Evaluating Earthquake ·Hazards 

in the Los Angeles RegionAn Earth-Science Perspective 

J. I. Ziony, Editor· 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1360 

An integrated set of studies describing methods for evaluating 

geologically controlled earthquake hazards as a basis 

for reducing future losses 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1985 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

library of Congress Cataloging-in-Publication Data 

Evaluating earthquake hazards in the Los Angeles region-An earth-science perspective. 

(U.S. G~ological Survey professional paper ; 1360) 

Bibliography: p. 471 

Supt. of Docs. no.: I 19.16:1360 

1 . Earthquakes--California-Los Angeles region. I. Ziony, Joseph I. II. U.S. Geological Survey professional paper 1360. 

QE535.2.U6E93 1985 363.3'495'0979494 85-600239 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, DC 20402 
FOREWORD 

Devastating earthquakes have sporadically struck many populated centers of the United States (for example, Boston, Mass., in 1755; Charleston, S.C., in 1886; San Francisco, Calif., in 1906; Long Beach, 

Calif., in 1933; Tacoma and Seattle, Wash., in 1949 and 1965; Anchorage, Alaska, in 1964; and San Fernando, Calif., in 1971). Although a damaging earthquake at a given locality in the United States is a 

relatively rare event, the likelihood of truly catastrophic loss of life and property is increasing as 

development and construction accelerate in the 39 States that lie in regions of major or moderate potential for large earthquakes. 

Beginning with Clarence E. Dutton's investigations of the 1886 Charleston earthquake, scientists of the 

U.S. Geological Survey have studied earthquakes and their effects. The great Alaska earthquake of 1964 

and the 1971 San Fernando earthquake awakened officials to the threat facing many urban areas and 

stimulated geologists and seismologists to analyze the conditions that control the distribution of earthquake damage. The United States Congress, recognizing that the potential for large earthquakes is a national concern, enacted the Earthquake Hazards Reduction Act. of 1977 (Public Law 95-124), which 

establishes objectives to (1) develop earthquake-resistant engineering-design methods; (2) predict earthquakes and characterize seismic hazards; (3) develop model codes fodand use and construction; and (4) 

prepare plans for responding to major destructive earthquakes. Within these broad objectives, two major goals of the Geological Survey have been to improve methods of evaluating geologically controlled 

earthquake effects and to delineate earthquake hazards in major urban regions at high seismic risk. 

Studies for Seismic Zonation of the San Francisco Bay Region (U.S. Geological Survey Professional 

Paper 941-A) was a solid advance in the assessment of earthquake hazards. That report presented 

methods for evaluating earthquake, surface-faulting, ground-shaking, and ground-failure potential and 

described a multidisciplinary approach to seismic zonation. Subsequent earth-science maps and evaluations of California's San Francisco Bay region prepared by the Geological Survey were the bases for 

derivative maps that are now being used in engineering design, land use planning, and emergencyresponse planning to reduce future earthquake losses. 

Evaluating Earthquake Hazards in the Los Angeles Region-An Earth-Science Perspective, which 

builds on the foundations laid by the San Francisco Bay region studies, indicates how rapidly the science 

of earthquake hazard assessment is evolving. For example, innovative new concepts for predicting the 

extent and severity of strong shaking and of earthquake-triggered landsliding have resulted from 

research in the Los Angeles region. In presenting state-of-the-art methods, this volume describes the 

potential for damaging geologic and seismologic effects and demonstrates the application of evaluative 

techniques to selected areas of that region. We expect to publish more detailed maps of hazard potential 

for much of the region over the next several years. The hazard-evaluation methods described herein can 

also be used for evaluating and mapping earthquake hazards in other urban areas such as Salt Lake 

City, Utah, Seattle, Wash., and Anchorage, Alaska, all of which are vulnerable to earthquake damage. 

The ultimate benefits of studies such as those reported in this volume are the reduced loss of life, injury, and property damage and the continued functioning of vital services and economic activities following a potentially destructive earthquake. To achieve these benefits, scientists, engineers, and planners 

must cooperate in the development of useful technical products. In turn, officials in both the private 

sector and in the government must determine which actions acceptable to the general public can best 

reduce future earthquake losses. 

Dallas L. Peck 

Director, U.S. Geological Survey 

Foreword Ill 

CONTENTS 

FOREWORD III 

ABSTRACT IX 

INTRODUCTION 1 

J. I. Ziony and W. J. Kockelman 

The earthquake threat, 1 • Purpose and content of this volume, 4 • Opportunities 

for reducing earthquake hazards, 8 • Users of information for reducing earthquake hazards, 11 • Looking toward the future, 13 

GLOSSARY 15 

CONVERSION TABLE 23 

EARTHQUAKE AND SURFACE-FAULTING SOURCES 

GEOLOGIC AND SEISMOLOGIC SETTING 25 

R. F. Yerkes 

Plate-tectonic evolution of California, 25 • Present plate-tectonic setting, 25 • Effects of continuing deformation, 27 • Pattern of active faults, 32 • Pattern of clamaging earthquakes, 32 • Pattern of modern seismicity, 33 

EVALUATING EARTHQUAKE AND SURFACE-FAULTING POTENTIAL 43 

J. I. Ziony and R. F. Yerkes 

Potentially active faults of the region, 43 • Hazards from active faults, 60 • Examples of surface faulting and related effects from southern California earthquakes, 65 • Predicting the future behavior of faults, 69 • Implications for reduction of earthquake hazards, 89 

EARTHQUAKE GROUND MOTION 

PREDICTING EARTHQUAKE GROUND MOTION: AN INTRODUCTION 93 

R. D. Borcherdt 

Developing a data base for ground-motion estimation on a regional scale, 93 • 

Predicting earthquake intensities, 94 • Predicting quantitative characteristics of 

ground shaking, 95 • Estimating ground shaking for a postulated event, 97 • 

Common means for characterizing earthquake shaking, 97 

MAPPING QUATERNARY SEDIMENTARY DEPOSITS FOR AREAL VARIATIONS IN 

SHAKING RESPONSE 101 

J. C. Tinsley and T. E. Fuma~ 

Mapping surficial geologic units, 101 • Surficial geologic maps, 105 • Description 

of map units, 105 • Using physical properties of surficial geologic units to estimate 

relative shaking response, 112 • Mapping shear-wave velocity groups, 114 

MAPPING SHEAR-WAVE VELOCITIES OF NEAR-SURFACE GEOLOGIC MATERIALS 

127 

T. E. Fumal and J. C. Tinsley 

Geologic factors affecting shear-wave velocity, 128 • Shear-wave velocity studies 

in the Los Angeles region, 129 • Shear-wave velocities in late Quaternary sedimentary deposits, 130 • Shear-wave velocities in pre-late Quaternary bedrock 

materials, 135 • Preparing regional maps of shear-wave velocity, 135 

Contents V 
PREDICTING SEISMIC INTENSITIES 151 

J. F. Evernden and J. M. Thomson 

Why ground-motion parameters saturate at high magnitude, 152 • Method for 

predicting seismic intensities, 156 • Correlating intensity with strong-motion 

parameters, 160 • Applying the intensity prediction method, 170 • Using seismic 

intensities to predict earthquake losses, 184 • Mathematical details of model for 

predicting intensities, 201 

PREDICTIVE MAPPING OF EARTHQUAKE GROUND MOTION 203 

W. B. Joyner and T. E. Fumal 

Predictive equations, 204 • Using local shear-wave velocity to improve predictions 

of site effects, 205 • Characterizing earthquake sources, 208 • Applying the 

method, 212 • Dependence of probabilistic ground-motion estimates on param-

. eters of the magnitude-frequency relation, 216 

PREDICTING RELATIVE GROUND RESPONSE 221 

A.M. Rogers, J. C. Tinsley, and R. D. Borcherdt 

Previous studies, 221 • Comparative ground response in the Los Angeles region, 

224 • Geologic and geotechnical parameters affecting ground response, 

226 • Comparing ground response with geologic factors, 233 • Clustering sites to 

reflect ground-response variability, 236 • Predicting geographic variation in 

ground response, 241 • Validity and limitations oftechnique, 246 

PREDICTING EARTHQUAKE GROUND-MOTION TIME-HISTORIES 249 

P. A. Spudich and S. H. Hartzell 

The earthquake rupture process, 249 • How ground motions are simulated, 

252 • Mathematical details, 254 • Green's functions and their approximation, 

255 • Detailed example of ground-motion simulation, 260 

EARTHQUAKE-TRIGGERED GROUND FAILURE 

EVALUATING LIQUEFACTION POTENTIAL 263 

J. C. Tinsley, T. L. Youd, D. M. Perkins, and A. T. F. Chen 

Liquefaction and resulting ground failure, 266 • Method for evaluating liquefaction potential, 267 • Mapping liquefaction susceptibility, 268 • Liquefaction susceptibility in the Los Angeles region, 276 • Determining liquefaction opportunity, 

297 • Liquefaction potential maps and their limitations, 314 

PREDICTING AREAL LIMITS OF EARTHQUAKE-INDUCED LANDSLIDING 317 

R. C. Wilson and D. K. Keefer 

Landslides in historical earthquakes worldwide, 319 • Examples of landslides in 

California earthquakes, 323 • Numerical models for earthquake-induced landslides, 327 • Severity of shaking as a function of magnitude and distance, 332 • 

Predicting the limits of landsliding from an earthquake, 335 • A hypothetical site 

evaluation, 338 

EARTHQUAKE-RELATED PHENOMENA OFFSHORE 

IDENTIFYING POTENTIALLY ACTIVE FAULTS AND UNSTABLE SLOPES OFFSHORE 347 

S. H. Clarke, Jr., H. G. Greene, and M.P. Kennedy 

Acquiring and interpreting marine geophysical data, 350 • Potential geologic 

hazards in the offshore Los Angeles region, 357 

VI Contents 
EVALUATING TSUNAMI POTENTIAL 375 

D. S. McCulloch 

Tsunami generation and propagation, 376 • California tsunami history, 387 • 

Tsunami potential in coastal southern California, 392 • Tsunami hazard reduction, 402 • California tsunamis from 1812 to 1975, 409 

APPLICATIONS 

PREDICTED GEOLOGIC AND SEISMOLOGIC EFFECTS OF A POSTULATED 

MAGNITUDE 6.5 EARTHQUAKE ALONG THE NORTHERN PART OF THE 

NEWPORT-INGLEWOOD ZONE 415 

J. I. Ziony, J. F. Evernden, T. E. Fumal, E. L. Harp, S. H. Hartzell, W. B. Joyner, D. K. Keefer, 

P. A. Spudich, J. C. Tinsley, R. F. Yerkes, and T. L. Youd 

Geology of the demonstration area, 415 • The postulated earthquake, 417 • Surface faulting and deformation, 419 • Seismic intensities, 420 • Horizontal acceleration, velocity, and response spectral values, 423 • Time-histories of ground 

motion, 430 • Liquefaction-related ground failure, 434 • Landsliding, 436 • 

Other effects, 441 

USING EARTH-SCIENCE INFORMATION FOR EARTHQUAKE HAZARD REDUCTION 443 

W. J. Kockelman 

Anticipating damage to critical facilities, 443 • Adopting seismic safety plans, 

449 • Retrofitting highway bridges, 454 • Regulating development in potential 

surface fault rupture areas, 457 • Strengthening or removing unsafe masonry 

buildings, 461 • Other examples, 465 

REFERENCES CITED 471 

PHOTOGRAPH CREDITS 

p.42, aerial view northwestward along the San Andreas fault near San Bernardino (D. M. Morton, USGS); p. 100, aerial view above Pomona 

northeastward along eastern San Gabriel Mountains and part of upper Santa Ana River basin (D. M. Morton, USGS); p. 126, determining 

seismic velocities of near-surface geologic materials by using a truck-mounted recording system (l. ). Hwang, USGS); p. 150, computer-generated map showing Modified Mercalli intensities for 1952 Kern County earthquake (U.S. Geological Survey Professional Paper 1223); p. 248, 

San Onofre Nuclear Generating Station (J. I. Ziony, USGS); p. 316, landslide triggered by 1971 San Fernando earthquake on western side 

of Golden State Freeway (J. I. Ziony, USGS); p. 374, damage to railroad in Seward, Alaska, from tsunami waves generated by 1964 Alaska 

earthquake (U.S. Coast and Geodetic Survey, now the National Ocean Survey); p. 470, Olive View Hospital after 1971 San Fernando earthquake (Reuben Kachadoorian, USGS). 

Contents VII 
VIII Earthquake Hazards in the Los Angeles Region 
Evaluating Earthquake Hazards 

in the Los Angeles RegionAn Earth-Science Perspective 

ABSTRACT 

Potentially destructive earthquakes are inevitable in 

the Los Angeles region of California, but hazards prediction can provide a basis for reducing damage and loss. 

This volume identifies the principal geologically controlled earthquake hazards of the region (surface 

faulting, strong shaking, ground failure, and tsunamis), 

summarizes methods for characterizing their extent and 

severity, and suggests opportunities for their reduction. 

Two systems of active faults generate earthquakes in 

the Los Angeles region: northwest-trending, chiefly 

horizontal-slip faults, such as the San Andreas, and 

west-trending, chiefly vertical-slip faults, such as those 

of the Transverse Ranges. Faults in these two systems 

have produced more than 40 damaging earthquakes 

since 1800. Ninety-five faults have slipped in late 

Quaternary time (approximately the past 750,000 yr) 

and are judged capable of generating future moderate 

to large earthquakes and displacing the ground surface. 

Average rates of late Quaternary slip or separation 

along these faults provide an index of their relative activity. The San Andreas and San Jacinto faults have slip 

rates measured in tens of millimeters per year, but most 

other faults have rates of about 1 mm/yr or less. Intermediate rates of as much as 6 mm/yr characterize a 

belt of Transverse Ranges faults that extends from near 

Santa Barbara to near San Bernardino. The dimensions 

of late Quaternary faults provide a basis for estimating 

the maximum sizes of likely future earthquakes in the 

Los Angeles region: moment magnitude (M) 8 for the San 

Andreas, M 7 for the other northwest-trending elements 

of that fault system, and M 7.5 for the Transverse 

Ranges faults. Geologic and seismologic evidence along 

these faults, however, suggests that, for planning and 

designing noncritical facilities, appropriate sizes would 

be M 8 for the San Andreas, M 7 for the San Jacinto, 

M 6.5 for other northwest-trending faults, and M 6.5 to 7 

for the Transverse Ranges faults. The geologic and 

seismologic record indicates that parts of the San Andreas and San Jacinto faults have generated major 

earthquakes having recurrence intervals of several tens 

to a few hundred years. In contrast, the geologic 

evidence at points along other active faults suggests 

recurrence intervals measured in many hundreds to 

several thousands of years. The distribution and character of late Quaternary surface faulting permit estimation of the likely location, style, and amount of future 

surface displacements. 

An extensive body of geologic and geotechnical information is used to evaluate areal differences in future 

levels of shaking. Bedrock and alluvial deposits are differentiated according to the physical properties that 

control shaking response; maps of these properties are 

prepared by analyzing existing geologic and soils maps, 

the geomorphology of surficial units, and geotechnical 

data obtained from boreholes. The shear-wave 

velocities of near-surface geologic units must be 

estimated for some methods of evaluating shaking potential. Regional-scale maps of highly generalized shearwave velocity groups, based on the age and texture of 

exposed geologic units and on a simple two-dimensional 

model of Quaternary sediment distribution, provide a 

first approximation of the areal variability in shaking 

response. More accurate depictions of near-surface 

shear-wave velocity useful for predicting ground-motion 

parameters take into account the thickness of the 

Quaternary deposits, vertical variations in sediment 

. type, and the correlation of shear-wave velocity with 

standard penetration resistance of different sediments. 

A map of the upper Santa Ana River basin showing 

shear-wave velocities to depths equal to one-quarter 

wavelength of a 1-s shear wave demonstrates the threedimensional mapping procedure. 

Four methods for predicting the distribution and 

strength of shaking from future earthquakes are 

presented. These techniques use different measures of 

strong-motion severity: seismic intensities, peak horizonAbstract IX 
tal acceleration and velocity (or response spectral 

values), amplification factors relative to ground motion 

on bedrock, and time-histories of ground motion. 

Maps of predicted seismic intensities for the Los 

Angeles region are useful for emergency-preparedness 

planning and for estimating losses from future earthquakes. A computer-based technique for predicting 

earthquake intensities incorporates (1) a numerical 

model of the earthquake source, (2) a mathematical 

expression for the rate of attenuation in the crust of the 

region, (3) an empirical correlation of geologic ground 

conditions with differences of expected intensity, and (4) 

a digitized map of geologic ground conditions for the 

area studied. Comparison of observed intensities from 

the 1971 San Fernando earthquake with strong-motion 

records indicates that intensity correlates directly with 

expected levels of shaking from 0.5 to 3 Hz (periods of 

approximately 0.3-2 s), frequencies of concern to ordinary structures. Example applications of the predictive method to the Los Angeles region include predicting 

intensities for a postulated great earthquake on the San 

Andreas fault; calculating cumulative maximum intensities for a suite of 87 postulated earthquakes representative of the principal potentially active faults; deducing 

the likely fault sources for the earthquakes of 1812 from 

candidate predicted intensity maps; and mapping the 

estimated root-mean-square acceleration for a potential 

Los Angeles basin earthquake. The technique of predicting intensities can be extended to estimate losses 

from future earthquakes by incorporating empirical correlations between observed intensities and percentage 

of damage experienced by various types of structures. A 

comparison of predicted losses to wood-frame structures for possible earthquakes shows that a moderatesize earthquake in the Los Angeles basin would cause a 

much higher loss than a great earthquake on the San 

Andreas fault. 

Predictive mapping of peak horizontal acceleration 

and velocity and of horizontal response spectral values 

provides an appraisal of areal shaking potential that is 

useful for engineering design and building codes. The 

technique relies on equations derived from regression 

analyses of an extensive set of strong-motion records. 

These equations link the ground-motion parameters to 

earthquake magnitude, source distance, and site conditions. The site effect can be expressed in terms of the 

shear-wave velocities of near-surface geologic materials. Thus, predictive maps of ground-motion values for 

a single postulated earthquake can be made by applying 

the predictive equations and taking into account the 

areal differences in shear-wave velocities. The uncertainty associated with the frequency of occurrence and 

the size of future earthquakes from multiple potential 

sources can be evaluated by means of a newly develX Earthquake Hazards in the Los Angeles Region 

oped approach that uses fault-slip rates to compute the 

ground motion that will be exceeded at a specified annual probability. Predictive maps for the upper Santa 

Ana River basin made by using this method show the 

areal distribution of ground-motion values exceeded at a 

return period of 500 yr for future large earthquakes on 

the San Andreas, San Jacinto, and Cucamonga faults. 

Areal variations in shaking potential are also 

estimated by comparing measurements of ground motions from distant underground nuclear explosions 

recorded at 98 sites in the Los Angeles region. Because 

local ground response from these low-strain signals correctly predicts ground-motion amplification for higher 

strain levels .caused by nearby large earthquakes, the 

data provide a way of assigning amplification factors 

relative to shaking on crystalline bedrock. At periods 

less than 0.5 s, the most pronounced differences in 

observed site responses correlate with differences in 

sediment void ratios, thicknesses of surficial deposits, 

and depths to basement rocks; resonant effects having 

large amplifications over narrow frequency bands are 

observed for sites underlain by Holocene deposits 10 to 

20 m thick. At periods greater than 0.5 s, the most important geologic factors are depth to basement rocks and 

thickness of Quaternary sediments. When recorded motions are compared with what is known about geologic 

conditions at each site, the principal factors that affect 

amplification can be grouped, and distinctive types of 

sites can be identified through cluster analysis. These 

site types then become the basis for predictive mapping 

of relative shaking response. To demonstrate the mapping procedure, the areal distribution of expected 

amplification factors for part of the Los Angeles basin is 

shown for three period bands (3.3-10, 0.5-3.3, and 

0.2-0.5 s); locally, the spectral amplification is predicted 

to be as much as 61/2 times greater than the shaking 

levels on crystalline bedrock. 

Earthquake-resistant design of critical structures 

commonly requires elaborate estimates of the characteristics of ground motion at a particular site. Timehistories of ground motion from postulated earthquakes 

are predicted by estimating how each point on a slipping 

fault will be displaced, determining the ground motions 

caused by each point, and then summing the groundmotion contributions from all points to obtain the total 

motion at a given distant site. The method depends on 

assumptions concerning the detailed character of the 

expected rupture propagation and the velocity structure 

of the Earth's crust in the region analyzed. The timehistory of ground motion caused by slip of a single point 

on a fault is called a Green's function. Green's functions 

can be determined theoretically by solving the wave 

equation in a model of the crust, or they may be obtained 

empirically by using recordings of small earthquakes in 
the desired crustal structure. Economical methods of 

computing Green's functioo.s by using simplifying 

assumptions are reviewed. 

Secondary geologic effects such as liquefaction within 

the alluvial basins and landsliding within the upland 

areas can be expected as a result of strong shaking during future earthquakes. Liquefaction potential is 

evaluated by preparing two types of maps-one showing 

the susceptibility of sediment to liquefy with shaking 

and the other expressing the probabilities that critical 

levels of shaking needed for liquefaction will be attained. Areas of susceptible sediments are delineated by 

analyzing the physical properties of the late Quaternary 

alluvial deposits, grouping these deposits according to 

their probable content of cohesionless sand or silt, and 

determining whether they are saturated with ground 

water at depths of less than about 15 m. Holocene sand 

and silt, especially if deposited during the past few hundred years, are the most susceptible to liquefactionrelated ground failure; these materials are mapped on 

the basis of soil-profile development, geomorphic expression, and geotechnical properties such as standard 

penetration resistance. Areas of the Los Angeles region 

deemed most vulnerable to liquefaction during future 

earthquakes include the flood plains of the Los Angeles, 

Santa Ana, and San Gabriel Rivers; parts of the San Fernando Valley and the Oxnard Plain; coastal and harbor 

areas of Long Beach and Marina Del Rey; and floodcontrol basins. The opportunity for liquefaction at a site 

containing susceptible sediments can be estimated by 

considering the earthquake potential and applying an 

empirically determined relation between earthquake 

magnitude and the limiting distances for liquefactionrelated ground failure. Regional liquefaction opportunity is mapped by summing, for points on a map, the expected annual rates of occurrence of earthquakes of M 5 

or greater from those fault sources that influence each 

point. Individual sites will experience ground shaking 

strong enough to cause liquefaction in susceptible sediment on an average of once every 30 to 50 yr. 

The extent and severity of future earthquake-induced 

slope failure can be fully evaluated only when detailed 

information about the geologic and topographic controls 

on slope stability is available. Although such information is not yet complete for the Los Angeles region, a 

twofold approach has been developed to assess the 

areal limits of earthquake-triggered landslides for 

postulated earthquakes of specified size. The maximum 

distances from an earthquake source at which various 

classes of landslides can occur (given susceptible slopes) 

are estimated on the basis of worldwide data for historical earthquakes that have triggered landslides. The 

probability distribution of threshold levels of shaking 

capable of triggering slope failure can then be mapped 

by extending the Newmark method of slope-stability 

analysis; the procedure depends on newly established 

correlations between earthquake magnitude, critical 

displacement of a slope, and intensity of shaking for a 

given earthquake-source distance. The likelihood of 

slope failures from a postulated earthquake is evaluated 

for a sample site in the Santa Monica Mountains. 

Faults and zones of potential slope instability on the 

sea floor off the Los Angeles region have been identified 

and evaluated by means of specialized remote-sensing 

methods. Acoustic reflection profiles reveal those faults 

that offset Quaternary sediments of the sea floor and 

also show potentially unstable slopes on which subaqueous sediment slides, mass flows, and gas-charged 

sediments occur. A regional analysis of these profiles indicates offshore counterparts to the onshore faults of 

the San Andreas system and the Transverse Ranges. 

Many of these offshore faults may generate moderate to 

large earthquakes and offset the sea floor. Scattered 

zones of sea-floor sliding as large as 60 km2 are mapped 

along the outer edge of the Santa Monica and San Pedro 

shelves and cover several hundred square kilometers in 

the central Santa Barbara Basin. Furthermore, potentially unstable gas-charged sediments apparently are 

widespread in the Santa Monica and San Pedro Basins. 

Some zones of sea-floor instability could fail during 

shaking caused by nearby large earthquakes. 

Tsunamis are a threat to coastal areas, although the 

hazard in the Los Angeles region is much less than that 

in many other regions along the circum-Pacific border. 

A number of methods for predicting tsunami wave 

heights and frequency of occurrence from both distant 

and local sources are summarized. Predictive models for 

distantly generated tsunamis indicate that wave heights 

of 2 m are exceeded on the average of once every 500 yr, 

except locally along Santa Monica and San Pedro Bays 

and near Ventura, where wave heights of 3 m are 

exceeded on the average of once every 500 yr. A preliminary appraisal of the potential for locally generated 

tsunamis suggests that wave runup heights as great as 4 

to 6 m could be caused by sea-floor faulting in the Santa 

Barbara Channel; wave runup heights no greater than 2 

to 3 m are estimated for the dominantly strike-slip faults 

farther south. Earthquake-triggered sea-floor slides having the dimensions observed in the offshore region are 

unlikely to cause tsunamis. 

To demonstrate the various hazard-evaluation 

methods discussed in this volume, the geologically controlled effects expected from a postulated M 6.5 earthquake along the northern part of the Newport-Inglewood 

fault zone are evaluated. Predict.ed effects include: 

1. Secondary faulting (normal-oblique slip) at the 

ground surface along one or more late QuaterAbstract XI 
nary faults exposed in the Baldwin and Rosecrans Hills and possible subsurface slip along 

reverse faults at the northern end of the 

Dominguez Hills. 

2. Shaking intensities of Modified Mercalli intensity 

VII distributed widely throughout the Los 

Angeles basin and the San Fernando Valley and 

scattered areas of intensity VIII as far as 18 km 

from the main fault. 

3. Strong shaking lasting about 10 to 15 s. Peak groundmotion values of about 0.4 g acceleration, 90 to 

100 cm/s velocity, 1.2 g pseudoacceleration 

response, and 160 to 180 cm/s pseudovelocity 

response near the earthquake source zone. Peak 

ground-velocity values at the northwestern end 

of the fault zone will be higher than those at the 

southeastern end if the subsurface tectonic rupture propagates northwestward from the postulated epicenter. 

4. Liquefaction in highly susceptible, water-saturated, 

cohesionless Holocene alluvial sediments as 

much as 18 km from the earthquake source zone. 

XII Earthquake Hazards in the Los Angeles Region 

5. Rock or soil falls and slides, the most common 

earthquake-triggered slope failures, occurring 

chiefly in upland areas within about 40 km of the 

earthquake source zone. 

6. Minor harmonic waves {seiches) in enclosed small 

bodies of water. 

Earth-science information can be used by planners, 

engineers, and decisionmakers to solve specific 

earthquake-related problems in southern California. Examples of the geologic and seismologic information used 

and the actions taken to reduce the hazard are discussed for the problems of anticipating damage to 

critical facilities, adopting seismic safety plans, 

strengthening highway bridges, regulating development 

in areas of potential surface faulting, and strengthening 

or removing unsafe masonry buildings. Effective 

measures for reducing future earthquake losses can 

result if adequate scientific data and interpretations are 

available and are thoughtfully applied by engineers, 

planners, and others responsible for public safety. 
INTRODUCTION 

By J. I. Ziony and W. J. Kockelman 

THE EARTHQUAKE THREAT 

In July 1769, a Spanish expedition led by Captain 

Gaspar de Portola, civil and military governor of the 

province of Mexico, marched northward from San Diego 

and became the first documented group of Europeans to 

set foot on the plain near Los Angeles (Bancroft, 1884, 

p. 146): 

on the 28th, when the governor and his 

followers were on the Santa Ana River, four 

violent shocks of earthquake frightened the Indians into a kind of prayer to the four winds, and 

caused the stream to be named also Jesus de los 

Temblores. Many more shocks were felt during 

the following week; yet the foreigners were 

delighted with the region, noting the agricultural 

possibilities . . . . 

This seismologic "greeting" introduced the newcomers 

to a distinctive feature of the Earth's crust in the Los 

Angeles region of California-the sporadic occurrence 

of strong earthquakes. Earthquakes at first were of little 

concern, but their occurrence became more significant 

as the Spanish proceeded to build missions and settle 

the region. The year 1812, recorded as "el aiio de los 

temblores" in mission archives, was marked by two major earthquakes that killed at least 40 people and 

severely damaged coastal missions from near Dana 

Point to near Point Arguello and others as far inland as 

the San Fernando and San Gabriel valleys. Many of the 

more than 40 additional strong earthquakes that have 

shaken parts of the region since 1812 have resulted in 

loss of life and property (table 1). We now know that 

similar earthquakes will occur as the inevitable result of 

the ongoing dynamic crustal processes characteristic of 

the region. 

Today the Los Angeles region (fig. 1) is inhabited by 

more than 11 million people and is one of the key industrial, commercial, and cultural centers of the United 

States. As its population and development expand, so 

does its vulnerability to destructive earthquakes. The 

1971 San Fernando earthquake, a moderate-sized event 

whose epicenter was on the margin of the Los Angeles 

metropolitan area, dramatically demonstrated how 

vulnerable a complex modern urban society is to the 

damaging effects of nearby earthquakes (fig. 2). 

Even though the losses shown in table 1 are significant, they do not accurately reflect the actual risk to the 

Los Angeles region. Many of the damaging earthquakes 

listed in the table preceded major development in 

southern California, and none was as strong as the 

largest magnitude possible in the region. A recent 

assessment of the earthquake hazards in California 

(Federal Emergency Management Agency, 1980) concludes that catastrophic earthquakes are inevitable in 

the Los Angeles region. The probability that a large 

earthquake will occur sometime during the next 30 yr 

along the San Andreas fault near Los Angeles is currently estimated to be 40 percent or greater (Lindh, 

1983; Wesson and Wallace, 1985). Projected losses of 

billions of dollars and estimated casualties of tens of 

thousands (table 2) would surpass the results of any 

previous natural disaster in the Unitlild States. A 

catastrophic earthquake would severely strain the 

emergency-response and recovery capabilities of 

Federal, State, and local governments and profoundly 

impact the economies of the State and the Nation. 

Earthquakes of sufficient size threaten lives and 

damage property by setting off a chain of effects that 

disrupts the natural and manmade environments. Widespread strong ground shaking is a geologic effect that 

can cause buildings to distort or fail. Vibratory earthquake motion, in turn, can induce secondary geologic effects such as liquefaction, landsliding, and related 

ground failure hazardous to structures or can generate 

sudden fluctuations of water levels in lakes, reservoirs, 

and wells. Some earthquakes are accompanied by permanent offset or distortion of the ground surface that 

can rupture or warp structures. Rare large surface 

displacements occurring within the marine environment 

can trigger seismic sea waves (tsunamis) that may 

damage coastal facilities thousands of miles from the 

earthquake source. Primary and secondary geologic effects that cause exceptionally severe damage to structures or lifelines may result in major nongeologic effects 

Introduction 1 
.. .. FIGURE 1.-Geographic setting of the Los Angeles region and environs. County boundaries shown by heavy broken lines. 

' ·• 1. . ' · 1 1 1, 1 .) , _-., , '-----.._ ~---------.... • ~- • .c ' ' \ r--/ .r---.. "\.'\\.Jr \ \\\. 1 ll t r r ~ 

/ 't 

J 
TABLE 1.-Losses from southern California earthquakes, 1812-1979, 

in which Jives were lost or damage was known to have equaled or 

exceeded $100,000 

[Modified from U.S. Geological Survey (1981, table 1). NA, data not available] 

Dollar loss at 

Year Location Lives lost time of quake 

1812 ------San Juan Capistrano 40 NA 

1899------ San Jacinto 6 NA 

1915 ------Imperial Valley 6 900,000 

1918------ San Jacinto and Hemet 0 200,000 

1925 ------Santa Barbara 13 8,000,000 

1926------ Santa Barbara 1 NA 

1933 ------ Long Beach 115 40,000,000 

1940------ Imperial Valley 9 6,000,000 

1941------ Santa Barbara 0 100,000 

1941------ Torrance and Gardena 0 1,100,000 

1949 ------Terminal Island 0 9,000,0001 

1951 ------Terminal Island 0 3,000,0001 

1952 ------Kern County 14 60,000,000 

1955------ Terminal Island 0 3,000,0001 

1961------ Terminal Island 0 4,500,0001 

1971 ------ San Fernando 65 504,950,000 

1978 ------ Santa Barbara 0 12,000,000 

1979------ Imperial Valley 0 30,000,000 

1

Subsurface damage to oil wells; no damage to surface structures reported. Earthquakes may 

have been triggered by oilfield operations. 

(widespread fires, flooding of populated areas caused 

by failure of large dams, or release of toxic or radioactive materials) that could be more catastrophic than the 

initial effects of the earthquake. A more complete, nontechnical explanation of the various hazards posed by 

earthquakes has been presented by Blair and Spangle 

(1979). 

Because the hazards to life and property resulting 

from the primary and secondary effects of earthquakes 

may vary substantially throughout a region, measures to 

reduce earthquake hazards must necessarily begin by 

delineating geographic areas having different potentials 

for fault offset or distortion of the land surface, strong 

ground shaking, ground failure, or other geologically 

controlled effects. This volume presents methods for 

characterizing these types of earthquake hazards on a 

regional scale and provides earth-science information 

vital to actions that could be taken in the Los Angeles 

region to reduce future earthquake losses. 

PURPOSE AND CONTENT 

OF THIS VOLUME 

The Los Angeles region became a major focus for 

seismic hazard research following the 1971 San Fernando earthquake, which stimulated national interest in 

earthquakes and expanded the resources available for 

earthquake studies. Earthquake prediction-the specifi4 Earthquake Hazards in the Los Angeles Region 

TABLE 2.-Estimated losses in Los Angeles and Orange Counties from 

two postulated large earthquakes 

(Losses from the failure of dams and transportation or communication systems and consequential losses such as unemployment and other economic impacts excluded. Summarized. from 

Federal Emergency Management Agency {1980) and Steinbrugge and others {1981). Uncertainties associated with loss-estimation procedures suggest that actual losses to buildings could 

vary upward or downward by a factor of as much as two to three] 

Postulated earthquake 

Magnitude 8.3 Magnitude 7.5 

on San Andreas on Newport-Inglewood 

fault zone 

Deaths -------------------- 3,Q00--12,5001 4,400-21,000' 

Hospitalized injured---------12,Q00--50,0001 17,600--84,0001 

Long-term homeless---------------52,000 192,000 

Damage to buildings and--------------25 62 

contents (in billions of 

1980 dollars). 

1

Depending on time of day. 

cation of the time, place, and magnitude of an impending 

earthquake-is one goal of this research. Thus, some efforts have centered on monitoring the Earth's crust with 

a variety of instruments to detect possible fluctuations 

in geophysical signals that might foreshadow a major 

imminent southern California earthquake and permit its 

prediction within a time frame of a few days, weeks, or 

months. Progress toward short-term prediction has been 

slower than scientists had hoped, but there has been 

substantial progress in making long-term earthquake 

predictions (for example, determining the probability 

during the next several decades of a future large earthquake on the San Andreas fault) and in better 

understanding how earthquakes occur (Wesson and 

Wallace, 1985). Earthquake hazard assessment-the 

specification of the potential for destructive effects of 

future earthquakes-is another goal. Truly remarkable 

progress has been made on the earth-science aspects of 

this subject, as evidenced by the findings presented in 

this volume. 

All strategies for reducing future losses from earthquakes rely on the ability to predict the geographic 

distribution and severity of the potentially damaging 

geologic and seismologic effects that commonly accompany major earthquakes-strong shaking, fault offset of 

the land surface, and disruption of the ground by liquefaction or landsliding. These hazards are the topics of 

the following chapters. 

This professional paper provides an overview of the 

principal geologically controlled earthquake hazards in 

the Los Angeles region and summarizes the methods 

that earth scientists use to evaluate and characterize 

those hazards. Although the volume was initially 

planned to address the general public as well as earth-
quake experts and researchers in related fields, this 

goal has been only partially achieved because of the 

c::omplexity of the scientific problems associated with 

many of the hazards and the diversity of the potential 

audience. Most of the chapters emphasize the scientific 

bases for mapping and assessing geologically controlled 

earthquake hazards and thus will be of greatest interest 

to geologists and seismologists. Some chapters treating 

hazard-reduction issues have been written to be understood by planners, engineers, and decisionmakers who 

need to use earth-science information in specific situations to reduce those hazards. Our hope is that all 

readers, whatever their background or expertise, will 

gain a better understanding of the earthquake hazards 

facing the Los Angeles region and of the opportunities 

for reducing the risk to life and property. 

A glossary (p. 15) containing the principal technical 

terms used in this volume will assist the nonspecialist. A 

table for converting from metric to English units of measure is on p. 23. 

Most of the earth-science research summarized in 

this report has been conducted by scientists and 

engineers of the U.S. Geological Survey, the California 

Division of Mines and Geology, various universities, and 

private consulting firms, chiefly using funds provided by 

the Earthquake Hazards Reduction Program of the Geological Survey. Research activities have included detailed geologic and seismologic studies of faults, investigations of the factors that influence seismic shaking, 

and analysis of the geotechnical controls on liquefaction 

and landsliding. Many of the methods described in the 

following chapters have evolved from hazard-evaluation 

techniques first developed in a multidisciplinary study 

of seismic zonation in the San Francisco Bay region (Borcherdt, 1975), where the resulting earth-science products have been successfully used to reduce hazards. The 

studies in both the San Francisco Bay and the Los 

Angeles regions have significantly improved our ability 

to predict and map the geologic effects of future earthquakes. Because knowledge of the behavior of faults 

during late Quaternary time and of the distribution and 

character of sediments deposited during that time span 

is crucial to evaluating earthquake hazards, these topics 

have received special attention. Subdivisions of Quaternary time as used in this volume are shown on the accompanying geologic time chart (inside front cover). 

This volume examines in sequence the causes of 

earthquakes in the Los Angeles region, the major 

geologic hazards likely to be associated with future 

earthquakes and the methods for evaluating and mapping those hazards, and examples of the impact of earthscience information on the decisionmaking processes 

that result in hazard reduction. The geologic factors 

that control the location and size of earthquakes and 

their rupture characteristics are evaluated in two 

chapters that describe: 

• The plate-tectonic framework within which 

earthquakes occur in the Los Angeles region 

(Yerkes, p. 25). 

• The identification of active faults, their potential 

for generating earthquakes and rupturing or distorting the land surface, and estimates of the 

likely size and frequency of major earthquakes 

along them (Ziony and Yerkes, p. 43). 

Strong shaking, the chief threat posed by an earth" 

quake because of the large area commonly affected, receives particular attention in seven chapters describing 

different aspects of that hazard: 

• An introduction to available methods of predicting the extent and severity of strong shaking and 

the applicability of different predictive techniques to reducing earthquake hazards (Borcherdt, p. 93). 

• How the late Quaternary sedimentary deposits 

of alluvial basins are differentiated and mapped 

to help characterize variations in the severity of 

future shaking (Tinsley and Fumal, p. 101). 

• A technique for regrouping geologic units on the 

basis of their geotechnical properties and shearwave velocities for prediction of future shaking 

levels (Fumal and Tinsley, p. 127). 

• Why it is useful to predict seismic intensities, 

how maps of predicted intensities are prepared 

for postulated earthquakes, and how these techniques can be applied to estimating future losses 

from earthquakes (Evernden and Thomson, 

p. 151). 

• The quantitative prediction of ground-motion 

values by applying newly developed equations 

that link peak acceleration, peak velocity, and 

response spectra to earthquake magnitude, geologically determined fault slip rates, and site 

geology Ooyner and Fumal, p. 203). 

• The use of ground motions from nuclear explosions in Nevada, recorded in the Los Angeles 

region, combined with geologic information obtained during the course of urban development, 

to map the relative shaking response expected 

for areas having different geologic characteristics (Rogers and others, p. 221). 

• The methods for simulating numerically the timehistory of ground motion at a site from a postulated earthquake, information needed by structural engineers for the earthquake-resistant 

design of special facilities such as large dams 

and nuclear powerplants (Spudich and Hartzell, 

p. 249). 

Introduction 5 
A 

B 

FIGURE 2.-The 1971 San Fernando earthquake demonstrated the vulnerability of a modern urban society to the damaging effects of a nearby 

earthquake. A, Damage at the Veterans Administration Hospital resulted in 47 deaths. Collapsed buildings were constructed in 1926, before 

earthquake-resistant design was required. The building at the left, constructed after 1933 and designed to resist strong shaking, did not sustain significant structural damage. (Photograph copyright 1971 by The Los Angeles Times.) B, Collapsed highway overpasses and bridges at the 

interchange of the Foothill and Golden State freeways. Because the earthquake occurred early in the morning, only three deaths resulted from 

this damage. However, the principal highway link between northern and southern California was temporarily cut, and traffic had to be 

rerouted for several months. (Photograph by R. E. Wallace, U.S. Geological Survey.) C, Overturned equipment at the Sylmar electrical converter station. Power distribution to more than 600,000 customers in southern California was disrupted because of widespread damage to 

electrical power facilities. (Photograph by T. L. Youd, U.S. Geological Survey.) D, The Lower Van Norman Dam, overlooking the heavily 

populated San Fernando Valley, was damaged nearly to catastrophic failure when part of the hydraulic-fill embankment and the concrete lining slid into the reservoir. About 80,000 people living downstream from the dam had to be evacuated as a precautionary measure. (Photograph 

by J.I. Ziony, U.S. Geological Survey.) 

Strong shaking from major earthquakes commonly 

triggers secondary geologic processes that can result in 

localized but severe effects. These effects are the topics 

of chapters describing: 

• A procedure for identifying the depositional and 

hydrologic environments in the Los Angeles 

region that have a potential for liquefaction, the 

. temporary transformation of earth materials 

into a liquefied state that is the chief cause of 

ground failure in areas of low relief during prolonged strong shaking (Tinsley and others, p. 263). 

• The empirical and theoretical methods for 

predicting the areal limits of earthquaketriggered slope failures in upland areas (Wilson 

and Keefer, p. 317). 

The Continental Shelf offshore of the Los Angeles 

region poses distinctive hazards that are important to 

coastal development. These hazards are discussed in 

two chapters describing: 

• The methods for identifying both faults that 

could offset the sea floor and potentially 

unstable sea-floor slopes that might fail and the 

general distribution of these potential hazards 

(Clarke and others, p. 347). 

• The character of tsunamis (seismic sea waves), 

methods of predicting their occurrence and 

severity, and an evaluation of their threat to the 

southern California region (McCulloch, p. 375). 

A summarizing chapter demonstrates how the preceding techniques can be used to predict the diverse and 

widespread geologic and seismologic effects of a potential earthquake along the northern part of the NewportInglewood zone [Ziony and others, p. 415). Specific 

predictions concern the location and severity of ground 

shaking, surface faulting, liquefaction, and landsliding 

associated with a moderate-sized earthquake. 

The final chapter [Kockelman, p. 443) illustrates how 

earth-science information is used to reduce earthquake 

hazards. It gives examples of specific earthquakerelated problems faced by planners, engineers, and 

decisionmakers in southern California and discusses the 

geologic and seismologic information used, the actions 

taken, and the impact of each action or decision. 

OPPORTUNITIES FOR REDUCING 

EARTHQUAKE HAZARDS 

that avoid or accommodate the potential effects of 

earthquakes. Some earthquake hazards, such as fault 

offset of the land surface, have definite areal limits and 

can be avoided by careful land-use planning and 

development. Others, such as strong ground shaking, 

generally cannot be avoided, and attempts must be 

made to design and build structures that will accommodate distortion and minimize the possibility of lifethreatening failures. Whatever strategy is selected, 

various levels of government, private groups, corporations, and quasi-public organizations can play important 

roles in reducing earthquake hazard or damage. 

An environment totally free of the risk of earthquake 

losses cannot be created in an earthquake-prone region. 

Choices mu~t be made between known or perceived 

risks and the expected costs of reducing them. The actions chosen for hazard reduction depend on judgments 

of acceptable risk [that level of exposure to loss for 

which no action is considered appropriate). Risks acceptable to individuals may not be considered acceptable by society. In dealing with the earthquake threat to 

the Los Angeles region, individual citizens must decide 

where to purchase homes and what measures to take to 

protect themselves against earthquake effects. Private 

firms or corporations that site and operate facilities 

must also make choices, as must governmental bodies 

that set standards for the construction of facilities 

important to the continuing function and safety of a 

modern urban society. Whatever the decisions, they 

should be based on an understanding of the likely 

hazards and how they can be reduced. 

A wide range of opportunities for reducing earthquake hazards is available to planners, engineers, and 

decisionmakers, both public and private (see list, p. 10). 

Techniques such as seismic-resistant design or the 

strengthening of unsafe structures are well known in the 

engineering profession. In the planning profession, an 

effective technique is public acquisition of hazardous 

areas; other planning techniques such as regulating 

development or posting warnings in potentially hazardous areas are obvious and practical but require consistent enforcement. Other techniques successfully used in 

reducing landslide, flood, windstorm, and soil hazards 

could be applied to earthquakes. These techniques and 

others listed on p. 10 may be used in a variety of combinations to help reduce earthquake hazards. 

Preparing Development Studies 

·and Plans 

Although earthquake damage is inevitable in the Los Wise planning and development involve selecting the 

Angeles region, it can be reduced by adopting strategies best possible location, density, and arrangement of land 

8 Earthquake Hazards in the Los Angeles Region 
uses to minimize exposure to earthquake hazards and 

thus reduce earthquake damage. Such planning may include project reviews, environmental assessments, and 

appraisals of existing hazardous buildings, transportation networks, utility systems, and critical facilities and 

their relation to zones of potential surface faulting or 

ground failure. Land-use development based on sound 

information about earthquake hazards and implemented 

over an extended period of time can be among the most 

effective measures for saving lives and minimizing 

disruptions in case of an earthquake (U.S. Office of 

Science and Technology Policy, 1978, p. 54). Responsibility and authority for preparing and implementing 

land use or development plans are usually assigned to 

city and county governments, but State agencies and 

private corporations have key responsibilities. 

Designing and Building Safe Structures 

Modern experience with earthquakes in urban areas 

shows that properly designed and constructed facilities 

can withstand nearby large earthquakes. Thus, one of 

the most effective ways to reduce the loss of life and 

property from earthquakes is to ensure that appropriate 

engineering design and material standards are followed 

when structures are erected. More restrictive design 

standards generally result in a nominal increase in construction costs; in many instances, however, a better 

design of the building layout or configuration may be 

achieved at no additional cost and in some situations 

may actually save money (U.S. Office of Science and 

Technology Policy, 1978, p. 37). 

Careful supervision of construction is very important, 

because the best earthquake-resistant design can be 

compromised by poor construction practices. Some complex forms of design and construction require special 

training or expertise for local building officials. 

Discouraging New or Removing 

Existing Hazardous Development 

Economical methods of reducing earthquake losses include discouraging development in potentially hazardous areas by means of public-information programs, 

posted warnings, public recording of the hazard, special 

assessments, tax credits, lenders' policies, publicfacility service-area policies, and disclosure to realestate buyers. Historically, financial institutions have 

funded projects in areas known to be hazardous, developers have built on them, and people have occupied 

them. Sometimes, rebuilding in the same manner and in 

the same location will immediately follow a disaster, and 

government loans or other subsidies may even be used. 

Therefore, government funding incentives or disincentives can be important techniques for discouraging such 

development. 

Removal of unsafe structures is sometimes the most 

effective safety measure. According to the Executive Office of the President (1978, p. 12), "Most deaths and injuries in earthquakes have been caused by collapsing 

buildings-generally older buildings and often those 

made of unreinforced masonry, although some modern 

buildings are also vulnerable. The public's vulnerability 

to earthquakes over the coming years will be dominated 

by these existing hazardous structures." 

Regulating Development 

It is costly and difficult to retrofit, strengthen, 

remove, or convert existing structures, and it is 

unrealistic to assume that all future development in exceptionally hazardous .areas can be discouraged. Thus, 

regulating development in areas susceptible to earthquake damage may be a more efficient and economical 

way to avoid earthquake hazards and reduce damage. 

Cities and counties have the authority to prepare and 

implement land use and development plans in their jurisdictions. The adoption and administration of city or 

county zoning, subdivision, building, hea"lth, and safety 

ordinances are authorized or, in some cases, required 

by the California Legislature. The Field and Garrison 

acts, for example, are statewide laws passed in 1933 

and 1939, respectively, requiring earthquake-resistant 

design, construction, and examination of certain public 

school buildings. Numerous programs underway at the 

local level include plans for strengthening or removing 

existing unsafe buildings. 

Preparing for and 

Responding to Disasters 

Preparedness and response planning for anticipated 

emergencies enable an impacted area to better cope 

with any disaster and hence to reduce hazards and 

damage. Comprehensive plans for dealing with the effects of large earthquakes are particularly important 

because such events are different from other disasters 

Introduction 9 
Some opportunities for using geologic and seismologic information to reduce 

earthquake hazards 

Preparing development studies and plans: 

Circulation or transportation studies and plans 

Community facility and utility inventories and plans 

Environmental impact assessments and reports 

Land use and open-space inventories and plans 

Land-subdivision lot layouts 

Multihazard risk analyses and reduction plans 

Redevelopment plans (preearthquake and postearthquake) 

Seismic- and public-safety plans 

Designing and building safe structures: 

Building strengthening or retrofitting 

Critical facility siting and design 

Engineering, geologic, and seismologic reports 

Public-facility and utility reconstruction or relocation 

Reconstruction after earthquakes 

Repair of dams 

Site-specific investigations and hazard evaluations 

Discouraging new or removing existing hazardous development: 

Capital-improvements expenditures 

Costs of nonsubsidized insurance 

Disclosure of hazards to real-estate buyers 

Financial incentives and disincentives 

Policies of private lenders 

Posted warnings of potential hazards 

Public acquisitions of hazardous areas 

Public-facility- and utility-service area policies 

Public information and education 

Public records of hazards 

Removal of unsafe structures 

Special assessments and tax credits 

Regulating development: 

Building and grading ordinances 

Design and construction regulations 

Hazard-zone investigations 

Land use zoning districts and setback requirements 

Special hazard-reduction ordinances 

Subdivision ordinances 

Preparing for and responding to disasters: 

Anticipating damage to critical facilities 

Damage inspection, repair, and recovery procedures 

Disaster training exercises 

Earthquake prediction response plans 

Earthquake preparedness plans 

Emergency response plans . 

Monitoring and warning systems 

Personal preparedness actions 

in that they are infrequent, usually unpredicted, and 

potentially catastrophic. Planning currently being done 

for the Los Angeles region under the Southern California Earthquake Preparedness Project is an excellent 

example of the complex efforts necessary to set up an 

earthquake preparedness and response system. 

Personal preparedness applicable to the home, 

school, and place of work is a very important phase of 

what should be an unbroken chain of tasks extending 

from long-term mitigation before an earthquake through 

response during an earthquake to recovery and 

10 Earthquake Hazards in the Los Angeles Region 

reconstruction after an earthquake (Kockelman, 1984). 

The last chapter in this volume discusses several 

techniques that may be used to reduce earthquake 

hazards. Many of the opportunities presented in the list 

on p. 10 have also been discussed by the U.S. Office 

of Science and Technology Policy (1978, p. 20-67), the 

California Legislature Joint Committee on Seismic Safety 

(1974, p. 45-180) and Blair and Spangle (1979, p. 67-78). 

Adequate geologic and seismologic information, similar 

to that discussed in the following chapters, is a prerequisite for the effective use of these opportunities. 
USERS OF INFORMATION FOR 

REDUCING EARTHQUAKE 

HAZARDS 

Opportunities and responsibilities for reducing earthquake hazards reside in all segments of society. Actual 

and potential users of earthquake-hazard information 

such as that contained in this volurrie include many people at community, State, and national levels, both public 

and private. Some potential users are shown in the list 

on p, 12 under various general headings. Users also 

include scientists and engineers who use the information to resolve scientific or technical questions, planners 

and decisionmakers who must consider hazards in the 

context of other land use "apd development criteria, and 

interested citizens who must consider the likelihood of 

future earthquakes before making personal decisions. 

Various levels of government, business, industry, and 

the services sector, voluntary organizations, professional societies, and special-interest groups play important roles in reducing earthquake hazards. Their 

contributions have been discussed in reports prepared 

by the U.S. Office of Science and Technology Policy 

(1978) and the California Legislature Joint Committee 

on Seismic Safety (1974). Blair and Spangle's (1979) 

report describing the governmental framework for 

reducing earthquake risk places special emphasis on 

California State agencies, programs, and mandates to 

local government. 

City, County, and 

Areawide Government Users 

City and county governments are empowered and 

obligated to provide for the public health, safety, and 

welfare of their citizens and are required by the California Legislature (1971) to prepare seismic-safety plans. 

The adoption and administration of city and county zoning, subdivision, building, grading, and safety ordinances are authorized or required by the California 

Legislature under various sections of the California 

Government and the Health and Safety codes. Because 

the principal governmental resource at the site of a 

disaster is usually the local government, local government agencies will of necessity be heavily involved in 

taking preventive actions as well as in coordinating onthe-scene response to and recovery from disasters. 

Local government will continue to be the primary agent 

for direct action in resolving seismic-safety problems 

(California Legislature Joint Committee on Seismic Safety, 1974, p. 31). Seismic safety can also be an integral 

part of the functions, programs, and plans of areawide 

agencies, such as the Southern California Association of 

Governments, and the various public-utility and school 

districts. 

Federal Government Users 

• The Federal Government plays a crucial role in 

stimulating State and local governments to develop and 

improve their seismic-safety policies. Many direct 

Federal efforts to reduce risks have evolved from a national commitment to provide disaster relief to States 

and localities devastated by earthquakes. Federal agencies are also responsible for the seismic safety of their 

own facilities. In addition, the U.S. Government, through 

the Federal Emergency Management Agency (which 

leads the National Earthquake Hazards Reduction Program), formulates plans for national actions in response 

to catastrophic earthquakes (Schnell and Herd, 1984). 

These plans include large-scale preparedness for, response to, and recovery from major damage or loss of 

life and also may include search, rescue, and evacuation, provision for medical care, food, and shelter, police 

protection, and other emergency help. 

State Government Users 

The State of California has the ultimate non-Federal 

public responsibility for the health, safety, and welfare 

of its people. State agencies incorporate their own 

seismic-safety standards into their operations and also 

work with local governments to encourage community 

seismic-safety efforts. Officials in almost every California State government agency need to consider seismic 

safety in carrying out their duties. Blair and Spangle 

(1979, p. 24) note that the "location and construction of 

public facilities, management of State lands, provision of 

services, and delegation of powers and responsibilities 

to local governments should all reflect an awareness 

that damaging earthquakes are inevitable." 

The California Legislature has led the way in defining 

and coordinating the State's role in reducing seismic 

risk. Passing the Field and Riley acts, creating the 

Seismic Safety Commission, requiring a seismic-safety 

plan for each city and county, and passing the AlquistPriolo Act requiring special studies in areas of potential 

surface fault rupture are some examples of the Legislature's seismic-safety actions. 

Other National Users 

Voluntary organizations (which provide aid to victims 

of disasters), national institutes, and scientific and 

Introduction 11 
Some potential users of geologic and seismologic information for reducing 

earthquake hazards in the Los Angeles region 

City, county, and areawide government users: 

Building, engineering, planning, and safety departments 

County boards of supervisors 

Mayors and city council members 

Multicity and multicounty planning, development, and preparedness agencies 

Offices of emergency services ~ 

Police, fire, and sheriffs departments 

Public works departments 

School districts 

Southern California Association of Governments 

Southern California Earthquake Preparedness Project 

State government users: 

Building Standards Commission 

Coastal Commission 

Department of General Services 

Department of Housing and Community Development 

Department of Insurance 

Department of Real Estate 

Department of Transportation 

Department of Water Resources 

Division of Mines and Geology 

Earthquake Prediction Evaluation Council 

Governor's earthquake safety councils and task forces 

Legislature and legislative committees 

Mining and Geology Board 

National Guard 

Office of Emergency Services 

Office of Planning and Research 

Office of the State Architect 

Public Utilities Commission 

Seismic Safety Commission 

Federal Government users: 

Army Corps of Engineers 

Bureau of Land Management 

Bureau of Reclamation 

Congress and congressional staffs 

Department of Housing and Urban Development 

Department of Interior 

Department of Transportation 

Environmental Protection Agency 

Farmers Home Administration 

Federal Emergency Management Agency 

Federal Housing Administration 

Federal Insurance Administration 

Federal Power Commission 

Forest Service 

General Services Administration 

National Bureau of Standards 

National Oceanic and Atmospheric Administration 

Nuclear Regulatory Commission 

Small Business Administration 

Other national users: 

Applied Technology Council 

American Association of State Highway and Transportation Officials 

American Public Works Association 

American Red Cross 

Association of Engineering Geologists 

Association of State Geologists 

Earthquake Engineering Research Institute 

International Conference of Building Officials 

National associations of cities, counties, and states 

12 Earthquake Hazards in the Los Angeles Region 
Other national users-Continued 

National Association of Insurance Commissioners 

National Institute of Building Sciences 

Natural Hazards Research and Applications Center 

Professional and scientific societies (including geological, engineering, architectural, and 

planning societies) 

Private and quasi-public users: 

Civic and voluntary groups 

Communication and transportation industries 

Concerned citizens 

Construction companies 

Consulting planners, geologists, architects, and engineers 

Extractive, manufacturing, and processing industries 

Financial and insurance institutions 

Landowners, developers, and real-estate salespersons 

Structural Engineers Association of California 

Utility companies 

University departments (including geology, civil engineering, architecture, urban and regional 

planning, and environmental studies departments). 

professional organizations make major and significant 

contributions to seismic safety. Research workers from 

many disciplines, including seismology, geology, earthquake engineering, and the social sciences, play a major 

role in reducing earthquake hazards by helping local, 

State, and Federal planners and decisionmakers formulate and evaluate their plans, programs, and procedures. Experts from the research community, for example, provide technical advice to special advisory 

groups that prepare model building codes. Scientific and 

professional organizations are major contributors to the 

worldwide exchange of information through publications and technical meetings. 

Private and Quasi-Public Users 

The private (including corporate) sector exercises 

perhaps the strongest influence on engineering design 

and land development in the United States. In choosing 

where to locate and how to construct facilities, industrial and commercial developers are sensitive to tax and 

other incentives offered by State and local governments, 

to favorable labor and retail markets, to transportation 

networks, and to terrain and water-resource conditions. 

Often, natural hazards are not weighted heavily in these 

development considerations unless they are likely to affect the facilities within their amortized lifetime or 

period of ownership. According to the Executive Office 

of the President (1978, p. 29): 

Business, industry, and the services sector play 

the lead roles in constructing new buildings and 

in developing land. Seismic design provisions in 

local codes ... are minimum standards. 

Thoughtful businessmen interested in providing 

a safe environment for their consumers and 

employees, and in protecting their capital investment will want to give careful consideration to 

earthquake hazq.rds in planning, constructing 

and maintaining their facilities . . . . In some 

instances short-term profits may be reduced to 

increase the long-term benefits of saving lives, 

reducing property damage, and maintaining the 

functioning of the economy in the face of a major 

earthquake. Private financial institutions, including lending agencies and insurance companies, must continue their important role. 

The effective use of geologic and seismologic information to avoid damage or to reduce loss requires a considerable effort on the part of both the producers and 

the users of the information. Unless· scientific and 

engineering results are specifically tailored, the effective user community is limited to other geologists, seismologists, and engineers. If users do not become proficient in interpreting and applying technical information, 

the information is likely to be misused or even neglected 

in the decisionmaking process. Studies by Kockelman 

(1975, 1976, 1979) on the use of earth-science information by city, county, and regional planners and decisionmakers in the San Francisco Bay region showed that the 

most effective use of hazard information was achieved 

when maps that clearly depicted the location, susceptibility, and severity of the hazards were provided. Furthermore, hazard reduction was more likely when agencies had geologists or engineers on their staffs. Their 

skills permitted a broader use of the technical materials, 

and agencies were able to make interpretations from the 

information for their own purposes. 

LOOKING TOWARD THE FUTURE 

The research results summarized in this volume 

demonstrate the progress that earth scientists have 

Introduction 13 
made in predicting the location and severity of the 

potentially destructive geologic and seismologic effects 

of future earthquakes in the Los Angeles region. These 

results, however, do not represent the final word in 

characterizing such effects. Further improvements can 

be expected as a more detailed earth-science data base 

for the region is developed and as predictive methods 

are tested and refined. 

A comprehensive geologic data base is the most 

crucial prerequisite for improving evaluations of earthquake hazard potential. Essential components of such a 

data base would include (1) detailed geologic maps that 

emphasize late Quaternary deposits, (2) measurements 

of the geotechnical and hydrologic properties of those 

deposits throughout the major alluvial basins, and (3) information on slope steepness and strength of geologic 

materials in upland areas. These data at present are 

variably incomplete for the Los Angeles region. The 

hazard potential maps used in this volume are chiefly at 

scales of 1:250,000 (1 in. ""4 mi) or smaller. More detailed characterizations-for example, at 1:24,000 scale 

(1 in. ""2,000 ft) - are desirable for many hazard reduction activities, but, for much of the Los Angeles region, 

the basic geologic data have not yet been acquired in the 

detail that permits mapping potentially hazardous conditions at large scales. Furthermore, improved estimates 

of fault slip rates, which are vital to assessing the earthquake potential, must await detailed analysis of geologic 

relations along the numerous potentially active faults of 

the region. Acquisition of geologic and geotechnical information such as that described here requires a sustained effort over a considerable time. 

Differing scientific opinions about the prediction of 

earthquake ground motion also need to be resolved. The 

influence of geologic conditions on ground shaking, in 

particular, is incompletely understood (in this volume, 

for example, compare the views of Evernden and Thomson with those of Rogers and others concerning the effect of water-saturated alluvium on expected levels of 

shaking). A technical question deserving further investigation is what percentage-loss factors are appropriate in applying the intensity prediction method of 

Evernden and Thomson to estimating future earthquake 

losses. These topics are among the many scientific and 

technical issues that need additional study before 

estimates of the potential hazards and losses from 

future earthquakes in the Los Angeles region can be improved. 

14 Earthquake Hazards in the Los Angeles Region 

Even though many of the results reported here 

are preliminary and further research is still needed, the 

methods described can be applied to evaluating and 

mapping similar hazards in other earthquake-prone 

regions of the United States. The challenge now is to ensure that these techniques are used where they are 

needed, that the resulting scientific products are 

disseminated to planners and engineers, and that decisionmakers at all levels of government and in the private 

sector take this information into account in selecting 

ways to reduce earthquake hazards. 

Acknowledgments 

We gratefully acknowledge the many helpful comments of Robert D. Brown, Jr., and Robert L. Wesson, 

both of the U.S. Geological Survey, who reviewed an 

earlier manuscript of Professional Paper 1360. Their 

suggestions concerning the scope and content of the subject material significantly improved this volume. 

A report of this size and complexity requires a major 

editorial and graphics preparation effort by the Office of 

Scientific Publications of the U.S. Geological Survey. 

Special thanks go to Kathie R. Fraser, the technical editor 

of this volume, for expertly coordinating the processing 

and production of the report at a continent's distance 

from the authors. She was especially adept in helping the 

scientists communicate their concepts to a broader audience. We also acknowledge the contributions of the 

graphics units in Reston, Va., and Menlo Park, Calif., for 

helping produce carefully crafted illustrations. 

The following illustrations have been used to introduce the principal topical headings: Earthquake and 

Surface-Faulting Sources, a photograph by A. T. F. Chen 

(U.S.Geological Survey) of surface faulting from the 1971 

San Fernando earthquake; Earthquake Ground Motion, 

an aerial photograph from Newsweek magazine of 

damage to the Veterans Hospital in 1971; EarthquakeTriggered Ground Failure, a 1971 aerial photograph of 

the damaged Van Norman Dam, by R. H. Gordon 

(Gordon Air Photo); Earthquake-Related Phenomena Offshore, a portion of an orthographic drawing by T. R. 

Alpha (U.S. Geological Survey); Applications, a portion of 

a map by the California Division of Mines and Geology. 
GLOSSARY 

[Terms set in bold type are defined elsewhere in the glossary] 

Acceleration. The time rate of change of velocity of a reference point during an earthquake. Commonly 

expressed in percentage of gravity (g, equal to 980 cm/s2). 

Accelerogram. The record from an accelerograph showing ground acceleration as a function of time. 

Accelerograph. A compact, rugged, and relatively inexpensive instrument that records the signal from 

an accelerometer. Film is the most common recording medium. 

Accelerometer. A sensor whose output is almost directly proportional to ground acceleration. The conventional strong motion accelerometer is a simple, nearly critically damped oscillator having a 

natural frequency near 20 Hz. 

Acoustic reflection profiling. Method using sound waves to map geologic features on and beneath the 

sea floor. A pulse of sound is transmitted downward through the water from a ship-mounted or towed 

acoustic source. The acoustic energy reflected from the sea floor and from the interfaces between 

distinctive underlying geologic units is recorded by the survey vessel. Continuous profiles show a 

cross section of acoustically distinct units plotted as a function of acoustic-wave traveltime beneath 

the ocean surface and of distance along the survey track. 

Active fault. A fault that is considered likely to undergo renewed movement within a period of concern to 

humans. 

Aftershocks. Secondary tremors that may follow the largest or main shock of an earthquake sequence. 

Such tremors can extend over a period of weeks, months, or years. 

Alluvium. Loosely compacted gravel, sand, silt, or clay deposited by streams. 

Amplification. An increase in seismic signal amplitude within some range of frequency as waves propagate through different Earth materials. The amplitude may be decreased in another frequency band. 

Amplitude. Zero-to-peak value of any wavelike disturbance. 

Angle of internal friction. A measure of the shear strength of rock or sediment related to the intrinsic 

frictional resistance on a potential shear fracture. 

Anticline. A upwardly convex fold in originally planar sedimentary rocks. Commonly adjacent to a 

syncline, a fold that is downwardly convex. 

Arias intensity. A ground-motion parameter derived from an accelerogram and proportional to the integral over time of the acceleration squared. Expressed in units of velocity (meters per second or centimeters per second). 

Artesian. Refers to ground water confined under pressure greater than that produced by water table 

conditions. 

Aquiclude. A body of relatively impermeable rock or sediment that impedes the flow of ground water. 

Aquifer. A water-bearing body of porous and permeable rock or sediment. 

Attenuation. A decrease in seismic signal amplitude as waves propagate from the seismic source. Attenuation is caused by geometrical spreading of seismic wave energy and by the absorption and scattering of seismic energy in different Earth materials. 

B horizon. Soil horizon characterized by the accumulation of clay minerals, iron compounds, and (or) 

calcium carbonate. Commonly reddish colored. 

Bandpass. Refers to a range (or band) of frequencies passed by a filtering operation that suppresses 

other frequencies. 

Basement. Igneous and metamorphic rocks that underlie the main sedimentary rock sequences of a 

region and extend downward to the base of the crust. 

Bedrock. Relatively hard, solid rock that commonly underlies softer rock, sediment, or soil. 

Glossary 15 
Body wave. Seismic wave propagated in the interior of the Earth. P and S waves are examples. 

Bulk density. The weight of a material divided by its volume, including the volume of its pore spaces. 

Clast. Fragment of rock produced by mechanical weathering of older materials. 

Cluster analysis. A procedure for arranging data into homogeneous subgroups based on their mutual 

similarities and hierarchical relations. 

Coherent slides. Landslides that consist of a few relatively intact blocks of rock or soil that move 

together. The basal failure surface of most such slides is several meters or tens of meters below the 

land surface. 

Cohesionless. Refers to a sediment whose shear strength depends only on friction, because there is no 

bonding between the grains. Typical of clay-free sandy deposits. 

Colluvium. Loose soil or rock fragments on or at the base of gentle s'lopes or hillsides. Deposited by or 

moving under the influence of rainwash or downhill creep. 

Compressional wave. See P wave. 

Convolution.A mathematical operation describing the interaction of two functions, such as a signal and a 

filter, that may result in a change of wave shape. 

Corner frequency. That frequency at which the curve representing the Fourier amplitude spectrum of a 

recorded seismic signal abruptly changes slope. 

Creep. Slow, more or less continuous movement that may occur either along faults owing to ongoing tectonic deformation or along slopes owing to gravitational forces. 

Critical acceleration (Acl· The minimum value of ground acceleration required to overcome the resistance 

of a particular slope to earthquake-induced sliding. 

Critical displacement (Ucl· The minimum ground displacement required if a slope is to continue sliding 

after seismic shaking stops. In this volume, the assigned values are 10 em for coherent slides and 

2 em for disrupted slides and falls. 

Critical facilities. Structures whose ongoing performance during an emergency is required or whose 

failure could threaten many lives. May include (1) structures such as nuclear power reactors or large 

dams whose failure might be catastrophic; (2) major communication, utility, and transportation 

systems; (3) involuntary- or high-occupancy buildings such as prisons or schools; and (4) emergency 

facilities such as hospitals, police and fire stations, and disaster-response centers. 

Crust. The outermost major layer of the Earth, ranging from 10 to 65 km in thickness worldwide and 

about 20 km thick in coastal California and characterized by P wave velocities less than about 8 km/s. 

Damping. The reduction in amplitude of an oscillation owing to absorption of energy within a material. 

See also Geometrical attenuation. 

Design earthquake. The postulated earthquake (commonly including a specification of the ground motion 

at a site) that is used for evaluating the earthquake resistance of a particular structure. 

Dip. Inclination of a planar geologic surface (for example, a fault or a bed) from the horizontal. 

Directivity. An effect of a propagating fault rupture whereby earthquake ground motion in the direction 

of propagation is more severe than that in other directions from the earthquake source. 

Displacement. The difference between the initial position of a reference point and any later position. (1) 

In seismology, displacement is usually calculated by integrating an accelerogram twice with respect 

to time and is expressed in centimeters. (2) In geology, displacement is the permanent offset of a 

geologic or manmade reference point along a fault or a landslide. 

Disrupted slides and falls. Landslides that are broken during movement into chaotic masses of small 

blocks, rock fragments, or individual grains. The basal failure surface of most such slides is within a 

few meters of the land surface. 

Earthquake hazard. Any physical phenomenon associated with an earthquake that may produce adverse 

effects on human activities. 

Effective stress. The average stress transmitted directly from particle to particle of a rock or sediment 

mass that controls how the mass deforms. Effective stress perpendicular to an arbitrary surface in a 

saturated porous material is the difference between the applied normal stress and the pore-water 

pressure. 

16 Earthquake Hazards in the Los Angeles Region 
Elastic dislocation theory. In seismology, a theoretical description of how an elastic Earth responds to 

fault slip, as represented by a distribution of displacement discontinuities. 

Epicenter. The point on the Earth's surface vertically above the point (focus or hypocenter) in the crust 

where a seismic rupture initiates. 

Fault. A fracture along which there has been significant displacement of the two sides relative to each 

other parallel to the fracture. Strike-slip faults are chiefly vertical fractures along which rock 

masses have shifted horizontally. Dip-slip faults are chiefly inclined fractures along which rock 

masses have shifted vertically. If the rock mass above an inclined fault is depressed, the fault is 

termed normal slip, whereas the term reverse slip (or thrust) indicates that the side above the fault is 

elevated. Oblique-slip faults have significant components of both strike and dip slip along them. 

Fault-plane solution. An analysis to determine the attitude of the causative fault and its direction of slip 

from the radiation pattern of seismic waves for an earthquake recorded at numerous stations. The 

analysis most commonly uses the direction of first motion of P waves and yields two possible orientations for the fault rupture and the direction of seismogenic slip. From these data, inferences can be 

made concerning the principal axes of stress in the region of the earthquake. 

Fault scarp. Steplike linear landform coincident with a fault trace. Caused by geologically recent offset 

of the land surface. 

Fault trace. Intersection of a fault with the ground surface; also, the line commonly plotted on geologic 

maps to represent a fault. 

Filter. In seismology, a physical system or a mathematical operation that changes the waveform or 

amplitude of a signal. 

Filtering. Attenuation of certain frequency components of a seismic signal and the amplification of 

others. For a recorded signal, the process can be accomplished electronically or numerically in a 

digital computer. Filtering also can occur naturally as seismic energy passes through the Earth. 

First motion. On a seismogram, the direction of ground motion as the P wave arrives at the seismometer. 

Upward ground motion indicates an expansion in the source region; downward motion indicates a 

contraction. 

Focal-mechanism solution. See Fault-plane solution. 

Focus. The point within the Earth where an earthquake rupture initiates. See also Hypocenter. 

Fourier amplitude spectrum. The relative amplitude at different component frequencies as derived from 

a time series by Fourier analysis. 

Fourier transform. The mathematical operation that resolves a time series (for example, a recording of 

ground motion) into functions showing the relative amplitude and phase components of the signal. 

Free field. Refers to ground motion measurements that are not influenced by manmade structures. 

Frequency. Number of cycles occurring in unit time. Hertz (Hz), the unit of frequency, is equal to the 

number of cycles per second. 

Fundamental period. The longest period for which a structure shows a maximum response. The 

reciprocal of natural frequency. 

Geodetic. Refers to the determination of the size and shape of the Earth and the precise location of points 

on its surface. 

Geometrical attenuation. That component of attenuation of seismic wave amplitudes owing to the radial 

spreading of seismic energy with distance from a given source. 

Geomorphology. The study of the character and origin oflandforms. 

Geotechnical. Refers to the use of scientific methods and engineering principles to acquire, interpret, 

and apply knowledge of Earth materials for solving engineering problems. 

Green's function. A mathematical entity that, in reference to earthquake shaking, is used to represent 

the ground motion caused by instantaneous slip on an individual part of a fault. 

Ground motion. General term referring to the qualitative or quantitative aspects of shaking of the Earth's 

surface from earthquakes or explosions. 

Glossary 17 
Ground response. See Ground motion. 

Halfspace. A mathematical model bounded by a planar surface but otherwise infinite. Properties within 

the model are commonly assumed to be homogeneous and isotropic, unlike the Earth itself, which is 

heterogeneous and anisotropic. 

Hertz (Hz). A unit of frequency. Expressed in cycles per second. 

Hydrostatic stress. The stress component in the Earth that is uniform in magnitude in all directions. 

Hypocenter. The point within the Earth where an earthquake rupture initiates. See also Focus. 

Intensity. A subjective numerical index describing the severity of an earthquake in terms of its effects on 

the Earth's surface and on humans and their structures. A condensed version of the Modified Mercalli intensity scale appears on the inside back cover of this volume. 

Isoseismal. A line on a map bounding points of equal intensity for a particular earthquake. 

Kinematic. Refers to the movement patterns that result in a particular deformation. 

Lateral spreads and flows. Landslides that commonly form on gentle slopes and that display rapid 

fluidlike flow movement. 

Least-squares fit. An approximation of a set of data having a curve such that the sum of the squares of 

the differences between the observed points and the curve is a minimum. 

Liquefaction. Process by which water-saturated sediment temporarily loses strength, usually because of 

strong shaking, and behaves as a fluid. 

Lithology. The description of rock composition and texture. 

Lithosphere. The outer solid portion of the Earth, including the crust and uppermost mantle. 

Love wave. A type of seismic surface wave having a horizontal motion that is transverse to the direction 

of propagation. 

Magnetic polarity reversal. A change of the Earth's magnetic field to the opposite polarity. Polarity 

reversals in sequences of magnetized rocks are detected by analysis and, when compared with 

standard polarity time scales, are used to estimate geologic ages. 

Magnitude. A number that characterizes the size of an earthquake, based on measurement of the maximum motions recorded by a seismograph for earthquake waves of a particular frequency. Scales 

most commonly used in the Western United States are (1) local magnitude (Md (commonly referred to 

as "Richter magnitude"), (2) surface-wave magnitude (M5), and (3) body-wave magnitude (mb). None 

of these scales satisfactorily measures the largest possible earthquakes because each relates to only 

certain frequencies of seismic waves and because the spectrum of radiated seismic energy changes 

with earthquake size. The recently devised moment magnitude (M) scale, based on the concept of 

seismic moment, is uniformly applicable to all sizes of earthquakes. 

Mantle. That part of the Earth's interior between the metallic core and the crust. 

Microzonation. Geographic delineation on a regional or local scale of areas having different potentials 

for hazardous effects of earthquakes (including geologic effects such as surface faulting, strong 

ground shaking, and ground failure). 

Newmark analysis. A numerical technique that models a potential landslide as a rigid friction block 

resting on a slope and uses a strqng-motion record to calculate the expected displacement of the 

block under earthquake shaking. 

Natural frequency(ies). The discrete frequency(ies) at which a particular elastic system vibrates when it 

is set in motion by a single impulse and not influenced by other external forces or by damping. The 

reciprocal of fundamental period. 

Normal stress. That stress component perpendicular to a given plane. 

Orthogonals. In oceanography, map lines constructed perpendicular to known or predicted wave fronts. 

Orthogonals are used to estimate the relative distribution of tsunami wave energy arriving at a coast 

line. 

Oscillation. The alternating motion or vibration of a reference point. 

Oscillator. A mass that undergoes alternating motion. In earthquake engineering, an idealized massspring system that is used as a model of the response of a structure to earthquake ground motion. 

P wave. A seismic body wave that involves particle motion (alternating compression and extension) in the 

direction of propagation. 

18 Earthquake Hazards in the Los Angeles Region 
Peak value. Largest value of acceleration, velocity, or displacement recorded for a particular earthquake time-history. 

Pedogenic. Pertaining to processes that add, transfer, transform, or remove soil constituents. 

Perched ground water. Ground water separated from the underlying main body of ground water by an 

unsaturated zone. 

Period. The time interval required for one full cycle of a wave. 

Period band. That range of periods being considered in an analysis of ground motion. 

Permeability. A measure of the ability of fluid to pass through the pore spaces of a rock or sediment. 

Phase. (1) A stage in periodic motion, such as oscillation, measured with respect to a given initial point 

and expressed in angular measure. (2) A pulse of seismic energy arriving at a definite time. 

Physiographic. Refers to the character and distribution of landforms. 

Plate tectonics. A well-proven theory that considers the Earth's crust and upper mantle to be composed 

of a number of large, thin, relatively rigid plates that move relative to one another. Interaction along 

their boundaries commonly results in earthquake and volcanic activity. 

Poisson distribution. A probability distribution that characterizes discrete events occurring independently of one another in time. 

Pore-water pressure. Stress transmitted by the water filling the voids of rock or sediment. 

Pseudoacceleration response. The product of the relative displacement response and the square of the 

angular frequency of an oscillator. 

Pseudovelocity response. The product of the relative displacement response and the angular frequency 

of an oscillator. 

Quasi-harmonic decomposition. Technique whereby the filtering of a seismogram results in a sequence 

of narrow-band seismograms that are used to estimate the time pattern of individually arriving P 

wave pulses. 

Radiometric. Pertaining to the measurement of geologic time by the analysis of certain radioisotopes in 

rocks and their known rates of decay. 

Rayleigh wave. A seismic surface wave causing an elliptical motion of a particle at the free surface, with 

no transverse motion. 

Recurrence interval. The average time span between events (such as large earthquakes, ground shaking 

exceeding a particular value, or liquefaction) at a particular site. 

Reflection. The energy or wave from a seismic source that has been returned (reflected) from an interface between materials of different elastic properties within the Earth. 

Reflector. An interface between materials of different elastic properties that reflects seismic waves. 

Refraction. (1) The deflection of the ray path of a seismic wave caused by its passage from one material 

to another having different elastic properties. (2) Bending of a tsunami wave front owing to variations 

in the water depth along a coast line. 

Refraction diagram. Map of the time-dependent positions of known or predicted tsunami wave fronts. 

Regression analysis. A statistical technique applied to data to determine, for predictive purposes, the 

degree of correlation of a dependent variable with one or more independent variables. 

Relaxation theory. Concept wherein radiated seismic waves of an earthquake result when stored strain 

within the Earth is released at the time of slip along a fault; adjacent fault blocks reach new states of 

equilibrium. 

Rigidity. See Shear modulus. 

Residual. The difference between the measured and the predicted values of some quantity. 

Resonance. An increase in the amplitude of vibration in a body when the frequency(ies) of the shaking 

force is close to the natural frequency(ies) of a shaking body. 

Response. The motion in a system resulting from shaking under specified conditions. 

Response spectrum. A curve showing the response of a series of simple harmonic oscillators of different 

natural frequency(ies) subjected mathematically to a particular earthquake ground motion. 

Response spectra, commonly plotted on tripartite logarithmic graph paper, show the variation of 

spectral acceleration, displacement, and velocity of the oscillators as a function of vibration frequency and for various levels of damping. 

Glossary 19 
Return period. See Recurrence interval. 

Root mean square. Square root of the mean square value of a random variable. 

Rupture front. The instantaneous boundary between the slipping and unslipped parts of a fault during 

an earthquake. 

Rupture velocity. The speed at which a rupture front propagates during an earthquake. 

S wave. A seismic body wave that involves a shearing motion in a direction perpendicular to the direction of propagation. When it is resolved into two orthogonal components in the plane perpendicular 

to the direction of propagation, SH denotes the horizontal component and SV denotes the orthogonal 

component. 

Sag pond. A small enclosed depression commonly filled with water; formed where recent faulting of the 

land surface has impounded drainage. 

Sand boil. Sand and water ejected to the ground surface as the result of liquefaction at shallow depth; 

the conical sediment deposit that remains as evidence of liquefaction. 

Saturation. (1) In seismology, the leveling off of ground-motion parameters with increasing earthquake 

magnitude. (2) In hydrogeology, the degree to which the pores of a sediment or rock are filled with 

water. 

Seiche. Oscillation of the surface of an enclosed body of water owing to earthquake shaking. 

Seismic hazard. See Earthquake hazard. 

Seismic impedance. Seismic P wave velocity multiplied by the bulk density of a medium. 

Seismic wave. An elastic wave generated by an impulse such as an earthquake or an explosion. Seismic 

waves may propagate either along or near the Earth's surface (for example, Rayleigh and Love 

waves) or through the Earth's interior (P and S waves). 

Seismicity. The geographic and historical distribution of earthquakes. 

Seismic moment. A measure of the size of an earthquake based on the area of fault rupture, the average 

amount of slip, and the shear modulus of the rocks offset by faulting. Seismic moment can be calculated from the amplitude of long-period seismic waves. 

Seismic risk. The probability of social or economic consequences of an earthquake. 

Seismic zonation. Geographic delineation of areas having different potentials for hazardous effects from 

future earthquakes. Seismic zonation can be done at national, regional, and local scales. See also 

Microzonation. 

Seismogenic. Capable of generating earthquakes. 

Seismogram. A record of ground motion or of vibrations of a structure caused by an earthquake or an 

explosion. 

Seismograph. An instrument system for amplifying and recording the signals from seismometers. 

Seismometer. The sensor or instrument used to detect seismic wave energy and to transform it into an 

electrical voltage. 

Separation. The distance between any two parts of a reference plane (for example, a sedimentary bed or 

a geomorphic surface) offset by a fault, measured in any plane. Separation is the apparent amount of 

fault displacement and is nearly always less than the actual slip. 

Shear modulus. The ratio of shear stress to shear strain of a material during simple shear. 

Shear stress. That stress component giving rise to tangential force across a given plane. 

Shear wave. See S wave. 

Slip. The relative displacement of formerly adjacent points on opposite sides of a fault, measured in the 

fault surface. 

Slip model. A kinematic model that describes the amount,. distribution, and timing of slip associated with 

a real or postulated earthquake. 

Slip rate. The average rate of displacement at a point along a fault as determined from geodetic 

measurements, from offset manmade structures, or from offset geologic features whose age can be 

estimated. It is measured parallel to the dominant slip direction or estimated from the vertical or 

horizontal separation of geologic markers. 

20 Earthquake Hazards in the Los Angeles Region 
Soil. (1) In engineering, all unconsolidated material above bedrock. (2) In soil science, naturally occurring 

layers of mineral and (or) organic constituents that differ from the underlying parent material in 

their physical, chemical, mineralogic, and morphologic character because of pedogenic processes. 

Soil profile. The vertical arrangement of soil horizons down to the parent material. Commonly subdivided 

into A, B, and C horizons. 

Source. (1) The geologic structure that generates a particular earthquake. (2) The explosion used to 

generate acoustic or seismic waves. 

Spectral amplification. A measure of the relative shaking response of different geologic materials. The 

ratio of the Fourier amplitude spectrum of a seismogram recorded on one material to that computed 

from a seismogram recorded on another material for the same earthquake or explosion. 

Spectral ratio. See Spectral amplification. 

Spectrum. The distribution or range of values of a characteristic of a physical system. In seismology, 

commonly a curve showing amplitude and phase as a function of frequency or period. 

Standard deviation. The square root of the average of the squares of deviations about the mean of a set 

of data. Standard deviation is a statistical measure of spread or variability. 

Standard penetration resistance. A measure of relative density expressed by the number of blows (blow 

count) needed to push a probe a standard distance into sediment. The "standard penetration test" 

determines the number of blows required to drive a standard sampling spoon 1 ft into the sediment by 

repeatedly dropping a 140-lb weight from a height of 30 in. 

Station. A ground position at which a geophysical instrument is located for an observation. 

Strain. The percentage of change in the length, shape, or volume of a body subjected to deformation. 

Stratigraphy. The study of the character, form, and sequence of layered rocks. 

Stress. Force per unit area acting on a surface within a body. Six values are required to characterize 

completely the stress at a point: three normal components and three shear components. 

Stress drop. The difference between the stress across a fault before and after an earthquake. 

Strike. Trend or bearing, in relation to north, of the line defined by the intersection of a planar geologic 

surface (for example, a fault or a bed) and a horizontal surface. 

Strong motion. Ground motion of sufficient amplitude and duration to be potentially damaging to 

engineered structures. 

Subduction. In plate tectonics, the process whereby one plate of the lithosphere descends beneath 

another. 

Subsidence. Downward settling of the Earth's surface with little or no horizontal motion. May be caused 

by natural geologic processes (such as sediment compaction or tectonic activity) or by human activity 

(such as mining or withdrawal of ground water or petroleum). 

Surface faulting. Displacement that reaches the ground (or sea floor) surface during slip along a fault. 

Commonly accompanying moderate and large earthquakes having focal depths to 20/ km, surface 

faulting also may accompany aseismic tectonic creep or natural or man-induced subsidence. 

Surface wave. Seismic wave that propagates along the Earth's surface. Love and Rayleigh waves are 

examples. 

Tectonic. Refers to crustal rock-deforming processes that affect relatively large areas. 

Thixotropic. Refers to the ability of certain colloidal materials, such as some clays, to weaken or change 

structure when shaken but to regain strength with time. 

Time-history. The sequence of values of any quantity (such as a ground-motion parameter) during the 

time span of an event. 

Time series. See Time-history. 

Transform fault. A special variety of strike-slip fault along which the displacement changes form or 

stops. Commonly connects oceanic spreading ridges and subduction zones. 

Traveltime curve. A graph of arrival times of P or S waves recorded at different points as a function of 

distance from the seismic source. Seismic velocities can be computed from the slopes of the resulting 

curve. 

Glossary 21 
Tsunami. An impulsively generated sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major sea-floor slides, or exploding volcanic 

islands. 

Tsunamigenic. Refers to those earthquake sources, usually along major subduction zone plate boundaries, such as those bordering the Pacific Ocean, that can generate tsunamis. 

Tsunami magnitude (Mt1· A number used to compare sizes of tsunamis generated by different earthquakes and calculated from the logarithm of the maximum amplitude of the tsunami wave measured 

by a tide gauge distant from the tsunami source. 

Velocity. The time rate of change of displacement of a reference point during an earthquake. Can be 

calculated by integrating an acceleration record once with respect to time. Expressed in centimeters 

per second. 

Velocity structure. A generalized regional model of the Earth's crust that represents crustal structure by 

layers having different assumed seismic velocities. 

Void ratio. The ratio of the volume of void space in a rock or sediment to the volume of solid material. 

Water table. The upper surface of a body of unconfined ground water at which the water pressure is 

equal to the atmospheric pressure. 

Wavelength. The distance between successive points of equal amplitude and phase on a wave (for example, crest to crest or trough to trough). 

22 Earthquake Hazards in the Los Angeles Region 
FACTORS FOR CONVERTING METRIC UNITS TO 

INCH-POUND UNITS 

Most quantitative information in this volume is given in the International System of Units (SI or metric), 

the measurement system commonly used by scientists. The inch-pound (English) units of measurement, 

however, may be more familiar to many readers. The following conversion table is for the convenience of 

those who prefer English units. 

Multiply SI unit By To obtain inch-pound unit 

Length 

millimeter (mm) 0.0394 inch (in) 

centimeter (em) .394 inch (in) 

meter (m) 3.28 foot (ft) 

kilometer (km) .62 mile (mi) Oand) 

kilometer (km) .54 mile (mi) (nautical) 

Area 

square meter (m2) 10.76 square foot (ft2) 

square kilometer (km2) .386 square mile (mi2) 

Volume 

cubic meter (m3) 35.31 cubic foot (ft3) 

cubic kilometer (km3) .24 cubic mile (mil) 

Density 

gram per cubic centimeter (g/cm 3) 62.43 pound per cubic foot Ob/ft3) 

Conversion Table 23 
Earthquake and SurfaceFaulting Sources 
GEOLOGIC AND SEISMOLOGIC SETTING 

By R. F. Yerkes 

INTRODUCTION 

This discussion of the geologic and seismologic setting 

of the Los Angeles region shows why and where earthquakes occur in that area. The basic framework for the 

discussion is the concept of plate tectonics, which 

relates many of the Earth's large-scale geologic processes to movement in marginal areas of relatively rigid 

crustal or lithospheric "plates" that are in slow, constant motion (5-10 cm/yr) relative to one another. One of 

these margins, the San Andreas fault system, forms the 

broad boundary between the Pacific (oceanic) and the 

North American (continental) plates and passes obliquely through coastal California. Because this boundary 

transects or borders several of the State's major metropolitan centers, it is one of the most extensively urbanized tectonic plate boundaries on Earth. 

We outline the evolution of coastal California in terms 

of plate tectonics and show how the Los Angeles region 

straddles the junction between two major active fault 

systems-the northwest-trending San Andreas and the 

east-trending Transverse Ranges-that are responding 

to present plate motions. We also describe the types of 

permanent deformation associated with movement 

along these faults and document the spatial and temporal distribution of historical damaging earthquakes 

associated with those movements. 

PLATE-TECTONIC EVOLUTION 

OF CALIFORNIA 

Plate tectonics, a global-scale process that has been 

going on for millions of years, involves relative movement of very large plates of the Earth's lithosphereblocks averaging about 100 km thick and thousands of 

kilometers across. Most seismic and volcanic activity is 

concentrated along boundaries between these plates. 

Three types of plate boundaries are recognized: 

spreading ridges, where oceanic plates are formed and 

spread laterally away from each other; transform 

faults, where plates slide horizontally past each other 

along strike-slip faults between spreading ridges; and 

subduction zones, where one plate (oceanic) dives 

beneath another. Tracing the history of the plates and 

their boundaries is a major component of modern geologic and seismologic studies (see, for example, Ernst 

(1981)). 

Figure 3 is an interpretive map of the California 

region and its relation to both ancient and present tectonic plates. The following general history is envisioned. 

The inactive subduction zone off central California and 

Baja California, Mexico, presumably was the boundary 

between the once-continuous Farallon oceanic plate and 

the North American continental plate (Dickinson, 1981). 

About 29 m.y ago, a portion of the Farallon plate disappeared by subduction, and an ancestral segment of the 

East Pacific Rise (a spreading ridge now bounding the 

Farallon remnants) first contacted the subduction zone. 

The complex interactions set up by this encounter led to 

the development of the San Andreas system of transform faults and subsequent attachment of the displaced 

coastal terrane to the Pacific plate (see Dickinson and 

Snyder (1979) for details). Before 5 m.y. ago, transform 

slip occurred on equivalent faults west of the modern 

San Andreas, some of which are now offshore. 

In plate-tectonic terms, all of California west of the 

San Andreas fault consists of' several pieces of crust 

that have been transported in a relatively northwestward direction along the boundary as part of the Pacific 

plate. In the part of California considered here, the 

latest phase of this process ended before late Miocene 

time more than 5 m.y. ago (see geologic time-scale chart, 

inside front cover). Since then; continuing deformation 

has caused chiefly reorientation, folding, and faulting of 

the many separate unrelated pieces or "miniplates" 

that make up the region. 

PRESENT PLATE-TECTONIC 

SETTING 

The present San Andreas system is the locus of 

relative motion between the North American and Pacific 

Geologic and Seismologic Setting 25 
• Seattle 

0 

I 

0 

I 

100 

100 

I 

I 

200 

/ /""" ' 

200 

I 

I 

300 

I 

400 

300 

I 

I 

400 MILES 

I 

500 KILOMETERS 

/ ' 

/ ""'' / ' / ' --------......... 

/ '... ~- ----------- / 

CALIFORNIA 

--....... '- San ........ ~ ---4----"'..., ..... ............... -._~ 

--, TR CONT. 

......... ........ _ _ _.,_ __ _._ 

PACIFIC OCEAN 

FIGURE 3.-Inferred relationships between San Andreas transform fault (SAF), Transverse Ranges (TR), and the Pacific and North American 

plates. Displacement on faults parallel to the long dimension of the map is parallel to the fault (strike slip); displacement on faults having other 

trends, such as reverse faults of the Transverse Ranges, is chiefly vertical (dip slip). The large arrow shows the motion of the Pacific plate 

relative to the North American plate (about 56 mm/yr averaged over last 5 m.y.). Vectors labeled "TR cont." indicate the inferred maximum 

contraction across the Transverse Ranges since the Gulf of California began opening about 5 m.y. B.P. Adapted from Atwater (1970), Dickinson and Snyder (1979), and Moore (1981). 

plates. The overall motion between these plates continues, perhaps at an accelerated rate; the average over 

the last 3 m.y. is at least 56 mm/yr in a right-lateral 

sense (Moore, 1981). The most recent estimate for 

average relative motion along the San Andreas zone 

north of the Tranverse Ranges is at least 33 mm/yr 

Cfhatcher, 1979); the 23-mm/yr difference presumably 

reflects both relative movement along other faults of the 

San Andreas system and associated folding and faulting 

within and along the boundaries of the Transverse 

Ranges. 

In southern California, the surface trace of the San 

Andreas itself may not represent the plate boundary at 

26 Earthquake Hazards in the Los Angeles Region 

depth. One hypothesis is that the subsurface plate 

boundary is deflected more than 100 km northeast of the 

surface trace opposite the Transverse Ranges (Yeats, 

1981). The deflection of the San Andreas-called the 

"big bend"-presumably is related to north-south contraction and east-west extension in the Transverse 

Ranges-Mojave Desert region. 

The techniques for dating geologic materials and 

modeling geologic processes that have been developed 

and applied over the last few decades show very clearly 

that southern California west of the San Andreas fault is 

geologically very young (although it locally contains very 

old rocks derived from elsewhere) and is at the "leading 

edge" of continent-forming processes. 
--4_ 

-.... ~ D --~--~ .... 

EXPLANATION 

Active transform fault 

• 4 Active subduction zone 

.._ __ ~ 

t 

9 

Inactive subduction zone 

Active spreading ridge 

North American plate 

Pacific plate 

Remnant of Farallon 

plate 

.... ....._ ___ _...._ _,, 

---4_ __ _._ __ _._ 

EFFECTS OF CONTINUING 

DEFORMATION 

The deformational processes now operating in 

southern California are dominated by the intersection of 

the San Andreas and the Transverse Ranges fault systems (fig. 4); the effects of this intersection are evident in 

the local scenery, such as the spectacular southern face 

of the San Gabriel Mountains overlooking the Los 

Angeles-San Bernardino metropolitan area (fig. 5), or in 

the occurrence of transitory events such as earthquakes. Although these fault systems are part of a longterm continuing process now at least 5 m.y. old, they are 

currently responding to strain related to motion of the 

Pacific and North American plates either by horizontal 

(right-lateral) slip (faulting and earthquakes) on faults of 

the San Andreas system or by vertical (reverse) slip on 

Transverse Ranges faults. The effects of this deformation include (1) mountain building caused by sporadic 

displacement along reverse faults (for example, as much 

as 2 m of absolute uplift during faulting that accompanied the 1971 San Fernando earthquake); (2) basinal 

development exemplified by the extremely deep, long, 

narrow east-trending Santa Barbara Channel-Ventura 

basin, which is filled with young sediment and has 

flanks overturned by reverse faulting; (3) widespread 

deformation of late Quaternary marine and nonmarine 

terrace deposits, locally rising relative to sea level at 

long-term rates of 4 to 10 mm/yr or 4 to 10 km/m.y. (Lajoie and others, 1979); {4) generation of earthquakes in 

the upper 15 km of the crust; and (5) widespread 

regional uplift (Castle, 1978} and strain accumulation 

(Savage and others, 1981) shown by analysis of horizontal and vertical survey data. 

The distribution of most of these effects is shown in 

figure 6, which also shows epicenters of selected welllocated earthquakes for which fault-plane solutions 

(analyses of instrumentally well recorded earthquakes 

Geologic and Seismologic Setting 27 
DESERT 

AI 

I 

PACIFIC OCEAN 

0 50 100 MILES 

1----r----'-----.----___J 

0 50 100 KI LOMETERS 

EXPLANATION 

FAULTS 

Soli d where well kn own, 

das hed where poorl y known 

REVERSE 

Ill! II' 

Scarp fa ces 

viewer 

Scarp faces away 

from viewer 

STRIKE-SLIP 

~ 

Right-late ral 

--::>"" 

Left-lateral 

FIGURE 4.-Present relative motions of crustal blocks. Blocks in the foreground move northwest with the Pacific plate and represent the Peninsular 

Ranges; those representing the Transverse Ranges (shaded) generally are bounded by reverse faults and prominent scarps. Modified from 

Anderson (1971). 

for which the sense and orientation of the generating 

fault displacement can be derived) are available. These 

epicenters are distributed throughout the region, and, 

although most represent earthquakes of local magnitude 

(MJ1 5 or less, they reflect the same strain field 

reflected by several larger earthquakes for which solutions are available-generally north-south compression. 

The maximum measured long-term rates of uplift occur 

1

Magnitude is a measure of the size or strength of an earthquake based on seismograph 

records and therefore dependent on wave path, site effects, and instrumental frequency 

response. Local magnitude {ML) was devised for southern California earthquakes (Richter, 

1935, 1958). A widely applicable measure independent of frequency and wave path, moment 

magnitude (M) is numerically coincident with ML in the range 3 to 7 (Hanks and Kanamori, 

1979). See Ziony and Yerkes (this volume) for more details. 

28 Earthquake Hazards in the Los Angeles Region 

along the coast west of Ventura (Lajoie and others, 

1979), in an area of intense seismicity and active folding 

and reverse faulting. Although measured rates are 

sparse for inland parts of the Transverse Ranges, those 

areas are also characterized by geologically recent 

reverse faulting, and estimated long-term rates of uplift 

for those areas are comparable. Figure 6 also shows the 

surface traces of major Quaternary faults, classified by 

age of latest movement at the surface. Those faults or 

fault segments that show geologic evidence of Holocene 

rupture also generally are seismically active. Not shown 

on the map are results of leveling surveys that indicate 

local areas of very rapid historic uplift-for example, 
FIGURE 5.-Aerial view west along the southern front of the eastern San Gabriel Mountains. The south-facing scarp at right center (right of 

powerline) is the southernmost fault of the 1-km-wide Cucamonga segment of the Transverse Ranges frontal fault zone. The fault scarp is compound (the result of at least eight successive ruptures), slopes as steeply as 30°, is as much as 16m high, and is about 5 km long; the lastrupture occurred between 500 and 1,000 yr B.P. The scarp cuts late Pleistocene and Holocene fan deposits of Day Canyon but does not cut the 

most recent deposits in active streams (right foreground). Mesozoic and older rocks of the mountain block have been thrust hundreds of meters 

up and southward (left) over the fan deposits by recurrent movements on the north-dipping reverse faults at a long-term average rate of about 

3 mm/yr (Matti and others, 1982). The young alluvial lowland at the left extends almost continuously for 85 km from San Bernardino (20 km 

behind viewer) to Pasadena. (Photograph taken September 1960; copyrighted by J. S. Shelton. Used by permission.) 

Geologic and Seismologic Setting 29 
Santa Monica Mts 

FIGURE 6.-Major Quaternary faults, directions of inferred maximum compressive stress (P axes) derived from fault-plane solutions, and localities 

of estimated long-term uplift rates (Lajoie and others, 1979). MC indicates Malibu Coast fault; Npt-lngwd, Newport-Inglewood fault; PV, Palos 

Verdes Hills fault; Ry, Raymond fault; RM, Red Mountain fault; SF, San Fernando fault; SM, Santa Monica fault. Epicenters represent selected 

instrumentally located earthquakes from 1933 (event 26) to 1981 (event 66) for which well-constrained fault-plane solutions are available 

(event numbers from tables 3 and 4). 

30 Earthquake Hazards in the Los Angeles Region 
- 39 ., San Gabriel Mts 

~ , ~ dre 

1 ,- 59 954 

'-...4... 

~' \_ 

\ 

........_ 

,

,

, ......._ 

~ 

~ ~~ "' ...... 

'\~ ' 64 

·~ 

' '-..... .......... ""-

, 

"" ',~ 

" " " 

Geologic and Seismologic Setting 31 
Point Conception during early years of this century 

(Yerkes and others, 1981) and the more extensive, transitory southern California uplift which is centered over 

the Mojave Desert but includes the Transverse Ranges 

(Castle, 1978). 

Another means of describing the continuing regional 

deformation is to integrate all known slip rates of faults 

into a kinematic model. On this basis, long-term horizontal convergence rates across the Santa Barbara Channel-San Cayetano-Sierra Madre-Cucamonga zone may 

exceed 10 mm/yr (Yeats, 1981), about 20 percent of the 

Pacific-North American plate motion. Such rates are 

consistent with other measured rates of deformation in 

the Transverse Ranges and are the highest modeled for 

any southern California fault west of the San Jacinto 

zone. 

Thus, we see at several scales and through several independent lines of evidence the effects of north-south 

crustal shortening throughout the Transverse Ranges, 

effects generally associated with horizontal right-lateral 

movement along the plate boundary (the San Andreas 

and associated faults of coastal California). The compressive effects of deformation so characteristic of the 

Transverse Ranges have long been attributed to convergence between the "big bend" of the San Andreas 

fault and the Pacific plate, but this hypothesis does not 

account for similar effects east of the "big bend," nor is 

the origin of the "big bend" itself well understood. It is 

important to recognize that the Los Angeles region occupies the junction between two major intersecting 

zones of active faults, that the deformational processes 

probably are as active now as they have ever been (Atwater and Molnar, 1973), and that these processes are 

expected to continue at least at present rates. 

PATTERN OF ACTIVE FAULTS 

Figure 7 shows the pattern of major Quaternary 

faults in the Los Angeles region and epicenters of welllocated earthquakes of M1 ~ 3 for 1970 through 1981. The 

lowland area of the region is dominated by two seismically active fault systems-the northwest-trending 

right-lateral strike-slip San Andreas and its members 

(from east to west, the San Jacinto, the WhittierElsinore, and the Newport-Inglewood) and the westtrending reverse faults of the Transverse Ranges, the 

southernmost of which transects most members of the 

San Andreas system but not the San Andreas itself (see 

fig. 6). The lowland area also occupies the junction between two major physiographic provinces, the structural trends of which are controlled by the fault 

systems-the Peninsular Ranges province east and 

south of the Los Angeles basin, major elements of which 

parallel the San Andreas system, and the Transverse 

32 Earthquake Hazards in the Los Angeles Region 

Ranges province northwest, north, and northeast of the 

basin, elements of which trend generally east-west, 

transverse to the San Andreas system. The boundary between the two provinces is marked by a zone of westtrending reverse faults, which forms, for example, the 

steep southern slope of the San Gabriel Mountains (fig. 

5). The damaging 1971 San Fernando earthquake occurred in this zone. 

The northwest-trending Newport-Inglewood zone of 

faults and folds traverses the densely urbanized 

western Los Angeles basin and, at its northern end, is 

overridden by or merges with the east-trending Santa 

Monica zone of reverse faults. The onshore segment is 

about 60 km long from the Santa Monica zone at the 

northwest to the Santa Ana River at the southeast, 

beyond which the zone extends offshore toward San 

Diego. At least three damaging earthquakes have occurred along the onshore segment during historic time. 

The Newport-Inglewood zone has a relatively high rate 

of seismicity but a very low estimated long-term slip rate 

( < 1 mm/yr) (Woodward-Clyde Consultants, 1979). 

PATTERN OF DAMAGING 

EARTHQUAKES 

Because of the strong correlation (in California) between damaging earthquakes (M ~ 5) (table 3) and geologically young faults mappable at the surface, the distribution of such earthquakes and faults in time and space is 

the best available index to the location of future damaging earthquakes. Figure 8 shows the epicenters and 

isoseismal patterns of 42 known damaging (MM ~ VII)2 

earthquakes, their relation to mapped Quaternary 

faults, and urbanized areas. Most damaging onshore 

earthquakes can be associated with known Quaternary 

faults, as Allen and others (1965) recognized. These 

faults also have been seismically active over the 11-yr 

period from 1970 to 1981. Even allowing for location 

errors for preinstrumental events, the map provides 

strong evidence that most Quaternary faults are 

seismically active. The lack of historical earthquakes on 

fault segments such as the San Cayetano, the Sierra 

Madre, and the Cucamonga in the Transverse Ranges 

cannot be interpreted as evidence of less hazard there; 

this lack is more likely to indicate earthquake recurrence intervals that exceed 180 yr, the time span since 

the beginning of written history in southern California. 

2

MM ~VII indicates a Modified Mercalli intensity equal to or greater than VII. Intensity is a 

measure of the effects of an earthquake at a given place based on observation. Intensity varies 

with magnitude but is highly dependent on the observer's experience, the site geology, and the 

distance from the earthquake source. MM VII is the lowest intensity at which damage to 

masonry of ordinary workmanship and mortar (not reinforced or designed to resist lateral 

forces) appears. Several intensity scales are in use; the Modified Mercalli scale uf 1931 or its 

successor (the 1956 version} is commonly used in the United States (Richter, 1958, p. 137). See 

inside back cover for a complete description of scale. 
An association between Holocene rupture and 

seismicity furnishes strong presumption of fault activity, 

but there have been prominent events in which one or 

both of these criteria have been missing or not recognized. For example, a major damaging earthquake 

(event 5) (fig. 6, table 3) and extensive surface rupture 

occurred in 1857 on a segment of the San Andreas fault 

that has been relatively quiet since; yet Allen (1981) has 

concluded that this segment still poses great seismic 

hazard. Furthermore, the occurrence of the 1971 San 

Fernando earthquake (event 39) (fig. 6, table 3) and surface rupture on a reverse fault having a well-developed 

young surface scarp but no recognized historical rupture or seismicity indicates that such faults also may 

generate damaging earthquakes. 

The maps shown in figures 6, 7, and 8 identify six 

major sources of historical damaging earthquakes in 

southern California-the "big bend" segment of the San 

Andreas fault, the San Jacinto fault zone, the NewportInglewood zone, and the Santa Barbara Channel, San 

Fernando, and Raymond(?) faults of the Transverse 

Ranges. The San Andreas and White Wolf faults in the 

"big bend" area have produced the two largest 

southern California earthquakes of historic time (1857, 

M 7.9; 1952, M 7.5). 

In terms of numbers of damaging earthquakes, the 

San Jacinto fault zone has been the most prolific in 

historical time. At least 10 events have taken place 

(1858-1980) over a fault length of about 200 km (table 3); 

about half of these events have caused damage in the 

San Bernardino-Riverside area. 

The Newport-Inglewood zone and the Santa Barbara 

Channel faults each have generated several damaging 

earthquakes (table 3). As their reconstructed damage 

patterns indicate (Toppozada and others, 1981), the 

1812 earthquakes were by far the largest associated 

with either zone. 

In terms of exposure to damaging earthquakes, the 

3,380 km2 of urbanized Los Angeles basin constitute 

about 5 percent of the onshore area mapped in figure 7, 

but faults in the basin area have generated 10 (24 percent) of the 42 historical damaging earthquakes. All of 

the urbanized basin area has been shaken at MM <?:VII at 

least once in the last 180 yr, about 91 percent has been 

shaken twice or more, about 57 percent has been shaken 

three times or more, about 27 percent has been shaken 

four times or more, and about 9 percent has been 

shaken five times or more. 

PATTERN OF MODERN SEISMICITY 

This section summarizes the distribution of instrumentally recorded seismicity and its relation to the 

regional and local tectonic framework. Abundant evidence shows that, in California, faults are the principal 

loci of stress release at and above seismic depths (Allen, 

1975), generally within 10 to 15 km of the surface. Expo~ed fault traces represent roughly planar surfaces of 

shear that result from opposing movements of adjoining 

rock masses; along the plate boundary, this movement 

results from widespread, generally north-south compressive strain. The shearing is resisted by a frictionlike 

process that permits either intermittent impulsive slip 

(rupture), which causes earthquakes, or continuous slow 

movement (creep), which occurs sometimes without 

detectable earthquakes. Specific identification of 

earthquake-generating fault movements requires the 

ability to map earthquakes in three dimensions, especially where inclined fault surfaces are involved. Welllocated fault-plane solutions assist greatly in correlating 

surface and seismic evidence about the type and attitude of fault rupture (table 4), especially on inclined 

faults. 

Figure 9 shows the relation of the Los Angeles region 

to the rest of California in terms of the 1980 and 1981 

record of ML <?: 1.5 earthquake epicenters mapped by 

seismograph networks that have been greatly augmented since about 1970. In central California, most 

earthquakes occur along mapped vertical faults of the 

northwest-trending San Andreas system that have Holocene right-lateral strike slip; dense alignments of small 

events are concentrated along segments that are_known 

to be creeping (Allen, 1981). South of the Transverse 

Ranges in the Los Angeles region, similar alignments occur along the San Jacinto fault and, to a lesser degree, 

along portions of the Elsinore and Newport-Inglewood 

zones, which also are elements of the San Andreas 

system. The pattern of epicenters north and south of the 

Transverse Ranges thus reflects to a prominent degree 

the distribution of right-lateral strike slip on vertical 

faults that make up the active plate boundary. That this 

boundary zone is about twice as wide south of the 

Transverse Ranges as it is to the north perhaps reflects 

east-west extension south of the Transverse Ranges. 

In and near the Transverse Ranges, however, the pattern of seismicity is much more diffuse (see also fig. 8). 

Instead of prominent northwest-trending alignments 

coincident with the traces of vt;Jrtical faults, there are 

short arcuate patterns, such as those northeast of Santa 

Barbara Channel; tight clusters, such as those at San 

Fernando just to the east; or short east-west trends, 

such as those near the Anacapa fault. Fault-plane solutions show that the seismicity is along reverse or 

reverse-oblique north-dipping faults that can be mapped 

at the surface. East of the San Jacinto zone, some 

seismicity can be associated with reverse or reverseoblique displacement on the Banning and Mission Creek 

Geologic and Seismologic Setting 33 
34 

EXPLANATION 

MAJOR FAULT 

~ ---:1"" 

Holocene Quaternary 

Arrows show sense of strike slip; barbs on upthrown side of reverse 

or thrust fault; dashed where location uncertain, dotted where buried. 

Santa Ynez 

EPICENTER OF DAMAGING EARTHQUAKE (MM;;.VII) Number refers to table 3. 

0 

Preinstrumental 

0 

0 

0 

0 

ML 

;;.7 

;;.6<7 

;;.5<6 

<5 

Instrumental 

0 

0 

0 

0 C) PACIRC OCEAN 

FIGURE 7.-Epicenters of 42 known damaging earthquakes (MM ~VII) from 1800 to 1978, major Quaternary faults, and 1970 to 1981 record of welllocated epicenters of ML ~ 3 earthquakes (in brown). MC indicates Malibu Coast fault; M Ck, Mission Creek fault; Npt-Ingwd, NewportInglewood fault; OR, Oak Ridge fault; PI, Pleito fault; PV, Palos Verdes Hills fault; Ry, Raymond fault; RM, Red Mountain fault; SF, San Fernando fault; SM, Santa Monica fault; S Sn, Santa Susana fault; Vta, Ventura fault; WW, White Wolf fault. 1970 to 1981 seismicity furnished by 

P. T. German, U.S. Geological Survey, Pasadena, Calif.; relative magnitude of event indicated by size of circle. 

34 Earthquake Hazards in the Los Angeles Region 
32 

San Gabriel Mts 

Geologic . an d Seismologic Setting 35 
TABLE a.-Historical (180G-1980) damaging (MM intensity ~VII) earthquakes 

[Event numbers correspond to numbers used in fig. 6] 

Event 

no. 

1------

2------

3------

4------

5------

6------

6a-----

7------

8------

9------

10------

11------

12------

13------

14------

15------

16------

17------

18------

19------

20------

21------

22------

23------

24------

25------

26------

Year 

1800 

1812 

1812 

1855 

1857 

1858 

1892 

1893 

1899 

1899 

1902 

1907 

1910 

1912 

1915 

1916 

1918 

1919 

1920 

1923 

1925 

1926 

1927 

1929 

1930 

1930 

1933 

27------ 1937 

28------ 1941 

29------ 1941 

30------ 1941 

31------ 1942 

32------ 1947 

33------ 1948 

34------ 1952 

Month 

Nov. 

Dec. 

Dec. 

July 

Jan. 

Dec. 

Feb. 

Apr. 

July 

Dec. 

July 

Sep. 

May 

Dec. 

Jan. 

Oct. 

Apr. 

Feb. 

June 

July 

June 

June 

Nov. 

July 

Aug. 

Aug. 

Mar. 

Mar. 

July 

Oct. 

Nov. 

Oct. 

Apr. 

Dec. 

July 

Day 

22 

8 

21 

11 

9 

16 

24 

4 

22 

25 

28 

20 

15 

14 

12 

23 

21 

16 

22 

23 

29 

29 

4 

8 

5 

31 

11 

25 

1 

22 

14 

21 

10 

4 

21 

Time' 

21:30 

15:00 

19:00 

04:15 

16:00 

10:00 

07:20 

19:40 

20:32 

12:25 

06:57 

01:54 

15:47 

04:31 

02:44 

22:32 

15:57 

02:48 

07:30 

14:42 

23:21 

13:50 

16:46 

11:25 

00:40 

01:54 

16:49 

07:50 

06:57 

08:41 

16:22 

15:58 

23:43 

11:52 

Latitude, Longitude, 

oN. ow. 

33.0 

33.7 

34.2 

34.1 

35.3 

34.0 

32.6 

34.3 

34.3 

33.8 

34.72 

34.2 

33.7 

34 

34.73 

34.9 

33.75 

35 

33.97 

34 

34.3 

34.5 

34.6 

33.9 

34.3 

33.952 

33.62 

33.41 

34.37 

33.8 

33.78 

32.97 

34.98 

33.93 

35.00 

117.3 

118.12 

119.9 

118.1 

119.8 

117.32 

115.7 

118.72 

117.5 

117.0 

120.4 

117.4 

117.4 

119 

120.23 

118.9 

117.00 

119 

118.37 

117.25 

119.8 

119.72 

120.9 

118.04 

119.5 

118.682 

117.97 

116.26 

119.58 

118.2 

118.25 

116.0 

116.55 

116.38 

119.02 

M 

6.5 

6.9 

7.1 

6 

7.9 

6.5 

6.8 

5.5 

6.7 

6.8 

5.4 

6 

6 

5 

5.8 

5.6 

6.8 

5 

4.7 

6.0 

6.8 

5.5 

7.3 

4.7 

5 

5.2 

6.2 

6 

6.0 

4.9 

5.4 

6.6 

6.5 

6.0 

7.5 

Maximum 

intensity 

[MM) 

VII 

VII 

VIII 

VIII 

IX+ 

IX 

IX+ 

VIII 

VIII 

IX 

VIII 

VII 

VII 

VII 

VIII 

VII 

IX 

VII 

VIII 

VII 

IX 

VII 

IX 

VIII 

VII 

VII 

IX 

VII 

VIII 

VII 

VII+ 

VII 

VII 

VII 

XI 

Area of 

MM2:7, 

in km3 

Fault or 

zone 

2,9203 Rose Canyon(?) 

8,500 Newport-Inglewood 

13,000 Santa Barbara 

Channel. 

7753 Raymond(?) 

57,000 San Andreas 

2,9203 San AndreasSan Jacinto. 

6,600 Laguna .Salada 

(Elsinore). 

2053 Santa Susana(?), 

Simi(?). 

4,300 San Andreas(?) 

4,700 San Jacinto 

202 Los Alamos 

7703 San Jacinto(?) 

7753 Elsinore(?) 

553 Offshore(?) 

540 Los Alamos 

260 

7,000 San Jacinto 

553 White Wolf 

34 Newport-Inglewood 

1,3203 San Jacinto 

3,800 Santa Barbara 

Channel. 

2003 Santa Ynez(?) 

2,200 Offshore Point 

Arguello. 

40 Norwalk 

553 Santa Barbara 

Channel. 

1 

Remarks and 

sources4 

One strong foreshock 

and many strong 

aftershocks; 1. 

1 

~ 36G-km surface 

rupture; 1, 2. 

1 

1, 33 

1 

1 

1, 3 

Two large 

aftershocks in 4 

days (4, 5, 6). 

3, 4, 6 

4, 6 

4, 6 

4, 5, 6 

4, 5a, 6 

3, 4, 7 

4, 6 

4, 8, 9 

3, 4, 6 

Many strong 

aftershocks; 4, 6, 

10, 36, 37. 

4, 6 

4, 6, 11, 12, 36 

4,6, 13 

4, 6 

95 Anacapa 4, 6, 14 

2,835 Newport-Inglewood Twelve aftershocks 

~ML 5 by Oct. 2; 

6, 15, 16, 17, 

775 San Jacinto 

5953 Santa Barbara 

Channel. 

40 NewportInglewood(?). 

1553 NewportInglewood(?). 

34, 36. 

6, 15, 18 

Plus many strong 

aftershocks; 6, 15. 

6, 15, 19 

6, 15 

2,9203 San Jacinto 3, 6, 15 

4,700 Unknown, probably 6, 15, 17, 35 

not Manix. 

5,000 Mission Creek 

30,000 White Wolf 

6, 15, 20 

Eleven aftershocks in 

4 days: 1 ML ~6. 

4 ML~5.5, 6 ML~5; 

53-km surface 

rupture (6, 15, 21). 
TABLE 3.-Historical (1800--1980) damaging [MM intensity ;;:: VII) earthquakes-Continued 

Event 

no. Year 

35------ 1954 

36------ 1968 

37------ 196~. 

38------ 1970 

39------ 1971 

40------ 1971 

41------ 1973 

42------ 1978 

1

GMT. 

2

Location modified. 3Estimated. 

Month 

Jan. 

Apr. 

Apr. 

Sep. 

Feb. 

Mar. 

Feb. 

Aug. 

4Numbers refer to the following sources: 

1. Toppozada and others (1981) 

2. Agnew and Sieh (1978) 

3. Thatcher and others (1975) 

4. Toppozada and others (1978) 

5. Beal (1915) 

Sa. Branner (1917) 

6. Coffman and von Hake (1973a) 

7. Townley (1918) 

8. Taber (1920) 

9. Richter (1970] 

10. Toppozada and Parke (1975) 

11. Byerly (1930) 

12. Hanks (1979) 

13. Wood and Richter (1931) 

14. Gutenberg and others (1932) 

15. Real and others (1978) 

Latitude, Longitude, 

Day Time1 'N. 'W. 

12 23:33 35.0 119.02 

9 02:28 33.19 116.13 

28 23:20 33.34 116.35 

12 14:30 34.27 117.54 

9 14:00 34.41 118.40 

31 14:52 34.29 118.52 

21 14:45 34.07 119.04 

13 22:54 34.40 119.68 

19. Bravinder (1942) 

20. Richter and others (1958) 

21. Neumann and Cloud (1955) 

22. Murphy and Cloud (1956) 

23. Cloud and Scott (1972) 

24. von Hake and Cloud (1971) 

25. Scott (1973) 

26. Coffman and von Hake (1973b) 

27. Whitcomb and others (1973) 

28. Coffman and von Hake (1975) 

29. Lee and others (1978) 

30. Stover and von Hake (1980) 

31. Coffman and von Hake (1972) 

32. Corbett and johnson (1982) 

33. Strand (1980) 

34. Rodgers (1973) 

Maximum Area of 

inten~ity MM;,:7, 

M (MM) inkm' 

5.9 VII+ 540 

6.5 VII 1,330 

5.8 VII 420 

5.4 VII 1753 

6.6 IX 2,600 

5.1 VII 85 

5.3 VII 425 

5.6 VII 330 

Fault or 

zone 

White Wolf 

Coyote Creek 

(San Jacinto). 

San Jacinto 

North San Jacinto 

San Fernando 

San Fernando 

Anacapa 

Santa Barbara 

Channel. 

Remarks and 

sources4 

6, 15, 22 

6, 15, 23 

6, 15, 24 

6, 15, 31 

Four aftershocks in 

43 min: 2 ML ;;:: 5.5; 

15-km surface rupture; 15, 25, 27. 

26, 27 

15, 28 

Plus many small 

aftershocks; 29, 

30, 32. 

16. Richter (1935) 35. Beeby and Hill (1975), Lindh and others (1978) 

17. Richter (1958) 36. Toppozada and Parke (1982) 

18. Wood (1937) 37. Toppozada and Parke (1975) 

faults. Reverse faulting along this entire east-west belt 

generally marks the southern margin of such mountain 

ranges as the Santa Monica, the San Gabriel, and the 

San Bernardino Mountains. 

The "cloud" of seismicity in the San Benardino Mountains is poorly understood. The few available fault-plane 

solutions are compatible with right-lateral strike slip on 

mapped vertical northwest-trending faults similar to 

those in the Mojave Desert to the north; none correlate 

with the south-dipping reverse faults that border the 

mountains on the north. The presence of this seismicity, 

as opposed to the relative lack in the adjoining San 

Gabriel Mountains, presumably is related to contrasting 

structure and shear resistance at depth. 

The dense north-trending alignment of epicenters immediately east of the San Bernardino Mountains includes three events associated with historical surface 

rupture; the ruptures are aligned more nearly with the 

zone of epicenters than they are with the regional trend 

of faults in the Mojave Desert. The approximate coincidence of this alignment with the eastern boundary of 

seismicity, the eastward change in habit to normal 

faulting, and the sharp eastward rise in heat flow 

(Lachenbruch and others, 1978) suggest an association 

with ongoing adjustments of the plate boundary. 

SUMMARY 

Metropolitan southern California lies along the broad 

boundary between two of the Earth's moving crustal 

plates. Continuing deformation along the boundary, 

caused by generally north-south compression derived 

from relative motion of the plates, is expressed chiefly 

as right-lateral strike slip on vertical faults of the 

northwest-trending San Andreas system both north and 

south of the Transverse Ranges. In turn, this displacement is expressed as prominent alignments of earthquake epicenters that coincide with and directly reflect 

the fault traces and movement on them. In the TransGeologic and Seismologic Setting 37 
0 

121 ° 

35 ·- r= ~--~r-~ ----~~--~------~-------------- -4~~-- -------

0 

EXPLANATION 

EPICENTER OF DAMAGING EARTHQUAKE (MM;a. vn) 

(Epicenters keyed to figure 7) 

0 

Prelnstrumental ML Instrumental 

0 ... 7 0 

0 ... 6< 7 0 

Q ;a.S<6 0 

0 <5 0 

ISOSEISMAL PATTERN 

~~-3-, 

\ I ..... __ ..,

Boundary of MM;a. VII shaking; numeral shows 

number of events affecting area (1800-1978). 

I 

10 

10 

I 

I 

20 

20 

I 

I 

30 

I 

40 

30 40 

I I 

~ KILOMETERS 

SO MUS 

I 

2 

FIGURE B.-Epicenters and isoseismal _patterns of 42 known damaging (MM2:VII) earthquakes from 1800 to 1978 in relation to urbanized areas 

(in brown), Epicenters and patterns for preinstrumental events have been reconstructed, largely by Toppozada and others (1981), from contemporary records, 

38 Earthquake Hazards in the Los Angeles Region 
\ 

I 

\a 

I 

I 

\ 

(j(~~ Y 

I 

I ~"' I G 

I 

I 

\ 

)'"" \ "" \ "" \ 

118' 

---------'\..l " I 

"""' '" - '-, 

\ 

·~ ~- \ ) 

"-, I 

'-.y / .............. ___ _....... 

)' 

0 

0 

Geologtc . an d Seismologtc . Setting 39 
TABLE 4.-Selected earthquakes having known fault·plane solutions 

[Event numbers correspond to numbers used in fig. 6) 

Event 

no. 

43------

44------

45------

46------

47------

48------

49------

50------

51------

52------

53------

54------

55------

56------

57------

56------

59------

60------

61------

62------

63------

64------

65------

66------

1

GMT. 

Year 

1959 

1965 

1969 

1972 

1972 

1972 

1973 

1974 

1975 

1975 

1975 

1976 

1976 

1976 

1977 

1978 

1977 

1978 

1978 

1979 

1979 

1980 

1980 

1981 

Month 

Oct. 

Oct. 

Oct. 

Jan. 

July 

Sep. 

Aug. 

Dec. 

Mar. 

May 

Nov. 

Jan. 

Oct. 

Nov. 

Mar. 

May 

June 

June 

Dec. 

Mar. 

June 

Feb. 

May 

Sep. 

2

Numbers refer to the following sources: 

1. Gawthrop (1975) 

2. Lee and others (1979) 

3. Cockerham and Eaton (1982) 

Day 

1 

17 

30 

17 

27 

23 

6 

6 

24 

31 

5 

1 

15 

30 

17 

14 

27 

19 

29 

15 

30 

25 

29 

4 

Time' 

04:35 

09:45 

15:36 

05:49 

01:12 

03:23 

23:29 

13:45 

10:32 

14:39 

17:20 

15:56 

16:18 

20:59 

06:30 

21:07 

00:34 

15:50 

Latitude, Longitude, 

34.48 

33.98 

34.38 

34.30 

34.72 

34.78 

33.97 

34.12 

34.50 

34.52 

34.13 

34.01 

33.75 

34.08 

34.46 

33.68 

34.11 

34.81 

33.92 

34.32 

34.23 

33.52 

34.94 

33.68 

120.49 

116.78 

120.84 

120.26 

118.95 

120.25 

119.45 

118.26 

118.89 

116.49 

117.34 

117.88 

118.02 

118.12 

117.98 

116.04 

117.95 

117.77 

118.34 

116.44 

116.89 

116.55 

120.78 

119.10 

4. C. H. Cramer and J. M. Harrington (written communication, 1978} 

5. Teng (1979) 

6. McNally and Pechmann (1981) 

7. Buika and Teng (1979) 

B. Pechmann and others (1980) 

9. P. German (written communication, 1982) 

10. Sanders and others (1981) 

11. Corbett and Piper (1981) 

12. Kanamori and McNally (1981) 

13. Beeby and Hill (1975), Lindh and others (1978) 

verse Ranges, however, the north-south compression is 

expressed by a large component of vertical deformation-folding and mountain building through reverse or 

reverse-oblique displacement on east-trending inclined 

faults. The resulting patterns of seismicity can be 

associated with specific faults only through correlation 

of surface geologic evidence with seismic evidence by 

means of well-located fault-plane solutions. Even so, 

nearly all historical damaging earthquakes in the Los 

40 Earthquake Hazards in the Los Angeles Region 

4.5 

4.9 

3.7 

2.7 

3.0 

3.0 

5.0 

4.4 

2.7 

5.2 

3.0 

4.0 

2.8 

2.5 

3.0 

2.2 

2.9 

3.0 

2.5 

5.2 

4.9 

5.6 

4.8 

5.3 

Fault or 

zone 

Point Conception 

area. 

Banning(?) 

Off Point 

Conception 

Santa Barbara. 

Channel. 

Unknown 

Alamos-Baseline 

Santa Cruz Island 

Santa Monica(?) 

Unknown 

Galway Lake 

San Jacinto 

Unknown 

NewportInglewood(?). 

Raymond 

San Andreas 

San Andreas 

Sierra Madre(?) 

Mirage Valley 

Newport-Inglewood 

Homestead Valley 

San Bernardino 

Mountains. 

San Jacinto 

Hosgri 

North of Santa 

Barbara Island. 

Type 

Left-reverse oblique 

Reverse 

Left-reverse oblique 

Reverse 

Thrust 

Left-reverse oblique 

Left-reverse oblique 

Reverse 

Reverse 

Right lateral 

Right lateral 

Right lateral 

Reverse 

Reverse 

Right-reverse 

oblique. 

Right lateral 

Reverse 

Reverse 

Reverse 

Right lateral 

Strike slip 

Right lateral 

Reverse 

Right lateral 

1 

12 

1 

2 

2 

1 

1 

7 

2 

Remarks and 

sourcesz 

6.8-km surface 

rupture; 13. 

6 

5 

5 

6 

6 

12 

4 

6 

5 

3-km surface 

rupture; 8. 

9 

10 

3 

11 

Angeles region (42 in 180 yr) and many smaller earthquakes can be associated with recognized Quaternary 

faults that are seismically active today. Essentially all 

urbanized areas of the region lie within range of one or 

more of these damaging earthquakes. We expect this 

deformational process to continue at least at present 

rates; present evidence indicates that future damaging 

earthquakes will occur on or near a recognized fault 

that shows evidence of geologically recent activity. 
31 ' 

126' 

0 

0 0 

+ 

0 

: 0 

+ 

0 

MAGNITUDE ( Mtl 

+ + 

5.0 5.9 0 

4.0 4.9 0 

3.0 3.9 0 

2.0 2.9 0 

1.5 1.9 

0 50 100 MILES 

I I I 

I I 

0 50 100 KILOMETERS 

APPROXIMATE SCALE 

0 

'>o §!O 

's 

0 

~ 

0 

0 

0 

~" 0 

O(!J <9 0 

-f' 0 '0 

0 . 0 c\0 

.. 

0 

0 

0 0 

0 

'C:oP' 

0 

0 

0 

0 0 

+ 

0 

114' 

+ + 

0 ~ 0 

,o ;., ~ 

t 

' 0 0 

+ 

0 ., ~ 

oo'"t 

0 

0 

0 0 0 0 

0 

0 

0 

0 0 

FIGURE 9.-Epicenter map of California. ML ~ 1.5 epicenters for 1980 and 1981 and explanation of symbols. Box shows area of figures 6, 7, and 8. 

Map compiled and plotted by J. P. Eaton (U.S. Geological Survey, Menlo Park, Calif.) from unpublished data supplied by F. W. Lester (U.S. 

Geological Survey, Menlo Park, Calif.), C. E. Johnson (U.S. Geological Survey, Pasadena, Calif.), L. K. Hutton (California Institute of Technology, 

Pasadena, Calif.), A. S. Ryall (University of Nevada, Reno, Nev.), and A.M. Rogers (U.S. Geological Survey, Golden, Colo.). 

Geologic and Seismologic Setting 41 
42 Earthquake Hazards in the Los Angeles Region 
EVALUATING EARTHQUAKE AND SURFACE-FAULTING 

POTENTIAL 

By J. I. Ziony and R. F. Yerkes 

INTRODUCTION denly during earthquakes or slowly during a process 

called creep. Cumulative displacements of tens to hunThe Los Angeles region of California has been . dreds of kilometers can result if the fault continues to 

dissected by a complex pattern of faults produced over slip over a long span of geologic time. Individual 

millions of years during markedly different episodes of episodes of movement, however, are small-generally 

crustal deformation. Although many of these faults ap- less than a few meters-and are commonly separated in 

parently are no longer capable of movement, others are time by tens, hundreds, or thousands of years. 

responding to ongoing strain accumulation associated A fault on a local scale is a more or less planar surwith large-scale shifting of plates of the Earth's crust. face whose geometry can be characterized by strike 

As Yerkes (this volume) has discussed, current earth- (trend or bearing of the intersection of the fault with the 

quake activity is associated with the northwest-trending Earth's surface in relation to north) and dip (inclinati::m 

strike-slip faults of the San Andreas system and the from the horizontal). Geologists classify faults according 

west-trending, dominantly reverse-slip faults of the to the primary type of movement along them-that is, 

Transverse Ranges. Several faults have undergone strike slip, dip slip, or oblique slip (fig. 10). 

movement in historical time and generated damaging Strike-slip faults are chiefly vertical faults that have 

earthquakes; undoubtedly, they will slip again. Further- shifted rocks on one side of the fault horizontally in relamore, the geologic or geophysical attributes of other tion to the opposite side. Depending on whether the rock 

faults suggest that they, too, may be capable of mass on the opposite side has shifted to the right or to 

earthquake-generating movements within a time span of the left, the designation of right lateral or left lateral is 

concern to residents of the region. used. The San Andreas fault is the classic example of a 

To avoid or to accommodate the destructive effects of right-lateral strike-slip fault. Dip-slip faults have 

earthquakes, planners and engineers need to know changed the elevation of a rock mass on one side of the 

which faults are likely to slip suddenly again and what fault relative to the opposite mass. These faults are 

the likely results of such movement would be. The mostly inclined rather than vertical. If the side above 

specific information needed includes the distribution of the fault is depressed, the fault is termed normal slip; 

active faults, their relative activity, the likely size and the term reverse slip is applied if the side above the fault 

frequency of large earthquakes along them, and their is elevated. Oblique-slip faults have significant compotential for rupture at the Earth's surface. This ponents of both strike and dip slip along them. 

chapter describes the potentially damaging geologic effects directly associated with movement along faults, 

the techniques presently available for identifying and Active Faults 

evaluating those effects, and current knowledge about 

the fault hazards of the Los Angeles region. Subsequent 

chapters will address other geologic. effects such as the 

strong shaking and the resulting ground failure that are 

indirect products of sudden fault slip. 

POTENTIALLY ACTIVE FAULTS OF 

THE REGION 

Faults and Their Character 

A fault is a fracture within the Earth's crust along 

which significant movement has occurred either sudActive faults are those faults that are considered likely to undergo renewed movement within a period of concern to humans (Wallace, 1981). Faults that currently 

are slipping, that display earthquake activity, or that 

have had historical surface rupture clearly are active. 

· Ex~ept in these limited cases, however, it is difficult to 

differentiate with certainty between faults capable of 

future movement and those that cannot move under the 

state of stress existing in the Earth's crust. Known active faults display a wide range of behavior, and the dynamic processes that result in fault movement are 

understood only partially. 

Earthquake and Surface-Faulting Potential 43 
STRIKE r-- '"'-{ 

SLIP 

Left lateral 

DIP SLIP 

OBLIQUE 

Reverse oblique SLIP Normal obi i que 

FIGURE 10.-Types of faulting common in the Los Angeles region, 

characterized by the sense of displacement of the blocks on opposite sides of the fault. Movement on oblique-slip faults has both 

strike- and dip-slip components. 

An approach that has proved useful in identifying active faults is to determine the age of the most recent 

movement along a fault. Designation of a fault as active 

can be based on the assumption that the more recent the 

faulting, the more likely any future movement. Because 

different faults can lie dormant for different lengths of 

time before they slip again, however, there is no universally applicable time span for evaluating fault activity 

(see "Determining the Future Behavior of Faults"). Both 

historical and geologic evidence suggests that some 

faults may remain dormant for hundreds or thousands 

of years between major displacements. 

This chapter considers those faults that show 

evidence of offset during late Quaternary time (approximately the past 750,000 yr) (see inside front cover) as 

candidates for future rupture in response to the present 

tectonic stress field. We have three reasons for selecting the late Quaternary as the appropriate time span 

within which to assess the potential activity of faults in 

the Los Angeles region. 

1. Time spans of a few tens of thousands of years or 

less appear inadequate to judge fault activity, 

because large historical earthquakes and surface faulting have occurred worldwide along 

some faults that lacked evidence of historical or 

Holocene (the past 10,000 yr) activity. 

2. The many late Quaternary deposits found in much of 

the Los Angeles region contain widespread 

datable markers for evaluating fault activity. 

Coastal sequences of marine terrace deposits are 

44 Earthquake Hazards in the Los Angeles Region 

reliably dated back to 120,000 yr ago, according 

to various dating methods (Lajoie and others, 

1979). In the Ventura basin, the ages of several 

volcanic ash layers interspersed with the Pleistocene sediments are accurately known (SarnaWojcicki and others, 1984). Inland, nonmarine 

alluvial deposits as old as about 750,000 yr locally (Bull and others, 1979; Meisling, 1984) are exposed extensively along the fault-bounded fronts 

of the major upland areas. 

3. Geologic evidence in and near the Transverse 

Ranges suggests that major changes in the 

tectonic stress field of the region took place during early Pleistocene time, from about 1.7 m.y. 

to about 750,000 yr ago. These changes were 

marked by the accelerated uplift and subsidence 

of major topographic elements of the Transverse 

Ranges, the initiation of slip along some faults, 

and the sharply accelerated rates of slip along 

other faults (Yeats, 1977, 1983; Stein and Thatcher, 1981; Meisling and Weldon, 1982b). Thus, 

many faults that were developed under earlier 

stress conditions may not be able to slip in the 

current stress field. 

Distribution of Late Quaternary Faults 

in the Los Angeles Region 

Faults in the Los Angeles region that show evidence of 

movement in late Quaternary time are shown in figure 

11 and listed in table 5. Several of these faults have offset stratigraphic or physiographic features that suggest 

surface movements within Holocene time. A few have 

displaced the ground surface during historical time, 

which, for southern California, begins with the Spanish 

explorations in 1769. 

As Yerkes (this volume) has pointed out, the present 

tectonic regime of the Los Angeles region is marked by 

interaction between two distinct systems of geologically 

young faults-the San Andreas fault and related 

northwest-trending faults, which have dominantly rightlateral strike-slip movement, and the west-trending 

faults of the Transverse Ranges, which have dominantly 

reverse-slip displacements. Ninety-five late Quaternary 

faults belonging to these systems have been identified in 

the region. The details of their geologic and seismologic 

character and sources of information about these faults 

are summarized in table 5. A discussion of the major 

faults, fault groups, or fault zones follows. Numbers in 

parentheses refer to the individual faults as listed in 

figure 11 and table 5. 

San Andreas fault zone.-The San Andreas fault zone 

is the dominant active fault in California. The main ele-
ment of the boundary between the Pacific and the North 

American tectonic plates, it extends as a continuous surface feature from Cape Mendocino in northern California for more than 1,000 km to east of San Bernardino in 

southern California. Within the Los Angeles region, the 

San Andreas fault zone (1) trends southeastward along 

the margin of the Antelope Valley and extends through 

Cajon Canyon to form part of the southern boundary of 

the San Bernardino Mountains (fig. 12). Two great 

historicaf earthquakes marked by extensive surface 

faulting have occurred along this fault-the renowned 

1906 San Francisco earthquake and the lesser known 

but possibly more severe 1857 Fort Tejon earthquake. 

San Jacinto fault zone.-Echelon segments (including 

2-8) of the San Jacinto fault zone extend from near San 

Bernardino southeastward more than 300 km through 

the Imperial Valley and into northern Baja California, 

Mexico. The zone at its northern end appears to merge 

with the San Andreas fault. For the past century, the 

San Jacinto fault zone has been the most active 

earthquake-generating feature in southern California; it 

has produced at least 10 earthquakes of about local 

magnitude (ML) 6.0 or greater since 1890. 

Elsinore fault zone and related faults.-The 

northwest-trending Elsinore fault zone (including 13-20) 

extends nearly 200 km from the Mexican border to the 

northern edge of the Santa Ana Mountains. Beyond the 

city of Corona, the Chino fault (11) continues the trend of 

this zone almost to Pomona. The Whittier fault (12), 

which extends northwest from the Elsinore fault zone, 

forms part of the eastern margin of the densely populated Los Angeles basin. 

Newport-Inglewood fault zone.-The NewportInglewood fault zone is a broad zone of discontinuous 

faults (25-31) and folds striking southeastward from 

near Santa Monica across the Los Angeles basin to 

Newport Beach. Faults having similar trends and projections occur offshore of San Clemente and in San 

Diego (the Rose Canyon and La Nacion faults). Altogether, these various faults constitute a system more 

than 240 km long that extends into Baja California, Mexico. A near-shore segment of the Newport-Inglewood 

fault zone was the source of the destructive 1933 Long 

Beach earthquake; this zone thus represents a major 

hazard to the densely populated Los Angeles basin. 

Palos Verdes Hills fault.-The Palos Verdes Hills are 

separated from the rest of the Los Angeles basin by a 

major southwest-dipping fault that elevates rocks on the 

west. The Palos Verdes Hills fault (35) has an onshore 

extent of about 15 km. It has, however, been mapped 

northwestward into Santa Monica Bay, where it apparently is truncated by or merges with west-trending 

faults of the Transverse Ranges. Segments of the fault 

also have been identified in San Pedro Bay nearly 30 km 

south of Long Beach. 

San Pedro Basin fault zone.-The San Pedro Basin 

fault zone (38) is a poorly known offshore zone of 

echelon northwest-trending faults that extends from 

near Point Dume southeastward into the San Pedro 

Channel east of Catalina Island. 

Faults of the Santa Cruz-Catalina sea-floor escarJr 

ment.-The faults of the Santa Cruz-Catalina sea-floor 

escarpment (39) include a number of faults that generally coincide with a prominent escarpment on the sea floor 

that extends southeastward from the eastern end of 

Santa Cruz Island. The character of these faults is less 

well known because of incomplete data. The escarpment 

bifurcates between Santa Barbara Island and Santa 

Catalina Island. The occurrence of the ML 5.2 1981 Santa Barbara Island earthquake along this escarpment indicates that these faults pose an earthquake hazard. 

Faults of the Mojave Desert.-The strike of a series of 

youthful faults occurring in the Mojave Desert is uniformly more northerly than that of the San Andreas 

fault. Within the region addressed in this report, these 

faults include the Mirage Valley (41), the Helendale (42), 

and the Lenwood (43) faults. 

Faults along the margins of the San Bernardino Mountains.-The northern edge of the San Bernardino Mountains is delineated by an arcuate group of discontinuous 

faults (93) that have various trends and that generally 

dip southward into the mountain mass. The distribution 

and history of these faults are poorly understood and 

are currently being investigated. 

South of the San Bernardino Mountains, the Banning 

fault zone (95), a complex band of north-dipping faults, 

extends eastward for about 50 km. Although the Banning is shorter than many other faults, it is a key tectonic element, because it appears to link segments of the 

San Andreas fault to the northwest and the southeast. 

Faults of the southern margin of the western Transverse Ranges.-The southern . boundary of the western 

Transverse Ranges is formed by an overlapping group of 

west- to east-northeast-trending late Quaternary faults. 

These faults, which dip steeply to moderately northward, comprise an essentially continuous narrow belt 

more than 300 km long that adjoins many of the major 

urban centers of the Los Angeles region. 

Offshore, the faults include the Santa Rosa Island 

fault (76) and the Santa Cruz Island fault (77). The 

Anacapa (Dume) fault (78), probably an offshore extension of the Santa Cruz Island fault, appears to link with 

the Santa Monica fault (80). Onshore, the Santa Monica 

fault and the Hollywood fault (81) are subparallel 

elements along the northern margin of the Los Angeles 

basin. The Raymond fault (82) follows the same general 

trend and extends through Pasadena to intersect the 

Earthquake and Surface-Faulting Potential 45 
1200 1190 

34 45' ,----------------------------------------------------,---------------- -----------

~ 

EXPLANATION 

----Fault with historical surface rupture 

----Fault with Holocene (past 10,000 years) 

surface rupture 

---- Fault with late Quaternary (past 750,000 

years) surface rupture 

Identification number of fault listed in table 5 

0 10 20 30 MILES 

0 10 20 30 40 KILOMETERS 

SANTA MONICA MOUNTAINS 

39 

33°15' 39 

12~00.-------------------------------------------------L--------------------------=~ 

119° 

FIGURE 11.-Faults that may generate damaging earthquakes or surface rupture in the Los Angeles region. The latest surface displacements on 

these faults are known to have occurred either during historical time (since 1769 for southern California), during Holocene time, or during late 

Quaternary time. Identification numbers are keyed to table 5, which lists the faults and summarizes their geologic and seismologic character. 

46 Earthquake Hazards in the Los Angeles Region 
116' 45' 

34'45' 

OLa ncast~:·----~---- ~\~~@~' 117' 

MOJAVE DESERT 

) 

~" ~ 83 

SAN GABRIEL MOUNTAINS 

@ o.. Pasadena 85 

~"rbank 

~-------= ~ @ @ 

0 Los Angeles 

"67) 

\~ 

WhittierO 

~ ~ 

_ong Bea c~ 

~ 0 Santa Ana 

0 Victorville 

BERNARDINO MOUNTAINS 

0 San Clemente 

-

---------------~~----------------=-~~'-~~C----------------------------, 118' 1~1,.7'c- --,;116'45 33'15' ' 

Earthqua k e a nd Surface-Faulting Potential 47 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region 

(For available geologic information on fault slip rates and recurrence intervals for major earthquakes, see tables 10 and 11, respectively. Evidence of faulting age: OS, offset stratigraphy; P, faultproduced physiographic features; W, ground-water impediment within late Quaternary alluvial deposits. Type of faulting: R, reverse; N, normal; SR, right-lateral strike slip; SL, left-lateral strike slip; 

RRO, reverse right oblique; RLO, reverse left oblique; NRO, normal right oblique; NW, normal left oblique] 

Map number and fault Geometric aspects 

1 San Andreas fault zone------------Numerous subparallel faults of 

varied length in zone 

generally 0.3-1.5 km wide (as 

wide as 4 km near Palmdale 

and Lake Hughes). Zone 

strikes N. 65°-70° W. but 

near Banning strikes N. 40° 

W. Most faults are approximately vertical, although SE. 

from Cajon Pass generally 

dip 55°-60° NE. The most 

recently active element 

within zone typically composed of linear segments 0.5 

to 11 km long arranged in 

echelon manner in belt as 

wide as 100 m. Scattered 

splay faults locally diverge 

from trend of main zone. 

Subsidiary south-dipping 

faults common on southern 

side of zone adjacent to 

Antelope Valley. Fault zone 

extends as continuous surface feature from near Banning NW. more than 1,000 

km to Cape Mendocino. 

Connected by Banning fault 

(95) to Indio segment of San 

Andreas fault NE. of Imperial Valley. 

San Jacinto fault zone: 

2 Glen Helen-----------------Single strand. Strikes 

N. 40°-60° W. Presumed vertical dip. Length at least 

8km. 

3 San Jacinto-----------------Several strands in zone as wide 

as 0.3 km. Strikes N. 40"-60° 

NW. Dips 35° NE. to vertical. Length approximately 

25 km. 

4 Lytle Creek-----------------Single strand. Strikes N. 45° 

W. Dips 65° SW. Length at 

least 12 km. 

5 Claremont------------------Single strand composed of 

closely overlapping breaks. 

Strikes N. 40°-55° w. Dip 

vertical or steeply N E. 

Length approximately 65 km. 

Age and evidence 

of latest 

surface faulting 

Historical (1857) SE. to Wrightwood. Holocene (OS, P) from 

Wrightwood to near Banning. Splay and subsidiary 

faults chiefly late Quaternary 

(OS, Pj. 

Holocene (P, W) 

Late Quaternary (OS) 

Late Quaternary [OS, W) 

Holocene (OS, P, W); historical 

creep ncar Hemet possibly 

related to subsidence due to 

ground-water withdrawal. 

48 Earthquake Hazards in the Los Angeles Region 

Type of 

late 

Quaternary 

offset 

SR 

SR 

SR, RRO 

RRO 

SR 

Seismicity 

Source of 1857 Fort Tejon 

earthquake (estimated M 

7 .9), whose epicenter probably was in the 

Parkfield-Cholame area of 

central California. Possible 

source of july 22, 1899, 

earthquake (estimated ML 

6.5) near San Bernardino. 

Diffuse belt of scattered 

small earthquakes 

associated with fault zone. 

Closely associated small 

earthquakes. Geometrically 

compatible fault-plane 

solutions. Possible source 

for two damaging earthquakes of ML 2o6 (1899, 

1907). 

Numerous small earthquakes 

near fault trace. 

Geometrically compatible 

fault-plane solutions. 

Numerous small earthquakes 

near fault trace. 

Geometrically compatible 

fault-plane solutions. 

Scattered small earthquakes 

near fault trace. Possible 

source for four damaging 

earthquakes of MI.~ 6 

{1890, 1899, 1918, 1923). 

Sources of information 

Mapping, Quail 

Lake-Wrightwood: 

Barrows and others (1985) 

Mapping, Quail 

Lake-Palmdale: 

Beeby (1979) 

Kahle {1979) 

Kahle and others (1977) 

Kahle and Barrows {1980) 

Mapping, 

Palmdalt>-Wrightwood: 

Barrows and others (1976) 

Barrows (1979, 1980) 

Schubert and Crowell 

(1980). 

Mapping, 

Wrightwood-Banning: 

j. C. Matti (unpublished 

data, 1983). 

Miller {1979) 

Morton and Miller (1975) 

Ross (1969) 

Slip/recurrence: 

Davis and Duebendorfer 

{1982). 

Rasmussen (1982a) 

Rust (1982) 

Sieh (1978a, c, 1984) 

Weldon and Sieh (1981) 

Seismicity: 

Green (1983) 

Hileman and Hanks {1975) 

C. E. johnson (unpublished 

data, 1982). 

Cramer and Harrington 

(1984, in press). 

Pechmann (in press) 

Sharp (1972) 

Thatcher and others (1975) 

Cramer and Harrington 

(1984, in press). 

C. E. Johnson [unpublished 

data, 1982). 

Morton (1975, 1976) 

Cramer and Harrington 

(1984, in press). 

C. E. johnson (unpublished 

data, 1982). 

Mezger and Weldon (1983) 

Morton (1975, 1976) 

Fell (1987) 

Given (1981) 

Green [1983) 

C. E. Johnson [unpublished 

data, 1982). 

Morton (1978) 

Sharp (1972) 

Thatcher and others (1975) 
TABLE 5.-Geologic and seismologic· characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

San Jacinto fault woe-Continued: 

6 Casa Lorna-----------------Several closely overlapping 

echelon strands. Strikes N. 

35°-40° W. Dips 50"-70° 

NE. Length approximately 

18 km. 

7 Hot Springs-----------------Single strand. Strikes east-west 

to N. 45° W. Dips steeply 

NE. Leogth approximately 

29 km. 

8 Clark---------------------- Single strand composed of 

closely overlapping breaks. 

Strikes N. 50°-60° W. Dips 

vertically to 6() 0 NE. Length 

at least 85 km. 

9 Rialto-Colton-------------------·-Two echelon strands. 

Strikes N. 45°-55° W. 

Presumed vertical dip. 

Total length 26 km. 

10 Central Avenue-----------------Presumed single strand. 

Strikes N. 35° W. 

Dip unknown. 

Length at least 8 km. 

11 Chino------------------------ Single strand. 

Strikes N. 35°-50° W. 

Dips 60°-65° sw. 

Length at least 18 km. 

12 Whittier-----------------------One to three subparallel 

strands in zone as wide as 

1.2 km. Strikes 

Elsinore fault zone: 

N. 65°-80° NE. Dips 

65°-80° NE. Length at least 

40km. 

13 Main Street-----------------Several overlapping strands. 

Strikes N. 60°-800 W. 

Presumed to dip steeply SW. 

Length approximately 7 km. 

14 Fresno-Eagle---------------- Single strand. Strikes N. 

55°-65° W. Dips 

15°-50° SW. Length at least 

16km. 

15 Tin Mine-------------------Single strand. 

Strikes N. 50° W. 

Vertical dip. Length approx· 

imately 5 km. 

Age and evidence 

of latest 

Surface faulting 

Holocene (OS, P, W); creep 

movement since at least 

1939, possibly related to sub· 

sidence due to ground·water 

withdrawal. 

Probably late Quaternary (P) 

Holocene (OS, P) 

Late Quaternary (W); no sur· 

face expression. 

Late Quaternary (W); no sur· 

face expression. 

Late Quaternary (OS, P, W) 

Late Quaternary (OS, P) 

NW. of Brca Canyon; 

Holocene (OS) SE. to near 

Santa Ana River. 

Probably Holocene (P) 

Late Quaternary (P) 

Late Quaternary (P) 

Type of 

late 

Quaternary 

offset 

Nor NRO 

R or RRO 

SR and RRO 

SR 

RRO 

RRO 

R or RRO 

R or RRO. 

SR 

Seismicity 

Scattered small earthquakes 

near fault trace. 

Scattered small earthquakes 

at southern end of fault 

trace. 

Numerous closely associated 

small earthquakes along 

northern and southern sectors. Geometrically compatible fault-plane solution. 

Possible source for ML 6 

earthquake in 1937. 

Numerous small earthquakes 

nearby. 

Scattered small earthquakes 

SW. of fault trace. 

Numerous small earthquakes 

closely associated with 

fault. 

Sources of infonnation 

Given {1981) 

Fett (1967) 

Morton (1978) 

Proctor (1962, 1974) 

Rasmussen (1981, 1982b) 

C. E. johnson (unpublished 

data, 1982). 

Given (1981) 

Sharp {1967) 

Given (1981) 

Sanders and I<anamori (1984) 

Sharp (1967, 1972, 1981a) 

Thatcher and others {1975) 

California Department of 

Water Resources (1970). 

C. E. johnson (unpublished 

data, 1982). 

Morton (1976) 

Ziony and others (1974) 

Durham and Yerkes (1964) 

Heath and others (1982) 

C. E. johnson (unpublished 

data, 1982). 

Weber (1977) 

Durham and Yerkes (1964) 

Hannan and others (1979) 

C. E. johnson (unpublished 

data, 1982). 

Lamar (1972, 1973) 

Morton and others (1973) 

Yerkes (1972) 

Hart and others (1979) 

Weber (1977) 

Weber (1977) 

Weber (1977) 

Earthquake and Surface-Faulting Potential 49 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Elsinore fault zone-Continued: 

16 Glen Ivy North--------------Single strand of closely overlapping breaks. Strikes N. 

40°-55° W. Dips 70° SW. 

except for vertical to steeply 

NE. dip near Lake Elsinore. 

Length at least 28 km. 

17 Glen Ivy South---------------Single strand. Strikes N. 

35°--65° W. Dips 

45°-50° SW. Length 7 km. 

18 Wildomar------------------ One to five subparallel strands 

in 7.0ne locally 0.7 km wide. 

Strikes N. 45°-65° W. Dips 

steeply SW. Length at least 

40km. 

19 Willard-------------------- Several discontinuous echelon 

strands. Strikes N. 50°-55° 

W. Presumed to dip steeply 

NE. Total length at least 35 

km. 

20 Wolf Valley-----------------Single strand. Strikes 

N. 55°-75° W. Presumed vertical dip. Length 6 km. 

21 Murietta ---------------------- Several overlapping strands. 

Hot Springs. Strikes N. 80° E. to N. 70° 

W. Dips 80°-85° S. Length 

at least 12 km. 

22 Norwalk---------------------- Presumed single strand. 

Strikes N. 65°-85° W. 

Dips steeply N E. 

Length at least 14 km. 

23 Faults in----------------------Four subparallel faults in zone 

West Coyote 2.0 km wide. Strikes N. 

Hills. 10°-45° W. Dips 70° SW. to 

55° NE. Lengths from 1 to 

1.5km. 

24 Peralta Hills--------------------Single strand. 

Strikes N. 80° W. to N. 80° 

E. Dips 0°-60° N. Length at 

least 8 km. 

Age and evidence 

of latest 

surface faulting 

Holocene (OS, Pi 

Holocene (P) 

Holocene (OS, P) 

Late Quaternary (OS, P ) 

Late Quaternary (OS, P, W) 

Late Quaternary (OS, P, W) 

Possibly late Quaternary (P) 

Late Quaternary (OS); historical 

{1968) surface rupture along 

westernmost fault probably 

related to withdrawal of oil 

and gas. 

Late Quaternary (OS, P) 

SO Earthquake Hazards in the Los Angeles Region 

Type of 

late 

Quaternary 

offset 

NRO 

RRO 

NRO 

NRO 

SR 

N 

R(?) 

RLL 

R 

Seismicity 

Numerous closely associated 

small earthquakes at 

northern end. Possible 

source of ML 6 earthquake 

in 1910. 

Numerous closely associated 

small earthquakes. 

Scattered small earthquakes 

nearby. 

Scattered small earthquakes 

nearby. 

Numerous closely associated 

small earthquakes. 

Scattered small earthquakes 

NE. of fault trace. Possible 

source for damaging 1929 

earthquake (ML 4.7). 

Numerous small earthquakes 

neamy. 

Sources of information 

C. E. johnson (unpublished 

data, 1982). 

Langenkamp and Combs 

(1974). 

Millman {1985) 

Rockwell and others (1985) 

Weber (1977) 

C. E. johnson (unpublished 

data, 1982). 

Langenkamp and Combs 

(1974). 

Millman (1985) 

Weber (1977) 

C. E. johnson [unpubiished 

data, 1982). 

Kennedy (1977) 

Lamar and Swanson (1981) 

Langenkamp and Combs 

(1974). 

Weber (1977) 

C. E. johnson (unpublished 

data, 1982). 

Hart and others (1979) 

Langenkamp and Combs 

(1974). 

Kennedy (1977) 

Weber (1977) 

Hart and others (1979) 

C. E. johnson (unpublished 

data, 1982). 

Kennedy (1977) 

Kennedy [1977) 

Lamar (1973) 

C. E. johnson [unpublished 

data, 1982). 

Richter (1958) 

Yerkes [1972) 

Morton and others (1973) 

Yerkes (1972) 

Bryant and Fife (1982) 

Fife and others (1980) 

C. E. johnson (unpublished 

data, 1982). 

Morton and others (1973) 

Schoellhamer and others 

(1981). 
TABLE 5.-Geologic and seisrnologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Newport-Inglewood fault zone: 

25 Inglewood------------------Single strand locally offset by 

short north- and 

NE.-trending faults. Strikes 

N. 5°-30° W. Dips 70° W. 

Length at least 13 km. 

26 Potrero-------------------- Single strand. Strikes N. 25" 

W. Dips 77° W. at surface, 

82' W. at depth. Length 

7km. 

27 Avalon-Compton-------------Single strand. 

Strikes N. 20 '-30' W. 

Presumed vertical. 

Length at least 4 km. 

28 Cherry-Hill ----------------- Single strand. 

29 Reservoir HillSeal Beach. 

Strikes N. 39"-50" W. 

Dips 80' E. 

Length at least 9 km. 

------------Single strand. 

Strikes N. 59" W. 

Dips near vertical. 

Length at least 12 km. 

30 Newport-Inglewood---------- One to three closely spaced 

(North Branch). strands. Strikes N. 40'-60' 

W. Dips steeply SW. Length 

at least 18 km. 

31 Newport-Inglewood----------Single strand. Strikes N. 45' 

(South Branch). W. Dips steeply SW. Length 

at least 10 km and possibly 

joins similarly oriented fault 

offshore Dana Point. 

32 Faults offshore of----------------Two echelon strands. Strikes 

San Clemente. N. 45"-55" W. Dip 

unknown. Length of each 

fault at least 25 km. 

33 Pelican Hill--------------------Several strands. 

Strikes N. 15'-35' W. 

Dips 75 ° W. at surface but 

45' W. at depth. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (OS, P); surface faulting since 1957 

locally along north-trending 

faults in response to 

withdrawal of oil and gas. 

Late Quaternary (P, W) 

Late Quaternary (P. W); 

historical (1941, 1944) 

faulting within 1.5 km of surface along subsidiary southdipping reverse faults. 

Late Quaternary (OS, P, WJ 

Late Quaternary (OS, P, W) 

Holocene (OS, W); possible 

historical surface faulting 

(1933) at Newport Mesa. 

Late Quaternary (P) 

Late Quaternary (OS, P) 

Late Quaternary (OS) along 

subsidiary fault. 

Type of 

late 

Quaternary 

offset 

N orNRO 

N orNRO 

SR(?) 

R or RRO 

NRO orSR 

SR 

SR 

SR(?) 

N orNRO 

Seismicity 

Numerous small earthquakes 

nearby. Geometrically 

compatible fault-plane 

solution. Possible source 

of 1920 earthquake (M1 4.9). 

Numerous small earthquakes 

nearby. 

Scattered small earthquakes 

nearby. Epicenters of 1941 

(ML 4.9) and 1944 (M1 4.5) 

lie SW. of fault trace. 

Numerous small earthquakes 

lie east of trace. Fault 

overlies aftershock zone of 

1933 Long Beach earthquake (M 6.2). 1941 Torrance-Gardena earthquake 

(ML 5.4) located SW. of 

fault trace. 

Numerous small earthquakes 

near trace. Fault overlies 

aftershock zone of 1933 

Long Beach earthquake (M 

6.2). 

Scattered small earthquakes 

near trace. Fault is adjacent to aftershock zone of 

1933 Long Beach earthquake (M 6.2). 

Scattered small earthquakes 

near trace. Fault is adjacent to aftershock zone of 

1933 Long Beach earthquake (M 6.2). 

Concentrations of small 

earthquakes locally along 

traces. 

Scattered small earthquakes 

west of trace. 

Sources of infonnation 

Barrows (1974) 

Buika and Teng (1979) 

Castle and Yerkes (1976) 

Poland and others (1959) 

). C. Tinsley (unpublished 

data, 1983). 

Barrows (1974) 

Buika and Teng (1979) 

Poland and others (1959) 

Bravinder (1942) 

Buika and Teng (1979) 

Mariner (1948) 

Poland and others (1959) 

Hileman and others (1973) 

C. E. johnson (unpublished 

data, 1982). 

K. R. Lajoie (unpublished 

data, 1983). 

Poland and Piper (1956) 

Yerkes and others {1965) 

Hileman and others (1973) 

C. E. Johnson (unpublished 

data, 1982). 

Pola.nd and Piper (1956) 

California Department of 

Water Resources (1966, 

1968). 

Guptill and Heath (1981) 

Hileman and others (1973) 

C. E. johnson (unpublished 

data, 1982t 

California Department of 

Water Resources (1968) 

Hileman and others (1973( 

C. E. johnson (unpublished 

data, 1982). 

Poland and Piper (1956) 

Clarke and others (this 

volume). 

C. E. johnson (unpublished 

data, 1982). 

Castle (1966) 

Morton and others (1973) 

). E. Slosson (personal communication, 1973). 

Earthquake and Surface-Faulting Potential 51 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

34 Charnock and------------------Two fault strands. 

Overland A venue. Strikes N. 35' W. 

Presumed vertical dip. 

Length at least 10 km. 

35 Palos Verdes Hills---------------Several echelon strands locally 

in a zone as wide as 2 km. 

Strikes N. 20'...00' W. Onshore segment generally not 

exposed. Dip 70° SW. in 

subsurface of Palos Verdes 

Hills, although exposed subsidiary fault dips 75' NE. 

Total length at least 80 km. 

36 Redondo Canyon----------------Presumed single strand. Strikes 

N. 80°--85° E. Dip unknown. 

Length approximately 13 km. 

37 Cabrillo -----------------------Several echelon strands. 

Strikes N. 20'-50' W. 

Dips 50°-75° onshore. 

Length approximately 18 km. 

38 San Pedro Basin----------------Series of separate, left-stepping 

fault zone. echelon strands in zone 

locally as wide as 5 km. 

Strikes N. 35'-50' W. 

Presumed vertical dip. 

Length of individual strands 

4-12 km; length of entire 

zone at least 70 km. 

39 Faults of the--------------------Echelon strands in zone locally 

Santa Cruz- 4 km wide. Strikes N. 

Catalina sea-floor 

escarpment. 

Faults of Mojave Desert region: 

50°-60° W. Length of individual strands 5 to 40 km; 

length of entire zone at least 

120 km. 

40 Llano----------------------Single strand. Strikes N. 65° 

W. Presumed dip to SW. 

Length at least 6 km. 

41 Mirage Valley---------------Several echelon strands, each 

1-7 km long, locally in zone 

3 km across. Strike N. 

40°-50° W. Presumed vertical dip. Total length of 

zone approximately 30 km. 

42 Helendale------------------ Numerous echelon strands, 1 

to 4 km long, forming narrow linear zone as wide as 1 

km. Strands strike N. 

45°-50° W. Presumed ver~ 

tical dips. Total length of 

wne at least 90 km. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (OS); no surface expression. 

Holocene (OS) in San Pedro 

Bay. Late Quaternary (OS, P) 

onshore and probably 

overlain by Holocene 

alluvium. Inferred late 

Quaternary (OS) in Santa 

Monica Bay. 

Holocene (P) 

Holocene (OS) offshore 

Late Quaternary (OS) 

Possibly late Quaternary (P) 

Holocene {P) monoclinal 

folding. 

Late Quaternary; overlain by 

unfaulted Holocene alluvial 

fan deposits. 

Holocene (P) 

52 Earthquake Hazards in the los Angeles Region 

Type of 

late 

Quaternary 

offset 

SR(?) 

R or RRO 

R(?) 

Nor NRO 

SR or RRO 

SR 

R 

SR(?) 

SR 

Seismicity 

Numerous small earthquakes 

nearby. Geometrically 

compatible fault-plane 

solutions. 

Numerous small earthquakes 

near and west of fault 

trace. Geometrically compatible fault-plane solution 

in Santa Monica Bay. 

Scattered small earthquakes 

near trace. 

Scattered small earthquakes 

ncar fault trace. 

Numerous small earthquakes 

near and east of fault 

traces. Geometrically compatible fault-plane solutions. 

Source of 1981 Santa Barbara Island earthquake 

(ML 5.2) and aftershotks. 

Closely associated small 

earthquakes. 

Sources of information 

Buika and Tcng (1979) 

Poland and others (1959) 

Buika and Teng {1979) 

Clarke and others {this 

volume). 

Hileman and others (1973) 

Junger and Wagner (1977) 

Nardin and Henyey (1978) 

Poland and others (1959) 

Woodring and others (1946) 

Yerkes and others {1965) 

Nardin and Henyey (1978) 

Yerkes and others (1967) 

Clarke and others (this 

volume). 

Darrow and Fischer {1 983) 

Hileman and others (1973) 

Lajoie and others (1979) 

Woodring and others (1946) 

Hileman and others (1973) 

Junger and Wagner (1977) 

Nardin (1981) 

Yerkes and Lee (1979a, b) 

C. E. [ohnson (unpublished 

data, 1982). 

Corbett and Piper (1981) 

C. E. johnson (unpublished 

data, 1982). 

Junger and Wagner (1977) 

Yerkes and Lee (1979a, b) 

Guptill and others (1979) 

Ponti and Burke (1980) 

Ponti and Burke (1980) 

G. S. Fuis (unpublished data, 

1983). 

C. E. johnson (unpublished 

data, 1982). 

Miller and Morton {1980) 

Morton and others (1980) 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Faults of Mojave Desert region (Continued): 

43 Lenwood-------------------Numerous closely overlapping 

echelon strands, 1-5 km 

long, forming continuous 

narrow zone. Strands strike 

N. 25°-40° W. Presumed 

vertical dips. Total length of 

zone at least 65 km. 

Faults within Transverse Ranges: 

44 Santa Ynez-----------------One to seven strands in zone 

as wide as 0.3 km. Strikes N. 

80' W. to N. 85' E. Dips 

45°-80° S., generally 

steepens eastward. Total 

length 130 km; late Quaternary length approximately 80 

km. 

45 San jose (A)-----------------One to two strands. Strikes N. 

60° W. Dip unknown. 

46 Mission RidgeArroyo Parida. 

Length approximately 13 km. 

------------Single strand. Strikes N. 80° E. 

to N. 85' W. Dips steeply S. 

near Santa Barbara but dips 

6(J0-80° N. further east. 

Length approximately 40 km. 

47 More Ranch----------------One to two strands. 

Strikes N. 80' W. to N. 80' 

E. Dips 75'-85' S. Length at 

least 14 km. 

48 Mesa-Rincon Creek----------Single strand. Strikes N. 60° 

W. to east-west. Dips 

65°-35° S. near surface; 

probably vertical at depth. 

Length approximately 37 km. 

49 Lavigia --------------------One to two strands. Strikes N. 

50'-75' W. Dips 45" SW. 

Length at least 7 km. 

50 Shepard Mesa---------------Single strand. 

Strikes N. 60"-70' W. 

Dips 70" S. Length 6 km. 

51 Carpinteria----------------- Single strand. 

Strikes N. 75' W. 

Dips 40° S. 

Length 4 km. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (P). Possible 

historical fault creep at 

northern end. 

Possibly Holocene (OS) along 

one strand near Lake 

Cachuma. Late Quaternary 

(OS, P) as far east as near 

Wheeler Springs 

Late Quaternary (OS) 

Late Quaternary (OS. P); apparently overlain by unfaulted Holocene alluvium. 

Late Quaternary (OS. P) 

Late Quaternary (OS, P) 

Late Quaternary (OS) 

Late Quaternary (OS. P) 

Late Quaternary (OS) 

Type of 

late 

Quaternary 

offset 

SR 

SL 

N(?) 

N 

R 

R 

R 

R 

R 

Seismicity 

Closely associated small 

earthquakes. 

Scattered small earthquakes 

near trace. Mission Ridge 

fault possible source of 

1978 earthquake (ML 5.1). 

Scattered small earthquakes 

near trace. 

Scattered small earthquakes 

near trace. 

Scattered small earthquakes 

near trace. 

Sources of information 

Church and others (1974) 

G. S. Fuis (unpublished data, 

1983). 

C. E. johnson (unpublished 

data, 1982). 

Miller and Morton (1980) 

Morton and others (1980) 

Darrow and Sylvester (1983) 

Dibblee (1966) 

Keaton (1978) 

Yerkes and Lee (19798, b) 

j. I. Ziony (unpublished data, 

1981). 

R. E. Troutman (unpublished 

data, 1984). 

Dibblee (1966) 

Olson (1982) 

Dibblee (1966) 

jackson and Yeats (1982) 

Yerkes and Lee (1979a, b) 

Rockwell (1983) 

Rockwell and others (1984) 

Yeats and Olson (1984) 

Dibblee (1966) 

K. R. Lajoie (unpublished 

data, 1983). 

Upson (1951) 

Yerkes and Lee (1979a, b) 

Dibblee (1966) 

jackson and Yeats (1982) 

Yerkes and Lee (1979a, b) 

Dibblee (1966) 

Olson (1982) 

jackson and Yeats (1982) 

jackson and Yeats (1982) 

K. R. Lajoie (unpublished 

data, 1983). 

A. M. Sarna-Wojcicki (unpublished data, 1982). 

Earthquake and Surface-Faulting Potential 53 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Faults within Transverse Ranges-Continued: 

52 Red Mountain---------------Several strands in zone 

1 km wide. Strikes N. 85' W. 

toN. 60° E. Dips 55°--65° N. 

near surface; 70°-75° N. at 

depth; 85° N. at western 

end. Length approximately 

38km. 

53 Fault Y--------------------Probably several strands. 

Strikes east-west to N. 80° E. 

Dip unknown. Length 

approximately 33 km. 

54 }avon----------------------Single strand. 

Strikes N. 80' W. 

Dips 68'S. 

Length at least 4 km. 

55 Pitas Point-Ventura----------Presumed single strand. 

Strikes N. 70° W. to eastwest. Dips steeply north. 

Length at least 50 km. 

56 Santa Ana------------------Two strands at western end. 

Strikes east -west. Dip inferred steeply south. Length 

13km. 

57 Faults near-----------------Five separate strands. 

Oak View. Strikes N. 60' E. Dips 

30°-60° SE. May become 

bedding-plane faults at 

depth. Length from 1 to 3 

km. 

58 Lion Canyon----------------Single strand. 

Strikes N. 60' E. 

Dips 30'-50' S. 

Length approximately 15 km. 

59 San Cayetano---------------T"'{o strands about 0.5 km 

apart west from Sespe Creek; 

single strand to east. Strikes 

N. 60' W. to N. 70' E. Dips 

5°-35° N. near surface, 

55'-70' N. at depth. Length 

approximately 40 km. 

60 Faults of Orcutt--------------Eight separate strands. 

and Timber Strikes N. 80' E. 

Canyons. Dip 55°-70° N. near surface. 

May become shallow 

bedding-plane faults at 

depth. Lengths from 2 to 6 

km. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (OS, P); 

southern branch overlain by 

unfaulted Holocene marine 

terrace deposits (2,000-6,000 

yr ll.P.). 

Holocene (P) 

Holocene (OS) 

Holocene (OS, P) 

Late Quaternary (P. W) 

Holocene (OS, PI 

Late Quaternary (OS, P) 

Holocene (OS, P) 

Late Quaternary (OS, P) 

54 Earthquake Hazards in the Los Angeles Region 

Type of 

late 

Quaternary 

offset 

RLO 

R(?) 

R 

RI.O 

R(?) 

R 

R 

R 

R 

Seismicity 

Numerous dosely associated 

small earthquakes. 

Geometrically compatible 

fault-plane solutions. 

Scattered small earthquakes 

near trace. 

Closely associated small 

earthquakes near eastern 

end. Geometrically compatible fault-plane solutions. Possible source of 

1941 Santa Barbara earthquakes (M 6.0). Alternate 

possible source lor 1978 

Santa Barbara earthquake 

(ML 5.1). 

Scattered nearby small earthquakes. Geometrically 

compatible fault-plane 

solution. 

Sources of information 

jackson and Yeats (1982) 

K. R. Lajoie (unpublished 

data, 1983). 

A. M. Sarna-Wojcicki {unpublished data, 1982). 

Yeats and others (1981, in 

press). 

Yerkes and Lee (1979a, b) 

Crippen and others (1982) 

Yerkes and Lee (1979a, b) 

Yerkes and others (1981) 

A. M. Sarna-Wojcicki and 

others (in press). 

Corbett and johnson (1982) 

Greene and others (1978) 

Lee and others (1978, 1979) 

A. M. Sarna-Wojcicki (unpublished data, 1976). 

Yerkes and Lee (1979a, b) 

Keller and others (1980) 

Rockwell and others (1984) 

Keller and others (1982) 

Rockwell (1983) 

Rockwell and others (1984) 

Yeats and others (1981) 

Schleuter (1976) 

Keller and others (1980) 

Cemen (1977) 

Keller and others {1982) 

Rockwell (1982, 1983) 

Schlueter (1976) 

Yerkes and Lee (1979a, b) 

Keller and others {1980) 

Rockwell (1983) 

Yeats and others (1981)-· 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Faults within Transverse Ranges-Continued: 

61 Holser--------------------- Several closely spaced strands. 

Strikes N. sao E. to N. 70° 

W. Dips 60'-70' S. Length 

approximately 12 km. 

62 Clearwater----------------- One to two strands. Strikes N. 

80° W. to east-west. Generally dips 70'--80' N. but locally 25'--40' N. Late Quaternary length approximately 14 

km. 

63 San Gabriel-----------------Several echelon strands in zone 

(central portion). 0.5 km wide. Strikes N. 

45'--65' W. Dips 50'--80' N. 

Late Quaternary length at 

least 32 km. 

64 Oak Ridge------------------One to three strands in zone as 

much as 0.5 km wide. 

Strikes N. 60' W. to N. 50' 

E. Generally dips 65°-80° S. 

but south of Fillmore dips 

5°-30° s. near surface. 

Length approximately 100 

km. 

65 Springville------------------Two strands in zone about 0.6 

km wide. Strikes N. 65'-75' 

E. Dips 55'--80' N. Length 

about 9 km. 

66 Camarillo------------------ Single strand. 

Strikes east-west. 

Presumed vertical dip. 

Length at least 6 m. 

67 Simi---------------------- Single strand that bifurcates at 

western end. Strikes N. 

70'--80' E. Dips 60'-75' N. 

Length approximately 31 km. 

68 Santa Susana----------------Several strands in zone as 

much as 1 km wide. Strikes 

N. 75' W. to N. 50' E. Dips 

0°-30° N. near surface; 

55'--60' N. at depth. Length 

28 km. 

69 San Fernando---------------Five major echelon strands. 

Strikes N. 75' E. to N. 70' 

W. Dips 15°-50° N. near 

surface, 35 o N. at depth. 

Total length at least 15 krn. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (OS, P) 

Late Quaternary (OS) near San 

Francisquito Canyon but 

overlain by unfaulted late 

Quaternary river terrace 

deposits elsewhere. 

Holocene {OS, W) near Castaic. 

Late Quaternary (OS, P) between Newhall and Big 

Tujunga Canyon. 

Late Quaternary (W. P); 

possibly Holocene south of 

Fillmore (P) and offshore. 

Late Quaternary (P, W) 

Late Quaternary (P, W) 

Late Quaternary (OS, P); 

overlain by unfaulted 

Holocene alluvium {about 

4,000 yr B.P.). 

Late Quaternary (OS); overlain 

by unfaulted Holocene 

stream terrace deposits (approximately 10,000 yr B.P.). 

Locally at northeastern end, 

historical surface faulting accompanied 1971 San Fernando earthquake. 

Surface faulting accompanied. 

1971 San Fernando eerthquake. 

Type of 

late 

Quaternary 

offset 

R 

R(?) 

Nor NRO 

R 

R(?) 

R(?) 

R 

RW 

RW 

Seismicity 

Numerous closely associated. 

small eerthquakes near 

western end. Geometrically compatible fault-plane 

solution south of Santa 

Paula. Western end possible source of 1925 Santa 

Barbara earthquake (M 

6.8). 

Closely associated small 

earthquakes, including ML 

3.1 event in 1969. 

Scattered associated small 

earthquakes, including ML 

4.6 event neer Gillibrand 

Canyon in 1976. 

Geometrically compatible 

fault-plane solutions. 

Source of 1971 San Fernando earthquake (M 6.6) and 

aftershocks. Geometrically 

compatible fault-plane 

solutions. 

Sources of information 

Cemen (1977) 

Stitt (1983) 

Weber (1978, 1982) 

Lns Angeles County 

Engineer, unpublished 

data, 1965). 

Stanley (1966) 

Cotton and others (1983) 

NeUigan (1978} 

Stitt (1983) 

Weber (1978, 1982; unpublished data, 1984). 

Ricketts and Whaley (1975} 

Rieser (1976) 

Weber and Kiesling (1975) 

Yeats and others (1981, 1982) 

Yerkes and Lee (1979a, b) 

Jakes (1979) 

Gardner (1982) 

. Jakes (1979) 

Jakes (1979) 

C. E. johnson (unpublished 

data, 1982). 

Hanson (1981) 

Weber and Kiesling (1975) 

Leighton and others (1977} 

Lung and Weick (1978) 

Sirnila and others (1982) 

Weber (1975) 

Yeats and others (1977) 

Yerkes and Lee (1979a, b) 

Allen and others (1975) 

Barrows (1975) 

Bonilla (1973) 

Kahle (1975) 

Sharp (1975) 

U.S. Geological Survey Staff 

(1971). 

Weber (1975) 

Earthquake and Surface-Faulting Potential 55 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Faults within Transverse Ranges-Continued: 

70 Mission Hills----------------Presumed single strand. 

Strikes N. 80° E. to east-west. 

Dips 80° N. near surface, 

45• N. at depth. Length at 

least10km. 

71 Northridge----------------- Several echelon strands in zone 

0. 7 km wide. Strikes N. 

70°-80° W. Dips 35° N. near 

surface, 80° N. at depth. 

Length approximately 15 km. 

72 Verdugo ------------------- Presumed multiple strands in 

zone 0.5-1.0 km wide. 

Strikes N. so•-7o• W. Infer· 

red to dip 45•--oo• NE. 

Length at least 20 km. 

73 Eagle Rock-----------------Single strand. Strikes N. oo• 

W. to east-west. Dips 

15°-30° N. at western end. 

Length at least 5 km. 

74 San Rafael------------------Echelon strands. 

Strikes N. oo•-7o• W. 

Presumed near-vertical dip. 

Total length approximately 

6km. 

75 Possible fault---------------- Presumed single strand. 

in North Strikes N. so• E. 

Hollywood. Presumed vertical dip. 

Faults along southern margin of 

Transverse Ranges: 

Length approximately 2 km. 

76 Santa Rosa Island------------Single strand. Regionally arcuate, striking N. so• W. at 

western end and N. 60° E. at 

eastern end. Dip unknown. 

Length at least 72 km. 

77 Santa Cruz Island------------One to three echelon strands in 

zone as wide as 0.5 km. 

Strikes N. 70•-ao• W. Dips 

7o•-7s• N. Length at least 

68km. 

78 Anacapa [Dume)-------------Presumed single strand in 

west; multiple strands in 

east. Strikes N. 80° W. toN. 

oo• E. Inferred to dip 

moderately north. Length at 

least45 km. 

79 Malibu Coast----------------Several subparallel strands in 

zone as wide as 0.5 km. 

Strikes east·west and dips 

45•-ao• N. Length at least 

27 km. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary or Holocene 

[OS, P, W). 

Late Quaternary or Holocene 

(P, W). 

Holocene [OS, P, W) 

Possibly late Quaternary [OS, 

P). 

Possibly late Quaternary [P) 

Possibly Holocene [P) 

Late Quaternary [OS, P) 

Late Quaternary [OS, P) 

Probably late Quaternary [P) 

Late Quaternary [OS) 

56 Earthquake Hazards in the los Angeles Region 

Type of 

late 

Quaternary 

offset 

R[?) 

R? 

R[?) 

R[?) 

RLO 

RLO 

R 

R 

Seismicity 

Several aftershocks of 1971 

San Fernando earthquake 

are closely associated with 

fault. 

Scattered small earthquakes 

near trace. 

Probable source of April 1, 

1945, earthquake [M1 5.4). 

Generally lacks small earthquakes. Possible source of 

ML 5.0 earthquake near 

Anacapa Island in 1973. 

Source of 1973 Point Mugu 

earthquake (M 5.3) and 

aftershocks. Geometrically 

compatible fault-plane 

solution. 

Numerous small earthquakes 

nearby. 

Sources of information 

Kowalewsky (1978) 

Saul (1975) 

Shields (1978) 

Barnhart and Slosson (1973} 

Shields (1978) 

Weber (1980) 

C. E. johnson [unpublished 

data, 1982). 

Weber (1980) 

Weber (1980) 

Weber (1980) 

Weber (1980} 

Hileman and others (1973) 

Junger (1976, 1979) 

Kew (1927) 

Junger (1976, 1979) 

Patterson (1979) 

Yerkes and Lee (1979a, b) 

Junger and Wagner (1977) 

Lee and others (1979) 

Yerkes and Lee (1979a, b) 

K. R. Lajoie (unpublished 

data, 1983). 

Y crkes and Wentworth 

(1985). 

C. E. johnson (unpublished 

data, 1982}. 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Faults along southern margin of Transverse Ranges-Continued: 

80 Santa Monica---------------One or more strands. 

Geometry poorly known. 

Strikes N. 60°--80° E. 

Presumed to dip 45°-65° 

NW. at depth; some nearsurface traces are vertical. 

Length at least 40 km. 

81 Hollywood ----------------- Presumed single strand. 

Geometry poorly known. 

Strikes N. 80° W. toN. 60° 

E. Inferred to dip about 60' 

N. Length approximately 17 

km. 

82 Raymond------------------ One to three strands locally in 

wne 0.4 km wide. Strikes N. 

80' W. to N. 70' E. Dips 

50'-55' N. Length 22 km. 

83 Sierra Madre----------------One to five anastomosing 

strands in zone as wide as 1 

krn. Four distinct salients. 

Strikes N. 55° W. to eastwest. Dips 15°-50° NE. and 

north. Total length approximately 65 km. 

84 Duarte---------------------One to two subparallel strands 

locally in zone 1.5 km wide. 

Strikes N. 60° W. toN. 70' 

E. Presumed to dip steeply 

NE. Length approximately 

14 km. 

85 Clamshell- --------------- Several subparallel strands in 

Sawpit Zone. zone as wide as 1 km. 

Strikes N. 60' E. Dips 

35'-70' NW. Length approximately 16 km. 

86 Cucamonga-----------------Two to three subparallel 

strands in zone as wide as 1 

km. Strikes N. 70° E. to eastwest. Dips moderately to 

steeply north. Length at least 

25 km. 

87 Indian Hill------------------Presumed single strand. 

Strikes east-west 

Dip presumed steeply north. 

Length approximately 9 km. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (OS, P, W) 

Possibly Holocene (P) 

Holocene (OS, P, W). Overlain 

by unfaulted soil {1,600 yr 

B.P.). 

Holocene (OS, P) between Big 

Tujunga and Dunsmore 

Canyons. Elsewhere, late 

Quaternary (OS, P, W). Overlain by unfaulted Holocene 

alluvium in several places. 

Late Quaternary (W); possibly 

Holocene {P, W) along northern strand near Azusa. 

Late Quaternary (OS) 

Holocene (OS, P) along 

southern strands. Late 

Quaternary (OS) along northem strand. 

Late Quaternary (P, W) 

Type of 

late 

Quaternary 

offset 

RLO 

R or RLO 

R or RLO 

R 

R 

R 

R 

SL{?) 

Seismicity 

Small earthquakes closely 

associated with eastern 

end. Geometrica)ly compatible(?) fault-plane solution. 

Some small earthquakes 

associated with eastern 

end. 

Scattered small earthquakes 

lie north of fault trace. 

Possible source of 1855 

Los Angeles earthquake 

(Modified Mercalli intensity VIII). Geometrically 

compatible fault-plane 

solution. 

Few and scattered small 

earthquakes. 

Numerous small earthquakes. Geometrically 

compatible fault-plane 

solutions. 

Scattered small earthquakes 

nearby. 

Sources of information 

Buika and Teng (1979) 

Crook and others (1983) 

Hill (1979) 

Hill and others (1979) 

McGill {1981, 1982) 

Real (in press) 

Crook and others {1983) 

Hill and others (1979) 

Weber {1980) 

Bryant (1978) 

Crook and others (in press) 

Real (in press) 

Weber {1980) 

Yerkes (this volume) 

Crook and others (in press) 

Pechmann (in press) 

Crook and others (in press) 

Morton {1973) 

Crook and others (in press) 

Matti and others (1982, in 

press) 

Morton and Matti (in press) 

Morton and others (1982) 

Pechmann (in press) 

California Department of 

Water Resources {1970). 

Cramer and Harrington 

{1984, in press). 

C. E. johnson (unpublished 

data, 1982). 

Earthquake and Surface-Faulting Potential 57 
TABLE 5.-Geologic and seismologic characteristics of late Quaternary faults in the Los Angeles region-Continued 

Map number and fault Geometric aspects 

Faults along southern margin of Transverse Ranges-Continued: 

88 San Jose (B)-----------------Single strand. 

Strike N. 45°--llO• E. 

Dip presumed steeply north. 

Length approximately 22 km. 

89 Red Hill--------------------Presumed single strand. 

Strikes N. 20• W. to N. 70° 

E. Dip inferred steeply north. 

Length approximately 13 km. 

90 "Barrier 1"------------------Presumed single strand. 

Strikes N. 45 • E. 

Dip unknown. 

Length at least 5 km. 

91 Inferred fault---------------- Presumed single strand. 

near Fontana. 

Faults along margins of San 

Bernardino Mountains: 

Inferred from seismicity to 

strike N. 45• E. Dip 

unknown. Length at least 8 

km. 

92 Cleghorn------------------- Single strand. Strikes N. 6()• 

W. toN. 75° E. Dip near vertical. Length at least 23 km. 

93 North Frontal---------------Numerous discontinuous arFault Zone of cuate strands averaging 2-4 

San, Bernardino km long, locally in a zone as 

Mountains. wide as 6 k:m. Strikes N. 10° 

E. toN. so• W. Dips from 

10°-70° SE. or SW. One 

5-km-long NW.-striking segment is vertical. Total length 

of zone at least 50 km. 

94 Faults of the----------------Several arcuate echelon 

Crafton Hills 

(Crafton, Chicken 

Hill, and Casa 

Blanca faults). 

strands, each 2--ll km long. 

Strikes N. so•--llQ• E. 

95 Banning ------------------- Two to three strands in zone 

locally 4 km wide. Northern 

strand strikes N. 70° W. to 

N. as• W. and dips 35•-7o• 

N. South em strands are 

complex, arcuate segments 

3-10 km long that strike N. 

65° W. to N. so• E. and 

presumably dip moderately 

north. Total length of zone at 

least 45 km. 

Age and evidence 

of latest 

surface faulting 

Late Quaternary (W); overlain 

by unfaulted Holocene 

alluvium. 

Late Quaternary (P, W) except 

Holocene (P) at eastern end. 

Late Quaternary (W); no surface expression. 

Possibly late Quaternary; no 

surface expression. 

Probably Holocene (P) 

Late Quaternary (OS, P); 

overlain by unfaulted. active 

Holocene alluvial fans. 

Late Quaternary (OS, P) 

Holocene (OS, P. W) 

58 Earthquake Hazards in the Los Angeles Region 

Type of 

late 

Quaternary 

offset 

SL(?) 

SL(?) 

SL(?) 

SL(?) 

SL 

R (except 

vertical 

(NW.-striking 

strand may 

be SR) 

N(?) 

R (except 

NW .-striking 

segments 

probably SR). 

Seismicity 

Scattered small earthquakes 

nearby. Geometrically 

compatible fault-plane 

solutions. 

Scattered small earthquakes 

nearby. Geometrically 

compatible fault-plane 

solutions. 

Numerous closely associated 

small earthquakes. 

Numerous closely aligned 

small earthquakes. Composite fault-plane solutions 

suggest left-lateral strikeslip faulting. 

Numerous small earthquakes 

near eastern end of trace. 

Numerous closely associated 

small earthquakes near 

eastern part of zone. 

Numerous closely associated 

small earthquakes. 

Geometrically compatible(?) fault-plane solutions. 

Sources of information 

California Department of 

Water Resources (1970). 

Cramer and Harrington 

(1984, in press). 

C. E. johnson (unpublished 

data, 1 982). 

California Department of 

Water Resources (1970). 

Cramer and Harrington 

(1984, in press). 

Hadley and Combs (1974) 

C. E. johnson (unpublished 

data, 1982). 

Morton (1976) 

California Department of 

Water Resources (1970). 

Cramer and Harrington 

(1984, in press). 

Hadley and Combs (1974) 

C. E. johnson (unpublished 

data, 1982). 

Morton (1976) 

Cramer and Harrington 

(1984, in press) 

Hadley and Combs (1974) 

Morton (1976) 

C. E. johnson (unpublished 

data, 1982). 

Meisling and Weldon (1982a, 

b). 

Meisling (1984) 

C. E. johnson (unpublished 

data, 1982). 

Meisling (1984) 

Miller (in press) 

Green (1983) 

j. C. Matti (unpublished 

data, 1983). 

Morton (1976) 

Allen (1957) 

Green (1983) 

Matti and Morton (1982) 

Yerkes (this volume) 

C. E. johnson (unpublished 

data, 1982). 
FIGURE 12.-Vertical aerial photograph of the northwestern San Bernardino Valley showing urbanization across the surface traces of the San 

Andreas fault zone, which here marks the southern boundary of the San Bernardino Mountains. Arrows point to the most recently active trace 

of the fault, the trace that offsets deposits and landforms of Holocene age. Future large earthquakes, accompanied by surface faulting and 

deformation, can be expected along this trace. (From U.S. Geological Survey photograph VOOB-2-48, scale approximately 1:80,000; taken in 

September 1975.) 

Sierra Madre fault zone. The densely populated San 

Gabriel Valley is separated on the north from the San 

Gabriel Mountains by the geometrically complex zones 

of the Sierra Madre (83), Duarte (84), and Cucamonga 

(86) faults. 

Several isolated late Quaternary faults that probably 

are Transverse Ranges structures lie south of the main 

mountain front. These faults include principally the San 

Jose B (88) and the Red Hill (89) faults, which extend 

through the Pomona area. 

Faults within the western Transverse Ranges.-A 

broad band of late Quaternary faults traverses the interior of the western Transverse Ranges from beyond 

Santa Barbara eastward to Pasadena, where it merges 

with the southern boundary of the Transverse Ranges. 

The faults comprising the band are discrete arcuate 

elements that chiefly dip northward. Segments of this 

band were responsible for several historical damaging 

earthquakes near Santa Barbara and for the 1971 San 

Fernando earthquake. 

The faults in the area around Santa Barbara, Ventura, and the Oxnard Plain have east to northeast 

trends. The major faults that have been active in late 

Quaternary time include the Santa Ynez (44), More 

Ranch (47), Mission Ridge-Arroyo Parida (46), Red 

Mountain (52), and Pitas Point-Ventura (55) faults. East 

of these faults are the San Cayetano (59), Oak Ridge (64), 

and Simi (67) faults. 

The band of faults within and adjacent to the San Fernando Valley mostly strikes west-northwest. From west 

to east, these faults include the Santa Susana (68), San 

Fernando (69), and Sierra Madre (83) fault zones, which 

are closely linked segments of the same system. The central part of the San Fernando Valley is transected by the 

Northridge fault (71), which may merge eastward with 

the northwest-trending Verdugo fault (72) adjacent to 

Earthquake and Surface-faulting Potential 59 
Burbank. North of the valley, several segments of the 

San Gabriel fault (63) locally offset late Quaternary 

deposits, although other segments of this long fault 

apparently do not. 

Although nearly 100 faults having late Quaternary 

offsets have been identified, others that may have ruptured as recently probably exist but are not now 

recognizable as geologically youthful. Unrecognized 

faults that have the potential to cause damaging earthquakes may underlie many of the areas covered by 

Quaternary alluvial deposits. Other such faults undoubtedly exist along the sea floor offshore of southern 

California, especially in the Santa Barbara Channel. 

Thus, we emphasize that figure 11 is not a final and complete accounting of the potentially active faults of the 

region. Indeed, it is expected that, as additional geologic 

and seismologic research is conducted, other active 

faults will be identified. 

HAZARDS FROM ACTIVE FAULTS 

Slip along a fault may result in one or more geologic 

effects that can damage or destroy structures and injure 

their inhabitants. Ground shaking and surface faulting 

are the effects of principal concern when rupture occurs along faults in the Los Angeles region. A related 

effect-the possible generation of tsunami waves by 

earthquakes beneath the sea-may be of concern to 

coastal parts of the region. For certain structures like 

pipelines, canals, and coastal facilities, the regionalscale uplift and subsidence that accompany some large 

earthquakes may pose a minor hazard. 

Earthquake Generation 

Sudden slip along all or part of a fault surface within 

the Earth's crust releases elastic strain energy that has 

accumulated within the nearby rocks and radiates that 

energy in the form of earthquake waves. Figure 13 is an 

idealized model of an earthquake source typical of the 

Transverse Ranges. Vibrational waves are propagated 

large distances in all directions away from the fault. As 

they pass through an area, they produce the shaking effects that are the predominant cause of earthquake 

damage. The severity of ground shaking at any point 

depends upon (1) the size of the earthquake, (2) the 

distance to the ruptured part of the fault plane, and 

(3) the local geologic conditions that either amplify or attenuate (reduce) the earthquake waves. Methods for 

predicting the severity of shaking and the effects of local 

geologic conditions on that shaking are discussed in 

subsequent chapters of this volume. Here we consider 

only the energy release associated with earthquakes. 

60 Earthquake Hazards in the Los Angeles Region 

EARTH'S SURFACE 

FAULT PLANE 

FIGURE 13.-Model of typical earthquake source (modified from Boore, 

1977). Rupture first begins at a point within the Earth's crust, 

termed the focus or hypocenter, and spreads across part of the existing fault plane. Surface faulting occurs when the rupture propagates to the Earth's surface; the surface rupture does not 

necessarily coincide with the epicenter, the point on the Earth's 

surface directly above the hypocenter. The fault illustrated here is 

a reverse oblique-slip fault whose orientation is specified by its 

angles of strike and dip. The dimensions of an earthquake source 

at depth can usually be estimated from the distribution of carefully 

located aftershocks, the smaller earthquakes that commonly follow 

the main shock. In southern California, earthquake hypocenters 

generally are less than 15 km deep. The intersection of the fault 

with the ground surface, called the fault trace, is the line observed 

by geologists and plotted on maps (for example, fig. 11). If a significant component of vertical movement occurs along the fault, a low 

step, or scarp, may be formed along the fault trace. Fault scarps 

are the most obvious expression of active faults at the Earth's 

surface. 

The most common expression of the size of an earthquake is magnitude, which is a number based on measurement of the maximum motions recorded by a seismograph for earthquake waves of a particular frequency. 

The concept of magnitude was introduced by Richter 

(1935), who defined it as the logarithm of the maximum 

recorded amplitude written by a seismograph of specified sensitivity 100 km from the earthquake (observations at distances other than 100 km are corrected to the 

standard distance by using empirical curves). The local 

magnitude scale, termed M1, was originally devised for 

southern California earthquakes, which are generally 

less than 15 km deep. Later, other magnitude scales 

were developed for more distant and deeper earthquakes: Ms estimates the strength of distant shallowfocus earthquakes from long-period seismic waves that 

propagate near the surface of the Earth, and mb 
TABLE 6.-Seismic moments, magnitudes, and likely fault sources for larger earthquakes in southern 

California since 1857 

[Moments and magnitudes are chiefly from Hanks and others [1975), Hanks and Kanamori (1979), and Kanamori and Regan (1982)] 

Moment, Magnitude 

Date x 10" dyne-em ML Ms 

Jan. 9, 1857 ---------900 

Dec. 25, 1899 ------- 15 

Apr. 21, 1918 ------- 15 6.8 

July 23, 1923 -------- 1 6'1· 

June 29, 1925 ------- 20 6'1· 

Nov. 4, 1927 --------100 7.3 

Mar. 11, 1933 ------- 2 6.3 6'/• 

May 19, 1940 ------- 30 6.4 6.7 

July 1, 1941 ---------- .9 5.9 5.9 

Oct. 21, 1942 -------- 9 6.5 6'h 

Apr. 10, 1947 ------- 7 6.2 6.4 

Dec. 4, 1948 -------- 1 6.5 6.5± 

July 21, 1952 --------200 7.2 7.7 

Mar. 19, 1954 ------- 4 6.2 

Apr. 9, 1968 -------- 6 6.4 6.7 

Feb. 9, 1971 -------- 10 6.4 6.6 

Feb. 21, 1973 -------- .1 5.9 5.2 

Oct. 15, 1979 -------- 7 6.6 

estimates the strength of distant earthquakes of any 

focal depth from seismic waves that penetrate deep 

within the Earth. Each scale has limitations; none 

satisfactorily measures the very largest earthquakes 

because each relates to only certain frequencies of 

seismic waves and because the spectrum of radiated 

seismic energy changes with earthquake size. Other 

limitations on seismogram-derived magnitudes include 

uncertainties with regard to the attenuation characteristics of the Earth's interior through which the earthquake waves pass and the effect of geologic conditions 

near the instrument on recorded amplitudes. The different magnitude scales have been discussed in greater 

detail by Lee and Stewart (1981), Chung and Bernreuter 

(1981), and Nuttli and Hermann (1982). 

A more fundamental measure of the size of an earthquake is seismic moment, which relates the strength of 

an earthquake directly to the physical attributes of the 

fault slip generating the event. Seismic moment is defined as the product of the area of the rupture, the average amount of slip, and the shear modulus (or strength) 

of the rocks involved. Seismic moment can be estimated 

from geologic information obtained after an earthquake 

(for example, the length of surface faulting or aftershock 

zone and the measured amounts of slip) or from analysis 

of seismograph recordings; it can also be estimated from 

the dimensions of shaking intensity patterns observed 

from an earthquake. Hanks and others (1975) have discussed seismic moment in greater detail. 

A new magnitude scale based on the concept of 

seismic moment was recently devised (Hanks and 

Kanamori, 1979). Termed the moment magnitude (M) 

M Probable fault source 

7.9 San Andreas 

6.8 Claremont (San Jacinto zone) 

6.8 Claremont (San Jacinto zone) 

6.0 Claremont (San Jacinto zone) 

6.8 In Santa Barbara Channel 

7.3 Offshore Point Arguello 

6.2 Newport-Inglewood zone (offshore) 

7.0 Imperial (San Jacinto zone) 

6.0 In Santa Barbara Channel 

6.6 Coyote Creek (San Jacinto zone) 

6.5 In Mojave Desert 

6.0 Mission Creek 

7.5 White Wolf 

6.4 Coyote Creek (San Jacinto zone) 

6.5 Coyote Creek (San Jacinto zone) 

6.6 San Fernando 

5.3 Anacapa 

6.5 Imperial (San Jacinto zone) 

scale, it is uniformly applicable to all sizes of earthquakes. The M scale is approximated by ML in the 

magnitude range 3 to 7 and by Ms in the magnitude 

range 5 to 7%. Because the M scale avoids many of the 

limitations of traditional instrumental magnitude scales 

and still relates well to other scales in the appropriate 

magnitude ranges, seismologists and geologists are 

using it more frequently to express earthquake size or 

strength. Other advantages are that the rate of occurrence of earthquakes having different M values can be 

related directly to the slip rate on faults (Molnar, 1979) 

and that the moment magnitude for both past and future 

earthquakes can be estimated directly from the assumed dimensions of fault rupture (Wallace, 1982). 

Because M is a newly developed quantity, it has been 

determined only for some of the most important past 

earthquakes. Table 6 compares the seismic moments 

and magnitudes of the larger earthquakes in southern 

California since 1857. This chapter will use M values, 

where they have been computed, to express the size of 

earthquakes being discussed. 

Like other magnitude scales, M uses small numbers to 

express vast differences in earthquake size. In absolute 

terms of radiation of seismic energy, energy release increases about 32 times with each increase in magnitude 

unit (table 7). Because the amount of energy radiation 

reflected in the various magnitude scales increases 

geometrically, small differences in magnitude are much 

more significant at the higher ends of the scales than 

they are at the lower ends. The difference in radiated 

energy between earthquakes of M 7.9 and M 8.0, for 

Earthquake and Surface-Faulting Potential 61 
TABLE 7.-Comparison of differences in magnitude and radiated 

energy for any two earthquakes 

[Modified from a table by K. R. Lajoie (Blair and Spangle, 1979)] 

Difference in 

magnitude 

Difference in 

radiated energy 

5--------------------------------32,000,000 

4 -------------------------------- 1,000,000 

3-----------------------------------32,000 

2------------------------------------1,000 

1---------------------------------32 (31.6} 

.1------------------------------------1A 

example, is about one million times larger than the difference between earthquakes of M 3.9 and M 4.0. 

Although wider areas may be damaged by larger earthquakes, however, damage is not proportional to the 

radiated energy. 

Regardless of the method used to express the strength 

of an earthquake, a fundamental relation that holds for 

all magnitude scales has been observed-the amount of 

earthquake energy released is related to the size of the 

fault area that has slipped and to the amount of the 

displacement. Figure 14 shows that larger areas of fault 

rupture generally result in larger earthquakes. 

Surface Faulting and Related 

Permanent Ground Deformation 

When slip along a fault plane extends to the Earth's 

surface, the effects can have profound significance for 

buildings, dams, pipelines, and other structures that 

straddle or cross the fault trace. These effects include 

rupture and offset of the land surface, local warping 

and tilting of the ground near the fault trace, and, less 

commonly, uplift or subsidence of adjoining areas. 

These permanent ground deformations, although they 

affect smaller areas than the shaking effects of an 

earthquake affect, can damage or even destroy structures. Examples of structural damage caused by surface 

faulting and distortion that accompanied a modern 

earthquake in an urban area are shown in figure 15. 

Whether slip along a fault during an earthquake 

reaches the ground surface depends on the size, depth, 

and orientation of the earthquake rupture surface. 

Large shallow earthquakes in California commonly are 

accompanied by surface faulting or deformation. Generally, surface faulting is associated with earthquakes 

having hypocenters shallower than 15 km and magnitudes of M 5.5 or greater. Under special circumstances, 

surface rupture has occurred in association with earthquakes as small as M 2.5 (Yerkes and others, 1983); offsets for such shocks, however, are typically small. 

62 Earthquake Hazards in the Los Angeles Region 

Comparison of worldwide data on historical surface 

faulting indicates that larger magnitude earthquakes 

are associated with longer surface faults and greater 

displacements (Bonilla and Buchanan, 1970; Slemmons, 

1977; Mark and Bonilla, 1977; Scholz, 1982). About 444 

km of the surface trace of the San Andreas fault in 

northern California, for example, ruptured during the 

1906 San Francisco earthquake (M 7.7). In California, 

surface rupture has accompanied many of the moderate 

to large historical earthquakes. Maximum values of 

historical surface rupture length and surface displacement are presented in table 8 for the major types of 

faulting that have occurred in California. 

Surface faulting is rarely confined to a simple narrow 

line. More commonly, a complex fault pattern results 

where the main fault zone is complicated by branching 

and secondary faults. Occasionally, secondary faults 

may be as far as 70 km from the main fault zone. The 

pattern of surface rupture commonly reflects the mode 

of faulting, the pattern of the dip-slip surface faults 

being more complex than that of the strike-slip surface 

faults. 

The amount of surface displacement along historical 

ruptures has varied greatly in short distances. Commonly, the displacement is not symmetrical along the fault 

(f) 

a: 

w 105 

tw • 

::2: 

0 

M5 = log A + 4.15 

• ...J 

:;2 

w 

a: 

<t: 104 

:::> 

0 

(f) 

z 

<i. 

w 

0 

• a: 103 

<t: 

w 

u • a: 

:::> 

0 

(f) 

w 

~ 

<t: 

:::> 

0 

I 

ta: 

<t: 

w 

6.0 7.0 8.0 9.0 

MAGNITUDE 

FIGURE 14.-Comparison of area of earthquake rupture surface 

with surface-wave magnitude (modified from Wyss, 1979, fig. 2}. 

Solid circles, open circles, and solid and open triangles indicate 

data from various investigators for historical earthquakes 

worldwide. Progressively larger areas of fault rupture generally 

result in larger earthquakes. 
FIGURE 15.-Examples of surface displacement that accompanied the 

1971 San Fernando earthquake. A, Damage to sidewalk and pavement along Foothill Boulevard about 1 km east of the San Fernando 

airport. The scarp, which is about 1 m high, resulted from reverse 

left-oblique fault slip. View looks northwest along Foothill 

Boulevard. (Photograph by J. I. Ziony, U.S. Geological Survey.) B, 

Damage to house, sidewalk, and pavement near Pacoima Wash. 

View looks westward. The concrete floor slab was offset and 

tilted, and the house had to be razed (Youd and others, 1978, fig. 

4A). C, Simplified cross section illustrating faulting and damage 

(Youd and others, 1978, fig. 4B). 

trace but may reach a maximum near one end of the 

fault and may show several high points in offset along 

the fault trace (fig. 16). 

Surface faulting commonly is accompanied by permanent horizontal or vertical distortion within a few 

meters to several hundred meters of the main fault. 

Usually, the distortion, which can tilt the ground surface, is minor in comparison with the amount of fault offset. Sometimes, however, the distortion is a substantial 

proportion of or even exceeds the fault offset. The ratio 

of vertical distortion to vertical fault offset, for example, 

was two to one along the part of the Coyote Creek fault 

that was activated by the 1968 Borrego Mountain earthquake in Imperial Valley (Clark and others, 1972). 

Not all surface displacements along faults occur suddenly in direct association with earthquakes. Fault 

creep is slow, differential movement caused chiefly by 

aseismic tectonic processes. It also can be artificially 

induced by human activity, such as the withdrawal of 

fluids from shallow parts of the Earth's crust. 

Tectonic creep has been recognized along faults in 

several parts of California, particularly in central 

California (Herd, 1979; Wesson and others, 1975) and in 

the Salton Trough region. The most notable example occurs along the San Andreas fault south of the San Francisco Bay region, where creep accounts for as much as 

32 mm/yr of contemporary right-lateral slip (Burford 

and Harsh, 1980). Monitoring studies there have shown 

that tectonic creep occurs either as discrete small increments of slip within intervals of hours or days or as 

nearly uniform motion. Commonly, the creep rate along 

a fault shows variations both with position along the 

fault and with time. 

Short-term tectonic creep, termed afterslip, occasionally is associated with surface faulting. The amount 

of such slip may approach the amount of sudden slip 

TABLE 8.-Maximum values of length of surface rupture and amount 

of surface displacement from historical earthquakes in California 

(Derived from Bonilla and others (1984, table 3) and Slemmons (1977, table 16). Moment magnitude estimates from Hanks and Kanamori (1979). Rupture length and displacement maximums 

for a given fault type are not necessarily from the same earthquake] 

Fault type 

Length of 

surface rupture, in km 

Normal slip--------------91 

Normal oblique slip------11()2 

Reverse oblique siip-------52• 

Strike slip--------------4444 

:1950 Fort Sage Mountain earthquake (ML 5.6). 

1872 Owens Valley earthquake (M 7.8). 31952 Kern County earthquake (M 7 .5). 41906 San Francisco earthquake (M 7.7). 5

1971 San Fernando earthquake (M 6.6). 61857 Fort Tejon earthquake (M 7.9). 

Maximum surface 

displacement, in m 

0.61 

6.42 

2.1" 

9.46 

Earthquake and Surface-Faulting Potential 63 
80 

(j) 

a: 

w 70 1-

w 

~ 

i= 60 z 

w 

u 

z 50 

fl..-

:::i 

(j) 40 

1-

160 days after earthquake 

I 

S2 

a: 30 

-1 

<l:: 

1- 20 z 

0 

4 days after earthquake !::::! 

a: 

0 10 I 

0 

SE 

0 5 10 25 30 NW 

DISTANCE ALONG IMPERIAL FAULT, IN KILOMETERS 

FIGURE 16.-Horizontai component of surface offset measured along the rupture trace of the Imperial fault following the October 15, 1979, 

Imperial Valley earthquake (modified from Sharp and others, 1982, fig. 101). The 1979 surface rupture was about 30 km long and overlapped 

the northern half of the surface rupture associated with the 1940 Imperial Valley earthquake. The amount of displacement is distributed 

asymmetrically along the rupture and is greatest near its southeastern end. Significant creep occurred after the main shock. One hundred and 

sixty days following the earthquake, the location of maximum right slip was shifted slightly northwestward, and postearthquake creep accounted for a significant proportion of the total surface displacement. 

directly associated with the main ground rupture event. 

For example, average horizontal displacement along the 

Imperial fault increased from about 27 to 31 em just 

after the October 15, 1979, Imperial Valley earthquake 

to 41 to 45 em 6 months later (Sharp and others, 1982). 

Tectonic creep has not yet been observed in the Los 

Angeles region, although creep from other causes has 

been recognized along several faults. Surficial displacements of as much as 18 em have occurred during the 

past three decades in the Baldwin Hills, near the northern end of the Newport-Inglewood fault zone, along a 

series of north- to northeast-trending short normal 

faults. Although these faults probably originated as tectonic features, their contemporary displacements are 

attributed to differential subsidence caused by withdrawal of petroleum and gas from an underlying oilfield 

(Castle and Yerkes, 1976). 

Creep also has been observed along the Casa Lorna 

and Claremont strands of the San Jacinto fault zone 

north of Hemet (Fett and others, 1967; Proctor, 1962). 

The dominantly dip-slip movement probably results 

chiefly from compaction of sediments caused by withdrawal of ground water from a narrow alluvial basin 

bounded by the faults; maximum subsidence of this 

basin has averaged 3.5 to 4.0 cm/yr since 1939 (Morton, 

1978). Evidence that subsidence has occurred at rates of 

about 2 to 6 mm/yr for the past 15,000 to 42,000 yr 

(Lofgren, 1976), however, suggests that tectonic processes may contribute to the contemporary fault slip. 

64 Earthquake Hazards in the Los Angeles Region 

Tsunami Generation 

Large earthquakes that originate beneath or near the 

sea sometimes are accompanied by tsunamis. A 

tsunami-an ocean wave generated by rapid displacement of a large volume of sea water-results either from 

vertical faulting or warping of the sea floor or from 

large-scale submarine landsliding. Waves of destructive 

size and force may strike nearby coasts or may travel 

thousands of miles across the open ocean to hit distant 

shorelines. As a tsunami enters shallow waters, its 

velocity diminishes, but the wave heights increase (occasionally to several tens of meters), the result being 

potentially destructive effects. 

Within the Pacific basin, damaging tsunamis are most 

common along the margins of coastal Alaska, the Japanese islands, and the islands of the mid-Pacific Ocean. 

Coastal California also has experienced destructive 

tsunamis. The harbor in Crescent City in northern California, for example, was badly damaged and 11 people 

were drowned when the distant 1964 Alaska earthquake generated a train of sea waves. 

As McCulloch (this volume) discusses in greater 

detail, small tsunamis of local origin have struck coastal 

southern California sporadically. The Santa Barbara 

Channel earthquake of December 21, 1812, reportedly 

caused waves that inundated the lower reaches of the 

coast between Santa Barbara and Goleta. Other small 

tsunamis have occurred near the Los Angeles region, 
perhaps the best documented being a 2-m-high wave 

generated by the 1927 Point Arguello earthquake. 

Regional Tectonic Deformation 

Uplift and subsidence on a regional scale accompany 

some large earthquakes, especially those associated 

with large components of dip-slip displacement. Although the amounts of uplift or subsidence rarely exceed a few . meters, vertical deformation can have 

adverse effects on facilities along coast lines and on 

pipelines and canals inland. 

The area of uplift or subsidence is determined by fault 

dimensions and displacement and can extend over tens 

of square kilometers to hundreds of thousands of square 

kilometers. The great Alaska earthquake of 1964, for example, which resulted from reverse-slip motion along a 

low-angle fault of regional extent, was accompanied by 

vertical uplift and subsidence of an area of more than 

285,000 km2 ; local changes in elevation exceeded 11 m. 

In the Los Angeles region, tectonic deformation on a 

much smaller scale has been documented for the 1971 

San Fernando earthquake (Savage and others, 1975) 

and suggested as likely for the 1933 Long Beach earthquake (Gilluly and Grant, 1949). 

EXAMPLES OF SURFACE 

FAULTING AND RELATED 

EFFECTS FROM SOUTHERN 

CALIFORNIA EARTHQUAKES 

The range of surface faulting effects likely to be 

associated with future major earthquakes in the Los 

Angeles region can best be illustrated by considering 

three historical southern California earthquakes that 

ruptured the land surface. The 1857 Fort Tejon earthquake is representative of the largest event likely to 

occur along the San Andreas fault; the 1968 Borrego 

Mountain earthquake was a moderate-sized event 

within the Peninsular Ranges along the dominantly 

strike-slip San Jacinto fault zone; the 1971 San Fernando 

earthquake is an example of a destructive earthquake 

along one of the dominantly dip-slip faults within the 

Transverse Ranges. 

1857 Fort Tejon Earthquake 

The 1857 Fort Tejon earthquake is the largest event 

known to have affected the Los Angeles region since exploration of the area by the Spanish in 1769. Although 

this earthquake occurred before the advent of seismograph recordings, a comparison of the amount of fault 

slip that it generated with that generated by the instrumentally measured 1906 San Francisco earthquake (Ms 

81f4, equivalent to M 7.7) indicates that the Fort Tejon 

event was clearly larger (Sieh, 1978a); Hanks and 

Kanamori (1979) assign it M 7.9. 

Although the 1857 event was named for Fort Tejon, 

which is located south of Bakersfield, historical accounts of foreshock activity strongly suggest that the 

epicenter was actually located along the central part of 

the San Andreas fault near Cholame, northeast of San 

Luis Obispo, and that the earthquake rupture surface 

propagated several hundred kilometers southeastward 

into the Los Angeles region (Sieh, 1978b). 

No systematic observations of the earthquake effects 

were made immediately after the event. Contemporary 

accounts, however, indicate that surface faulting 

accompanied by strike-slip offsets of several meters extended along the San Andreas fault from Cholame at 

least to Lake Elizabeth near Palmdale, a distance of 

about 230 km. A modern geomorphic analysis of offset 

stream channels crossing the fault has documented that 

surface ruptures apparently extended southeastward to 

near Wrightwood (Sieh, 1978a). The total length of surface faulting thus probably exceeded 360 km (fig. 17). 

Detailed character of the rupture trace can only be inferred, because no fault mapping was done at the time 

of the earthquake. The 1857 break is believed to be 

restricted to the geomorphically most prominent trace in 

the San Andreas fault zone, although it is likely that subsidiary faulting occurred along some parallel strands 

within a kilometer or so of the main trace. Geomorphic 

expression of several subsidiary faults adjacent to the 

San Andreas near Palmdale, for example, is fresh 

enough to suggest that these fault elements also slipped 

in 1857 (Barrows and others, 1976). 

Estimates of the style and amount of slip have been 

made by analysis of displaced small drainage features 

that cross the main fault trace (Sieh, 1978a). Stream 

channels are offset systematically in a right-lateral 

sense; there is little or no vertical component. Slip along 

the fault apparently reached a maximum of about 9.5 m 

in the Carrizo Plain west of Bakersfield and diminished 

rapidly toward the southeast. Along the margin of the 

Antelope Valley, slip is estimated to have been between 

3 and 4.5 m. 

Locally, dip-slip components of displacement probably 

accompanied the earthquake. Fresh-looking meter-high 

scarps across alluvial fans, for example, may record 

subsidiary faulting along the southwest-dipping Elkhorn 

thrust, which lies about 3 km northeast of the San 

Andreas fault in the southern Carrizo Plain. 

1968 Borrego Mountain Earthquake 

The M 6.5 Borrego Mountain earthquake of April 9, 

1968, was generated by sudden slip on the northwestEarthquake and Surface-Faulting Potential &5 
MONTEREY • FRESNO N 

~ 

SAN LUIS OBISPO • 

\ 

\ 

CHOLAME 

VALLEY 

LAKE 

50 100 MILES 

r----.I -- ---~ 

50 100 KILOMETERS 

1 

• BAKERSFIELD 

• 11; • . 

¥VRIGHTWOOD 

'.? SAN BERNARDINO 

LOS ANGELES 

I 

-1 . ~ 

FIGURE 17.-Extent of surface fault rupture (heavy line) along the San Andreas fault associated with the 1857 Fort Tejon 

earthquake (modified from Sieh, 1978a, fig. 2). Right-lateral surface offset reached a maximum of about 9.5 m in the 

Carrizo Plain and was about 2 to 4 m between Lake Elizabeth and Wrightwood. 

striking Coyote Creek fault, an element of the San Ja- Offsets along the main trace were chiefly right latercinto fault zone about 100 km southeast of Hemet al, and the maximum measured strike slip was 38 em. In 

outside the Los Angeles region. The main shock was ap- . contrast, outlying surface ruptures that diverged from 

proximately midway along a broad, complex zone of the trend of the main fault had large vertical comaftershocks about 60 km long. Surface-faulting and ponents of offset, locally as great as 23 em. Compression 

deformation effects of this earthquake were intensively and distortion, which produced locally complex patterns 

studied (Allen and others, 1972; Burford, 1972; Clark, of surface deformation, characterized the areas at the 

1972; Clark and others, 1972; Sharp and Clark, 1972) ends of the echelon fault segments (fig. 18B). Studies of 

and are summarized below. the patterns of the 1968 faulting and earlier movements 

Surface faulting occurred along 31 km of the Coyote recorded by offset of preexisting physiographic features 

Creek fault in three distinct bands of echelon fractures showed that the 1968 displacements in every case 

trending approximately N. 30°-50° W. (fig. 18A). Most of matched the sense of earlier slip events along the Coyote 

the ground displacement took place within 20 m of the Creek fault. 

trace, although some occurred as much as 500 m away. Aseismic creep continued for several years after the 

Isolated evidence of faulting was observed as much as earthquake and was concentrated mainly along the cen3 km from the main trace. tral and southern sectors of the fault, which had ex66 Earthquake Hazards in the Los Angeles Region 
.. , 

* ~ Epicenter of main shock 

April 9, 1968 Magnitude 6.5 

0 

f 

0 

I 

1 

I 

2 

I 

3 

2 

I 

I 

4 

I 

4 

I 

5 KILOMETERS 

5 MILES 

I 

\\ 

I 

FIGURE 18A 

FIGURE 18.-Surface faulting associated with the Borrego Mountain earthquake of April 9, 1968. A, Major surface ruptures along the Coyote 

Creek fault (generalized from Clark, 1972, pl. 1). B, Surface faulting along the northern segment of the 1968 rupture (portion from Clark, 1972, 

pl. 1). Note the left-stepping echelon pattern of many of the breaks. C, Relation of the Coyote Creek fault, which was the source of the 1968 

earthquake, to the three distant faults-the San Andreas, the Superstition Hills, and the Imperial-along which minor surface offsets were 

triggered at distances as great as 70 km from the epicenter (modified from Allen and others, 1972, fig. 52). 

perienced the least amount of coseismic slip. Locally, 

postearthquake creep was as much as 18 em. 

Interestingly, the Borrego Mountain earthquake triggered small (1-2.5 em) right-lateral surface displacements along three subparallel faults at distances of as 

much as 70 km from the main shock (fig. 18C). The faults 

that ruptured sympathetically were the Imperial fault 

(for 22 km), the Superstition Hills fault (for 23 km), and 

the southern San Andreas fault north of the Salton Sea 

(for 30 km). 

Earthquake and Surface-Faulting Potential 67 
.5 

.5 

B 

_5 zoo--

EXPLANATION 

120 50 

""""~~---' l---<-- ..____---J9LL W10~ 

Surface rupture 

Arrow and number indicate apparent direction and amount of horizontal displacement, 

in millimeters. Left-lateral offsets are further identified with L L. Number without 

symbol represents amount of vertical displacement, in millimeters; number on 

up thrown side. W 10m, width of fracture zone, in meters 

(80-100) 

''~'-'''''' ~'~"''' Displacements in parentheses were measured in June 1968 . All others were 

measured in April 1968 

Bfl n .. --.:.:.... 

1 MILE 

FIGURE 18B 

68 Earthquake Hazards in the Los Angeles Region 
Borrego 

Springs 

l . 

· 

116'00' 

covo;!u~~EEK '-.. ss 

33'00' SUPERSTITION ..... ~ 

HILLS FAULT 

0 5 10 MILES 

0 

\1111 

5 10 KILOM TER ~ 

~ 

UNITED _? TATE -- -------- t----- - --- --MEXICO C 

FIGURE 18C 

1971 San Fernando Earthquake 

Tectonic surface rupturing that caused extensive 

damage to parts of the heavily populated San Fernando 

Valley accompanied theM 6.6 1971 San Fernando earthquake. The surface-faulting effects have been documented in detail (U.S. Geological Survey Staff, 1971; 

Kamb and others, 1971; Barrows, 1975; Kahle, 1975; 

Weber, 1975; Sharp, 1975, 1981a; Youd and others, 

1978). 

The zone of surface ruptures was about 15 km long, 

extending from the western side of San Fernando to Big 

Tujunga Canyon. Displacements were the result of 

reverse left-oblique slip of as much as 2.1 m along the 

San Fernando fault zone, which dips north about 55°. 

Detailed mapping showed that five separate segments of 

this fault zone were activated at the surface during the 

earthquake. Nearly all of the tectonic surface offsets 

were restricted mostly to the upper block, or hanging 

wall, of the fault zone. The zone of surface faulting coincided with a buried ground-water barrier formed by 

pre-1971 faulting in the Holocene alluvial deposits of the 

valley and was aligned with fault-produced geomorphic 

features of late Quaternary age. 

The character of ground deformation varied along 

each segment. The distal parts of the fault zone were 

marked by relatively simple rupture zones less than 

about 5 m wide. In contrast, fractures comprising the 

west-central segment that traverses the alluviated San 

Fernando Valley were much more complex (fig. 19). This 

segment consisted of a main belt of thrusting about 75 to 

200m wide and bordered on the north by a broad (1-1.5 

km wide) zone of discontinuous, mostly normal-slip 

faults having small offsets (several millimeters). 

Subsidiary faulting along short faults in the foothills 

occurred at distances of as much as 2 km from the main 

trace. Some of these offsets indicated as much as 1 m of 

reverse left-oblique slip. 

Secondary faulting accompanied by small amounts of 

left-lateral and reverse slip was observed along about 

450 m of the Santa Susana fault northwest of the primary faulting (Weber, 1975). Similar rupturing may 

have occurred along a short segment of the Buck Canyon-Watt fault near its junction with the San Gabriel 

fault 8 km northeast of San Fernando. 

The earthquake was also accompanied by permanent 

ground distortion, including uplift (fig. 20) and horizontal 

displacements. Comparison of precise leveling surveys 

made before {1968-70) and after the earthquake shows 

that changes in elevation formed an east-west arch that 

affected much of the northern San Fernando Valley 

(Savage and others, 1975; Yerkes and others, 1974). The 

greatest changes were in the foothills east of the valley, 

where maximum uplift was about 2 m. Because maximums in the patterns of uplift coincide with topographic highs, such deformation probably was the most 

recent result of ongoing (but sporadic) geologic processes. Horizontal displacements, locally of more than 

2 m and occurring over a broad area, showed an abrupt 

discontinuity along the zone of surface faulting in the 

pattern and amount of horizontal distortion (Yerkes and 

others, 1974). 

The preceding three examples illustrate some of the 

kinds of surface faulting and deformation that might accompany future major earthquakes in the Los Angeles 

region. The faults that produced these effects could slip 

again in the near future and perhaps duplicate their 

historical surface offsets. Other faults within the region 

have attributes similar to those discussed, and major 

earthquakes along these faults could produce comparable patterns of surface rupture and distortion. The 

next section addresses ways of identifying which faults 

might be the source of future seismic events and 

estimating the likely character of future earthquakes 

and tectonic surface deformation along those faults. 

PREDICTING THE FUTURE 

BEHAVIOR OF FAULTS 

Identifying Active Faults 

Geologists and seismologists use various criteria 

based on current manifestations or the history of a fault 

to infer its potential for future rupture. These criteria include historical surface faulting or creep, historical and 

Earthquake and Surface-Faulting Potential 69 
,··-._ 

' • *: oYf:~< '(~I 

_}, 

FIGURE 19.-Western segments of tectonic surface ruptures produced by dominantly reverse left-oblique faulting associ1!ted with the 1971 San 

Fernando earthquake (U.S. Geological Survey Staff, 1971, fig. 2). Note the complexity of the Sylmar segment, which traverses the alluvium of 

the San Fernando Valley, in comparison with the relatively simple traces of the Tujunga segment that separates bedrock foothills from 

alluvium. 
~ ... \ 

, . t.:man 

P•ci' 

-~·· 

, < -.,;:'\ 

"'-

"" < 

< 

' > f 

' t 

/ 

'/. 

_, <v 

"<-or•h .. ParQJma Pari< ,. 

,r 

~ 

Tectonic rupture, showing dip 

Queried where tectonic origin is doubtful; 

where surface expression is poor 

Boundaries of 'io:n~: d~niii:ni~ main tectonic 

ruptures in Sylmar segment of San Fernando 

fault zone 

0.30C 

Magnitude of shortening across tectonic 

ruptures or other compressional features, 

in meters 

0.40L 0.04R 

Left Right 

Magnitude of lateral component of movement, 

in meters 

L or R without number signifies 

0 . 01 m 

Direction of shorteiiiligat tectonic ruptures 

or component of shortening on features 

other than surface ruptures 

~ 

.40 

u 

Vertical component of relative movement 

Dot. or D on downthrown side of rupture, U on 

upthrown side. Magnitude of vertical component 

of movement given in meters 

'II 

0 .5 1 KILOMETER 

... 

· -· Fenton Av~. )'": .. ~ . 

,; ~ 

·g~- 1' 

Earthquake and Surface-Faulting Potential 71 
GABRIEL MOUNTAINS 

PACOIMA 

RESERVOIR 

/ 

/ 

/ 

/ 

/ 

/ 

s---- . -tO· 

VA HOSPITAL / 

/'/ 

~LIVE VIEW • ~----=-------- + 7.0 ___ 

---

0 

0 

\ 

" ", ....._ ~ . . . LOWER VAN • + 7

·

5 

~-~---.:::::" NORMAN LAKE • + 0 5 

• • _,...- -rO-r _.-~--r-

.. / 

f _.l.--L_ 

~ ...>-- _.l...- • 

SAN FERNANDO VALLEY 

2 MILES 

2 3 KI LOMETERS 

--

-..!..._ 

TUJUNGA VALLEY 

HANSEN LAKE 

FIGURE 20.-Relative elevation changes (in meters) in the northern San Fernando Valley determined from surveys before and after the 1971 earthquake (from Savage and others, 1975, fig. 2). The steepest gradient (where changes of elevation contours are spaced most closely) generally 

coincides with the zone of surface faulting. Contours of elevation changes are dashed where inferred and hachured where subsidence occurred. Solid circles are surveyed points. 

contemporary seismicity, contemporary accumulation of 

strain as revealed by repeated geodetic surveying 

across faults, episodes of slip in the recent geologic past 

as deduced from displaced rock or soil units of known 

age, and physiographic features that record geologically 

young movements at the ground surface. 

Although our understanding of the behavior of faults 

is incomplete, enough is known to show that the manner 

and frequency of movements along these faults can vary 

greatly. Some faults can be dormant for thousands of 

years and then slip suddenly tens of meters, whereas 

other faults release strain through frequent small earthquakes or by more or less continuous creep. Because the 

range in fault behavior is great, earth scientists do not 

currently agree as to what criteria differentiate with 

certainty between an active fault and one that will remain inactive. 

An approach commonly used to designate active 

faults is to consider how recently displacements have 

occurred along them (Ziony and others, 1973). Geologic 

evidence along a fault is evaluated to determine the age 

of the youngest faulted material or the age of the 

72 Earthquake Hazards in the Los Angeles Region 

youngest landforms produced by faulting. A fault then 

can be assigned to the age class (for example, historical, 

Holocene, or late Quaternary) that most closely brackets 

the time span containing its youngest slip event. 

Systematic regional evaluations of faults have been 

made by Wentworth and others (1970) for the Los 

Angeles basin, by Ziony and others (1974) for coastal 

southern California, by Buchanan-Banks and others 

(1978) for coastal central California, and by Pampeyan 

(1979) for the San Francisco Bay region. 

Which time span is chosen to designate a fault as 

active depends on the likely consequences of renewed 

faulting. In evaluating the locations of structures intended for human occupancy, for example, the State of 

California uses evidence of offset during Holocene time 

(approximately the past 10,000 yr) to designate a fault 

as active (Hart, 1980). Longer spans of geologic time are 

used for types of construction whose possible failure 

would pose high risks to the public. Thus, for the siting 

of large dams, the U.S. Bureau of Reclamation considers 

a fault active if it has experienced slip during the past 

100,000 yr. The U.S. Nuclear Regulatory Commission, 
which is responsible for approving the siting and design 

of nuclear power facilities, considers faults that have 

slipped several times during the last 500,000 yr as 

active. 

A complication in identifying potentially active faults 

is that, although most such faults in California displace 

young alluvial deposits or topographic features, active 

faults in certain tectonic settings do not reach the 

Earth's surface. The ML 6.7 1983 Coalinga earthquake 

in central California demonstrated that damaging 

seismogenic slip can occur on a concealed fault that is 

manifested at the surface only by recurrently active 

young folds (Stein and King, 1984). The earthquake was 

generated by thrusting in basement rocks along a lowangle active fault that does not completely penetrate the 

overlying Cretaceous and late Cenozoic sedimentary 

rocks (Yerkes and others, 1984). 

Faults in the Los Angeles region that show evidence of 

movement at or near the Earth's surface within the past 

approximately 750,000 yr are indicated in figure 11. 

Although additional studies along other faults in the 

region may subsequently reveal evidence for geologically recent activity, we are reasonably confident that the 

suite of historical, Holocene, and late Quaternary faults 

identified in this chapter contains those faults that are 

most likely to cause damaging earthquakes. Table 5 

summarizes what is known about. the physical characteristics of each fault, our current appraisal of the 

age of the most recent displacement, the type of geologically recent slip, and the evidence for associated 

earthquakes. 

Evaluating Relative Activity 

Simply designating a fault as active does not adequately predict its future behavior. Significant differences between the degrees of activity of active faults 

may exist and must be considered. Two faults that have 

both been active in Holocene time, for example, may 

have vastly different intervals and amounts of recurrent 

movement. Geologists and seismologists now recognize 

that the slip rate, the size and recurrence intervals of 

earthquakes, and the amount of slip per movement event 

provide a more precise and useful ch.aracterization of 

fault activity than the age of the latest offset alone 

provides. 

Analysis of the slip rates of faults provides one means 

for assessing degrees of activity. Rates can be obtained 

directly from observed or geodetically measured historical offsets along faults that are currently creeping. 

For most active faults, however, slip rates must be 

deduced from the displacement of geologically young 

markers. The average rate of slip for a length of geologic 

time is calculated by dividing the cumulative net displacement of a stratigraphic or physiographic marker 

by the amount of time elapsed since the marker was first 

displaced by the fault. Most commonly, this time span is 

assumed to be the age of the displaced marker as 

mell.sured by radiometric dating techniques, as estimated from stratigraphic relations, or as inferred from 

physiographic expression. 

Geologically determined slip rates provide a measure 

of only the long-term average displacement rate along 

the fault. Faults, however, do not necessarily move at 

constant rates of slip. Although the inferred average slip 

rate along part of the San Jacinto fault zone, for example, during the past 730,000 yr B.P. is about 8 to more 

than 12 mrnlyr, comparison of measured offsets from different segments of that-time-span indicates that the slip 

rate fluctuated, dropping as low as 1 to 2 mrnlyr for 

parts of that period (Sharp, 1981b). Fluctuating rates of 

slip during the past 2 m.y. also have been documented 

for the Oak Ridge fault (Yeats, 1977). Most commonly, 

however, the average slip rate is the only estimate that 

can be obtained, because data are insufficient to show 

changes in the slip rate of an individual fault. 

Comparison of the average rates of slip for different 

active faults in a region can provide a quantitative 

measure of their relative activity. Provisional classifications of faults according to rates of long-term averag~ 

slip have been proposed by Matsuda (1975, 1977), Slemmons (1977), Cluff (1978), and Knuepfer and others 

(1981). Table 9 is an example of such a classification. An 

assessment of the degree of activity, based on this 

classification, has been completed for the faults of Japan· 

(Research Group for Active Faults of Japan, 1980). 

Geologic slip rates have been estimated for many of 

the major faults in the Los Angeles region (Lamar and 

others, 1973; Anderson, 1979). The estimates for different faults, however, have been computed by using 

measured offsets representing widely different spans of 

geologic time; in some cases, offset geologic features as 

old as 6 to 17 m.y. provide the basis for estimating the 

TABLE 9.-Degree of fault activity from long·term slip rates during late 

Quaternary time 

[From Matsuda (1977) and Slemmons (1977)] 

Average slip rate, 

Class Degree of activity in mmlyr 

AA---- Very high 

A----- High 

B ----- Moderately high 

C ----- Moderate 

10-100 

1.0-10 

.1-1.0 

.01-Q.1 

Comments 

Restricted to major 

plate boundaries. 

Generally welldeveloped 

physiographic 

evidence 

of recent faulting. 

Earthquake and Surface-Faulting Potential 73 
TABLE 10.-Late Quaternary slip rates estimated for some faults of the Los Angeles region 

(Data chiefly from compilation by Clark and others (1984) listing sources of information for each fault. Data for Cleghorn and Ord Mountain faults from Meisling (1984). Rates reported are those without major uncertainties. --, no preferred rate] 

Fault (map number) Minimum 

San Andreas (1)----------------- 20.0 

San Jacinto zone, Clark (8)--------- 8.0 

Chino (11)--------------------- .02 

Newport-Inglewood zone: 

Inglewood (25)---------------- .12 

North Branch (30)------------- .1 

Palos Verdes Hills (35)------------ .02 

Santa Ynez (44)----------------- .15 

Arroyo Parida (46)--------------- .35 

More Ranch (47)---------------- .2 

Red Mountain [52)--------------- .4 

Javon Canyon [54)--------------- .7 

Ventura [55)-------------------- .8 

Faults near Oak View [57)--------- .27 

San Cayetano [59)--------------- .88 

Faults of Orcutt and------------- .05 

Timber Canyons (60). 

Santa Cruz Island (77)------------ .2 

Santa Cruz Island (77)------------ .86 

Malibu Coast (79)--------------- .04 

Santa Monica (80)--------------- .27 

Raymond (82)------------------ .1 

Sierra Madre (83)---------------- .36 

Cucamonga (86)---------------- 2.9 

Cleghorn (92)------------------- 2.0 

Ord Mountain (93)--------------- .04 

Slip rate, in mm/yr 

Maximum 

30.0 

>12.0 

.06 

.6 

1.2 

.3 

10.1 

.4 

>.3 

1.5 

2.5 

2.4 

1.34 

2.9 

2.36 

>.56 

.09 

.39 

.22 

4.0 

6.4 

16.0 

.7 

Preferred 

25.0 

1.0 

>.3 

.13 

3.3 

0.1 

Component' 

H 

H 

v 

v 

v 

v 

T 

v 

v 

D 

T 

D 

T 

T 

T 

v 

H 

T 

v 

v 

v 

T 

H 

v 

1

T, true slip rate; H, horizontal component of slip rate; V, vertical component of slip rate; D, dip component of slip rate. 

long-term slip rate. It is highly doubtful whether rates 

averaged over more than a few million years are representative of slip rates associated with the current tectonic stress field. 

Comparison of rates of offset for only late Quaternary 

time provides a more reliable basis for characterizing 

the present relative activity of faults in the Los Angeles 

region. Marine and nonmarine deposits of late Quaternary age, which are widespread in the region, serve as 

markers for fault displacements and can be dated locally with reasonable precision by using various absolute 

and relative dating techniques. Measured offsets of late 

Quaternary deposits or of physiographic features that 

can be related to these deposits are known for about 

half of the faults listed in table 5. Most of the measurements, however, are of a component of the displacement 

(for example, the vertical separation or throw) rather 

than of true slip; therefore, the computed rates in many 

cases are less than the actual slip rates. Furthermore, 

the ages of offset deposits or geomorphic features can 

be reliably estimated for less than half of the localities 

where offsets (either separation or slip) have been 

74 Earthquake Hazards in the Los Angeles Region 

measured. Thus, rates of displacement can be estimated 

for less than 25 percent of the potentially active faults of 

the region. 

Known late Quaternary slip rates are summarized for 

the Los Angeles region in table 10. These values may 

change as new information about the ages of the offset 

features or the amounts of offset comes to light. 

Although true slip rates can be calculated for a few 

faults, most data are for either the horizontal component, the vertical component, or the dip component (and 

thus give less than the true rate). The most common 

parameter available for comparing the relative activities of different faults is the vertical component of the 

slip rate. Although component rates are less than true 

slip rates, they can be useful if the ratio of vertical slip 

to horizontal slip along a fault is known. Thus, horizontal 

component rates computed for the dominantly strike-slip 

San Andreas, San Jacinto, and Cleghorn faults closely 

approximate their true rates, because these faults have 

large ratios of horizontal to vertical slip. Similarly, rates 

of vertical separation can be used to estimate true rates 

for faults known to be dominantly dip slip. Even where 
120° 

0 25 KilOMETERS 

118° 

."' 

'""" 

\ 

\ 

EXPLANATION 

SLIP RATE 

(mm/yr) 

---10- 30 

---3-9 

--- 1- 2 

e Locality where slip rate is known (table 10) 

0 Locality where only vertical or horizontal 

component of slip rate is known (table 10) 

-·-·- < 1 

FIGURE 21.-Late Quaternary faults of the Los Angeles region classified according to known or inferred rates of slip within the past several hundred thousand years. Rates from faults having no constraining geologic offsets are provisionally assigned on the basis of connection with faults 

of known rate, tectonic setting, and geomorphic expression. 

slip ratios are uncertain, comparing component rates 

for individual faults having similar trends provides a 

gross estimate of their relative activity. 

Vertical component rates for the chiefly reverse-slip 

faults of the Transverse Ranges, for example, approximate their true slip rates, if it is assumed that vertical 

separations measured across these faults are equivalent to the vertical components of slip. That this assumption is not strictly correct is shown by oblique-slip 

historical surface offset along the San Fernando fault 

and by a dominant slip vector for the province that 

plunges 55° NE., determined from earthquake faultplane solutions (Yerkes and Lee, 1979b, fig. 3). This 

assumption is, however, a reasonable working hypothesis that can be tested against variations in assumed 

fault dip and slip-vector orientation. Geometric analysis, 

for example, shows that the vertical component rate for 

a pure reverse-slip fault dipping 70° will be about 94 

percent of the true slip rate, whereas the vertical component rate for an oblique-slip fault of similar dip would 

be about 67 percent of the true slip rate. For shallower 

faults, of course, vertical separation is a much less accurate measure of slip. Nevertheless, vertical component rates can estimate true slip rates within a factor of 

two for the faults of the Transverse Ranges. 

Integrating the sparse and mostly incomplete data 

from table 10 into a provisional slip-rate map for the 

region (fig. 21), we have assigned faults to one of four 

categories representing estimated ranges in true slip 

rate by taking into account available slip-rate data, 

probable styles of fault displacement, and possible connections with other faults of known rate. We have also 

compared known vertical component rates and relative 

geomorphic expression; of faults having similar tectonic 

settings. Systematic areal differences in estimated slip 

rates are shown on the provisional -map-the San AnEarthquake and Surface-Faulting Potential 75 
dreas and San Jacinto faults have slip rates measured in 

tens of millimeters per year, from 2 to 30 times greater 

than those of other active faults in the region. The next 

most active system is the belt of faults that extends 

diagonally across the Transverse Ranges from near Santa Barbara to San Bernardino. Individual faults in this 

system have rates that range from 1 to 6 mm/yr, the 

higher rates occurring where the belt is narrow and 

composed of only a few faults (for example, along the 

southern boundary of the Transverse Ranges eastward 

from Pasadena). In contrast, rates for the southern 

boundary faults of the Transverse Ranges west from 

Pasadena appear to be less than 1 mm/yr. Although few 

data are available for the northwest-trending fault 

systems that lie west of the San Jacinto fault, estimates 

of about 1 mm/yr for each appear consistent with what 

is known. · 

Reliable geologic data with which to closely estimate 

a late Quaternary slip rate for the Elsinore fault zone in 

the Los Angeles region are not yet available. Proposed 

slip rates range widely-from about 0.8 mm/yr (Lamar 

and Swanson, 1981) to about 7 mm/yr (Kennedy, 1977)-

and are based on apparent horizontal separations of 

sedimentary facies boundaries rather than on unambiguous measurements of slip. We provisionally assign a 

rate of about 1 mm/yr to the fault zone. Studies in progress southeast of Corona (Millman, 1985), however, suggest that a higher rate could be appropriate on the basis 

of apparent lateral offets of presumed middle to late 

Pleistocene alluvial fan deposits. Pinault and Rockwell 

(1984) have proposed a Holocene slip rate of about 

4 mm/yr for the southern Elsinore fault zone about 

20 km north of the California border with Mexico. 

Closely constrained late Quaternary slip rates have 

not yet been determined for the Newport-Inglewood and 

the Palos Verdes Hills fault zones, which pose a major 

earthquake threat to the densely populated Los Angeles 

basin. For the Newport-Inglewood zone, WoodwardClyde Consultants (1979) estimate an average slip rate 

of 0.5 mm/yr since late Miocene time on the basis of inferred right-lateral displacements of geologic markers 3 

to 5 m.y. old; this value may not be representative of the 

offset rate during the past several hundred thousand 

years, however. Late Quaternary rates of vertical separation of 0.6 and 0.3 mm/yr have been calculated locally 

for the Newport-Inglewood and Palos Verdes Hills fault 

zones, respectively. Becau~e the geometry of the zones 

suggests dominantly right-lateral displacement, the vertical components of the offset rate probably are a fraction of the actual slip rate. Displaced late Pleistocene 

marine-terrace shoreline angles •near San Diego (Kern, 

1977) suggest a slip rate of 1.2 to 1.4 mm/yr for the Rose 

Canyon fault, a probable southern extension of the 

Newport-Inglewood zone. Thus, we can reasonably 

76 Earthquake Hazards in the Los Angeles Region 

assign provisional slip rates of about 1 mm/yr to each of 

these fault zones. 

New methods of seismic risk analysis that use geologically determined slip rates to estimate the average rate 

of seismic moment release on a fault have been proposed recently (for example, Anderson, 1979; Wesnousky and others, 1982; Joyner and Fumal, this volume). 

The spatial and size distributions of future earthquakes 

in Japan, for instance, have been predicted from Quaternary slip-rate data (Wesnousky and others, 1984). 

Although these promising methods can be used to estimate seismic hazard for the Los Angeles region on the 

basis of existing slip-rate information, more reliable estimates will require considerable improvement in the 

knowledge of slip rates for the entire suite of late 

Quaternary faults. 

Determining Earthquake Potential 

A fault can generate earthquakes when it is suitably 

oriented to slip within the tectonic stress field of the 

Earth's crust and when it lies within rocks strong 

enough to store large amounts of strain energy for sudden release. How can we decide which active faults will 

generate future damaging earthquakes, and what will 

be the likely size and frequency of occurrence of these 

earthquakes? 

Instrumentally recorded seismicity, although it indicates only the short-term patterns of release of earthquake energy, is a key tool for assessing the ability of a 

fault to produce earthquakes. The seismogenic nature of 

a fault is established where there is a close spatial relation between fault geometry and earthquakes. Comparison of fault-trace maps (fig. 11) with earthquake 

epicenter maps for the region is a first step in identifying seismogenic faults; this approach is severely limited, 

however, where faults are inclined rather than vertical, 

as they are in the Transverse Ranges, or where they are 

closely spaced. The earthquake-generating ability of a 

fault is established with greater certainty where geologic and seismologic information is detailed enough to 

accurately map earthquake hypocenters and to associate them with a specific fault at depth (for example, 

the Red Mountain fault) (fig. 22). The strongest evidence 

that a fault is seismogenic is found in cases where earthquakes are aligned along a fault in three dimensions and 

where focal mechanism solutions agree with the orientation and sense of movement from geologic data. 

Absence of seismicity along a fault alone, however, 

does not imply a lack of potential for future damaging 

events. For the Los Angeles area, there are only about 

50 yr of reasonably good instrumental recordings of 

seismicity and only about 200 yr of written history with 

which to compare earthquake occurrences and the distribution of geologically youthful faults. Experience both 
- ~N 

+-_J~~+---~~~~~L_ ________ ev --~ 

10 + 

+-

FIGURE 22.-North-south cross section through the Red Mountain fault 

northwest of Ventura showing closely associated small earthquakes from 1970 to 1975 (modified from Yeats and others, 1981, 

fig. 8). Hypocenters (small solid circles) are projected from nearby 

points onto the plane of the cross section; vertical and horizontal 

bars around hypocenters give error limits in the original locations 

of the earthquakes. The position of the Red Mountain fault to 

depths of about 4 km (solid line) is accurately defined by numerous 

oil wells (approximately vertical lines) that intersect it at points 

shown by large solid circles. Several fault-plane solutions are in 

agreement with the geologic evidence that the fault movement is 

predominantly reverse and has a minor left-slip component (Yerkes 

and Lee, 1979b). Contacts between geologic units are dashed 

where approximately located. 

locally and worldwide has shown that these spans of 

time are much too short for appraising the long-term 

seismic behavior of faults. Large earthquakes often occur along faults that have little or no previous record of 

seismicity. Furthermore, the reconstruction of earthquake history for those parts of the world having the 

longest historical records (for example, Turkey, China, 

and Japan) indicates that there are large long-term temporal and spatial variations in earthquake activity 

(Allen, 1975). Because of these inherent difficulties in 

using instrumental or historical seismicity, scientists 

have increasingly relied on the late Quaternary geologic 

history of faulting as a guide to estimating the 

seismogenic nature of faults. 

A complication in assessing earthquake potential is 

that not all active faults are capable of causing damaging earthquakes. The dimensions of some faults may be 

too small in terms of potential rupture surface to produce significant earthquakes. Furthermore, a few faults 

release all their elastic energy by aseismic creep. 

Others may be shallow features that are not deep 

enough to penetrate high-shear-strength rocks that can 

store large amounts of elastic strain energy. In the Ventura area, for example, several active faults that offset 

late Quaternary deposits are postulated to result from 

flexural-slip folding that involves only shallow strata 

(Yeats and others, 1981; Yeats, 1982). Consequently, 

these particular faults may pose no earthquake hazard, 

although movements along them may rupture the ground 

surface. 

Estimating the maximum earthquake for a fault.-

Modern engineering practice for the design of important 

structures such as dams, large buildings, and nuclear 

power reactors includes the calculation of expectable 

ground-motion values based chiefly on estimates of the 

maximum sizes of earthquakes that could be generated 

by nearby or distant faults. Methods used to estimate 

the size of future earthquakes include (1) analysis of the 

regional earthquake history to determine the largest 

event associated with a particular fault, (2) comparison 

of the earthquake history of a particular fault with the 

histories of other faults in analogous structural or 

tectonic settings (for example, fig. 23), and (3) use of empirically determined magnitude-fault length relations. 

Each approach has limitations and problems that introduce large uncertainties into the estimation of maximum magnitude. 

Seismologists and geologists have recognized for 

several decades that the size of an earthquake generally 

increases as the dimensions of the activated fault surface increase. Empirical relations between dimensions 

of faulting and earthquake magnitude have been derived from studies of historical large earthquakes 

worldwide. Correlations have been made between magnitude and fault length and between magnitude and 

maximum displacement (Bonilla and Buchanan, 1970; 

Mark and Bonilla, 1977; Slemmons, 1977; Bonilla and 

others, 1984). Figure 24, for example, shows one correlation between earthquake magnitude and length of 

surface rupture. 

These kinds of correlations are widely used by 

engineers for estimating the maximum earthquake likely 

for a particular fault and a particular length of future 

rupture. A common approach is to base estimates on the 

assumption that half the total fault length can rupture in 

any single earthquake (for example, Wesson and others, 

1975). There is much uncertainty, however, about what 

proportion of a fault will rupture in a single event. 

Historical data indicate that major earthquakes have 

resulted from rupture of anywhere from a small fraction 

to nearly 100 percent of a preexisting fault surface. Furthermore, because faults commonly have discontinuous 

and complex patterns and are locally concealed by 

young deposits or by bodies of water, there are inherent 

difficulties in accurately determining the length of a 

fault. 

Earthquake and Surface-Faulting Potential 77 
-------------------------------- N.25 .------------------------------~ 

SAN SAN WHITE 

FERNANDO GABRIEL SAN ANDREAS WOLF 

~0~ \ Basement 

-" --- 0 -;--- (j) 

fJro a: 0 

TO ' A\ 

TO Basement UJ 

(j) 

UJ 

...J 5 

-~ Ih:: 10 UJ 

0 

15 

- ..... - - - I_")'\ 1971 • Basement 

" 

SAN FERNANDO I 

M 6.5 

I 

""' I 

""" ""' I 

I 

0 

0 5 

f-- 5 UJ 

/Basement 

~ 

0 Basement ...J 

riA 10 :,.,:-

z 

1952 KERN COUNTY~ I- 15 f-- M5 7.7 c._ 

UJ 

I 0 

20 

5 10 MILES 

10 15 KILOMETERS 

FIGURE 23.-Vertical section, offset 80 km along the San Andreas fault, through the hypocenters of the 1952 Kern County and 

the 1971 San Fernando earthquakes (Wesson and others, 1974, fig. 1). Both the White Wolf and the San Fernando faults, 

which generated these earthquakes, are reverse left-oblique slip faults that dip toward the San Andreas fault. Similarities 

in the tectonic settings of the two faults were used as one of the bases for inferring that a future earthquake as large as 

M 7.5 is possible for the Sierra Madre-San Fernando-Santa Susana system of faults. TQ indicates Tertiary and Quaternary sedimentary rocks; T, relative movement toward reader; A, relative movement away from reader. Arrows indicate 

the general direction oflateral compression to which the earthquakes are attributed. 

Because of these uncertainties and difficulties, any 

estimate of future earthquake size based on these empirical correlations must be viewed with great caution. 

Even though estimates of the maximum earthquake commonly are expressed as numbers (sometimes to tenths of 

an integer), such estimates are crude approximations 

only. 

Although studies of fault hazards in other regions (for 

example, Wesson and others, 1975) have estimated maximum magnitudes for individual faults on the basis of 

empirical relations between fault length and magnitude, 

we do not consider the application of this procedure appropriate for the faults of the Los Angeles region. First, 

many of the Los Angeles faults are overlapping echelon 

segments of longer zones, and knowledge of their configuration and possible linkage at depth is insufficient to 

define with reasonable certainty their effective lengths 

for possible earthquake generation. Second, the basic 

data for magnitude-fault length relations are sparse, 

especially for reverse faults, and show a wide scatter, 

which implies considerable uncertainty in those 

relations. 

General constraints on the size of future earthquakes 

likely to occur in the Los Angeles region are, however, 

provided by considering the historical record of large 

earthquakes, the 15- to 2D-km limiting depth for instrumentally recorded seismicity in the region, and the 

range in dimensions of the late Quaternary faults. 

78 Earthquake Hazards in the Los Angeles Region 

Table 6 lists the magnitudes and seismic moments for 

the larger earthquakes in southern California since 

1857. By far the largest event was the 1857 earthquake 

(M 7 .9, corresponding to an estimated moment of 9 x 1()27 

dyne-em), which was more than 4 times greater in moment than the next largest event and 10 to 100 times 

greater than the other listed events. 

The 1857 event, which was associated with more than 

360 km of surface rupture along the south-central San 

Andreas fault as far south as Wrightwood, probably approaches being the largest earthquake that might occur 

on that fault. A somewhat greater event might occur if a 

future San Andreas earthquake caused rupture along 

the entire south-central trace, including the San Bernardino area. Raleigh and others (1982) have suggested that 

the entire San Andreas fault in southern California, including that segment east of Indio, could rupture in a 

single great earthquake event; such throughgoing rupture, however, may not be mechanically feasible in light 

of the apparent truncation of the Holocene surface trace 

of the south-central San Andreas by the west-trending 

Banning fault. 

As table 6 shows, the most prolific source in terms of 

numbers of major earthquakes is the San Jacinto fault 

zone, which has generated 8 of the 18 listed events. 

These earthquakes have been as large as M 7 (moment of 

3 x 1()26 dyne-em). Although the fault zone extends for 

more than 300 km, individual fault segments are about 
8.5 

• 

p.: 

8.0 

• • 

• Ui 

~ 

UJ 

0 7.5 • ::> • • t:: 

z 

(!) 

<( 

~ 

UJ 

:,£ 

<( 7.0 ::> 

0 

I 

t0: 

<( 

UJ • ~ • 6.5 • 

• 

~ 

6.0 10 500 

LENGTH OF SURFACE RUPTURE, IN KILOMETERS 

FIGURE 24.-Length of surface-fault rupture of historical earthquakes worldwide in relation to magnitude for all types of 

faults (modified from Bonilla and others, 1984, fig. lA). Because of the statistics involved in estimating maximum 

values, line A-A' is used to estimate the most likely earthquake magnitude associated with a given length of surface 

rupture, whereas line B-B' is used to estimate the most likely rupture length associated with a given ellrthquake 

magnitude. 

85 km or less in length and, in contrast to the San 

Andreas fault zone, are discrete echelon segments 

whose end points are 5 to 10 km apart. These spatial 

characteristics, together with the fact that each historical event has involved only one fault segment of the 

zone, suggest that M 7 is probably the maximum earthquake size for the San Jacinto fault zone. This value 

probably is a reasonable upper bound for the other 

major northwest-trending zones in the region-the 

Newport-Inglewood and Elsinore fault zones-which 

are similar in overall length but have generally shorter 

fault segments. 

Estimating the maximum earthquake for faults of the 

Transverse Ranges is especially difficult. Individual late 

Quaternary faults are as long as 80 km, and many of 

them appear to link, the suggestion being that two or 

more adjoining faults might rupture simultaneously to 

generate much larger earthquakes. The occurrences of 

the 1927 Point Arguello earthquake (M 7.3) offshore from 

the western Transverse Ranges and of the 1952 Kern 

County earthquake (M 7.5) along a reverse fault just 

north of the Transverse Ranges suggest that events of 

comparable magnitude may be possible within the province. Wesson and others (1974) have concluded that a 

ML 71f2 to 73/4 (equivalent to M 7.5) event is a reasonable 

maximum magnitude to expect along the Sierra MadreSan Fernando-Santa Susana fault system on the basis of 

the regional seismic history, the analogous tectonic settings of the 1952 Kern County and 1971 San Fernando 

earthquakes (fig. 23), and the combined lengths of those 

faults. Similar arguments can be applied to the Santa 

Cruz Island-Anacapa-Santa Monica-HollywoodRaymond fault system and to comparable belts of late 

Quaternary faults in the Ventura-Santa Barbara Channel area. 

In summary, an upper limit of about M 8 (seismic moment of about 1028 dyne-em) for earthquakes in the Los 

Angeles region is compatible with the historical data 

and with what is known about the geometry of the faults; 

future earthquakes approaching this size probably will 

be restricted to the San Andreas fault zone. The largest 

earthquake likely along the other northwest-trending 

Earthquake and Surface-Faulting Potential 79 
zones of the San Andreas system is estimated to be M 7 

'(seismic moment of 3 x 1()26 dyne-em). An upper bound of 

about M 7.5 appears appropriate for the major reverseslip fault systems within the Transverse Ranges. 

Estimating likely earthquake size for ordinary planning and design purposes.-Although maximummagnitude events are important to the seismic design of 

critical structures, such earthquakes imply rupture 

along most of the area of a fault plane and thus generally can be expected to recur only rarely. More significant 

for ordinary planning and design purposes, therefore, is 

the likely size of an earthquake that has a reasonable 

probability of occurring during the lifetime of most 

structures (about 50 to 100 yr). 

The concept that individual active faults repeatedly 

generate major earthquakes of the same size (termed 

characteristic earthquakes) was recently proposed by 

Schwartz and Coppersmith (1984). They suggest that 

long fault zones do not break along their entire length 

during surface-faulting earthquakes but, instead, rupture along the same discrete segments. The distribution 

of slip associated with major earthquakes along each 

segment would be expected to be repeated during successive large events. If this assumption is correct, the 

characteristic earthquake model implies that the most 

likely earthquake size for particular faults could be 

determined from the geologic attributes that influence 

segmentation of a fault zone. 

A growing body of geologic evidence suggests that the 

south-central segment of the San Andreas fault, which 

includes that portion in the Los Angeles region, is ruptured repeatedly by a characteristic large event such as 

the 1857 earthquake (Sieh, 1981; Schwartz and Coppersmith, 1984). The evidence for this conclusion is (1) 

marked differences in long-term slip rates (33-64 mm/yr 

at Wallace Creek, west of Bakersfield, in comparison 

with 20-30 mm/yr at Cajon Canyon near San Bernardino) that are consistent with a model of repeated 

1857-type events having maximum displacement in the 

sector west of Bakersfield and (2) geologic data on 

recurrence at scattered sites along the south-central 

segment suggesting that large events of about the same 

size occur repeatedly along this segment of the San Andreas fault (see "Estimating the Likely Frequency of 

Damaging Earthquakes"). Since the 1857 earthquake, 

this part of the fault appears to be locked and displays a 

low rate of seismicity. On the basis of what is known 

about the Holocene displacement history of the San Andreas fault, the probability of occurrence of 1857-type 

earthquakes along the fault is currently estimated to be 

about 1 percent/yr but about 40 percent within the next 

30 yr (Lindh, 1983). Thus, an earthquake of about M 8 

appears credible for ordinary planning and design 

purposes. 

80 Earthquake Hazards in the Los Angeles Region 

Possible guides to selecting design earthquakes for 

noncritical structures for the other strike-slip faults of 

the region are their historical seismicity and their inferred lengths of Holocene surface rupture. The Claremont and Clark faults (highly seismic elements of the 

San Jacinto fault zone), for example, have Holocene 

lengths of about 65 and 85 km, respectively; the former 

is the probable source for three major historical earthquakes, two of which were M 6.8. A M 7 event thus seems 

reasonable for either of these two faults. In contrast, 

current levels of seismicity along the Palos Verdes Hills, 

Newport-Inglewood, Whittier, Elsinore, and similar 

northwest-trending fault zones are much lower, and 

their Holocene traces are mostly less than 20 km long 

(the implication being that, within the past few thousand 

years, these faults probably did not generate earthquakes whose associated rupture surfaces exceeded a 

few tens of kilometers in length). Thus, M 6.5 design 

earthquakes are reasonable for these faults. 

Considerable uncertainty exists about the design 

earthquakes for noncritical structures to be applied to 

the dominantly reverse-slip faults of the Transverse 

Ranges. Many of these faults appear to link into systems 

100 km or more long (fig. 11). The segments having 

demonstrated Holocene offset, however, are discontinuous and range from a few kilometers to a few tens of 

kilometers in length, the suggestion being that the 

associated earthquakes have not been greater than 

about M 7. Segmentation into separate fault elements of 

20 to 30 km is especially evident for the systems of faults 

that form the southern boundary of the Transverse 

Ranges, possibly because of mechanical interaction with 

the northwest-trending strike-slip faults that characterize the region farther south. 

Data on surface faulting from the 1971 San Fernando 

earthquake (Sharp, 1975, 1981) and from ancient seismic events deciphered from the geologic record along 

several faults (Bonilla, 1973; Matti and others, 1982; 

Crook and others, in press; Sarna-Wojcicki and others, 

in press) indicate that Transverse Ranges reverse faults 

typically produce about 0.5 to 2 m of vertical separation 

during a major earthquake event. On the basis of all the 

foregoing evidence, we conclude that M 6.5 to 7 events 

are appropriate design earthquakes for such faults 

when noncritical structures are considered. 

In summary, our current judgment, based largely on 

the segmented character of faulting during Holocene 

time, is that credible earthquakes for ordinary planning 

and design purposes are San Andreas fault, M 8; San 

Jacinto fault zone, M 7; other northwest-trending late 

Quaternary faults, M 6.5; and late Quaternary reverse 

faults of the Transverse Ranges, M 6.5 to 7. These 

estimates will be highly speculative until considerably 
more information becomes available on the recurrence 

of major faulting events along individual faults. 

Estimating the Likely Frequency 

of Damaging Earthquakes 

An approximate measure of the historical frequency 

of damaging earthquakes in the Los Angeles region is 

provided by the record since 1800 (Yerkes, this volume, 

table 3), which indicates that some part of the area has 

been shake{\ by a moderate or large event on the average of about once every 4 yr. How often, however, can a 

specific fault be expected to generate a damaging earthquake? This question, of particular significance to planning and engineering design decisions, can be answered 

satisfactoril~ at present for only a few faults in the 

region. 

With the exception of the San Jacinto fault zone, 

which has generated at least 10 major earthquakes 

since 1890, the historical seismic record of southern 

California is inadequate to reliably estimate the frequency of potentially damaging events for a particular 

fault or fault zone. Evidence of ancient earthquakes 

locally preserved in the geologic record along some of 

the late Quaternary faults can, however, be used to 

demonstrate the ability of such faults to produce significant earthquakes and to estimate the time intervals between such events. 

The study of prehistoric earthquakes has emerged as 

a powerful technique in evaluating the recurrence intervals of major earthquakes along faults (Clark and 

others, 1972; Sieh, 1981; Wallace, 1981; Sieh and Jahns, 

1984). Because moderate and large seismic events commonly are accompanied by surface faulting and related 

deformation or by secondary effects of shaking such as 

liquefaction-produced sand boils (see Tinsley and 

others, this volume), careful analysis of deposits or 

physiographic features along a fault may reveal discrete 

episodes of past earthquake-induced deformation. The 

historical seismic record for many faults worldwide that 

generate large earthquakes suggests that events of approximately the same size are repeated through time 

along individual faults. The concept of an average 

recurrence interval for a specific fault may be applicable to many faults (Sieh, 1981). Although the time 

intervals between events may range from tens to hundreds of years, they are commonly more or less regularly spaced over periods of several hun'dred to a thousand or so years. 

To reconstruct the prehistoric earthquake history of a 

fault, geologists search within Holocene or late Pleistocene deposits near the fault for evidence of repeatedly 

offset stratigraphic or physiographic features (see Sieh 

and Jahns (1984) for a well-documented study at a site 

along the San Andreas fault in central California), for 

sediments whose character suggests derivation from 

local fault scarps (fig. 25), or for sedimentary features 

·indicative of past liquefaction events. These studies 

generally require three-dimensional exposures of geologic relations, so that subtle features can be observed 

and documented in great detail; usually, excavation by 

trenching has been required to expose critical stratigraphic relations and datable materials that can provide time constraints on the inferred events. 

The number of discrete seismic events identified at a 

site along a fault depends both on preservation of the 

geologic evidence for each event and on the geologist's 

ability to discern the relevant evidence. Because some 

major earthquakes that have produced small surfacefaulting displacements may go unrecognized, geologic 

estimates of earthquake recurrence will always represent the maximum time intervals between major earthquakes and the minimum number of events. 

If discrete episodes of past earthquakes cannot be 

clearly discerned from the geologic record preserved 

along a fault, an average recurrence interval for major 

events can be estimated approximately by dividing the 

amount of slip for a particular time period by the 

displacement or slip for a single event inferred to be 

characteristic of that fault. Matti and others (1982, in 

press), for example, have observed that fault scarps 

developed in alluvial deposits formed during the past 

13,000 yr along strands of the Cucamonga fault west of 

San Bernardino show systematic increments in height of 

about 2 m; applying 2 m as an average value for fault 

slip accompanying a surface-faulting earthquake event, 

they have inferred 18 episodes of ground displacement 

and estimated a recurrence interval of about 700 yr for 

the Cucamonga fault. The slip-rate method presumes, 

however, that the slip events are essentially equal in 

size and that all slip is seismic. If the assumed value of 

the single-event displacement is not representative of 

the long-term behavior of that particular fault or if a 

substantial part of the total slip is due to creep movement, estimates of average recurrence interval using 

this method can be grossly inaccurate. 

Recurrence intervals of major earthquakes have been 

estimated so far for only a handful of faults in the Los 

Angeles region (table 11). The sparse data that have 

been obtained suggest that the San Jacinto and San Andreas faults have generated potentially damaging earthquakes in intervals of several tens to a few hundred 

years (for any particular fault segment). In contrast, the 

other potentially active faults in the region have estimated recurrence intervals of many hundreds to several 

thousands of years. 

Earthquake and Surface-Faulting Potential 81 
(f) 

a: 

UJ 

fUJ 

~ 

7 

6 

5 

4 

3 

2 

0 

f~\X./~ Holocene colluvium and allu vium 

EJ Holocene deb ris apron 

Holocene stream terrace gravel 

Upper Pleistocene or 

lower Holocene colluvium 

Tertiary or Quaternary bedrock 

FIGURE 25.-Geologic relations on canyon wall exposing the Javon Canyon fault near Pitas Point about 10 km northwest of Ventura (modified from 

Sarna-Wojcicki and others, in press). The reverse-slip fault offsets by approximately 4 m a stream-terrace platform estimated to be about 

3,500 yr old and thus implies a long-term average slip rate of about 1.1 mm/yr. The small fault (1) and the superposed aprons of angular rock 

fragments (2, 3, 4, 5) immediately adjacent to the Javon fault are interpreted to represent discrete slip events on the fault and to record 

separate vertical displacements ranging from 0.5 to 1.3 m. These geologic relations have been used to infer that four or five moderate-sized 

prehistoric earthquakes occurred about 350 to 1,000 yr apart, the average recurrence interval being approximately 700 yr. 

The best geologic information on earthquake recurrence in the Los Angeles region is for the San Andreas 

fault (fig. 26). At Pallett Creek, about 30 km southeast of 

Palmdale, the most complete record of prehistoric earthquakes known for a single fault anywhere in the world 

has been deciphered by detailed stratigraphic analysis 

of deposits of a late Holocene marsh exposed by trenching (Sieh, 1978c, 1984). The depositional environment of 

the ancient marsh was ideal for rapid burial and preservation of earthquake-induced deformation that occurred 

during its 2,()()(}-yr history. Reasonably precise time constraints on individual earthquake episodes are possible, 

because the sedimentary sequence contains abundant 

carbonaceous layers that have been dated by the 14C 

method. Evidence for distinct earthquake episodes in82 Earthquake Hazards in the Los Angeles Region 

eludes sand-boil deposits and other features induced by 

liquefaction; buried fault scarps and fissures; and 

lateral offsets of some horizons. The initial study of the 

Pallett Creek site (Sieh, 1978c) identified nine large 

earthquakes (including the 1857 event) since about 500 

A.D., for a suggested average recurrence interval of 

about 160 yr; more recent investigations (Sieh, 1984) 

have extended the record back to about 0 A.D. and have 

postulated the occurrence of 12 significant earthquakes 

since about 260 A.D., for an average recurrence interval of about 145 yr. 

Prehistoric events also have been reconstructed from 

trenched Holocene deposits along the San Andreas fault 

near Three Points, about 45 km northwest of Palmdale, 

and at San Emigdio Creek, about 2-5 km west of Gorman 
TABLE H.-Geologically determined estimates of the recurrence intervals of major earthquakes for a given point along some late Quaternary 

faults of the Los Angeles region 

Fault (map no.) 

Recurrence interval,• 

inyr 

San Andreas (1)--- 65-270 

San Jacinto------- 30--150 ARI [SM) 

fault zone 

(2-8). 

San Fernando (69)- 100--300 

Cucamonga (86!--- 700 ARI [SM) 

Javon Canyon (54)-- 350--1,000 

Elsinore fault----- 300--2,000 ARI (SM) 

zone (13-20): 

Glen Ivy North -- 200--300 

(16). 

Wildomar (18)--- 2,000--3,000 

Raymond [82)----- 3,00G--4,500 ARI 

Red Mountain (52)- More than 4,500 

[south branch). 

Sierra Madre (83)-- More than 1,000 

to 10,000. 

Santa Susana (68)-- More than 10,000 

Remarks 

Twelve events within past 1,700 yr 

Assumes range of slip rate (8-12 mm/yr) and 

range of estimated event displacements 

(0.4-1.2 m) during past 730,000 yr. 

Two events since about 100--300 yr ago. 

Assumes 18 displacements averaging 2 m 

within past 13,000 yr. 

Four or five events within past 3,500 yr. 

Assumes slip rate of 0.8 mrnlyr during past 

5 m.y. and range of estimated event 

displacements [0.3-1.2 m). 

Three or more events since about 

750 yr ago. 

One or two events since about 

4,000 yr ago. 

Eight events in past 36,000 yr, three events 

in the past 10,000 yr. 

Overlain by unfaulted deposits about 4,500 yr 

old. 

Overlain by unfaulted deposits between about 

1,000 and 10,000 yr old. 

Overlain by unfaulted deposits about 

10,000 yr old. 

Sieh (1984) 

Sharp (1981b) 

Bonilla (1973) 

References 

Matti and others (1982, in press) 

Sarna-Wojcicki and others (in press) 

Lamar and Swanson (1981) 

Rockwell and others (1985) 

Lamar and Swanson (1981) 

Crook and others (in press) 

Yeats and others (in press) 

Crook and others (in press] 

Leighton and others (1977), Lung and Weick 

(1978). 

1

Range of recurrence interval given, except where average recurrence interval {ARI) indicated. SM, recurrence interval derived from sli~rate method. 

just north of the area shown in figure 11. Although the 

Holocene record at these localities is much less complete than that at Pallett Creek, at least two pre-1857 

earthquakes have been inferred at each of these sites 

(Rust, 1982; Davis and Duebendorfer, 1982); the dates of 

both events correlate reasonably well with the dates of 

inferred events at Pallett Creek. This correlation suggests that the San Andreas fault along the southern 

margin of the Antelope Valley probably is repeatedly 

ruptured by large surface-faulting earthquakes of 

approximately the same size. 

Predicting the Character of .Surface 

Deformation Associated with Future 

Movement along Faults 

Surface faulting and permanent ground distortion induce shearing; compressional, tensional, and rotational 

strains that can damage or destroy even well-built structures. Predicting the likely distribution and severity of 

such processes is vital to developing hazard-mitigation 

strategies that would avoid or accommodate these effects; therefore, earth-science researchers have paid 

particular attention to the characteristics of faulting at 

the ground surface. Methods for predicting the patterns 

of rupture and distortion and for estimating the amounts 

of future surface offset have been developed and are 

now being widely applied (Bonilla, 1970, 1982; Wesson 

and others, 1975; Slemmons, 1977; Wallace, 1977). 

Data for evaluating surface-rupture hazards in the 

Los Angeles region are still incomplete. The likely location and type of future surface offset can be predicted 

with relative confidence from studies of offset late 

Quaternary deposits. It is possible to obtain rough 

estimates of the amount of surface displacement for individual events by using empirical relations based on 

worldwide historical observations. It is, however, very 

difficult to assess the actual likelihood of surface rupture along specific late Quaternary faults in the region. 

Only a few of the larger earthquakes in the region have 

been accompanied by tectonic surface rupture. For example, although the 1971 San Fernando earthquake 

generated surface faulting, three earthquakes of comparable size or larger along the Claremont fault of the 

San Jacinto fault zone apparently were not accompanied 

by surface-fault rupture. 

Location and pattern of surface faulting.-Worldwide 

evidence from historical surface-faulting events shows 

that nearly all ground ruptures have closely followed 

preexisting fault traces. Displacements have occurred 

Earthquake and Surface-Faulting Potential 83 
EVENT 

z 

1800 A.D.-

X 

v 

T 

R 

1000A.D.- N 

F 

D 

c 

B 

A 

0 A.D.-

DATE RECURRENCE 

(A. D.) INTERVAL 

1857 

137 ± 50 

1720 ± 50 

170±86 

1550 ± 70 

200 ± 86 

1350 ± 50 

270 ± 82 

1080 ± 65 

65 ± 119 

1015 ± 100 

80 ± 131 

935±85 

90 ± 113 

845 ± 75 

110 ± 99 

735 ± 60 

145±81 

590 ± 55 

240 ± 97 

350 ± 80 

90 ± 120 

260 ± 90 

FIGURE 26.-Dates of H! large earthquakes, along with their recurrence intervals, inferred from geologic relations in Holocene marsh 

deposits along the San Andreas fault at Pallett Creek about 30 km 

southeast of Palmdale (from Sieh, 1984, tables 2-4). The events are 

assigned letter designations in reverse alphabetical order starting 

with the youngest (1857). The uncertainty in each date is shown by 

a vertical bar and plus or minus values. Recurrence intervals for 

the events shown average 145 yr but vary from about 65 to about 

270 yr. Events X, V, T, R, and F each were accompanied by about 1 

to 2 m of strike-slip displacement of the ground surface and apparently were similar in size to the M 7.9 1857 earthquake. Events N 

and I produced lateral offsets of only a few centimeters at Pallett 

Creek and presumably were smaller earthquakes. Reliable 

estimates of the sizes of events A, B. C, and D have not been 

established. 

repeatedly along or near the same fault plane and nearly always with the same sense of offset (strike, dip, or 

84 Earthquake Hazards in the Los Angeles Region 

oblique slip) as that which can be inferred for the recent 

geologic past. The location and pattern of future surface 

faulting thus can be predicted, within reasonably close 

limits, from geologic relations commonly discernible at 

the Earth's surface. 

Surface faulting normally produces a complex pattern of ruptures that includes (1) a main fault trace and 

(2) subsidiary faults of lesser displacement that may occur many meters or even several tens of kilometers from 

the main break (Bonilla, 1970). Statistical data on all 

types of faulting suggest that 90 percent of the total surface faulting in any one event will be within 5 km of the 

main break and that most of the secondary faulting will 

be within 15 km of the main trace; displacements along 

subsidiary faults generally are less than 30 percent of 

the maximum displacement on the main fault (Bonilla, 

1982). The main trace · at the ground surface can be a 

single rupture or can consist of parallel, branching, or 

interlacing fractures. Studies of historical examples 

show that the width of the zone of faulting adjacent to 

the main trace has varied from a few centimeters to 

hundreds of meters, depending on the type of faulting, 

the magnitude of the associated earthquake, and the 

near-surface geologic materials along the fault trace. 

Although the maximum distance to the most distant 

secondary fault is about the same for all types of 

faulting, the main traces of strike-slip faults generally 

are narrow and simple in comparison with the traces of 

normal-, reverse-, or oblique-slip faults (Slemmons, 1977; 

Bonilla, 1982). 

Physiographic features produced by surface faulting 

(fig. 27) are particularly useful to delineate fault traces 

likely to rupture the ground surface again. Scarps, 

linear valleys and ridges, sag ponds, and offset drainage 

channels in distinctive aligned patterns result from 

repeated rupture at the Earth's surface. By observing 

and accurately mapping these features, geologists can 

delineate patterns of likely future surface faulting. 

Geologic maps of the late Quaternary faults shown in 

figure 11 provide a general guide to the location and pattern of future surface displacement in the Los Angeles 

region. The existing maps of many of these faults, 

however, were prepared for purposes other than 

evaluation of surface-rupture potential and at scales 

that are too small for complete and accurate mapping of 

all significant fault traces. Special-purpose geologic 

mapping and analysis that document the evidence for 

the youthfulness of individual fault traces and of faultproduced topographic features are available for some of 

the major faults. Parts of the San Andreas, San Jacinto, 

and Elsinore fault zones and the Ventura, San Fernando, 

Sierra Madre, Cucamonga, Raymond, Hollywood, and 

Verdugo faults have been mapped in sufficient detail 

(1:24,000 to 1:6,000 scale) to accurately depict the loca-
Offset drainage channel 

Bench 

Offset drainage channel 

Linear valley or trough 

FIGURE 27.-Landforms typically developed along active strike-slip faults (from Wesson and others, 1975, fig. 11). Landforms developed along 

active reverse-, normal-, and oblique-slip faults commonly are more complex and discontinuous in pattern. 

tion of fault traces that are candidates for future surface displacement. 

Maps of Special Studies Zones for fault-rupture 

hazard as designated by the California Division of Mines 

and Geology {Hart, 1980) are available for many of the 

Holocene faults in the Los Angeles region {fig. 28); the 

geologic evidence for Holocene surface displacements 

has been tabulated by Hart and others {1977, 1978, 

1979). Faults designated for special studies to date include the San Andreas fault; the San Jacinto zone; the 

Ventura, San Fernando, Raymond, and Cucamonga 

faults; the Newport-Inglewood zone; and Holocene 

segments of the Sierra Madre, Whittier, and Elsinore 

fault zones. These 1:24,00Q-scale maps delineate recently active fault traces inferred from stratigraphic offsets, 

physiographic evidence, or geophysical techniques and 

are detailed enough to depict the major fault traces. 

More detailed geologic studies, including trenching, are, 

however, necessary to accurately locate and describe 

all evidence bearing on the rupture hazard for specific 

sites. Lamar and Scrivner {1983) have summarized the 

geologic evidence obtained from trenching investigations that bears on the recency of faulting within many 

of the Special Studies Zones in the Los Angeles region. 

Type and amount of displacements.-The type of 

future movement likely to occur on a fault can be estimated from the prevalent style of its geologically recent 

movements {strike slip, dip slip, or oblique slip). 

Although a fault that has been in existence for millions 

of years may have slipped in different ways in the geologic past, the type of slip that has characterized it for 

the last several hundred thousand years probably is the 

most reliable indicator of future slip. For currently 

active faults, seismologic {fault-plane solutions) or geodetic evidence of slip direction also can be used to infer 

the likely type of displacement. The slip characteristics 

of the late Quaternary faults in the Los Angeles region 

are given in table 5. 

The amount of future displacements likely to occur 

along specific faults can also be estimated from offsets 

in historical earthquakes or inferred from analysis of 

geologic relations along a fault. Amounts of prehistoric 

offset can be inferred from the morphology of fault 

scarps (Wallace, 1977, 1981), from systematically offset 

Earthquake and Surface-Faulting Potential 85 
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FIGURE 28.-Index to maps of Special Studies Zones for fault-rupture hazard in the Los Angeles region (from Hart, 1980). These maps, compiled and issued by the California Division of 

Mines and Geology, show [at a scale of 1:24,000) (1 in. = 2,000 ft) the traces of Quaternary faults within selected major Holocene fault zones as a guide for delineating the legal boundaries of areas within which site-specific investigations for active faults (as defined by the Alquist-Priolo Act of the State of California) are required when structures are planned for 

human occupancy. As new information on the location and recency of faulting becomes available, these maps are revised. 
~--- 20 ~ ~-- ~ 

z z w w • 

:::?: 10 p.' :::?: • w • w u u • • • 

<t: • <t: •• • • -' 5 . • : • -' a. a. • • ~ • • .. •• (/) •• • OCil ~ • • 0(/) • a:: • • • wa::: • ww • • • • • Ul- uw • 

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6.0 6.5 7.0 7.5 8.0 8.5 5 10 50 100 500 

EARTHQUAKE MAGNITUDE (M 5 ) LENGTH OF SURFACE RUPTURE, IN KILOMETERS 

A B 

FIGURE 29.-Empirical relations useful for estimating the maximum surface displacements likely for future earthquakes (modified from Bonilla 

and others, 1984, figs. 2A, 3A). Based on worldwide data on historical surface faulting. A, Relation between maximum surface displacement 

and earthquake magnitude, M5. B, Relation between maximum surface displacement and length of surface rupture. Lines show least-squares 

fit to data for all types of faults. Because of the statistics involved in estimating maximum values, lines labeled A-N are used to estimate the 

most likely maximum surface displacement associated with a given magnitude earthquake (A) or length of surface rupture (B). Lines labeled 

B-B' are used to estimate the most likely earthquake magnitude (A) or length of surface rupture (B) associated with a given maximum surface 

displacement. 

stream channels crossing fault traces (Wallace, 1981; 

Sieh and Jahns, 1984), or from geologic relations exposed in trenches cut across faults (Bonilla, 1973; Sieh, 

1978c). In the Los Angeles region, for example, geomorphic analysis of fault scarps along strands of the 

Cucamonga fault suggests that the strands have ruptured repeatedly during the past 13,000 yr in events that 

averaged about 2 m of vertical offset (Matti and others, 

1982, in press). 

Another technique for estimating the amount of likely 

displacement uses the empirical relations that link 

displacement with various parameters determined from 

analysis of historical earthquake observations 

worldwide (Bonilla, 1970, 1982; Bonilla and others, 

1984). These relations can provide approximate limits 

on the amount of surface-fault displacement to be expected for different types of faults. Thus, maximum surface displacement can be estimated for an earthquake 

of a particular magnitude along a specific type of fault 

(fig. 29A); although data are too sparse to draw conclusions for specific types of faults, larger values of 

displacement within the same range of magnitudes are 

generally associated with reverse-slip faults. Alternatively, if geologic mapping provides a basis for 

limiting the likely total length of future surface rupture, 

empirical relations can be used to estimate the maximum displacement (fig. 29B). 

Although historical surface-faulting events in the Los 

Angeles region are too few to use as a guide to the likely 

maximum amounts of future displacements, the data 

base of historical surface offsets in all of California 

(table 8) provides a general frame of reference for what 

might be expected for different types of faulting. Approximate upper limits on the amount of future displacements associated with earthquakes on specific types of 

faults also can be estimated from the relation between 

maximum fault offset and length of surface rupture (fig. 

29B) by assuming that future surface-faulting events 

will not exceed the mapped lengths of late Quaternary 

fault traces in the Los Angeles region .. For the San Andreas fault, which is hundreds of kilometers long, the implied upper bound would be about 10 m. Similarly, the 

San Jacinto and other northwest-trending strike-slip 

fault zones have single strands that are as long as 85 km, 

the implication being that horizontal surface displacements of as much as 4 m are possible. Most other late 

Quaternary faults in the region are less than 40 km long, 

and displacements on these faults are unlikely to exceed 

2 to 3 m per event. 

Regional tectonic deformation.-The geologic and 

historical records provide rough clues to the patterns of 

regional tectonic deformation that could be associated 

with future earthquakes. Late Quaternary marine and 

nonmarine terraces, which are excellent markers for 

reconstruction of past crustal movements, indicate that 

regional uplift and subsidence are continuing; although 

these processes are sporadic, they reflect ongoing deformation that has elevated or depressed the same areas 

repeatedly during the recent geologic past. 

The land surface of the Los Angeles basin and adjacent uplands exemplifies this pattern of ongoing vertical 

deformation (fig. 30). Continued uplift of the hills and 

mountains and subsidence of the lowland areas are 

reflected in the folded and faulted near-surface rocks. 

Earthquake and Surface-Faulting Potential 87 
FIGURE 30.-0blique aerial phoiograph looking north along the Inglewood fault in the Baldwin Hills at the northern end of the Los Angeles basin. 

The Santa Monica and Hollywood faults form the southern margin of the Santa Monica Mountains, which extend approximately northeastward across the top of the photograph. The Baldwin Hills and Santa Monica Mountains are the result of repeated episodes of tectonic uplift 

and folding during late Quaternary time. Future moderate to large earthquakes along these potentially active faults may be accompanied by 

uplift, warping, or tilting of these upland areas. (Photograph by Spence Air Photos, February 1967. Reproduced by permission of the Department of Geography, University of California, Los Angeles.) 

Thus, the series of hills along the Newport-Inglewood 

zone express the trend and vertical uplift of subsurface 

faulted anticlines. Although some aseismic deformation 

cannot be precluded, much of the folding probably ac88 Earthquake Hazards in the Los Angeles Region 

companied moderate or large earthquakes along the 

Newport-Inglewood fault zone. 

Regional tectonic warping associated with two 

historical earthquakes in the region shows what future 
effects are possible. The 1933 Long Beach earthquake 

(M 6.2) apparently caused uplift and subsidence over an 

area of at least 260 km2 east of the Newport-Inglewood 

fault zone; the deformed area comprised a northwesttrending upwarp having a maximum uplift of 18 em 

centered on the Alamitos Plain and extended southeast 

from near Compton (Gilluly and Grant, 1949). The 1971 

San Fernando earthquake (M 6.6), as noted earlier, was 

associated with a broad uplift of perhaps 600 km2 on the 

upthrown (northern) side of the north-dipping reverse 

fault. Tectonic uplift locally exceeded 2 m (Savage and 

others, 1975) and was accompanied by small amounts of 

horizontal expansion and contraction distributed in a 

complex pattern across the uplift (Yerkes and others, 

1974, fig. 8). 

The future patterns of uplift and subsidence caused 

by earthquakes can be estimated by numerical modeling 

from elastic dislocation theory. The distribution of vertical surface deformation from idealized strike-slip and 

dip-slip faults has been calculated on the basis of this 

theory (for example, Chinnery, 1965; Barnett and 

Freund, 1975; Freund and Barnett, 1976). The theory 

also has been applied successfully to deduce the 

character of slip at depth from the observed surface 

deformations of several major dip-slip earthquakes in 

southern California (Jungels and Frazier, 1973; Savage 

and others, 1975; Stein and Thatcher, 1981). An inverse 

application of these latter modeling techniques can be 

used to define the approximate limits and amounts of 

vertical deformation likely to be associated with a 

postulated future earthquake. That is, one could calculate the expected pattern of uplift and subsidence by 

assuming the geometry of the causative fault and the 

direction, amount, and distribution of slip. 

We conclude that large-scale uplift and subsidence 

resulting from future earthquakes in the Los Angeles 

region will reflect the established patterns of vertical 

deformation indicated by the physiography of the 

region. Tectonic elevation changes will be related to the 

geometry of the earthquake-generating fault and may 

extend over hundreds of square kilometers. The largest 

changes in elevation will be associated chiefly with the 

dip-slip faults of the Transverse Ranges. Regional uplift 

and subsidence may, however, accompany components 

of vertical faulting along some strike-slip faults. 

Although the maximum changes in elevation probably 

will be no more than a few meters, such movements 

occurring along the coast could pose a significant ftmctional hazard to coastal facilities. The overall impact of 

such tectonic distortion accompanying future earthquakes in the Los Angeles region will be small in comparison with damage caused by shaking, landslides, and 

surface-fault rupture. 

IMPLICATIONS FOR REDUCTION 

OF EARTHQUAKE HAZARDS 

Potentially damaging future earthquakes are the inevitable result of the tectonic environment of the Los 

Angeles region. Although the events themselves cannot 

be prevented, many of their destructive effects can be 

avoided or accommodated-and property damage, injuries, and loss of life significantly limited-by using information on the expected location and character of fault 

hazards. Reduction of earthquake hazards begins with 

the recognition that the faults described in this chapter 

are the likely sources of future moderate- to largemagnitude earthquakes and that any associated surface 

faulting or distortion will be localized along their traces. 

This information can be applied to (1) develop and implement governmental land use policies and bujldjng codes, 

(2) provide technical data for use in decisions about the 

siting and design of structures, and (3) stimulate 

emergency preparedness actions by governmental agencies, the corporate community, and the general public. 

Because the dominant strategy in earthquake-hazard 

reduction is to design structures that will accommodate 

earthquake shaking (design for surface rupture is 

generally impractical), the size of future earthquakes 

that might occur along the different faults is a key issue 

for which geologic and seismologic data can provide important constraints. Although building codes, which apply to ordinary structures such as dwellings and other 

low-rise construction, specify lateral force (shaking) 

requirements based indirectly on regional estimates of 

seismic hazard, modern engineering practice for larger 

or more critical structures develops seismic design 

parameters through a series of analytical steps that includes the specification of a design earthquake (both 

location and size), the largest event that it is appropriate 

to design a particular structure or class of structures to 

withstand (Hays, 1980). 

Specification of a design earthquake represents a 

qualitative judgment that incorporates understanding of 

the tectonic and seismologic environment, the physical 

characteristics of nearby faults, and an assessment of 

the acceptable level of risk for a particular type of structure. For critical facilities such as nuclear power reactors or large dams that necessitate extremely large 

factors of safety, the design earthquake usually is the 

maximum event that can be expected from a nearby 

seismic source, even though such an event might occur 

only once in several thousand years. The earthquake 

size chosen for the design of most other types of structures, however, is usually that which might reasonably 

occur within the lifetime of the structure-50 to 100 yr. 

Earthquake and Surface-Faulting Potential 89 
In special design situations (for example, LNG Seismic 

Review Panel, 1981), different levels of shaking 

parameters are based on the largest sizes of earthquakes that might be expected to occur over different 

spans of time-for example, a recurrence of a few hundred years, a few thousand years, or a few tens of 

thousands of years. 

Potential surface faulting is the earthquake hazard 

most amenable to loss-reduction strategies, because it is 

a localized hazard that is easily studied and delineated 

by direct geologic observations. The potentially destructive effects of surface faulting and associated ground 

distortion are commonly reduced by siting structures to 

avoid future displacements; in special cases, structures 

such as pipelines are designed to accommodate those 

displacements without destruction or loss of function. 

Selective siting to avoid zones of potential rupture is 

the most effective way to reduce risks from this hazard. 

This strategy, which relies on the ability of geologists to 

identify and map fault traces that may be the loci of 

future movement at the ground surface, is being implemented in California through the Alquist-Priolo 

Special Studies Zones Act of 1972. This act specifies 

that no structures for human occupancy are permitted 

on or within 50 ft of an active fault (defined as a fault 

that has had surface displacement during Holocene 

time). Geologic maps compiled by the California Division 

of Mines and Geology identify fault zones showing 

evidence of Holocene surface displacement along one or 

more segments and form the legal basis for delineating 

zones within which city and county governments must 

regulate development (Hart, 1980). Usually, these local 

agencies require further detailed geologic investigations, including trenching, to assess the presence or 

absence of fault-rupture hazards for specific sites. 

Avoiding fault traces may be impossible for structures of extended dimensions, such as pipelines or 

canals, or for large special structures whose siting is 

controlled by other factors. For those structures that 

cannot be selectively sited, special engineering design is 

necessary to accommodate likely differential surface 

movements. In these cases, estimates not only of the expected location of future faulting but also of the style 

and amount of fault slip are needed to guide engineering 

judgments. 

Because earthquake-associated regional uplift or subsidence is not localized, avoidance is not usually a practical strategy. In the Los Angeles region, the potential 

for future vertical deformation from earthquakes is 

reflected in the series of broadly warped late Quaternary marine terrace deposits along the coast, whose 

uplift-at long-term rates as high as 10 mm/yr (Lajoie 

and others, 1979}--probably reflects numerous episodes 

90 Earthquake Hazards in the Los Angeles Region 

of regional warping associated with past large earthquakes. The adverse consequences of uplift or subsidence for facilities being built along the coast are best 

reduced by designing to accommodate such effects. 

SUMMARY 

Fault hazards in the Los Angeles region can be anticipated by evaluating the currently available geologic 

and seismologic information. Although the data base is 

incomplete and some methods of hazard assessment are 

still evolving, enough is known to identify most of the 

hazardous faults and predict the areal distribution and 

type of future surface displacements along them (and, 

less confidently, the likely amounts of surface rupture). 

The sizes and frequency of significant earthquakes likely to occur along these faults can be estimated, although 

with much less certainty. 

We can now identify, in the Los Angeles region, nearly 100 fault strands having surface offsets in late 

Quaternary time. Many of these faults, especially those 

showing displacements in Holocene time, are the 

sources of large historical earthquakes or have produced recent small earthquakes or both. These late 

Quaternary faults are likely to generate future destructive earthquakes and associated surface rupture and 

tectonic deformation. 

These faults differ greatly in degree of activity and 

severity of hazard. Studies now in progress seek to 

determine geologically recent rates of offset along these 

faults as an index of their relative activity. The most 

reliable estimates of slip rates, averaged over the past 

several hundred thousand years, are for the San Andreas fault (20--30 mm/yr) and the San Jacinto fault zone 

(8 to more than 12 mm/yr). Estimated offset rates for 

most other faults are less than 1 mm/yr, except for a belt 

of Transverse Ranges faults that extends from near Santa Barbara to San Bernardino and has rates of slip or 

vertical separation as high as 6 mm/yr. Slip rates of 

about 1 mm/yr are reasonable assumptions for the Palos 

Verdes Hills and Newport-Inglewood fault zones. 

Preliminary findings on earthquake recurrence suggest that parts of the San Andreas and San Jacinto fault 

zones have generated major earthquakes at intervals of 

several tens of years to a few hundred years. The time 

intervals between major earthquakes on other faults appear to be many hundred to several thousand years. 

Additional study of late Quaternary faults is needed to 

adequately assess the recurrence intervals for 

moderate to large earthquakes on many faults. 

The type of future surface displacement likely to 

occur on many faults is known. The San Andreas fault 
and most other northwest-trending faults will have 

dominantly right-lateral strike-slip motion, but significant vertical components of slip (chiefly reverse) locally 

can be anticipated along parts of the San Jacinto, 

Elsinore, Whittier, Newport-Inglewood, and Palos 

Verdes Hills fault zones. Chiefly reverse slip is likely 

along the faults of the Transverse Ranges, although 

significant left-lateral strike-slip components can be expected along the Santa Ynez, Santa Cruz Island, and San 

Fernando faults. 

Earthquakes as large as M 8, accompanied by as 

much as 10 m of chiefly horizontal surface offset, can be 

expected along the San Andreas fault. The largest 

earthquake likely to occur along the other major fault 

zones in the Los Angeles region is estimated to be M 7.5; 

such earthquakes can generate as much as 3 m of surface offset. Except on the San Andreas fault, maximummagnitude events probably are very rare. Thus, we 

judge that earthquakes of M 6.5 to 7, accompanied by as 

much as 2 m of surface displacement, are appropriate 

design earthquakes for ordinary planning purposes for 

most other faults of the region. 

Large surface-faulting displacements along the 

reverse-slip faults in the Santa Barbara Channel may 

generate local t~unamis that could be hazardous to 

coastal facilities. In addition, tectonic upwarp and subsidence of broad areas may accompany some future 

large earthquakes in the Los Angeles region, although 

historical events suggest that the changes in elevation 

probably will not exceed a few meters at any point. 

Surface uplift and subsidence are more likely to be 

associated with major earthquakes along the westtrending faults of the Transverse Ranges, because vertical displacements are characteristic of those faults. 

Planning and engineering decisions can reduce many 

of the potentially hazardous effects of faulting through 

the twin strategies of avoidance and accommodation. Of 

all the earthquake hazards, surface fault rupture is the 

most easily addressed because its potential effects are 

areally restricted and can be reliably predicted. Thus, 

for example, detailed geologic maps now available for 

many of the potentially active faults of the Los Angeles 

area provide a guide for selective siting of construction 

under the State of California's Alquist-Priolo Special 

Studies Zones Act. 

On the other hand, the seismic shaking that results 

from sudden rupture along a fault is widespread and 

generally must be accommodated through engineering 

design. Reduction of this hazard depends not only on an 

estimate of the likely size of a future earthquake but also 

on a knowledge of how seismic energy is modified as it 

passes through the complex geologic structure of the 

Earth. The problem of predicting the location and severity of the shaking effects-the major challenge of earthquake hazard reduction-is discussed in the following 

chapters. 

Earthquake and Surface-Faulting Potential 91 
Earthquake Ground 

Motion 
PREDICTING EARTHQUAKE GROUND MOTION: 

AN INTRODUCTION 

By R. D. Borcherdt 

INTRODUCTION 

The damaging effects of earthquakes, with the exception of those associated with tectonic surface displacements, are caused by strong ground shaking. Ground 

shaking generally causes the most widespread effects 

not only because it propagates to considerable distance 

from the earthquake source but also because it may trigger secondary effects associated with ground failure 

and water inundation. Consequently, accounting for the 

effects of strong ground motion generated by future 

large earthquakes is a major factor in safeguarding life 

and property. 

Reducing loss of life and property from strong ground 

shaking requires conscientious application of 

earthquake-resistant design and construction practices, 

development of adequate land use policies, and implementation of appropriate measures to strengthen 

vulnerable structures. For the design of critical structures at specific sites (such as nuclear powerplants, 

dams, and high-rise structures), it is feasible to collect 

detailed geologic and seismologic data sets on which to 

develop elaborate estimates. For routine construction 

and development of land use policy, collection of such 

data sets is not feasible, and more generalized predictions on a regional scale are necessary. This chapter 

provides the framework for subsequent chapters concerned with ground-motion estimation on both a regional 

and a site-specific basis. In brief, these chapters are 

concerned with development of geologic and geotechnical data bases useful for making ground-motion 

estimates on a regional scale (Tinsley and Fumal; Fumal 

and Tinsley), regional estimates of earthquake intensities (Evernden and Thomson), estimates of quantitative 

measures of ground motion on a regional scale Ooyner 

and Fumal), regional delineations of potential variations 

in local ground response (Rogers and others), and sitespecific estimates of potential ground-shaking timehistories (Spudich and Hartzell). These chapters, which 

are addressed to a broad audience, summarize currently available data sets and methodologies pertinent to 

predicting ground motion for seismic zonation, land use 

policy development, and site-specific design of critical 

structures. 

Earlier work on developing ground-motion estimates 

in the San Francisco Bay region for seismic zonation 

purposes (Borcherdt, 1975) found broad public interest 

and application in most city and county seismic safety 

plans (Kockelman, 1975; Kockelman and Brabb, 1979). 

The work emphasized the importance of local geologic 

conditions in determining the character of strong 

ground shaking and showed the existence of resonancetype wave propagation phenomena capable of increasing the amplitude of certain frequencies of ground 

snaking significantly at . sites underlain by different 

types of alluvial deposits (Borcherdt, 1970; Borcherdt 

and Gibbs, 1976). This work resulted in regional predictions of maximum expected earthquake intensity, attenuation relations for strong shaking with distance 

(Page and others, 1975), geographic delineation of potential variations in shaking owing to local geologic conditions, and model estimates of strong shaking at specific 

sites for an earthquake of given size and location. These 

studies have contributed to a rapidly evolving research 

effort in strong-motion seismology, which, together with 

significant improvements in the strong-motion data 

base, has resulted in a number of advances pertinent to 

understanding the nature of ground motions generated 

by large earthquakes. Many of these advances are applied in subsequent chapters to the problem of 

estimating future strong ground motions and resultant 

earthquake intensities for the Los Angeles region. 

DEVELOPING A DATA BASE 

FOR GROUND-MOTION 

ESTIMATION ON A 

REGIONAL SCALE 

Local geologic conditions are known to strongly influence the character of earthquake-generated ground 

Predicting Earthquake Ground Motion 93 
shaking (Wood, 1908; Kanai, 1952; Borchardt, 1970, 

1975; Rogers and others, 1980). Consequently, quantitative estimates of strong ground shaking and its effects on a regional scale must account for these influences and be based on earth-science data available 

throughout the region of interest. The data most readily 

available on a regional scale are geologic data 

presented in the form of geologic maps. Most standard 

geologic maps, however, are compiled for inferring 

geologic history and are not easily adapted to many 

special-purpose interpretive products. For example, 

most geologic maps differentiate bedrock units in considerable detail but only crudely differentiate young, unconsolidated sedimentary deposits of interest for 

estimating the severity of future shaking or the potential 

for liquefaction-induced ground failure. Lajoie and 

Helley (1975) used inferences regarding age and depositional environment based on physical characteristics of 

map units to differentiate sedimentary deposits in the 

San Francisco Bay region. Tinsley and Fumal (this 

volume) have extended this methodology to the Los 

Angeles region. They discuss the compilation of an extensive physical-property data base, the geologic data 

base available for portions of the region, and the 

methodology for delineating Quaternary sedimentary 

deposits in the Los Angeles region. Such compilations 

provide the regional basis for deriving special-purpose 

interpretative maps. 

To extend the available geologic and physicalproperty data bases for preparing regional estimates of 

future ground shaking, an extensive program was 

undertaken to collect seismic velocity and geologic logs 

in all major sedimentary units in the San Francisco Bay 

region (Gibbs and others, 1975, 1976, 1977, 1980) and 

the Los Angeles region (Fumal and others, 1981, 1982, 

1984). Results of this program show that the seismic 

velocities of different units correlate with variations in 

measured ground motions and observed earthquake intensities (Borchardt and others, 1979). In addition, 

detailed comparative studies conducted by Fumal (1978) 

have defined surficial units in terms of geotechnical and 

geologic parameters that have distinguishable seismic 

velocities and, in turn, distinct response characteristics 

(Borchardt and others, 1979). The availability of geologic 

and geotechnical parameters on a regional scale allows 

near-surface seismic velocities to be mapped on a 

regional scale for delineating variations in future 

ground response. 

Fumal and Tinsley (this volume) summarize the 

seismic-velocity data base collected for the Los Angeles 

region. They define seismic-velocity units on the basis of 

a detailed comparative study of geologic and geotechnical parameters. These definitions are used in conjunction with thickness information to map average 

shear-wave velocity over a thickness of one-quarter 

94 Earthquake Hazards in the Los Angeles Region 

wavelength at a reference period of 1 s. Shear-wave 

velocity maps provide a basis for estimating future 

ground motion on a regional scale. Methodologies for 

preparing predictive ground-motion maps are discussed 

in subsequent chapters. 

PREDICTING EARTHQUAKE 

INTENSITIES 

Predicted earthquake intensities are especially useful 

for reducing earthquake hazards on a regional scale. 

Because earthquake intensities are based on a direct 

assessment of the effects of ground shaking on manmade 

structures and natural features, estimated earthquake 

intensities provide a regional assessment of potential 

earthquake losses from future damaging earthquakes. 

Predicted intensity maps developed for the San Francisco Bay region (Borchardt and others, 1975a) and the 

Los Angeles region (Evernden and others, 1981) have 

been used extensively by Federal, State, county, and city 

planning agencies as well as by the public for both land 

use planning (Kockelman, 1979, 1980) and predisaster 

response planning (Davis and others, 1982a, b). Maps 

showing predicted intensities provide estimates on a 

regional scale of the severity of expected earthquake effects and as such are especially useful for seismic-risk 

and seismic-hazard evaluations. A discussion of seismic 

intensity and commonly used intensity scales is provided 

for additional reference in appendix 1; an abridged version of these scales appears on the inside back cover. 

General factors influencing earthquake intensities 

are characteristics of the earthquake source (such as 

size, fault depth and extent, and rupture type), seismic 

energy transmission characteristics of the regional 

crustal structure, and local site conditions. A subsequent chapter (Evernden and Thomson, this volume) 

discusses a general predictive model for earthquake intensities that accounts for each of these factors and applies the model to predict maximum expected earthquake intensities on a regional scale for the Los Angeles 

region. On the basis of intensity predictions for a suite of 

possible California earthquakes, Evernden and Thomson 

extend the procedures of Blume and others (1980) to provide estimates of dollar loss expected for wood-frame 

construction. Because such estimates are dependent on 

the location and extent of urbanization relative to the 

earthquake source, they indicate the relative seismic 

risk associated with the major seismogenic faults in 

California. 

The amount of damage that a particular structure 

experiences during an earthquake depends on the structure's design and construction characteristics. Consequently, the severity of damage to an individual struc-
ture is not always a reliable indicator of ground shaking. 

To investigate the reliability of earthquake intensity as 

an indication of ground shaking, Evernden and Thomson 

compare observed intensities from the 1971 San Fernando earthquake with instrumental recordings of strong 

shaking in different frequency bands. Their results indicate that predicted earthquake intensities correlate 

directly with expected levels of shaking in the frequency 

band 0.5 to 3 Hz. This correlation suggests that 

predicted intensities might be used in conjunction with 

present building codes for the earthquake-resistant 

design of particular types of structures in the Western 

United States. In the past, earthquake intensities have 

been used for design purposes primarily in regions such 

as the Eastern United States, where few instrumental 

recordings of strong motion have been obtained. 

Although predicted earthquake intensities may not 

provide a quantitative estimate of the amplitude and frequency characteristics of strong ground shaking and do 

not predict whether a particular structure will fail, they 

do delineate potential regional variations in the severity 

of expected effects of earthquake-generated strong 

ground shaking. As such, they are especially useful for 

regional hazard assessments as well as for the development of future land use policies and disaster response 

plans. 

PREDICTING QUANTITATIVE 

CHARACTERISTICS OF 

GROUND SHAKING 

Earthquake-resistant design codes are based on quantitative estimates of ground shaking in the form of either 

time-history parameters or spectral parameters. Thus, 

estimating these parameters on both a site-specific and 

a regional basis is a fundamental component of efforts 

to reduce losses from future earthquakes. Methodologies for making quantitative estimates in the Los 

Angeles region are presented in subsequent chapters. A 

detailed description of parameters used to quantitatively describe strong ground shaking for engineering 

design is presented in appendix 1. 

The basic data set required for making quantitative 

estimates of ground shaking consists of instrumental 

recordings of damaging earthquakes obtained near the 

sources of those earthquakes. Unfortunately, recordings 

of ground motions for many types of potential earthquakes at distances of engineering interest have not yet 

been obtained; significant improvements have been 

made in the strong-motion data set within the last 

decade, however, the most notable addition being the 

recordings from the Imperial Valley earthquake of 1979. 

These recent data have been incorporated in groundmotion estimates derived in subsequent chapters. 

Estimating Peak Acceleration, 

Velocity, and Response 

Spectral Parameters 

Joyner and Fumal (this volume) have used a regional 

map of near-surface shear-wave velocities (Fumal and 

Tinsley, this volume) in conjunction with parameters 

derived from instrumental recordings of strong-motion 

data to estimate ground-motion parameters for future 

earthquakes of specific magnitude and location and to 

estimate the exceedance level of certain ground-motion 

parameters at a specified annual probability. The 

predictive method presented by Joyner and Fumal (this 

volume) is based on attenuation relations specifying the 

statistical regression of parameters such as peak 

horizontal acceleration, velocity, and response spectral 

values on earthquake magnitude, source distance, and 

local site conditions. Characterization of the local site 

conditions is based on the premise that ground-motion 

body-wave amplitudes can be expected, in many situations, to be approximately inversely proportional to the 

corresponding seismic-wave velocity as mapped by 

Fumal and Tinsley (this volume), which in turn is based 

in part on the delineation of Quaternary deposits provided by Tinsley and Fumal (this volume). The technique 

presented by Joyner and Fumal (this volume) can be used 

to provide ground-motion estimates at specific sites as 

well as on a regional scale. To account for the uncertain 

times and sizes of future events, data on fault-slip rate 

(Ziony and Yerkes, this volume) are incorporated to 

estimate regional and site-specific ground-motion 

parameters that will be exceeded at a specified annual 

probability. 

These regional and site-specific quantitative estimates of ground-motion parameters are expected to be 

useful in the earthquake-resistant design of both noncritical and critical structures. The set of strong-motion 

data used by Joyner and Fumal (this volume) permits 

estimates of expected ground-motion amplitude level 

averaged over relatively broad frequency bandwidths. 

Some local geologic deposits, however, are known to 

amplify ground shaking considerably over relatively 

narrow frequency bandwidths owing to resonant effects 

(Borcherdt, 1970; Borcherdt and others, 1975c). Rogers 

and others (this volume) have used recordings of a variety of seismic events to develop an empirical data base 

for predicting the frequency-dependent nature of 

ground response in detail. 

Estimating Regional' Variations in 

Local Ground Response 

Rogers and others (this volume) have used strongmotion recordings of the 1971 San Fernando earthPredicting Earthquake Ground Motion 95 
quake, recordings of distant nuclear explosions, and the 

extensive geologic and seismic data bases compiled by 

Tinsley and Fumal (this volume) to prepare a quantitative estimate of potential variations in ground 

response over the frequency bandwidth of engineering 

design interest. On the basis of comparative groundresponse measurements at 37 locations, Rogers and 

others (1984) have found that local ground response 

determined from low-strain signals from distant nuclear 

events can be used to predict ground response to signals 

of higher strain levels like those generated by the San 

Fernando earthquake. This conclusion suggests that 

comparative measurements of ground shaking recorded 

at 98 sites in the Los Angeles region from distant 

nuclear explosions can be used to provide quantitative 

estimates of ground response for future damaging earthquakes. In general, these comparative measurements 

show that levels of ground shaking at periods of less 

than 0.5 s at sites underlain by Holocene and Pleistocene sedimentary deposits are commonly three to four 

times greater than those at sites underlain by crystalline 

rock. Resonant effects having larger amplifications over 

narrow frequency bands are observed for sites underlain by Holocene deposits 10 to 20 m thick. For periods of 

shaking greater than 0.5 s, levels of ground shaking 

generally increase as the thickness of Quaternary 

deposits increases. 

By using cluster analysis techniques, Rogers and 

others (this volume) demonstrate how these data on 

measured ground response can be matched with the 

geologic and geotechnical information to predict relative 

ground response over bands of different periods for a 

set of map units. The resulting predictive groundresponse maps for the Burbank-Los Angeles-Compton 

urban corridor provide a quantitative estimate of the 

frequency-dependent amplitude variation expected in 

ground motions owing to local site conditions. Such 

maps would be useful for regional planning and for 

general earthquake-resistant design. 

Site-Specific Prediction of 

Ground-Shaking Time-Histories 

Design of critical structures at specific sites (such as 

nuclear powerplants, high-rise buildings, and dams) 

often requires an elaborate and accurate description of 

the characteristics of the ground motions likely to be 

experienced during the life of the structure. In rare instances, the ground motions likely to be generated may 

96 Earthquake Hazards in the Los Angeles Region 

have been previously recorded at the site, but, in most 

cases, no such recording exists, and design must be 

based on theoretical model estimates derived from data 

recorded elsewhere. The recent growth of the strongmotion data set has contributed to a rapidly evolving 

research effort in strong-motion seismology; this 

research is directed toward the development of theoretical models to describe the nature of the earthquake 

rupture process and the resulting generation and propagation of seismic shaking. Spudich and Hartzell (this 

volume) have discussed these recent developments and 

their application to the problem of predicting groundmotion time-histories at specific sites. 

Spudich and Hartzell (this volume) describe the 

nature of the earthquake rupture process, including 

deceleration and acceleration of rupture fronts caused 

by stress and strength heterogeneities on the fault surface, and its role in generating high-frequency ground 

motions significant to earthquake-resistant design. They 

review models describing the nature of the rupture 

process and its generation of seismic waves as inferred 

from strong-motion data recorded from the 1979 Imperial Valley earthquake. They also examine published 

techniques for calculating Green's functions, which permit computation of ground shaking at any point on the 

Earth's surface, given a linear model of the Earth's 

structure and a mathematically tractable representation of a physical model of the earthquake source. Their 

review discusses several methods for describing wave 

propagation, including the equivalent Green's function 

representation for several linear Earth models having 

layered and continuous velocity gradients. 

Spudich and Hartzell (this volume) discuss sitespecific simulations made by Apsel and others (1981) for 

postulated earthquakes on the Mojave segment of the 

San Andreas fault and on the Newport-Inglewood fault 

zone. Such deterministic simulations are reasonably 

successful in reproducing frequencies of recorded 

strong-motion time-histories of less than 1 to 2 Hz. 

Limitations are imposed on higher frequencies by a lack 

of knowledge regarding details of the rupture timehistory and the intervening crustal structure. Stochastic 

simulations of the source rupture characteristics and 

detailed crustal structure determinations help remove 

these limitations. The success of the simulation procedures in reproducing recorded ground motions suggests that, in those cases for which elaborate estimates 

are feasible, reasonably confident predictions of 

ground-shaking time-histories can be developed for 

earthquake-resistant design. 
ESTIMATING GROUND SHAKING 

FOR A POSTULATED EVENT 

Measures designed to safeguard life and property 

from the destructive effects of strong ground shaking 

may use any or all of the various methodologies for 

estimating strong ground shaking discussed herein, including regional estimates of earthquake intensity, 

generalized estimates on a regional scale of parameters 

used in earthquake design codes, regional delineations 

of potential variations in local ground response, and 

elaborate predictions of ground-motion time-histories. 

These various techniques are applied to a postulated 

earthquake (M 6.5) on the northern part of the NewportInglewood fault zone in a later chapter (Ziony and 

others, this volume). This composite analysis illustrates 

the application of the various methodologies for assessment of seismic hazards owing to potential strong 

ground motion in the Los Angeles region. 

APPENDIX 1.-COMMON MEANS 

FOR CHARACTERIZING 

EARTHQUAKE SHAKING 

The severity of ground motion from an earthquake 

can be characterized either qualitatively-from the 

observed or expected effects of strong shaking on man 

and his structures-or quantitatively-from parameters that can be instrumentally recorded. Detailed 

descriptions of parameters commonly used to characterize ground motion are given by Richter (1958), Page and 

others (1975), and Hays (1980). A summary of these 

parameters follows. 

A qualitative measure of shaking.-Seismic intensity 

is a numerical index based on subjective analysis of the 

observed effects upon humans, manmade structures, 

and the Earth's surface. Several different intensity 

scales have been defined. The Modified Mercalli intensity scale (inside back cover), which was adopted in 1931 

by the U.S. Coast and Geodetic Survey (now the National 

Ocean Survey), is in most common usage. Although this 

scale is currently used for most earthquake investigations in the United States, some researchers prefer the 

older Rossi-Forel intensity scale, because its units appear to scale better with physical measurements of 

ground motion (Evernden and others, 1973, 1981). At the 

higher intensities (X, XI, and XII), the Modified Mercalli 

scale describes effects that relate chiefly to ground 

failure and do not necessarily indicate increased levels 

of shaking. 

lsoseismal maps depict the geographic distribution of 

different grades of intensity observed for particular 

earthquakes. Because the patterns on these types of 

maps commonly are influenced by local geologic conditions, methods for predicting intensities of future large 

earthquakes have received particular attention in 

hazard-analysis research (for example, Borcherdt and 

others, 1975c; Evernden and others, 1973, 1981). 

Quantitative measures of shaking.-The severity of 

ground motion can be expressed in quantities that may 

be scaled or computed from on-scale recordings of 

strong shaking instrumentally recorded from damaging 

earthquakes. The most common strong-motion recordings are accelerograms that depict ground shaking as a 

function of time (fig. 31) in a format proportional to 

acceleration for band frequencies considered to be of 

engineering significance. Maximum, or peak, amplitude 

parameters obtained from accelerometers are commonly used in engineering design. These parameters include 

peak acceleration, peak velocity, and peak displacement. Typically, peak acceleration occurs at frequencies in the range 2 to 10 Hz, whereas the dominant 

frequencies of velocity and displacement are in the 

ranges 0.5 to 2 Hz and 0.06 to 0.5 Hz, respectively (Page 

and others, 1975). 

The response of structures to strong ground shaking is 

dependent not only on the amplitude of shaking but also 

on the frequencies and duration of shaking. Response 

spectra provide a useful means of characterizing the 

relative frequency content of shaking. Response spectra, defined as the maximum response of a suite of 

linear, damped, single-degree-of-freedom oscillators 

subjected to a specified time-history of motion (fig. 32), 

provide estimates useful for calculating actual structural response. Response spectra typically are plotted 

on tripartite logarithmic paper and show the variations 

of peak spectral velocity, acceleration, and displacement as a function of vibration period. Each different 

representation of response spectra has a particular 

physical significance for building design (see Hays, 

1980, p. 35). Joyner and Fumal (this volume) present a 

method for estimating pseudoacceleration and pseudovelocity response spectral values on a regional scale. 

Predicting Earthquake Ground Motion 97 
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(f) 

a: 

UJ 

f- (f) 

UJ UJ 

~ I 

u f- ~ z 

UJ 

u ~ 

~ 0 

f-' 

0 z 

UJ f-' 

z ~ 

UJ UJ u ~ <l: UJ 

u 

<l: 

_J 

0.. 

(f) 

_J 

0.. 0 

~ c 0 

50 0 5 10 

20 

15 

TIME, IN SECONDS 

FIGURE 31.-Recordings of N. 14° E. component of horizontal ground motion at Pacoima damsite for 1971 San Fernando earthquake (from Page 

and others, 1975). Velocity (B) and displacement (C) records are obtained by integrating accelerogram (A) once and twice, respectively. 

98 Earthquake Hazards in the Los Angeles Region 
M 

M 

M 

M 

k0.08 k0.18 k0.5 k10.0 

0.08 0.18 0.5 1.0 5.0 10.0 

FREQUENCY, IN HERTZ 

>- 127.0 t:: 

u 

0 

_J 

Ll.J 

> 50B Ll.J 

> en 

t-en 25.4 --E <t: c (.) 

_J ·-

Ll.J 

a: 12.7 

0 

0 

:::> 

Ll.J 

(f) 5.1 Cl... 

0.1 02 0.5 2 5 50 

FREQUENCY, IN HERTZ 

)7 Story 3-7 Story 1-2 Story 

FIGURE 32.-Response spectra portray the variations of ground-motion parameters as a function of vibration period (modified from Hays, 1980, fig. 32). Top, Schematic ensemble of single-degree-of-freedom 

oscillators. M and k represent the mass and spring constants of the equivalent mechanical system. 

Middle, Response spectra derived from the 1940 Imperial Valley earthquake accelerogram. Heavy 

lines show response calculated assuming damping factors of 0, 2, 5, and 10 percent, respectively. 

Bottom, Bar graph showing ranges of natural frequencies for buildings of different heights in relation 

to schematic ensemble and response spectra. 

Predicting Earthquake Ground Motion 99 
100 Earthquake Hazards in the Los Angeles Region 
MAPPING QUATERNARY SEDIMENTARY DEPOSITS 

FOR AREAL VARIATIONS IN SHAKING RESPONSE 

By J. C. Tinsley and T. E. Fumal 

INTRODUCTION 

Areal differences in damage caused by shaking from 

earthquakes commonly can be related to variations in 

near-surface geologic materials (Milne, 1908; Lawson 

and others, 1908; Kanai, 1952; Gutenberg, 1957; 

Medvedev, 1962; Borchardt, 1970; Borcherdt and 

others, 1975; Rogers and others, 1979; Fumal, 1978; 

Fumal and Tinsley, this volume; Rogers and others, this 

volume; Evernden and Thomson, this volume). In particular, ground shaking often is greatest on young, loose 

sedimentary deposits. The 1933 Long Beach earthquake, 

for example, caused greater damage in Compton than it 

did in Long Beach (Wood, 1933, p. 49, 52). Wood has 

ascribed this difference mainly to variations in Quaternary geology. Campbell (1976) has also studied the 1933 

Long Beach earthquake and has shown that, for a given 

distance from the Newport-Inglewood fault zone, the 

damage at sites underlain by "unconsolidated soils" 

was greater than that at sites underlain by "consolidated soils." Long Beach is sited chiefly on relatively 

well consolidated late Pleistocene sedimentary deposits, 

whereas Compton is located on poorly consolidated, 

water-saturated Holocene alluvial deposits of the Los 

Angeles River and its tributaries (Thomas and others, 

1961; Yerkes and others, 1965). These observations, and 

similar ones made elsewhere in the world, demonstrate 

the importance of determining the distribution and 

characteristics of the Quaternary sedimentary deposits 

upon which most of the world's urban centers are sited. 

For the Los Angeles region, we present a technique 

for differentiating Quaternary sedimentary deposits 

that we hope will be transferrable to other areas. First, 

we describe a reconnaissance technique for dividing 

such deposits according to age and grain-size distinctions. This technique is used to prepare small-scale surficial geologic maps of parts of the major alluvial basins 

of the region (fig. 33). These maps are fundamental data 

sets for identifying areal variations in the physical properties of the alluvial sediment and of the adjacent 

uplands. Then, sediment age and grain size are related 

to secondary parameters such as shear-wave velocity, 

which are useful for predicting shaking response during 

earthquakes. The approach that we follow is derived 

from studies done in the San Francisco Bay region by Lajoie and Helley (1975) but incorporates studies of the 

shear-wave velocities of near-surface alluvial materials 

in the Los Angeles region (Fumal and Tinsley, this 

volume). Comparing selected physical properties of the 

rock and sediment units with measurements of shearwave velocity permits identification of areal groupings 

having distinct ranges in shear-wave velocity. On the 

basis of a two-dimensional model of sedimentation pattern, we present a series of regional maps grouping the 

surficial deposits according to distinctive ranges in 

shear-wave velocity; these maps provide an approximate characterization of relative shaking response. 

MAPPING SURFICIAL 

GEOLOGIC UNITS 

Techniques of traditional geologic mapping evolved 

chiefly in response to the needs of the mineral industries; consequently, standard geologic maps commonly 

emphasize the detailed distribution and character of 

bedrock units, including lithology, age, and rock structure (bedding, foliation, lineation, fractures, folds, and 

faults). In contrast, areas underlain by relatively 

uncemented or loose alluvium or other sediment without 

apparent structural or stratigraphic mineral potential 

commonly are depicted as a single map unit. Variations 

in the physical properties of Quaternary alluvial 

deposits that pertain to the delineation of geologic 

hazards such as ground shaking or ground failure are 

not usually distinguished on standard geologic maps. 

Because urban areas at risk from earthquakes commonly are located on Quaternary alluvial deposits, conventional geologic maps usually are not adequate for 

evaluating earthquake hazards. For this reason, during 

Shaking Response of Quaternary Sediments 101 
34'30' 119'00' 

Santa 

Santa 

Susana 

118'00' 117'00' 

GABRIEL MOUNTAINS 

Santa Ana Valley 

INDEX MAP LOCATION 10 15 20 25 KILOMETERS I I I I 

FIGURE 33.-Index map of the Los Angeles region showing areas mapped and evaluated for this study. 

the past two decades, specialized mapping techniques 

directed specifically at identifying and evaluating earthquake hazards in alluvial deposits have evolved (Borcherdt, 1970; Borcherdt and others, 1975; Lajoie and 

Helley, 1975). 

We have adapted the approach of Lajoie and Helley 

(1975) and have mapped surficial deposits in the Los 

Angeles region. Principal sources of information include 

topographic maps, aerial photographs, soil maps, descriptive accounts of excavations (including logs of 

water wells, oil wells, and other boreholes), trenches 

and foundations, and exposures in cliffs, streambanks, 

quarries, and roadcuts. Geologic units are defined and 

mapped on the basis of geologic and genetic criteria 

such as geomorphic expression, inferred depositional 

environment, soil-profile development, and grain size. 

For the most part, work was done chiefly in the office, 

but, locally, we have incorporated our own field 

observations. 

Topographic Maps 

Topographic maps represent the landscape by using 

topographic contour lines, bathymetric contour lines, 

culture symbols, stream courses, and many additional 

symbols. Older topographic maps showing the pre-urban 

landscape are especially valuable for making inferences 

102 Earthquake Hazards in the Los Angeles Region 

about the character and distribution of Quaternary 

sediments, especially if their contour intervals are 

small. The principal basin areas of Los Angeles County, 

for example, were mapped by the U.S. Geological Survey 

at a scale of 1:24,000, at a contour interval of 5 ft, 

during the 1920's and early 1930's. These early maps 

clearly outline many principal physiographic elements 

of the pre-urban landscape, including mountains, foothills, canyons, and other features underlain by consolidated rocks; areas likely to be underlain by streamtransported sediment such as alluvial channels, alluvial 

fans, river flood plains and marshes; and areas likely to 

be underlain by other sedimentary deposits, including 

beach deposits, windblown dune deposits, and coastal 

estuarine muds. In contrast to modern topographic maps 

(which have contour intervals of 20 to 40 ft), the closely 

spaced contour lines of the early vintage maps reveal 

many landforms having only subtle topographic expression and now obliterated. 

Aerial Photographs 

Black-and-white vertical aerial photographs first 

became available for extensive areas of the Los Angeles 

region in the late 1920's; when these photographs are 

viewed in overlapping stereographic pairs, they afford a 

three-dimensional view of the landscape, including 
alluvial deposits, drainages, and many other geomorphic 

features or landforms. The margins of landscape 

features noted on topographic maps (such as subtle 

channels, swamps, flood plains, dunes, and other landforms) often can be delineated more precisely by using 

aerial photographs than by using maps alone. Thedeposits associated with these landforms may have 

distinctive physical properties; thus, a geologic map 

emphasizing surficial deposits reflects the distribution 

of the physical properties that may be significant in 

evaluating geographic variations in shaking response. 

Soil Maps and Soil Stratigraphy 

Before extensive urban development in the Los 

Angeles region, the U.S. Department of Agriculture 

mapped soils in the area to encourage use of the best 

farming practices and cultivation of the most appropriate crops (Holmes and others, 1915; Nelson and others, 

1915, 1916). We use these soil maps as guides to the 

areal distribution of physical and chemical characteristics of agricultural soils; thus, these maps may reflect 

basic differences in the grain sizes and in other physical 

and chemical age-dependent attributes of the deposits in 

which the soil forms. For example, a soil on an alluvial 

fan mapped by the U.S. Department of Agriculture as a 

stony soil phase typically contains boulders and may be 

difficult or impossible to plow and hence of limited 

agricultural value. However, we use grain-size information (presence of boulders) to infer that the alluvial unit 

is very coarse grained. 

The characteristics of a soil profile can indicate the 

' age of the land surface if certain conditions are met. A 

soil profile may be moderately developed or well developed, as indicated by the presence of a clay-enriched 

zone (B horizon) in which clay, iron oxides, and other 

products of weathering have been concentrated over a 

long period of time. Or, the profile may be poorly 

developed, as is the case chiefly on flood plains, natural 

levees, and channels of modern rivers and on young 

alluvial fans. Jenny (1941, 1961) has shown that, as a soil 

develops, the profile's characteristics are functions of 

the type of parent material, the climate, the vegetation, 

the topographic position in the landscape, and the age. 

In areas where all these "state factors" (soil-forming 

parameters) (with the exception of age) are similar, the 

chemical and physical characteristics in soil profiles 

may reflect the duration and intensity of weathering, 

and differences among profiles may reflect the time required to form the soil. The soil profile can serve as a 

rapid means of distinguishing rather young alluvial 

deposits from rather old ones-a sort of clock that 

begins to run when deposition or erosion of sediment 

proceeds at a rate that is slower than the rate of soilprofile development. 

In the Los Angeles region, McFadden (1982) has 

recognized seven stages of soil formation and has shown 

that Jenny's (1941) soil-formation factors vary within a 

narrow enough range for us to conclude that alluvial 

deposits characterized by well-developed soil profiles 

have been subjected to weathering conditions to greater 

profile depths for a significantly longer period of time 

and hence are older than alluvial deposits characterized by relatively thin, poorly developed soil profiles. 

Well-developed soil profiles occur on alluvial fans or 

river flood plains or on shallow marine sedimentary 

deposits that have been tectonically uplifted or folded 

and no longer receive sediment from the present 

drainage network. Poorly developed soil profiles occur 

along the channels, levees, and flood basins of current 

streams graded to modern sea level and include areas 

where sediment transport and deposition ensued before 

construction of the largely successful civil-engineering 

efforts to control floods and debris flows in the Los 

Angeles region. 

Differences in soil-profile development can be correlated with the age distinctions of the underlying 

deposits. Radiocarbon dates from the Los Angeles 

region (Hastorf and Tinsley, 1981) indicate that 

moderately developed and well-developed soil profiles 

characterized by diagnostic subsurface horizons containing noteworthy clay accumulations, reddening 

owing to oxidation of ferrous iron compounds to hematite, and increased bulk density are associated with 

weathering and soil formation in alluvial deposits dated 

as late Pleistocene and older. Conversely, poorly 

developed soil profiles lack much pedogenic accumulation of clay, ferric oxides, and increased bulk density 

and are usually less than about 10,000 yr old. Holocene 

deposits generally lack the conspicuous chemical and 

physical alterations of the sediment, including clast 

weathering, a reduction of pore volume, and an increase 

in soil strength, that commonly distinguish pre-Holocene 

deposits from Holocene deposits. This trend is shown by 

penetrometer studies and shear-wave velocity studies, 

which will be discussed in a later section of this chapter. 

Rates and processes of soil genesis in the Los Angeles 

region (McFadden, 1982) and elsewhere (Birkeland, 

1984) are reasonably well documented and clearly help 

to distinguish between Holocene and Pleistocene 

deposits, especially where the surface soil profile can be 

examined. Analyses of soil profiles using the techniques 

of soil stratigraphy (Birkeland, 1984) have been used in 

part by many workers, including Eckis (1934), Thomas 

and others (1961), McCoy and Sarna-Wojcicki (1978), 

Poland (1959), Lamar (1970), and Cox and Morton (1978) 

Shaking Response of Quaternary Sediments 103 
TABLE 12.-Approximate age and geologic and geomorphic setting of selected soil series mapped in 

the Los Angeles region by the U.S. Bureau of Soils, 1915-1920 

Soil series Age 

Altamont -----Holocene and 

Pleistocene. 

Diablo -------Holocene and 

Pleistocene. 

Holland ------Holocene and 

Pleistocene. 

Antioch ------Pleistocene 

Madera ------Pleistocene 

Montezuma ---Pleistocene 

Placentia -----Pleistocene 

Pleasanton ---Pleistocene 

Ramona -----Pleistocene 

Chino -------Holocene 

Hanford -----Holocene 

Tujunga ------Holocene 

Dublin -------Holocene 

Yolo --------Holocene 

Oakley -------Holocene 

Geologic and geomorphic setting 

Soils formed on bedrock 

Colluvium and residual mantle; chiefly slightly calcareous to noncalcareous; formed on slopes and on rolling hills or mountainous terranes underlain by sandstone, siltstone, and shale. 

Colluvium and residual mantle; often moderately to highly calcareous; formed on slopes and on rolling hills or mountainous 

terranes underlain by calcareous shale, sandstone, siltstone, 

or impure limestone. 

Residual soils, chiefly noncalcareous, formed chiefly on granitic 

and schistose rocks. 

Soils formed on Quaternary alluvial deposits 

Alluvial fans and fluvial terrace deposits derived chiefly from 

sedimentary rocks; reddened to 5YR hue. 

Dissected alluvial fans and fluvial terrace deposits derived 

chiefly from igneous and sedimentary rocks; B horizon commonly is reddened and enriched in clay and has a hardened 

zone (duripan) that may not disintegrate in water. 5YR and 

2.5YR hues. 

Dissected alluvial fans and fluvial terrace deposits derived 

chiefly from sedimentary rocks; commonly calcareous and 

relatively high in organic matter. 

Dissected alluvial fans and fluvial terrace deposits derived 

chiefly from granitic rocks; deeply reddened (5YR-10R hues) 

and clay-enriched B horizon. 

Alluvial fans and fluvial terrace deposits derived chiefly from 

from schistose metasedimentary rocks; may be reddened 

(5YR hue). 

Alluvial fans and fluvial terrace deposits derived chiefly from 

granitic and sedimentary rocks; may be reddened (7.5-2.5YR 

hues). 

Alluvial fans and in flood-basin areas derived from granitic 

and schistose rocks; typically fine textured, calcareous, poorly 

drained (2.5Y hue). 

Alluvial fans and on flood plains derived from granitic and schistose rocks; coarse-textured soils indicate channel and levee 

geomorphic associations; fine-textured soils occupy geomorphic positions intermediate between levee deposits and floodbasin deposits; generally well drained (lOYR hue). 

Alluvial fans associated with active channels draining granitic terranes; generally well drained (10YR hue). 

Alluvial fans and flood plains derived from sedimentary rock; 

commonly has a flood-basin association (2.5Y hue). 

Alluvial fans and flood plains of drainages from sedimentary 

terranes; coarse-textured phases occur generally in welldrained basin settings; fine-textured phases frequently indicate less well drained basin areas (2.5Y hue). 

Eolian dunes, chiefly adjacent to littoral areas (10YR hue). 

104 Earthquake Hazards in the Los Angeles Region 
100 

percent sand 

1 00 percent clay 

EXPLANATION 

f71 Medium-grained 

~ sediment 

100 

percent silt 

FIGURE 34.-Soil textural classes and gram-siZe designations of 

alluvial sediments (after Soil Survey Staff, 1975, p. 471). 

to help distinguish Holocene deposits from late Pleistocene deposits in the Los Angeles region. Our study 

substantiates and incorporates many of the inferences 

of these earlier workers. 

SURFICIAL GEOLOGIC MAPS 

Geologic maps delineating areas underlain by Quaternary sedimentary deposits, Tertiary and pre-Tertiary 

sedimentary rock, and pre-Tertiary plutonic and 

metamorphic rock have been prepared for five alluvial 

basins in the Los Angeles region: (1) the San Fernando 

Valley, (2) the San Gabriel Valley, (3) the Los Angeles 

basin, (4) the Oxnard Plain, and (5) the upper Santa Ana 

River basin (fig. 33). We have divided the alluvial 

deposits into four grain-size categories and two 

inferred-age categories (Pleistocene and Holocene) by 

using the techniques described above; the mapping was 

done by J. C. Tinsley at 1:24,000 scale. The mapped 

grain-size designations are very coarse, coarse, 

medium, and fine. The geologic age is based chiefly on 

the profile characteristics of soils mapped by the U.S. 

Department of Agriculture's Bureau of Soils, consistent 

with modern established principles of soil stratigraphy 

(Birkeland, 1984) and with field studies of soils and soil 

genesis in the Los Angeles region (McFadden and 

others, 1980; McFadden and Tinsley, 1982, p. 15). 

Representative soil series identified from the early soil 

surveys and the geologic age designations used in this 

chapter are shown in table 12. The relations among the 

soil textures and the grain-size designations of the 

alluvial sediments are presented in figure 34. The 

generalized areas of bedrock were compiled from the 

geologic map of California (scale 1:250,000) (Rogers, 

1965, 1969; Jennings, 1962; Jennings and Strand, 1969). 

The map units shown in figures 35, 36, 37, 38, and 39 are 

described briefly from youngest to oldest. 

DESCRIPTION OF MAP UNITS 

Holocene Deposits 

(Less than 10,000 Yr Old) 

Qyf (fine-grained Holocene alluvium).-Chiefly poorly 

sorted, plastic, locally carbonaceous sandy silt, silt, silty 

clay, and clay in poorly drained flood basins adjacent to 

coastal marshlands, on distal parts of alluvial fans, in 

localized tectonic depressions along recently active 

faults, and in parts of alluvial plains adjacent to uplands 

composed of fine-grained sedimentary rock. Occasional 

lenses and small channels of well-sorted sand and fine 

gravel; occasional marine and estuarine pelecypod and 

gastropod shells and foraminifer tests in and near 

coastal marshes. Contains fossils of living vertebrate 

species and may contain freshwater pelecypod and 

gastropod shells. Interfingers with and grades both 

laterally and upstream into medium-grained alluvium; 

overlies late Pleistocene alluvium and bedrock; 0 to 50 m 

thick in coastal basins and generally less than 10 m 

thick in inland basins on alluvial plains and on lower 

parts of alluvial fans. 

Qym (medium-grained Holocene alluvium).-Loose, 

moderately well drained, moderately sorted to wellsorted sand and silty sand forming alluvial plains and 

natural levees along streams. Locally contains thin beds 

of well-sorted clay, silt, gravel, and occasional cobbles 

and boulders. Contains freshwater pelecypod and 

gastropod shells. Intermediate in char~cter and lateral 

extent between fine- and coarse-grained alluvium with 

which it interfingers; generally overlies late Pleistocene 

alluvium; generally less than 50 m thick in coastal 

basins and less than 10 m thick in inland basins. 

Qyc (coarse-grained Holocene alluvium).-Loose, welldrained, moderately sorted, highly permeable sand and 

gravel deposited by modern streams and forming 

natural levees and flood plains and higher parts of 

alluvial fans; gravel predominates near stream channels 

and toward fan heads. Locally contains beds and lenses 

of well-sorted silt, sand, and gravel; contains freshwater 

pelecypod and gastropod shells. Interfingers with 

medium-grained alluvium and very coarse grained alluvium. Generally overlies late Pleistocene deposits and 

bedrock. Thickness ranges from 50 m in large canyons 

and near fan heads to 5 m or less on alluvial plains, 

stream channels, and alluvial fans. 

Qyvc (very coarse grained Holocene alluvium).-

Loose, very well drained, very highly permeable cobbly 

and bouldery gravel and interstitial sand forming channel deposits and alluvial fan deposits on fan heads and 

in channels of principal canyons draining steep mountainous terranes. Pebbles and sand become dominant 

downfan and laterally away from stream channels issuing from major canyons. Locally contains beds of wellsorted silt, sand, and gravel; contains fossils of living 

Shaking Response of Quaternary Sediments 105 
11 8'30' 118'15' 

2 

I 1 ! 

I 

1 3 MILES 

EXPLANATION 

G 

Artificial fill 

B B B ~ 01 

c Very coarse Coarse- Medium- Fine-grained 01 

.., grained grained grained sediment 0 

0 sediment >- sediment sediment (silt and J: a: 

Chiefly undifferentiated ~ Tertiary 

G 

and pre- ~ ~ Tertiary sedimentary rocks and in- ffi 

terbedded intrusive and extrusive rocks f-

(cobbles and (gravel) (sand) clay) <C 

boulders) z 

a: 

U.J 

fB B B G <C 

01 ::l c 0 

Very coarse Coarse- 01 

Medium- Fine-grained .., 

,S grained grained grained sediment "' sediment sediment sediment (silt and ·o:; 

(cobbles and (gravel) (sand) clay) 0:: 

boulders) 

L:J 

~ }'a:-

U.J <C 

~ Chiefly intrusive and metamophic rock, o. b: 

undifferentiated ~ 

Contact-Queried where doubtful 

FIGURE 35.-Age and textural character of surficial geologic materials in the San Fernando Valley. 

vertebrate species and freshwater pelecypod and 

gastropod shells. Thickness ranges from 50 m in fan 

heads and canyons to 5 m or less on upper parts of 

alluvial fans where deposits interfinger with coarse-and 

medium-grained alluvium. Overlies late Pleistocene 

alluvium and bedrock. 

106 Earthquake Hazards in the Los Angeles Region 

Pleistocene Deposits 

(10,000 to 1,700,000 Yr Old) 

Qof (fine-grained Pleistocene alluvium).-Weathered, 

slightly indurated and consolidated to moderately in-
EXPLANATION 

B B B B <II 

Very coarse Coarse- Medium- Fine-grained u 

c 

<II Chiefly undifferentiated GJ Tertiary GJ and pre- r ~ grained grained grained sediment 0 Tertiary sedimentary rocks and in- ffi 0 > sediment sediment sediment (silt and J: a: terbedded Intrusive and extrusive rocks 1-

(cobbles and (gravel) (sand) clay) ~ 

z boulders) a: 

~ }'~ "'-1 

1- "'-!~ 

B B B G ~ a:-

<II ;:) Chiefly intrusive and metamophic rock, Q.. ~ c 

<II 0 undifferentiated ~ Very coarse Coarse- Medium- Fine-grained u 

.9 grained grained grained sediment "' sediment sediment sediment (silt and ] 

(cobbles and (gravel) (sand) clay) Q.. Contact 

boulders) 

FIGURE 36.-Age and textural character of surficial geologic materials in the San Gabriel Valley. 

Shaking Response of Quaternary Sediments 107 
118'30' 

34'00' 

33'45' --r2 3 • 5 kilOMETERS 

I 

I I 

I I I 

I 2 3 MILES 

B B 

Very coarse Coarsegrained grained 

sediment sediment 

(cobbles and (gravel) 

boulders) 

EJ El 

Very coarse Coarsegrained grained 

sediment sediment 

(cobbles and (gravel) 

boulders) 

B 

Mediumgrained 

sediment 

(sand) 

El 

Mediumgrained 

sediment 

(sand) 

118'15' 

EXPLANATION 

·-~····)! sediment 0 > (silt and :r a: clay) < z 

a: 

11.1 

,_. 

G )' 

< :J 

CJ 

Fine-grained ~ sediment .i 

(silt and -£ 

clay) 

Chiefly undifferentiated Tertiary and pre· ~ 0 G }i:: 

Tertiary sedimentary rocks and In· ffi 

terbedded Intrusive and extrusive rocks 1-

Chiefly Intrusive 

~ and metamophic rock , a:-

a. 

~~ ~ 

undifferentiated ~ 

Contact 

FIGURE 37.-Age and textural character of surficial geologic materials in part of the Los Angeles basin. 

108 Earthquake Hazards in the Los Angeles Region 
EXPLANATION 

G 

Artificial fill 

~ B 8 

Coarse- Medium- Fine-grained 

grained grained sediment 

sediment sediment (silt and 

(gravel) (sand) clay) 

Chiefly undifferentiated late Pleistocene sediment 

B 

Chiefly undifferentiated middle and early Pleistocene 

and some latest Tertiary sedimentary rock 

5 KILOMETERS 

3 MILES 

., 

= ., 

... 

.2 

0 

:I: 

Chiefly undifferentiated Tertiary and preTertiary sedimentary rocks and interbedded Intrusive and extrusive rocks 

FIGURE 38.-Age and textural character of surficial geologic materials in the Oxnard Plain area. 

Shaking Response of Quaternary Sediments 109 
34'07'30" 

34'00' 

5 KILOMETERS 

I I I I 2 3 MILES 

FIGURE 39.-Age and textural character of surficial geologic materials in the upper Santa Ana River basin. 

110 Earthquake Hazards in the Los Angeles Region 
EJ 

Very coarse 

grained 

sediment 

(cobbln and 

boulden) 

B 

EXPLANATION 

J 

0 

Artlfld•lftll 

B B 0 Coarse

grained 

· Mediumgr•lned Fine-grained 

sediment ~ > :c "' sediment sediment (aUt •nd < (gravel) ( .. nd) clay) z 

"' "" G ~ 

~ t· 

~ ~ 

Fine-grained ~ C1 

Coarse· Mediumgr•lned grained sediment i Hdlment sediment (aUt and ~ 

(gr•vel) ( .. nd) clay) 

Chlely undlllerentlated G Tertl•ry 

0 and pre· I= ~ Tertiary aedlmenlary rocks and In· ffi terbedded lntrultve and extrusive rocks 1-

L.:.:J r::;.:l } ""< . ~ Chiefly "'I= intrusive and metamophlc rock, c.. ffi undifferentiated tContact 

Shaking Response of Quaternary Sediments 111 
durated and well-consolidated, poorly drained deposits 

on lower parts of older dissected alluvial fans and flood 

basins. Consists chiefly of silt and clay and contains 

occasional lenses of gravel and sand. Commonly subsurface but is exposed along flanks of anticlinal uplifts 

and along uplifted fault blocks. Relict soils commonly 

reddened to 5YR and redder hues (Munsell notation) 

(Munsell Soil Color Charts, 1975). Less permeable than 

Holocene alluvium. Locally contains freshwater gastropod and pelecypod shells and extinct vertebrate fossils. 

Overlain by Holocene deposits along lower parts of alluvial plains and along some margins of anticlinal folds; in 

coastal basins is incised by channels that are partially 

to completely filled with Holocene alluvium. Maximum 

thickness unknown but is at least 300 m in coastal 

basins. Nonmarine in inland areas, marine and 

estuarine in parts of coastal basins. 

Qom (medium-grained Pleistocene alluvium).-

Compact to very dense, moderately drained, moderately 

sorted, moderately permeable sand containing lenses of 

small gravel, silt, and clay. Exposed on inactive alluvial 

fans and alluvial plains in intermediate positions between channels and flood-basin deposits in surface and 

subsurface localities. Locally contains freshwater 

pelecypod and gastropod shells and extinct vertebrate 

fossils. Maximum thickness unknown. Overlies bedrock 

and underlies Holocene alluvium. 

Qoc (coarse-grained Pleistocene alluvium).-

Weathered, slightly consolidated to well-consolidated 

and indurated alluvial fan and flood-plain deposits consisting primarily of gravel, sand, and some silt. Relict 

soils commonly reddened to 5YR and redder hues 

(Munsell notation). Permeable but less so than Holocene 

equivalent. Interfingers with and overlies marine 

deposits in parts of coastal basins; overlain by Holocene 

deposits on upper parts of alluvial fans and alluvial 

plains; incised by channels that are partially filled with 

Holocene alluvium. Maximum thickness unknown but is 

at least 300 m in coastal basins where marine beds provide control on the base of the Quaternary section. 

Qovc (very coarse grained Pleistocene alluvium).-

Weathered, slightly consolidated to well-consolidated 

and indurated alluvial fan and flood-plain deposits consisting primarily of bouldery and cobbly gravel and sand 

and locally containing some beds of silt. Relict soils commonly reddened to 5YR and redder hues (Munsell color 

notation). Permeable but less so than the texturally 

equivalent Holocene unit. Interfingers with and overlies 

marine deposits in coastal basins; interfingers with 

coarse- and medium-grained Pleistocene alluvium in inland valleys on alluvial fan heads and in stream channels. Incised by channels that are partially filled with 

Holocene alluvium. Maximum thickness unknown but is 

at least 300 m along mountain fronts. 

112 Earthquake Hazards in the Los Angeles Region 

Tertiary and Mesozoic Deposits 

Ts (Tertiary and pre-Tertiary sedimentary rock, undifferentiated).-Weathered to slightly weathered shale, 

siltstone, sandstone, and conglomerate. Poorly to well 

sorted. Moderately soft to well-cemented and wellindurated strata. Chiefly marine origin; some nonmarine 

units. Underlies alluvial deposits and overlies basement 

rocks. Maximum aggregate thickness exceeds 10 km in 

deepest parts of major coastal basins, but thickness 

varies markedly across the Los Angeles region. 

Mz (Mesozoic and pre-Mesozoic crystalline and 

metasedimentary rocks, undifferentiated).-Comprises 

the basement complexes exposed in principal mountain 

ranges and encountered in exploratory borings near 

basin margins. Includes basement terrane rocks of the 

Santa Monica Mountains, the San Bernardino Mountains, the San Jacinto Mountains, the northern Perris 

block, and the northern Santa Ana Mountains. 

USING PHYSICAL PROPERTIES 

OF SURFICIAL GEOLOGIC UNITS 

TO ESTIMATE RELATIVE 

SHAKING RESPONSE 

This section describes a method for using several 

physical properties of sediments as a guide to approximating their likely relative response to seismic shaking. 

Grain size and sorting are sediment properties that depend chiefly on the depositional environment. Other 

physical properties of sediments that significantly influence its strength and hence correlate broadly with its 

shear-wave velocity include consistency (for cohesive 

soils) and relative density (for cohesionless soils) as 

measured with a penetrometer (Fumal and Tinsley, this 

volume). These properties also are related to and tend to 

increase with the geologic age of the deposit and also 

with its thickness (Lajoie and Helley, 1975, p. 49; Fumal 

and Tinsley, this volume; Rogers and others, this 

volume). 

We use shear-wave velocity (Vs) as an index of the 

strength, relative density, and induration of the sediment and thus as a means of approximating the response of a deposit to seismic shaking. Medvedev (1962) 

has shown that seismic impedance (defined as the product of the shear-wave velocity and the bulk density, V5 ·p) 

is useful for estimating relative shaking response. 

Amplification of seismic waves in layered media is proportional to the contrast (difference) in the impedances 

of superposed deposits (Medvedev, 1962). Lajoie and 

Helley (1975) and Borcherdt and Gibbs (1975) have 

shown that, for layers of a given thickness, relative 
TABLE 13.-Comparison of relative buik density, penetration resistance, shear-wave velocity, and 

calculated impedance values of surficial geologic units 

[--, no data available] 

Geologic 

unit 

Bulk 

density,' 

in glcm3 

Average 

penetration,• 

in blows/ft 

Shear-wave 

velocity,'•' 

in rn/s 

Impedance' 

!Vs·pJ 

Holocene 

Qyf ------------- 1.6 ± 0.2 

Qyrn ------------ 1.6±0.2 

Qyc ------------- 1.6±0.2 

Qyvc ------------ 1.6±0.2 

14±8 

14±8 

150-270 (200) 

195-285 (230) 

290-355 (320) 

350-375 (365) 

210-490 (320) 

270-510 (370) 

410-640 (510) 

490-675 (580) 

Pleistocene 

Qof ------------- 1.9 ± 0.3 

Qom ------------ 1.9 ± 0.3 

Qoc ------------- 1.9 ± 0.3 

Qovc _________ :___ 1.9 ± 0.3 

34±18 

34±18 

200-360 (305) 

270-740 (430) 

330-680 (495) 

445-830 (650) 

320-790 (580) 

430-1630 (820) 

530-1500 (940) 

710-1,830(1,240) 

Tertiary and Mesozoic 

Ts -------------- 2.4 

Mz ------------- 2.7 

Refusal 

Refusal 

300-1,300 

1,150-1,8005 

720-3,120 

3,100-4,860 

1

Bulk densities (p) for Quaternary deposits from McFadden (1982) and Los Angeles County Flood Control District (unpublished data, 

195()-1980). 

2

From CAL TRANS freeway borings; 5 to 10 ft subsurface, 141J.lb hammer, J().in. drop. Penetrometer tests not reliable in gravelly and 

bouldery deposits. Refusal indicates failure to advance the penetrometer through the Earth materials. 3

Holocene and Pleistocene values from Fumal and Tinsley (this volume, table 18). Mean value in parentheses. 4

Mean value in parentheses. 

!ivaiue may be lower for weathered crystalline rock. 

shaking response should be greatest where the surface 

geologic units have the lowest impedance values (finegrained Holocene) and where the impedance contrast 

between the surface layer and a subjacent layer is the 

greatest. The impedance contrast and the relative shaking response for a given thickness of fine-grained 

Holocene deposits overlying Tertiary sedimentary rock, 

for example, should be higher than those of the same 

thickness of fine-grained Holocene deposits overlying 

Pleistocene fine-grained sediments. 

Selected physical properties are shown in table 13 for 

the surficial geologic units that we mapped in the Los 

Angeles area: (1) penetration resistance (blows per foot), 

taken from penetrometer studies made by the California 

Department of Transportation (CAL TRANS), (2) range 

and mean values of shear-wave velocity (V5) within each 

geologic unit measured to depths of 30 m by using 

downhole techniques, and (3) relative impedance values 

calculated by using bulk density values for near-surface 

sites (McFadden, 1982) and bulk density measurements 

of sediment sampled below the principal zone of soil formation during soil-engineering studies of storm-drain 

facilities in the Los Angeles region (Los Angeles County 

Flood Control District, unpublished data, 1950-1980). 

Shear-wave velocities have been measured at 84 sites 

in the Los Angeles region, chiefly in· Holocene and 

Pleistocene alluvial deposits. The alluvium is grouped 

according to geologic age and physical properties (grain 

size, consistency, and relative density). Correlations are 

then recognized with respect to shear-wave velocities. 

Relative density and consistency of sediment, as measured by the standard penetrometer test, are correlated 

with geologic age (Fumal and Tinsley, this volume). Thus, 

geologic maps showing age and grain size are sufficient 

for regional studies of areal variations in relative shaking response. Fumal and Tinsley (this volume) show that 

standard penetrometer tests, where they are available, 

afford a basis for further subdividing certain classes of 

sediment (primarily sand and clay) to reduce the 

variance with respect to measured shear-wave velocities. In this chapter, however, standard penetrometer 

data are not incorporated into the definitions of the 

geologic map units or of the shear-wave velocity groups. 

Therefore, although the geologic map units are more 

broadly applicable to the Los Angeles region, the precision of the results obtained from using the twodimensional model of sediment distribution for estimating relative ground shaking is correspondingly reduced. 

Shaking Response of Quaternary Sediments 113 
TABLE 14.-Comparison of mean shear-wave velocities and shear-wave velocity groups for surficial 

geologic units in the Los Angeles region 

Mean shear-wave velocity 

Mean± 1 s.d., Number of Range, Shear-wave 

Age and texture in m/s sites studied in m/s velocity group 

Holocene sediment: 

Fine grained ----------------- 200±20 23 15Q-270} 

(silt and clay). 

Medium grained ------------- 230± 30 38 195--285 

( < 15 percent gravel). 

Coarse grained and ----------- 330±30 12 29Q-375 

very coarse grained 

(> 15 percent gravel; 

cobbles and 

boulders). 

Pleistocene sediment: II 

Fine grained ----------------- 305±50 18 20Q-360 

(silt and clay). 

Medium grained ------------- 430±115 57 27Q-740 

( < 15 percent gravel). 

Coarse grained and ----------- 535± 125 23 33Q-830 III 

very coarse grained 

(> 15 percent gravel; 

cobbles and 

boulders). 

Sedimentary rock ---------------- 530±250 27 30Q-13001 IV 

Crystalline rock ----------------- 1,130±440 12 67Q-1,9001 v 

1

Range includes V5 values for moderately weathered crystalline rocks. 

MAPPING SHEAR-WAVE 

VELOCITY GROUPS 

For regional evaluation, we classify the eight Pleistocene and Ho)ocene surficial geologic units into three 

shear-wave velocity groups (table 14): group I, which includes Holocene fine- and medium-grained deposits 

(Vg < 285 m/s); group II, which includes very coarse grained 

and coarse-grained Holocene deposits and fine- and 

medium-grained Pleistocene deposits (290 m/s < Vs < 7 40 

m/s); and group III, which includes coarse-grained Pleistocene sedimentary deposits (3JO m/s < V5 < 830 m/s). Areas 

underlain directly by sedimentary or crystalline rock 

are divided into two units solely on the basis of lithology. 

Group IV consists of areas underlain by sedimentary 

rock and by sedimentary rock interbedded with intrusive or extrusive igneous rocks; group V consists of 

areas underlain by crystalline (chiefly granitic and 

metamorphic) rock. 

Table 14 shows that the average shear-wave velocity 

decreases within each age category as the sediment 

becomes finer in texture, a trend suggesting that shaking effects on fine-grained deposits may be more severe 

than those on coarse-grained deposits for a given 

114 Earthquake Hazards in the Los Angeles Region 

thickness and layered sequence of materials at a given 

distance from an earthquake source. Thus, future levels 

of shaking are expected to be most severe in areas 

delineated as group I; the expected level of shaking 

would decrease relatively from group I through group V. 

In fact, the character of ground shaking at a point on the 

Earth's surface during an earthquake depends on additional factors not specifically addressed by this general 

approach. These factors include the distance from the 

causative fault, the orientation of the fault, the sense in 

which the earthquake energy is released or focused, the 

size of the earthquake, the basin geometry, and the 

presence of subsurface configurations of layers suitable 

for trapping or amplifying seismic energy in narrow 

periods of interest for engineering purposes. 

Rationale for Projection of 

Surficial Physical Properties 

Data to Depth 

Information on the subsurface character of Quaternary sedimentary deposits in the Los Angeles region is 

severely limited for many of the alluvial basins. This 
/ 

I 

\ I I 

I / ' 

EXPLANATION 

· 0 o ·o o · a .. 

· QyvcQ. . . . · 0 o. o . .. 

- Qyf ' 

Qyvc : Very coarse-grained bouldery alluvium 

Qyc : Coarse grained gravelly alluvium 

Qym: Medium grained sandy alluvium 

Qyf: Fine-grained silty, clayey alluvium 

OJ 0 

Oovc : Very coarse grained bouldery alluvium 

Ooc : Coarse grained gravelly alluvium 

Oom: Medium-grained sandy alluvium 

Qof: Fine-grained silty or clayey alluvium 

Crystalline igneous and metamorphic rock 

Fault: arrows indicate relative sense of displacement 

FIGURE 40.- Generalized depositional model of Quaternary sedimentary deposits in the Los Angeles region. This simplistic model implies that, for 

sediment of a given grain-size distribution, the locus of deposition has been relatively constant during Quaternary time. To the extent that these 

conditions are met, the texture of sediment at the surface of the ground may indicate the texture of the geologic units at depth. 

limitation has forced us to adopt a two-dimensional 

model of sediment deposition (fig. 40) to evaluate what is 

actually a three-dimensional problem, even though the 

model has inherent shortcomings and uncertainties. The 

grain-size designations mapped at the surface are 

assumed to represent the grain size of the sediment to 

depths that would influence shaking response. The 

depositional model reflects the distance from the source, 

the nature and types of the rock in the source terranes, 

and the facies that a given deposit may represent within 

the depositing alluvial system. Coarse materials at the 

surface near the San Gabriel Mountains, for example, 

are assumed to overlie areas underlain by coarsegrained materials to depths sufficient to influence 

shear-wave propagation and seismic response. Joyner 

and Fumal (this volume) suggest that a thickness equal to 

one-quarter wavelength of a 1-s shear wave is useful in 

determining a minimum depth of significance for 

evaluating strong ground motion. Regional geologic relations within the Quaternary sediments support this 

assumption; evidence confirming both the broad applicability and the shortcomings of this approach is indicated by studies of alluvial deposits and ground-water 

basins and logs of borings within the Los Angeles region 

(Eckis, 1928; California Water Rights Board, 1962; 

Thomas and others, 1961) and in other basins elsewhere 

(Schumm, 1977). That is, the coarsest Quaternary 

deposits occur adjacent to upland areas as alluvial fans 

and channel deposits of high-gradient streams that 

drain intensely jointed and fractured, chiefly crystalline 

igneous and metamorphic terranes. In contrast, finegrained deposits occur chiefly either (1) in flood plains 

Shaking Response of Quaternary Sediments 115 
as the uppermost deposits of fluvial fining-upward sequences or (2) in distal parts of all Quaternary sedimentary basins of the region and generally throughout those 

Quaternary alluvial basins having source areas of 

siltstone- and shale-rich rocks. This general trend (grain 

size as a function of depositional environment and 

distance from source) is demonstrated by a transect 

along the Los Angeles River from the Los Angeles Civic 

Center to the Los Angeles harbor area using shallow 

boreholes (table 15) and deeper water wells (table 16). 

Locations of borings are .shown in figures 41A and 41B. 

Relative proportions of coarse alluvium intersected by 

borings decrease downstream as the proportions of finegrained alluvium increase downstream. 

Generalized Maps of Shear-Wave 

Velocity Groups 

Using tables 13 and 14, we can assign ranges of V8 to 

the geologic units in figures 35, 36, 37, 38, and 39. When 

these geologic units are grouped into units having 

distinct ranges of shear-wave velocity, maps of nearsurface V8 can be prepared (figs. 42, 43, 44, 45, 46). 

These maps provide a first approximation of likely shaking response in terms of the model presented above. 

In the absence of information concerning additional 

geologic factors that commonly influence shaking 

response (depth to basement rocks, Holocene thickness, 

vertical variations in sediment type, and so on) (Rogers 

and others, this volume), these maps could provide a 

reasonable first approximation of relative shaking 

response. Although representing highly generalized 

areal differences in shear-wave velocity, these maps 

could be used for earthquake microzonation and for 

general planning to reduce hazards from future strong 

shaking. The next chapter will show how more precise 

estimates, which are useful in seismic design, can be 

derived by accounting for sediment thickness and vertical variations in lithology to depths equal to onequarter wavelength of a 1-s shear wave. 

TABLE 15.-Percentage of sediment designated as "aquiclude" (nonwater-bearing) as opposed to 

chiefly medium- and coarse-grained sediment designated as "aquifer" (water-bearing) horizons in the 

subsurface of the coastal plain area of Los Angeles County, after Thomas and others (1961) 

[Wells listed in sequence from proximal (near) to distal (far) positions with respect to source of sediments. Proportion of lines in a section 

increases generally in a downstream direction, but trend reflects local sources of sediment. Locations of arrays are shown in fig. 41A] 

State well 

no. 

Section 

thickness, 

inft 

Aquiclude 

thickness, 

inft 

Proportion of 

fine sediment, 

in percent 

Proportion of 

medium and coarse 

sediment, in percent 

Section K-K'-K", Los Angeles Civic Center, Dominguez Gap to Terminal Island 

2S/13W-10P6 -------- 700 275 39 61 

2S/t3W-15M3 ------- 700 345 49 51 

2S/13W-15P8 -------- 690 350 51 49 

2S/13W-22P2 -------- 660 365 55 45 

2S/13W-34A2 ------- 640 415 65 35 

2S/t3W-{)3Rl -------- 600 285 48 52 

3S/t3W-11El -------- 600 210 35 65 

3S/13W-15Hl ------- 575 200 35 65 

3S/13W-22H7 ------- 560 314 56 44 

3S/13W-26L2 -------- 560 357 64 36 

3S/13W-26Nl ------- 550 286 52 48 

3S/t3W-35Pl -------- 550 314 57 43 

4S/13W-{)3Rl -------- 540 236 44 56 

4S/13W-15A2 ------- 530 314 59 41 

4S/13W-23M1 ------- 520 143 27 73 

4S/13W-27H1 ------- 520 136 26 74 

4S/13W-35M3 ------- 510 428 84 16 

5S/13W-{)3K1 -------- 500 286 57 43 

116 Earthquake Hazards in the Los Angeles Region 
TABLE 15.-Percentage of sediment designated as "aquiclude" (nonwater-bearing) as opposed to 

chiefly medium- and coarse-grained sediment designated as "aquifer" (water-bearing) horizons in the 

subsurface of the coastal plain area of Los Angeles County, after Thomas and others (1961)-Continued 

State well 

no. 

Section 

thickness, 

inft 

Aq•JicluJe 

thir::kness, 

inft 

Proportion of 

fine sediment. 

in percent 

Proportion of 

medium and coarse 

sediment, in percent 

Section Q-Q', along the Orange-Los Angeles County line from the Puente Hills to Seal Beach 

3S/11W-12J1 -------- 693 329 47 53 

3S/11W-12P2 -------- 700 200 29 71 

3S/11W-26B1 -------- 507 357 70 30 

3S/11W-26E1 -------- 464 300 66 34 

3S/11W-27N1 ------- 457 271 59 41 

3S/11W-34E1 -------- 450 243 54 46 

4S/11W-05A1 ------- 436 293 67 33 

4S/11W-05P4 -------- 428 200 47 53 

4S/11W-08E2 -------- 428 236 55 45 

4S/11W-18J1 -------- 427 293 69 31 

4S/11W-30M1 ------- 414 286 69 31 

4S/12W-25H1 ------- 408 229 56 44 

5S/12W-02B4 -------- 406 129 32 58 

5S/12W-02R1 -------- 402 236 59 41 

5S/12W-11G1 -------- 402 193 48 52 

5S/12W-10A1 ------- 400 229 57 43 

Section M-M'-M", from Whittier Narrows Dam south to the Pacific Ocean west of Seal Beach 

2S/11W-06J1 -------- 800 15 

2S/11W-12A6 ------- 800 180 

2S/12W-13D7 -------- 780 175 

2S/12W-23B4 -------- 750 150 

2S/12W-27G5 -------- 750 180 

2S/12W-28J6 -------- 690 150 

3S/12W-04D2 -------- 725 230 

3S/12W-04Q2 ------- 665 220 

3S/12W-09L1 -------- 700 350 

3S/12W-16L1 -------- 690 415 

3S/12W-28H3 ------- 675 435 

3S/12W-33F1 -------- 650 400 

4S/12W-09B3 -------- 640 490 

4S/12W-16H1 ------- 630 360 

4S/12W-21M4 ------- 630 215 

4S/12W-28H10 ------- 625 230 

SUMMARY 

Geologic conditions in Quaternary sediments vary 

across a region and commonly influence shaking 

response during earthquakes. Delineating surficial 

geologic units in order to evaluate areal differences in 

shaking response from future earthquakes requires 

knowledge of the surface and subsurface distribution of 

Quaternary sedimentary deposits according to their 

wave-propagation characteristics. In th,e absence of 

2 98 

22 78 

22 78 

20 80 

24 76 

22 78 

32 68 

33 67 

50 50 

60 40 

64 36 

62 38 

76 24 

57 43 

34 66 

37 63 

detailed subsurface information for all the alluvial 

basins in the Los Angeles region, a two-dimensional 

model of the areal distribution of Quaternary 'sediments 

according to age and grain size is used to characterize 

likely relative ground response by means of readily 

available data. Derivative maps that broadly characterize the near-surface shear-wave velocities across a wide 

geographic region provide a first approximation of the 

likely areal variability in relative shaking response from 

future earthquakes. 

Shaking Response of Quaternary Sediments 117 
TABLE 16.-Relative proportions of gravel. sand, and silt and (or] clay expressed as a percentage of 

total alluvial stratigraphic thickness as logged in CAL TRANS exploratory boreholes 

[Boreholes mainly along State highways 11 and 7 (Harbor and Long Beach freeways) from near the Los Angeles Civic Center to the Long 

Beach and Los Angeles areas (north to south) across the Los Angeles river flood plain. Locations of boreholes shown schematically in fig. 

41B. tr, trace] 

Silt and 

Freeway Borehole Borehole Gravel,• Sand,' clay,• 

no. no. 1 depth, in ft in percent in percent in percent Comments 

101 53-722-B3 48 0 13 87 Siltstone is local 

sediment source. 

5 53-1183-B3 35/335 36 64 0 

5 53-1360-B2 23 75 25 0 

5 53-601-B3 35 67 33 tr 

7 53-2505-B12 56/225 18 27 55 Siltstone is local 

sediment source. 

7 53-1152-B2 40 38 42 20 

7 53-840-Bfi 75 5 90 5 

7 53-833-B4 55 0 47 58 

7 53-828-B5 90 7 82 11 

7 53-824-B5 68 0 76 24 

7 53-2143-B17 90 tr 68 32 

7 53-1210-B4 70 6 77 17 

7 53-725-B3 33 0 946 6 

11 53-538-B1 27 59 41 0 

11 53-793-Bl 45 78 0 22 

11 53-856--B2 26 46 54 0 

11 53-906--B3 40 20 80 0 

11 53-926-Bfi 60 0 77 23 

11 53-981-B3 40 0 826 18 

11 53-955-B3 50 0 886 12 

11 53-960-B1 48 0 856 15 

11 53-964-B3 56 0 80 20 

11 53-976--B2 35 0 100 0 

1

CALTRANS borehole code. For example, in 53-7583-83, 53 denotes Los Angeles County, 7583 is bridge or structure number, and 81 

is boring number. 2

Includes intervals containing gravelly sand, sandy gravel, clayey gravel, pebbly sand, and very coarse detritus such as cobbles and 

boulders. 3

Includes intervals containing silty sand or clayey sand. 4Includes intervals containing sandy or silty clay and sandy or clayey silt. 5

35/33 denotes 35-ft boring that penetrated 33 ft of alluvium before entering bedrock. Percentages computed relative to thickness of 

alluvium. 6 All sand logged as fine sand. 

118 Earthquake Hazards in the Los Angeles Region 
V'l 

::r 

Ql 

'1f/!:" 

:r 

(JQ 

~ "C 

118'30' r0 33'45' 

:I 

~ 

s. 

~ c 

;. 

... 

:I 

Ql 

~ A 

118'15' 

R11481 

• E11351 

~11351 H71561 

l2(641 

_Dominguez Hills ~521 • /J 

'\ ~;:!571 /~ R1(441" 

A2(591 

M112711

" 

H11261 

u• 

(601 

M ' 

0 5 10 KilOMETERS 

0 5 MilES 

118'00' 

J1(471 

P2(291. 

811701 

N11591_y'E11661 

• E1154l 

118'30' ,...--

33'45' 

B 

118'15' 

o Burbank 

0 Pasadena 

53-906 

53-926 

53-981 

53-955 

53-960 

53-964 53-1210 

0 5 )0 KILOMETERS 

0 5 MilES 

~ 3' 

tD 

:I 

... FIGURE 41.-A, Distribution of water wells listed in table 15. Percentage of fine-grained materials in the subsurface is shown in parentheses by each well. B, Distribution of water wells 

listed in table 16. 

"' 

... 

... 

I.C 
\ 

\ .. 

\ , 

t 

34'15' 

J!'' 

l 

' t 

Symbol 

5 KILOMETERS 

f--'-TI..Li-J..,I 1r'--r11 

1 2 3 MILES 

EXPLANATION 

Shear·wave Shear·wave 

velocity group velocity range (m / s) 

150 :sV, <285 

II 200 < V,<740 

Ill 330 :sv, :s830 

IV 300 :sv. :s 1,300 

v 670 :sv, <1900 

118'15' 

FIGURE 42.-Generalized shear-wave velocity groups in the San Fernando Valley. Surficial textural characteristics are assumed to extend to 

depths of significance to shaking response. 

120 Earthquake Hazards in the Los Angeles Region 
Symbol 

\, ___ _:,._J, 

.._ ~:~fi 

.. 

.. -~ > .... }. ,. ,~, 

,~!. 

EXPLANATION 

~hear-wave 

velocity group 

II 

Ill 

IV 

v 

150 :sV, <285 

200 <V, <740 

330 :sv. :s830 

300 :sV, :s 1,300 

670 :sV, <1900 

118'00' 

5 KILOMETERS 

f-_L-,,...li_.J.I 'I _!_--,JI I

1 2 3 MILES 

117'45' 

IV l 

l._ 

FIGURE 43.-Generalized shear-wave velocity groups in the San Gabriel Valley. Surficial textural characteristics are assumed to extend to depths 

of significance to shaking response. 

Shaking Response of Quaternary Sediments 121 
34'00' 

/ 

33145' 

3 4 5 KILOMETERS 

3 MilES 

EXPLANATION 

Shear-wave Shear-wave 

velocity group velocity range (m / s) 

II 

Ill 

IV 

v 

ISO sV, <285 

200<V, <740 

330 sV,s830 

300 sV, s 1,300 

670 sv, <1900 

FIGURE 44.-Generalized shear-wave velocity groups in part of the Los Angeles basin. Surficial textural characteristics are assumed to extend to 

depths of significance to shaking response. 

122 Earthquake Hazards in the Los Angeles Region 
Symbol 

~ 

I I 

I I 1 2 

EXPLANATION 

Shear-wave Shear-wave 

velocity group velocity range (m / s) 

150 ,;;V, < 285 

II 200 <V, < 740 

Ill 330:SV,,;;830 

IV 300,;;V,,;l,300 

5 KILOMETERS 

I' 

3 MILES 

FIGURE 45.-Generalized shear-wave velocity groups in the Oxnard Plain area. Surficial textural characteristics are assumed to extend to depths 

of significance to shaking response. 

Shaking Response of Quaternary Sediments 123 
FIGURE 46.-Generalized shear-wave velocity groups in the upper Santa Ana River basin. Surficial textural characteristics are assumed to extend 

to depths of significance to shaking response. 

124 Earthquake Hazards in the Los Angeles Region 
EXPLANATION 

Shear-wave Shear-wave 

Symbol velocity group velocity range (m / s) 

150 sV, < 285 

II 200<V,<740 

Ill 330 sV, s 830 

IV 300 sV, s1,300 

v 670 sV, < 1900 

5 KILOMETERS 

II II 

2 3 MILES 

Shaking Response of Quaternary Sediments 125 
126 Earthquake Hazards in the Los Angeles Region 
MAPPING SHEAR-WAVE VELOCITIES OF 

NEAR-SURFACE GEOLOGIC MATERIALS 

By T. E. Fumal and J. C. Tinsley 

INTRODUCTION 

The distribution of damage caused by earthquake 

ground shaking commonly reflects areal differences in 

local geologic conditions. Damage on thick deposits of 

unconsolidated sediments, for example, is frequently 

observed to be much greater than that on bedrock at 

nearby locations. To map geographic variations in shaking response, parameters are needed that can be used to 

predict these variations in ground motion due to differences in site geology. Recent studies indicate that 

shear-wave velocity is a critical factor in determining 

the amplitude of ground motion Gayner and Fumal, this 

volume) and thus might be a useful parameter in preparing predictive maps of strong ground motion. 

Measurements of near-surface shear-wave velocities 

are now available for many sites in the San Francisco 

Bay and Los Angeles regions of California (Gibbs and 

others, 1975, 1976, 1977, 1980; Fumal and others, 1981, 

1982, 1983). Comparisons between the shear-wave 

velocity data and several measures of ground motion 

demonstrate the potential usefulness of shear-wave 

velocity for predicting site effects on ground motion. For 

the San Francisco Bay region, Borcherdt and others 

(1978) have found that average shear-wave velocity to a 

depth of 30 m correlated inversely with intensities from 

the 1906 San Francisco earthquake. The intensities experienced at sites having mean shear-wave velocities of 

300 m/s, for example, were about two units higher than 

those experienced at sites at the same distance from the 

ruptured fault ·but having velocities near 800 m/s. A 

similar inverse correlation was found between average 

shear-wave velocity and amplifications of low-strain 

ground motion generated by nuclear explosions. Joyner 

and Fumal (this volume) present a relation between site 

shear-wave velocity and peak horizontal ground velocity 

measured at strong-motion stations in central and southern California. 

If maps of mean shear-wave velocity were available, 

these important relations could be used to prepare maps 

showing predicted levels of various ground-motion 

parameters. Unfortunately, it is expensive and time consuming to measure seismic velocities at the large 

number of sites necessary to adequately characterize a 

geologically complex region. As an alternative, we have 

identified relations between shear-wave velocity and 

several other physical properties of geologic materials 

that can be mapped more readily on a regional scale. 

We have developed a method for assigning shearwave velocities to the mapped geologic units in the San 

Francisco Bay region (Fumal, 1978). According to this 

method, the geotechnical measures that show useful 

correlations with shear-wave velocity are texture (relative grain-size distribution) and standard penetration 

resistance for unconsolidated sedimentary deposits and 

fracture spacing, hardness, and lithology for bedrock 

materials. 

In this chapter, we extend our analysis to include the 

Los Angeles region. We first briefly review the factors 

that affect shear-wave velocity and discuss correlations 

between seismic velocity and other physical properties 

of the geologic units. We next examine the shear-wave 

velocities of the various geologic units in the Los Angeles 

region and determine which units or groups of units 

have distinct velocity characteristics. Finally, we 

demonstrate how these velocity units, together with information on the three-dimensional distributions of 

sedimentary deposits and bedrock materials, can be 

used to construct a map of mean shear-wave velocity for 

the urbanized upper Santa Ana River basin. In a subsequent chapter Gayner and Fumal, this volume), this map 

is used to prepare predictive maps of selected groundmotion parameters. Our technique of mapping mean 

shear-wave velocities of near-surface geologic materials 

differs from the more simplified approach described by 

Tinsley and Fumal (this volume) in that it accounts for 

Shear-Wave Velocities of Near-Surface Materials 127 
areal variations in the thickness of sedimentary deposits 

and vertical variations in lithology. 

GEOLOGIC FACTORS AFFECTING 

SHEAR-WAVE VELOCITY 

Shear-wave velocity is dependent on the rigidity of the 

structure of a soil or rock mass and is controlled by the 

porosity of the structure and the forces holding the 

structure together, including cohesion, friction, cementation, and effective stress. The primary physical properties that control the velocities of shear waves in 

sediments are different from those in rock and so will be 

discussed separately. 

Soil 

Hardin and Drenevich (1972) have conducted laboratory studies investigating the effects of numerous factors on the shear modulus in soils. The shear modulus is 

equal to the product of the soil density and the square of 

the shear-wave velocity. For the soils that we studied, 

density variations are small (1.7-2.15 g/cm3) and correlate with the shear-wave velocity, so that the shear 

modulus is proportional to the square of the shear-wave 

velocity. We would therefore expect that the soilcondition factors found by Hardin and Drenevich to 

have the most important effect on shear modulus-void 

ratio and effective mean principal stress (or degree of 

saturation in partially saturated cohesive soils}-are 

also important for shear-wave velocity. 

Hardin and Drenevich found that void ratio (the ratio 

of the volume of voids to the volume of solids) is one of 

the most important parameters affecting the shear 

modulus in both clean sands and cohesive soils. Void 

ratio is dependent on the grain-size characteristics of 

the soil (primarily mean particle size and sorting 

(Meade, 1968)) and the packing density of the soil particles. We have used soil texture (relative grain-size 

distribution) as a partial measure of void ratio. Texture 

is particularly useful, as it can be readily determined in 

the field by techniques developed by the U.S. Soil Conservation Service (Soil Survey Staff, 1951). The sedimentary deposits in the San Francisco Bay region were 

divided into four textural categories based on grain-size 

distribution: (1) clay and silty clay, (2) silt loam and 

sandy clay, (3) sand, and (4) gravel. In these sediments, 

shear-wave velocity generally increases as mean grain 

size increases. 

Void ratio is also dependent on the packing density of 

the soil particles. The relative density of sands is frequently estimated directly by using the results of the 

128 Earthquake Hazards in the Los Angeles Region 

Standard Penetration Test (SPT) and the classification 

given by Terzaghi and Peck (1967). For cohesive soils, 

Terzaghi and Peck have suggested using the SPT to 

estimate the unconfined compressive strength (twice the 

undrained shear strength), which increases as void ratio 

decreases. Furthermore, because the SPT sampler penetration primarily involves dynamic soil shear behavior, 

Schmertman (1978) has suggested that it is reasqnable 

to expect a correlation between N values (resistance, 

measured in blows per foot) and shear-wavl;l velocities. 

We found that, for the San Francisco data, $ear-wave 

velocity increases as penetration resistance increases 

for both cohesionless and cohesive soils, and we used 

these relations to subdivide the clay and silty clay and 

sand categories. 

In addition to void ratio, mean principal effective 

stress is a very important factor controlling shear 

modulus in laboratory samples at a given strain amplitude (Hardin and Drenevich, 1972). It is reasonable, 

then, to expect an increase in shear-wave velocity with 

depth in sedimentary deposits even if there is little textural variation. This relation was confirmed at several 

sites in the San Francisco Bay area on thick sections of 

loose to medium-dense sands. Most often, however, 

changes in velocity correlated with changes in texture, 

soil stiffness, or age. Many sites having layers of stiff 

clay and silt or dense sand 15 to 25 m thick showed no 

significant increase in velocity with depth, an indication 

that factors other than effective stress controlled velocity in these deposits. 

Time-dependent processes, including thixotropic 

hardening of clays and cementation, can increase the 

rigidity of the sediment structure beyond values solely 

attributable to void ratio and effective stress. Laboratory studies (Hardin and Black, 1968; Stokoe and 

Richart, 1973) show that these effects can increase 

shear velocity by 1 to 2 percent for silty sand and by 10 

to 15 percent for kaolinite clay per log cycle of time. For 

natural sediments, our field measurements indicate that 

these time-dependent velocity increases are much more 

important than they appear to be from laboratory studies and may become the dominant factor controlling 

shear velocity (Fumal, 1978) (see fig. 50). 

Rock 

Studies by Walsh and Brace (1966) have suggested 

that the elastic behavior of rock depends very strongly 

on the total porosity of the rock mass in the form of both 

cracks and intergranular pores. They found that the effect of narrow elliptical cracks on the elastic moduli is 

nearly the same as that of an equal concentration of 

roughly spherical pores, in spite of the fact that the 
porosity in the case of the pores is much greater than 

that in the case of the cracks. Thus, formation of cracks 

in a rock could significantly lower the elastic modulus 

(and hence the seismic velocity) without changing the 

total porosity appreciably. Furthermore, Walsh and 

Brace have found that the longest cracks, such as joints 

and bedding-plane partings, have the greatest effect. An 

estimate of fracture spacing therefore should correlate 

with shear-wave velocity. 

The hardness (relative resistance to penetration) (see 

fig. 55) of the intact rock also affects the shear-wave 

velocity. Hardness, a measure of the strength and toughness of rock, is related to the lithology and the characteristic fabric of each rock type. Igneous rocks have 

crystalline fabrics consisting of interlocking crystals 

and are generally hard. Sandstones, on the other hand, 

have a cemented fabric in which the space between 

grains is partially or completely filled with cement. 

Sandstones display a wide variation in hardness depending on the degree of induration. 

The fracture spacing and hardness of bedrock materials are strongly affected by weathering processes. 

Weathering causes the progressive disintegration of 

rock through both mechanical and chemical processes. 

Mechanical weathering primarily involves the opening 

of existing fractures as well as the formation of new 

ones. Chemical weathering generally decreases the 

hardness of the intact rock through dissolution of 

cement and decomposition of mineral grains. Both 

weathering processes act to decrease shear-wave 

velocity. 

Data from the San Francisco Bay region show that 

shear-wave velocity increases as the hardness of the 

intact rock and the fracture spacing increase (the fracture spacing has the ·dominant effect). These two properties, plus lithology, were used to define seven categories of bedrock materials having distinct velocity 

characteristics (Borcherdt and others, 1978). 

The physical properties of the bedrock materials at 

each site vary with depth depending on the degree of 

weathering. The depth to which the bedrock has been 

significantly altered by weathering processes varies 

considerably from site to site because of differences in 

lithology and permeability. Rock types such as chert, 

porcelaneous shale, and serpentine are little affected by 

weathering even at shallow depths, whereas granitic 

rock may be significantly weakened to depths greater 

than 30 m. Velocities were obtained for moderately 

weathered and fresh rock at most sites. The difference 

between these values increases as the strength of the 

fresh rock increases-80 to 250 m/s for low- to mediumstrength sedimentary rocks to 750 to 1,050 m/s for highstrength igneous rocks. 

SHEAR-WAVE VELOCITY STUDIES 

IN THE LOS ANGELES REGION 

Shear-wave velocities were measured by using the 

downhole technique at 84 sites in the Los Angeles basin 

and vicinity (fig. 47). Most sites were chosen to provide 

geologic and seismic data to compare with groundmotion measurements made at nuclear-explosion 

recording stations (48 sites) and strong-motion stations 

(23 sites). A few sites were selected to provide additional data from particular sedimentary deposits. 

At each site selected, rotary-wash equipment was 

used to drill a borehole to a depth of about 30 m; a few 

holes in very hard rock were as shallow as 21 m. 

Representative samples of each dominant type of 

material encountered were recovered during drilling. 

Generally, three to five Pitcher sampler, split-spoon, or 

diamond-core samples were taken at each site. Geologic 

logs, including soil texture and color and estimates of 

hardness and fracture spacing in rocks, were compiled 

for each hole from descriptions of the samples and a 

field log based on continuous monitoring of drill cuttings 

and roughness and rate of drilling, on-site inspection of 

samples, and inspection of nearby outcrops (fig. 48A). 

The geologic logs were examined, and estimates of the 

age (usually Holocene or late or middle Pleistocene) 

were made for the sedimentary deposits encountered in 

each hole by geologists experienced in mapping in the 

Los Angeles region 0. C. Tinsley and D. Ponti, personal 

communication, 1982). 

Shear waves were generated at the ground surface by 

a horizontal traction source similar to the' one developed 

by Kobayashi (1959) and discussed by Warrick (1974). 

Recordings of seismic signals were made in the boreholes by using a three-component geophone package 

usually at intervals of 2.5 m. Velocities were calculated 

for depth intervals determined from changes in the 

slopes of traveltime curves (fig. 48B). To minimize the effects of picking errors, these depth intervals are a 

minimum of 5 m (three traveltime measurements) for 

materials having velocities less than 350 m/s and 7.5 m 

(four traveltime measurements) for stiffer materials. 

Because physical properties were determined by field 

methods, they are generally only relative evaluations of 

the average properties of the sediment or rock mass. 

Measurements of standard penetration resistance, density, and seismic-wave velocity were the only quantitative determinations made. Although this procedure 

may lack refinement, it is potentially widely applicable 

to other seismically active areas having similar geologic 

units. 

Comparison of the interval shear-wave velocities with 

the physical properties indicated on the geologic logs 

shows correlations for the Los Angeles area that are 

Shear-Wave Velocities of Near-Surface Materials 129 
34' 00' 

• 

Santa Barbara • 

EXPLANATION 

0 Quaternary sed im entary deposits 

0 

I 

0 

10 

I 

10 20 

20 

I I 

30 

I 

30 

I 

40 MILES 

I 

40 KILOMETERS 

17' 00' 

• 

FIGURE 47.-Locations of sites in the Los Angeles region at which seismic velocity and geologic data have been obtained from drill holes to depths 

of 30 m. Stippled area is the demonstration area in the upper Santa Ana River basin. 

very similar to those for the San Francisco Bay region. 

For ease of discussion, we have divided the geologic 

materials of the Los Angeles region into two broad 

categories based on degree of induration: (1) unconsolidated to moderately consolidated sedimentary deposits and {2) bedrock. The first group is comprised of all 

deposits ranging in age from Holocene through middle 

Pleistocene less than about 250,000 yr old. The second 

group includes all older materials. The velocity 

characteristics of each category will be discussed 

separately. 

SHEAR-WAVE VELOCITIES 

IN LATE QUATERNARY 

SEDIMENTARY DEPOSITS 

Correlation with Physical Properties 

Unconsolidated to moderately consolidated sedimentary deposits are greater than 30 m thick at 58 sites and 

130 Earthquake Hazards in the Los Angeles Region 

5 to 21 m thick at 15 others. Because of the large number 

of velocity measurements for these materials, it was 

convenient to analyze separately the data from three 

subareas: {1) the Los Angeles basin, (2) the San Fernando and Antelope '-valleys, and (3) the Ventura-Oxnard 

area. Only the Los Angeles basin results, which are 

generally similar to those for the other subregions, will 

be illustrated. The following discussion, however, applies to all three areas. The means, ranges, and standard deviations of the complete data set are listed in 

accompanying tables, along with separate listings for 

groups that show significant geographic variation. 

The results of measurements in the Los Angeles basin 

subarea are summarized in figure 49, which shows 

average velocity over the depth intervals obtained from 

traveltime curves. Because these sediments are for the 

most part thickly bedded, the velocity intervals generally correspond to materials having relatively homogeneous physical properties. From two to five such 

velocity intervals were determined for each site. Figure 

48C shows, for an individual site, how the velocities 

calculated by using the traveltime curves are plotted as 

interval velocities in figure 49. 
------ 0 

Sand, dark brown to 

yellowi sh brown, 

dense 

5 5 

10 10 

Clay and silty clay, 

olive grey mottled, 

.:_,7; strong brown, 

very stiff 

Loamy sand, 

20 yellowish 

brown, medium 

to very coarse 

Grading to sand , 

25 fine 

to medium 

Silt loam, olive 

30 ----

A 

(f) 

a: 

UJ 

1-

UJ 

::;;;: 15 z 

I 

I-

"-

UJ 

0 

20 

25 

TIME, IN MILLISECONDS 

10 30 

• FirstS arrival 

.t. FirstS peak 

410 Velocity, in 

meters per second 

8 

70 90 

(f) 

a: 

UJ 

1-

UJ 

::;;;: 

l 

z 15 

I 

I-

"-

UJ 

0 

20 

25 

SHEAR-WAVE VELOCITY, IN METERS PER SECOND 

EXPLANATION 

~ Clay, silty clay I Sand 

c 

FIGURE 48.-A, Geologic log for a site in the Los Angeles basin. B, Traveltime curve for the same site. C, Method for combining and plotting these 

data on the interval velocity graph shown in figure 49. 

Figure 49 groups the sediments according to texture 

and standard penetration resistance. Although some of 

the resulting groups have wide ranges in velocity and 

there is overlap between groups, these parameters have 

the advantage of being widely available for urban 

regions because the requisite tests ordinarily are conducted during routine engineering studies. The means, 

ranges, and standard deviations of the velocities of each 

group are shown for the complete data set in table 17. 

The sediments of the Los Angeles region are divided 

into five categories according to grain-size distribution: 

(1) clay and silty clay, (2) silt loam and sandy clay, (3) 

sand, (4) gravelly sand and gravel ( > 20 percent gravel), 

and (5) cobble to boulder gravel. The data in figure 49 

show that shear-wave velocity increases as mean grain 

size increases. Because of the greater proportion of 

sand having high void ratios sampled in the Los Angeles 

area, this trend is not as pronounced here as it is in the 

San Francisco region. 

SPT results for three of the textural groups in the Los 

Angeles region are shown in figure 50. The N value 

(resistance, measured in blows per foot) for a given sample is plotted versus the mean shear-wave velocity for 

the depth interval containing that sample. Values for 

several age designations are given. We have applied 

corrections to the standard penetration values for very 

fine or silty sand below the water table (after Terzaghi 

and Peck, 1967) and for effective overburden pressure 

in sands (after Bazarra, 1967) (equivalent to CN (Seed 

and others, 1983) for 96 kPa ::5 a0 ::5 48 kPa). Presumably, 

overburden pressure also affects N values in cohesive 

soils, but no correction was found in our literature search. 

The wide scatter shown in figure 50 is similar to that 

found in the San Francisco Bay region. In addition to 

variations in equipment and measurement technique, 

differences in sampling scale may account for a significant part of this scatter. Penetration resistance is recorded cumulatively over a 0.3-m interval and is very 

sensitive to small inhomogenieties. The shear-wave 

velocity, on the other hand, is an average value over 5 to 

25m. 

Consequently, the good correlation for clay (correlation coefficient 0.97) is remarkable, and the N value can 

be used to predict shear-wave velocity with some confidence for these sediments. Although the scatter for 

sand is much greater (correlation coefficient 0.81) than 

that for clay, the relations between penetration 

Shear-Wave Velocities of Near-Surface Materials 131 
SHEAR-WAVE VELOCITY, IN METERS PER SECOND 

100 

0 

200 300 400 500 600 700 800 

n 

I I I I I I I I I I I I I I I 

I'! 5 

EXPLANATION 

Clay and silty clay 

fr ~ I Medium to stiff (4-sN s 15) 

II Very stiff to hard (N> 15) 

~ Ill Silt loam and sandy clay 

Sand 

f-- I IV Loose to medium (N-s 30) 

v Dense to very dense (N> 30) 

VI Gravelly sand and gravel 

·' VII Cobble to boulder gravel : 

: 

r-- ~ 

10 

(f) 

a: 

L.U 

f--

L.U 

::?; 

~ 15 :r:' 

f--

~ 

L.U 

0 

20 

r-

: 

~ 25 

30 I J _l _I 11 LJ_l J _l J J _l _l J _l ! I I I I 

II VI 

Ill VII 

IV v 

FIGURE 49.-Shear-wave velocities for depth intervals determined from traveltime curves in unconsolidated to moderately consolidated sedimentary deposits in the Los Angeles basin subarea. The deposits are divided into groups according to texture and standard penetration resistance 

N (number of blows per foot). Means (solid circles) and standard deviations (bars) of velocity for each unit in the Los Angeles region are shown 

along the lower abscissa. 

resistance and shear-wave velocity are very similar for 

both groups. We have subdivided these two categories 

by using relations between penetration resistance and 

other index properties of the soils given by Terzaghi and 

Peck (1967). For cohesive soils, penetration resistance 

serves as an index of consistency (relative firmness). We 

have subdivided the clays and silty clays into two 

groups: medium to very stiff (4 ~ N ~ 15} and very stiff to 

hard (N> 15). No significant thicknesses of soft to very 

soft (N < 4) clays were found at our sites in the Los 

Angeles area. For sands, penetration resistance has been 

related to relative density and is most useful for N < 50. 

132 Earthquake Hazards in the Los Angeles Region 

We have subdivided the sands into two groups: loose to 

medium dense (N ~ 30} and dense to very dense (N > 30}. 

Because of the corrections applied to the data for sands, 

this boundary is lower than that (N = 40} used in the San 

Francisco Bay region. 

The relation between penetration resistance and 

shear-wave velocity is poor for the silt loam and sandy 

clay group (correlation coefficient 0.62}. It was not used 

to subdivide that group, although the distribution of 

velocity in these sediments is bimodal (two distinct 

subsets). The distribution of velocity is also bimodal for 

the gravelly sand and gravel and the cobble to boulder 
TABLE 17 .-Shear-wave velocities in late Quaternary sedimentary deposits of the Los Angeles region 

[N, number of blow per foot from standard penetration resistance tests] 

Shear-wave velocity 

No. of Mean, Standard Range, 

Physical property unit velocity intervals in mls deviation in mls 

Clay and silty clay: 

Medium to very stiff (4 ~ N ~ 15) ------------------ 8 175 30 140-225 

Very stiff to hard (N> 15) ----------------------- 7 270 50 2Q0-340 

Silt loam and sandy clay--------------------------- 29 260 80 160-360 

Sand: 

Loose to medium dense [N ~ 30) ------------------ 40 235 35 14Q-285 

Dense to very dense [N> 30) 

Los Angeles-Ventura ----------------------- 29 400 100 27()-610 

San Fernando-Antelope Valleys -------------- 26 485 70 31Q-740 

Totru ---------------------------------- 55 440 110 27Q-740 

Gravelly sand and gravel: 

Los Angeles --------------------------------- 7 485 110 305-680 

Ventura ------------------------------------ 5 445 150 30Q-620 

San Fernando-Antelope Valleys ----------------- 16 410 90 29Q-540 

Totru ----------------------------------- 28 435 105 29Q-680 

Cobble to boulder gravel --------------------------- 8 580 185 35().-830 

gravel groups. Penetration resistance is not very useful 

in these coarse-textured sediments, nor are .most other 

geotechnical tests, because of the difficulty of sampling. 

To investigate the importance of time effects in the 

Los Angeles region, the in situ shear-wave velocities 

were compared with expected values calculated by using equations derived from laboratory investigations. 

Void ratios of samples collected were calculated from 

measured bulk densities (assuming 100 percent saturation) and plotted versus interval shear-wave velocity in 

figure 51. Expected shear-wave velocity was calculated 

for each sample by using equations suggested by Hardin 

and Richart (1963): 

relation between void ratio and in situ shear-wave 

velocity (fig. 51). The velocities of late and middle 

Pleistocene sediments are significantly higher than 

those of Holocene sediments for the entire range of 

measured void ratios. Furthermore, it was found that in 

situ velocities for the Holocene deposits are generally 

within 10 percent of the values expected from equations 

1 and 2, whereas velocities of late and middle 

Pleistocene deposits are 15 to 80 percent higher than the 

calculated velocities. 

Although shear-wave velocity is inversely related to 

void ratio, there is considerable scatter in the data. For 

Holocene sediments, penetration resistance appears to 

be a better predictor of velocity than void ratio is, 

V5 =(111-50.9e)u00.25 (for u0>96 kPa) 

V5 = (90.2 - 42.4e )u0 °·30 (for u0 ::5 96 kPa) 

(1) especially for clays. For late and middle Pleistocene 

sediments, shear-wave velocity is nearly independent of 

where Vs is in meters per second, e is the void ratio, and 

u0 is the mean principle effective stress. As a simplifying 

assumption, u0 was taken to be equal to the overburden 

pressure. The actual effective stress is probably lower 

because of pore pressures; thus, the calculated shearwave velocity is a maximum value. 

We determined that whether the sample was taken 

with a Pitcher barrel or a split spoon and whether it was 

taken above or below the water table have little effect 

on the relation between void ratio and shear-wave 

(2) void ratio for values less than 0.5, whereas, for values 

between 0.9 and 0.5, void ratio seems to predict velocity 

somewhat better than N value does. As there is with 

penetration resistance, there is significant variation of 

void ratio within mappable geologic units (see, for example, Rogers and others, this volume, fig. 114). Thus, 

although the addition of void-ratio data would probably 

not be an improvement over a classification based on 

texture and standard penetration alone, such data could 

serve as an alternative where they are available. 

velocity. Texture is somewhat important, since void 

ratios of fine-grained sediments are higher than those of 

sands and gravelly sands for a given shear-wave velocity. The age of the deposit, however, strongly affects the 

Correlation with Sedimentary Units 

The previous section has shown that the shear-wave 

velocities of near-surface sedimentary deposits can be 

Shear-Wave Velocities of Near-Surface Materials 133 
0 

z 

0 

u 

w 

(f) 

a: 

UJ 

a_ 

(f) 

a: 

UJ 

1-

UJ 

::2' 

~ 

~­

u 

0 

-' 

UJ 

> 

UJ 

> 

~ cl:: 

<t 

UJ 

::c 

(f) 

sao - I r---. -T-T~; -~. ·······~ 

I ' I I I I ! 

400 --~ +-+ . I ~ .. , ' I I ' 

300 -l-+_ ······· 6 •. +-1-._, TI 

I

, '[; , , I . ~ : I I i i I 

200 t---· t.' "-'--···~' _J -~EX ~L ~A~ ON !_ ............ ___; 

I

' Holocene : 1 , ! A i ! 

' · Late and Middle Pleistocene · ' i I o I i Pliocen~-Pieis~ocene 100 '-----'----l.--L _ _L _ _j__j___L___; 

0 10 20 30 40 50 60 70 80 

500 

400 

300 

200 

100 

PENETRATION RESISTANCE, IN BLOWS PER FOOT 

134 Earthquake Hazards in the Los Angeles Region 

~ FIGURE 50.-Variation of shear-wave velocity with standard penetration resistance for three textural groups of sedimentary deposits in 

the Los Angeles region. A, Clay and silty clay; B, silt loam and 

sandy clay; C, sand and gravelly sand. Lines are least-squares fits 

to the data that give the equations shown. The correlation coefficients for these equations are 0.97 (clay), 0.62 (silt), and 0.81 

(sand). Penetration tests were performed in conjunction with 

rotary-wash drilling; the cathead and rope technique was used to 

drop a 42.5-kg hammer a distance of 76 em. 

related to several readily determined physical properties. Knowing the areal distribution of these properties 

would aid in estimating ground response from future 

earthquakes. Unfortunately, such information can be obtained only indirectly, if at all, from most geologic maps. 

Although areas underlain by unconsolidated sedimentary deposits are most susceptible to ground shaking 

hazards, these areas generally are not subdivided on 

ordinary regional-scale geologic maps. 

Recent mapping in the Los Angeles region has provided geologic maps of sedimentary deposits that are 

more useful for evaluating earthquake hazards. Tinsley 

and Fumal (this volume) describe techniques based on 

Lajoie and Helley's (1975) methods of classifying and 

mapping alluvial deposits according to age and texture. 

Each age category (Holocene and late and middle 

Pleistocene) is divided into fine-, medium-, and coarsegrained and very coarse grained units, which correspond to chiefly silt and clay, sand, gravelly deposits 

( > 15 percent gravel), and bouldery and cobbly deposits, 

respectively. 

Shear-wave velocities measured in these mappable 

units in the Los Angeles basin are shown in figure 52. 

Means, ranges, and standard deviations of the velocities 

for each unit in the entire region are presented in table 

18. For the late and middle Pleistocene medium- and 

coarse-grained units, significant variation was found 

between the Los Angeles basin and the San Fernando 

Valley-Antelope Valley areas, and separate values are 

shown. Each mappable unit in the Los Angeles region 

has distinct shear-wave velocity characteristics, reflecting the important influence of age and texture on the 

physical properties that control velocity. 

The relations between the velocity units based on 

physical properties (fig. 49) and the mapped geologic 

units (fig. 52) are shown schematically in figure 53. Each 

textural group has two distinct ranges of velocity, which 

correspond to the Holocene and late and middle Pleistocene age groups. For the clays and sands, the age divisions nearly coincide with the divisions based on standard penetration resistance (Holocene clays, however, 

can have N values as high as 20, a few sands having 

N ~ 30 are late Pleistocene, and some Holocene sands 

have N> 30). The distinct velocities in silt loams and 

sandy clays of different ages are not, however, reflected in 
the penetration test results. Although the clay and silty 

clay and the silt loam and sandy clay categories have 

distinct velocity characteiistics, they generally cannot be 

mapped separately. Each of the fine-grained Holocene 

and fine-grained late and middle Pleistocene groups thus 

include portions of both the clay and silt units. 

Because the late and middle Pleistocene medium- and 

coarse-grained deposits have rather wide ranges in 

shear-wave velocity, a means of subdividing them would 

be desirable. Studies of shear-wave velocity in late 

Quaternary stratigraphic units mapped in the Antelope 

Valley (Ponti and Burke, 1980; Ponti and others, 1981) 

show that shear-wave velocity systematically increases 

as the age of the deposit increases (fig. 54). These units 

can be differentiated in the field by the degree of soilprofile development. In particular, deposits older than 

about 100,000 yr can be distinguished from younger 

deposits by a pronounced reddening of the soil. Additional studies are in progress to determine whether this 

trend in shear-wave velocity exists in other basins; if it 

does, reddening of the soil may provide an easily recognizable means of subdividing the late and middle Pleistocene medium- and coarse-grained sediments for 

purposes of mapping shear-wave velocity. 

SHEAR-WAVE VELOCITIES 

IN PRE-LATE QUATERNARY 

BEDROCK MATERIALS 

Shear-wave velocities were measured in bedrock 

materials at 42 sites in the Los Angeles region. Rocks at 

most of these sites comprise two categories: (1) middle 

Miocene to early Pleistocene sedimentary rocks and (2) 

granitic rocks of the San Gabriel, San Bernardino, and 

Santa Monica Mountains. Because a much wider range 

of materials was sampled in the San Francisco Bay 

region, data from that region were relied on to a large 

extent in developing criteria for estimating shear-wave 

velocities of bedrock map units in the Los Angeles 

region. 

In the San Francisco Bay region, shear-wave velocity 

increases as both the hardness of the intact rock and the 

fracture spacing increase; the effect of the fracture 

spacing is dominant (Fumal, 1978). These two properties, together with lithology, were used to define seven 

categories of bedrock materials having distinct velocity 

characteristics. Figure 55 shows interval velocities obtained in moderately weathered to fresh bedrock in the 

Los Angeles region grouped into these categories. 

Ranges of velocity for these units in the San Francisco 

Bay region are shown for comparision. Results from the 

two regions compare very favorably. Means, ranges, 

Cl 

z 

0 

u 

UJ 

UJ 

a: 

UJ 

"-

800 

700 

~ 600 UJ 

fUJ 

:::;; 500 

~- 400 

u 

0 

--' 

~ 300 

UJ 

> 

~ 200 

r.i: 

~ 100 I 

UJ 0.30 0.40 0.50 0.60 0. 70 0.80 0.90 1.00 1.10 1.20 

VOID RATIO 

FIGURE 51.-Variation of measured shear-wave velocity with void 

ratio for Holocene (solid circles) and late and middle Pleistocene 

(open triangles) sediments in the Los Angeles region. Data are 

primarily for sand and fine-grained sediments, along with some 

gravelly sand. Solid lines are visually determined approximate fits 

to the data. 

• and standard deviations of the velocities for the combined data set are presented in table 19. 

Standard geologic maps ordinarily contain very little 

information about the relative hardness and fracture 

spacing of bedrock units and are thus unsatisfactory for 

estimating shear-wave velocity. In the San Francisco 

Bay region, Wentworth and others (1985), recognizing 

the need for engineering data for bedrock materials, 

have prepared detailed descriptions of hardness, fracture spacing, and other geotechnical properties of the 

geologic units in San Mateo County. These descriptions 

can be used in conjunction with the velocity data to 

assign velocity categories to each map unit or groups of 

similar units. 

For the Los Angeles basin, Wentworth and others 

(1970) have grouped the numerous mapped bedrock 

units into eight engineering-geologic units based on 

lithology, induration or rock hardness, and the degree of 

parting developed along bedding planes. Although this 

compilation is generalized and restricted areally, it provides a useful grouping of the units for estimating shearwave velocities in the Los Angeles basin and in other 

areas where comparable geologic units are present. 

These engineering-geologic units are presented in table 

20, along with the velocity units from table 19 assigned 

to them and equivalent geologic units. 

PREPARING REGIONAL MAPS 

OF SHEAR-WAVE VELOCITY 

The correlations between shear-wave velocity, 

physical properties, and geologic units can be used to 

Shear-Wave Velocities of Near-Surface Materials 135 
TABLE 18.-Shear-wave velocities in mappable late Quaternary sedimentary units in the Los Angeles 

region 

Shear-wave velocity 

No. of Mean, Standard Range, 

Geologic unit velocity intervals in mls deviation in m/s 

Holocene 

Fine ------------------------------------------ 23 

~edium --------------------------------------- 38 

Coarse ---------------------------------------- 10 

Very coarse------------------------------------- 2 

200 

230 

320 

365 

20 

30 

25 

20 

15(}-270 

195-285 

29(}-355 

35(}-375 

Late and middle Pleistocene 

Fine ------------------------------------------ 18 305 50 20(}-360 

~edium: 

Los Angeles-Ventura -------------------------- 31 

San Fernando-Antelope Valleys ----------------- 26 

395 

470 

100 27(}-620 

115 31(}-740 

Total ----------------------------------- 57 430 115 27(}-740 

Coarse: 

Los Angeles-Ventura -------------------------- 7 

San Fernando-Antelope Valleys ----------------- 10 

550 

460 

85 45(}-680 

70 45(}-680 

Total ----------------------------------- 17 495 85 33(}-680 

Very coarse------------------------------------- 6 650 155 445-830 

construct maps of estimated mean velocity for use in 

predicting ground response. To illustrate the method, we 

have prepared maps for the upper Santa Ana River 

basin. As Joyner and others (1981) proposed, we calculated mean shear-wave velocities over depths equal to 

one-quarter wavelength of a 1-s shear wave. For the upper Santa Ana River basin, the corresponding depths 

range from 100 m for alluvium to 400 m for hard granitic 

rock. This method requires extrapolating the nearsurface data to these greater depths. Unfortunately, 

reliable shear-wave velocity measurements from deep 

boreholes are scarce. Seismic measurements obtained 

from two holes in central California (Warrick, 1974; 

Joyner and others, 1981) give values of 380 m/s for largely fine-grained Pleistocene alluvium and 630 m/s for 

interbedded medium- and coarse-grained Pleistocene 

alluvium over the depth interval of about 40 to 180 m. 

These values are comparable to those that we have obtained at 30 m and suggest that extrapolating the 

shallow data for alluvium to greater depths gives 

reasonable approximations. Increases in velocity with 

depth in fresh bedrock are largely controlled by the closing of cracks (Walsh and Brace, 1966). Actual shearwave velocities in these materials therefore may be 

somewhat greater than the assigned values if fractures 

close appreciably in the upper 400 m. 

The method that we use for mapping near-surface 

seismic velocity variations is shown schematically in 

figure 56, along with sample calculations that will be 

discussed in more detail later. Two types of geologic 

information are required: (1) a map showing the areal 

136 Earthquake Hazards in the Los Angeles Region 

extent of exposed geologic materials and (2) the distribution and thicknesses of concealed geologic materials 

as depicted on geologic cross sections and on maps 

showing the thickness of alluvial deposits (isopach 

maps). Mean shear-wave velocities are assigned to exposed geologic map units by comparing them with similar materials in the Los Angeles and San Francisco Bay 

regions (tables 18 and 19). The geologic map and subsurface data are used to compile a set of the distinct types 

of geologic profiles in the basin. Mean velocities are 

then calculated for each profile over a depth equal to 

one-quarter wavelength of a 1-s shear wave. Those profiles or groups of profiles that have significantly different mean velocities are then used to prepare a map of 

mean shear-wave velocity to a depth of one-quarter 

wavelength of a 1-s wave for the demonstration area. 

Descriptions of the exposed geologic materials in the 

upper Santa Ana River basin and a map of their areal 

distribution (scale 1:125,000) have been compiled by Cox 

and Morton (1978). Mean shear-wave velocities assigned to the mapped geologic units are presented in 

table 21, and a map of the units themselves is shown in 

figure 51. The Holocene units mapped in this basin are 

equivalent to those in the Los Angeles area, so their 

velocities are used directly. Very little information concerning the thickness or subsurface texture of mapped 

late and middle Pleistocene units is available at this 

time; therefore, the mean shear-wave velocity obtained 

for all late and middle Pleistocene sediments in the Los 

Angeles area (435 m/s) is assumed for these deposits. An 

estimate of mean shear-wave velocity in the bedrock 
SHEAR-WAVE VELOCITY, IN METERS PER SECOND 

Vl 

cc 

UJ 

fUJ 

::?: 

~ 

:r:-

fa._ 

UJ 

0 

5 

10 

15 

20 

25 

Hf 

--Hm 

500 600 

He Hvc 

----

Pf 

Pm 

Pc 

700 BOO 

HOLOCENE 

I Hf Fine 

Hm Medium 

He Coarse 

LATE PLEISTOCENE 

I Pf Fine 

Pm Medium 

Pc Coarse 

Pvc Very coarse 

Pvc 

FIGURE 52.-Shear-wave velocities for depth intervals determined from traveltime curves for Holocene and late and middle Pleistocene sedimentary units in the Los Angeles basin subarea defined according to age and texture. Means (solid circles) and standard deviations (bars) for each 

unit in the Los Angeles region are shown along the lower abscissa. Note that the very coarse grained Holocene unit was not sampled in the Los 

Angeles basin subarea. 

materials was made by determining from map descriptions which of the physical property units listed in table 

19 comprise each map unit. 

Thicknesses of Holocene sediments compiled from 

California Department of Transportation borehole logs 

and water-well drillers' logs show that these sediments 

are probably less than 15 rn thick across most of this 

basin (S. Carson and J. C. Matti, written communication, 

1983). We used an average value of 7 rn in calculating 

shear-wave velocities. Maps showing total thicknesses 

of late Quaternary alluvium at a scale of 1:125,000 and 

a contour interval of 100 ft are available for nearly all 

of the study area except a narrow strip north of the 

Cucamonga fault (California Department of Water Resources, 1970; California Division of Mines and Geology, 

1976). 

A set of distinct types of geologic profiles was cornpiled by using Cox and Morton's (1978) geologic map and 

subsurface data on thickness and distribution of concealed geologic materials. For areas where the 

Shear-Wave Velocities of Near-Surface Materials 137 
wC/J ii:it: Fine 

uz Medium ~::l 

C/JU 

i:U(3 

__10 Coarse a.._~ 

wo t-w Very :)<.9 coarse 

---- N -s 15 

Clay N > 15 

~ Silt loam a: 

w Sandy clay a.. 

0(/) 

g:t:: 

__~z 

---- N -s 30 

<(::l Sand u 

(/) '-...,_ 

N >30 >-

:r: 

a.. Gravelly 

sand 

and gravel 

Cobble to 

boulder 

gravel 

(/) Fine 

t- wz 

Z::l Medium 

w 

uu 

o-

__~<.9 Coarse 

oo 

:r:c) Very w 

(.9 coarse 

0 100 200 300 400 500 600 700 

SHEAR-WAVE VELOCITY, IN METERS PER SECOND 

FIGURE 53.-Relation between units defined on the basis of physical properties and Holocene and late and middle Pleistocene geologic units. Patterns are the same as those in figures 49 and 52. N is standard penetration resistance measured in blows per foot. The length of the box for 

each unit is equal to two standard deviations of the shear-wave velocity data for that unit. 

thickness of alluvium was greater than about 101 m, 

four profiles were constructed, each consisting of 7 m of 

one of the Holocene units overlying 94 m of late and middle Pleistocene deposits, plus one profile consisting entirely of late and middle Pleistocene sediments. For the 

other areas having alluvium at the surface, three or four 

profiles were constructed, one at each of the 10o-ft 

thickness contours, and so consisted of 7 m of one of the 

138 Earthquake Hazards in the Los Angeles Region 

Holocene units present in that portion of the study area 

overlying 84.5, 54, or 23.5 m of late and middle 

Pleistocene alluvium overlying the appropriate bedrock. 

Forty-seven distinct types of geologic profiles were identified in the upper Santa Ana River basin. 

Mean shear-wave velocities were calculated over a 

depth equal to one-quarter wavelength of a 1-s wave for 

each of these profiles (see fig. 56 for sample calculation). 

800 
SHEAR-WAVE VELOCITY, IN METERS PER SECOND 

EXPLANATION 

STRATIGRAPHIC ESTIMATED AGE 

UNIT (years B.P.) 

I Os 5,000-10,000 .. 

0 4 40,000-80,000 

0 3 100,000-150,000 

5 

10 -

.. 

0 2 250,000 (.{) 

a: 

LJJ 

1-

LJJ 

:2 

~ 15 

:C 

1-

Cl... 

LJJ 

0 

20 

25 

FIGURE 54.- Shear-wave velocities for depth intervals determined from traveltime curves for late Quaternary stratigraphic units in the Antelope Valley as mapped by Ponti and Burke (1980) and Ponti and others (1981). Approximate ages are assigned through correlation with a 

similar dated sequence in the San Joaquin Valley (D. Ponti, personal communication, 1982). 

For each profile, the thickness of each geologic unit was 

divided by the mean shear-wave velocity assigned to 

that unit to give a traveltime through that layer. These 

layer traveltimes were summed downward through the 

profile until a total traveltime of 0.25 s was reached. 

The total thickness transited was divided by 0.25 s to 

give the mean shear-wave velocity for that profile. 

Those profiles that had shear-wave velocities differing 

from each other by more than 7 percent were judged to 

be significantly different. We divided the 47 geologic 

profiles into 15 groups, each having a distinct mean 

shear-wave velocity. These groups of profiles were used 

to prepare the map of mean shear-wave velocity to a 

depth of one-quarter wavelength of a 1-s wave for the 

upper Santa Ana River basin shown in figure 58. 

For areas where the thickness of alluvium is less than 

about 100 m, the calculated mean shear-wave velocity 

changes rapidly depending on depth to bedrock. Velocity 

also changes laterally, to a lesser degree, along sediment thickness contours, being lower where the surface 

layer is composed of fine- or medium-grained Holocene 

alluvium. These rapid areal changes of velocity are difficult to present clearly on a small-scale map such as 

figure 57. For this reason, mean shear-wave velocity in 

these areas of thin alluvium is depicted on the map as 

contours of equal velocity by using values obtained from 

geologic profiles composed of late and middle Pleistocene sediment overlying bedrock. Where the surface 

layer is composed of fine- or medium-grained Holocene 

alluvium, the total profile thicknesses were adjusted 

(8-9 m thinner}, so that the calculated mean shear-wave 

velocities equaled those obtained for the late and middle 

Pleistocene sediment over bedrock profiles. For this 

reason, the contours depicted in figure 58 make slight 

incursions toward the bedrock areas where fine- or 

medium-grained alluvium is exposed at the surface. 

The general features of the method for mapping 

shear-wave velocity presented here are widely apShear-Wave Velocities of Near-Surface Materials 139 
SHEAR-WAVE VELOCITY, IN METERS PER SECOND 

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

or-~,~~--r-.-.-~-.--r-o--r-.--r-.--.-.-.,-~or~-o--r-o--r-.--r-~-r-.-.--r-.--.-.-. 

5 

10 

20 

25 

30 

~ IV ~ VI ~ 

ROCK TYPE HARDNESS FRACTURE SPACING 

~ Sandstone Soft Moderate and wider 

Shale Firm to soft Close 

II Bill Sandstone Hard to firm Moderate and wider 

Shale Firm to soft Close 

Igneous Firm to soft Close in hard 

with hard masses 

~ masses 

Ill Igneous } Hard to firm Close to moderate 

Sedimentary 

Igneous Firm to soft Close to moderate 

with hard in hard masses 

masses 

IV ITd Igneous , } Hard to firm Close to moderate 

sandstone 

v • Sandstone } Firm to hard Moderate and wider 

conglomerate 

VI D Sandstone Hard to firm Moderate and wider 

VII m Igneous Hard Close to moderate 

' and wider 

140 Earthquake Hazards in the Los Angeles Region 
TABLE 19.-Shear-wave velocities in pre-late Quaternary bedrock materials for the Los Angeles basin 

and San Francisco Bay region 

[Physical property units defined by using lithology, hardness, and fracture spacing as shown in fig. 55] 

Shear-wave velocity 

Physical property unit No. of samples 

Mean, 

in m/s 

Standard 

deviation 

Range, 

in rnls 

I --------------------------------- 19 

II -------------------------------- 19 

111--------------------------------21 

385 

550 

770 

45 

55 

70 

3()(}-455 

455-655 

67Q-900 

IV -------------------------------- 8 

v -------------------------------- 4 

VI-------------------------------- 5 

VII ------------------------------- 6 

945 

1,080 

1,265 

1,690 

50 87G-1,000 

35 1,03o-1,100 

45 1,21o-1,310 

130 1,50G-1,900 

plicable. The details of the procedure used for a particular area, however, are dependent on the quality of 

the available geologic data, especially subsurface data. 

In most areas, such as the upper Santa Ana River basin, 

the character of subsurface alluvium is poorly known. 

The geologic materials in these areas can be represented by a small number of representative geologic profiles. In the Los Angeles basin, the distribution and 

thicknesses of the subsurface sedimentary layers are 

better known. In this area, we calculated mean shearwave velocity at several hundred points along cross sections through the basin. A map of mean shear-wave 

velocity was constructed (Ziony and others, this volume) 

by contouring the values at these points. 

The map prepared for the upper Santa Ana River 

basin (fig. 58) shows striking contrasts between the 

velocities of the two predominant types of geologic 

materials exposed there (unconsolidated sedimentary 

deposits and hard granitic rocks). Because the sedimentary deposits are generally more than 100 m thick, the 

map shows that the lowest estimated velocities are 

relatively uniformly distributed over the valley floor, including most of the heavily urbanized areas. In sharp 

contrast, in those areas where the sedimentary deposits 

are less than 100 m thick, the shear-wave velocity increases very rapidly approaching the high velocities 

estimated for the hard granitic rocks. 

~ FIGURE 55.-Shear-wave velocities for depth intervals determined 

from traveltime curves in bedrock materials in the Los Angeles 

region. These materials are divided into groups according to fracture spacing, hardness, and lithology. Terms for fracture spacing 

and hardness are those proposed by Ellen and others (1972). For 

fracture spacing, very close is 0 to 1 em, close is 1 to 5 em, 

moderate is 5 to 30 em, wide is 30 to 100 em, and very wide is more 

than 100 em. Hardness is the response of the material to a geologic 

hammer. Hard indicates that the hammer bounces off with a solid 

sound; firm, the hammer dents with a thud, and the pick point 

dents or penetrates slightly; and soft, the pick point penetrates. 

Ranges of velocities for these units in the San Francisco Bay region 

are shown along the lower abscissa. 

SUMMARY 

Recently developed relations between mean shearwave velocity and strong-ground-motion parameters indicate that seismic velocity can be used to characterize 

local geologic conditions for predicting ground response 

from future earthquakes. In order to prepare maps of 

mean shear-wave velocity for this purpose, we established correlations between seismic velocity and other 

more readily obtainable physical properties of the geologic materials. These correlations can be applied to a 

particular area by using data concerning the areal 

distribution, physical properties, and thickness of the 

geologic units present to estimate and map shear-wave 

velocity. 

We analyzed seismic and geologic data from 84 sites 

in the Los Angeles region. These data suggest several 

useful correlations between shear-wave velocity and 

soil texture, standard penetration resistance, rock hardness, fracture spacing, and lithology. The late Quaternary sedimentary deposits are grouped into five categories on the basis of mean grain size: (1) clay and silty 

clay, (2) silt loam and sandy clay, (3) sand, (4) gravelly 

sand and gravel, and (5) cobble to boulder gravel. Shearwave velocity generally increases as mean grain size 

increases in these deposits. Standard penetration 

resistance, an indicator of consistency (clays) or relative 

density (sands), can be used to subdivide {1) clay and 

silty clay into medium to stiff (4 ::5 N ::515) and very stiff to 

hard (N> 15) categories and (2) sand into loose to medium 

(N ::5 30) and dense to very dense (N> 30) categories. For 

bedrock materials, shear-wave velocity increases as the 

hardness of the intact rock and the fracture spacing in 

the rock mass increase, the latter having the dominant 

effect. Lithology is important primarily for differentiating between hard sedimentary rocks and hard 

igneous rocks. These three physical properties were used 

to define seven categories of bedrock materials in the Los 

Shear-Wave Velocities of Near-Surface Materials 141 
TABLE 20.-Shear-wave velocity units assigned to the engineering-geologic units for bedrock materials in the Los 

Angeles basin 

Engineering-geologic unit' 

Bedrock 

velocity 

unit' 

Chiefly soft sedimentary rocks -----------------------------1 

Mixed soft and hard sedimentary ---------------------1 and II 

rocks with well-developed beddingplane parting. 

Mixed soft and hard sedimentary -----------------------II-V 

rocks lacking well-developed bedding-plane parting. 

Mixed soft to hard serpentinite ------~---------------II and III 

and related rocks. 

Mixed soft to hard volcanic and 

shallow intrusive rocks: 

Fragmental rocks -----------------------------II and III 

Flow rocks: 

Moderately weathered ---------------------------IV 

Fresh ----------------------------------------VII 

Chiefly hard sedimentary rocks ---------------------IV and V 

with well-developed bedding-plane parting. 

Chiefly hard sedimentary rocks ---------------------------VI 

without well-developed bedding-plane parting. 

1

From Wentworth and others (1970. table 1). 2

From table 19. 

142 Earthquake Hazards in the Los Angeles Region 

Equivalent geologic 

units 

San Pedro Formation 

Niguel Formation 

Fernando Formation 

Capistrano Formation 

Sycamore Canyon Member of Puente Formation 

Vaqueros, Sespe, and Santiago Formations in 

Santa Ana Mountains and San Joaquin Hills. 

Trabuco Formation in Santa Monica Mountains 

Modelo Formation 

Puente Formation, exclusive of Sycamore Canyon 

Member. 

Monterey Shale 

Upper Topanga Formation of Durrell (1954) 

Hollycrest Formation of Neuerburg (1953) 

San Onofre Breccia. 

Griffith and Cahuenga Beds of Neuerburg (1953) 

Sespe Formation in Santa Monica Mountains 

Silverado Formation 

Williams Formation 

Ladd Formation 

Trabuco Formaton in Santa Ana Mountains 

Topanga Formation in San Jose Hills and area 

southwest of Pasadena. 

Unnamed serpentinite and gneissic rock on Santa 

Catalina Island. 

El Modena Volcanics 

Glendora Volcanics 

Conejo Volcanics of Blackerby (1965) 

Middle Topanga Formation of Durrell (1954). 

Unnamed extrusive and intrusive rocks of Palos 

Verdes Hills, Santa Catalina Island, and San 

Joaquin Hills. 

Lower Topanga Formation of Durrell (1954) 

Topanga Formation in Santa Ana Mountains and 

San Joaquin Hills. 

Vaqueros Formation in western Santa Monica 

Mountains. 

Martinez Formation 

So-called Chico Formation of Santa Monica 

Mountains. 

Granitic rocks in Santa Monica and San Gabriel 

Mountains and in mountains northwest of 

Pasadena. 

Santa Monica Slate 

Bedford Canyon Formation 

Catalina Schist 

Schist (Franciscan?) in Palos Verdes Hills 

Metamorphic complex in San Gabriel Mountains 

and mountains northwest of Pasadena. 
USING 

Measured or 

assumed values 

of mean 

shear-wave 

velocity 

(Vs) 

ASSIGN V5 

to exposed 

geologic units 

Ohm, 230 m/s 

Qp, 435 m/s 

Mz, 1760 m/s 

Map of 

exposed 

geologic units 

CALCULATE Vs to a depth of 

'!. wavelength of a 1-s wave 

CONSTRUCT 

basic types of 

geologic profiles 

= 0.030 s 

plus 

for each profile by using 54 m + 435 m/s = 0.124 s 

assigned V5 for each 0.154 s 

component of profile 

Subsurface data 

on thickness 

and 

distribution of 

geologic units 

Qp 

61 m 

0.25 - 0.154 = 0.096 s 

DETERMINE which profile 

types are significantly 

different (differences in 

V5 are greater than 

7 percent) 

~ MAP distribution of 

distinct profile types 

(contours where 

alluvium is less than 

100m thick) 

169m = 1

1760 m/s 1 X 0.096 S 

230m 

I 

I 

I 

230m 

0.25 s 

I 

I 

I 

0.25 s 

= 920 m/s = Vs 

FIGURE 56.- Method used to construct a map of average shear-wave velocity to a depth of one-quarter wavelength of a 1-s wave. Calculations for 

a sample geologic profile are also shown. 

Shear-Wave Velocities of Near-Surface Materials 143 
0 2 4 6 8 10 MILES 

0 2 4 6 8 10 KILOMETERS 

FIGURE 57.-Assigned mean shear-wave velocities for geologic map units in the upper Santa Ana River basin. Values shown are based on correlation with similar materials in the Los Angeles basin. Geologic data were compiled by Cox and Morton (1978). 
GEOLOGIC UNIT 

Fine-grained Holocene alluvium 

Medium-grained Holocene alluvium, 

Eolian sand 

Coarse-grained Holocene alluvium 

Very coarse grained Holocene alluvium 

Late Pleistocene sediments 

Pliocene and Pleistocene nonmarine 

sediments, Puente Formation 

Potato Sandstone (Dibblee, 1964) 

Tertiary volcanic rocks 

Pre-Tertiary crystalline rocks 

with closely spaced fractures 

Pre-Tertiary crystalline rocks 

with widely spaced fractures 

ASSIGNED MEAN Vs 

(m/sec) 

210 

230 

320 

365 

435 

420 

550 

770 

1150 

1760 

Shear-Wave Velocities of Near-Surface Materials 145 
FIGURE 58.-Mean shear-wave velocity calculated over a depth of on&quarter wavelength of a 1-s shear wave for the upper Santa Ana Rh 

basin. 

146 Earthquake Hazards in the Los Angeles Region 
COMPUTED MEAN SHEAR-WAVE VELOCITY, m/sec 

AREAS OF BEDROCK 

OR ALLUVIUM 

> 100m THICK 

0 

I 

0 

I 

2 

2 

I 

410 

435 

550 

770 

1150 

1760 

I 

4 

I 

6 

4 

I 

AREAS OF ALLUVIUM < 100m THICK 

I 

8 

Peninsular 

Ranges 

640 

1010 

1380 

6 8 

I I I 

San Gabriel -

San Bernardino Mountains 

10 MILES 

I 

545 

745 

945 

10 KILOMETERS 

Shear-Wave Velocities of Near-Surface Materials 147 
TABLE 21.-Assigned shear-wave velocities of exposed geologic units in the upper Santa Ana River 

basin 

Assigned mean 

Bedrock shear-wave 

velocity velocity, 

Geologic map unit' unit' in m/s 

Holocene sediments' 

Very coarse grained alluvium --------------------------------------------- 365 

Coarse-grained alluvium ------------------------------------------------- 320 

Medium-grained alluvium ------------------------------------------------ 230 

Fine-grained alluvium --------------------------------------------------- 210 

Eolian sand -------,.---------------------------------------------------- 230 

Late and middle Pleistocene sediments• 

~~:;;~~:;:~n::~;~~vium} --------------------------------------------- 435 

Medium-grained alluvium 

Fine-grained alluvium 

Pliocene and Pleistocene nonmarine sediments 

San Timoteo Beds of Frick (1921) ---------------------------------- I and II 420 

Tertiary rocks 

Sedimentary rocks: 

Puente Formation ------------------------------------------

Potato Sandstone (Dibblee, 1964) -------------------------------

Volcanic rocks: 

Glendora Volcanics ----------------------------------------

(largely andesite breccias in map area). 

I and II 

II 

III 

Pre-Tertiary crystalline rocks with widely spaced fractures 

Granitic rocks: 1 

Relatively unweathered• ----------------------------------

Deeply weathered• 

VII 

Pre-Tertiary crystalline rocks with closely spaced fractures 

420 

550 

770 

1,760 

Granitic rock } 

Met~~;~:~: rocks: ----------------------------------------IV and VII 1,150 

1

From Cox and Morton (1978). 2

From table 19. 3Equivalent to Holocene map units of the Los Angeles basin. 4

Although these deposits show an apparent correlation between V and texture, age is probably more important for medium--grained to 

very coarse grained deposits. Since these deposits have not been subdivided according to age and since the texture in the subsurface is 

not well known, these deposits have been combined. 

"Probably comparable to the three hardest granitic sites in the San Gabriel-San Bernardino Mountains. 

"Thin ( < 5 m) layer of deeply weathered material over fresh rock. 

Angeles and San Francisco Bay regions having distinct 

shear-wave velocities. 

Geologic maps incorporating data on physical properties are becoming available for the Los Angeles region. 

Tinsley and Fumal (this volume) describe a mapping 

scheme that divides Holocene and late and middle Pleistocene alluvium into four textural categories, each 

having distinct shear-wave velocity characteristics. 

148 Earthquake Hazards in the Los Angeles Region 

Detailed studies in the Antelope Valley suggest that 

velocity increases with age in the late and middle Pleistocene alluvium. The distinct reddening of soils 

developed on deposits older than about 100,000 yr may 

be a useful criterion for estimating shear-wave velocity. 

Wentworth and others (1985) have provided detailed 

descriptions of hardness and fracture spacing for all 

mappable bedrock units in San Mateo. County (near San 
Francisco). A similar, although much more general, map 

compilation prepared for the Los Angeles basin by 

Wentworth and others (1970) is useful for determining 

which physical property group or groups comprise each 

mappable bedrock unit and thereby provides a basis for 

estimating shear-wave velocity for bedrock materials. 

Regional maps of mean shear-wave velocity can be 

constructed by using these correlations between shearwave velocity, physical properties, and geologic map 

units. Two types of geologic information are required: (1) 

a map showing the areal extent of exposed geologic 

materials and (2) subsurface data on the distribution 

and thicknesses of concealed geologic materials. Subsurface data are the more difficult to obtain; the quality 

of data available determines the procedure for estimating mean shear-wave velocity. In most areas, such 

as the upper Santa Ana River basin, the character of 

subsurface alluvium is poorly known. Estimated mean 

shear-wave velocity in these areas is largely dependent 

on the texture and age of the surficial deposits and the 

depth to bedrock. In the upper Santa Ana River basin, 

we have compiled a set of a small number (15) of representative geologic profiles having distinct mean 

shear-wave velocities. We have used these profiles to 

construct a map of shear-wave velocity to a depth of 

one-quarter wavelength of a 1-s wave. In the Los 

Angeles basin, more detailed geologic data are available. The subsurface sedimentary deposits there occur 

in alternating fine- and coarse-grained layers that are 

continuous over large areas of the basin. The distribution and thicknesses of these layers are relatively well 

known. In this area, we calculated mean shear-wave 

velocity at several hundred points along cross sections 

through the basin rather than for a few representative 

profiles. These points were contoured to provide a map 

of mean shear-wave velocity. Subsequent chapters of 

this volume Ooyner and Fumal, Ziony and others) illustrate how these maps of mean shear-wave velocity 

can be used to construct predictive maps of earthquake 

ground-motion parameters. 

Shear-Wave Velocities of Near-Surface Materials 149 
4 

40° 4 40° 

4 4 

5 4 

5 

55 

5 

5 

6 5 

38° 5 38° 

5 

150 Earthquake Hazards in the Los Angeles Region 
PREDICTING SEISMIC INTENSITIES 

By J. F. Evernden and J. M. Thomson 

INTRODUCTION 

J'he main purposes of this chapter are to describe the 

technique used to calculate seismic intensities for any 

postulated earthquake within any region of the conterminous United States, to show the strong correlation of 

certain parameters of strong-motion records with 

seismic intensities, and to demonstrate how the method 

of predicting intensities can be applied to answer important questions about the potential for strong ground 

shaking in the Los Angeles region. We also will apply 

known relations between intensity and percent loss for 

different structures to estimate future loss or replacement costs due to shaking from various postulated 

California earthquakes. 

Intensity is the only one of the several commonly used 

measures of ground shaking from earthquakes that correlates directly with damage to ordinary structures and 

can be accurately predicted for a postulated earthquake. Although many investigators in engineering 

seismology currently emphasize prediction of groundmotion quantities that can be instrumentally recorded 

(such as peak acceleration and peak velocity), we 

believe that seismic intensity is a more useful measure 

of shaking potential. For example, it is well known that 

peak acceleration shows a poor correlation with 

damage and risk. Blume (1981, p. 16) has stated: 

All too often, peak acceleration is misguidedly 

used as a direct measure of earthquake 

damage potential. It is convenient to discuss an 

earthquake that has just occurred in terms of 

its location, magnitude, and peak acceleration. 

But, as time goes on, magnitude and acceleration may no longer be so relevant. There is a 

vast gap between peak instrumental acceleration and the base shear coefficients used to 

design buildings .... They can be reconciled 

only if all the many factors related to the earthquake are considered ... .it follows that the 

spikes observed on records have little or no 

structural design significance .... We need to 

continue to record acceleration and to treat it 

as a valuable tool but to recognize that it is not 

a reliable index of damage potential. 

Possible reasons for this poor correlation are (1) weak 

correlation at best between peak acceleration and 

magnitude for large earthquakes because of saturation 

of recorded ground motion, (2) peak accelerations that 

often occur at frequencies outside the band of relevance 

to structural damage and intensities, and (3) inadequate 

correlation between peak acceleration and spectral 

energy distribution (see Hanks and McGuire (1981) for 

statements to the same effect). Available data suggest 

that, on the average, there is a correlation of timedomain peak acceleration versus frequency with intensity (Medvedev, 1962; Trifunac and Brady, 1975). 

Trifunac and Brady (1975) reported that scatter in the 

data of peak acceleration versus intensity is so great as 

to render the mean correlation useless for interpretive 

purposes. Finally, peak acceleration is devoid of any 

measure of signal persistence; thus, it would be surprising if such a parameter showed a satisfactory correlation with damage and thus with intensity. 

What is required for purposes of estimating future 

levels of earthquake shaking is a quantity that is both 

(1) clearly correlatable with damage and risk and (2) 

predictable. The earliest leaders in the field of earthquake microzonation recognized that the only truly 

useful and available quantity is intensity (Medvedev, 

1962, 1976; Richter, 1958, 1972; Friedman, 1969, 1975). 

They recognized and exploited the fact that the very 

definition of intensity units guarantees a correlation of 

shaking parameter (that is, intensity value) with damage 

or risk to structures of the type used in specifying the intensity units and thus establishes for this parameter the 

first of the two previously noted characteristics of a 

truly useful microzonation parameter. A recent quote 

(Smolka and Berz, 1981, p. 23) on the same theme is: 

Although intensity is subjective by nature and 

is by definition linked to the loss extent, it is the 

only measure available which takes into account such important damage factors as the 

spectral characteristics and the duration of 

earthquake ground motion in addition to its 

Predicting Seismic Intensities 151 
severity. Therefore, Mercalli intensity is still 

superior to all known objective quantities such 

as, e.g., instrumental intensity (Hausner intensity, Arias intensity) or spectral acceleration, 

which have failed up to now in reflecting the 

whole of important damage factors. 

A point not specifically addressed here but also of great 

importance is stated by Smolka and Berz (1981, p. 23): 

"The use of intensity permits the inclusion of historical 

earthquakes in the seismic risk analyses .... The seismic 

risk study for Switzerland shows in an exemplary 

fashion how historical data can be incorporated into a 

risk analysis." Lomnitz (1981, p. 34) has stated, "If peak 

horizontal acceleration is not necessarily an appropriate predictor of earthquake damage, is there a 

better parameter which answers to the requirements 

for this purpose? As we have suggested, such a 

parameter has existed for many years: it is the seismic 

intensity as measured on the Mercalli scale." 

None of these workers chose to place in the record the 

fact that intensities are predictable in a useful context; 

that is, it is possible, from the seismologically and 

geologically established parameters of an earthquake 

and region Oength of break and depth of focus of the 

earthquake, regional attenuation factor, groundcondition scaling), to predict observed patterns of intensities in different regions. We have attempted to fill this 

gap in documentation by publishing a series of papers 

(Evernden and others, 1973, 1981; Evernden, 1975b). 

Before discussing the predictive method and its applications, however, it is important that a somewhat confusing phenomenon be addressed and explained. All 

measures of ground motion relative to seismic intensity 

as usually defined saturate for high-magnitude earthquakes in California, saturation meaning that all of 

these parameters cease increasing as length of break 

exceeds 20 km or so. The chapter begins with an explanation of this phenomenon, and the several topics 

mentioned above then follow in order. 

Those who may wish to compare the predicted intensities of this volume or of a forthcoming series of USGS 

maps with those of other authors (Blume and others, 

1980; Davis and others, 1982a, b) should realize that the 

latter have based their analyses on maps of predicted 

intensity provided by the USGS. The differences between succeeding maps for the same postulated earthquake in the same region are an expression of improved 

estimates of seismic ground conditions, not of different 

modes of calculation. 

152 Earthquake Hazards in the Los Angeles Region 

WHY GROUND-MOTION 

PARAMETERS SATURATE AT 

HIGH MAGNITUDE 

The observational fact that maximum shaking intensities, local magnitude, and peak acceleration saturate 

(that is, cease increasing) at magnitudes above M 6.53 

has been well known for some years. Although efforts to 

correlate maximum intensity with magnitude have been 

made, they have all foundered on the observation that 

maximum shaking intensity for M 6.5 earthquakes in 

California is as large as it is for M 8.3 earthquakes. Inspection of any catalogue of intensity maps will illustrate this point. 

Hanks and Johnson (1976) pointed this out by study of 

seismograms, and Blume (1981, p. 15) stated it in an 

engineering context: 

If one studies the many structures that have 

been exposed over the years to nearby largemagnitude earthquakes, it becomes fairly 

clear that the amplitude of ground shaking 

during very large magnitude events does not 

increase much, if at all, over that during events 

of, say, M 61!2 or M 7. The shaking will last 

longer and, of course, will extend over much 

greater areas during the great events, but 

there seems to be some sort of limit, or saturation level, for local magnitude. 

It may be useful to stress that the frequency range of 

relevance in this saturation is frequencies of 0.3 Hz or 

so and higher (that is, all frequencies of relevance to intensities as usually defined). Hanks and McGuire (1981) 

limited the range of applicability of their statistical relation between peak acceleration and magnitude to 

magnitudes of M 6.5 or less because of the saturation effects at higher magnitudes. The work of Joyner and 

Boore (1981) agrees as to the absence of any useful correlation of peak acceleration and magnitude at higher 

magnitudes. Joyner and Boore did report a best-fit leastsquares correlation of magnitude and peak horizontal 

acceleration, but this correlation is such that the eightyfourth percentile of the M 6.5 distribution is equal to the 

fiftieth percentile of the M 7.5 distribution. Factors 

other than magnitude must more significantly influence 

observed near-field values of acceleration. The later 

•See appendix 2 for definition of M as used in this chapter. 
~ 103 

a: 

w 

:I: 

a: 

w .. ll.. ...... C/) 

... , 

',UR= 0.3 z 

0 ' a: ' 10' ' Sd ' ~ ' ' ' 

z /', 

UR = 0.3 ', 

t-= ' z ' w ' \ 

~ \ 

w \ 

u \ 

~ 10 \ 

\ 

ll.. \ C/) \ 

Ci I 

I 

....J I <( I 

a: e = 5 x 10' I 1- R0 = 1 km \ u \ w Vp = 6.1 km/s \ ll.. I C/) Vs = 3.5 km/s 

Azimuth 30° 

Takeoff angle 30° 

Distance 20 km 

------ p 

SH 

0.1 

0.1 10 100 

FREQUENCY, IN HERTZ 

FIGURE 59.- Theoretically predicted spectra of compressional (P) and 

shear (SH) waves versus rupture velocity for a 2-km fault rupture 

(distance of 20 km) (Minster, 1973). Rupture velocity (in kilometers 

per second) indicated by U R" 

discussion of the record obtained at Pacoima Dam for 

the 1971 San Fernando earthquake is an example of this 

relation. 

The failure of local magnitude to significantly increase as the length of break of California earthquakes 

exceeds 20 km or so is just another expression of the 

phenomenon of saturation of ground-motion parameters 

for high-magnitude earthquakes in California. 

Understanding the reasons for this saturation is vital 

for interpreting observed seismograms and predicting 

expected levels of ground motion. Therefore, a somewhat elaborate explanation of the phenomenon will be 

included. Although the explanation could be presented 

in a variety of ways, the route chosen is the physical 

model of the earthquake source expressed in relaxation 

theory, because it is capable of predicting all spectral 

values and because it makes all the necessary assumptions within a physical description of the earthquake 

process. Although rupture velocity is an assumed 

parameter in each prediction, the correctness of the 

value chosen when studying any specific seismogram 

can be checked by spectral examination of the 

seismogram. 

Saturation of compressional wave spectra of earthquakes has been recognized for some time (Evernden, 

1975a) and is a phenomenon explained by models of an 

earthquake based upon a relaxation source (Evernden 

and Archambeau, in press, in preparation). However, 

the waves causing major damage and those generally 

analyzed by strong-motion seismograms are horizontal 

shear waves rather than compressional waves. For such 

waves, relaxation theory (Archambeau, 1968; Archambeau and Minster, 1978; Minster, 1973; Evernden and 

Archambeau, in press, in preparation) predicts a flat 

long-period displacement source spectrum and two corner frequencies that scale with the ratio of rupture 

velocity to length of break. The amplitudes of frequencies between the two corner frequencies are inversely 

proportional to the square of the frequency (f-2

) if the 

rupture velocity approaches the shear-wave velocity, 

and the amplitudes of frequencies higher than the second corner frequency scale inversely as the cube of the 

frequency (f- 3). Source spectral relationships versus 

rupture velocity as predicted by relaxation theory are 

shown in figure 59 (Minster, 1973). Note the dependence 

of spectral shape on rupture velocity. Figure 60 indicates how these spectra are predicted to scale with 

size of an earthquake, for an assumed rupture velocity 

of 0.95 Vs. For ease of drawing, all roundings of corners 

predicted on figure 59 are ignored on figure 60. Since 

figure 60 is intended to be illustrative of general relations, amplitudes are expressed in terms of logarithms 

of seismic moment M0 , so that readers can see the implied relations of spectral corner frequencies and spectral falloff as a function of event size for California 

earthquakes. The relation developed by Evernden and 

others (1981) (log M0 = 23.04 + 1.91 log (length of break)) 

can be used to relate moment M0 to rupture length and 

thus to magnitude for southern California earthquakes. 

The loci of both corner frequencies in figure 60 (left and 

right) are lines having slopes of f- 3, their exact locations 

depending on stress drop and rupture velocity. All 

amplitudes scale linearly with stress drop, figure 60 being intended to model stress drops of about 75 bars. It is 

important to note that the locus of points for the righthand corner frequency is the asymptote for all highPredicting Seismic Intensities 153 
28 

27 

26 

25 

i= 

z 

w 

~ 24 

0 

~ 

u 23 ~ 

~ w 

~ 22 

(!) 

0 

..J 

Loci of corner 

frequencies 

R = Rupture velocity 

Length of break 

f -' slope 

frequency>> R 

0.001 O.D1 0.1 1.0 10 100 1000 

FREQUENCY, IN HERTZ 

FIGURE 60.- Theoretically predicted horizontal shear-wave source 

spectra for earthquakes (relaxation model, rupture velocity 

UR=0.95 V5 ). 

frequency amplitudes; that is, the source spectral curve 

beyond the right-hand corner frequency is common for 

all earthquakes. 

To understand the physical bases for the predicted 

relations in figures 59 and 60, it is helpful to consider 

the correlative values of frequency, R (the ratio of rupture velocity and length of break), and spectral 

behavior. For frequencies distinctly less than R (see fig. 

60) or, equivalently, for wavelengths long relative to 

length of break, the earthquake is effectively modeled as 

a point source, all movement at the fault taking place in 

a small fraction of all relevant periods. The result is a 

flat amplitude versus frequency relation. At frequencies 

distinctly greater than R or, equivalently, for wavelengths small relative to length of break, the potential 

radiation at each point of the fault at such frequencies is 

complete. One can think in terms of the fault's appearing infinitely long at such short wavelengths (that is, 

long enough that energy radiation at a point is no longer 

influenced by length of the fault). The result is that 

amplitudes at such frequencies will be the same for all 

earthquakes having lengths of break sufficiently large 

154 Earthquake Hazards in the Los Angeles Region 

(that is, saturation of amplitudes), and a plot of 

amplitude versus frequency for a given earthquake will 

follow a f-3 relationship. At frequencies between the 

above two extremes, the amplitude versus frequency 

relationship steepens in some manner from being flat to 

having a f-3 slope. For shear waves and for a rupture 

velocity about 0.95 times the shear-wave velocity in the 

rocks surrounding the fault, the slope of the amplitude 

versus frequency is predicted to follow a f- 2 relation for 

about an order of magnitude increase in frequency as 

shown in figure 60. If the rupture velocity were actually 

to reach the shear-wave velocity (V J, the f-2 slope would 

be maintained to infinite frequencies. Note that, on the 

f-2 leg of the spectral curve, amplitudes increase by only 

a factor of three for a tenfold increase in amplitude at 

low frequencies. As noted above, the sharp corners of 

the spectral curves in figure 60 are artificial (see fig. 

59), as the three conditions discussed above are gradational in their applicability. As regards observations at 

some distance from the source, a variety of factors 

associated with propagation and interference effects 

will lead to further rounding of the predicted corners 

and to irregularity in details of the observed spectra. 

Do these theoretical predictions agree with observations? Tucker and Brune (1973) have published shearwave displacement spectra for many of the small aftershocks of the 1971 San Fernando earthquake. They 

found that long-period spectra were indeed flat and that 

the rate of high-frequency falloff to the right of the lefthand corner frequency of figure 60 did indeed tend to 

follow an f- 2 relationship, establishing that the rupture 

velocity of most of these small earthquakes did approach the shear-wave velocity of the rocks around the 

failure zone. Tucker and Brune paired observational 

data of level of long-period shear-wave spectrum (which 

scales with seismic moment for a fixed stress drop) and 

corner frequency. Their data for two different ranges of 

stress drop are shown in figure 61. The predictions of 

relaxation theory agree with their observations. 

For large earthquakes in California, effectively total 

release of all 1- to 2-s energy at the center of the break 

after fault lengths exceed 20 km or so means that peak 

value of acceleration at frequencies relevant to intensities, as well as local magnitude and intensity, will not 

increase as the length of break increases further. Total 

energy radiated in the bandpass will increase with increasing length of break, but energy density at these frequencies will not increase. Therefore, near-field values 

of ground motion should not increase as length of break 

exceeds 20 km or so, except for the fortuitous location of 

a recording instrument near a shallow asperity or 

strong point on the fault or fortuitous aspects of instrument siting. For large earthquakes in California, factors 

such as ground condition, heterogeneity of source and 
propagation path, and so on can influence near-field 

amplitudes much more than "magnitude" of the event 

can. 

If the spectra in figure 60 are replotted in the format 

in common use in earthquake engineering, figure 62 is 

obtained. If the roundings of figure 59 were included, a 

zone of nearly uniform velocity versus frequency would 

exist. The important fact illustrated by this figure is that 

spectral curves versus magnitude (as indicated by seismic moment) do not scale vertically on such a plot. Highfrequency accelerations saturate. Figure 62 shows 

clearly that peak accelerations at damage-relevant 

frequencies do not continue to increase for large 

earthquakes. 

To further clarify the character of strong-motion 

seismograms and resultant implications for correlation 

with intensity, one horizontal component of the strongmotion records of the 1971 San Fernando earthquake as 

recorded at Pacoima Dam is analyzed in two different 

ways: bandpassed seismograms and quasi-harmonic decomposition of the seismogram into a set of undispersed 

(that is, body-wave) arrivals. Figure 63 presents an example of the first technique as applied to the S. 16° E. 

horizontal-motion strong-motion record obtained at 

Pacoima Dam for the 1971 San Fernando earthquake. A 

set of such filtered traces provides a very clear picture 

of the frequency versus time structure of the seismogram. For simplicity, figure 63 presents the original 

seismogram and filtered seismograms for the three 

bandwidths from 0.1 to 1, 1 to 10, and 10 to 20 Hz only. 

Peak acceleration values for each trace are indicated in 

the figure. Peak accelerations at frequencies less than 1 

Hz are associated with the beginning of the seismogram 

and thus probably with the initial deep rupturing of the 

San Fernando fault. The high frequencies associated 

with this deep rupturing apparently have been lost 

already owing to scattering or attenuation (or else they 

never existed, perhaps implying low initial rupture 

velocity). The peak accelerations occurred approximately 8 s after initial motion, too late to be an aspect of the 

main rupturing. 

The second technique (quasi-harmonic decomposition) 

allows an even better look at the pattern of energy 

release for this earthquake. Figure 64 illustrates the 

decomposition of the same seismogram used in the 

analysis above. The technique consists of analyzing the 

seismogram in terms of coherent, undispersed, reasonably broad band arrivals, the shape of the arrivals 

within the time domain being dictated by the results of 

decomposition and comparison of the resultant suite of 

narrow-band seismograms, not by an ad hoc assumption 

of arrival shape. The program does require specification of the minimum number of narrow-band filtered 

seismograms on which an arrival at a common time ap23 .-----------.------------.-----------, 

i= 

z 

22 

~ 21 

0 

~ 

u 

~ 

~ 

UJ 

~ 

(!) 20 

0 

....1 

19 

18 L----------- ------------L------------" 

1 10 

FREQUENCY, IN HERTZ 

FIGURE 61.-Theoretically predicted horizontal shear-wave spectra 

(solid lines) for earthquakes (relaxation model) and observed spectral data (solid circles) for aftershocks of the 1971 San Fernando 

earthquake [rucker and Brune, 1973.) Spectra are shown both 

idealized (with sharp corner frequencies) and actual (with smooth 

curves connecting straight-line segments). Dashed lines indicate 

different values of stress drop. 

pears. If this minimum number is reached, the data for 

this time interval are processed for definition of an arrival. Complete description of the technique will not be 

attempted here, since such an elaboration is in the process of being published by C. B. Archambeau. The first 

trace on figure 64 is the original seismogram, the third 

through thirty-third traces are the individual arrivals 

defined by decomposition, and the second trace is the 

reconstituted seismogram based on summing of the 31 

traces below. The complete failure to reproduce the 

longer periods at the beginning of the seismogram 

results from the narrow-band character of that part of 

the record. All of the later high-frequency portion of the 

seismogram appears to be a series of individual pulses 

Predicting Seismic Intensities 155 
i= 

z 

w 

~ 

0 

~ 

u 

~ 

S!? 

w 

~ 

(.!) 

0 

..J 

29 

28 

27 

0.01 0.1 

FREQUENCY, IN HERTZ 

1.0 

FIGURE 62.- Theoretical spectra of figure 60 replotted in the format 

generally used in earthquake engineering. 

or spikes of very similar shape, not a coherent continuous signal. The marked grouping in time of the 

stronger pulses suggests a limited source volume, while 

their character of high-frequency spikes suggests an 

origin near the seismometer. This analysis suggests that 

the value of peak acceleration on a near-source strongmotion record is largely a matter of pure chance. This 

value is critically controlled by the fortuitous disposition 

of seismometers and strong spots at shallow depth on 

the fault surface. It may have very little to do with the 

magnitude of the earthquake, whereas the ground motion at lower frequencies is more closely linked to the 

magnitude of the earthquake. Attempts to synthesize the 

high-frequency part of the spectrum after the event 

must be somewhat arbitrary, as there will never be 

enough seismometers to yield a unique interpretation of 

structure of the fault surface. 

If one desires or is compelled by seismic design 

regulations to continue using quantities such as peak acceleration, it might be advisable to consider maximum 

acceleration in a set of narrow-band spectral windows 

rather than peak acceleration from the entire seismogram, assuming that such a suite of values can be shown 

to have some useful correlation with damage or risk for 

particular types of structures. This point will be investigated later. 

156 Earthquake Hazards in the Los Angeles Region 

METHOD FOR PREDICTING 

SEISMIC INTENSITIES 

A computer-based procedure for calculating intensity 

patterns for specified earthquakes has been developed 

(Evernden and others, 1973, 1981; Evernden, 1975b). 

The procedure has been tested by extensively comparing predicted and observed patterns of intensity for 

numerous historical earthquakes throughout the conterminous United States and eastern Asia. As noted 

earlier, this computer program has been used by both 

State and Federal agencies to estimate, for emergency 

preparedness planning, the likely levels of shaking intensity for various potential earthquakes. For example, 

intensities have been predicted for possible earthquakes 

affecting major California population centers (U.S. Geological Survey, 1981). 

A brief summary and flow diagram (fig. 65) of the procedures of calculation are presented here (see app. 2 for 

mathematical details). The ingredients of the intensity 

modeling technique are (1) a law expressing the rate of 

attenuation of intensity-related seismic waves in the 

region to be investigated; (2) a correlation of geologic 

ground condition and expected relative intensity (saturated alluvium is used as a reference ground condition); 

(3) a map giving the distribution of the several defined 

seismic ground conditions throughout the region to be investigated; and (4) a mathematical model of the earthquake source (including location, length of break, and 

depth of focus), plus a scheme of calculation that conceptually radiates energy from each segment of the 

fault, attenuates each such increment according to element 1, calculates a quantity intended to simulate the 

root-mean-square (RMS) acceleration over a time window of 10 to 20 s (matter of choice) centered on the 

strongest arrival (that is, from nearest point on fault), 

converts this RMS acceleration into a predicted intensity on saturated alluvium, and then, by using the data 

from elements 2 and 3, calculates the predicted intensity 

for the site ground condition. The present computer program can provide either Rossi-Forel or Modified Mercalli intensities. A description of the Modified Mercalli 

scale, with Rossi-Forel equivalents, is presented on the inside back cover of this volume. 

An attenuation map of the region under consideration 

is an essential first step toward predicting intensities 

successfully. Figure 66, a first attempt at such a map for 

the conterminous United States, is based on study of the 

intensity patterns of earthquakes throughout the country. The second step is to correlate length of break, 
Maximum value = 1.1715 g SEISMOGRAM 

Maximum value=0.2791 g 0.1-1Hz 

Maximum value=0.9231 g 1-10Hz 

Maximum value=0.2003 g 1Q-20 Hz 

TIME, IN SECONDS 

FIGURE 63.-Strong-motion seismogram recorded at Pacoima Dam for the San Fernando earthquake of February 9, 1971. S. 16° E. component. The 

upper curve is the original accelerogram. Lower curves are filtered versions of the upper accelerogram, the band of frequencies used for each 

curve being indicated on the figure. 

Predicting Seismic Intensities 157 
~ ~ 

~ 

--v 

A 

11 

l 

A. "-! 

J~/L Ill.. 

IJ 

TIME, IN SECONDS 

FIGURE 64.-Quasi-harmonic decomposition of the S. 16° E. component of the Pacoima Dam record from the 1971 San Fernando 

earthquake (see fig. 63). 

depth of focus, and intensity pattern on saturated 

alluvium in each of the different regions defined by the 

attenuation parameter. All the details of the procedures 

and data required to construct figure 66 and to achieve 

the above correlation have been presented by Evernden 

(1975b) and Evernden and others (1981) and are not 

repeated here. Note that we do not say "correlate 

magnitude and intensity pattern." Ongoing seismologic 

research ultimately may establish such a correlation on 

a regional basis. However, many current users of "magnitude" have an erroneous concept in mind. Properly 

used, magnitude is a scale of the relative sizes of earthquakes by certain very specific measurements recorded 

on a very specific instrument within a region of uniform 

attenuation characteristics. By using careful calibration 

procedures and definitions, events of "equivalent" 

magnitude can be defined in different regions but only 

after such careful calibration and after somewhat arbitrary assertion of the definition of "equivalence." For 

Ms and mb, two routinely used magnitude 

measurements based on long-range observations, such 

calibration and definition are possible by largely accepted procedures. Consistent interregional definition of 

"local" magnitudes, however, has not been achieved, so 

little detailed meaning can be attached to many such 

values today for areas where attenuation is different 

from that in southern and western California, particularly when the formula developed by Richter for ap158 Earthquake Hazards in the Los Angeles Region 

plication to earthquakes in southern California (a region 

of very high attenuation) is used indiscriminately in 

regions having different attenuation characteristics. 

The extent of interpretive error and confusion that can 

so result has been suggested by Evernden and others 

(1981). Correct procedures using conventional seismologic data are available for solving this problem, but 

they are laborious and time consuming and have not 

been applied throughout the United States. A procedure 

applicable in all regions for defining local magnitude by 

means of intensity data has been described by Evernden 

and others (1981) and used by Evernden (1983). 

The third step required is correlation of geologic 

ground condition with seismic ground condition (expected intensity relative to saturated alluvium). Two 

procedures are used. We followed Borcherdt (1970) in 

achieving intercalibration by means of the relative 

amplitudes of seismic waves recorded at sites on 

various rock and sediment types in the San Francisco 

Bay region. Because Borchardt's data were not correlated with depth to water table, we followed 

Medvedev (1962) in decreasing the predicted intensity 

by one unit if the water table was at a depth of 10 m or 

more in Quaternary alluvium. No adjustment is made for 

depth to water table in any other materials. 

This empirically developed scale for geologic units in 

the San Francisco Bay area was extended to all units on 

the 1:250,000-scale map sheets of the Geologic Atlas of 

California (California Division of Mines and Geology 

[1958-1969]) on the basis of similarity of relevant rock 

properties, the resultant correlations being given in 

table 22. Expected relative intensities of the seismic 

ground-condition units in table 22 are given in table 23. 

The fact that these modes of calibration of relative 

intensities achieved an excellent correlation with observations confirmed the much earlier demonstration by 

Medvedev {1962) that differences in intensity on ground 

of various types are directly linked to measurable, quantitative aspects of the several rock or sediment types. 

Because intensities on all rock or sediment types (even 

the highest shaking intensities) can be explained by 

linear scaling from relative amplitudes of low-amplitude 

waves (Evernden and others, 1973), it is established that 

high shaking intensities are primarily an aspect of 

elastic response, not of inelasticity or other aspects of 

ground failure. Of course, if amplitudes become too high 

in water-saturated cohesionless sand or silt (Tinsley and 

others, this volume), the ground may liquefy and fail, 

and nonshaking aspects of damage may result. Shaking 

damage, however, is predictable by a model based on 

scaling by means of low-amplitude elastic behavior of all 

rock and sediment types. 

Given the above correlations, the final requirement is 

a theoretical model of the earthquake source. A detailed 
I Select grid dimensions for study area }- I 

_ Length of rupture 

Specify earthquake Define regional 

r- Depth of focus attenuation source parameters factor 

Location of end 

points of rupture 

Compute energy released 

from rupture 

Determine ground 

f---' 111 conditions for 

each grid point 

Assign relative 

intensity increments 

"' 

Geologic 

unit 

Depth to 

water table 

Compute RMS acceleration over a 10-to 20-s 

time window for each grid point 

t 

~~ Compute local intensity for 

standard ground conditions 

at each grid point 

Integrate predicted intensity with relativ,e 

intensity increment for each grid poin' 

Convert computer output to desired format 

and print map of study area 

FIGURE 65.-Flow chart for predicting seismic intensity values for a specified earthquake in a given region. 

description of the model used has been given by Evernden and others (1981) and is repeated in a condensed 

version in appendix 2. Only one point need be stressed 

here. The model as now implemented calculates essentially RMS acceleration over a time interval of potentially 20 s, including arrivals as much as 10 s before the arrival from the nearest point of the fault break to arrivals 

as much as 10 s after that arrival. The intent of this procedure is to build signal persistence into the calculation 

of intensity. The original calculation is for saturated 

alluvium. The last step in the program is to make the correction for the actual seismic ground condition at the 

site by using data described above. 

Given all of these parameterized and modeled factors, 

accurate predictions are possible. Evernden and others 

(1981) and Evernden (1982) have presented samples of 

Predicting Seismic Intensities 159 
FIGURE 66.-Generalized attenuation map for the conterminous United States expressed in values of k (k is 

defined in app. 2.) 

observed and predicted intensities for numerous earthquakes, so none will be given here. The discussions in 

those papers indicate that intensity fulfills the second 

required characteristic of a useful microzonation 

parameter; that is, it is predictable in a detailed and 

useful manner. 

A major difficulty in using predicted intensity maps in 

the future is the current tendency of those who make 

and use intensity maps to ignore one of the critical 

facets of the definitions of intensity units-the fact that 

these definitions are related to very particular types of 

structures. Today, changes in construction practice 

commonly are ignored in assigning intensities. When 

definitions based on pre-1940 construction are applied 

to post-1940 construction, confusion in understanding 

and interpretation results (see later discussion of San 

Fernando, Coyote Lake, and Imperial Valley earthquakes). Unless this practice ceases, it is certain that interpretation of future published intensity maps and their 

prediction will become impossible. If intensity prediction is to remain useful, it will be essential to apply old 

definitions rigorously and to generate all auxiliary and 

corollary definitions required to achieve uniform 

estimates of intensity in spite of variations in building 

types and modes of construction. As an effective example of such calibration, the current definitions of 

160 Earthquake Hazards in the Los Angeles Region 

Modified Mercalli intensities used in the People's 

Republic of China are in terms of Chinese structures, 

these definitions having been established only after 

careful analysis and comparison. It was only because of 

this effort by the Chinese that the analysis reported by 

Evernden (1983) was successful. 

CORRELATING INTENSITY WITH 

STRONG-MOTION PARAMETERS 

Previous Studies 

Several investigations of correlations between intensities and acceleration data derived from strong-motion 

seismograms have been published, one of the first having been Medvedev's (1962) (see fig. 67). His technique 

was to measure frequency versus acceleration directly 

from analog records of U.S. strong-motion seismograms 

and to plot maximum acceleration at various periods 

versus intensity as interpreted from "U.S. 

Earthquakes," an annual publication of the U.S. Coast 

and Geodetic Survey (USCGS), now the National Ocean 

Survey. These procedures were the best available at the 

time, and the plotted data in figure 67 indicate the cor-
TABLE 22.-Correlation of geologic units on 1:250,000-scale geologic map of California with groundcondition units for California 

Geologic map 

units 1 

Ground-condition 

unit 

Granitic and metamorphic rocks ----------------------------------------------- A 

(Kjfv, gr, bi, ub, JT RV' m, mV, PpV, PmV, 

Cv, Dv, pS, pSv, pCc, PCgr, pC, epC, Tl) 

Paleozoic sedimentary rocks -------------------------------------------------- B 

(Ms, PP, Pm, C, CP, CM, D, S, pSs, 0, E) 

Early Mesozoic sedimentary rocks---------------------------------------------- C 

(Jk, Ju, JmE, Tr, Kjf) 

Cretaceous through Eocene sedimentary rocks ------------------------------------ D 

(Ec, E, Epc, Ep, K, Ku, KE) 

Undivided Tertiary sedimentary rocks ------------------------------------------- E 

(QTc, Tc, TE, Tm) 

Oligocene through middle Pliocene sedimentary rocks ------------------------------ F, 

(PmEc, PmE, Me, Muc, Mu, Mmc, Mm, ME, de, d) 

"Pliocene-Pleistocene" sedimentary rocks ---------------------------------------- G 

(Qc, OP, Pc, Puc, Pu) 

Tertiary volcanic rocks ------------------------------------------------------ H 

(Pv, Mv, Olv, Ev, QTv, Tv) 

Quaternary volcanic rocks ---------------------------------------------------- I 

(Qrv,Qpv) 

Quaternary sedimentary deposits ---------------------------------------------- J 

(Qs, QaE, Qsc, Of, Qb, Qst, QE, Qq, Qt, Qm) 

1

From California Division of Mines and Geology [1958-1969]. 

TABLE 23.-Relative expected intensity for ground-i:ondition units 

Ground-condition 

unit 

Relative intensity 

compared to 

saturated alluvium Ul 

read from the published intensity maps of the earthquakes, found a quite poor correlation. A few comments 

on their procedures, as regards both use of peak acceleration and use of intensities directly read from the 

published map of Scott (1973) for the 1971 San Fernando 

Derived from geologic map of California': earthquake, seem necessary in order to make clear why 

A ------------------------------------------- - 3·

00 we used somewhat different procedures in the analysis B ------------------------------------------- -2.60 

c ------------------------------------------- _ 2_20 that follows. Peak accelerations are often at frequencies 

D ----==:..-:.:.==-.=--_-:..··::::.:-_-::=-.:--==:.::.::..:.=:::.-::.:...--::-::-_-·=Lao- -that-are-outside-the-band-relevant-to-intensity-deter--- . -- ---- _ 

E ------------------------------------------- -1.70 minations. Peak accelerations (or peak velocities) from 

F ------------------------------------------- -1.50 records filtered to include only the range of frequencies 

G ------------------------------------------- - l.OO relevant to intensities should show better correlation 

H ------------------------------------------ -2.70 

r ------------------------------------------- _ 2_70 with intensities. Because a major factor in observed inJ (saturated alluvium) --------------------------- .oo tensities is almost certainly the length of time over 

Alluvial units based on depth 

in feet to water table: 

J2 ------------------------------------------- 0.00 

L3 ------------------------------------------ -1.00 

M•------------------------------------------ -1.50 

1From California Division of Mines and Geology J1958--1969). 2

o fl<water tahle<30 ft. 3

30 ft<water table<100 ft. 1100 ft <water table. 

relation achieved. Trifunac and Brady (1975), using 

peak acceleration data without regard to frequency 

from the strong-motion records of the 1971 San Fernando earthquake and other earthquakes and intensities 

which amplitudes of relevant frequencies persisted at 

significant amplitude, an even better correlation might 

be achieved by comparing intensity and a parameter 

related to signal amplitude over a relevant period of 

time. Such parameters will be defined and investigated 

below. A few comments on the appropriate intensity 

values to use are required. Trifunac and Brady (1975) 

simply read values according to latitude and longitude 

from Scott's (1973) map for the 1971 San Fernando 

earthquake. However, as discussed elsewhere (Evernden, 1975b), maps such as Scott's have the major flaw of 

nearly all intensity maps. They accentuate the highest 

intensities in a region but totally ignore the lower intensities. Thus, the hard rock terranes in the general vicinity of the 1971 San Fernando earthquake are simply not 

Predicting Seismic Intensities 161 
0.40g -----------.... .......... T 6. 6. 

- EXPLANATION 

0.30 .......... 0) INTENSITY: 6. 

~ 0.25 6. 6. 8 

1 0.20 lf5f'Ci • 7 0.18 

6.. 

6. 

0 0 .16 6 co 0.14 6.. ~ 5 1 0.12 6.~ >- 0.1g t-- t 0.0 0 

c:n 0.08 Ol •• 0 0 

2 ,..... LU 0.07 z 1 t-- 0.06 

~ 0.05 z 

t 0 

0.04 i= <0 <t: 

l 0.03 a: 

LU 

....1 

0.025 LU t u 0.02 u 1.0 O.D18 <t: 

1 0.016 

0.014 

0.012 

0.01 

0.009 

0.008 

0.007 

0.006 

0.005 

0.004 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 

PERIOD, IN SECONDS ~ 

FIGURE 67.-Acceleration data at different periods in comparison with Modified Mercalli intensity (from Medvedev, 1962, fig. 4.12). Heavy lines 

divide diagram into several fields where points representing a particular intensity predominate. 

observable from Scott's map-not because high intensities were observed at such sites but rather because 

the lack of damage reports led to blank areas that were 

later encompassed in the surrounding alluvial areas. 

Analysis of Data from the 1971 San 

Fernando Earthquake 

Table 24 presents the "observed" and predicted intensities determined by us for strong-motion sites on 

alluvium for the 1971 San Fernando earthquake; sites on 

"thin alluvium" are not included, as we were unsure 

about the meaning of such statements as regards the appropriate corrections from saturated alluvium. The 

definition and source of the "observed" intensities 

should be understood clearly. The values used are derived as follows: 

1. Assume that Scott's (1973) isoseismal map for the 

San Fernando earthquake effectively contours intensity on saturated alluvium (see earlier comment on general prevalence of this practice), as 

regions of shallow ground water are scattered 

throughout the area. 

2. Interpret Scott's intensity boundaries as being at 

half-magnitude points; that is, the boundary between VI and Vis interpreted as 5.5. 

162 Earthquake Hazards in the Los Angeles Region 

3. Read intensities from Scott's map to one-tenth intensity unit. 

4. Decrease values from Scott's map for depth to water 

table (WT), using data of Maley and Cloud (1973) 

or data supplied by J. C. Tinsley (0.0 adjustment if 

WT < 20 ft, - 0.5 if 20 :=:; WT < 30 ft, - 1.0 if WT ~ 30 

ft). 

These intensity values will be markedly different from 

those used by Trifunac and Brady (1975). As the predicted values are also corrected for depth to water 

table, the agreement of ob.served and predicted values 

in table 24 is an indication of the agreement of predicted 

and observed intensities on saturated alluvium; that is, 

values and rate of dieoff are as predicted in our model. 

The incorporation of depth of water table was not essential for table 24 other than to point up the occasional site 

that needs further investigation. However, such adjustment is vital in comparing intensity and strong-motion 

parameters (figs. 68A-70E). 

We used predicted intensities at all sites, whether 

alluvial or otherwise, to compare with strong-motion 

parameters under the assumption that, because predicted agree with observed where we are sure of ground 

condition, the predicted values are preferred over 
TABLE 24.-"0bserved" and predicted intensities for the 1971 San Fernando earthquake for sites on 

alluvium 

(Based on values reported by Scott (1973) but adjusted for depth to water table as discussed in text. Some "observed" Modified Mercalli 

intensity values may differ by as much as one intensity unit from those read from Scott's map. All localities are in Los Angeles unless 

otherwise indicated. Measurements were taken as close to ground level as possible] 

Latitude, Longitude, Modified Mercalli intensity' 

Location oN. ow. "Observed" Predicted 

9841 Airport Blvd.--------------------- 33.946 118.386 5.6 5.7 

Anza, Anza Post Office----------------- 33.556 116.674 4.8 4.0 

San Bernardino, Hall of Records ---------- 34.106 117.284 4.6 5.0 

Long Beach, 205 W. Broadway----------- 33.769 118.194 5.8 5.0 

Glendale Municipal Service Building ------ 34.133 118.247 6.3 6.5 

Pasadena, CIT, Athenaeum ------------- 34.139 118.121 6.0 6.3 

Costa Mesa, W. 19th St. ---------------- 33.644 117.926 3.6 4.4 

5260 Century Blvd. -------------------- 33.945 118.372 5.6 5.7 

Orange, 4000 W. Chapman Ave. ---------- 33.781 117.893 5.3 4.7 

Santa Ana, Orange County Engineering ---- 33.750 117.867 5.7 4.6 

Building. Colton, Edison Building ______ _: _________ 34.059 117.313 5.4 5.0 

234 Figueroa St. ---------------------- 34.056 118.257 6.2 6.1 

Alhambra, 900 S. Fremont Ave. ---------- 34.085 118.149 6.2 6.1 

250 E. First St. ------------------------ 34.050 118.241 6.5 6.6 

222 Figueroa St. ---------------------- 34.057 118.251 6.0 6.6 

7080 Hollywood Blvd. ------------------ 34.101 118.344 6.3 6.4 

Hemet Fire Station -------------------- 33.730 116.979 3.8 3.6 

San Juan Capistrano ------------------- 33.489 117.671 5.0 4.8 

Long Beach State College --------------- 33.776 118.113 5.8 5.9 

8639 Lincoln Ave. --------------------- 33.960 118.419 5.6 5.7 

Pasadena, CIT, Millikan Library ---------- 34.137 118.125 6.2 6.3 

1640 S. Marengo St. ------------------- 34.060 118.213 5.7 6.1 

Fullerton, 2600 Nutwood Ave. ----------- 33.878 117.881 4.7 4.9 

Hollywood, 1760 N. Orchid Ave. --------- 34.103 118.339 6.6 6.4 

646 S. Olive Ave.---------------------- 34.047 118.254 6.3 7.1 

435 N. Oakhurst Ave. ------------------ 34.078 118.391 6.5 6.3 

808 S. Olive Ave. ---------------------- 34.035 118.251 6.3 6.0 

8244 Orion Blvd. ---------------------- 34.221 118.471 7.0 7.0 

Gorman, Oso Pumping Plant ------------ 34.801 118.718 5.0 5.2 

Pearblossom, Pumping Plant ------------ 34.508 117.922 5.6 5.7 

Port Hueneme ----------------------- 34.150 119.200 5.5 5.6 

Palmdale Fire Station ------------------ 34.578 118.113 5.1 6.0 

120 N. Robertson Blvd. ----------------- 34.076 118.383 6.5 6.8 

Beverly Hills, 450 N. Roxbury Dr. --------- 34.069 118.406 6.5 6.7 

6430 Sunset Blvd. --------------------- 34.097 118.329 5.9 6.4 

6464 Sunset Blvd. --------------------- 34.097 118.331 5.9 6.4 

3407 Sixth St. ------------------------ 34.063 118.295 6.4 6.2 

Terminal Island ---------------------- 33.765 118.225 6.0 5.9 

UCLA Reactor Lab -------------------- 34.067 118.450 6.3 6.2 

3440 University Ave. ------------------- 34.023 118.283 5.6 6.0 

14724 Ventura Blvd. ------------------- 34.152 118.455 6.7 7.1 

15250 Ventura Blvd. ------------------- 34.154 118.464 6.2 6.6 

15107 Vanowen ---------------------- 34.195 118.128 5.6 6.5 

Vernon CDM Building ----------------- 34.000 118.200 5.6 5.9 

15910 Ventura Blvd. ------------------- 34.160 118.480 6.1 6.6 

3470 Wilshire Blvd. -------------------- 34.061 118.299 6.5 6.2 

4680 Wilshire Blvd. -------------------- 34.061 118.331 6.4 6.2 

Whittier Narrows Dam ----------------- 34.020 118.053 5.5 5.7 

Wheeler Ridge ----------------------- 35.018 118.985 4.7 4.4 

3710 Wilshire Blvd. -------------------- 34.062 118.307 6.4 6.2 

9100 Wilshire Blvd. -------------------- 34.067 118.389 5.9 6.2 

1 Arabic numerals are used here instead of the standard roman numerals, so that gradations in Modified Men::alli intensities can be 

shown. 

Predicting Seismic Intensities 163 
ROSSI-FOREL INTENSITIES ROSSI-FOREL INTENSITIES 

2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 

0 

Slope = 2.63 -1 Slope=2.30 

z Sigslope = 0.2423 Sigslope= 0.1645 

0 z 

i= 0 8 i= <! <! 0 a: 

w - 1 0 a: oo 0 oo _J w w 0 f"o _J 

u w @0 u 0 u 

<! u -2 oo oo <! 

~ oO (/) 

::::> ~ ~ £; x - 2 <! (.9 

~ 0 

_J 

(.9 

0 

_J -3 

FULL BANDWIDTH FULL BANDWIDTH - 3 

2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 

MODIFIED MERCALLI INTENSITIES MODIFIED MERCALLI INTENSITIES 

A B 

ROSSI-FOREL INTENSITIES ROSSI-FOREL INTENSITIES . 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 

Slope = 2.23 Slope = 2.49 

Sigslope = 0.1060 Sigslope=0.1469 

oCO 

0 0 0 ~ ~ u 

u 0 

0 0 _J 

w _J 

w > 

> 0 (/) 0 ~ 0 

~ oo £; ::::> 0 ~ 0 (.9 

X 0 

<! _J 

~ 

(.9 

0 

_J 

FULL BANDWIDTH 

3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 

MODIFIED MERCALLI INTENSITIES MODIFIED MERCALLI INTENSITIES 

c D 

FIGURE 68.-Comparisons of intensities and parameters of full bandwidth (0.1-25 Hz) strong-motion seismograms from the 1971 San Fernando earthquake. A, Intensity versus peak acceleration. B, Intensity versus RMS acceleration in a 10-s time window centered on the peak 

value. C, Intensity versus peak velocity. D, Intensity versus RMS velocity in a 10-s time window centered on the peak value of the velocity. Slope 

is the slope of the least-squares linear fit of log (strong-motion parameter) to Rossi-Forel intensities under the assumption that only predicted 

intensity values may be in error. Sigslope is the standard deviation of the Slope value. 
z 

0 

i= 

<X: 

a: 

UJ 

...J 

UJ 

u 

u 

<X: 

~ 

:J 

~ 

x 

<X: 

~ 

(.!) 

0 

...J 

(.!) 

0 

...J 

2 

- 1 

- 2 

/ 

- 3 

2 

2 

0 

- 1 

2 

ROSSI-FOREL INTENSITIES 

3 4 5 6 7 8 9 

Slope = 2.45 

Sigslope = 0.1636 0 

0 0 / oo0 

0 / 

/;; 0 

/ 

/ 

BAND 2 

3 4 5 6 7 8 9 

MODIFIED MERCALLI INTENSITIES 

A 

ROSSI-FOREL INTENSITIES 

3 4 5 

Slope= 2.61 

Sigslope = 0.1954 0 

0 

00 

0 

6 7 8 

0 

9 

BAND 2 

10 

10 

10 

3 4 5 6 7 8 9 10 

MODIFIED MERCALLI INTENSITIES 

c 

ROSSI-FOREL INTENSITIES 

2 3 4 5 6 7 8 9 10 

- 1 

Slope= 2.24 0 

Sigslope=0.1289 

0 

z 

0 

~ - 2 

a: 0 UJ 0 ...J 

UJ 

u 

u 

<X: 

en 

~ 

!£ - 3 

(.!) 

0 

...J 

BAND 2 

2 3 4 5 6 7 8 9 10 

MODIFIED MERCALLI INTENSITIES 

B 

ROSSI-FOREL INTENSITIES 

2 3 4 5 6 7 8 9 10 

Slope = 2.49 

Sigslope = 0.1648 

0 

~ u 

0 

...J 0 UJ 0 > 0 0 en 

~ 

!£ / 

(.!) o / o 

0 /t ...J 

/ - 1 / 

/ 

BAND 2 

2 3 4 5 6 7 8 9 10 

MODIFIED MERCALLI INTENSITIES 

D 

FIGURE 69.-Comparisons of intensities and parameters of strong-motion accelerograms from the 1971 San Fernando earthquake. A, Intensity 

versus peak acceleration on accelerograms filtered to include only frequencies between 0.5 and 3 Hz (band 2}. B, Intensity versus RMS acceleration in a 10.s time window centered on the peak value for accelerograms filtered to include only frequencies between 0.5 and 3 Hz (band 

2}. Squares indicate values on hard rock. C, Intensity versus peak velocity on velocity seismograms filtered to include only frequencies between 

0.5 and 3 Hz (band 2}. D, Intensity versus RMS velocity in a 10-s time window centered on the peak value of velocity seismograms filtered to include only frequencies b~tween 0.5 and 3 Hz (band 2). Slope is the slope of the least-squares linear fit of log (strong-motion parameter) to RossiForel intensities under the assumption that only predicted intensity values may be in error. Sigslope is the standard deviation of the Slope 

value. 
2 

- 2 

z 

0 

~ a: 

w 

-' 

w 

u 

u 

~ 

(/) 

::::!: - 3 

[£ 

(!) 

0 

-' 

2 

2 

- 2 

z 

0 

t= 

~ 

a: 

w 

-' 

w 

u 

u - 3 ~ 

(/) 

::::!: 

[£ 

(!) 

0 

-' 

- 4 

2 

ROSSI-FOREL INTENSITIES 

3 4 5 6 7 8 

Slope= 2.86 

Sigslope= 0.2008 

3 

3 

0 

4 

0 

0 

0 

0 

5 

0 

6 7 

MODIFIED MERCALLI INTENSITIES 

A 

ROSSI-FOREL INTENSITIES 

4 5 6 7 8 

Slope= 5.62 

Sigslope= 1.282 0 

0 

0 

0 oO ~ o8 7 ooo 00 

I 0 

Qf}~ 0 0 0 

0 

l m 0 

I 

I 

I 

I 

3 4 7 

MODIFIED MER CALLI INTENSITIES 

c 

9 10 

8 9 10 

9 10 

8 10 

166 Earthquake Hazards in the los Angeles Region 

z 

0 

i= 

- 1 

2 

~ - 2 w 

-' 

w 

u 

u 

~ 

(/) 

::::!: 

a: 

(!) 

0 

-' 

z 

0 

t= 

~ 

a: 

w 

-' 

w 

u 

u 

~ 

(/) 

::::!: 

[£ 

(!) 

0 

-' 

- 3 

- 4 

2 

2 

- 2 

- 3 

- 4 

2 

I 

ROSSI-FOREL INTENSITIES 

3 4 5 

Slope= 2.74 

Sigslope= 0.2987 0 

8 0 9<e 

0 0 

6 7 8 9 10 

3 4 5 6 7 8 9 10 

3 

MODIFIED MERCALLI INTENSITIES 

B 

ROSSI-FOREL INTENSITIES 

4 5 6 7 8 

Slope = 4.13 

Sigslope = 1.290 

0 

0 

~ 0 

o I 

I 

I 

I 

I 

I 

I 

9 

BAND 4 

3 4 5 6 7 8 

MODIFIED MERCALLI INTENSITIES 

D 

10 

10 
2 

- 2 

z 

0 

i= 

<( 

a: 

UJ 

_J 

UJ 

u 

u - 3 

<( 

U'l 

~ 

~ 

(.9 

0 

_J 

- 4 

2 

ROSSI-FOREL INTENSITIES 

3 4 5 

Slope = 4.83 

Sigslope = .8403 

0 0 

oo/ oCOk 0 

I 

I 

I 

I 

I 

3 4 5 

6 

0 

l o 

0 

0 

0 

0 

6 

MODIFIED MERCALLI 

E 

7 8 

0 

7 

INTENSITIES 

9 10 

8 9 10 

~FIGURE 70.-Comparisons of intensities and parameters of strongmotion accelerograms of the 1971 San Fernando earthquake. A, 

Intensity versus RMS acceleration in a 20-s time window centered 

on the peak value for accelerograms filtered to include only frequencies less than 0.5 Hz (band 1}. B, Intensity versus RMS 

acceleration in a 10-s time window centered on the peak value for 

accelerograms filtered to include only frequencies between 3 and 

10 Hz (band 3}. C, Intensity versus RMS acceleration in a 10-s time 

window centered on the peak value for accelerograms filtered to 

include only frequencies between 10 and 25 Hz (band 4}. D, Same 

type of data as C but only for sites on hard rock. E, Same type of 

data as C but only for sites on alluvium. Slope is the slope of the 

least-squares linear fit of log (strong-motion parameter) to RossiForel intensities under the assumption that only predicted intensity 

values may be in error. Sigslope is the standard deviation of the 

Slope value. 

extrapolated values in areas where the local ground 

condition is not alluvium. 

The correlation of numerous strong-motion parameters with intensity currently is being investigated. The 

analysis reported here will be concerned solely with 

data of the 1971 San Fernando earthquake and with 

only a few of the strong-motion parameters. No data acquired above the first floor in any building have been 

used. The parameters to be discussed are: 

1. Peak acceleration and RMS acceleration in a 10-s 

time window centered on the peak value of the 

unfiltered accelerograms of the 1971 San Fernando earthquake as prepared by the California Institute of Technology (CIT) (figs. 68A, 68B). 

2. Peak velocity and RMS velocity in a 10-s time window 

centered on the peak value of the digitized calculated velocity seismogram as prepared by CIT 

(figs. 68C, 68D). 

3. Peak acceleration and RMS acceleration in a 10-s 

time window centered on the peak value of the 

CIT accelerogram filtered to include only frequencies between 0.5 and 3 Hz (band 2) (figs. 69A, 

69B). 

4. Peak velocity and RMS velocity in a 10-s time window 

centered on the peak value of the CIT velocity 

seismograms filtered to include only frequencies 

between 0.5 and 3 Hz (figs. 69C, 69D). 

5. RMS acceleration in a 20-s time window centered on 

the peak value of the CIT accelerograms filtered 

to include only frequencies lower than 0.5 Hz 

(band 1) (fig. 70A). 

6. RMS acceleration in a 10-s time window centered on 

the peak value of the CIT accelerograms filtered 

to include only frequencies between 3 and 10 Hz 

(band 3) (fig. 70B). 

7. RMS acceleration in a 10-s time window centered on 

the peak value of the CIT accelerograms filtered 

to include only frequencies between 10 and 25 Hz 

(band 4). Figure 70C includes all sites; figure 70D 

includes only sites on hard rock; figure 70E includes only sites quite certainly on alluvium. 

It is a feature of the model for calculating intensities 

that acceleration is assumed to increase by a factor of 

two for each one-unit increase in Rossi-Forel intensity, 

analysis having shown that Rossi-Forel intensities so 

scale, whereas Modified Mercalli intensities do not. 

Therefore, the solid line on all figures is a theoretical 

line along which the parameter plotted versus intensity 

increases by a factor of two for each one-unit increase 

in Rossi-Forel intensity. The line is positioned to pass 

through the centroid of the data. The dashed line is a 

linear least-squares fit to the data under the assumption 

that there is only error in the predicted intensity. The 

Slope parameter in the upper left-hand corner of each 

figure is the slope of the dashed line; the Sigslope value 

is the standard deviation of the slope. The value of the 

strong-motion parameter used for each station is the 

greater of the two values obtained from the pair of orthogonal horizontal instruments. Slightly greater values 

might be obtained by search through all azimuths, but 

marked changes, particularly for the RMS values, seem 

unlikely. There is distinct uncertainty about some of the 

predicted intensities on the basis of available data. 

The strong-motion records obtained near Pacoima 

Dam either are anomalous relative to all other data or 

Predicting Seismic Intensities 167 
require special explanation. They can be made concordant by assigning a shaking intensity of IX or so to the 

small ridge on which the instruments were located. Such 

assignment is certainly incorrect for nearby areas. Scott 

{1973, p. 28) noted that the caretaker's house at the dam, 

a one-story wood-frame house 2 ft off the ground on a 

concrete perimeter foundation, suffered only minor 

damage, and its brick chimney was undamaged. Other 

wooden structures in the immediate area were undamaged, and another unsupported brick chimney did 

not fall. The assignment of very high intensity to this 

general area apparently was based largely on massive 

rock slides. Although rock slides are a described aspect 

of high intensity, they are certainly a poor criterion, as 

so many factors other than shaking are critical to 

generation of such slides. Also, the model cannot predict 

such high intensity at a rock site for a source at the 

known depth of the San Fernando earthquake. A suggested explanation for the high accelerations recorded 

near Pacoima Dam is a focusing of energy in the small 

ridge on which the instrument is placed. We have not 

used the Pacoima Dam data in the least-squares analysis but have plotted the datum point for that locality at 

RFI VII in figures 68, 69, and 70. 

Inspection of figures 68A and 68B indicates that RMS 

acceleration on the unfiltered accelerograms over a 1Q-s 

time window centered on the peak value achieves 

markedly better agreement with the predicted intensities than does peak acceleration on the same accelerograms, an expected result in light of an analysis 

published by Hanks {1979). Therefore, at the very least, 

it would seem appropriate to use RMS acceleration 

rather than peak acceleration from such accelerograms 

for damage prediction. It is interesting that peak velocity versus predicted intensity {fig. 68C} achieves the 

lowest values of Slope and Sigslope of any parameter, 

although not significantly better than RMS acceleration 

in figures 68B {seismogram) and 69B {band 2). One point 

to be noted throughout these figures is that the parameters having the lowest Sigslope values have the lowest 

Slope values, the suggestion being that the theoretical 

Slope of 2.0 is probably indistinguishable from observations. It would seem probable that the value of Slope in 

figure 68C is smaller than that in figure 68D simply 

because of statistical scatter. 

Inspection of figures 69A and 69B {acceleration data 

for band 2) again shows that RMS acceleration achieves 

better agreement with intensity data than does peak acceleration. However, the fact that the least-squares data 

for figure 69B are not significantly better than those for 

figure 68B suggests, in conjunction with figures 70A 

through 70C, that the RMS values of acceleration of the 

total seismogram are largely controlled by the data of 

band 2. Note that all Slope and Sigslope values of figures 

168 Earthquake Hazards in the los Angeles Region 

70A through 70C {bands 1, 3, and 4) are greater than 

those for figure 68B, particularly for bands 1 and 4. 

These results indicate that RMS values of acceleration 

in bands 1, 3, and 4 decrease more rapidly with decreasing intensity than do those of band 2. Since intensity and 

epicentral distance are strongly correlated for sites on a 

given rock type, the behavior in bands 3 and 4 for sites 

on alluvium is probably the result of greater attenuation 

with increasing frequency. The apparently similar 

behavior in band 1 would require a markedly different 

explanation. 

Relations Between Intensity and 

Root-Mean-Square Acceleration 

A set of interesting relations can be found by analysis 

of the RMS acceleration data considering Slope and intercept data for all frequency bands for all stations, for 

stations on alluvium, and for stations on hard rock. 

Several strong-motion instruments at sites of uncertain 

ground condition are excluded from the following 

analysis, as are instruments on Miocene and Eocene 

sediments. 

For band 2 {0.5-3 Hz), the fields of RMS acceleration 

for sites on hard rock and alluvium largely overlap {fig. 

69B), this overlap implying that the 3.0 adjustment of 

predicted intensity for sites on hard rock leads to consistent estimates of RMS acceleration in band 2 for the 

same predicted intensity, an expected result. Also, it 

was noted above that the least-squares fit of RMS acceleration and predicted intensity in band 2 yielded a 

Slope value in close agreement with that used in the intensity prediction model {2.2 ± 0.1 versus 2.0, where 

scaling intensity is predicted Rossi-Forel intensity), supporting the case for validity of the model parameterization. These clear statistical correlations of observed acceleration data and predicted intensities seem sufficient 

to justify using the observed relations of intensity and 

RMS acceleration in band 2 to convert the predicted intensity map to a predicted band 2 RMS acceleration 

map. Such a map will be presented later (fig. 78). 

The data of band 4 (10-25 Hz) are markedly different 

from those of band 2 (figs. 70C, 70D, 70E). The Slope 

value is high on all of these figures, being somewhere 

around 4.5 to 5 rather than 2.2, as for band 2, the result 

being that RMS acceleration in band 4 decreases as the 

square of the rate appropriate to band 2. Amplitudes 

decrease at essentially the same rate on both hard rock 

and alluvium, thus confirming another assumption of the 

mod.el that decay rate is related to the shaking response 

of the bedrock, not to the behavior of surficial materials, 

which influences the level of ground motion and the 

spectral composition of ground motion for a given basement input. At the same intensity {band 2 RMS accelera-
ROSSI-FOREL INTENSITIES ROSSI-FOREL INTENSITIES 

2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 

0 0 

ALLUVIUM HARD ROCK Intensity 

- 1 - 1 ,'l_ cutoff 

z z on 

0 0 / hard rock 

i= i= , <( <( ~ " a: - 2 a: w 

_J 

w 

_J 

- 2 ~-- / / w w u u /. ,// u u <( <( " (f) (f) // ~ - 3 ~ - 3 /' / ~ ~ 

<.:) <.:) /// 

0 0 ,// _J BAND 1 ----- _J BAND 1 ------ - 4 BAND 2 "/ BAND 2 

BAND 3----- BAND 3 ----- BAND 4 ------ / BAND 4 -------

- 5 

2 3 4 5 6 7 8 9 10 3 4 5 6 7 9 10 

MODIFIED MERCALLI INTENSITIES MODIFIED MERCALLI INTENSITIES 

A B 

FIGURE 71.-Comparisons of intensities and RMS accelerations of the 1971 San Fernando earthquake in all frequency bands. A, Alluvium sites. B, 

Hard rock sites. 

tion), RMS acceleration on hard rock in band 4 is about 

10 times that on alluvium. However, this tenfold increase is simply the result of the same intensity's being 

at much shorter range on hard rock than it is on 

alluvium, the much higher Slope value for data of band 4 

leading to much more rapid decrease with distance of 

band 4 RMS values than of band 2 values. In fact, RMS 

acceleration values in band 4 are higher on alluvium 

than they are on granite at the same distance. In terms 

of RMS values versus frequency, the signals on alluvium 

and hard rock at the same range are very similarly 

shaped, the values for all bands being several times 

greater on alluvium than they are on hard rock. It should 

be remembered that we are speaking here of RMS acceleration values over time windows of about 10 s, not peak 

acceleration values, which have been generally used in 

the past. For peak acceleration, values are higher on 

hard rock than they are on alluvium at the same range, 

this peak value generally occurring in band 4. If one considers RMS acceleration as being a more useful predictor of expected shaking damage than peak acceleration, 

there is no basis in the data of the 1971 San Fernando 

earthquake for considering hard rock sites as being at 

the same risk as alluvium sites at any frequency. 

These relations as well as others are displayed in 

figures 71A (alluvium sites) and 71B (hard rock sites). 

Curves for all four bands are included. An interesting 

point is that all bands have similar RMS values at short 

range (that is, at the maximum possible shaking intensity 

on each rock type). Such a relation is predicted by 

seismic source theory (that is, a flat source spectrum in 

acceleration for all frequencies above the left-hand 

corner frequency, this corner frequency for the shear 

waves of the 1971 San Fernando earthquake being at a 

frequency of 0.2 to 0.1). The comparison of spectral composition and level at equal intensity on both alluvium 

and hard rock is obvious. The comparison at equal 

range can be approximated by comparing values at intensity I on hard rock with intensity I+ 2.5 to 3 on 

alluvium. The statements made earlier derive from such 

a comparison. It can also be seen in the figures that the 

spectral behavior with intensity is very similar in bands 

2 and 3, band 3 having the slightly greater Slope value. 

The fact that Slope values are steeper for band 1 than 

they are for band 2 was noted earlier. Note that the 

Slope value for hard rock sites is greater than 4 and that 

the Sigslope value is apparently small. The critical point 

here may be that intensity IV on hard rock is at a range 

of only 50 km, so that nearly all observations for band 1 

on hard rock are in the near field for waves having 

periods of several seconds or longer. Thus, the explanation of the high rate of falloff at long periods may be that 

it is an expression of the presence in these data of the 

theoretically predicted near-field terms of elastic 

theory, terms displaying higher rates of falloff than the 

usually observed far-field terms. 

Predicting Seismic Intensities 169 
It is concluded that RMS values of acceleration do indeed show better agreement with intensity than do peak 

acceleration values, even if peak values are band 

limited. It also is concluded that data bandpassed to include only energy in the intensity-relevant band (band 2) 

achieve better fit to observed intensities than do data 

from any other band. It does appear that, at least for the 

data of the 1971 San Fernando earthquake, RMS acceleration in a 1D-s time window from the unfiltered 

seismogram achieves as good a fit to intensity data as 

does RMS acceleration in the 0.5- to 3-Hz bandpass. 

Finally, it appears that the assumption that Rossi-Forel 

intensities increase by one unit for a doubling of the 

ground-motion parameter is supported by these data, in 

conformance with earlier analyses. 

The scatter of data in band 2 relative to predicted intensities is influenced by uncertainty in detailed ground 

condition, uncertainty in optimum bandpass and optimum parameter, and by the fact that virtually none of 

the strong-motion records can be considered as recordings of free-field ground motion. Although only records 

from first floors or basements were used, the fact that 

most of the sites were in tall buildings means that the 

recordings obtained will be influenced to some degree 

by building response. From a seismologist's point of 

view, there ·should be many more true free-field measurements of strong ground motion. 

Obviously, we favor a quantitative use of intensities 

during all phases of damage and risk analysis. As 

generally defined or used, intensity is a narrow-band 

parameter, although definitions do frequently intermix 

phenomena of markedly different effective periods. We 

recommend attempting to define spectrally determined 

intensities following the spirit of Medvedev. Such an effort might well bring into focus the long-period spectral 

contrasts of larger earthquakes. 

APPLYING THE INTENSITY 

PREDICTION METHOD 

In this section, we present examples of how the computer program for predicting intensities can be used to 

address different questions of concern regarding the 

earthquake shaking potential in the Los Angeles region. 

Importance of Ground-Condition 

Assumptions 

A point stressed previously but requiring recurrent 

statement is that predicted intensities are linked directly and importantly to the assumed ground conditions. 

One simply must not inspect a map of predicted intensities without also consulting the map of assumed 

ground conditions for the particular study area. Figure 

170 Earthquake Hazards in the Los Angeles Region 

72 gives the presently assumed ground conditions 

throughout the Los Angeles region. In the region, all 

areas shown on the 1:250,00D-scale map sheets of the 

Geologic Atlas of California (California Division of Mines 

and Geology (1958-1969]) as alluvium of any type are 

treated as having similar physical characteristics; 

variations in ground response are regarded solely as a 

function of depth to water table (less than or greater 

than 30 ft). The detailed analysis of Quaternary 

sedimentary deposits recently completed by Tinsley and 

Fumal (this volume) was not available in time to be used 

in the present study. In addition, ground-water levels (a 

major control over shaking intensity) can undergo radical seasonal and long-term changes. Proper future use 

of predicted intensity maps made today is possible only 

if changes or differences from the ground conditions 

assumed today are incorporated into the analysis. Also, 

the minimum cell size used for the studies in this chapter 

is 1fz minx 1

h min (that is, about 3,000 x 2,500 ft). Details 

of geology below that scale are lost on the maps. Proper 

use of the maps requires that one note the ground condition used for the prediction at the point of interest and 

modify the prediction based on the relative ground 

response of the actual site under consideration and the 

assumed ground response for the appropriate grid element. The requisite scale for converting from geologic 

units to ground response or seismic units is presented in 

table 23. 

The depth to water table is an important ground 

parameter for sites on valley alluvium. Shaking intensity 

drops about one intensity unit for an increase of depth to 

water table from 0 to 30 ft relative to ground level. It 

may drop another half unit for an increase of depth to 

water table from 30 to 100 ft or more. That is, intensities 

can change from, say, IXlfz to VIII (from extremely 

severe shaking to only strong shaking) by simply changing the depth to water table. The most important single 

step that a community located on thick alluvium can 

take to protect itself from extreme earthquake-induced 

shaking is to lower the water table to about 50 ft; the 

worst possible thing that it can do is to raise the water 

table to the surface. 

Predicting Intensities for a Specific 

Earthquake 

Maps showing the distribution of predicted intensities 

from individual postulated earthquakes are useful in 

estimating future damage patterns and in preparing 

emergency response plans. For example, Davis and 

others (1982a, b) have used our predictive method to 

evaluate the effects of hypothetical great earthquakes 

along the San Andreas fault on lifeline systems 
(transportation, water, and communication networks) in 

the Los Angeles and San Francisco metropolitan areas. 

As examples of calculating intensities for specific 

earthquakes, we model in this volume both a 30.km-long 

rupture on the northern part of the Newport-Inglewood 

zone (see fig. 74; table 25, event 9A, for location and 

parameters of this earthquake), and a repeat of the 1857 

Fort Tejon rupture on the San Andreas fault. 

The predicted intensities for the Newport-Inglewood 

earthquake are presented· by Ziony and others (this 

volume, figs. 213, 214) for comparison with results from 

other methods of predicting earthquake ground motion. 

Two major reasons for modeling this earthquake are the 

anticipated level of damage and our interpretation of 

the earthquake of December 8, 1812 (see later section). 

The entire course of the postulated fault break is within 

areas that have been nearly completely urbanized or industrialized in the past 50 yr since the Long Beach 

earthquake of 1933, an earthquake that occurred on the 

same fault system immediately south of the postulated 

earthquake. The 1933 earthquake was a significantly 

larger earthquake than generally considered (Evernden 

and others, 1981); it has been assigned too small a 

stature in the hierarchy of historical California earthquakes because of an accident of history. The 1933 Long 

Beach earthquake was the first significant earthquake 

to occur after the USCGS changed from Rossi-Forel intensities to Modified Mercalli intensities (MMI), and the 

large differences in meaning of some of the highest shaking intensities, although fully documented by the USCGS 

at the time of change, apparently were ignored by most 

investigators. By using Modified Mercalli intensities, the 

occurrence of intensity IX was nearly eliminated, an obvious aspect of the published intensity maps of both the 

1933 Long Beach and 1952 Kern County earthquakes. If 

the intensity map of the Long Beach earthquake had 

been described in Rossi-Forel units, there would have 

been a large area of intensity IX and a consequent 

realization of the larger size of the earthquake. In 1952, 

after the Kern County earthquake, amazement at the 

limited area of intensity MMI IX for an earthquake 

associated with such violent ground displacement was 

expressed in print. 

Other features that may have contributed in some 

measure to assigning too small a size to the 1933 Long 

Beach earthquake were that most of the rupture was 

offshore and that much of the area surrounding the onshore portion of the rupture was undeveloped. The entire area is now heavily developed, and the hypothetical 

earthquake that we model is immediately north of the 

portion of the Newport-Inglewood fault that ruptured in 

1933. The entire line of modeled rupture is on land. 

We include in this section predicted values of 

Modified Mercalli intensities for a postulated repeat of 

the 1857 Fort Tejon earthquake on the San Andreas 

fault. Given that average repeat times for major earthquakes on the Mojave Desert section of the San Andreas 

fault are about 150 yr and that it is over 125 yr since the 

iast great earthquake along this segment of the San Andreas fault, the probability of a repeat within the next 

few decades must be considered high. Therefore, it is 

important to determine just what shaking levels are to 

be expected. The State of California (Davis and others, 

1982a) has published such a study, basing its predictions of damage to lifelines on intensity estimates provided by us. Since giving the State those estimated intensities, we have extensively refined the data relative to 

depth to ground water from information provided by 

J. C. Tinsley of the USGS. This refinement is the basis for 

any differences in predicted intensities between the 

maps published by Davis and others (1982a) and those 

published here as figure 73. 

Figure 73 indicates that very little of the vast residential area in the Los Angeles basin will experience 

markedly damaging intensities as a result of this great 

earthquake. Note that at no place in the Los Angeles 

basin are damaging intensities predicted to be as high 

as they were in the 1971 San Fernando earthquake. 

Most of the basin will experience no greater intensity 

that MMI VII. Comparison of predicted intensities for 

the modeled earthquake on the northern part of the 

Newport-Inglewood zone (Ziony and others, this volume, 

figs. 213, 214) with those for the 1857 Fort Tejon repeat 

(fig. 73) show clearly that the Newport-Inglewood earthquake will produce higher intensities within the Los 

Angeles basin. 

A comment on the character of the predicted intensity 

maps presented in this volume may be useful. Because 

no damage occurs to modern structures at intensities of 

less than VI, such low intensities are not shown on the 

maps; all areas of predicted intensity V or less are 

shown without symbol. The small-scale maps published 

in this volume are intended only to illustrate the mode of 

presentation to be followed on larger scale versions of 

these maps to be published elsewhere by the USGS at a 

scale of 1:250,000. 

Intensities on these maps are shown as either singlestroke or block numbers. Single-stroke numbers are relevant to the lower half of an intensity unit (for example, 

single-stroke 6 covers intensities from 5.50 to 6.0), and 

block numbers are relevant to the upper half (for example, solid 6 covers intensities from 6.0 to 6.5). 

Predicting Maximum Potential 

Intensities Across the Region 

We have extended our computing program to generate maps showing the composite maximum predicted inPredicting Seismic Intensities 171 
\ 

FIGURE 72.-Assumed ground conditions for the onshore Los Angeles region. Map units are explained in table 22. Base from parts of the Los 

Angeles, Long Beach, San Bernardino, and Santa Ana 1 o x 2 o sheets. 
.· : dfo' "' ~ ·r'r' 

HUNTINGTON 

·., ;'")) ..... 

-!.<- Newpo~. 

·J- ~ 

! 

--C';.y- -------~---------------- ----------- ------ -1+ : ,-1,/«' ! '(! .~\.J i P')ir,~ 

! San Clernente 
TABLE 25.-87 postulated earthquakes used to calculate composite maximum intensities for the Los 

Angeles region 

[Events marked with asterisks are modeled as reverse-faulting earthquakes. Rupture lengths are shown in f!g. 74] 

Event Fault zone 

1A ------- San Andreas 

1B ------- San Andreas 

2A ------- San Jacinto 

2B ------- San Jacinto 

2C ------- San Jacinto 

20 ------- San Jacinto 

2E ------- San Jacinto 

3 --------Central Avenue 

4 -------- Chino 

5* ------- Whittier 

6A ------- Elsinore 

6B ------- Elsinore. 

6C ------- Elsinore 

60 ------- Elsinore 

7 -------- Murrieta 

8* ------- Norwalk 

9A ------- Newport-Inglewood 

9B ------- Newport-Inglewood 

9C ------- Newport-Inglewood 

90 ------- Newport-Inglewood 

9E ------- Newport-Inglewood 

lOA ------ Palos Verdes Hills 

lOB ------ Palos Verdes Hills 

loG ------ Palos Verdes Hills 

100 ------ Palos Verdes Hills 

11A ------San Pedro Basin 

11B ------ San Pedro Basin 

llC ------ San Pedro Basin 

12A ------ Santa Cruz-Catalina escarpment 

12B ------ Santa Cruz-Catalina escarpment 

12C ------ Santa Cruz-Catalina escarpment 

120 ------ Santa Cruz-Catalina escarpment 

12E ------ Santa Cruz-Catalina escarpment 

12F ------ Santa Cruz-Catalina escarpment 

13* ------ Llano 

14 ------- Mirage Valley 

15A ------ Helendale 

15B ------ Helendale 

16A ------ Lenwood 

16B ------ Lenwood 

17 ------- Camp Rock 

18 ------- Cleghorn 

19A * ----- North Front-San Bernardino Mountains 

19B ------ North Front-San Bernardino Mountains 

19C ------ North Front-San Bernardino Mountains 

190 ------ North Front-San Bernardino Mountains 

20 ------- Crafton 

21* ------ Banning 

22A ------ Santa Ynez 

22B ------Santa Ynez 

22C ------ Santa Ynez 

23* ------ More Ranch 

24 ------- Mission Ridge 

25 ------- Arroyo Parida 

26* ------ San Cayetano 

27 ------- Mesa-Rincon Creek 

28* ------ Red Mountain 

174 Earthquake Hazards in the los Angeles Region 

Length of break, 

inkm 

320 

68 

27 

20 

50 

18 

45 

7 

18 

30 

18 

29 

22 

27 

15 

12 

30 

22 

22 

27 

30 

27 

29 

21 

24 

18 

25 

28 

23 

19 

30 

27 

30 

30 

6 

30 

30 

30 

25 

27 

30 

23 

15 

11 

13 

14 

20 

30 

31 

29 

29 

25 

27 

23 

32 

24 

27 

Magnitude 

(M] 

8.1 

7.2 

6.6 

6.4 

7.0 

6.4 

6.9 

5.8 

6.4 

6.7 

6.4 

6.7 

6.5 

6.6 

6.2 

6.1 

6.7 

6.5 

6.5 

6.6 

6.7 

6.6 

6.6 

6.4 

6.5 

6.3 

6.6 

6.6 

6.5 

6.4 

6.7 

6.6 

6.7 

6.7 

5.7 

6.7 

6.7 

6.7 

6.5 

6.6 

6.7 

6.5 

6.2 

6.0 

6.2 

6.2 

6.4 

6.7 

6.7 

6.6 

6.6 

6.6 

6.6 

6.5 

6.7 

6.5 

6.6 
TABLE 25.-8;:: postulated earthquakes used to calculate composite maximum intensities for the Los 

Angeles region-Continued 

Event Fault zone 

29A • ----- Pitas Point-Ventura 

29B* ----- Pitas Point-Ventura 

30A * ----- Oak Ridge 

30B* -----Oak Ridge 

30C* -----Oak Ridge 

30D* ----- Oak Ridge 

31* ------Simi 

32* ------ Holser 

33 ------- San Gabriel 

34* ------ Santa Susana 

35* ------ Northridge 

36* ------ San Fernando 

37* ------ Verdugo 

38A • ----- Sierra Madre 

38B* -----Sierra Madre 

39* ------ Cucamonga 

40 ------- Santa Rosa Island 

41A • -----Santa Cruz Island 

41B* -----Santa Cruz Island 

42A • ----- Anacapa 

42B* ----- Anacapa 

43A • ----- Santa Monica 

43B* -----Santa Monica 

44* ------ Malibu Coast 

45* ------Hollywood 

46* ------ Raymond 

47 ------- Indian Hill 

48 ------- San Jose 

49 ------- Red Hill 

50 ------- Fontana 

tensities from multiple postulated events in the same 

region. If enough earthquake sources in a region are 

considered, the resulting map can delineate those areas 

having the greatest long-term exposure to shaking 

hazards. As a first approximation of the areal shaking 

potential in the Los Angeles region, we recently evaluated a suite of six potential earthquakes and mapped 

the maximum expected values of Modified Mercalli intensity (Evernden, 1982, fig. 9; U.S. Geological Survey 

Staff, 1982, fig. 1). 

To demonstrate predicted intensity maps that might 

be used for microzonation or in regional planning, we 

have generated the cumulative maximum predicted intensities at points within the Los Angeles region 

resulting from a suite of expectable earthquakes along 

the principal active faults. The 87 events used were 

specified by J. I. Ziony and represent his current appraisal of the earthquake potential of the principal late 

Quaternary faults of the region. Distinctive fault 

segments were identified from their surficial geologic 

character and were the basis for postulating rupture 

lengths. Larger earthquakes might be possible if actual 

Length of break, Magnitude 

inkm (M) 

25 6.6 

24 6.5 

19 6.4 

25 6.6 

24 6.5 

32 6.7 

27 6.6 

10 6.0 

30 6.7 

26 6.6 . 

14 6.2 

19 6.4 

20 6.4 

28 6.6 

24 6.5 

25 6.5 

25 6.5 

30 6.7 

28 6.6 

32 6.7 

20 6.4 

26 6.6 

23 6.5 

29 6.6 

24 6.5 

14 6.2 

10 6.0 

20 6.4 

12 6.1 

8 5.9 

ruptures were to spread to two or more adjacent fault 

segments during a single earthquake. However, such 

spreading would have little effect on predicted nearfield maximum potential intensities, because such intensities saturate in the neighborh~od of M 6.2. The 87 

potential earthquakes used are shown in figure 74 and 

listed in table 25. The calculated maximum intensities at 

each site resulting from these 87 earthquakes are 

plotted in figure 75. 

These calculated intensities can serve two purposes: 

(1) to delineate areas of potentially hazardous shaking 

and (2) to delineate areas having little chance of experiencing high, damaging intensities. These maps can 

be considered as a conservative prediction of future 

shaking levels across the Los Angeles region. Although 

we know the potentially active faults, we do not know 

when any will slip, and so we calculate intensities from 

all of them. As Ziony and Yerkes (this volume) point 

out, the repeat times for major earthquakes along segments of the San Andreas and San Jacinto fault zones 

range from several tens of years to a few hundred years; 

in contrast, repeat times along other active faults probPredicting Seismic Intensities 175 
f r"-'.tr Pt 

34 00' 

/ 

30 

APPROXIMATE SCALE 

Onwrr1 Bf' o!l d :.< 

PcJrt HiJPneme 

,. 

"~ { 

t\r H,!r J•t...nj t:~»' ,f,l ... / 

\ 

' ( ./ 

) 

( 

1 

' 

40 KILOMETERS 

\ 

6 ~ ~ 

\

1

>_lf'l 

SANrA >1' ·.-rc ~ ~ 

E: ~:.egLm, 

Manha jtan Be 

rmosa 

R<icJondo '-'..,;. 

Pa~>" r~ 

Fr ,"; ,.w,l~ 

·-----~; 

c;::...->~ j f:...,'~'~v~ '-~~ 1 .. / 

c. " G~_-'-~-t~-.J (~\ ) 

2.---/ "---;,. 

::=:~-~j() 

( 

\'-

\ \ 

\

- J '-..--.. 

·'-.._ 

I , \., \ 

) \___ _ _) 

) 

\, 

7 r') ,, 

•• 5'-</ ...... ~ j 

--- ~-

33'15''----L-i-"-"------~---~-----------_J_ ________ _:__.::.:·--::::::__:·:::_-___________ _ 

FIGURE 73.-Predicted Modified Mercalli intensities in the onshore Los Angeles region from a repeat of the 1857 Fort Tejon earthquake on the San 

Andreas fault. Heavy line indicates trace of postulated seismic rupture. Base from parts of the Los Angeles, Long Beach, San Bernardino, and 

Santa Ana 1 o x 2 o sheets. Arabic numerals are used instead of the standard Roman numerals, so that gradations in Modified Mercalli intensities can be shown. Single-stroke characters indicate intensities in the lower half of an intensity band; hollow characters indicate intensities 
-iii 

'", ·Avakm 

>o 

HUNT NGTON 5 

--:------, - :--- --- _,.__ Agua 1b1ll . - t-1rn-.:n;, 

\ : 

~-ahutll.o Mt 

Sf<:(; 

·~' ~t \ 

p"""'" vr""' 

~lom<tr Mtn-'L 

in the upper half. For example, intensities 5.50 to 5.99 are indicated by the singl&-Stroke character 6; intensities 6.00 to 6.50 are indicated by a 

hollow 6. Intensity 10 is indicated by an asterisk. All areas of intensity V or less are shown without symbols, because little damage to modem 

structures occurs at those intensities. 

y'J 
Santa 

Rosa I 

0 

FIGURE 74.-Map of Los Angeles region showing rupture lengths for 87 postulated earthquakes (table 25). These events were selected by J. I. Ziony 

to be typical earthquakes that might occur along particular fault segments considered potentially seismogenic. The northern end of event 1A, a 

repeat of the 1857 Fort Tejon earthquake, lies about 150 km north of the map area. Coordinates of end points for the reverse-slip earthquakes 

(see table 25) were displaced horizontally 6 km in the downdip direction from the surface traces of the respective faults. 

ably range from many hundreds of years to several thousand years. We cannot say whether figure 75 does or 

does not represent the short-term hazard for any 

specific point. Given this basic uncertainty, these maps 

have relevance within the context of defining areas that 

must be avoided for structures that should have a nearvanishing probability of sustaining significant damage 

due to any potential earthquake. 

A second, inverse way of using these maps may be of 

more interest. As we can see by comparing figure 75 

with figure 72, figure 75 is distinctly more than a 

restatement of the ground-condition maps. In other 

words, great areas of alluvium have both a water table 

at least 30 ft below the surface and locations sufficiently 

removed from potentially active faults that predicted 

maximum intensities do not exceed MMI VII, a shaking 

level that has minimal effect on well-designed buildings. 

The very limited areas predicted to potentially experience intensities of MMI IX and X are very near active faults and presently have the water table at or very 

near the ground surface (for example, the Oxnard Plain 

in fig. 75). The maps in figure 75 are particularly useful 

for delineating favorable areas for siting facilities 

whose immunity from shaking damage at the time of an 

earthquake is vital. Of course, if hard rock sites are 

available, one need not be concerned with defining 

178 Earthquake Hazards in the Los Angeles Region 

alluvium sites of low expected intensity. However, some 

communities or organizations may find it necessary or 

desirable to exploit such alluvium sites. 

Locating Pre-instrumental 

Historical Earthquakes 

A third application based on the intensity prediction 

model is to use the model in conjunction with available 

observations of intensities, ground conditions, and 

mapped faults to estimate locations and magnitudes 

(lengths of rupture) of past earthquakes, including those 

for which instrumental recordings are not available. 

The locations and sizes of these earthquakes may have 

great significance in evaluating the earthquake hazards 

of a region. 

Evernden and others (1981) analyzed the intensity 

data of two past southern California earthquakes whose 

fault sources are not definitely known. With the quantity 

of data available, it was feasible to enfold the intensity 

prediction program within a statistical framework and 

to base predictions of location and size on minimization 

of a statistical parameter. The details of that statistical 

model have been given by Evernden and others (1981) 

and will not be repeated here. The earthquakes studied 

were the 1927 Point Arguello and 1933 Long Beach 
earthquakes. The 1927 earthquake was shown at very 

high statistical confidence to have been associated with 

rupture of the Hosgri fault offshore. A location even 

10 km farther at sea than the Hosgri fault is strongly rejected by available intensity data and the intensity 

model. A location on the Santa Lucia Bank fault zone is 

rejected at far greater than 0.99 confidence. Such a 

location is grossly inconsistent with the intensity data. 

The solution for the 1933 Long Beach earthquake was 

constrained to lie on the Newport-Inglewood fault zone 

because the seismologic data were unequivocal. The 

position and length were determined by the statistical 

model. The location found by the intensity data was consistent with conventional seismologic data but was more 

definitive in establishing a length of break of about 

30 km, the northern end of the break being onshore. The 

break shown as 9B on figure 74 is nearly that found for 

the 1933 Long Beach earthquake. 

In this chapter, we attempt to determine the locations 

of the two large earthquakes that occurred on December 8 and 21, 1812, the largest historical earthquakes to 

occur in southern California before the 1857 Fort Tejon 

earthquake. The available shaking data for these earthquakes can be derived from descriptions given by BanMisson 

croft (1885) from records of the Franciscan m1sswns 

then present in the area. It is clear that the records of 

low intensities (below those causing damage) are very 

incomplete; it is quite unreasonable, for example, to 

think that San Gabriel mission could have suffered considerable damage at the time of the December 8 earthquake while the earthquake was not felt at San Fernando mission. The scribes at one mission may have noted 

shaking equivalent to intensity IV, while others chose 

not to mention effects equivalent to intensities V and VI. 

The general paucity of earthquake records from such a 

seismically active area suggests that familiarity had 

bred lack of noteworthiness. Our analysis will assume 

that shaking inadequate to cause damage may or may 

not have been noted. Together with the constraints 

imposed by our model, the available data, and the reporting assumed above, all solutions are tightly constrained. For example, the use of an intensity no higher 

than IV ("felt but no damage") at Purisima tor the 

December 8 earthquake is controlled by no report of 

damage at San Fernando. 

The damage reports gleaned from Bancroft (1885) and 

our interpretations of the shaking intensities for the two 

earthquakes are as follows: 

Estimated intensity 

Damage' (MMI) 

Earthquake of December 8, 1812 

San Diego ------------- Possibly felt, but maybe not. Certainly no 

damage at mission. '!f V 

San Luis Rey -----------Not reported felt. No damage. '!OV 

San Juan Capistrano ----- Caused collapse of dome of cathedral but no 

reported damage to adobe buildings 

surrounding the cathedral. Bancroft stated 

that collapse of the cathedral was the 

result of poor construction. VII(?) 

San Gabriel ------------ Church badly cracked, losing top of its tower. 

Most mission buildings considerably 

damaged. VII(?) 

San Fernando ----------Not reported felt. No damage. '!fVI 

San Buenaventura ------- Not reported felt 

Santa Barbara ---------- Not reported felt 

Santa lnes ------------- Not reported felt 

Purisima -------------- Felt but no damage IV(?) 

San Luis Obispo -------- Not reported felt '!f IV 

December 21, 1812 

San Gabriel and south---- Not reported felt '!OV 

San Fernando ---------- Slight damage to church. Did not fall, 

apparently. VI(?) 

San Buenaventura ------- In addition to some serious cracks in the mission 

buildings, the new church was so badly 

damaged that part of the facade and all of 

the tower had to be torn down and 

rebuilt. VII(?) 

Santa Barbara ---------- Buildings of both mission and presidio damaged 

by a long series of shocks that lasted for 

several months. "Sea was troubled," new 

asphalt springs formed in all directions, 

cracks reported in the mountains. People 

slept in open air for 3 months. 

Many aftershocks. VII 

Predicting Seismic Intensities 179 
Misson Damage' 

Estimated intensity 

(MMI) 

December 21,_ 1812--Conlinued 

Santa Ines ------------- Corner of the church came down, as did all of 

the roofs in the mission. VII(?) 

Purisima -------------- Two large earthquakes, the second bringing 

down the church and nearly all adobe 

buildings. Shaking so violent that it was 

difficult to stand. 

San Luis Obispo --------Not reported felt 

1

From Bancroft (1885). 

These data become much more understandable when disintegration and failure to repair, not from earththe ground conditions at the several missions are quake damage. Most of these missions were very weak 

considered: structures. 

Intensity Figure 76A models a rupture along the southern half 

difference of the Newport-Inglewood fault (9C and 9D of fig. 74) from 

saturated (41 km long, M 6.9) as a possible source of the December 

alluvium 8 earthquake. San Juan Capistrano has the highest pre-

--------------------- dieted intensity (MMI VIII). San Gabriel is next 

San Diego ----------- Eocene marine sediments -_ 1

1·.

8

8 (MMI VII). San Fernando is predicted as borderline 

San Luis Rey --------Eocene marine sediments 

San Juan Capistrano ___ Alluvium, possibly saturated 0 (MMI V-VI), and San Diego Oust off the map) and San 

Mission Ground condition 

San Gabriel---------- Holocene alluvium, possibly Luis Rey are predicted to have experienced MMI IV. San 

saturated. o Buenaventura, Santa Barbara, and Santa Ines are preSan Fernando -------- Holocene alluvium, possibly dieted to have experienced MMI III or less, while 

saturated. 0 Purisima, placed as it was on the flood plain of the Santa San Buenaventura ---- Late Pleistocene marine 

terrace deposits, well Ynez River, is predicted to have experienced MMI IV. 

drained. At terrace Thus, a 41-km break on the southern Newport-Inglewood 

back edge near bedrock fault zone explains all observations. Other models that 

hills and about 60 ft might be considered are ruptures on the Elsinore fault 

above Ventura River. - 1.5 

Santa Barbara -------Late Pleistocene zone (6A, 6B, and 6D of fig. 74) (73 km long, M 7.2) and on 

fanglomerate, well the southern half of the Palos Verdes Hills fault (10C and 

drained. 75 to 100ft 10D of fig. 74) (41 km long, M 6.9). The first model reabove Mission Creek. 

Santa Ines ----------Late Pleistocene river 

terrace gravels on 

Pliocene diatomaceous 

shale about 100 ft 

above Santa Ynez River. 

Purisima ------------ Holocene{?) alluvium near 

southern edge of Santa 

Ynez River flood plain, 

possibly saturated. 

San Luis Obispo ------ Cretaceous-Jurassic 

greywacke. 

-1.5 

-1.8 

0 

-2.0 

It may seem that the intensities that we are assigning 

to the sites damaged are too low. We think not. The 

buildings damaged were of such construction as to invite destruction even under moderate shaking. Bancroft 

noted that travelers in California in the 1820's commented upon the decrepit state of nearly all of the missions, their condition apparently resulting from simple 

180 Earthquake Hazards in the Los Angeles Region 

quires such great length to cause MMI IV at Purisima 

but consequently predicts MMI VI at San Luis Rey (fig. 

76B), which seems most unlikely. In addition, field 

evidence suggests that the modeled break is unlikely 

because fresh fault scarps have not been recognized 

along that part of the Elsinore fault zone. A break along 

the southern half of the Palos Verdes Hills fault lowers 

the predicted intensity at San Juan Capistrano (MMI VII) 

but not enough to invalidate the model (fig. 76C). The 

Palos Verdes Hills fault displays Holocene surface 

faulting on the San Pedro shelf (Ziony and Yerkes, this 

volume), whereas the Newport-Inglewood fault zone 

broke immediately north of the modeled portion in 1933. 

Our knowledge of the progressive occurrence of earthquakes along fault zones in many areas leads us to infer 

that the December 8, 1812, earthquake was on the 

southern half of the Newport-Inglewood fault zone. The 

apparent progression northward of historical earthquakes on this fault zone suggests that the detailed· 
study of the geologic and seismologic effects of a 

postulated break on the northern quarter of the 

Newport-Inglewood fault zone (Ziony and others, this 

volume) may be a pertinent scenario. 

The earthquake of December 21, 1812, was clearly at 

a far different location. The reports that many people 

left both Santa Barbara and San Buenaventura missions 

for as long as 3 months and that many aftershocks were 

felt at Santa Barbara (probably also at San Buenaventura but not noted in records by Bancroft) strongly suggest an east-west locus of rupture reasonably near both 

sites. For completeness, we demonstrate (fig. 77 A) that a 

large break (90 km long) along the San Andreas fault, 

positioned to give maximum predicted intensities at 

Santa Barbara, is inadequate to generate the required 

intensities at Santa Barbara, San Buenaventura, and 

Purisima. Because the greatest historical earthquake in 

southern California occurred along this very fault only 

45 yr later, a major earthquake along the same segment 

in 1812 seems unreasonable. 

More likely candidates for the locus of this earthquake are the Santa Ynez fault and the Pitas PointVentura fault (and its probable western extension). The 

major requirement of the model is· that MMI VI be 

reached at San Fernando and at least MMI VII be 

reached at Purisima. As will be seen, a rupture length of 

80 km or more is required. Assuming that several segments of the Santa Ynez fault can break as a unit, we 

model such a break in figure 77B (events 22A, 22B, and 

22C of fig. 74) (87 km long, M 7.3). MMI VII is predicted 

at Purisima, MMI IV at San Luis Obispo, MMI VII at 

Santa Barbara and Santa. Ines, MMI VI to VII at San 

Buenaventura, MMI VI at San Fernando, and lower 

values to the southeast. We must assume that MMI VI at 

San Fernando from the December 8 earthquake weakened the church structure but caused no detectable 

damage, whereas the same intensity 13 days later led to 

detectable damage requiring repairs. If only two of the 

three segments of the fault are used in the model, the intensities at either Purisima or San Fernando are 

predicted as too low. The problems with the model in 

figure 77B are that it gives no basis for the tsunami (McCulloch, this volume) apparently generated by the earthquake and that evidence of historical surface faulting 

along the fault has not been demonstrated. 

Figure 77C models a· rupture along the Pitas PointVentura fault and its probable western extension events 

(29A, 29B, and 23 of fig. 74) (90 km long, M 7.3). This 

earthquake is modeled as a thrust, so that a pseudodepth value of 20 is used rather than 25, and thus the 

locus of the energy release is moved 6 km to the north of 

the trace of the fault zone, such perturbations of the 

usual model for strike-slip earthquakes having been required to explain the high near-field intensities of the 

1971 San Fernando thrust earthquake (Evernden and 

others, 1981). The predicted MMI value at Purisima is 

low VII, an only marginally adequate value. Predicted 

intensity at Santa lnes is VI to VII, at Santa Barbara and 

San Buenaventura VIII, at San Fernando VI, and at San 

Gabriel V. Shortening of the fault rupture on the east 

would lower predicted intensities at San Fernando to V, 

an unacceptable result. On the other hand, a further extension on the west to increase predicted intensity at 

Purisima seems desirable. Thus, figure 77D add~ 10 km 

to the line shown on figure 74 (100 km long, M 7.4), the 

result being that the predicted MMI value at Purisima is 

slightly higher. There is no reason why the rupture could 

not be extended even farther west. 

Other potential earthquake sources offshore of Santa 

Barbara (fig. 74) have be(m modeled up to the maximum 

length consistent with present interpretations, and all 

fail to predict adequately high MMI values at Purisima, 

Santa Ines, and San Fernando. A location along the Pitas 

Point-Ventura trend, however, is consistent with many 

aftershocks being felt at Santa Barbara and San Buenaventura, with generation of a tsunami by this offshore 

thrust fault, and with numerous small fractures in the 

hanging wall block (the landward side of the fault) during subsequent aftershocks. We conclude that available 

intensity data, when interpreted within the confines of 

our model, indicate the earthquake(s) of 21 December, 

1812, to have been associated with rupture of about 100 

km along the offshore trend of the Pit!J.S Point-Ventura 

fault. In light of the reports from Purisima of two earthquakes about one-half hour apart, the second earthquake being much more violent, it may be that the 

eastern half of the fault ruptured first, this initial rupture being followed by an earthquake of essentially 

equivalent magnitude (M = 7.0) along the western half of 

the fault. No other known fault zone appears adequate 

to explain all observations. 

Predicting Root-Mean-Square 

Acceleration 

As we pointed out earlier and as figures 71A and 71B 

illustrate, RMS acceleration shows strong correlation 

with predicted intensity and rock type. In band 2, RMS 

acceleration is nearly independent of rock type, being 

only a function of intensity. Therefore, a direct conversion of predicted intensity to predicted RMS acceleration in band 2 is possible. Figure 78 gives the predicted 

RMS acceleration in band 2 for part of the Long Beach 

Predicting Seismic Intensities 181 
( 

'i ~ 

HUNTINGTON 

1 800' 

' ' ' ' 

·~~:< ' -: ~- J 

.._,-t:.,:>JiJloo 

\ 

::9 

i San Cler.1ente 

tensities 5.50 to 5.99 are indicated by the single-stroke character 6; intensities 6.00 to 6.50 are indicated by a hollow 6. Intensity 10 is indicated 

by an asterisk. All areas of composite maximum intensity of V or less are shown without symbol, because little damage to modern structures occurs at those intensities. 
..:.. -7 

Sa rlta 

' ' ------------------------------------+-----------------------------------4---------------------------------?A'"'""-"'*>' : : : : 

! i 

::

j :':! Oxnar,_1 Bf', i r-· \ 

i i Port Hcjenerne 

I . :c 

'----,-----,.;., __ }:/ P~•t• · , 

34··oo· t-hml -

0

- •••.. · ... ---l>rir::-7.-=--i?;H ""----J:;n~-L~=+=~------;------- --- :; ;~;:.~~~ _~.~ ---- ----:.r:: _______ , _________________ : _________ ::.----------------------------· ·-- -------------- --- ql\tii MQO ~:.·:::·;·.· _~~, 

~--~ SA,NTA lvfi'.:NfCA ,_, , _ ~ ~ ' ~ 

33' 

!~~ .. -:- : : E.i ]Seg1 

l j Manhatfan 

i S A N l A ,;; Hei mo~ i 11 o Ref onc ' .__ :\ ""- , i . ..._~.?(' ! Pat 

:J '\, ';., : ; } j ~: 't''"~.=J (~-; - T" : ~ : /'''~? :f( 

\ C! ' / 'c ' t ~ •~-,~ ;_;::\ s,4, • 

~ f ~~~,,;;;, ;;J ' '' ' (}\'Z T _'~ ' ?tf 3[) iv!JU>' j } '-"\ \ ~ , 

· :.:.· .-.·.(.' ,:.: ) ,_j ·~./ ~--, 1(J )() .. . 4iJ KiLO!vlt Tii:; 

LL.L;.,,l .. .L!" L ! _._l_ ! ! 

; '·(,. 1 

: : ' (._ ' 

' '-. : 

" : l--rL 

FIGURE 75.-Predicted composite maximum Modified Mercalli intensities in the onshore Los Angeles region for 87 postulated earthquakes (listed 

in table 25 and located in fig. 74). Base from parts of the Los Angeles, Long Beach, San Bernardino, and Santa Ana 1 ox 2 o sheets. Arabic 

numerals are used instead of the standard Roman numerals, so that gradations in Modified Mercalli intensities can be shown. Single-stroke 

characters indicate intensities in the lower half of an intensity band; hollow characters indicate intensities in the upper half. For example, in-
122 121 120 119 118 11? 36~--~~--~~--------.---------~~--------.---------~36 

35 

34 

A 

Pacific 

·ocean 

4 

35 

34 

33L---------~--------~----------~--------~----~L-~33 

122 121 120 119 118 11? 

FIGURE 76.-Predicted intensities for candidate fault ruptures to explain reported effects of the earthquake of December 8, 

1812. A, Southern half of the Newport-Inglewood fault zone (9C and 9D of fig. 74). B, Elsinore fault zone (6A, 6B, and 6D of 

fig. 74). C, Palos Verdes Hills fault zone (10C and 10D of fig. 74). Digitization scale is O.P x0.1 °. Calculation point is the 

center of the grid element. Numbers refer to the lower half of an intensity unit ("8" to intensities between 7.5 and 8.0); the 

associated letters refer to the upper half ("i" to intensities between 8.0 and 8.5). An asterisk refers to intensities between 

9.5 and 10.0. Two-letter symbols indicate locations of Franciscan missions (center of symbol). Intensities shown are for 

ground conditions of saturated alluvium. 

1 o x 2 o sheet from the postulated earthquake along the 

northernmost 30 km of the Newport-Inglewood zone. 

USING SEISMIC INTENSITIES TO 

PREDICT EARTHQUAKE LOSSES 

Correlating Intensity with 

Percent Loss 

A particularly important derivative application of 

predicted intensity maps is based on the fact that, 

because damage-causing intensities are defined in 

terms of type of building and extent of damage, it is 

possible to construct empirical graphs correlating 

building type, intensity, and level of damage (usually ex184 Earthquake Hazards in the Los Angeles Region 

pressed as percent of value); such graphs are possible 

for structures that suffer damage owing to frequencies 

within the intensity-related bandpass (band 2, corresponding to 0.5-3.0 Hz). This principle certainly applies to wood-frame structures and has been shown to 

apply to unreinforced concrete buildings also. Thus, 

figure 79 presents empirically derived curves of percent 

damage versus intensity for pre-1940 California woodframe construction, post-1940 California wood-frame 

construction, and both residential and commercial 

unreinforced concrete construction. The first curve is 

from Evernden and others (1981), and the last three are 

derived from Gulliver (in press). These graphs allow 

direct conversion of predicted intensity to predicted 

average percent loss from shaking (assuming that 

buildings of the relevant type are at the sites of 

predicted loss), leading to the suite of maps presented in 

figures 80 through 83 for the modeled Newport-
122 121 120 119 118 117 36~--~~--~----~--~--------~.---,-----,-,-------~36 

35 

34 

A 

Pacific 

Ocean 

35 

5 e 

34 

33L---------4-----~--~--------~~--------~----~L-~33 

122 r21 120 119 118 117 

122 121 120 119 118 117 36~--~----~~------~----------~-,------.---~----~36 

35 

34 

8 

Pacific 

Ocean 

5 

4 

35 

e 

34 

336===~~==~=-~== --~===---~~~--== ~~~~~~~33 

122 121 120 119 118 117 

FIGURE 77.-Predicted intensities for candidate fault ruptures to explain reported effects of the earthquake of December 21, 1812. A, 90-km rupture on the San Andreas fault (portion of 1A of fig. 74). B, Santa Ynez fault (22A, 22B, and 22C of fig. 74). C, Pitas Point-Ventura fault (29 and 

23 of fig. 74). D, Same as C plus 10 km added on the western end. Digitization scale is 0.1 o x 0.1 o. Calculation point is the center of the grid ele-
122 121 120 119 118 117 36~--~~--~----------~----~----~--------~----------~36 

35 

34 

8 

Pac1f1c 

Ocean 

e 

35 

33~--------~----------~--------~----------~----~~~33 

122 121 120 119 118 117 

122 

36 

35 

34 

c 

12 1 

Pac1fic 

Ocean 

120 1 19 1 18 

4 

35 

34 

33~--------~--------~--------~~--------~------L-~33 

122 121 120 119 118 117 

Predicting Seismic Intensities 185 
122 121 120 119 1 18 11? 36 ~-- ~---,----------.----------,--------~,--,------,36 

4 

35 35 

e 

34 34 

Pacific 

Ocean 

c = 20 

c 

33 33 

122 12 1 120 1 1 9 1 1 8 1 1 ? 

122 1 2 1 120 1 1 9 1 1 8 1 1 ? 

36 36 

4 

35 35 

5 e 

34 

~---------L----------L---------~--------~~----~--~33 

1 1? 

ment. Numbers refer to the lower half of an intensity unit ("8" to intensities between 7.5 and 8.0); the associated letters refer to the upper half 

("i" to intensities between 8.0 and 8.5). An asterisk refers to intensities between 9.5 and 10.0. Two-letter symbols indicate locations of Franciscan missions (center of symbol). Intensities shown are for ground conditions of saturated alluvium. 
118"15' 118"00'' 

HUNTINGTON 

3T ' ·, 30' -- -- ----- -- ------- - -

' ,:, '!' ·, 

--------- '< :~<> o.\ _-- --------------- j 

APPROXIMATE SCALE 

10 MILES 

10 KILOMETERS 

FIGURE 78.-Predicted root-mean-square (RMS) acceleration over a 

10-s window in band 2 (frequencies of 0.5-3.0 Hz) in part of the 

Long Beach 1 o x 2 o sheet from a postulated earthquake along the 

northernmost 30 km of the Newport-Inglewood zone. Numbers 

designate the following ranges in RMS acceleration: 5, > 0.016 to 

0.032 g; 6, > 0.032 to 0.064 g; 7, > 0.064 to 0.128 g; 8, > 0.128 to 0.256 

g. Heavy line is the trace of the postulated seismic rupture, which 

extends northwestward about another 10 km into the Los Angeles 

basin. 

Inglewood earthquake. Figure 79 and a comparison of 

figures 80 through 83 with figure 213 of Ziony and 

others (this volume) illustrate the well-known truth that 

poorly designed structures can collapse at comparatively low intensities. Death and destruction resulting from 

earthquakes are more a matter of poor construction and 

poor planning than of high intensity. 

A direct parameter of damage such as predicted percent loss may be more immediately useful in interpretation and analysis than the more abstruse intensity. 

However, the limitations of maps such as figures 80 

through 83 is that they give the average percent structural damage to be expected only if relevant buildings 

exist within the area. A much more useful map would be 

one correlating actual building distribution and 

predicted level of damage. Such a map would require 

availability of a digitized census of relevant building 

188 Earthquake Hazards in the Los Angeles Region 

types. As no such data base presently exists for the Los 

Angeles region, we cannot present a map based on such 

correlation, although it would be one of the more useful 

derivative products of predicted intensity maps. A 

version of this type of map could express predicted percentage and (or) number of homeless on a grid or areal 

basis and thus immediately and clearly flag the areas 

requiring major post-earthquake relief efforts. Gulliver 

(in press) has assembled much of the data required to 

implement such a map for the Los Angeles region. 

Maps indicating predicted dollar loss, both by 

building type and by total structural loss, could be 

developed. At present, such sophisticated maps are 

beyond the capabilities of available building inventories 

or data bases. The programming required to generate 

such maps after the data bases become available is a 

matter of a few hours, given presently available programs, but man-years may be required to assemble the 

relevant data. For the time being, predictions of dollar 

loss to wood-frame structures from shaking and total 

loss to all structures must depend on generalized loss 

estimation schemes such as the one developed by Blume 

and others (1980) and slightly modified by Evernden and 

others (1981). Because the results of that analysis may 

be of interest and are as sophisticated as we can now 

do, they are presented here, along with the description 

of the mathematical procedures as well as some additional comments. 

It must be stressed that all damage estimates given 

below are for structural and architectural damage due 

to shaking alone. Potential losses resulting from damage 

to contents of buildings, dam failure and consequent inundation, rupturing of dikes, extensive fires, and other 

hazards are not included, nor are indirect costs resulting from disruption of a variety of services and 

industries. 

Predicting Dollar Loss for WoodFrame Construction 

For use as a guide to relative risks associated with different faults and potential earthquakes on these faults, 

we have written a simple computer program that estimates replacement value for wood-frame construction 

damaged by the modeled earthquakes (Evernden and 

others, 1981). The procedures, which closely follow 

those of Blume and others (1980), have been implemented for California and could be implemented in any 

region at any desired scale of population unit. As presently designed, the data sets required are: 

1. List of all California cities (or segments of cities) and 

unincorporated areas, including county, popula-
tion, latitude, longitude, and typical geologic 

ground condition. 

2. Estimated dollar value of wood-frame construction in 

a city of 75,000 in California. Value used is $1.06 

billion (Blume and others, 1980) and is appropriate to 1977. Application of this analysis in 

subsequent years will require determination of 

the proper scaling relationship in order to get 

values appropriate to the year of concern. 

3. Table of percentage of damage (P) to wood-frame 

construction versus Rossi-Forel intensity (RFI) or 

Modified Mercalli intensity. The following table, 

for example, is based on values given by Freeman 

(1932) and Blume and others (1980) and is equivalent to the curve for pre-1940 construction in 

figure 79: 

(i) if ::sRFI <5.9 P=O 

(ii) 5.9 ::s RFI < 6.0 P = (RFI- 5.90) 

(iii) 6.00 ::s RFI < 6.80 p = (RFI- 6.00) X 0.25 + 0.1 

(iv) 6.80 ::s RFI < 7.40 P = (RFI - 6.80) x 0.5 + 0.3 

(v) 7.40 ::sRFI <7.85 P=(RFI-7.40)x1.11+0.6 

(vi) 7.85 ::s RFI < 8.25 p = (RFI- 7.85) X 2.25 + 1.1 

(vii) 8.25 ::s RFI < 8.70 P = (RFI- 8.25) x 3 33 + 2.0 

(viii) 8.70 ::s RFI < 9.05 p = (RFI- 8.70) X 7.14 + 3.5 

(ix) 9.05 ::s RFI < 9.50 p = (RFI- 9.05) X 6.67 + 6.0 

(x) 9.50 ::s RFI < 10.0 P = (RFI- 9.50) x 6.00 + 9.0 

(xi) 10.00 ::s RFI P = 12 

The procedure of calculation is straightforward: 

A. For each community: 

1. Calculate expected RFI (or MMI) by standard 

formula and using appropriate ground condition. 

2. Calculate estimated percent damage (P) to woodframe or other construction (table above or 

figure 79). 

3. Calculate estimated replacement value by using 

parameters given above or modified for changed 

value of structures since 1977. Answer in billions of dollars. 

B. For each county: 

Sum estimated replacement values for all communities in county. 

C. For State: 

Sum estimated replacement values for all counties. 

D. Sort loss amounts by percent loss and print table of 

distribution of losses by percent loss. 

Estimates of Dollar Loss for Potential 

California Earthquakes 

A condensed set of estimated future losses to woodframe construction is given in tables 26 through 28 for 

the modeled Newport-Inglewood earthquake and possi10 -

rz 

UJ 

u 

cr: 

UJ 

a.. 

~ 

Cf) 

Cf) 

0 

-' 

1. 0 

ROSSI-FOREL INTENSITIES 

6 7 8 9 

Unreinforced concrete, ------......... } 

commercial 

Unreinforced concrete, 

residential 

5 

MODIFIED MERCALLI INTENSITIES 

10 

FIGURE 79.-Percent loss from shaking versus intensity versus various 

types of structures (data from Evemden and others, 1981; Gulliver, 

in press). 

ble repeats of the Fort Tejon (1857) and San Francisco 

(1906) earthquakes. The first part of each table gives 

totals by counties and Statewide for two ground conditions (saturated alluvium and one intensity unit lower 

than expected on saturated alluvium), using intensity 

versus damage scales for pre-1940 wood-fraine construction (Evernden and others, 1981) and post-1940 

wood-frame construction (Gulliver, in press). The second 

part of each table tabulates losses against percent 

damage, this table well illustrating that predicted 

damages in southern California, particularly for the Fort 

Tejon repeat, are based on summing low levels of 

damage over the great number of structures at risk. 

Compare the second parts of all three tables to see how 

concentration of structures near the pertinent fault 

leads to much higher damage. 

Predicting Seismic Intensities 189 
11 8"15' 11 8" 00' 11 8"30' 118"15' 118°00' 

HUNTINGTON 

/ (,_ 

10 MILES 

10 KILOMETERS 

FIGURE 80.-Predicted percent damage to pre-1940 wood-frame construction in part of the Long Beach 1 o x 2 o sheet as a result of 

shaking from a postulated earthquake along the northernmost 

30 km of the Newport-Inglewood zone. Numbers designate the percent loss if this type of construction is present. Heavy line is the 

trace of the postulated seismic rupture, which extends northwestward about another 10 km into the Los Angeles basin. 

Effects of Improved Construction Practices 

Further discussion of these tables is essential if they 

are to be of use to readers. In the first place, the "J 

(saturated alluvium)" columns are certainly not based 

on the appropriate ground condition for nearly any of 

the communities in either northern or southern California. The reason for inclusion of those columns will be apparent in a later discussion. The "Pre-1940 J -1" column is that used by Evernden and others (1981) and 

assumes relevance of the curves of intensity versus 

damage for pre-1940 structures. We must admit that the 

estimates of damage under "Post-1940 J -1" are much 

lower than one's intuition might suggest. Are figures 

such as those given in the far right-hand columns to be 

believed? Three recent California earthquakes suggest 

that they have merit. 

190 Earthquake Hazards in the Los Angeles Region 

3~ 

oo·:· 

<5'"7'"t-

~ 

o..,.o 

('>~ 

""'"t-

. . ' 

' 

HUNTINGTON BEACH'"'~ 

'lr.f'; <" ' \ ' 33° : ~----------- ----------------------- ----------------------------------- ~ 30' APPROXIMATE SCALE 

I 

10 MILES 

I 

10 KILOMETERS 

FIGURE 81.-Predicted percent damage to post-1940 wood-frame construction in part of the Long Beach 1 ox zo sheet as a result of 

shaking from a postulated earthquake along the northernmost 

30 km of the Newport-Inglewood zone. Numbers designate the percent loss if this type of construction is present. Heavy line is the 

trace of the postulated seismic rupture, which extends northwestward about another 10 km into the Los Angeles basin. 

First, consider the 1971 San Fernando earthquake. 

Assuming a deep water table at all sites and using the 

damage curve appropriate to pre-1940 construction 

predict a replacement value of $258 million for woodframe construction, whereas use of the damage curve 

appropriate to post-1940 construction predicts a total 

replacement value of $85 million. Detailed corrections 

for the actual ground-water levels would increase this 

figure. Steinbrugge and Schader (1973) reported a 

minimum loss figure of $114 million. That figure agrees 

much more closely with the predicted value based on the 

pattern of pre- and post-1940 construction in the San 

Fernando area than with that predicted from the 

pre-1940 curve. 

Second, consider the 1979 Coyote Lake earthquake, 

which occurred in the southern San Francisco Bay 

region. Figure 84 illustrates that the available data (ML, 
118"30' 

34° 

oo";-

118"15' 118"00' 

HUNTINGTON 

33°:_- --------------------------------- -~-- ----------------------------- --- _j 30' 

APPROXIMATE SCALE 

I 

10 MILES 

I 

10 KILOMETERS 

FIGURE 82.-Predicted percent damage to unreinforced concrete 

residential structures in part of the Long B11ach 1 o x 2 o sheet as a 

result of shaking from a postulated earthquake along the northernmost 30 km of the Newport-Inglewood zone. Values indicate percent loss if this type of construction is present. Solid numbers (1-9] 

indicate corresponding percent Joss. Hollow numbers designate the 

following ranges in percent loss: 0, > 9 to 10 percent; 1, > 10 to 12 

percent; 2, > 12 to 16 percent; 3, > 16 to 20 percent; 4, > 20 to 25 

percent. Heavy line is the trace of the postulated seismic rupture, 

which extends northwestward about another 10 km into the Los 

Angeles basin. 

intensity pattern, and length of break) all agree when interpreted in terms of expected correlations for an earthquake in western California. Evernden (1983) has 

presented a description of figures of this type and a 

demonstration of the sensitivity of such plots to event 

parameters and k value. The test imposed by a figure 

such as figure 84 is that agreement exists between the 

model and the observations only if the observations lie 

along a vertical line on the figure. The intensities for this 

earthquake were largely determined by nonstructural 

data. Given the agreements shown in figure 84, table 29 

was calculated for a variety of relations between intensity and damage. In addition, the level of damage incurred in Gilroy, Calif., and reported by Kustu (1981) is 

included. Intensities were calculated for saturated 

118"30' 

34° 

00' 

< "V..z.. 

~ 

0~0 

118"15' 118"00' 

HUNTINGTON 

0":>--y~ 

' ~ 

31':_----------------------------------- -~ -- --- _,_-------------------------J 30' 

APPROXIMATE SCALE 10 MILES 

10 KILOMETERS 

FIGURE 83.-Predicted percent damage to unreinforced concrete commercial structures in part of the Long Beach 1 ox 2° sheet as a 

result of shaking from a postulated earthquake along the northernmost 30 km of the Newport-Inglewood zone. Values indicate percent Joss if this type of construction is present. Solid numbers (1-9] 

indicate corresponding percent loss. Hollow numbers designate the 

following ranges in percent loss: 0, > 9 to 10 percent; 1, > 10 to 12 

percent; 2, > 12 to 16 percent; 3, > 16 to 20 percent; 4, > 20 to 25 

percent. Heavy line is the trace of the postulated seismic rupture, 

which extends northwestward about another 10 km into the Los 

Angeles basin. 

alluvium m and for water table at 30 ft or greater a- 1). 

The value of intensity used for calculating damage was 

the one of this pair that was closer to the reported intensity. Under "Losses, predicted," the column headed 0 

uses this intensity and the pre-1940 damage curve. The 

sequence of columns to the right is for losses calculated 

when relevant intensity is decreased in half-intensity 

increments, it being presumed that the protection 

achieved by post-1940 construction can be expressed as 

an increment of intensity protection. About 88 percent 

of all houses in Gilroy and Hollister have been built since 

1940. Therefore, losses observed should give some idea 

of the protection achieved by the change in building 

codes. Direct interpretation of table 29 would suggest 

that a protection of greater than one full intensity unit is 

Predicting Seismic Intensities 191 
TABLE 26.-Calculated replacement costs for wood-frame construction (pre- and post-1940) damaged 

by postulated earthquake along northernmost 30 km of the Newport-Inglewood zone using different 

assumptions of ground conditions 

[Losses are for shaking only and exclude damage to building contents] 

County 

J (saturated 

alluvium) 

Los Angeles ------------2.764 

Orange --------------- .156 

Riverside -------------- .005 

San Bernardino --------- .007 

Santa Barbara ---------- .001 

Ventura --------------- .015 

All of State ------------2.948 

Pre-19401 

Loss, in billions of 1977 dollars 

J-1 

0.697 

.045 

.000 

.000 

.000 

.003 

.746 

J (saturated 

alluvium) 

0.927 

.058 

.000 

.001 

.000 

.004 

.991 

Post-1940' 

j-1 

0.260 

.007 

.000 

.000 

.001 

.000 

.268 

Ratio of percent loss to cumulative loss 

Loss percent 

j (saturated 

alluvium) 

:s; 1 -----------0.159 

S2 ----------- .418 

:s; 3 -----------1.281 

S4 -----------1.570 

S5 -----------2.199 

:s; 6 -----------2.948 

:s; 7 -----------2.948 

1

From Evemden and others (1981). 2

From Gulliver (in press). 

Pre-1940' 

achieved by post-1940 building requirements. It is interesting to note that, in addition to a change in building 

code since 1940, there is now a generally enforced 

home-loan requirement that a termite inspection 

precede the sale of a dwelling. This factor, whose enforcement has nothing to do with earthquake design, 

may be as or more important in preventing damage at 

the time of an earthquake than most of the provisions in 

the building code. 

Third, consider the 1940 and 1979 Imperial Valley 

earthquakes. For brevity, we will only note a fact that 

anyone can confirm by inspecting the intensity maps for 

those earthquakes. That fact is that the reported patterns for the lower intensities for those two earthquakes 

in southern California were essentially identical. Modeling of those earthquakes would have predicted this identity on the basis of their observed surface breaks, the 

length of break into Mexico for the 1940 earthquake 

having little effect on the intensities in southern California. Also, strong-motion records obtained at the same 

site for the 1940 and 1979 earthquakes were very 

similar. Actually, the peak velocity on the 1979 record 

was nearly twice that on the 1940 record, peak accelerations on bqth being similar (fig. 85). Although the 

1940 record persisted longer than the 1979 record did, 

the period of high amplitudes was essentially the same 

192 Earthquake Hazards in the Los Angeles Region 

j-1 

0.404 

.746 

.746 

.746 

.746 

.746 

.746 

J (saturated 

(alluvium) 

0.427 

.991 

.991 

.991 

.991 

.991 

.991 

Post-1940' 

J-1 

0.268 

.268 

.268 

.268 

.268 

.268 

.268 

for both records, the average peak values on the 1979 

record being distinctly higher. Given the fact that intensity values scale by powers of two of the strong-motion 

parameter (see earlier discussion), the low-amplitude 

persistence of the 1940 record seems highly unlikely to 

have influenced intensities in any significant way. The 

minor differences between the 0.5- to 3-Hz filtered accelerograms for the two earthquakes can be seen in figure 

85. It is pertinent in this regard to note that the Imperial 

County Services Building failed at the moment of the 

peak velocity shown on figure 85 (Rojahn and Mark, 

1982), the one markedly different parameter between 

the 1940 and 1979 records. This incident would suggest 

that failure in 1940 was probably more closely linked to 

the time of high amplitudes than to the time of persistent 

low amplitudes. On this basis of evaluation, the record 

of the 1979 earthquake implies the higher level of 

destructive ground motion. 

Therefore, it seems probable that ground shaking was 

at least as strong along the fault in 1979 as it was in 

1940. However, reported intensities in the hardest hit 

areas were at least an intensity unit lower for the 1979 

earthquake than they were for the 1940 earthquake. 

The seemingly logical conclusion to draw from these 

relations is that the reported lower near-range inten-
TABLE 27.-Calculated replacement costs for wood-frame construction (pre- and post-1940) damaged 

by postulated repeat of 1857 Fort Tejon earthquake, using different assumptions of ground conditions 

[Losses are for shaking only and exclude damage to building contents] 

Loss, in billions of 1977 dollars 

Pre-19401 Post-1940' 

J [saturated J [saturated 

County alluvium) j-1 alluvium) j-1 

Fresno ----------------0.007 0.000 0.001 0.000 

Kern ----------------- .035 .010 .013 .003 

Kings ----------------- .003 .001 .001 .000 

Los Angeles ------------1.328 .363 .466 .108 

Orange --------------- .134 .040 .051 .003 

Riverside -------------- .064 .017 .021 .006 

San Bernardino --------- .199 .051 .067 .019 

San Diego ------------- .002 .000 :000 .000 

San Luis Obispo -------- .015 .004 .005 .001 

Santa Barbara ---------- .020 .006 .007 .000 

Tulare ---------------- .003 .000 .000 .000 

Ventura --------------- .047 .013 .017 .002 

All of State ------------1.858 .505 .650 .144 

Ratio of percent loss to cumulative loss 

Pre-19401 

J [saturated 

Loss percent alluvium) 

~1 -----------0.449 

~2 ----------- .975 

~3 -----------1.427 

~4 -----------1.617 

~5 -----------1.743 

~6 -----------1.790 

~7 -----------1.792 

~8 -----------1.793 

~ 12 -----------1.858 

1

From Evemden and othern (1981). 2

From Gulliver (in press). 

sities for the 1979 earthquake resulted not from lower 

levels of ground shaking but from improved structural 

design. 

We conclude that the damage data of these four 

earthquakes support the case for assuming that 

post-1940 wood-frame construction does indeed reduce 

predicted losses to wood-frame construction by a factor 

of about three. One can make the case that the righthand column in all of these tables is that appropriate for 

estimating average damage to most California woodframe homes in future earthquakes. 

Other Estimates of Dollar Loss 

However, before blithely accepting all of these conclusions, one must at least pay some attention to an 

assessment by the Federal Emergency Management Administration (FEMA) (1980) that predicts a $25 billion 

total loss to all building types as the result of a repeat of 

Post-1940' 

J [saturated 

J-1 [alluvium) J-1 

0.439 0.498 0.137 

.483 .620 .144 

.485 .623 .144 

.500 .623 .144 

.505 .643 .144 

.505 .650 .144 

.505 .650 .144 

.505 .650 .144 

.505 .650 .144 

the 1906 San Francisco earthquake. Although not published in the ·cited document, this total includes a $10.6 

billion loss to wood-frame construction; the mode of calculation used to achieve the latter figure has been described by the analyst, K. V. Steinbrugge (oral.presentation and written notes, 1980). When the curve for 

pre-1940 construction was used, nearly every parameter value used in our calculations was within a few percent of that used by Steinbrugge. One factor-percent 

loss to wood-frame structures-was not. Steinbrugge 

made no correlation of site, distance from fault, geology, 

or expected intensity with resultant percent structural 

damage. He assumed that there would be an average of 

12-percent loss to all wood-frame structures in the San 

Francisco Bay region (all six counties of table 30). As 

can be seen in figure 79, this assumption presumes that 

all communities in the region will experience intensity X 

and are of pre-1940 construction. As a matter of fact, no 

communities (not even downtown San Francisco) exPredicting Seismic Intensities 193 
TABLE 28.-Calculated replacement costs for wood-frame construction (pre- and post-1940) damaged 

by postulated repeat of 1906 San Francisco earthquake, using different assumptions of ground conditions 

(Losses are for shaking only and excludP damage to building contents J 

Loss, in billions of 1977 dollars 

Pre-1940' Post-194()2 

I (saturated I (saturated 

County alluvium) I-1 alluvium) I-1 

Alameda ------------------------ 0.907 0.240 0.315 0.079 

Contra Costa --------------------- .231 .060 .079 .021 

Humboldt ----------------------- .010 .003 .004 .001 

Marin -------------------------- .231 .079 .105 .026 

Merced ------------------------- .003 .000 .001 .000 

Monterey ------------------------ .099 .026 .033 .009 

Napa --------------------------- .012 .003 .004 .001 

Sacramento ---------------------- .009 .000 .000 .000 

San Benito ----------------------- .012 .003 .005 .001 

San Francisco -------------------- 1.034 .357 .502 .124 

San Mateo ----------------------- .819 .347 .449 .117 

Santa Clara ---------------------- 1.236 .416 .543 .139 

Santa Cruz ----------------------- .106 .040 .053 .013 

Solano -------------------------- .037 .010 .013 .003 

Sonoma ------------------------- .079 .021 .028 .007 

Stanislaus ----------------------- .005 .000 .001 .000 

Yolo---------------------------- .002 .000 .000 .000 

All of State----------------------- 4.855 1.608 2.142 .543 

Ratio of percent loss to cumulative loss 

Pre-19401 Post-194()2 

Loss percent 

I (saturated 

alluvium) 

:s; 1 ------------------- 0.047 

:52------------------- .095 

:s; 3 ------------------- .208 

:s; 4 ------------------- .249 

:s; 5 ------------------- .268 

:56------------------- .625 

:s; 7 ------------------- .921 

:s; 8 ------------------- 1.457 

:s; 9 ------------------- 2.049 

:s; 10 ------------------ 2.302 

:s; 11 ------------------ 3.975 

:s; 12 ------------------ 4.855 

1

From Evernden and others (1981). 2

From Gulliver (in press). 

perienced such intensity in 1906, and most wood-frame 

structures in the region have been built since 1940. As 

Freeman (1932) noted long ago, average percent loss in 

the areas hardest hit by earthquakes in the first part of 

this century seldom if ever exceeded 5 percent of value. 

The San Francisco earthquake of 1906 was no exception. In a document published in 1979 (Algermissen and 

Steinbrugge, 1979), an estimate of loss 'to all one- to fourfamily dwellings (nearly all of the wood-frame structures) in the greater San Francisco Bay area as a result 

of a repeat of the 1906 San Francisco earthquake was 

194 Earthquake Hazards in the Los Angeles Region 

I (saturated 

I-1 (alluvium) I-1 

0.058 0.064 0.186 

.357 .204 .544 

.599 .498 .544 

1.144 .779 .544 

1.537 1.429 .544 

1.608 1.696 .544 

1.608 2.142 .544 

1.608 2.142 .544 

1.608 2.142 .544 

1.608 2.142 .544 

1.608 2.142 .544 

1.608 2.142 .544 

given as $1.51 billion (1970 dollars). This figure is 

similar to the one calculated by Evernd{m and others 

(1981) and in this chapter by using the pre-1940 curve. 

Therefore, the logic behind assuming the 12-percent loss 

is unclear. 

To demonstrate fully the level of uncertainty of present estimates of damage, consider the calculated values 

in table 30. In this table, the value of all wood-frame 

residences in the six San Francisco Bay region counties 

is assumed to be $88 billion. Five models are used for 

calculating replacement values: 
1. As used by Steinbrugge for the FEMA report (that is, 

12-percent damage throughout the six counties). 

2. Geology as given by Helley and others (1979) and intensity scaling of the geologic units following R. D. 

Borcherdt (personal communication, 1983); a few 

modifications dictated by historical intensity data 

have increased predicted intensities in all cases 

(H/B). 

3. Ground conditions as above with one intensity unit 

protection (RFI) achieved through 1940 building 

code (H/B-1). 

4. Water table assumed to be at a depth of at least 30 ft 

throughout all regions shown as Quaternary 

alluvium on the geologic map of California; all 

such sites assumed to have the properties of recent alluvium a -1). 

5. Ground conditions as above with one intensity unit 

(RFI) protection achieved by the 1940 building 

code (U -1)- 1). 

Note that the values given in columns 3 and 5 of table 30 

are predictable as the most credible in the table on the 

basis of the analysis given above of the 1971 San Fernando, 1979 Coyote Lake, and 1940 and 1979 Imperial 

Valley earthquakes, considering that only a small fraction of bay area residences are on saturated alluvium. 

There is no evidence of a quantitative analysis that rejects the general notion that post-1940 structures in the 

San Francisco Bay region will suffer damage as predicted in columns 3 and 5. These results contrast significantly with the $10.6 billion obtained by following the 

procedures used for the FEMA study. The FEMA report 

(Federal Emergency Management Agency, 1980, p. 21), 

however, noted the uncertainties in loss estimation: 

" .. . Methodologies for estimates of this type are approximate at best. Consequently, the figure shown ... may 

vary upward or downward by as much as a factor of 

two or three." The results that we present in this 

chapter are at the lower limit of or beneath the uncertainty range of the FEMA results. One concludes that 

the range of results from various loss estimation techniques currently in practice is at least as great as the 

uncertainties given by FEMA. 

In this era of rapidly fluctuating building prices, 

current-dollar damage assessments are poor estimators 

for planning disaster relief and subsidization. A far 

more useful parameter is an average percent structural 

damage, as there are empirical data that allow correlation of the average percent damage with an estimation 

of the percent of homeless anticipated (Gulliver, in 

press). Therefore, this parameter of percent damage is 

included in table 30 in the column labeled "Percent 

damage." 

Table 31 and figure 86 indicate potential California 

earthquakes that have been modeled for estimates of 

rTTT"TI ' I , 1-,-1----.1---;l" ' l" l -,-- 1 -;-1--.-1-,

1

.,.,,,

1 ;-1 1

,-,-1 -;-1 ----.-- 1 ----,_ 10" 

1000 

CJ) 

a: 

LL 

f--

LL 

:if 

0 100 ...J 

;;;; 

~ 

r:E 

10 

2L, IN KM 1000 100 

I (MX) 10 9 

ML I I I I I I I I I 

8 7 

Parameters from data: 

I (MX). ML, R1 values 

k (1.75), c (25) 

Parameters found : 

2L = 8.5 km 

Av1= 1.1x10" cm' 

10 

8 7 

I I 1....,1 

6 

I I 

5 

1015 

CJ) 

a: 

LL 

f--

LL 

:if 

i= 

z 

LL 

u 

10" LL 

a: 

<l: 

:J 

a 

CJ) 

~ 

5 

<l: 

10" 

1 

I I 

FIGURE 84.-Data for 1979 Coyote Lake earthquake. Parameters from 

data: k=1.75 (attenuation function); C=25 (artificial number 

reflecting assigned depth of postulated earthquake (approximately 

15 greater than depth)); I(MX), maximum intensity; ML' local 

magnitude; Ri' radius of area within intensity contour. Parameters 

found: 2L = 8.5 km (length of fault break); AVI = 1.1 x 1014 km2 (area 

with intensity VI contour). Values of Modified Mercalli intensity 

are given in arabic numerals rather than roman numerals, so that 

gradations in intensity can be indicated. 

losses to wood-frame construction. All values in this 

table are based on the curve for pre-1940 construction. 

Appro'ximate conversion to wood-frame losses predicted 

for post-1940 construction is achieved by dividing the 

loss values in table 31 by a factor of three (see tables 

26-28). A vital point to note in table 31 is the comparatively low loss expected from a repeat of the 1857 

Fort Tejon earthquake. Virtually any large earthquake 

in the San Francisco Bay region would cause a comparable level of damage, and maximum-size potential 

earthquakes on the San Andreas and Hayward faults 

would cause much greater damage than a repeat of the 

1857 earthquake. In addition, several comparatively 

small earthquakes in southern California would cause 

as much or more damage than an 1857 repeat. Most particularly, a M 6.7 earthquake modeled for a rupture 

along the Santa Monica fault would cause more than 

twice the damage expected from an 1857 repeat. Of 

course, the reasons for this relation between earthquake size and caused damage are locations of the pertinent faults relative to manmade structures and the high 

Predicting Seismic Intensities 195 
I I I I I I I I I I I I I 

Max. value = .3487 g 

Max. value = .0282 g 

Max. value = .2589 g 

Max. value =.2183 g 

TABLE 29.-Predicted and actual losses to wood-frame construction in the southern San Francisco 

Bay region due to 1979 Coyote Lake earthquake 

[nfr, not reported] 

Modified Mercalli 

intensity Apparent Losses, in millions of doUars 

Predicted' ground Predicted 

City Observed J~O' I~ 1' condition 0" 0.5' 1.0' 1.5' Actual 

Salinas -------------------- VI 5.9 5.1 0 1.46 0.65 0 0 n!r• 

San Juan Bautista ------------ VI 6.5 5.7 -1 .23 0 0 0 nlr 

Gilroy --------------------- VII 7.2 6.3 0 2.18 .91 0.53 0.276 0.057 

Milpitas-------------------- VI 5.9 5.3 0 .75 .33 0 0 nlr 

Morgan Hill ---------------- VI 7.2 6.3 -1 .34 .17 0 0 nlr 

San Martin ----------------- VI 7.3 6.4 -1 .08 .04 .02 0 nlr 

San Jose-------------------- v 6.2 5.4 -1 0 0 0 0 nlr 

Sunnyvale ------------------ VI 5.8 5.1 0 2.02 0 0 0 n/r 

Santa Cruz ----------------- VI 5.9 5.3 0 .96 .43 0 0 nlr 

Hollister ------------------- VII 6.5 5.6 0 .63 .32 .19 0 .026 

Total ------------------------------------------------- 8.65 2.85 .74 .27 .07 

1 Arabic numerals are used here instead of the standard roman numerals, so that gradations in Modified Mercalli intensities can be 

shown. 2

J"" 0 is predicted intensity under assumption of water table at surface in alluvial areas. 3

J"' 1 is predicted intensity under assumption of water table at a depth of 30 ft in alluvial areas. 4Pred.icted loss for predicted intensity under J ==O or J:l that most closely agrees with the observed intensity. 5

Predicted. loss for intensities 0.5, 1.0, or 1.5 less than used under the column headed 0. Since an observed intensity VII encompasses 

predicted intensities of 6.5 to 7.5, modeling such as that used here can estimate only approximately the appropriate correction for 

post-1940 construction. 

"If observed intensity were 6.8 rather than 7.2 (water table down 10ft within model), dollar loss (1.5)•0. 7

From Kustu (1981). 

~atio of populations in Hollister and Gilroy) x {ratio of damage ratios in these two cities) x {damage in Gilroy). 

I I I I I I I I I I I I I I I I I I I I I I I I 

SEISMOGRAM Max. value = .4869 g 

.1-.5 Hz Max. value = .0245 g 

.5-3 Hz Max. value = .3151 g 

3-10Hz Max. value = .2832 g 

... ~ ...... .. 

I I I I I I I I I I 

SEISMOGRAM 

.1-.5 Hz 

.5--3 Hz 

3-10Hz 

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

TIME, IN SECONDS 

A 

TIME, IN SECONDS 

8 

I I 

FIGURE 85.-Selected acceleration and velocity records for the Imperial Valley earthquakes of May 18, 1940, and October 15, 1979. All records 

are from the same site at El Centro, Calif. {32.80° N., 115.54° W.). Figures present full bandwidth seismograms and seismograms filtered for 

bands 1, 2, and 3. Maximum values are given for each record. A, Ground acceleration for earthquake of May 18, 1940 {180° component). B, 
'I '1'1' 1- 1"1'1'1"1 '1'1'1"1 '1'1'1"1 """~-.1'1'1'"1'1'1'1"1'1.-""-, 1"1'1'1"1 '1'1'1"1 '1'1'1-ri 'l'l'l"l"""~"l'l'l'l"l'l'l'lrrrTIO'rrTO-ro 

Max. value = 32.3230 cm/s SEISMOGRAM Max. value = 42.5130 cm/s SEISMOGRAM 

Max. value = 11 .3370 cm/s .1-.5 Hz Max. value = 13.1466 cm/s .1-.5Hz 

Max. value = 28.6859 cm/s .5-3 Hz Max. value = 36.3207 cm/s .5-3 Hz 

Max. value = 7.6658 cm/s 3-10Hz Max. value = 9.7693 cm/s· 3-10Hz 

LL~LL~_L~~LLI~i~I-LI ~1~1-Li Li~I~I-ILL~I~i-ILLI~-L~~LL~_L~I LI~_L~_LLL~LL~I~I-ILLI~I~i-ILLI~I~I-LI LI~I~I_ILLi~I~LL~-L~~~ 

TIME, IN SECONDS 

c 

I I I I I I I I I I I I I I I I I lllilillli 

Max. value = 36.4730 cm/s SEISMOGRAM 

Max. value = 27.9296 cm/s .1-.5 Hz 

Max. value = 20.4745 cm/s .5-3 Hz 

Max. va lue = 3.5238 cm/s 3-10Hz 

I I I I I II I I I I I I I I I I 

TIME, IN SECONDS 

E 

TIME, IN SECONDS 

D 

I I I I I I I I I I I I I I I I I I I I I I I I I I 1 

Max. value = 67.7660 cm/s SEISMOGRAM 

Max. value = 40.7498 cm/s .1-.5 Hz 

Max. value = 27.4606 cm/s .5-3 Hz 

Max. value = 10.0339 cm/s 3-10Hz 

---.~~···M-1 - - I I I I I I I I I ! I I I I t I 

TIME, IN SECONDS 

F 

Ground acceleration for earthquake of October 15, 1979 (180° component). C, Ground velocity for earthquake of May 18, 1940 (180° component). D, Ground velocity for earthquake of October 15, 1979 (360° component). E, Ground velocity for earthquake of May 18, 1940 (270° component). F, Ground velocity for earthquake of October 15, 1979 (270° component). 
TABLE 30.-Calculated replacement costs (in billions of 1977 dollars) for wood-frame construction damaged by shaking from postulated repeat of 

1906 San Francisco earthquake 

(Based on various assumptions about percent loss and geologic ground conditions. Replacement values are totals; percent damages are averages] 

FEMA1 H/B2 H/B-1' J -1' 0-1)-1' 

Replacement Percent Replacement Percent Replacement Percent Replacement Percent Replacement Percent 

County value damage value damage value damage value damage value damage 

Alameda -------------------- 2.8 12 0.223 0.9 0.055 0.2 0.363 1.5 0.099 

Contra Costa ----------------- 1.3 12 .051 .5 .011 .1 .092 .8 .025 

Marin ----------------------- .5 12 .073 1.9 .023 .6 .119 3.1 .031 

San Francisco ---------------- 2.0 12 .189 1.2 .054 .3 .546 3.3 .145 

San Mateo ------------------- 1.4 12 .400 3.4 .137 1.2 .530 4.5 .130 

Santa Clara ------------------ 2.6 12 .508 2.4 .133 .6 .636 3.0 .159 

Total/average -------------- 10.6 12 1.44 1.6 .413 .5 2.29 2.6 .589 

1Values used in calculating total building losses for Federal Emergency Management Agency (1980), according to K. V. Steinbrugge (oral and written communications. 1980). 

:!various ground conditions as given by Helley and others (1979) and relation of ground condition and intensity from R. D. Borchardt (personal communication, 1982). Pre-1940 construction. 3

Same as HIB but for post·1940 construction {assumed to give one Rossi-Forel intensity unit protection). 

"Treated all Quaternary deposits on geologic map of California as being of same character and having water table at 30 ft. 5

Same as J -1 but for post-1940 construction {assumed to give one Rossi-Forel intensity unit protection). 

TABLE 31.-Predicted replacement value of wood-frame constructon damaged by shaking from potential earthquakes in 

western California 

[Based on earthquake intensity loss curve for pre-1940 construction. Typical ground conditions assumed to be alluvium with water tab]e 30 ft or more below ground 

surface. Excludes damage to building contents. Modified from Everndcn and others (1981, table 25)] 

Predicted replacement 

value for 

wood-frame 

Ends of break construction, 

Symbol Latitude, Longitude, Length, in billions of 

Fault [fig. 86) oN. ow. inkm Magnitude 1977 dollars 

San Andreas (1906 repeat) ------- 1 36 51.00 121 33.10 400 8.3 1.72 

4015.90 124 27.20 

Hayward -------------------- 2A 38 00.61 122 22.92 100 7.4 1.14 

37 11.76 121 44.62 

Hayward -------------------- 2B 37 48.89 122 13.73 50 7.0 .54 

37 24.46 121 54.58 

Hayward -------------------- 2C 37 27.53 121 52.28 20 6.4 .11 

37 11.76 121 44.62 

Calaveras (1911 repeat) --------- 3 37 09.10 121 34.90 11 6.1 .02 

37 14.20 121 39.90 

San Gregorio ----------------- 4 37 05.68 122 18.31 30 6,7 .04 

36 50.47 122 10.47 

Zayante --------------------- 5 37 02.43 121 53.64 15 6.3 .02 

36 56.55 121 47.03 

Hosgri ---------------------- 6 37 29.90 129 54.50 80 7.3 .01 

34 12.20 121 05.90 

Hosgri (1927 repeat) ------------ 7 34 36.00 120 38.80 70 7.2 .02 

35 11.90 120 54.50 

Nacimiento (1952) ------------- 8 35 44.20 121 07.70 20 6.4 !S .001 

35 52.10 12116.90 

Santa Barbara ---------------- 9A 34 28.20 120 04.80 40 6.9 .023 

34 25.70 119 39.10 

Near Santa Barbara: 

1925 repeat --------------- 9B 34 27.70 120 00.10 29 6.7 .015 

34 25.90 119 41.40 

1978 repeat --------------- 10 34 22.20 119 43.00 4 5.4 .003 

34 23.34 119 45.44 

San Andreas (1857 repeat) ------- 11 34 18.30 117 31.50 300 8.1 .51 

35 45.10 120 17.80 

Offshore San Clemente --------- 12 33 34.05 117 56.10 40 6.9 .16 

33 18.65 117 36.92 

198 Earthquake Hazards in the Los Angeles Region 

0.4 

.2 

.8 

.9 

1.1 

.7 

.7 
TABLE 31.-Predicted replacement value of wood-frame constructon damaged by shaking from potential earthquakes in 

western California-Continued 

Predicted replacement 

value for 

wood-frame 

Ends of break construction, 

Symbol Latitude, Longitude, Length, in billions of 

Fault (fig. 86) oN. ow. inkm Magnitude 1977 dollars 

Newport-Inglewood ----------- 13A 33 54.50 118 17.40 45 6.9 .90 

33 36.30 117 58.80 

Newport-Inglewood ----------- 138 33 54.50 118 17.40 22 6.5 .53 

33 45.50 118 08.10 

Newport-Inglewood ----------- 13C 33 45.40 118 08.10 22 6.5 .33 

(1933 repeat). 33 36.30 117 58.80 

Newport-Inglewood ----------- 13D 34 02.69 118 25.77 42 6.9 1.05 

33 45.50 118 08.10 

whittier --------------------- 14 33 58.99 118 00.00 20 6.4 .35 

33 55.14 117 47.80 

Raymond ------------------- 15 34 12.18 118 01.95 10 (C=20)' 6.0 .26 

34 10.35 118 07.80 (C=25)' 

Elsinore: 

South ------------------- 16A 33 25.80 117 00.00 70 7.2 .04 

33 00.00 116 27.00 

North ------------------- 168 33 40.54 117 22.93 30 6.7 .03 

33 29.19 117 09.27 

San Fernando (1971 repeat) ------ 17 34 22.78 118 30.31 19 (C=20)' 6.4 .26 

34 18.62 118 16.55 

San Jacinto ------------------ 18A 34 03.04 117 11.80 30 6.7 .06 

33 51.89 117 02.44 

San Jacinto ------------------ 188 34 08.96 117 16.76 38 6.8 .09 

33 51.89 117 02.44 

Malibu Coast ----------------- 19 34 06.10 118 56.44 31 (C=20)' 6.7 .38 

34 05.10 118 33.17 

Santa Monica ---------------- 20 34 06.10 118 33.17 32 (C=20)' 6.7 1.14 

34 10.01 118 09.27 

Rose Canyon ----------------- 21A 32 53.11 117 18.05 51 7.0 .28 

32 30.41 116 58.79 .072 

Rose Canyon ----------------- 218 32 48.85 117 14.44 32 6.7 .23 

32 34.67 117 02.40 .oo• 

1

For thrust earthquakes, a C value of 20 is used {rather than 25, as used for strike-slip earthquakes). 2 Assumes that typical ground condition in San Diego results in shaking two intensity units less than that for saturated alluvium. 

rates of attenuation of intensity-relevant energy in 

western and southern California. 

Although the San Jacinto fault is the most seismically 

active fault in southern California today, its location and 

the apparently limited maximum size of earthq!.lakes 

that occur on it render it a limited regional threat, 

although, it certainly is of great significance to San Bernardino and environs. Because the earthquakes hypothesized for the San Jacinto fault are assumed to be 

located on the northern 30 or 39 km of that fault, even a 

doubling of the rupture length by extension southward 

would not significantly increase predicted structural 

damage. The losses calculated for San Diego as the 

result of hypothesized earthquakes on the Rose Canyon 

fault are based on intensities assuming ground-motion 

characteristics equivalent to one and two intensity units 

less than predicted for saturated alluvium. Since most of 

the city is built on bedrock or raised marine terraces, 

figures based on saturated alluvium seem inappropriate 

as estimators of predicted damage, although they cer· 

tainly are appropriate at particular sites. 

Although other fault breaks could have been modeled, 

the examples given illustrate the numerous possibilities 

that exist for extensive damage in southern California 

and demonstrate that the San Andreas fault is not the 

primary threat to the Los Angeles region. A fact of great 

importance is that the calculations given in table 31 indicate that damage to wood-frame structures amounting 

to more than five times that incurred at the time of the 

1971 San Fernando earthquake is not to be expected. 

Given the limited data bases presently available, the 

only route to estimating total loss for all structures is by 

Predicting Seismic Intensities 199 
124° 

\ 

\ 

\ 

0 

0 50 

123° 122° 121° 

0 

APPROXIMATE SCALE 

50 100 150 MILES 

1 DO 150 KILOMETERS 

Bakersfield 

0 

FIGURE 86.-Postulated earthquakes in western California that were modeled for estimating losses to wood-frame construction listed in table 31. 

From Evernden and others (1981, fig. 25). 

200 Earthquake Hazards in the Los Angeles Region 
empiricism based on very limited data sets. Blume and 

others (1980) multiplied wood-frame losses by a factor of 

2.0 to get total losses when using the curve appropriate 

to pre-1940 wood-frame structures for estimating woodframe losses. Steinbrugge apparently used a factor of 

2.39 in the FEMA study discussed above. If one estimates wood-frame losses by the post-1940 curve, one 

should use a multiplication factor of four or five to empirically estimate losses to all structures. 

SUMMARY 

Of the several commonly used measurements of 

ground shaking associated with earthquakes, only 

seismic intensity has the properties of correlating 

directly with expected damage to structures of a 

specific bandpass (aproximately 3--0.5 Hz) and of being 

predictable with high accuracy. Given these unique 

properties, it is the logical parameter to incorporate into 

computer-based schemes for estimating local and 

regional seismic risk and damage. Maps showing predictions of intensity for any potential earthquake in the Los 

Angeles region can be easily prepared. These maps can 

be used to estimate losses to wood-frame construction 

caused by shaking resulting from such potential earthquakes and illustra~e the relative risks associated with 

different faults in California. 

APPENDIX 2.-MATHEMATICAL 

DETAILS OF MODEL FOR 

PREDICTING INTENSITIES 

A long curved fault (only possible in regions where 

k = 1%) is assumed to be a series of uniform point 

sources as closely spaced as desired. The formula used 

is 

(

10n.B+1.5Ml1/ l n ]1/ a=A n 'Y E (Ri + C)-k-r 'Y 

·=1 

(3) 

(effectively equation 7 of Evernden and others (1973), 

where 'Y = 4 and the coefficient of M is 0.864 rather than 

0.80) and 

I= Rossi-Forel intensity. 

M = Ms = ML Oocal magnitude) up to Ms = 6.5. 

n = number of equally spaced subevents used in the 

model to achieve nearly uniform release of energy 

along the fault break. 

e = 1011·

8 +l.sM =energy (ergs) released by an earthquake 

of magnitude M (Richter, 1958, p.366). 

Ri = distance, in kilometers, from point i of n points on 

a fault to the point of observation. 

C = pseudodepth term chosen to give proper nearrange dieoff of intensities. Intensity values beyond 

50 to 100 km are nearly insensitive to variation in 

expected values of C for earthquakes in the United 

States. 

k= term controlling rate of dieoff of a (acx.1-k) and 

thus effectively of I. 

'Y = log (energy arriving at a point)/(a) or a= (energy arriving at a point)11

"Y. 

A= 0.779 =arbitrary leading coefficient selected to 

give correct intensity values at a uniform ground 

condition for a particular earthquake. Once set for 

the normalizing earthquake, it cannot be changed. 

The value used was set to give identical shortrange I values as given by Evernden and others 

(1973), where 'Y = 4. 

The points of the "fault" are distributed over a length 

(2L) appropriate to theM value (or an M value is used appropriate to the length of break 2L) (see discussion below). 

When shorter or straight faults are considered, equation 

3 can be slightly altered to simplify analysis and 

manipulation and to escape the multipoint aspect of 

energy release. Details of this formulation of equation 3 

have been given by Evernden and others (1981). 

A brief discussion of the role of the several defined 

factors in controlling predicted intensities follows. 

L and M.-When this discussion is limited to conditions appropriate to southern California, empirical data 

of this area indicate a general correlation between L 

and M. Associating a 2L of 10 km with an M of 6.0 and a 

2L of 400 km with an M of 8.25 leads to M = (3.2667 +log 

Oength of break)/0.711. Table 32 gives a tabular presentation of this formula. 

Leading coefficient.-The coefficient used is arbitrary and was chosen as appropriate for predicting I 

values on saturated alluvium, the control data used being intensity values for the San Francisco earthquake of 

1906. 

I= 3(0.5 +log a) (4) Mode of calculating RMS acceleration.-For long 

(Richter, 1958), where 

a= "acceleration." 

fault breaks such as the 1906 San Francisco and the 

1857 Fort Tejon, it is appropriate to consider energy 

from only a small portion of the fault, because energy 

Predicting Seismic Intensities 201 
TABLE 32.-Magnitude (M) 

relative to length of break (2L) and 

energy density Oog eoJ 

[Applicable only to regions of ks1.75.] 

M 2L log eD 

4 ------ 0.4 18.2 

5 ------ 2 19.0 

5.5 ----- 4.5 19.4 

6 ------ 10 19.8 

6.5 ----- 23 20.2 

7 ------ 50 20.6 

7'12 ---- 116 21.0 

8 ------ 265 21.4 

8.25 ---- 400 21.6 

8.5 ----- 600 21.8 

9 ------ 1,350 22.2 

202 Earthquake Hazards in the Los Angeles Region 

from distant parts arrives so late that it is of no importance for influencing intensity. For such earthquakes, 

the program calculates a as the square root of the sum 

of the squares of the a values arriving at the station 

from those points on the fault having traveltimes such 

that they arrive in a time window of 20 s centered 

around the arrival from the closest point on the fault. 

Use of this time-window procedure led to changing k 

from 2.0, as Evernden and others (1973) had used, to 

1.75, as they used in all subsequent papers. Evidence for 

the validity of this change is that it then became possible 

to accurately predict intensities for all magnitudes from 

about 5.5 to 8.25, a very powerful check on the accuracy 

of the scaling parameters. Further details have been 

given by Evernden and others (1981). 
PREDICTIVE MAPPING OF 

EARTHQUAKE GROUND MOTION 

By W. B. Joyner and T. E. Fumal 

INTRODUCTION 

This chapter describes methods for the predictive 

mapping of quantities used in the engineering design of 

earthquake-resistant structures. The most useful such 

quantities are horizontal response spectral values, but 

we also discuss peak horizontal acceleration and velocity. The response spectrum is the basis, either directly or 

indirectly, of most earthquake-resistant design. It is 

used directly as input in the dynamic analysis of structures and indirectly in building codes as the basis for the 

relation between the lateral design force coefficient and 

the period (Applied Technology Council, 1978). The 

response spectrum is useful because it represents the 

response to a given ground motion of a simple set of 

mathematical models of structures. It can be defined as 

the response of a set of single-degree-of-freedom 

oscillators (for example, mass-spring systems) having 

different natural periods and damping. An example is 

given in figure 87, which shows the response spectrum 

computed for one of the horizontal components of 

ground motion recorded in the 1979 Imperial Valley 

earthquake at station number 7 of the El Centro array. 

Among the different kinds of response spectra, we make 

use in this chapter of pseudovelocity response spectra 

and pseudoacceleration response spectra. The pseudovelocity response is defined as the product of the relative displacement response and the angular frequency 

of the oscillator; the pseudoacceleration response is 

defined as the product of the relative displacement 

response and the square of the angular frequency of the 

oscillator. 

Although response spectral values are the most useful 

parameters for earthquake-resistant design, we include 

discussions of peak horizontal acceleration and velocity 

because they have commonly been used to characterize 

earthquake ground motion. In fact, the conventional 

method for estimating response spectral values uses 

peak horizontal acceleration to scale some normalized 

spectral shape such as the Nuclear Regulatory Commissian's Regulatory Guide 1.60 spectrum (U.S. Atomic 

Energy Commission, 1973). Such a procedure would be 

generally valid only if the shape of the response spectrum were independent of earthquake magnitude, 

source distance, and recording site conditions. In fact, a 

number of independent studies (McGuire, 1974; 

Trifunac and Anderson, 1978; Joyner and Boore, 1982a, 

b) have shown that the shape of the response spectrum 

is strongly dependent on magnitude and site conditions. 

This problem is largely avoided by Newmark and Hall's 

(1969) scaling method, which scales the short-period 

portion of the spectrum by peak acceleration, the intermediate portion (about 0.3 to 2.0 s) by peak velocity, 

and the long-period portion by peak displacement. The 

ideal approach, however, is to predict response values 

directly, as McGuire (1974), Trifunac and Anderson 

(1978), and, incorporating data from the 1979 Coyote 

Lake and Imperial Valley earthquakes, Joyner and 

Boore (1982a, b) have done. 

The two basic elements in any method of making predictive ground-motion maps are (1) predictive equations 

giving the dependence of the ground-motion parameters 

on variables such as magnitude, distance and nearsurface geologic conditions and (2) a means of specifying 

the location and magnitude of future earthquakes. The 

predictive equations used here are derived from regression analysis of strong-motion accelerograph data from 

shallow earthquakes in western North America. Previously published equations are modified to incorporate 

an improved method of predicting site effects using local 

shear-wave velocity. Shear-wave velocity is estimated 

by the methods of Fumal and Tinsley (this volume). As 

for the magnitude and location of the earthquakes, 

predicted ground motion can be mapped for a postulated earthquake of specified magnitude and location, or 

the ground-motion value that will be exceeded at a 

specified annual probability can be mapped, taking into 

account potential earthquakes on a number of faults. In 

the latter case, fault slip rates are used to characterize the earthquake potential of different faults. 

Predictive Ground-Motion Mapping 203 
w·o 

C/lz 

z o O u O..w 

(/) (f) 

w 

a:: a: 

w >- a_ 

t:: (/) ua: 

ow _Jtl:J 

w2 

> - O f0~ ::J u w 

C/JZ 

o._-

40.0 

20.0 

10.0 

4.00 

tors that tend to limit (or enhance) motion near the 

source. Using a value of h that is independent of 

magnitude is equivalent to assuming that the curve 

showing the attenuation of the predicted parameter 

with distance has the same shape independent of 

magnitude; in other words, the change in the predicted 

parameter for a given change in magnitude is the same 

at every distance. Boore and Joyner's {1982; Joyner and 

Boore, 1981, 1982a, b) examination of the data for peak 

horizontal acceleration, velocity, and response spectra 

does not support a magnitude-dependent shape. Campbell {1981) has arrived at a different conclusion with 

respect to peak horizontal acceleration, but, in spite of 

this difference and other differences in assumptions and 

method, his predictions for peak horizontal acceleration 

and those of Joyner and Boore (1981) differ by only small 

2 5

8 "'--'----"'-''-.----'-.o"".2._L___j.~.__j__-=L__:~2C>...t.'-----~~L...J,""1 o---.:,..L:,J20 amounts in comparison with statistical uncertainty. 

UNDAMPED NATURAL PERIOD. IN SECONDS The measure of distance used is the shortest distance 

to the vertical projection of the fault rupture on the surFIGURE 87.-Pseudovelocity response spectra for the 1979 Imperial 

Valley earthquake. El Centro array, station 7, 230° component 

(Brady and others, 1980). Spectra are shown for 0, 2, 5, 10, and 20 

percent of critical damping. 

PREDICTIVE EQUATIONS 

To calculate the effect of earthquake magnitude and 

distance on ground-motion values, we use the predictive 

equations developed by Joyner and Boore (1981, 1982a, 

b) from analysis of strong-motion recordings: 

logy= c0 + c1(M-6) + ciM-6)2 + c3 log r + c4r + S 

5.0::s;M::s;7.7 

r = (d2 + h2)112 

S = 0 (rock sites) 

S = c5 (soil sites) 

(5) 

where y is the ground-motion parameter to be predicted, 

M is moment magnitude (Hanks and Kanamori, 1979), 

and d is the shortest distance from the site where 

ground motion is being predicted to the vertical projection of the earthquake fault rupture on the surface of the 

Earth. The parameters c0 through c5 and h have been 

determined from the strong-motion data by a two-stage 

regression procedure described by Joyner and Boore 

(1981, 1982a, b). The predictive equations for peak 

horizontal acceleration are illustrated in figure 88, 

those for peak horizontal velocity in figure 89, and those 

for horizontal response spectra in figures 90, 91, and 92. 

The parameter h is a fictitious depth introduced to 

allow for the fact that the source of the peak motion (or 

the maximum response in the case of response spectral 

values) may not be the closest point on the rupture surface. The value obtained for h incorporates all the fac204 Earthquake Hazards in the Los Angeles Region 

face of the Earth rather than the shortest distance to the 

rupture, because the introduction of the parameter h 

makes allowance for, among other things, the fact that 

the source of the peak motion (or maximum response) 

may lie at some depth below the surface. Using the 

shortest distance to the rupture surface for d in equation 5 would be, in effect, compensating twice for the 

effect of depth. In making predictive ground-motion 

maps, we must, of course, use the same definition of 

distance d that was used in developing the predictive 

equations from the strong-motion data. The actual 

distribution of ground motion close to a specific earthquake, particularly directly over a dipping fault, will undoubtedly be more complex than these simple equations 

predict, but we believe that these relations are a sound 

basis for making useful ground-motion estimates even 

close to the earthquake. 

Moment magnitude (Hanks and Kanamori, 1979) is defined as 

(6) 

where M0 is the seismic moment in dyne-centimeters. 

Determination of the seismic moment of potential earthquakes, therefore, permits the use of equation 5 to 

estimate ground motion. 

Table 33 gives the parameters of the predictive equations for the larger of two horizontal components of 

pseudovelocity response (5-percent damping), peak 

acceleration, and peak velocity. Table 34 gives the corresponding parameters for the random horizontal component. The estimated standard deviation of an individual prediction, uY, is also given in tables 33 and 34. The 

quantities c6 and V0 in tables 33 and 34 have to do with 

improved estimates of site effects obtained by using site 
0) 

z 

z · 

0 

~ 0:: 

w 

_J 

w 

u 

u 

<( 

_J 

<( 

fz 

0 

!:::! 

0:: 

0 

:r: 

1.0 

0.01 

M 

7.5 

6.5 

5.5 

o. oo 1 L.LLLLUL..--!--..l.......L.L..L.LJ..J..J..._....__L......L~.L1.1 o..._o_L_L_J_J 

DISTANCE, IN KILOMETERS 

FIGURE 88.-Predicted value of peak acceleration for the randomly 

oriented horizontal component as a function of distance and moment magnitude. Curves are dashed where not constrained by 

data. 

shear-wave velocity as discussed in the following section. The parameters given in table 34 for the predictive 

equations for the random component of peak horizontal 

acceleration and velocity were obtained from the values 

given by Joyner and Boore (1982b) for the larger of two 

horizontal components by changing the constant term c0 

by an amount determined by averaging the difference 

between the logarithm of the larger peak and the 

average logarithm of the two peaks over a selected 

subset of the data set used by Joyner and Boore (1982b). 

The coefficient c2 of the quadratic term in magnitude 

is not significantly different from zero at the 9D-percent 

confidence level for peak acceleration and peak velocity 

Uoyner and Boore, 1981) and so is given on tables 33 and 

34 as zero. Also for the response spectral values at most 

periods, c2 is not significantly different from zero at the 

9D-percent confidence level, but the values obtained at 

different periods are consistent enough to convince 

Joyner and Boore (1982b) that inclusion of the quadratic 

term is warranted. The maximum resulting difference in 

predicted values, with and without the quadratic term, 

is only about 20 percent. The c2 coefficient warrants 

special interest because, for the response spectral 

values, it is of such sign and size that it causes the curve 

of response versus magnitude for constant distance to 

level off with increasing magnitude, an effect commonly 

referred to as saturation. 

The data set from which the predictive equations 

were determined contained no events having magni-

~~ - 0 ~u - w UC/J 10.0 ~---­

Oo:: 

_Jw 

~a... 

_J(/) 

<(0:: 

t-W 

ztow N::?: 1.0 

a:f= 

oz 

M 

7.5 

:r:~ 6.5 

5.5 

0. 1 L...L...LLl..Ll.L_.J.._L.J....LL.l.LlL-.J..._J___i_.L..L.I.~~ ........... _J_J 

1 10 

DISTANCE, IN KILOMETERS 

FIGURE 89.-Predicted value of peak velocity for the randomly 

oriented horizontal component as a function of distance and moment magnitude at rock sites (heavy line) and soil sites (thin line). 

Curves are dashed where not constrained by data. 

tudes outside the range 5.0 to 7.7; the equations thus 

should not be used outside that range. For magnitudes 

greater than 7.7, we use the values computed from the 

predictive e<~,uations for a magnitude of 7.7. The predictive equations are constrained by data at soil sites for 

the entire distance range of interest for magnitudes less 

than 6.5. For values of d less than 15 km and magnitudes 

greater than 6.0 at rock sites and for values of d less 

than 25 km and magnitudes greater than 7.0 at all sites, 

the predictive equations are not constrained by data, 

and the predicted values should be treated with caution. 

Examples presented in this chapter show such values by 

dashed contour lines. 

USING LOCAL SHEAR-WAVE 

VELOCITY TO IMPROVE 

PREDICTIONS OF SITE EFFECTS 

The use of a simple rock-versus-soil classification to 

account for site effects in the predictive equations 

described in the previous section is necessitated by 

limited knowledge of the geology at the strong-motion 

sites. We have, however, measured shear-wave velocity, 

in drill holes to depths generally equal to or greater than 

30 m, at 33 of the strong-motion sites where data used in 

deriving the predictive equations were recorded. Included in these 33 locations are most of the sites in the 

Predictive Ground-Motion Mapping 205 
data set Uoyner and Boore, 1981) for the 1971 San Fernando earthquake. We use these shear-wave velocity 

data to derive a modification of the predictive equations 

intended to improve the prediction of site effects. The 

method is described briefly here; a fuller discussion is 

planned for submission to the Bulletin of the Seismological Society of America. The development of predictive 

equations in terms of site shear-wave velocity permits us 

to make predictive ground-motion maps using the methods described by Fumal and Tinsley (this volume) for 

mapping shear-wave velocity. 

There is a basis in traditional seismologic theory 

(Bullen, 1965; Aki and Richards, 1980) for using local 

shear-wave velocity to estimate the site effect on 

ground-motion amplitude. If we neglect losses caused by 

reflection, scattering, and anelastic attenuation, the 

energy along a tube of rays is constant, and the amplitude is inversely proportional to the square root of the 

product of the density and the propagation velocity. If 

we include a correction for the change in the crosssectional area of the ray tube caused by refraction in a 

medium where velocity is a function of depth, the amplitude of ground motion is proportional to 

(cos i)-112 (pV)-112 

where pis the density, Vis the propagation velocity, and 

i is the angle of incidence measured from the vertical. 

The variations in density are relatively smali and tend to 

correlate with the shear-wave velocity. Because propagation velocity tends to increase with depth, incidence 

angles are small near the surface, and the factor in cos i 

can be neglected. Thus, amplitude is approximately proportional to the reciprocal of the square root of the propagation velocity. As Joyner and others (1981) proposed 

in analyzing data from the 1979 Coyote Lake earthquake, we use shear-wave velocity, measured over a 

depth of one-quarter wavelength of the period of concern, for predicting the site effect on ground motion. 

This method of predicting site effects does not account 

for resonance effects, which involve reinforcing multiple reflections. Narrow-band measures of ground motion such as Fourier spectra or undamped response 

spectra are certainly affected significantly at some sites 

by resonance. Broader band measures such as we propose to predict, however, will in general be less affected. Resonance effects appear in undamped response 

spectra as sharp peaks at the resonant frequency. Such 

peaks are substantially reduced in the 5-percent 

damped spectral values that we propose to predict. 

To develop the modified predictive equations, we consider sites in the strong-motion data set for which shearwave velocity data are available and take the residuals 

of log y with respect to the values predicted by equation 

206 Earthquake Hazards in the Los Angeles Region 

0 

z 

0 

u 

w 

(/) 

a: 

w 

0.... 

(/) 

a: 

w 

t:u 100 ~ 

i= 

z 

w 

u 

z 

w 

(/) 

z 

0 

0.... 

(/) 

w 

a: 

~ 

u 

0 

__.J 

w 

> 

0 

0 

:::l 

w 

(/) 

0.... 

10 

~----- / ~ / M 

/ 

7.5 

--------------- ;;/ /_ / - t /~---- 6.5 

~ -----

5.5 

1L_ __ _L __ L_L_LL~LL ____ L__L_L_L~~ 

0.1 1.0 10.0 

PERIOD, IN SECONDS 

FIGURE 90.-Predicted pseudovelocity response spectra for 5-percent 

damping at rock sites (heavy line) and soil sites (thin line) for d = 0 

and M = 5.5, 6.5, and 7.5. Spectra correspond to the randomly 

oriented horizontal component. Curves are dashed where not constrained by data. 

5 for rock sites. A linear regression is done between 

those residuals and the logarithm of the average shearwave velocity to a depth of one-quarter wavelength of 

the period of interest. This analysis requires extending 

the downhole shear-wave velocity profile in many cases 

to depths substantially greater than the deepest measurement, with the help of whatever geologic data are 

available. Ground-motion data show some variation between earthquakes in addition to variations caused by 

differences in magnitude. To avoid confusing variation 

caused by site conditions with variation between earthquakes, the regression is done using the equation 

(7) 

where Rii is the residual for earthquake i at site j, Vi is 

the average shear-wave velocity to the appropriate 
M =6.5 

0 

z 

0 

u 

w 

(f) 

a: 

w 

Q_ 

(f) 

a: 

w 0 fw 100 

L 5 fz 

w 10 

u 

z 

w 20 (f) 

z 

0 

Q_ 

(f) 

w 

a: 

>- 10 

t::: 

u 

0 

_J 

w 

> 

0 

0 

:::> 

w 

(f) 

Q_ 

1.0 10.0 

PERIOD, IN SECONDS 

FIGURE 91.-Predicted pseudovelocity response spectra for 5-percent 

damping at soil sites for M = 6.5 and d = 0, 5, 10, 20, and 40 krn. 

Spectra correspond to the randomly oriented horizontal 

component. 

depth at site j, and pi and c6 are parameters determined 

by the regression. Figure 93 shows a log-log plot of the 

residuals against shear-wave velocity for peak horizontal ground velocity. The regression using equation 7 

gives the slope of the straight line relating the logarithm 

of ground motion residual to the logarithm of site shearwave velocity, but it does not give a unique intercept. 

We obtain the intercept by requiring that the average 

site effect term calculated by using the shear-wave 

velocity be the same as the average calculated for the 

same group of stations by using the simple rock-versussoil classification. The resulting site effect term can be 

cast in the form 

(8) 

where V is the local shear-wave velocity and V0 is a 

M=7.5 

0 

z 

0 

u 

w 

(f) ,..-----

/ ' 0 a: 

w / ,..-------...... Q_ /// .......... 5 (f) 

a: 

w // ....----.......... 10 fw 100 j/ / 

L ;_/ / 

f= h'/ // 20 z 

w 

u h'l/ 

z ll/ d=40 

w 

(f) t71 

z 11 0 I Q_ 

(f) 

w 

a: 

>- 10 

t::: 

u 

0 

_J 

w 

> 

0 

0 

:::> 

w 

(f) 

Q_ 

1.0 10.0 

PERIOD. IN SECONDS 

FIGURE 92.-Predicted pseudovelocity response spectra for 5-percent 

damping at soil sites for M = 7.5 and d =0, 5, 10, 20, and 40 krn. 

Spectra correspond to the randomly oriented horizontal component. Curves are dashed where not constrained by data. 

reference velocity. Values of c6 and V0 are given in 

tables 33 and 34 for the various ground-motion quantities to be predicted, except for peak acceleration and a 

few of the short-period response values for which the 

correlation between the logarithm of ground-motion 

residual and the logarithm of shear-wave velocity is not 

statistically significant at the 9(}-percent level. 

To avoid problems resulting from the ground-motion 

variation between earthquakes, data from a single 

earthquake (the 1971 San Fernando earthquake) are 

used to compare the effectiveness of the two methods of 

accounting for site effects. Analysis of the peak horizontal velocity data from the San Fernando earthquake 

shows a significant reduction in residual variance when 

shear-wave velocity rather than the twofold site 

classification is used to predict the site effect. For 

response spectral values at 1.0 s, the reduction is not 

Predictive Ground-Motion Mapping 207 
TABLE 33.-Parameters in the predictive equations for the larger of two horizontal components of pseudovelocity response (cm/s) at 5·percent 

damping and of peak acceleration (g) and velocity (cm/s) 

[Co through G. and hare used in equation 5 and were determined from strong~motion data by a two-stage regression procedure Uoyner and Boore, 1981, 1982a, b). oy is the standard error of an individual prediction by equation 5. G. and V0 are used in equation 8 and were determined by a regression procedure described in the textJ 

Period, h. c •. v •. 

ins Co c, c, inkm c, in krn- 1 c, in m/s c. a y 

Pseudovelocity response 

0.1 ------------------ 2.24 0.30 -0.09 10.6 -1.0 -0.0067 -0.06 0.27 

.15 ------------------ 2.46 .34 -.10 10.3 -1.0 -.0063 -.05 0.27 

.2 ------------------ 2.54 .37 -.11 9.3 -1.0 -.0061 -.03 0.27 

.3 ------------------ 2.56 .43 -.12 7.0 -1.0 -.0057 .04 650 -0.20 0.27 

.4 ------------------ 2.54 .49 -.13 5.7 -1.0 -.0055 .09 870 -.26 0.30 

.5 ------------------ 2.53 .53 -.14 5.2 -1.0 -.0053 .12 1050 -.30 0.32 

.75 ------------------ 2.46 .61 -.15 4.7 -1.0 -.0049 .19 1410 -.39 0.35 

1.0 ------------------ 2.41 .66 -.16 4.6 -1.0 -.0044 .24 1580 -.45 0.35 

1.5 ------------------ 2.32 .71 -.17 4.6 -1.0 -.0034 .30 1780 -.53 0.35 

2.0 ------------------ 2.26 .75 -.18 4.6 -1.0 -.0025 .32 1820 -.59 0.35 

3.0 ------------------ 2.17 .78 -.19 4.6 -1.0 .0 .29 1620 -.67 0.35 

4.0 ------------------ 2.10 .80 -.20 4.6 -.98 .0 .24 1320 -.73 0.35 

Peak acceleration 

0.49 0.23 0.0 8.0 -1.0 -0.0027 0.0 0.28 

Peak velocity 

2.17 0.49 0.0 4.0 

significant. In both cases, the reduction in variance is 

not large in comparison with the total variance, and it is 

not well determined because of the limited number of 

sites for which we have shear-wave velocity data. For 

these reasons, a separate value of aY for the case when 

the site effect is predicted from shear-wave velocity is 

not given. The fact that the reduction in variance is 

relatively small should not be taken to mean that it does 

not matter much which method of predicting the site 

effect is used. At a typical site, it may make little difference which method is used, but, at some sites, the difference is large, and we believe that the use of shear-wave 

velocity will give better estimates. 

CHARACTERIZING 

EARTHQUAKE SOURCES 

If the magnitude and location of an earthquake are 

specified, as they are for the postulated earthquake 

described by Ziony and others (this volume), the predictive equations described in the preceding two sections 

are all that is needed to make predictive ground-motion 

maps. On the other hand, we may wish to determine the 

level of ground motion that has a specified annual probability of being exceeded, given one or more seismogenic 

faults. Methods of solving this classic problem in 

engineering seismology are discussed by Cornell (1968), 

208 Earthquake Hazards in the Los Angeles Region 

-1.0 -0.0026 0.17 1190 -0.45 0.33 

Der Kiureghian and Ang (1977), Algermissen and 

Perkins (1976), and McGuire (1978). When these computations are made, the statistical variation in groundmotion values about the expected value given by the 

attenuation relation is commonly neglected but need not 

be (McGuire, 1978). Historical seismicity data are commonly used to define the activity of the sources, but 

geologic data on fault slip rates may also be used 

·(McGuire and Shedlock, 1981). In California, particularly, the use of slip-rate data is appealing because the 

historical record is relatively short and geologically 

determined slip-rate data of relatively high quality are 

becoming available (Allen, 1975). 

One very important advantage of using slip rate to 

characterize the seismicity is· that, by doing so, one can 

make ground-motion estimates that are to a good approximation independent of assumptions concerning the 

details of the magnitude-frequency relation. We illustrate the proposition here with a simple example; a 

demonstration that the proposition holds true in general 

is given in appendix 3. For the example (fig. 94), we take 

a site 10 km from a strike-slip fault having a slip rate of 

0.4 cm/yr, and we estimate the value of peak horizontal 

acceleration that is exceeded at an average return 

period of 500 yr. The first case that we consider is a 

sequence of earthquakes all of the same size and occurring at an average rate of once every 250 yr (fig. 94A). 

To satisfy the specified slip rate, each of these events 
TABLE 34.-Parameters in the predictive equations for the randomly oriented horizontal component of pseudovelocity response (cm/s) at 5-percent 

damping and of peak acceleration (g) and velocity (cm/s) 

[Co through es and h are used in equation 5 and were determined from strong-motion data by a two-stage regression procedure Qoyner and Boore, 1981, 1982a, b). o is the standard error of an individual prediction by equation 5. ee and V 0 are used in equation 8 and were determined by a regression procedure described in the text] Y 

Period, h. c •• v •. 

ins Co c, c, inkm c, inkm~ 1 c, in rnls c, (] 

y 

Pseudovelocity response 

0.1 ------------------ 2.16 0.25 -0.06 11.3 -1.0 -0.0073 -0.02 0.28 

.15 ------------------ 2.40 .30 -.08 10.8 -1.0 -.0067 -.02 .28 

.2 ------------------ 2.46 .35 -.09 9.6 -1.0 -.0063 -.01 .28 

.3 ------------------ 2.47 .42 -.11 6.9 -1.0 -.0058 .04 590 -0.28 .28 

.4 ------------------ 2.44 .47 -.13 5.7 -1.0 -.0054 .10 830 -.33 .31 

.5 ------------------ 2.41 .52 -.14 5.1 -1.0 -.0051 .14 1020 -.38 .33 

.75------------------ 2.34 .60 -.16 4.8 -1.0 -.0045 .23 1410 -.46 .33 

1.0 ------------------ 2.28 .67 -.17 4.7 -1.0 -.0039 .27 1580 -.51 .33 

1.5 ------------------ 2.19 .74 -.19 4.7 -1.0 -.0026 .31 1620 -.59 .33 

2.0 ------------------ 2.12 .79 -.20 4.7 -1.0 -.0015 .32 1620 -.64 .33 

3.0 ------------------ 2.02 .85 -.22 4.7 -.98 .0 .32 1550 -.72 .33 

4.0 ------------------ 1.96 .88 -.24 4.7 -.95 .0 .29 1450 -.78 .33 

Peak acceleration 

0.43 0.23 0.0 8.0 -1.0 -0.0027 0.0 0.28 

Peak velocity 

2.09 0.49 0.0 4.0 

must have a slip of 100 em. By definition, the median 

peak horizontal acceleration for earthquakes of this 

magnitude will be exceeded for half of the events, or 

once every 500 yr. So, the quantity that we seek to 

estimate is the median peak horizontal acceleration for 

the magnitude corresponding to a slip of 100 em. To 

determine the magnitude, we first calculate the seismic 

moment. The definition of seismic moment is 

Mo = ~-tULW (9) 

where 1-' is the rigidity, U is the slip, L is the length of the 

rupture, and W is the width measured in the plane of the 

rupture. Slip is proportional to length (Bonilla, 1967; 

Slemmons, 1977; Sykes and Quittmeyer, 1981; Scholz, 

1982; Bonilla and others, 1984); that is, 

U = etL (10) 

where a is the constant of proportionality. Combining 

equations 9 and 10 gives the equation used for calculating moment: 

(11) 

Given the moment, the moment magnitude is obtained 

from equation 6. We obtain a magnitude of 7.0 for the 

earthquake having 100 em of slip and occurring once 

-1.0 -0.0026 0.17 1190 -0.45 0.33 

every 250 yr. In the calculations, a value of 3.4 x 

1011 dyn/cm2 is assumed for the rigidity, a value of 10 km 

is assumed for the width, and a value of 1.1 x 10-s is assumed for a (see table 35). Equation 5 gives 0.33 g for the 

median peak horizontal acceleration 10 km from a 

magnitude 7.0 event. So, 0.33 g is the estimate corresponding to an average return period of 500 yr. To 

show the insensitivity of the estimate to the magnitudefrequency relationship, we compare the result obtained 

for the sequence of earthquakes having 100 em of slip 

once every 250 yr with that obtained for a sequence having 20 em of slip once every 50 yr (fig. 94B). Proceeding 

as before, we obtain a magnitude of 6.0 for the 20-cm 

events. Since there are 10 of these events in 500 yr, the 

value of peak horizontal acceleration that is exceeded at 

an average return period of 500 yr is the value corresponding to the ninetieth percentile of the probability 

distribution curve. If it is assumed that the logarithm of 

peak horizontal acceleration is normally distributed and 

that the standard deviation uY is as given in table 34, that 

value is 0.44 g (equation 5). The difference between 0.33 

and 0.44 g is small in comparison with the variation indicated by the given value of uY. This relative insensitivity to the magnitude-frequency relation results from the 

compensating action of two opposing effects. Smaller 

magnitude events give smaller median ground-motion 

estimates, but, the smaller the magnitude, the larger the 

number of events and the higher the percentile corPredictive Ground-Motion Mapping 209 
_J 

<( 

=:> 

0 

(/) 

w 

a: 

0 -

+ Rock site 

<> Soil site 

<> <> 

<> 

<> <>$ <+ + 

<> 

<> «>o <> + <> 

<> <> 

o<> 

<> 

<> 

<> + + 

<> 

+ ::~-+ -

0 + 

<> 

+ 

- 1 . 0 '-'--'----'--'-'-I __ ....______J__-"---'--'----L.L.l-'-1--c___---'--...L-J 

100 1000 

SHEAR-WAVE VELOCITY. 

IN METERS PER SECOND 

FIGURE 93.-Residuals of the logarithm of peak horizontal ground 

velocity with respect to the values predicted for rock sites by equation 5, plotted against average shear-wave velocity to a depth of 

one-quarter wavelength of a 1-s wave. The plot shows that there is 

a good correlation between site effects and site shear-wave 

velocity. 

responding to the estimate for a 500-yr return period. 

This compensation obviously depends on the constraint 

that the magnitude-frequency relation satisfy the given 

slip rate. 

The example above suggests a very simple method for 

making predictive maps showing ground-motion values 

that are exceeded at an average return period T,. 

Whatever the real earthquake sequence along a fault, it 

is replaced for purposes of calculation by a simple sequence of earthquakes all of the same magnitude and 

occurring at an average rate of twice per time period T,. 

Since the median ground-motion value for that magnitude will be exceeded for half of the events, it will be exceeded at a return period equal to T,. The median value 

is calculated by using the predictive equations of the 

preceding sections and is used in making the map, provided that the calculated magnitude does not exceed the 

largest magnitude possible on the fault. The largest 

possible magnitude can be calculated by using the total 

length of the fault with equations 6, 9, and 10. If the 

largest possible magnitude is less than the magnitude 

calculated for earthquakes occurring at an average rate 

of twice per time period T,, the real earthquake sequence is replaced by a sequence of earthquakes, all of 

which are of the largest possible magnitude and which 

occur at an average rate chosen to satisfy the slip rate. 

210 Earthquake Hazards in the Los Angeles Region 

The predictive equations are then used to calculate a 

ground-motion value for the probability level determined 

by the average number of events per time period T,, as 

in the second part of the simple example. 

To understand the method, it is important to remember that the return period T, is not chosen on any basis 

having to do with the rate of occurrence of earthquakes 

but rather corresponds to a probability level that is of 

interest to the user of the map and is determined by considerations of acceptable risk. 

A further simplification used in making the predictive 

maps is considering each fault separately. At each 

point, the maps portray the value of ground motion that 

will be exceeded at a specified probability as a consequence of earthquakes on only one fault-the fault for 

which the computed value is largest. This approximation will be relatively good at points close to the faults, 

and such points are the most important from the standpoint of the shaking hazard. To get an idea of the 

significance of the error made by using this approximation, consider a mapped area containing only two faults. 

In general, the locus of points for which the groundmotion level corresponding to the specified probability 

level is identical for both faults will fall along a curved 

line. If both faults are taken into account, the true probability level along that locus is twice that given by the 

approximate method. Everywhere else, the difference 

between the true level and the approximation is smaller. 

As appendix 3 shows, the difference in ground-motion 

level corresponding to a factor of two in probability is 

relatively small. 

Describing the simple method more precisely, we seek 

to map the ground-motion value that is exceeded at a 

certain annual rate N,, which is the reciprocal of the 

average return period T,. (It is more convenient to work 

with the annual rates at which the mapped value is exceeded rather than with the annual probability that it is 

exceeded. The two quantities are approximately the 

same, and one can be computed exactly from the other if 

necessary.) For the given value of N and a given fault 

slip rate iJ, we define the moment r(Molrer of what we 

will call the reference earthquake as follows. We divide 

U by 2N, to obtain the mean slip U ref for the reference 

earthquake: 

(12) 

Combining equations 11 and 12, we obtain an expression for the moment of the reference earthquake: 

(13) 

where wtot is the maximum width of that portion of the 
A 

7.0 

0.33 

50 PERCENT t 

6.0 

5.0 

0.1 g 1.0 g 

ACCELERATION LU 

0 

:::> t: 4.0 -t-------,--------,-----------,--------,-----~ 

z 0 

<..? 500 

<( 

~ RECURRENCE INTERVA~IN YEARS 

1-

z 

LU 

~ 7.0 

0 

~ 

6.0 

5.0 

4.0 

-

-

-

0 

8 

90 PERCENT 

0.1 g 1.0 g 

ACCELERATION 

500 

RECURRENCE INTERVAL, IN YEARS 

FIGURE 94.-Schematic diagram of a simple example illustrating that probabilistic ground-motion estimates are insensitive to the details of 

the magnitude-frequency relation, provided that the slip rate is constrained. A, Earthquakes occurring once every 250 yr. B, Earthquakes 

occurring every 50 yr. 

fault capable of generating earthquakes. We are assuming 

here that the reference earthquake will be large enough to 

rupture the maximum width. (For typical California 

faults, this assumption implies an earthquake of moment 

magnitude larger than about 6.0 to 6.5.) We also define a 

moment (M0)lim' which represents the largest earthquake 

that the fault is capable of generating. Combining equations 9 and 10, we obtain 

(14) 

where 1101 is the total length of the fault. 

If the calculated value of (M0)rer is less than (M0)lim' we 

take the median ground-motion value for a moment of 

(Molrer as the value that will be exceeded at the annual rate 

of N,. We are representing the earthquake sequence by an 

equivalent simple sequence of earthquakes of equal moment (Molrer occurring at an annual rate 2N,. The median 

ground-motion value for moment (M0)rer will be exceeded, 

by definition, for half the events, for a corresponding annual rate of N,. If (M0)lim is less than the calculated value 

of (M0)ref' then an earthquake of moment (Molrer is not 

possible, and we represent the earthquake sequence by an 

equivalent sequence of earthquakes of equal moment 

(M0) 1im occurring at an annual rate Mof(M0) 1im, where M0 is 

the long-term rate of moment release on the fault obtainable from the slip rate and the definition of moment 

(equation 9). We calculate the ground-motion value z that 

is exceeded at an annual rate N, by solving the equation 

where P[y~ z I (M0)

1

im] denotes the probability that the 

ground motion y will exceed value z given the occurrence 

of an earthquake of moment (M0 )

1

im. The equation can be 

rewritten 

Predictive Ground-Motion Mapping 211 
TABLE 35.-Values of a for strike- and reverse-slip earthquakes in California 

Mo. 

Earthquake in dyn-cm 

L, 

inkm 

W, 

inkm References 

Strike-slip earthquakes 

San Francisco (t906) ----------- 4.0 x t0' 7 450 10 0.58 x 10- 5 Thatcher (1975) 

Parkfield (1966) --------------- t.4 x tO'• 25 7 

Borrego Mountain (t968) ------- t.O x tO'• 45 11 

Imperial Valley (t979) ---------- 6.0 x t0'5 35 to 

.94 x to-• Tsai and Aki (t969) 

Eaton and others (t970) 

Lindh and Boore (198t) 

t.32 x 10- 5 Hamilton (t972) 

Hanks and Wyss (t972) 

Hanks and others (t975) 

Swanger and Boore (1978) 

1.44 x to-• H. Kanamori (oral communication, t98t) 

Chavez and others (t982) 

Sharp and others (t982) 

T. H. Heaton (oral communication, t982) 

Average for strike-slip earthquakes ------------------------ t.t x to-• 

Revel'tiiHIIip earthquakes 

Kern County (1952) ------------ 1.5 x t0'7 70 23 

San Fernando (t971) ----------- t.O x t0'6 20 16 

3.91 x 10- 5 Dunbar and others (t980) 

D. M. Boore and H. Kanamori (unpublished data, t979) 

4.60 x to-• Allen and others (t973) 

Hanks and others (t975) 

Average for reverse-slip earthquakes ----------------------- 4.3 x to-• 

1 Mo 11 2 a= --;-r.::-,where!'=3.4x10 dyn/cm. !'LW 

N = Mo [1-F(x)] 

r (Mo)lim (15) 

where x = Uog z-log Z1im]/a, F is the cumulative normal 

probability distribution function, log Z1

im is the mean of 

the logarithm of the ground-motion value given by the 

predictive equations for the moment (Molum• and a is the 

standard deviation of the logarithm of an individual 

observation. Strictly speaking, the value used for a should 

not be the value representing ground motion in general 

obtained from the analysis of the strong-motion data set 

but rather should be the value representing individual 

observations of ground motion at the same site from 

earthquakes at generally different locations on the same 

fault. We do not have a reliable estimate for the latter 

value, however, and therefore use the former in the belief 

that the resulting error will be acceptably small. 

APPLYING THE METHOD 

To map predicted ground motion from an earthquake 

of specified magnitude and location, we compile data on 

212 Earthquake Hazards in the los Angeles Region 

shear-wave velocity to a depth of one-quarter wavelength of the period of interest, as Fumal and Tinsley 

(this volume) describe. These data, together with equations 5 and 8, define a predicted value of ground motion 

at every point and are all that is necessary to make the 

map. Maps of this kind for peak acceleration, velocity, 

and response at 0.2 and 1.0 s for 5-percent damping for 

the randomly oriented horizontal component are given 

in the chapter on the postulated earthquake in the 

Newport-Inglewood zone (Ziony and others, this volume). 

If data adequate for estimating shear-wave velocities 

are not available, equation 5 can be used with the 

twofold rock-versus-soil classification of sites, or a map 

can be made for some reference site condition with the 

understanding that allowance for local site effects will 

be made separately. 

If we wish to map an estimate of the ground motion 

that will be exceeded at an annual rate Nr, we need to 

know the location, the dimensions, and the long-term slip 

rates of the relevant fault zones. For each fault, we 

calculate moments (M0)rcr and (M0)um by using equations 

13 and 14. (We use a value of 3.4 x 1011 dynlcm2 for p. in 

equations 13 and 14. For a, we use values derived in 
table 35 for strike-slip and reverse-slip faults in California.) If (M0)rer is less than (M0 )

1

im, we take as our estimate 

the mean value given by equations 5, 6, and 8 for the moment (M0)rer· If (M0)

1

im is less than (M0)ref' we take as our 

estimate the solution of equations 5 and 15, using for a in 

equation 15 the value of a given in tables 33 or 34. If the y 

moment magnitude is greater than 7.7, the value used in 

equation 5 is 7.7. The ground-motion value mapped at 

each site is the largest estimate obtained after all the 

seismogenic faults in the region have been considered. 

Contour lines are dashed-an indication that the predictive equation~ are not constrained by data-at rock 

sites for distances less than 15 km and magnitudes 

greater than 6.0 and at all sites for distances less than 

25 km and magnitudes greater than 7.0. 

To illustrate the application described in the preceding paragraphs, maps of the upper Santa Ana River 

basin have been compiled showing, for the randomly 

oriented horizontal component, the values of peak acceleration (fig. 95), peak velocity (fig. 96), pseudoacceleration response at 0.2 s for 5-percent damping (fig. 97), and 

pseudovelocity response at 1.0 s for 5-percent damping 

(fig. 98) that are exceeded at an annual rate N, of 0.002. 

This rate, which represents a return period of 500 yr, 

was chosen simply to illustrate the method. It is essentially the same rate as that implicit in the zoning maps of 

the United States contained in the Applied Technology 

Council's (1978) study, "Tentative Provisions for the 

Development of Seismic Regulations for Buildings." 

Figures 95 and 96 are included because they show peak 

horizontal acceleration and velocity, which are more 

familiar measures of earthquake ground motion, but we 

believe that maps of response values such as those 

shown in figures 97 and 98 will prove more useful for 

earthquake-resistant design and seismic zonation. 

The map of shear-wave velocity data used in making 

figures 96 and 98 is figure 58 of Fumal and Tinsley (this 

volume). Three major seismogenic faults need to be considered in the upper Santa Ana River basin study area: 

the San Andreas, the San Jacinto, and the Cucamonga. 

The essential data on these faults are taken from Ziony 

and Yerkes (this volume) and are shown in table 36, 

along with the derived quantities used in making the 

maps in figures 95 through 98. The fault zones are 

assumed to extend from the surface to a depth of 10 km, 

and the widths are therefore 

W=~ sin 8 

in kilometers, where 8 is the dip angle. The dip is also 

taken into account in determining the vertical projection 

of the rupture zones on the surface of the Earth. As we 

noted previously, the distance d in equation 5 is 

measured from that projection of the rupture surface. 

Contours in figure 96 show predicted peak horizontal 

velocities of 200 and 400 cm/s, values greatly in excess 

of the largest ever measured. We know of no reason to 

believe that such values could not occur, but data are 

not available to support them, as the dashed contours indicate. The map of predicted pseudovelocity response at 

1.0 s (fig. 98) also shows values in excess of the largest 

ever measured but not by nearly as large a factor as 

those in figure 96. It is gratifying that the factor is not so 

large in figure 98 in view of the greater engineering utility of predicted response maps. 

Whether the maps show ground motion from a 

specified earthquake or ground motion that is· exceeded 

at a specified rate from multiple sources, the exact 

technique by which the maps are made is of secondary 

importance. The predicted values could be calculated 

over a dense grid of points and the contours interpolated 

between grid points. Various short cuts are possible. It 

is obviously not necessary to calculate a value for every 

grid point. The technique that we used for the sample 

maps in this chapter and for the maps in the chapter on 

the postulated earthquake (Ziony and others, this 

volume) was to prepare, for each source zone and each 

ground-motion contour value, a table of distances corresponding to a selected set of near-surface shear-wave 

velocity values. The distance of each contour from a 

rupture zone was scaled off on the map, taking into account the areal distribution of shear velocities. 

SUMMARY 

PrediCtive maps of peak horizontal acceleration, 

velocity, and response spectral values can be prepared 

by new methods based on predictive equations that give 

ground-motion values in terms of magnitude, distance, 

and site conditions. The equations are modified to improve the prediction of site effects qy using the local 

shear-wave velocity of near-surface geologic materials. 

Predictive ground-motion maps can be made for ground 

motion from an earthquake of specified magnitude and 

location; samples of such maps are included in a later 

chapter (Ziony and others, this volume). Predictive maps 

can also be made showing the ground-motion value that 

will be exceeded at a specified annual probability taking 

into account future earthquakes on a number of faults. 

We have demonstrated that probabilistic estimates of 

near-fault ground motion from earthquakes on a single 

fault are, to a good approximation, independent of .the 

parameters of the magnitude-frequency relation, provided that the relation is constrained by the fault slip 

rate. On the basis of this proposition, a simple method is 

developed for making predictive maps showing probabilistic estimates of ground motion from earthquakes on 

Predictive Ground-Motion Mapping 213 
117'47'30" 

117' 47'30" 

FAULT 

•POMONA 

0 

RIVERSIDE 

• 

PEAK ACCELERATION (g) 

0 

0 

33'52'30" '----------·~_\_____:,~ _______________ _ _,..... 

4 10 

4 6 8 10 12 KILOM ETERS 

FIGURE 95.-Map of the upper Santa Ana River basin showing, for the randomly oriented horizontal component, the value of peak acceleration 

that is exceeded at an annual rate of 0.002 (return period of 500 yr). Dashed contours correspond to combinations of magnitude and distance 

for which the predictive equations are not constrained by data. 

-------------------..... 34' 15' 

PEAK VELOCITY (cm/s) 

12 MILES 

117' 00' 

0 4 8 10 12 MILES 

4 8 10 12 KILOMETERS 

POMONA 

• 

FIGURE 96.-Map of the upper Santa Ana River basin showing, for the randomly oriented horizontal component, the value of peak velocity that is 

exceeded at an annual rate of 0.002 (return period of 500 yr). Dashed contours correspond to combinations of magnitude, distance, and site 

conditions for which the predictive equations are not constrained by data. Note the geometric contour interval. 

117'00' 
117'47'30" 

• POMONA 

--

0 

·.s 

" ' ' ' ' ' " " 

PSEUDOACCELERATION RESPONSE (9) AT 0_. 2s 

0 4 8 10 

' ' " 

SAN BERNARDINO 

33'52'30"'------ ---'-------- - --- - --- -----''------...--

FIGURE 97.-Map of the upper Santa Ana River basin showing, for the randomly oriented horizontal component, the value of pseudoacceleration 

response at 0.2 s and 5-percent damping that is exceeded at an annual rate of 0.002 (return period of 500 yr). Dashed contours correspond to 

combinations of magnitude and distance for which the predictive equations are not constrained by data. 

PSEUDOVELOCITY RESPONSE (cm/s) AT 1.0 s 

117"47'30" FAULT 

12 MILES 

c--· ..., • POMONA / i 

.... ,,_/ 

c!J' 

33' 52'30' '-------------------------- ~ "'-...../' 

FIGURE 98.-Map of the upper Santa Ana River basin showing, for the randomly oriented horizontal component, the value of pseudovelocity 

response at 1.0 s and 5-percent damping that is exceeded at an annual rate of 0.002 (return period of 500 yr}. Dashed contours correspond to 

combinations of magnitude, distance, and site conditions for which the predictive equations are not constrained by data. Note the geometric 

contour interval. 
TABLE 36.-Assumed parameters for principal earthquake sources in the upper Santa Ana River basin area 

[Data on fault type, dip, and slip rate from Ziony and Yerkes (this volume)] 

u.• Ltot.' wtot' 

Fault Type in cm/yr Dip inkm inkm Mref Mlim (M,~im 

San Andreas (Mojave segment)--------- Strike slip 3.0 Vertical• 400 10 8.1 7.8 0.0068 

San Jacinto zone -------------------- Strike slip 1.0 Vertical 75 10 7.5 6.8 .012 

(Glen Helen and Claremont faults). 

Cucamonga------------------------ Reverse slip .3 45° N. 25 14 6.5 6.7 

1

Estimated average late Quaternary slip rate. In making the maps, a preliminary value of 0.3 cm/yr was used for the slip rate on the Cucamonga. That value falls at the lower end of the range 0.29 

to 0.64 crnlyr given by Ziony and Yerkes (this volume). 2

Maxirnum Holocene length. 3

Dips 60° NE. southeastward from San Bernardino. 

any number of faults for which slip rates are known or 

can be reliably estimated. A suite of maps for the upper 

Santa Ana River basin illustrates the latter method. 

APPENDIX 3.-DEPENDENCE OF 

PROBABILISTIC GROUND-MOTION 

ESTIMATES ON PARAMETERS 

OF THE MAGNITUDE-FREQUENCY 

RELATION 

In this chapter, we have described a simple system for 

estimating the ground-motion values that will be exceeded at a specified annual rate. In this appendix, we 

attempt to show that the resulting values are good approximations of the values that would be obtained if 

more conventional magnitude-frequency relations were 

used. The usual form for describing the rate of occurrence of earthquakes of different magnitudes is that 

given by Gutenberg and Richter {1954; Ishimoto and 

Iida, 1939): 

log N=a-bM 

where N is the annual number of events having 

magnitudes greater than or equal to M and a and b are 

constants. The Gutenberg-Richter relation must be truncated at a maximum magnitude Mmax to avoid an infinite 

rate of moment release. There are two options. The 

cumulative distribution given above can be truncated, or 

the corresponding density distribution can be truncated. 

Both options are considered here. If the cumulative 

distribution is truncated, the resulting relation includes 

as a special case, for b = 0, the characteristic earthquake model in which all of the earthquakes are the 

same size. The simple model described in the text is a 

characteristic earthquake model. 

216 Earthquake Hazards in the los Angeles Region 

We show in this appendix that probabilistic groundmotion estimates are insensitive to the parameters of the 

magnitude-frequency relation as long as the slip rate is 

satisfied. This matter is of some importance because, in 

the general case, there may not be a good basis for 

choosing values for the parameters. Values near one are 

commonly used for b, but a growing body of opinion in 

recent years holds that, for individual faults, much 

lower values may be appropriate (Singh and others, 

1981; Schwartz and others, 1981; Lahr and Stephens, 

1982; Wesnm1sky and others, 1983). Mmax is commonly 

taken as the magnitude corresponding to rupture of the 

entire length of the fault zone, but in general there is no 

basis for assuming that earthquakes so large actually 

occur. 

We first consider the case of a Gutenberg-Richter 

cumulative distribution truncated at a maximum magnitude Mmax' Following Brune {1968) and Molnar {1979), 

we apply the definition of moment magnitude given in 

equation 6, introduce a maximum moment (M0)max' and 

require that the long-term rate of moment release in the 

earthquake sequence equal a known value M0 • The 

resulting equation is 

MoMo 13 

N{Mo)={1-{3) {1-H(Mo-{Mo)max)} {16) (Mo)!,~ 

where N(M0) is the annual number of earthquakes having moments greater than or equal to M0 , H represents 

the Heaviside function, and {3 is a constant equal to 2/3 

b. As we noted before, Mo for a fault can be obtained 

from the slip rate (corrected if necessary for aseismic 

slip) and the definition of moment (equation 5). We 

distinguish between (Mohim' the largest moment permitted by the size of the entire fault, and (M0)max' the largest 

moment that is implied by our adopted magnitudefrequency relation. (M0)max should never be larger than 
(M0 )1im' but, in general, nothing prevents us from 

postulating a smaller value. 

For general values of {j, we calculate the groundmotion value z that will be exceeded at an annual rate 

N, as the solution of the equation 

where 

J

oo L(M0 ) 

Nr = --n(Mo) P(y~ z I Mo) dMo 

O Ltot 

n(Mo) = _ dN(M0) 

dM0 

(17) 

L(M0) is the rupture length corresponding to moment M0 , 

and P(y~ z I M0) is the probability that the ground motion 

y will exceed value z given the occurrence of an earthquake of a moment M0 • The quantity n(M0)dM0 is the annual number of earthquakes in the moment range dM0 

for the entire fault. Multiplication by the ratio L(M0)/L101 

gives the annual number of earthquakes that rupture 

that portion of the fault adjacent to a specific site, the 

assumption being that earthquakes along other parts of 

the fault can be neglected. That assumption is good for 

sites where the distance to the fault is small in comparison to the rupture length. 

P(y~z I M0)=1-F(x) (18) 

where F is the cumulative normal probability distribution function, 

x =(log z -log Z)la (19) 

log Z is the mean of the logarithm of the ground-motion 

value for the moment M0 , and a is the standard deviation. 

We consider in turn the three factors of the integrand 

in equation 17. Obviously, 

L (M0) 

where Lmax is the rupture length corresponding to moment (M0)max· Assuming that earthquakes of moment M0 

are large enough to rupture the maximum width of the 

fault zone, we can obtain, with the aid of equations 9 

and 10, 

L (M0) Lmax Mol/2 

Ltot (Mo)m~; (20) 

(For earthquakes smaller than the moment corresponding to rupture of the maximum width, the exponents 

should be 1/3 where they are 1/2 in equation 20. Repeating the analysis with exponents of 1/3 instead of 1/2 

gives results not greatly different from the results presented here.) By differentiating equation 16 (Molnar, 

1979; Anderson and Luco, 1983), we can obtain 

where o is the Dirac delta function. 

If we define 

q =(log z -log zm.Jia (22) 

where log zmax is the mean of the logarithm of the 

ground-motion value for the moment (M0)max' then substitution in equation 19 gives 

X= q +(log zmax -log Z)la (23) 

If we can express log z in the form 

where M is the magnitude corresponding to moment M0, 

then we obtain 

(24) 

Substituting from equations 18, 20, and 21 into equation 

17 gives 

(25) 

where 

- d ( [ ~ ] -P ) } ( 1-F(x)) (Mo)max (26) 

and x is given by equation 24. To simplify equation 25, 

we assume that an earthquake of moment (Molrer is large 

Predictive Ground-Motion Mapping 217 
1.0.-------------------,------------------, 

:::. 

'§ 

1'\.J 

Cl 

.2 0 

I 

"' Cl 

0 

- 1.0 L_ ________________ ~ ____ _l __________ ~ 

- 1.0 0 

Mmax - Mref 

1.0 

FIGURE 99.-Difference between the ground-motion value predicted by 

the simple model and the value predicted by using a magnitudefrequency relation of the Gutenberg-Richter type whose cumulative distribution curve is truncated at a maximum magnitude Mmax· 

Other symbols are explained in the text. A value of one for the c,lu 

ratio is appropriate for peak horizontal acceleration and for shortperiod horizontal response spectra. Note that the difference is 

normalized by u, the standard deviation of an individual prediction 

from the predictive equation. 

enough to rupture the maximum width of the fault zone, 

and we use the definition of moment given in equation 9 

to obtain 

(Molrer= ~tUrefLref Wt t 

Substituting from equation 12 gives 

u 

(Mo)rer = IL ----- 4.r Wtot 2N, (27) 

By differentiating the definition of moment, we obtain 

(28) 

Solving equations 27 and 28 for M0 in terms of (Molrer 

gives 

(29) 

Substituting from equation 29 into equation 25 and rearranging give 

218 Earthquake Hazards in the Los Angeles Region 

1.0 .-------------r-----------, 

A 

c,jo-=2.0 

b 

.:;:::. 0 'Gi 

~ Cl 

.2 

I 

... 

Cl 

.2 [3=% 

- 1.0 

[3=0 

- 1.5L_ ________________ ~------L---------~ 

-1.0 0 1.0 

Mmax - Mref 

FIGURE 100.-Difference between the ground-motion value predicted 

by the simple model and the value predicted by using a magnitudefrequency relation of the Gutenberg-Richter type whose cumulative distribution curve is truncated at a maximum magnitude Mmax· 

Other symbols are explained in the text. A value of two for the c1/u 

ratio is appropriate for peak horizontal velocity and for 

intermediate-period horizontal response spectra. Note that the difference is normalized by u, the standard deviation of an individual 

prediction from the predictive equation. 

As we did previously, we assume that earthquakes of 

moment (M0),.,1 are large enough to rupture the maximum 

width of the fault zone, and we use equations 9 and 10 to 

obtain further simplification: 

I = 1 [(Mo)max] 1/2 

2(1- {3) (M0),.,1 

(30) 

Equations 26 and 30 can be rewritten in terms of moment magnitude, a step that we do not bother to show 

here. Equations 24, 26, and 30 constitute a system that 

we solve by successive approximation using numerical 

integration to obtain values of q for given values of 

(M0)max/(M0),.,1

• Once we find q, we can use equation 22 to 

obtain 

or, equivalently, 

(31) 

The left-hand side of equation 31 is the difference be-
1.0~---------------.-----------------. 

c c, /CJ'=1.0 

~ Q) 

~ 

Ol 

.2 

I 

"' Ol 

.2 

- 1.0L-______________ ~L_--------------~ 

-1.0 0 1.0 

FIGURE 101.-Difference between the ground-motion value predicted 

by the simple model and the value predicted by using a magnitudefrequency relation of the Gutenberg-Richter type whose density 

distribution curve is truncated at a maximum magnitude Mmax' 

Other symbols are explained in the text. A value of one for the c,/a 

ratio is appropriate for peak horizontal acceleration and for shortperiod horizontal response spectra. Note that the difference is normalized by a, the standard deviation of an individual prediction 

from the predictive equation. 

tween the ground motion predicted by equation 17 and 

that predicted by the simple model, normalized by a. The 

difference is shown in figures 99 and 100 by curves for 

{3 = 0 and {3 = 213, plotted against (Mmax- M,.rl• where 

Mmax and Mrer are the moment magnitudes corresponding 

to moments (Molmax and (M0)ref' The curves in figure 99 

are for the ratio e1la= 1, which approximates the value 

appropriate for peak acceleration and short-period 

response; the curves in figure 100 are for the ratio 

e11a = 2, which approximates the value appropriate for 

peak velocity and intermediate-period response Gayner 

and Boore, 1981, 1982a, b). Except for large values of 

(Mmax- Mrerl• the differences are relatively small in comparison with a. This circumstance is fortunate in that it 

frees us from the necessity of establishing accurate 

values of {3 and Mmax· Although figures 99 and 100 show 

large differences between the predictions of the simple 

model and those of equation 17 for small values of {3 and 

large values of (Mmax- Mrerl• we contend that the simple 

model is generally the more appropriate basis for 

ground-motion predictions. The falloff of the curves for 

{3 = 0 at large (Mmax- M,.rl on figures 99 and 100 

represents assumed earthquake sequences consisting of 

very large magnitude events occurring at a very low annual rate. If we could really be confident that such sequences were representative of the real seismicity, we 

could use them as a basis for predicting ground motion. 

1.0 r-------------------,---------------------, 

~ '§ 

1'\.J 

Cl 

.2 0 

I 

"' Cl 13=2/3 .2 

- 1.0 

- 1.5L_ ________________ L_ ______________ ~ 

- 1.0 0 1.0 

FIGURE 102.-Difference between the ground-motion value predicted 

by the simple model and the value predicted by using a magnitudefrequency relation of the Gutenberg-Richter type whose density 

distribution curve is truncated at a maximum magnitude Mmax· 

Other symbols are explained in the text. A value of two for the c,/a 

ratio is appropriate for peak horizontal velocity and for 

intermediate-period horizontal response spectra. Note that the difference is normalized by a, the standard deviation of an individual 

prediction from the predictive equations. 

In general, however, there is no basis for confidence, 

and those sequences represent an imprudent basis for 

prediction. 

Figures 99 and 100 are based on equation 16, which 

represents a cumulative distribution curve of the 

Gutenberg-Richter type truncated at a maximum moment (M0)max as described by Molnar (1979). An alternative, perhaps more appealing on physical grounds, is 

to truncate the density distribution rather than the 

cumulative distribution. To compare this alternative 

with the simple model, the analysis described above was 

repeated, except that equation 21 was replaced by the 

following equation: 

n(M0

) = (1 - {3)Mo M~/3-l (32) 

(MJ~~ 

The results, shown in figures 101 and 102, are quite 

similar to those obtained by using equation 21, shown in 

figures 99 and 100. 

The same simple model that we propose as a basis for 

making ground-motion predictions can be used to 

estimate the effect on those predictions of using different values of the annual rate N, at which it is assumed 

Predictive Ground-Motion Mapping 219 
that the predicted value will be exceeded. According to 

equation 13, the reference moment (M0)ref for the simple 

model scales as N, -z. From the c1 coefficient of tables 33 

and 34 and the definition of moment magnitude given in 

equation 6, we see that peak horizontal acceleration and 

short-period response scale approximately as (M0)rer' 

which is equivalent to N, - 113 , and that horizontal velocity 

and intermediate-period response scale approximately 

as (M0)rer' which is equivalent to N, - 213 • In other words, 

220 Earthquake Hazards in the Los Angeles Region 

a change by a factor of two in N,, or equivalently in 

probability, corresponds to a change by a factor of 0.79 

in peak acceleration and by a factor of 0.63 in peak 

velocity. The result for peak horizontal acceleration is 

approximately the same as that obtained by a completely different method by Algermissen and Perkins (1976), 

who gave as a rule of thumb that peak horizontal acceleration scales as N, -o.43• 
PREDICTING RELATIVE GROUND RESPONSE 

By A. M. Rogers, J. C. Tinsley, and R. D. Borcherdt 

INTRODUCTION 

The character of ground shaking at a point on the 

Earth's surface generated by an earthquake is influenced by distance from the causative fault, characteristics of the earthquake source, and geologic conditions 

within the Earth's mantle and crust. Geologic conditions 

at or near a site are known to exert an especially significant influence on the nature of ground shaking (Milne, 

1898; Lawson and others, 1908; Kanai, 1952; Gutenberg, 

1957; Medvedev, 1962; Borcherdt, 1970; Murphy and 

others, 1970; Rogers and others, 1979). In the Los 

Angeles region, Wood (1933) noted that the 1933 Long 

Beach earthquake caused more damage in Compton 

than it did in Long Beach and ascribed this difference to 

local geologic effects. For the same earthquake, Campbell (1976) showed that, for a given distance from the 

Newport-Inglewood zone, damage at sites underlain by 

unconsolidated soils was greater than that at sites 

underlain by consolidated soils. Certain frequencies of 

strong shaking may be amplified considerably by thin 

low-velocity surface layers, and the overall spectral 

level of ground motion may increase as the seismic 

velocity of near-surface materials decreases and (or) as 

the thickness of sediments increases (Murphy and 

Hewlett, 1975; Borcherdt and Gibbs, 1976; Rogers and 

others, 1979). Although the importance of local geologic 

conditions has long been recognized, the quantitative 

prediction of the influence of these conditions on ground 

shaking by either empirical or theoretical models is still 

in the developmental stage. 

PREVIOUS STUDIES 

Problems central to the theoretical or empirical 

prediction of site response are related to differences in 

wave types, angles of incidence, azimuth of approach, 

and Earth heterogeneity (Hudson and Douglas, 1975; 

Murphy and Hewlett, 1975; Esteva, 1977) and to the 

question of nonlinear soil behavior (Seed and Idriss, 

1970; Hardin and Drnevich, 1972). Relative changes in 

the proportions of body- and surface-wave energy as a 

function of epicentral distance, for instance, might alter 

the ground response in a manner not predicted by 

either theory or empiricism. Nevertheless, site-specific 

velocity models have been used with linear or nonlinear 

models of shear-wave propagation in a layered geologic 

column to obtain theoretical estimates of local siteresponse effects (Kanai, 1952; Kanai and Yoshizawa, 

1958; Murphy and others, 1971; Lastrico, 1970; Joyner 

and Chen, 1975). Comparisons of theory and observed 

data indicate that theoretical models can often be used 

to predict site response (Borcherdt and Gibbs, 1976; 

McEvilly and Johnson, 1980; Joyner and others, 1981). 

Simple one-dimensional models frequently are used 

because they provide first-order approximations of site 

response. These models also apply to either radial or 

transverse components of motion because the angle of 

incidence through near-surface low-velocity sediments 

is nearly vertical (Murphy and others, 1970). The disadvantage of these models is that essential subsurface 

data are not available everywhere; furthermore, the 

models are not applicable in all situations. 

Empirical methods are not limited in the same manner 

that most theoretical solutions are. Because measurements of site response incorporate the effects of waves 

arriving from many directions (backscattering) and the 

effects of both body and surface waves, they provide a 

smoothed estimate to the solution of the more complex 

problem, reflecting the effects of true Earth geometry. 

Underground nuclear explosions were first used as distant seismic sources in empirical studies of site effects 

by Borcherdt (1970) and Murphy and others (1971). Lowstrain measurements of small earthquakes or distant 

nuclear explosions obtained over a region on a variety 

of local site conditions can directly provide a map of 

potential geographic variations in site response (Murphy and Hewlett, 1975; Hays and Algermissen, 1982; 

Hays and King, 1982). Correlation of site response and 

known geologic data is also a useful technique for extrapolating relative shaking effects over a broad region 

or for making estimates at specific sites. Borcherdt and 

Gibbs (1976), for example, have established a relation 

between the age of surficial deposits and the mean specPredicting Relative Ground Response 221 
tral amplification in the San Francisco Bay region that 

has enabled them to produce a regional map showing expected geographic variations in shaking intensity. These 

studies and those of Mueller and others (1982), King 

(1982), and Rogers and others (1984) suggest that, for 

many situations, effects of local site conditions may 

predominate over other effects such as changing source 

azimuth, wave type, and angle of incidence. These 

studies have shown that changes in mean spectral 

amplification from low-level ground motions are correlated with geologic structure, measured in-situ shearwave velocities, and changing earthquake intensities 

and spectral levels; these correlations suggest that, in 

many cases, site effects can be predicted empirically as 

well as theoretically. 

Using nuclear explosions to study or predict site 

amplification assumes that site effects produced by lowlevel ground motions from distant nuclear explosions 

are similar to those that would be observed during 

strong shaking. A significant question of engineering interest is, "To what extent can ground-response measurements determined from low levels of shaking (small 

strains less than 10- 5), such as those recorded from distant nuclear explosions, be extrapolated to predict 

ground response at higher levels of shaking induced by 

nearby damaging earthquakes?" Laboratory-based 

studies suggest that soils behave in a nonlinear fashion 

when strain levels exceed about 10- 5 (Seed and Idriss, 

1970) or 10- 4 (Turner and Stokoe, 1982). That is, at 

strains of this level or greater, soils begin to lose 

strength (as reflected by a decrease in shear modulus, 

which causes increased wave amplitudes) and to increase wave attenuation or damping (as reflected by an 

increase in the damping coefficient, which causes 

decreased wave amplitudes). Theoretical modeling of 

soils suggests that, at certain frequencies, the ratio of 

surface to base-input motion for soils undergoing 

nonlinear high-strain behavior will be lower than the 

ratio for the same soils responding in a linear manner to 

lower base-input motions. This behavior is due to the 

fact that the effects of increased damping dominate the 

effects of reduction in shear modulus (Borchardt and 

others, 1975; Joyner and Chen, 1975). The changes in 

soil properties produced by nonlinearity increase the 

fundamental resonant period of site shaking and lower 

the resonant peak level. For the most part, however, 

these effects of nonlinear soil behavior have not been 

observed in strong-ground-motion records. 

On the contrary, field data suggest that highamplitude soil response is similar to low-amplitude soil 

response, perhaps for strains up to 10- 3• Using recordings of nuclear events at two Nevada Test Site locations 

(Murphy and others, 1971), Rogers and Hays (1978) have 

shown that site response measured at strains of 10- 3 

222 Earthquake Hazards in the Los Angeles Region 

and 10- 4 are essentially equal. Joyner and others (1981) 

have demonstrated that linear theoretical models 

predict the site response at a recording site in the area 

of the Coyote Lake, Calif., earthquake for strains as 

large as 10- 4 • Rogers and others (1984) have compared 

site response measured by using distant nuclear explosions (strains near 10- 5

) with site response at the same 

locations measured by using data from the 1971 San 

Fernando earthquake (strains near 10- 3) and have 

found that the two data sets are equivalent within the 

expected variability of the statistics (fig. 103). Field 

observations of earthquake damage also suggest that 

high-amplitude soil response and low-amplitude soil 

response are similar. 

A high correlation between mean spectral amplification was determined for sites near San Francisco from 

Nevada Test Site nuclear explosions and from observed 

1906 earthquake intensities, up to San Francisco intensity level 4 (Borchardt and others, 1975). Espinosa and 

Algermissen (1972) found a correlation between the 

thickness of alluvial sediments, mean spectral amplification derived from low-level ground motions generated by 

small earthquakes, and damage to highrise buildings in 

the 1967 Caracas, Venezuela, earthquake. These studies 

provide evidence supporting the assumption that soil 

responds to very high levels of damaging shaking 

without significant nonlinear behavior. These studies 

also support the argument that differences between 

wave types and other factors caused by ground motions 

resulting from distant low-level sources and those 

caused by nearby strong earthquakes have only secondorder significance in comparison with the site-response 

phenomena. These results suggest that, for in situ soils, 

the changes produced in the shear modulus and in the 

damping factors by strong shaking are smaller than the 

changes suggested by the results of laboratory testing of 

samples. 

Soils have been observed to sustain large damaging 

ground motions that include soil amplification effects. In 

addition to the examples cited in the introduction, table 

37 shows that ground motions as large as 0.7 g and 

108.8 cm/s have been recorded on soils. In the Italian 

earthquakes cited in table 37, accelerations (at some 

sites as large as 0.5 g) recorded on thin soils (less than 

20 m) were higher by factors of as much as four in comparison with those recorded on thick soils or rock. These 

cases may or may not have exhibited nonlinear behavior 

but, nonetheless, demonstrate large damaging ground 

motions at sites underlain by soil. Even though nonlinear 

behavior can limit the magnitude of ground motions on 

soils, the upper limits of shaking on soils still appear to 

be high in some cases. 

The effect of nonlinear soil response may also be 

restricted to a small area surrounding the causative 
6 

5 

o~ _<( 4 

1-1- <(<( 

a:o 

...Ja: 

<(<( 3 a:w 1-...J 

uu 

UJ:::> 

a..z 2 (/)~ 

A 

c 

0 

0 

0 

0 

SPECTRAL RATIO 

(EARTHQUAKE DATA) 

~--~~----~~--~~----~~----~~~ 

5 -

o~ 

- <( 4 - t-1- <(<( 

a:o 

...Ja: 

<(<( 

a:w 1-...J 

uu 

UJ:::> 

B;~ 

3 1-

2 r0 0 

SPECTRAL RATIO 

(EARTHQUAKE DATA) 

-

-

-

-

-

6 

5 

o~ _<( 

1-1- <(<( 

4 

a:o 

...Ja: 

<(<( 3 -a: UJ 1-...J 

uu 

W:J 

a..z 2 (/)~ 

B 

D 

SPECTRAL RATIO 

(EARTHQUAKE DATA) 

6 

~--~~--~~----~~--~~--~~--~ 

5 ro~ 

- <( 4 r-- 1-1- <(<( 

a:o 

...J a: 3 r- <(<( 

a:w 1-...J 

uu 

W:J 

B;~2 r1 -

0 0 

0 

-

-

-

-

-

Q L----L- I ___ L_I ___ --~1 ____ ~1--~ 

0 2 3 4 5 6 

SPECTRAL RATIO 

(EARTHQUAKE DATA) 

FIGURE 103.-Comparisons of the geometric mean spectral ratios in four period bands determined from ground-motion recordings of distaU:t 

underground nuclear explosions and from the 1971 San Fernando earthquake (from Rogers and others, 1984). A, 0.2 to 10.0 s. B, 0.2 to 0.5 s. C, 

0.5 to 1.0 s. D, 1.0 to 3.3. s. These data indicate that small ground motions obtained from distant sources can be used to estimate differences in 

ground response from nearby damaging earthquakes. 

fault (Hays and Algermissen, 1982). A magnitude 7 to 7.5 

earthquake, for instance, develops velocities on soil 

sites exceeding 100 cm/s at distances of less than 7 to 13 

km from the fault (dependent on the magnitude) Uoyner 

and Boore, 1981). For soil sites having 20G-m/s shearwave velocities, strains of 5 x 10- 3 will be developed 

Predicting Relative Ground Response 223 
TABLE 37.-Peak ground motions and estimated strains recorded at selected sites underlain by unconsolidated sediments 

[--, no data] 

Earthquake Station 

1966 Parkfield ----------------------- 2 

1979 Imperial Valley------------------- 6 

1972 Ancona, Italy, and 1976 Friuli, Italy ---

Acceleration, 

in g 

0.48 

.72 

Up to 

0.5 

within this zone. Observations discussed in this section 

indicate that this strain level may still be below the level 

of significant nonlinear behavior. Because damaging 

motions on soils (Modified Mercalli intensities greater 

than or equal to VI) occur at distances of 60 to 100 km 

from the fault (Howell and Schultz, 1975), the region of 

damage within which nonlinear soil response is possible 

is about 2 to 9 percent of the total area of damage, if a 

30-km rupture is assumed. Where the fault passes 

through developed regions, the zone of nonlinear 

behavior may be the area of greatest life loss, but a high 

percentage (as much as 90 percent) of the economic loss 

occurs outside this zone (Algermissen and others, 1972). 

Where the fault passes outside the developed zone or 

the earthquake is too small to induce nonlinear soil 

response, this behavior will not be a factor at all [for example, the 1967 Caracas, Venezuela, earthquake and 

the 1977 Romanian earthquake). 

COMPARATIVE GROUND 

RESPONSE IN THE 

LOS ANGELES REGION 

Comparative ground response to distant nuclear explosions was measured at 98 sites throughout the Los 

Angeles region. When these measurements are coupled 

with available geologic and geotechnical data, they provide an extensive data base to delineate potential 

geographic variations in strong ground shaking. Threecomponent recordings of Nevada Test Site nuclear explosions were made at each site. A total of 19 nuclear 

explosions were used; because some sites were reoccupied for several events, 159 three-component records 

were obtained. Sites for the study (fig. 104) were chosen 

to obtain as complete a sample of underlying geologic 

conditions and as broad a geographic coverage as possi224 Earthquake Hazards in the Los Angeles Region 

Velocity, Estimated 

in cmls strain References 

78.1 5 x 10- 3 Earthquake Engineering Research Laboratory 

108.8 5x10- 3 

to 1o-• 

(1969-1975). 

Nuclear Regulatory Commission (1980) 

Porcella and Matthiesen (1979) 

Mueller and others (1982) 

Chiaruttini and Siro (1981) 

ble. Because the seismic source lies between 400 and 

450 km from the recording sites, the effects of azimuthal 

variations in the energy radiated by the source and the 

major portions of the crustal propagation paths are 

similar for all sites. 

The response characteristics of each site over the 

period band 0.2 to 10 s were computed by using Fourier 

spectral ratios (Borcherdt and Gibbs, 1976). The Fourier 

spectral ratios (F) were computed from 

k= O, ... ,n 

i= 1, ... ,m 

j= v, t, r 

where silkiT) corresponds to the smoothed Fourier 

amplitude spectra for a signal of length T at frequency 

kiT for the jth component at the ith station and s0j [kiT) 

designates the corresponding smoothed amplitude spectra computed from a simultaneous recording at the 

reference station. The ratios were computed only at 

those frequencies for which a signal-to-noise ratio 

greater than a factor of two existed for both spectra. 

The noise level was determined by examining the spectra of a time segment before the arrival of the signal on 

each component of motion. These data, including processing techniques, copies of recorded time-histories, and 

spectral ratios, have been compiled and discussed by 

Rogers and others (1980). 

A site located on crystalline rock (CIT) [fig. 104) was 

reoccupied for every recorded nuclear explosion. By using CIT spectra (s0 j [kiT)) as the base rock site, it was 

possible to minimize the effects of source, transmission 

path, and instrument response in the spectral ratios 

(Rogers and others, 1979). Thus, the spectral ratios are 

assumed to reflect only frequency-dependent site 

amplification effects. The ·spectral ratio technique has 

been used by a number of investigators to obtain a first-
A 

c 

119'24' 34'22' 

I I I ' I I I 1) 

0 5 I 

10 

I 

10 MILES 

I 

15 KILOMETERS 

119"00' 

34'00' '-------------------- _1 

IN SET 

0 

I ' I ' II 1 11 

0 5 KILOMETERS 

118"40' 118"00' 

34' 23' ,------,-,-----------------, 

34'00' 

0 5 I " ' I I 'lfil l 0 5 10 

D 118"00' 34'25' 

B 

SAWTOOTH 

MOUNTAIN 

, RED 

MOUNTAIN 

5 MILES 

I I I I I L I 

1 18"25' 

34,30. '----L---"------"5--"K'-'ILO"'M""E"' TE""RS,___---' 

CALIFORNIA 

0 50 100 MILES 

hJ,J 

0 50100 KILOMETERS 

I 17'20' 

SAN GABRIEL MOUNTAINS 

34'00' 

>5'"1 "'t;, 

"1 

-<7--v 

'1 

0 5 10 MILES '\ 

I I I I I I I . LAKE 

IIT1'ri1 ,TI I I--'--"-'1-T'I "/-. . ELSINORE 

0 5 10 15 KILOMETERS ~~ (j 

U" 

FIGURE 104.-Locations of sites (triangles) in the Los Angeles region at which ground-motion recordings of underground nuclear explosions at the 

Nevada Test Site were obtained. Strong-motion recordings of the 1971 San Fernando earthquake were also available at some of these locations, indicated by the solid triangles. Open triangles indicate that only nuclear test recordings are available at a site. Station names and locations are taken from Rogers and others {1980). 

Predicting Relative Ground Response 225 
order approximation of the site amplification of local 

geologic deposits (Kanai and others, 1956; Gutenberg, 

1957; Borcherdt, 1970; Rogers and others, 1979). The 

ease with which the extraneous effects are removed 

from nuclear-event recordings is one of the prime 

motivations for using such events; nearby earthquakes 

produce recordings in which site amplification, source, 

and propagation-path phenomena are intertwined and 

difficult to study individually (Hanks, 1975). 

In the case of ground motions from distant nuclear explosions, the effects of site conditions dominate on the 

recorded time-histories. Figure 105, for example, shows 

time-histories from a single Nevada Test Site nuclear explosion recorded simultaneously at eight sites. The example illustrates several effects of local site conditions 

commonly observed on recorded time-histories from distant sources of shaking. Maximum amplitudes of motion 

recorded on the alluvial sites, for instance, are several 

times larger than those recorded on the sedimentary- or 

crystalline-rock sites. The duration of ground motion at 

the alluvial sites is generally longer than that at the rock 

sites. The degree of amplification occurring in the longperiod peak amplitudes of these records is greatest at 

sites underlain by the thickest sediments. Comparison of 

all three components of ground motion recorded at each 

site (Rogers and others, 1980) shows that the amplification of horizontal ground motions is commonly larger 

than that of vertical motions. In the following discussion, 

only the horizontal components of ground motion are 

emphasized, because they are the most important in 

structural engineering. 

The amplitude spectral ratios computed for the simultaneous recordings shown in figure 105 are presented in 

figure 106, where station CIT has been used as the 

reference station. The ratios show that the effects of site 

conditions relative to those at CIT are strongly frequency dependent and that amplification occurs for many of 

the sites over most of the frequency band for which a 

good signal-to-noise ratio exists. Horizontal amplification factors in the range 2 to 7 are apparent for the 

lower frequency ground motions ( < 1 Hz) for those sites 

on thick sections of alluvium; lower amplifications are 

apparent at these periods for sites underlain by thin sections of alluvium. Considerable amplification at the 

intermediate frequencies (1-2 Hz) and at the higher frequencies (2-5 Hz) is readily apparent at several of the 

sites, the horizontal amplification at site FS4 being indicative of a predominant ground-resonant frequency. 

Note that resonance is not a factor for the thick alluvial 

sites, which display relatively flat spectra across the entire observed frequency range. The spectral ratios for 

the GOC and CIT sites show that the spectral levels of 

the two crystalline-rock sites are very similar for the 

lower frequencies, but the intermediate-frequency and 

226 Earthquake Hazards in the Los Angeles Region 

higher frequency motions recorded at GOC are larger 

than those recorded at CIT. Site 3838, located on sedimentary rock, indicates a uniformly higher response in 

comparison with the response at CIT over most of the 

frequency band. 

Amplification does not produce large peaks in the 

time-history for FS4 because the frequency of maximum 

incoming energy is not coincident with the resonance 

peak frequency. This result points out the pitfall of examining peak ground-motion parameters for site effects. 

A site may have a strong amplification effect that is not 

necessarily reflected by the peak accelerations, for 

instance. 

The spectral ratios are similar for most of the nuclear 

explosions analyzed. An example of the spectral geometric means and their geometric standard deviations is 

shown in figure 107, together with data from the individual events used to compute the statistics. Additional examples have been computed by Rogers and others 

(1980), who have shown that the geometric standard 

deviation averages 1.38 independent of frequency (this 

result is seen more clearly in their log-log plots). By comparison, this dispersion is lower than that associated 

with the empirical prediction of root-mean-square acceleration on rock (Hanks and McGuire, 1981). 

The spectral ratios computed from shaking induced 

by distant nuclear explosions suggest that the observed 

ground motions varied significantly from site to site, 

depending on the type of underlying geologic deposits. 

At many sites, amplification is strongly frequency 

dependent. The level of spectral response at alluvial 

sites commonly is higher than that at rock sites, and the 

amplitude and duration of shaking depend on the thickness of the underlying sediments. Sites having thin 

alluvium tend to amplify shaking over a narrow frequency range, whereas sites having thick alluvium amplify 

shaking over a broad frequency range. These general 

conclusions are consistent with similar data and a 

similar interpretation reported by Borcherdt and Gibbs 

(1976) for the San Francisco Bay region. 

GEOLOGIC AND GEOTECHNICAL 

PARAMETERS AFFECTING 

GROUND RESPONSE 

The diverse geologic framework of southern California offers a unique opportunity to study variations in 

earthquake-generated ground shaking as a function of 

geologic setting. Crystalline rocks, for example, are exposed in rugged mountains more than 3 km above sea 

level and, in the deepest parts of the Los Angeles basin, 

are buried beneath at least 10 km of sedimentary rock 
ALLUVIUM 

0.031 

0.000 

- 0.031 

0.031 

0.000 

- 0.031 

0.031 

0 

z 

0 0.000 u 

UJ 

en 

c: - 0.031 

UJ 0.031 

c.. 

en 0.000 c: 

UJ 

1-

UJ - 0031 

~ 0.031 

1-

z 

UJ 0.000 u 

z 

>-' - 0.031 

0.031 

1- 3838 SEDIMENTARY ROCK 

u 

0 0.000 

.....J 

w 

> - 0.031 

0.031 GOC CRYSTALLINE ROCK 

0.000 

- 0.031 

0.031 CIT 

0.000 

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 

TIME, IN SECONDS 

FIGURE 105.-Radial component time-histories of ground motion from a distant underground nuclear explosion in Nevada 

recorded simultaneously at eight sites in the Los Angflles region and grouped according to the type of geologic materials 

immediately beneath each recording station. The amplitude levels at locations underlain by alluvium clearly are greater 

than those at locations underlain by rock. The degree of amplification also appears to be related to the thickness of 

underlying alluvium: HOI, Holiday Inn, 300 m; MIL, Millikan Library, 372 m; A TH, Athenaeum, 372 m; GMB, Glendale 

Municipal Building, 120m; FS4, Fire Station 4, 15 m. GOC, CIT, and 3838 are rock sites. 
ALLUVIUM /CRYSTALLINE ROCK 

12.0 12.0 MIL.RCIT ATH RCIT 12.

0 ,----,1--.-1-'1--.-1---, 

9.0 9.0 9.0 - -

6.0 vi' r I 6.0 

3.0 3.0 0 

i= 

<! 

a: 0.0 0.0 3.0 4.0 5.0 3.0 5.0 

-

'\;-\ -

I I 3.0 4.0 5.0 

6.0 -

3.0~~ 

o.o ,__ __ _,__I __ _,I __ _L_ __ _,__ _ __, 

0.0 1.0 2.0 _J 

<! 

a: 

1- GMB.RCIT u 12.0 12.0 

UJ 

a_ 

(/) 

9.0 9.0 

6.0 6.0 

3.0 ~~ 3.0 

1.0 2.0 3.0 4.0 5.0 0.0 

0.0 

~ 1.0 3.0 5.0 

SEDIMENTARY ROCK/CRYSTALLINE ROCK 

3838.RCIT 12.0 I I I I 

9.0 - -

6.0 - -

3.or-~ rvv~ --

o.o I I I I 

0.0 1.0 2.0 3.0 4.0 5.0 

CRYSTALLINE ROCK/CRYSTALLINE ROCK 

12.0 I 

GOC.RCIT 

I I I 

9.0 - -

6.0 - -

3.0 

-~I j\rJ~ r ('..\ -

\ 

0.0 I I 

0.0 1.0 2.0 3.0 4.0 5.0 

FREQUENCY, IN HERTZ 

FIGURE 106.-Spectral ratios of the radial components of ground motion (see fig. 105) recorded on sites having geologic conditions different from 

the crystalline-rock site (CIT). These diagrams show that spectral site amplification ranges from about 1 to greater than 12; the highest ratios 

occur at sites underlain by alluvium. Site FS4 displays a resonant frequency between 2 and 3 Hz, whereas other sites have more uniform 

amplification, averaging as much as 6 in some frequency bands. 

and alluvium (Yerkes and others, 1965). The youngest 

deposits in the basins of the Los Angeles region consist 

chiefly of unconsolidated to partly consolidated alluvialfan and river flood-plain sediment. These deposits range 

228 Earthquake Hazards in the los Angeles Region 

in thickness from 0 to 10 m near basin margins to, 

perhaps, more than 50 m in coastal basins. Sand and 

mud occur in ancient and modern shore areas; windblown sands are present locally in inland basins. Basin 
fill, mostly of Quaternary age and some of Pliocene age, 

ranges widely in texture; gravel, cobbles, and boulders 

occur chiefly near mountain fronts and in channels on 

alluvial fans emanating from the mouths of major canyons, and silt and some clay commonly are deposited on 

flood plains tens of kilometers from the mountains. 

The 98 recording sites used in this study encompass a 

broad range of the variations in depth to basement rock 

and in the texture and physical properties of basin fill. 

Geologic and geotechnical information about the uppermost few tens of meters of basin fill at each groundmotion recording site was compiled from logs of soilengineering boreholes, water wells, and ·limited field 

investigations (Gibbs and others, 1980; Fumal and 

others, 1981, 1982; J. C. Tinsley, written communication, 

1982). The soil-engineering logs, chiefly of foundation 

studies, are from files maintained by city, county, State, 

and Federal agencies and from geotechnical consulting 

firms. These records describe the near-surface sediment in terms of its grain size, moisture content, and dry 

density. Many of these boreholes penetrate the uppermost 5 to 10 m of the alluvial deposits, although foundation studies for major structures may penetrate up to 

30m or more. 

The general geologic character and the thickness of 

surficial sediments in the depth range from 15 to 300 m 

have been inferred from drillers' lithologic logs of water 

wells and from geophysical logs of oil and water wells 

filed with State and local agencies. Studies of the 

regional hydrology (Poland, 1959; Poland and others, 

1956, 1959; Thomas and others, 1961; California Water 

Rights Board, 1961; Dutcher and Garrett, 1963; California Department of Water Resources, 1966) describing 

the geologic and hydrologic setting of the late Quaternary alluvial basins have been incorporated where 

pertinent. 

For each recording site, several engineering and 

water-well logs were examined, and the most representative data-usually obtained from the borings closest to, 

if not beneath, the site-were used to characterize each 

site. We regard three thickness parameters as significant for characterizing the sites: (1) the total thickness 

of sedimentary deposits, expressed as the depth to the 

crystalline igneous and (or) metamorphic rocks underlying the basins; (2) the approximate thickness of semiconsolidated sediment, expressed as the approximate thickness of the Quaternary (less than 1.7 m.y. old) deposits; 

and (3) the approximate thickness of unconsolidated or 

poorly consolidated sediments, expressed as the approximate thickness of Holocene (less than 10,000 yr old) 

sediment. The lithologic and time-stratigraphic horizons 

bounding these rock units commonly correspond to 

physically significant interfaces in the subsurface 

across which the shear-wave velocities and relative densities of the sediment may change (Fumal, 1978; Gibbs 

and others, 1980; Fumal and others, 1981, 1982) and 

thus alter the response characteristics of the site. 

A number of geotechnical factors (table 38) were 

chosen to characterize the recording sites either 

because they have some direct application in a theoretical model of site response and (or) because they have 

been reported to have some influence on ground shaking 

in past studies. Parameters such as mean percentage of 

silt and clay, void ratio, and depth to water table have 

been reported to influence site response (Barash (1969) 

has summarized many of these studies), whereas shearwave velocity, Holocene deposit thickness, Quaternary 

deposit thickness, depth to cementation, and depth to 

basement rocks are all parameters that might be used 

directly in a theoretical model of site effects. The 

alluvium-to-rock spectral ratios were reduced to a small 

set of numbers by computing the geometric mean spectral ratio over 10 period bands. Because a high degree of 

correlation was observed between the mean spectral 

values in some of these period bands, only three nonoverlapping bands were used in further analysis. These 

bands are referred to as the short-period (0.2-D.5 s), 

intermediate-period (0.5-3.3 s), and long-period 

(3.3-10 s) bands. A discussion of the geotechnical 

parameters thems~lves follows. 

Mean .void ratio.-Void ratios (e) are computed from 

dry-density (GD) data obtained from the foundationengineering data by using the relation e = (GS/GD) -1, 

where GS is the density of the solids without voids. For 

most soils, GS varies from 2.65 to 2.70. By assuming the 

lower value for sand and the higher value for clay, mean 

e values were computed for each alluvial site, generally 

for the upper 8 m. At layered sites having several values 

of e, the depth-weighted mean was computed. Mean e 

rather than mean shear-wave velocity was used in this 

study to characterize the sites for several reasons. First, 

laboratory studies by Hardin and Drnevich (1972) have 

indicated that e and shear modulus are inversely 

related, and Rogers and others (1979) have determined 

that site response increases as e increases, a result that 

might be predicted from the relation between e and 

shear-wave velocity. Figure 108 uses data from Los 

Angeles and San Francisco to show this relation. The 

curve fit to these data can be used to estimate shearwave velocity from e. Second, data on void ratios were 

readily available from engineering boreholes and were 

therefore a useful and inexpensive way to estimate 

near-surface shear-wave velocity. Data on void ratios 

were also available at nearly twice as many sites as 

data on shear-wave velocity; because of the effort and 

expense involved in collecting borehole measurements, 

the shear-wave velocities were not available for many 

sites until this study was almost complete. Third, void 

Predicting Relative Ground Response 229 
FS4. V BACKBEACH FS4. V ICEBERG 

32.0 32.0 I I 1 

24.0 24.0 - -

16.0 16.0 f- -

8.0 8.0 f- -

0.0 0.0 J ~ I- - ~,~~ 

0.0 1.0 2.0 3.0 4.0 5.0 a.o 1.0 2.0 3.0 4.0 5.0 

FS4. T BACKBEACH FS4. T ICEBERG 

32.0 32.0 

0 

i= 

24.0 24.0 

<t 

a: 

...J 16.0 16.0 

\ <t 

a: 

fu 

w 

a.. 8.0 8.0 (/) 

0.0 0.0 

0.0 1.0 2.0 3.0 4.0 5.0 0.0 1.0 2.0 3.0 4.0 5.0 

FS4. R BACKBEACH FS4. R ICEBERG 

24.0 24.0 

16.0 16.0 

8.0 8.0 

1.0 2.0 3.0 4.0 5.0 3.0 4.0 5.0 

FREQUENCY, IN HERTZ 

A B 

FIGURE 107.-Comparison of spectral ratios computed for stations FS4 (alluvium) and CIT (crystalline rock) for distant nuclear explosions. A, 

Backbeach. B, Iceberg. C, Fondutta. Components of shaking are vertical (V), transverse (T), and radial (R). The geometric mean spectral ratio 

(solid line) and one geometric standard deviation about the mean (dashed and dotted lines) are also shown (D). The geometric standard devia230 Earthquake Hazards in the Los Angeles Region 
FS4. V FONDUTTA 

32.0 I I I I 32.0 

24.0 1- - 24.0 -

16.0 1- - 16.0 1-

8.0 t- - 8.0 1-

0.0 ~ ~~,r- 0.0 0.0 1.0 2.0 3.0 4.0 5.0 0.0 

FS4. T FONDUTTA 

32.0 32.0 

0 24.0 24.0 F 

<{ 

a: 

...J 

<{ 16.0 16.0 

a: 

1-

u 

w 

0.. 

(f) 8.0 8.0 

0.0 

0.0 1.0 2.0 3.0 4.0 5.0 0.0 

0.0 

FS4. R FONDUTTA 

32.0 

24.0 24.0 

16.0 16.0 

8.0 8.0 

0.0 

0.0 1.0 3.0 4.0 5.0 

c 

FREQUENCY, IN HERTZ 

I 

v-.· 

1.0 

1.0 

FS4. VAvG 

I I I 

-

-

-

,, 

~~ I" 

,t·~ ' .... .... 

.. ( ··· 

2.0 3.0 4.0 5.0 

FS4. TAvG 

·.~~ ~ 

FS4. RAvG 

I, 

/I 

I, 

I 

I I 1 

I'· 

, t: I } j\ • 

, : ·r ~~ 11 1 '•I II I 

'''··~ ,~··· : .. :···.:· .. ~ 

D 

5.0 

5.0 

tion in this case averages to a factor of about 1.3 across the frequency band. Similar examples for other stations have been shown by Rogers 

and others (1984). These diagrams demonstrate the reproducibility of the spectral ratios between distant nuclear events. 

Predicting Relative Ground Response 231 
TABLE 38.-Geotechnical parameters and the percentage of stations 

for which each parameter was available 

Parameter 

Stations for which 

parameter was available, 

in percent 

Mean void ratio (o-8 m) -------------------------- 82 

Mean percentage of silt and ---------------------- 37-95 

clay (four depth intervals). 

Thickness of Quaternary------------------------- 100 

Age ----------------------------------------- 100 

Thickness of Holocene -------------------------- 99 

Depth to water table ---------------------------- 97 

Textural type --------------------------------- 99 

(very coarse to fine). 

Depth to crystalline basement --------------------- 100 

Depth to cementation --------------------------- 91 

Mean borehole shear-wave ----------------------- 42 

velocity (four depth intervals). 

ratios were frequently measured at the building where 

the nuclear-event recordings were made, whereas 

shear-wave velocity measurements sometimes had to be 

taken tens to hundreds of meters away. Thus, in some 

cases, an e value computed for the recording site may be 

a more relevant measure of the shaking response at the 

recording site than a shear-wave velocity measurement 

made some distance away. Even though the void ratio is 

generally known only in the upper 8 m, which represents 

only a fraction of the near-surface wavelength in the 

short-period band, the high correlation observed in this 

period band between void ratio and shaking response indicates that the near-surface void ratio reflects information about the mean shear-wave velocity over a deeper 

sediment section. This supposition is supported by the 

highly significant correlation coefficient {- 0.6) in our 

data between mean void ratio in the upper 8 m and 

mean shear-wave velocity in the upper 30 m. 

Mean percentage of silt and day.-The mean percentage of silt and clay was determined from the lithologic 

descriptions of boreholes for selected thicknesses of 8, 

15, 30, and 122 m by summing the total incremental 

thicknesses of sediment logged as silt or clay within the 

interval, dividing that sum by the thickness of the interval, and then multiplying the quotient by 100. 

Thickness of Quaternary.-The base of the Quaternary sedimentary deposits was selected arbitrarily at 

the base of the marine San Pedro Formation in the 

coastal basin areas and at the base of the nonmarine{?) 

sand and gravel that comprise the freshwater-bearing 

alluvium in the interior basins. Some of these basinal 

nonmarine{?) deposits are almost certainly preQuaternary in age, but correlations among these deposits are not reliable. 

Age.-Recording sites were classed according to the 

geologic age of the underlying surficial deposits-for 

232 Earthquake Hazards in the Los Angeles Region 

example, Holocene alluvium, Pleistocene alluvium, Tertiary sedimentary rock, Tertiary volcanic rock, or preTertiary crystalline igneous and metamorphic rock 

{crystalline basement). Sites were classed as rock sites 

where a thin alluvial veneer had been excavated and 

had been removed during construction of the building 

that housed the recording instrument. 

Thickness of Holocene.-Holocene deposits are commonly associated with historical flooding and are 

capped by soils having minimally developed profiles. In 

practical terms, in the field, the base of the Holocene 

section is placed generally at the top of the uppermost 

red or reddish-brown buried soil. Early Holocene 

deposits may have nonclayey {cambic) B horizons or nonreddened clay-enriched B horizons, except within historically active flood basins {McFadden and Tinsley, 1982). 

Depth to water table.-The distance from the ground 

surface to free ground water, expressed here as "depth 

to ground water" (including perched water), was determined from logs of boreholes located near each 

instrument site and from selected maps and records 

maintained by the California Department of Water 

Resources, the Los Angeles County Flood Control 

District, and the City of Los Angeles Department of 

Water and Power. 

600 

0 

z 

0 

u 

w 

(/) 

a:: 

w 

c. 

(/) 

a:: 

w 

1-

w 

~ 

~ 

~ 300 

~ u 

0 

...J 

w 

> 

a:: 

< w 

I 

(/) 

100 

0.3 0.4 0.5 0.6 0.7 0.8 0.9 

VOID RATIO (e) 

FIGURE 108.-Relation between mean shear-wave velocity in the upper 

10 m and mean void ratio in the upper 8 m. Solid triangles are data 

from the San Francisco region (Fumal, 1978), and open triangles 

are data from the Los Angeles region. The curve , which is a leastsquares fit to all of the data, can be used to estimate shear-wave 

velocity (V sJ for sediments in cases where only void-ratio (e) data 

are available. 
Textural type.-The grain-size distribution of the surface sediment at the instrument site was classified as 

very coarse, coarse, medium, or fine, depending on the 

texture of the surface soil as mapped by the U.S. Department of Agriculture or the U.S. Bureau of Soils. Very 

coarse grained deposits contain boulders and cobbles, 

coarse-grained deposits contain gravel, medium-grained 

deposits contain chiefly sand, and fine-grained deposits 

contain chiefly silt and clay. 

Depth to crystalline basement.-The depth to basement rock is the vertical distance from the land surface 

to crystalline igneous or metamorphic rock. Depths to 

basement, which may exceed 10 km in the Los Angeles 

basin (Yerkes and others, 1965, p. A4), have been estimated from electric logs, lithologic logs, and gravity 

models, such as McCulloh's {1957, 1960) model. 

Depth to cementation.-Depth to cementation is defined as the distance from the land surface to sediments 

described in drilling logs as "cemented." The 

stratigraphic position at which this effect is noted apparently varied from driller to driller as well as from 

place to place. 

Shear-wave velocity.-Borehole shear-wave. velocity 

measurements were made to a depth of 30 m at 41 of the 

98 nuclear recording sites (Gibbs and others, 1980; 

Fumal and others, 1981, 1982, 1984). Mean shear-wave 

velocity was computed for depth intervals of 0 to 2, 0 to 

5, 0 to 15, and 0 to 30 m. 

COMPARING GROUND RESPONSE 

WITH GEOLOGIC FACTORS 

We will first explore the dependence between 

response data and geotechnical parameters to determine which factors have the strongest influence on site 

response in each period band. Having determined the 

most important factors, we will then present an empirical technique for predicting site response on the 

basis of these variables, whereby recording sites are 

grouped or clustered on the basis of similarity among · 

the most important geologic site factors in a given period 

band. Grouping of the sites is accomplished by using the 

techniques of cluster analysis and discriminant analysis 

of cluster trials. To use these techniques, the mean siteresponse values and the geologic variables first must be 

assembled into a 98-station by 27-variable matrix, which 

permits us to easily extract relevant columns for 

analysis. After the clusters are formed, a geographic 

area is classified into one of the clusters on the basis of 

its geologically distinctive characteristics for a given 

period band, and the geometric mean cluster response is 

assigned as the response for that area. Although it is impractical to show all the details of the process leading to 

the final results of this study, we will examine the more 

important stages in the following discussions. 

To examine the relation between site response and 

geologic parameters, the most straightforward approach is to group the sites according to variations in 

one of the geologic factors and to compute the mean 

response for each group, as table 39 does. These results 

indicate that, for the Los Angeles region, (1) levels of 

shaking at sites underlain by Holocene and Pleistocene 

sedimentary deposits are three to four times greater 

than those at sites underlain by crystalline rock for all 

period bands; {2) the void ratio has a strong influence on 

short-period response (void ratios in the 0.8 to 0.9 range 

indicate a mean response on soil that is six times greater 

than that on crystalline rock and three times greater 

than that on soils having low void ratios); and (3) 

amplitudes in the long-period band generally increase as 

the thickness of Quaternary deposits and (or) the depth 

to basement increases. The apparently anomalous finding (table 39} that the response of sites on Miocene rock 

is higher than that of sites on Pliocene rock may be attributed to causes other than age. Three of the Miocene 

rock sites are on ridges or areas of high topography and 

may be affected by topographic amplification (Boore, 

1972; Rogers and others, 1974). The results given in 

brackets in table 39 are computed exclusive of these 

topographically high sites and show a closer correspondence between the two age groups at short and intermediate periods. In addition, the Pliocene rock sites 

that we have used are all located in downtown Los 

Angeles within an area of about 1 km2 and thus do not 

represent an even geographic distribution of sites. The 

Pliocene rock sites in our sample may be characterized 

by anomalously low response, which reflects factors 

that we have not considered in our analysis. We have no 

means by which to analyze this possibility, however. The 

dependence of the response variables on each of the 

geologic factors was ex$lmined for each period band by 

grouping on one factor; table 39 shows some of the 

stronger interrelations between these variables, but a 

more elaborate analysis enabled us to study these interactions and others in more detail. 

The smoothing techniques of exploratory data 

analysis (Mosteller and Tukey, 1977; Velleman and 

Hoaglin, 1981) can be applied to determine the influence 

of one factor on the response variable, given a body of 

data in which several factors are changing simultaneously. The chief problem is that, for a limited data set, it 

may not be possible to hold several factors constant 

while studying the influence of another; these smoothing 

techniques can be a helpful analysis tool for data satisfying certain assumptions. Figure 109, for instance, 

shows the smoothed short-period spectral ratio versus 

Holocene deposit thickness and void ratio. The broad 

Predicting Relative Ground Response 233 
TABLE 39.-Comparision of mean ground response (relative to crystalline rock) from distant underground nuclear 

explosions recorded at sites within the Los Angeles region 

[Geometric standard deviation in the response variable for these groups ranges from about 1.6 to 1.9. Short period, 0.2 to 0.5 s; intermediate period. 0.5 to 3.3 s: 

long period, 3.3 to 10.0 s] 

Age of 

surficial 

materials Short period 

Holocene------ 3.4 

Pleistocene ---- 3.2 

Pliocene ------ 1.4 

Miocene ------ 2.5 [1.9)1 

Mesozoic ----- 1.7 

Void ratio' Short-period 

0.2-{).4 -------- 2.3 

0.4-{).6 -------- 3.1 

0.6-{).7 -------- 3.0 

0.7-{),8 -------- 4.2 

0.8-{).9 -------- 6.2 

Quaternary 

thickness, 

in meters 

Intermediate period 

3.3 

3.1 

1.6 

2.2 [1.8)1 

1.1 

Intermediate period 

Long period 

2.6 

2.6 

2.0 

1.4 (1.3)1 

0.8 

Long period 

0 --------------------------------------------------- 1.6 1.3 

1.4 

2.9 

3.1 

5.9 

3.1 

D-75 ------------------------------------------------ 2.3 

75-200 ----------------------------------------------- 3.6 

20D-500 ---------------------------------------------- 3.6 

50D-1000 --------------------------------------------- 4.1 

> 1000 ----------------------------------------------- 3.4 

Depth to 

basement, 

in kilometers Intermediate period Long period 

0 ---------------------------------------------------· 1.1 0.8 

1.3 

2.5 

4.1 

3.9 

o-2 --------------------------------------------------- 2.6 

2-4 --------------------------------------------------- 2.8 

4-6 ----------------------------------------;;,----------- 3.8 

> 6 --------------------------------------------------- 3.8 

1

Bracketed value excludes topographically high sites. 2 Average for uppermost 8 m. 

peak in the Holocene thickness plot near 15 m is due to 

the shift through this period band of the fundamental 

resonance period of the Holocene layer. The general increase in the short-period response as void ratio increases is caused principally by the increase in shearwave velocity between Holocene and Pleistocene 

deposits. For comparative purposes, theoretical spectral ratios were computed by using a horizontally 

layered SH-body-wave model and assuming viscous 

damping. The physical properties of the geologic column 

used in this modeling were generated by computer from 

the geologic data matrix; variable surface-layer 

velocities, fixed lower layer velocities, and depths to 

velocity contrasts were determined by Holocene and 

Quaternary deposit thicknesses and depth to basement, 

as figure 110 outlines. Surface-layer velocities were 

234 Earthquake Hazards in the Los Angeles Region 

either measured borehole shear-wave velocities or computed from void ratios (fig. 108). The theoretical spectral 

ratios and the mean spectral values were processed in 

exactly the same fashion as the observed quantities. The 

concordance between observed data and theory supports our interpretation of the observed behavior and 

shows the utility of theoretical models for predicting 

mean site response. Although similar analysis of other 

factors indicates that variables such as depth to basement and Quaternary thickness have an effect on the 

short-period response, these variables and others are of 

secondary importance in comparison with Holocene 

deposit thickness and near-surface void ratio. 

Identifying the chief geologic factors that control 

intermediate- and long-period response is more difficult 

than identifying those that control short-period response 
0 

A 

.-----,-~----,~-----,----~~------1 

c\0 -

0 

0 -

0 

-

0 0 -

2 - -

1 - -

L_--~~----~I _____ L_I ____ IL_ __ ~ 

0 15 30 45 60 75 

HOLOCENE THICKNESS, IN METERS 

B 

.---~~--~~----,-~--~~------1--,-1--, 

0 

0 0 0 

6 1-- -

5 1-

~ a: 4 f-

...J 

<t: 

a: 

t; 3 -

w 

0.. 

(/) 

2 -

1 -

8 

0 

0 

8 

§ 

-

-

L-~,L_~'---~~--~~---~'--L-1~ 

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 

VOID RATIO 

FIGURE 109.-Smoothed short-period spectral ratios at sites on 

Holocene deposits in comparison with Holocene thickness (A) and 

void ratio (B). To minimize the influence of void ratio in A, only sites 

having void ratios greater than 0.65 were included. A circle indicates theoretical values; a square indicates observed values. 

because a larger number of variables may be involved. 

Some factors, such as Quaternary thickness and depth 

to basement rocks, are highly interdependent, because 

the deep parts of the Los Angeles basin have continued 

to subside during the Quaternary. Moreover, the deeper 

structural features and shear-wave velocities may not 

be as well determined as the geotechnical factors controlling the short-period response, and the amount of 

data (for the number of variables involved) may be too 

limited to fully explore the problem. Some consistent 

behavior in these two period bands is observed, nevertheless. For thin Quaternary soils and sedimentary-rock 

deposits, for instance, the response in these two bands is 

low, whereas, for thick deposits, high response is 

observed, as table 39 and figures 111 and 112 show. 

Although the SH-body-wave model partially predicts this 

behavior, the correspondence between observed and 

predicted values is poorer at longer periods, probably 

because the theory applied does not model the behavior 

of surface waves as they propagate through laterally inhomogeneous layers. Attempts to model surface waves 

in such media, however, have shown that surface-wave 

amplitudes increase as the waves propagate from thin 

layers to thicker ones (Drake and Mal, 1972; Murphy 

and Hewlett, 1975) and thus qualitatively support the 

results discussed above. Examination of factors other 

than Quaternary thickness and depth to basement indicates that the other factors have only secondary influence on the site response in these period bands. 

After studying earthquake intensities in the Soviet 

Union, Medvedev (1962) reported that the presence of 

shallow ground water in alluvial sediments apparently 

increased the intensity of seismic shaldng. On the basis 

of this conclusion, Evernden and Thomson (this volume) 

have increased predicted intensities by one unit where 

saturated alluvium occurs near the surface. We 

reevaluated Medvedev's (1962, figs. 2.1-2.7) data in 

light of the results of our study in the Los Angeles region. 

For the types of sites that Medvedev examined, as the 

depth to the water table decreased to less than 10 m, the 

thickness of the soil deposits increased to between 10 

and 20 m. Thus, Medvedev's observation that the highest intensities occur at sites having shallow water tables 

( < 10 m) can be attributed to resonant effects associated 

with soils between 10 and 20 m thick rather than to the 

effect of differences in depth to the water table. Our interpretation is supported by the lack of correlation between shear-wave velocities or site response and depth 

to water table in San Francisco (Borcherdt and Gibbs, 

1976; Fumal, 1978). In Los Angeles, sites having a water 

table at less than 10 m have a distribution of void ratios 

whose mean is slightly higher than that of sites where 

the water table is deeper; furthermore, the number of 

Pleistocene sites in this group is proportionately larger 

than that in the group where the water table is shallow. 

Both of these occurrences may be due to some depositional or geomorphologic causes; in the data of this 

Predicting Relative Ground Response 235 
HOLOCENE 

PLEISTOCENE, 

PLEISTOCENP 

TERTIARY 

ROCK 

CRYSTALLINE 

BASEMENT 

t.t , 

tP,=QTHK-tH 

, 

tP2= QTHK-tP1 

tT=+b-QTHK 

SHEAR 

VELOCITY (m/s) 

{Vm Vs 

350 

600 

1500 

3000 

DENSITY (g/cm3 ) 

1.46 

2.10 

2.10 

2.35 

2.50 

.. 

Q 

50 

200 

200 

500 

-

REMARKS 

V5 =42.9+94.1/e2 

tP1 NOT ALLOWED 

TO EXCEED 100 m 

ONLY PRESENT 

WHEN 

OTHK-tH> 100 m 

ONLY PRESENT 

WHEN 

tb> OTHK 

FIGURE 110.-Shear-wave-velocity model used to compute theoretical damped SH-wave response. The values for the symbols used in this figure 

either are calculated as shown or come from the geologic data matrix described in the text and table 38. th is the thickness of Holocene 

deposits; e, void ratio; V5, shear-wave velocity calculated from the equation shown; V m' borehole shear-wave velocity; tP and t 2, Pleistocene 

deposit thicknesses; tQ, Quaternary deposit thickness; tT' thickness of the Tertiary section; tb, depth to crystalline rock. The qualfty factor, Q, is 

assumed in the model to include the effects of material attenuation. 

study, however, these correlations are not strong 

enough to demonstrate a clear dependence between 

water table and site response. Thus, in the Los Angeles 

region, the lack of correlation between depth to the 

water table and mean short-period response or other 

factors controlling site response suggests that depth to 

water table apparently is not a reliable predictor of 

variation in shaking level, a view that conflicts with 

Evernden and Thomson's (this volume). 

CLUSTERING SITES TO REFLECT 

GROUND-RESPONSE VARIABILITY 

Sites having similar response characteristics can be 

clustered by computing some analytical measure of 

similarity between a list of items on the basis of their attributes. In our analysis, the items are recording sites, 

and the attributes are the geotechnical properties of 

each site (note that we do not use the response factor as 

an attribute, because we are attempting to predict 

response as a function of the geologic properties of a 

site). The clustering algorithm (Anderberg, 1973; Hartigan, 1975; IMSL, 1982) uses a computing rule to determine those items most nearly alike and the similarity 

level at which clusters of similar items are alike. The 

results can be plotted simply as an inverted hierarchical 

tree of similarity nodes (fig. 113). In this example, sites 5 

and 6 are more nearly alike than any other pair, and 4 

236 Earthquake Hazards in the los Angeles Region 

and 5 are more dissimilar than 1, 2, 3, and 4 or 5, 6, 7, 

and 8. The definition of clusters is determined by specifying the level of similarity below which clusters form. 

At similarity level one, 5 and 6 form a cluster; at level 

two, 1 and 2 and 5, 6, and 7 form two clusters; at level 

three, 1, 2, 3, and 4 and 5, 6, 7, and 8 form two clusters. 

The choice of a similarity level below which clusters 

form is subjective and, in practice, may change across 

the cluster diagram. 

Once a set of clusters is formed by this procedure on a 

chosen set of factors, it is possible to analyze the degree 

to which these factors define unique groups by means of 

discriminant analysis (Morrison, 1969, 1974; Cooley and 

Lohnes, 1971; Nie and others, 1975), which determines 

the significance of each factor's discriminating power 

by using the statistics of factors within and between 

clusters. A set of discriminant functions is computed 

that permits calculation of the probability that a single 

member of a cluster belongs to that cluster or any other 

cluster; given a table of these probabilities, it is possible 

to calculate the percentage of sites that have been correctly classified. 

Our application of this procedure was a trial-anderror process, during which some of the data analysis 

described above was done concurrent with the cluster 

and discriminant analysis. At the start, the site-response 

data were divided into rock and alluvial groups, and 

then clusters were examined in which many or all of the 

measured factors were part of the clustering model. 
A 

5 

<.) 

~ 0 

0 0 0 0 

0 0 0 

0 0 ©0 

i= 

<( 

a: 

.....1 

<( 

a: 

1-

u 

w 

a.. 

(/) 

0

o 2 4 6 8 10 12 

4.5 

0 

~ a: 

.....1 

<( 3 

a: 

1-

u 

w 

a.. 

(/) 

1.5 

B 

DEPTH TO BASEMENT, IN KILOMETERS 

0 

0 

0 

10 100 1000 10000 

QUATERNARY THICKNESS, IN METERS 

FIGURE 111.-Smoothed intermediate-period spectral ratio compared 

with depth to basement rock (A) and Quaternary thickness (B). A 

circle indicates theoretical values; a square indicates observed 

values. 

This approach, however, produced too many clusters, 

each of which had too few station members. The number 

of factors in the clustering process was reduced in a 

series of trials by gradually discarding factors that 

A 

6 

8J 0 

0 

0 0 0 0 0 0 

OlElJ 0 0 0 

0 

ocj 0 0 

0 oO 

i= 0 CO go~ 0 <( <€! a: 

~ ~0 bO 0 B 0 .....1 0 <( 

a: ~~ 8o 

1-

u § w 0 a.. 

(/) 0 

~ 

0

o 2 4 6 8 10 12 

4.5 

0 

i= 

<( 

a: 

.....1 

<( 

a: 

1-

u 

w 

a.. 

(/) 

DEPTH TO BASEMENT, IN KILOMETERS 

B 

L__L_LLLUUL-_L-LLLUUL--L-~~~L_~--~~ 

10 100 1000 10000 

QUATERNARY THICKNESS, IN METERS 

FIGURE 112.-Smoothed long-period spectral ratios compared with 

depth to basement rock (A) and Quaternary thickness (B). A circle 

indicates theoretical values; a square indicates observed values. 

discriminated poorly between clusters on the basis of 

statistics produced by the discriminant analysis. Some 

continuous variables were categorized into discrete 

ranges to satisfy certain requirements of the analysis 

Predicting Relative Ground Response 237 
1 

~ a: 

:5 

~ 

U5' 

(.!) 

z 

Ci5 

<( 

w 

cr:: 

u 

w 

0 

2 34 56 7 8 

STATION NUMBER 

LEVEL 3 

LEVEL 2 

LEVEL 1 

FIGURE 113.-A simple example of the clustering technique showing 

the cluster tree and the clusters that form at various levels of 

similarity. 

techniques. In some cases, relevant ranges in this classifying scheme were apparent from the preliminary data 

analysis. For unconsolidated sediment thickness, for example, sites were classified into three ranges of 

thickness: 

>Om and <11m 

>11m and <20m 

>20m 

These values are based on the behavior of the shortperiod response as a function of this variable. Comparison of the mean response values in the three period 

bands for each cluster set examined revealed that some 

cluster parameters reduced the response variance in 

each cluster better than others, in accord with the 

results of the preliminary data analysis (figs. 109, 111; 

table 39), which showed that the most important factors 

in each period band should be different. Ultimately, 

those cluster sets selected were chosen (1) because they 

had the lowest dispersion in the defining variables and 

because they used those factors having the strongest effect in a given period band, (2) because the probability of 

misclassification was low, and (3) because there was 

enough data in each cluster in the set to estimate the 

mean cluster properties. The final sets of clusters are a 

compromise between the many clusters that would be 

required to preserve all the complexity in the site 

response as a function of site geology and the requirement that each cluster contain enough cases to estimate 

its average response with acceptable variance. · 

Figure 114 shows the set of two rock clusters and 

eight alluvial clusters that was derived for the short238 Earthquake Hazards in the Los Angeles Region 

period band. This figure can be understood by using 

cluster 4A as an example. That cluster includes sites 

having a depth to basement rock of more than 0.5 km, an 

unconsolidated sediment thickness greater than 20 m, 

void ratios in the 0.6 to 0.7 range, and a geometric mean 

spectral ratio (hereafter shortened to spectral ratio) of 

about 3.6. The response predicted by using these 

clusters preserves the important features of site 

behavior noted above. For a given unconsolidated sediment thickness, for instance, the spectral ratio increases as the void ratio increases (for example, 

compare clusters 1A, 3A, and 6A). The spectral ratio 

also increases, for a constant void ratio, as the unconsolidated sediment (mostly Holocene sites) thickness increases to the critical range (for example, compare 

clusters 6A, 7 A, and 8A). Note that the thin unconsolidated sediment clusters contain most of the Pleistocene 

sites; those unconsolidated Pleistocene sites in the 

thickness range 11 to 20 m, however, are grouped with 

the Holocene sites in this range. The spectral ratio of 

rock sites 1R and 2R is typically lower than that of the 

alluvial clusters, as one might predict on the basis of 

their shear-wave velocities. A comparison of clusters 1A 

and 2A shows that sites underlain by shallow alluvium 

over crystalline rock (2A) have a spectral ratio two 

times higher than that of the same type of site overlying 

a deep sedimentary basin; this difference further emphasizes the importance of high-impedance contrasts at 

shallow depths. Even though we were able to divide the 

sites into only 10 clusters, which result in a moderate 

range in the. geologic and spectral ratio factors in each 

cluster, a useful result can be demonstrated by comparing average spectral level with shaking intensity. Borchardt and others (1975) have shown that a factor of two 

in mean spectral level corresponds to a change in intensity units of 1 MM (Modified Mercalli); we infer, then, 

from the data in figure 114, that these clusters predict 

the true spectral ratio of a site more closely than one 

intensity-unit increment for 90 percent of the cases, 

because the geometric 90-percent confidence interval is 

less than a factor of two (1.45). 

Figure 115 shows the clusters derived for the 

intermediate- and long-period bands. In principle, 

clustering for the intermediate-period band should be 

determined separately; it is known, for instance, that 

Holocene sites more than 30 m thick produce high spectral ratios in this period band. Because no clustering 

scheme was discovered for this band that was significantly better than that derived for the long-period band, 

however, these two bands are treated similarly. These 

cluster sets show that the spectral ratio increases as 

depth to basement rock increases up to 6 km; spectral 

ratios decrease slightly for greater sediment thicknesses. At the shorter periods in the intermediate-period 
0 

i= 

<t: 

a: 

_J 

<t: 

1.0 a: 

1-

u 

w 

a.. 

CJ) 

0.8 

0 0.6 

~ a: 

0 

0 

> 0.4 

15 

10 

8 

6 

5 

4 

3 

2 

1 

0.8 

0.6 

0.5 

l 

I 1 I 

15 

10 

8 

6 

5 

4 

3 

2 

0.8 

0.6 

0.5 

1.0 

0.8 

0.6 

0.4 CJ) 

a: 

w 

1-

w 

0.2 

11 m s: SED. < 20 m l 

SED.2: 20 m 

SED. < 11 m // 1-

z 

w 

0.2 

[ 11m s: SED. < 20m 

l SE0 .2: 20m 

SED.< 11m 

w~ 

z 

wz 

u 

gcn 

OCJ) 

:X:~ ~ 

~ 

:X: 

1-

s: 0.5 km J > 0.5 km 

1R 2R 

L__j 

UJ 

z 

:J 

....J 

<l: 

t-

(/) 

>-

a: 

u 

>-

a: 

~ z 

UJ 

~ 

iS 

UJ 

(/) 

ROCK 

/ • 

1A 2A 3A 

• • • 

4A 5A 6A 

ALLUVIUM 

• 

[ s: 0.5 km 

• > 0.5 km 

7A 8A 

~ 

w 

CJ) 

<t: 

co 

~ 

~ a.. 

w 

0 

SITE RESPONSE CLUSTER NUMBERS 

FIGURE 114.-Site clusters for short-period ground motions in the Los Angeles region. Solid circles indicate the geometric mean of the short-period 

spectral ratios, the mean void ratio, the unconsolidated sediment thickness, and the depth to basement rock for a given cluster. Vertical bars 

indicate the range in a variable, and side ticks indicate the 90-percent confidence intervals. 

band, this decrease may be caused partially by wave attenuation in both the soil and the rock column. Although 

the cause of this behavior in the long-period band is not 

clear, it is also predicted by the SH-wave results shown 

in figures 111 and 112 and may be produced by the first 

mm1mum in the theoretical spectral ratio that occurs 

near 6 s owing to destructive wave interference. The 

geometric mean spectral ratios at rock sites range up to 

two, whereas those at soil sites can reach up to about 

five for clusters having a depth to basement rock in the 

Predicting Relative Ground Response 239 
10.0-

8.0 

1 II II n 

0 6.0 

16 IIP i= 4.0 

-T ,JH J <( 

a: 2.0 ...J 

1

1 l1I-c <( 1.0 Il a: 

1-

u 0.4 UJ 

a.. 

(/) 

0.2 

15.00 -

(/) 10.00 ! a: 

UJ 

1- 5.00 I UJ 1= ~ I 

0 2.00 I ...J l: I 

Q 

z 1.00 

~--- 0.50 I z I UJ 

~ 0.20 UJ 

(/) 

<( 

OJ 0.10 

0 

1- 0.05 

I 

1-

a.. 

UJ 

0 

0.01 

4000 

(/) 2000 I (/) 

UJ 1000 z 

:.::: 1 ~(/) 400 :I :co: 1 1-llJ 

1- 200 I >-UJ 

a:~ 

<( 

zz 100 

a:-

UJ 1 1- 40 <( 

::) 

d 20 

10 

~ I2R 3R 1

1A 2A 3A 4A 5A 6A 7A 8A I 

UJ >- z cr: ALLUVIUM 

::::; <l: ....J f-

<l: z 

f- UJ 

CJl 2 >-

cr: 0 u UJ 

CJl 

ROCK 

SITE RESPONSE CLUSTER NUMBERS 

FIGURE 115.-Site clusters for intermediate- and long-period ground motions in the Los Angeles region. Top 

scale: Open circles and solid circles indicate the geometric mean of the intermediate- and long-period spectral ratio values, respectively. Bottom scales: Solid circles indicate the geometric mean depth to basement 

rock or Quaternary thickness. The range and the 90-percent confidence intervals for each factor are indicated by vertical bars and side ticks, respectively. 

10.0 

8.0 

6.0 

4.0 

2.0 

1.0 

0.4 

0.2 

15.00 

10.00 

5.00 

2.00 

1.00 

0.50 

0.20 

0.10 

0.05 

0.01 

4000 

2000 

1000 

400 

200 

100 

40 

20 

10 
4- to 6-km range. The low spectral ratio {0.7) for sites 

underlain by very thin soils is not completely understood. Several of the sites that have the lowest 

amplification factors in this cluster lie within mountain 

ranges, however. Long-period surface waves may have 

unusually low amplitudes relative to CIT in such locations because surface-wave energy can be reflected by 

the boundaries of the ranges (Aki, 1969; Murphy and 

Hewlett, 1975; Johnson, 1979). 

PREDICTING GEOGRAPHIC 

VARIATION IN 

GROUND RESPONSE 

Cluster sets such as those described above can be 

used to map the relative ground response (in comparison with that at sites on crystalline bedrock) expected 

for a particular region from future earthquakes. As a 

demonstration of the methods and techniques, we have 

prepared a set of predictive ground-response maps for a 

small area approximately centered on the Los Angeles 

Civic Center (figs. 116A, 116B, 116C). In brief, our proposed procedure associates geographic areas having 

particular geologic attributes with a given site-response 

cluster. The spectral ratio for that cluster is then assigned to the geographic area. 

We will discuss the procedures used to produce the 

relative ground-response map for the short-period band 

(fig. 116C) as an example of the general technique. 

Figure 117 schematically illustrates the method. The 

first two steps are {1) to prepare a cluster diagram for 

the study area that relates observed spectral ratios to 

geologic factors influencing levels of shaking and (2) to 

assemble a suite of maps that show rock and sediment 

types, depths to basement rocks, thicknesses of unconsolidated (Holocene and Pleistocene) sediments, and the 

distribution of void ratios characteristic of unconsolidated sediments. The third step combines the 

geologic maps assembled in step 2 into groups that 

reflect the geographic distribution of the important 

cluster factors for a given period band. The easiest 

method is to visually compare the geologic data maps (by 

using transparent overlays), noting where two or more 

sets of geologic attributes are coincident, and then draw 

zone boundaries. An area of high void ratio, for instance, may coincide with one or more of the three 

categories of unconsolidated sediment thickness. Where 

it coincides with an area in the thick category, cluster 

7 A is assigned to the area; where it coincides with an 

area in the thin catagory, cluster 6A is assigned, and so 

on. In the final step, each zone associated with a particular cluster is assigned a response value on the basis 

of spectral ratios from figure 114. This procedure was 

judged more reasonable than attempting to contour the 

response values, because it is known from damage 

studies that site response can vary rapidly over very 

short distances, particularly for low structures. Step 

changes in response can thus occur as a function of 

near-surface variations in geology, and this method of 

mapping predicted response reflects this behavior, at 

least for the short-period map. The long- and 

intermediate-period maps are prepared in the same 

manner, but, because ground response at these periods 

changes more gradually as a function of variable 

geologic factors, these maps are more nearly like contour maps on which transitions from low to high 

response occur over broad zones. 

The map showing predicted relative ground response 

for long periods (fig. 116A) is of significance to structures more than 30 stories high. It predicts that low 

response will characterize areas underlain by rock and 

thin alluvial deposits; the highest levels of response will 

occur in areas where the depth to basement rock ranges 

from 4 to 6 km, and slightly lower levels are predicted in 

the deepest parts of the basin. The lowest response will 

be where crystalline basement is located at or near the 

surface in the Santa Monica Mountains and Verdugo 

Mountains areas. South of Burbank and west of 

Pasadena, the relatively thin alluvium in the intermontane basin areas and along the Los Angeles River valley 

near the eastern end of the Santa Monica Mountains 

and north of the Los Angeles Civic Center also will exhibit a low response. Response is expected to increase to 

the northwest (San Fernando Valley), to the east (San 

Gabriel Valley), and to the south (Los Angeles basin). 

The southwestern part of the map shows a relatively low 

response where crystalline basement rock is about 3 km 

deep along the Newport-Inglewood zone. 

The map showing predicted relative ground response 

for intermediate periods (fig. 116B) is of significance to 

5- to 3Q-story structures. This map is similar to the longperiod map. The chief difference is that the response in 

this period band of areas covered locally by a thin 

veneer of alluvial deposits and overlying crystalline 

basement rock or Tertiary sedimentary rock (1A, 2A, 

and 4A of fig. 115) is expected to be higher than that in 

the long-period band. 

The map showing predicted relative ground response 

for short periods (fig. 116C), which is most relevant to 

buildings in the two- to five-story class, has been 

prepared for only the central third of the area shown in 

the intermediate- and long-period maps. The lowest 

response is predicted for areas underlain by crystalline 

and sedimentary rock, and the highest response occurs 

in regions where thicknesses of near-surface alluvium 

(11-20 m) and high void ratios (~0.7) produce significant 

resonant response in this period band. In some respects, 

Predicting Relative Ground Response 241 
2.2 

4.6 

4.6 

3.4 

2.2 

A 

OBURBANK 

LOS ANGELES 

CIVIC CENTER 

0 

3.4 

COMPTON 

0 

... ........... ....... . ................. .... ........................ 

3 4 MILES 

I I 

I I 

5 6 KILOMETERS 

1.1 

PASADENA 

0 

qJf d-u 2.2 

c=b~ 

\ 

I 

4.6 

3.4 

FIGURE 116.-Predicted relative ground response for part of the Los Angeles basin. Numbers are mean amplification 

factors compared with levels of shaking at sites on crystalline basement rock. A, Map for the long-period band 

(3.3-10 s) of significance to buildings 30 stories high or more. Stippling outlines area shown in C. B, Map for the 

242 Earthquake Hazards in the Los Angeles Region 
4.5 

34'00' 

3.6 

B 

0 

4.5 

I 

z 3 

3.6 

\ 

q OMPTON t 

3 4 MILES 

I I 

I I 

5 6 KILOMETERS 

PASADENA 

0 

2.1 

?-, ·-? 

3.6 

4.5 

intermediate-period band (0.5-3.3 s) of significance to buildings 5 to 30 stories high. Stippling outlines area shown 

in C. C, Map for the short-period band (0.2-{).5 s) of significance to buildings two to five stories high. 

Predicting Relative Ground Response 243 
34'00' 

c 

~\...~$ LOS f:>. / . . . -·-·--

· ~ 

11 8"15' 

3 4 MILES 

I I 

I I 

5 6 KILOMETERS 

FIGURE 116.-Continued 

244 Earthquake Hazards in the Los Angeles Region 
DETERMINE SITE RESPONSE CLUSTERS 

AND THEIR MEAN SPECTRAL RATIOS 

\ I 

COMPILE MAPS RELATING GEOLOGIC 

FACTORS THAT INFLUENCE SHAKING 

IN THE STUDY REGION TO OBSERVE 

SPECTRAL RATIOS 

COMPARE GEOLOGIC DATA MAPS TO 

IDENTIFY AREAS OF COINCIDENT ATTRIBUTES 

PERTINENT TO SITE-RESPONSE CLUSTERS 

5 

7 8 

5 

4 

9 8 9 8 

6 6 7 6 

DELINEATE RELATIVE-RESPONSE UNITS 

MAP SHOWING DISTRIBUTION 

OF BEDROCK AND SEDIMENT 

MAP SHOWING DEPTH 

TO BASEMENT ROCKS 

MAPS SHOWING THICKNESS OF 

UNCONSOLIDATED HOLOCENE 

AND PLEISTOCENE SEDIMENT 

MAP SHOWING VOID 

RATIOS OF SEDIMENTS 

AND ASSIGN THEIR MEAN SPECTRAL RATIO 

COMPARED TO CRYSTALLINE BEDROCK 

FIGURE 117.-Procedure used to construct the predicted relative ground-response maps shown in figure 116. 

this map closely resembles a surficial geologic map; 

thus, sedimentologic details of the alluviated valleys, including those of the Los Angeles River valley, are expressed clearly by the mapped response units. The 

southwestern part of the map depicts an area where silt 

(characterized by high void ratios) deposited by the Los 

Angeles River thins to the west and wedges out along the 

eastern flank of the Newport-Inglewood zone, where 

deformed Pleistocene deposits characterized by low 

void ratios are exposed. It should be noted that high 

response at short periods may occur at sites underlain 

by rock if these sites are near the crest of a ridge or 

other pronounced topography, as the range of high 

response for clusters 1R and 2R (fig. 114) shows. 

Predicting Relative Ground Response 245 
VALIDITY AND LIMITATIONS 

OF TECHNIQUE 

In a qualitative way, data from several other studies 

support this study's conclusions about the importance of 

unconsolidated sediment thickness. As noted above, 

Chiaruttini and Siro (1981) have observed accelerations 

at sites underlain by thin soils ( < 20 m) that were greater 

than those observed on rock or thicker soil sites by factors of four or five. The difference in the behaviors of 

thin and thick soil is not so great in the data of this study, . 

but this discrepancy may be due to the fact that we have 

no data for periods shorter than 0.2 s, where peak 

acceleration energy commonly occurs and attenuation 

effects become strong. We infer from Chiaruttini and 

Siro's data that material attenuation may have an important effect at sites underlain by thick soils and for 

ground motions in the period range where peak acceleration energy occurs. This conclusion is also supported 

by the work of McEvilly and Johnson (1980), who have 

found that Q factors, which measure attenuation of 

seismic energy, must be between 6 and 40 for shear 

waves in order to explain the amplitude levels on their 

accelerograms. 

The effect of near-surface sediment thickne~s can 

also be seen in the data of Minakami and Sakuma (1948) 

for the 1946 Nankai, Japan, earthquake. The highest 

levels of ground motion were observed in regions where 

the thickness of fine sand was in the 10- to 20-m range 

(figs. 103-109). Ooba (1957, fig. 10) has shown that, for 

the 1944 Tonankai, Japan, earthquake (M 8.0), the 

highest percentage of collapsed houses(> 50 percent) occurs where the thickness of clayey overburden is in the 

15- to 35-m range, and the lowest ( < 10 percent) occurs in 

regions underlain by thinner sediment or rock. 

The clustering scheme proposed here to predict site 

response can be partially tested by applying it in other 

areas where strong ground motion has been recorded 

and sufficient data about site conditions are available. 

We classify the Richmond recording station (McEvilly 

and Johnson, 1980), for instance, into clusters 7 A (short 

period) and 4A (intermediate period) and Coyote Lake 

earthquake recording station 2 ijoyner and others, 1981) 

into clusters 6A (short period) and 2A (intermediate 

period). At both sites, the predicted mean response for 

both period bands ranges between 3 and 5, and the 

observed response ranges between 3 and 4. 

This clustering scheme, however, cannot be applied to 

all site conditions. If, for example, near-surface mean 

shear-wave velocity is considerably less (say, 100 m/s) or 

greater (say, 400 m/s) than the mean value for sites displaying resonant conditions in Los Angeles (about 

200 m/s), then resonant conditions in the short-period 

band would occur at one-half or twice the thickness 

246 Earthquake Hazards in the Los Angeles Region 

range, respectively, of this study, and the mean spectral 

values would also be modified by as much as twice or 

one-half the levels of this study. Thus, in regions where 

shear-wave velocities are exceptionally low, at least 

three additional high void-ratio clusters having different 

ranges of near-surface sediment thickness would be required. Applying these clusters to other regions requires 

critical evaluation of the important geotechnical factors 

to determine if sites in the region, in fact, fit the clusters 

of this study, which do not represent all geologic 

conditions. 

SUMMARY 

Local geologic conditions can significantly influence 

the relative levels of ground shaking caused by earthquakes. Based on the generally valid assumption that 

the relative responses of different sites are approximately equivalent for both low and high levels of 

motion, comparative studies of ground motion recorded 

within a region provide a reliable method for estimating 

the shaking effects likely to be caused by future 

earthquakes. 

We have analyzed the geographic variation in relative ground response at 98 locations within the Los 

Angeles region by using a collection of ground-motion 

recordings from a series of underground nuclear test explosions at the Nevada Test Site. The mean spectral 

levels of the site responses from these distant events 

were evaluated in three period bands of engineering importance as a function of the underlying geotechnical 

conditions at each site. These properties were collected 

from a wide range of sources, including engineering 

borehole and water-well logs in city files, geologic and 

gravity maps, and a limited number of measured shearwave velocities in near-surface sediments. In preliminary evaluations of the data, we determined, for instance, that the levels of shaking experienced by sites 

underlain by Holocene and Pleistocene sediments are 

three to four times greater than those experienced by 

sites underlain by crystalline rock for periods less than 

0.5 s and that ground motions at periods greater than 

0.5 s increase as Quaternary thickness and (or) depth to 

basement rock increases. 

The geotechnical factors having the strongest influence on site response in each period band were identified by means of statistical clustering techniques. The 

results indicate that, at periods less than 0.5 s, the most 

significant factors controlling ground response are 

mean void ratio in the near-surface layers, unconsolidated sediment thickness (principally Holocene deposit 

thickness), and depth to basement rock, those sites having near-surface sediment thickness in the 10- to 20-m 
range demonstrating site resonance effects. At periods 

greater than 0.5 s, depth to basement rock and the 

thickness of Quaternary sediments were found to be 

controlling factors. 

These clusters were used in a procedure developed to 

produce maps of relative ground response for part of the 

Los Angeles basin. The clusters can also be used to 

make estimates of shaking effects at specific locations, if 

the necessary geotechnical information is available for 

the site. This technique has important implications for 

earthquake hazard reduction in Los Angeles and elsewhere, because it can be used to predict future relative 

ground response from geotechnical data that are ordinarily obtained in the course of urban development. 

The utility of the technique is further enhanced by provisions permitting ground-response estimates to be made 

for period bands pertinent to structures of different 

sizes. This mapping procedure may be useful for seismic 

zonation in other earthquake-prone urban areas, if clusters applicable to the specific geologic framework of the 

region being studied can be determined. 

Predicting Relative Ground Response 247 
248 Earthquake Hazards in the Los Angeles Region 
PREDICTING EARTHQUAKE GROUND-MOTION 

TIME-HISTORIES 

By P. A. Spudich and S. H. Hartzell 

INTRODUCTION 

Engineers are often called upon to design facilities 

that are to be built at specific sites near known active 

faults. To do so, the engineer may require an estimate of 

the ground motions that would occur at the site owing to 

an earthquake on a nearby fault. If the facility to be 

built is simple, an estimate of anticipated peak values of 

ground motion (for example, acceleration, velocity, or 

duration) may be all that is required. In many cases, 

however, the engineer may need to know anticipated 

ground-motion time-histories at the site. If soil tests 

reveal a buried sand layer at the site that is prone to .liquefaction, for example, the engineer may need to know 

how many cycles of seismic loading the sand layer will 

be subjected to and how large this loading will be. The 

engineer may require ground-motion time-histories in 

order to calculate response spectra for the structure, 

and, if damaging levels of ground motion are anticipated, the engineer may need to know whether the 

damaging motion will occur as a single pulse or as a 

series of oscillations that cause progressive inelastic 

deformation with each cycle. 

If the engineer is lucky, a strong-motion accelerogram 

may already exist that is a suitable example of the worst 

shaking anticipated; that is, a record will exist that has 

been recorded at the proper distance from an earthquake of the desired size and mechanism in a similar 

geologic structure. Often a suitable strong-motion 

recording cannot be found, however; perhaps a record 

the correct distance from the right size event exists, for 

example, but the recording site is hard rock, unlike the 

thick layer of alluvium that characterizes the proposed 

facility's site. Similarly, the observed record may have 

rather low levels of motion owing to the effects of rupture propagation away from the recording site, whereas 

a worst-case scenario for the proposed facility would include rupture propagation toward the site. Lack of 

strong ground-motion data for many such situations of 

interest has necessitated development of theoretical 

techniques for predicting ground-motion time-histories 

of hypothetical earthquakes. 

This chapter discusses some of the techniques used to 

calculate these theoretical ground-motion time-histories, 

the information necessary to make a relevant calculation, and the approximations commonly used to make the 

calculations tractable. These methods are applicable to 

ground-motion evaluation in any earthquake-prone 

region. In a later chapter (Ziony and others, this 

volume), we demonstrate, for the Los Angeles region, 

how ground-motion time-histories are calculated for a 

postulated magnitude 6.5 earthquake on the NewportInglewood zone. 

This paper is structured to be readable by both a 

general audience and a more specialized audience of 

people who may have to use the results obtained by 

studies like the one conducted by Apsel and others 

{1981) and discussed in this paper. Sections of this paper 

having the word "detail" or "detailed" in their headings 

contain caveats, explanations, and interpretations that 

the general audience may safely skip. 

THE EARTHQUAKE RUPTURE 

PROCESS 

Although the details of the earthquake rupture process are largely unknown, the gross features are understood theoretically and observationally, and a reasonable model of an earthquake source can be specified by 

a handful of parameters. This section examines these 

parameters and comments on how well they might be 

predicted in a simulation of earthquake rupture. 

Let us start by examining a very simple model of an 

earthquake source-a cra~k that grows on a· plane surface in an infinite homogeneous medium. We assume 

that a uniform tectonic shear stress is applied parallel 

to the plane to drive the crack, as figure 118 shows, and 

we also assume that slip initiates at some point on the 

plane (the earthquake hypocenter). Subsequently, the 

Ground-Motion Time-Histories 249 
Tectonic shear 

stress 

Direction of 

fault slip 

FIGURE 118.-ldealized ruptUring fault at time !3• The yet unbroken 

part of the fault is stippled, and the actively slipping part is unstippled. Contours show positions of the rupture front at times t,, ! 2, 

and t,. The fault slips in the direction of applied stress. Slip timehistories for A, B, and C are shown in figure 119. The dashed 

arrow shows the motion of material on the opposite side of the 

fault. 

slipping area will grow and spread away from the hypocenter. If we define the rupture front as the boundary 

between the slipping and the unslipped regions of the 

fault plane, the position of the rupture front at three successive times t11 t2, and t3 will be as figure 118 shows. 

The shape of the rupture front will be either circular or 

elliptical, and the front itself will advance at a velocity 

dependent on direction. In the direction perpendicular 

to the applied stress, the rupture will travel at the speed 

of a Rayleigh wave in the medium (- 0.92 V5, where V5 is 

the shear-wave velocity); in the direction parallel to the 

applied stress, the rupture will travel at the Rayleighwave speed if the cohesion between the two sides of the 

fault is great, or it will travel as fast as the P-wave 

velocity if the fault cohesion is low (Mikumo and 

Miyatake, 1978). Everywhere within the ruptured area 

(the unstippled region of fig. 118), the offset of the two 

sides of the fault will be parallel to the applied stress. 

In general, observational studies of earthquakes, such 

as those summarized by Geller (1976), show rupture 

velocities to be about 60 to 90 percent of the shear-wave 

velocity in the surrounding rock, in rough agreement 

with theory. Recently, Olson and Apsel (1982), Archuleta (1984), and Spudich and Cranswick (1984) have 

250 Earthquake Hazards in the Los Angeles Region 

found evidence for rupture velocities near the P-wave 

velocity in the 1979 Imperial Valley, Calif., earthquake. 

To return to the idealized earthquake source in figure 

118, if the tectonic stress and the cohesion between the 

two sides of the fault are uniform everywhere, there is 

nothing to stop the rupture from expanding indefinitely; 

consequently, the relative offset or slip between the two 

sides of the fault will grow endlessly. The rupture front 

can be stopped, however, if the rupture encounters a 

region of the fault where the tectonic stress is not large 

enough to overcome the fault's resistance to rupture. 

Thus, nonuniformities in either the tectonic stress or the 

strength of the fault-zone materials or both will cause 

the rupture process to stop. We can examine, for example, the time-histories of slip at points A, B, and C 

(fig. 118) for the cases of a rupture that stops, shown by 

the dotted lines in figure 119 (Archuleta and Frazier, 

1978), and a rupture that continues indefinitely, shown 

by the solid lines in figure 119 (Kostrov, 1964). In either 

case, slip at A, B, and C is initiated by the passage of the 

rupture front at times t1 , t2 , and t3• Slip ceases, however, 

only if the rupture front stops at a boundary. If we 

follow Boatwright (1981) and say that healing initiates 

when the slip function deviates from that expected for a 

fault without boundaries, we can see in figure 119 that 

the healing starts earliest at point C, nearest the fault 

boundary, and that it propagates away from the boundaries. An apt analogy would be an automobile accident 

in which the lead car (rupture front) in a long string of 

vehicles smashes into an obstacle and causes a chainreaction collision among the following vehicles. As each 

vehicle smashes into the one ahead (healing), the collision propagates backward through the line of cars, 

even though all the cars are moving forward. The last 

car to come to a stop is the one farthest from the initial 

obstacle. 

Although we have apparently been talking about circular or elliptical faults, the same principles apply to 

long strike-slip faults. Figure 120 shows a theoretical 

calculation by Archuleta and Day (1980) of rupture 

propagation along a strike-slip fault resembling the San 

Andreas fault near Parkfield in central California. The 

actively slipping region of the fault is shown at 2-s intervals after rupture initiation. In this case, the first 

barriers encountered by the rupture front are the left 

side, the bottom, and the top of the fault, and healing 

propagates inward from these boundaries. 

From theoretical studies like those of Kostrov (1964), 

Archuleta and Frazier (1978), and others, we can make 

a reasonable guess that, during an earthquake, the slip 

time-history at any point will look like the slip timehistory for an unbounded fault until information from 

the boundaries reaches that point and initiates healing, 
FIGURE 119.-Slip time-histories of points A, B, and C (fig. 118) under 

two assumptions: (1) there are no boundaries to stop the rupture 

front, so slip continues indefinitely (solid line), and (2) the rupture 

front stops at a boundary, and slip ceases at internal points (dotted 

line). Crosses indicate the points at which healing is initiated; open 

circles, points at which healing is completed. 

as figure 119 shows. Boatwright {1981) has elaborated 

on this presumption and has used it to study aftershocks 

of the 1975 Oroville, Calif., earthquake. 

Before proceeding to more complicated models of rupture, let us examine the major features of the ground 

motions caused by these simple models. The most well 

known effect of a propagating rupture is to amplify 

energy radiated in the direction of rupture and to 

diminish energy radiated opposite the direction of 

rupture (Ben-Menahem, 1961). This effect, termed directivity, has been observed in many theoretical and observational studies (for example, Boatwright and Boore, 

1982; Hartzell and Heimberger, 1982) and is apparent in 

the ground-motion calculations that we present for the 

hypothetical Newport-Inglewood event later in this 

volume (Ziony and others, this volume). The magnitude 

of this effect is related to the average rupture velocity. A 

second effect, which is of great engineering signifi8s 

0 10 20 30 MILES 

I I I I 

I 

0 10 20 30 KILOMETERS 

FIGURE 120.-Rupture-propagation model for long strike-slip fault, 

adapted from Archuleta and Day (1980). Diagrams of fault plane at 

2-s intervals after rupture initiation. Unstippled area is actively 

slipping. Stippled area to the right has not yet broken; stippled area 

to the left has been healed and now exhibits a net static offset. 

Hypocenter shown by asterisk. 

cance, is that most of the high-frequency energy is radiated from the rupture front itself and that this energy is 

radiated most profusely under two circumstances: {1) 

when the rupture front accelerates or decelerates and 

(2) when the rupture front crosses a region of the fault 

where the amount of slip varies from place to place 

(Madariaga, 1977; Spudich and Frazer, 1984). In the 

simple rupture models that we have discussed thusfar, 

where the rupture front propagates uniformly until it 

hits the boundary of the fault, almost all the high-frequency radiation occurs when the rupture front stops at 

the fault boundary. This characteristic is a well-known 

feature of the simple Haskell {1964) fault model. 

The theoretical observation that most· high-frequency 

energy is radiated by changes in the velocity of the rupture front and by spatial variations in the amount of slip 

has important implications for the high-frequency 

ground motions caused by earthquake source models 

Ground-Motion Time-Histories 251 
• 

EPICENTER 

function to vary randomly, with certain statistical properties, over the fault surface while maintaining the con- !, stant shape of the slip time-function over the fault. 

SURFACE RUPTURE 

SE STANCE. IN KILOMETERS NW Bouchon allowed both the amplitude and the shape of 

50 his slip functions to vary over the fault plane in accordg:? 0 +.:.:.:"'" .~ .. t_~..,., :.: .· ... r-------''---...._----:=-'-~---h.,..,.,r---r.- ::r---'=~ ance with Das and Aki's (1977a) theoretical study of 

~ fault rupture, and he included a small number of high- w 

5 10 15 20 25 30 35 40 45 

~ 5 strength barriers to rupture on the fault. Apse! and his 

;;2 coworkers allowed an even greater degree of random-

~ 10 ness by adding a random component to the local rupture 

~ velocity, the rupture direction, the slip direction, and the 

~ 15 slip time-function at each point. Their work will be 

FIGURE 121.-Possible heterogeneity of rupture during the 1966 

Parkfield, Calif., earthquake, modified from Aki (1979). Unstippled 

area was postulated to have slipped during the earthquake; the 

stippled area remains locked. Dashed lines have been added to 

close contours. 

that are more realistic than those discussed above. 

Since both the state of stress on a fault and the strength 

of the fault material may be quite heterogeneous over a 

real fault surface, we might expect that, during an 

earthquake, the rupture front will advance very irregularly and that some regions of the fault will be so 

strong that the rupture front will jump past them and 

leave them unbroken. The result might be a pattern of 

broken and unbroken regions on the fault similar to that 

shown in figure 121, which is the pattern suggested by 

Aki (1979) for the 1966 Parkfield earthquake. Several 

theoretical studies, including those of Das and Aki 

(1977a, b), Mikumo and Miyatake (1978), and Day (1982), 

have shown that, in the presence of stress and strength 

heterogeneities, rupture fronts can advance unevenly 

and even jump around unyielding regions of the fault 

(termed barriers). Because high-frequency radiation is 

generated by nonuniform rupture-front motion and an 

irregular slip distribution, the pattern of preexisting 

stress and strength on the fault will control the highfrequency ground motions that the earthquake 

generates. 

Unfortunately, the distribution of stress and strength 

on real faults is unknown, so that it is impossible at this 

point to predict deterministically the details of how any 

particular active fault would rupture. Hence, beginning 

with Haskell (1966) and Aki (1967), investigators have 

tried to discover the statistical distribution of material 

properties or rupture parameters on the fault surface in 

an effort to simulate higher frequency ground motions. 

Considerable work on the statistical nature of earthquake slip functions has been done more recently by Aki 

and others (1977), Andrews (1981), Papageorgiou and 

Aki (1983), and many others that they cite, and incoherent source behavior has been used in various 

forms by Bouchon (1978), Boore and Joyner (1978), and 

Apse! and others (1981). In their study, Boore and Joyner 

allowed the rupture velocity or the amplitude of the slip 

252 Earthquake Hazards in the Los Angeles Region 

discussed below. 

HOW GROUND MOTIONS 

ARE SIMULATED 

Conceptually, the problem of calculating earthquake 

ground-motion time-histories (henceforth called simply 

ground motions) can be divided into two parts, the first 

being the determination of what happens at the earthquake source to generate seismic waves and the second 

being the determination of how those waves are altered 

by the geologic structures that they pass through as they 

propagate away from the source. This section will 

describe Green's function summation methods, which 

are mathematical methods for calculating earthquakegenerated ground motions. We concentrate on these 

particular methods for several reasons; they are the 

easiest to understand, they explicitly separate the 

action of the earthquake source from the subsequent 

propagation of seismic waves, they have been the most 

commonly used methods in practice, and any other 

method can be expressed equivalently as a Green's 

function summation method without approximation. 

The basic idea underlying Green's function summation methods is that, at a particular observation point, 

the overall ground motion caused by a large earthquake 

can be obtained by summing contributions to the ground 

motion from slip along many small segments of the 

causative fault. To do so, one must first specify how 

each segment of the fault slips during the earthquake 

and determine, for each small segment of the fault, how 

the ground at the observation point moves when only 

that part of the fault slips. Once we know the groundmotion time-histories caused at the observation point by 

slip on each individual segment of the fault, we can 

determine the ground motion caused by the large event 

simply by adding all the ground-motion time-histories 

caused by individual segments of the fault. 

The ground motion caused by instantaneous slip on an 

individual segment of a fault is usually represented by a 

mathematical entity called a Green's function. For 
y 

-0: zUl tr=: o .. : ~1 - ::::;w 

(/) 2 0 TIME. IN SECONDS 

z 

1A 1. ---~ --?Observation 

'1r-r-/ pomt 

ing ground mot1on at 

observation point (Green's 

function) caused by 

instantaneous unit slip at 

Indicated source point 

FIGURE 122.-Depictions of Green's functions in an x-y-z coordinate 

system. Individual points on the fault surface F undergo instantaneous unit-amplitude slip, as the graphs indicate. The ground motion caused at the observation point by a single point source is a 

Green's function. Green's functions at points A, B, and C differ 

from one another because of varied epicentral distances from the 

observation point, varied source depths, and differences in 

geologic structure along the travel paths. The Green's functions 

must be further modified before they can be added together to 

simulate the rupture of the fault surface. 

simplicity, let us assume that these small segments of a 

fault are points on that fault. To define a Green's function, imagine that we allow a single point on the fault to 

slip instantaneously from zero offset to unit offset and 

then stop (point A in fig. 122). The ground-motion timehistory caused at the observation point by this individual source point is called by seismologists the 

Green's function for the source point. Thereason for introducing Green's functions is that, once the Green's 

function for a point on a fault is known, the ground motions caused by any arbitrarily complicated slip of that 

individual point can be easily obtained from the Green's 

function by the mathematical operation of convolving 

the slip time-history of the point with the Green's function (Bracewell (1965, p. 24-35) provides a simple 

description of convolution). Hence, to determine the 

ground-motion con' -ibution of each point on the fault, 

we first determine the Green's functions for each point 

on the fault (points A, B, and C in fig. 122). Green's functions from different points on the fault will in general 

differ from one another because the distances between 

the source and the observation point will vary, and the 

geologic structures through which the waves pass will 

also vary. We then convolve each Green's function with 

the slip time-history of the source point to get the point's 

total contribution. 

The next step is the specification of the hypothetical 

earthquake source. The earthquake source may be 

specified completely by knowing the slip function (that 

is, the slip time-history) at every point on the fault. To 

I 

F 

Time 

,..--=== 

Time 

Time 

Time 

Time 

FIGURE 123.-Slip functions at various points on a hypothetical fault 

surface F. Note that slip initiates later at points farther from the 

hypocenter owing to the delay of the rupture in propagating from 

the hypocenter to each point. Both the shape and the amplitude of 

the slip functions may vary irregularly over the fault. Only one 

component of slip is shown. 

manufacture a sensible source model, we rely on the 

basic properties of earthquake rupture described 

previously. Figure 123, for example, shows slip functions at six points on a fault surface F that might result 

from a hypothetical earthquake that ruptures the fault 

surface. Note that each slip function starts at zero offset 

and ends with a constant offset, consistent with the 

premise that earthquakes result in a permanent offset 

between the two sides of the fault. Note also in figure 

123 that, at each point on the fault surface, the shape 

and the amplitude of the slip functions are different, and 

slip initiates at different times. If we were to make plots 

like these for both components of slip at every point on 

the fault, the earthquake source would be completely 

characterized. Such a source description is called a 

kinematic description, because it specifies the motion of 

every point on the fault surface rather than the forces 

acting on every point. 

Once we have a complete description of the action of 

each point on the fault F and a description of what motions are caused at the observation point per unit slip at 

each point on F (the Green's functions), we can find the 

total motion at the observation point simply by summing 

the contributions from each point on the fault. Consider, 

for example, a hypothetical earthquake in which the slip 

function at each point on the fault is simply instantaneous unit-amplitude slip whose onset time varies over 

the fault surface. In this case, the total motion at the 

observation point would be a simple sum of the Green's 

functions, each function being delayed in time to take into account the delayed action of its source point. Now 

imagine that the amplitudes of the source slip also vary 

from point to point on the fault. In this case, the Green's 

Ground-Motion Time-Histories 253 
Fault 

segment Slip Convolution Green's 

dFi function * function 

* 

* --4vv--

2 Q- L 

Vi * fl..ttvvv 

3 / 

*~ 

N 

Time *-v!vv = 

Ground motion 

contributed by 

dF i 

+ 

+ --.JVV\. + 

Total 

at 

ground 

a pomt 

motion ~~ 

FIGURE 124.-Schematic illustration of ground-motion simulation. The 

left-hand column shows slip functions for several small areas of 

the fault, shown in figure 123. The center column shows the 

Green's functions caused by instantaneous unit slip on each part of 

the fault. The right-hand column shows the ground motion caused 

at the observation point by the slip function in the left-hand column 

(a convolution of the slip function and the Green's function). The 

results of these convolutions are automatically scaled to account 

for slip-function amplitude and delay. The total ground motion at 

the observation point (lower right-hand corner) is a sum of the contributions from each part of the fault (right-hand column). 

functions would not only be delayed, as they were 

before, but would also be multiplied by the amplitudes of 

their respective source points before being summed. In 

the most general case, where the shape of the slip function varies from point to point on the fault, as figure 123 

shows, each Green's function would be convolved by its 

respective slip function before being summed. This procedure is shown schematically in figure 124. 

A convenient aspect of Green's function summation 

methods is that the Green's functions are largely independent of the earthquake being simulated; they depend only on the geologic structure and the locations of 

the fault surface and the observation points, not on the 

details of how the earthquake ruptures. Hence, the 

Green's functions can be calculated once and stored for 

repeated use in simulating many different earthquakes 

as long as the fault surface and the observation sites remain the same. Often, calculating the Green's functions 

is the bulk of the computational labor. In this case, a 

wide variety of hypothetical earthquakes in the same 

study area can be simulated with relatively little effort if 

the Green's functions have been calculated previously 

254 Earthquake Hazards in the Los Angeles Region 

and stored for reuse, as we have done (Ziony and others, 

this volume). 

To calculate the ground motions from a postulated 

earthquake, all that one needs, in theory, is a complete 

specification of the slip function on every point of the 

fault and a complete knowledge of the Green's functions 

connecting each point on the fault with each observation 

point. Since neither of these goals has been attained in 

practice, we discuss how approximations of each are 

commonly obtained. 

MATHEMATICAL DETAILS 

Before proceeding, we pause to clarify a few terms used 

in the preceding discussions and in ensuing ones. We 

have used the term Green's function to refer to the ground 

motions caused by instantaneous slip at a point on a fault. 

Other authors assume different sources of waves for their 

Green's functions; some, for example, use point-force 

sources applied at the fault surface, whereas others use 

point-force sources applied at the observation point and 

evaluate their Green's functions on the fault surface. In 

addition, instead of using a step function for the source 

time-function (fig. 122), some use delta functions. Other 

details involve the directions of motion. Slip on the fault 

surface can occur in any direction parallel to the surface 

and can be broken into strike-slip and dip-slip components. Hence, a more complete specification of the 

Green's functions requires that we determine ground motions at the observation point caused by a strike-slip point 

dislocation and a dip-slip point dislocation. In addition, 

each source will generally cause motions in all three orthogonal directions (x, y, and z) at the observation point. 

Hence, if the Green's function is to be specified completely, it must be expressed in the form: 

G85(JCo, t; y, 0) 

Gd•(:xo, t; y, O) 

where G is the three-component vector consisting of the 

motions in the x, y, and z directions and the ss and ds 

superscripts denote strike-slip and dip-slip sources, 

respectively; y is the slipped point on the fault, Xo is the 

observation point, and the argument (Xo, t; y, O) specifies 

that the motions are caused by a source acting at position 

y and time 0 and are observed at Xo and time t. 

In general, the slip that occurs as a function of time can 

be different at every point on the fault surface, so that we 

would characterize the strike-slip and dip-slip components of slip by SSS(y, t) and gd•(y, t), where y is a point on 

the fault. When we use the phrases slip function of the 

earthquake or slip model of the earthquake, we are referring to SSS(y, t) and sd•(y, t) for every point on the fault. 

When we say slip function at a point, we mean SSS(y0 , t) 

and gd•(y0 , t), where Yo is the particular point in question. A 
less general description of slip on the fault would be 

s(y, t)=a(y)T(t), where a(y) is the amplitude of the slip 

functions, which may vary with position on the fault, and 

T(t) is the shape of the slip functions, which in this case is 

the same for all points on the fault surface. Clearly, if 

s(y1, t)=5T(t) and s(y2, t)=T(t), the slip functions have the 

same shapes and different amplitudes. 

Thus, the ground displacement at observation point 

Xo may be wri~en 

U(Xo, t)= ~ I I [s"(y, t) *Gss(Xo, t; y, 0) 

dt F 

+ sd'(y, t) *Gd'[Xo, t; y, 0)] dF 

(33) 

where y is a point on the fault surface F, the asterisk 

denotes temporal convolution (Bracewell, 1965), and 

where the d/dt compensates for our use of a step function 

rather than a delta function as the Green's function's 

source time-function. Imagine that we break F up into N 

subfaults dF; having center point Y; and that, within dFi' 

s(y, t) and G(Xo, t; y, 0) are approximately constant with 

respect to y. Then we can rewrite the integral as a sum of 

contributions from each subfault 

d 

u (Xo. t)= dt 

N 

E [sss(yi, t) *Gss(Xo, t; yi' 0) 

i=l (34) 

This technique is almost identical to the procedure used 

by Heaton and Heimberger (1979) to simulate the 1971 

San Fernando earthquake, by Hartzell and Heimberger 

(1982) to simulate the 1979 Imperial Valley earthquake, 

and by us (Ziony and others, this volume) and has been 

well summarized by Heaton (1982). 

GREEN'S FUNCTIONS AND 

THEIR APPROXIMATION 

Although great progress has been made recently in 

understanding seismic wave propagation in the Earth, 

two obstacles force seismologists to use approximate 

Green's functions in ground-motion simulations. This 

section discusses those obstacles, the approximations 

used, and their effect on the relevance of the resulting 

predicted time-histories of shaking. We stress that the 

effect of each approximation is to diminish the accuracy 

of the calculations for some types of waves in certain 

frequency bands and certain geologic structures. Consequently, in choosing an approximation, the user must 

know which types of waves will be the most important 

contributors to strong ground motions in the situation 

being simulated and must choose the method that most 

accurately represents those types of waves. 

The first obstacle to accurate calculation of Green's 

functions is the fact that the Earth's velocity structure is 

rarely known well enough to allow an exact calculation 

of Green's functions, even in principle. In particular, we 

cannot detect most of the heterogeneities that are 

responsible for scattered waves in the Earth. Aki and 

Chouet (1975) have pointed out that most of the energy in 

the S-wave codas of local earthquakes is due to latearriving S waves scattered from random heterogeneities. If such heterogeneities are not included in velocity 

models, the Green's functions obtained from the model 

will lack the scattered waves that exist in reality. 

Although this problem may not be very severe for calculations at frequencies of 1 Hz, for which the associated 

seismic wavelengths are long, the problem is quite 

severe at frequencies of 20 Hz. 

Details of Uncertainties Due to 

Poorly Known Velocity Structure 

To calculate seismic waves accurately up to frequencies of 10 Hz in a region where the minimum shear-wave 

velocity is 1.5 km/s, we need to know details about the 

seismic velocity, the density, and the attenuation structures having a spatial resolution of 75 m. In most regions 

of interest, this goal is unattainable. So, can we say, in 

general, how well these structures are known and how 

our imperfect knowledge of structure affects the reliability of Green's function calculations? 

The degree of detail in which a velocity structure is 

known is dependent on the type of data from which the 

structure was derived and the method used to analyze 

those data. Generally, P-wave velocity is the only 

physical property of the crust that is easily observed in 

any detail, because it is easy to generate P waves artificially (for example, by explosions or vibrator trucks) 

and difficult to generate S waves. When an S-wave 

velocity structure cannot be observed directly, it is 

derived from a P-wave velocity structure by assuming a 

fixed ratio of P- and S-wave velocities in various 

materials (Hamilton, 1979). Density can be measured 

directly by means of gravity surveys, or it can be inferred from the P-wave velocity by using empirical relations, such as those given by Hamilton (1978). Fortunately, seismic waves are not affected much by density 

variations (Wiggins and Heimberger, 1974), so accurate 

density estimation is not crucial. P- and S-wave attenuations are very difficult to measure directly, and, usually, 

Ground-Motion Time-Histories 255 
educated guesses are made on the basis of what few 

observations do exist. Of all the physical properties 

listed above, the lack of a directly measured S-wave 

velocity structure and· the poor knowledge of S-wave attenuation introduce the largest. uncertainties into 

Green's function calculation. Although poor knowledge 

of V8 affects all frequencies of ground motion, uncertainties in S-wave attenuation become progressively more 

important for computations at higher frequencies. 

Hence, a good knowledge of S-wave attenuation is quite 

important in calculating peak accelerations. 

Since P-wave velocity is the most easily observed 

physical property of the crust, how well is it typically 

known? A very dense multichannel seismic-reflection 

survey can resolve details of the P-wave velocity structure 100 to 200 m in extent within the top few kilometers 

of the crust. Such information rarely exists, however, 

and is often proprietary. Good-quality modern seismic 

refraction analysis, such as that done by McMechan 

and Mooney (1980), is capable of resolving details about 

1 km in vertical extent and 2 to 3 km in horizontal extent. 

Work of this type usually interprets the refraction data 

in terms of seismic velocity models that vary both vertically and horizontally and can therefore deal adequately with major lateral changes of velocity structure. 

Most available velocity structure information, however, 

comes from an earlier style of refraction data analysis, 

which interpreted the data in terms of a stack of layers 

of constant-velocity material separated by flat or dipping planes (Biehler and others, 1964). Although this 

type of analysis is quite appropriate for some places, it 

is not especially reliable for others, such as those 

characterized by horizontal variation in structure. In 

particular, it is completely incapable of resolving 

crustal heterogeneities having limited horizontal extent 

(say, a few kilometers). 

Computational Limitations 

The second obstacle to accurate Green's function 

calculation is the computational effort required. The 

most powerful and general methods for calculating 

Green's functions are the finite-element and the finitedifference methods (Boore, 1972). These methods can, in 

principle, calculate the complete seismic wavefield in 

Earth models having an arbitrary three-dimensional 

velocity structure, but the computational effort is great. 

Of course, it should be noted that the computational effort required by a finite-element analysis yields a truly 

complete solution. Rather than generating ground motions at only 10 sites, for example, as the ground-motion 

simulation for the postulated earthquake along the 

Newport-Inglewood zone does (Ziony and others, this 

volume), a comparable finite-element analysis, like the 

256 Earthquake Hazards in the Los Angeles Region 

one described below, would generate ground motions at 

a grid of 63,000 sites in the Los Angeles basin. Moreover, because the finite-element analysis accounts for 

the effects of horizontal variations in basement depth 

and in near-surface shear-wave velocity, it is an extremely powerful, albeit expensive, tool for seismic 

zonation. 

Consider, for example,· the computational effort that 

would be required by a finite-element method for 

calculating ground motions in the Los Angeles basin 

from a magnitude 6.5 earthquake on the NewportInglewood fault. If the method of Archuleta and Frazier 

(1978) is used to calculate 30-s ground-motion timehistories at 63,000 sites for frequencies ranging from 0 

to 2 Hz, approximately 19 million words of computer 

storage would be required, and the calculation would 

take about 40 hr on a fast, currently available computer 

such as the CRA Y -1. 

Since, in practice, the large amounts of computer time 

required to use the finite-element or finite-difference 

method in routine calculations of Green's functions in 

the frequency band of engineering interest are not made 

available, other more approximate, less computationally 

expensive methods are generally used. Two principle 

alternatives exist at present. The distinction between 

them is that, in one, the geologic structure is approximated by a simpler structure in which Green's functions can be obtained exactly, and, in the other, the 

exact geologic structure is used but the Green's functions are obtained only approximately. 

In the first alternative, the true Earth's structure is 

approximated by a laterally homogeneous structure 

(that is, a structure in which seismic velocities, densities, and attenuations vary only with depth and are independent of horizontal position). Once this approximation is made, it is possible to calculate complete Green's 

functions (that is, Green's functions that contain the 

complete seismic response of the approximate structure, including all possible body and surface waves). We 

will refer to such Green's function calculation methods 

as lateral homogeneity methods. It is important to note 

that, when one assumes lateral homogeneity of the 

geologic structure, absolute horizontal position becomes 

irrelevant, and the only meaningful horizontal variable 

is the location of the observation point relative to the 

seismic source. The lateral homogeneity approximation 

is usually a reasonable first approximation of the true 

Earth structure, because the material properties of the 

Earth generally vary more with depth than they do with 

horizontal position. In many regions of greatest interest 

for earthquake hazards evaluation, such as the Los 

Angeles region, where crystalline uplands are adjacent 

to deep alluvial basins, the approximation of lateral 

homogeneity is not always good, however. 
To date, the lateral homogeneity approximation has 

been used in almost all practical ground-motion simulations. Ground motions from the 1971 San Fernando 

earthquake were simulated by Bouchon (1978), Heaton 

and Heimberger (1979), and Heaton (1982), all of whom 

used a laterally homogeneous Earth model consisting of 

a uniform halfspace. The 1966 Parkfield earthquake 

was simulated by Bouchon (1979), who used a uniform 

layer overlying a halfspace, and by Archuleta and Day 

(1980), who used an Earth model consisting of two 

uniform layers overlying a halfspace. More complicated 

laterally homogeneous models, shown in figure 125, 

have been used in simulations of the 1979 Imperial 

Valley earthquake (Hartzell and Heimberger, 1982; 

Olson and Apsel, 1982; Hartzell and Heaton, 1983; Archuleta, 1984) and in studies of the Los Angeles region 

(Apsel and others, 1981; Ziony and others, this volume). 

If it is important to retain lateral variations in the 

geologic structure, then one must currently choose 

Green's function methods that give only approximate 

Green's functions. The most widely used of these approximate methods are the body-wave methods (also 

called ray methods), which construct the seismic 

response of the medium from a finite sum of discrete 

body waves (such as direct P and S waves). The resulting Green's functions are necessarily incomplete 

because neither surface waves nor most of the infinite 

possible number of body waves is included. An additional strength of body-wave methods is that they are 10 

to 100 times faster computationally at high frequencies 

(10 Hz) than lateral homogeneity methods are. As more 

strong ground-motion data are gathered from earth~ 

quakes, it is becoming clear that horizontal variations in 

geologic structure can affect the strength of the ground 

motions. Liu and Heaton (1984) have presented an excellent example of how the structures of the San Fernando 

Valley, the Santa Monica Mountains, and the Los 

Angeles basin altered the character of the ground motions from the 1971 San Fernando earthquake. Consequently, research on body-wave methods, which are 

appropriate for laterally varying structure, is currently 

quite active. Both Hong and Heimberger (1978) and 

Nowack and Aki (1984) have used body-wave methods to 

study amplification of ground motion in sedimentary 

basins, and Rial (1984) has examined how the damage 

patterns observed in the 1967 Caracas, Venezuela, 

earthquake could be predicted by body-wave theory. 

Cormier and Spudich (1984) have used body-wave 

methods to show that ground motions can be amplified 

in fault zones owing to their geologic structure. Both 

Bernard and Madariaga (1984) and Spudich and Frazer 

(1984) have devised extremely simple and efficient 

methods for combining body-wave Green's functions 

with earthquake rupture models. 

Details of Choosing a Green's 

Function Method 

Clearly, to choose between these methods in a sitespecific simulation, one must decide how important surface waves are in the study situation, how strong the 

horizontal variations in geology are at the site, and how 

well a finite sum of body waves would approximate the 

actual Green's functions. Although these questions are 

difficult to answer a priori, certain considerations can 

be addressed. Surface waves, for example, start to 

become an important component of ground motion only 

at epicentral ranges that are about two to three times 

the seismic source depth; thus, if one is simulating 

ground motions from an earthquake whose rupture surface is confined to depths greater than 3 km, surface 

waves will be unimportant at horizontal distances less 

than about 10 km but may be very important at distances greater than 20 km. Additional discussion of the 

characteristics of surface and body waves has been 

presented by Spudich and Orcutt (1982). 

When the importance of horizontal variation in 

geologic structure is assessed,· the scale of variation 

must be considered. For example, accelerograms from 

both the 1979 Coyote Lake and Imperial Valley earthquakes were recorded in alluvial basins, but the scal~s 

of the basins vary dramatically. Figure 126 shows cross 

sections of the Santa Clara Valley (Mooney and Luetgert, 1982), site of the Coyote Lake earthquake, and the 

Imperial Valley (from line 1E-2W of Fuis and others 

(1982)). Although one could find a laterally homogeneous 

velocity model that would be a reasonable approximation of the Imperial Valley structure between the fault 

and accelerometer sites 1 through 11, one would be 

hard pressed to find a laterally homogeneous model that 

would approximate the velocity structure between the 

Calaveras fault and any of the Santa Clara Valley accelerometer sites. In fact, Cormier and Spudich (1984) 

have shown that the Santa Clara Valley velocity structure amplified ground motions in the Calaveras fault 

zone. For this reason, lateral homogeneity methods for 

calculating Green's functions have been used quite successfully in simulating ground motions caused by the 

Imperial Valley earthquake but have been of lesser utility in simulating Coyote Lake ground motions (Bouchon, 

1982; Liu and Heimberger, 1983). 

Lateral homogeneity methods have been studied intensively. In such techniques, the Earth models used 

consist of stacks of layers whose material properties 

and thicknesses vary. In some methods, the layers are 

required to be perfectly uniform, whereas, in others, the 

material properties may vary smoothly with depth 

within each layer. Although this second type of Earth 

structure is more realistic, the uniform-layer models can 

Ground-Motion Time-Histories 257 
9 

8 

7 

(J) 

w 

....J 

6 

w 

<.9 5 

z 

<( 4 

(J) 

0 3 Apsel and others (1981) ------

....J 

2 

1o 

Cl 9 

z 

0 

u 8 UJ 

(f) 

>- U5 7 a: w UJ 

....J f-

....J UJ 6 

<( ~ 

0 

> ...J 5 ;;2 

....J z 

<( i;' a: 

4 Hartzell and 

Heimberger (1982) 

w u 3 c.. 0 

...J 

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UJ 

> 

~ 1 $: 0 2 

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0 5 

....J 

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Olson and 

-----Apsel (1982) 

10 12 25 50 

u. 

4 I ---Bouchon 

~ (1979) 

a: 3 Archuleta and 

<( 

c.. 2 

Day (1980) 

1 

0 2 4 6 8 10 

DEPTH, IN KILOMETERS 

FIGURE 125.-Graphs of laterally homogeneous P-wave velocity structures used in groundmotion simulations in the Parkfield, Imperial Valley, and Los Angeles regions of California. 

Note the varying depth scales. 

be made arbitrarily close to a smooth Earth model by 

taking many very thin, uniform layers whose material 

properties change gradually between layers Oike the 

two Imperial Valley models in fig. 125). Of course, the 

cost of calculating Green's functions rises as the number 

of layers in the Earth model increases; because the cost 

of computing Green's functions by these methods is gen258 Earthquake Hazards in the Los Angeles Region 

erally the major expense in ground-motion simulation, 

the motivation for calculating them once and storing 

them for later reuse is strong. 

Of the uniform-layer methods, one of the first and 

most widely used is the generalized ray theory (GRT) of 

Heimberger (1968) and Heimberger and Harkrider 

(1978). Although the GRT is extremely powerful in some 
SANTA CLARA VALLEY 

ill ~ 0.0 -,------~~-------------------------------.rn~--~------~~---------r- ~ 3.4 w 

1-

~ 1.0 

0 

_J 

:;:2 2.0 z 

:r:· 

b:: 3.0 w 

0 

6.0 

4.3 

CALAVERAS FAU LT ZONE 6.0 

14 16 

DISTANCE, IN KILOMETERS 

IMPERIAL VALLEY !'. 

£ tJ1 ~&i&ffi &&l£ && ffi ~------~~====~~====~~~==~~~-=~~~====~~----------------~ 

-_-_-:::$===~~~::==--=--=------------~l~===--=--=--=----;-;-~~;~;:;-===--=-~ -~----- --- ~Q!I!L .D. _2!~_r.Q.Cjg; 35- ------===_:-: ____ ::. _ _.._..--- _,...,..._..._ 

~ 4 

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w 

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- --- ------ ---- Subbasement 

0 

8 

30 40 50 60 70 

DISTANCE, IN KILOMETERS 

FIGURE 126.-Cross sections of P-wave velocity structures in the Santa Clara Valley (A) and the Imperial Valley (B) of California. 

Accelerometer sites are indicated by numbered triangles. A, Numbers inside the cross section are the P-wave velocities (in kilometers per second) of the labeled units. B, Dashed lines are isovelocity contours. I and B indicate surface traces of the Imperial 

and Brawley faults, respectively. The Imperial Valley cross section is taken from line 1E-2W of Fuis and others (1982). Note the 

difference in the vertical and horizontal scales in both cross sections. 

applications (Burdick and Orcutt, 1979), one drawback 

is that it does not automatically generate complete 

Green's functions for the layered medium. As Hartzell 

and Heimberger (1982) have shown, this shortcoming 

can be very inconvenient for ground-motion synthesis. 

Consequently, other methods for generating the complete response of uniform-layer models have been 

developed (Kind, 1978; Herrmann, 1979; Bouchon, 1980; 

Kennett, 1980; Harvey, 1981; Apsel and Luco, 1983) and 

have been used in ground-motion simulations by 

Bouchon (1978, 1979, 1982), Apsel and others (1981), 

and Olson and Apsel (1982). 

To overcome the expense of using finely layered Earth 

models to approximate continuous velocity-depth profiles, several investigators have determined methods to 

generate complete Green's functions for arbitrary 

smooth or discontinuous velocity profiles (Alekseev and 

Mikhailenko, 1980; Cormier, 1980; Kennett and Illingworth, 1981; Olson and others, 1984; Spudich and 

Ascher, 1983). Such techniques have been used in 

ground-motion simulations by Hartzell and Heimberger 

(1982), Hartzell and Heaton (1983), Archuleta (1984), Liu 

and Heimberger (1983), and Ziony and others (this 

volume). 

Ground-Motion Time-Histories 259 
Two drawbacks common to all these methods of 

generating complete Green's functions in laterally 

homogeneous Earth models are that they are expensive 

to use in the frequency band of engineering interest 

{1-20 Hz) and that they require the use of an often 

unrealistic Earth model. For these reasons, considerable 

interest is being shifted toward body-wave methods for 

calculating Green's functions. Several methods exist for 

calculating body-wave Green's functions (Hong and 

Heimberger, 1978; McMechan and Mooney, 1980; 

Cerveny, 1983), and several more are under development. The chief pitfall of using such methods, mentioned 

earlier, is the possibility that an impractically large 

number of body waves must be included in the Green's 

functions in some Earth models. Hong and Heimberger 

(1978) have shown a good example in which one or two 

body waves alone are insufficient. In certain situations, 

however, the complete seismic response of a geologic 

structure may be well represented by a few body waves. 

If, for example, a particular geologic structure contains 

very few reflectors (abrupt velocity discontinuities), 

body waves traveling directly from source to receiver 

without reflection will probably be the most important 

waves. If, in addition, surface waves are not important, 

for the reasons noted above, then the ground motions 

resulting from an earthquake in this structure may well 

consist primarily of direct body waves. Spudich and 

Cranswick (1984) have shown that these conditions 

prevailed at a site 5.6 km from the M5 6.9 Imperial 

Valley earthquake of 1979. The ground motions at that 

site consisted primarily of the direct P and S waves only. 

A body-wave method like that of Spudich and Frazer 

(1984) would be well suited for synthesizing the ground 

motions observed by Spudich and Cranswick. 

Empirical Green's Functions 

Of course, all the Green's function calculation 

methods mentioned above are theoretical calculations 

based on an inferred approximate Earth model. Empirically obtained Green's functions may also be used. 

Hartzell (1978), for example, used recordings of small 

earthquakes as Green's functions for a larger earthquake simulation. If the small earthquake occurs on the 

same fault surface as the hypothetical large event and if 

recordings of the small earthquake are available at the 

sites where simulated ground motions for the hypothetical large event are desired, the recordings are in some 

respects ideal Green's functions, because their source is 

virtually a point in space and the effects of wave propagation in the local structure are included exactly. This 

use of small-earthquake recordings as Green's functions 

may prove to be very important, but its utility depends 

260 Earthquake Hazards in the Los Angeles Region 

on the existence of a very good set of recordings. Other 

studies using this approach have been done by 

Kanamori {1979), Hartzell (1982), and Irikura (1983). 

DETAILED EXAMPLE OF 

GROUND-MOTION SIMULATION 

Apsel and others (1981) have simulated ground 

· motions in the Los Angeles basin caused by a magnitude 

7.5 event on the "big bend" segment of the San Andreas 

fault and by a magnitude 6.8 event on the NewportInglewood fault near Long Beach. Because of the size of 

the events, the large horizontal distances between 

points on the faults and sites in the basin, the geologic 

complexity of the region, and the frequency bandwidth 

covered, this study was particularly difficult to execute. 

Although we will comment on some of the techniques 

used, a cursory review such as this one is not sufficient 

to judge the validity of the results of such a large study. 

The following discussion concentrates on the San 

Andreas event simulation. 

Green's functions.-Apsel and Luco's (1983) method, 

which requires a laterally homogeneous, uniform-layer 

Earth model, was used to generate Green's functions in 

the o- to 5-Hz frequency band. Because of the lateral 

variations between the geologic structures of the San 

Andreas fault and points in the Los Angeles basin, a 

1o-Iayer velocity model representing a composite of 

velocities observed at different depths in southern 

California was used (fig. 125). In the top 15 km, the 

velocity structure used by Apsel and others (1981) was 

appropriate to the Los Angeles basin specifically and included the low-velocity materials that velocity logs in oil 

wells have shown to exist at shallow depths. For deeper 

structure, they used velocities derived from regional 

traveltime studies. Certainly, the assumption of lateral 

homogeneity in this study is an important one, and, 

although we cannot comment on its validity without further study, one might be able to check its validity by 

determining what part of the Earth model transmitted 

most of the seismic energy and by checking the lateral 

homogeneity assumed for that depth range. If, for example, it were determined that 95 percent of the seismic 

energy stayed trapped in the top 5 km of the model of 

Apsel and others (1981), then the lateral homogeneity 

assumption might break down if the top 5 km of the San 

Gabriel Mountains differed considerably from their 

model. On the other hand, the lateral homogeneity 

assumption may be much better for the deeper structure. In this light, it is interesting to consider the observations of Liu and Heaton (1984). 

Because of the relatively high frequencies and the 

long epicentral ranges that Apsel and his coworkers 
dealt with, they were forced to include attenuation (Q) in 

their Earth model. They pointed out that their calculated 

peak accelerations are strongly influenced by the Q of 

the Earth model and that uncertainties in Q could lead to 

uncertainties in the computed peak accelerations of 

more than a factor of two. 

Slip model.-The slip model used in this study was a 

kinematic model in which many parameters were derived from dynamic models of earthquake rupture and 

in which a degree of randomness was added to the 

source behavior. Our description of this slip model is intended to convey only the general principles. 

The shape of the slip time-function at each point on 

the fault was selected to be a simple function approximating the shapes of slip functions observed in dynamic 

rupture models such as those of Archuleta and Frazier 

(1978) (fig. 119). This shape was held constant over the 

entire fault surface. At each point on the fault, the 

theoretical arrival time of a rupture front propagating 

at 0.9 of the local shear-wave velocity was determined. 

Rather than allowing slip to initiate at each point at the 

theoretical arrival time of the rupture front, Apsel and 

his coworkers allowed slip to initiate at a random time 

delay (generally less than 1 s) after the theoretical time. 

In this way, they introduced the irregular propagation of 

rupture discussed in the section describing the earthquake rupture process. Additional randomness was 

added by allowing the direction of rupture advance to 

vary irregularly from the overall along-strike direction, 

by allowing the slip mechanism at each point on the fault 

to vary randomly about a predominantly strike-slip 

mechanism, and by allowing the amplitude of the slip 

function to vary randomly about a mean amplitude at 

each point on the fault. The amount of random variation 

was chosen on the basis of simulations of several earthquakes for which local strong-motion data existed. Thus, 

the slip model of Apsel and others (1981) was intermediate between the essentially dynamic model of Archuleta 

and Day (1980) and the entirely kinematic model of 

Bouchon (1979). 

Green's function summation.-The Green's function 

summation technique that Apsel and others (1981) used 

was also essentially a point-source summation like that 

of Hartzell and Heimberger (1982), although Apsel and 

his coworkers used a different method of interpolating 

Green's functions and used additional measures to ensure that the distribution of point sources on the fault 

surface was dense enough. 

SUMMARY 

Time-histories of ground motion from a hypothetical 

earthquake can be predicted by determining how each 

point on a fault is displaced during the event, calculating the ground motions caused by each individual 

point on the fault, and then summing the contributions to 

get the total ground motion of the hypothetical event at 

distant sites. Some methods for simulating ground motions use essentially this procedure (for example, Ziony 

and others, this volume), whereas, in other methods (for 

example, Archuleta and Frazier, 1978), the action of the 

earthquake source is calculated along with the propagation of seismic waves away from the source. Even in 

these cases, however, the validity of the calculated 

ground motions may be tested by determining whether 

the fault slipped in a realistic way, whether a realistic 

Earth structure was used, and whether the method used 

to calculate seismic-wave propagation was accurate. 

The ground motion caused by sudden slip at any point 

along a ·fault can be represented by a mathematical entity called a Green's function. If ground- motion calculations explicitly use Green's function summations, 

calculation of those functions is often the bulk of the 

computational labor, but, if they are stored, they may be 

summed repeatedly, relatively effortlessly, to simulate a 

wide variety of hypothetical earthquakes in the same 

study area. 

At present, the theory for calculating complete 

Green's functions (that is, Green's functions containing 

the complete response of the Earth model) is most fully 

developed for Earth models in which material properties 

vary with depth only; such models assume no horizontal 

change in geologic structure. In more realistic models, 

where horizontal variation in geologic structure occurs, 

incomplete Green's functions can be calculated for individual body waves, such as direct P or S waves, or for 

waves that have undergone a specified number of reflections and mode conversions. The complete response 

of laterally varying media cannot be determined easily 

except in very simple circumstances, although it can 

always be obtained with great computational effort by 

using three-dimensional finite-element or finitedifference calculations. In many instances, however, the 

bulk of the ground motion observed at a specific site may 

consist primarily of direct P and S waves, and, in these 

cases, it may be possible to simulate ground motions in 

the laterally varying structure with little computational 

effort. 

Incomplete knowledge of the geologic structure of a 

region and uncertainties about seismic source behavior 

are important obstacles to the prediction of ground motions. One way around the obstacle of Green's function 

determination might be to use seismograms from small 

earthquakes as Green's functions. Purely theoretical 

attempts to circumvent these voids in our knowledge, 

however, will probably rely on a more statistical 

description of seismic source action and seismic-wave 

propagation. 

Ground-Motion Time-Histories 261 
Earthquake-Triggered 

Ground Failure 
EVALUATING LIQUEFACTION POTENTIAL 

By J. C. Tinsley, T. L. Youd,4 D. M. Perkins, and A. T. F. Chen 

INTRODUCTION 

Liquefaction, a process by which water-saturated 

sediment loses strength and may fail during strong shaking, commonly accompanies moderate to great earthquakes throughout the world. Research into the process 

and consequences of liquefaction was stimulated by 

catastrophic ground failures triggered by the 1964 

Alaska earthquake (Hansen, 1965; McCulloch and 

Bonilla, 1970); the 1964 Niigata, Japan, earthquake 

(Seed and Idriss, 1967); the 1967 Caracas, Venezuela, 

earthquake (Seed and Alonso, 1973); and the 1971 San 

Fernando, Calif., earthquake (Youd, 1971; Seed and 

others, 1975). These and subsequent studies of other 

earthquakes have firmly linked liquefaction to certain 

hydrologic and geologic conditions. Liquefaction as a 

process is now relatively well understood. The environments that favor the occurrence of liquefaction can 

be delineated with reasonable precision, and the geographic variation in liquefaction potential can be used 

in planning the reduction of earthquake hazards. 

Liquefaction-related ground failures have occurred 

during past earthquakes in southern California. The 

great 1857 Fort Tejon earthquake caused fissuring of 

the ground in the beds of the Los Angeles, San Gabriel, 

Santa Clara, and Santa Ana Rivers. Sand boils occurred 

at Santa Barbara and in the flood plain of the Santa 

Clara River (Agnew and Sieh, 1978). During the 1933 

Long Beach earthquake, liquefaction-generated ground 

failures damaged parts of Compton, Huntington Beach, 

and Long Beach (Barrows, 1974). Figure 127 shows 

liquefaction-related ground failure manifested as slumping and cracking along the Balsa Bay causeway near 

Huntington Beach in Orange County, Calif. During the 

1973 Point Mugu earthquake, ground failures due to liquefaction were noted in the estuarine areas near Port 

Hueneme and along the lower reaches of Calleguas 

Creek (Weber and Kiessling, 1976). During th,e 1979 and 

1981 earthquakes in the Imperial Valley, locally extensive ground failures damaged roads, utilities, irrigation 

'Now at Department of Civil Engineering, 370 Clyde Building, Brigham Young University, 

Provo, UT 84602. 

canals, and other agricultural facilities (Y oud and Wieczorek, 1982, 1984). In all these instances, a range of 

liquefaction-related effects was reported-from minimal ground cracking causing negligible damage, to sand 

boils, lateral spreads, and slumping causing greater 

damage. During the 1971 San Fernando earthquake, for 

example, liquefaction-related ground failures severely 

damaged facilites at the San Fernando Juvenile Hall (fig. 

128A), inflicted major damage to the newly constructed 

Jensen Water Filtration Plant, and triggered nearcatastrophic failure of the Lower Van Norman Reservoir Dam (fig. 128B) (Seed and others, 1975). Future rna" 

jar earthquakes undoubtedly will cause comparable 

liquefaction-related ground failure in parts of the 

alluvial basins of the Los Angeles region. 

This chapter reviews how liquefaction potential is 

evaluated and then defines the relative liquefaction 

potential for six areas in five alluvial basins in the Los 

Angeles region (fig. 129). Our regional assessments consider the geologic age and type of sedimentary deposits, 

the ground-water depth, and the likelihood that earthquakes strong enough to cause liquefaction will occur. 

The occurrence of liquefaction is limited chiefly to 

certain mappable geologic and hydrologic settings and 

to regions of high seismicity. Water-saturated, cohesionless, granular sediment situated at depths less than 

30 ft subsurface constitutes the principal environs of the 

liquefaction process. These geologic conditions are 

widespread in parts of each of the six areas considered 

in this chapter: the San Fernando Valley, the San 

Gabriel Valley, the coastal basin in Los Angeles County, 

the flatland area of Orange County, the upper Santa 

Ana River basin, and the Oxnard Plain. 

Acknowledgments 

This report is based in large measure on the logs of 

several thousand exploratory boreholes and wells filed 

by numerous public and private agencies and organizations. We are indebted to the following for their important contributions, including access to records, in 

discussions or in reviews: California Division of Mines 

Evaluating Liquefaction Potential 263 
)~ ~:- .,..> ... , · 

f ·'.f":; 

r· ~.: .. "" ...... _J • ~ 

.· ~-

i 

.:...o . , 

-

...... 

t 

-.. 

FIGURE 127.-Damage to causeway across Bolsa Bay northwest of Huntington Beach as a result of the 1933 Long Beach earthquake. Slumping 

and cracking of the road were probably due to liquefaction of the underlying fill or the Holocene sediment of Bolsa Bay. (Photograph from the 

City of Long Beach Public Library Historical Collection.) 

and Geology, Los Angeles; California Department of 

Water Resources, Southern District, Los Angeles; 

California Department of Transportation, Division of 

Structures, Sacramento; California Division of Oil and 

Gas, Long Beach; City of Los Angeles Department of 

Building and Safety and Department of Water and 

Power; County of Los Angeles Department of the County 

Engineer (Geologic Section), Department of Facilities 

(Architectural Division), Department of Public Works 

(Soils Section), Flood Control District (Materials 

Engineering Division and Water Conservation Division, 

Groundwater Studies and Operations Section), and 

Department of Roads; Southern California Rapid Transit 

264 Earthquake Hazards in the Los Angeles Region 

District, Rapid Transit Department; Metropolitan Water 

District of Southern California; U.S. Army, Corps of 

Engineers, Los Angeles District; and LeRoy Crandall and 

FIGURE 128.-A, Damage to San Fernando Juvenile Hall facility caused ...... 

by lateral spreading ground failure during the February 9, 1971, 

San Fernando earthquake. (Photograph by T. L. Youd, from U.S. 

Geological Survey Professional Paper 733.) B, Lower Van Norman 

Dam Reservoir. Slumping of the concrete lining on the northern 

side of the dam was caused by the 1971 San Fernando earthquake. 

Considerable water had been emptied by the time the photograph 

was taken. Subsequent investigation of the failure indicated that 

part of the hydraulic fill comprising the earthen dam had failed 

owing to liquefaction (Seed and others, 1975). (Photograph by R. E. 

Wallace, from U.S. Geological Survey Professional Paper 733.) 
A 
34'30' 119'00' 

Santa 

s .... 

COASTAL BASIN 

Of LOS ANGELES 

COUNTY 

118'00' 

ill Whittier 

GABRIEl 

~I

MOUNTAINS 

"'<,"..._ ~.:>~ if-£;·'o ,_, '1:"0.;;),· ~ G Anaheim ov.' (j 0 

117'00' 

Santi Ana Vliity 

v /.f 

Long 613:' ORANGE each~ COUNTY 

0 5 10 15 20 1 , 1 1 1 1 

0 5 1'o 

INDEX MAP LOCATION 

33'30' L_ ____ _L _________ __L __________ _L_ ____ ;t:_ ____ ...J._~--------___J 

FIGURE 129.-Six areas for which liquefaction potential has been analyzed in the Los Angeles region-the San Fernando Valley, the San Gabriel 

Valley, the coastal basin in Los Angeles County, the flatland area of Orange County, the upper Santa Ana River basin, and the Oxnard Plain. 

Associates, Consulting Geotechnical Engineers, Los 

Angeles. C. A. Hastorf, E. J. King, E. Layman, J. P. 

McCalpin, J. M. McManus, D. M. Merritts, M. Nicholson, 

R. J. Preston, D. J. Ponti, D. Sato, K. Seals, S. L. Wert, and 

K. M. Williams assisted in procuring and processing the 

data used in this report. 

LIQUEFACTION AND 

RESULTING GROUND FAILURE 

Liquefaction is defined as "the transformation of a 

granular material from a solid state into a liquefied 

state as a consequence of increased pore-water pressures" (Youd, 1973, p. 1). The process of liquefaction 

must be distinguished from the effects of ensuing ground 

failure, which actually result in damage. Youd (1980) 

suggested that displacement accompanying ground failure must exceed about 10 em for significant damage to 

affect most structures. Four types of ground failure commonly result from liquefaction (Youd, 1978a, b): lateral 

spread, flow failure, ground oscillation, and loss of bearing strength. These modes of ground failure and the 

nature of the damage that they are likely to cause are 

discussed below. 

Lateral spreads include the lateral displacement of 

surficial blocks of sediment as a result of liquefaction in 

266 Earthquake Hazards in the Los Angeles Region 

a subsurface layer. Once the process of liquefaction 

transforms a subsurface layer into a fluidized mass, 

gravitational forces plus inertial forces resulting from 

the earthquake may cause the mass to move downslope 

or toward a cut slope or free face (for example, an incised river channel, an irrigation canal, or an openconduit storm drain). The historical record indicates 

that lateral spreads most commonly occur on gentle 

slopes that range between 0.3° and 3°; lateral 

displacements commonly amount to several meters, 

perhaps tens of meters if soil conditions are especially 

favorable for liquefaction and if earthquake shaking is 

of sufficient duration. This mode of ground failure is 

especially destructive to pipelines, utilities, bridge piers, 

and other structures having shallow foundations, particularly those located in flood-plain areas adjacent to 

river channels. Lateral spreads resulting in ground 

displacements of only a few feet caused damage at 

every major pipeline that broke in San Francisco during 

the 1906 earthquake (Y oud, 1978a, p. 47); hence, liquefaction was responsible for the severely compromised 

ability to fight the fires that caused about 85 percent of 

the damage to that city. 

Ground oscillation takes place if liquefaction occurs 

at depth and if the slopes are too gentle to permit lateral 

displacement. Following liquefaction at depth, overlying 

soil blocks that are not liquified may decouple from one 
another and oscillate on the liquified substrate. The 

resulting ground oscillation is often observed as a 

traveling ground wave. Ground settlement, the opening 

and closing of fissures, and sand boils may accompany 

the oscillations. Overlying structures and subgrade 

facilities commonly sustain damage through this mode of 

ground failure. 

Flow failure constitutes the most catastrophic mode of 

ground failure caused by liquefaction. Usually developing on slopes greater than 3 o, the flows are comprised 

chiefly of liquefied soil or blocks of intact material riding 

on a liquefied substrate. Flow failures commonly displace soil masses by tens of meters; in favorable circumstances, flow failure has displaced materials by tens of 

kilometers at velocities of tens of kilometers an hour. 

Flow failures can occur on land or under water; the extensive damage to Seward and Valdez, Alaska, during 

the 1964 Alaska earthquake was caused by submarine 

flow failures. 

Loss of bearing strength can occur under a structure 

when the soil loses strength and liquefies. Large deformations can then occur within the soil mass and allow 

buildings to settle and tip; if the structures are buoyant, 

they may float upward. Among the more spectacular examples of this failure mode was the tilting of structures 

in the Kwangishicho apartment complex, where four 

buildings tipped as much as 60° during the 1964 Niigata, 

Japan, earthquake, and buried septic tanks rose as much 

as 3ft. 

METHOD FOR EVALUATING 

LIQUEFACTION POTENTIAL 

Although a number of methods for evaluating the liquefaction hazard have been proposed (for example, 

Seed and Idriss, 1971; Seed and others, 1983; Roth and 

Kavazanjian, 1984), the techniques applied in this 

chapter combine those of Youd and Perkins (1978) and 

Youd and others (1975) updated to incorporate new information, including liquefaction failure in clay-bearing 

sediments (Seed and others, 1983), and rely on geologic 

and hydrologic mapping and basinal stratigraphic 

analyses by J. C. Tinsley and on his compilations of field 

mapping by others. Preliminary results of some of our 

findings were reported by Youd and others (1978), 

Tinsley and Youd (1979), and King and others (1981). 

This chapter incorporates much hydrologic and geotechnical data from public and private sources not compiled 

in earlier regional studies of liquefaction. As a result, 

we have identified several areas that contain or are likely to contain shallow or perched ground water and that 

have not been recognized previously. 

The procedure used to determine areal variations in 

liquefaction potential requires the development of a liquefaction susceptibility map and a liquefaction opportunity map. A liquefaction susceptibility map delineates 

areas where liquefiable materials are most likely to be 

present and is based chiefly on generalizations pertaining to the geology and hydrology of late Quaternary 

deposits in a sedimentary basin. The liquefaction opportunity map shows return periods for earthquake shaking 

strong enough to generate liquefaction in susceptible 

materials and is based on an appraisal of regional 

earthquake potential. These two maps are then considered together to determine liquefaction potential, the 

relative likelihood that an earthquake will cause liquefaction in water-saturated cohesionless silts and sands 

that may be present. 

The concept of a liquefaction potential map merits a 

brief discussion, because the liquefaction susceptibility 

maps presented in this chapter can be regarded as 

liquefaction potential maps as well. As originally proposed by Youd and Perkins {1978), a liquefaction potential map is derived by superimposing a liquefaction susceptibility map and a liquefaction opportunity map. A 

liquefaction potential map thus would express the concept that the probability of liquefaction-induced ground 

failure in certain areas may be greater than that in 

other areas, either owing to differences in the physical 

properties of near-surface earth materials (liquefaction 

susceptibility) or to differences in the return periods of 

earthquakes strong enough to induce liquefaction in 

susceptible materials (liquefaction opportunity). Our 

ability to estimate the size and frequency of future 

earthquakes expected from the numerous potentially active faults and fault zones in the Los Angeles region is 

improving (Ziony and Yerkes, this volume), but we are as 

yet unable to determine that statistically significant 

changes in liquefaction opportunity occur across the 

region. In the study area, liquefaction potential is controlled chiefly by regionally mappable differences in the 

liquefaction susceptibility of late Quaternary basin 

sediments rather than by areal differences in earthquake potential. The liquefaction susceptibility maps in 

this chapter, therefore, also serve as liquefaction potential maps because the current seismic model of earthquake potential suggests that the liquefaction opportunity is generally constant across the Los Angeles region. 

Liquefaction potential maps delineate areas where a 

relative potential for liquefaction and associated ground 

failure may exist. Maps drawn at regional scales, however, are not sufficient for evaluating the actual liquefaction potential at a specified site. Site-specific geotechnical studies, using procedures and techniques such 

as those summarized by Seed and others (1983), are reEvaluating Liquefaction Potential 267 
TABLE 40A.-Sediment-source factors determining the nature of late Quaternary basin sediment in 

the Los Angeles region 

Factors Effects 

High topographic relief --------------------- Efficient erosional slope processes deliver sediment readily to streams. 

Semiarid, Mediterranean climate -------------- Intense episodic rainfall promotes removal of loose 

soil and rock on steep slopes. 

Vegetation -------------------------------Frequent fires remove vegetation and spall rock 

and expose steep slopes. 

Bedrock characteristics --------------------- Fractured and deformed sedimentary, igneous, 

and metamorphic terranes yield sediment to 

high-gradient streams. Largest clasts are 

determined by fracture spacing in bedrock 

areas; soft siltstone and shale yield chiefly 

silt and clay. 

quired to evaluate the liquefaction potential beneath an 

individual parcel of land. 

Users of these regional maps must consider that a 

potential for liquefaction does not necessarily indicate a 

similar potential for any other specified type of ground 

failure. Ground failures, however, commonly occur as a 

consequence of liquefaction and hence should be ·anticipated in areas where susceptible, water-saturated, 

cohesionless granular sediment may exist. 

MAPPING LIQUEFACTION 

SUSCEPTIBILITY 

The geologic and hydrologic factors that affect liquefaction susceptibility are (1) the age and type of 

sedimentary deposit, (2) the looseness of cohesionless 

sediment, and (3) the depth to perched or other ground 

water. Liquefaction susceptibility maps compiled for the 

Oxnard Plain, the flatland area of Orange County, and 

the upper Santa Ana River basin reflect susceptibility 

categories based on the age and type of sedimentary 

deposits as reported in the literature and on the depth to 

free water or other ground water as compiled from 

published or unpublished sources. For the Los Angeles 

basin, the San Fernando Valley, and the San Gabriel 

Valley areas, the liquefaction analyses incorporate new 

and unpublished geologic and hydrologic mapping by the 

senior author as well as limited geologic data compiled 

from published studies. 

Age and Type of Sedimentary Deposit 

In general, analyses. of historical occurrences of liquefaction indicate that the more recently a sediment has 

268 Earthquake Hazards in the Los Angeles Region 

been deposited, the more likely it is to be susceptible to 

liquefaction and that certain types of deposits, such as 

river-channel and flood-plain deposits, are more susceptible to liquefaction than other deposits, such as alluvialfan deposits (Youd and Perkins, 1978). Sediment source 

factors partly determining the nature of late Quaternary 

sediment in the Los Angeles area are shown in table 

40A. The effect of selected transport processes on grain 

size, sorting, and bedding characteristics in different 

sedimentary deposits is shown in table 40B. These factors and processes chiefly determine the physical 

characteristics of sediment deposited at various places 

within a region. The distribution of particle sizes (sorting) and the packing (the grain-to-grain arrangement] of 

the sand particles influence liquefaction susceptibility. 

Sand and silty sand are the textural classes that have 

the greatest likelihood of liquefaction. Gravelly sand or 

deposits containing less than 15 percent clay are less 

likely to liquefy. Bouldery and cobbly gravels or deposits 

containing more than 15 percent clay are not known to 

liquefy. The standard penetration test (SPT) is used by 

engineers as an index to show how densely packed the 

sediment is. For a given particle-size distribution, the 

more loosely packed the sediment, the lower the 

penetrometer resistance and the more likely the sediment is to liquefy during earthquake shaking. 

To assess liquefaction susceptibility, we have subdivided the late Quaternary deposits of the Los Angeles 

region into three informal stratigraphic units according 

t~ relative age: the latest Holocene deposits, formed 

chiefly during the past 1,000 yr; the earlier Holocene 

deposits, formed chiefly during the remainder of the 

Holocene from 1,000 to about 10,000 yr ago; and the 

undifferentiated late and middle Pleistocene marine and 

nonmarine deposits, formed chiefly during the past 

0.5 m.y. The criteria and characteristics used to identify 
TABLE 40B.-Erosional and transport processes controlling grain-size, sorting, and bedding characteristics of sedimentary deposits 

[A comprehensive summary of the identification and classification of principal sedimentary paleoenvironments has been given by Rigby 

and Hamblin (1972)) 

Process Deposit 

Wind -----------------------------------Chiefly fine-grained and very fine grained sand, 

silt; very well sorted; preserved as dunes in 

coastal and inland basin areas; also as 

patchy, thin deposits on alluvial fans and 

flood plains; forms overthickened soil horizons in fine-grained sediment and silt coats 

on clasts in bouldery gravels. 

Beach and coastal terrace------------------- Fine- to coarse-grained sand; some gravel and 

boulders present in high-energy settings; 

chiefly well-sorted, laminated deposits mantle 

wave-eroded benches along modern and tectonically uplifted shorelines. 

Coastal lagoon or marsh --------------------Fine- and medium-grained sand; the proportion of 

silt and clay depends on the degree of winnowing in the depositional environment. 

River channel, levee, and flood basin ----------- Grain size generally decreases as distance from 

sediment-source area increases. 

Channel facies: Boulders, cobbles, gravel, and 

sand; moderately to poorly sorted; scour and 

fill and cross stratification are common sedimentary structures; deposits are well to 

poorly stratified; scale of sedimentary structures depends on size of stream. 

Levee facies: Chiefly coarse- and medium-grained 

sand, often containing some gravel; often well 

bedded and cross stratified; moderately well 

sorted. 

Flood-basin facies: Chiefly fine-grained and very 

fine grained sand, silt, and some clay; often 

thinly laminated, moderately well sorted; 

commonly burrowed; interfingers with channel and levee facies. 

Alluvial fan ------------------------------Boulders, gravel, and sand in braided channels 

and bars emanating from canyons draining 

mountainous areas; sediment size decreases 

downslope; deposits commonly are well stratified but may be crudely stratified and 

poorly sorted; deposited by braided stream 

channel, sheet-flood, and debris flow processes in piedmont areas. 

Debris flow ------------------------------Very poorly sorted deposits of sand, silt, and clay 

(matrix) that form a high-density aqueous 

slurry capable of entrainment and transport 

of boulders weighing tons. 

and map these deposits are discussed below. The maps 

showing surficial deposits differ from those done to map 

relative shaking response (Tinsley and Fumal, this 

volume) in that the surficial geologic maps presented in 

this chapter depict two Holocene stratigraphic units, 

whereas the surficial geologic maps presented by 

Tinsley and Fumal (this volume) do not distinguish between younger and older Holocene deposits. Identifying 

the youngest Holocene deposits is critical for evaluating 

liquefaction susceptibility. These deposits typically are 

less than 4 m thick, however-too thin to be a significant 

factor in evaluating site-dependent variations in seismic 

shaking in period bands of interest for most structural 

engineering considerations Uoyner and Fumal, this 

volume; Rogers and others, this volume). 

Evaluating liquefaction Potential 269 
TABLE 41.-Diagnostic soil-profile characteristics of Holocene and late Pleistocene deposits in the Los 

Angeles basin 

Soil horizon Description 

Latest Holocene deposits 

A -------------------------------------- < 1 ft thick 

B -------------------------------------- Absent 

C -------------------------------------- Unoxidized or only slightly oxidized; clasts 

unweathered. 

Earlier Holocene deposits 

A -------------------------------------- 1 to 3 ft thick 

B -------------------------------------- Cambic, poorly developed textural B,1 <1ft thick 

C --------------------------------------Oxidized to depth of <6ft; cla~ts slightly weathered 

Late Pleistocene deposits 

A -------------------------------------- < 1 ft thick 

B -------------------------------------- Prominent textural B1; thickness ranges from 2 to 

15ft; may be reddened [rubified). 

C --------------------------------------Oxidized to >6 ft; may be reddened [rubified); 

clast weathering is moderate to deep. 

1

Textural B refers to the horizon in which weathering products (including both translocated and authigenic clay and metallic oxides) 

accumulate as soil formation proceeds from negligible to advanced states at the Earth's surface. 

Youngest Holocene Deposits 

(Map Unit Qya2) 

Youngest Holocene deposits are composed chiefly of 

boulders, gravel, sand, silt, and clay known or inferred 

to have been deposited in very recent alluvial-fan, 

stream, river, swamp, lake, windblown dune, or beach 

depositional environments. This unit delineates those 

alluvial areas believed to contain the youngest sediment 

(D-1,000 yr old) that is least well consolidated (Y oud and 

Perkins, 1978) and is most likely to liquefy as a result of 

moderate or large earthquakes. These deposits are identified chiefly from historical records and from anecdotal 

accounts of major floods occurring before extensive urbanization of the alluvial basins. Where urbanization 

has not obliterated the uppermost parts of these 

deposits, the relative degree of soil-profile development 

is also useful; the diagnostic soil-profile characteristics 

are summarized in table 41. 

The limits of historical flooding have been established 

chiefly on the basis of two sources: (1) unpublished field 

notes and maps (1:24,000 scale), on file with the Los 

Angeles County Flood Control District, that describe and 

delineate areas flooded during major storms in 1934, 

1938, 1941, 1943, 1944, 1952, 1954, and 1956 and (2) 

flood records for major drainage basins in southern 

California, including reports by Troxell and Peterson 

270 Earthquake Hazards in the Los Angeles Region 

(1937) and Troxell (1942). Other data used include 

photointerpretive studies of 1928 and 1938 black-andwhite aerial photography at scales of 1:24,000 or 

greater. The 1928 photography is the C-300 series obtained from the Fairchild Collection at Whittier College, 

Whittier, Calif.; the 1938 photography is from the U.S. 

Archives, Washington, D.C., and was flown 3 to 5 

months following the devastating floods of March 1938. 

Photographic and topographic features used to infer 

areas recently inundated include changes observed in 

the configuration of active drainage channels from 1928 

to 1938; areas where row crops, orchards, or other 

cultural features were disrupted or washed out; areas 

adjacent to stream courses where channels are incised 

5 ft or less below the natural levees; and areas 

characterized by prominent or fresh bar-and-swale 

channel morphology typical of distributary channels on 

alluvial fans and on flood plains of braided rivers. In our 

analysis, we have excluded localized areas inundated 

when water backed up owing to plugged culverts and 

also areas identified by the Los Angeles County Flood 

Control District as having been inundated by sheet 

flooding-a form of inundation that occurs commonly 

when intense precipitation accumulates on a tract of 

land and runs off as a thin sheet of water rather than as 

overflow from a channel system or breached levee. In all 

cases, our interpretations identify and delineate the 

youngest parts of a very youthful depositional system, 
because these areas are most likely to contain sediments 

susceptible to liquefaction. 

Earlier Holocene Deposits (Map Unit Qya1) 

Deposits mapped as earlier Holocene are differentiated chiefly where (1) there is no recorded history of 

flooding, (2) the topographic position of the area is slightly higher in the landscape than that of areas mapped as 

youngest Holocene deposits, (3) channels commonly 

show a somewhat subdued bar-and-swale microtopography in comparison with latest Holocene deposits, and 

(4) pedogenic soils are characterized by weakly 

developed, nonreddened but perceptibly oxidized C 

horizons (B horizons, if they are present, may exhibit 

small amounts of translocated clay typical of soil stage 

S5 in the San Gabriel Mountains soil stratigraphy of 

McFadden (1982) and McFadden and Tinsley (1982)). 

These characteristics are summarized in table 41. 

Late Pleistocene Deposits (Map Unit Qoa) 

Areas mapped as Pleistocene deposits were differentiated chiefly according to the relative degree of soilprofile development. These deposits generally are exposed along the margins of youthful anticlines, along 

topographic benches and terraces near the margins of 

valleys, and along the rising blocks adjacent to reverse 

faults having a history of deformation of Quaternary age 

or younger. These deposits are characterized by surface 

soils having moderately developed to well-developed 

textural B (argillic) horizons. Distinguished readily from 

Holocene soils by physical and chemical soil-profile 

characteristics, including degree of clast weathering, 

all but the latest Pleistocene soils contain appreciable 

ferric iron and are reddened (rubified) from initial hues 

of 2.5 Y or 10 YR to hues of 5 YR, 2.5 YR, or 10 R, according to the Munsell system of color notation and descrip-

, tion (Munsell Soil Color Charts, 1975). These soil profile 

characteristics are summarized in table 41; soil chronosequences and stages of soil-profile development for the 

San Gabriel Mountains area have been described fully 

by McFadden (1982) and briefly by McFadden and 

Tinsley (1982). These soil profiles commonly display 

characteristics developed under climatic conditions that 

allowed soil moisture to penetrate somewhat more deeply in the profile than conditions today would permit, an 

indication that these soil profiles developed during one 

or more of the cooler or wetter climatic episodes that 

characterize the Pleistocene epoch in western North 

America. 

In areas underlain by late Pleistocene deposits, the 

original constructional landforms typically have been 

deformed tectonically and (or) dissected by erosion; in 

relatively undissected areas, primary depositional 

topography has been strongly modified or obliterated by 

later erosional and depositional processes. Five Pleistocene stratigraphic units have been grouped and mapped 

as undifferentiated late Pleistocene deposits for the purpose of evaluating liquefaction susceptibility. 

Youd and Hoose (1977) have estimated from the historical record that, on the basis of geologic age alone, 

relatively well sorted, saturated river-channel deposits 

no more than several hundred years old (corresponding 

in age to our latest Holocene unit) would have a very 

high susceptibility to liquefaction-induced ground failure. Earlier Holocene river-channel deposits are presumed to have a high susceptibility, and deposits of 

Pleistocene age and older are presumed to have low and 

very low susceptibilities, respectively. Similar relations 

are noted for flood-plain and alluvial-fan deposits, 

although the estimated relative susceptibility is less for 

alluvial-fan and flood-plain deposits, which tend to be 

less well sorted than river-channel deposits. In general, 

saturated, cohesionless sediment would have very high 

or high susceptibility if it is of latest Holocene age, 

high or moderate susceptibility if it is of earlier Holocene age, and low to very low susceptibility if it is of 

Pleistocene age or older, depending on the depositional 

environment. 

Penetration Resistance and 

Liquefaction Susceptibility 

We verified our qualitative estimates of liquefaction 

susceptibility based on the age of the generalized 

geologic deposits mapped in the Los Angeles County 

area by comparing these estimates with calculated liquefaction susceptibilities determined from a sample of 

Standard Penetration Test (SPT) data taken from these 

deposits. To make these calculations, we applied a 

technique developed by Seed and others (1983) and used 

a computer code of that technique prepared by Chen 

(1984). The technique described by Seed and others 

(1983) incorporates several empirical constants and 

relations that have been revised from time to time as 

data have been accumulated. This technique is presently the most widely used procedure for evaluating liquefaction susceptibility in engineering practice. The 

general criteria that we derived from Seed and others' 

(1983) procedure are plotted in figure 130. Our analysis 

is discussed below. 

Evaluating Liquefaction Potential 271 
We extracted standard penetration data from borehole logs supplied to us by several public agencies and 

private consultants. Most of the data came from subsurface investigations conducted by or for the California 

Department of Transportation in conjunction with construction of freeways in the Los Angeles area. Only SPT 

data from sediment listed as sand, sandy silt, silty sand, 

and silt were used in the analysis. Test data from sediment logged as clayey, gravelly, or cobbly were not 

used. 

In our analysis, borehole sites were plotted on surficial geologic maps, and the thicknesses of strati-

. graphic units sampled by the SPT were determined as 

follows. The thicknesses of the two Holocene units were 

inferred from lithologic information on logs of the SPT 

and nearby holes and from our regional geologic mapping studies. Criteria used to assign thicknesses to the 

informal generalized stratigraphic units include identifying subsurface features logged by the drillers such as 

(1) an oxidized (reddened) clay-rich layer, which may indicate a late Pleistocene soil formed on a landscape now 

covered by Holocene deposits; (2) a dark-gray or 

organic-rich sand, silt, or clay layer greater than 1 ft in 

apparent thickness and overlying nonreddened but 

slightly oxidized layers, which may be a now-buried soil 

that formed on early or middle Holocene deposits; (3) at 

sites where ancient soils were not logged and apparently may not be preserved, an estimated maximum thickness of the latest Holocene unit of about 12 ft (this value 

generating approximately 8 cycles of strong ground motion and a 0.2-g maximum surface acceleration at the 

borehole sites in question and a nearby M 8.0 event 

generating approximately 20 cycles of strong ground 

motion and a 0.5-g maximum surface acceleration (Seed 

and others, 1983, p. 471). The three ground-water conditions considered are ground-water level at the ground 

surface, ground-water level at a depth of 10 ft, and 

ground-water level at a depth of 30 ft. These water 

levels are those postulated to exist at the time of the 

earthquake, not necessarily those obtained when the 

SPT was conducted. The water level observed during 

the penetration test is recorded on the borehole log; the 

water level at the time of the penetration test typically 

was below the level of the penetration test in most instances for the data that we obtained and have shown in 

figure 130. 

The liquefaction susceptibility calculated for each 

datum and for each ground-water condition was then 

placed into one of four categories: 

1. Results indicating that liquefaction would occur during a M 6.5 event are listed in the high susceptibility category. 

2. Results indicating that liquefaction would not occur 

during a M 6.5 event but would occur during an 

M 8 event are listed in the moderate susceptibility 

category. 

3. Results indicating that liquefaction would not occur 

even if an area were shaken by a M 8 event are 

listed in the low susceptibility category. 

is based on a maximum average cumulative thickness of 

sediment deposited during and (or) following major historical floods in 1938, 1944, and 1956, as observed by 4. 

the Los Angeles County Flood Control District); and (4) 

also at sites without apparent buried soil profiles, a 

base for the Holocene series arbitrarily inferred where 

SPT data points that lie above ground-water level for 

the postulated water condition being analyzed 

(not the water level observed at the time of the 

test) were tabulated as "above ground water" 

the penetration data indicate an abrupt increase of and are considered nonliquefiable. 

resistance sustained through several layers but not 

ascribable to a gravel layer. The thickness of the 

stratigraphic horizons inferred from the borehole logs 

broadly corresponds to and is seemingly confirmed by 

thicknesses noted at those few places in the field where 

sections of the late Pleistocene and Holocene deposits 

are exposed, such as in foundation excavations, quarries, railroad cuts, and stream incisions. 

The liquefaction susceptibility indicated by each SPT 

datum was evaluated by using the technique of Seed and 

others (1983) for the two earthquake conditions and 

three ground-water conditions depicted in figure 130. 

Soil properties assumed in the calculation are a dry unit 

weight of 100 lb/ft3 (dry density of 1.6 g/cm3), a relative 

density generally greater than 60 percent, and a mean 

grain size less than 0.15 mm (silty sediment). The two 

earthquake conditions are a nearby M 6.5 event 

272 Earthquake Hazards in the Los Angeles Region 

The results from our analysis are listed in table 42. 

In summary, the tabulation shows that liquefaction 

susceptibility is strongly a function of the age and depth 

of the sediment and the depth to ground water. For a 

ground-water level at the surface, the data indicate that 

most of the latest Holocene sand and silt is highly liquefiable, that the earlier Holocene sediment is moderately 

liquefiable, and that the Pleistocene sediment generally 

has moderate to low susceptibility. When the ground 

water is at a depth of 10 ft, only a fraction of the data 

from any unit indicates a high susceptibility, but those 

parts of the latest and earlier Holocene units that are 

below the water table generally have moderate susceptibility. For a ground-water level at 30 ft, nearly all the 

sediment in all three stratigraphic units either is above 

the postulated water level or has low susceptibility. 
0.--------------,-------------,,--------------,-------------.--------------,-------------, 

10 

~ ---

20 

tUJ 

UJ 

u.. 

~ 

r.' 

ta.. 

UJ 

Cl 

30 

40 

50 

0 10 20 30 40 50 60 

UNCORRECTED STANDARD PENETRATION RESISTANCE, IN BLOWS PER FOOT 

FIGURE 130.-Criteria used for estimating liquefaction susceptibility in the Los Angeles region, calculated by using the procedure developed by 

Seed and others (1983). Assumptions used in making the calculation include peak horizontal accelerations of 0.2 and 0.5 g for the M 6.5 and 

M 8.0 earthquakes, respectively; a uniform dry unit weight of the sediment of 100 lb/ft3 ; silty sediment (mean grain size less than 0.15 mm); a 

relative density generally greater than 60 percent; and values of w (depth to free ground water) as indicated. 

Depth to Ground Water 

The final factor considered in regional mapping of liquefaction susceptibility is the depth to ground water, including water that is perched. Perched ground water 

refers to unconfined ground water separated from an 

underlying main body of ground water by an unsaturated zone (Bates and Jackson, 1980). Liquefaction 

susceptibility generally decreases as the depth to water 

increases, for two reasons. First, the greater the depth 

to ground water, the greater the normal effective stress 

acting on saturated sediment at any specified depth. Increasing the normal effective stress decreases susceptibility to liquefaction. Second, age, cementation, infilling of intergranular voids, alteration, and compactness 

of sediment generally increase with depth. Each of these 

Evaluating Liquefaction Potential 273 
TABLE 42.-Evaluation of liquefaction susceptibility (in percent) in cohesionless nongravelly sediment from standard penetration data taken in the 

upper 16 m of late Quaternary sediment in the Los Angeles area for three hypothetical positions of the water table using criteria developed by Seed 

(1983) 

[The total number of test results for each stratigraphic unit is found in the far right column. In the San Fernando Valley, for example, 76 percent of 153 penehation tests obtained in latest Holocene 

sediment indicate high susceptibility if the water level were at the ground's surface] 

Total, 

Water level at surface Water level at 10 ft Water level at 30 ft Standard 

Above Above Above PenetraAge High Moderate Low water High Moderate Low water High Moderate Low water tion Tests 

San Fernando Valley 

Latest Holocene --- 76 23 1 0 7 39 4 50 0 0 0 100 153 

Earlier Holocene --- 54 43 3 0 5 57 14 24 0 8 2 90 588 

Late Pleistocene --- 17 46 37 0 2 40 55 3 0 15 35 50 413 

San Gabriel Valley 

Latest Holocene --- 81 19 0 0 1 25 3 71 0 0 0 100 75 

Earlier Holocene--- 38 56 6 0 3 57 19 21 0 12 12 76 473 

Late Pleistocene --- 7 42 51 0 0 22 57 21 0 5 22 73 26 

Coastal basin, Los Angeles County 

Latest Holocene --- 81 19 0 0 0 

Earlier Holocene --- 34 48 19 0 3 

Late Pleistocene --- 6 39 55 0 0 

factors increases resistance to liquefaction. Thus, as the 

depth to ground water increases, the saturated sediments tend to be older and more compact and to have increased density and normal stress; consequently, the 

liquefaction susceptibility decreases (Y oud and others, 

1978). 

The following criteria are applicable to liquefaction 

susceptibility with respect to depth to ground water. For 

ground-water depths less than 10 ft, maximum possible 

susceptibility is very high. For water depths between 10 

and 30 ft, maximum possible susceptibility is high. For 

water depths between 30 and 50 ft, maximum possible 

susceptibility is low. For water depths greater than 

50 ft, maximum possible susceptibility is very low. These 

criteria, summarized in table 43, are based on those suggested by Youd and Perkins (1978) and used by Youd 

and others (1978); they are confirmed by the data compiled in table 42. 

Maps showing depth to ground water, including 

perched ground water, were compiled for each alluvial 

basin considered in this report. Unless otherwise 

specified, the lines shown on these depth-to-groundwater maps are not necessarily equipotential lines in 

the conventional usage of hydrologists. For example, 

hydrologists commonly describe a ground-water basin in 

two dimensions by using equipotential lines (lines connecting points having equal potential within the flowage 

system). Thus, the direction of flow is normal to the 

equipotential lines and is from areas of relatively higher 

274 Earthquake Hazards in the Los Angeles Region 

21 1 78 0 0 0 100 250 

49 30 18 0 16 16 68 1,131 

20 71 9 0 4 20 76 950 

potential toward areas of relatively lower potential, 

such as a basin outlet or a pumping well. The data in our 

study are not sufficient to show patterns of movement, 

recharge, or depletion, especially where the depth to 

water is identified from a single observation in a given 

boring. Our lines may be equipotential in some areas, 

but we commonly cannot determine if they are from our 

data; hence, our lines simply enclose or indicate areas 

within a stratigraphic unit where our data show that 

either perched or unconfined ground water has been 

found within the specified depth intervals. Where 

depths to water are not tightly constrained, lines are 

dashed; where depths are speculative or constrained by 

factors other than borehole data or water levels measured in wells, lines are dashed and queried. 

The ground-water data are from Federal, State, 

county, and city governmental agencies, private consultants, water purveyors, and private individuals; unless 

anonymity was requested, the sources are acknowledged. The data are not uniformly distributed, and, in 

areas where control is sparse, constructing the maps required considerable generalization, extrapolation, and 

interpretation. 

The reliability of these types of maps varies considerably across the Los Angeles region. Sources of 

uncertainty are described briefly, so that users may 

better comprehend the limitations of liquefaction susceptibility maps. 
The principal difficulty encountered in mapping 

shallow occurrences of ground water is that the network of observation wells used to chart the recharge 

storage and extraction of water is not designed to 

monitor shallow ground water in most areas. Monitoring 

of the deeper aquifers is emphasized to safeguard 

potable water supplies (California Department of Water 

Resources, 1961). Because shallow and (or) perched 

water-bearing layers tend to be irregularly distributed 

and often contain water of dubious or unreliable quality, 

these layers are not usually monitored and have 

recharge characteristics and transmissivities that are 

poorly known. In contrast, the water-monitoring network is excellent where it was developed for a specific 

purpose. For example, the Coastal Barrier and Replenishment Projects (systems of water-injection and observation wells administered by Los Angeles County) 

achieved their objective of safeguarding and even improving w~ter quality in parts of the county otherwise 

threatened by saltwater intrusion. The system of key 

and observation wells used within interior basins to 

monitor recharge of ground water from spreading 

grounds and injection wells is designed in part to 

monitor water levels, including those in shallow 

aquifers, but coverage is localized near spreading 

grounds and was never intended to be geographically 

comprehensive in its scope or to include perched-water 

occurrences. Thus, the hydrology of the shallowest 

undeveloped aquifers is poorly known, and the degree to 

which those ground-water occurrences contribute to the 

liquefaction susceptibility is poorly understood. 

Borings that penetrate to ground water are sparse in 

many areas. We have some coverage over many areas 

from borings for storm-drain construction, but these 

borings often are shallow (seldom more than 30ft deep). 

Thus, such data tend to imply the absence of ground 

water at very shallow depths, on the date and at the 

time specified for these studies, rather than to define the 

depth at which water is found. 

Ground water is commonly encountered during civil 

engineering studies, but water levels usually are not 

monitored for more than several hours. In the absence 

of routine ground-water observations, only by examining 

records of holes drilled in proximity to one another over 

a period of years can one obtain any assurance that 

water may persist from year to year, although the hydrology remains speculative. 

Water levels in some deep wells may have been 

higher than the phreatic surface in the surrounding surficial strata, owing to artesian pressures at depth. To 

reduce this source of uncertainty, we -have obtained 

well-casing perforation information for wells monitored 

by the California Department of Water Resources and 

the Los Angeles County Flood Control District and relied 

on wells perforated at appropriate intervals to aid in 

our interpretations. Knowing the depths at which well 

casings are perforated enables the analyst to exclude 

wells that tap more than one water-bearing layer or that 

do not tap only the shallow ground water. Perforation 

data indicate that relatively few wells unambiguously 

monitor shallow zones of ground water. 

Some water-depth measurements, especially along 

freeways or for certain large buildings or storm drains, 

were made two or three decades ago, and water levels 

may have changed in the interim. We retain high confidence in these data if additional, more recent 

geotechnical studies also show ground water to have 

been present or if there are monitored wells nearby 

showing reliable depth-to-water measurements. If subsequent confirmation of depth to water is lacking, map 

lines enclosing the occurrences of water are dashed and 

queried. 

Seasonal fluctuations in water levels affect our interpretations. If there is no adequate monitoring network, 

the only effective recourse is the historical record. 

Ground-water data from the middle 1940's may be the 

best approximation of what high ground-water conditions would probably be. The 1944-45 water year 

followed several relatively wet winters, before pumpage 

from ground-water basins reached the volumes occasioned by urbanization following World War II. To address this uncertainty, two sets of ground-water maps 

are presented for each of three basins in Los Angeles 

County. The first set shows shallow ground-water conditions based on records from 1945 or earlier; the second 

set shows conditions based on water depths reported 

chiefly from 1960 to 1978. The first set may be appropriate for evaluating liquefaction susceptibility 

seasonally or during wet years. During years when 

available moisture and ground-water recharge are 

average, the liquefaction susceptibility will be less widely distributed than it will during wet years. 

Since 1945, development of the ground-water basins 

has intensified; today, depending on pumping practices, 

water levels are generally lower than 1944-45 levels, 

although basins are carefully monitored and managed to 

reduce the likelihood of contamination and depletion. 

Development of the ground-water resource in southern 

California has been the single most effective step in 

reducing or eliminating the liquefaction hazard in many 

areas, because extractive pumping of ground water has 

lowered the water table in many areas to depths that 

make liquefaction unlikely. An exception may be an 

area in and near San Bernardino, east of the San Jacinto 

fault, where development of the ground-water resource 

has included recharge of the ground-water reservoir by 

using water brought from northern California through 

the California Aqueduct. 

Evaluating Liquefaction Potential 275 
TABLE 43.-Probable susceptibility of cohesionless. granular, nongravelly layers as criteria used to compile liquefaction susceptibility map 

Depth to ground water, in feet 

Sedimentary unit 0 to 10 10 to 30 30 to 50 50+ 

Holocene: 

Latest ------------------------------------Very high to high' Moderate' Low Very low 

Earlier ----------------------------------- High Moderate Low Very low 

Pleistocene: 

Late ------------------------------------- Low Low Very low Very low 

Middle and early ---------------------------Very low 

Tertiary and pre-Tertiary ------------------------ Very low 

Very low 

Very low 

Very low Very low 

Very low Very low 

1 Areas are mapped as having very high susceptibility if fluvial channel and levee deposits are known to be present; sediment deposited in other sedimentary 

environments is considered to have high susceptibility. 2Fluvial deposits having high susceptibility occur rarely and are not widely distributed; other sediments are moderately susceptible to liquefaction. 

As future water-management policies and practices 

evolve, the effect of a series of years in which precipitation is greater than normal may become marked. The 

city of Beverly Hills, for example, went out of the waterpumping business during the late 1970's and is now supplied by the Metropolitan Water District of Southern 

California. The city abandoned and destroyed its wells. 

The wetter-than-normal winters from 1978 to 1983 have 

caused ground-water recharge to parts of basins that 

are no longer so intensively pumped. As these basins 

recharge, ground-water levels may approach predevelopment levels, and areas that used to be mapped as 

swamps are likely to return to their formerly saturated 

state. Dewatering practices may be increasingly required over wider areas to protect property, especially 

in areas formerly identified as artesian and as swamps 

(cienegas) by Mendenhall (1905a, b). In general, as the 

depth to ground water decreases, the susceptibility to 

liquefaction increases. 

Errors may have been made in measuring or reporting 

the depth to ground water in some boreholes. To partially redress this source of uncertainty, we have arbitrarily eliminated from consideration those values that 

seemed to us to be truly aberrent or that could not be 

confirmed by nearby wells. 

Compilation of Liquefaction 

Susceptibility Maps 

The criteria delineated above and summarized in 

table 43 were used to compile the susceptibility maps 

presented in subsequent sections of this report. The surficial geologic map and the ground-water maps were 

superimposed to derive the susceptibility map. As 

climatic conditions or basin-management practices 

change, ground-water levels are likely to change, and 

276 Earthquake Hazards in the Los Angeles Region 

liquefaction susceptibility is likely to increase during 

wet cycles and decrease during dry cycles. These 

changes reflect a probable greater areal extent of 

shallow ground water or ground water persisting at 

shallower depth during a relatively wet cycle as opposed to a relatively dry cycle. 

LIQUEFACTION SUSCEPTIBILITY 

IN THE LOS ANGELES REGION 

For each of six areas, we now discuss the surficial 

geologic map, one or two ground-water maps, and the 

corresponding liquefaction susceptibility maps derived 

according to the methods presented in the preceding 

sections. The sources of the geologic, hydrologic, and 

geochronologic data are given, unless anonymity was requested by those persons or firms supplying the data. 

The six study areas are best grouped into two subsets 

corresponding to the relative amounts of effort expended in our analysis of the liquefaction problem. The 

data bases are not at all comparable in scope; major efforts in this study are focused on Los Angeles County 

and its principal basins (the San Fernando Valley, the 

San Gabriel Valley, and the Los Angeles basin proper). 

Reconnaissance maps of liquefaction susceptibility have 

also been compiled for the Oxnard Plain, the upper Santa Ana River basin, and the flatland area of Orange 

County by using the relative age and depth-to-groundwater criteria shown in table 42 to interpret existing 

maps showing surficial deposits and average groundwater conditions. Of the data bases assembled for these 

last three areas, the one for Orange County is the most 

comprehensive, having been put together by the California Division of Mines and Geology specifically for 

evaluating earthquake hazards, including liquefaction. 

The liquefaction potential of the upper Santa Ana River 

basin area currently is being mapped by S. A. Carson 
and J. C. Matti (U.S. Geological Survey). Their analysis 

will be based on improved mapping of surficial deposits, 

drilling and standard penetration studies of selected 

localities, and improved knowledge of the near-surface 

occurrences of ground water, in comparison with the 

reconnaissance-style mapping incorporated in this 

analysis. The liquefaction maps presented in this report 

showing the Oxnard Plain rely heavily on hydrologic 

mapping as published by the California Division of 

Mines and Geology. The criteria in table 42 were used to 

derive the liquefaction susceptibility maps; a few 

modifications were made on the basis of more recent but 

unpublished mapping in parts of the area near Ventura 

by A. M. Sarna-Wojcicki (U.S. Geological Survey). 

We now describe the surficial geologic maps, the 

ground-water maps, and the derivative liquefaction 

susceptibility maps of the San Fernando Valley, the San 

Gabriel Valley, the Los Angeles basin area of Los 

Angeles County, the flatland area of Orange County, the 

upper Santa Ana River basin area of Riverside and San 

Bernardino Counties, and the Oxnard Plain area of 

Ventura County. 

San Fernando Valley 

Surficial Geology 

The San Fernando Valley is located within the 

Transverse Ranges province and is bounded on the 

north and east by the San Gabriel and Verdugo Mountains, on the south by the Santa Monica Mountains, and 

on the west and northwest by the Simi Hills and the 

Santa Susana Mountains (fig. 129). The entire basin is 

drained by the Los Angeles River and its tributary drainages. The alluvium deposited by these streams chiefly 

reflects the types of rock exposed along the basin's 

perimeter, and these broad lithologic characteristics 

strongly influence the nature and distribution of 

deposits susceptible to liquefaction (table 42). The 

generalized surficial geology of the San Fernando Valley 

is shown in figure 131. The alluvial deposits and the 

ground-water-bearing characteristics of the alluvium in 

the San Fernando Valley have been analyzed comprehensively by the California Water Rights Board 

Referee (1962), and we use those data where they are 

applicable. 

Alluvial deposits in the eastern half of the San 

Fernando Valley are composed chiefly of cobbles, 

gravel, and sand; silt and clay often are relatively minor 

components. This alluvium was deposited chiefly by 

Pacoima Wash and Tujunga Wash, which drain mostly 

granitic and metamorphic rocks of the western San 

Gabriel Mountains. The sandy, highly permeable character of the deposits enables large volumes of ground 

water to percolate to depths exceeding 50 ft subsurface. 

Alluvium in the western half of the San Fernando 

Valley was deposited by small streams draining areas 

underlain by chiefly fine-grained Tertiary and preTertiary sedimentary rocks (the Simi Hills, the Santa 

Monica Mountains, and the Santa Susana Mountains). 

In contrast to the coarse-textured alluvial deposits of 

the eastern half, these flood-plain deposits contain a 

large proportion of fine-grained clayey alluvium. Vertical permeability is correspondingly reduced, perched 

water occurs commonly in sandy channel deposits, and 

the regional water table locally is relatively close to the 

ground surface. Exposures in foundation excavations indicate that sand, gravel, and silty sand occur chiefly as 

buried stream channels that traverse the subsurface 

from the surrounding uplands toward the Los Angeles 

River. It is these cohesionless, granular channel deposits 

that may be susceptible to liquefaction. Their distribution within the area is not known in detail, however. It 

may be possible to locate and map these channels by 

means of special-wavelength radar or seismic reflection 

techniques; the present data do not permit these 

deposits to be delineated. 

Ground Water 

The regional distribution of ground water for the year 

1944 is shown in figure 132 by contour lines (equipotential lines) drawn on the surface of the water table. 

Ground water flows normal to equipotential lines; thus, 

figure 132 indicates that the ground water generally 

flows along a gradient that is parallel or subparallel to 

the topography of the ground surface and is toward and 

along the Los Angeles River. The 1944 water year was 

characterized by high annual precipitation, as were the 

years 1943 and 1941. Consequently, the ground-water 

levels were high, and areas of near-surface ground 

water were especially, extensive in the 1944 water year. 

The 1944 water levels are the best documented, highest 

water levels for the San Fernando Valley on record 

(California Water Rights Board, 1962). 

A depth-to-ground-water map based on the data in 

figure 132 was superimposed on the surficial geologic 

map (fig. 131), and these two maps were then used to 

construct the "high-water-level" liquefaction susceptibility map shown in figure 133. Areas having depths to 

water of less than 10 ft were extensive in 1944 and include a corridor along the Los Angeles River, areas 

along tributary drainages, and areas near flood-control 

basins. 

Many of these areas were flooded historically (King 

and others, 1981), and the resultant deposits preEvaluating Liquefaction Potential 277 
2 3 5 KILOMETUS 

I I '• I 

1 2 3 MM.!S 

EXPLANATION a Late Holocene alluvium; gravel, sand, silt, and clay; 

unconsolidated, uncemented; herein restricted to 

areas that tlooded historically, including tidal marshes. Thickness 0 to 3 m. Age less than 1,000 yr. 

~ Undifferentiated Holocene alluvium; gravel, sand, silt, 

and clay; uncemented, unconsolidated. Thickness 0 

to 30m. Age 1,000 to 10,000 yr. Locally may include 

thin deposits of late Holocene alluvium 

8 Undifferentiated late Pleistocene aUuvtum; gravel, sand, 

silt, and clay; moderately to well consolidated; often 

slightly cemented; locally well cemented 

G Undifferentiated pre-Quaternary lithifled sedimentary 

rocks 

G Undifferentiated pre-Quaternary volcanic rocks 

G Mesozoic and older crystalline basement terranes ofthe 

San Gabriel, Verdugo, and Santa Monica Mountains 

areas 

0 Artificial fill 

FIGURE 131.-Generalized surficial geology of the San Fernando Valley. 

sumably include some of the youngest sediment in the 

basin. Where cohesionless granular materials are present as stream-channel and levee deposits, the sediments 

are interpreted to have a very high to high susceptibility 

to liquefaction. Areas having moderate susceptibility 

commonly occur adjacent to areas of very high to high 

susceptibility, chiefly along the Los Angeles River and 

its tributaries and in the Van Norman Reservoirs area 

west of San Fernando (fig. 129). 

Figure 134 illustrates depth to ground water, including perched ground water, in the San Fernando 

Valley compiled from several thousand exploratory 

boreholes that were drilled for engineering purposes 

278 Earthquake Hazards in the Los Angeles Region 

from 1950 to 1981. Few of these localities are used to 

monitor ground water, and the measured depths to 

ground water are subject to many of the uncertainties 

discussed in a preceding section of this chapter. Nevertheless, these data are distributed over about three 

decades and tend to confirm the occurrence of shallow 

ground water in areas along the Los Angeles River, near 

reservoirs, recharge facilities, and flood-control basins. 

In comparison with 1944 data, the major areas of 

shallow ground water are reduced in geographic extent, 

a reflection of the increased volume of water extracted 

from wells in the southeastern portion of the valley 

along the Los Angeles River. 
1 2 3 5 KILOMETERS' 

1 I' 1 11 

3 MILES 

EXPLANATION 

Boundary of valley 1111 

--500 ---- Une of equal ground water elevation; 

dashed where Inferred &om spal'lN! data 

Impediments to ground water flow 

Ground water cascades 

--?--?--

r-:::::1 

l2J 

Questionable Impediment or ground water 

cascade 

Areas of less than 10 feet depth to ground 

water as of 1944 

FIGURE 132.-1944 high ground-water conditions in the San Fernando Valley (modified from California Water Rights Board, 1962). 

Liquefaction Susceptibility 

A "low-water-level" liquefaction susceptibility map of 

the San Fernando Valley area derived from figures 131 

and 134 is shown in figure 135. Comparing figures 133 

and 135 shows that, since 1944, the increased depth to 

ground water has resulted in an apparent decrease of 

susceptibility, chiefly along the Los Angeles River. 

Areas of very high liquefaction susceptibility may exist 

where cohesionless, water-'saturated, granular sediment occurs chiefly as present and former streamchannel deposits in the Reseda-Canoga Park area, as 

figure 135 notes. Field observations, borehole logs, and 

the relatively fine grained nature of the source rocks 

suggest that linearly distributed stream-channel 

deposits, although of limited areal extent, are likely to 

be the most susceptible deposits in the Reseda-Canoga 

Park area. 

Evaluating Liquefaction Potential 279 
0 1 2 3 4 5 KILOMETERS 

1---j --'-I 'I L..l -'r' I -1'--r'l' 0 1 2 JMILES 

EXPU.NATION 

Very high 

High 

Moderate 

low 

Very low 

Bedrock areas 

FIGURE 133.-Relative liquefaction susceptibility in the San Fernando Valley based on 1944 ground-water data (compare with fig. 135). Relative 

susceptibility to liquefaction-related ground failure is interpreted as a function of the age of the saturated materials and the depth to ground 

water. VH designates areas likely to contain very young, relatively well sorted stream-channel and levee deposits where the depth to ground 

water is less than 10ft. 

San Gabriel Valley 

Surficial Geology 

The generalized surficial geology of the San Gabriel 

Valley is shown in figure 136. The San Gabriel Valley is 

located north and east of the Los Angeles Civic Center 

and is bounded on the north by the San Gabriel Mountains, on the east by the San Jose Hills, on the south by 

the Puente Hills, and on the west and southwest by the 

Verdugo Mountains and the Repetto Hills {fig. 129). Principal surface streams draining the basin include the 

Arroyo Seco along the western margin; the Rio Hondo 

and the San Gabriel River drain through the Whittier 

Narrows to the Los Angeles River. All other drainages 

are tributary to these principal drainages. 

280 Earthquake Hazards in the Los Angeles Region 

The alluvial deposits of the San Gabriel Valley consist 

chiefly of boulders, gravel, and sand derived from the 

San Gabriel Mountains. Fine-grained alluvium, often 

containing appreciable clay, is derived from the San 

Jose Hills, the Puente Hills, and the Repetto Hills and 

volumetrically dominates the sediment deposited along 

the southern margin of the basin. The channel and leveP 

deposits of present and former streams draining valleys 

underlain by Tertiary sedimentary rock, however, are 

likely to contain cohesionless, granular sediment susceptible to liquefaction. 

Ground water 

Two principal ground-water basins characterize the 

San Gabriel Valley: the Raymond basin and the San 
118'30' 118'15' 

1 2 3 5 KilOMETERS 

' ,' '• r' 1 2 3 MilES 

FIGURE 134.-Depths to near-surface ground water in the San Fernando Valley compiled from post-1944 water level data and data from engineering boreholes, chiefly from 1960 through 1975. Isobaths are in feet. 

Gabriel basin. These basins were recognized initially by 

Mendenhall (1908], who noted that they were separated 

by a prominent ground-water barrier subsequently 

recognized and named the Raymond fault by Eckis 

(1934]. Buwalda (1940] reported on the geology of the 

Raymond basin for the Pasadena Water Department. 

In the Raymond basin, ground water flows from north 

to south (Buwalda, 1940]. Before the extensive pumping 

that has lowered the water table in most areas along 

either side of the Raymond fault, ground water was 

forced to the surface along the fault zone, and numerous 

swamps, springs, and small perennial lakes indicated 

that shallow ground water was present (Mendenhall, 

1908]. Today, high ground water occurs seasonally and 

only in restricted areas along the Raymond fault zone 

(Crook and others, 1979]. Elsewhere in the Raymond 

basin, seasonal occurrences of shallow ground water 

are associated with flood-control basins and groundwater recharge operations. 

In the San Gabriel basin, ground water generally 

flows southwesterly, parallel to the topographic gradient from principal drainages of the San Gabriel Mountains and other hillslope areas toward and through the 

Whittier Narrows, as the contours drawn on the groundwater table for the year 1944 show (fig. 137] (California 

Department of Water Resources, 1966,'fig. 19]. 

The surficial geologic map (fig. 136] and a depth-toground-water map based on 1944 ground-water data 

(fig. 137] were superimposed to derive a liquefaction 

susceptibility map (fig. 138]. Areas of shallow ground 

water Oess than 10 ft to water] occur chiefly within and 

around the area now designated as the Whittier Narrows Flood Control Basin, where the liquefaction susceptibility is designated high to very high. This area is 

surrounded by an area of moderate susceptibility, 

where the water table is somewhat deeper (1G-30 ft subsurface) and older Holocene deposits are saturated. 

This area of moderate susceptibility extends up Walnut 

Creek between the San Jose Hills and the Puente Hills. 

Figure 139 illustrates the depth to shallow ground 

water, including perched ground water, compiled from 

several hundred exploratory borings and from several 

dozen water wells monitored by the State of California. 

Geologic structures known or presumed to influence the 

movement of ground water at shallow depths Oess than 

50 ft) include the Raymond fault and elements of the 

Evaluating Liquefaction Potential 2lrl 
EXPLANATION 

Very high 

High 

Moderate 

low 

Very low 

Bedrock areas 

FIGURE 135.-Relative liquefaction susceptibility in the San Fernando Valley based on the ground-water data shown in figure 134. Comparison 

with figure 133 shows that areas designated as having high and moderate susceptibility are much smaller. 

Sierra Madre fault along the southern margin of the San 

Gabriel Mountains; areas of shallow ground water from 

this study are shown where they are associated with 

those structures. 

Liquefaction Susceptibility 

Comparision of ground-water data from 1944 and 

from the post-1944 (chiefly 1965-75) period indicates 

that the areal extent of shallow ground water has been 

sharply reduced. This reduction is presumed to stem 

chiefly from the development of ground-water resources. A "low-water-level" liquefaction susceptibility 

map prepared from the data in figure 139 is shown in 

figure 140. The Whittier Narrows Flood Control Basin is 

classified as chiefly within the moderate susceptibility 

designation, reflecting a depth to ground water in the 

range of 10 to 30 ft subsurface. 

282 Earthquake Hazards in the los Angeles Region 

The extent of areas having high and moderate susceptibility to liquefaction is very sensitive to changes in the 

depth to ground water. Most of the San Gabriel Valley is 

at low or very low levels of risk from liquefaction, 

because the ground water is more than 30 ft subsurface; 

in many noncoastal basin areas, deposits at depths of 

30 ft or more are often Pleistocene in age, especially in 

the Raymond basin area. 

Los Angeles County Area of the 

Los Angeles Basin 

The Los Angeles basin is bounded on the north by the 

Santa Monica Mountains, on the west by the Pacific 

Ocean, on the south and southeast by the San Joaquin 

Hills and Santa Ana Mountains, and on the east by the 

Puente Hills and Chino Hills (fig. 129). The part of the 
118'00' 

2 3 4 5 KILOMETERS 

1

1 1

1 1

1 

1 2 3 MILES 

EXPLANATION 

~ Late Holocene alluvium; gravel, sand, silt, and clay; 

unconsolidated, uncemented; herein restricted to 

areas that flooded historically, including tidal marshes. Thickness 0 to 3m. Age less than 1,000 yr. 

~ Undifferentiated Holocene alluvium; gravel, sand, silt, 

and clay; uncemented, unconsolidated. Thickness 0 

to 30m. Age 1,000 to 10,000 yr. Locally may include 

thin deposits of late Holocene alluvium 

EJ Undifferentiated late Pleistocene aUuvium; gravel, sand, 

silt, and clay; moderately to well consolidated; often 

slightly cemented; locally well cemented 

B Undifferentiated early and middle Pleistocene deposits 

of gravel, sand, silt, and clay; locally well cemented 

G Undifferentiated pre-Quaternary lithified sedimentary 

rocks; Ts + Tv where co-mingled 

G Undifferentiated pre-Quaternary volcanic rocks 

G Mesozoic and older rocks of the San Gabriel, Verdugo, 

and Santa Monica Mountains areas 

0 Artificial fill 

FIGURE 136.-Generalized surficial geology in the San Gabriel Valley. 

Los Angeles basin situated in Orange County is discussed separately in a later section. 

Yerkes and others (1965) have described the structural and stratigraphic framework of the Los Angeles 

basin. The subsurface configuration of the Quaternary 

deposits is known chiefly from studies of the basinal 

hydrology. Mendenhall (1905a, b) first described the 

general occurrence of ground water and delineated the 

principal ground-water barriers, including the NewportInglewood fault zone. Subsequent regional hydrologic 

studies to determine safe yields from the various waterbearing zones and to safeguard the coastal aquifers 

Evaluating Liquefaction Potential 283 
1 2 3 4 5 KILOMETERS 

I I I 

1 1 

1 3 MILES 

EXPLANATION 

Boundary of valley fill 

--600--- Lines of equal elevation of ground water In 

wells 

---?- Faults affecting water-bearing materials. 

Dashed where Inferred; queried where location uncertain 

FIGURE 137.-1944 high ground-water conditions in the San Gabriel Valley (modified from California Department of Water Resources, 1966, 

fig. 19}. 

from saltwater intrusion include the works of Eckis 

(1934), Poland and others (1956, 1959), Poland (1959), 

Zielbauer and others (1961, 1962), and the California 

Department of Water Resources (1961, 1962). 

284 Earthquake Hazards in the Los Angeles Region 

Surficial Deposits 

The generalized surficial deposits of the Los Angeles 

area are shown in figure 141. The distribution of the 
EXPLANATION 

Very high 

High 

Moderate 

low 

Very low 

Be.lrock areas 

2 3 

I I 

I I 1 2 

118'00' 

5 KILOMETERS 

i' 

3 MILES 

FIGURE 138.-Relative liquefaction susceptibility in the San Gabriel Valley based on 1944 high ground-water conditions (compare with fig. 140}. 

Relative susceptibility to liquefaction-related ground failure is interpreted as a function of the age of the saturated materials and the depth to 

ground water. VH designates areas likely to contain very young, relatively well sorted stream-channel and levee deposits where the depth to 

ground water is less than 10ft. 

stratigraphic units as mapped reflects the continuing 

tectonic deformation of the area (Yerkes and others, 

1965; Yerkes, 1972), the distribution of the first- and 

second-order sources of sediment, and areas of 

historical flooding (Los Angeles County Flood Control 

District, unpublished maps and field notes, 1938-1956; 

Troxell, 1942). The youngest sediment occurs in the 

modern flood-plain areas of the Los Angeles, San 

Gabriel, Rio Hondo, and Santa Ana Rivers, which have 

caused multiple known episodes of inundation during at 

least the past 150 yr. 

These principal drainages flow west to the Pacific 

Ocean, across the uplifting area of Pleistocene deposits 

that crop out along the Newport-Inglewood zone of 

deformation. Early Holocene deposits crop out chiefly 

along the flood-plain margins, on the flanks of uplifting 

folds along the basin margins of the structural basin. 

Late Pleistocene deposits, locally including the early 

Pleistocene San Pedro Formation, are exposed in the 

broad northwest-trending outcrop shown along the 

western third of figure 141. The eastern half of the area 

of Pleistocene deposits lies along the Newport-Inglewood 

zone of folds and faults. The western half is comprised 

chiefly of Pleistocene and Holocene eolian sand, which 

overlies older Pleistocene marine and nonmarine strata. 

A small area of Holocene deposits containing sediment 

reworked from adjacent uplands along the NewportInglewood zone drains south and then west through 

Dominguez Gap. Tertiary and pre-Tertiary sedimentary 

rocks and Mesozoic and older plutonic and metamorphic 

Evaluating Liquefaction Potential 285 
FIGURE 139.-Depths to near-surface ground water in the San Gabriel Valley compiled from post-1944 water data, including data from engineering boreholes, chiefly for 1960 through 1975. !so baths are in feet. 

rocks frame the alluviated parts of the Los Angeles 

basin. 

Ground Water 

The distribution of near-surface ground water 

apparently has changed markedly because of the development and management of ground-water resources 

since 1905. The geologic framework is important to 

understanding evolving hydrologic conditions in the Los 

Angeles basin area, as figure 142 illustrates. The latest 

Tertiary and Quaternary deposits that fill the Los 

Angeles basin comprise an alternating sequence of relatively permeable and relatively less permable strata or 

zones. The relatively permeable zones are composed 

chiefly of gravel and sand; these aquifers yield copious 

286 Earthquake Hazards in the Los Angeles Region 

volumes of water to wells. The aquifers are separated 

by zones or layers of sediment (called aquicludes) that 

are relatively less permeable because they contain a 

relatively high proportion of silt and clay. The more clay 

rich the sediment, the less readily it yields water to 

wells. In some parts of the Los Angeles basin, the 

aquicludes are quite impermeable, and little, if any, 

water passes through them. In nearby areas, however, 

the aquicludes are quite "leaky," and ground water can 

pass upward or downward from one aquifer to another 

through confining aquicludes, if pressure gradients are 

favorable. A comprehensive description of the deeper, 

principal aquifers and aquicludes has been given by the 

California Department of Water Resources {1961); the 

hydrologic sections in that report characterize the 

hydrology of the area also shown in figure 141. Figure 

142, compiled chiefly from Mendenhall (1905a, b) and 
EXPLANATION 

High 

Moderate 

low 

Very low 

Bedrock areas 

2 3 

I 

1 1

1 

I 2 

118'00' 

5 KILOMETERS 

i' 

3 MILES 

117'45' 

FIGURE 140.-Relative liquefaction susceptibility in the San Gabriel Valley based on the ground-water isobaths presented in figure 139. Areas 

designated as high and moderate susceptibility are smaller relative to those based on the 1944 ground-water levels and are confined chiefly to 

the flood-control basins and ground-water recharge facilities near the Whittier Narrows. 

Conkling (1927), shows the decreasing extent of confined 

or "artesian" ground water in the deposits along the Los 

Angeles and San Gabriel Rivers before 1905, in 1905, 

and in 1928. The stippled areas contained water within 

8 ft of the surface as recently as 1935 (Los Angeles 

County Flood Control District, unpublished map, scale 

1:62,500). The depths to water measured in numerous 

shallow wells and tabulated by Mendenhall (1905a, b) 

indicate that shallow ground water was common within 

the artesian area shown by the solid line in figure 141. 

Because the near-surface aquicludes in this formerly 

artesian area are known to be somewhat "leaky" 

(California Department of Water Resources, 1961), we 

infer that, before the ground-water reservoir was 

pumped, many of these areas of shallow water could 

have been recharged from below by upward seepage 

through permeable zones in the aquicludes. 

Figure 143 is a "high-water-level" liquefaction 

susceptibility map derived by assuming that the depth to 

ground water was approximately as described by 

Mendenhall's (1905a, b) hydrographic contours. Floodplain areas containing latest Holocene deposits of cohesionless, granular sediments are assigned a very high 

susceptibility; the susceptibility is reduced as the sediment becomes older or as the depth to ground water increases (table 43). 

In figure 144, dashed lines are isobaths (lines that 

enclose areas found to contain ground water within the 

indicated limits of depth). These occurrences of ground 

water are based on relatively recent (195G-80) records 

Evaluating Liquefaction Potential 287 
118'15' 

34'00' 

33'45' 

3 5 KILOMETERS 

f-.._,J__,'r--'---r, I 

~ 3 MILES 

EXPLANATION 

~ Late Holocene alluvium; gravel, sand, silt, and clay; 

unconsolidated, uncemented; herein restricted to 

areas that flooded historically, Including tidal marshes. Thickness 0 to 3 m. Age less than 1,000 yr. 

~ Undifferentiated Holocene alluvium; gravel, sand, silt, 

and clay; uncemented, unconsolidated. Thickness 0 

to 30m. Age 1,000 to 10,000 yr. Locally includes deposits of late Holocene alluvium and eolian sand 

8 Undifferentiated late Pleistocene aUuvium; gravel, sand, 

silt, and clay; moderately to well consolidated; often 

slightly cemented; locally well cemented 

B Undifferentiated early and middle Pleistocene deposits 

of gravel, sand, silt, and clay; locally well cemented 

0 Undifferentiated pre-Quaternary lithlfled sedimentary 

rocks 

G Mesozoic and older rocks of the San Gabriel, Verdugo, 

and Santa Monica Mountains areas 

0 Artificial fill 

FIGURE 141.-Generalized surficial geology of the Los Angeles County portion of the Los Angeles basin. 

of water wells and of exploratory boreholes drilled for 

engineering studies. Comparing figure 143 with figure 

145 indicates that the extensive area of shallow ground 

288 Earthquake Hazards in the los Angeles Region 

water noted in the Los Angeles River area in 1905 had 

been reduced markedly following development of the 

ground-water resource. 
3<'00' 

33'45' 

/ 

'/, 

~~ :c" ·• •, ...... , .. ,,., ···.<fr 

0 · 1 2 3 4 5 kiLOMETERS 

3 MILES ',l flf\E'r 

~i:'<> ·i~ 'V:I tl•)' 

FIGURE 142.-Areas of artesian ground-water conditions have decreased as ground-water resources have been developed. The maximum 

pre-1905 extent of the artesian area is shown by a short dashed line; the limit of the artesian area in 1904 is shown by a solid line (Mendenhall, 

1905a, b); the limit of the artesian area in 1926 is shown by a heavy dashed line; areas containing shallow ground water 8ft or less below the 

ground surface as of October 1926 are shown by stippling (Conkling, 1927, pL 13). 

In the "low-water-level" map (fig. 145), areas having 

high, very high, or moderate susceptibility to liquefaction (if cohesionless, granular materials are present) 

occur in only a few localities and are restricted to areas 

near the mouth of a drainage such as Ballona Creek and 

in harbor areas of Los Angeles, near Long Beach and 

Los Alamitos (Randell, 1983). Apparently, the development of the ground-water resource has had an important beneficial effect on reducing the number and extent 

of areas where liquefaction can occur in the Los 

Angeles area. 

As ground-water management practices change, due 

care must be exercised to ensure that several consecutive seasons of relatively high precipitation do not 

recharge hydrologic basins to a point where shallow 

ground water once more becomes extensive and the 

liquefaction susceptibility correspondingly widespread. 

Evaluating Liquefaction Potential 289 
34'00' 

.-·\ 

/, 

33'45' 

0 1 2 3 4 5 KILOMETERS 

3 MILES 

118'15' 

EXPLANATION 

Very high 

High 

Moderate 

Low 

Very low 

FIGURE 143.-Extensive areas of probable high and moderate susceptibility to liquefaction in the Los Angeles basin, based on ground-water data 

from Mendenhall (1905a, b) and Conkling (1927). Much of the area shown in the central part of the map could have been recharged from 

pressurized water-bearing layers partially confined below the near-surface water-bearing layers. These layers may contain only perched 

water today. A comparison with figure 145 shows how the withdrawal of ground water has reduced the size of susceptible areas. 

Orange County Area of the 

Los Angeles Basin 

Surficial Geology 

The Orange County area comprises the southern half 

of the Los Angeles basin. Broadly upwarped and tilted 

Pleistocene marine terraces occur intermittently along 

the Pacific shoreline and the part of the NewportInglewood fault zone extending from Newport Bay north 

290 Earthquake Hazards in the los Angeles Region 

to Alamitos Bay. The extensive alluvial plain that extends inland to the San Joaquin Hills in the south and to 

the Santa Ana Mountains in the east contains in its uppermost part chiefly alluvial deposits of the Santa Ana 

River, plus contributions of sediment from smaller 

basins that drain the adjoining, mainly sedimentary 

terranes of the adjacent uplands. 

The distributions, thicknesses, and characters of the 

surficial deposits in the Orange County area have been 

mapped at a scale of 1:48,000 for purposes of seismic 
34"00' 

33145' 

118130' 

'7 . 

n 

';..-

2 3 5 KILOMETERS 

f--'-l,J'L-J.,' j--'----r'j 1 MILES 

118'15' 

FIGURE 144.-Ground-water levels compiled from post-1928 data in the Los Angeles basin area of Los Angeles County, Data include 

measurements made at selected wells monitored by the State of California and made in exploratory borings from 1960 through 1975. Isobaths 

are in feet. 

zonation by Sprotte and others (1980) and Sherburne 

and others (1981). The reader is referred to those 

publications for additional details. A highly generalized 

surficial geologic map compiled from Sprotte and others 

(1980), Rogers (1965), and Yerkes (1972) is shown in 

figure 146. 

Ground Water 

The extent of shallow ground water has been mapped 

in the flatland area of Orange County by Sprotte and 

others (1980). Figure 147 is an isobath map compiled 

from Sprotte and other (1980, pl. 1). The dashed lines 

enclose areas of equal depth to ground water, based on 

logs of exploratory borings undertaken for construction 

projects before 1955 and on drillers' logs of water wells 

excavated since 1920. The lines thus are not equipotential lines in the hydrologic sense but are isobath lines. 

The map is a compilation of the shallowest reported occurrences of ground water and is thus a conservative 

interpretation that represents a regional evaluation of 

Evaluating Liquefaction Potential 291 
34'00' 

f· 

/ 

33*45 ' 

/ 

2 3 5 KILOMETERS 

f-L,-'L-.J'r'-r', I 

~ i 3 MILES drt'er 

h:'t"!$t:l<<ltiU'· 

FIGURE 145.-Relative liquefaction susceptibility in the Los Angeles basin, based on depths to ground water measured from 1960 through 1975 

(compare with fig. 143). Relative susceptibility to liquefaction-related ground failure is interpreted as a function of the age of the saturated 

materials and the depth to ground water. VH designates areas likely to contain very young, relatively well sorted stream-channel and levee 

deposits where the depth to ground water is less than 10ft 

the "worst possible" ground-water conditions for considerations of seismic response (Sprotte and others, 

1980, p. 7). 

Liquefaction Susceptibility 

The depth-to-ground-water thresholds in table 43 and 

the depth-to-ground-water data in figure 147 have been 

used to derive a preliminary liquefaction susceptibility 

292 Earthquake Hazards in the los Angeles Region 

map (fig. 148). The highest susceptibility would be 

associated with the occurrences of cohesionless, 

granular materials and the shallowest (0-10 ft) depths 

to ground water. Stippled areas show positions of 

former drainage channels as given on 1890 U.S. Geological Survey topographic maps. These channels predate 

construction of storm drains and channelization of 

natural drainages and are likely to contain sediment 

susceptible to liquefaction. They are not, however, the 
3 4 5 KILOMETERS 

', i' 2 3 MILES 

..... -"""\\. Hasler r arm '-_.} 6 5 

I 

\~ 

I '· 

"' -.,.; 

EXPLANATION 

[5J late Holocene alluvium; gravel, sand, slit, and EJ Undifferentiated Pleistocene alluvium; gravel, 

clay; unconsolidated, uncemented; herein sand, slit, and clay; moderately to well conrestricted to areas that flooded historically. solidated often slightly to well cemented. 

Including tidal marshes. Thickness 0 to 3m. Thickness 0 to > 1,200 m. 

Age <1,000 yr. 

Undifferentiated Holocene alluvium; gravel, 

sand, silt, and clay; uncemented. unconsolidated; thickness 0 to 30 m. Locally includes thin elements of late Holocene 

alluvium. 

~ Pre-Quaternary lithifled rock units, undifferentiated. Chiefly includes Tertiary and preTertiary sedimentary rock, locally includes 

Tertiary intrusive and extrusive rock of the 

Santa Ana Mountains. 

FIGURE 146.-Generalized surficial geology of the flatland areas of the Orange County portion of the Los Angeles basin (from Sprotte and others, 

1980; Rogers, 1965; Yerkes, 1972). 

only channels to have traversed the coastal plain (Troxell, 1942), so channel deposits may occur in the near 

subsurface in other places as well as in those localities 

shown in figure 148. 

Evaluating Liquefaction Potential 293 
118'00' 117'45' 

':' 

5 l!'lQ.J 

2 3 5 KILOMETERS j / 

1----'--Tj -LI --'-' I,...--L___,.JI1 

1 2 3 MILES 

', . \ ""·'... 

FIGURE 147.-Generalized depth to ground water in the flatland areas of Orange County (modified from Sprotte and others, 1980). Isobaths (in 

feet) are dashed where approximately located and queried where ground-water data are sparse. 

Upper Santa Ana River Basin Area 

Surficial Geology 

The upper Santa Ana River basin area is shown 

relative to the other alluvial basins in the study in figure 

129. The alluvial basin is bounded on the north by the 

San Gabriel Mountains, on the east by the San Bernardino Mountains and the San Andreas fault, on the south 

294 Earthquake Hazards in the Los Angeles Region 

by Tertiary-Cretaceous sediments in the northern Santa 

Ana Mountains and the granitic rocks of the eastern 

basement complex of Yerkes and others, (1965), and on 

the west by the Tertiary sedimentary rocks of the Puente 

Hills, the Chino Hills, and the San Jose Hills (Durham 

and Yerkes, 1964). 

The generalized surficial deposit map compiled by 

Cox and Morton (1978) is the surficial geologic base map 

for our reconnaissance appraisal of liquefaction suscep-
Geologic Depth to ground water. In feet 

Unit 0-10 10-30 30-50 50 

0yl2 VH H-M vt 

Ov• H-VH H-M VL 

lloo M L VL 

To VL vt VL VL 

Because Oy1 Includes OV•2 • a worstcase susceptibility designation is 

assigned. For example, H-VH lor 

ground-water depth of 0 to 10 It Instead of susceptibility category H 

3 4 

I 

5 KILOMETERS 

I 

3 MILES 

-:-.i 

j ;J?Q.:J 

I I 

FIGURE 148.-Relative liquefaction susceptibility in the flatland area of Orange County. Stippled areas indicate positions of former drainage channels as shown on 1890 U.S. Geological Survey topographic maps. Relative susceptibility to liquefaction-related ground failure is interpreted as 

a function of the age of the saturated materials and the depth to ground water. VH designates areas likely to contain very young, relatively well 

sorted stream-channel and levee deposits where the depth to ground water is less than 10ft. 

Evaluating Liquefaction Potential 295 
tibility and is shown in figure 149. This map shows the 

two principal systems of sediment dispersal that 

dominate the region. One suite of alluvial deposits, 

derived from the rugged canyons draining the San 

Gabriel Mountains, forms coalesced alluvial fans that 

slope south from the piedmont of the San Gabriel Mountains to the Jurupa Hills and the Santa Ana River. The 

second suite, derived from the chiefly granitic rocks exposed northeast, east, and south of the Riverside-San 

Bernardino area, consists of the alluvial fans and fluvial 

terraces of drainages that are directly tributary to the 

Santa Ana River near the eastern part of the area 

shown in figure 149. 

Ground Water 

The ground-water map that we used to compile a liquefaction susceptibility map of this area (fig. 150) is a 

small-scale map generalized from a 1:48,000-scale 

ground-water map by Carson and Matti (1982) and 

shows the minimum depth to ground water in the upper 

Santa Ana River basin area. Carson and Matti (1982) 

analyzed the water-level data for the period from 1973 

through 1979, using wells monitored by the California 

Department of Water Resources. Their study shows that 

cycles of natural recharge and management of groundwater basins profoundly affect the temporal and spatial 

distribution of ground water. In parts of San Bernardino, rising water has invaded cellars, undermined road 

fills, and affected foundations. In several places where 

water levels have continued to rise since 1979, the areas 

underlain by shallow ground water have expanded 

beyond what is depicted in this report. Principal areas 

where shallow ground water was detected are located 

north of Pomona, within the Prado Dam Flood Control 

Basin, along the Santa Ana River basin, locally in Cajon 

Creek Valley, and along parts of the San Jacinto fault 

zone in the Riverside-San Bernardino area (Dutcher and 

Garrett, 1963). 

Liquefaction Susceptibility 

A "high-water-level" liquefaction susceptibility map 

was compiled from figures 149 and 150 by using the 

model developed in this chapter. Areas where shallow 

ground water resulted in a designation of high or 

moderate liquefaction susceptibility (if cohesionless 

granular materials are present) are shown in figure 151. 

Carson and Matti (1982) have identified 20 areas in 

which shallow ground water was detected by various 

water-monitoring agencies. Some of these areas contain 

shallow ground water only part of the year; other areas 

296 Earthquake Hazards in the Los Angeles Region 

have hydrologic settings in which shallow ground water 

occurs during much of the year in connection with 

natural and artificial recharge operations, groundwater barriers, flood-control operations, and other 

hydrologic basin management practices. Carson and 

Matti (1982) have given a more comprehensive discussion of the ground-water data used for this 

reconnaissance. 

Figure 151 indicates that the principal areas where 

liquefaction is likely to occur (if cohesionless granular 

sediment is present) include: 

1. The Santa Ana River channel and parts of the adjacent flood plains, from the San Jacinto fault to 

Prado Dam. 

2. The San Bernardino area, chiefly northeast of the 

San Jacinto fault and ground-water barrier. 

3. Several localities around the margin of the basin adjacent to fault systems that apparently are barriers to the subsurface movement of ground 

water or localities where impermeable layers 

may perch water seasonally. These localities include small areas near La Verne, south of 

Pomona, the Claremont area, the Upland area, 

the San Antonio wash area, and the San Antonio 

Canyon alluvial fan shown in the western and 

northwestern parts offigure 151. 

4. In the eastern part of figure 151, where shallow 

ground water has been reported in the Mentone 

area, in Lytle Creek Canyon Wash, in an area 

east of Yucaipa, and in San Timoteo Canyon and 

the Mill Creek area. 

Oxnard Plain Area 

A reconnaissance study of liquefaction susceptibility 

in the Oxnard Plain area of Ventura County was compiled by using the techniques presented in this chapter, 

a surficial materials map that identifies areas according 

to the age and grain size of sediments (McCoy and 

Sarna-Wojcicki, 1978), and a ground-water map based 

on historical high ground-water levels (Sprotte and 

Johnson, 1976). 

The Oxnard Plain, which represents the southwestern 

part of the onshore portion of the Ventura basin, is 

situated within the Transverse Ranges structural province. The Oxnard Plain is a relatively flat, alluviated 

area that extends inland from the Santa Barbara Channel shoreline and terminates along the base of South 

Mountain and the Camarillo Hills on the northeast and 

the Santa Monica Mountains on the east. The inland 

margin of the alluviated surface is about 100 ft above 

sea level. 
The Holocene deposits of the Santa Clara River, 

Calleguas Creek, and Camarillo Creek are extensive and 

contain locally abundant, cohesionless granular materials; the uppermost 50 ft of sediment within much of the 

Oxnard Plain corresponds to the Perched Water Zone of 

Sprotte and Johnson (1976, p. 227). 

Surficial Deposits 

The present and former flood plains of the principal 

drainage contributing sediment to the Oxnard Plain 

have been subdivided by McCoy and Sarna-Wojcicki 

(1978) according to sediment age and grain size; their 

map is reproduced in figure 152. The surficial deposits 

consist partly of unconsolidated or loosely consolidated 

gravelly sand and sand associated with present and 

former river channels; these cohesionless sediments are 

interbedded with lenses of silt, clay, and carbonaceous 

sediments (including peat), which represent deposits 

formed in flood-basin areas. Near the shoreline, deposits 

also include lagoonal or estuarine sediment and beach 

and eolian deposits. The distribution of cohesionless 

granular deposits in the near subsurface is not known 

with any degree of certainty except along principal 

drainages, but stream channels presumably have 

shifted position many times during the accumulation of 

late Pleistocene and Holocene deposits in the Oxnard 

Plain. 

Sprotte and Johnson (1976) have compiled maps showing depth to ground water in the Oxnard Plain; the maps 

are based on the shallowest depth at which ground 

water has been encountered historically. Thus, the 

ground-water map presented in figure 153 may represent excessively severe conditions in some areas. 

However, a comparison of Sprotte and Johnson's (1976) 

ground-water map with the shallowest depths to ground 

water measured in wells monitored by the California 

Department of Water Resources from 1970 to 1975 indicated that ground water commonly was found at 

depths broadly corresponding to the historical high level 

indicated by Sprotte and Johnson. In the absence of 

reliable hydrologic information concerning the uppermost aquifer zone in the Oxnard Plain and the intervals 

perforated in the monitoring wells, we conservatively 

use Sprotte and Johnson's (1978) data. 

Liquefaction Susceptibility 

A map showing "high-water-level" liquefaction 

susceptibility in the Oxnard Plain has been compiled according to the criteria in table 43 and is shown in figure 

154. Zones having the highest susceptibility coincide 

with the channels of the Santa Clara River and Calleguas Creek. Liquefaction effects were noted in both 

drainages following the Point Mugu earthquake of 

February 21, 1973 (Sprotte and others, 1975, pl. 8). An 

extensive area of historically high ground water occurs 

across much of the central Oxnard Plain, especially inland from Port Hueneme and Mugu Lagoon. Where the 

water table is 15 to 40 ft subsurface, areas are mapped 

as having moderate susceptibility at the most. Areas of 

chiefly Pleistocene deposits have low susceptibility to 

liquefaction. 

DETERMINING LIQUEFACTION 

OPPORTUNITY 

When soils are shaken in the laboratory, the 

likelihood of liquefaction increases with both the 

amplitude of applied motion and the duration of that motion. For earthquake ground motion, both amplitude and 

duration increase as magnitude increases. Hence, soil 

liquefaction due to strong ground shaking will be strongly influenced by earthquake magnitude. 

When a sufficiently large earthquake occurs, liquefaction effects are experienced at sites various 

distances from the earthquake rupture. The more susceptible sites liquefy at greater distances. The larger 

the magnitude of the earthquake, the greater the 

distance at which liquefaction is observed. Figure 155 

shows a curve from Youd and Perkins (1978) that 

estimates, for a given magnitude, the distance beyond 

which liquefaction is not expected to occur at a highly 

susceptible site. This curve is based on observations of 

the farthest distance from a fault rupture at which 

significant liquefaction has occurred in historical earthquakes. (Liquefaction that produces horizontal movement of 10 em or more is considered significant in terms 

of hazard to ordinary structures.) The role of ground 

motion and duration is implicit in the curve rather than 

being mathematically or physically modeled. The curve 

represents the locus of a threshold such that, if a site is 

at a distance that lies above the curve, the combination 

of earthquake ground-motion amplitude and duration is 

sufficient to cause significant liquefaction, provided 

that the geologic materials at the site are susceptible to 

liquefaction. (The liquefaction susceptibilities of some 

uncompacted artificial fill composed of sand can be 

higher than those of natural, fluvially deposited sediment; these artificial fills may have blow counts of less 

than three. Susceptible materials, as used in this 

chapter, are sand and silt layers of late Holocene origin 

whose standard penetration resistance is between 

about 3 and 20). Thus, if a specific site lies within the 

Evaluating Liquefaction Potential 297 
5 KILOMETERS 

I I II II 

0 1 2 3 MILES 

FIGURE 149.-Generalized surficial geology of the upper Santa Ana River basin (Cox and Morton, 1978). 

298 Earthquake Hazards in the Los Angeles Region 
EXPLANATION 0 Artificial fill 

8 late Holocene alluvium; gravel, sand, silt, and clay; 

unconsolidated, uncemented; herein restricted to 

areas that Oooded historically, including marshes. 

Thickness 0 to 3m. Age less than 1,000 yr. 

~ Undifferentiated Holocene alluvium; gravel, sand, silt, 

and clay; uncemented, unconsolidated. Thickness 0 

to 30m. Age 1,000 to 10,000 yr. locally may include 

thin deposits of late Holocene alluvium 

~ Undifferentiated late Pleistocene aUuvlum; gravel, sand, 

silt, and clay; moderately to well consolidated; often 

slightly cemented; locally well cemented 

G Undifferentiated pre-Quaternary lithified sedimentary 

rocks, Includes Tertiary volcanic rocks 

~ Mesozoic and older crystaUine basement terranes of the 

L..:.:J San Gabriel, San Bernardino, and Jurupa Mountains 

areas 

Evaluating Liquefaction Potential 299 
117'30' 

34'07'30" 

34'00' 

FIGURE 150.-Generalized depth to shallow ground water in the upper Santa Ana River basin (Carson and Matti, 1982). Contours (in feet) are 

dashed where data are sparse and solid where data are relatively abundant. 

300 Earthquake Hazards in the Los Angeles Region 
EXPLANATION 

Boundary of valley fill 

---50---- Line of equal ground water elevation; 

dashed where inferred &om sparse data 

---30--- Area containing perched ground water 

5 KILOMETERS 

I I I I 2 3 MILES 

Evaluating Liquefaction Potential 301 
FIGURE 151.-Relative liquefaction susceptibility in the upper Santa Ana River basin. Relative susceptibility to liquefaction-related ground failure 

is interpreted as a function of the age of the saturated materials and the depth to ground water. 

302 Earthquake Hazards in the Los Angeles Region 
EXPLANATION 

High 

Moderate 

low 

Very low 

Bedrock areas 

5 KILOMETERS 

1

1 1

1 

2 3 MILES 

Evaluating liquefaction Potential 303 
EXPLANATION 

G Artificial fill 

~ Late Holocene alluvium; gravel, sand, silt, and clay; 

L::J unconsolidated, uncemented; herein restricted to 

areas that flooded historically, including tidal marshes. Thickness 0 to 3m. Age less than 1,000 yr. 

8 Undifferentiated Holocene alluvium; gravel, sand, silt, 

and clay; uncemented, uncoqsolidated. Thickness 0 

to 30m. Age 1,000 to 10,000 yr. Locally may include 

thin deposits of late Holocene alluvium 

Undifferentiated late Ple15tocene alluvium; gravel, sand, 

silt, and clay; moderately to well consolidated; often 

slightly cemented; locally well cemented 

·.,i r:. -~ \ l 

[3 Undifferentiated middle and early Pleistocene 

sedimentary rock 0 Undifferentiated pre-Quaternary llthlfied sedimentary 

rocks 

~ Undifferentiated pre-Quaternary volcanic rocks /-:"' :.-"'·.,--

. '-if",::P':·r: 

1-

; r !-·__._ __ _ 

5 KILOMETERS I I I I 

3 MILES 

FIGURE 152.-Generalized surficial materials in the Oxnard Plain of Ventura County (modified from McCoy and Sarna-Wojcicki, 1978). 

304 Earthquake Hazards in the Los Angeles Region 
5 KILOMETERS f---L,-...J....._--'r---'--r' 3 MILES 

FIGURE 153.-Generalized depth to ground water in the Oxnard Plain of Ventura County. From hydrologic maps compiled by Sprotte and Johnson 

(1976) and water levels compiled by the California Department of Water Resources between 1970 and 1975. Contours in feet. 

threshold distance of an earthquake rupture, that site 

has an opportunity to liquefy. 

For an earthquake-prone region, we can model possible future earthquake locations by using what we call 

sources. A source may be either a source zone or a 

source fault. The source zone is a map area over which 

earthquakes are modeled as point ruptures that are 

equally likely anywhere in the zone. The source fault is a 

segmented line on a map over which ruptures of a length 

appropriate to the earthquake magnitude are equally 

likely anywhere; source faults may be contained within 

source zones. In general, the smaller magnitude earthquakes are assumed to occur as points in the source 

zones, and the larger magnitude earthquakes are 

assumed to occur as line ruptures on the source faults. 

The long-term relative rate of occurrence of the various 

magnitudes possible on those sources can be characterized from the regional seismicity by using a magnitudefrequency relation described by Gutenberg and Richter 

(1941, p. 102-107) and Richter (1958, p. 359): 

log N=a+bM 

where N is the number of shocks of magnitude M or 

greater per unit time and a and b are constants. Figure 

156 shows the source zones used for southern CaliforEvaluating Liquefaction Potential 305 
EXPLANATION 

Map 

Symbol 

H 

H-M 

M 

M-L 

L 

VL' 

Llquefacdon 

Susceptibility 

High 

High to moderate 

Moderate 

Moderate to low 

Low 

Very low 

(bedrock area) 

Approximate location of sand bolls and lurch 

cracks obaerwd following the Point Mugu 

eanhquake of February 21, 1973. Localldes 

compiled from Sprotte (1975, pl. 8) 

119'00" 

5 KILOMETERS 

3 MllfS 

FIGURE 154.-Relative liquefaction susceptibility within the Oxnard Plain of Ventura County. Relative susceptibility to liquefaction-related ground 

failure is interpreted as a function of the age of the saturated materials and the depth to ground water. 

nia, along with stippling to indicate those source zones 

in which either individual faults or parallel systems of 

faults were placed. 

Examples of Determining 

Liquefaction Opportunity 

Suppose a site lies within a modeled region. Then it is 

possible to calculate, by using the threshold locus curve 

(fig. 155), the fraction of the possible earthquake occurrences on a source for which the site will lie within the 

threshold distance of an earthquake of a given 

magnitude in one of the sources. For each source, there 

306 Earthquake Hazards in the Los Angeles Region 

is an expected annual rate of occurrence of that magnitude from that source. The product of that annual rate 

and the fraction of possible occurrences is the annual 

rate of liquefaction opportunity caused by an earthquake of that magnitude on that source. The calculation 

can be repeated for all possible magnitudes from that 

source, and the annual rates of opportunity can be accumulated. If all the sources are independent of one 

another, we can add together the annual opportunity 

rates for that site due to each source in the region. The 

result of this accumulation is the total liquefaction opportunity rate at the site (fig. 157B). Because this rate is 

usually very much less than 1.0, it is convenient to talk 

about it in terms of its inverse, which is called return 
0 

() .. "' -" ·c:; 

c: "' .. .. :;:( 0 c:Lt .J:; 'It 

> ., .. c: co ., :!2 ~~ . C» 

LIQUEFACTION z .,; .., .. U) m 

~ 

-

0 

~ .. OJOU 

- ., iija> .. 0... 

iii Clu ~ .J:; 

., '= 0 z ,;.. ~ 0 'It - ~ III co iii c: (') ., u iii .2 III > iii C» -o ~ u. c: 'It 0 .!!! ~ 10 0 (7) 

s "' .; :E 7 

"' ., 

~ 

co 

...,. 

., 

-

NO LIQUEFACTION 

DISTANCE, IN KILOMETERS 

FIGURE 155.-Relation of earthquake magnitude to the maximum threshold distance at which liquefaction has been observed. Based on historical 

data (Youd and Perkins, 1978; Youd and Wieczorek, 1982). 

period (the long-term average number of years between 

liquefaction opportunities at a site). We provide an example of this calculation in the following paragraphs. 

If the threshold model given in figure 155 is assumed 

to be correct, liquefaction in susceptible materials is 

possible whenever an earthquake of sufficient size occurs closer than a threshold distance from a site. In 

calculating liquefaction opportunity, it is important to 

understand the role played by an earthquake's rupture 

length in assessing the rate at which a given earthquake 

occurs within a given threshold distance. Figure 157A 

shows (1) the interaction between fault length, rupture 

length, and site location in determining how many earthquakes of a given magnitude might occur at distances 

less than or equal to a given distance from a fault source 

and (2) how the analysis differs when a point rupture is 

assumed instead of a rupture along a line source of 

earthquakes. 

As an example, consider a fault source 150 km long 

(fig. 157A). The potential earthquakes are assumed to 

occur on the fault. Let us now choose two sites, each 

situated so that a circle having a threshold radius of 

50 km includes one-third of the fault's length. For site A, 

the circle includes the middle third of the fault; for site 

B, the circle includes the end third of the fault. If potential earthquakes on the fault are represented as point 

ruptures equally likely anywhere on the fault, the 

circles around site A and around site B each include 

one-third of all such potential earthquake occurrences. 

If the potential earthquakes on the fault are not represented as point ruptures but as linear ruptures having 

appreciable lengths, however, the results differ depending on the lengths of the ruptures. If the ruptures are 

small enough, the results do not differ much from the 

results obtained by using point ruptures. Suppose, 

however, that an earthquake of sufficient magnitude 

ruptured the entire 15o-km length of the fault. All such 

ruptures would have part of the rupture segment lying 

within the circles surrounding each site; hence, all occurrences of earthquakes of this magnitude would contribute to ground motions at distances of 50 km or less 

from the sites, even though only one-third of the fault 

rupture lies within the 5o-km radius. Now consider an 

earthquake such that the expected rupture length is 

60 km. These ruptures can occur randomly on the fault, 

subject to the restriction that the rupture is contained 

Evaluating Liquefaction Potential 307 
FIGURE 156.-Source zones used in computing liquefaction opportunity for southern California. Zones in which all earthquakes are modeled as 

point sources are indicated by unstippled areas. Zones in which large-magnitude earthquakes (M2: 5.8) are placed on known fault traces and 

modeled as ruptures whose lengths are dependent on magnitude are indicated by heavy stippling. Zones in which large-magnitude earthquakes are modeled as ruptures on systems of parallel, equally spaced faults are indicated by light stippling. Labels on seismic sources correspond to those used by Thenhaus and others (1980) and Algermissen and others (1982). 

entirely within the fault. All such occurrences will produce some part of the rupture within the 5D-km circle 

from site A, because a 6D-km rupture on this fault must 

produce at least 10 km of rupture within the middle 

third of the fault. Only 55 percent (50/90) of such occurrences will lie within the 5D-km circle from site B, 

because the near end of a 6D-km rupture must lie within 

that 150- 60 = 90 km of fault nearest site B. Thus, the 

percentage of the larger magnitude earthquakes that 

produce ruptures lying within some radius of a site 

depends on the magnitude of the earthquake, the length 

of the fault rupture, and the portion of the fault that lies 

closest to the site. 

308 Earthquake Hazards in the Los Angeles Region 

An idealized example of the calculation of liquefaction opportunity is shown in figure 157B. Three different 

sites are located with respect to two faults. We assume 

that only M 7 earthquakes occur on fault AD and that 

only M 6 earthquakes occur on fault EJ; there are no 

other earthquake sources in this idealized example. On 

the basis of this model (fig. 155), liquefaction is possible 

at susceptible sites within 45 km of a M 7 earthquake 

rupture and at points within 7 km of a M 6 earthquake 

rupture. Thus, liquefaction is possible at site 1 (fig. 

157B) from fault AD only. Liquefaction is possible at site 

2 from both fault AD and fault EJ. Liquefaction is not 

possible at site 3 because site 3 is located more than 
~--------------------\-----------150km--------------------------------~ 

-------=~====~~~----~fk---------50km--------~ 

Site B --------------------------,,.JL-------------------- ~--__:_~~---------------------;>! 

Site A 

FIGURE 157 A.-Effect of assumed rupture length on the number of potential earthquakes occurring within a given distance of a site susceptible to 

liquefaction. A and B are two sites near a 150-km-long fault; one-third of the fault is contained within 50 km of eaclr site. For earthquakes 

treated as point ruptures, one-third of the earthquakes on the fault occur within 50 km of both site A and site B. For a given magnitude, 

however, if earthquakes are modeled by ruptures having lengths of 50 km and the ruptures occur randomly on the fault, part of the rupture of 

each potential earthquake will be within 50 km of site A. However, because all 50-km-long ruptures will have a left-hand endpoint within 

100 km of site B, only 50/100 (or halt) of the earthquakes will have some part of a rupture within 50 km of site B. 

45 km from any potential point of rupture on fault AD 

and more than 7 km from any potential point of rupture 

on fault EJ. 

To calculate liquefaction opportunity at sites 1 and 2 

(fig. 157B), we must know what percentage of the earthquakes that might occur on the faults will have some 

part of a rupture close enough to the sites that an earthquake could cause liquefaction in susceptible materials. 

The discussion of figures 157C, 157D, and 157E illustrates the calculation of these percentages. We assume 

that M 7 earthquakes occur along fault AD at an annual 

rate of 0.02 events per year and that M 6 earthquakes 

occur along fault EJ at an annual rate of 0.01 events per 

year. 

We need a measure of all possible ruptures of a given 

length that can be placed on a fault trace. To obtain 

such a measure, we will show that portion of the fault 

where the right-hand ends of these ruptures may lie. We 

assume that M 7 events have ruptures 32 km long, a 

value derived from Bonilla and others (1984, fig. 1E, 

p. 2392). In figure 157C, the location of the right-hand 

ends of all 32-km ruptures must lie at or to the right of 

point B, which is 32 km from the left-hand end of the 

fault. All points between C and D on the fault are within 

45 km of site 1. Hence, any rupture that has a right-hand 

endpoint between C and D will contain a point located 

less than 45 km from site 1. Therefore, the length of segment CD divided by the length of segment BD and 

Evaluating Liquefaction Potential 309 
oSite 1 

0 site 3 

10 20 30 40 50 KILOMETERS 

I 

I 

I 

\~ 

I"" 13 

I 

I 

I 

I 

FIGURE 157B.-Three sites located with respect to two potentially seismogenic faults. Fault AD is assumed to generate only M 7 earthquakes, and 

fault EJ is assumed to generate only M 6 earthquakes. Liquefaction is assumed to be possible within the threshold distances indicated for the 

two faults, if highly susceptible sediment is present. 

A 

-.......... 

' ' ' ' ' ' \ 

·\ 

\ 

'P 

0 Site 2 

Site 1 

10 20 30 40 KILOMETERS 

oSite3 

FIGURE 157C.-Determining the percentage of 32-krn-long ruptures (M 7) on fault AD that lies within 45 krn of site 1. All M 7 32-krn-long ruptures 

have right-hand endpoints lying on segment BD. Each rupture having a right-hand endpoint on segment CD also has a point on that rupture 

within 45 krn of site 1. 

310 Earthquake Hazards in the Los Angeles Region 
4 

Site 2 0 Site 1 

QSite 3 

FIGURE 157D.-Determining the percentage of 32-km-long ruptures on fault AD that lies within 45 km of site 2. All points on segment XY lie within 

45 km of site 2. Point Z is 32 km to the right of pointY. Each 32-km-long rupture having a right-hand endpoint on segment XZ also has a point on 

that rupture within 45 km of site 2. 

4 

QSite 1 

/ 

QSite 3 

FIGURE 157E.-Determining the percentage of 1G-km-long ruptures (M 6) on fault EJ that lies within 7 km of site 2. All 1G-km-long ruptures have 

right-hand endpoints on segment FJ. All points on segment GH lie within 7 km of site 2. Point I lies 10 km to the right of point H. Each rupture 

having a right-hand endpoint on segment GI also has a point on that rupture within 7 km of site 2. 

Evaluating Liquefaction Potential 311 
multiplied by 100 is the percentage of all possible M 7 

earthquakes· having a 32-km length of rupture that can 

cause liquefaction at site 1. 

The evaluation for site 2 is somewhat more complicated, both because we must consider contributions 

from both fault AD (fig. 157D} and fault EJ (fig. 157E} and 

because it is more difficult to specify the relevant line 

segment of fault AD. We now consider these hypothetical examples. 

All points at or between X and Y on fault AD lie within 

45 km of site 2 (fig. 157D}. Any M 7 earthquake rupture 

having a right-hand endpoint at or to the right of X and a 

left~hand endpoint at or to the left of Y will contain at 

l~ast one point that is located within 45 km of site 2. 

Because the M 7 ruptures are 32 km long and because 

location Z is 32 km to the right of Y, all 32-km-long earthquake ruptures having right-hand endpoints at or between X and Z will contain at least one point on the 

rupture within 45 km of site 2. Thus, the ratio of the 

length of segment XZ to the length of segment BD, multiplied by 100, is the percentage of all possible M 7 ruptures that can cause liquefaction at site 2. 

There is also a contribution to liquefaction opportunity from fault EJ at site 2. Figure 157E shows how we 

determine the percentage of M 6 occurrences whose 

ruptures have some part of a rupture within 7 km of site 

2. The ruptures from M 6 earthquakes are assumed to be 

10 km long, on the basis of Bonilla and others' (1984, 

p. 2392} data. The right-hand edges of all possible 1Q-km 

ruptures lie alongside segment FJ. All points along segment GH lie within 7 km of site 2. Point I is 10 km to the 

right of point H. Therefore, all M 6 ruptures having a 

right-hand endpoint along segment GI will have a part of 

the rupture within 7 km of site 2. The percentage of M 6 

occurrences that can cause liquefaction at site 2 is given 

by the ratio of the length of segment GI to the length of 

segment FJ. 

The percentage of M 7 events on fault AD that can 

cause liquefaction at site 1 (fig. 157C} is determined as 

follows. Fault segment CD is 72 km long and represents 

that portion of fault AD situated less than the threshold 

distance (45 km) from site 1. The length of segment BD 

represents the percentage of the total fault length that 

can generate M 7 ruptures and is given by the difference 

between the overall fault length and the rupture length; 

fault AD is 220 km long, and M 7 events produce ruptures 32 km long, so 220 km- 132 km = 188 km. Thus, 

the percentage of M 7 events on fault AD that can 

cause liquefaction at site 1 is given by CD/BD = 72 km/ 

188 km = 0.38 (or 38 percent). 

The percentage of M 7 events on fault AD that can 

cause liquefaction at site 2 (fig. 157D} is determined as 

follows. Fault segment XZ is 90 km long and represents 

the portion of fault AD situated at less than the 

312 Earthquake Hazards in the Los Angeles Region 

threshold distance (45 km) from site 2. Segment BD as 

calculated in the preceding paragraph is 188 km long. 

Thus, the percentage of M 7 events on fault AD that can 

cause liquefaction at site 2 is given by XZ/BD = 90 km/ 

188 km = 0.48 (or 48 percent). 

The percentage of M 6 events on fault EJ that can 

cause liquefaction in susceptible materials at site 2 (fig. 

157E} is determined as follows. Fault segment GI is 

19 km long and represents the portion of fault EJ situated at less than threshold distance (7 km) from site 2. 

The length of fault EJ that can generate 1D-km-long ruptures in M 6 earthquakes is given by FJ = EJ -10 km = 90 

km- 10 km = 80 km. Thus, the percentage of M 6 events 

on fault EJ that can cause liquefaction at site 2 is given 

by GI/FJ = 19 km/80 km = 0.24 (or 24 percent). 

The annual rate of liquefaction opportunity at site 1 is 

given by the product of the percentage of M 7 events on 

fault AD causing liquefaction at site 1 and the annual 

rate of occurrence of M 7 events for fault AD, assumed 

to be 0.02 per year. Thus, (0.38}(0.02} = 0.0076 liquefaction events per year or a return period of 

1/0.0076 = 131 yr. 

The annual rate of liquefaction opportunity at site 2 is 

given by the sum of the contributions owing to fault AD 

and fault EJ. The fraction of M 7 events from fault AD 

causing liquefaction at site 2 multiplied by the annual 

rate of occurrence of M 7 events amounts to 

(0.48}(0.02} = 0.0096 liquefaction events per year. The 

fraction of M 6 events from fault EJ causing liquefaction 

at site 2 multiplied by the annual rate of occurrence of M 

6 events on fault EJ, assumed to be 0.01 events per year, 

amounts to (0.24}(0.01} = 0.0024 liquefaction events per 

year. The sum of the annual liquefaction rates at site 2 

owing to M 7 events and M 6 events is equal to 

0.0096 + 0.0024 = 0.012 or a return period of 1/0.012 or 

83 yr. 

We have shown the calculation of annual rates and 

return periods for three sites and a simple model of 

earthquake recurrence. Calculations for actual sites 

would involve more complex models. These more sophisticated models would need to characterize activity on a 

fault by a suite of possible magnitudes assumed for each 

of a large number of source faults (and source zones) instead of a single earthquake magnitude. Thus, at a site, 

we would have to accumulate liquefaction opportunity 

rates due to each magnitude for each source close 

enough to the site to cause liquefaction. For each 

magnitude, we would aJso have to take into account a 

probabilistic distribution of future rupture lengths 

rather than just one rupture length. Figure 158 shows 

such a map for the Los Angeles region; this map uses a 

complex model discussed earlier in the text, a model for 

which we have considered, for each fault, not simply a 

single-magnitude earthquake or rupture length origi-
119' 118' 117' 116' 115' 114' 

35' (/ \ ---- ......... '-... /' / ......... "-... ' ' " ......... "-... '-... '-... "' '-... ~0 ......... ' '-... "' ' "' "' "' "' "' '-... " ......... / " " " '-... 

'-... " '-... 32 \ '-... '-... '-... .. 0'-... '-... <::\ 33 l '-... "' '-... '--- 44 '-... '-... '-... ---.,oo '\ 

I "' "' '-... 

"-... "' '-... " '\ 

34' 

\ "' "' " '\ '\ r - --- "-- "-- '-... 

\ \ '\ \ "' '-... '-... -'o 33 0" 

\ \ "' "' "' " \ '\ ". ". -'o 

"' "' "' "' \ " "-. ". so "- '\ \ \ '-... vo '-... "' '\ \ \ '-... '-... '-... ;: "' "' \ 

\ " "' '-... '-... """ '\ 33' \ 51 8o ""'- \ '\ " '-... ' \ \ 

'-... ) "' --- '-... 

50 100 150 KilOMETERS 

50 100 MilES 

n•L-----------~-----------L-----------L----------~----------~------------L---------~ 

FIGURE 158.-Return period of liquefaction opportunity in southern California. Contours represent the average number of years before an earthquake of M 5 or larger occurs closer to the site than the threshold radius of liquefaction given by the magnitud!Hiistance locus shown in figure 

155. 

nating from a fault but a suite of possible magnitudes 

and a suite of possible rupture lengths for each 

magnitude. 

Mapping Liquefaction Opportunity 

If the opportunity calculation is made for a large 

number of sites in a region and if the resulting return 

periods are plotted on a map, it is possible to contour the 

return period of opportunity. We have performed these 

calculations for the Los Angeles region by using the 

seismic source zones, faults, and earthquake occurrence rates of Thenhaus and others (1980) and Algermissen and others (1982). The result is shown in figure 

158. 

Because the radius of the opportunity threshold increases so rapidly as magnitude increases, the liquefaction opportunity map is dominated by those faults that 

can generate the larger magnitude earthquakes. One 

might therefore expect that the San Andreas fault would 

dominate the results in this region, and, certainly, it 

makes an important contribution. Other active faults in 

the Los Angeles region that lie closer to most urban sites 

than the San Andreas does, however, do make signifi· 

~ant contributions. Much of the Los Angeles region is 

within the threshold distance of the lower magnitude 

events expected on one or more relatively short faults. 

These lower magnitude events are estimated to occur 

about as frequently as the higher magnitude events on 

the San Andreas fault. As a result, the map shows a 

broad area in which the return period for liquefaction 

opportunity is about 30 to 50 yr. 

It must be pointed out that these values refer to the 

long-term average rate of opportunity at individual sites. 

If we consider the average rate of damaging earthquakes for the entire Los Angeles region, we would expect shaking strong enough to induce liquefaction to occur several times but at different sites in a 3D- to SD-yr 

time span, perhaps once every 6 to 8 yr somewhere 

within the region. Therefore, the values suggest that 

only one in four or five of these damaging earthquake 

events will be close enough to produce a liquefaction 

opportunity at any single site. 

The results presented on our map (fig. 158) depend 

largely on the models used for the . source and rate of 

earthquake occurrences. Because magnitude is so important in estimating liquefaction opportunity, the maxEvaluating liquefaction Potential 313 
imum magnitude assumed for a source fault and the b 

value of the relation log N =a+ bM (Gutenberg and 

Richter, 1941), which is assumed here to govern the 

relative rate of the larger events, significantly influence 

the calculations. The map also assumes a Poisson 

distribution of earthquake occurrences through time. 

Obviously, different models would yield different 

results. 

A Poisson distribution model implies that there is insufficient information to determine changes in earthquake probability for a given source as a function of 

time. Because of the detailed geologic information on 

earthquake recurrence being dev.eloped for the San Andreas fault (see Ziony and Yerkes, this volume), it may 

be possible in the future to validate a non-Poissonian 

model of earthquake occurrence for the larger magnitude events on that fault. For such a model, the largemagnitude earthquakes are less likely to occur in the 

early years after one such occurrence and are more 

likely after some longer time has passed. Thus, larger 

magnitude events may be more likely in the next two or 

three decades than the Poisson distribution would 

predict. Therefore, liquefaction opportunity rate would 

increase considerably (and return period would 

decrease) for some distance around the San Andreas 

fault. 

Instead of using the Gutenberg-Richter relation for 

the relative occurrence rates of the various magnitudes, 

a different model, such as the so-called characteristic 

earthquake model, might be applied. For this model, 

above a certain magnitude, only earthquakes of a particular magnitude occur on a fault. In this case, 

intermediate-magnitude earthquakes may not occur at 

all along the San Andreas fault; therefore, the liquefaction opportunity rate very near the fault may decrease 

significantly because of these earthquakes. There would 

also be a compensating smaller increase in opportunity 

rate for a greater distance around the fault because of 

some increase in the likelihood that the larger 

magnitude characteristic event would occur. 

It is also possible that applying slip-rate models to 

calculate future seismic rates (such as Joyner and Fumal 

(this volume) propose) on faults may change estimates of 

the rates of earthquake occurrence for the faults in the 

Los Angeles metropolitan area. Because the results in 

this area depend so strongly on the earthquake rates 

assumed for these faults, the return period for liquefaction in this area would be significantly affected. 

Finally, we emphasize that opportunity is a threshold 

measure. Opportunity tells us only how frequently that 

threshold is exceeded, not by how much. 

314 Earthquake Hazards in the Los Angeles Region 

LIQUEFACTION POTENTIAL MAPS 

AND THEIR LIMITATIONS 

Concomitant consideration of the liquefaction susceptibility maps (figs. 133, 135, 138, 140, 143, 145, 148, 151), 

which show those areas where susceptible materials 

are likely to occur, and the liquefaction opportunity map 

(fig. 158), which shows how often threshold severities of 

ground shaking are likely to impact the region, provides 

an assessment of the liquefaction potential across the 

Los Angeles region. The implication is that, every three 

to four decades, liquefaction-related phenomena are expected to occur at susceptible sites in southern California. Because liquefaction opportunity as presently 

evaluated does not vary significantly across the Los 

Angeles region, liquefaction potential is controlled chiefly by differences in liquefaction susceptibility of basin 

sediment; · thus, liquefaction susceptibility maps also 

serve as liquefaction potential maps. 

These studies of liquefaction potential that we have 

reported are not a substitute for a site-specific evaluation of liquefaction potential. The maps presented in this 

chapter are small scale and indicate general areas 

where susceptible materials are likely to be present. 

Areas shown as having very high, high, or moderate 

susceptibility are expected to be the loci of liquefaction 

in future earthquakes, if cohesionless, granular, watersaturated materials are present. Areas designated as 

having very low or low susceptibility are not expected to 

incur liquefaction-related ground failures during future 

earthquakes. Because we cannot guarantee that we 

have correctly mapped all shallow ground-water occurrences or denoted all occurrences of susceptible sediment, these maps are approximations; they do, however, 

provide a regional guide to those areas where liquefaction should be considered a potential hazard and where 

special investigations may be needed to assure the safety of some constructed works. 

SUMMARY 

Maps showing liquefaction susceptibility have been 

compiled for six areas in five basins in the Los Angeles 

area; for most basins, "low-water-level" and "highwater-level" cases have been mapped. These liquefaction susceptibility maps delineate areas in which any 

cohesionless granular layers are estimated to have very 

high, high, moderate, or low susceptibility to liquefaction. The liquefaction susceptibility of cohesionless 

granular layers is estimated from analyses of lithology, 

geologic age, depth to ground water, and SPT data. 
Analysis of areal seismicity provides a probabilistic 

estimate of the average return period (in years) of 

ground shaking severe enough to cause liquefaction in 

susceptible materials. Liquefaction potential is greatest 

where high water level, highly susceptible deposits, and 

frequent moderate to large (greater than M 5) earthquakes coexist. Within the Los Angeles region, a return 

period of about 30 to 50 yr is anticipated for ground motions sufficient to exceed the liquefaction threshold at a 

given susceptible site. 

Where the water table is less than 10 ft subsurface, 

fluvial silt and sand less than 1,000 yr old have very high 

susceptibility; older Holocene cohesionless deposits 

have high susceptibility, and Pleistocene cohesionless 

deposits have low susceptibility. Where the water table 

is 10 to 30 ft subsurface, Holocene cohesionless deposits 

are considered to have moderate susceptibility to liquefaction; Pleistocene cohesionless deposits generally 

have low susceptibility to liquefaction. Liquefaction is 

not likely to occur in any material when depth to ground 

water exceeds 30 ft. The susceptibility depends critically on depth to ground water, a parameter that may 

change abruptly in response to land use, ground-water 

recharge operations, patterns of ground-water extraction, or abnormal yearly precipitation. 

The maps do not delineate the type of ground failure 

that may occur. Lateral spreading has occurred on very -

gently sloping alluvial plains in southern California in 

past earthquakes; that mode of failure is likely to occur 

during future moderate to great earthquakes. 

These maps are small-scale, highly generalized 

models derived from widely scattered data; data in some 

well-explored areas are generalized and applied to entire map units in some instances. Thus, the maps are not 

a substitute for detailed studies of liquefaction potential 

at any particular site. Rather, the maps should serve 

their intended purpose of broadly delineating areas 

where the likelihood of earthquake-generated ground 

failure is greatest and where special consideration may 

be desirable. 

Evaluating Liquefaction Potential 315 
316 Earthquake Hazards in the Los Angeles Region 
PREDICTING AREAL LIMITS OF 

EARTHQUAKE-INDUCED LANDSLIDING 

By R. C. Wilson and D. K. Keefer 

INTRODUCTION from earthquake-induced landslides. The topographic, 

geologic, and seismologic conditions of some areas are 

Just as manmade structures can be damaged or nearly optimum for producing earthquake-induced landdestroyed by severe shaking from an earthquake, so, slides, and a large population lives on steep hillsides and 

too, can natural slopes weaken and fail (figs. 159-163). along deep, narrow canyons. This combination of steep 

The resulting landslides can undermine buildings and slopes and relatively dense population is most signifithereby cause severe foundation damage or collapse. cant in the eastern Santa Monica Mountains, but other 

Landslides can overrun people and structures, block upland areas at risk include the Baldwin, Puente, Palos 

roads, and sever lifelines such as water pipes, power Verdes, and San Rafael Hills, the canyons in the Verlines, or gas mains. Roads blocked by landslides can dugo Mountains, and the foothills of the San Gabriel, 

isolate communities and disrupt rescue and relief opera- Santa Ana, and San Bernardino Mountains. In addition, 

tions. Because a large earthquake in a mountainous earthquake-induced lateral-spread landslides can 

region can generate thousands of landslides in a few originate on or move down gentle slopes ( < 1 o in some 

minutes, the overall impact on the population is thus in- cases), so that areas of gently sloping to near-level 

creased far beyond that of any single landslide. ground underlain by saturated sandy materials may 

Earthquake-induced landslides have caused tens of also be at risk. During the 1971 San Fernando earththousands of deaths and billions of dollars in losses quake (M 6.6), landslides caused 135 million 1984 dollars 

worldwide in this century; in many earthquakes, the ' in damage to buildings, utilities, highways, and dams 

resulting landslides have caused as much or more (Kachadoorian, 1971; Youd, 1971; Califqrnia Division of 

damage than the other effects of seismic shaking. The Highways, 1975); one landslide on the Lower Van 

great 1964 Alaska earthquake, for example, caused an Norman Dam resulted in the temporary evacuation,of 

estimated 1.2 billion 1984 dollars in damage; 0.67 billion 80,000 people. The San Fernando earthquake was cen1984 dollars (56 percent of the total) was due to land- tered in the relatively sparsely populated foothills of the 

slides (W. R. Hansen, oral communication, 1977; Reuben San Gabriel Mountains, but a future large earthquake 

Kachadoorian, oral communication, 1977; T. L. Youd, located closer to population centers could cause hunoral communication, 1977). Landslides also caused at dreds of millions of dollars in damage and numerous 

least 48 of the 130 deaths reported in this earthquake casualties from landslides alone. 

(Keefer, 1984b). In a study of large (M> 6.9) Japanese 

earthquakes since 1964, Kobayashi {1981) determined 

that more than half of all earthquake-related deaths 

were caused by landslides. In several other foreign 

earthquakes, where particularly hazardous conditions 

were present, landslides have caused thousands of 

deaths. The most catastrophic of these landslides was a 

rock avalanche in the Peruvian Andes, which was triggered by an earthquake in 1970. This rock avalanche 

buried two cities and several villages and killed at least 

18,000 people (Plafker and others, 1971). 

The Los Angeles region, because of its mountainous 

terrain and seismic activity, faces a potential hazard 

This chapter describes a new method for predicting 

the areal limits of various types of landslides triggered 

by earthquakes such as those that could occur in the Los· 

Angeles region. The method is based both on studies of 

landslides in historical earthquakes and on a numerical 

analysis of dynamic slope stability. The first section of 

this chapter describes the characteristics of 

earthquake-induced landslides and the observed relations between earthquake magnitude and areal extent 

of landslides. The second section briefly describes 

known landslides that have occurred in representative 

California earthquakes. Then, the dynamic slope stabilEarthquake-Induced Landsliding 317 
FIGURE 159.-Rock falls along the Pacific Coast highway caused by the 1973 Point Mugu earthquake. Rock falls-individual boulders or disrupted 

masses of rock that descend slopes by bounding, rolling, or free falling-are the most abundant landslides (table 45) and the third leading 

cause of landslide-related deaths in historical earthquakes. 

ity analysis that links slope failure with levels of ground 

motion is discussed; a discussion of the severity of 

ground motion as a function of earthquake magnitude 

and distance follows. Relations are next developed for 

predicting the areal limits of ground motion sufficient to 

trigger landslides of various types, and maps are pre318 Earthquake Hazards in the Los Angeles Region 

sented showing the distribution of landslides predicted 

from a postulated M 6.5 earthquake on the NewportInglewood fault system. Finally, the relations between 

slope stability and shaking severity are illustrated by a 

hypothetical site evaluation for the postulated M 6.5 

event. 
FIGURE 160.-0blique aerial view of the prehistoric Blackhawk rock avalanche in the Lucerne Valley north of the San Bernardino Mountains. This 

rock-avalanche deposit contains about 300 million cubic meters of material; the maximum width of the lobe is 3 km, and the height of the raised 

distal rim is about 15 m. The triggering mechanism of this prehistoric landslide is uncertain, but it may have been an earthquake. (Photograph 

by J. S. Shelton; published with permission.) 

LANDSLIDES IN HISTORICAL 

EARTHQUAKES WORLDWIDE 

A recent study of worldwide data from historical 

earthquakes (Keefer and others, 1978; Keefer and Tannaci, 1981; Keefer, 1984a, b) shows that there are constraints on the types and distribution of landslides in 

seismic events. Following the principles of Varnes 

(1978), we classified earthquake-induced landslides 

primarily by material type and character of movement 

and secondarily by other attributes such as degree of internal disruption and degree of saturation. Material 

was classified as "rock" or "soil" on the basis of its 

state before landslide initiation. "Rock" signifies firm, 

intact bedrock. "Soil" signifies a loose, unconsolidated, 

or poorly cemented aggregate of particles that may or 

may not contain organic material. Many earthquakeinduced landslides are complex and involve two or more 

modes of movement and both rock and soil material; 

these landslides were classified according to the 

predominant mode of movement and material. 

Fourteen types of landslides were identified from 

historical earthquakes (Keefer, 1984b); most or all of 

them could occur in certain geologic environments in the 

Earthqu~ke-Jnduced Landsliding 319 
FIGURE 161.-Aerial view of coalescing disrupted soil slides caused by 

the 1976 Guatemala earthquake. Slides stripped away vegetation 

and sheets of sandy residual soil, generally less than 0.6 m thick, 

exposing white pumice bedrock. Slopes in the foreground are approximately 30 m high. Disrupted soil slides are chaotic jumbles of 

small blocks and soil grains that slide on planar or gently curved 

basal shear surfaces formed at soil-bedrock contacts or at boundaries between different soil layers. Hundreds of similar landslides 

in loose silty and sandy soils were triggered by the 1971 San Fernando earthquake. (Photograph taken from Harp and others 

(1981).) 

Los Angeles region. The fourteen types of landslides 

were grouped into three major categories-disrupted 

slides and falls, coherent slides, and lateral spreads and 

flows-on the basis of distinctions in movement, internal 

disruption, and geologic environments (table 44). 

Disrupted slides and falls (rock falls, rock slides, rock 

avalanches, soil falls, disrupted soil slides, and soil 

avalanches) are broken during movement into chaotic 

masses of small blocks, rock fragments, or individual 

soil grains. With the exception of rock avalanches, these 

landslides are generally shallow. They are detached 

from steep slopes and move at moderate to extremely 

rapid velocities (table 44). Coherent slides (rock slumps, 

rock block slides, soil slumps, soil block slides, and slow 

earth flows) are generally deeper seated and consist of 

a few relatively coherent blocks that slide at slow to 

very rapid velocities on moderate to steep slopes (table 

44). Lateral spreads and flows (soil lateral spreads, 

rapid soil flows, and subaqueous landslides5) involve 

some component of fluidlike flow. They move at rapid to 

extremely rapid velocities, commonly on gentle slopes. 

Several of these types of landslides are illustrated in 

figures 159 to 163. 

•Earthquake-induced subaqueous landslides are commonly complex, 

involving components of slumping, block sliding, lateral spreading, and 

(or) flow. They are grouped with lateral spreads and rapid flows, 

because most exhibit some component of fluidlike movement. 

320 Earthquake Hazards in the Los Angeles Region 

The most abundant landslides in the historical earthquakes studied by Keefer (1984b) were rock falls, 

disrupted soil slides, and rock slides (see list, this page), 

all of which are shallow, internally disrupted, and detached from steep slopes (table 44). All these types of 

landslides are likely to be abundant in moderate or large 

earthquakes in the Los Angeles region. Reports of subaqueous landslides, slow earth flows, rock block slides, 

and rock avalanches were rare in the historical earthquakes (see list, this page). The apparent rarity of subaqueous landslides is due partly to difficulties in observation. The reported numbers of the other three types, 

however, are probably good approximations of their 

actual numbers. In contrast to the worldwide record, 

rock slumps and block slides were relatively common in 

the 1971 San Fernando earthquake and probably would 

be abundant in future earthquakes in the Los Angeles 

region as well. 

The hazards presented by earthquake-induced landslides depend on their potential abundance, their movement characteristics, and the distribution of population 

and constructed works relative to likely sources of landslides. Although all types of earthquake-induced landslides pose some hazard to life, at least 90 percent of the 

landslide-caused deaths in the historical earthquakes 

studied resulted from rock avalanches, rapid soil flows, 

and rock falls (Keefer, 1984b). 

Rock avalanches and rapid soil flows, the two leading 

causes of death, are similar in that they can travel 

several kilometers at high velocities on slopes as gentle 

as a few degrees. Most deaths caused by these landslides resulted from burial of cities or towns on gently 

Relative abundances of earthquake-induced 

landslides in 40 historical earthquakes worldwide 

[Landslide type listed in order of decreasing total numbers. From Keefer (1984b)] 

Very abundant(> 100,000): 

Rock falls 

Disrupted soil slides 

Rock slides 

Abundant (10,000 to 100,000): 

Soil lateral spreads 

Soil slumps 

Soil block slides 

Soil avalanches 

Moderately common (1,000 to 10,000): 

Soil falls 

Rapid soil flows 

Rock slumps 

Uncommon (100 to 1,000): 

Subaqueous landslides 

Slow earth flows 

Rock block slides 

Rock avalanches 
FIGURE 162.-Aerial view of the Native Hospital slide, a large soil block slide in Anchorage, Alaska, caused by the 1964 earthquake. Soil block 

slides consist of one or a few coherent blocks that slide in a translational manner, exhibiting little or no rotation. Most have grabens at their 

heads and pressure ridges at their toes. Similar landslides, in somewhat different geologic environments, have been triggered by several 

southern California earthquakes, including the 1940 Imperial Valley, the 1952 Kern County, the 1966 Parkfield, and the 1971 San Fernando. 

(Photograph COIJrtesy of U.S. Army.) 

Earthquake-Induced Landsliding 321 
---...,=---=-= 

FIGURE 163.-Side-scan sonograph record of part of a subaqueous landslide offshore of the Klamath River, triggered by the Humboldt County, 

Calif., earthquake of November 8, 1980. The sinuous ridge running from the upper left to the lower right is the primary landslide toe. The lobes 

near center to the left of the toe are subsidiary flows. The direction of landslide movement is toward the lower left. Sonograph from Field and 

Hall (1982). 

sloping ground several kilometers from the sites of landslide initiation. These landslides are relatively uncommon in the worldwide historical record (see list, p. 320]; 

no rock avalanches and only a few earthquake-induced 

rapid soil flows are known from the historical record in 

the Los Angeles region. Rapid soil flows are common in 

the region during periods of high rainfall, however 

(Campbell, 1975). Furthermore, a single large rock 

avalanche or rapid soil flow could cause catastrophic 

damage. 

Rock falls, the third leading cause of death, are also 

the most abundant landslides in earthquakes and occur 

in virtually all types of rocks on slopes steeper than 40°. 

Areas at risk from rock falls are limited by the distances 

(as much as several hundred meters] that boulders can 

bounce or roll when they reach the bases of steep 

slopes. 

In addition to rock avalanches, rapid soil falls, and 

rock falls, leading causes of property damage among 

earthquake-induced landslides are soil slumps and soil 

lateral spreads. The propensity of such slumps and 

lateral spreads to cause property damage is due to their 

abundance (see list, p. 320) and to their occurrence on 

gentle slopes, where human development is common, 

322 Earthquake Hazards in the los Angeles Region 

and in manmade fill (Youd and Perkins, 1978; Keefer, 

1984b). Soil slumps and lateral spreads caused more 

than half of the landslide-related damage in the 1971 

San Fernando earthquake. Conditions favoring formation of lateral spreads in the Los Angeles region are 

discussed by Tinsley and others (this volume). 

Whether a particular slope produces a landslide during an earthquake depends on the strength of the hillside materials, the slope geometry, the ground-water 

conditions, and the level of shaking. Analytical techniques treating these factors are developed and presented later in this chapter. General types of geologic 

environments most likely to produce landslides during 

earthquakes in the Los Angeles region are shown in 

table 45. 

Maximum distances of landslides from the faultrupture zones of historical earthquakes are plotted in 

relation to magnitude in figure 164 for the three major 

categories of landslides. Approximate upper bounds 

were fitted to the data to show the greatest distance 

from the fault rupture at which an earthquake of given 

magnitude is likely to cause landslides in each category. 

Extension of the upper bounds to M < 5.3 is based on 

intensity data from U.S. earthquakes, which suggest that 
the smallest events likely to cause disrupted slides and 

falls, coherent slides, and lateral spreads and flows are 

M 4.0, M 4.5, and M 5.0, respectively. The estimate of a 

M 5.0 event as the smallest likely to cause lateral 

spreads and flows agrees with Kuribayashi and Tatsuoka's (1975, 1977), Youd's (1977), and Youd and 

Perkins' (1978) estimations that soil liquefaction is 

unlikely to occur in M < 5 events. 

Scatter in the data in figure 164 indicates that factors 

other than magnitude influence the maximum distance 

from the fault rupture at which landslides occur. Factors probably causing significant scatter includ.e earthquake focal depth, variations in the ground-motion 

characteristics of individual earthquakes, uncertainties 

in distances and magnitude determinations, and local 

geologic conditions. Geologic conditions particularly 

influence distances by controlling the distribution of 

susceptible sites, an effect most evident for small events 

where the area shaken is small and thus may contain 

only a few scattered susceptible slopes. 

EXAMPLES OF LANDSLIDES 

IN CALIFORNIA EARTHQUAKES 

Landslides caused by five earthquakes in California 

are discussed in this section to illustrate the range in 

potential for earthquake-induced landslides in the Los 

Angeles region. The earthquakes chosen are discussed 

in order of increasing magnitude. Because the effects of 

the 1857 Fort Tejon earthquake, the only great event to 

have occurred in southern California in historical time, 

are not well documented, we use the 1906 San Francisco 

earthquake to illustrate the potential for landslides in 

such a large California event. 

1978 Santa Barbara Earthquake 

The 1978 Santa Barbara earthquake (M 5.6), centered 

4 km offshore of Goleta Point (Lee and others, 1978), 

caused a few dozen small rock falls, rock slides, and soil 

falls scattered throughout an area of approximately 

200 km2 (Harp and others, 1980). These landslides were 

confined to steep roadcuts in the Santa Ynez Mountains 

and sea cliffs near Goleta Point. The landslides were 

primarily in weakly cemented and closely jointed 

sedimentary rocks and in residual and colluvial soils 

developed on them. Most of these landslides had 

volumes of only a few cubic meters. The largest rock 

fall-and the only one to cause reported damage-had a 

volume of about 100 m3 and blocked California State 

Highway 154 near San Marcos pass for 30 hours. 

One soil slump, near Elwood, was reported in the 

earthquake. This slump, in an uncompacted railroad embankment composed of excavated rock, soil, and waste 

lumber, was at least partially responsible for derailing a 

freight train that moved onto the embankment a few 

minutes after the earthquake (Harp and others, 1980). 

On the University of California's Santa Barbara campus, a lateral spread occurred in soft alluvial fill on the 

banks of Goleta slough (Miller and Felszeghy, 1978). 

1933 Long Beach Earthquake 

Documentation of landslides and other ground 

failures in the 1933 Long Beach earthquake (M 6.2) is incomplete. On and near the coast between Long Beach 

and Newport Beach, manmade fills in areas underlain 

by wet sand and mud settled and spread (Wood, 1933). 

In the Belmont Shore residential district of Long Beach, 

pavement was buckled, and cracks up to 100 mm wide 

opened along the banks of a filled canal (Maher, 1933), 

probably because of lateral spreading. Slumps were 

observed in manmade fills and unconsolidated sediments between Long Beach and Compton (Neumann, 

1935). The slumps and lateral spreads caused some 

localized damage (fig. 165). Sand boils were reported 

north of Newport Beach, at Huntington Beach, in the 

Alamitos-Seal Beach area, near the mouth of the Santa 

Ana River, at Balsa Chica, at Cabrillo Beach, and in the 

Compton area (Wood, 1933; Barrows, 1973; Oakeshott, 

1973). Rock falls and other landslides of undetermined 

type in mountainous terrain were reported from canyons in central Los Angeles County, from as far south as 

San Clemente, and from as far north and west as Anacapa Island (Maher, 1933; Neumann, 1935). 

1971 San Fernando Earthquake 

Landslides in the 1971 San Fernando earthquake (M 

6.6) were concentrated in about 250 km2 of mountainous 

terrain north of the surface fault rupture (fig. 166A) and 

also occurred throughout an additional 3,000 kmz 

stretching southward from the epicentral region to the 

Palos Verdes Peninsula (Coffman and von Hake, 1973) 

and eastward through most of the San Gabriel Mountains (Morton, 1971). These landslides caused at least 

135 million 1984 dollars in damage. 

The earthquake triggered several hundred rock falls, 

rock slumps, soil falls, disrupted soil slides, soil avalanches, and soil slumps (fig. 166B) (Morton, 1971, 1975; 

California Division of Highways, 1975; Yen and Trotter, 

Earthquake-Induced Landsliding 323 
TABLE 44.-Characteristics of earthquake-induced landslides 

[Modified from Keefer, 1984b] 

Type of 

Name movement Internal disruption' Dry 

Landslides in rock 

Disrupted slides and falls: 

Rock falls -------- Bounding, rolling, free High or very high X 

falling. 

Rock slides ------- Translational sliding High X 

on basal shear 

surface. 

Rock avalanches -- Complex, involving Very high X 

sliding and (or] 

flow 

as stream 

of rock 

fragments. 

Coherent slides: 

Rock slumps ----- Sliding on basal shear Slight or moderate ? 

surface; 

component 

ofheadward 

rotation. 

Rock block slides -- Translational sliding Slight or moderate ? 

on basal 

shear surface. 

Landslides in soil 

Disrupted slides and falls: 

Soil falls --------- Bounding, rolling, free High or very high X 

falling. 

Disrupted soil Translational sliding High X 

slides. --------- on basal shear 

surface or 

zone of 

weakened, 

sensitive 

clay. 

Soil avalanches --- Translational sliding; Very high X 

subsidiary flow. 

Coherent slides: 

Soil slumps ------ Sliding on basal shear Slight or moderate 

surface; 

component 

ofheadward 

rotation. 

Soil block slides --- Translational sliding Slight or moderate 

on basal shear 

surface. 

Slow earth flows -- Translational sliding Slight 

on basal shear 

surface; minor 

internal flow. 

324 Earthquake Hazards in the Los Angeles Region 

Water content 

Partly 

Moist saturated Saturated Velocity' Depth' 

X X X Extremely rapid Shallow 

X X X Rapid to Shallow 

extremely 

rapid. 

X X X Extremely rapid Deep 

X X X Slow to rapid Deep 

X X X Slow to rapid Deep 

X X X Extremely rapid Shallow 

X X X Moderate to Shallow 

rapid. 

X X X Very rapid to Shallow 

extremely 

rapid. 

x X X Slow to rapid Deep 

? X X Slow to very Deep 

rapid. 

X X Very slow to Generally 

moderate shallow; 

with very occasionrapid ally 

surges. deep. 
TABLE 44.-Characteristics of earthquake-induced landslides-Continued 

Name 

Type of 

movement Internal disruption' 

Water content 

Partly 

Dry Moist saturated Saturated Velocity' Depth• 

Landslides in soil-Continued 

Lateral spreads and flows: 

Soil lateral ------- Translation on basal 

spreads. zone of liquefied 

gravel, sand, or 

silt or weakened, 

sensitive clay. 

Rapid soil flows --- Flow 

Subaqueous ------

landslides. 

Complex, involving 

slumping, lateral 

spreading, and 

(or) flow. 

Generally moderate; 

occasionally 

slight; occasion· 

ally high. 

Very high 

Generally high or 

very high; 

occasionally 

moderate. 

X ? 

X X Very rapid Variable 

? X Very rapid to Shallow 

extremely 

rapid. 

X X Rapid to Deep 

extremely 

rapid. 

1

Siight: landslide consisting of one or a few coherent blocks. Moderate: landslide consisting of several coherent blocks. High: landslide consisting of numerous small blocks and individual soil 

grains and rock fragments. Very high: landslide almost completely disaggregated into individual soil grains or small rock fragments. 2

Extremely slow, less than 0.6 m/yr; very slow, between 0.6 and 1.5 m/yr; slow, between 1.5 m/yr and 1.5 m/mo; moderate, between 1.5 m/mo and 1.5 m/d; rapid, between 1.5 mid and 0.3 m/min; 

very rapid, between 0.3 m/min and 3 m/s; extremely rapid, more than 3 mls. Terminology from Varnes {1978). 3

Shallow, generally less than 3 m; deep, generally more than 3 m. 

1978; Clark and others, 1979). Rock falls were common 

in roadcuts and on steep cliffs in intensely jointed conglomerates, gneisses, and granites. Soil falls occurred in 

uncemented and weakly cemented sands and gravels 

along streambanks. Disrupted soil slides and soil avalanches involved loose, unsaturated layers of silty and 

clayey sand less than 1 m thick. Most rock slumps reactivated preexisting slumps. Soil slumps took place in 

weak, fine-grained highway and bridge-approach fills; 

slumps and roadcut failures caused an estimated 12 

million 1984 dollars in damage to highways (California 

Division of Highways, 1975). Landslides also damaged 

the Camp Karl Holton Juvenile Facilities and several 

buildings near the Olive View Hospital (Yerkes, 1973). 

Several soil lateral spreads occurred in the Van Norman Lakes area. The largest lateral spread, the Juvenile 

Hall slide, caused more than 58 million 1984 dollars in 

damage to the San Fernando Valley Juvenile Hall, the 

Sylmar electrical converter station, and adjacent highway structures, railroad facilities, pipelines, and canals 

(Youd, 1971; Youd and Olsen, 1971). This lateral spread 

involved alluvial-fan materials containing a subsurface 

zone of saturated, loose sandy silt and fine sand 

(Fallgren and Smith, 1973) which was inferred to have 

liquefied (Youd, 1971). The average surface slope of the 

landslide was only 1.5° (Youd, 1971). 

A potentially catastrophic liquefaction-induced landslide occurred on the upstream face of the Lower Van 

Norman Dam (Youd and Olsen, 1971; Seed and others, 

1975) (see Tinsley and others, this volume, fig. 128B). 

This landslide seriously weakened the dam and resulted 

in the temporary evacuation of 80,000 people living 

downstream. The cost of rebuilding the dam was estimated at 66 million 1984 dollars (Kachadoorian, 1971). 

The dam, constructed in several stages from 1912 

through 1940, consisted of a hydraulically placed sandfill embankment capped by several types of rolled fills; 

the main failure zone was in the hydraulic fill (Seed and 

others, 1975). 

1952 Kern County Earthquake 

The 1952 Kern County earthquake (M 7.5) and its 

aftershocks caused hundreds of landslides in the southwestern Sierra Nevada, the Tehachapi Mountains, and 

the San Gabriel Mountains (Buwalda and St. Amand, 

1955). Types of landslides included rock falls, rock 

slides, rapid soil flows, disrupted soil slides, and reactivations of existing coherent, deep-seated slides. Landslides blocked numerous highways, some for several 

weeks, and dammed several canyons, creating small 

lakes. The highest concentrations of landslides, including most reactivations, were on steep slopes near 

the surface expression of the fault-rupture zone, where 

shaking was presumably most severe. Rock falls were 

reported as far from the fault rupture as the Angeles 

Forest Highway between Vincent and Pasadena 

(Oakeshott, 1955). 

On the floor of the San Joaquin Valley, ground cracks 

were reported from an area of several hundred square 

kilometers between Arvin and Maricopa (Steinbrugge 

Earthquake-Induced Landsliding 325 
TABLE 45.-Geologic environments likely to produce earthquake-induced landslides in the Los Angeles region 

Landslide 

type Type of material 

Rock falls ---------- Rocks weakly cemented, intensely fractured, or 

weathered; contain conspicuous planes of 

weakness dipping out of slope or contain 

boulders in a weak matrix. 

Rock slides --------- Do. 

Rock avalanches ----- Rocks intensely fractured and exhibiting one of the 

following properties: significant weathering, 

planes of weakness dipping out of slope, weak 

cementation, or evidence of previous 

landsliding. 

Rock slumps -------- Intensely fractured rocks, preexisting rock slump 

deposits, shale, and other rocks containing 

layers of weakly cemented or intensely 

weathered material. 

Rock block --------- Rocks having conspicuous bedding planes or similar 

slides. planes of weakness dipping out of slopes. 

Soil falls ----------- Granular soils that are slightly cemented or 

contain clay binder. 

Disrupted soil ------- Loose, unsaturated sands 

slides. 

Soil avalanches ------ Do. 

Soil slumps--------- Loose, partly to completely saturated sand or silt; 

uncompacted or poorly compacted manmade 

fill composed of sand, silt, or clay; preexisting 

soil slump deposits. 

Soil block ---------- Loose, partly or completely saturated sand or silt; 

slides. uncompacted or slightly compacted manmade 

fill composed of sand or silt; bluffs containing 

horiwntal or subhorizontallayers of loose, 

saturated sand or silt. 

Slow earth --------- Stiff, partly to completely saturated clay and preflows. existing earth-flow deposits. 

Soil lateral --------- Loose, partly or completely saturated silt or sand; 

spreads. uncompacted or slightly compacted manmade 

fill composed of sand. 

Rapid soil flows ----- Saturated, uncompacted or slightly compacted 

manmade fill composed of sand or sandy silt 

(including hydraulic-fill earth dams and 

tailings dams); loose, saturated granular soils. 

Subaqueous -------- Loose, saturated granular soils 

landslides. 

Minimum 

slope 

inclination, 

in deg 

40 

35 

25 

15 

15 

40 

15 

25 

10 

5 

10 

.3 

2.3 

.5 

Remarks 

Particularly common near ridge crests and on spurs, 

ledges, artificially cut slopes, and slopes undercut by active erosion. 

Occasionally reactivate preexisting rock slide 

deposits. Particularly common in hillside flutes 

and channels, on artificially cut slopes, and on 

slopes undercut by active erosion. 

Restricted to slopes of >150-m relief that are undercut by active erosion. 

Particularly common on stream banks, terrace 

faces, coastal bluffs, and artificially cut slopes. 

Occasionally reactivate preexisting soil avalanche 

deposits. 

Particularly common on embankments built on soft, 

saturated foundation materials, in hillside cutand-fill areas, and on river and coastal flood 

plains. 

Particularly common in areas of preexisting landslides along river and coastal flood plains, and 

on embankments built on soft, saturated 

foundation materials. 

Particularly common on river and coastal flood 

plains, embankments built on soft, saturated 

foundation materials, delta margins, sand 

dunes, sand spits, alluvial fans, lake shores, 

and beaches. 

Particularly common on delta margins 

and Moran, 1954; Warne, 1955). The cracks, some of 

which were associated with soil slumps, block slides, 

and (or) lateral spreads, caused significant damage to 

agricultural land and building foundations (Steinbrugge 

and Moran, 1954). Slumps also caused minor damage to 

highway and bridge-approach fills in the epicentral 

region (Perry, 1955). The total area affected by landslides in this earthquake sequence was approximately 

7,000 km2 • 

326 Earthquake Hazards in the Los Angeles Region 

1906 San Francisco Earthquake 

The 1906 San Francisco earthquake (M 7.7) caused 

thousands of landslides in an area of 32,000 km2 stretch-
ing from Arcata on the north to near King City on the 

south. Landslides killed at least 11 and probably several 

dozen people and caused significant damage to buildings, roads, bridges, railroads, and other manmade 

structures. The summary of landslides and related effects caused by this earthquake is based on information 

compiled and interpreted by Youd and Hoose (1978). 

In mountainous terrain of the northern California 

Coast Ranges, the most numerous landslides were rock 

and soil falls, rock slides, disrupted soil slides, and soil 

slumps. Rock falls, soil falls, and rock slides affected 

300 km of coastal bluffs as well as many roadcuts and 

steep canyon walls. One person was killed by a rock fall. 

Many preexisting soil slumps were reactivated, probably because the earthquake occurred during a rainy 

season when preexisting landslides were marginally 

stable because of high ground-water levels. Rock 

slumps, block slides, and avalanches, rapid soil flows, 

and slow earth flows were reported in smaller numbers 

in the Coast Ranges. Two rock avalanches, each involving several hundred thousand or million cubic meters of 

material, killed at least 10 people in the Santa Cruz 

Mountains south of San Francisco. 

In areas of loose sandfill in downtown San Francisco, 

soil lateral spreads, ground settlement, and other soilliquefaction effects caused significant damage in three 

major zones totaling about 3 km2 in area. Among the 

many buildings damaged was the Valencia Street Hotel, 

which collapsed and burned, killing several dozen people. The collapse may have been partially caused by a 

lateral spread in the ground beneath the structure. 

Ground movements also broke two water mains, cutting 

off the water supply to a major part of San Francisco 

that subsequently was destroyed by fire. Outside San 

Francisco, soil lateral spreads and related phenomena 

occurred in alluvial, coastal, and filled areas (fig. 167). 

Many stretches of river flood plains several kilometers 

long were disrupted by cracks, settlements, and lateral 

spreads. 

NUMERICAL MODELS 

FOR EARTHQUAKE-INDUCED 

LANDSLIDES 

Whether a particular slope will fail during an earthquake depends on the answers to two questions: (1) how 

stable was the slope before the earthquake and (2) how 

severely did the earthquake shake the slope? Thus, we 

seek some way to numerically express both the preearthquake stability of the slope and the severity of the 

shaking in the same dimensional units, so that they can 

be directly compared with each other. 

In the next section, we develop mathematical models 

of the mechanics of landslides to measure and express 

the slope stability under both static (aseismic) and 

dynamic (seismic) conditions. In the following sections, 

we use statistical analyses of strong-motion data to 

measure the shaking severity. Finally, we discuss the 

relation of the shaking severity to the magnitude and 

distance from the seismic source. 

Mechanics of Slope Stability 

We begin the analysis by examining slope stability 

under static (aseismic) conditions. Figure 168 depicts a 

hypothetical landslide of the block-slide type. Two 

forces act on the center of mass of this potential landslide-the gravitational load (L), which is the downslope 

component of the weight of the landslide mass, and an 

opposing force (R), which is the resistance of the slope to 

deformation from downslope movements. The maximum 

resistance (Rmaxl is a function of the strength of the slope 

material and can be expressed as the integration of the 

shear strength over the area of the sliding surface. 

Following standard slope-engineering nomenclature, we 

express the static slope stability as the ratio of the maximum resistance to the load and call this ratio the .factor 

of safety (FS): 

FS= 

For a dynamic (seismic) situation, this analysis must 

be taken a step further. During an earthquake, seismic 

waves passing through the slope create an acceleration 

field (a(t)), which exerts an additional body force on the 

mass (m) of the potential landslide. During the time of 

strong shaking, this seismically induced force will 

fluctuate and sporadically add to the downslope load. If 

this downslope seismic force is large enough, the total 

downslope load (L+m a(t)) may exceed the maximum 

resistance, and the slope will undergo irreversible 

displacement. As Wilson and Keefer (1983) have done, 

we express this level of ground motion in terms of a 

critical acceleration (AJ, which is the seismic acceleration that, when multiplied by the mass, is equal to the 

difference between the maximum resistance and the 

gravitational load, 

or 

(

Rmax -L) mAc= LL L=(FS-1)L 

Earthquake-Induced Landsliding 327 
(/) 

....J 

....J(/) 

~ffi a:f0~ 

(/)0 

W....J §Q 

500 

200 

100 

(/) z 50 

0 - ww 

f-Z 

a_ 0 20 

~N 

(/)W o§ 

u..f- 0!5 

wa: 

u, 

Zf-

~S (f)<l: 

ou.. 

10 

5 

2 

;:a;;:2 

~~ 0.5 

x 

<l: 

:2 0.2 

A MAGNITUDE (M) 

c MAGNITUDE (M) 

328 Earthquake Hazards in the Los Angeles Region 

:2 

0 

a: U..(f) 

(/)a: 

ww of- _w 

....J:2; 

(/)0 

f-::::! 

z~ 

w 

a:z 

w-

:c - ow 

uZ 

0 u..N 

ow 

wa: 

U::l Zf- <l:a_ 

f-:::1 

(/)0: 

0~ ....J :2:::1 

::l<l: 

;:a;;u.. 

x 

<l: 

:2 

1000 

500 

200 

100 

50 

20 

10 

5 

2 

~ (/) 200 a: a: 

u..~ w w 100 

o:2 

:::JS 5o (/)_ 

0~ 

5~ 20 u_W 

0 6 10 WN 

u 

zw 5 <l:a: 

f-:::1 

~ll: 

0:::1 2 ;:a;; a;= 

::lf-

;:a;;....J _::I 

x<l: <l:u.. 

:2 0.5 

0.2 

8 

D 

I 

~ 

!I 

•sF 

IVe 

• 

• 

•FE 

MAGNITUDE (M) 

- ~ 

--;:?" ~~·= ... ········ •••••••• · //•" / ..... ·· 

/ (..······ 

/ /_..:.··· 

I .: . ...- / .. f I /.: 

I / f 

I I ! 

I I f 

I I 

- - - - Disrupted slides 

and falls 

--- ·- Coherent slides ....................... Lateral spreads 

and flows 

MAGNITUDE (M) 
so that 

Ac = (FS -1)L/m 

Therefore, 

Ac=(FS-1)g sin 8 

where g is the acceleration due to gravity and 8 is the 

slope angle. Thus, the critical acceleration is the 

minimum ground acceleration required to overcome the 

maximum resistance of the slope to sliding. To cause a 

landslide on a particular slope, the ground acceleration 

must exceed Ac for a finite length of time (the time requirement is examined in a following section). Henceforth, we will use the critical acceleration as the 

numerical measure of the stability of a slope and its susceptibility to an earthquake-induced landslide. 

If the slope steepness and the strength of the slope 

materials are known, we can estimate the critical acceleration of a shallow landslide on an infinitely long 

slope (fig. 168) from the equation 

A c' 

_c_ =- +(1-A) tan r/>' cos 8-sin 8 

g -yh 

where 8 is the slope steepness angle, 'Y is the specific 

weight of slope material, h is the thickness of the potential landslide, c' is the effective cohesion, r/>' is the effective friction angle of the slope material, and A is the ratio 

of pore pressure to overburden stress. Values of c' and r/>' 

appropriate for dynamic conditions, which Newmark 

(1965, p. 150) noted should be used, "may involve considerably reduced shearing strengths owing to the 

dynamic effects on the pore pressures." Values of c' and 

rf>' measured in standard undrained tests should yield 

reasonably conservative results. 

This infinite-slope analysis can be further generalized 

by grouping various types of slope materials into three 

broad lithologic categories, each having assumed average values of c' and rf>' (for dynamic conditions) (fig. 169). 

Figure 169 is a plot of Ac versus slope steepness for each 

category of slope material. If this plot is used, the 

qualitative slope-lithology combinations described in 

table 45 as being susceptible to seismically · induced 

landsliding can be seen to have relatively low values of 

Ac (<0.3 g). 

Newmark Analysis 

The critical acceleration (Ac) represents the ground 

motion necessary to begin the process of slope failure. 

Because small, irreversible displacements do not necessarily result in a slope failure of practical or engineering 

significance, however, how far the landslide would 

move must now be determined. This distance can be 

estimated by using a technique developed by Newmark 

(1965), which hereafter will be called the Newmark 

analysis. The Newmark analysis, which models the landslide as a rigid friction block resting on a slope, uses a 

record of ground acceleration versus time (a strongmotion record) to calculate the expected displacement 

of the block. This model is most directly applicable to 

translational, coherent slides (block slides and slow 

earth flows) (table 44) and, after slight modification, to 

rotational slumps. If yet another modification is introduced to account for the importance of tensile failure 

and more brittle behavior, the model can also be applied 

to the initial stages of disrupted landslides. The model, 

however, has only limited applicability to liquefactioninduced lateral spreads and flows. 

The significance of critical acceler(,ltion is illustrated 

in figure 170A, a plot of acceleration versus time for an 

actual strong-motion record. Superimposed on this 

strong-motion record is a horizontal line corresponding 

to the critical acceleration of a hypothetical slope. If the 

strong-motion record contained a peak acceleration less 

than the critical acceleration for our hypothetical slope, 

then the displacement of the block would be zero, and 

the slope would remain stable. When the ground motion 

does exceed the critical acceleration, however, the next 

...... FIGURE 164.-Maximum distance from the fault-rupture zone [surface or subsurface) to landslides in earthquakes of different magnitudes [from 

Keefer, 1984b}. California earthquakes in the data set as follows: CL, August 6, 1979, Coyote Lake; DC, March 22, 1957, Daly City; FE, 

February 9, 1971, San Fernando; HV, March 15, 1979, Homestead Valley; IV, May 19, 1940, Imperial Valley; KC, July 21, 1952, Kern County 

(not included by Keefer (1984b)); MD, January 24, 1980, Greimville-Mount Diablo; ML, May 25, 1980, Mammoth Lakes; PA, June 28, 1966, 

Parkfield-Cholame; SB, August 13, 1978, Santa Barbara; SF, April 18, 1906, San Francisco. Unlabeled points represent earthquakes outside 

California (identified by Keefer (1984b}}. Vertical bars indicate uncertainties, where they are known, in boundaries of fault-rupture zones, in 

locations of most distant landslides, or both. Horizontal bars indicate the range in reported magnitudes. Magnitudes greater than or equal to 

7.5 are generally moment magnitudes as defined by Kanamori (1977); magnitudes less than 7.5 are generally Richter surface-wave 

magnitudes. A, Maximum distance from the fault-rupture zone to a dl'srupted slide or fall. The solid line is an approximate upper bound enclosing all data. B, Maximum distance from the fault-rupture zone to a coherent slide. The solid line is an approximate upper bound enclosing all 

data. G, Maximum distance from the fault-rupture zone to a lateral spread or flow. The solid line is an approximate upper bound enclosing all 

reported occurrences. The dot-dash line is an upper bound determined by Youd and Perkins (1978} for soil liquefaction phenomena having 

displacements of at least 10 em in gently sloping Holocene flood-plain, deltaic, or eolian materials. D, Comparison of the upper bounds from A, 

B. and G. The dashed line is the bound for disrupted slides and falls; the dash-double-dot line is the bound for coherent slides; the dotted line is 

the bound for lateral spreads and flows. 

Earthquake-Induced Landsliding 329 
step is to integrate those portions of the strong-motion 

record that lie above the critical acceleration (fig. 

170A). 

The integration begins at point A (figs. 170A, 170B, 

170C), where the ground acceleration first exceeds the 

critical acceleration. We integrate over time that portion AB of the ground motion above Ac to calculate the 

velocity of the block (fig. 170B). At point B, the block 

reaches the maximum velocity for this acceleration 

pulse. After point B, when the ground acceleration 

drops below the critical acceleration, the block is still in 

motion because of its inertia but is now being decelerated by the friction that still exists beneath the block. 

Also, the ground acceleration may well swing around in 

the opposite direction and directly oppose the motion of 

the block (as it does at the end of the second pulse). Eventually, the motion of the block will cease, and the block 

will come to rest at point C. (The point at which the block 

again comes to rest occurs at some finite time after point 

B, the point where ground acceleration first falls below 

Ac.) Finally, the displacement of the block is calculated 

by integrating the velocity of the block over time (fig. 

170C). Note where points A, B, and C fall on the 

displacement-time curve. In this example, there is also a 

second pulse of ground acceleration exceeding Ac and 

producing a second displacement increment, which ends 

with a small displacement in the upslope direction. 

In his original report, Newmark (1965) was concerned 

with artificial embankments, and computed displacement was used as a design factor; one can either design 

the embankment to tolerate the seismically induced 

displacement without significant loss of strength or 

design a stronger embankment to reduce the seismic 

displacement. In either case, the resistance of the slope 

to sliding, expressed as Ac, can be treated as a constant 

during the dynamic analysis. In actual cases, however, 

as the displacement becomes significant, the slope 

material may lose some shear strength, and Ac thus may 

decrease (Goodman and Seed, 1966). If the displacement 

continues, the slope may lose so much strength that Ac 

will go to zero, and the slope will become statically 

unstable (FS < 1). In this case, the slope may continue to 

move even after the seismic shaking ceases. 

For a specified slope and known slope materials, we 

could, by careful laboratory measurements of strength 

versus strain, estimate the loss of strength of the slope 

(and thus the decrease in AJ as a function of displacement. Goodman and Seed (1966), for example, performed such an analysis for a laboratory-scale model of 

a slope in uncemented sand. Such an analysis, however, 

is restricted to slopes where the mechanical properties 

are well known. For a regional application, such as mapping susceptibility, it is simply not practical to consider 

330 Earthquake Hazards in the Los Angeles Region 

decreases in Ac as a function of displacement as an integral part of the numerical analysis. 

Instead, the numerical analysis of the strong-motion 

record is performed under the arbitrary assumption of a 

constant value of critical acceleration. The displacement thus calculated is then compared with a "benchmark" value of displacement, herein termed the critical 

displacement, beyond which it is likely that the slope 

would lose a significant amount of strength. If the computed value of displacement (assuming a constant Ac) is 

a small fraction of the value of the critical displacement, 

then the slope probably lost little strength and regained 

most of its stability when the seismic shaking ceased. In 

such a case, little damage would be expected, either to 

the slope itself or to overlying structures. If, however, 

the computed (constant Ac) displacement exceeds the 

critical displacement, then significant damage becomes 

a potential result of the seismic shaking; if the computed 

displacement greatly exceeds the critical displacement, 

then catastrophic failure of the slope could result. 

The actual value of the critical displacement may 

vary widely, depending on the mechanism of slope failure (rock fall, slump, block slide, and so on), the 

lithology, the slope geometry, and the previous history of 

slope movement. To quantify this parameter for regional 

application, we assign a value of 10 em for the critical 

displacement of coherent slides (table 44). This value is 

consistent with two ideas: 

1. In moving 10 em, a landslide will probably have 

broken most of the cohesive bonds along the slip 

surface and across the scarp at the top of the 

landslide and will also have begun to override 

the toe at the bottom. 

2. Ten centimeters is our estimate of the displacement 

that a typical house foundation could withstand 

before experiencing significant damage. This 

second reason would also apply to slope failures 

from lateral spreads and flows; thus, a value of 

10 em is also assigned for the critical displacement for landslides of these types. Youd (1980), 

in a study of damage to building foundations as 

a consequence of ground-failure displacement, 

found that most flexible buildings on wellreinforced foundations can withstand 10 em of 

extensional ground displacement before incurring significant damage. 

Rock falls and most other disrupted landslides (table 

44) involve a significant component of tensile failure, a 

mechanism more brittle than shear and for which the 

critical displacement is lower. So, we shall assume a 

value of 2 em for the critical displacement for disrupted 

landslides. 
FIGURE 165.-Damage to the Pacific Coast Highway from slumping or 

lateral spreading southeast of Huntington Beach during the 1933 

Long Beach earthquake. (Photograph from the City of Long Beach 

Public Library History Collection.) 

The Newmark analysis, commonly used in designing 

artificial embankments for more than 15 yr, has recently 

been checked against an actual case of earthquakeinduced failure on a natural slope (Wilson and Keefer, 

1983) and was demonstrated to be a valid predictor of 

the displacement of a landslide during seismic shaking. 

The Newmark analysis was also used with the plot in 

figure 169 to derive susceptibility units for an experimental seismic slope stability map of San Mateo 

County in California (Wieczorek and others, 1985). 

Relating Shaking Severity 

to Slope Stability 

In the preceding sections, we have discussed how the 

preearthquake stability of a slope can be expressed in 

terms of the critical acceleration [AJ, a function of slope 

steepness and material properties. The Newmark analysis also allows calculation of how far a landslide with a 

given Ac would move under the time-history of shaking 

represented by a particular strong-motion record. The 

displacement can be compared directly with the critical 

displacement (Uc = 2 or 10 em, depending on landslide 

type) to determine whether the slope would produce a 

landslide of practical significance. Now we need to 

describe the severity of seismic shaking in terms of a 

single number, independent of the sta"~Jility of any individual slope but expressed in the same physical units 

[acceleration), so that the severity can be compared 

directly with the stability. 

By taking the same given strong-motion record and 

repeatedly running the Newmark analysis [as depicted 

in fig. 170) for a family of values of Ac, from zero to the 

peak acceleration [A) of the record, a predicted 

displacement for each value of Ac can be calculated. In 

this way, we can calculate the response of any possible 

slope to the seismic ground motion represented by the 

given strong-motion record. [This procedure is analogous to the "response spectrum" analysis used in the 

engineering design of earthquake-resistant manmade 

structures.) 

Figure 171 is a plot of critical accelerations versus 

the corresponding displacements predicted from a 

number of strong-motion records. By taking the value of 

Ac that corresponds to a predicted displacement equal 

to the critical displacement (10 em for coherent landslides) for a given strong-motion record, a measure of 

the seismic shaking intensity that is directly related to 

slope stability can be derived. We abbreviate this value 

of Ac as [AJ10• Thus, the Taft record, for example, has an 

[Ac)10 = 0.03 g, whereas the Pacoima record has an 

(AJ10 = 0.33 g (fig. 171). 

The advantage of using the value of (Ac)10 to express 

the seismic shaking severity, as marked by the position 

of the Ac-displacement curve, is that it is expressed in 

the same physical units (acceleration) as our measure of 

seismic slope stability [AJ and is directly referenced to 

the critical displacement. The [AJ10 value gives the 

critical acceleration of the most resistant slope that 

would be expected to undergo significant displacement 

as a coherent slide for this level of seismic shaking. All 

slopes for which Ac> (Ac)10 should survive this shaking 

without significant failure. In the same way, we can 

reference the severity of seismic shaking to the critical 

displacement for disrupted landslides (Uc = 2 em) by deriving a value for (AJ2 • Therefore, [AJ10 and (Ac)2 become 

useful parameters for expressing seismic shaking 

severity for predicting earthquake-induced landslides. 

A somewhat less complicated way of expressing the 

severity of seismic shaking as recorded by a strongmotion record was developed by Arias (1970). Arias intensity (10 ) is defined as an integration over time of the 

acceleration squared (Arias, 1970): 

00 

Ia= ~ f[(a[t)]Z dt 

The Arias intensity is expressed in units of velocity, 

usually in meters per second. We can use the Arias intensity to replace the hundreds of points in a digitized 

Earthquake-Induced Landsliding 331 
118 30' 

A 6 MILES 

0 6 KILOMETERS 

FIGURE 166.-A, Locations of landslides (solid circles) in the area where slope failures triggered by the February 9, 1971, San Fernando earthquake were most abundant (Morton, 1971). B, Aerial view of landslides triggered in the Lopez Canyon area by the February 9, 1971, San Fernando earthquake. (Photograph by D. M. Morton.) 

strong-motion record with a single value and simplify 

the seismic input to the Newmark analysis by taking advantage of newly developed empirical relations between 

(AJ10, (Ach' and the Arias intensity (fig. 172). 

Figure 172 plots (AJ10 and (Ach versus the Arias intensity. Each data point represents a single strong-motion 

record in table 46 for which both the Arias intensity and 

the value of (AJ10 and (Ac)2 were calculated. Figure 172 

shows a linear logarithmic relation plotted between the 

Arias intensity and both (AJ10 and (Ac)2• For many cases, 

where only approximate estimates of (AJ10 or (AJ2 are 

required, we can avoid performing a number of 

Newmark analyses by simply calculating the Arias intensity and using the plot in figure 172. 

332 Earthquake Hazards in the Los Angeles Region 

SEVERITY OF SHAKING 

AS A FUNCTION OF 

MAGNITUDE AND DISTANCE 

Because strong-motion records are available for only 

a limited number of sites in a relatively small number of 

earthquakes, an independent technique is needed to 

estimate the distance over which a particular earthquake could trigger landslides on slopes having a given 

value of critical acceleration. To fill this need, we have 

developed an empirical relation for the severity of 

seismic shaking (as expressed by the Arias intensity) as 
FIGURE 166.-Continued 

a function of earthquake magnitude and distance from 

the seismic source. 

Because the data set of reported Arias intensity 

values is rather limited (table 47), two assumptions were 

used to constrain the statistical analysis: 

1. For a given distance from the seismic source, the 

logarithm of the Arias intensity is assumed to be 

a linear function of the magnitude of the earthquake as measured by the moment magnitude 

scale of Hanks and Kanamori (1979). 

2. For a given earthquake magnitude, an inverse square 

relation was assumed between the Arias intensity and the source distance. 

These two assumptions result in the following empirical 

magnitude-distance-Arias intensity relation: 

where M is the moment magnitude, r is the source 

distance (measured from the slip surface), K0 and Km are 

proportionality constants, Ku is the standard deviation of 

the distribution of values of Arias intensity for a given 

magnitude and distance, and P is exceedance probability (P = 0 for the mean (5o-percent exceedance probability) and P = ± 1 for one standard deviation above or 

below the mean (16- or 84-percent exceedance probability), respectively). 

The first assumption (that log Ia oc M) is supported by 

several relations from source-mechanism theory (Hanks 

and McGuire, 1981), which also allow the proportionality constant (Km) to be evaluated (W. Joyner, personal 

communication, 1983). The chain of reasoning laid out 

by Joyner is as follows: 

1. For a constant stress drop, the root mean square of 

the acceleration (ArmJ is inversely proportional 

to the square root of the corner frequency, fo 

(Hanks and McGuire, 1981). 

Earthquake-Induced Landsliding 333 
FIGURE 167.-Lateral spreading in Moss Landing caused by the April 18, 1906, San Francisco earthquake. Large areas in the Los Angeles region 

are susceptible to liquefaction-induced lateral spreading Cfinsley and others, this volume). (Photograph courtesy of Monterey County Historical 

Society, Inc., Salinas, Calif.) 

2. The corner frequency is inversely proportional to the 

cube root of the seismic moment M0 • 

3. The duration of seismic shaking (Td) is inversely proportional to the corner frequency (Hanks and 

McGuire, 1981); thus, Td oc M0

113• 

4. By definition, the Arias intensity is proportional to 

the integral of the acceleration squared over the 

time (Arias, 1970}, which is equal to A~sTd; so, 

and so, 

log 10 oc 2/3 M0 

5. By definition, the moment magnitude is equal to 

M = 2/3 log M0 -10.7 

(Hanks and Kanamori, 1979). 

6. Therefore, log Ia is proportional to M, and the proportionality constant Km = 1.0 (W. Joyner, personal 

communication, 1983). 

334 Earthquake Hazards in the los Angeles Region 

To have a common reference for magnitude, we corrected the reported Arias intensity values for a variety 

of magnitudes equivalent to a M 6.5 event for the same 

source distance (I a') by using the linear assumption; that 

is, log 10 '=log 10 +{6.5-M). We then compared these 

"corrected" values of Arias intensity with the log of the 

source distance (fig. 173) and derived the value of K0 

that best fits the data, K0 = - 4.1. The source distance 

was corrected for focal depth. The standard deviation 

was found to be K. = 0.44. Thus, our magnitude-distance 

relation for Arias intensity becomes 

log 10 = - 4.1 + M- 2 log r + 0.44 P 

Using this relation between magnitude, distance, and 

Arias intensity, we can estimate the seismic shaking 

severity at any site, given the magnitude of the event, the 

distance from the site to the seismic source, and the 

probability (P) of the actual Arias intensity's exceeding 

the predicted Arias intensity. For example, a site 20 km 

from a M 6.5 event would have a 5D-percent chance 
FS = Rmax 

L 

+ 

a (t) 

Ac = (FS- 1) g sin 0 

mg 

FIGURE 168.-Model of a potential landslide (shaded area) on a constant slope showing the interaction of the gravitational load (L), the 

resistance force (R), and the seismic acceleration field (a(t,)). The 

slope has a steepness angle equal to 9 ; the potential slide block has 

a thickness equal to h. The potential slide has a mass equal to m. 

The term g is acceleration due to gravity. 

(P = O) of experiencing an Arias intensity of 0.63 m/s or 

greater, corresponding to an (A)10 of 0.05 g (fig. 172). A 

site 50 km away would have a 5G-percent chance of exceeding I a= 0.1 m/s ((Ac)10 = 0.012 g) (fig. 172) but would 

also have a finite probability (3.5 percent, corresponding to P = 1.8) of experiencing an I a of 0.63 m/s or 

greater-the same value calculated for 20 km (for P = 0). 

PREDICTING THE LIMITS OF 

LANDSLIDING FROM 

AN EARTHQUAKE 

The relation between magnitude, source distance, 

and seismic shaking severity derived above provides a 

partial means of answering the question, "How far 

away can an earthquake of a given size trigger landslides?" We now need, however, an additional piece of 

information: "What is the minimum seismic shaking 

severity (as measured by 10

) at which landsliding is likely 

on susceptible slopes?" One approach to this question is 

to make a direct comparison of our magnitude-source 

distance-Arias intensity relation and the relations between magnitude and most distant landslides developed 

from our studies of historical earthquakes (fig. 164). We 

can make such a comparison simply by plotting the magnitude versus the source distance (r) for given values of 

Arias intensity and exceedance probabilities (fig. 174). 

After the statistical variations have been taken into account, the "best fits" to the historical earthquake data 

are (1) a value of I a= 0.5 m/s for coherent landslides (fig. 

174A), (2) 10 =0.15 m/s for disrupted landslides (fig. 

~ 

z 

0 

i= 

<! 

a: 

~ 0.3 ~'k-'~+----+-----'~--+---~ UJ 

u 

u 

<! 

...J 

<! 

u 

E 

a: y o. 1 t--+-'o,----;~-~--'-.1------=----+---"..--r-

'<I: " 

5% 

SLOPE 

70% 100% 

FIGURE 169.-Plots of critical acceleration (A,) versus slope steepness 

for three sets of lithologies: group A, strongly cemented rocks 

(crystalline rock and well-cemented sandstone); group B, weakly 

cemented rocks (sandy soil and poorly cemented sandstone); group 

C, argillaceous rocks (clayey soil and shale). The cohesion factor, 

c'/-yh, for group A assumes values of c' = 300 psf, 'Y = 100 pcf, and 

h = 10 ft. The angle of internal friction (<P) (peak strength, undrained 

conditions) is 35° for sands, sandstone, and crystalline rocks and 

zoo for clayey soils and shales. The solid lines depict dry slope 

materials, and the dashed lines depict saturation from the slide 

plane to the surface. 

174B), and (3) 10 = 0.5 m/s for lateral spreads and flows 

(fig. 174C). For these values of 10 , the historical data are 

completely contained within two standard deviations of 

the mean (P = ± 2), corresponding to exceedance probabilities of 2 and 98 percent, respectively. 

Using the relations in figure 172, we can convert the 

"threshold" values of Arias intensity to (AJ10 = 0.05 g for 

I a= 0.5 m/s (coherent slides and lateral spreads and 

flows) and (Ac)2 = 0.05 g for Ia = 0.15 m/s (disrupted 

slides). Thus, a value of critical acceleration of 0.05 g 

appears to be the approximate value of the susceptibility of the slopes that failed at the greatest distance from 

the source areas of these historical earthquakes. Of 

course, the actual slopes that failed almost certainly 

had a wide range of values of critical acceleration, just 

as we would expect a range of Ac values in any given 

region. To construct numerical models of the areal distribution of earthquake-induced landslides, however, a 

value of Ac = 0.05 g appears to be a useful approximation of a "lower bound" for the seismic stability of 

susceptible slopes, whatever the mechanism of failure. 

At first glance, this estimate (Ac = 0.05 g) for the 

critical acceleration of the "most susceptible slopes" 

appears to be rather high. Is it not possible for a slope to 

have a value of Ac = 0.01 g or even less? Why, in fact, 

should there be any lower limit to Ac? Is the value of 

Earthquake-Induced Landsliding 335 
PARKFIELD #2 

5 s 

.,z 50 

u<fl 

S~o cn1-Z 

u..wO 

0~~ 0 >-/-(f) 

t::~o: uuw 

0 "- _J~ 

UJ 

> 50 

8 5s 

c 5s 

FIGURE 170.-Algorithm for the Newmark analysis. A, Strong-motion 

record (1966 Parkfield earthquake, station 2) on which critical acceleration (Ac = 0.2 g) for a hypothetical slope has been superimposed. B, Velocity of block versus time. C, Displacement of block 

versus time. Point A, ground acceleration of block first exceeds 

critical acceleration; point B, block reaches maximum velocity; 

point C, motion ceases, and block comes to rest. 

Ac = 0.05 g for the lower bound merely an artifact of our 

numerical analysis? 

An argument can be made that there is, in fact, a 

practical minimum for the critical acceleration, below 

which slopes would have a high probability of failure 

from nonseismic causes over a time period much shorter 

than the return period for strong seismic shaking at any 

particular site. For example, heavy rainfall causes 

many landslides in the Santa Monica Mountains on a 

return period of 10 to 25 yr (Campbell, 1975), whereas 

the return period of strong seismic shaking in the same 

region is probably at least several decades. 

As an illustration, consider a hypothetical slope in 

cohesionless material (loose sandy soil) having an angle 

of friction of <1> = 30 o and a porosity of 25 percent. The 

slope steepness is 24 o. The optimum slide plane is 

located at a depth of 5 m, which is below a water table 

at 2.9 m depth. The critical acceleration of this slope is 

approximately Ac = 0.01 g, so the slope is highly susceptible to seismically induced failure. A rise in the water 

336 Earthquake Hazards in the Los Angeles Region 

table of only 19 em, however, would also cause this slope 

to fail under static conditions (FS = 1). If there are no 

losses from runoff or bedrock infiltration, this rise in 

water level would require only 1.8 in of rainfall in a 

period of a few hours-a fairly common occurrence in 

this area (return period less than 1 yr). On the other 

hand, a similar slope in similar materials having a slightly lower water table or a slightly gentler slope angle, 

such that Ac = 0.05 g, would require 9.2 in of rainfall 

within the same period of time-a much less common occurrence whose return period begins to approach that 

of strong seismic shaking. Therefore, a slope where 

Ac = 0.01 g would be much more likely to fail because of 

heavy rainfall than from seismic shaking. A slope where 

Ac = 0.05 g, on the other hand, would survive all but the 

heaviest rainfall yet still be highly vulnerable to failure 

under strong seismic shaking. 

We can now use our magnitude-source distanceArias intensity relation (fig. 173) to estimate the source 

distance from a given earthquake at which the probability that the seismic shaking severity will exceed any 

given value is 50 percent (P = 01. Taking ·I a= 0.5 m/s as 

the threshold shaking ·severity for coherent slides, we 

estimate this distance to be approximately 24 km for a 

M 6.5 event (fig. 174A). Figure 175 is a map of the Los 

Angeles area showing a hypothetical seismic source 

zone for a M 6.5 event on the northern NewportInglewood fault. A line is drawn 24 km from the source 

to indicate the area within which the chance that the 

ground motion will exceed the threshold severity is 

greater than 50 percent. Figure 175 also includes a line 

65 km from the source zone, corresponding to the 

predicted outer limit for coherent slides as determined 

from worldwide historical data (fig. 164). Beyond this 

65-km limit, coherent slides are unlikely during this 

event, even for susceptible slopes. In a middle zone, between 24 and 65 km from the fault rupture, the probability that shaking would be severe enough to cause 

coherent slides on susceptible slopes is finite but less 

than 50 percent. 

The same reasoning can be followed with regard to 

rock falls and other disrupted landslides. If the 

historical magnitude-distance relation for disrupted 

landslides (fig. 164A) is compared with the magnitudedistance-Arias intensity relation, the best fit to the 

historical data is obtained with an Arias intensity value 

of approximately 0.15 m/s (fig.174B). As we did above 

for coherent slides, we take this value of 10 as the threshold shaking severity for disrupted landslides and 

calculate a source distance corresponding to a 

5D-percent exceedance probability for this value. This 

distance is approximately 41 km. 
(f) 

a: 

LU 

ILU 

~ 

i= 

z 

LU 

u 

z 

t-" 

z 

LU 

~ 

LU 

u 

<{ 

_j 

Q_ 

(f) 

0 

1000 

500 

200 

100 

50 

20 

10 

5.0 

2.0 

1.0 

-1-1 

-1-

3<i.;::,.... 

- 1- 11 :::,... 3 :::::-~? 

.......... 4 '"'~2 "-1, '-""'2 ..... 5 .......... "4' ~2......_ 1'2 -......, 5 4..._ ~ 

"s, "4'-...~, ' 2, '-1 

b' ~-4, 2~ "'1 

\ \ '4, ' 2 ~ ., ., '\ '...... 

0.5 \ 3, 

5 

0.2 

0.1 

0.01 0.02 0.05 0.1 02 0.5 

CRITICAL ACCELERATION (g) 

1.0 

FIGURE 171.-Displacements predicted by the Newmark analysis as a 

function of assumed critical acceleration for several strong-motion 

records from California earthquakes. The stronger of the two 

horizontal components of the records was used in each case. Also 

indicated for reference are the values of critical displacement for 

coherent landslides (slumps, block slides, and earth flows) (10 em) 

and for disrupted landslides (falls, slides, and avalanches) (2 em). 

1, S. 16° E. component of horizontal ground motion recorded at 

Pacoima damsite from the 1971 San Fernando earthquake; 2, 1966 

Parkfield earthquake, station 2; 3, 1940 El Centro earthquake; 4, 

1966 Parkfield earthquake, station 5; 5, 1952 Taft earthquake. 

Figure 176 is a second map, similar to figure 175, 

whose lines show distances of 41 km (50-percent exceedance probability) and 112 km (historical limit from 

fig. 164A) from the source area of the postulated M 6.5 

event on the Newport-Inglewood fault. Again, the inner 

area denotes a zone having a high probability that shaking will exceed the threshold level required to cause 

1.00 

0.50 

log (Ac) 2 =0.61 log Ia - 0.81 

>- 0.20 I-

~ 

> <{ 

a: 0.10 (.9 

~ 

0. 0.05 

" :::5. 

a: 0.02 0 

lo g (Ac) 10= 0.791og Ia - 1.095 

S' 

i 0.01 

0.1 0.2 0.5 1.0 2.0 10.0 

ARIAS INTENSITY, IN METERS PER SECOND 

FIGURE 172.-(AJ10 (triangles) and (AJ2 (circles) versus Arias intensity 

(I.) for 10 strong-motion records. Regression lines are also plotted 

for log (AJ10 versus log 10 and log (AJ2 versus log 1

0 • The standard 

deviations for these regressions are 0.144 and 0.151, respectively. 

disrupted landslides from susceptible slopes (Ac < 0.05 g) 

(geologic characteristics as shown in table 45), a middle 

area (between 41 and 112 km) having less than a 50-percent (but still significant) probability that shaking will be 

severe enough to trigger such landslides, and a zone 

beyond 112 km where landslides are unlikely. 

Figure 177 is a third map, similar to figures 175 and 

176, depicting the probabilities of failure of slopes 

susceptible to lateral spreads, flows, or subaqueous 

landslides. Taking a value of I a= 0.5 m/s as the threshold 

shaking severity for landslides of these twes (fig. 175C), 

we plot an equidistance line 24 km from the source area 

of the postulated M 6.5 event on the Newport-Inglewood 

fault; this line corresponds to a 50-percent probability 

TABLE 46.-Measures of shaking severity for several strong-motion records 

(All earthquakes occurred in California, unless otherwise noted. A, acceleration; 1

0

, Arias intensity; (A,)10• critical acceleration for 

coherent landslides; (AJ2

• critical acceleration for disrupted landslides] 

(A).' (I~.' (A )to. (AJ,. 

Earthquake Record/component ing in mls in g ing 

1966 Parkfield----------------------------- Station 2/065 0.485 1.64 0.20 0.31 

1966 Parkfield ----------------------------- Station 5/085 .447 .96 .09 .21 

1979 Coyote Lake --- ----------------------- Station 6/050 .36 .71 .12 .24 

1979 Coyote Lake -------------------------- Coyote Creek/250 .206 .25 .02 .06 

1975 Kalapana, Hawaii---------------------- Hilo/344 .205 .20 .02 .05 

1971 San Fernando------------------------- Pacoima/164 1.22 9.16 .33 .52 

1978 Santa Barbara ------------------------- Goleta/180 .338 .93 .07 .15 

1952 Kern County-------------------------- Taft/111 .144 .48 .033 .065 

1940 Imperial Valley------------------------ El Centro/180 .293 1.61 .10 .15 

1978 Miyagi-Ken Oki, Japan ------------------ Tohoku Univ./000 .238 1.69 .11 .16 

1

The values of A and 1

0 reported in this table may vary slightly from those reported in tables 47 and in the standard catalogs. because 

of differences in digitization, time base, and correction factors. These differences should not affect the correlations developed in 

figure 172. 

Earthquake-Induced Landsliding 337 
TABLE 47.-Magnitude-distance--Arias intensity data 

(Strong-motion data compiled from Arias [1970], Dobry and others [1978], Vanmarcke and Lai [1980], and Joyner and Boore {1981]] 

Source Arias Corrected 

Moment distance intensity Arias intensity, 

magnitude (r), Acceleration (I.). (I.). 

Earthquake/station (M) inkm (A) in m/s in m/s 

Kern Countyffaft ------------ 7.4 43 0.179 0.59 0.074 

Parkfield/Station 2 ----------- 6.1 6.61 .498 1.71 4.30 

Parkfield/Station 5 ----------- 6.1 9.31 .434 .85 2.135 

Lower California/El Centro----- 6.5 53 .182 .62 .62 

Imperial/El Centro ----------- 7.0 12 .348 1.93 .61 

San Fernando/Castaic --------- 6.6 21 .271 .99 .79 

Eureka/Federal Building ------- 6.5 25 .257 .710 .71 

San Fernando/Orion ---------- 6.6 20 .255 1.28 1.02 

Lytle Creek/Wrightwood ------- 5.3 14 .198 .14 2.22 

Parkfield/Temblor------------ 6.1 161 .347 .45 1.13 

Ferndale/City Hall ----------- 5.6 25 .237 .105 .83 

San Fernando/Palmdale ------- 6.6 34 .113 .334 .265 

Kern County/Pasadena -------- 7.4 130 .053 .114 .014 

Hollister/City Hall ------------ 5.6 40 .065 .135 1.072 

San Francisco/Golden Gate ---- 5.3 11 .105 .05 .79 

San Francisco/State Bldg.------ 5.3 17 .085 .052 .82 

San Francisco/Alex. Bldg.------ 5.3 16 .043 .016 .25 

San Francisco/Oakland -------- 5.3 26 .04 .010 .16 

Borrego/San Onofre ---------- 6.6 122 .046 .035 .028 

Kern County/(A005) ---------- 7.4 85 .131 .29 .037 

Kern County/(A006) -,--------- 7.4 109 .053 .11 .014 

Borrego/(A020) -------------- 6.6 96 .029 .03 .024 

Long BeachNernon ---------- 6.3 53 .133 .23 .365 

San Jose/(A010) -------------- 5.8 10 .102 .075 .376 

Southern California/(B023) ----- 5.4 38 .033 .010 .126 

Wheeler Ridge/(B031) --------- 5.9 43 .068 .042 .167 

Central California/(U307) ------ 5.0 6 .057 .05 1.58 

Northern California/(U308) ----- 5.7 59 .075 .04 .25 

Torrance-Gardena/(V316) ------ 5.4 6 .055 .04 .50 

Southern California/(V329) ----- 5.0 6 .167 .100 3.16 

1

Source distances for the 1966 Parkfield earthquake adjusted for the surlace-rupture zone proposed by Lindh and Boore [1981). 

that the ground motion will exceed the threshold severity. We plot another equidistance line at 59 km from the 

fault to denote the predicted outer limit of lateral 

spreads, flows, and subaqueous landslides from a M 6.5 

event as determined from worldwide historical data (fig. 

164C) (Keefer, 1984b). Thus, areas having a high susceptibility to lateral spreads, flows, and subaqueous landslides (see table 45; Tinsley and others, this volume; 

Clarke and others, this volume) would have a high probability of failure in the postulated event if they were 

located within 24 km of the fault and a low probability of 

failure if they were located farther than 59 km from the 

fault. 

338 Earthquake Hazards in the Los Angeles Region 

A HYPOTHETICAL SITE 

EVALUATION 

To illustrate how the methods developed in this 

chapter might be applied, we will consider a residence 

on the northern slope of the eastern Santa Monica 

Mountains, near the city of Sherman Oaks. The lot has a 

grade of 25 percent (equal to a slope angle e of 14°), facing to the north. Would this site run a significant risk of 

damage from slope failure in an earthquake? 

The first step in answering this question would be to 

locate the property on a geologic map (Yerkes and 
10.0 ,. "Ll=O km 

~ .. , >-

!::: .,. (/) Ll=12 km 

.~,\. z 1.0 w • 

Iz • • ~ • (/) • ~ • a: 

~ 0.1 

0 

w log (/a*) = -4.1 + 1.0 M-21og r* Iu 

w 

a: 

a: 0.01 0 

u 

1.0 10.0 

DISTANCE FROM SOURCE (r), IN KILOMETERS 

FIGURE 173.-Corrected Arias intensity versus distance from the 

seismic source area. The values of Arias intensity were calculated 

from strong-motion records (table 46) and adjusted to be equivalent 

to a M 6.5 event at the same source distance, on the basis of an 

assumed log-linear relationship between magnitude and Arias intensity for a given distance . .:l, focal depth; r*, ..Jr> + .:l'; Ka, 0.44. 

Campbell, 1980). On doing so, we find that the lot is 

located within the Modelo Formation, a "siltstone, soft 

mudstone, and siliceous shale, [with] minor interbedded 

sandstone." Consulting table 45, we find that the slope 

of the lot is not steep enough to have a significant risk of 

rock falls, rock slides, or rock avalanches. The slope 

steepness (14°), however, closely approaches the minimum slope for rock slumps (8 ~ 15 °). Also, the shale 

units within the Modelo generally fit the "type of material" in which rock slumps occur (table 45), and some of 

the shale horizons may be weak enough to fit the criteria 

for soil slumps (8 > 10°) or soil block slides (8 >5°). If the 

colluvium is thick(> 3m) or, as is very likely, the house is 

built on a pad of artificial fill, the criteria for soil slumps 

or block slides may be met. If the bedding of the Modelo 

Formation dips out of the slope at this location, the 

likelihood of a block slide increases (see table 45). 

Although local codes required the cut-and-fill foundation pad for the house to meet a minimum specification 

of FS = 1.5, that value would correspond to a critical acceleration of only Ac = (FS -1) sin 8 = 0.12 g. Figure 169 

shows that the Modelo Formation (a group C lithology) 

on a slope of 14° would also have an Ac of roughly 0.12 g 

under moist (but not necessarily saturated) conditions. 

Should the earthquake occur after a period of heavy 

rainfall, the critical acceleration could be significantly 

lower, depending on the drainage of the lot, the local 

hydrologic conditions, and other site-specific factors. 

We shall take Ac=0.12 g as our reference value for 

subsequent calculations. 

Given this value of Ac, the property in question could 

sustain significant damage if it were subjected to 

seismic shaking more severe than (AJ10 =0.12 g. (We 

take 10 em as the value of the critical displacement 

because we are concerned about a slope failure of the 

slump or block slide type.) How likely is it that the 

postulated M 6.5 event on the Newport-Inglewood fault 

zone would cause such severe shaking on this site? 

From figure 172, we see that (Ac)10 =0.12 g correlates 

with an Arias intensity value of 1.65 m/s. Although this 

residence is well within the 5o-percent probability line 

for exceeding the threshold shaking severity for 

coherent slides (fig. 175), the threshold severity is only 

I a= 0.5 m/s, significantly less than the severity required 

to cause coherent sliding at this less susceptible site 

(10 = 1.65 m/s). Using the magnitude-source distance-Arias intensity relation, we calculate that the 

source distance from a M 6.5 event, which corresponds 

to a 5Q-percent exceedance proability for Ia = 1.65 m/s, is 

approximately 12.5 km. The residence under study is 

located approximately 16 km from the nearest point on 

the Newport-Inglewood fault trace involved in this 

scenario event. Thus, there is a less than even but significant (roughly one in three) chance that the shaking from 

this event would exceed 10 = 1.65 m/s and thus cause 

displacements of 10 em or greater, possible damage being a consequence. Even if this residence experienced 

little structural or foundation damage, however, utilities 

and road access could be severely impacted if there 

were nearby slope failures. 

Although this example deals with a specific site, the 

analytical methods presented in this chapter and the 

assumptions on which they are based are more appropriate for evaluating the potential for seismically induced landsliding on a regional scale. The results of 

these methods should be the beginning, not the end, of 

any evaluation of a specific site. For a more detailed 

assessment, a homeowner should engage a geologist or 

an engineer to perform a property inspection. 

SUMMARY 

Landslides have caused significant damage in 

historical southern California earthquakes and will 

probably pose substantial hazards in future moderate 

and large events in the Los Angeles region. The number, 

geographic extent, and hazard potential of landslides increases as earthquake magnitude increases; an event of 

about M 4 is the smallest likely to cause any landslides, 

Earthquake-Induced Landsliding 339 
1000 

~ 500 

0 

a: 

LL(f) 200 (f) a: UJUJ 

Ol-

- UJ 100 ...J~ (/)0 

1-...J 50 z- UJ:.:: 

a:z UJ- 20 J: - ow 

uz 

0 10 LLN 

Ow 

wa: 5 U:J 

Zl- <{0... 

t-:J (f) a: 2 

or'- ((Ac),o = 0.05 g) ~...J 

:J:J ePA :2~ 0.5 x N 

<{ 0 I 

:2 II II 

0.2 Cl.. Cl.. 

0.1 

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 

A MAGNITUDE 

1000 1000 

500 (/) 

500 ::: 

0 ...J(/) 

200 LLa:; 

a:UJ 200 

oti:i 

100 (/):2 100 oo 

<{:::! 

50 UJ:.O:: 50 a: 

a.z 

(/)-

20 

...J w· <rz 20 

a:O UJN 

10 1-UJ 10 

<I: a: 

5 

...J:J 

LLI- 5 

De• oo... 

UJ:J 

ua: 2 ((Acb = 0.05 g) zl 2 <{I- 0 FE• r-;' 1-...J II I/ N (/):J Cl.. -<I: Cl.. 0 I Ou_ / II II 0.5 :2:2 Cl.. Cl.. :JO 0.5 

:2a: 

- LL 

0.2 >< <{ 0.2 

:2 

0.1 0.1 

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 9.0 9.5 

8 MAGNITUDE c MAGNITUDE 

FIGURE 174.-Comparison of data on landsliding from historic earthquakes to the magnitude-source distance relation for Arias intensity. California earthquakes in the data set are as follows: CL, August 6, 1979, Coyote Lake; DC, March 22, 1957, Daly City; FE, February 9, 1971, San Fernando; HV, March 15, 1979, Homestead Valley; IV, May 19, 1940, Imperial Valley; KC, July 21, 1952, Kern County (not included by Keefer 

(1984b}); MD, January 24, 1980, Greenville-Mount Diablo; ML, May 25, 1980, Mammoth Lakes; PA, June 28, 1966, Parkfield-Cholame; SB, 

August 13, 1978, Santa Barbara; SF, April18, 1906, San Francisco. Unlabeled points represent earthquakes outside California (identified by 

Keefer (1984b}}. The heavy lines are the upper bound from historical data. The magnitude-source distance relation for Arias intensity is plotted as a locus of points corresponding to the Arias intensity that appears to provide the "best fit" to the historical data and to exceedance 

probabilities of P=O (50 percent), P=2 standard deviations (2 percent), and P= -2 standard deviations (98 percent). An average focal depth 

of 12 km is assumed for these plots. A, Coherent landslides (slumps and block slides). I

0 = 0.5 m/s. B, Disrupted landslides (falls, disrupted 

slides, and avalanches). 10 =0.15 m/s. C, Lateral spreads or flows. 10 =0.5 m/s. The dot-<lash curve is the upper bound postulated by Youd and 

Perkins (1978}. 
FIGURE 175.-Map of the Los Angeles basin and surrounding uplands showing zones of "" 

probability for coherent landslides from a hypothetical M 6.5 earthquake on the ~\) northern Newport-Inglewood fault zone (straight line in center of map). The outer a ~ 

oval-shaped line is the limit for coherent slides from a M 6.5 earthquake based on """' 

worldwide data from historical earthquakes (Keefer, 1984b). The inner oval-shaped o 0 

/ 

I \ 

line is the 50-percent probability line that corresponds to the source distance at r L, ____ L_ ____ L_ ___ _.J 

which the mean predicted Arias intensity (from fig. 174) is equal to the threshold . J 

shaking severity for coherent landslides {10 = 0.5 m/s). Most of the coherent land- ~ slides will occur within the 50-percent probability line. -;:J ~ ~~~ -

i 

\ 

I 

/ 

..... I ( 

whereas an earthquake of about M 8 or larger is capable 

of triggering tens of thousands of landslides throughout 

a region that extends to more than 400 km from the 

fault. 

·Studies of. historical events have shown that earthquakes trigger 14 types of landslides. In order of 

decreasing abundance, these are rock falls, disrupted 

soil slides, rock slides, soil lateral spreads, soil slumps, 

soil block slides, soil avalanches, soil falls, rapid soil 

flows, rock slumps, subaqueous landslides, slow earth 

flows, rock block slides, and rock avalanches. 

Although most or all types of earthquake-induced 

landslides pose some hazard to human life and property, 

historical evidence shows that the predominant hazards 

to life come from rock avalanches, rapid soil flows, and 

rock falls. Zones at risk from rock falls extend only a few 

hundred meters from the bases of steep slopes, but 

zones at risk from rock avalanches or rapid soil flows 

extend for several kilometers from the localities of landslide initiation. Leading causes of property damage, in 

addition to these three types of landslides, are soil 

slumps and soil lateral spreads. 

Materials that are most susceptible to earthquakeinduced landslides and the predominant types of landslides in each are (1) weakly cemented, weathered, or intensely fractured rocks (rock falls, slides, avalanches, 

slumps, and block slides); (2) more indurated rocks 

where prominent discontinuities dip out of slopes (rock 

falls and slides, block slides, avalanches, and, possibly, 

slumps); (3) loose, unsaturated sand (disrupted soil 

slides and soil avalanches); (4) loose, partly to completely saturated sand or silt (soil slumps, block slides, lateral 

spreads, subaqueous landslides, and rapid soil flows); 

(5) saturated soils containing sand and gravel layers 

alternating with sensitive clay (disrupted soil slides, soil 

avalanches, and rapid soil flows); (6) loess (rapid soil 

flows); (7) granular soils that are slightly cemented or 

contain a clay binder (soil falls); and (8) uncompacted or 

poorly compacted manmade fill containing little or no 

clay (soil slumps, block slides, lateral spreads, and rapid 

soil flows). 

The probability that a landslide will occur on a particular slope during a particular earthquake is a func-

~ FIGURE 176.-Map of the Los Angeles basin and surrounding uplands 

showing zones of probability for disrupted landslides from a 

hypothetical M 6.S earthquake on the Newport-Inglewood fault 

zone [straight line in center of map). The outer oval-shaped line 

probability line is the limit for disrupted landslides from a M 6.S 

earthquake based on worldwide data from historical earthquakes 

(Keefer, 1984b). The inner oval-shaped line is the so-percent probability line that corresponds to the source distance at which the 

mean predicted Arias intensity is equal to the threshold shaking 

severity for disrupted slides (10 = 0.1S rnls). Most of the disrupted 

landslides will occur within the so-percent probability line. 

Earthquake-Induced Landsliding 343 
-- \. 

\ 

A 'V I•E 

') - / 

I 

\ 

" -··- -."::1...._ 
tion of both the preearthquake stability of the slope and 

the severity of the seismic ground motion. The preearthquake stability of the slope is controlled by both the 

strength of the slope material and the steepness of the 

slope. The combinations of slope and lithology that are 

particularly vulnerable to earthquake-induced landsliding have been determined by a study of historical 

landslides and experience in postearthquake investigations and are listed in table 45. Another way to express 

the susceptibility of a slope to seismically induced landsliding is the critical acceleration (Ac), which can be 

calculated from the static factor of safety as determined 

by a standard slope stability analysis. 

The second factor (severity of the ground shaking required for earthquake-induced landsliding) has been investigated by using both empirical data from historical 

earthquakes and a numerical . technique developed by 

Newmark (1965). The Newmark analysis allows for inputs of both the static slope stability and a seismic 

strong-motion record; thus, slope stability and seismic 

ground motion are linked. The Newmark analysis computes the displacement of a rigid friction block, which is 

used to represent a potential landslide on the slope 

under study. We have defined the "critical displacement" as that beyond which the slope can be considered 

to have produced a landslide. We have assigned values 

of 10 and 2 ern as the critical displacements for coherent 

and disrupted landslides (table 44), respectively. The 

..... FIGURE 177.-Map of the Los Angeles basin and surrounding areas 

showing zones of probability for lateral spreads and flows from a 

hypothetical M 6.5 earthquake on the Newport-Inglewood fault 

zone (straight line in center of map). The outer oval-shaped line is 

the limit for lateral spreads and flows from a M 6.5 earthquake 

based on worldwide data from historical earthquakes (Keefer, 

1984b). The inner oval-shaped line is the so-percent probability 

line that corresponds to the source distance at which the mean 

predicted Arias intensity is equal to the threshold shaking severity 

for lateral spreads and flows (10 = 0.50 rnls). Most of the lateral 

spreads and flows will occur within the 5G-percent probability line. 

severity of seismic shaking required to cause coherent 

slides is thus defined as that which, according to the 

Newmark analysis, would produce a displacement of 

more than 10 ern on a slope having a given Ac (that is, 

(AJlO). 

Using both the theoretical and the historical-empirical 

studies, we can delineate three zones surrounding a 

seismic event: (1) a zone (within the 50-percent probability line) within which there is a high probability that 

susceptible slopes (Ac < 0.05 g) will fail; (2) a zone having a 

less than even but still finite probability that susceptible 

slopes will fail; and (3) a zone beyond the outer limit 

defined by data from worldwide historical events that is 

so far from the seismic source that the probability of 

landslides is very ,small, even on susceptible slopes. 

Three maps were prepared to show these zones for a 

postulated M 6.5 event-the first for coherent slides, the 

second for disrupted slides or falls, and the third for 

lateral spreads or flows. These maps, in combination 

with the geologic criteria for seismic landslide susceptibility (table 45) and existing geologic maps of the Los 

Angeles region, provide the basic tools for assessing the 

potential hazard from earthquake-induced landslides on 

a local level. A general analysis of which upland areas 

could experience the most significant damage from landslides in a postulated M 6.5 earthquake on the northern 

part of the Newport-Inglewood fault zone is presented 

by Ziony and others (this volume) . 

Earthquake-Induced Landsliding 345 
Earthquake-Related 

Phenomena Offshore 
IDENTIFYING POTENTIALLY ACTIVE FAULTS AND 

UNSTABLE SLOPES OFFSHORE 

By S. H. Clarke, H. G. Greene, and M.P. Kennedy6 

INTRODUCTION 

Evaluating the earthquake hazards associated with 

the offshore areas of the Los Angeles region poses 

distinctive challenges. Although many of the hazards 

are the same as those onshore (for example, ground 

shaking, fault rupture of the sea floor, and earthquakeinduced ground failure), specialized remote-sensing 

techniques are required to evaluate and map them in the 

marine environment. This chapter describes the principal method-acoustic reflec~ion profiling-available 

for analyzing geologic hazards offshore and summarizes 

present knowledge of the distribution of potentially active faults and unstable slopes in the offshore Los 

Angeles region (fig. 178). An additional earthquake 

hazard unique to the marine environment-tsunamis or 

seismic sea waves-is discussed by McCulloch (this 

volume). 

Previous Investigations 

Numerous studies of the geology of the southern 

California continental borderland and its significance to 

offshore development have been completed during the 

past 15 yr. The first regional study of structure and 

depositional history using acoustic reflection records 

was conducted by Moore (1969). Known and postulated 

faults, both offshore and onshore, were compiled for this 

area by Ziony and others (1974) and Jennings (1973, 

1977). Vedder and others (1974) summarized knowledge 

of the regional stratigraphy, structure, and geologic 

history of emergent and submergent parts of the 

southern California borderland. The geology and 

geologic hazards of the offshore Santa Monica and San 

Pedro Basins and the Gulf of Santa Catalina were 

6

Califomia Division of Mines and Geology, Scripps Institution of Oceanography, La jolla, 

CA 92093. 

studied by Greene and others (1975, 1979), Clarke and 

others (1983), and Edwards (1982) and those of the 

eastern Santa Barbara Basin by Greene and others 

(1978). The structure and stratigraphy of the Santa 

Monica and San Pedro Basins were mapped and described by Junger and Wagner (1977). Yerkes and Lee 

(1979a, b), Yerkes and others (1981), and Lee and others 

(1978, 1979) evaluated seismicity in relation to faults in 

the Santa Barbara Basin and the Transverse Ranges 

region, and Field and Edwards (1980) discussed processes of sea-floor mass movement and mapped zones of 

failure on slopes and basin margins throughout much of 

the southern California borderland. 

Nardin (1981) and Nardin and Henyey (1978) mapped 

the stratigraphy and structure and discussed the tectonic and depositional history of the Santa Monica and 

San Pedro Basin areas, and Malouta and others (1981) 

described Holocene depositional processes and the 

nature and rates of basin filling in the Santa Monica 

Basin. Quaternary stratigraphy, structure, and depositional processes in the Santa Barbara Basin were 

described and discussed by Fischer (1972) and Thornton 

(1981). Maps by Clarke and others (1985) and Vedder 

and others (1985) have summarized recent knowledge of 

the geology and geologic hazards of the inner and. midsouthern California continental borderland from the 

U.S.-Mexican border to the vicinity of Goleta (fig. 178). 

Physiographic Character 

The offshore region addressed in this chapter extends 

from west of Santa Barbara southeastward to the vicinity of Oceanside, a distance of about 280 km, and from 

the shoreline seaward an average distance of about 

35 km (fig. 178). The mainland shelf is the major physiographic feature along the eastern margin of this region. 

South of the Palos Verdes peninsula, between the Palos 

Verdes Hills and Newport Beach, the shelf is relatively 

broad (10--20 km wide) and is referred to here as the San 

Faults and Unstable Slopes Offshore 347 
~SCALE 

0 5 10 15tlllll I, I I I I I I 

I 

0 5 10 15 20 kii.OMfliiiiS 

Earthquake FIGURE Hazanls 1 78o-Principal in the L ph '~""ph" 0 ""'"~ of th• olhhore L i:<~g~----------- r--

os Angeles Reg" os Angeles region C 10n ° ontour inte al 

0 

rv IS 200 mo 

348 
Faults an d Unstable Slop es Offshore 349 
Pedro shelf. Farther south, between Newport Beach and 

Oceanside, the shelf is much narrower (3-9 km wide). 

The break in slope marking the western margin of the 

shelf is as shallow as 75 m in the northern part of the 

area off San Pedro Bay, but, farther south, it averages 

90 to 125 m in depth. Several prominent submarine canyons cutting the mainland shelf in the San Pedro Bay 

area include the San Pedro Sea Valley, which empties 

westward into the San Pedro Basin, and the San Gabriel 

and Newport Canyons, which cut the southern margin of 

.the shelf and drain southward into the Gulf of Santa 

Catalina. Newport Canyon forms the physiographic 

boundary between the San Pedro shelf and the narrow 

shelf segment south of Newport Beach. Water depth in 

the area south of the Palos Verdes peninsula ranges 

from approximately 20 to 30 m along the inner shelves to 

a maximum of about 900 m in the San Pedro Basin and 

the Gulf of Santa Catalina. Bedrock knolls (for example, 

Lasuen Knoll) rise as much as 420 m above the sea floor 

in these offshore basins. The Gulf of Santa Catalina is 

bounded on the west by bedrock ridges comprising 

Thirtymile Bank and the emergent Santa Catalina Island 

platform. 

North of the Palos Verdes peninsula, the shelf break 

occurs at water depths as shallow as 75 to 80 m in the 

vicinity of Santa Monica Bay; farther west, the depth of 

the break gradually increases to depths of 90 to 105 m. 

Here, the mainland shelf is cut by five submarine canyons-Redondo, Dume, Mugu, and Hueneme Canyons, 

which head near shore, and Santa Monica Canyon, 

which heads about 9 km offshore. These canyons empty 

southward and westward into the Santa Monica Basin. 

In addition, the slope between Dume and Hueneme Canyons is cut by several large submarine gullies. Water 

depths over the area range upward to a maximum of 

about 950 m in the southeastern end of the Santa 

Monica Basin and about 600 m in the Santa Barbara 

Basin southwest of Goleta. A bedrock knoll-Redondo 

Knoll.,.-rises about 420 m above the sea floor and forms 

a portion of the sill between the Santa Monica and San 

Pedro Basins. The area is bounded along its seaward 

margin by the Santa Cruz-Catalina Ridge, a bedrock 

ridge of exposed Tertiary sedimentary and volcanic 

rocks, and by the Channel Islands platform. The eastern 

terminus of the Channel Islands platform-the Anacapa 

Ridge-forms the physiographic boundary between the 

east-trending Santa Barbara Basin and the northwesttrending Santa Monica Basin. 

ACQUIRING AND INTERPRETING 

MARINE GEOPHYSICAL DATA 

Geologic features on and beneath the sea floor commonly must be evaluated by remote-sensing methods 

350 Earthquake Hazards in the Los Angeles Region 

rather than by direct observation. Although a variety of 

techniques is available for marine geologic studies, 

acoustic reflection profiling is presently the principal 

method used to map sea-floor and subbottom features. 

The basic principal of acoustic reflection profiling is 

echo sounding, in which a pulse of sound is generated 

and transmitted downward through the water from a 

ship-mounted or towed acoustic source. Some of this 

acoustic energy is reflected from the sea floor, and some 

is reflected from interfaces between subbottom units 

that can be differentiated by their acoustic characteristics. These acoustic units have physical properties such 

as bulk density and acoustic velocity that differ 

significantly from the properties of adjacent units. The 

reflected energy is received by sensors (hydrophones) in 

or towed by the survey vessel, and the signals are processed and recorded by analog or digital methods. The 

recorded signals are graphically presented as continuous acoustic reflection profiles (fig. 179); these profiles depict cross sections of acoustic units plotted as a 

function of acoustic traveltime beneath the sea surface 

(vertical direction) and distance along the survey track 

(horizontal direction). To determine the depth to a reflecting interface, the velocity of sound in acoustic units 

(including the water column) above the interface must 

be assumed or determined. By interpreting a series of 

acoustic reflection profiles obtained for an area, 

geologists can infer and map geologic features on and 

beneath the sea floor. Dobrin (1976) has published a 

comprehensive description of the acoustic reflection 

technique. 

Much of the information presented in this chapter is 

based on the interpretation of subbottom acoustic 

reflection records collected aboard the RN Sea Sounder 

during 1978 and 1979 (cruises S2-78-SC and S2-79-SC) 

and the RN S. P. Lee during 1981 (cruise L2-81-SC). 

These records consist of high-resolution profiles 

gathered with 12-kHz, 3.5-kHz, minisparker, and 

Uniboom systems and intermediate- to deep-penetration 

profiles gathered with a 16D-kJ sparker and dual 4D-in3 

air-gun systems. Subsurface features ranging upward in 

vertical dimension from approximately 1.0 to 1.5 m can 

be resolved on high-resolution data that vary in subbottom penetration from 150 to over 400 m. The 

intermediate- to deep-penetration data used to determine structures at greater depths beneath the sea floor 

can resolve features larger than about 15 m in vertical 

dimension and commonly record useful information at 

subbottom depths of well over 1 km. Ship positioning 

was accomplished by range-range triangulation and 

Loran C, augmented in remote locations by satellite 

navigation and ship's radar. Location accuracy of the 

acoustic data. ranges from about 15 m where precision 

equipment was used to about 250 m where ship's radar 

alone was used. 
A 

0.4 (/) 

0 

z 

0 

u 

w 

(/) 

0.8 z 

w· (/) ~ a: 

w 5 1- w w > ~ 1.2 <( 

a: 

1-

>- <( 

;: 

6 

1.6 ~ 

0 3 4 MILES 

0 2 4 KILOMETERS 

B 

300 0.4 

(/) 

0 

z 

0 

u 

w 

(/) 

600 0.8 z 

u.i 

~ (/) 

a: 5 w w 1-

w > <( ~ 900 1.2 a: 

1-

>- <( 

~ 0 

1200 1.6 ~ ...-" - ~-::::::-

FIGURE 179.-lntermediate-penetration acoustic reflection profile across the mainland shelf near Oceanside showing well-defined fault (Kennedy 

and others, in press). Vertical exaggeration 7:1. A, Acoustic reflection record. Note interruption and displacement of prominent reflectors, 

sea-floor offset, and bubble pulse (a). B, Line drawing of prominent reflectors. 

Faults and Unstable Slopes Offshore 351 
(/) 

a: 

w 

1-

w 

~ 

(/) 

a: 

525 

675 

825 

975 

525 

~ 675 w 

~ 

825 

A 

B 

0.7 

0.9 

1.1 

1.3 

0 3 MILES 

0 3 KILOMETERS 

0.7 

0.9 

1.1 

975-L--------------~--------~----------------------L1.3 

(/) 

0 

z 

0 

u 

w 

(/) 

z 

w 

~ 

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FIGURE 180.-lntermediate-penetration acoustic reflection profile across the eastern flank of the Coronado Bank, the Lorna Sea Valley, and the shelf off San Diego showing well-defined faults (solid lines), 

indicated by discontinuation and displacement of prominent reflectors, and inferred faults (dashed 

lines), indicated by bending, changes in dip, and relatively small displacements of prominent reflectors (Kennedy and others, in press). Vertical exaggeration 12:1. A, Acoustic reflection record. B, Line 

drawing of prominent reflectors. The fault at left juxtaposes Tertiary-Quaternary strata (TQ) and exposed bedrock block of Miocene (Tm) age. 

352 Earthquake Hazards in the Los Angeles Region 
Standard interpretive methods were used in analyzing the acoustic reflection data. Criteria for interpreting 

faults follow Greene and others (1973) and Kennedy and 

others (in press) and are, for well-defined faults (figs. 

179, 180), (1) distinct displacement of prominent reflectors, (2) an abrupt termination of prominent reflectors or 

the juxtaposition of intervals of prominent reflectors 

that have contrasting acoustic characteristics, or (3) an 

abrupt change in the dip of reflectors across a distinct 

boundary. For inferred faults (fig. 180), the criteria are 

(1) small displacement of prominent reflectors, in which 

the upper or shallow reflectors may be bent rather than 

broken, (2) prominent reflectors that are discontinuous 

and contrasting acoustic characteristics that are present on either side of an acoustically obscure disturbed 

zone, or (3) apparent changes in dip on either side of the 

disturbed zone. For questionable faults (mapped where 

obscure interruptions of acoustic reflectors are present 

in the subsurface), the criteria are (1) a shift in phase of 

reflectors that is not due to instrumental malfunction, (2) 

bent or broken reflectors that can be correlated with 

known faults on other lines, (3) termination of weak 

reflectors, or (4) any other zone of acoustic contrast, 

especially where the zone appears similar to and 

aligned with faults identified on adjacent lines. Faults 

(fig. 179) shown as cutting the sea floor are interpreted 

from disturbances in the uppermost sediment layers and 

(or) slight changes in the slope of the sea floor directly 

above the fault. Some questionable and inferred faults 

have been mapped where topographic lineaments appear to support the continuation of known faults. 

The strike of a fault is determined principally by correlation from one acoustic profile to another. Features 

that can be used to correlate faults from profile to profile typically include reflectors that are similar and 

displaced in the same direction and that have similar 

drag or other subsidiary folding associated with them. 

Contrasts in acoustic characteristics that appear 

similar across a fault on adjacent profiles can also be 

used to make correlations. 

Where fault planes dip more than about 35 o, the vertical exaggeration common to acoustic profiles 

precludes determining the dip, even though the records 

clearly indicate that a fault is present. Consequently, 

faults dipping 35 o or more are shown as vertical. Determining the amount and direction of movement on a fault 

is difficult. Only the apparent vertical component [dip 

separation) of offset can be measured on acoustic reflection profiles; the horizontal component (strike separation) can be determined only where piercing points of 

lines representing equivalent geologic features can be 

identified on opposite sides of a fault. 

The depth to the upper limit of a fault trace can be 

calculated from acoustic profiles by multiplying the 

acoustic velocity assumed or determined for the particular rock unit by half of the two-way acoustic 

traveltime obtained at the shallowest (stratigraphically 

highest) subsurface reflector cut by the fault. Generally, 

the stratigraphically highest point at which a fault can 

be identified in an acoustic reflection profile is at the 

base of the "bubble pulse"/ about 6 m beneath the 

ocean floor on high-resolution records and about 50 to 

60 m below the sea floor on intermediate-penetration 

records. An exception is sea-floor offset apparent on 

acoustic reflection records. 

An approach commonly used onshore to evaluate the 

recency of fault activity is to determine the age of the 

youngest deposit cut by a particular fault or the 

youngest landform offset by the fault; the time span (for 

example, Quaternary or Holocene) chosen to designate a 

fault as active then is selected on the basis of the likely 

consequences of renewed faulting on engineered structures (Ziony and others, 1974; Ziony and Yerkes, this 

volume). This type of evaluation is also the basis for 

identifying offshore faults as active. However, several 

factors complicate an evaluation of the offshore region: 

1. Faults (especially strike-slip faults) that displace 

rocks having similar acoustic characteristics on 

opposing fault blocks commonly are difficult to 

detect in acoustic reflection profiles. 

2. The ages of rock and sediment in the offshore region 

cannot always be closely determined. Correia- . 

tions of stratigraphic units commonly are based 

on similarities in acoustic character rather than 

on direct physical evidence such as bottom 

samples or cores from wells. 

3. Young deposits may not be present along some active 

offshore faults, and thus the ages of latest faulting cannot be closely constrained. Faults where 

only Tertiary or pre-Tertiary rocks are exposed 

at the sea floor might not be identified as geologically youthful in the absence of associated 

seismicity. 

4. Active faults in some tectonic settings in California 

do not penetrate rocks near the Earth's surface 

(Ziony and Yerkes, this volume, p. 73). The ML 

6.7 Coalinga earthquake, for example, apparently was associated with sudden fault slippage at depths of 4 to 12 km, whereas shallower 

deformation was expressed by folding (Stein 

and King, 1984). Faults that are limited to 

deeper and older strata might be interpreted 

from acoustic reflection data to be geologically 

7

The "bubble pulse" results from attenuating reverberations in the water column after the 

primary pulse has been produced. These reverberations are reflected back from the ocean bottom and appear as pseudo-sea-floor traces on the acoustic record (see fig. 179A), effectively 

masking any signals reflected from shallow structures immediately beneath the sea floor. 

Faults and Unstable Slopes Offshore 353 
old faults unless seismicity indicates contemporary activity. 

Because of these factors, the age of latest faulting as inferred from acoustic reflection profiles may not always 

be a reliable indicator of fault activity. 

Criteria used to infer conditions of sea-floor instability 

from acoustic reflection data have been described by 

Clarke and others (1983) and Kennedy and others (in 

press). Sea-floor instability here denotes conditions that 

result from mass movement and liquefaction of sea-floor 

sediment, phenomena that can be earthquake induced. 

Potentially unstable sea-floor conditions in the offshore 

Los Angeles region are associated with subaqueous 

sediment slides, subaqueous mass flows (including sediment creep), and, to a limited extent, accumulations of 

shallow gas. 

Subaqueous slides are mass movements of rigid or 

semiconsolidated sediment masses along discrete shear 

surfaces, accompanied by relatively little internal deformation (Dott, 1963). A side-scan sonograph record showing the sea-floor characteristics of a subaqueous slide 

offshore of northern California is presented by Wilson 

and Keefer (this volume, fig. 163). Slides are _commonly 

identified on acoustic reflection records (figs. 181, 182) 

by the presence (in longitudinal sections) of some or all 

of the following features: (1) a headscarp where the slip 

surface extends upward to and is expressed in the sea 

floor, (2) compressional ridges and folded and contorted 

subbottom reflectors resulting from small-scale thrusting and folding at the toe of the slide, (3) transverse (tensional) cracks in the body of the slide, (4) evidence of 

rotation or limited internal deformation of reflectors, 

and (5) the presence of a slip surface, which may be upwardly concave or planar, represented by a discrete 

failure plane or by an intensely deformed (and in some 

cases acoustically transparent) zone beneath the slide 

mass. The term slump is commonly applied to a slide 

that shows evidence of rotational movement along a 

curved slip surface; the term block glide is used for 

those slides having a relatively planar, usually gently 

dipping slide surface. Subaqueous slides may occur on 

slopes of less than 1 o and may range in size from simple 

failures covering tens of square meters to composite 

failure zones thousands of square kilometers in area 

and from a few meters to hundreds of meters thick 

(Moore, 1961; Heezen and Drake, 1964; Lewis, 1971; 

Hampton and Bouma, 1977). Subaqueous mass flows involve the downslope movement under gravity of watersaturated, unconsolidated sediment; the moving mass 

may behave plastically or as a very viscous fluid, and 

movement may be slow or rapid (Dott, 1963). Shear oc354 Earthquake Hazards in the Los Angeles Region 

curs extensively throughout the displaced mass rather 

than along a few discrete planes, as it does in slides. The 

velocity and displacement of flow characteristically 

decrease with depth below the sea floor, so that the 

deposit lacks a distinct slip surface. Subaqueous sediment flow deposits (fig. 183) are identified on acoustic 

reflection profiles by (1) the presence of anomalously 

thick sediment masses apparently detached from underlying strata, (2) the absence of an identifiable slip plane, 

and (3) acoustic transparency or chaotic internal structure. Sediment creep in the marine environment is a 

form of flow; it is a poorly understood, poorly documented phenomenon. As used here, this term refers to 

the slow, more-or-less continuous, downslope movement 

of the upper layers of unconsolidated sediment. The occurrence of creep is inferred on acoustic reflection 

records from the presence of hummocky sea-floor 

topography, deformed but identifiable acoustic bedding 

in the upper sediment layers, a downward decrease in 

the degree of deformation, and the apparent absence of 

a slip surface. Zones of sediment creep in the southern 

California borderland appear to extend to depths of 15 

to 20 m below the sea floor; they may be areally extensive and are commonly associated with other types of 

failure. 

Gas present as bubbles in the pore space of sediment 

can lower the shear strength of the enclosing sediment 

and thereby increase the likelihood of failure (Sangrey, 

1977); under some circumstances, gas-charged sediment 

can liquefy spontaneously when it is subjected to cyclic 

loading, as it is in earthquake shaking (Hall and Ensiminger, 1979). Gas accumulation in sediment (fig. 184) is 

suggested on medium- and high-resolution acoustic 

reflection profiles by (1) the presence of amplitude 

anm.nalies (apparent as enhanced or "bright" subbottom reflectors), (2) the sharp termination or displacement of reflectors commonly associated with acoustically turbid zones, (3) the absence of surface multiples 

indicating absorption of the seismic signal (Nelson and 

others, 1978), and (4) the presence in reflectors of "pull 

downs," apparent depressions resulting from the decreased velocity of sound in gaseous sediment and the 

consequent delayed arrivals of acoustic returns. Watercolumn anomalies on high-resolution acoustic profiles in 

some cases suggest gas bubbles in the water column, 

although other phenomena such as kelp and fish produce features that appear similar. Side-scan sonographs 

and underwater video or photographic coverage can 

show seep mounds or craters on the sea floor, as well as 

gas bubbles. Sampling and geochemical analyses, however, are needed to verify the presence of gas and identify its origin. 
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(slump) (from Kennedy and others, in press). Vertical exaggeration 9:1. A, Acoustic reflection record. 

B, Line drawing of prominent reflectors. Note the slip surfaces, the apparent drag folding of strata 

adjacent to slip surfaces, and the relative absence of internal deformation of reflectors. The zone of 

movement extends to a sub bottom depth in excess of 100 m. 

Faults and Unstable Slopes Offshore 355 
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FIGURE 182.- High-resolution acoustic reflection profile across the continental slope off Crescent City on the northern 

California continental margin showing subaqueous slides (retrogressive slumps) (from Kennedy and others, in press). Vertical exaggeration 13:1. A, Acoustic reflection profile. B, Line drawing of prominent reflectors. Note hummocky sea-floor 

surface produced by headscarps, back rotation and limited internal deformation of reflectors, and multiple slip surfaces. 

The wne of movement extends to a depth of approximately 20 m beneath the sea floor. 

356 Earthquake Hazards in the los Angeles Region 
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FIGURE 183.-High-resolution acoustic reflection profile across the slope of the Santa Barbara Basin showing a subaqueous flow deposit (from Edwards, 1982). Vertical exaggeration 8:1. Note the apparent absence of a slip surface and the acoustic transparency of the sediment mass. 

POTENTIAL GEOLOGIC HAZARDS 

IN THE OFFSHORE 

LOS ANGELES REGION 

The discussion of earthquake hazards in the offshore 

Los Angeles region is divided into three parts: principal 

Quaternary faults, sea-floor instability, and shallow gas 

accumulations. This arbitrary subdivision is only to 

facilitate discussion, and it should be borne in mind that 

these hazards are closely interrelated; that is, sudden 

fault movement may result in ground rupture and shaking and consequent sea-floor failure, which in turn is 

dependent in part on factors such as sediment thickness 

and composition, degree of induration, state of water 

and gas saturation, and sea-floor declivity. The discussion of principal Quaternary faults describes briefly the 

character and evidence for recency of rupture along the 

most prominent and geologically youthful faults in this 

region, faults that we consider to have the potential for 

generating earthquakes and producing fault offset of the 

sea floor. The discussion of inferred sea-floor instability 

summarizes the types and distribution of sea-floor 

failures in this region, as well as evidence leading to the 

conclusion that sea-floor failures may be earthquake induced. Finally, the discussion of hydrocarbon seepage 

and shallow gas accumulation briefly describes the 

nature and distribution throughout the region of gascharged sediment, deposits probably prone to failure by 

liquefaction and mass movement when they are subjected to earthquake shaking. 

Principal Quaternary Faults 

This section summarizes the geologic and seismologic 

character of the principal fault zones offshore (fig. 185) 

that have been active during Quaternary time (the past 

Faults and Unstable Slopes Offshore 357 
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FIGURE 184.-High-resolution acoustic reflection profile across the San Pedro shelf and escarpment showing acoustic anomalies possibly indicating the presence of gas-saturated sediment (Kennedy and others, in press). Vertical exaggeration 13:1. A, Acoustic reflection profile. B, 

Line drawing of prominent reflectors. Note amplitude anomalies (a) apparent as enhanced subbottom reflectors, the sharp termination of 

other reflectors at the margin of these anomalies, and the zone of acoustic transparency beneath the anomalies. These acoustic anomalies are 

in nearly flat lying Quaternary (Q?) sediment overlying an eroded flat-topped Miocene (Tm) bedrock ridge. 

1.7 m.y.). Our emphasis is on the ages of latest faulting 

along these zones as interpreted from acoustic reflection profiles. Yerkes (this volume) presents details of 

historical and instrumentally recorded seismicity for the 

entire Los Angeles region. Ziony and Yerkes (this 

358 Earthquake Hazards in the Los Angeles Region 

volume) discuss the character of the offshore faults and 

their onshore counterparts, summarize geologic 

evidence for the rates of fault slip and earthquake 

recurrence, and evaluate the potential for future earthquakes. Our analysis here considers evidence for fault 
displacement at or near the sea floor during Quaternary 

time instead of late Quaternary time, as Ziony and 

Yerkes (this volume) have done. The longer time span 

has been used because, for much of offshore southern 

California, the Pleistocene sedimentary rock sequence 

cannot be subdivided on acoustic reflection profiles with 

confidence. 

South of the Palos Verdes Hills, the predominant 

structural grain within the Gulf of Santa Catalina area 

trends northwest. Two major fault zones-the NewportInglewood and the Palos Verdes Hills-form the northeastern and southwestern boundaries, respectively, of a 

relatively undeformed structural block, named the 

Catalina block by Greene and others (1979). Faults of 

both zones are geologically youthful, locally displacing 

the sea floor and cutting Quaternary sediment within 

the offshore Los Angeles area. No single fault within 

either zone appears to continue uninterrupted for more 

than about 40 km. This pattern resembles other fault 

zones of California, onshore and offshore, that are composed of short, en echelon faults and folds in relatively 

narrow (1-10 km) zones. 

The Newport-Inglewood fault zone, which projects 

offshore at Newport Beach, appears to have influenced 

the development of the eastern slope of the Gulf of Santa 

Catalina physiographic basin. The zone is defined at the 

surface by discontinuous, generally northwest-trending 

faults and folds within Tertiary and Quaternary strata; 

these structural features and similarly aligned faults 

offshore form a discrete belt that extends for at least 

240 km from near the Santa Monica Mountains into 

Baja California. To the south, near Oceanside, faults 

aligned with the Newport-Inglewood zone step to the 

west and have been mapped southward offshore to the 

vicinity of La Jolla, where they appear to link with the 

Rose Canyon fault zone, which Legg and Kennedy (1979) 

have suggested may connect with the Vallecitos-San 

Miguel fault zone in Mexico. Onshore and northwest of 

Newport Beach, the fault zone extends northward 

across the western Los Angeles basin and appears to 

terminate abruptly at the Santa Monica fault (Barrows, 

1974; Ziony and others, 1974; Jennings, 1977). Moody 

and Hill (1956) and Harding (1973) have postulated a 

right-slip wrench tectonic model for the NewportInglewood fault zone in the Los Angeles basin. We have 

noted apparent offsets and en echelon folds suggesting 

this same sense of motion offshore along the southern 

extension of the zone (for example, Scripps Submarine 

Canyon appears to be a right laterally offset head of La 

Jolla Submarine Canyon (Greene and others, 1979)). 

The Newport-Inglewood fault zone has a measured 

right-lateral strike-slip displacement of 1,000 to 2,000 m 

in lower Pliocene strata (Yerkes and others, 1965) and 

probably 3,000 m in middle Miocene strata (Hill, 1971); 

apparent vertical separation across the fault zone is 

locally more than 1,000 m at the buried basement surface (Yerkes and others, 1965). Additionally, this zone of 

faulting apparently overlies the aftershock zone of the 

1933 Long Beach earthquake (M 6.2) (Barrows, 1974; 

Ziony and Yerkes, this volume, table 5). Offshore, faults 

aligned with the Newport-Inglewood fault zone are 

observed near or seaward of the shelf edge on several 

acoustic reflection lines between Laguna Beach and 

Oceanside. Where this zone can be mapped on the 

mainland shelf, it is characterized by a gentle 3- to 

5-m-high upwardly convex "bulge" of the erosional surface on Tertiary bedrock landward of the fatllt trace 

(fig. 186). This bulge is, in some locations, mirrored in 

the overlying Quaternary sediment and the sea floor, 

and Quaternary sediment commonly thins over these 

low-relief bedrock highs. The fault extends to the sea 

floor in areas devoid of Quaternary sediment. Locally, 

the erosional surface on Tertiary bedrock shows an apparent vertical separation of 5 to 7 m, seaward 

(western) side down. Where Quaternary sediment is 

present, it is buttressed against this scarp, and, on one 

profile, Holocene sediment appears to be offset by a 

fault aligned with the Newport-Inglewood zone. In a recent comprehensive review of acoustic reflection data 

from the shelf off Oceanside, Greene and Kennedy 

(1981) noted that faults of this zone extend to the sea 

floor, where they "questionably offset Holocene sediment"; an acoustic reflection survey for the Southern 

California Edison Company similarly indicated that, in 

this area, faults aligned with the N~wport-Inglewood 

zone appear locally to displace marine terrace deposits 

of probable Holocene age (U.S. Nuclear Regulatory Commission, 1981, para. 2.5.1.12(4)(d)). Although this 

evidence is not definitive, it strongly supports a history 

of deformation on offshore faults aligned with the 

Newport-Inglewood fault zone that extends to the present time. 

The Palos Verdes Hills fault zone extends from northern Santa Monica Bay southeastward; across the Palos 

Verdes peninsula and the San Pedro shelf to the vicinity 

of Lasuen Knoll, a distance of more than 110 km. The 

segment of the fault zone near San Pedro is well defined 

and continuous. The fault zone steps southwestward in 

the vicinity of Lasuen Knoll; the splay passing southwest 

of Lasuen Knoll extends for 80 km or more southeastward to its intersection with elements of the Coronado 

Bank fault zone that pass along the eastern edge of Coronado Bank offshore of San Diego (Greene and others, 

1979). The Coronado Bank fault zone has, in turn, been 

postulated by Legg and Kennedy (1979) to continue 

southward and to join the Agua Blanca fault zone in Baja California. If it does so, these faults comprise a complex multipart Quaternary zone of deformation more 

Faults and Unstable Slopes Offshore 359 
---- EXPLANATION 

Fault known to cut Holocene deposits or 

reach sea ftoor; dashed where 

inferred or approximately located 

---Fault known to cut Quaternary deposits; 

dashed where inferred or approximately 

located 

--Fault known to cut Tertiary rocks. Younger 

deposits absent. Dashed where 

" " / 

/ 

inferred or approximately located 

I 

FIGURE 185.-Principal Quaternary faults in the offshore Los Angeles region. Data sources are indicated in text. Contour interval is 250m. 

Bathymetry from U.S. Coast and Geodetic Survey (1967a, b). 

360 Earthquake Hazards in the Los Angeles Region 

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BATHYMETRY FROM l.___j 

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Faults and Unstable Slopes Offshore 361 
sw NE .I .. 

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FIGURE 186.-High-resolution acoustic reflection profile showing a strand of the Newport-Inglewood fault zone on the mainland shelf about 28 km 

south-southeast of Laguna Beach. Vertical exaggeration 11:1. Note the upwardly convex "bulge" of the erosional surface on Tertiary rrJ 

bedrock, the buttressing of acoustically transparent Holocene (Qh) sediment against the seaward margin of this bulge, and the slight deformation of the sea floor above the fault. 

than 440 km long that we consider to be the result of 

wrench faulting. The Palos Verdes Hills fault zone in the 

vicinity of the Palos Verdes Hills shows an 1,800-m vertical separation, southwestern side up, of Catalina 

Schist basement (Yerkes and others, 1965); a series of 

elevated marine terraces in the Palos Verdes Hills 

shows that this movement continued into late 

Pleistocene time. Abrupt changes in the configuration of 

the basement surface and differences in the thickness 

and lithology of Tertiary rocks juxtaposed by the fault 

suggest important components of strike-slip offset as 

well (Yerkes and others, 1965). The generally accepted 

sense of offset on the Palos Verdes Hills fault is 

dominantly right lateral, suggested by its northwestern 

trend and by fold axes that diverge westward from the 

fault in the vicinity of the Palos Verdes uplift. Its inter362 Earthquake Hazards in the Los Angeles Region 

section with the north-dipping Anacapa fault in Santa 

Monica Bay is not well understood but coincides with a 

dense cluster of earthquake epicenters recorded since 

1976 (R. F. Yerkes, oral communication, 1983). 

The Palos Verdes Hills fault zone in the Los Angeles 

Harbor area and on the San Pedro shelf is a complex en 

echelon to anastomosing group of fault splays comprising a zone 1.5 km wide ih which no single fault trace can 

be mapped for more that about 10 km (Dames and Moore 

and MESA2, 1983). Here, faults of this zone offset 

Holocene sediment and (or) the sea floor (Greene and 

others, 1975; Junger and Wagner, 1977; Clarke and 

others, 1983; Dames and Moore and MESA2 , 1983), although, throughout much of the Gulf of Santa Catalina, 

these faults appear to cut only units of Pleistocene age 

or older. Figure 187 shows a fault (probably correspond-
0 1 MILE 

0 1 KILOMETER 

FIGURE 187.-High-resolution acoustic reflection profile showing a principal strand of the Palos Verdes Hills fault zone on the San Pedro shelf 

about 15 km south of Long Beach. Vertical exaggeration 9:1. The basal Holocene reflector shows a vertical separation of 3m, and the sea floor 

is offset about 1 m, southwestern side up. Qh, Holocene; Qpl, Pleistocene; Tm, Miocene. 

ing to fault S-4 of Dames and Moore and MESA2 {1983)) 

of the Palos Verdes Hills fault zone that lies along the 

northeastern flank of the Palos Verdes uplift; this fault 

offsets the basal Holocene reflector approximately 3 m, 

southwestern side up, and produces a scarp 1 m high at 

the sea floor. The presence of a "topographic anomaly," 

considered to reflect tectonic upbowing of the sea floor 

above the Neogene bedrock units southwest of this fault, 

further suggests Holocene activity along this fault 

strand {Dames and Moore and MESA2 , 1983). Holocene 

activity on the Palos Verdes Hills fault zone is also suggested by seismologic data from the San Pedro shelf and 

the northern Gulf of Santa Catalina {Hileman and 

others, 1973; Teng and Henyey, 1975). 

A potentially active segment of the Palos Verdes Hills 

fault zone-the Cabrillo fault-was mapped principally 

as an inferred fault by Woodring and others {1946) for 

about 3.5 km from the central Palos Verdes Hills to 

Cabrillo Beach, where, in seacliffs, it is seen to dip 

northeasterly {southwestern side upthrown) and cut 

Miocene strata. Greene and others {1975) extended the 

trace southward offshore to near the head of the San 

Pedro Sea Valley, where it is shown as offsetting the 

base of Holocene sediment; however, the fault as Greene 

and his coworkers drew it is not aligned with other 

structural elements on the San Pedro shelf, and the connection of onshore and offshore strands of the fault 

seems questionable. Nardin and Henyey {1978) mapped 

the Cabrillo fault for 9 km southeastward across the San 

Pedro shelf along a different trace but did not discuss its 

age or structural significance. In a recent study for the 

U.S. Geological Survey {Dames and Moore and MESA2, 

1983), investigators mapped the Cabrillo fault as a zone 

of disruption 11 km long and 500 m wide and occupying 

a position similar to that mapped by Nardin and Henyey 

{1978) but, at its southeastern end, joining the Palos 

Verdes Hills fault. The presence of two 1.2-m-high southfacing "scarps" in late Quaternary sediment and lowrelief "topographic anomalies" thought to have been 

produced by tectonic deformation of the sea floor is considered by the Dames and Moore and MESA2 study as 

evidence of latest Holocene activity. We have mapped a 

fault on high- and intermediate-resolution acoustic 

reflection profiles in the position shown for the Cabrillo 

fault {fig. 185) by the Dames and Moore and MESN investigators. This fault closely approaches or reaches the 

Faults and Unstable Slopes Offshore 363 
sw NE 

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75~~¥.+~~~44+H~~+H+h~+rirh¥T+H+4~~~~~~~--+tt~~~~~-------------,---f-0.1 z 

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FIGURE 188.-High-resolution acoustic reflection profile showing the Cabrillo fault on the San Pedro shelf about 9 km southeast of San Pedro. Vertical exaggeration 10:1. Note that this fault cuts Miocene strata to the sea floor, but there is no apparent sea-floor offset. QPI, Pleistocene; Tm, 

Miocene. 

sea floor in Miocene strata, but there is no apparent surface displacement [fig. 188). On balance, it seems possible that the Cabrillo fault is an active 15-km-long strand 

of the Palos Verdes Hills fault zone, but additional 

documentation of the age and nature of offset is 

desirable. 

The length, trend, and character of the offshore 

Newport-Inglewood-Rose Canyon and Palos Verdes 

Hills-Coronado Bank fault zones are comparable to 

those of the Whittier-Elsinore and San Jacinto fault 

zones onshore. Short, en echelon, second-order faults 

are associated with each major fault zone and commonly splay from the primary faults at angles ranging from 

20° to 40°. Second-order fold axes are similarly related 

to these fault zones. These structural relations follow 

the stress pattern for wrench faulting described by 

Moody and Hill (1956) and Wilcox and others (1973} and 

suggest that each of these major fault zones may represent a throughgoing, right-slip fault within the underlying basement rock. Major structural and physiographic 

364 Earthquake Hazards in the Los Angeles Region 

features within and bounding the Catalina block are 

also compatible with the wrench tectonic model. The La 

Jolla Submarine Canyon near San Diego, for example, 

appears to be a graben formed as a result of tension 

associated with dilation within the Catalina block. 

Similarly, the Coronado Bank and Point Lorna in the 

San Diego area appear to be horsts produced by 

compression. 

The presence of the Palos Verdes Hills fault on the 

Palos Verdes peninsula is indicated by vertical separation of the Catalina Schist basement, the elevation of the 

Palos Verdes Hills largely during late Tertiary and 

Quaternary time, and the presence of deformed strata 

of early to late Pleistocene age along the northeastern 

flank of the Palos Verdes Hills (Woodring and others, 

1946; Schoellhamer and Woodford, 1951; Yerkes and 

others, 1965). The Palos Verdes Hills fault appears to 

extend northwestward across Santa Monica Bay, cuts 

the head of Redondo Canyon, and terminates against or 

merges with the Anacapa fault southeast of Point Dume 
(fig. 185); whether Holocene motion is taken up principally along this strand of the fault is problematic, 

however. In Santa Monica Bay, the Palos Verdes Hills 

fault cuts strata ranging in age from Pliocene to Quaternary, although major fault motion appears to be preQuaternary Ounger and Wagner, 1977). An alternative 

view of activity along the Palos Verdes Hills fault in 

Santa Monica Bay was taken by Nardin and Henyey 

(1978), who considered that right-lateral offset along 

this fault southeast of Redondo Canyon is accommodated in Santa Monica Bay by south-over-north 

reverse faulting along the Redondo Canyon fault, a highangle fault first mapped by Emery (1960, p. 79) (see also 

Yerkes and others, 1967; Junger and Wagner, 1977) 

along the southern wall of Redondo Canyon and the narrow shelf adjacent to the Palos Verdes Hills (fig. 185). 

Nardin and Henyey cited as evidence the apparent 

absence of large vertical offsets along the Palos Verdes 

Hills fault in Santa Monica Bay northwest of Redondo 

Canyon and the presence of large vertical separation 

and Holocene displacements on the Redondo Canyon 

fault and on the Palos Verdes Hill fault on land and farther to the southeast in San Pedro Bay. The Redondo 

Canyon fault joins the main strand of the Palos Verdes 

Hills fault at or near the coast line and cuts the sea floor 

and Holocene deposits on the shelf south of the head of 

Redondo Canyon Ounger and Wagner, 1977; Nardin and 

Henyey, 1978; Nardin, 1981). Seismicity data for Santa 

Monica Bay are inconclusive as to whether recent motion on the Palos Verdes Hills fault is accommodated on 

the strand mapped across Santa Monica Bay by Junger 

and Wagner {1977) or along the Redondo Canyon fault. 

The length of the Palos Verdes Hills fault from its 

juncture with the Redondo Canyon fault to the vicinity of 

Lasuen Knoll, a segment characterized by continuous to 

intermittent offsets of Holocene strata, is approximately 

70 km, however. 

Other northwest-trending zones of faulting in the offshore San Pedro-Santa Monica Basin area include (1) 

the San Pedro Basin fault zone and (2) a zone of en 

echelon faults that lies along the crest and slope of the 

Santa Cruz-Santa Catalina Ridge (fig. 185). The San 

Pedro Basin fault zone consists of steeply dipping, en 

echelon, generally left-stepping faults extending from 

the southeastern sill of the San Pedro Basin northwestward along the northern flank of Redondo Knoll to the 

vicinity of Dume Canyon, a total distance of about 85 km 

Ounger and Wagner, 1977). This fault zone appears, at 

its northwestern terminus, to join or terminate against 

the Anacapa fault. Faults of the San Pedro Basin fault 

zone vertically displace Pliocene strata 200 m or more 

near the mouth of Dume Canyon, whereas, farther 

southeast, near Redondo Knoll, Miocene rocks show a 

minimum displacement of 500 m. Nardin (1981) indicated that sediment of late Pleist~cene age or 

younger-and locally the sea floor-may be displaced 

by faults of the San Pedro Basin fault zone in both the 

San Pedro and the Santa Monica Basins. Faults showing 

vertical separation are predominantly northeastern side 

down, although apparent reversals of relative vertical 

offset suggest a component of strike slip (Nardin, 1981). 

Seismicity data show clusters of epicenters associated 

with youthful faults in the vicinity of Dume Canyon, near 

the juncture of the Anacapa fault and the San Pedro 

Basin fault zone, and in the San Pedro Basin northeast of 

the San Pedro Basin fault zone; relatively few epicenters 

are evident in the San Pedro and Santa Monica Basins 

southwest of the San Pedro Basin fault zone. This 

distribution of faults and epicenters suggests that the 

San Pedro Basin fault zone forms the southwestern 

margin of a major structural block. Nardin (1981) indicated that this block may be a tipped graben resulting 

from a combination of compression and right shear in a 

broad transform margin. The extent of the San Pedro 

Basin fault zone may be greater than figure 185 shows, 

if, as Junger and Wagner (1977) and Nardin (1981) suggested, it adjoins faults that extend farther southeast 

through the Gulf of Santa Catalina and the San Diego 

Trough to or beyond the Mexican border. However, a 

southeastward continuation of the fault zone is not indicated by recent mapping in the Gulf of Santa Catalina 

(Greene and others, 1979; Clarke and others, 1983). 

A northwest-trending zone of faulting as wide as 4 km 

has been mapped along the base and flank of the bathymetric ridge extending from Santa Catalina Island to the 

Santa Cruz Island platform, where it appears to merge 

with the east-trending Santa Cruz Island fault (Edwards, 

1982). These faults dip steeply and are predominantly 

downthrown to the northeast, toward the Santa Monica 

Basin; they cut rocks of Miocene and Pliocene age, and 

Quaternary strata are cut locally (Edwards, 1982). This 

fault zone has been identified as the source of the 1981 

Santa Barbara Island earthquake (ML 5.2) (Corbett and 

Piper, 1981). Individual faults of this zone appear to be 

discontinuous, generally a few kilometers to as much as 

about 30 km long, although the zone itself may extend 

for more than 100 km. A sinuous, west-northwesttrending, 27-km-long fault that cuts Quaternary sediment in the Santa Monica Basin and Miocene rocks on 

the crest and flank of the ridge is mapped in the area of 

complex folding and faulting where the ridge abuts the 

Channel Islands platform south of Santa Cruz Island [Edwards, 1982). A fault of similar length is present low on 

the slope of the ridge northwest of Santa Catalina 

Island, where it reaches the sea floor and juxtaposes 

volcanic and sedimentary rocks of Miocene age Ounger 

and Wagner, 1977). 

Faults and Unstable Slopes Offshore 365 
West-trending structures along the southern margin 

of the Transverse Ranges abut the northwest-trending 

structural grain to the south along a 200-km-long zone of 

late Quaternary dislocation comprising the Santa 

Monica-Malibu Coast, Anacapa, Santa Cruz Island, and 

Santa Rosa Island faults (fig. 185). These are northdipping reverse faults, and at least two-the Santa 

Monica and Santa Cruz Island faults-show components of left-lateral offset. The Santa Monica fault extends for 40 km along the southern margin of the Santa 

Monica Mountains and forms the southern structural 

boundary of the Transverse Ranges province in this 

area. Vertical separation of basement rocks is estimated 

to be as much as 2,400 to 3,660 m, and a large amount of 

left-lateral strike slip is inferred to account for the juxtaposition of dissimilar pre-upper Miocene rocks across 

this fault (McCulloh, 1960; Campbell and Yerkes, 1976). 

Elements of the Santa Monica fault appear to cut upper 

Pleistocene terrace deposits at several localities onshore (Yerkes and Lee, 1979b), and two west-trending 

faults that are probable offshore extensions of the Santa 

Monica fault may cut Holocene sediment in northern 

Santa Monica Bay (Greene and others, 1975, pl. 10). 

The Santa Monica fault apparently bifurcates 

westward in northern Santa Monica Bay (fig. 185). The 

northern branch-the Malibu Coast fault-cuts the 

coast north of Point Dume; the southern branch extends 

westward offshore as the Anacapa fault. The Malibu 

Coast fault is a narrow, north-dipping zone of reverse 

faults 25 to 30 km long that juxtaposes dissimilar basement and younger rocks along its entire length and for 

which 60 to 90 km of left-lateral strike slip has been inferred (Campbell and Yerkes, 1976). This fault, which 

separates the Santa Monica Mountains from the lowlying coastal plain to the south, has thrust upper 

Miocene strata more than 15 m over upper Pleistocene 

terrace deposits near Malibu Canyon and has cut 

Pleistocene strata at other localities onshore (Yerkes 

and Lee, 1979b). Offshore, the Malibu Coast fault appears to terminate in Pleistocene deposits on the slope 

near Mugu Canyon, where a vertical displacement of 

200 m in Miocene rocks has been noted Ounger and 

Wagner, 1977). The Anacapa fault forms the southern 

structural boundary of the Transverse Ranges province 

in the offshore. This fault extends as one or two northdipping strands along the northern slope of Santa 

Monica Bay to the Santa Cruz Island platform, a 

. distance of about 45 km. Major offset on the Anacapa 

fault appears to have taken place during Pliocene time. 

Junger and Wagner (1977, fig. 7) indicated north-side-up 

vertical separations of several hundred meters in lower 

Pliocene strata south of Point Dume and substantially 

greater offsets in Miocene rocks. They also show Ounger 

and Wagner, 1977, fig. 4) Quaternary sediment to be cut 

366 Earthquake Hazards in the Los Angeles Region 

locally in the general vicinity of Dume Canyon, but, 

elsewhere, the Anacapa fault appears to terminate in 

Pliocene strata. However, the Anacapa fault is 

associated with the Santa Monica and Santa Cruz Island 

faults, both of which show well-documented late Quaternary offset, and the identification of this fault as the 

probable source of the 1973 Point Mugu earthquake 

(M 5.3) and its aftershocks (Lee and others, 1979; Yerkes 

and Lee, 1979b; Yerkes, this volume) suggests that it is 

active. 

The Anacapa fault appears to merge westward with 

the Santa Cruz Island fault near the base of the Channel 

Islands platform southeast of Anacapa Island Ounger 

and Wagner, 1977; Edwards, 1982). The Santa Cruz 

Island fault continues as a narrow zone westnorthwestward for nearly 70 km to its juncture with the 

Santa Rosa Island fault near the western coast of Santa 

Cruz Island (fig. 185). Throughout most of its length, the 

Santa Cruz Island fault is steeply north dipping and lies 

in the prominent central valley of Santa Cruz Island, 

where it juxtaposes dissimilar pre-Tertiary and Tertiary 

basement, volcanic, and sedimentary rocks Ounger, 

1976). This fault cuts Quaternary strata on the Channel 

Islands platform east of Santa Cruz Island, and the 

westward offshore continuation of the fault cuts Quaternary deposits with a minimum of 15 m of vertical separation Ounger and Wagner, 1977; Junger, 1979; Edwards, 

1982). On Santa Cruz Island, stream deflections of up to 

300 m in a left-lateral sense suggest at least that much 

late Quaternary lateral displacement Ounger, 1979; Patterson, 1979). The Santa Cruz Island fault is a possible 

source for the 1973 Anacapa Island earthquake (ML 5.0) 

(Ziony and Yerkes, this volume, table 5). 

Faults within the eastern Santa Barbara Basin and 

the northeastern Transverse Ranges are characterized 

by thrust and high-angle reverse displacements, generally subordinate left slip, great structural relief, and 

moderate to large amounts of late Quaternary vertical 

offset. These displacements reflect the profound northsouth compression that has (and is presently) shaping 

this region. Several faults-most notable among them 

the Oak Ridge (Montalvo) and McGrath faults and the 

Pitas Point-Ventura fault-extend offshore into the 

eastern Santa Barbara Basin (fig. 185). The Oak Ridge 

fault-the dominant structural feature of the eastern 

Santa Barbara Basin-is a west-trending zone of deformation comprising folds and faults that can be traced 

for nearly 100 km, from the eastern Ventura Basin 

westward and offshore into the Santa Barbara Basin. 

The Oak Ridge fault dips shallowly to steeply southward 

and is characterized by thrusting, reverse faulting, and 

isoclinal folding. On land, it occupies a narrow zone that 

generally follows the Santa Clara River westward to the 

coast south of Ventura. East of Ventura, strata of 
Miocene age and older show an apparent stratigraphic 

separation of 2,000 m or inore and, in places, have been 

thrust over upper Pleistocene strata (Baddley (1954) as 

cited by Yerkes and Lee (1979b)). Although sea-floor 

displacement is not observed along the fault trace, upper Pleistocene strata offshore locally show an apparent 

vertical displacement of more than 135 m (Greene and 

others, 1978). The McGrath thrust-a branch to the 

south of the Oak Ridge fault-extends only about 3 km 

offshore. The McGrath fault dips gently south in the offshore, similar to the Oak Ridge fault, and cuts strata as 

young as late Pleistocene in age (Greene and others, 

1978). The western part of the Oak Ridge fault has been 

suggested by Ziony and Yerkes (this volume, table 5) as a 

possible source for the 1925 Santa Barbara earthquake 

(M 6.8). 

The Pitas Point-Ventura fault is a 5D-km-long northdipping reverse or left-oblique fault that has been 

traced along the northern side of the Santa Clara River 

valley and the foothills of the Santa Ynez Mountains 

before it extends offshore at Ventura. Offshore, 3 km 

southeast of Pitas Point, this fault displaces an upper 

Pleistocene erosion surface 25 m, northern side up, and 

cuts the base of the overlying Holocene sediment 

(Greene and others, 1978). About 15 km southeast of 

Santa Barbara, the Pitas Point fault dips steeply northward and displaces late Pleistocene strata (Yerkes and 

Lee, 1979a); still farther west, it joins the Pitas Point 

thrust of Weaver and others (1969). The Ventura fault, 

inferred to be an onshore extension of the Pitas Point 

fault, dips steeply north and cuts Holocene sediment 

near Ventura (S<~:rna-Wojcicki and others, 1976). Vertical separation at the base of upper Pleistocene strata 

has been estimated as 275 m (Ogle and Hacker, 1969), 

and a component of left slip is indicated by related folds 

and by the fault-plane solution of a 1970 earthquake 

(ML 3.6) associated with this fault (Lee and others, 1979; 

Yerkes and Lee, 1979b). Luyendyk and others (1983), 

using high-resolution acoustic reflection data, have 

mapped a curvilinear step in the sea floor on the shelf 

between Goleta and Rincon Point, about 5 to 7 km north 

of and roughly parallel to the trace of the Pitas 

Point-Ventura fault. They interpreted this step as the 

expression of a 33-km-long, south-dipping reverse fault 

that shows as much as 10 m of sea-floor offset and p,robable offsets of "Holocene materials." They named this 

feature the Goleta-Rincon fault and correlated it in part 

with "fault Y" as mapped by Yerkes and Lee (1979a). 

The Pitas Point-Ventura fault has been suggested by 

Ziony and Yerkes (this volume, table 5) as the source for 

the 1941 Santa Barbara earthquake (M 6.0) and the 1978 

Santa Barbara earthquake (ML 5.1). Evernden and 

Thomson (this volume) concluded, from patterns of 

observed and predicted seismic intensities, that the 

Pitas Point-Ventura fault and possible eastward extensions could have generated the large earthquake of 

December 21, 1812, which severely damaged missions 

throughout the western Transverse Ranges. 

Sea-Floor Instability 

Much of the southern California continental borderland is characterized by slopes having thick accumulations of poorly consolidated or unconsolidated 

fine-grained sediment of Quaternary age. Because this 

sediment is typically water saturated, its shear strength 

is commonly lower than that of corresponding sediment 

exposed onshore. As a consequence, many failures in 

the marine environment are larger and occur on lower 

slopes than typical failures on land. In fact, failures on 

submarine slopes of less than 4° are commonplace (see, 

for example, Lewis, 1971; Prior and Coleman, 1977), and 

failures on slopes as low as 0.25 o have been documented 

(Field and others, 1982). Zones of sea-floor failure commonly measure in the range of kilometers on a side and 

may be much larger, covering areas in the range of tens 

of thousands of square kilometers (Selnes, 1982). Forces 

acting to trigger movement in accumulations of unconsolidated sediment are those that tend to increase the 

load on the sediment mass or to reduce the shear 

strength. These forces may be static (for example, imposed by loading associated with high rates of sedimentation) or cyclic (for example, imposed by storm waves 

or earthquake shaking). Thus, proximity to sources of 

sediment supply, proximity to seismogeriic faults, and 

wave climate, as well as sea-floor declivity, are critical 

factors to consider in evaluating susceptibility to failure. 

The interrelation of these and other potential influencespromoting failure is complex and has been discussed in 

greater detail as it relates to slope stability in the offshore Los Angeles region by Field and Edwards (1980). 

Most submarine failures that we have noted appear to 

be composite rather than single events, and it is usually 

impossible to determine, through a remote-sensing study 

using standard equipment, the nature, scale, timing, and 

rate of motion of the individual slides and flows that contribute to failure. Zones of past failure should be viewed 

as having an unknown potential for renewed movement. 

As a consequence of having failed already, some may be 

more stable than unfailed accumulations of sediment on 

the adjacent slopes; others, however, may have unchanged or even reduced stability. Consequently, the 

geologic and engineering properties of past failures and 

of the adjacent slopes must be studied on a case-by-case 

basis. Earthquake-induced sea-floor slides are rarely 

reported for historical earthquakes worldwide, probably because of difficulties in documenting such failures 

Faults and Unstable Slopes Offshore 367 
in the marine environment (Wilson and Keefer, this 

volume). Wilson and Keefer's (this volume) figure 164C 

shows the estimated limiting distances, for earthquakes 

of different magnitudes, of liquefaction-related failures 

such as subaqueous slides. 

Geotechnical and sedimentologic evaluations of two 

widely separated zones of sea-floor failure (off San 

Mateo Point 70 km southeast of Los Angeles and in the 

Santa Barbara Basin 15 km southeast of Gaviota) provide evidence that sea-floor failures off southern 

California may be earthquake induced (Edwards and 

others, 1980; Edwards, 1982). Each zone of failure off 

San Mateo Point is about 1.5 km wide, 3.5 km long 

(downslope), and 50 m thick and comprises multiple 

discrete slumps on slopes of 4 o or less. The heads of 

these failures are at water depths of about 600 m, and 

their toes lie at depths of about 750 m, in the southern 

part of Newport Submarine Canyon. The failure off 

Gaviota is about 2 km wide and 2 km long and is a mass 

flow deposit that heads in 395 m of water and toes at a 

depth of 510 m. Geotechnical studies of cores from these 

deposits and from undisturbed sediment on the adjacent 

slopes suggest that horizontal ground accelerations of 

0.13 to 0.17 g would be sufficient to initiate failure on 

the 3 o to 4 o slopes characteristic of much of this region. 

Strong shaking from earthquakes is thought to be the 

triggering mechanism, because these failures occur well 

below the water depths at which cyclic loads imposed 

by surface waves are significant. According to Seed and 

others (1976), the mean ground acceleration produced in 

deep cohesionless soil by an earthquake of magnitude 

6.5 at an epicentral distance of 45 km is 0.1 g; the mean 

acceleration plus one standard deviation under these 

conditions is slightly less than 0.2 g (reported by Edwards and others, 1980). Numerous historical earthquakes of about M 6 or greater-large enough to have 

generated ground motions at this level or greater-are 

reported for the offshore and coastal Los Angeles region 

(Yerkes, this volume, table 3). Clearly, ground motions 

theoretically capable of triggering the massive failures 

observed on submarine slopes throughout this region occur repeatedly. Although not taken from the southern 

California offshore, additional documentation that seafloor failures can be earthquake induced has been provided by a recent study of the Klamath River delta on the 

northern California shelf (Field and others, 1982). Geophysical surveys conducted before and after a ML 6.5 

earthquake (November 9, 1980) centered 75 km northwest of Eureka indicated that failure by liquefaction and 

sediment flowage on very low slopes over a 12D-km2 area 

was triggered by that earthquake. 

Sea-floor failures in the offshore San Pedro Bay-Gulf 

of Santa Catalina area have been mapped and described by Greene and others (1975), Richmond and 

368 Earthquake Hazards in the Los Angeles Region 

others (1981), Edwards and others (1980), and Clarke 

and others (1983). Numerous sediment slides are present in the Gulf of Santa Catalina area, the majority in the 

northern part between San Mateo Point and the San 

Pedro shelf (Clarke and others, 1983) (fig. 189). These 

areas of failure, in general, are characterized on highresolution acoustic reflection records by a hummocky 

sea-floor surface and, in the subsurface, by steeply dipping, more-or-less distinct reflectors extending upward 

to or near the sea floor. These reflectors are interpreted 

as geologically young slip surfaces, and the areas comprise a continuous series of rotated and displaced sediment masses. Zones of failure typically occur on slopes 

of 4 o or less, at water depths ranging from 250 to 

900 m, and extend to a depth of as much as 50 m below 

the sea floor. Where the dimensions of these zones of 

failure could be determined, they range in area from 

about 1 to about 12 km2 • 

A rotational slump covering an area of 8 to 9 km2 is 

located near the base of the San Pedro escarpment 15 to 

20 km south of Point Fermin at water depths of 700 to 

850 m (fig. 189). Two other failures flanking the San 

Pedro shelf have been mapped by Greene and others 

(1975). The larger of these failures covers an area of 

about 10 km2 and apparently involves strata of early 

Pliocene age and younger at water depths of 200 to 

700 m about 5 km south of Point Fermin. A second failure, located just below the shelf edge 15 km southeast of 

Point Fermin, covers 3 km2 and involves probable 

Pleistocene and Holocene deposits. Two areas of rotational slumping are also present on the eastern slope of 

the Gulf of Santa Catalina within about 10 km of Oceanside. These failures, both of which involve late Quaternary deposits, cover areas of about 15 and 10 km2 and 

head at water depths of about 200 and 500 m. 

Sediment masses interpreted as subaqueous flow 

deposits are located in two areas at or near the base of 

the slope between Newport Beach and Dana Point, at 

water depths ranging from about 400 to 700 m. These 

areas are characterized, on high-resolution acoustic 

reflection records, by upwardly convex, hummockyappearing bulges of the sea floor and the disruption or 

absence of shallow subbottom reflectors. The larger of 

the areas was determined to cover nearly 60 km2 and to 

extend to a depth of 40 m or more below the sea floor. 

These deposits probably represent repeated episodes of 

relatively recent, small-scale mass movement. 

Evidence of sediment creep was noted on the eastern 

slope of the Gulf of Santa Catalina off Newport Beach 

and off Oceanside. The zones of creep are about 3 to 

5 km in their downslope dimension and extend from 

water depths of 200 to 250 to about 500 m. Creep in this 

region appears from acoustic reflection records to affect sediments to a maximum depth of about 20 m below 
the sea floor; in the areas off Newport Beach, creep 

zones appear to merge downslope with sediment slides. 

Sea-floor failures in Santa Monica Bay between the 

Palos Verdes peninsula and Point Dume have been 

described by Greene and others (1975), Haner and 

Gorsline (1978), and Edwards (1982). Rotational slumps 

up to 3 km in breadth are present in Santa Monica Canyon, especially along its oversteepened southern and 

eastern walls; typically, however, these failures are 

smaller, averaging about 1 km2 in area (fig. 189). These 

failures commonly lack a modern sediment drape, an indication that they are geologically youthful (Edwards, 

1982). Additional zones of failure are present on the 

slope between Santa Monica Canyon and Point Dume. A 

zone of individual slides 4.5 to 7.5 km long and about 9 to 

40 m thick has been mapped by Haner and Gorsline 

.(1978) as extending diagonally across the slope between 

Dume Canyon, at a depth of 580 m, to the slope off 

Malibu, at a depth of about 220 m; the upper part of this 

slide zone coincides approximately with the trace of the 

Anacapa fault east of its juncture with the San Pedro 

Basin fault zone. Parts of the lower Santa Monica Canyon are filled at depths of about 600 to BOO m by a major 

slide that covers an area of 15 km2 • In addition, an extensive zone of sediment creep is mapped below the shelf 

break as covering an area of at least 35 km2 on the 0.8 o 

to 2.7° slope north of the upper reaches of Santa Monica 

Canyon (Haner and Gorsline, 1978; Edwards, 1982). 

Submarine slides in the northern Santa Monica Basin 

are associated principally with the Hueneme and Mugu 

Submarine Canyons. Hueneme Canyon is cut through a 

thick section of poorly consolidated Pleistocene sediment and, perhaps partly as a consequence, is the site of 

several rotational slumps, the largest being 4 to 5 km2 in 

area and extending from water depths of 100 to about 

450 m (Greene and others, 1978). Other smaller failures 

are present along the western side of the upper part of 

Hueneme Canyon (near its head), in upper Mugu Canyon, and on the slope between these two canyon systems 

(Greene and others, 1975, 1978). These slides are 

mapped at water depths of 50 to 600 m and are typically 

1 km2 or less in area, although Edwards (1982) reported 

an area of sediment slides (possibly block glides) measuring 30 km2 in area on the extensively gullied slope 

west of Dume Canyon at depths between 100 and 500 m. 

Evidence for downslope sediment creep is extensive 

and commonly occurs in association with failures within 

and between the Hueneme and Mugu Canyon systems 

and on the Hueneme fan (Greene and others, 1978; 

"unstable sediment masses" of Edwards, 1982). A large 

single area of creep deformation extends for nearly 

15 km just below the shelf break west of Hueneme Canyon and appears to affect slope deposits down to a 

water depth of about 250 m. 

Extensive zones of failure are also present in the 

Santa Barbara Basin. According to Richmond and 

others (1981, p. 11), "over 20 percent of the central 

Santa Barbara Basin is covered by areas of unstable 

sediment moving downslope toward the center of the 

basin." Two principal areas of mass movement are 

delineated, each covering more than 150 km2 ; these 

areas comprise multiple failures and show evidence of 

sediment disturbance that extends, in many places, to 

depths of more than 90 m below the sea floor. 

Hydrocarbon Seepage and 

Shallow Gas Accumulation 

Natural gas of biogenic and thermogenic origin may 

be present in marine sediment. Biogenic gas-principally methane-is derived from bacterial alteration of 

organic material in sediment (Claypool and Kaplan, 

1974). Thermogenic gas, characterized by relatively 

high levels of hydrocarbons heavier than methane, is a 

byproduct of petroleum formation (Bernard and others, 

1976). The presence of thermogenic gas in sediment can 

reflect an overpressured zone that is discharging gas 

into the overlying strata either directly or through a conduit such as a fault or a bedding plane. Gas of either 

type present as bubbles in the pore space of sediment 

can increase pore pressure and reduce the shear 

strength of the enclosing sediment and thus enhance the 

likelihood of failure (Sangrey, 1977). Additionally, sediment containing dissolved gas can liquefy spontaneously 

when it is subjected to cyclic loading, like that caused by 

earthquake ground motion (Hall and Ensiminger, 1979). 

Consequently, identifying areas of possible shallow gas 

accumulation is an important adjunct of studies of sediment instability in the offshore. Indications of shallow 

gas accumulation from acoustic reflection records (see 

criteria on p. 354) are in themselves inconclusive if 

there is no direct measurement of gas content in cores 

or underwater sonographic or photographic evidence of 

gas seepage at the sea floor. Nonetheless, acoustic 

reflection data commonly provide useful indications of 

the presence of gas in sediment offshore. Oil and gas 

seeps and areas of possible shallow gas accumulation 

identified from acoustic reflection studies in the offshore Los Angeles region are shown in figure 189. 

Wilkinson's (1971) study of California oil and gas 

seeps shows that oil seepages were reported from the 

San Pedro shelf near Point Fermin and from the northeastern slope of the San Pedro Basin and that gas (probably methane) seepage was reported from near shore in 

the vicinity of Huntington Beach (fig. 189). Additional 

seeps were mapped by Greene and others (1975) on the 

inner shelf seaward of the Palos Verdes Hills and off 

Faults and Unstable Slopes Offshore 369 
8.~ c: 0 i:i:IL 

~ 

~~ ...lire 

() 0 

EXPLANATION 

Areas of sea-floor mass transport 

from sediment slides and 

flows, undifferentiated 

~ Areas of downslope sediment creep 

/ 

/ 

I 

' 

I ' -"" ( 

,.-) 

,__ Areas of acoustic anomaly 

possibly indicating shallow gas 

.../\lfj Oil or gas seep 

FIGURE 189.-Sea-floor failures, hydrocarbon s~ps, and areas of shallow gas accumulation in the offshore Los Angeles region. Areas of sea-floor 

mass transport and sediment creep have been compiled from the following sources: Santa Barbara Basin from Richmond and others (1981); 

Santa Monica Bay and the Santa Monica Basin from Edwards (1982), Greene and others (1975, 1978), and Haner and Gorsline (1978); San 

Pedro Bay, the San Pedro Basin, and the Gulf of Santa Catalina from Clarke and others (1983), Edwards (1982), and Greene and others (1975). 
10 

I I I 

10 15 20 KILOMETERS 

CONTOUR INTERVAL 250 METERS 

BATHYMETRY FROM 

NOS. 1206 N- 15 

NOS. 1206 N-16 

Areas of acoustic anomaly and oil and gas seeps have been compiled from the following sources: Santa Barbara Basin from Richmond and 

others (1981) and Wilkinson (1971); Santa Monica Bay and the Sal'l.ta Monica Basin from Edwards (1982), Greene and others (1975), and 

Wilkinson (1971); San Pedro Bay, the San Pedro Basin, and the Gulf of Santa Catalina from Clarke and others (1983), Greene and others (1975), 

Richmond and others (1981), and Wilkinson (1971). Contour interval is 250m. Bathymetry from U.S. Coast and Geodetic Survey (1967a, b). 
Point Fermin. Acoustic anomalies in the water columnpossibly seeps-were reported by Richmond and others 

(1981) from the San Pedro shelf in the vicinity of both 

the Cabrillo and the Palos Verdes Hills fault zones. We 

identified a single water-column anomaly-possibly a 

seep-on the San Pedro shelf about 16 km south of Long 

Beach; this anomaly lies above folded and faulted strata 

of probable late Miocene age and in close proximity to 

deformation associated with the offshore extension of 

the Palos Verdes Hills fault zone. 

Four small areas of acoustic anomaly thought to 

reflect the presence of gas in sediment were mapped by 

Clarke and others (1983) at shallow subbottom depths on 

the San Pedro shelf (figs. 184, 189). Three areas are in 

relatively shallow water 15 to 20 km south of Long 

Beach; two are in dipping strata of probable late Tertiary and Quaternary age, and one of them appears to 

be associated with an offshore strand of the Palos 

Verdes Hills fault zone. The third area, south of Long 

Beach, is in horizontally bedded strata of Quaternary 

age at a subbottom traveltime depth of 30 to 35 milliseconds. The fourth area is mapped about 7 km southwest 

of Newport Beach 10 to 20 milliseconds beneath the sea 

floor in flat-lying Quaternary sediment. Several additional areas of acoustic anomaly thought to reflect the 

presence of gas were reported by Richmond and others 

(1981) from the San Pedro shelf and the adjacent northern slope of the Gulf of Santa Catalina; these anomalies 

range in size from about 1 to 12 km2• Elsewhere, acoustic 

anomalies are reported in isolated localities from the 

slope southwest of Dana Point and Oceanside, at water 

depths in excess of 500 m and at traveltime depths 

below the sea floor of 50 to more than 350 milliseconds 

(Richmond and others, 1981). 

Hydrocarbon seeps are widespread in Santa Monica 

Bay; many oil ;md gas seeps apparently are associated 

with the northwest-trending Palos Verdes Hills fault 

zone, especially near the head of Redondo Canyon (fig. 

189) (Wilkinson, 1971; Greene and others, 1975; Edwards, 1982). Flow rates per seep of 12 to 15 bbl/d of oil 

and an undetermined amount of gas have been estimated for these seeps (Wilkinson, 1971). A second eastwest-trending cluster of seeps-principally oil 

seeps-occurs in northern Santa Monica Bay, where it 

may be associated with the offshore Santa Monica fault 

(Greene and others, 1975, pl. 10). Methane seepage from 

the sea floor off Malibu Point in northern Santa Monica 

Bay was reported following the 1971 San Fernando 

earthquake (Clifton and others, 1971); subsequent radioisotope analysis of the evolved gases indicate that they 

are Holocene in age and probably biogenic in origin 

(H. E. Clifton, oral communication, 1983). These seeps 

372 Earthquake Hazards in the Los Angeles Region 

had a linear trend initially considered to have been fault 

controlled but now seen as probably following the trend 

of an ancient filled channel. Elsewhere in this area, Edwards (1982) has indicated (1) a cluster of possible gas 

seeps in the northern San Pedro Basin aligned with and 

apparently associated with the San Pedro Basin fault 

zone south and west of the Palos Verdes peninsula and 

(2) a group of predominantly gas seeps in the northern 

Santa Monica Basin. 

Areas of oil and gas seepage in the northern Santa 

Barbara Basin east of 120° W. are mostly associated 

with the offshore Rincon anticlinal trend and with eastwest trending faults between Rincon Point and Goleta 

Point (Wilkinson, 1971). The most voluminous of these 

areas of seepage is off Coal Oil Point near Goleta, where 

about 250 active oil or gas-oil seeps (not shown on 

fig. 189) are located primarily along or near the crests of 

highly faulted anticlines covered by a relatively thin 

veneer of unconsolidated sediment (Fischer and Stevenson, 1973). 

Areas of acoustic anomaly interpreted by Edwards 

(1982) to reflect the presence of gas-charged sediment 

are distributed throughout the Santa Monica Basin. 

These areas underlie much of the shelf of the northeastern Santa Monica Bay between Point Dume and 

Redondo Canyon, where they extend seaward as much 

as about 13 km, and the Ventura shelf in the vicinity of 

Hueneme and Mugu Canyons, where they extend 6 to 

10 km offshore. Both areas extend from the shallow 

waters of the inner shelf seaward to water depths of 

about 250m. Large areas characterized by blotchy, 

intermittent subbottom reflections thought to result from 

gas accumulation in basin sediment occupy most of the 

Santa Monica Basin, including the Hueneme and Mugu 

submarine fan complexes, and the northwestern part of 

the San Pedro Basin between the Palos Verdes peninsula and Santa Catalina Island. These reflections appear to lie 30 to 50 ms below the sea floor (Edwards, 

1982, fig. A-9). 

SUMMARY 

Acoustic reflection profiling-a marine geophysical 

method for remotely mapping geologic features on and 

beneath the sea floor-has been used to identify potentially active faults and areas susceptible to slope 

failures offshore from the Los Angeles region. A complex offshore network of Quaternary fault zones poses 

hazards to coastal and offshore development from fault 

offset, ground shaking, earthquake-induced ground 

failure, and possible tsunamis. South of the Los Angeles 
basin, faults of the 240+-km-long Newport-InglewoodRose Canyon fault zone apparently cut Holocene strata 

off Laguna Beach and Oceanside; this seismically active 

fault zone is associated with at least one major damaging earthquake, the 1933 Long Beach event (M 6.2). The 

Palos Verdes Hills-Coronado Bank fault zone cuts Holocene deposits along much of the 7Q-km distance between 

Redondo Canyon and Lasuen Knoll. Holocene deformation also may be associated with the Cabrillo fault, an 

apparent splay from the Palos Verdes Hills fault zone on 

the San Pedro shelf. 

Farther north, activity on several faults in the San 

Pedro Basin, the Santa Monica Basin, and the eastern 

Santa Barbara Basin is reflected by the regional seismicity, even though these faults have not been conclusively shown to cut Holocene strata. These faults include the San Pedro Basin fault zone, faults of the Santa 

Catalina-Santa Cruz Island escarpment (source of the 

ML 5.2 1981 Santa Barbara Island earthquake), and 

faults of the 20o-km-long zone of late Quaternary deformation comprising the Santa Monica-Malibu Coast, 

Anacapa (source of the M 5.3 1973 Point Mugu earthquake), and Santa Cruz Island (possible source of the ML 

5.0 1973 Anacapa Island earthquake) faults. In addition 

to continuing seismic activity along this zone, the Santa 

Monica fault apparently cuts Holocene sediment in the 

northern Santa Monica Bay. West-trending, high-angle 

reverse and thrust faults of the eastern Santa Barbara 

Basin are characterized by great structural relief and 

evidence of recent deformation. Most notable among 

these faults are the Oak Ridge fault, which cuts late 

Quaternary strata and is a possible source of the 1925 

Santa Barbara earthquake (M 6.8), and the Pitas PointVentura fault, which cuts Holocene sediment onshore 

and offshore and may have generated several moderate 

to large historical earthquakes that affected the Santa 

Barbara region. 

Much of the offshore Los Angeles region is 

characterized by slopes having thick deposits of watersaturated, fine-grained sediment that is prone to failure 

by sliding, flowing, and liquefaction, even on low slopes. 

Geotechnical analyses of recently deposited sediment in 

the eastern Santa Barbara Basin and off San Mateo 

Point southeast of Los Angeles indicate that, on the 3 o to 

4 o slopes common in this region, sea-floor failures can 

be expected to result from ground shaking associated 

with earthquakes having magnitudes within the range of 

those recorded from the offshore Los Angeles region. 

Evidence of geologically youthful sea-floor mass movement is common on acoustic reflection profiles 

throughout the offshore Los Angeles region. Large sediment gravity slides extending to 50 m below the sea floor 

cover areas of up to 12 km2 along the eastern slope of the 

Gulf of Santa Catalina but are most common between 

San Mateo Point and the San Pedro shelf. Rotational 

slumps cover more than 20 km2 on the slopes flanking 

San Pedro Bay and are also mapped off Oceanside in 

two zones having a combined area of about 25 km2• 

Subaqueous flow deposits are extensive in deeper water 

below the eastern slope of the Gulf of Santa Catalina 

between Newport Beach and Dana Point, covering an 

area of more than 60 km2 to a depth of up to 40 m below 

the sea floor. Deformation inferred to result from sediment creep extends as much as 20 m below the sea floor 

on this slope off Newport Beach and off Oceanside. Gas 

seeps and areas of acoustic anomaly thought to represent shallow gas accumulations in Quaternary sediment 

are present on the San Pedro shelf and on the eastern 

slope of the Gulf of Santa Catalina. 

Farther northwest, geologically youthful slumps and 

slides are abundant in Santa Monica Canyon, on the 

slope between Santa Monica Canyon and Point Dume, on 

the slope between Dume Canyon and Malibu, in the 

vicinity of Hueneme and Mugu Canyons, and in the central Santa Barbara Basin, where zones of failure cover 

areas of hundreds of square kilometers and extend to 

depths of 90 m or more beneath the sea floor. Deformation from downslope sediment creep is extensive below 

the shelf break north of Santa Monica Canyon, in the 

vicinity of Hueneme and Mugu Canyons, and on the 

Hueneme submarine fan. 

Hydrocarbon seeps are common in Santa Monica Bay, 

where they appear to be associated with offshore 

segments of the Palos Verdes Hills fault zone and the 

Santa Monica fault, and in the central Santa Barbara 

Channel off Coal Oil Point. Extensive areas of gascharged sediment underlie much of northeastern Santa 

Monica Bay, the Ventura shelf, the northwestern part of 

the San Pedro Basin, and most of the Santa Monica 

Basin. 

Faults and Unstable Slopes Offshore 373 
374 Earthquake Hazards in the Los Angeles Region 
EVALUATING TSUNAMI POTENTIAL 

By D. S. McCulloch 

INTRODUCTION 

Tsunamis-impulsively generated wave trains-are 

among the most destructive and life-claiming natural 

phenomena to ravage coastal areas (see list, opposite). 

Although most coasts of the Pacific basin have a long 

history of tsunami-caused death and destruction, 

tsunami damage to coastal California has been relatively slight in historical time. The only tsunami to cause appreciable damage and loss of life along the California 

coast occurred on March 27, 1964, as a result of the 

great Alaska earthquake (fig. 190). Even though earlier 

tsunamis produced little damage in California, extensive 

development of some of the affected coast line over the 

last 100 yr has increased the risk of loss of life and property damage. 

This chapter reviews the major physical phenomena 

related to the generation, propagation, and runup of 

tsunami waves and summarizes the historical tsunami 

record of California to provide a basis for understanding 

the tsunami potential in coastal southern California. 

The chief methods for reducing losses from future 

tsunamis-warning systems, hazard maps, and public 

awareness-are also discussed. 

During the last quarter-century, increasing concern 

for coastal hazards has prompted considerable study of 

tsunamis. Some impetus for these studies has been provided by recent large tsunamis (1960 Chile, 1964 

Alaska), by concern for the safety of coastal nuclear 

reactors, and by the need to assess coastal flood 

hazards as a basis for assigning insurance risk. 

Recent advances in seismology have made possible a 

better understanding of the relation between tsunamis 

and tsunamigenic earthquakes, in terms of both the 

energy released and the configuration of the associated 

sea-floor displacement. Increased understanding of 

earthquake generation at the subducting margins of colliding lithospheric plates permits time and space modeling of large tsunamigenic earthquakes around the 

margin of the Pacific Ocean. Finally, development of 

high-speed computer-aided multidimensional numerical 

models permits simulation of tsunamis and analysis of 

their coastal impact. Readers interested in pursuing this 

subject might see Wiegel's (1970) and Murty's (1977) 

excellent expositions on tsunamis, Hwang and Lee's 

Some major tsunamis during the last 275 yr 

• 1707 Japan Great Hoei Tokaido-Nankaido 

tsunami; 30,000 dead, 7,763 houses 

destroyed. 

• 1737 Kamchatka Runup of 30 to 60 m; great loss 

of life and property. 

• 1755 Portugal Runup of 15 m in Lisbon; waves 

hit coasts of North Africa and England and 

reached as far north as Holland. Waves 

crossed Atlantic; 3-m wave runup heights in 

San Martin in the West Indies. More than 

60,000 killed in Lisbon. 

• 1868 Chile Runup of 14 m; 25,000 dead; 

wrecked most ships in the harbor and overwhelmed and devastated the city. U.S. Gunboat Wateree carried 3.2 km inland and left 

stranded. Waves affected Hawaii, New 

Zealand, and Japan. 

• 1877 Chile Waves 3 to 4 min Samoa, 2.5 to 6 m 

in Japan, 1 to 6 m in Australia and New 

Zealand. 

• 1883 

• 1896 

• 1933 

• 1946 

• 1960 

• 1976 

Indonesia Explosion of Krakatoa, a 

volcanic island. Wave runup of 35 m; at 

least 36,417 people killed along the shores 

of Java, Sumatra, and Borneo. 

Japan Great Meiji Sanriku tsunami, Honshu. 27,000 deaths; runup greater than 30 m 

at Umnak, Alaska, and 17 m in Hawaiian 

Islands, where 159 were killed and 488 

houses were destroyed. 

Japan Sanriku tsunami, Honshu. Runup 

28 m; 3,022 dead, 8,900 homes and 8,200 

boats destroyed. 

East Aleutians Runup greater than 30 m. 

There were 241 deaths and 36 million dollars of damage to the Hawaiian Islands. 

There was one death in California and damage to coastal Chile. 

Chile Runup 23 m in Chile, 5.5 m in Japan. 

Coastal towns and ships destroyed in Chile; 

more than 1,000 deaths. Considerable damage in Japan, where 4,885 structures were 

destroyed and 199 killed. There was major 

damage and 61 deaths at Hila, Hawaii. 

Philippines Mora Gulf, 5.9 m runup. Possibly 5,000 deaths. 
FIGURE 190.-A house tom from its foundations and penetrated by an automobile during the 1964 tsunami at Crescent City, Calif. (Photograph 

used by permission, W. Griffin, Crescent City Printing Co., Crescent City, Calif.) 

(1979) volume on the proceedings of a National Science 

Foundation tsunami workshop, Houston's (1979) and 

Bernards and Goulet's {1981) state-of-the-art reviews of 

tsunami research, Pararas-Carayannis and others' 

(1982) annotated bibliography of tsunami-related phenomena, and Lockridge and Smith's (1984) annotated 

map of tsunamis in the Pacific basin. 

Acknowledgments 

The author thanks the following, who read all or part 

of this chapter and offered helpful suggestions: E. N. 

Bernard, Pacific Marine Environmental Laboratory, 

National Oceanic and Atmospheric Administration 

(NOAA); J. R. Houston, Coastal Engineering Center, U.S. 

Army Corps of Engineers; R. T. Lenaburg, Federal 

Emergency Management Agency; R. L. Slingerland, 

Pennsylvania State University; T. J. Sokolowski, Alaska 

Tsunami Warning Center, NOAA; R. L. Wiegel, Universi376 Earthquake Hazards in the Los Angeles Region 

ty of California, Berkeley; and H. C. Wagner, R. F. 

Yerkes, and J. I. Ziony, U.S. Geological Survey (USGS). 

The author also thanks the following, who kindly supplied information and discussion: B. Edwards and P. 

McClellan, USGS; J. Harrison, U.S. Army Corps of Engineers; L. S. Hwang and F. Wu, Tetra Tech; J. W. Joy, 

Marine Advisors; J. Kellerher, Redwood Research, Inc.; 

Y. Kobayashi, Kyoto University; and, finally, Reuben 

Kachadoorian, USGS, with whom the author examined 

1964 tsunami damage in Whittier, Alaska, and whose 

careerlong association with the USGS was an inspiration to his colleagues. 

TSUNAMI GENERATION 

AND PROPAGATION 

Commonly cited causes of tsunamis are tectonic 

displacement of the sea floor associated with large, 
U1 

a: 

80 

No tsunami 

000 0 0 

-3 

Tsunami I 

generated I 

I 

' -2 I - • • I Dtsastrol!s I tsunami ~ 60 llJ 

~ 00 0 0 

2 

0 I • g 

~ 00000 

~ g4o 0 0 

2 -2 - 2 

ooooooo o6ioo:oz o -i0~-~1 ,t _, -, 3 

000 0 0 

J: 

t 

llJ 

Cl 

....1 

ooooooooooooo 

0 0 

- 2 ' • • 

<( 20 u ooooooo'ijooooo -2 

0-1 _, ,4 2 

•• • I• • .. , , 5 

• 

0 

U00 0 

ooooooooooo 

0 0 

-2-1 

•• o I 

• I 

, 

, 0~~~~~~~~~~~~ -2 _, 

.. ---.'.-'~'--~---------J 

5 6 7 8 9 

EARTHQUAKE MAGNITUDE (ML) 

FIGURE 191.-Relation between the magnitude (ML) and focal depth (H) 

of submarine earthquakes and the occurrence and size of associated tsunamis (!ida, 1970). Open circles indicate no tsunami; solid 

circles indicate tsunamis, the accompanying number being the 

nearest whole tsunami magnitude (see table 48). !ida divided the 

data into three fields: no tsunami, tsunami generated, and 

disastrous tsunami. The limiting magnitude for tsunamigenic earthquakes, excluding three "tsunami earthquakes" in which the 

released seismic energy is abnormally small (solid line), is 

ML ~ 6.3 + 0.005 H, and the limit for disastrous tsunamis having a 

magnitude of more than two (dashed line) is Mr.~ 7.7 +0.007 H. 

shallow earthquakes; sea-floor landslides; rock falls into 

bays and oceans; exploding volcanic islands (for example, Krakatoa and Santorini); and underwater nuclear 

explosions (for example, Bikini Atoll) (Wiegel, 1970; 

Furneaux, 1964; Galanopoulos and Bacon, 1969). 

Other suggested causes include earthquake-related 

horizontal tectonic displacement of a basin (on the upper plate of a megathrust) containing a confined or 

semiconfined water body (Tudor, 1964; Plafker, 1972). 

Studies of the tsunami hazard to coastal nuclear reactors (Marine Advisors, 1965) have considered the 

remote possibility of waves generated by meteor impact. 

The name tsunami does not have universal meaning. 

Many who use the term are concerned with long-period 

waves that travel great distances and are generated by 

large-scale tectonic sea-floor displacement associated 

with large earthquakes. Others call these large panoceanic waves "seismic sea waves" and reserve the 

name tsunami for waves generated by smaller events 

such as explosions and subaerial and submarine landslides that affect a much smaller area. In this chapter, 

we follow Wiegel (1970), who takes the broader view of 

wave mechanics and applies the name to all impulsively 

generated waves, whether of local or transoceanic 

scale. 

The terms used to describe tsunami wave height are 

also ambiguous. Rigorously defined, height is the vertical distance from the crest to the trough (double 

amplitude) of the tsunami wave before it runs up on the 

land. Runup elevation or runup height is the highest 

altitude above tide level that the water reaches as it 

runs up on the land. However, height is often used 

synonymously with runup height or to indicate the 

height of the wave crest at some specific location during 

runup; predicted runup heights may be referred to mean 

sea level. Context is often the best guide to meaning. 

Earthquake-Generated Tsunamis 

It is generally accepted that large tsunamis are the 

result of seismotectonic deformation in which there is 

appreciable and relatively rapid vertical displacement 

(uplift and (or) subsidence) of many hundred to more 

than a thousand square kilometers of the sea floor. Iida 

(1963a) showed that, for tsunamis generated by seismic 

events associated with thrusting along the Japan-Kurile 

Trench, the larger the earthquake and the shallower its 

focus, the larger the associated tsunami (fig. 191). He 

presented a revision of the tsunami magnitude scale proposed earlier by Imamura (1949) and related the runup 

height of the tsunami to the associated amount of energy 

(table 48). He also related tsunami size or magnitude to 

Richter magnitude, (that is, local magnitude MJ (fig. 

192A) and demonstrated that tsunami period increases 

as earthquake magnitude increases (fig. 192B). Several 

workers (Iida, 1963a, b; Van Darn, 1964) recognized that 

the size of the tsunami is related to the area of the 

displaced sea floor. 

TABLE 48.-Magnitude, energy, and runup heights of tsunamis in 

Japan 

[From !ida (1963a)] 

Tsunami 

magnitude 

classification' 

Tsunami energy, 

in ergs (foot-pounds) 

5 -------- 25.6 X 1()23 (18.9 X 1014) 

4.5 ------ 12.8 X 1023 (9.4 X 1014) 

4 -------- 6.4 X 1()23 (4.7 X 1014) 

3.5 ------ 3.2 X 1()23 (2.4 X 1014) 

3 -------- 1.6 X 1()23 (1.2 X 1014) 

2.5 ------ .8 X 1()23 (.59 X 1014) 

2 -------- .4 X 1()23 (.29 X 1014) 

1.5 ------ .2 X 1()23 (.15 X 1014) 

1 -------- .1 X 1023 (.074 X 1014) 

.5 ------ .05 X 1()23 (.037 X 1014) 

0 -------- .025 X 1()23 (.018 X 1014) 

- .5 ------- .0125 X 1()23 (.0092 X 1014) 

-1 -------- .006 X 1023 (.0044 X 1014) 

-1.5 ------ .003 X 1()23 (.0022 X 1014) 

- 2 -------- .0015 X 1()23 (.0011 X 1014) 

1

From Imamura (1949). 

Maximum runup height, 

in meters (feet) 

>32 (>105) 

24-32 (79-105) 

16- 24 (52.5--79) 

12- 16 (39.2-52.5) 

8- 12 {26.2-39.2) 

6- 8 (19.7-26.2) 

4-6 (13.1-19.7) 

3-4 (9.9-13.1) 

2- 3 (6.6-9.9) 

1.5-- 2 (4.9-6.6) 

1-1.5 (3.2-4.9) 

.75-- 1 (2.5--3.2) 

.50-.75 (1.6-2.5) 

.30-.50 (1.0-1.6) 

<.30 (<1.0) 

Tsunami Potential 377 
100 

ci 50 

Q(l) 

a:o 

wz Cl.o 

-u 20 ::!:w 

<(Vl 

Zz 

::J- 10 (/) 

1--

5 

5 

8 

UJ 

0 

::J 

4 

!::: 2 z 

(.!) 

<( 

::!: 

~ <( 

z 

::J 

~ 0 

-1 

5 

A 

1 

rr 

1 

I 

l( 

j 

6 7 8 9 

EARTHQUAKE MAGNITUDE (ML) 

• 

~ ~ 

_.....- • 

-~ • 

6 7 8 

EARTHQUAKE MAGNITUDE (ML) 

FIGURE 192.-A, Relation between tsunami magnitude and earthquake 

magnitude (ML) (!ida, 1963a). B, Relation between the maximum 

period of a tsunami and the associated earthquake magnitude (ML) 

(!ida, 1963b). 

To refine the relations between tsunami size and seafloor deformation, Abe (1973, 1975) examined several 

coastal Japanese earthquakes. Using seismic-wave first 

motions and the polarity of the initial waves in the 

tsunami wave train, he established the attitude of the 

fault slip plane and the sense of real displacement (uplift 

and (or) subsidence) of the sea floor. He approximated 

the area of displaced sea floor by examining the aftershock distribution and by projecting the tsunami wave 

fronts back to the source area from a dense onshore 

tide-gauge network. Finally, by comparing tsunami wave 

heights at the edge of the source area with the 

amplitude of the sea-floor displacement (calculated from 

seismic movement and fault area), Abe demonstrated 

that tsunami wave heights at the source area were approximately the same as the amplitude of the displaced 

sea floor. He interpreted his findings as strongly indicating that large tsunamis are generated by tectonic 

deformation rather than by large submarine landslides 

and slumps, whose time constants would be larger than 

those observed. Abe (1975) noted that the relation between the area of the fault-rupture surface (S) defined 

378 Earthquake Hazards in the Los Angeles Region 

by the one-day aftershock distribution and the tsunami 

source area (S1) is S = 0.8 S1 (fig. 193), and Kanamori 

(1977) indicated that the aftershock distribution 

measured several months after the main event (Sm) 

averages about 75 percent larger than the 24-hr 

distribution (Sm""' 1.4 S1

). 

In 1977, Kanamori pointed out that recorded earthquake ground motions used for assigning magnitudes in 

conventional scales saturate (cease to increase) in great 

earthquakes when the rupture dimension(~ 100 km) exceeds the wavelength of the waves used to calculate Ms 

and therefore fail to account for all the energy released 

(Kanamori, 1977) (see Evernden and Thomson (this 

volume) for an explanation of why ground-motion 

parameters saturate). Kanamori related the overall 

physical deformation at the earthquake source (rigidity 

of faulted rocks, average fault displacement, and area 

of the fault-rupture surface) and the change in elastic 

strain and proposed a new moment magnitude scale 

(Mw, now indicated by the M of Hanks and Kanamori 

(1979)) for earthquakes in which the stress drop is 

complete . 

Moment magnitudes gave Abe (1979) the opportunity 

to compare the tsunami size with a more accurate 

estimate of the strain energy or seismic energy released 

during large earthquakes. He proposed a new tsunami 

magnitude scale, Mt' calculated from the logarithm of 

the maximum amplitude of the far-field tsunami waves 

measured by tide gauges; that is, Mt =log H + B, where 

(/) 

a: 

UJ 

1--

UJ 

::!: 

0 104 ....J 

sz 

UJ 

a: 

<( 

::J 

0 

(/) 

~ 

v) 

103 

Kurile• 

•Sanriku 

Kurile • • Tokachi 

Tonankai e 

Nemuroe/ 

""'"'"•~"' 

103 104 

S,, IN SQUARE KILOMETERS 

eNankaido 

FIGURE 193.-Relation between the calculated area of the faultrupture surface (S) and the size of the related tsunami source area 

(S1

) as given by Abe (1975). The linear relation of the exponential 

function iss= 0.8 sr 
UJ 

0 

;:) 

!::: 

z 

~ 9 

~ 

~ 

<1: 

z 

;:) 

1/) 

I8 

8 9 10 

MOMENT MAGNITUDE (M) 

FIGURE 194.-Relation between tsunami magnitude (M1

) and earthquake moment magnitude (M) for earthquakes derived by Abe 

(1979) from H (observed maximum amplitude of tsunami waves, in 

miles) and B (a constant depth that depends on the source region 

and the recording station) to calibrate his M1 tsunami magnitude 

scale. Standard deviation is indicated by bars. 

H is the maximum observed tsunami amplitude (in 

meters) and B is a constant that depends on both the 

source region and the behavior of the tsunami at the 

tide-gauge station. Abe evaluated H and B by using 14 

large dip-slip earthquakes (M 7.8-9.5) that occurred 

around the Pacific and for which there were good runup 

tide-gauge measurements. A comparison of tsunami 

magnitude and moment magnitude for the calibration 

earthquakes shows good agreement (fig. 194). 

Several large earthquakes have produced tsunamis 

apparently too large for the associated stress drops. 

Kanamori (1972) called such events tsunami earthquakes. Fukao (1979) examined two tsunami earthquakes and suggested that seismogenic thrust faulting 

occurred between oceanic and overlying continental 

plates in a subduction zone but that the fault did not 

reach the sea floor. The displacement on the deep thrust 

placed a sudden load on the overlying, normally ductile 

sediment wedge at the edge of the continent. This wedge 

then failed by brittle fracture along one or more steeply 

dipping secondary faults that broke to the surface and 

displaced the sea floor. The steep dip of the secondary 

faults contributed to the vertical component of sea-floor 

offset, and, presumably, the low rigidity of the sediment 

wedge accounted for the low stress drop. 

Tsunami size is related not only to the size and rate of 

displacement of the source area but also to the shape 

and sense of motion of the source area (up and (or) 

down). As Wiegel (1970) noted, the large tsunamis of Mt 

9.4 and Mt 9.1 of the M 9.4 1960 Chile and the M 9.2 1964 

5 

~ 4 

UJ 

0 

;:) 

!::: 3 z 

(!) 

<1: 

~ 2 

~ 

<1: 

z 

;:) 1 1/) 

I0 

v v 

10 20 

/ 

/_ v 

./ v 

/ 

/ 

50 1 00 200 500 1 000 2000 5000 1 0000 

WATER DEPTH (H) AT EPICENTER, IN METERS 

FIGURE 195.-Relation between Imamura-Iida tsunami magnitude 

(table 48) and water depth at the epicenter of the associated earthquake (Iida, 1963a). 

Alaska earthquakes, respectively, were produced by 

uplift of elongate areas of sea floor (Plafker, 1972), 

which accounts for the large associated tsunamis. 

Model experiments (Takahasi (1963), cited by Wiegel 

(1970)) indicate that, when an elongate source is raised 

or lowered, the wave having maximum amplitude 

travels perpendicular to the long axis of the source. In 

addition, when an elongate source is raised, the amplitude of the larger wave decreases more slowly (1/r112 or 

1fr113, where r is radial distance from the source area) 

than that of the smaller wave that travels perpendicular 

to the short axis of the source (which decreases by 

1fr.312). By contrast, when the source area is more equidimensional, the resulting wave has a more circular 

wave front. A circular wave loses amplitude quickly 

because of radial spreading and dispersion, and its 

amplitude decreases in proportion to 1/r. 

Tsunami size is also related to water depth at the 

epicentral area. Iida (1963a) showed that, for 

earthquake-generated tsunamis observed in Japan, 

there is an upper bound relation between water depth 

and tsunami magnitude (fig. 195). The physical reason 

for this relation is not fully understood. As Iida noted, 

the increase in tsunami magnitude with water depth is 

too large to be explained by amplification due to reflection as the wave approaches the shore. 

It is generally accepted that offshore strike-slip 

faulting, in which displacement of the sea floor is 

primarily lateral, has not caused tsunamis, but proof remains elusive. Historically, there was no observed 

coastal tsunami thought to have resulted from the 1906 

horizontal displacement on the San Andreas fault (see 

discussion of event 26, app. 4) and none within San Francisco Bay associated with the 1868 displacement on the 

Hayward fault. However, mathematical and laboratory 

modeling indicate that a significant tsunami could be 

generated by lateral displacement of a major submarine 

Tsunami Potential 379 
ridge such as the Gorda Escarpment off Cape Mendocino (Garcia, 1972). 

Large-scale tsunamis are not single waves but a long 

train of waves. If deformation occurs on a shelf, the 

shelf may act as a partially resonant chamber; energy is 

reflected back onto the shelf both from the shore and 

from the deep water at the continental slope (Tuck, 

1979). The cross-shelf width largely determines the 

length of the chamber and hence the length of the 

tsunami. When the cross-shelf length of the deformation 

is large and close to the natural mode of chamber 

oscillation, the excitation may be greatest. Tuck 

estimated that, as the gravity water waves oscillate 

back and forth between the shore and the slope, 

perhaps 25 percent of the waves escape into the deep 

ocean. The returning waves lose energy through dispersion along the shoreline. Thus, there is a general 

decrease in the energy of successive waves that are 

propagated shoreward and seaward off the shelf. 

In general, long-period tsunamis are associated with 

sea-floor deformation of the continental shelf, and 

shorter period tsunamis are associated with deformation in deeper water. Large tsunamis generated on continental shelves (1952 Kamchatka, 1960 Chile, 1964 

Alaska) had periods greater than 40 min. Main waves 

from deep-water Aleutian tsunamis (1946, 1957) had 

very short period waves of 7 to 10 and 10 to 15 min 

(Kajiura, 1979). 

Tsunami Wave Propagation 

As long-period tsunami waves cross the deep ocean, 

they behave as linear nondispersive gravity waves. 

Their periods may exceed 1 hr, amplitudes are probably 

less than 1 m, and wavelengths are on the order of 40 to 

200 km (Wu, 1979). Because of their great wavelengths, 

tsunamis act as shallow-water waves that feel the bottom when the water depth is less than one-twentieth to 

one-twenty-fifth the wavelength. Thus, wave velocity is 

dependent in part on water depth such that velocity 

equals the square root of the acceleration of gravity 

times the water depth. The initial wave in the wave train 

appears, from model studies (Prins, 1958; Weigel, 1970), 

to travel slightly faster. In the open ocean, where 

wavelengths are large and water depths equal or exceed the average ocean depth (38,000 m, as given by 

McLellan (1965)), tsunamis may travel at great speeds of 

550 to 800 km/hr (Wiegel, 1970). 

The direction of wave travel from the source to the affected shore is largely determined by refraction. 

Because wave velocity is depth dependent; waves are 

slowed as the water shoals, the wave crest is bent or 

380 Earthquake Hazards in the Los Angeles Region 

refracted, and the travel path is altered so that it 

becomes more perpendicular to the bottom contours. 

Refraction can be expressed by 

sin ex: 2 ~ 

sin ex: 1 vt 

where ex: 1 and ex: 2 are angles between adjacent wavefront positions and their respective bottom contours and 

V1 and V2 are the corresponding wave velocities. For 

wave-path prediction, refraction diagrams of the timehistory of the successiv~ wave-front positions can be 

drawn, given the original wave position, the wave velocity, and the sea-floor configuration (fig. 196). On refraction diagrams, orthogonals (rays normal to the moving 

wave front) can be drawn to indicate the direction of 

wave travel and also to evaluate changes in tsunami 

wave amplitude. Where orthogonals converge, energy is 

concentrated, and wave amplitude increases. Where orthogonals diverge, the tsunami wave is stretched, and 

amplitude decreases. 

As a tsunami wave passes above a sea-floor irregularity, it may lose energy by reflection. If the slope of the 

irregularity is gradual and the length of the slope is a 

moderate multiple of the wavelength, there is practically no reflection. The larger the irregularity and the more 

steplike it becomes (for example, at the edge of the continental shelf), the greater the reflection and, therefore, 

the less the energy that continues landward. Steplike irregularities may do more than reduce energy in the 

transmitted wave. Wu (1979) noted that strong reflection over a steplike irregularity may produce considerable change in the tsunami waveform near the step. For 

predictive purposes, it is important to know the waveform that may strike a coast. Thus, with regard to both 

amplitude and waveform, reflection is an important 

parameter in evaluating tsunami hazard. 

Because of their small height, tsunamis go undetected 

by ships at sea; however, compressional waves generated at the sea floor in the epicentral area are transmitted through the water, and ships struck by such seaquakes report an experience akin to running aground or 

striking another vessel. Energy in the compressional 

wave may be considerable. The 32,50Q-ton tanker Ida 

Knudsen, sailing in 4,900 m of water approximately 

35 km from the epicenter of a 1969 M8 8.0 earthquake 

west of Gibraltar, suffered such extensive damage to its 

hull girders and beams, equipment, and machinery that, 

although later extensively rebuilt, it was at first listed as 

a total loss (Hove and others, 1982). Seaquakes are more 

than just an interesting phenomenon. Hove and others 

(1982) analyzed the damage to the Ida Knudsen and 11 

other ships hit by seaquakes (table 49) and concluded 

that offshore structures in seismically active areas 
A 

8 

c 

should be designed to withstand earthquake loads 

similar to those predicted for shore-sited structures. 

They note that the seismically induced forces may be 

large and of long duration and that the force delivered 

tp the structure is largely independent of the water 

depth. These forces have generally been ignored in the 

design of floating structures. 

Tsunami Runup 

When long-period tsunami waves encounter shoaling 

water as they approach a shoreline, fundamental properties of the waves change in a progressively nonuniform way, and predicting wave behavior becomes more 

difficult. As each wave runs up a sloping sea floor, the 

increased frictional drag decreases the speed of the 

wave and shortens its wavelength. The energy within 

each wave is crowded into progressively less water. 

Because the volume of water in a tsunami wave is large, 

it cannot dissipate significant energy by breaking along 

its leading edge, as do waves having shorter 

wavelengths, and the crowding takes place so rapidly 

that the energy cannot be lost by dispersion. Tsunami 

waves adjust by increasing their height. Waves that 

were 1 m or so high in the ocean may reach heights in 

excess of 20 m during runup. If successive waves in the 

tsunami wave train are similar, they are affected in a 

similar way as they cross shoaling water; they undergo 

a similar decrease in velocity, and their periods remain 

nearly constant. In an area where tsunami waves are 

coming ashore, it is of great importance for people to 

know that intervals between successive major waves 

may be similar. 

In the real world of nonuniform sea-floor slope and irregular coastal configuration, the local sea-floor 

bathymetry and the shape of the shoreline can have a 

large effect on refraction, reflection, and the formation 

of secondary waves by reflection, diffraction, and the 

setting up of high-amplitude resonant waves in semienclosed bays and harbors. To estimate how high a 

tsunami wave will be as it crosses the coastline, these 

local effects must be considered and add to the complexity of runup predictions. 

Tsunamis come ashore in several ways. Shepard 

{1948, p. 49) described the arrival of the April 1946 

~FIGURE 196.-Wave refraction and orthogonal diagrams for three major tsunamis that have affected the California coast. A, 1952 Kamchatka (Keulegan and others, 1969). B, 1960 Chile (Hisamoto and 

Murayama, 1962). C, 1964 Alaska (Wilson and T~rum, 1968). Successive wave-front positions are shown in hour and half-hour increments (Chile and Alaska) or 16.5-min intervals (Kamchatka). 

Tsunami Potential 381 
TABLE 49.-Parameters of earthquakes, vessels damaged by associated seaquakes, and seismic forces experienced by the vessels 

(Modified from Hove and others {1982). --. no data] 

Depth to 

Region of Magnitude hypocenter, 

earthquake Mb Ms inkm Vessel 

Nicaragua ------------------ 7.0 160 Magician 

Eagle 

Solana 

Mexico -------------------- 8.1 Sevenur 

Northern Sun 

Arizona 

Mexico -------------------- 7.7 100 Unknown 

Solomon Islands --- 6.1 7.3 Ninghai 

Peru ------------- 6.3 Belmont 

Gibraltar --------- 6.5 8.0 14 Ida Knudsen 

Peru-Ecuador ------ 6.3 7.6 15 Bergensfjord 

Thessaloniki ------- 6.1 6.4 3 Troyka 

tsunami at Oahu generated by the M 8.4 Aleutian 

earthquake: 

The waves were probably low as they came in 

to the coast. At our residence we estimated 

that the second wave which broke over the 

outer reef was about 16 feet high, not any 

higher than the storm waves that were breaking at the time. At the coast it was possible to 

see over the advancing wave from a height of 

eye level of about 18 feet above the tide. 

However, unlike normal waves the tsunami 

kept on coming rather than dissipating its 

energy where it encountered the reef. 

Some tsunami waves look like a rapid rise in tide. In 

the 1964 Alaskan earthquake, the low-lying shore of 

Kodiak Island was inundated by at least five successive 

tsunami waves (Kachadoorian and Plafker, 1967, 

p. F22). One resident described the first wave as "a nonturbulent rapid rise of tide." The wave reached a height 

of 2.6 to 3.8 m. The second wave arrived about 20 min 

later and was reported by several eyewitnesses as a 

surge of about 1.8 m followed by a rise to about 4.3 m. 

The third wave reached about the same height. 

Although the description of the waves as a nonturbulent 

rapid rise of tide may sound benign, these waves were 

anything but. They reached a maximum runup height of 

about 10 m. As they surged in and out across the city, 

they tore buildings apart, demolished waterfront industrial buildings, wreaked havoc on the fishing fleet, 

and severely scoured the land surface (Kachadoorian 

and Plafker, 1967, p. F24): 

382 Earthquake Hazards in the Los Angeles Region 

Distance from Duration 

Water depth, ship to epicenter, of quake, Acceleration, 

inm in km ins in percent g 

3,400 330 100 <1 

3,400 340 120 <1 

1,500 80 7 16 

3,000 100 60 10 

2,500 230 180 3 

2,500 260 75 2 

500 90 9 

4,000 50 20 

110 170 15 3 

4,900 20 (60) 75 

3,000 100 40 7 

20 35 10 15 

The violent incoming and outgoing waves 

destroyed more than 212 structures. About 

200 of them were on land and approximately 

15 were private and commercial docking facilities. The inland structures included 158 

homes, 25 commercial structures and about 20 

miscellaneous buildings. 

To the south at Crescent City, Calif., tsunami waves from 

this same earthquake had the same general aspect 

(Tudor, 1964, p. 65-66): 

One observer related that as the first wave 

moved into the city bringing logs and debris 

with it, the water rose rapidly with the small 

waves riding the crest. Front Street was 

covered in places with considerable water and 

logs which partially blocked traffic. As the 

first wave subsided, officers of the City Police 

and .Sheriffs Department moved into the area 

to survey the damage and to deal with the 

sightseers and possible looters. They began 

moving the public out almost immediately as 

the second wave started building up. The second and third waves seemed of lesser magnitude than the first and to hit with less force. 

But the fourth wave was fast in rising; it hit the 

city hardest, such that it left in its wake a large 

area of total destruction. One reporter said the 

wave came into the city in fingers of water. 

Another observer reports the first wave in the 

city at 0009 PST, 28 March. Two more waves 

came and both threw driftwood onto the street 
at 0030 and 0045. Then, at 0140, the water 

began pouring onto the streets, slowly, then 

more swiftly. When this wave receded cars, 

refrigerators, gas tanks, and debris of all sorts 

floated toward the sea. It was this highest 

wave that was responsible for the 12 dead. 

In areas near the tsunami source but also less commonly in areas remote from the source where the wave 

height is large or the slope is very low (for example, in a 

river channel) or when a wave encounters runoff of a 

preceding wave, the wave may come ashore as a bore 

having an abrupt front accompanied by a roaring, 

breaking frontal zone. Eaton and others (1961, p. 139) 

described the arrival of a bore at Hilo, Hawaii, 

generated by the 1960. Chilean earthquake: 

At first there was only the sound, a dull rumble 

like a distant train, that came from the 

darkriess far out toward the mouth of the bay. 

By 1:02 a.m. all could hear the loudening roar 

as it came closer through the night. As our eyes 

searched for the source of the ominous noise, a 

pale wall of tumbling water, the broken crest 

of the third wave, was caught in the dim light 

thrown across the water by the lights of Hilo. It 

advanced southward nearly parallel to the 

coast north of Hilo and seemed to grow in 

height as it moved steadily toward the bayshore heart of this city. At 1:04 a.m. the 

20-foot-high nearly vertical front of the inrushing bore churned past our lookout, and we 

ran a few hundred feet toward safer ground. 

Turning around, we saw a flood of water pouring up the estuary. The top of the incoming current caught in the steel-girder roadway of the 

south half of the bridge and sent a spray of 

water high into the air. Seconds later, brilliant 

blue-white electrical flashes from the north 

end of Kamehameha A venue a few hundred 

yards south of where we waited signalled that 

the wave had crossed the sea wall and buffer 

zone and was washing into the town with 

crushing force. Flashes from electrical short 

circuits marked the impact of this wave as it 

moved swiftly southeastward along Kamehameha A venue. Dull grating sounds from 

buildings ground together by the waves and 

sharp reports from snapped-off power poles 

emerged from the flooded city now left in 

darkness behind the destroying wave front. At 

1:05 a.m. the wave reached the power plant at 

the south end of the bay, and after a brief 

greenish electrical arc that lit up the sky above 

the plant, Hilo and most of the Island of Hawaii 

was plunged into darkness. 

Many of the forms taken by tsunami waves were well 

documented during the tsunami that accompanied the 

1983 Nihonkai-Chubu earthquake beneath the Japan 

Sea. The tsunami, which struck the northwestern coast 

of Honshu, Japan, Korea, and coastal Siberia, is probably the most photographed major tsunami ever to occur 

(Osamu, 1984; Bertero and others, 1985). In areas adjacent to shallow parts of the shelf, where the waves were 

strongly influenced by the bottom, the waves were 

multicrested, dispersively deformed bores and acted as 

short-period waves. Where the shelf was deeper nearshore, the waves had long periods more typical of 

tsunamis. Locally, the waves were refracted and reflected by coastal irregularities and, in some areas, reflected obliquely back intQ the oncoming wave train, 

adding amplitude to the coq1bined wave (Mach-stem 

wave). 

Tsunamis may be preceded by drawdown along the 

shore when the initial part of the wave train is a trough. 

Drawdown can be dramatic. The constant sound of surf 

may disappear in an eerie quiet. If coastal residents 

recognize the withdrawal of the sea as a precursor to a 

tsunami, a withdrawal can provide adequate warning. 

Saint-Amand (1961, p. 12) described such an incident 

associated with the tsunami generated by the M 9.5 1960 

Chilean earthquake: 

Then, suddenly, they noted that the sea was 

beginning to retreat from the shores, exposing 

the ocean floor to distances well beyond the 

lowest tides. When this happened, the fire 

alarms were sounded, and firemen and carabineros systematically went through the streets 

warning everyone of the impending danger. 

The people fled afoot and on horseback to the 

hills and waited. Those on horseback made 

repeated trips to save the old and infirm. After 

15 to 30 minutes, the sea returned, advancing 

upon the shore in a wave that was, in places, 

over 20 feet high. The wave rushed over the 

land, covering and carrying away the houses, 

killing the animals that could not be evacuated, 

and carrying off some of the people who, for 

one reason or another, had not left their 

homes .... In Quele ... according to press 

reports, nearly 500 people were lost because 

they returned to their houses too soon or 

because they had failed to heed the warning of 

Tsunami Potential 383 
the receding water. In several villages along 

the southern coast, such as Carelmapu ... the 

mariscadores, or shellfish collectors, took advantage of the recession of the sea to wander 

over the exposed sea floor collecting shellfish 

in their baskets. When they had collected more 

than the usual quantity of mussels and locos, 

they returned to the shore, climbed upon the 

hills, and waited for the water to return. The 

waves continued all afternoon. The third or 

fourth wave was reported as the highest. A 

group of mapuchis or Araucanian Indians sacrificed a 7-year-old boy to the gods of the sea to 

calm the remorseless surf. 

Where drawdown is not recognized as a precursor, 

the loss of life has been high. Immediately Jollowing the 

1964 Alaska earthquake at the small fishing village of 

Chenega on Chenega Island in Prince William Sound, the 

water withdrew to an estimated depth of 40 m and a 

distance of about 600 m offshore (Plafker and others, 

1969). Drawdown exposed the rocky floor of the shallow 

cove that lay directly in front of the village. The following tsunami was about 12 m high. It overwhelmed and 

destroyed most of the houses. Many of the children and 

some of the adults recognized the danger and sought 

protection at the school house, which was built on high 

ground, but 23 people (about one-third of the village 

population and nearly one-fifth of all those killed in 

Alaska by the earthquake) were lost to the wave. 

Unfortunately, a warning drawdown does not always 

precede the first wave. Tide-gauge records from the 

western coasts of North and South America and from 

islands in the Pacific (Spaeth and Berkman, 1967) all 

show that the 1964 Alaskan earthquake produced a 

wave train in which the first wave was a crest. Tudor 

(1964, p. 4) noted that the U.S. Coast Guard observed a 

7-ft drop in water level at Fort Point (the tide-gauge station beneath the southern end of Golden Gate Bridge at 

San Francisco) just seconds before the arrival of the 

first positive wave. It seems unlikely that people on the 

beach would have taken what must have been a relatively short wavelength trough as an indication of an approaching tsunami or that, even having recognized it as 

such, they would have had time to reach higher ground. 

Landslide-Generated Tsunamis 

Earthquake-triggered subaerial and submarine landslides have caused many highly destructive local 

tsunamis. It has also been suggested that earthquakeinduced submarine landslides may cause tsunamis of 

transoceanic scale. There is no question that earth384 Earthquake Hazards in the Los Angeles Region 

quakes do cause very large submarine slides. For example, in the M 7.9 1923 Kanto earthquake in Japan, approximately 70 km3 of unconsolidated sediment slumped 

from the floor and sediment-filled submarine canyon 

tributaries beneath Sagami Bay into the Japan Trench 

(Shepard, 1933), and Edgers and Karlsrud (1982) listed 

11 slides that ranged in volume from 1 to 800 km3 that 

are known or conjectured to have been generated by 

earthquakes. There is, however, little evidence that submarine landslides are responsible for significant 

tsunami waves that affect regions remote from the slide. 

Furthermore, as Abe (1973) noted, the deformation of 

the sea floor predicted from seismic events quantitatively satisfies tsunami parameters (size and rate of 

displacement of sea floor), whereas submarine slides 

have too slow a time constant. 

There are, nevertheless, many instances of highly 

destructive local tsunamis generated by slides. 

Subaerial landslides and rock falls that slid or fell into 

water have generated local tsunamis having runup 

heights of as much as 525 m (Lituya Bay, Alaska), nearly 

one and one-half times the height of the Empire State 

Building, and have resulted in catastrophic loss of life 

(Miller, 1960; Slingerland and Voight, 1979). In 1792, an 

earthquake triggered a slide of about 0.5 km3 of volcanic 

debris from the slopes of Mount Shimabara on the 

Japanese island of Kyushu. The slide impacted Shimabara Bay and generated three tsunami waves that 

crossed the bay, reached a height of 10 m, and killed 

more than 15,000 people in the vicinity of Kumamoto. 

One of the primary causes of death in the 1964 

Alaskan earthquake was waves generated by slides 

from the fronts of fan deltas. Unlike the previously noted 

slides, which were largely or entirely subaerial, most of 

the material that slid from these fan deltas was below 

water level before sliding. In many cases, as the sliding 

mass became fully submerged, water rushed in to fill the 

void left by the slide. In some places, the velocity of the 

water was high enough that inertia carried it well inshore, to runup heights of at least 10 m. Some of these 

waves decimated the shores of Alaskan coastal communities (Coulter and Migliaccio, 1966; Lemke, 1967; 

Kachadoorian, 1965; McCulloch, 1966). At Kenai Lake, 

they broke off spruce trees near the ground and 

uprooted others, some as much as 0.5 m in diameter. 

These trees were driven like battering rams as far as 

100 m ashore. Some trees were stripped of nearly all 

their bark and limbs. Those that remained standing had 

bark and limbs torn from the sides exposed to the wave. 

Large blocks of frozen sediment, some weighing an 

estimated 50 tons, were pulled from the sinking slide 

mass and carried ashore with the trees (McCulloch, 

1966). Slide-generated waves of this kind are not confined to Alaska. A similar wave resulting from an 
A 

8 

D 

FIGURE 197.-Schematic sequential cross sections showing waves 

generated by a subaqueous slide. A, Preslide conditions. B, Start of 

sliding; local drawdown at the head of the slide. C, Wave overtopping the delta margin. D, Generation of a mound of water by upward displacement of the slide toe. E, Unstable mound sinking and 

generating waves (probably a series) that radiate away from the 

oscillatory mound. Modified from Kachadoorian (1965}. 

earthquake-triggered slide may have been responsible 

for the destruction of Port Royal on the island of Jamaica 

in 1692 (Heath, 1748; Link, 1960). 

The 1964 Alaska submarine slides also generated 

waves that appear to have been caused by water forced 

upward or laterally by the moving slide debris. Upward 

water displacement was common. Seward, Valdez, and 

Whittier, for example, were first flooded by waves 

resulting from water rushing landward to replace the 

sinking slides. All three towns were then struck by a 

wave or wave train that radiated from what was often 

described as a "mound of water" that formed some 

distance from shore (fig. 197) (Grantz and others, 1964; 

Kachadoorian, 1965; Coulter and Migliaccio, 1966; 

Lemke, 1967; Wilson and T~rum, 1968). At Whittier 

(Kachadoorian, 1965, p. B6), eyewitnesses described the 

formation of the mound " . .. as if something seemed to be 

exploding underneath the water." Postearthquake 

soundings and bottom sampling showed that the water 

mound formed approximately above the deposited slide 

mass. At Valdez, Wilson and T~rum (1968) suggested 

that the water mound resulted from upward rotation of 

the toe of a large slide that started as a rotational 

failure and then disintegrated into a thin blanket 

downslope. 

Waves generated by horizontal displacement of water 

below the water surface occurred at Kenai Lake. Such 

horizontal currents (turbidity currents) generated by 

submarine slides have been examined theoretically and 

experimentally (for example, Hampton, 1972) and are inferred to have been formed where submarine cables 

have been cut beyond the limits of earthquake-triggered 

slides (Heezen and Ewing, 1952). In a few cases, such as 

at Kenai Lake and at Lake Zurich in Switzerland 

(Kuenen, 1950) where the slide mass was partially 

subaerial, the current-generating slides have been 

observed directly, but, where slides are entirely submarine and were found by later sounding, the contemporaneity of the slides and the currents is inferrential. 

At Kenai Lake, slides from partially subaerial fan deltas 

traveled across a nearly flat lake floor and forced water 

ahead of them. The water burst to the surface along the 

shoreline, where it broke off spruce trees and stripped 

the vegetation and soil from the steep, rocky lake shore. 

Runup heights of 6 to 8 m were common, the maximum 

being 33m. 

Not all submarine slides that generate tsunamis are 

triggered by earthquakes. On October 16, 1979, approximately 30 km of the French Riviera coast, from near the 

Italian border to Antibes, including the shore at Monaco 

and the port city of Nice, were struck by two waves 

approximately 3 m high that smashed beach-front 

homes, hurled automobiles into buildings, and claimed 

10 lives (San Francisco Examiner, 1979). The Monaco 

Observatory recorded no earthquake at this time. As 

Gennesseaux and others (1980) and Auffret and others 

(1982) described, a lowering of the sea level was seen at 

about the time that a fill 300 m wide by 300 m long slid 

beneath the sea. The fill had been placed on the delta of 

the Var River to extend an airport runway, and postslide 

soundings indicated a water depth of 50 m where the fill 

had been. Gennesseaux and others (1980) suggested that 

the volume of the slide (minimum of 300 m2 x 50 

m = 4.5 x 106 m3) was too small to have generated the 

tsunami and that the waves were probably caused by 

two much larger slides (total volume 400 x 106 m3), identified by post-tsunami soundings, that were dislodged 

from the walls of two submarine valleys downslope from 

Tsunami Potential 385 
,.._ _ _ _ A ----+1 

A 

A=2h 

A=h 

A= ?h h 

B 

FIGURE 198.-A, Laboratory model for generating impulsive waves 

(Wiegel, 1970). The length (A) and displacement (h) of the box and 

the water depth (d) can be varied. B, Recorded waves generated by 

the model. A single displacement of the block produces a train of 

oscillatory waves, and changes in the model configuration shift the 

position of the high-amplitude waves in the wave train. 

the failed fill. The slides traveled downslope to the base 

of the continental slope and generated turbidity currents that traveled beyond the slides and cut submarine 

cables 80 and 110 km offshore of Nice. 

Slide-generated waves pose a clearly recognized 

hazard to reservoirs, harbors, and lakes, where they 

may endanger lives, overtop or breach dams, or destroy 

waterside property. Thus, there has been some effort to 

develop predictive models of such waves. Some models 

are largely theoretical and are based on principles of 

fluid dynamics. Others are largely empirical, and 

results may depend on specific physical aspects of the 

386 Earthquake Hazards in the Los Angeles Region 

models. Some are general case studies designed to examine how variations in the input energy (for example, 

differences in size, density, failure angle, velocity, 

degree of submersion of slide mass before sliding, or 

water depth) affect wave generation; still others are 

concerned with a specific site, such as a reservoir (for 

example, Davidson and Whalin, 1974), and are designed 

to examine the kinds of waves that will be generated by 

a specific slide falling or sliding into a water-filled basin 

of a specific bathymetry. An excellent summary o£ 

model studies has been given by Wiegel (1970). 

Some aspects of slide-generated waves have been 

deduced from field study and eyewitness accounts of actual waves. Applying such observations to other areas is 

difficult or inappropriate because of significant diffenmces in parameters such as the character and 

mechanism of failure of the slide mass and the bathymetry of the basin. Furthermore, it is difficult to form a 

generalized quantitative model from such observations 

because of large uncertainties in the time-history of 

water response to slide impact. 

As a result, much that is known or conjectured about 

slide-generated tsunamis is deduced from laboratory 

scale models. In one very instructive type of model 

(Prins, 1958; Wiegel and others 1970), a block representing a slide is either dropped or rapidly raised at the end 

of an elongate water-filled tank, and recorders at several locations along the tank record the passing wave 

train (fig. 198). The depth, height, and length of the displaced water can be changed independently to examine 

their effect on the wave train (fig. 198). As Wiegel and 

others (1970) noted, changes in depth, height, and length 

of the displaced water can change the position of the 

highest amplitude wave in the wave train (fig. 198) and 

the characteristics of the leading waves (fig. 199). For a 

given set of conditions, the wave train stays the same if 

the block is raised or lowered, except that the first wave 

is a crest if the block is raised and a trough if the block is 

dropped. 

In a laboratory model more appropriately applied to 

movement of a submerged landslide, Wiegel (1955) 

found that, for a given slide (block) moving into water of 

a given depth, the steeper the failure slope, the longer 

the period and the greater the amplitude of the major 

wave produced by the slide. 

Some studies of slide-generated waves integrate 

several approaches; for example, Slingerland and 

Voight (1979) compared field data, empirical models, 

and theoretical studies of waves generated by slides and 

rock falls that were largely or entirely subaerial. They 

concluded that maximum wave height at a large 

distance from the slide can be computed and that, for 

detailed wave analysis, either scale models or a 

numerical approach can be used. One such numerical 
model (Raney and Butler, 1975) deals adequately with 

wave nonlinearity and considers complex basin geometry and thus takes into account amplification or reduction in wave height due to refraction. As Slingerland and 

Voight (1979) noted, application of this numerical model 

is difficult because it is highly sensitive to parameters 

that are difficult to predict-the size of the slide mass, 

the time-history of emplacement of the slide mass in the 

water, and the deceleration of the mass as it is immersed. Nevertheless, they concluded that this approach provides a technique for establishing conservatively safe estimates of the risk of tsunamis generated 

by subaerial slides or rock falls. 

CALIFORNIA TSUNAMI HISTORY 

Most of the world's major tsunamis have been 

generated at subduction-convergent plate boundaries 

along the margin of the Pacific Ocean (fig. 200). Over the 

past 200 yr, nearly a third of all major tsunamis have 

occurred along deep-sea trenches bordering Japan, the 

Aleutians, and South America. Dip-slip fault displacements associated with large (M ~ 7) shallow earthquakes 

that accompany thrusting at these subduction zones occur at appropriate rates and are accompanied by 

changes in elevation of an area of sea floor large enough 

to produce large tsunamis. Fortunately for California, 

the major tsunamis generated at the Pacific-Eurasian 

plate boundary in the western Pacific that have 

repeatedly decimated the Japanese coast are reduced to 

small, generally undamaging but detectable waves after 

crossing the Pacific. However, this statement is not true 

for all distantly generated tsunamis. The five major 

distantly generated tsunamis that have affected the entire California coast during the post-1812 period of 

record are shown in table 50. 

Appendix 4 lists the heights of distantly and locally 

generated tsunamis reported along the California coast 

since the earliest reported tsunami of 1812. The 

~re-1940's data base is poor because most west coast 

tide gauges were only recently installed. Most 

pre-1940's reports are from San Diego and San Francisco, where tide gauges were installed in 1854. 

Because a uniform data base for the entire coast is lackFIGURE 199.-A, Characteristic wave types formed by landslides and ..... 

in the laboratory model shown in figure 198. Water particles in 

oscillatory waves move in closed orbits, showing no net forward 

motion, whereas water particles in solitary waves (which travel 

wholly above mean water level) and bores have a forward translation (modified from Slingerland and Voight, 1979). B, Relation between source length (A) water depth (d), vertical displacement (h), 

and characteristics of the leading wave in the laboratory model 

shown in figure 198 (Prins, 1958). 

h 

d 

OSCILLATORY WAVE 

SOLITARY WAVE 

Mean water 

level 

CONOIDAL WAVE 

Mean water 

level 

BORE 

Mean water 

level 

A 

0. 1 L_ _ ___j_ _ _l____L---'---__l_j_j_J-,Lc __ _L____j__'---l___L_L_l___j_J 

0.1 

8 ~ 

d 

10.0 

Tsunami Potential 387 
(,I,) 

g; 

, 

Ill 

::I. 

:r 

~ 

c 

Ill 

~ 

:r: 

Ill 

N 

Ill 

a. 

<ll 

:r 

-:r 

I'D 

r0 

<ll 

> 

:I 

~ 

~ 

H cs· 

:I 

c: 

; 

·-l 

20°~~· ~ 

oo 

.~~ 

~:. "-• i: • 

·~ 

EXPLANATION 

A Active volcanoes 

1964 (57) 

I 

--

Approximate locqtion of significant tsunami. Numbers are 

year and (approximate tsunami 

magnitude) 

Subducting margin. Solid areas 

indicate zones nearly filled by 

rupture zones of known large 

shocks. Open areas are zones 

of long-term relative quiescence for large shocks 

180° 

PACIFIC 

PLATE 

160° 140° 120° 

NORTH AMERICA 

PLATE 

100° 

60° 

40° 

20° 

oo 

20° 

40° 

FIGURE 200.- Tsunamigenic lithospheric plate boundaries in the Caribbean Sea and the Pacific Ocean (Kelleher, 1979). Tsunami magnitude is log2 H. where H is the 

tsunami height in meters. 
TABLE 50.-Major distantly generated tsunamis that have affected the entire California coast since 1812 

Places of Cost of U.S. 

Earthquake Tsunami major impact damage, in millions 

Date Source location magnitude' magnitude [M1)' in United States Fatalities• of 1981 dollars 

1946 ----- East Aleutian Trench 

1951 ----- Kamchatka Trench 

1957 ----- Central Aleutian Trench 

1960 ----- Chile Trench 

1964 ----- Gulf of Alaska 

Abe(l979~ 

2

Bernard and Goulet (1981). 

8.4(M5) 9.3 

9.0 (M) 9.0 

9.1 (M) 9.0 

9.4 (M) 9.4 

9.2 (M) 9.1 

ing, tsunami heights are listed several ways in the 

appendix. 

Refraction diagrams showing sequential wave-front 

positions and orthogonals for three of the major distantly generated tsunamis that have affected California are 

shown in figure 196. Despite the fact that these major 

tsunamis were generated to the north, west, and south 

of California, refraction on the California continental 

margin locally gave the waves an easterly travel direction toward the coast.· 

The largest recorded waves generated by the five major distantly generated tsunamis listed in table 50 are 

shown in figure 201. Wav~ heights are given as the 

largest crest-to-trough tide-gauge measurement (Spaeth 

and Berkman, 1967). As noted earlier, runup heights can 

be significantly higher than tide-gauge measurements. 

For comparison, some 1964 Alaska tsunami runup 

heights along the northern and central California coast 

(Magoon, 1965) are also given in figure 201. The highest 

1964 wave at Crescent City was not measured by a tide 

gauge. As Wiegel noted, the tide gauge broke, and the 

wave washed over the top of the building housing the 

gauge. There were, however, some probably reliable 

eyewitnesses who established a 2D-ft height for this 

wave, for there were " ... three gentlemen sitting on top 

of ... [another] building at the time of the tsunami keeping very close track of where the wave was" (Wiegel, 

1969, p. 62). 

Wave-height variation (fig. 201) demonstrates the influence of the local sea-floor configuration in determining tsunami wave height along coastal California. 

Despite great differences in the source locations of 

these distantly generated tsunamis, some sites consistently experience high or low waves. Van Darn 

(1979b) attributed the generally low tsunami heights experienced by southern California to a combination of the 

generally low glancing angles of the main open-ocean 

tsunami waves and the reflection and (or) wave transformation as the waves cross the complex basin-ridge 

bathymetry of the wide southern California borderland 

Hawaiian Islands 173 119.2 

Hawaiian Islands 0 2.1 

Hawaiian Islands 0 10.5 

Hawaiian Islands 61 66.9 

Alaska, California, 119 282.3 

Hawaiian Islands. 

terrane (see fig. 204). This complex submerged 

physiography does more than just reduce the amplitude. 

Tide-gauge records of tsunami waves along this coast 

exhibit a long "ringing" that may last several tens of 

hours after the arrival of the first tsunami wave. Wilson 

(1971) suggested that the ringing may be produced by 

oscillation of the water mass on the shelf rather than being a long wave train in the tsunami that is propagated 

across the borderland. It is well known that tsunamis 

can excite waves within harbors to oscillate at some frequency determined by harbor configuration. The ringing 

is most pronounced at Santa Monica Bay; however, the 

ringing is probably not determined by oscillation within 

Santa Monica Bay, which is wide open to the Pacific, for 

Raichlen (1979) has shown that wave energy is concentrated at approximately the same ringing frequencies at 

Santa Monica, Los Angeles Harbor, and the La Jolla promontory. He suggested that all three bathymetrically different sites are therefore probably responding to 

shelfwide oscillation rather than to locally generated 

waves. 

The frequency distribution of the waves may be affected by the oscillation of water on the shelf, but the 

duration of oscillation may be related in part to continued input of energy from the Pacific. Analysis of a 

long-period-wave recorder in operation at La Jolla during and after the 1960 Chile tsunami (Miller and others, 

1962) indicates, as might be expected, that highfrequency oscillation decreased rapidly but that lower 

frequency tsunami-related waves were still detectable 

above background waves for a week after the arrival of 

the tsunami. Similar waves decaying at about the same 

rate were recorded on a long-period-wave recorder at 

Wake Island by W. G. Van Darn (unpublished data, cited 

by Miller and others (1962, p. 39)) following the 1957 

Aleutian tsunami. It is generally thought that Wake 

Island is so small in relation to the size of passing 

tsunami waves that tide-gauge records there show no 

significant interaction between the island and the passing tsunami (Van Darn, 1970). Thus, in the open Pacific, 

Tsunami Potential 389 
METERS FEET 

6 

5 

4 

2 

0 

Observed runup 

heights for 1964 

Alaska tsunami 

(Magoon, 1965) 

Fort Bragg 

Eureka Santa Cruz 

Bodega Point Arena 

1 0 ' Davenport 

Half Moon 

Bay 

San 

Francisco 

8' Drakes Bay 

Monterey 

Moss 

Landing 

FIGURE 201.-Crest-to-trough heights of the highest waves from five 

major tsunamis recorded by tide gauges along the California coast 

(drawn from data of Abe, 1979; Spaeth and Berkman, 1967; 

Wiegel, '1969). Some sites generally experience large waves (Crescent City and Santa Monica Bay), but, in general, waves tend to be 

lower in southern California. Tide-gauge heights are usually exceeded by the highest runup heights, as shown on the inset graph of 

runup heights of the 1964 tsunami. 1, 1964 Alaska, M 9.2, M1 9.1; 2, 

1960 Chile, M 9.5, ~ 9.4; 3, 1952 Kamchatka, M 9.0, M1 9.0; 4, 1976 

east Aleutian Trench, M5 8.4, M1 9.3; 5, 1957 central Aleutian 

Trench, M 9.1, M1 9.0. Modified from Magoon (1965). 

tsunami energy appears to persist over periods of 

several days. The occurrence of long-duration oscillations presents no hazard if wave amplitude is low, but, 

in areas like Santa Monica Bay, the currents that these 

oscillations produce may put considerable loads on 

moored structures and contribute to scouring. At Santa 

Monica Bay, waves with crest-to-trough measurements 

of about 1 m (approximately half the height of the 

390 Earthquake Hazards in the Los Angeles Region 

largest wave) were still occuring 17 to 19 hr after the arrival of the first wave of the 1964 Alaskan tsunami. 

Total tidal amplitude at the time of the tsunami was 

about 1.5 m; thus, in every 20-min crest-to-trough 

tsunami wave period, the bay experienced about 70 percent of the full tidal reversal that normally occurs every 

6 hr. 

Another important peculiarity of tsunami wave 

behavior observed along the California coast is the occurrence of high runup in bays and behind hooks that 

appear to have the best protection from approaching 

tsunamis (Wiegel, 1970; Willard Bascom, unpublished 

report, 1946, cited by Wiegel (1970)). The 1946 Aleutian 

tsunami probably produced no wave at the city of Monterey, on the southern side of Monterey Bay, but water 

rose to 3.5 m at Santa Cruz on the northern side of the 

bay. Waves from the 1964 Alaskan tsunami were 2.3 m 

at Monterey but almost twice as high (4.3 m) at Santa 

Cruz. Wilson and T~rum (1968) suggested that the deep 

submarine Monterey Canyon bisecting the bay may 

favor northward refraction of wave energy entering the 

bay. Half Moon Bay also experienced high waves during 

these tsunamis (4.6 m in 1946 and 2.9 m in 1964) and a 

possible height of 4.6 m in 1859. 

Locally generated tsunamis, usually attributed to 

coastal earthquakes, have produced 13 possible recorded events from 1812 to 1975 (table 51). Reports of these 

locally generated tsunamis are so sketchy that there is 

often doubt not only as to what was seen but also as to 

where observations were made. It has been suggested 

that event 1 is a misdated and mislocated description of 

event 2, the tsunami that resulted from an estimated M 7 

to 7.5 earthquake beneath Santa Barbara Channel. The 

1812 Santa Barbara Channel tsunami was once 

reported to have had a height of 5 m at Gaviota and 9 to 

10.5 m at Santa Barbara, but a more recent assessment 

suggests a runup of only 3 to 4 m at Gaviota and a still 

smaller runup at Santa Barbara (see discussion, app. 4). 

Event 23 was originally described as "[a] tidal wave, the 

largest in the history of Santa Barbara ... " (Holden, 

1898, p. 152). Although originally accurately attributed 

to a high tide, it has since erroneously been ascribed to a 

tsunami (see app. 4). Half Moon Bay (event 12, 1859) is 

reported to have had a 4.6-m runup, but Iida and others 

(1967) suggested that this height may be exaggerated. 

As noted above, however, well-documented high runup 

has occurred at Half Moon Bay. These high waves 

resulted from distantly generated tsunamis, and Iida 

and others (1967a) suggested that the source for the 

1859 runup may have been Chile rather than San Francisco. The only other locally generated tsunami that produced significant waves resulted from the M 7.3 1927 

earthquake off Point Arguello, which produced local 

runup of 1.8 m at Surf and 1.4 m at Port San Luis, 13 and 
TABLE 51.-High waves along California coast (1812-1975) correctly or erroneously attributed to 

locally generated tsunamis 

Event' Year Area affected Waves reported 

1 ----- 1812 San Francisco(?], Santa Barbara(?] In Santa Barbara, "covered ground 

where plaza now is" (app. 4). 

2 ----- 1812 North shore of Santa Barbara 

Channel. 

6 ----- 1854 San Francisco(?], Benicia(?] 

10 ----- 1855 Capistrano 

12 ----- 1859 Half Moon Bay 

13 ----- 1862 San Diego Bay 

19 ----- 1879 Santa Monica Bay 

21 ----- 1885 San Francisco 

23 ----- 1896 Santa Barbara 

26 ----- 1906 San Francisco 

33 ----- 1923 Cape Mendocino 

37 ----- 1927 Point Arguello 

39 ----- 1930 Santa Monica Bay 

42 ----- 1933 Long Beach 

1

Numbers taken from appendix 4. 

66 km north along the coast from Point Arguello, respectively (Byerly, 1930). 

Four local tsunamis were observed along the southern 

California coast during the period of record from 1812 

to 1975. For three of these events (events 10, 19, and 42), 

wave heights were not indicated. Although it is difficult 

to say with assurance for the older events, it is probable 

that, if the waves had been high or had caused much 

damage, they would have been reported; thus, they were 

probably small. The 1862 tsunami in San Diego Bay 

(event 13) also produced a small runup ( < 1 m?), and 

Agnew (1979) has suggested that the event may have 

been caused by shoreline slumping. Thus, with the exception of the 1812 Santa Barbara and the 1927 Point 

Arguello tsunamis, locally generated tsunamis have 

posed little hazard to the coast of southern California. 

The 1964 Alaskan earthquake generated the only 

tsunami that caused extensive damage to California during the period from 1812 to 1975. The cost of damage 

was approximately $13,375,000 adjusted to 1971 dollars 

and $32,260,000 in 1983 dollars (table 52). For comparison, the cost of California earthquake damage 

resulting from 26 earthquakes during the same period 

(1812-1971) was $7,200,000,000 adjusted to 1971 

dollars (Alfors and others, 1973) and $17,366,400,000 in 

1983 dollars. Although the cost of tsunami damage was 

only 0.2 percent of earthquake damage, the bulk of the 

cost was incurred in Crescent City, where 11 of the 13 

3- to 4-m runup at Gaviota (see app. 4) 

Sea wave following shocks or shock 

Two unusually heavy sea waves 

0-m withdrawal in San Francisco Bay, 

4.0-m runup in Half Moon Bay. 

<1m 

Affected Santa Monica 

A series of waves 

High tide erroneously reported as 

tsunami. 

0.1-m drawdown followed by series of 

waves having 5-cm amplitudes. 

Flooding at mouth of Navaro 

River. 

0.3- to 0.0-m run up 

1.8-m runup at Surf, 1.5-m runup at 

Port San Luis. 

Local oscillations to about 0.6 m 

Uncertain records 

tsunami deaths in California also occurred. Damage to 

the 34-block downtown section of Crescent City was 

described by Tudor (1964): 54 houses were destroyed, 

and 3 7 were damaged; 42 business establishments were 

totally destroyed, 108 sustained major damage, and 29 

experienced minor damage. Houses floated free of foundations and grounded in streets, as did .large logs. 

Wiegel (1969) pointed out that cars and single-story 

frame structures float in relatively shallow water; in the 

current velocities of perhaps 30 milhr that probably occurred in Crescent City, both can become destructive 

agents. There was also heavy damage in the harbor; 15 

boats capsized, and Citizens Dock was heavily damaged 

by buoyant forces and by a heavily loaded lumber barge 

that was forced against it by the current surge. Damage 

TABLE 52.-Cost of 1964 tsunami damage to California coast 

[From Alfors and others (1973)] 

Location Damage, in 1971 dollars 

Crescent City ----------------------------

Long Beach -----------------------------

Los Angeles -----------------------------

Marin County ---------------------------

Noyo Harbor ---------------------------- "' 

11,000,000 

100,000 

275,000 

1,000,000 

1,000,000 

13,375,0001 Total -------------------------------

1

$32,260,000 (1983 dollars). 

Tsunami Potential 391 
in the rest of California from the 1964 tsunami was 

caused largely by high-velocity current surges in ports, 

marinas, and narrow entrances to bays. Thus, most 

damage was to boats, related harbor facilities, and 

moored navigation aids. Magoon (1965) reported 

damage to boats and marine facilities at Noyo River, the 

fishing port at Fort Bragg, Bodega Bay, Tomales Bay, 

Bolinas, San Francisco Bay, Santa Cruz and Santa Cruz 

Harbor, Moss Landing, Monterey Harbor, and Los 

Angeles. Some of the damage was detailed by Spaeth 

and Berkman (1967, p. 24): 

... Mendocino County reported that approximately 100 fishing boats in Noyo Harbor suffered damage with 10 being sunk. A dredge in 

the harbor was carried upstream about onefourth mile and grounded on a sandbar. Estimates of the damage ranged from $250,000 to 

$1 million. In Marin County, approximately $1 

million worth of damage was done to small 

boats and berthing facilities, mostly in Loch Lomond Harbor in San Rafael. Los Angeles County Civil Defense reported $100,000 to $200,000 

damage to six small-boat slips, pilings, and the 

Union Oil Company fuel dock; $75,000 damage 

due to scouring action on the harbor sides in 

Los Angeles County Harbor; and 8 docks with a 

value of $100,000 destroyed in Long Beach 

Harbor. 

San Diego escaped damage from the 1964 tsunami, but 

high currents resulting from the 1960 Chilean tsunami 

tore out several hundred feet of rotted wharfage (Van 

Dorn, 1979b). 

TSUNAMI POTENTIAL IN 

COASTAL SOUTHERN CALIFORNIA 

Potential for Local 

Fault-Generated Tsunamis. 

In southern California, displacement between the 

North American and the Pacific plates is accommodated 

in part by movements along strike-slip faults, some of 

which are in the offshore borderland. Geologic structures in the Transverse Ranges, including the Santa Barbara Channel and the offshore Point Arguello area to 

the west, lie athwart the strike-slip motion and are experiencing compressive tectonic deformation (Yerkes, 

this volume). It is not surprising that the only welldocumented local tsunamis thusfar recorded in 

392 Earthquake Hazards in the Los Angeles Region 

southern California (the 1812 Santa Barbara and the 

1927 Point Arguello tsunamis) were generated in this 

compressive tectonic geologic setting. There is, 

however, some suggestive evidence that episodes of vertical displacement capable of tsunami generation may 

be associated with the offshore extension of the Palos 

Verdes Hills reverse fault to the southwest in an area 

otherwise dominated by strike-slip displacement. 

Before much was known of offshore California 

geology, it was proposed that the tsunami accompanying 

the 1927 (M5 7.3) earthquake off Point Arguello was 

generated by submarine landsliding or by displacement 

along an east-west fault (Marine Advisors, 1965). Sliding 

can probably be eliminated as a cause. Recent mapping 

of the offshore Point Arguello area has delineated submarine slides 20 and 60 km northwest of Point Arguello, 

but these slides are nested retrogressive slumps that 

resulted from progressive upslope failures in which 

no slump had appreciable downslope displacement (McCulloch and others, 1980). In addition, the tsunami was 

recorded at Honolulu and Hilo (fig. 202) (Iida and others, 

1967a), and, as noted above, it is doubtful that submarine slides can generate transoceanic tsunamis. 

There is some evidence that the Point Arguello earthquake may have had significant dip-slip displacement. 

Gawthrop {1978a) located the 1927 epicenter on the 

southeastern end of the long, seismically active 

northwest-trending Hosgri fault (Hoskins and Griffiths, 

1971; Wagner, 1974; McCulloch and others, 1980; Lindh 

and others, 1981) (fig. 203). The epicenter has been 

placed farther offshore by others (Byerly, 1930; Smith, 

1975; Hanks, 1979). Displacement accompanying the 

earthquake deduced from fault-plane solutions has been 

described as primarily oblique right-lateral strike slip 

accompanied by some northeastern-side-up dip slip 

(Gawthrop, 1978a) or as primarily vertical dip slip, 

northeastern side up, accompanied by only minor strikeslip displacement (Yeh, 1975). Geodetic measurements 

(Savage and Prescott, 1978) indicate that the fault displacement associated with the 1927 earthquake had a 

large component of thrust and no appreciable right slip. 

A fault-plane solution of a more recent M1 5.1 earthquake (May 20, 1980), located nearly coincident with 

Gawthrop's 1927 epicenter location, indicated very 

nearly pure dip-slip northeastern-side-up displacement 

on a northwest-striking high-angle reverse fault (Eaton, 

1984). 

Other potentially tsunamigenic faults occur offshore 

of Point Arguello. Northwest-trending seismically active 

faults as long as 70 km, some having sea-floor expression as long as 40 km, lie within and bound the Santa 

Lucia Bank, a structural high at the upper edge of the 

continental slope (McCulloch, and others, 1980). Faultplane solutions (Gawthrop, 1975, 1978b) for the two 
-' 

~ w 

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< 1.5 w 

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z 

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0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 

HAWAIIAN STANDARD TIME, NOVEMBER 4,1927 

FIGURE 202.-Tide-gauge record at Hilo, Hawaii, showing the beginning of the tsunami wave train generated by the November 4, 1927, Point 

Arguello earthquake in California. The wave train began at about 8:30a.m. with a drawdown and had a maximum range of about 1 ft. The 

earthquake epicenter was approximately 3,950 km from Hilo, and the wave traveled approximately 750 kmlhr (The Volcano Letter, 1931). 

122' 121 ' 120' 

36' .------ -== 

FIGURE 203.-0ffshore faults and the locations of associated 

epicenters for which first-motion determinations have been made 

in the vicinity of Point Arguello, Calif. (after McCulloch and others, 

1980). First-motion diagrams are lower hemisphere plots; white indicates dilation, and black indicates compression. Larger diagrams 

are generally well constrained first-motion determinations. The 

1927 Point Arguello earthquake (1) is shown as located by 

Gawthrop (1975); first motion is as given by Yeh (1975). First motions for events 3 through 6 and 8 through 12 from Gawthrop 

(1978b); for 2 and 7 from Gawthrop (1975); for 13 from Eaton 

(1984). 

main shocks (ML 5.4-5.6) of a 1969 earthquake swarm 

centered on the southwestern end of Santa Lucia Bank 

indicate pure dip slip, southwestern side up, on steep 

southwest-dipping high-angle reverse faults (fig. 203). 

Within the constraints of epicenter location, these 

events may have occurred on the faults having sea-floor 

expression. If the long sea-floor expression of these 

faults represent single-event displacements, the faults 

are capable of producing large earthquakes. Thenhaus 

and others (1980) estimate a recurrence interval of 230 

years for 6.4 :s M8 < 7.0 earthquakes in this area. Thus, 

these faults may have the potential to generate 

tsunamis. 

Another potential source area for local faultgenerated tsunamis lies to the east along the major 

geologic boundary between the Santa Barbara Channel 

and the adjoining Transverse Ranges, where seismically 

active northeast-dipping reverse faults separate the 

rocks beneath the Santa Barbara Channel to the south 

from the elevated and folded rocks of the Transverse 

Ranges to the north (Yerkes and Lee, 1979). Active tectonic deformation along this boundary is also indicated 

by the fact that the highest short- and long-term uplift 

rates in California are found along this coast (Yerkes 

and others, 1981). Surface fault rupture accompanied 

by sea-floor displacement is a distinct possibility 

beneath the Santa Barbara Channel. This area has experienced large, damaging earthquakes (Yerkes, this 

volume). On December 21, 1812, two large earthquakes 

Tsunami Potential 393 
of estimated M 7 to 7.5 probably occurred beneath the 

channel, and Spanish mission structures were severely 

damaged for a horizontal distance of about 185 km along 

this geologic boundary (Toppozada and others, 1981; 

Yerkes and others, 1981); comparing the reported 

damage pattern with predicted intensities from several 

possible fault sources suggests that fault rupture probably occurred beneath the northern Santa Barbara 

Channel (Evernden and Thomson, this volume) along the 

Pitas Point-Ventura fault and its possible western extension. In 1971, a M 6.6 earthquake inflicted severe 

damage to San Fernando at the eastern end of the zone 

of faulting and produced surface rupture for at least 

15 km and a total measured vertical offset of 2.20 m 

(Burford and others, 1971). Lee and Ellsworth {1975) 

suggested a maximum credible earthquake of M1 7.3 in 

the Santa Barbara Channel, although Ziony and Yerkes 

(this volume) suggest that it might be as large as M 7.5. If 

the relations between tsunami size, earthquake magnitude, and hypocentral depth established for Japanese 

earthquakes can be applied in this very different 

geologic environment, the occurrence of a sea-floorrupturing earthquake having a magnitude of 7.5 and a 

hypocentral depth of 4 to 14 km could produce a tsunami 

having a magnitude of 2 accompanied by a runup height 

of 4 to 6 m (figs. 191, 192). 

Still farther to the south, offshore of Huntington and 

Newport Beaches, Holocene deposits less than approximately· 10,000 yr old are offset along an appreciable 

length of the offshore Palos Verdes Hills fault (Greene 

and others, 1975; Junger and Wagner, 1977; Darrow 

and Fischer, 1983; Clarke and others, this volume). Maximum observed displacement of the base of the Holocene 

deposits on this fault is approximately 3 m, and the maximum observed offset of the surface of the Holocene 

deposits at the sea floor is 1 m. From a tsunamigenic 

point of view, a worst case might presume a single 3-m 

vertical offset of the sea floor. If one makes the common 

assumption that half (35 km) the mapped trace of the 

fault (70 km) can break as a single rupture (Bonilla and 

others, 1984) and that the maximum probable magnitude 

of an earthquake associated with this fault is Ms 7.3 

(Thenhaus and others, 1980), a 3-m surface offset is not 

unreasonable in terms of what is known about relations 

between fault length, earthquake magnitude, and surface displacement from a study of worldwide faulting 

(Bonilla and others, 1984). If good reason is found to discount a 3-m single-event offset, there is still possible concern for a repeat of the observed 1-m offset. If seismicity 

rates determined by Thenhaus and others (1980) are 

used, a recurrence interval of about 135 yr for a 

6.4 ~ Ms < 7 earthquake that would be capable of producing a 1-m single-event displacement (Bonilla and others, 

1984) can be estimated. Thus, the recurrence interval is 

394 Earthquake Hazards in the Los Angeles Region 

short enough to be of concern. A very rough approximation of the potential tsunami can be made. If one assumes a M 7 event at a hypocentral depth of about 10 km 

(using estimates by Wood (1933) and Woodward-Clyde, 

Inc. (1979) for the hypocentral depth of the M 6.2 1933 

Long Beach earthquake that occurred just toward shore 

of this fault) and the relation between magnitude and 

hypocentral depth (fig. 191), this earthquake could be 

tsunamigenic. And, if the relation between earthquake 

and tsunami magnitude for Japanese tsunamigenic 

earthquakes is valid in this case (fig. 192A), this earthquake could generate a magnitude 1 tsunami having a 

maximum runup of 2 to 3 m. The upper bound relation 

between tsunami magnitude and water depth at the 

epicenter [fig. 195) (the shallower the water, the less efficient the energy coupling between the water and the 

deforming sea floor) suggests, however, that, if the offshore Palos Verdes Hills fault were to offset the shallow 

shelf, water depth would be an important factor in 

reducing wave height. 

Potential for Local 

Slide-Generated Tsunamis 

Interpretations of a relatively dense network of subbottom acoustic reflection profiles on which it is possible to see both the surface topography and the internal 

structure of submarine landslides have revealed many 

slides within zones of mass soil failure that lie about 3.5 

to 14 km offshore of the Los Angeles region in water 

depths of 250 to 750 m (fig. 204) (Field and Edwards, 

1980; Clarke and others, this volume). Dimensions of 

single slides are usually considerably smaller than those 

ofthe zones in which they occur. Seismic shaking, which 

reduces the shear strength of ocean-floor sediment by 

cyclic loading, may be a cause of the observed sliding. 

Geotechnical studies (Edwards and others, 1980) suggest that ground motion whose horizontal acceleration is 

in excess of 0.13 g at the sea floor, which can be expected in this area [Thenhaus and others, 1980; Spudich 

and Orcutt, 1982), should be sufficient to produce 

failure. In fact, the geotechnical measurements suggest 

that much of the unfailed sediment is metastable and 

subject to sliding, and it is difficult to understand why 

sliding is not more widespread. Geotechnical studies of 

slides off Alaska (Schwab and Lee, 1983) have shown 

that slope failures occur given the proper combination 

of water content in the sediment (35 to 45 percent, a 

reflection of porosity and grain-size distribution) and 

seismic shaking during which the effective acceleration 

(not just the peak acceleration) exceeds the critical acceleration (the threshold acceleration at which a given 

slope starts to fail). Although the presumption has been 
EX PLAN AT ION 

(ffljiiiJJJfl> Zones of mass failures: 

I- Field and Richmond ( 1980) 

2- Greene and others ( 1975) 

3- Richmond (In press) 

4 - Haner and Gorsline ( 1978) 

5- Field and Edwards ( 1980) 

6- Nardin and others ( 1979) 

0 10 20 30 Kilometers 

0 5 10 15 Nautical miles 

Contours in meters 

Angeles 

FIGURE 204.-Known sediment failures in the southern California borderland (Field and Edwards, 1980). Contours in meters. 

Tsunami Potential 395 
Water level 

Do 

FIGURE 205.-Schematic cross section of a submarine landslide scarp 

showing the parameters used to estimate the amplitude of a slidegenerated wave (after Striem and Miloh, 1975). Do is the water 

depth at the base of the slope, D5 is the water depth to the center 

of gravity of the slide, £ is the distance from the center of gravity 

to the edge of the slide, and h is the slide thickness. 

that earthquakes may trigger slides off southern California, opportunities for observing such slides are rare, 

and there have been no direct observations of slides that 

were initiated or moved during southern California 

earthquakes. The only offshore California submarine 

slide known to have been initiated by an earthquake is a 

large liquefaction-induced failure off northern California that occurred in conjunction with a M 7.2 earthquake (Field and others, 1982). 

To estimate the tsunami that might be generated by an 

earthquake-triggered slide, we must assume the dimensions of a representative slide. B. D. Edwards (oral communication, 1983), who has examined most of the nearshore zones of mass failure offshore of Los Angeles, 

estimated the following parameters for a representative 

slide block: 

Length --------- 5 km 

Width --------- 5 km 

Thickness ------ 50 m 

Volume -------- 1.25 km3 

Density -------- 1.6 g/cm3 

Total weight ---- 2 x 1012 kg 

In falling 100 m, the block represents an energy output 

of 0.147 x 1()23 erg, which, if it is fully converted to wave 

generation, is comparable to an energy input associated 

with tsunamis of 2- to 3-m runup heights (table 48). 

However, Wiegel (1970) has shown, in a dropping-block 

model, that only 1 .to 2 percent of the potential energy is 

converted to wave generation. The energy output would 

thus be reduced to 0.00147 x 1023 erg, and the runup 

height would be reduced to about 1 m. Waves of this 

height are insignificant and would probably lose 

396 Earthquake Hazards in the Los Angeles Region 

amplitude exponentially as they traversed the long 

distance to the shoreline. If this approximation is valid, 

it suggests that tsunamis generated by slides of the 

dimensions known along the southern California coast 

pose no tsunami hazard. 

The wave generated by the postulated representative 

slide block can also be estimated by using an equation 

developed by Striem and Miloh (1975) that Murty (1979) 

applied to a wave generated by a submarine slide investigated by Prior and others (1982) at Kitimat Arm, 

British Columbia. The model assumes that the wave 

energy is uniformly distributed over the width of the 

slide and, consistent with Wiegel's observations, that 

only a very small fraction of the potential energy released by the slide is converted to wave energy. The 

equation takes the form 

As figure 205 shows, D5 is the water depth at the center 

of gravity of the slide, D0 is the water depth at the base 

of the slope, f is the distance from the edge to the center 

of gravity of the slide, h is the slide thickness, 1J- is the 

assumed percentage of energy transferred from the 

slide to the wave, and o is the density of the slide divided 

by the density of water. Substituting the values from the 

postulated slide block (Ds = 600 m, D = D 0 

= 700 m, £ = 2,500 m, h =50 m, ll = 0.01, and o = 1.6) 

yields a calculated wave height H of 0.14 m. 

The fact that this small wave should have approximately the same order of magnitude runup as the wave 

estimated by the preceding model suggests that there is 

little hazard of tsunamis generated by slides of the 

dimensions observed off the southern California coast. It 

is stressed that this calculation is sensitive to the assumed slide-to-wave energy transfer (1 percent), which 

is derived from laboratory models, and that this 

parameter is not well evaluated in actual cases. 

Potential for Distantly Generated 

Tsunamis 

Several approaches have been used to predict the frequency of occurrence and the height of distantly 

generated tsunamis that might affect coastal California. 

One relates tsunami height to tsunami frequency from 

historical California data. Another combines longer 

term historical data from the shores of the entire Pacific 

with numerically simulated tsunamis in the source areas 

thought to be most threatening to California and examines the height and frequency of occurrence of the 

predicted waves. A third identifies existing seismic gaps 
in distant tsunamigenic areas, evaluates which might 

produce the most damaging tsunami in California, and 

considers the probability of a large tsunamigenic earthquake in that seismic gap. 

California Tsunami Record 

Using recorded tsunami heights, Wiegel (1970) 

described a tsunami height distribution function for 

Japan, for Hila, Hawaii, and for several California sites 

(fig. 206). The distribution functions demonstrate the 

relation between expected wave height and frequency 

and can be used for estimating recurrence intervals. 

The San Diego curve is added by using data from appendix 4. For moderate and large tsunamis (heights above 

approximately 1.5 m), these curves suggest that wave 

height is related to the log of the frequency. 

As figure 206 indicates, the recurrence interval for 

large tsunamis is approximately 100 yr in California and 

10 yr in Japan. The difference in recurrence interval 

reflects the generation of local tsunamis along the 

Japan-Kurile Trench and the sensitivity of Japan to distant tsunamis as opposed to (1) the absence of significant locally generated tsunamis along the California 

coast, (2) the transoceanic dieoff of tsunamis generated 

off Japan, and (3) the relative insensitivity of California 

to distantly generated waves. Figure 206 also shows that 

waves from distantly generated tsunamis tend to be 

smaller in southern California. 

Long-Term Historical Data and 

Mathematical Models 

Tsunamis can be simulated by using mathematical 

models that specify the location, geometry, and amount 

of elevation change in a source area, the paths of the 

resulting waves, and the effects of shoaling on wave 

amplitude as waves approach a coast line (for example, 

Brandsma and others, 1978; Houston, 1980; Hwang and 

others, 1972). By combining historical data and 

numerical modeling, the U.S. Army Corps of Engineers 

has predicted 100- and 500-yr runup elevations for the 

U.S. west coast for the Federal Insurance Administration to use as a basis for calculating flood-insurance 

rates (Garcia and Houston, 1975; Houston and Garcia, 

1974, 1978; Houston and others, 1975; Houston, 1980). 

Because no historical record was long enough or complete enough to make statistically valid predictions for 

most of the California coast, these predictions are based 

on numerical models of distantly generated tsunamis 

and the historical record of tsunamis elsewhere in the 

Pacific. These models indicate that the California coast 

is most sensitive to tsunamis generated along the 

Alaska-Aleutian and Peru-Chile margins. For modeling 

purposes, these two source areas were divided into 12 

segments, and 5 tsunamis ranging from 2.5 to 4.5 in 

intensity (in increments of 0.5) were modeled in each 

segment by using a numerical finite difference model 

(Garcia, 1976). The modeled tsunami is initiated by an 

uplift of the sea surface assumed to be identical to the 

uplift of the sea floor. The tsunamis are presumed to be 

large, made up of linear nondispersive waves having 

wavelengths greater than 160 km. The wave trains are 

propagated across a wide-spaced computational grid 

representing the Pacific Ocean (using actual water 

depths along wave paths) to the base of the California 

continental slope. 

On reaching a water depth of 500 m at the base of the 

slope, wave trains predicted for the 5 tsunamis in each 

of the 12 segments were propagated up the continental 

40 

35 

f--

w 

w 

LL 

~ 30 o.: 

::J 

z 

::J 

a: 

a: 25 0 

f--

:r 

(!) 

w 

:r 20 w 

> <t 

3: 

~ 15 <t 

z 

::J 

(JJ 

f--

::!: 

::J 10 ::!: 

x 

<t 

::!: 

5 

0 

RECURRENCE INTERVAL, IN YEARS 

0.6 0.4 0.2 0.1 O.Ql 

AVERAGE YEARLY FREQUENCY OF TSUNAMIS 

OF EQUAL OR GREATER HEIGHT 

1000 

0.001 

FIGURE 206.-Comparison of maximum height or runup with frequency and recurrence interval for tsunami waves in Japan, California, 

and Hawaii. Modified from Wiegel (1970). 

Tsunami Potential 397 
5 

Rincon 

Island 4 

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Los Angeles 

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0 0.5 1.0 1.5 2.0 2.5 0 0.5 1.0 1.5 2.0 2.5 0 0.5 1.0 1.5 2.0 2.5 

ELAPSED TIME, IN HOURS ELAPSED TIME, IN HOURS ELAPSED TIME, IN HOURS 

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4 

3 

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Bay -

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z' o e--'----\Pd-- -1----+--------1 

0 

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0 0.5 1.0 1 2.5 .5 2.0 2.5 0 0.5 1.0 1.5 2.0 2.5 0 0.5 1.0 1.5 2.0 

ELAPSED TIME, IN HOURS ELAPSED TIME, IN HOURS ELAPSED TIME, IN HOURS 

5 

San Diego 4 

3 

1-

lJ.J 2 lJ.J 

LL. I 

,,..., 

I 

FIGURE 207.-Comparison of actual tide-gauge recordings (solid line) of 

the 1964 Alaska tsunami along the California coast and waves 

simulated by a numerical model (dashed line) of the same tsunami 

(Houston, 1980). 

~ 

z' 0 

I / 

0 

t= 

<t: - 1 

> lJ.J 

..../ 

lJ.J 

- 3 

- 4 

- 5 

0 0.5 1.0 1.5 2.0 2.5 

ELAPSED TIME, IN HOURS 

slope and across the continental shelf by means of a 

shallow-water numerical model. The resulting waves 

were described for 199 shoreline locations from Point 

Conception to the Mexican border. The shallow-water 

model is a finite difference model, developed by 

Leendertse (1967) and modified by Butler (1978), that 

treats the shoaling waves as nonlinear through a finemesh computational grid in which grid size is decreased 

to accommodate the increasing effect of local bathymetry as the shoreline is approached. Verification of the 

model was made by comparing a simulation of the 1964 

tsunami with tide-gauge records from the available 

seven southern California tide-gauge records of the 

398 Earthquake Hazards in the Los Angeles Region 

actual tsunami (fig. 207). As Houston (1980, p. 9-10) 

concluded, 

[fhe] numerical model calculation agrees 

reasonably well with the tide gage records 

[however] the tide gages do not record 

tsunamis without distortions of amplitude, 

period and phase. The greatest amplitude difference [approximately 0.6 m] is for the second 

wave crest at Santa Monica . .. However, the 

tide gage may have had response problems 

while recording the wave crest since the 

recording appears to be truncated and there 
are unusual high frequency oscillations in the 

truncated region of the wave form. 

To make predictions, temporal distributions of intensity must be known. Houston (1980) used the Imamura-Iida 

intensity scale (table 48) as modified by Soloviev (1970), 

where 

intensity= logzfv'2 height (meterslavgl 

so as to use a generally representative average runup 

-rather than risk skewing the data to an unrepresentative runup at a single point along the coast. By combining this measure of intensity with the recorded tsunami 

histories for the two major source areas and by assuming a linear distribution between frequency and intensity, Houston established predictions for tsunamis of a 

given intensity (i) that would be generated in any given 

year along the Peru-Chile Trench: . 

n(i) = 0.074e- 0·

63; 

and along the Alaskan-Aleutian margin: 

n(i) = 0.113e- 0·

71; 

This approach presumes that tsunamis have a Poisson 

distribution-that is, a frequency distribution of single 

noncontagious events in which the probability of a single 

event is · small and the number of events is large 

(McCulloch and Pitts, 1948). Elevations of the waves expected to be equaled or exceeded once every 100 to 

500 yr were then calculated from the numerically simulated tsunamis (fig. 208}. The predicted wave heights, 

shown above the shoreline, incorporate the effect of 

astronomical tides by means of an analytical solution 

used to determine the combined tsunami and 

astronomical-tide cumulative probability distribution 

(Houston, 1980}. These predicted heights above the 

shoreline are considered by Houston to equal runup 

elevations for most of southern California, except that 

runup elevations may be lower where waves flood lowlying or estuarine areas or higher where waves encounter steep topography at or near the shoreline. 

Although the limits of coastal flooding or inundation 

resulting from the predicted waves were not determined 

in this study, Houston and Butler (1979} have developed 

and applied a two-dimensional numerical model for inundation that they have tested against the observed 

1964 tsunami inundation at Crescent City. 

In assessing the foregoing predicted recurrence intervals and heights of the 10D- and 50D-yr tsunamis, the 

reader should be aware that (1) workers in the field 

disagree on whether the tsunami record is long enough 

to allow extrapolation to future events, especially large 

events (Hwang and Lee, 1979, p. 272-277); (2) the 

predicted heights are not maximum credible heights and 

do not presume coincidence of the highest tsunami wave 

with peak high tide or with storm-induced high-water 

setup and superimposed storm waves; and (3) the 

designations 10D- and 50D-yr tsunamis do not mean that, 

for any specific time period, it will be 100 or 500 yr between such events, because these calculated recurrence 

intervals are a statement of probability over a time 

period many times greater than the predicted intervals. 

Seismic Gaps 

The third method of tsunami prediction is based on 

recognition of seismic gaps and provides a model for 

predicting which portions of tsunamigenic subducting 

margins are likely to produce large tsunamis in the near 

future (McCann and others, 1979). Analysis of the 

seismic histories of areas adjacent to seismic gaps has 

provided accurate forecasts (location and magnitude) of 

large earthquakes (Ohtake and others, 1977). In 1970, 

J. A. Kelleher recognized a seismic gap at the Shumagin 

Islands along the Aleutian Trench. This spatial gap in 

seismic activity along an otherwise seismically active 

convergent plate boundary that has not had a large 

(M> 7.0) earthquake for several decades is one of several 

later described by Kelleher (1972), Kelleher and others 

(1974), and Sykes (1971) along island arcs of the Pacific 

margin. In 1981, L. S. House and others iqentified the 

Unalaska gap, adjacent to the Shumagin gap. 

The California coast is sensitive to tsunamis that 

might be generated in the Shumagin or Unalaska gaps. 

This sensitivity has been demonstrated by numerical 

simulation of hypothetical tsunamis generated at subduction zones around the Pacific to provide an estimation of the maximum credible tsunami waves that might 

occur along the west coast of the United States (Brandsrna and others, 1978). In this study, tsunamis were 

simulated at 34 sites along island arcs and trenches 

around the Pacific margin (fig. 209); it was presumed 

that each site was capable of producing sea-floor 

displacements somewhat larger than those of the 1964 

Alaska and 1960 Chile earthquakes. The simulated 

tsunamis were propagated across the Pacific to 

specified offshore locations through a finite difference 

grid having a minimum water depth of 180 m. Maximum 

wave heights (departure from still water) for each location produced by any of the 34 simulated maximum 

credible tsunamis are shown in figure 209. With the exception of one station off southern California (station 

16), which is controlled by a tsunami at Samoa (area 3, 

fig. 209), the maximum wave heights along the west 

Tsunami Potential 399 
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FIGURE 208.-Heights of the 100- and 500-yr tsunamis along the southern California coast (Santa Barbara to San Diego) as predicted by numerically modeled tsunamis. Modified from 

Houston (1980). Wave heights given for each numbered coastal location are the values predicted as the wave crosses the shoreline and include the effects of astronomical tides. Runup 

elevations may be higher where waves encounter steep topography at or near the shoreline or lower where waves flood low-lying or estuarine areas. 
METERS 

CANADA ------ B UNITED STATES 

48" 

2 • Grays Harbor 47" 

NORTH 3 • 46" 

AMERICA 

4 • 45° 

5 • 44° 

6 • 43° 

7 4ZO 

8 41 ° 

9 40" 

PAC IFI C O C EAN 10 39° 

11 38" 

12 37" 

13 36° 

14 35° 

15 34° 16 

17 

18 

19 31° 

I I I 

4 7 

FEET 

FIGURE 209.-A, Locations of mathematically simulated tsunamis at subduction margins around the Pacific Ocean. B, Maximum absolute wave 

displacement from still water at stations located at a water depth of 180 m along the California coast as calculated by simulated maximum 

credible tsunamis located at numbered sources shown in A (Brandsma and others, 1978). 

coast of the United States were produced by tsunamis 

along the Aleutian Trench and the Alaskan coast (areas 

24 and 25), which contain the Shumagin and Unalaska 

gaps. Of these two sources, Brandsma and others (1978, 

p. 145) said: 

The waves generated at source 24 exceed 

those generated at source 25 at some locations 

in spite of the latter's closer proximity and better directional orientation to the west coast. 

This effect probably arises from the fact that 

more of the displacement of source 24 occurs 

in water than is the case for source 25; consequently, source 24 imparts a greater potential 

energy to the water. 

Independent lines of evidence have convinced several 

workers that a great earthquake is imminent in the 

Shumagin gap, where stress appears to be accumulating. House and Boatwright (1980) interpreted two recent moderate-sized earthquakes (Mb 5.8 and 6.0) accompanied by relatively high stress drop as indicating 

the release of locally high stress concentration 

associated with heavy stress loading in the gap. They 

see these events as precursors to a great earthquake. 

Hauksson (1983) has described recent moderate earthquakes in the gap as having a doughnut-shaped distribution, which Magi (1969) demonstrated is a typical 

distribution preceding a large event within the 

doughnut. An unusual deep aseismic-slip event detected 

by a tiltmeter array occurred beneath the Shumagin 

Islands between 1978 and 1980 and is thought by 

Beavan and others (1983a, b) to have contributed to increased stress in the shallower locked main-thrust zone. 

The historical record is also interpreted by some as 

indicating the imminence of a great earthquake in the 

Shumagin gap. Davies and others (1981) and Sykes and 

others (1981) concluded, from a review of about 200 yr 

of historical documents, that at least half the Shumagin 

gap ruptured in major earthquakes in 1788 and 1847 

and may have ruptured again between 1899 and 1903. 

Average recurrence times for large events in the gap 

are therefore 50 to 75 yr, or, if it is assumed that no rupture occurred between 1899 and 1903, recurrence time 

is 91 yr. These investigators conclude that a great earthquake is likely within the next 10 to 20 yr in the 

Shumagin gap. Recent calculations of the probability for 

large earthquakes (M~ 7.8) along the Aleutians Uacob, 

1983) indicate that the Shumagin gap shows the highest 

probability (17-90 percent) of a great earthquake before 

1993. 

A comparison of seismic events in the Shumagin gap 

and tsunami history is informative. Iida and others 

(1967a) reported a 1788 Alaska-generated tsunami 

observed on the Alaska peninsula and in the Shumagin 

Islands. Their catalogue records no Alaska-generated 

Tsunami Potential 401 
tsunami in 1847 or between 1899 and 1903, when Davies 

and others (1981) and Sykes and others (1981) have suggested major ruptures in the Shumagin gap. Large earthquakes in the Shumagin gap should produce tsunami 

runup at San Francisco. Using the relations of earthquake magnitude to fault rupture area (Mw =log S + 4) 

derived from Kanamori (1977) and that of far-field 

tsunami amplitude to earthquake magnitude (1pg 

H = Mw- B) from Abe (1979), Blackford (1981) estimated 

that a M 8.8 earthquake could occur in the gap and that 

it should produce a wave with a crest-to-trough measure 

in excess of 0.64 m at San Francisco. The excess will depend on wave directivity. No tsunami between 1899 and 

1903 has been identified on records of tide gauges installed in San Francisco and San Diego in 1854. 

Opinions differ about possible recurrence intervals of 

great earthquakes at subduction margins. Plafker (1972, 

1978) noted that the apparent contradictions between 

recurrence intervals on the order of 100 yr indicated by 

seismologic data and intervals of 300 to 500 yr as suggested both by dated uplifted marine terraces (each 

uplift representing movement along a megathrust 

associated with a major earthquake) and by the amount \( 

of time required for the small rates at which the 

lithospheric plates are converging across the eastern 

Aleutian and the southern Peru-Chile Trenches account 

for the large amounts of net slip that accompanied the 

large 1964 Alaskan and 1960 Chilean thrust-fault earthquakes. Sykes and others (1981) suggested that the apparent long repeat times may reflect movement of a 

secondary imbricate fault within the upper plate that 

does not move with every major slip event on the main 

plate boundary. 

TSUNAMI HAZARD REDUCTION 

Tsunami Warning Systems 

Most hazards related to geologic events (for example, 

earthquake shaking, flooding, landslides, and tsunamis) 

can be greatly reduced in the long term by appropriate 

structural design and land use and in the short term by 

warning systems that allow sufficient time to avoid the 

hazard. The cost of inadequate tsunami warning 

systems has been high (Spaeth and Berkman, 1967, p. 5): 

After the devastating Aleutian tsunami of 

April 1, 1946, military and civilian sources 

criticized the U.S. Coast and Geodetic Survey 

for the lack of warning in the Hawaiian 

Islands. The critics correctly pointed out that 

seismic waves from this earthquake were 

402 Earthquake Hazards in the Los Angeles Region 

recorded at Honolulu and other observatories 

within minutes after the occurrence of the 

earthquake; and consequently, the tsunami 

could have been predicted. The error in this 

criticism lay in the fact that seismograph 

records were changed only once each day, and 

until the film records were developed, no 

knowledge of an earthquake occurrence was 

normally available. In addition, the great majority of underwater earthquakes does not 

cause tsunamis, and no arrangements were in 

effect to verify the existence of a tsunami 

through actual observations. 

As Shepard and others (1950, p. 392) reported: 

On the morning of April 1, 1946, the Hawaiian 

Islands experienced the most disastrous 

tsunami in their history. More than 150 persons were killed, principally by drowning, and 

163 others were badly injured. Hundreds of 

houses and other small buildings were 

destroyed or badly damaged. Property damage 

probably amounted to $25,000,000. 

And again (Hellmuth and others, 1963, p. 1126-1127): 

... 9 hours after the [1960 Chilean) earthquake, ... the following message was sent 

from Hawaii: This is a tidal wave alert bulletin. 

A violent earthquake in Chile has caused a 

tidal wave that is radiating in all directions 

over the Pacific Ocean. It is estimated that the 

first wave will reach the Island of Hawaii at 

midnight Hawaiian time and 30 minutes later 

at the Island of Oahu. Its destructive effects 

will last several hours. The intensity of the 

wave cannot be predicted. The southern part 

of Hawaii will be the first to be affected and 

will be the first indication of the damage that 

might be produced in other parts and other 

islands of the Hawaiian group. The times have 

been calculated for the arrival at other Pacific 

islands based on the best data obtainable; they 

are not very exact: Tahiti 0230 hours, 

Christmas Island 0400 hours, .Samoa 0500 

hours, Fiji and Canton 0600 hours, Johnston 

0700 hours, and Midway 0830 hours .... At 

0654 the first wave arrived at the Hawaiian 

Islands, producing great damage in Hila; but 

the activity of the Magnetic Observatory at 

Honolulu did not cease. At 1211 on 23 May, the 

state of alarm on the Hawaiian Islands terminated, but the waves of the tsunami con-
tinued their destructive voyage until they were 

stopped and then reflected by the coasts of 

Japan, Russia, New Zealand, Australia, etc. 

Unfortunately, it was Saturday afternoon in Tokyo, and 

the Japanese Meteorological Agency, which is responsible for issuing tsunami warnings, had closed at noon; 

thus, no warning was issued in Japan (Yoshimasa 

Kobayashi, oral communication, 1983). Iida and others 

(1967a) reported the widespread destruction-199 

people killed or missing, 4,875 structures wrecked or 

washed away, and 7,534 boats wrecked or lost. 

Tsunami warnings for tsunamigenic earthquakes occurring along coastal British Columbia, Washington, 

Oregon, and California are issued from the Alaska 

Tsunami Warning Center (ATWC), operated by the National Weather Service, in Palmer, Alaska. The following procedure is used (T. Sokolowski, written communication, 1983): 

The warning services are based on seismic 

data. Real-time seismic data, from more than 

75 remote sites, are continually telemetered to 

the A TWC and used to locate earthquakes. An 

alarm system is attached to several site signals 

that are telemetered from California and 

Alaska. Since the Center must react to earthquakes 24 hours a day, personnel are required 

to live within a specified travel time from the 

Center. [The office is manned 5 days a week, 8 

hours per day and, during nonoffice hours, 

personnel are made aware of large earthquakes by a radio-alarm system that is connected to the Center's seismic alarm system.) 

The seismic data are processed interactively 

and automatically to determine earthquake 

locations (±50 km), Richter magnitude (± 0.3), 

and tsunami arrival time ( ± 20 mins ). Tide data 

are telemetered in real-time from 8 remote 

Alaskan sites to the Center, but from the continental U.S. west coast states, data are requested via teletypewriter and telephones. 

The issuance of a tsunami WARNING is based 

upon the magnitude of the earthquake. A 

warned area includes those places that are 

within 3 hours of water wave travel time from 

the epicenter. The appropriate remaining 

areas, outside the warned area, are placed in 

a WATCH status. 

If an earthquake occurs in the west coast 

areas, with a magnitude greater than 6.75 and 

less than 7.5, an earthquake information 

message would be disseminated to the ATWC's 

recipients. The tide site's data about the 

epicenter would be requested to ensure that a 

tsunami was not generated. If the magnitude is 

7.5 or greater, a WARNING would be issued 

and the tide site's data obtained. 

Upon confirmation from tide gage data that a 

tsunami has been generated, the previously 

designated WATCH status areas are upgraded 

to a WARNING status. If an area has received 

a WARNING and subsequent tide data shows 

no tsunami activity, the WARNING and 

WATCH are cancelled. 

Once the decision has been made to issue a warning 

or a watch, the messages are transmitted on the National Warning System (NAWAS) telephone line. In 

California, the message goes to the Federal Emergency 

Management Agency (FEMA) and to the State of California Office of Emergency Planning, which is manned 

24 hr a day. 

The watch or warning is immediately relayed by 

telephone to local coastal county offices, such as 

sheriffs' departments, that are also open 24 hr a day. 

The message must be acknowledged by the recipient, 

who is immediately sent the same message by teletype. 

These ·telephone links are also checked three times a 

day. 

Both Hawaii and Alaska have rapid-response 

regional-warning networks that issue tsunami warnings 

in those· areas on the basis of earthquake magnitude 

alone. Washington, Oregon, and California have no 

similar regional warning system that can respond rapidly to a locally generated tsunami. A period of approximately 21 min (6 min for the arrival of the first seismic 

wave and 15 min for the arrival of the five to six large 

surface waves necessary for analysis) would be required before the decision could be made to issue a 

warning for a tsunami generated off southern California. Additional time would be required to relay the 

warning to local agencies and to translate the warning 

into action. 

Although there is no historical record of a recent 

locally generated tsunami along the Washington, 

Oregon, and northern California coasts, there is both 

seismologic and geologic evidence that the subduction 

zone at which the Gorda and Juan de Fuca plates are 

converging at rates of about 3 to 4 cm/yr with the North 

American plate (fig. 200) may be the site of a future 

great tsunamigenic earthquake. Heaton and Kanamori 

(1984, p. 939) describe the Juan de Fuca plate boundary 

as a " ... 500 km long seismic gap ... [that] ... represents 

one of the most remarkable to be found in the circumPacific seismic belt," and their comparison of the age, 

convergence rate, and seismicity of the Juan de Fuca 

plate with those of other actively subducting plates 

Tsunami Potential 403 
leads them to suggest the possibility of a future great 

earthquake at this subduction zone. Geologic evidence 

that this subduction zone should be considered 

tsunamigenic is presented by P. D. Snavely, Jr. (written 

communication, 1985): 

Landward tilting in the Oregon and Washington Coast Range and the Olympic Peninsula 

has been documented using tide gauges and 

geodetic leveling of uplifted marine terraces. 

Landward tilt and crustal shortening shown by 

thrust faults and folds on the outer Oregon 

shelf and slope are characteristic of many 

other subduction zones that have experienced 

major thrust earthquakes. Interpretations of 

multichannel seismic-reflection profiles across 

the continental slope of California, Oregon, 

and Washington support episodic underthrusting of the Gorda and Juan de Fuca plates 

beneath the North American plate on a long 

time scale. This convergence has produced a 

series of elongate en echelon anticlinal ridges 

bounded by thrust faults. These ridges have 

bathymetric expression and uplift abyssal 

sediments as much as 1,100 m. If one accepts 

the consensus of geologic data that faulting 

and folding along the lower slopes are the 

result of episodic events that uplifted abyssal 

sediments 400-1,000 m -above their original 

depositional positions, these dramatic uplifts 

of elongated anticlinal ridges, tens of kilometers long, are capable of generating destructive tsunamis. 

There is also the possibility that the northern offshore 

San Andreas fault might be capable of producing a 

tsunami. This fault is marked for much of its length by a 

scarp that offsets the modern sea floor (Curray and 

Nason, 1961; McCulloch and others, 1980; event 26, app. 

4), and a conservative worst-case model should probably 

assume several meters of vertical displacement on the 

fault. 

In tsunamigenic areas, where time is critical, the 

absence of a regional warning system automatically 

triggered by a large local earthquake can be costly. The 

May 26, 1983, Nihonkai-Chubu earthquake (M 7.7) occurred beneath the Sea of Japan about 140 km west of Honshu, 1 min or so after 12 noon Uapan Times, 1983; 

Osamu, 1984; Bertera and others, 1985). At 12:12, the 

first wave of 29 em was observed at Aomori. A tsunami • 

warning for the Sea of Japan side of Honshu and central 

Tohoku was issued to the disaster prevention section of 

the Japanese Meteorological Agency at 12:18 (Hokubei 

Mainchi, 1983): 

404 Earthquake Hazards in the Los Angeles Region 

... After receiving the warning at 12:18 p.m., 

an official in charge ran up from his office on 

the second floor to the radio room on the 

seventh floor. 

The official, according to the investigation, 

started to activate the warning system at 

12:20p.m .... 

The wireless tidal wave warning system is 

designed to simultaneously convey a warning 

to all the 69 villages and towns. The system, 

however, did not work due to the official's 

mistake .... 

In the procedure the official was supposed to 

depress three buttons to connect the system 

with the fire station headquarters, offices of 

cities, towns and villages, as well as welfare 

offices. The official pushed only the button for 

the fire station headquarters, failing to touch 

the remaining two .... 

According to McKean and Mobs (1983, p. 18, 21): 

Akimasa Otomo, a Japanese man, saw it happen. Shortly after noon on May 26, while tying 

up at a dock 36 miles from Akita, a prefectural 

capital on the northwest coast of Honshu, he 

saw a group of schoolchildren swarm out of an 

excursion bus and run toward the beach for a 

seashore lunch. Suddenly the water beneath 

Otomo receded-and then began to rise. He 

recognized the ominous signs. "I knew this was 

a tsunami. .. and rushed to higher ground," he 

later recalled. When he looked back, "I saw all 

the children floating and their bodies being 

carried out to sea." As soon as the huge wave 

receded, he rushed back to his boat, cast off 

and was able to pick up ten of the children. 

Others saved themselves by grabbing onto 

rocks or clinging to pieces of shed that had 

been swept away with them. But 13 of the 43 

young picnickers drowned. 

Elsewhere, along the westeru coast of Honshu 

and the southwestern tip of Hokkaido, in an 

arc of destruction extending some 500 miles, 

86 others perished in a series of great waves. 

The earthquake (measuring 7.7 on the Richter 

scale) that caused the waves claimed three 

more victims inland. Between the quake and 

the tsunami waves, which rose to 20 feet in 

places, 52 houses were washed away, 139 

destroyed, and 491 others damaged. Farms 

were flooded, roads split open, railway tracks 

torn up, and 14 bridges swept away. Fishing 

vessels and other craft caught close to shore or 
in harbors were hard hit; at least 225 of them 

sank outright and 414 others were carried out 

to sea or dumped on docks or village streets. 

Across the Sea of Japan, waves almost 30 feet 

high hit the Siberian coast and battered 

Korean fishing villages .... 

Even if it had been issued properly, the warning that 

should have been given at 12:20 would have come too 

late for the many people killed by this tsunami, for, by 

then, the tsunami was sweeping over the Oga Peninsula. 

Experience should have alerted the warning agency, for 

the 1983 tsunami was not a unique event for the west 

coast of Japan. The recent M 7.5 1964 -Niigata earthquake, also beneath the Sea of Japan, generated a 

tsunami that had runup heights of as much as 5.8 m (Iida 

and others, 1967a) and killed five(?) people (Kobayashi, 

1981). A regional warning system automatically triggered by the occurrence of these earthquakes might 

have reduced the death toll greatly. 

The shortcomings of warning systems are well recognized and are of considerable concern to those involved 

in the study and prediction of tsunamis. The principal 

needs are: 

• Techniques for rapid determination of earthquake 

source mechanisms (distinguishing nontsunamigenic 

strike slip from possibly tsunamigenic dip slip) for 

remote and local earthquakes. 

• Techniques for more rapid collection and analysis 

of seismological and tidal data and distribution of 

warnings. 

• Reasonable estimates of probable runup heights and 

areas of inundation in the path of the tsunami. 

Although several techniques (Brune and others, 1960; 

Ben-Menahem, 1961) have been devised for determining 

the source mechanisms of remote earthquakes by examining low-amplitude long-period Rayleigh surface 

waves, analysis time for such techniques is long, or else 

records of Rayleigh waves are not routinely available 

because seismographs dedicated to determining the 

magnitudes of large seismic events are insensitive to 

such waves. Fumumoto (1969) noted that Rayleigh waves 

traversing the Earth's surface generate acoustic waves 

in the overlying air that propagate upward into the high 

atmosphere and produce detectable waves in the 

ionosphere. He suggested that observations of 

ionospheric waves might be used to indicate the source 

mechanisms of distant earthquakes. More recently, 

Ward (1979) has demonstrated that the ratio of "ringing 

waves" (long-period compressional P waves that bounce 

between the top and the base of a water layer) to body 

waves can be related to focal depth, thrust or steep-dip 

focal mechanisms, and shallow structures-all parameters common to tsunamigenic earthquakes. He concluded that real-time observation of the ringing P waves 

that accompany large earthquakes in tsunamigenic 

areas provides a diagnostic tool for helping to establish 

tsunami potential. Kanamori and Given (1982) devised a 

rapid method of using Rayleigh-wave spectra at a long 

distance from the earthquake to determine both seismic 

moment and source mechanism within 10 min of receiving the seismograph data. Kanamori is presently investigating a method for near-field determination of 

seismic moment and source mechanisms using bodywave information. Thus, techniques for rapid determination of source mechanisms are available, and 

techniques for more rapid determination are being 

developed. 

Designs and hardware for improved regional tsunami 

warning systems to deal with the remaining problems of 

rapid data acquisition, analysis, runup prediction, and 

warning issuance are presently available (Van Darn, 

1979a; Bernard and others, 1982). These systems 

receive seismograph and tide-gauge data automatically 

by satellite and transmit them to a computer for 

analysis. Given the proper store of historical data and 

modeling parameters, a computer could determine the 

existence of a tsunami and its likely travel path, wavearrival times, and estimated runup heights. The systems 

could automatically issue warnings to locations in 

jeopardy. Bernard and others (1982) estimate that the 

rapid-response and analytical network proposed for 

developing nations of the Pacific could reduce the time 

between the occurrence of an earthquake and the issuance of a tsunami warning from about 1 hr to several 

minutes for areas now without regional warning 

systems. Thus, the analytical tools and hardware for 

rapid-response tsunami warning systems appear to have 

been developed. Now they await deployment. 

Inundation Maps and Land 

Use Planning 

In light of the tragic loss of life, the cost of property 

damage, and the disruption of commerce and personal 

lives suffered as a result of the 1964 Alaskan tsunami 

along the west coast of the United States, one might expect communities that were seriously affected to have 

incorporated some level of protection for their -citizens 

against the recurrence of such a tsunami. In fact, not all 

have done so. Although the city of. Kodiak, on Kodiak 

Island, was heavily damaged in the 1964 tsunami, it has 

not incorporated consideration of the tsunami hazard 

into its land use planning process (Preuss, 1982). 

Tsunami Potential 405 
Considerable incentive to recognize the tsunami 

hazard is now provided by the National Flood Insurance 

Program, which makes available low-cost federally subsidized insurance that cannot be cancelled by the 

Federal Government. To qualify for program participation, a community must adopt special construction requirements for buildings in areas that can be expected 

to be flooded in the 100-yr event (owing to storm or 

tsunami coastal flooding or river overflow). These 

building requirements must meet or exceed standards 

set by FEMA. The water elevations and the inundation 

limits for the 100-yr event are established by FEMA. For 

critical structures (such as nuclear reactors, hospitals, 

hazardous-waste storage areas, and record centers), 

FEMA specifies the higher water elevations and larger 

inundation areas of a 500-yr tsunami. 

The inundation area for the 100-yr event is divided 

into two major zones of structural requirements-a V 

zone, in which the anticipated water depth is greater 

than 3 ft and breaking waves are probable, and an A 

zone, in which the anticipated water depth is less than 

3 ft and there are no breaking waves. Each zone is further divided into 30 subdivisions for fixing appropriate 

insurance rates (Federal Emergency Management Agency, 1982). Construction requirements within the V zone 

include fixing the minimum height of building floors 

above sea level (sea level is referred to the 1929 National Geodetic Vertical Datum), using pile foundations 

to anchor structures that otherwise might float free and 

be damaged by or damage other structures, prohibiting 

use of erodable fill for structural support, and prohibiting structures seaward of the mean-lower-lowwater shoreline. 

Inundation maps have been made for coastal California counties (Flood Insurance Rate Maps, available 

through FEMA, Flood Map Distribution Center, 6930 

San Tomas Rd., Baltimore, MD 21227-6227). These maps 

are updated as experience dictates or as new data 

become available. Participating communities are given a 

grace period to adjust their building ordinances to the 

revised inundation maps. If they do not, they lose their 

option to obtain flood insurance through participation in 

the National Flood Insurance .Program, access to Federal Housing Administration and Veterans Administration loans, and possibly the right to qualify for Federal 

Disaster Relief in identified flood-hazard areas. If an applicant for or holder of a Small Business Administration 

loan were to lose Federal insurance, he would have to 

seek more costly, nonsubsidized cancelable insurance 

from the private sector. The National Flood Insurance 

Program exerts influence on the developer who does not 

wish to conform to FEMA standards, because an entire 

community can be denied Federal insurance if it grants 

a single variance adjudged by FEMA not to meet its 

406 Earthquake Hazards in the Los Angeles Region 

standards. In southern California, the cities of San Diego 

and Morro Bay and the counties of Orange, Los Angeles, 

Ventura, and Santa Barbara either have or will soon 

adopt building requirements that qualify them for 

Federal flood insurance (R. T. Lenaburg, oral communication, 1983). 

The most recent FEMA study of flood hazard to 

selected areas of southern California, from Morro Bay 

to the Mexican border (Lee and others, 1982), evaluated 

the following flood-generating mechanisms: 

• Runup of swell generated by intense offshore winter 

storms in the north Pacific. 

• Runup of wind waves generated by landfalling storm 

systems. 

• Runup of swell generated by tropical cyclones of Baja 

California. 

• Runup and surge from landfalling tropical cyclones. 

• Runup from tsunamis generated along the AleutianAlaskan and Peru-Chile Trenches. The 100- and 

500-yr tsunami heights developed by Houston (1980) 

were used (see fig. 208). 

As Lee and others (1982, p. 1) noted: 

Each of the above mechanisms is considered to 

act alone. That is, the joint occurrence of any 

combination of the above mechanisms to produce a flooding event is considered to be irrelevant to the determination of flood elevations 

with return periods of less than 500 years. The 

influence of the astronomical tides on coastal 

flooding is also an important factor in each of 

the above mechanisms. Each flood producing 

event from any of the above mechanisms can 

occur with a random phase of the astronomical 

tide. 

With the exception of damage in Crescent City, where 

the business district was severely affected by the 1964 

tsunami, most tsunami damage to California has been 

sustained by marine-oriented structures. Rail, ship, and 

highway freight often meet at dockside, where materials 

either are stored in bulk for local redistribution or await 

transport elsewhere. Tsunami inundation should be an 

important consideration when designating facilities for 

both long- and short-term storage of hazardous materials. Experience at Niigata and in Alaska (Whittier, 

Seward, and Valdez) has shown that petroleum storage 

facilities near dockside may rupture, and burning oil 

may be carried ashore on the tsunami waves. Direct 

wave damage to a storage facility is not always the 

problem, however. At Crescent City, a wave slammed a 

gasoline truck through a garage door. The impact 
dislodged an electrical junction box and ignited an oil 

tank farm, which burned for three days (Spaeth and 

Berkman, 1967). Accordingly, caution suggests that 

events external to the design of facilities for storing 

hazardous materials in or adjacent to a probable 

inundation area should be considered in assessing the 

integrity of such facilities. 

Public Awareness 

Reduction in tsunami hazard can also be attained 

through public awareness, both in long-term and immediate response. A. well-informed populace can respond on short notice and without panic to warnings of 

imminent danger if it knows what to do, as the people of 

London did during the nightly bombing raids on their 

city in World War II. When danger occurs only rarely 

and false alarms are raised, fewer people will respond. 

Tsunami predictions involving the fewest possible false 

alarms are highly desirable; however, when a population is transient, both education and an understanding 

of the hazard become a problem. Furthermore, if the 

recurrence interval of large tsunamis like the 1964 

Alaska tsunami is 100 yr or longer, it will be difficult to 

sustain concern for the hazard. Prominent markers 

could be erected throughout areas inundated by 

historical tsunamis to show the highest recorded water 

height-a passive daily reminde~ of what did happen 

and could happen again. Such markers might encourage 

recognition of tsunami hazards for both long- and shortterm land use. 

Experience suggests that, in regions where tsunamis 

are frequent, routine public education and practice 

drills are helpful. At Sanriku, on the eastern shore of 

Japan's Honshu Island, where the Great 1896 Meiji 

Sanriku tsunami killed 27,000 people and the 1933 

tsunami killed 3,022 people, the public has been trained 

to literally run for the hills if they feel an earthquake, 

and escape routes have been widened to accommodate 

the rush (Yoshimasa Kobayashi, oral communication, 

1983). In contrast, no such routine training is given on 

the western shore of Honshu Island. Had the west coast 

residents sought inland refuge, the 1964 Niigata and 

1983 Nihonkai-Chubu tsunamis would have caused 

many fewer deaths. 

Even where tsunamis are rare, as they are in the Los 

Angeles region, certain individual actions could save 

lives: 

• If you are on low ground near the coast and a large 

earthquake occurs in your area, move to high ground. 

There may be no time to either issue or receive an official warning. 

• If you recognize a premonitory drawdown of the sea, 

move to high ground. 

• The first tsunami wave may not be the highest. In major tsunamis, later waves commonly have the highest 

runup heights. 

• Periods between successive major waves may be 

similar. Thus, you may have time between waves to 

move to higher ground or to assist in rescue efforts. 

• Do not assume that, because the incoming tsunami 

wave is not breaking or because it is just coming in 

like a rapidly rising tide, it will not be destructive. 

The forces contained in this high-velocity, often 

debris-laden torrent are extremely destructive during 

runup and runoff. 

• Do not assume that areas behind beaches generally 

shielded from storm waves will be immune from high 

runup. Tsunami runup heights have historically been 

higher in some such areas along the California coast. 

• Do not go to the beach to watch a tsunami coming in. 

Not only might you hamper rescue efforts, but you 

may also have made your last sightseeing trip. 

SUMMARY 

Tsunamis are impulsively generated water waves 

that, throughout recorded history, have claimed hundreds of thousands of lives and wreaked havoc on 

coastal towns and cities. Most are caused when hundreds to more than a thousand square kilometers of the 

submerged continental shelf or slope are rapidly 

displaced several meters vertically during a large earthquake. Damage may be confined to the nearby coast, but 

waves may cross oceans and devastate distant shorelines. Local highly destructive tsunami waves are also 

generated when earthquake-triggered rock falls and 

avalanches or landslides fall or slide into water bodies 

or, in rare cases, when volcanic islands explode. 

The size of tsunamis caused by seismotectonic seafloor displacement can be related to the energy released 

by the earthquake, to the hypocentral depth and the 

water depth at the epicenter, and to the area and vertical displacement of the affected sea floor. The size of 

tsunamis generated by rock falls or slides can be estimated by theoretical, laboratory, and empirical models. 

Tsunamis are long wave trains. While they cross deep 

oceans, wave heights are about 1 m, but wavelengths 

may exceed 100 km, and waves may travel hundreds of 

kilometers per hour. Even at oceanic depths, tsunami 

waves interact with the sea floor. This interaction partially determines the travel direction of the wave. As 

tsunamis encounter shoaling coastal water, increasing 

interaction with the sea floor shortens the wavelengths, 

and the waves become steeper, sometimes reaching 

Tsunami Potential 407 
heights of several tens of meters. Many tsunamis come 

ashore as rapid successive rises of sea level. Less commonly, they come roaring ashore with a steep, breaking 

frontal wave. Both forms can cause extreme damage. 

Buildings torn from foundations, uprooted trees, cars, 

and even whole lines of railway cars may arm successive waves with tremendous destructive force. 

Historically, California has suffered little tsunami 

damage. The only tsunami to cause extensive damage 

during the period from 1812 to 1964 was generated by 

the 1964 Gulf of Alaska earthquake. The cost of damage 

from this tsunami, adjusted to 1983 dollars, was about 

$32.2 million, or about 0.2 percent of the dollar loss from 

California earthquakes during the same time period. 

Damage from the 1964 tsunami was most severe at Crescent City, where waves as high as 7 m overwhelmed 30 

blocks of the city. Damage was less severe to the south 

but extended to Los Angeles. The wide, physiographically complex offshore borderland may decrease tsunami 

effects in southern California. 

Both distant and locally generated tsunamis present a 

long-term hazard to southern California, but the risk is 

much lower than that from the more common, geologically controlled earthquake hazards. Distantly generated tsunamis of concern are those that may be 

produced along Pacific subduction margins. Large 

earthquakes in the Chile, Kamchatka, and Aleutian 

Trenches and the Gulf of Alaska have produced 

tsunamis recorded along the entire west coast of the 

United States. Mathematical simulation of tsunamis 

generated along the Pacific subduction margins suggests that California is most sensitive to tsunamis 

originating in the eastern Aleutian Trench and the Gulf 

of Alaska. Locally generated tsunamis also occur along 

California. The best documented affected the northern 

shoreline of the Santa Barbara Channel (1812) and the 

shoreline near Point Arguello (1927). Both were related 

to large earthquakes, and the tsunami from the Port 

Arguello event was recorded from San Francisco in central California to La Jolla near the Mexican border and 

was observed in the Hawaiian Islands. Seismically active faults that reach the sea floor may be capable of 

producing future tsu~amis in these areas, and similar 

faults may produce tsunamis off the Los Angeles area. 

Movement of earthquake-triggered submarine slides of 

the dimensions of existing slides found off the Los 

Angeles area does not appear to present a serious 

tsunami hazard. 

Despite the fact that there have been locally generated tsunamis along the California coast, predictions of 

tsunami size and frequency consider only those 

tsunamis that are distantly generated. The three predictive methods used are based on (1) an analysis of the 

California tsunami record, (2) a combination of mathe408 Earthquake Hazards in the Los Angeles Region 

matically simulated tsunamis and analysis of the longer 

term Pacific tsunami record, and (3) an identification of 

seismic gaps around the Pacific margin, where large 

tsunamigenic earthquakes can be expected, and an 

assessment of when such an earthquake might occur. 

The first method suggests that large tsunamis along the 

California coast have a recurrence interval of about 100 

yr. The second predicts the heights of the 100- and 

500-yr tsunamis along the coast. The third has identified 

a seismic gap along the Aleutian Trench (Shumagin gap), 

where geologic evidence suggests that a large tsunamigenic earthquake may soon occur. 

The tsunami hazard in the Los Angeles region is much 

less than that in many other places along the circumPacific border. Predictive models for distantly 

generated tsunamis indicate that wave heights of 2 m 

are exceeded on the average of once every 500 yr, except locally along Santa Monica Bay and San Pedro Bay 

and near Ventura, where wave heights of 3 m are exceeded on the average of once every 500 yr. A 

preliminary appraisal of the potential for locally 

generated tsunamis suggests that wave runup heights as 

great as 4 to 6 m could be caused by sea-floor faulting in 

the Santa Barbara Channel; wave runup heights no 

greater than 2 to 3 m are estimated for the dominantly 

strike-slip faults farther south. Earthquake-triggered 

sea-floor slides having the dimensions observed in the 

offshore region are unlikely to cause tsunamis. 

Warnings for distantly generated tsunamis are issued 

to California, Oregon, and Washington by the Alaska 

Tsunami Warning Center. No provision exists, however, 

for timely warning of tsunamis generated locally along 

the northern California, Oregon, or Washington coasts, 

where a large local tsunami generated by subductionrelated faulting is a possibility. Although tsunami warnings have been .limited to the estimated time of firstwave arrival, studies indicate that it is now feasible to 

include expectable wave heights and inundation areas. 

Such inclusions will greatly reduce the tsunami hazard. 

Reduction of the tsunami hazard is one of the aims of 

the Federal Flood Insurance Program, which makes lowcost insurance available to coastal communities that 

follow restrictive building standards set by the Federal 

Government for areas subject to tsunamis or stormwave flooding. The predicted 100-yr tsunami is used as a 

basis for noncritical structures such as dwellings and 

businesses, and the 500-yr tsunami is used as a basis for 

critical structures such as nuclear reactors, schools, 

and hospitals. Most southern California coastal communities have adopted building codes that meet or exceed requirements for participation in this program. 

Finally, public awareness of tsunami behavior can help 

the individual greatly reduce his personal risk. 
APPENDIX 4.-CALIFORNIA TSUNAMIS FROM 1812 TO 1975 

The information presented in this appendix has been compiled from a number of sources. Most entries are direct 

quotations taken from those sources. Many of the reference works cited in this quoted material have not been consulted directly by the author and thus do not appear in the list of references for this chapter. The sources used are 

designated by the following letter symbols: I, catalog of Pacific tsunamis (Iida and others, 1967); A, tsunamis recorded at San Diego (Agnew, 1979); W, tsunamis recorded at San Francisco (Wiegel, 1970); M, wave heights 

(Magoon, 1965); MA, Marine Advisors (1965). Because reported tsunami wave measurements are not uniform, the 

following terms are used to indicate the size of tsunami waves. Range or maximum rise or fall is the maximum peakto-trough value recorded on a tide gauge and can be significantly smaller than runup height. Height is the maximum 

departure from mean sea level as determined from the tide-gauge record or runup height. Amplitude is used where 

the definition of wave height is unclear. Wave arrival dates are given in local time. Earthquake magnitudes are as 

given by Iida and others (1967) or as recalculated by Abe (1979). 

Event Year 

1 1812 

2 1812 

3 1840 

4 1851 

5 1854 

6 1854 

7 1854 

8 1854 

Remarks 

Month unknown. Earthquakes possibly near San Francisco. Report based on second-hand 

communication that " .. .in 1812 the earthquakes were so severe as to cause tidal waves 

which covered the ground where the plaza now is." Iida and others (1967a) suggested possibly 

mislocated report of December 21 waves at Santa Barbara, but Wood (1916) cited these 

waves as evidence for displacement on a fault across San Francisco Bay rather than a more 

seaward fault. 

December 21. This tsunami has received considerable attention because it was locally 

generated by an earthquake of estimated M 7 to 7.5 within or near the Santa Barbara Channel 

and because the reported waves were so large. There is, however, reason to suspect that the 

waves were not as large as reported. According to Houston (1980, p. 5-6), " ... Wood and 

others (1966) reported that run-up heights of a tsunami generated by the 1812 Santa Barbara 

earthquake reached 50 ft at Gaviota, 3D-35 ft at Santa Barbara, and 15 ft or more at Ventura 

in southern California. Berkeley (cited by Wood and others (1966) as a basis for their reported 

run-up heights) has shown that the run-up for this possible tsunami was not nearly as large as 

reported. Professor G. D. Louderback (unpublished data) used an old report that said that the 

sea flowed 112-mile inland and plotted the information on a present day topographic map in the 

vicinity of Gaviota Canyon. This yielded a 5D-ft run-up level for the sea water. However, the 

study by Marine Advisors, Inc. (1965), discovered that the old report may have referred to an 

estuary (El Estero) near Santa Barbara that is approximately at sea level. In addition, they 

learned that there were no reported drownings even though Indian villages were on the beach 

at the time and many people were there. (The mission padres kept meticulous records of Indian births, deaths, and other statistics). Other f}vidence indicates that there may have been a 

run-up as great as·10 to 12 ft at Gaviota and a smaller run-up at Santa Barbara (Marine Advisors, Inc., 1965)." 

January 16-18. Earthquake and tsunami near Santa Cruz (I). Marine Advisors (1965) indicated 

report of tsunami is erroneous. 

November 13. Earthquake at San Francisco Bay. Motion of the waters of the bay. Perhaps a 

seiche, not a tsunami (1). 

July 24. No source is knm.yn, but the tidal observer at San Diego (Cassidy, 1862) noted that, on 

this date, "Water rose and fell nearly a foot in 10 minutes-currents set up also; harbor 

calm." (A) 

October 26. Earthquake at San Francisco and Benicia. Sea wave following shock or shocks. 

Observed at San Francisco(?) and Benicia(?) (1). 

November 1. Earthquake location unknown. At Angel Island in San Francisco Bay, water went 

"from calm sea with no wind; water rose several feet with high waves, lasting half hour." 

Perhaps a distant tsunami (1). 

December 23. Japan, 34° N., 138° E.; M8 8.4. Range 0.1 m at San Diego (A) and 0.2 mat San 

Francisco (1). · 

Tsunami Potential 409 
Event Year 

9 1854 

10 1855 

11 1856 

12 1859 

13 1862 

14 1868 

15 1868 

16 1868 

17 1872 

18 1877 

19 1879 

20 1883 

21 1885 

22 1896 

23 1896 

Remarks 

December 24. Japan, 33.2° N., 135.6° E.; Ms 8.4. Great Ansei Nankaido tsunami. Considerable 

damage and many deaths in Japanese islands. Height 0.3 m at San Francisco and 0.3 at San 

Diego (I). 

July 10 or 11. Earthquake near Los Angeles. Point San Juan (San Juan Capistrano). Two 

unusually heavy sea waves after last of four shocks (I). Yerkes (this volume) located this earthquake onshore, along the Raymond fault. 

August 23. Japan, 42° N., 141 o E.; M 6.9. Recorded on the coast of California (A). Great damage 

and loss of life in Hokkaido and Sanriku (I). 

September 24. Earthquake location not firmly known. Tsunami location has been reported as 

San Francisco, but observation may be of the October 5 Chilean tsunami; water "receded 15 

feet and returned suddenly" or "left the bay for several seconds." Reports seem greatly exaggerated if at San Francisco. Maximum runup heights of 4.6 m at Half Moon Bay (1). 

May 27. Earthquake at San Diego caused a small tsunami in San Diego Bay. This event is the 

only locally generated tsunami that has affected San Diego. It was associated with an earthquake that caused the most intense shaking known in San Diego. The tide gauge was being 

repaired at the time, so there is no quantitative record of the event, but an eyewitness account 

by tidal observer Andrew Cassidy has been preserved. At the time of the earthquake, Cassidy 

was on the beach. He wrote that, "The water in the Bay did not appear to be much agitated 

notwithstanding the sea run-up on the beach between 3 and 4 feet, and immediately returned 

to its usual level." The value of 3 to 4 ft probably refers to the horizontal distance along the 

beach; the wave height would have been much less. It is possible that one of the earthfalls 

noted by Cassidy along the bank might have generated the wave (A). 

April 2. Hawaii, 19.3° N., 155.3° W. (Wood, 1914). Height 0.1 mat San Diego (A). Range 0.15 m 

at San Francisco (W). 

August 13. Chile, 18.5° S., 71 oW. Amplitude 0.8 mat San Diego (A). 

August 14. Near Arica, northern Chile. Ms 8.5. Height 0.3 m at San Diego. Montessus de 

Ballore (1907) referred to a report by Schmick (1879) of a 21-m runup at San Pedro. Gutenberg 

and Richter (1954) gave the reported height as 18 m but indicated that it was most probably a 

mistake. Known as the Great Peru earthquake and tsunami, reported to have caused 25,000 • 

deaths (I). Range 0.43 m at San Francisco (W). 

August 23. On this date, a tsunami was recorded at San Diego, San Francisco, and Astoria. 

Relative arrival times infer a source in the northwestern Pacific (A). 

May 9. Chile, 21.5° S., 71 o W.; Ms 8 to 8.5. Height 0.3 m at San Francisco. Great Chilean 

tsunami caused considerable damage to Chile, Peru, and Japan (I). Range 0.37 m at San Francisco (W). 

August 10. San Fernando earthquake. Tsunami reported to have affected Santa Monica, but 

no details available (I). 

August 27. Explosion of Krakatoa Island in the Sunda Strait. Waves caused widespread 

damage and loss of life in Indonesia. Waves felt in Japan, Australia, New Zealand, Hawaiian 

Islands, Alaska, and California (I). Range 0.1 m at San Francisco (W). 

November 19. Epicenter unknown. In San Francisco, a series of waves occurred (I). 

June 15. Sanriku, Japan, 39.6° N., 144.2° E.; Ms 7.6. Great Meiji Sanriku tsunami. Disastrous; 

caused 27,122 deaths and 9,247 injuries. 10,617 houses swept away, 2,456 damaged (I). Range 

0.15 m at San Francisco (W). 

December 17. In a catalogue of earthquakes on the Pacific coast, Holden (1898, p. L52-L53) 

cited the following description of high water at Santa Barbara: "A tidal wave, the largest in 

the history of Santa Barbara, washed over the boulevard at 8 o'clock this morning, carrying 

back with it a large section of that beautiful and expansive driveway. The boulevard was built 

some five years ago and bulkheaded so securely that it was thought to be impervious to the action of the waves but the bounding billows carried off a portion of asphaltum and solid 

masonry, heavy framework and iron in its receeding grasp nearly fifty feet square and eight 

feet deep. A large sand hill between the boulevard and ordinary high tide was carried com410 Earthquake Hazards in the Los Angeles Region 
Event Year 

24 

25 

26 

1902 

1906 

1906 

Remarks 

pletely out to sea." Although Holden presented this description with no c9mment, its inclusion 

in his catalogue indicates that he attributed it to an earthquake-generated tsunami or to a 

tsunami of unknown cause. Neither Holden's (1898) or Townley and Allen's (1939) catalogue of 

California earthquakes notes the occurrence of a local earthquake on this date. More recently, 

this same high-water event was noted by Iida and others (1967a), who reported it as an 

isolated tsunami not related to a distantly generated tsunami. An account of this same event in 

the December 17, 1896, edition of the Daily Independent (now the Santa Barbara News Press) 

indicated that the erosion was caused by an abnormally high tide: "The flood tide this morning 

was one of the highest ever known in this city, and the boulevard suffered considerable 

damage. Between seven and eight o'clock the water was at the highest point and the waves 

washed over the one hundred foot driveway, carrying seaweed to the farthest side and filling 

the car track with sand. At the Chapala Street crossing on the boulevard, the tide had 

unrestricted entry to the driveway. A hole about eight feet deep and extending across the base 

of the sulfur water fountain necessitated immediate repairs to prevent further damage, and a 

force of men filled the break with bags of sand as a temporary measure. The tide has not been 

so high for years; even the big washout last spring not being so extensive, the water then coming in under a heavy southeast wind. This time there was no wind for a week. The grassy sand 

hill between Chapala and State Street on the beach has been washed out, exposing the 

boulevard front nearly the entire distance. The tide will be unusually high for the rest of the 

week." 

February 2 or 26. El Salvador. Much damage to coast of El Salvador and Guatemala; 185 

deaths. Observed in San Diego, but no details available (I). 

January 31. Offthe coast of Ecuador, 1 oN., 81.5° W.; M 8.8. Recorded at San Diego (A). 

April 18. San Francisco on San Andreas fault. Ms 8.25. Sea dropped 0.1 m at Fort Point 

(southern end of Golden Gate Bridge) and returned to normal. Started a series of waves having 

an amplitude of 5 em (I). The Fort Point tide-gauge record was shown by Lawson and others 

(1908, p. 370), who ascribed the initial lowering (without an immediate rise) to a possible minor 

downward displacement of the sea floor west of the San Andreas fault on the floor of the Gulf 

of the Farallones and the delayed succeeding two or three waves (40. to 45-min periods and 

1-to 2-in amplitude) to east-west oscillations of San Francisco Bay. It is conceivable that the initial negative wave was caused by the lowering of a geologically young fault-bounded graben 

(2 to 3 km wide and 22 km long) that Cooper (1971) mapped along the western side of the San 

Andreas fault in the Gulf of the Farallones. Undoubtedly, there was movement on the San Andreas fault along the eastern boundary of the graben in 1906, but it is not known if it was 

acompanied by downward displacement of the graben. 

Lawson and others (1908, p. 371) cite.d evidence for high water that may have been caused by a 

local tsunami: "The only other report indicating that the level of the ocean was affected along 

the coast is by W. W. Fairbanks, of Point Arena, who says: 'I have endeavored to learn of any 

unusual action of water along the sea-coast, and can relate but one instance of anything approaching the character of a tidal wave. On the day of the shock I traveled by wheel and on 

foot from Albion to Point Arena, 25 miles. At the mouth of Navarro River, at 8 o'clock on the 

morning of the 18th, I learned from reliable sources that a section of about 10 acres of low, 

flat land about the mouth of this river was entirely submerged for some minutes immediately 

after the shock."' The San Andreas fault passes out to sea at Point Arena and parallels the 

coast for about 115 km until it comes ashore near Shelter Cove. For most of its offshore length, 

it is marked by a geologically young sea-floor offset (Curray and Nason, 1961; McCulloch and 

others, 1980). The sea-floor scarp faces west (maximum vertical offset 27 m) to near Noyo Submarine Canyon (latitude 39°33' N.) and then faces east (maximum vertical offset 9 m) until it 

passes into the shallow Tolo Bank area off Shelter Cove. Although there was no welldocumented tsunami along the coast from the 1906 earthquake and no account of a distantly 

recorded tsunami, a cautiously conservative worst-case model should probably assume the 

Tsunami Potential 411 
Event Year 

27 1906 

28 1917 

29 1917 

30 1918 

31 1919 

32 1922 

33 1923 

34 1923 

35 1923 

36 1925 

37 1927 

38 1928 

39 1930 

40 1931 

41 1933 

42 1933 

43 1938 

44 1938 

45 1944 

46 1946 

47 1946 

48 1952 

Remarks 

possibility of several meters of sea-floor displacement along the northern California offshore 

· San Andreas fault. 

August 17. Coastal Chile, 33° S., 72° W.; M 8.2. The Great Valparaiso earthquake. 0.7 to 0.8 m 

of uplift intermittent along 350 km of coast. Height 0.1 m at San Diego; observed at San Francisco (1). A second great earthquake (Ms 8.2) occurred on this date, 30 min earlier, in the 

Aleutians. 

May 2. Kermadec Islands, 29° S., 177° W.; Ms 8. Recorded on the west coast of the United 

States (A). 

June 25. Tonga, 15.5° S., 173° W.; Ms 8.3. Recorded on the west coast of the United States (A). 

September 8. South Kurile Islands, 45.5° N., 151.5° E.; Ms 8.25. Observed in San Francisco (1). 

April30. Tonga, 19° S., 172.5° W.; Ms 8.3. Recorded in California (A). 

November 10. Central Chile, 28.5° S., 70° W.; M 8.5. Height 0.2 mat San Diego (A) and 0.2 mat 

San Francisco (1). 

January 22. Cape Mendocino, 40.5° N., 124.5° W.; M 7.2. Range 0.03 to 0.06 m (MA). 

February 4. East coast of Kamchatka, 54° N., 161 o E.; M 8.3. Height 0.2 mat San Diego (A) and 

0.1 m at San Francisco (1). 

April 14. East coast of Kamchatka, 56.5° N., 162.5° E.; M 7.2 (Gutenberg and Richter, 1954). 

Height 0.1 mat San Diego (A) and 0.2 mat San Francisco (1). 

October 4. Epicenter and magnitude unknown. 0.34 m at Long Beach. Source unknown. 

Possibly of meteorological origin. Only tide-gauge records for this event exist (I). 

November 4. Off Point Arguello, Calif.; Ms 7.3 (Gawthrop, 1978a). Townley and Allen (1939, 

p. 251) reported "a small sea wave recorded on tide gages at San Diego and San Francisco, 

and observed at Surf and Port San Luis. At Surf the rise in water was 6 ft (1.8 m); at Port San 

Luis it was 5 ft (1.5 m)." Range 0.006 m at La Jolla (Byerly, 1930). Wave recorded in Hawaiian 

Islands (1). Well-documented, locally generated tsunami; probably generated by dip-slip fault 

displacement of sea floor. See discussion in text. 

June 16. Offshore southern Mexico, 16.25° N., 98° W.; M 8. Height 0.1 mat La Jolla and <0.1 m 

at San Francisco (1). 

August 31. Santa Monica Bay, 33.9° N., 118.6° W.; M 5.25. Amplitude 0.6 mat Santa Monica. 

Possibly landslide-triggered seiche (MA). 

October 4. Solomon Islands, 10.5° S., 161.75° E.; Ms 7.9. Recorded at Santa Barbara (1). 

March 2. East of Honshu, 39.2° N., 144.5° E.; M 8.4. Great Sanriku tsunami. Height 0.2 m at 

San Francisco, 0.1 m at Santa Monica, 0.2 m at Los Angeles, and < 0.1 m at La Jolla (A, 1). 

March 10. Long Beach, 33.6° N., 118.0° W.; M 6.25. Height 0.1 m at Long Beach. Uncertain 

records (1). 

May 19. Strait of Macassar, 1 o S., 120° E.; M 7.6. Height < 0.1 mat Santa Monica (1). 

November 10. Shumagin Island, Alaskan Peninsula, 55.5° N., 158° W.; M 8.2. Observed in Santa Monica (1). 

December 7. Near Honshu, 33.7° N., 136° E.; M 8.1. Height 0.1 mat San Diego (A) and 0.1 mat 

Terminal Island (1). 

Aprill. Southern Alaska, 52.75° N., 163.5° W.; M 7.4. Range 0.43 mat La Jolla and 0.37 mat 

San Diego (A). Heights of 0.9 m at Crescent City, 0.3 m at San Francisco, 3.5 m at Half Moon 

Bay, 0.3 mat Alameda, 0.1 mat San Mateo, 3.5 mat Santa Cruz, 1.2 mat Avila, 0.7 mat San 

Luis Obispo, 0.8 m at Port Hueneme, 0.4 m at Los Angeles, 0.3 m at La Jolla, and 0.2 m at San 

Diego (1). In light of the small heights reported for most stations, the 3.5-m values at Santa Cruz 

and Half Moon Bay are surprising; however, the Santa Cruz Sentinel reported that a 15-ft 

wave occurred at Half Moon Bay and that a man was killed when he was washed out to sea 

from Cowles Beach at Santa Cruz. 

December 21. Nankaido, Japan, 33° N., 135.6° E.; M 8.1. Height 0.3 mat Crescent City and 0.1 

m at San Francisco (1). 

March 4. Hokkaido, Japan, 42.5° N., 143° E.; M 8.1. Range 0.02 mat La Jolla (A). Height 0.2 m 

at Crescent City, 0.6 m at San Francisco, and 0.8 m at Los Angeles (1). 

412 Earthquake Hazards in the Los Angeles Region 
Event Year 

49 1952 

50 1956 

51 1957 

52 1958 

53 1960 

54 1963 

55 1964 

56 1966 

57 1968 

58 1975 

Remarks 

November 5. Off east coast of Kamchatka, 52.7° N., 159.5° E.; M 9.0. Range 0.24 mat La Jolla 

and 0.7 m at San Diego (A). Height 1.1-m at Crescent City, 0.6 m at San Francisco, 1.0 m at 

Avila, 0.7 mat Port Hueneme, 0.7 mat Los Angeles, and 0.4 mat San Diego (I). 

March 30. Kamchatka, 55° N., 160.9° E. Height 0.1 mat Avila (I). 

March 9. Rat Islands, 51.3° N., 175.8° W.; M 9.1. Range 0.6 m at La Jolla and 0.45 m at San 

Diego (A). Height 0.7 mat Crescent City, 1.7 mat Bodega Harbor, 0.2 mat San Francisco, 0.6 m 

at Avila, 0.3 mat Los Angeles, 0.5 mat Anaheim Bay, 0.3 mat La Jolla, and 0.2 mat San Diego 

(I). 

November 7. South Kurile Islands, 44.5° N., 148.9° E.; M 8.3. Height 0.1 mat Port Hueneme (I). 

Range 0.9 m at San Francisco (W). 

May 22. Coast of central Chile, 39.5° S., 74.5° W.; M 9.5. Range 2.7 + mat Santa Monica and 

1.52 m at Los Angeles (S); 1 m at La Jolla and 1.5 m at San Diego (A). Height 3.7 m at Crescent 

City, 0.5 mat San Francisco, 1.5 mat Port Hueneme, and 0.7 mat San Diego (I). 

October 12. South Kurile Islands, 44.8° N., 149.5° E.; M 8.5. Height 0.5 mat Crescent City (I). 

March 27. Southern Alaska, 61 oN., 147.8° W.; M 9.2. Range 0.7 mat La Jolla and 1.1 mat San 

Diego (A). Height 6.3 m at Crescent City, 1.3 m at San Francisco, 0.6 m at Los Angeles, and 0.6 

m at La Jolla (I). Crest to trough of largest recorded wave 2.3 m at San Francisco, 1.65 m at 

Alameda, 3.17 + m at Avila, 1.80+ m at Rincon Island, 2.0 m at Santa Monica, 1.0 m at Los 

Angeles, 0.85 mat Alamitos Bay, 0.55 mat Newport Bay, 0.67 mat La Jolla, and 1.13 mat San 

Diego (S). Maximum runup height above mean-lower-low water 3.8 m at Humboldt Bay, 3.8 m 

at Fort Bragg, 3.7 m at Point Arena, 2.5 m at Drakes Bay, 2.9 m at Half Moon Bay, 3.8 m at Santa Cruz, 4.3 mat Capitola, 2.1 m at Moss Landing, and 2.3 mat Monterey (M). 

October 17. Peru, 10.7° S., 78.7° W.; M 8.1. Height 0.1 mat Crescent City and <0.1 mat San 

Diego (I). 

May 15. East of Honshu, 29.9° N., 129.4° E.; M 8.2. Amplitude 0.1 mat La Jolla (A). 

November 29. Hawaii, 19.3° N., 155° W.; M5 7.1. Amplitude 0.3 m at La Jolla, 0.12 mat San 

Diego, and 0.37 mat Imperial Beach (A). 

Tsunami Potential 413 
7 

<7 

<7 

Applications 

8 

<7 

For a Magnitude 8.3 Earthquake on the Son Andreas Fault in 

Southern California 

SEISMIC INTENSITY DISTRIBUTION 

Cotnp1led by 

JamH F. Do¥it, John H Btnnell, Gltnn Borchardt, 

J11dy W Colt, JOfMS E. Kol'llt, Solem J Rlct ond Niehotl A. Sil¥0 

1982 

EXPLANATION 

wi:J• 

Ross,·Fort~llnl•ns,ty Scot• 

<7 • Noslgmlicontdomogtl 

7 ·Strong Shod. Ovttrlllrowofmovobllt objtlcls; 

toll of p/oslttr; ringing of cllurch bttJ/s; 

gt~ntlrol ponic, wilfloul domogt~ to buildmgs. 

8- V•ry Strong Shock. Fall of ch1mnt1ys; crocks 

m tht1 walls of Dulldmgs 

9- E¥1remttly Strong Shock Por/10/ or to/of 

dt~slrfJCIIon of som• bu1/d"'gs. 

s 

GROUND FAILURE 

Surf(}Cfl Fwll R11plurt1 

lor ScMorio Eorthquoktt. 

Ar.os of high gro•nd wot•r (</Om) wflll 

poltlnliol for ground failure, including 

li(!Utlfaction and stlllltlmtlnl. 

~ 

~ 

High Palttntiol 

Modttraltl or 

1./nknown Poten1101 

7 
PREDICTED GEOLOGIC AND SEISMOLOGIC EFFECTS OF 

A POSTULATED MAGNITUDE 6.5 EARTHQUAKE 

ALONG THE NORTHERN PART OF THE 

NEWPORT-INGLEWOOD ZONE 

By J. I. Ziony, J. F. Evernden, T. E. Fumal, E. L. Harp, S. H. Hartzell, 

W. B. Joyner, D. K. Keefer, P. A. Spudich, J. C. Tinsley, R. F. Yerkes, 

and T. L. Youd8 

INTRODUCTION 

The geologic and seismologic effects of a specified 

future earthquake in the Los Angeles region can be anticipated by applying the techniques of hazard evaluation described in the preceding chapters. Predictions of 

the distribution and severity of expected effects could 

be the basis for land use, engineering design, and 

emergency preparedness actions to reduce potential 

losses. The reliability of the forecasts, however, varies 

with the geologic information that is available, with the 

validity of methods used, and with the type of hazard 

that is addressed. 

This chapter is intended primarily to demonstrate 

some of the methods described in this volume rather 

than to predict the effects of a particular future earthquake. The Los Angeles basin and environs have been 

chosen for this demonstration because the area is the 

most densely populated part of the region and because it 

contains a wide range of geologic conditions that are 

reasonably well known in three dimensions. In this example, we consider the likely effects of surface faulting 

and related deformation, ground shaking, liquefaction, 

and landsliding that might be expected from a moderatesized earthquake on the northern part of the NewportInglewood zone. Although the term "prediction" 

commonly is used with respect to forecasting the time, 

location, and magnitude of an impending earthquake, 

the term as used in this chapter refers to estimating effects that would result if an earthquake of postulated 

size and location were to occur. We have no information 

8

Now at Department of Civil Engineering, 370 Clyde Building, Brigham Young University, 

Provo, UT 84602. 

that the occurrence of an earthquake such as that 

postulated is imminent. 

The effects predicted in this chapter should be considered only as approximations of what might occur. 

Many of the techniques applied here are still in their 

developmental stages, and their scientific validity has 

not been conclusively established. In particular, there 

are significant differences in scientific opinion concerning the relative influence of different geologic factors on 

levels of ground shaking. Furthermore, the results of 

some techniques are highly sensitive to the simplifying 

assumptions about the geologic conditions, and small 

changes in the assumed conditions commonly yield 

results that are markedly disparate. Readers also are 

cautioned that the maps and evaluations presented here 

should not be used for site-specific purposes because 

the geologic information varies in completeness across 

the demonstration area and because testing of subsurface materials usually is required to reach conclusions 

about a site. Finally, possible effects in the adjacent 

offshore area generally are neglected because there are 

no detailed data about the character of sea-floor 

sediments. 

GEOLOGY OF THE 

DEMONSTRATION AREA 

The demonstration area includes parts of the Los 

Angeles basin, the Santa Monica Mountains, the San 

Fernando Valley, the Verdugo Mountains, the San 

Gabriel Valley, and the Palos Verdes Hills (fig. 210). 

Crystalline basement rocks and Tertiary sedimentary 

rocks characterized by relatively high shear and compressive strengths are exposed in the upland areas, 

Effects of the Postulated Earthquake 415 
118' 30' 

Artificial f ill 

Holocene alluvium 

Pleistocene alluvium 

EXPLANATION 

Tertiary and pre- Tertiary bedrock 

---- Contact 

Late Quaternary fault, 

dotted where concealed 

<> 

I I I I I I I I 

• 

Projected trace of deep 

rupture associated with 

earthquake 

Predicted surface faulting 

Epicenter of postulated 

earthquake 
whereas weaker Quaternary sedimentary deposits 

underlie the lowland areas. The area straddles the 

northwest-trending Newport-Inglewood zone of deformation and such predominantly east-trending reverse 

faults as the Santa Monica, Hollywood, and Raymond 

faults, which form the southern boundary of the 

Transverse Ranges. The Newport-Inglewood zone, 

which extends southeastward from Beverly Hills, is expressed topographically by an aligned series of low hills 

that rise as much as 120 m above the adjacent plains; 

structurally, the zone at the surface is a series of discontinuous north- to northwest-striking faults, northwest- to 

west-trending folds, and numerous short subsidiary normal and reverse faults. The structural style of the 

Newport-Inglewood zone suggests right-lateral strikeslip faulting at depth (Harding, 1973; Barrows, 1974). 

The fault-plane solution for the main shock of the 1933 

Long Beach earthquake (Woodward-Clyde Consultants, 

1979) that probably occurred on an offshore element of 

the Newport-Inglewood zone is compatible with such 

motion. 

The configuration of the crystalline basement rock 

surface buried beneath the Los Angeles basin has been 

reasonably outlined by numerous wells drilled for 

petroleum and by analyses of gravity measurements 

(McCulloh, 1960; Yerkes and others, 1965, fig. 2). 

Southwest of the Newport-Inglewood zone, the basement 

rock surface generally is at depths of 1.5 to 4 km (except 

in the Palos Verdes Hills, where it locally is more than 

300 m above sea level) and slopes gently northeastward. 

Northeast of the Newport-Inglewood zone, the same surface is dominated by a large synclinal trough that extends southeastward beyond Santa Ana and is as deep 

as 10 km. The rocks between the crystalline basement 

and the ground surface chiefly are Tertiary and early 

and middle Pleistocene sedimentary rocks. 

The lowland areas are blanketed by late Quaternary 

deposits, whose distribution and character will strongly 

influence the ground-motion and ground-failure effects 

of any earthquake. Along and west of the NewportInglewood zone, these deposits include as much as 75 m 

of late Pleistocene marine and nonmarine terrace 

sediments; farther east, these deposits grade laterally 

into flood-plain deposits (gravel, sand, and silt) as much 

as 105 m thick. Holocene alluvial fan and flood-plain 

deposits form much of the surface of the southern San 

Fernando Valley and the western San Gabriel Valley 

and extend along the Los Angeles and San Gabriel 

..... FIGURE 210.-Generalized geologic map of demonstration area showing the epicenter of the postulated M 6.5 earthquake, the presumed 

trace of the associated fault rupture at depth along the NewportInglewood zone, and predicted locations of associated surface 

faulting. 

Rivers. Clayey and organic-rich Holocene marsh 

deposits adjoin and locally extend several kilometers inland from the mouths of the major streams that enter the 

ocean at Marina Del Rey, Wilmington, and Seal Beach; 

similar deposits also occur locally at the northern end of 

the Baldwin Hills. 

Ground water occurs at depths of 15 m or more in 

much of the demonstration area (Tinsley and others, this 

volume, figs. 134, 144). Extensive zones of shallow (less 

than 10 m deep) ground water underlie the flood plains 

and flood-control basins of the Los Angeles and San 

Gabriel Rivers, occur within the Ballona and Dominguez 

Gaps, and adjoin the marina and harbor areas along the 

coast, however. Scattered but areally significant occurrences of ground water at depths of less than 10 m, 

presumed to be perched; also are present near Beverly 

Hills, Hollywood, Southgate, and Downey and in a narrow belt just east of the Newport-Inglewood zone. The 

ground-water levels _fluctuate seasonally and in 

response to changes in management practices in the 

ground-water basins (for example, increased pumping 

or recharging of aquifers). 

THE POSTULATED EARTHQUAKE 

For the purpose of demonstration, we postulate an 

earthquake associated with right-lateral seismic slip at 

depth along the northernmost 30 km of the NewportInglewood zone. In California, breaks of this length commonly generate earthquakes of moment magnitude (M) 

6.5. Such slip is considered credible because the 

geometry of the exposed echelon faults and folds of the 

Newport-Inglewood zone is compatible with repeated 

strike-slip motion along a throughgoing fault or faults 

within the underlying basement rocks (Harding, 1973; 

Yeats, 1973; Barrows, 1974). 

The earthquake hypocenter is placed beneath the 

southeastern corner of the Dominguez Hills about 5 km 

south of Compton. The location and slip character of this 

event are shown in figures 210 and 211. Primary tectonic rupture having a pure right-lateral strike-slip motion is assumed to propagate northwestward for 30 km 

along a vertical fault at depths of between 3 and 13 km. 

The unidirectional rupture propagation of this hypothetical event is similar to that which may have occurred during the 1933 Long Beach earthquake (on the 

basis of its aftershock pattern) and would resemble the 

rupturing that occurred north of the epicenter of the 

1979 Imperial Valley earthquake, which, like the Long 

Beach earthquake, was a dominantly strike-slip event. 

Fault slip is postulated to average 70 em, reaching a 

maximum of 140 em about 10 km northwest of the hypocenter. The model permits ground warping and secondEffects of the Postulated Earthquake 417 
/ 

/ / 

/ 

BALDWIN 

HILLS 

DOMINGUEZ 

GAP 

HYPOCENTER 

' ' ' ' ' ' 

r 

Vl 

a: 

w 

1-

w 

::;; 

0 

--' 

"' 

FIGURE 211.-Schernatic model of faulting associated with the postulated earthquake. Fault rupture is assumed to start 10 krn 

below the southeastern margin of the Dominguez Hills and to spread northwestward for a distance of 30 krn along a 

throughgoing vertical fault presumed to underlie the Newport-Inglewood zone. Primary tectonic rupture having a right-lateral 

strike-slip sense of displacement occurs at depths between 13 and 3 krn; the average slip is 70 ern. Ground warping and 

secondary faulting having significant components of vertical offset are predicted to occur at and near the Earth's surface. 

ary faulting having significant components of vertical 

offset at and near the Earth's surface. 

A comparison (table 53) of the characteristics of the 

postulated event with those of the 1933 Long Beach 

earthquake, which occurred offshore near the southern 

part of the Newport-Inglewood zone, is useful. The 

418 Earthquake Hazards in the Los Angeles Region 

postulated event is slightly larger than the 1933 Long 

Beach earthquake and is similar in size to the 1971 San 

Fernando earthquake. The example earthquake thus is 

a moderate-sized event that could occur along any late 

Quaternary fault of adequate length in the region; it 

does not necessarily represent the largest earthquake 

that might occur along the Newport-Inglewood zone. 
TABLE 53.-Comparison of postulated earthquake with the 1933 Long Beach earthquake 

Earthquake 

Parameter Postulated 

Moment magnitude------------------------- 6.5 

Moment, in 1(}25 dyne-em--------------------- 6 

Location of epicenter: 

Latitude, 0 N. --------------------------- 33.85 

Longitude, 0 W. ------------------------- 118.22 

Depth of hypocenter, in km ------------------- 10 

Seismic rupture: 

Length, in km -------------------------- 30 

Width (vertical extent), in km --------------- 10 

Average slip, in m ----------------------- .7 

Sense of slip --------------------------- Right lateral 

'offshore. 

SURFACE FAULTING AND 

DEFORMATION 

By J. I. Ziony and R. F. Yerkes 

Right-lateral ·slip at depth associated with the 

postulated earthquake is expected to be manifest at and 

near the ground surface in secondary faulting and in 

warping and localized uplift. 

The historical record of earthquake-related deformation along the Newport-Inglewood zone is used, together 

with methods of evaluating surface-faulting potential 

described by Ziony and Yerkes (this volume), to estimate 

what deformation of the ground surface might occur. 

Although surface-fault rupture was not recognized at 

the time of the 1933 Long Beach earthquake, recent 

trenching investigations near Newport Beach (about 

20 km southeast of the demonstration area) have documented historical surface rupture that could have occurred during that event (Guptill and Heath, 1981). At a 

site on Newport Mesa, as much as 30 em of vertical 

separation of a post-1920 manmade fill has been observed across the northern branch of the Newport-

. Inglewood fault; stratigraphic differences in late 

Pleistocene river terrace deposits offset by the fault, 

together with the geometry of the shear zone, indicate a 

major component of strike-slip faulting. Because nearly 

the entire main-shock and aftershock zone of the 1933 

earthquake was offshore of this site, we believe that the 

surface rupture at Newport Mesa may represent slip 

1933 Long 

Beach 

6.2 

2-6 

33.62 

117.971 

10 

22-30 

15(?) 

0.31--{).46 

Right lateral 

References 

Hanks and Kanamori (1979) 

Toppozada and Parke (1982) 

Hanks and Kanamori (1979) 

Woodward-Clyde Consultants (1979) 

Toppozada and Parke (1982) 

Toppozada and Parke (1982) 

Woodward-Clyde Consultants (1979) 

Woodward-Clyde Consultants (1979) 

Evernden and others (1981) 

Woodward-Clyde Consultants (1979) 

Woodward-Clyde Consultants (1979) 

Woodward-Clyde Consultants (1979) 

along a secondary fault rather than displacement along 

the primary seismogenic rupture. 

Historical faulting also has occurred in the shallow 

subsurface near Gardena in association with two 

modest-sized earthquakes (ML 4.9 in 1941 and ML 4.5 in 

1944) centered in the Dominguez Hills area (Bravinder, 

1942; Martner, 1948). As offsets in the metal casings of 

producing oil wells have documented, several centimeters of slip occurred at depths as shallow as 1 km 

along minor south-dipping reverse faults along the 

western side of the Newport-Inglewood zone during 

each event. These offsets probably represent secondary 

faulting along faults that are suitably oriented to slip in 

response to north-south compression associated with 

primary strike slip at greater depths within the 

Newport-Inglewood zone. 

We predict surface faulting totaling as much as 16 km 

along the Avalon-Compton fault, the Potrero fault, and 

the west-dipping main strand of the Inglewood fault (fig. 

210). Each of these faults has experienced significant 

offset during late Quaternary time and, on the basis of 

physiographic expression, appears to have repeatedly 

offset the present land surface. The style of geologically 

recent displacements along these faults and their orientation (striking about north-south and dipping steeply 

westward) with respect to the trend of the NewportInglewood zone suggest that surface rupture along them 

will be normal-right oblique slip. On the basis of the slip 

parameters of the postulated earthquake (average slip 

70 em, maximum about 140 em approximately 10 km 

northwest of the hypocenter), we estimate that surface 

Effects of the Postulated Earthquake 419 
fault displacement could range from a few to a few tens 

of centimeters, depending on how the slip at depth is accommodated by deformation within the overlying 

sedimentary rocks. The geomorphic expression of these 

faults suggests that vertical components of offset may be 

as large as the horizontal component. The main zones of 

surface rupture along the faults will range in width from 

several centimeters to a few meters, but small shears 

and permanent ground distortion are likely to extend to 

distances as great as several tens of meters. 

Within the Baldwin Hills, minor faulting at the ground 

surface also may occur along the east-dipping western 

strand of the Inglewood fault and along some of the 

northeast-striking faults that intersect the main trace of 

the Inglewood fault. Ground cracking and normal-slip 

movements of a few millimeters or centimeters also may 

be triggered along the system of short north-northeaststriking faults in the northern Baldwin Hills that has 

periodically experienced subsidence-induced creep 

(Castle and Yerkes, 1976). 

One or more of the numerous east-trending reverse 

faults in the subsurface between the Rosecrans and 

Dominguez Hills probably will experience as much as a 

few centimeters of reverse slip in association with the 

postulated earthquake. Although such rupture is not 

likely to extend to the ground surface and pose a 

surface-faulting hazard, it could disrupt production 

from the oil and gas wells that penetrate these faults. 

Warping and uplift of the land surface probably will 

accompany the postulated earthquake. This distortion 

will be most pronounced adjacent to the zone of surface 

faulting and in the Rosecrans and Dominguez Hills, 

which coincide with large exposed anticlines. By 

analogy with the 1933 Long Beach earthquake, with 

which was associated a northwest-trending uplift of the 

land surface centered about 3 km east of the NewportInglewood zone opposite Seal Beach (Gilluly and Grant, 

1949), uplift and subsidence resulting in elevation 

changes locally of as much as a few tens of centimeters 

can be expected. It is difficult to predict the distribution 

of such elevation changes, but they are likely to be largest around the southern third of the postulated earthquake rupture zone. 

SEISMIC INTENSITIES 

By J. F. Evernden 

Seismic intensities are predicted for the postulated 

earthquake by using the method discussed by Evernden 

and Thomson (this volume). The computer-based technique incorporates a numerical model of the earthquake 

420 Earthquake Hazards in the los Angeles Region 

source, a mathematical expression for the rate of attenuation in the crust of the region, an empirical correlation of geologic ground conditions with differences 

in expected intensity, and a digitized map of geologic 

ground conditions for the area studied. 

To carry out the calculations, the following assumptions are made: 

1. The regional attenuation factor (k) is 1% (Evernden 

and others, 1981). 

2. Although the event is postulated as a unidirectional 

rupture propagating northwestward from an 

epicenter at 33°51' N., 118°13' W., the 

predicted seismic intensities are insensitive to 

propagation direction. Thus, the earthquake is 

modeled as a rupture spreading from the center 

(33°58' N., 118°18' W.) toward both ends at 

shear-wave velocity. 

3. The parameter related to depth of focus [C) is set at 

25, the value appropriate for all strike-slip 

faults in California. 

We categorized the rock and sediment units of the Los 

Angeles region according to the geologic groundcondition units of Evernden and Thomson [this volume, 

table 22). Geologic ground-condition maps were 

prepared by digitizing the 1:250,000-scale Los Angeles, 

Long Beach, San Bernardino, and Santa Ana sheets of 

the Geologic Atlas of California (California Division of 

Mines and Geology [1958-1969]) on a %-minx 1!2-min 

grid. The relative intensity values that we assign to the 

different geologic ground-condition units are from 

Evernden and Thomson (this volume, table 23); these 

values are based on empirically determined relations 

for groups of geologic units of comparable age and 

lithology in the San Francisco Bay region and have not 

yet been verified directly through detailed comparisons 

of ground-motion recordings on geologic units of the Los 

Angeles region. As presently applied in southern 

California, our method for assessing shaking potential 

assumes that the physical characteristics of all Quaternary alluvium are similar, unlike procedures used in the 

San Francisco Bay region and unlike another technique 

discussed in this chapter that considers variations in the 

shear-wave velocities of the alluvial deposits (Fumal and 

Joyner, p. 423). Alluvium, however, is differentiated as 

saturated or unsaturated depending on whether the 

water table is known to be shallower or deeper than 

10 m (on the basis of modern data from Tinsley and 

others (this volume)). Figure 212 is a map of the demonFIGURE 212.-Geologic ground conditions and relative intensity in- ...... 

crements used in computing predicted intensities in the demonstration area. Units correspond to those presented by Evernden and 

Thomson (this volume, tables 22, 23). 
00 ' 

45' 

VIGA 

I 

I 

I 

Man hat :an Beacr , I 

I 

I 

He :mosa Beacll 

118°30' 

0 

APPROXIMATE ·sCALE 

5 

10 

118°15' 

10 MILES 

15 KILOMETERS 

1 1 1 I 
0 

APPROXIMATE ·sCALE 

5 

10 

10 MILES 

15 KILOMETERS 
stration area showing geologic ground conditions and 

corresponding relative intensity increments used in 

calculating the seismic intensities. 

Calculations of expected intensity are sensitive to the 

depth to the water table. Shaking intensities on alluvium 

where the water table is deeper than 10 m will be one intensity unit lower than those on alluvium where the 

water table is near the ground surface. The predicted 

values for alluviated areas thus are subject to modifications if better estimates of the present ground-water 

distribution become available or if ground-water levels 

change by several meters. Levels may vary because of 

seasonal fluctuations in rainfall or because of changes 

in management of the ground-water basins (either increased pumping or recharging of aquifers). 

The predicted intensities for the postulated M 6.5 

earthquake are presented in figures 213 and 214. These 

maps show that ground shaking of Modified Mercalli intensity VI or greater will affect approximately 6,400 km2 

of the onshore region and that most of the alluviated 

parts of the Los Angeles basin and the San Fernando 

Valley will experience shaking of intensity VII (see inside . back cover for an abridged description of this 

scale). Sm~ll areas of intensity VIII are predicted for the 

southern San Fernando Valley, near Marina Del Rey, in 

the Long Beach area, and for other scattered localities 

in the Los Angeles basin assumed to have saturated 

alluvium. Intensities of VII can be expected at distances 

of as much as 40 km from the modeled rupture where 

shallow ground water may be present (for example, 

near Pomona). 

Intensities of VI will occur in the Santa Monica Mountains, the Palos Verdes Hills, and other upland areas of 

Tertiary or older bedrock that ring the Los Angeles 

basin. Shaking of this severity is predicted as far a;; 

80 km from the modeled rupture (for example, near 

Oxnard and near San Bernardino) in areas underlain by 

saturated alluvium. 

..... FIGURE 213.-Predicted Modified Mercalli intensities for the 

postulated M 6.5 earthquake in the demonstration area onshore. 

The heavy line is the trace of the postulated seismic source. Singlestroke characters indicate intensities in the lower half of an intensity band; hollow characters indicate intensities in the upper half. 

For example, intensities 5.50 to 5.99 are indicated by the singlestroke character 6; intensities 6.00 to 6.50 are indicated by a 

hollow 6. Onshore areas of intensity V or less are shown without 

symbol. 

HORIZONTAL ACCELERATION, 

VELOCITY, AND RESPONSE 

SPECTRAL VALUES 

By T. E. Fumal and W. B. Joyner 

We calculated predicted values of peak horizontal acceleration, velocity, and response spectra for the 

postulated earthquake by using the method described by 

Joyner and Fumal (this volume). This method relies on 

equations linking ground-motion parameters to earthquake magnitude, source distance, and site conditions. 

The magnitude and location of the postulated earthquake are specified; thus, it was necessary only to 

compile data on site conditions to apply the predictive 

equations. Because the three-dimensional geology of the 

Los Angeles basin is relatively well known, we used 

shear-wave velocity rather than a rock-versus-soil classification to predict the effects of site conditions on 

ground motion. 

Figure 215 shows, for the demonstration area, the 

geographic variation in the mean shear-wave velocity 

calculated over a depth equal to one-quarter wavelength of a 1-s wave. The method used to make this map 

is, in general, the same as that described by Fumal and 

Tinsley (this volume) for the upper Santa Ana River 

basin but varies in detail because the subsurface 

distribution of Quaternary deposits is better known in 

the Los Angeles basin. Published reports describing the 

ground-water geology of the Los Angeles basin, the San 

Gabriel Valley, and the San Fernando Valley (California 

Department of Water Resources, 1961, 1966; California 

Water Rights Board, 1962) were the main sources of 

geologic data used to prepare the map of mean shearwave velocity. 

The report on the Los Angeles basin (California 

Department of Water Resources, 1961), which covers 

most of the demonstration area, includes a map showing 

the distribution of exposed geologic units, 14 cross sections shoWing the distribution of subsurface Quaternary 

sedimentary units to depths of 100 to 400 m, maps showing the thickness and the elevation of the bases of 10 major aquifers, and descriptions of geologic units present 

in the demonstration area. We used these descriptions, 

along with table 18 of Fumal and Tinsley (this volume), to 

assign mean shear-wave velocities to each Quaternary 

unit on the basis of age and texture (table 54). 

Effects of the Postulated Earthquake 423 
Mtn 

7 

~\ ( ;! r '\ ( ..,;~;• (). ,-

10 20 MILES 

0 10 20 KILOMETERS 

APPROXIMATE SCALE 

FIGURE 214.-Predicted Modified Mercalli intensities for the postulated M 6.5 earthquake for the entire onshore Los Angeles region. The hachured 

line delineates the demonstration area. The heavy line is the trace of the postulated seismic source. Single-stroke characters indicate intensities in the lower half of an intensity band; hollow characters indicate intensities in the upper half. For example, intensities 5.50 to 5.99 are in-
118.00' 

HUNTINGTON 

., Wilsona Gardens )6Z• 

' " 

, 

dicated by the single-stroke character 6; intensities 6.00 to 6.50 are indicated by a hollow 6. Onshore areas of intensity V or less are shown 

without symbol. 
118°30' 118°15' 

COMPUTED MEAN 

SHEAR-WAVE 

VELOCITY, 

IN METERS 

PER SECOND 

II 240 

II 265 

II 290 

II 315 

350 

34°00' 375 

~ 400 

, 

~ J 

~ 420 ' 

0 -· II 550 

·-:._ E' s( 9 J 

I II ~- 775 ( 

/ 

MAI'.HATTAN D _. 980 -

I'' 

D 1270 

Ht::.rp· So. BE: j D 1610 

RfDONDO BEA 

It 

Pa ,>< \ 

'' t Seal 

0 2 4 6 MILES ~I 

0 2 4 6 8 KILOMETERS .._ fl \ I I 

FIGURE 215.-Mean shear-wave velocity in the demonstration area calculated over a depth corresponding to one-quarter wavelength of a 1-s shear wave. Boundaries 

shown between velocity zones are gradational. 

426 Earthquake Hazards in the Los Angeles Region 
TABLE 54.-Mean shear-wave velocities assigned to exposed and subsurface Quaternary geologic 

units in the Los Angeles basin on the basis of age and sediment texture 

Geologic unit' 

Dominant 

sediment texture 

Assigned shear-wave 

velocity, 

in mls 

Holocene 

Dune sand and semiperched --------------- Medium 

aquifer. 

230 

Bellflower aquiclude--------------------- Fine 210 

Gaspur-Ballona aquifer ------------------- Medium and coarse 250 

Upper and middle(?) Pleistocene 

Older dune sand and semiperched ---------- Medium 

aquifer. 

430 

Lakewood Formation: 

Bellflower aquiclude ----------------- Fine 310 

420 

310 

430 

445 

Exposition-Artesia aquifers ------------Fine, medium, and coarse 

Aquiclude ---------------------- Fine 

Gage aquifer ------------------------ Medium 

Gardena aquifer --------------------- Medium and coarse 

Middle Pleistocene 

San Pedro Formation: 

Aquifers (Silverado, ------------------ Medium and coarse 

Hollydale, Jefferson, Lynwood, 

445 

and Sunnyside). 

Aquicludes ------------------------- Fine 310 

'california Department of Water Resources (1961). 

These velocities, assigned to the different geologic 

units, were then used to calculate mean shear-wave 

velocity over a depth equal to one-quarter wavelength of 

a 1-s wave at more than 400 points along cross sections 

in the Los Angeles basin and the San Gabriel and San 

Fernando Valleys. We calculated mean velocities at an 

additional 350 points between the cross-section lines by 

using the maps of the thickness and the elevation of the 

bases of major aquifers. At each point chosen, the thickness of each subsurface geologic unit was divided by the 

mean shear-wave velocity assigned to that unit to give a 

traveltime through that layer. These layer traveltimes 

were summed downward through the profile until a total 

traveltime of 0.25 s was reached. The total thickness of 

sediment involved was divided by 0.25 s to obtain a 

mean shear-wave velocity for each site. As many as 11 

superposed layers had to be considered in these velocity 

calculations at a given site. 

The geologic units vary continuously in thickness from 

site to site, resulting in a very complex threedimensional distribution of sedimentary deposits. Mean 

shear-wave velocity at a site, however, is most strongly 

dependent on the thickness of Holocene deposits and the 

proportion of fine- to medium- and coarse-grained sediment within the Pleistocene deposits; consequently, 

shear-wave velocity is relatively constant over large 

areas. For the parts of the demonstration area underlain by thick Quaternary deposits, we have delineated 

seven shear-wave velocity zones (first seven zones in fig. 

215). Although the velocities assigned to these zones differ significantly (more than about 7 percent) from one 

another, mean shear-wave velocities calculated for sites 

within each zone differ by no more than 10 m/s from the 

assigned velocity. Because thicknesses of the geologic 

units vary continuously, the boundaries between each of 

these seven zones are gradational. 

We assigned mean shear-wave velocities to the bedrock units exposed in the demonstration area (table 55) 

by using both the classification of engineering-geologic 

units for the Los Angeles basin (Wentworth and others, 

1970) and velocities measured in bedrock materials in 

the Los Angeles and San Francisco Bay regions. Each 

bedrock unit was assumed to be at least as thick as the 

one-quarter wavelength depth (100-400 m), so that the 

mean shear-wave velocity over this depth interval was 

taken to be equal to the mean shear-wave velocity 

assigned to that geologic unit in table 55. We differentiated the bedrock units exposed in the demonstration 

Effects of the Postulated Earthquake 427 
TABLE 55.-Mean shear-wave velocities assigned to bedrock units 

exposed in the Santa Monica and Verdugo Mountains and the Palos 

Verdes Hills 

Assigned mean shearwave velocity, 

Geologic unit in m/s 

Pico, Fernando, Modelo, Upper------------- 420 

Topanga of Durrell (1954), Monterey, 

and Puente Formations. 

Topanga Formation in area ----------------- 775 

southwest of Pasadena. 

Middle Miocene volcanic rocks ------------- 980 

and Lower Topanga Formation of 

Durrell (1954). 

Undivided Martinez and Chico-------------- 1,270 

Formations and Chico Formation. 

Granitic rocks, Catalina Schist, and ---------- 1,610 

Santa Monica Slate. 

area into five groups having distinct mean shear-wave 

velocities. We delineated an additional shear-wave 

velocity unit in the relatively small sections of the 

demonstration area where thin Quaternary sediments 

overlie bedrock having a strongly contrasting mean 

shear-wave velocity. 

Several features of the mean shear-wave velocity map 

shown in figure 215 should be noted: 

1. The lowest velocities occur in the Y -shaped area in 

the southeastern quarter of the demonstration 

area underlain by Holocene deposits. These 

deposits are up to 50 m thick, much thicker than 

equivalent units in the upper Santa Ana River 

basin demonstration area (Fumal and Tinsley, 

this volume}. 

2. Mean velocities at sites underlain by predominantly 

medium- and coarse-grained Pleistocene 

sediments· are about 1.7 times greater than 

velocities at sites underlain by the thickest 

Holocene deposits. 

3. The greatest contrast in mean shear-wave velocity 

occurs in the northern part of the demonstration 

area, where unconsolidated sediments and soft 

sedimentary rocks abut hard crystalline rocks, 

whose mean shear-wave velocities are about 

four times greater. 

Using figure 215 and applying the methods given by 

Joyner and Fumal (this volume} to the postulated earthquake, we made predictive maps showing peak horizontal acceleration, velocity, and response spectra at 0.2 

and 1.0 s for 5-percent damping (figs. 216A, 216B, 216C, 

216D}. 

For peak acceleration, the site-condition term in the 

predictive equation is not significant. Thus, the contours 

428 Earthquake Hazards in the Los Angeles Region 

shown in figure 216A are not affected by local geology 

and are smooth curves. We predict that the highest value of peak horizontal acceleration attained at the fault 

trace will be about 0.42 g. This value decreases by onehalf about 13 km from the fault trace. Predicted values 

of pseudoacceleration response at 0.2 s (fig. 216C) are 

slightly affected by the site-condition term, so that a 

twofold rock-versus-soil classification is used in the 

predictive equation. We predict that the highest value of 

pseudoacceleration response at 0.2 s attained at the 

fault trace will be near 1.16 g. This value will decrease 

by one-half about 14 km from the fault trace. 

In contrast, the site-condition terms in the predictive 

equations for both peak velocity and pseudovelocity 

response at 1.0 s are statistically significant. Thus, the 

contours of predicted values are markedly irregular. As 

we noted previously, the range of mean shear-wave 

velocity is not large (24D-400 m/s) within most of the 

demonstration area underlain by Quaternary deposits. 

In figures 216B and 216D, the variations in distance 

from the fault trace at which a given level of ground motion is expected to occur are generally less than 2 km 

over this range of mean shear-wave velocity. We predict 

that the highest values of peak velocity at the fault trace 

will reach 90 to 100 cm/s, depending on site mean shearwave velocity. These values will decrease by one-half 

about 7 km from the fault trace. For pseudovelocity 

response at 1.0 s, we predict that the highest values attained at the fault trace will be 160 to 180 cm/s, depending on site mean shear-wave velocity. These values will 

decrease by one-half about 8 km from the fault trace. 

The most noticeable effects of local geology on the 

predicted ground-motion values occur in the northern 

part of the demonstration area, where the shear-wave 

velocity contrasts are greatest between the soft 

sedimentary deposits and the hard crystalline rocks of 

the Santa Monica and Verdugo Mountains. Values of 

pseudovelocity response at 1.0 s, for example, are predicted to be greater than 50 cm/s in the southernmost 

San Fernando Valley but less than 25 cm/s in the Santa 

Monica Mountains at an equal distance from the fault 

trace. 

FIGURE 216.-Geographic variation in predicted ground-motion values ...... 

(for the random horizontal component) in the demonstration area 

for the postulated earthquake. The heavy line is the trace of the 

postulated seismic source. A, Peak acceleration (in percent of 

gravity). The maximum value reached at the fault trace is about 

0.42 g. B, Peak velocity (in centimeters per second). Maximum 

values reached at the fault trace range from about 90 to 100 cm/s, 

depending on site condition. C, Pseudoacceleration response (percent of gravity) at 0.2 s and 5-percent damping. The maximum 

value reached at the fault trace is about 1.16 g. D, Pseudovelocity 

response (in centimeters per second) at 1.0 s and 5-percent damping. Maximum values reached at the fault trace range from about 

160 to 180 cm/s, depending on site condition. 
BAY 

A 

• 

BAY 

c 

LOS ANGELES 

0 

/ 

L ANGELES 

BAY 

BAY 

LOS ANGELES 

• 

-?. 

.LOS ANGELES~~ 

0 2 4 8 10 MILES I I I I I I I 

0 2 4 6 8 10 KILOMETERS 

Effects of the Postulated Earthquake 429 
Comparison of figures 216A, 216B, 216C, and 216D 

shows that predicted values of peak velocity and 

pseudovelocity response at 1.0 s attenuate more rapidly 

in the region near the fault than values of peak acceleration and pseudoacceleration response at 0.2 s do. This 

characteristic of the predictive equations is required by 

the existing strong-motion data. 

Although the postulated earthquake would be generated by a unilateral rupture propagating from southeast 

to northwest, our methods do not take into account the 

direction of rupture propagation. Figures 216A through 

216D, therefore, do not show directivity effects on 

ground-motion values. The map patterns thus are the 

same as they would be if the propagation had been in the 

other direction or if the rupture had been bilateral. The 

following section on predicted ground-motion timehistories considers unidirectional rupturing and thus 

shows results that reflect directivity. 

TIME-HISTORIES OF GROUND 

MOTION 

By S. H. Hartzell and P. A. Spudich 

Time-histories of ground motion from the postulated 

earthquake can be predicted by assuming how each 

point on the slipping fault might be displaced, determining the ground motions caused by each point, and then 

summing the ground-motion contributions from each 

point to obtain the total motion at a given distant site. 

The results depend greatly on assumptions concerning 

(1) the velocity structure of the Earth's crust in the 

demonstration area and (2) the detailed character of the 

expected rupture propagation. Methods of simulating 

ground-motion time-histories commonly use Green's 

functions, mathematical expressions that estimate 

ground shaking caused by a single point source for an 

appropriate crustal model. These techniques, described 

by Spudich and Hartzell (this volume), are used in this 

section to simulate ground velocity from the hypothetical 

earthquake in the frequency range of 0.05 to 2.0 Hz for 

10 sites within the Los Angeles basin. The particular 

sites are selected to illustrate variations in predicted 

ground motion at different positions around the postulated rupture zone of the earthquake. The suite of 

ground motions that we predict is only one of many possible suites that could be caused by a moderate-sized 

earthquake on the Newport-Inglewood zone and probably represents neither the largest nor the smallest 

possible motions for a M 6.5 earthquake. 

To simplify calculation of the required point shear 

dislocation responses (or Green's functions), several 

430 Earthquake Hazards in the Los Angeles Region 

l 

5 (/) 

~ cc 

UJ 

1-

UJ 

~ 

0 

...J 

:;2 

~ 

I. 

1-

0.. 10 UJ 

Cl 

EXPLANATION 

--East of zone 

---- West of zone 

15 

FIGURE 217.-Velocity structure assumed for the Los Angeles basin for 

compressional (P) and shear (S) waves. A different structure is 

used on the eastern and western sides of the Newport-Inglewood 

zone to account for differences in depths to basement rocks. 

Calculations use data on rock density and depth to basement from 

McCulloh (1960) and Yerkes and others (1965). P-wave velocity 

structure is based on Teng and others (1973) and Hill and others 

(1977). S-wave velocity structure is calculated from P-wave velocity structure by assuming a Vp/Vs ratio of VP = V, vJ below 6.5 km 

and varying the ratio smoothly to VP = 1.9 V, at the surface. 

assumptions are made about the Earth's seismic velocity, density, and attenuation structure in the demonstration area. The Earth structure is laterally homogeneous; 

that is, the physical properties vary only with depth. 

This assumption is reasonable, because the fault zone 

and the points at which ground motions are calculated 

in this study all lie within the Los Angeles basin. A 

different laterally homogeneous structure, used on opposite sides of the Newport-Inglewood zone in the manner shown in figure 217, however, reflects considerably 

greater thickness of sedimentary rocks on the eastern 

side of that zone. For sites on the eastern side of the 

zone, Green's functions for the east-side structure are 

used to calculate ground motions. When ground motion 

for sites on the western side of the zone is computed, 

Green's functions for the west-side structure are used. 

A further assumption is that the shear-wave velocity at 

the surface of the Los Angeles basin is about 500 m/s, 
SE 

1112 ~ ~~~~~ 26 20 18 16 14 12 10 8 6 4 ~ 0 

DISTANCE ALONG FAULT, IN KILOMETERS 

FIGURE 218.-Assumed distribution of slip on a hypothetical rupture surface between depths of 3 and 13 km. Contours (in centimeters) represent 

amounts of final slip. The hypocenter is indicated by an asterisk. Nearby sites at which ground velocity is calculated are indicated by CTC 

(Century City), HWP (Hollywood Park), and CPA (Compton Airport). 

which is higher than the velocities estimated for late 

Quaternary sediments by Fumal and Joyner (table 54). 

This assumption enabled us to reduce the computation 

time of the calculations. Had a lower near-surface 

velocity been chosen (for example, 375 m/s), the ground 

motions that we calculated might have been 10 to 20 

percent larger. Finally, the Earth structure is assumed 

to have a perfectly elastic response and no attenuation 

of seismic energy. This approximation is probably acceptable at the low frequencies being calculated. 

Green's functions were calculated for the velocity 

structures given in figure 217 by using the discrete 

wavenumber-finite-element method (Olson and others, 

1984). The depth range over which Green's functions 

are needed is controlled by the top and bottom depths of 

the postulated rupture surface. The required epicentral 

distances at which Green's functions are needed are 

controlled by the distances from the postulated rupture 

surface to the sites where ground motion is to be computed. In this study, additional Green's functions are 

obtained by the interpolation method of Hartzell and 

Heimberger (1982). This interpolation is an approximation and assumes that the Green's functions are known 

at a spatial interval small enough that the variation in 

the waveforms between adjacent Green's functions is 

not great. 

The assumed model of slip across the rupture surface 

is shown in figure 218. The furthest extent of the 

postulated rupture fills a rectangular region from a 

depth of 3 km down to a depth of 13 km. The amplitudes 

of the offsets in figure 218 are chosen to be compatible 

with a total moment of 6 x 1025 dyne-em, corresponding 

to a moment magnitude of about 6.5. Tlie distribution of 

slip has been arbitrarily selected, but some of its 

features are similar to those inferred for the 1979 

Imperial Valley earthquake (Olson and Apsel, 1982; 

Hartzell and Heaton, 1983; Archuleta, 1984). Although 

the slip distribution used here is reasonable for the postulated earthquake, we stress that it is only one of an 

infinite number of possible configurations. 

For computational purposes, the modeled rupture surface is divided into a regular gridwork of point shear 

dislocation sources spaced 0.37 km apart both horizontally and vertically. Enough point sources are used so 

that, when their individual responses are added 

together, the earthquake appears as a uniform rupture 

rather than as a series of discrete sources. In a propagating rupture, seismic waves tend to pile up on one 

another in the direction of rupture propagation. This effect is called directivity (Boore and Joyner, 1978; 

Archuleta and Frazier, 1978). Similarly, at an azimuth 

opposite to the direction of rupture propagation, seismic 

waves tend to be stretched out in time. This stretching 

out reveals the individual sources on the rupture surface. Thus, the accuracy of the point-source-summation 

approximation to a uniform rupture can depend on the 

frequency of the calculation and on the azimuth of the 

site in relation to the strike of the rupture surface. Furthermore, the analysis is sensitive to assumptions about 

the rupture velocity. Figure 219A shows the model of the 

rupture front that is used in this simulation. The rupture 

velocity is assumed to be 0.8 times the shear-wave 

Effects of the Postulated Earthquake 431 
NW 

5 

9 (f) 

c:: 

11 ~ w 

L---~L----L~--~u_---- -----LL---~ 13 ~ 

...J 

~ 

r~----,-,----,-,----,-.r---,---r--,-----, 3 z 

5 ~ a... 

7 ~ 

9 

11 

10 

DISTANCE FAULT, IN KILOMETERS 

FIGURE 219.-Contours of the position of the rupture front at 2-s intervals after initiation of the earthquake. A, Rupture history used in 

calculations. B, An alternate rupture history. Hypocenter is indicated by asterisk. 

velocity on the eastern side of the Newport-Inglewood 

zone. A rupture velocity 0.8 times the shear-wave velocity is consistent with inferred rupture for moderate to 

large earthquakes (Geller, 1976) and with rupture 

velocities obtained from numerical studies of shear 

cracks (Andrews, 1976). Use of a different rupture 

history (for example, the one in figure 219B) can yield 

markedly different amplitudes of ground velocity, 

although the waveforms are similar. The alternate rupture history is for a rupture velocity 0.8 times the shearwave velocity west of the Newport-Inglewood zone. 

The predicted ground-motion time-histories are shown 

in figures 220A, 220B, and 220C for the components of 

velocity normal to the rupture surface, parallel to the 

rupture, and vertical, respectively. Ground-motion 

velocities are shown for 10 sites within the Los Angeles 

basin; the station names and their predicted peak 

velocities are given in table 56. The main conclusions 

that can be drawn from the amplitude distributions are 

that (1) strong shaking from the postulated earthquake 

lasts for about 10 to 15 s; (2) the component normal to 

the rupture surface has the largest amplitudes; and (3) 

both the directivity of the moving rupture and the radiation patterns of different seismic phases are important 

in evaluating the amplitude of the ground motion at 

specific sites. 

The component of ground motion normal to the rupture surface in figure 220A is mainly SH waves (horizontally polarized shear waves). This component is largely 

symmetric across the fault zone (compare, for example, 

432 Earthquake Hazards in the Los Angeles Region 

the predicted motions at LAX and USC). The normal 

component of velocity is relatively unaffected by the different depths to basement on the northeastern and 

southwestern sides of the fault zone. Velocities of this 

component toward the northwestern end of the fault are 

generally larger than those toward the southeastern 

end. The larger amplitudes to the northwest are due to 

directivity from the northward-propagating rupture 

(compare, for example, CTC and LBA). The normal components at CTC and HWP are particularly large for two 

reasons: (1) they lie close to the trace of the rupture surface near the SH-wave radiation pattern maximum, and 

(2) a significant portion of the postulated fault slip lies to 

the south of each site, between each site and the 

hypocenter. We note that the peak ground velocities normal to the seismic slip surface (table 56), which are the 

largest motions, agree reasonabaly well in magnitude 

with those predicted by Fumal and Joyner (fig. 216B). 

The main discrepancy is that the peak velocity distribution predicted by our model is skewed to the northwest 

because of our explicit inclusion of the effect of directivity, which is absent from figure 216B. 

The component of ground motion parallel to the rupture surface in figure 220B and the vertical component 

in figure 220C are mainly P (compressional waves), SV 

(vertically polarized shear waves), and surface waves. 

These two components do not show the symmetry across 

the fault that the normal component does (compare, for 

example, LAX and USC). Larger surface waves are 

generated on the eastern side of the fault zone because 

of the greater thickness of sedimentary rocks on that 

side (see, for example, the vertical component at USC). 

The peak values at USC, HWC, and LAX are relatively 

large because these sites lie near a P-SV radiation pattern maximum (45° off the strike of the postulated subsurface fault) for the large dislocations south of HWP 

(fig. 218). In contrast, COM at an azimuth of about 90° 

from the strike of the rupture surface is near a radiation 

pattern minimum (fig. 220C). The parallel and vertical 

components of velocity for LBA are small because of the 

northwestward directivity. These components are 

largest for CPA because of vertical directivity from the 

hypocenter, which lies at about a 60° angle under the 

station. That is, the parallel and vertical components at 

CPA are large for the same reasons that the normal components of CTC and HWP are large. 

Figure 221 illustrates the effect at site HWP of using 

the alternate rupture history depicted in figure 219. 

Although the waveforms are similar, the amplitudes are 

significantly increased in the new rupture history. At 

the other sites, the increase in amplitude is much less. 

These observations can be understood by considering 

figures 218 and 219. We see from figure 219 that, in the 
A 118'30' 

80 centimeters L___2,0 

per second l seconds 

0 5 10 

KILOM ETERS 

HWC•~22 6 

CTC A ..._ STM• • -.J n----85.9 

42 3 usc• 3o 7 34 

oo· 

B 118' 30' 

25 centimeters ~0 

per second l seconds 

.coM 6 

Jw------79.7 

ROB 

• ------------ 6.9 r 

0 

_ _,L=B"-'-A_,_•_3_

5 

5 10 

KILOMETERS 

34 

00' 

c 118' 30' 

15 centimeters 1_____2, 0 

per second l seconds 

0 5 10 

KILOMETERS 

HWC. 5 

CTf----lv----11 .7 

STM. 

~5.3 usc. 11.5 

.coM 6 

HWP. ~7.1 

LAX 

5.4 CPA ~ ·~v----16 0 

LBA. 

4 

FIGURE 220.-Predicted ground-motion time-histories of velocity components for 10 sites in the Los Angeles basin (see table 56 for station designations). All time-histories are plotted at the same 

horizontal and vertical scales for ease of comparison. Numbers to 

the right of each time-history indicate the peak amplitude of the 

trace (in centimeters per second). Heavy line is the trace of the 

-------- ------- --- -- Hwc~ ~2~ --- -- --------- ~;!::::~::~; ~:;;:::~~~!~~;t~:!~:~~!ty~;=~~~---------- ------ CTC face. C, Vertical component of velocity. 

STM 14.4 

1o. usc. 17.8 

.coM 

----J'...y--9.4 

~10.3 

CPA ~ •--Jr---26.8 

TABLE 56.-Peak velocities (in cm/s) from postulated earthquake 

computed for 10 sites within the Los Angeles basin 

Component 

Normal to Parallel to 

Site Location rupture rupture Vertical 

CTC ---- Century City 85.9 14.4 11.7 

HWP ---- Hollywood Park 79.7 10.3 7.1 

STM ---- Santa Monica 42.3 10.5 5.3 

CPA ----Compton Airport 37.6 26.8 16.0 

USC ---- University of Southern 30.7 17.8 11.5 

California. 

LAX ---- Los Angeles Airport 22.8 11.3 5.4 

HWC --- Hollywood Cemetery 22.6 12.5 8.5 

RDB ---- Redondo Beach 6.9 8.1 2.3 

COM --- City of Commerce 5.6 9.4 1.6 

LBA ---- Long Beach Airport 3.5 3.3 1.4 

Effects of the Postulated Earthquake 433 
VELOCITIES FOR ASSUMED RUPTURE HISTORY 

Parallel 10.3 

cm/s 

Normal 79.7 

Vertical 7.1 

VELOCITIES FOR ALTERNATE RUPTURE HISTORY 

Parallel 16.4 

Normal 135.3 

Vertical 7.8 

0 10 seconds 

I 

FIGURE 221.-Comparison of time-histories of ground velocity for the 

same site-HWP (Hollywood Park}-using the two different rupture histories shown in figure 219. Numbers to the right of each 

time-history indicate peak values. Different vertical scales are 

used for the two rupture histories to demonstrate that the 

waveforms are similar even though peak values are different. 

alternate rupture history, the upper part of the fault 

plane ruptures a little faster. Site HWP is particularly 

sensitive to this change in rupture velocity because of 

the larger values of slip at shallow depths just south of 

HWP (fig. 218). These shallower dislocations lie between 

HWP and the hypocenter and are involved in a directivity effect, which is in turn strongly dependent on the rupture velocity. Thus, we see that a fairly complicated interplay can exist between the rupture history, the 

distribution of slip, the location of the site, and the 

resulting ground motion. 

434 Earthquake Hazards in the Los Angeles Region 

LIQUEFACTION-RELATED 

GROUND FAILURE 

By J. C. Tinsley and T. L. Youd 

Liquefaction-related ground failure is expected to 

occur in association with the postulated earthquake at 

scattered localities within relatively flat alluvial areas. 

Figures 135 and 145 (Tinsley and others, this volume) 

delineate relative liquefaction susceptibility for the onshore part of the demonstration ~rea by using methods 

described by Tinsley and others (this volume). These 

figures are based on our assessment of the age and type 

of sedimentary deposits and the depth to ground water 

as compiled from modern data. We analyzed the 

physical properties of the late Quaternary alluvial 

deposits, grouped them according to their densities and 

their probable contents of loose cohesionless sand or 

silt, and determined whether they are saturated with 

ground water at depths of less than about 15 m. 

Holocene sediments, especially those deposited during 

the past few hundred years, are the most susceptible to 

liquefaction-related ground failure. Sea-floor sediments 

susceptible to liquefaction may also be present on or 

along the margins of the Santa Monica and San Pedro 

shelves (Clarke and others, this volume, fig. 189), but we 

lack sufficient information on their distribution and 

character to consider them in this analysis. 

For the postulated earthquake (M 6.5), we predict that 

significant liquefaction effects will occur at distances 

not more than 18 km from the surface projection of the 

fault rupture. This inference is based on the empirical 

relation between earthquake magnitude and the greatest distance at which liquefaction effects in gently sloping Holocene sediments are observed with respect to the 

seismic source (Y oud and Perkins, 1978; Tinsley and 

others, this volume, fig. 155). Observations of liquefaction generated by the 1979 Imperial Valley earthquake 

of comparable magnitude indicate that the greatest 

likelihood of liquefaction-related ground failures probably will be within 5 or 6 km of the surface projection of 

the fault rupture (Youd and Wieczorek, 1982). 

We predict that, within 18 km of the seismic rupture, 

ground failure due to liquefaction may occur at scattered localities within areas designated as having very 

high and high susceptibility (that is, where deposits are 

very young and where ground water is less than 10 ft 

subsurface). Figure 222 shows the geographic distribuFIGURE 222.-Predicted relative potential for liquefaction-related ...... 

ground failure from the postulated earthquake in the demonstration area. The oval-shaped dashed line, 18 km from the trace of the 

seismic source (heavy line), is the predicted areal limit for liquefaction effects causing ground displacements exceeding 0.1 m. 
34'00' 

33'45' 

// ---------------........ , 

/ ........ / 11 8'30' ......... 

" " 

VL* 

EXPLANATION 

High potential 

-

where cohesionless 

granular sediments are present 

Moderate potential where cohesion less 

granular sediments are present 

low potential where cohesionless 

granular sediments are present 

" " 

Areas underlain by bedrock units!*) 

or alluvial areas where little or 

no potential eldsts 

" " " 

0 

I I 

5 MI LES 

I 

0 5 KILOMETERS 

11 8'15' 

...___ ___________ ___ 

Effects of the Postulated Earthquake 435 
tion of ground within which liquefaction is likely during 

the postulated earthquake. These areas include all 

beach areas, the present and former tidal marshes and 

sloughs near Marina del Rey, the Los Angeles and Long 

Beach harbor areas, and parts of the flood-plain and 

tidewater areas of the Los Angeles and San Gabriel 

River basins. Liquefaction is less likely (but not unlikely) 

to occur in those areas designated as having moderate 

susceptibility. Areas having moderate susceptibility 

contain deposits that are ,water saturated at greater 

depths, are older, or are more deeply buried in comparison with areas containing highly susceptible 

materials. Areas designated as having low or very low 

susceptibility are unlikely to sustain ground failures by 

liquefaction, either because the deposits are unsaturated or because they are well consolidated and (or) 

cemented. 

Nature of Liquefaction Failures 

"Ground failure" is herein regarded as a permanent 

ground disruption exhibiting either (or both) horizontal 

and vertical components of displacement. Modes of 

liquefaction-induced gtound failure include lateral 

spreading and ground settlement caused by lateral 

displacement of liquefied materials or by compaction of 

cohesionless, granular, water-saturated sediment, 

respectively. Ground failure is considered to be significant if the differential displacement exceeds 0.1 m, the 

threshold required to damage common structures and 

engineering works (Youd and Perkins, 1978; Youd, 

1980). 

Lateral spreading is most likely to occur where loose, 

water-saturated, sandy sedimentary deposits and poorly 

compacted fills are situated near a free face (for example, storm-drain channels, sloughs, and waterfront 

areas). Once the granular water-saturated deposit has 

been transformed to a fluidized state, the liquefied mass 

is free to move toward the free face and to carry with it 

any engineered works constructed on or within its 

volume. Differential settlement is likely to occur along 

buried channels of former streams, in beach areas, 

along former sloughs in tidewater areas, and in sandy 

channel-fill deposits and natural levees of principal 

streams such as the Los Angeles and San Gabriel Rivers, 

Ballona Creek, and Compton Creek. 

The differential settlements and displacements that 

result from liquefaction-related ground failure likely 

will include disturbances and disruptions of public and 

private utilities services, including surface and subgrade water, gas and sewerage facilities, storm drains, 

irrigation works, channelized surface drainages, and 

shallow-seated foundations of structures. 

436 Earthquake Hazards in the Los Angeles Region 

Limitations of Prediction 

The ground-water data presently available for the 

demonstration area constitute a principal source of 

uncertainty in these predictions of liquefaction potential. There are very few well or control points used by 

State and local agencies to monitor shallow or perched 

ground water. Consequently, many occurrences of 

shallow ground water have been compiled from foundation investigations conducted before construction of 

storm drains, freeway overpasses, and public and 

private structures. The depth below grade at which any 

free or perched water was reported became the water 

depth used to evaluate liquefaction susceptibility. 

Because little is known concerning the hydrologic setting of these shallow occurrences of ground water, a 

seasonal recharge factor reflecting irrigation practice 

or rainfall doubtless controls the amount of, depth to, or, 

locally, the presence or absence of free ground water in 

near-surface sediment. We are unable to address this 

uncertainty in this study. The zones of potential liquefaction delineated in figure 222 are assumed to represent average or typical ground-water conditions that 

reflect average levels of precipitation and volumes of 

ground-water extraction. Water levels following winter 

rains are certain to be higher than water levels 

measured during the summer and autumn months. Consequently, seasonally and during sequences of years of 

above-average precipitation, the areas susceptible to 

liquefaction may be slightly larger than those shown in 

figure 222. Conversely, seasonally and during drought 

years, the areas susceptible to liquefaction may be 

smaller than those shown. Any change in the pattern of 

management (extraction or recharge) of the groundwater resource may also grossly modify the occurrence 

of shallow ground water and thus modify the limits of 

areas susceptible to liquefaction. 

Figure 222 does not provide a site-specific prediction 

of liquefaction-related ground failure. Detailed geotechnical studies, including direct testing of subsurface 

materials, are required to identify specific sites where 

water-saturated, loose, cohesionless sediment occurs 

and where significant lateral or vertical components of 

ground displacement are possible. 

LANDSLIDING 

By E. L. Harp and D. K. Keefer 

Strong shaking from the postulated earthquake is expected to trigger the local failure of many slopes within 

upland areas in and adjacent to the demonstration area. 

Figure 223 shows the predicted 50-percent probability 
0 10 20 MILES 

0 10 20 30 KILOMETERS 

FIGURE 223.-Fifty-percent probability limits of ground motion from the postulated earthquake that exceeds threshold levels necessary to trigger 

landslides of different types on susceptible slopes onshore in the Los Angeles region. Darker shaded areas are uplands, which are most likely 

to contain susceptible slopes. Oval-shaped line A is the so-percent probability limit for coherent failures (slumps and block slides). Oval-shaped 

line B is the so-percent probability limit for disrupted failures (rock and soil falls and slides). The likelihood of ground motion sufficient to trigger landslides increases toward the postulated zone of seismic rupture (heavy line). A few landslides may occur outside the so-percent probability limits at distances as great as 6S and 112 km from the seismic source for coherent and disrupted failures, respectively. (See Wilson and 

Keefer (this volume, figs. 17S, 176) for the geographic outer bounds of perceptible slope failure relevant to the postulated earthquake.) 

Effects of the Postulated Earthquake 437 
limits of ground motion that would exceed threshold 

levels necessary to trigger landslides of different types 

on susceptible slopes. The limits were determined by using the newly established correlations (Wilson and 

Keefer, this volume) between earthquake magnitude, 

critical displacement of a slope, and intensity of shaking 

for an earthquake source distance appropriate to a 

M 6.5 earthquake. Susceptible slopes are those areas 

where lithologic, hydrologic, and. slope characteristics 

are optimum for failure under seismic shaking. Because 

accurate slope and material-properties data are not 

available for the demonstration area, we can address 

the distribution of susceptible slopes in a general way 

only. Most landslides triggered by the postulated earthquake probably will occur within the ellipses shown in 

figure 223, but a few could occur at greater distances. 

The reader is referred to figures 175 and 176 (Wilson 

and Keefer, this volume) for the outer limits of perceptible slope failures for a M 6.5 earthquake as determined 

from worldwide data on historical earthquake-induced 

landsliding. 

Areas of potential sea-floor instability also have been 

identified along the margins of the Santa Monica and 

San Pedro shelves (Clarke and others, this volume, figure 189) that are within the estimated 59-km limiting 

distance for subaqueous slides triggered by M 6.5 earthquakes (Wilson and Keefer, this volume, figs. 164C, 177). 

The geotechnical character of these potentially unstable 

slopes is not known well enough, however, to judge 

which, if any, might fail during the postulated 

earthquake. 

Although many types of landslides are triggered by 

earthquakes (Keefer, 1984; Wilson and Keefer, this 

volume, table 44), for the postulated earthquake we consider only the most common types likely to occur on land 

and the categories of slopes that generally will fail. Furthermore, we restrict our predictions of landslide occurrence to upland areas. Liquefaction-related ground 

failure within alluvial deposits of adjacent valleys has 

been discussed in the preceding section. Our analysis of 

landslide occurrence from the postulated earthquake is 

heavily influenced by what is known about slope failures 

during the 1971 San Fernando earthquake. Much of the 

upland areas likely to sustain landslides have similar 

vegetative cover and topography and, in the case of the 

Santa Monica Mountains and the Verdugo Hills, share 

many of the same lithologic units as the area affected by 

landslides in the San Fernando earthquake. 

The predominant landslide types generated will be 

shallow disrupted failures (soil slides, rock falls, and 

rock slides). As many as a few hundred landslides of 

each of these types are likely to occur. Most soil slides 

probably will occur in thin (generally less than 2 m) colluvial and residual soils on slopes; most probably will 

438 Earthquake Hazards in the Los Angeles Region 

originate on slopes between 35 o and 45 o, but a few may 

occur on slopes as gentle as 15°. Except for a few areas 

where cliffs steeper than 50° are abundant, most of the 

rock falls and rock slides will be restricted to roadcuts 

and other artificially cut slopes, because upland areas 

adjacent to the Los Angeles basin have few natural 

slopes in excess of 45 o, the lower limit for most rock 

slide occurrences. The local climate and vegetation influence the slope limits for rock falls and rock slides. 

Although historical earthquake data worldwide establish general minimum slope values for rock falls and 

rock slides as 40° and 35°, respectively (Wilson and 

Keefer, this volume, table 45), upland areas likely to be 

affected by the postulated earthquake generally do not 

have bedrock slopes of less than 50° or talus slopes of 

less than 45 o. Most of the upland areas having slopes 

less than 45° to 50° are grassy or covered with brush 

rather than being bedrock or covered with talus. Few 

rock falls or rock slides are likely on these colluvial or 

residual soil-covered slopes. 

Only a few deep-seated rotational slumps and block 

slides in rock are expected. We cannot predict exactly 

where these may occur, because the data from historical earthquakes define relations between susceptible materials and slopes for rock slumps and block 

slides only in a general way. Worldwide experience 

from historical earthquakes has indicated that large 

preexisting slumps and block slides generally do not 

reactivate from seismic shaking (Wilson and Keefer, this 

volume; Harp and others, 1981; Keefer, 1984). 

The postulated earthquake also will probably trigger 

several tens (possibly up to a few hundred) of slumps 

from those older artificial fills that have not received 

enough compaction to meet modern grading standards. 

Typical of such deposits that have shown high susceptibility in past earthquakes are fills for housing 

developments, railroad embankments, outer edges of 

road and highway embankments, dikes, and bridge 

abutments. Soil falls and slumps are expected along the 

banks of stream channels that have not been lined with 

concrete but will pose little hazard because of small 

slope heights and lack of adjacent development. 

Although the postulated earthquake is expected to 

trigger a few scattered landslides as far distant as the 

outer bounds shown in figures 175 and 176 (Wilson and 

Keefer, this volume), landslides will be concentrated 

within the 50-percent probability exceedance lines for 

both disrupted and coherent failures, which are at 41 

and 24 km, respectively, from the postulated fault rupture (fig. 223). Slope failures (except for those related to 

liquefaction) will occur chiefly within several upland 

areas, where slopes exceed 10°. These areas are the 

Baldwin and Dominguez Hills, the eastern Santa Monica 

Mountains, the Palos Verdes Hills, the central Santa 
Monica Mountains and Pacific Palisades, the Verdugo 

Mountains and the adjacent San Gabriel Mountains, 

and the Puente Hills. Environments where the earthquake is most likely to produce slope failures from the 

earthquake within these areas are discussed individually below and are summarized in table 57. 

shallow soil slides. We expect the incidence of soil slides 

to be highest within slopes underlain by the Culver sand, 

the Baldwin Hills sandy gravel, and the Inglewood Formation of Weber (1982), judging from the susceptibility 

of these units to these types of failures during the 

1978-79 rainfall season and because of their generally 

noncohesive nature (Weber, 1982). 

Baldwin and Dominguez Hills 

The most common landslide type generated in the 

Baldwin and Dominguez Hills by the earthquake will be 

A few deep-seated slumps could occur in the Inglewood Formation and in artificial fill. Many of the slopes 

in the Baldwin Hills have been modified by cut and fill, 

and, where older fill slopes have not been compacted 

sufficiently to meet modern grading standards, they may 

TABLE 57.-Areas, geologic materials, and slopes most likely to fail in the postulated earthquake, with types of landslides 

Area Landslide type 

Baldwin and Dominguez Hills ----Soil slides 

Eastern Santa Monica Mountains -- Rock falls and rock slides 

(east of Sepulveda Canyon). 

Soil slides 

Deep-seated slumps and 

block slides. 

Most susceptible 

geologic materials 

Soil developed on weakly cemented 

sandstone of the Culver sand, 

Baldwin Hills sandy gravel, 

and Inglewood Formation of 

Weber (1982). 

Massive conglomerate of Topanga 

Canyon Formation. 

All units susceptible; most intensely fractured, fragment size 

small. 

All units susceptible 

Shale units of Modelo and Topanga 

Canyon Formations. 

Palos Verdes Hills --------------Deep-seated slumps and block Altamira Shale Member of Manslides. terey Formation. 

Central Santa Monica ----------- Rock falls and rock slides Conglomerate of Coal Canyon ForMountains-Pacific Palisades. mation; conglomerate and 

sandstone of Tuna Canyon Formation; alluvial fan deposits 

of Pacific Palisades. 

Soil slides 

Deep-seated slumps and block 

slides. 

Verdugo Mountains and --------- Soil slides 

adjacent San Gabriel 

Mountains. 

Rock falls and rock slides 

Puente Hills ------------------ Soil slides 

Rock falls and rock slides 

All areas --------------------- Slumps 

Modelo Formation and parts of 

Topanga Canyon Formation. 

In Santa Monica Mountains: Fernwood Member of Topanga 

Canyon Formation; in Pacific 

Palisades: Topanga Canyon, 

Tuna Canyon, Modelo, and 

Sespe Formations. 

Granitic, metamorphic, and igneous rock (occupies most of 

area). 

Same as above 

La Vida Member of Puente 

Formation. 

Conglomerate in Sycamore Canyon 

Member of Puente Formation 

' and lower member of Fernando Formation. 

Poorly consolidated artificial fill 

Most susceptible 

slopes 

Natural slopes, ts•-so• 

Falls: natural and artificial slopes 

steeper than so•. 

Slides: slopes steeper than 4S • 

Natural slopes with colluvial or residual soil, 20•-so•. 

Slopes steeper than ts•, generally 

in areas where failures already exist. 

Slopes steeper than ts• 

Slopes steeper than so• (rock falls) 

and 4S 0 (rock slides) in 

Topanga Canyon area and 

along Palisades. 

Soil-covered slopes between 20• 

and so•. 

Slopes steeper than ts• 

Slopes between ts• and so• having 

soil cover. 

Slopes steeper than so• (rock falls) 

and 4S0 (rock slides). 

Slopes between 15• and so• 

Slopes steeper than 3S • 

Embankments steeper than to• 

Effects of the Postulated Earthquake 439 
fail. The susceptibility of artificial-fill embankments has 

been well documented in many earthquakes (Harp and 

others, 1980; California Division of Highways, 1975; 

Asada and others, 1980; Keefer, 1984). 

Eastern Santa Monica Mountains 

Nearly all lithologic units in the eastern Santa Monica 

Mountains are susceptible to shallow soil slides involving mantles of colluvium, residual soil, or weathered 

bedrock. Soil slides will occur mainly on slopes between · 

zoo and 50°, a maximum incidence occurring on slopes 

of 35° to 45° (on the basis of the occurrence of soil slides 

in the Santa Monica Mountains under conditions of 

heavy rainfall (Campbell, 1975) and the geometric and 

slope characteristics of shallow soil slides from the 1971 

San Fernando earthquake (Yen and Trotter, 1978)). The 

steepest portions of canyons on the southern flank of the 

Santa Monica Mountains are the most likely sites for soil 

slides. Canyons on the northern flank of the range may 

also experience soil slides in areas underlain by the 

Modelo Formation, a unit that has shown high susceptibility to soil slides under high-intensity rainfall (Weber, 

1979). 

Rock falls and rock slides are likely in some roadcuts 

and other artificial slopes. Intensely fractured units 

such as the Santa Monica Slate and fine-grained parts 

of the Modelo Formation, which, upon failure, produce 

angle-of-repose piles of small rock fragments, are likely 

to produce the most rock falls; such rock falls, however, 

may be individually less hazardous than those produced 

by massive, less fractured rocks such as conglomerate 

and breccia of the Topanga Canyon Formation, from 

which boulder-sized fragments could dislodge. Long, 

steep slopes in the Cahuenga Peak and Mount Hollywood areas that have massive outcrops of Topanga Canyon conglomerate may produce rock falls that could gain 

sufficient momentum on the 40° to 50° slopes to travel 

several hundred meters. 

Palos Verdes Hills 

The Palos Verdes Hills contain many active, deepseated slump-earth flow-type landslides that are 

climate controlled and undergo accelerated movement 

in response to winter storms (Ehlig, 198Z). The best 

known is the Portuguese Bend-Abalone Cove landslide 

complex, chiefly within the Altamira Shale Member of 

the Monterey Formation, which could accelerate locally 

because of earthquake ground motion. Scattered areas 

outside the boundaries of existing landslides within the 

Altamira Shale Member may also slump or slide as 

440 Earthquake Hazards in the Los Angeles Region 

blocks. Scattered rock falls can be expected along the 

near-vertical cliffs bordering the ocean but will likely be 

thin (1-3 m) failures. 

Central Santa Monica Mountains 

and Pacific Palisades 

Rock falls and rock slides are likely to be numerous in 

the south-central Santa Monica Mountains and in the 

Pacific Palisades. Particularly susceptible are the late 

Pleistocene alluvial-fan deposits forming the Pacific 

Palisades that border the ocean near Santa Monica. 

These deposits contain near-vertical joints and support 

near-vertical slopes but have low cohesion (McGill, 

198Z). Rock falls, including large boulders, are likely 

north of the mouth of Topanga Canyon, where massive 

conglomerate of the Coal Canyon Formation forms nearvertical slopes several hundred meters high; it is here 

that a large (greater than 100,000 m3) rock fall avalanche may be triggered. Rock falls also may occur from 

other lithologic units where slopes are 50° or steeper. 

Rock slides will form under slope conditions similar to 

those under which rock falls form, except that they will 

occur on slopes of 45° or greater. 

Soil slides will be common on slopes between zoo and 

50° in colluvial or residual soils. The Modelo Formation, 

a slide-prone unit in the 1971 San Fernando earthquake 

(Morton, 1971), and similar beds of the Topanga Canyon 

Formation are the most susceptible units. 

Slumps and block slides exist within clayey and silty 

members of the Topanga Canyon Formation, the Tuna 

Canyon Formation, the Modelo Formation, and the Sespe 

Formation in the Pacific Palisades (McGill, 198Z), and 

extensive landslide deposits are present in the Fernwood Member of the Topanga Canyon Formation 

(Yerkes and Campbell, 1980). A few of these landslides 

may be reactivated during the postulated earthquake. 

Verdugo and San Gabriel Mountains 

The Verdugo Mountains and parts of the San Gabriel 

Mountains east of the San Fernando Valley could experience scattered soil slides, rock falls, and rock slides. 

Most of the Verdugo Mountains and adjacent areas of 

the San Gabriel Mountains consist of moderately steep 

slopes (up to 50°) underlain by closely fractured 

crystalline basement rocks. The soils developed on these 

rocks are characteristically granular, noncohesive, and 

thin (generally less than Z m). These soils occupy most 

slopes except those greater than 45 o where crystalline 

basement rocks are exposed. These soils are highly 
susceptible to soil slides when they are strongly shaken, 

but, because they are farther away from the postulated 

seismic source, they probably will have fewer failures 

than similar susceptible slopes in the eastern Santa 

Monica Mountains. Tertiary and Quaternary rocks and 

soils developed on slopes in the mountains immediately 

north of San Fernando will have few landslides in comparison with the 1971 San Fernando earthquake, 

because they are farther from the seismic source. 

Puente Hills 

Scattered rock falls and rock slides could occur from 

steep slopes formed by outcrops of resistant conglomerate of the Sycamore Canyon Member of the Puente 

Formation and the lower member of the Fernando Formation. Most of these slopes are located in the area 

north of Turnbull Canyon, the area just east of Whittier, 

and north of La Habra. A few scattered soil slides are 

also expected. 

Seasonal Influences on 

Earthquake-Induced 

Landslide Susceptibility 

The potential for earthquake-induced slope failures 

changes seasonally. Although seasonal effects on the 

potential for rock falls and rock slides would be slight, 

the susceptibility of some slopes to slumps and block 

slides would be increased by seasonally high groundwater levels. Moreover, intense rainfall at the time of 

the postulated earthquake could affect the behavior of · 

earthquake-triggered soil slides, especially in terms of 

runout distance. If slopes were nearly saturated at the 

time of the earthquake, the shaking could liquefy the 

more cohesionless granular soils and mobilize the soil 

slide material into debris flows. Because of the fluid 

nature of debris flows, they can attain speeds as great 

as several tens of kilometers an hour if suitable runout 

paths exist. The characteristics of debris flows in the 

Santa Monica Mountains and their hazards have been 

well documented from past intense storms (Campbell, 

1975; Weber 1979, 1980), but there are few data to 

estimate how much greater the occurrence of debris 

flows would be if an earthquake occurred when the soil 

was nearly saturated. 

OTHER EFFECTS 

The postulated earthquake is not likely to generate a 

tsunami because the source zone of the earthquake is 

entirely on land and is associated with dominantly 

strike-slip displacement. Furthermore, the known areas 

of sea-floor instability offshore from the Los Angeles 

region are not large enough to generate tsunamis if 

these areas suddenly fail owing to earthquake shaking 

(McCulloch, this volume). Other water-related earthquake phenomena can be expected, however. Seismically 

induced fluctuations of water levels in lakes, reservoirs, 

tanks, and wells commonly accompany earthquakes of M 

5 or greater and have been associated with moderatesized earthquakes in southern California (W aananen and 

Moyle, 1971, 1972). Shaking from the 1971 San Fernando 

earthquake, for instance, generated a 0.6-m surge in the 

Van Norman Reservoir and induced seiches (oscillations 

of the surface of an enclosed body of water) in countless 

swimming pools as far as 70 km from the epicenter. 

Water levels in wells as distant as 500 km from the epicenter exhibited measurable changes. Comparable effects could accompany the postulated earthquake. 

SUMMARY 

A moderate-sized (M 6.5) earthquake along the northern part of the Newport-Inglewood zone would generate 

a variety of geologic and seismologic effects that could 

be hazardous to people and property. The expected 

distribution and severity of these effects can be estimated by using many of the hazard-evaluation techniques described in the previous chapters. 

Fault rupture of the land surface, generated by 

secondary faulting along as much as 16 km of late 

Quaternary faults exposed in the Baldwin, Rosecrans, 

and Dominguez Hills, is expected. Oblique normal slip as 

great as a few tens of centimeters may occur locally. 

Minor movement along reverse faults in the subsurface 

near the Rosecrans Hills could cut nearby oil and gas 

wells. Tectonic elevation changes of as much as a few 

tens of centimeters also are expected near the earthquake source zone. 

Ground shaking of Modified Mercalli intensity VI or 

greater will affect about 6,400 km2 • Most of the 

alluviated parts of the Los Angeles basin and the San 

Fernando Valley will experience shaking of intensity 

VII, but intensities of VIII are predicted for some areas 

in the southern San Fernando Valley, near Marina Del 

Rey, in the Long Beach area, and locally elsewhere 

within about 18 km of the trace of the northern NewportInglewood zone. Peak ground-motion values of about 

0.4-g acceleration, 90- to 10D-cm/s velocity, 1.2-g 

pseudoacceleration response, and 160- to 18D-cm/s 

pseudovelocity response are predicted near the surface 

trace of the earthquake source zone. Numerical modeling of an idealized tectonic rupture assumed to be 

Effects of the Postulated Earthquake 441 
associated with the earthquake suggests that strong 

shaking will last about 10 to 15 s; if the tectonic rupture 

propagates northwestward from the postulated epicenter at Dominguez Gap, the components of shaking 

velocity normal to the trend of the rupture will be 

markedly higher toward the northwestern end of the 

Newport-Inglewood zone. 

Although liquefaction-related ground failure may 

occur at distances as great as about 18 km from the 

earthquake source, the areas where liquefaction is most 

likely are the beaches, the area near Marina del Rey, 

the Los Angeles and Long Beach harbor areas, and 

parts of the Los Angeles and San Gabriel River flood 

plains. Strong shaking also is expected to trigger land442 Earthquake Hazards in the Los Angeles Region 

slides locally, rock and soil falls and slides being the 

predominant types of failure. These disrupted failures 

are most likely in the upland areas within about 40 km of 

the northern Newport-Inglewood zone. A few slumps 

and block glides may be reactivated, or new ones may be 

formed, along susceptible slopes generally within about 

24 km of the earthquake source. 

Strong shaking also will cause oscillation of the surfaces of enclosed small bodies of surface water Oakes, 

reservoirs, tanks, and swimming pools) at distances of 

up to several tens of kilometers. Levels of water in wells 

locally will fluctuate temporarily to distances of a few 

hundred kilometers. 
USING EARTH-SCIENCE INFORMATION 

FOR EARTHQUAKE HAZARD REDUCTION 

By W. J. Kockelman 

INTRODUCTION 

The preceding chapters have summarized what is 

currently known about the major earthquake hazards in 

the Los Angeles region and have described methods that 

might be used to further evaluate the severity and 

distribution of such hazards. This information is 

valuable to soc-iety only if it is used by planners, 

engineers, decisionmakers, and the public to take action 

that will reduce the potentially destructive effects of 

future earthquakes. 

Recently, earthquake hazard reduction in California 

has generated much interest; the creation of the 

Southern California Earthquake Preparedness Project 

(1981), which is making use of scientific information to 

develop prototypical emergency plans, is an example of 

that interest. This chapter illustrates, through five 

examples, the range of applications of geologic and 

seismologic information used by planners, engineers, 

and decisionmakers to reduce earthquake hazards in 

the Los Angeles region. Among the users are State 

legislators, State agencies, county planning commissioners, county board supervisors, mayors, council 

members, city and county planners, State engineers, 

local building inspectors, and real-estate sellers. The examples include the entire State, a metropolitan region, a 

2,740-miZ (7,097 km2) county, a city of almost three 

million people, and individual lots and acreages offered 

for sale. The selection of these five examples does not 

imply endorsement by the U.S. Geological Survey. 

Each example presents a summary of the problems or 

needs faced by the users, the earth-science information 

used or available, the specific action taken, the methods 

and procedures used to carry out each action, and brief 

comments on the impact of each plan or decision and its 

adaptation for earthquake hazard reduction by other 

users. The users applied the earth-science information 

available at the time; they can revise, update, or amend 

their plans and decisions as newer or better information 

becomes available. Examples of similar uses of geologic 

and seismologic information have been reported elsewhere (Kockelman, 1975, 1976, 1979, 1980; Kockelman 

and Brabb, 1978; Robinson and Spieker, 1978; Blair and 

Spangle, 1979; Brown and Kockelman, 1983). 

I gratefully acknowledge the many helpful comments 

of those who reviewed this chapter in draft form: James 

Kahle, Theodore Smith, and Earl Hart, geologists, California Division of Mines and Geology; Albert McCurdy, 

Deputy Director, Santa Barbara County Current Planning Division; David Doerner, geologist, Santa Barbara 

County Resource Management Department; James Gates 

and Guy Mancarti, bridge engineers, California Department of Transportation; Earl Schwartz, Chief, Conservation Bureau, Los Angeles Department of Building and 

Safety; Glenn Johnson and Victor Hernandez, Citywide 

Planning Division, Los Angeles City Planning Department; Rachel Gulliver Dunne, senior geologist, Dames 

and Moore, and former President, Los Angeles Board of 

Building and Safety Commissioners; William Spangle 

and George Mader, William Spangle and Associates; 

J. Laurence Mintier, planning consultant, formerly of 

the California Office of Planning and Research; and 

Richard Andrews, Assistant Director, California Office 

of Emergency Services, and former Executive Director, 

California Seismic Safety Commission. 

ANTICIPATING DAMAGE TO 

CRITICAL FACILITIES 

Scenarios can be used to assess the impact of a major 

future earthquake. A scenario is usually thought of as a 

synopsis or outline of a play or a movie; thus, a scenario 

for an earthquake can be considered a synopsis or outline of a large seismic event and its severe impacts on an 

urban region. Our first example shows how a scenario 

can be used to assess the effects of a future earthquake 

on principal lifelines for emergency planning purposes. 

An analysis of readiness can then be used to provide 

planning insights, recommend further work, and serve 

as a basis for making or improving emergency preparedness, response, recovery, and reconstruction plans. 

Using Earth-Science Information 443 
Property losses to buildings and their contents, 

deaths, injuries requiring hospitalization, and failure of 

critical facilities9 and other facilities were estimated for 

seven postulated earthquakes in California, including a 

ML 8.3 event on the southern San Andreas fault system 

in the Los Angeles-San Bernardino region, by the 

Federal Emergency Management Agency (FEMA) (1980, 

p. 15-26). FEMA and the California Office of Emergency 

Services then conducted an analysis of readiness and 

discussed Federal, State, and local responses and 

response planning (Federal Emergency Management 

Agency, 1980, p. 27-32, 43-51). In addition, the National 

Oceanic and Atmospheric Administration (Algermissen 

and others, 1973) made a study of earthquake losses in 

the Los Angeles area; Blume and others (1978) predicted 

damage to structures in southern California; and the 

U.S. Geological Survey (USGS) (1981) presented detailed 

scenarios for the seven postulated earthquakes affecting major California population centers, including the 

Los Angeles and San Diego metropolitan regions. 

Many critical facilities, particularly lifelines, are 

vulnerable to the effects of eaqhquakes. Landslides and 

rock falls, for example, can block highways and railways; surface fault ruptures can damage highways, runways, and railbeds or break sewer, water, or fuel pipelines and thereby cause pollution and fire hazards. 

Strong shaking can cause transmission lines and overpass structures to fail, and power transmission and 

highway and railway use will be interrupted; liquefaction and the resulting ground failures can cause failure 

of bulkheads, piers, and quays and thereby disrupt 

shipping. 

A radio network may use a complex combination of 

telephone lines, microwave circuits, satellite interfaces, 

and underground cables. According to Davis and others 

(1982, p. 68), the failure of one link in this "electronic 

chain" can· effectively disable a large portion of the 

system. Most of southern California's water supply arrives by way of three major aqueduct systems-the Los 

Angeles Aqueduct from the eastern Sierra Nevada 

Mountains, the California Aqueduct from northern 

California, and the Colorado River Aqueduct. Both the 

Los Angeles and the Colorado River Aqueducts cross the 

San Andreas fault; the California Aqueduct closely 

parallels the San Andreas fault for over 160 mi (100 km) 

and crosses the fault at four locations (see fig. 226). 

""The tenn "critical facilities" is used here to ioclude (1) lifelines such as major communication. utility, and transportation facilities and their connections to emergency £acUities; (2) unique 

or large structures whose failure might be catastrophic, such as dams or buildings where explosive, toxic, or radioactive materials are stored or handled; (3) high-occupancy buildings such 

as schools, chun::hes, hotels, offices, auditoriums, and stadiums; and (4} emergency facilities 

such as police and fire stations, hospitals, communications centers, and disasteN-esponse 

centers. 

444 Earthquake Hazards in the Los Angeles Region 

Earth-Science Information 

Evernden and others (1981) have developed procedures for predicting the intensities of any hypothetical 

earthquake at any location in the conterminous United 

States. Their computer model calculates the groundshaking parameter of Rossi-Forel or Modified Mercalli 

intensity on a grid of reference points throughout 

a region by using equations that include the influence of 

the distance from the fault source, the attenuation, and 

the geology of the area. They published a series of intensity maps for specific earthquakes, including a 

magnitude 8.3 event on the southern part of the San Andreas fault. Their work includes a map of southern 

California (Evernden and others, 1981, pl. 1) showing 10 

ground-condition units correlated to geologic units 

digitized on a %-minx %-min grid and 8 categories of 

predicted Rossi-Forel intensities for an event similar to 

the 1857 Fort Tejon earthquake. 

Geologic information at a scale of 1:250,000 is available from the California Division of Mines and Geology 

(CDMG) Geologic Atlas of California. Information on 

ground water and liquefaction is available from the 

USGS, the CDMG, and other sources, including Youd 

and others (1979), Fife and others (1976), and local and 

metropolitan water departments. 

Decision 

Using an intensity map provided by the USGS, the 

CDMG prepared a planning scenario for the Governor's 

Emergency Task Force on Earthquake Preparedness 

based on a repeat occurrence of the great Fort Tejon 

earthquake of January 9, 1857 (Davis and others, 1982). 

The map was based on the method described by Evernden and others (1981) and was modified according to additional geologic information. The scenario assumed 

that a magnitude . 8.3 earthquake on the southern San 

Andreas fault would produce: 

• Two hundred miles (320 km) of surface rupbJre from Cholame Valley in northern San Luis 

Obispo County to near San Bernardino. 

• Intense shaking continuing for at least 60 s 

throughout the planning area. 

• Slip (predominantly horizontal) on the fault 

reaching a maximum of 33 ft (10 m) within a 

zone generally less than 330ft (100m) wide. 

• No concurrent secondary movement on other 

faults. 

• Aftershocks, with some events as large as 

magnitude 7 continuing for several weeks. 
Zones roughly paralleling the postulated surface rupture along the San Andreas fault are shown on a map 

(fig. 224) as isoseismal areas (that is, areas within which 

the anticipated seismic intensities are comparable). 

Each zone is assigned an intensity rating based on the 

Rossi-Forel (RF) scale. According to Davis and others 

(1982, p. 34): 

Regionally, the isoseismal values diminish 

to intensity 7 or less (R-F) southward and 

westward across the Los Angeles Basin 

toward the coast at successively greater 

distances from the fault. In the Long 

Beach and Huntington Beach areas, the 

Santa Clara Valley, and Ventura-Oxnard 

areas farther west, the groundwatersaturated substrates are considered to be 

intensity 8 (R-F) with ground failure potential. These regional patterns associated 

with the scenario event are of sufficient 

plausibility to form a credible basis for 

valuation of general effects upon lifelines 

that service the greater Los Angeles area 

and adjacent communities. 

Davis and others' (1982) map showing the distribution 

of seismic intensity (fig. 224) is intended for emergency 

planning purposes only and is based on the following 

hypothetical chain of events: the specified earthquake 

occurs, various localities in the planning area experience a specific type of shaking or ground failure, 

and certain critical facilities undergo damage and 

others do not. Because the scenario is based on the occurrence of a specific earthquake on the San Andreas 

fault, it is not valid for the assessment of possible 

damage produced by an earthquake on any other fault 

or by a different earthquake on the San Andreas fault 

(Davis and others, 1982, p. 23). 

Application 

Davis and others (1982, p. 35-116) developed individual scenarios showing damage to critical facilities, 

specifically lifelines such as highways, airports, 

railroads, marine facilities, communication lines, watersupply and waste-disposal facilities, and electrical 

power, natural gas, and petroleum lines. The scenarios 

for lifelines are based on evaluation of earthquakeengineering literature, comments by numerous engineers and officials of public agencies, and judgments by 

the authors. This assessment of the effects of the earthquake on lifelines was made to establish a regional pattern of ground shaking and ground failure (fig. 224) and 

to evaluate the resulting performance of lifeline 

segments throughout the Los Angeles region. The communications map, for example, assesses telephonesystem performance following the postulated earthquake (fig. 225). Other maps (those for water-supply and 

waste-disposal facilities, for example) (fig. 226) show the 

location of and estimates of damage to facilities. Most of 

the planning maps for the scenario contain notations 

that are explained in the text; for example, the notation 

W12 on a Metropolitan Water District transmission 

pipeline shown in figure 226 reads, "Water deliveries 

through the MWD Upper Feeder will be temporarily 

' interrupted by pipe rupture where this major transmission line crosses the Santa Ana River." 

According to Davis and others (1982, p. 9), most of the 

lifelines will sustain significant damage that could require a major emergency-response effort. Each scenario 

map is accompanied by a discussion of the general patterns of effects of the earthquake: 

Interstate 5 from the San Joaquin Valley 

and Interstate 15 through Cajon Pass will 

be closed, leaving U.S. 101 along the coast 

as the only major viable route open from 

the north. Highway connections with San 

Diego will remain open. (p. 37) 

Not all of the (telephone) systems in the 

greater Los Angeles region are set up to 

process emergency calls automatically on 

previously established priority bases. 

Thus overloading of equipment still in 

service could be very significant. (p. 67) 

Two of the three major aqueduct systems 

that import water to southern California 

will be ruptured by displacement of the 

San Andreas fault, and supply will not be 

restored for a three- to six-month period. 

(p. 85) 

Each planning map is accompanied by specific examples 

of anticipated damage: 

In San Bernardino County, Interstate 15 

will be closed by settlement of major fills 

and rockfalls in Cajon Canyon. Other 

freeway damage along Interstate 15E to 

the south, including major damage to the 

Interstate 15E/10 interchange will result 

in closure of this route south to Riverside 

and Interstate 10 to the east. (p. 39) 

Norton Air Force Base near San Bernardino could experience some shaking of an 

intensity high enough to damage runways 

through the secondary effects of ground 

Using Earth-Science Information 445 
111• 

;;....,.,.j!,!!!!!!.!i'R~--!2!.,!!!!!!~1<0 (XIOOOJ FEET 

Magnitude 8.3 Earthquake on the San Andreas Fault in 

Southern California 

SEISMIC INTENSITY DISTRIBUTION 

Compiled by 

James F. Davis, Jahn H. Bennett, Gl enn Borchard I, 

J11dy W. Cola, Jamu E. Kahle, Salem J. Rice a nd Michael A. Silva 

1982 

EXPLANATION 

Ross1 · For•f ln l• t~sity (fflfMsify dolo 

modi f i1d by C. O.M. G. from U.S G1ologicof 

Sur¥6y0pttt1Fi/6/mporl 81·ff5, 1981). 

Ross,-For• f lfl /6t1Sify Scot• 

< 7 - No Slgndico"' domogtt 

7 - Stroflg Shock. 0 ¥tlrlhrow of movobftt obt#cts; 

foil of ploslttr; rit~ t~ g of church btl/Is; 

gttt~ tlrol po"'C, without domogtt to Dulldmgs 

8 - Vttry trot~g Shock. Foil of mt~tt s; crocks 

'" !htt wolfs of Duitdit~ . 

9 - Extrttmttly Str ong Shock Porti o / or toto/ 

dttstrucliofl of somtt Duildit~g . 

GROU ND FAI LURE 

Surfoctt Foulf Ruptur~ 

for Sc~fiOrio Eor thquoktt 

Arttos of high grotmd wotttr ( </Om) wi th 

potttMi ol f or ground foi lurtt, including 

/iqutt foc t i on ot1d stJIII•m•nt. 

~ 

~ 

Hi gh Po!Mii ol 

Modt1r olt1 or 

Ut~known Pot ttfiiJo f 

FIGURE 224.-Predicted seismic intensity distribution from an 1857-sized earthquake along the south-<:entral San Andreas fault for part of the Los 

Angeles region. Compilation by Davis and others (1982) shows areas subject to surface fault rupture, liquefaction or other ground failure, and 

predicted intensity corresponding to the Rossi-Forel scale. Richter (1958, p. 651) aligned the Rossi-Forel (arabic numerals) and Modified Mercalli (roman numerals) intensity scales as follows: 1 (I), 1 to 2 (II), 3 (III), 4 to 5 (IV), 5 to 6 (V), 6 to 7 (VI), 8- (VII), 8 + to 9- (VIII), 9 + (IX), and 

10(X-XII). 

446 Earthquake Hazards in the Los Angeles Region 
1111 

For o Magnitude 8.3 Earthquake on the Son Andreas Fault in Southern California 

COMMUNICATIONS 

(Telephone Systems) 

Compil•d bJ 

JOtMI F. Oo.tl, Jcmn Cott•r ond Polly A. LowrJ 

Till$ map p0111'd•$ Ofl OSS#S$lriMII Df 1•1·~ $y$1_,1 

~rfo,,onc• fotlowifl9 Ill• sc•n(lriO .orlllqutlt.. rM tns•um.nts • 

ar1 1Jo11H on (I matrix at onliCi!HIIH • .,.,,, willl D margin 

fw conling•nci••· s,~st•m •ff•cliY•n•ss" ill a su/Jj.cli¥1 

rDiing at Ill• tt/Jilil¥ of •m~rg•nc,Y r•11pons• og•nci•s to 

us• Ill• t•l•piiDn• s,~st•ms . 

I . !jl Q~aeoe ~ 0 o I 2 3 0 I z 3 0 I 2 3 0 I z 3 

U DAYS AFTER EVENT 

FIGURE 225.-Impact of scenario San Andreas earthquake on communications (telephone systems) for part of the Los Angeles region. Compilation 

by Davis and others (1982) shows the percentage of telephone-system effectiveness in four zones designated A, B, C, and D up to 3 days after 

the postulated earthquake. 

Using Earth-Science Information 447 
For a Magnitude 8.3 Earthquake on the San Andreas Fault in 

Southern California 

WATER SUPPLY M[J WASTE~ FACILITIES 

Compiltcl by N 

Jo,.,.. F 0o¥tt, .lotln H Bennett, Glenn Borchard I, 0 Jo..- E )(ollie, Solem J. A1et ond M1choel A S1lwo W E 

1982 Q EXPLANATION 5 

~ Locollon of damage assessment (see text for details) 

!!:!!L M.Wn ':,~~,.;q~::::~tSstOn p,pe!tfle 

PERRIS RES SILVERWOOD LAKE 

SAN DIMAS RES. 

® 

~ 

~~ 

Waste Water Pipeline 

Reservoir copocdy ~ IOO,OOOA.F. 

Reservoir capacity: tqOOO-IOOPOOA.F 

ReserYOir copocJiy.· J,OOO-IO.OOOA.F 

Water Treatment Plant 

waste Water Treatment Plant 

Treatment Plant: damaged/shutdown 

Surface Faull Rupture for Scenario Earthquake 

FIGURE 226.-lmpact of scenario San Andreas earthquake on water-supply and waste-disposal facilities for part of the Los Angeles region. Compilation by Davis and others (1982} shows the location of and estimates of damage to specific facilities (aqueducts, pipelines, reservoirs, and 

treatment plants) from the postulated earthquake. The damage to specific facilities labeled W and numbered on the map are explained in the 

text accompanying the map. 
failure. Some damage could also occur to 

runways at Los Alamitos Armed Forces 

Reserve Center, but this may not be great 

enough to disrupt emergency operations. 

(p. 51) 

The several hydroelectric-power plants 

located on the California and Los Angeles 

aqueducts in northwestern Los Angeles 

County and the Devil Canyon Power Plant 

near San Bernardino will be out of service 

for an extended period of time due to 

major damage to both of the aqueduct 

systems. (p. 100) 

Each planning map for the scenario is also accompanied by planning needs: 

Emergency planners need to identify major emergency routes that can be most 

readily opened immediately following the 

earthquake .... alternative emergency 

routes should be selected which are at 

grade, wide, not flanked by buildings 

which are likely to be damaged, and not 

likely to be obstructed by fallen powerlines or other obstructions. (p. 40--41) 

Selection of air cargo delivery sites will influence the manner in which off-loaded 

personnel and supplies will be distributed 

by helicopters, highway, rail, or marine 

transport. Preferred airports need to be 

identified. (p. 52) 

Plans should be developed to ensure gas 

availability for those users who have 

priority emergency responsibilities. 

(p. 110) 

Each planning map is also accompanied by some recommendations for further work: 

An inventory of commercial and amateur 

broadcasting capabilities should be 

undertaken and the resulting information 

employed in developing the regional 

emergency communications plan. (p. 83) 

Further analysis should be undertaken to 

confirm the tentative conclusion that up to 

50 percent of the total power supply could 

be lost by this or a similar scenario earthquake and evaluate utility capabilities 

necessary to accomplish timely repairs to 

various damaged facilities. (p. 104) 

Plans for fire control should be developed 

for areas where tl;J.ese pipelines cross the 

San Andreas fault. Plans should also exist 

to ensure distribution of fuel supplies to 

airports selected for emergency activity 

and to other locations where fuel supplies 

for emergency response activities will be 

needed. (p. 115) 

Comments 

Each planning map contains a caveat to users concerning the assessment of damage: 

The conclusions regarding the performance of facilities are hypothetical and not 

to be construed as site-specific engineering evaluations. For the most part, 

damage assessments are strongly influenced by the seismic intensity distribution 

map for this planning area. There is 

disagreement among investigators as to 

·the most realistic model for predicting 

seismic intensity distribution. None have 

been fully tested and each would yield a 

different earthquake planning scenario. 

Facilities that are particularly sensitive to 

emergency response will require a detailed geotechnical study. 

The damage assessments are ~ased upon 

this specific scenario. An earthquake of 

significantly different magnitude or epicentrallocation on this or any one of many 

other faults in the planning area will 

result in a markedly different pattern of 

damage. 

It should be stressed that the lifeline damages anticipated in the scenario are for planning purposes only, 

and some may consider them overly pessimistic. In 

emergency planning, however, it is important to consider the worst possible disruptions of lifelines after a 

major earthquake so as to be better able to prepare, respond, and recover. 

ADOPTING SEISMIC 

SAFETY PLANS 

The California Legislature (1971, sec. 65300 and 

following) requires that each city and county prepare 

and adopt a comprehensive, long-term general plan for 

Using Earth-Science Information 449 
the physical development of the county. In addition to 

other elements, this general plan must include: 

A seismic safety element consisting of an 

identification and appraisal of seismic 

hazards such as susceptibility to surface 

ruptures from faulting, to ground shaking, 

to ground failures, or to the effects of 

seismically induced waves such as tsunamis and seiches. 

The seismic safety element shall also include an appraisal of mudslides, landslides, and slope stability as necessary 

geologic hazards that shall be considered 

simultaneously with other hazards such 

as possible surface ruptures from faulting, ground shaking, ground failure, and 

seismically induced waves. 

All counties in the Los Angeles region have prepared 

and adopted seismic safety plans (Orange County Environmental Management Agency, 1975; Los Angeles 

County Department of Regional Planning, 1974; Riverside County Planning Department, 1978; Santa Barbara 

County Planning Department, 1979; San Bernardino 

County Planning Department, 1979; San Diego County 

Environmental Development Agency, 1975; Ventura 

County Environmental Resources Agency, 1974). Santa 

Barbara County's plan is presented here to illustrate 

how a seismic safety plan is prepared and adopted. 

Santa Barbara County lies in the Transverse Range 

and southern Coast Range provinces. The county includes 2,740 mi2 (7,097 km2) and four channel islands. 

Because of its excellent climate, Santa Barbara County 

has been experiencing a rapid growth in population. According to the Santa Barbara County Planning Department (1979, p. 14), the county is not yet so urbanized that 

planning is in the "too little and too late" category. The 

department's report stated that 

.. .in the past, rapid population growth in 

California has pushed new urbanized 

development into geologically unfriendly 

terrain, where even minimal precautions 

were not observed because of ignorance 

of facts that were often readily available. 

Planning can avoid the areas least feasible for development from a geologic point 

of view. 

For more than two centuries, significant earthquakes 

have been felt or have caused damage in Santa Barbara 

County. Strong shaking and major damage from earthquakes occur an average of every 15 to 20 yr. 

450 Earthquake Hazards in the Los Angeles Region 

Earth-Science Information 

Much geologic and seismologic information is available and is referred to in the report by the Santa Barbara County Planning Department (1979, p. 181-190). 

Basic geologic maps, for example, have been prepared 

by Dibblee (1950, 1966, 1973) and Woodring and 

Bramlette (1950). Various USGS papers on ground-water 

supply (Evenson and Miller, 1963; Muir, 1968; Upson, 

1951; Worts, 1951) have been used to identify areas of 

possible liquefaction. A report on recency of faulting by 

Ziony and others (1973) is frequently cited, as is a report 

on seismicity by Hamilton and others (1969). The discussions of seismic risk refer to methods for calculating 

recurrence intervals on the basis of long-term slip rates 

on the fault as developed by Wallace (1970), Clark and 

others (1972), and Lamar and others (1973). 

Decision 

The county planning department used a consultative 

team headed by a firm of city and regional planners (Livingston and Associates) and a firm of consulting engineers and geologists (Moore and Taber). The county 

board of supervisors unanimously adopted the county 

seismic safety plan on January 22, 1979. The planning 

department and the investigative team were assisted by 

area advisory committees and others, including the 

California Earth Science Corporation, Lindvall-Richter 

and Associates, and R. M. Norris and R. W. Webb of the 

University of California, Santa Barbara. The Santa Barbara County Planning Department (1979, p. 7) stated 

that: 

The study consisted primarily of a 

thorough review of the general geology of 

Santa Barbara County and its compilation 

onto base maps, and an investigation of 

the main geologic and soil problems, with 

emphasis on those associated with faults 

and earthquakes. Specific geologic and 

soil problems that were considered, 

together with their effect on land use 

planning, were ground rupture, ground 

shaking, tsunamis and seiches, soil liquefaction, landslides and slope stability, 

expansive soils, soil creep, compressible 

and collapsible soils, high groundwater, 

erosion and shoreline regression, and 

subsidence. 

The county was divided into four study areas mainly 

on the basis of population patterns and potential 
development. According to the Santa Barbara County 

Planning Department (1979, p. 33), geologic, soil, and 

seismic factors "affect the suitability of land for various 

uses and ... should be considered, along with other factors, in land-use planning in order to eliminate or 

minimize their adverse effects .... " The department 

also developed the following tabulation, which provides 

a rough classification of factors to be considered in 

land-use planning: 

Critical: 

Ground rupture from fault movement 

Tsunamis and seiches 

Liquefaction 

Sometimes critical: 

Ground shaking 

High ground water 

Subsidence (normally correctable with engineering) 

Slope stability and landslides 

Soil creep 

Less critical: 

Expansive soils 

Compressible and (or) collapsible soils 

The county planning department (p. 33) concluded that: 

Ground rupture from fault offset and 

tsunamis and seiches are the only geologic 

problems for which there are no really 

feasible engineering solutions, and which 

could be considered as dominant factors 

in planning (assuming fairly frequent occurrence). Items lower on the list should 

also be taken into account during development, and probably should be given some 

consideration in planning land use or 

density. 

"Seismic Safety and Safety Element," a report prepared by the Santa Barbara County Planning Department (1979), includes a description of each geologic and 

seismologic hazard. The fundamentals of engineering 

seismology (including earthquake intensity, magnitude, 

frequency, recurrence intervals, and duration of shaking) are discussed; general seismicity and a condensed 

earthquake history are presented; a three-zone seismotectonic map for each study area is shown; earthquake 

recurrence intervals for the San Andreas and Big Pine 

faults are estimated; 47 faults classified as either active, 

potentially active, or inactive are described; five major 

areas subject to inundation by future tsunamis are identified; areas subject to liquefaction are mapped (fig. 

227); and areas subject to landsliding are identified and 

mapped. 

Application 

Geologic and seismologic information was compiled 

and transferred to USGS 71f2-min quadrangle maps 

(topographic series) at a scale of 1:24,000 (1 in=2,000 ft) 

for the four study areas. A reproducible mylar geologic 

map of the county at a scale of 1:96,000 (1 in= 8,000 ft) 

is on file at the county's public works department. The 

geologic maps show major bedrock units, surficial 

geologic units, faults, and folds. 

·The hazards were evaluated and rated according to 

their severity by applying geologic and engineering 

judgments. The areal extent and severity of the hazards 

were shown on the topographic base maps for the study 

areas. The data were then transferred to 5-acre (2 ha) 

grid base maps, and the ratings for individual hazards 

were encoded to produce computerized maps. Each 

geologic hazard evaluated was given one of three 

ratings-high, moderate, or none to low (fig. 227). 

The Santa Barbara County Planning Department 

(1979) then assigned a composite number, on the basis of 

known geologic hazards, as an overall indication of the 

difficulty of developing any particular area. The department devised a system for rating geologic hazards for a 

given area on both an individual and a collective 

basis-a system that could be implemented by computer. The resulting cumulative value was designated 

the geologic problem index (GPI). The GPI values for the 

four study areas were obtained by multiplying each 

geologic hazard by a weighting factor that took into account the seriousness of the hazard, the difficulty of 

alleviating it, and the frequency of its occurrence. The 

GPI values were then divided into five categories ranging from low through moderate to severe. 

The GPI was calculated for each 5-acre (2 ha) cell in 

the computer-analysis areas for each study area and 

then assigned to the appropriate severity category and 

displayed on a computer-produced map (fig. 228). These 

computer GPI maps thus reflect a summation of the ratings delineated on the geologic hazard maps (fig. 227). 

Recommendations then were made by the Santa Barbara County Planning Department (1979) concerning 

land use planning, subdivision procedures, grading 

codes, building codes, and land-stability insurance. The 

land use planning section, for example, contains the 

following recommendation concerning areas designated 

as severe on the GPI index: 

These areas should be given primary consideration for minimum development and 

use. They could be planned as natural 

areas, or for recreational or agricultural 

use. If development is permitted, it should 

generally be of low density. (p. 139) 

Using Earth-Science Information 451 
0' f 000' _ __.... UQU!fACTION 

VANDENBERG 

AIR FORCE BASE 

"' 

" 

" ................... . 

FIGURE 227.·-Liquefaction susceptibility for part of the Lompoc study area, prepared by the Santa Barbara County Planning Department (1979) at an original scale of 1:96,000. The white areas and lighter patterns within the computer-analysis area boundary indicate a low problem rating. The darker patterns indicate a moderate problem rating. No high problem areas are included in the region shown. 
FIGURE 228.-Summary of geologic hazards in the Lompoc study area, prepared by the Santa Barbara County Planning Department {1979) at an original scale of 1:96,000. The lighter patterns indicate low 

to moderate hazards. The darker patterns indicate moderate to severe hazards. 
One of the recommendations concerning subdivision 

procedures is that geologic reports should generally be 

required when the property contains or is near an active 

or potentially active fault or has a moderate to severe 

GPI. 

In addition, the county planning department made 

recommendations for future studies such as updating 

basic geologic maps, investigating potentially active 

faults, installing additional seismic instrumentation, and 

inventorying existing structures to determine their 

physical conditions and locations relative to potential 

geologic problems. 

Comments 

This example illustrates how a county planning 

department, assisted by planning, engineering, and 

geotechnical consultants, compiled, evaluated, digitized, 

and rated a wide range of geologic and seismologic information. The Santa Barbara County Planning Department (1979, p. 138) concluded that the time and effort 

expended on developing the GPI system for the county 

were well spent and that, 

[as] a planning aid, it shows the range in 

occurrence and severity of geologic problems within the County, providing 

valuable input necessary to the development of an intelligent plan for land use. 

The individual problem rating maps can 

be used by developers and by the various 

governmental agencies responsible for 

their supervision and guidance as an index to the specific geologic problems that 

can be expected in a particular area. 

RETROFITTING HIGHWAY 

BRIDGES 

The 1971 San Fernando earthquake represented a 

major turning point in the development of seismic design 

criteria for bridges. Gates (1976, p. 2301), a senior 

bridge engineer in the California Department of 

Transportation (CAL TRANS), reported that, before the 

earthquake, very little bridge damage was caused 

directly by vibrational effects; however, 

[after] the 1971 San Fernando event ... we 

observed a significant amount of vibrational effects on bridge structures .... 

454 Earthquake Hazards in the Los Angeles Region 

These effects were the result of very large 

vertical and horizontal ground accelerations, possibly exceeding 0.5 g .... The 

total damage to highway bridges in San 

Fernando was about $6,500,000. The major damage, especially the vibrational 

damage, was concentrated within the narrow region close to and possibly within 

the causative fault zone of the magnitude 

6.6 event. 

One of the problems was a design feature deliberately 

built into bridges and overpasses throughout the United 

States during the 1950's and 1960's. Bridge and overpass superstructures traditionally were not attached to 

the supporting piers and abutments to accommodate expansion and contraction caused by temperature 

changes; the weight of the roadbed was expected to hold 

them in place. The flaw in this design feature was not 

realized until the 1971 earthquake, when the ends of 

many bridges in the San Fernando Valley fell off the 

abutments or hinge seats upon which they sat. 

CAL TRANS has found that 1,133 of the approximately 

13,000 bridges throughout the State need attention and 

is now focusing on retrofitting the unrestrained joints of 

these bridges Q. H. Gates, written communication, 1981). 

Earth-Science Information 

After the 1971 San Fernando earthquake, a map 

showing maximum credible ground acceleration on bedrock from future California earthquakes was prepared 

by the CDMG (Greensfelder, 1972). The method used 

assumed that faults active in Quaternary time would indicate the distribution of future earthquake epicenters 

(Greensfelder, 1973). According to Gates (1976), each of 

the selected faults was then assigned a maximum probable earthquake magnitude based on Bonilla's (1970) 

data on fault rupture length. A set of curves relating 

peak ground acceleration, distance from fault rupture, 

and magnitude based on Seed and Schnabel's (1972) 

work was used to plot peak ground-acceleration values 

for bedrock sites on each fault. These values were then 

contoured to produce a map covering all of California, a 

portion of which is shown in figure 229. Gates (1976) 

discussed how this map information is combined with 

soil data and used as a basis for the seismic design 

criteria for California's bridges. 

More recently, probabilistic estimates of the levels of 

ground shaking have been made. Thenhaus and others 

(1980), for example, showed earthquake shaking anticipated in California coastal and Outer Continental 

Shelf areas on a series of six maps at a scale of 
35° 

EXPLA NAT IO N 

POTENT! AllY ACTIVE fAUlTS 

! 

Approximately located 

Number in parentheses is the maximum expected earthquake 

magnitude for the faul t 

Lines and arrows divide the San Andreas fault into four tectonic 

sec tions 

Queries at the ends of a fault indicate lock of strong ev1dence 

for its activity 

BEDROCK ACCELERATION CO NTOURS 

Units ore decimal fractions of the acceleration of gravity, from 

O.lOg to 0.50g . (O.lg Contour added by Deparotment of 

TranSportation for official use only) 

PREDOMINANT PERIOD OF BEDROCK ACCELERATIONS 

Acceleration range 

~0 .2 g 

O.l-0.2 g 

Predominant period 

0.35 seconds 

0.40 seconds 

Mean duration of motion 20·30 seconds 

0 20 40 60 MILES 

0 20 40 60 KILOMETERS 

FIGURE 229.-Maximum credible ground acceleration on bedrock from future earthquakes, prepared by Greensfelder (1972) at an original scale 

of 1:2,000,000 to show potentially active faults and acceleration contours for part of southern California. Numbers next to a fault name indicate the maximum assumed magnitude for an earthquake on that fault. 

1:5,000,000. The maps show values of peak horizontal 

acceleration and peak horizontal velocity on rock that 

have a 9G-percent probability of not being exceeded in 

10, 50, and 250 yr, the return periods being approximately 100, 500, and 2,500 yr, respectively. Algermissen and others (1982) showed earthquake shaking 

anticipated for the contiguous United States on a series 

of six maps. The maps show maximum values of horizontal acceleration and horizontal velocity in rock that have 

a 9G-percent probability of not being exceeded in 10, 50, 

and 250 yr. Hays (1980) reviewed the current procedures for specifying the characteristics of ground 

motion needed for earthquake-resistant design. 

Decision 

One of the major conclusions drawn after the 1971 

San Fernando earthquake was that deficiencies in 

details, especially at connections of major structural 

components, played a major role in all of the collapse 

failures of bridges. According to Gates (1976, p. 2302), 

Using Earth-Science Information 455 
A 

8 

Temporary deck 1 (k_Hinge Deck ace ess 

cover plate\ /pening 

l_ I f 

I 1Concrete bolster 

lr 

m 

r 

-

A -I ~ -t - 1,.:; Jl "-'--' 

Soff1t access openmg \ , Steel cover plate 

SECTION THROUGH HINGE 

6" cored hole 

End anchorage 

SECTION A-A 

~H inge (l Bent 

1 '/.'' galvanized high strength rods 

SECTION 

1

12 x 8 x 0' --8" Elastomeric bearing pad 

--::('~ d anchorage 

ck1ng dev1ce 

Detail A 

FIGURE 230.-Hinge connections designed to make concrete highway 

bridges earthquake resistant (Mancarti, 1981). Cross sections and 

details for cable restrainer (A) and high-strength rod restrainer (B) 

are shown. 

the decision was then made (1) to develop rational 

design criteria that take site-dependent characteristics 

into consideration, (2) to incorporate improved details 

into all bridges being designed and constructed, and (3) 

to evaluate and determine priorities for upgrading the 

earthquake resistance of existing bridges. Two factors 

selected for inclusion in the design criteria were the 

456 Earthquake Hazards in the Los Angeles Region 

location of the site relative to active faults and the effect 

of maximum credible earthquakes originating on individual active faults. 

A CAL TRANS bridge engineer (Mancarti, 1981, p. 1, 

2), in discussing highway bridge retrofit, described the 

types of restrainers (steel cables, rods, hinges, and 

bearing-support hardware) used to tie bridge superstructures together as well as to tie superstructures to 

substructures and stated that the main purpose is 

. . . to prevent spans from separating at 

hinges or falling off their bearing supports 

and to make structures seismically resistant to the extent that while they may sustain localized damage, they will not collapse catastrophically. It is also desirable 

that highway structures be rendered 

capable of carrying emergency traffic, 

with quickly performed temporary repairs 

so as to provide transportation lifelines 

for a stricken community immediately 

after a disaster. 

The new designs for hinges have substantial cable 

restrainers (for example, multiple units of seven %-in 

(19 mm) cables that form a tendon inside a pipe (fig. 

230A)). These restrainers allow bridges to move in small 

increments; their joints can open or close as much as 1 

to 3 in (25-76 mm), depending on the maximum amount 

needed to accommodate temperature changes. Wendell 

Pond, in a bulletin of the California State Division of 

Highways (1972, p. 3), observed that, once this movement has occurred, the restrainers are designed to limit 

further movement and to prevent collapses such as 

those that occurred during the 1971 San Fernando 

earthquake. 

Application 

Since 1971, CAL TRANS has been involved in retrofitting existing bridges. Its program began almost immediately after the 1971 San Fernando earthquake. The 

initial goal of the retrofitting program was to tie bridge 

superstructures together at hinges and bearings and to 

tie superstructures to substructures at bearing supports. CAL TRANS concentrated first on the hinges in 

the continuous structures and developed a fairly simple 

hinge restrainer unit for use in concrete box girder 

bridges (fig. 230A); Mancarti (1981, p. 3) stated that, 

"Components were easily fabricated from standard, 

available hardware and our retrofit contractors quickly 

developed the knack of installing them in structures at a 

reasonable price." Because the unit did not have a high 
enough load capacity for certain superstructure configurations in highly seismic areas, CAL TRANS developed a high-strength rod restrainer (fig. 230B). A unit 

composed of four symmetrically placed P/4-in (31.75 

mm) high-strength rods is rated at 600,000 lb design 

load. Units using one, two, or four rods have been successfully installed. They possess the additional advantage of requiring smaller holes to be cored through existing concrete elements (Mancarti, 1981, p. 4). 

Selection of structures for retrofit is currently based 

on a priority system. Mancarti (1981, p. 1) reported that 

this system 

... takes into account the bedrock acceleration at the structure site, the estimated 

cost to retrofit the structure, the cost of 

replacement in the event of loss, the ratio 

of the replacement cost to the retrofit 

cost, the length and availability of 

detours, and the average daily traffic on 

the main line as well as other factors 

which reflect the importance of the structure in the system. 

This rating technique has been put on the CAL TRANS 

computer in conjunction with an ongoing program for 

structure replacement and improvement; structures are 

then ranked for inclusion in the annual State transportation improvement program. To date, over half of these 

structures have been retrofitted at a cost of $24 million. 

According to J. H. Gates (written communication, 1981), 

current budget allocations will permit completion of all 

bridges identified as deficient by 1990. 

Comments 

The average CAL TRANS retrofit project consists of 

adding steel restrainer cables at hinge and expansion 

joints to prevent spans from collapsing. The potential for 

collapse can be minimized even if extensive damage occurs. The design criteria and priority system selected 

can be easily modified as estimates of likely shaking are 

refined and as new developments are made in earthquake engineering. 

J. H. Gates (written communication, 1981) reported 

that the CAL TRANS-designed details for restraineP 

units have evolved to the point where the systems are 

performing satisfactorily in the field, although none 

have been tested by a natural earthquake. CAL TRANS 

engineers warn that retrofitting will not keep an overpass bridge from collapsing if the fault rupture of a major earthquake is under or adjacent to the structure. 

REGULATING DEVELOPMENT IN 

POTENTIAL SURFACE FAULT 

RUPTURE AREAS 

As Ziony and Yerkes (this volume) discussed, many 

potentially active fault zones underlie the Los Angeles 

region. The surface traces of these faults are likely to be 

the sites of significant displacement during future major 

earthquakes. It is difficult and costly to design and build 

structures to withstand fault displacement. Even an inch 

or two (25-50 mm) of sudden fault movement can severely damage some structures. The probability that an 

earthquake will destroy buildings and kill or injure 

people becomes significant where high-density urban 

development or. critical facilities straddle active faults. 

Thus, the dominant strategy for reducing the hazard 

from surface rupture is to avoid potential surface fault 

rupture areas. 

If new fault traces are discovered or new areas are 

designated as hazardous, existing structures may be 

deemed unsafe. Many schools, hospitals, and other 

public and private developments have been built on or 

near the surface traces of previously unrecognized 

active faults. The 1971 San Fernando earthquake in 

southern California, for example, damaged structures 

erected over an active fault whose trace was not 

generally recognized at the time of development. Much 

of the damage associated with fault rupture can be 

limited if construction on active faults is avoided. Utility 

lines and transportation facilities can be located, 

designed, and operated to reduce outages and other 

disruptions. Some of the methods for using earth-science 

information and hazard mapping in land use planning 

and regulations have been discussed by Blair and 

Spangle (1979). 

Reconstruction, however, commonly takes place in the 

same hazardous areas after an earthquake. Youd and 

others (1978, p. 111), for example, observed that, after 

the San Fernando earthquake, " ... buildings had been 

repaired, new buildings have been built, and a freeway 

interchange has been constructed across the trace of 

the 1971 fault rupture." 

Earth-Science Information 

In California, many potentially active and recently active faults have been identified and mapped at various 

scales. A preliminary map showing recency of faulting 

(Ziony and others, 1974) shows the location of presently 

known or inferred faults in the coastal region of 

southern California and what is currently known about 

the recency of displacement along each fault. Maps by 

Using Earth-Science Information 457 
FIGURE 231.-Hypothetical fault traces showing possible complexities 

of faulting and demoo.strating the necessity for detailed geologic investigations within a broad zone astride a known fault rupture 

trace. 

the USGS and the CDMG are available chiefly at scales 

of 1:24,000 or smaller for many individual faults or fault 

rupture zones. Examples include Sharp's (1972) map of 

the San Jacinto fault zone, Sarna-Wojcicki and others' 

(1976) map of the Ventura fault, Barrows and others' 

(1976) map of the Palmdale segment of the San Andreas 

fault zone, and Weber's (1977) map of the Elsinore and 

Chino faults. 

The trace of an active fault cannot always be seen at 

the surface. It may be concealed, and the geologist may 

have to approximate its location. Displacements do not 

always occur along a single fault trace; branching, 

braided, and en echelon fault segments may result in 

wide zones of disturbance (fig. 231). Therefore, 

regulatory measures for avoiding or reducing the 

hazards of fault rupture commonly require detailed 

geologic investigations to accurately identify and 

evaluate all the strands of the faults. Once a trace has 

458 Earthquake Hazards in the Los Angeles Region 

been completely located, specific regulations (such as 

prohibiting certain uses or requiring specific buildings 

to be set back from the active strands) can be applied. 

Decision 

In response to public concern and because of the 

availability of scientific information, the California 

Legislature (1972) enacted the Alquist-Priolo Special 

Studies Zones Act. The act provides for public safety by 

restricting development near or over the surface traces 

of active faults. In addition, the act provides for geologic 

reports, approval of projects by cities and counties, exemptions for altering and adding to existing structures, 

disclosure of hazards by property sellers and their 

agents, and the charging of reasonable project approval 

application fees. 

To assist the cities and counties, the act requires the 

State Geologist to delineate Special Studies Zones that 

include all "potentially and recently active" traces of 

the San Andreas, Calaveras, Hayward, and San Jacinto 

faults and other faults that he deems "sufficiently active 

and well defined" to constitute a potential hazard from 

surface fault rupture. For the purpose of the act, a fault 

is considered "sufficiently active" if there is evidence of 

surface displacement along one or more of its segments 

or branches during the last 11,000 yr; a fault is considered "well defined" if its trace is clearly detectable 

by a trained geologist as a physical feature at or just 

below the ground surface (Hart, 1980, p. 5-6). 

The State Geologist initially delineated zones about 

one-quarter of a mile (400 m) wide. Currently, the zones 

delineated are about 400 to 600ft (13Q-200 m) wide. The 

best information available has been used to delineate 

surface traces of well-known faults on about 300 

quadrangle maps (fig. 232). Special Studies Zones are 

established by selecting turning points located at obvious features on either side of a mapped fault trace. 

The zone boundaries are drafted as straight lines connecting these points. Because fault traces vary (some 

have branching segments, curved or discontinuous 

traces, or wide areas of crushed rock), the zones are irregular and may exceed one-quarter of a mile (400 m) in 

width. Maps similar to figure 233 show faults, historical 

offsets and the years of their occurrence, displacement 

caused by creep, and lineaments seen on aerial 

photographs. Currently, the CDMG is evaluating those 

faults identified as "sufficiently active and well 

defined." Results, methods of evaluation, recommended 

zoning and zone revisions, and some of the problems encountered during evaluation have been summarized by 

Hart and others (1977, 1978, 1979). 
\ 

N G 

-

N 

t 0 

I 

0 

E L E s 

R A N G E 

I 

20 MILES 

I 

20 KILOM,FTERS 

FIGURE 232.-Part of the index to the Special Studies Zones maps showing faults zoned for special geologic studies (Hart, 1980). The official 

name of each quadrangle map and the year issued or revised are indicated. Part of the cross-hatched quadrangle is shown as figure 233. Information about the availability of the maps and their updating can be obtained from the Fault Evaluation Program Supervisor, California Division of 

Mines and Geology, Suite 100, 380 Civic Dr., Pleasant Hill, CA 94523. 

Application 

The State Geologist uses USGS 71!2-min quadrangle 

maps {topographic series) as the base for delineating 

Special Studies Zones. Information is transferred from 

published and unpublished fault and geologic maps to 

·the quadrangle maps, each of which lists specific 

references to the sources of that information. The 

geologic reports of Sarna-Wojcicki and others {1976) 

and Weber and others {1975), for example, are cited as 

the references used to compile the Ventura fault data 

for the Saticoy and Ventura quadrangle maps. As of 

January 1, 1982, Special Studies Zones encompassed 25 

counties and more than 70 cities in California; 

reproducible master copies of pertinent quadrangles 

have been provided to each affected city and county. 

The California Legislature {1972, sec. 2623) provides 

that cities and counties shall require, before approval of 

a project in a Special Studies Zones, "a geologic report 

defining and delineating any hazard of surface fault 

rupture" and that approval shall be in accord with the 

policies and criteria established by the California Mining and Geology Board. 

The California Mining and Geology Board (Hart, 1980, 

app. B) has prepared and adopted specific and detailed 

criteria prohibiting specific development in Special 

Using Earth-Science Information 459 
\ 

2708 ' p -=-" 2707 

2715 

20 2737 

r.,.·:-,·- . ,_ ... ',/ . 

...,.,. · : : __ ,-

...... 2759 -

,: 

( ' 

" 21 o.· " ... ~ t. ,. ~ 0 ··: /.~'();.:. ····;: ... c:: jlj 1 r 

.=,r: ~ 1!.·' . • ~ ', i 

I 

' ' 

p 

·, 

2638 

~- ·········• 

" I"'"''"''' . ........ .. : ......... . 

Water 

~1ti' Pa mdale-ilfllil 

/ 

............ : ... · 

., i U!\. I ,••·· · • 

. ·s .· • . .• . 26 L. 0 

~.Ll,~ J~ 

R 

FIGURE 233.-Part of the Ritter Ridge quadrangle map used by the California Division of Mines and Geology (1979) to show the boundaries of the 

Special Studies Zones (lighter lines) and their turning points (circles) along part of the San Andreas fault southwest of Palmdale. Traces of 

potentially active faults (heavier lines) are indicated by solid lines where accurately located, by a long dash where approximately located, by a 

short dash where inferred, and by dots where concealed. Geologic reports defining the hazard of surface fault rupture are required before 

development within a Special Studies Zone. 

460 Earthquake Hazards in the Los Angeles Region 
Studies Zones until a geologist, registered in California 

and retained by each city or county, has evaluated the 

geologic report that must accompany an application for 

development. The fault information shown on a quadrangle map (fig. 233) does not fulfill the requirement for 

a "geologic report"; cities and counties must require 

that a developer retain a registered geologist to evaluate 

sites within the Special Studies Zones to determine if a 

potential hazard from any fault exists. If a city or county 

finds that no undue hazard exists, the geologic report 

may be waived, if the State Geologist approves. The 

CDMG can provide information on the availability of 

waiver forms, maps showing Special Studies Zones, 

guidelines for evaluating surface fault ruptures, indexes 

to zone maps, and indexes to geologic reports within the 

zones. 

The act and the criteria allow cities and counties to 

establish more restrictive policies and criteria. One 

criterion initially adopted by the board provided that 

"[no] structure for human occupancy ... shall be ... 

placed across the trace of an active fault. ... " The area 

within 50 ft (15 m) of an active fault is assumed to be 

underlain by active branches of that fault until an investigation by a registered geologist proves otherwise. In 

1976, the California Legislature (1972, sec. 2621.6(a)) 

amended the original act to exclude " ... a single-family 

wood frame dwelling not exceeding two stories when 

such dwelling is not part of a development of four or 

more dwellings" and therefore removed such buildings 

from the board's criteria. Some cities and counties, 

however, retain the 5D-ft (15 m) setback for all structures for human occupancy; others, like the Portola 

Valley Town Council (1973), require greater setbacks in 

certain instances. The California Mining and Geology 

Board now recommends that a geologic report be required if the single-family dwelling lies on or within 100 

ft (32 m) of the trace of an historically active fault or 

other known active fault. 

The California Association of Realtors (1977) has 

published an instruction booklet on the legal obligations 

of Realtors10 to disclose geologic hazards that relate to 

the use of real estate. The California Association of 

Realtors (1981) includes, in its real-estate purchase contract form, a place for attaching information about 

Special Studies Zones. The California Association of 

Realtors (1978) has also prepared a disclosure form for 

Special Studies Zones that can be attached to the con: 

tract. The last paragraph of this form provides a space 

for the number of days that a prospective buyer has, 

from the time that a seller accepts his purchase offer, to 

make further inquiries concerning the use of the prop1

"'rhe word Realtor denotes a member of the National Association of Real Estate Boards. 

erty under the Special Studies Zones Act and provides 

that, where inquiry discloses conditions unsatisfactory 

to the buyer, the buyer may cancel the contract. 

Comments 

This example illustrates how earth-science information can be used by State legislators, State geologists, 

city and county officials, consulting geologists, and realestate buyers to avoid the hazards of surface fault rupture. The act's provisions, the board's criteria, and local 

ordinances discourage the construction of certain 

public and private buildings over faults that may creep 

or move suddenly during a major earthquake. This 

method of providing for public safety can be adapted to 

other types of potential ground failure, such as landslides or liquefaction, and to States other than California where similar hazards exist and where adequate 

scientific information is available. The fault rupture 

information on Special Studies Zones maps is used 

directly by cities and counties for other earthquake 

hazard reduction opportunities such as seismic safety 

elements, environmental assessments, and project 

reviews. 

STRENGTHENING OR REMOVING 

UNSAFE MASONRY BUILDINGS 

Officials of the city of Los Angeles know that the city 

will be subjected to intense ground shaking during a 

moderate or major earthquake. In the seismic safety 

plan adopted by the Los Angeles City Council as required by the California Legislature (1971), the Los 

Angeles Department of City Planning (1974, p. 1) stated 

that shaking 

... causes the greatest amount of damage 

from earthquakes occurring in rather 

populous areas. It is estimated the majority of structural failure that has been 

caused by earthquakes results from: (1) 

shaking which damages the structure 

directly, (2) shaking which causes soil 

failure beneath the foundation of a structure, and (3) shaking which causes the soil 

beneath the foundation to densify and settle, thus causing the structure to fail. 

The department noted that ground shaking can result 

in loss of life, personal injuries, property damage, and 

economic and social dislocations but that most of this 

Using Earth-Science Information 461 
loss is preventable. Consequently, to keep loss to a 

minimum, the Los Angeles Department of City Planning 

(1974), in an environmental impact repcrt, specified 

policies and programs regarding geologic evaluation, existing development, new development, critical facilities, 

emergency preparednesss, and postdisaster recovery. 

The major earthquake-related problem faced by the 

city is the strengthening or removal of existing hazardous buildings. The policies adopted concerning existing 

development include recommendations that: 

• Buildings that do not meet requirements for seismic safety should be 

strengthened or removed in an orderly 

manner. 

• Priorities for seismic upgrading of existing buildings should be based on the 

hazard to life, the type of occupancy, 

the location of the structure, and the 

capability of the structure to withstand 

earthquake forces. 

Some specific ways listed to implement these policies 

are: 

• Giving priority to pre-1934 unreinforced masonry structures, starting 

with structures that are most hazardous to life. 

• Considering an amended building code 

that would evaluate existing pre-1934 

unreinforced masonry structures on 

their ability to meet an acceptable level 

of seismic safety. 

• Considering an ordinance that would 

require building owners to conduct 

structural surveys and (or) seek State 

or Federal funding to identify structures that do not meet lateral force 

requirements. 

In 1976, the mayor of Los Angeles established a task 

force to explore and evaluate the range of possible city 

responses to an earthquake prediction. The Los Angeles 

City Task Force on Earthquake Prediction (Dunne, 1978, 

p. 21) identified unreinforced masonry structures built 

before 1934 as the greatest life hazard in an earthquake 

and recommended that "priorities for reinforcement, 

decreasing occupancy levels, or demolition should be 

established before we are confronted with a credible 

earthquake prediction." 

A complete inventory of pre-1934 masonry buildings 

was conducted by specially trained city building inspectors to document the nature and extent of the problem 

462 Earthquake Hazards in the Los Angeles Region 

and then was made available to building owners and 

other interested persons. There are at present approximately 8,000 pre-1934 unreinforced masonry buildings 

in the city of Los Angeles (fig. 234). These buildings have 

been classified by the Los Angeles City Building Department (1979, p. 3) as follows: 

Use 

Commercial -------

Industrial ---------

Apartment --------

Hot~ -------------

Public ------------

Other-------------

Total ----------

Number 

4,108 

2,393 

811 

268 

134 

162 

7,876 

More than 80 percent of these structures are commercial and industrial buildings providing places of employment for an estimated 70,000 workers. About 14 percent 

are residential apartments and hotels containing nearly 

46,000 units housing perhaps 137,000 persons (Los 

Angeles City Planning Department, 1980, p. F-iii). 

Because these structures are vulnerable to total collapse or to the shedding of outside walls under moderate 

to strong ground shaking, they present a substantial risk 

to their occupants and to passersby. The department 

concluded that, "It is the consensus of seismic safety experts that these pre-1934 unreinforced masonry buildings represent the greatest single threat to life and limb 

in Los Angeles in the event of a major quake." According to the Los Angeles City Planning Department (1979, 

p. 4), the unreinforced masonry buildings constructed 

before 1934 were found to be more vulnerable to earthquake forces than anyone had realized when they were 

designed and built: 

This fact was dramatically demonstrated 

during the Long Beach quake occurring in 

March of 1933 and the San Fernando 

Valley quake and aftershock of February 

and March of 1971. Earthquake resistance in buildings has deteriorated over 

the years due to factors such as: decreases in the strength of construction 

materials, fire damage, foundation settlement, alterations that have weakened 

structural elements, and damage sustained in past earthquakes. 

Earth-Science Information 

Many estimates of potential ground shaking and its effects are available for the Los Angeles region-for ex-
CANcx;A PARK 

WINNETKA 

WOODlAND HILLS 

N 

t 

0 

0 

RESEDA 

WEST VAN NUYS 

19 

BRENTW(X)O 

PAOFIC PAliSADES 

15 

10,000 FEET 

FIGURE 234.-The number of unreinforced masonry buildings originally verified in the field for each census tract by 

the Los Angeles Department of Building and Safety (Los Angeles City Planning Department, 1979) are shown here 

by community area. Similar diagrams are available showing the number of dwelling units in apartment buildings or 

the number of guest rooms in hotels and motels. Unnumbered areas are outside the city's corporate limits. 
ample, maximum credible ground acceleration (fig. 229) 

(Greensfelder, 1972), earthquake losses (Algermissen 

and others, 1973), seismic risk zones (International Conference of Building Officials, 1979, fig. 1, p. 145), probabilistic estimates of maximum horizontal ground 

motion (Thenhaus and others, 1980), predicted intensities (Evernden and others, 1981), and maximum 

horizontal acceleration and horizontal velocity (Algermissen and others, 1982). Using Algermissen and others' 

(1973) estimates for losses from a major earthquake in 

the Los Angeles area and assuming that 70 percent of 

those losses would be within the Los Angeles city limits, 

the Los Angeles City Planning Department (1979, p. 4) 

estimated that, if a structural improvement program 

was not implemented, up to 8,500 deaths and 34,000 

injuries could be caused by damage to unreinforced 

masonry buildings. 

Decision 

After 2 yr of deliberation, an ordinance amending the 

building code of the city of Los Angeles was formulated 

by the Los Angeles Earthquake Safety Study Committee 

(1978) and submitted to the city council in 1979. The ordinance was designed to reduce earthquake hazards by 

requmng the strengthening or removal of pre-1934 

buildings that have bearing walls of unreinforced 

masonry. The strengthening standards were not identical to those required for new construction but were 

especially adapted to the type of construction used in 

these older buildings and to their typical weaknesses. 

Because the cost of compliance was expected to be 

high, the Earthquake Safety Study Committee requested 

that a detailed cost study be prepared. The city council 

authorized and funded a structural engineering cost 

study, which was carried out by Wheeler and Gray, Consulting Engineers, under contract to the Los Angeles 

Department of Building and Safety (Los Angeles City 

Planning Department, 1979, app. G). The consultants 

evaluated a four-story apartment building, two-story 

apartments over a one-story industrial building, a onestory warehouse, a one-story warehouse with a mezzanine, and a two-story commercial and office building. 

According to the study, total compliance costs calculated for these five actual buildings ranged from $6.22 to 

$12.08 per square foot. The estimated cost of anchoring 

the walls to the floors and roof ranged from $1.00 to 

$1.60 per square foot. 

Some of the advantages of the proposed ordinance, as 

noted by the Los Angeles City Planning Department 

(1980), were that (1) the city's greatest single hazard to 

464 Earthquake Hazards in the Los Angeles Region 

life would be substantially reduced and casualties 

reduced perhaps fivefold; (2) buildings not worth repairing would eventually be demolished and land possibly 

made available for more productive use; and (3) repair 

or demolition would provide work for the construction 

industry. 

Some of the disadvantages of the proposed ordinance 

were that (1) some of the city's lowest priced housing 

would be demolished; (2) tenants would probably have to 

be temporarily relocated while remedial work was carried out; (3) rents in affected buildings would have to be 

increased to amortize the expense of repairs; and (4) interruption of normal business during remedial construction would impose severe hardships on many small 

businesses and perhaps force layoffs and closures. 

The Los Angeles City Planning Department (1980, 

p. F -iv) made a number of recommendations for 

mitigating some of the ordinance's adverse impacts. In 

the case of historical buildings, for example, adverse impacts and measures to alleviate them were assessed as 

follows: 

Adverse impacts.-Some buildings demolished under 

the proposed ordinance could have historical significance. Loss of irreplaceable cultural resources could 

result. 

Recommended or code-required mitigation measures.-Proposed regulations have been prepared to incorporate the provisions of the State Historical Building 

Code into the ordinance. These regulations provide 

alternative requirements for designated historical structures to facilitate their preservation. 

Net mitigated adverse impacts.-Historical buildings 

will not be exempted from remedial measures, but the 

special provisions should make it unlikely that any 

would have to be demolished. 

The alternative of upgrading existing buildings to 

meet current standards for new buildings was considered in 1976 but not adopted by the city council. The 

alternative of no ordinance was considered but, according to the Los Angeles City Planning Department (1980, 

p. F -vii), would have tended 

... to preserve the status quo, leaving any 

remedial measures to the discretion of 

building owners. It is considered unlikely 

that many would choose to make the necessary investment. The likely result would 

be heavy casualties and property damage 

in the event of a major earthquake. 

The proposed ordinance was approved and adopted by 

an 11 to 3 vote of the Los Angeles City Council on 

January 7, 1981 (fig. 235). 
Application 

The ordinance provides systematic procedures and 

standards for identifying and classifying buildings 

having unreinforced masonry bearing walls; these procedures and standards are based on a building's present use and occupancy. Priorities, time periods, and 

standards are also established under which buildings 

are required to be structurally analyzed and anchored. 

Where analysis determines deficiencies, the ordinance 

requires that a building be strengthened or demolished. 

The ordinance applies to all buildings having bearing 

walls of unreinforced masonry that were constructed or 

under construction before October 6, 1933, or for which 

a building permit was issued prior to October 6, 1933, 

the effective date of the city's first seismic building 

code. The ordinance does not apply to detached one- or 

two-story single-family dwellings and detached apartment houses containing less than five dwelling units and 

used solely for residential purposes. 

Affected buildings are classified according to type of 

function and occupancy as essential, high-risk, mediumrisk, and low-risk buildings (fig. 235, sec. 91.6803). The 

strengthening standards and time schedules for notification and compliance vary with the risk category. A 

structural analysis of each individual building is also required in order to determine the remedial measures 

necessary to meet the appropriate standards. A specific 

time schedule is provided (fig. 235, sec. 91.6805). 

An alternative compliance schedule, intended to 

lessen the financial and social impacts of the ordinance, 

gives a building owner the option of performing a portion of the remedial work within 1 yr of notification in 

exchange for a longer time in which to reach full compliance. The work to be performed within a year involves the anchoring of unreinforced masonry walls to 

the roof and to each floor of the building with bolts and 

washers. This procedure yields an immediate and substantial improvement in safety for perhaps one-fifth the 

cost of full compliance (Los Angeles City Planning 

Department, 1979, p. 5). The compliance schedule, including the anchoring alternative, has the following 

features: 

• All affected buildings are scheduled to be 

strengthened within 14 yr. 

• It will take at least 4 yr to notify all affected 

owners. 

• Building owners have the option, after notification, of either anchoring all the building 

walls within 1 yr or strengthening the entire 

building within 3 yr. 

• If the walls are anchored within 1 yr of notification, 1 to 7 yr more (depending on the building risk classification) are allowed for full 

compliance. 

In addition, the ordinance provides for service of orders, 

appeals, and enforcement. Various analyses and design 

factors, such as allowable stresses of construction 

materials, alternate materials, and minimum acceptable 

quality of existing unreinforced masonry walls, are 

specified. As of January 8, 1983, the Los Angeles Department of Building and Safety has issued 895 orders to 

owners to meet minimum seismic standards. Over 200 of 

those so notified have chosen to use the wall-anchor 

alternative and are now in the automatic extension 

period (Earl Schwartz, oral communication, 1983). A Los 

Angeles city councilman (Hal Bernson, written communication, undated) emphasizes that 

... this is a life safety rather than a property ordinance. That is, the level of 

seismic resistance that we provided in the 

ordinance does not necessarily guarantee 

than the structure will come through a 

major earthquake intact, or even usable. 

It is intended to assure that the structure 

will not collapse outright. This resulted 

from a compromise between optimum 

engineering goals and rehabilitation 

costs. Other cities may, and have, set their 

compromise at a different point,. 

Comments 

According to the Los Angeles Earthquake Safety 

Study Committee, compliance with the provisions of this 

ordinance could reduce the number of deaths within the 

Los Angeles city limits from 8,500 to 1,500 and the 

number of injuries from 34,000 to 8,000 for a single 

future earthquake. It was estimated by the Los Angeles 

City Planning Department (1979, p. 4) that a major earthquake in the Los Angeles area would result in structural 

damage to about two-thirds of all old unreinforced 

masonry buildings. Implementation of the ordinance 

would reduce this structural damage by approximately 

three-fourths and save an estimated $900 million in 

building costs. 

OTHER EXAMPLES 

Many other examples of how geologic and seismologic 

information is or might be used to reduce earthquake 

Using Earth-Science Information 465 
Ordinance No. 154,~7 

An ordinance addine Division 68 of Article 1 of Chapter IX of the 

~o;x'fs1?~~e~u~~i"ni9!~al ode relative to earthquake hazard reduction 

Section 1. Artrcle 1 of Chapter IX of the Los Angeles Municipal 

Codb 1\l'1~1'5'~ ~m.:_n~~~~~'lfuaA~~i'j.\'J..'t lk D'k"gbucTION IN EX- ISTING BUILDINGS SEC. 91.6801. PURPOSE: The purpose of this Division is to promote public safety and welfare b(s reducln~ the risk of death or rnjury that ma'b;esulf from 

b~,,3t~e; ~o~~t~~~e~u~~~~e ~9¥.t~'g~t~r~~ftd~a~~~~e .,::~"aid'~~ recognPzed for their sustalnlng.of life hazardous ~amage as a result of partfal or complete collapse during past moderate to strong earth· quakes. The provisions of this Division are minimum standards tor struc· tural seismic resistance established primarily to reduce the risk of life ross or in(ury and wHI not necessarily rrrevenf loss of life or Injury 

:ifh1~:~ es~~t~d"aur~~~ cttTsa8TJ~rt, e:~~'~"~o~u;~~~Pr;"~~~~tf~~~~:~ 

tr~f:~s tf. ~~~'rr8h~=~h~!'~~~~ f6li\~~r ~:~~~rf~~tems to be altered 

This B'ivlsion provides srcstematic procedures and standards for 

b~,rJi~~~:~~~C:."~n c:~:r~fJ~:~e n1 ~fs~~~~~~~~~ffe~ trr:::op~/i~: ~~~sf:~~ dards are also established under which these buildings are required to 

~lns~~U~~Ii~~~~J~:,Iy~~Sfa~~vf:lg~or~u~~:r1ht~e b~7rdrn~S roet~ stre~thened or demolishtW. 

under f1~~~s8~f-tn'fes~~t~f t~!oe~~~~o~~~~d~~~rni~t~~~i~~~=~~:~~~hf~ eluded in this Division. SEC. 91.6802. SCOPE: The provisions of this Division shall apply to all builings con- structed or under construction prior to OctoDer 6, 1933, or for which a 

ft~~dj~~eP~f~!t ~~Ji~!~~~ ~~~! ~':,?e~~~~~~:C. ~~S~~~c~~rl~~~~,f~ as defined herein. • EXCEPTION: This DiVIsion shall not apply to detached one or 1;; ~~~ s'"¥h~anmNJe dd~~lir~~ ~~~sd:~~c~:~daf~~lr;r~: ~~~~~~~~rt;~~~ 

poselEc. 91.6803. DEFINITIONS: For !3urposes of this Division, the a~pllcable definitions in Section~ls'.-e~?J1aTn~~Mi~g of~~~· ~~~~fn"gd ho"u~~~gw~n~~C::,~\~n~vbther 

;;ep'!!fi~~ ~~~~i~Xs~a~~n~c~~~~~~\,~~n':n~~gJ1~~~t~~e~~~:~to~r:~J~6~~ munication centers. High Risk Building: Anfc buildin~, not classified an essential 

~f~~~~~o~:6}1%cf~c~~~U:n,~~~~d ~:_de ermined by Section 91.3301 (d) 

_ EXCEPTION: A high risk building shall not include the followmg:l. Any building having exterior walls braced with masonry crosswalls or wood frame crosswalls spaced less than 40 feet apart in each story. 

2. AnY. building used for its intended purpose, as determined by 

the ~~~f6rti~a,ntB~Yrd i~~s:tht~/ :U~~J~~~ed~1e~ated as an historical 

building by an appropnate Federal, State or ~ity jurisdiction. Low Risk Building: Any building, not classified an essential buildinfl.; having an occupant load as del-ermined by Section 91.3301 (d) 

of leAAed~"J R~~uG~i7~~ng: Any building, not classified as a high risk 

~W~~~"~voSe~~;;~1~JAg~ <~~~~~irogoc~~vi~~t:rir ~~~~~nt toad as dPterunreinforced Masonry Bearing ~all: A masonry wall having all of the following charactenstics: 1. Provides the vertical support for a floor or roof. 2. The total su'ferimposed load is over 100 pounds per linear foot. 3. The area o reinforcin~ steel is less than 50 percent of that requlr~~~y it2~b~n ~WWJ\:U~i?I~~~'};TioNs: The rating classifications as exhibited in Table No. 68-A are 

~~~f,b~es1:~~~hi~d o~~d s~~~h r~~i~d~~~a~~~W~aW~ns~opfh~f b~~a~i~~~r The totar occupant load of the en~ire building as ~termined by Sec- tion 91.3301 (d) shall be used to determine the rating classification. 

builcTI~~ e ~~~?r~~t:Crto t~~t ~~1e~~~d~~tl~i~R;;~i~~s7Stfn~t~~Pssmf~ forces may be placed in separate rating classifications. 

TABLE NO. 68-A 

RATING CLASSIFICATIONS 

Type of Buildinq Classification 

Essential Building I 

High Risk Building II 

Medium Risk Building III 

Low Risk Building IV 

SEC. 91.6805. GENERAL REQUIREMENTS: The owner of each building Within the scope of this Division shall cause a structural analysis to be made of the building by_ a civil or structural engineer or arthitecf licensed by the State of California; 

and, if the bulldillQ does not meet the minimum earthquake standards specified in this Division, the owner shall cause it to be structurally altered to conform to such standards; or cause the building to be demolished. The owner of a building within the scope of this Division shall 

g>e~g~¥m~i~r f~~er;:f!~)/!W~"nt:h~e~t!~~~hti~~Yt:,.,~fs~ubmitting to the 

a_ Within 270 days after the service of the order, a structural 

~:~r,s~sha~r~~~~~~~~st;vr~~~ f~:ubbj~atnt~ ~~~vr~eb~t~fm~~a{~~ quirements of this Division; or b. Within 270 days after the service of the order, the structural 

g~~~~~~ ~~~efs~a,.r;,s tb ~o~~~~f~PfhS:~f~~~c~~a:e~~,~~~~n1i gJ tti~ Division; or 

tion ~·~ ~~n~~~~~r~~~ ~~~6~d~~~'ee ~lt~rh~~~uf~=~~~~~ ts~~~r,t:J r~ Section 91.6808 (c); or d. Within 270 dav.s after the service of the order. plans for the demolition of the building. 

own::~1:"afl ~gfaT~~ ~u~~~~t~d :r~if,Pfo'"::,~~n~~ ~hned~g~a;lttW:me tr~: ~uir'd construction or demofftion within the time limits set forth in 

or~er '~~~~~~~·iX~~~~:~~~d!~~\~ h;iJ ~itiGo~~~lf~~~ (~l~ date the 

466 Earthquake Hazards in the los Angeles Region 

TABLE NO. 68-B 

TIME LIMITS FOR COMPLIANCE 

Required Action Obtain Building By Owner Permit Within 

complete Structural Alterations or 

Building 

Demolition 

wall Anchor Installation 

1 year 

180 days 

Commence 

construction 

Within 

180 days* 

270 days 

*Measured from date of building permit issuance. 

Complete 

Construction 

Within 

3 years 

1 year 

Owners electing to comply with Item c of this Secti_on are also re- Quired to comply wTth Items D or d of this Section provided, however, that the 270-day per-iod provided for In such Items D and d and the time limits for obtaining a building permit~ commencing construction and 

6~Wcfi~~~~gm~fa~~us~\ ~~rt~~'n -f~{Rf ~b~ 6/-V3us~t~l)~ :!l:~~t~~~ a~~ cordance with Table No. 68-C. Each such extended tim~ limit, except 

l~: ~~: ~~~ 6r~~,c~n;.r;;.~~~~7~ ~~~~~d~c..r~~n;n~~~~6~ t~1~6~f~~T. l-~'int~~eedl~~i~h~bJi~d'i~e;;~:;,9t~~7:!~~~1on shall commence to run 

TABLE NO. 68-C 

EXTENSIONS OF TIME AND SERVICE PRIORITIES 

Ratinq 

classification 

I 

{Highut Priority) 

II 

IV 

(LQwest Priority) 

Occupant 

LOad 

100 or more 

100 or more 

More than 

50, bu< 

less than 

100 

More than 

"· but 

less than 

51 

Extension of Time 

if Wall Anchors 

are Installed 

1 year 

3 years 

5 years 

6 years 

' years 

Less than 20 7 year5 

Minimum Time 

Periods for 

Service of Order 

90 days 

1 year 

2 yea.r5 

J years 

4 years 

~!)c5:r\if~ Df1Pr~r~+~~~~~!~t~ent shall issue_an_order:. a_s pro- vided in Section 91.6806(bl. to the owner of eac~ puJid1ng w1thm, the scope of this Division in accordance. with the mm1mum t•me_p~nods for service of such orders set forth 1n Table No. 68-C. The mm1mum time period for the service of such orders shaH be measured fr~m the effective date of this Division. The Departm!=tn! shall upon rece.•Pt of.a written request from the owner, order a bUIIdtng to _comply w1th th.1s Division fcr1or to the normal service date for sucfl bu1ld1ng set forth tn 

this ~~ftcoonritents of Order. The order shall be_ written af"!d shaH be 

~r;:~:~ ae~t~~6Jne6~~~! 1a~f ~Ju~f1~t~~e:s~;s~~~~1~r~e~~~g~n ufh~n p~r~ 

~~~·,,'fs~~li·f~ nt~Cf1h:n~u~r~~ge ~~s cg~~,o~~fet~~ i~~~db~ t~~h6:~~~~ ment to be within the SCOP.e of ~his Dlv1sion and, thereJa:re. ts requ~red to meet the minimum seismic standards of this OtvtS!On The order shall specify the rating class~flcatlon at the. building and shall be a~­ companied by a copy of Sect1on 91.68p5 whtch sets lorth the owner s 

alte~~~tA,veie~7~~~~ g::'d~~!¥'h~~~~~~~~~er,son in char e or ~ont.rol of the buflding may apP.eal the Departm!=tnt s l.n!tial d~ermmat1on that the buildmg is witt-jin the scope of thts DiviSion to the Board of Building and Salety Commissioners. Such appeal shall be filed !Vith the Board within 60 days from the service date of the order descnbed in Section 91.6806(b). Any such appeal shall be decl~ed.by the Board 

n~~rt:~aWaGe6o~:J: ~~te~:nrnga~ep~~ata~hpergcfl:~! 'iof~~~· ~~;~,cf.fd rherefor, by the Def,artment and ttie grounds thereof shall be St?ted 

f~a~~y s'!7dt~~t'~,cil~e fa~:cr-:p~e~~~n~~ ~~-~io~O~frhn~eeo~y tn~~~~~~ 

Mun1ci~:!~~drerequests tor slight modifications from any otl-fer: de~er:­ minaWons, orders or actions by the Department pursuant to t~ts D•"::•· sion, shall be made In accordance with the procedures established '" 

Sectir~) ~~~;raatlon. At the tim.e that the DeP,arrment seryes t.he aforementioned order, the Supertntender:-t of Butldmg shall f1ie JJY•th the Office of the County Recorder a certlftcate statlnglhat the subJect building is within the scope of Division 68 - Earlhquake Hazard Reductton in Existing Buildings- of the Los Angeles Municipal Code. The certificate shan also sfate that the owner thereof has been ordered to structurally analyze the building and to structurally alter 

or d1f"t~~s~~~~r,erei;oe1f~~~~'ee~li~~~isf~~n~8 ~o~o;oe~i~1f~tn the 

scope of this Divls~on, or Is structurally capable of resisting minimum seismic forces required by this Divtsion as a result ol structural 

~Nif1~~'8ff~~ea~f ~~=~~~~nt~hki~Cr'a~~t=~~~~:fi~~t~u~!~~?n!~,~~~ t~: 

grJ,~~o~f 6~h~s~~~,~~~~~~~i~~z~;J>W.~u~\1~~ir~e~:r~W~~ lrj,~~~~~i ~ of the Los Angeles Municipal Code. 

of t~:>s~b'i~;tct~f2,tri If l~tTs f'oni~~rpy~h:~R.e~~~n 6~dc;rar~s~~d c~nt{h ~ Department pursuant~o this Division within any of the time llmlfs set forth in Section 91.6t!S, the SuP.erlntendent of Building shall order tha1 

~~1if"st~~t ~':-~~~n~ase b:ec~t~~~PWe~h~i1g~ ~u~lg:.:;91 i~e:C: ~it~c:~~ order has not been accomplished within 90 dav.~_after the date the building has been ordered vacated or such add1t1onal time as m~y 

~:~eo~fonn~~a~~~~~da~hc~ ~i'~dt~~~~~~~;rg;:~t~~~f,~tn "9f.bfO~~,·l,~ 

this~~e-91.6807. HISTORICAL BUILDINGS: (a) General The standards and procedures established by this Division shall aPply In all respects to an historical building except that as a means to preserve. original .archltect!Jral e.l~ments and facilitate restoration, an histoncalbulldm~ may. '"addtt1on, comply 

with(l,h)e rfn~~~~~do(:il~onkA~:Of~{;h ~~ ~~:~t~~isting or re-erected 

walls of abode construclion shall conform to the followtng: l. Unreinforced abode masonry wall shall not exceed a height or length to thickness ratio of 5, for exterior bearlng_walls and must bEJ 

~a~Y~~~i~~hu~r~~~~~ra:gt~~~a~g:6,~~~:st~d ~t~f~,~~~~~~d~h 
hazards in the Los Angeles region can be cited under 

several general headings. 

Preparing Development Studies 

and Plans 

Earthquake hazard reduction techniques under this 

heading include land use planning and reconstruction 

after earthquakes (Spangle and Associates, Inc., and 

others, 1980); preearthquake planning for postearthquake rebuilding (Spangle and Associates, Inc., and 

others, 1981); environmental impact analyses of growth 

forecast (Southern California Association of Governments, 1982); Long Beach city seismic safety element 

(Woodward-McNeill and Associates, 1975); derived seismic zones for the city of Simi Valley (Envirocom Corporation, 1974); seismic safety study for the city of San Diego 

(Woodward-Gizienski and Associates and F. Beach 

Leighton and Associates, 1974); risk determination and 

land use suitability (Riverside County Planning Department, 1978, p. 11-1-11-9); criteria for preparing environmental impact reports (Los Angeles County Department 

of Regional Planning, undated); guidelines for preparing 

and implementing city and county general plans and 

plan elements (California Office of Planning and 

Research, 1980); and a policy map for special management areas (Los Angeles County Department of Regional 

Planning, 1980, p. 11-41). 

Designing and Building Structures 

Earthquake hazard reduction techniques under this 

heading include guidelines for preparing geologic and 

seismologic reports (Association of Engineering 

Geologists, 1973); guidelines for preparing engineeringgeologic reports (Ventura County Department of Public 

Works, 1974); guidelines for preparing geologic reports 

on offshore operations and facilities (California Division 

of Mines and Geology, 1975); review of the adequacy of 

the seismic design basis of nuclear generating stations 

(U.S. Nuclear Regulatory Commission, 1981, p. 97-108); 

dynamic stability analysis of hydraulic fill dams by the 

California Department of Water Resources Gansen and 

others, 1976); evaluation of geologic hazards along an 

existing water main (Los Angeles County Department of 

..... FIGURE 235.-Part of the Los Angeles City Council (1981) earthquake 

hazard reduction ordinance requiring owners of buildings having 

unreinforced masonry bearing walls constructed before October 6, 

1933, to obtain a structural analysis. If the building does not meet 

the minimum standards, the owner is required to strengthen or 

remove it according to a specific time schedule. 

County Engineering, 1977); study of a roadcut failure 

and recommendations for corrective measures (Los 

Angeles County Department of County EngineeringFacilities, 1979); homebuilders guide for earthquake 

design (U.S. Department of Housing and Urban Development, 1980); design and construction of police communication and emergency operating center (Los 

Angeles County Sherifrs Department, undated); study of 

the minimum earthquake forces to be used in the design 

and construction of structures (International Conference of Building Officials, 1979, sec. 2312); and 

recommendations concerning the seismic safety and 

engineering design of a proposed liquefied natural gas 

terminal (LNG Seismic Review Panel, 1981). 

Discouraging New or Removing 

Hazardous Development 

Earthquake hazard reduction techniques under this 

heading include an instructor's guide for a "hands-on 

earthquake learning package" (Southern California 

Earthquake Preparedness Project and Environmental 

Volunteers, Inc., 1983); recommendations for reducing 

hazardous buildings (California Seismic Safety Commission Hazardous Building Committee, 1979); developing 

awareness among members of the architectural profession (American Institute of Architects Research Corporation, 1975); earthquake advisor's handbook for 

wood-frame houses (University of California Center for 

Planning and Development Research, 1982); getting 

ready for a large earthquake (Sunset Magazine, 1982); 

estimating potential insured earthquake loss (California 

Department of Insurance, 1982); and guidelines for 

earthquake disaster prevention (United Nations, 1976, 

p. 39-55). 

Regulating Development 

Earthquake hazard reduction techniques under this 

heading include guidelines for determining credible and 

probable earthquakes (California Building Safety Board 

Geotechnical Subcommittee, 1975); State regulations for 

designing and constructing elementary and secondary 

school buildings (California Education Code, section 

39140 and following) and community colleges (section 

81130 and following), for repairing, reconstructing, or 

replacing unsafe school buildings (section 39210 and 

following, section 81160 and following), and for making 

geologic- and soil-engineering studies of public school 

sites (sections 39002, 81003 and following); recommendations for reducing landslide damages (California 

Using Earth-Science Information 467 
Assembly Select Committee on Landslide Prevention, 

1980); fault investigation and evaluation of potential for 

surface rupture before land subdivision (EberhartAx:ten and Associates, Inc., 1980); model ordinance for 

an earthquake building code (Wiggins and Moran, 1971, 

app. F); ordinance for earthquake hazard reduction in 

existing buildings as part of a redevelopment plan (Santa Ana City Council, 1981); seismic design guidelines for 

Southern California Edison Company electrical substation facilities (Ostrom, 1976; Conway and others, 1978); 

siting criteria for liquefied natural gas facilities (California Public Utilities Commission, 1979); cost-benefit 

analyses based on isointensity maps and computed for 

different building codes (Pate and Shah, 1980); and fault 

rupture zone information and its disclosure (San Fernando Valley Board of Realtors, Inc., 1976). 

Preparing for and 

Responding to Disasters 

Earthquake hazard reduction techniques under this 

heading include risk analysis, facility design, and 

emergency response planning (Southern California Gas 

Company, written communication, 1979); emergency 

response planning (Metropolitan Water District of 

Southern California Earthquake Committee, 1978); 

automated database for disaster preparedness planning 

and response (Hoffman and others, 1983); educational 

program and school emergency preparedness and 

response (Los Angeles Unified School District, 1975); inspection of State water project facilities following an 

earthquake (California Department of Water Resources, 

1981); and planning for earthquake prediction response 

(Los Angeles City Office of the Mayor, 1980). 

SUMMARY 

The examples presented or listed in this chapter 

include anticipating damage to critical facilities; preparing, adopting, or implementing seismic safety 

studies, plans, and programs; retrofitting highway 

bridges; regulating development in areas subject to fault 

rupture; strengthening or removing unreinforced 

masonry buildings; and many others. The collective effect of these activities is to provide greater public safety, health, and welfare for individuals and their 

communities. 

The examples are typical of the problems faced by 

planners, engineers, and decisionmakers and the actions that they could take to reduce the effects of future 

468 Earthquake Hazards in the Los Angeles Region 

earthquakes. Their innovative responses are based on 

the use of geologic and seismologic information to 

reduce earthquake hazards and property damage. Each 

plan or decision was influenced by many factors-the 

nature of the geologic hazard, public concern, strong 

community interest, State enabling legislation, the 

availability of scientific information, and the ability of 

geologists, engineers, planners, and lawyers to incorporate the information into a study, plan, program, or 

regulation. 

The criteria and methods used in each example can 

be valuable to other urban regions where similar earthquake hazards exist and where adequate scientific information is available. The adaptation to and adoption 

by other jurisdictions and users depend on similarities 

in public awareness, enabling legislation, targeted 

issues, order of priorities, community interests, and 

abilities of planners, engineers, and decisionmakers. 

Some of the geologic and seismologic information 

needed for prudent land use and general planning in the 

Los Angeles region is available but generally not at the 

level of detail and scale needed for engineering and 

decisionmaking. Even greater detail at larger scales 

ranging from 1:1,200 to 1:12,000 (1 in= 100 to 1,000 ft) is 

needed for other purposes, including development planning, site investigation, ordinance administration, project review, and permit issuance. Public staffs and consulting firms either have or can develop this information 

in greater detail and at larger scales. 

Earthquake hazard research is continuing, the information base is improving, the methods for evaluating 

hazards are being perfected, and new reduction techniques are being tested. Planners, engineers, and decisionmakers (both public and private) need to recognize 

these facts and use the latest information, methods, and 

techniques, but they cannot be expected to have the 

training or experience necessary to understand and use 

untranslated scientific information. Therefore, if nonscientists are to benefit from this information, it must be 

interpreted and transferred to usable maps. Such information includes recurrence intervals for major earthquakes, relative intensities of ground shaking, susceptibility to landsliding, locations of active faults, potential 

for liquefaction, and predicted geologic effects of 

postulated earthquakes. 

Within the Los Angeles region, planners, engineers, 

and decisionmakers (public and private) live and work in 

a complex enviro~ment. Moreover, the geologic environment is just one aspect of their life and work. Other 

aspects include social, economic, political, and esthetic 

considerations, some of which are more apparent or 

more important to individual planners, engineers, or 

decisionmakers and their constituents. 
Even with adequate research, accurate information, 

usable products, effective communication, and proper 

use of the appropriate earthquake hazard reduction 

techniques, the lasting effectiveness of such techniques 

depends on many other factors, including: 

• Continued awareness and interest by 

the public and their decisionmakers. 

• Meticulous updating of hazard· information and maps by geologists, seismologists, and geotechnical engineers. 

• Careful revision of enabling legislation 

(if needed) by legislative bodies. 

• Accurate site investigations by 

registered geologists or geotechnical 

engineers. 

• Conscientious administration of regulations by inspectors. 

• Consistent enforcement by government 

officials. 

• Sustained support of inspection and enforcement officials by political leaders. 

• Judicious adjustment of regulations by 

administrative-appeal bodies. 

• Skillful advocacy by public officials and 

informed interpretation by the courts, if 

the regulations are challenged. 

• Concern for individual, family, and 

community health, safety, and welfare 

by home buyers and real-estate 

developers. 

Using Earth-Science Information 469 
470 Earthquake Hazards in the Los Angeles Region 
REFERENCES CITED 

Introduction 

Bancroft, H. H., 1884, History of California, 1542-1800, v. 1, in The 

works of Hubert Howe Bancroft, v. 18: San Francisco, A. L. Bancroft, 744 p. . 

Blair, M. L., and Spangle, W. E., 1979, Selsmic safety and land-use planning-Selected examples from California: U.S. Geological Survey 

Professional Paper 941-B, 82 p. 

Borchardt, R. D., ed., 1975, Studies for seismic zonation of the San Francisco Bay region: U.S. Geological Survey Professional Paper 

941-A, 102 p. 

California Legislature, 1971, Planning and zoning law, as amended: 

Sec. 65302(!), West's annotated California Government Code. 

California Legislature joint Committee on Seismic Safety, 1974, Meeting 

the earthquake challenge-Final report to the Legislature, january 

1974: California Division of Mines and Geology Special Publication 

45,223 p. 

Executive Office of the President, 1978, The National Earthquake 

Hazards Reduction Program: Washington, D.C., 30 p. 

Federal Emergency Management Agency, 1980, An assessment of the 

consequences and preparations for a catastrophic California 

earthquake-Findings and actions taken: Washington, D.C., 59 p. 

Hopkins, D. M., 1975, Time stratigraphic nomenclature for the 

Holocene epoch: Geology, v. 3, no. 1, p. 10. 

Izett, G. A., 1982, The Bishop ash bed and some older, compositionally 

similar ash beds in California, Nevada, and Utah: U.S. Geological 

Survey Open-File Report 82-582, 44 p. 

Kockelman, W. j., 1975, Use of U.S. Geological Survey earth-science 

products by city planning agencies in the San Francisco Bay 

region, California: U.S. Geological Survey Open-File Report 

75-276, 110 p. 

___ 1976, Use of U.S. Geological Survey earth-science products by 

county planning agencies in the San Francisco Bay region, California: U.S. Geological Survey Open-File Report 76-547, 186 p. 

Geologic and Seismologic Setting 

Agnew, D. C., and Sieh, K. E., 1978, A documentary study of the felt effects of the great California earthquakes of 1857: Bulletin of the 

Seismological Society of America, v. 68, no. 6, p. 1717-1729. 

Allen, C. R., 1975, Geological criteria for evaluating seismicity: 

Geological Society of America Bulletin, v. 86, no. 8, p. 1041-1057. 

___ 1981, The modern San Andreas fault, in Ernst, W. G., ed., The 

geotectonic development of California (Rubey volume I): Englewood Cliffs, N.j., Prentice-Hall, p. 511-534. 

Allen, C. R., St. Amand, P., Richter, C. F., and Nordquist, j. M., 1965, 

Relationship between seismicity and geologic structure in the 

southern California region: Bulletin of the Seismological Society of 

America, v. 55, no. 4, p. 753-797. 

Anderson, D. L., 1971, The San Andreas fault: Scientific American, 

v.225,no.5,p.52-68. 

Atwater, Tanya, 1970, Implications of plate tectonics for the Cenozoic 

tectonic evolution of western North America: Geological Society of 

America Bulletin, v. 81, no. 12, p. 3513-3536. 

Atwater, Tanya, and Molnar, P., 1973, Relative motion of the Pacific 

and North American plates deduced from sea-floor spreading in 

the Atlantic, Indian, and south Pacific oceans, in Kovach, R. L., and 

___ 1979, Use of U.S. Geological Survey earth-science products by 

selected regional agencies in the San Francisco Bay region, California: U.S. Geological Survey Open-File Report 79-221, 173 p. 

___ 1984, Reducing losses from earthquakes through personal preparedness: U.S. Geological Survey Open-File Report 84-765, 13 p. 

Lindh, A. G., 1983, Preliminary assessment of long-term probabilities 

for large earthquakes along selected fault segments of the San Andreas fault system in California: U.S. Geological Survey Open-File 

Report 83-63, 15 p. 

Ruddiman, W. F., and Mcintyre, A., 1984, Ice-age thermal response and 

climatic role of the surface Atlantic Ocean, 40° N. to 63° N.: Geological Society of America Bulletin, v. 95, p. 381-396. 

Schnell, M. L., and Herd, D. G., eds., 1984, National Earthquake 

Hazards Reduction Program-Report to the United States Congress, fiscal year 1983 activities: U.S. Geological Survey Circular 

919, 148p. 

Steinbrugge, K. V., Algermissen, S. T., Lagorio, H. J., Cluff, L. S., and 

Degenkolb, H. j., 1981, Metropolitan San Francisco and Los 

Angeles earthquake loss studies-1980 assessment: U.S. Geological Survey Open-File Report 81-113,46 p. 

U.S. Geological Survey, 1981, Scenarios of possible earthquakes affecting major California population centers with estimates of intensity and ground shaking: U.S. Geological Survey Open-File Report 

81-115, 35 p. 

___ 1984, Geologic time chart, in Stratigraphic notes, 1983: U.S. 

Geological Survey Bulletin 1537-A, p. A1-A4. 

U.S. Office of Science and Technology Policy, 1978, Earthquake 

hazards reduction-Issues for an implementation plan: Washington, D.C., Executive Office of the President, 231 p. 

Wesson, R. L., and Wallace, R. E., 1985, Predicting the next great 

earthquake in California: Scientific American, v. 252, no. 2, 

p. 35-43. 

Nur, A., eds., Proceedings of the Conference on Tectonic Problems 

of the San Andreas Fault System: Stanford University Publications, 

Geological Sciences, v. 13, p. 136-148. 

Beal, C. H., 1915, The earthquake at Los Alamos, Santa Barbara County, California, january 11, 1915: Bulletin of the Seismological 

Society of America, v. 5, no. 1, p. 14-25. 

Beeby, D. j., and Hill, R. L., 1975, Galway Lake fault; a previously unmapped active fault in the Mojave Desert, San Bernardino County, 

California: California Geology, v. 28, no. 10, p. 219-221. 

Branner, j. C., 1917, The Tejon Pass earthquake of October 22, 1916: 

Bulletin of the Seismological Society of America, v. 17, no. 1, 

p. 51-59. 

Bravinder, K. M., 1942, Los Angeles basin earthquake of October 21, 

1941, and its effect on certain producing wells in Dominguez field, 

Los Angeles County, California: American Association of 

Petroleum Geologists Bulletin, v. 26, no. 1, p. 388-399. 

Buika, j. A., and Teng, T. L., 1979, A seismicity study for portions of the 

Los Angeles basin, Santa Monica basin, and Santa Monica Mountains, California: University of Southern California Geophysical 

Laboratory Technical Report 79-9, 191 p. 

References Cited 471 
Byerly, Perry, 1930, The California earthquake of November 4, 1927: 

Bulletin of the Seismological Society of America, v. 20, no. 2, 

p. 53-B6. 

Castle, R. 0., 1978, Levelling surveys and the southern California uplift: 

U.S. Geological Survey Earthquake Information Bulletin, v. 10, no. 

3,p. 88-92. 

Cloud, W. K., and Scott, N. H., 1972, Intensity distribution and field effects, in The Borrego Mountain earthquake of April 9, 1968: U.S. 

Geological Survey Professional Paper 787, p. 142-153. 

Cockerham, R. S., and Eaton, J. P., 1982, The Point Sal. California, 

earthquake of May 29, 1980: Earthquake Notes, v. 53, no. 1, p. 51. 

Coffman, J. L., and von Hake, C. A., 1972, eds., United States earthquakes 1970: Washington, D.C., National Oceanic and Atmospheric Administration, 81 p. 

___ 1973a, Earthquake history of the United States (revised through 

1970): National Oceanic and Atmospheric Administration Publication 41-1, 208 p. 

___ 1973b, United States earthquakes 1971: Washington, D.C., National Oceanic and Atmospheric Administration, 176 p. 

___ 1975, United States earthquakes, 1973: Washington, D.C., National Oceanic and Atmospheric Administration, 112 p. 

Corbett, E. J., and Johnson, C. E., 1982, The Santa Barbara earthquake 

of 13 August 1978: Bulletin of the Seismological Society of 

America, v. 72, no. 6, pt. A, p. 2201-2226. 

Corbett, E. J., and Piper, K. A. 1981, Santa Barbara Island, California 

earthquake, September 4, 1981 [abs.]: EOS, Transactions of the 

American Geophysical Union, v. 62, no. 45, p. 958. 

Dickinson, W. R., 1981, Plate tectonics and the continental margin of 

California, in Ernst, W. G., ed., The geotectonic development of 

California (Rubey volume 1): Englewood Cliffs, N.J., Prentice-Hall, 

p.1-28. 

Dickinson, W. R., and Snyder, W. S., 1979, Geometry of triple junctions 

related to San Andreas transform: Journal of Geophysical 

Research, v. 84, no. 2, p. 561-572. 

Gawthrop, William, 1975, Seismicity of the central California coastal 

region: U.S. Geological Survey Open-File Report 75-134, 87 p. 

Gutenberg, B., Richter, C. F., and Wood, H. 0., 1932, The earthquake in 

Santa Monica Bay, California, on August 30, 1930: Bulletin of the 

Seismological Society of America, v. 22, no. 2, p. 138-154. 

Hanks, T. C., 1979, The Lompoc, California, earthquake (November 4, 

1927; M-7.3) and its aftershocks: Bulletin of the Seismological 

Society of America, v. 69, no. 2, p. 451-462. 

Hanks, T. C., and Kanamori, H., 1979, A moment magnitude scale: Journal of Geophysical Research, v. 84, no. 5, p. 2348-2350. 

Kanamori, H., and McNally , K., 1981, Seismicity studies for earthquake 

prediction in southern California using a mobile seismicity array: 

U.S. Geological Survey Open-File Report 81-282, p. 17-33. 

Lachenbruch, A. H., Sass, J. H., and Galanis, S. P., 1978, New heat-flow 

results from southern California [abs.]: EOS, Transactions of the 

American Geophysical Union, v. 59, no. 12, p. 1051. 

Lajoie, K. R., Kern, J. P., Wehmiller, J. F., Kennedy, G. L., Mathieson, 

S. A., Sarna-Wojcicki, A. M., Yerkes, R. F., and McCrory, P. A., 

1979, Quaternary marine shorelines and crustal deformation, San 

Diego to Santa Barbara, California, in Abbott, P. L., ed., Geological 

excursions in the southern California area, original papers and 

field trip roadlog prepared for the Geological Society of America 

Annual Meeting, November, 1979: San Diego, Calif., San Diego 

State University, Department of Geological Sciences, p. 3-15. 

Lee, W, H. K., Johnson, C. E., Henyey, T. L., and Yerkes, R. F., 1978, A 

preliminary study of the Santa Barbara, California, earthquake of 

August 13, 1978, and its major aftershocks: U.S. Geological Survey 

Circular 797, 11 p. 

Lee, W. H. K., Yerkes, R. F., and Simirenko, M., 1979, Recent earthquake activity and focal mechanisms in the western Transverse 

Ranges, California: U.S. Geological Survey Circular 799-A, 26 p. 

472 Earthquake Hazards in the Los Angeles Region 

Lindh, A., Fuis, G., and Mantis, C., 1978, Seismic amplitude 

measurements suggest foreshocks have different focal mechanisms than aftershocks: Science, v. 201, no. 4350, p. 56-59. 

Matti, J. C., Tinsley, J. C., Morton, D. M., and McFadden, L. D., 1982, 

Holocene faulting history as recorded by stratigraphy within the 

Cucamonga fault zone: A preliminary view, 1982, in Tinsley, J. C., 

Matti, J. C., and McFadden, L. D., eds., Late Quaternary 

pedogenesis and alluvial chronologies of the Los Angeles and San 

Gabriel Mountains areas, southern California: Geological Society 

of America Annual Meeting, Cordilleran Section, 78th, Anaheim, 

Calif., 1982, Guidebook 12, p. 29-44. 

McNally, K. C., and Pechmann, J., 1981, Recent seismicity changes 

along the San Andreas fault near Palmdale, California, in 

Kanamori, H., and McNally, K., Seismicity studies for earthquake 

prediction in southern California using a mobile seismographic array: U.S. Geological Survey Open-File Report 81-282, p. 176-195. 

Moore, G. W., 1981, Plate perimeters and motion vectors, in Drummond, 

K. J., chairman, Plate-tectonic map of the circum-Pacific region: 

American Association of Petroleum Geologists, scale 1:10,000,000, 

northeastern sheet. 

Murphy, L. M., and Cloud, W. K., 1956, United States earthquakes 

1954: U.S. Coast and Geodetic Survey Publication 793, 110 p. 

Neumann, Frank, and Cloud, W. K., 1955, Strong-motion records of the 

Kern County earthquakes, in Oakeshott, G. B., ed., Earthquakes in 

Kern County during 1952: California Division of Mines and Geology 

Bulletin 171, p. 205-210. 

Pechmann, J. C., Hutton, L. K., Johnson, C. E., Ebel, J. E., Given, J. W., 

Cole, D. M., and German, P. T., 1980, Epicentral locations for the 

Homestead Valley earthquake sequence, March 15, 1979: California Geology, v. 33, no. 5, p. 11D-114. 

Real, C. R., Toppozada, T. R., and Parke, D. L., 1978, Earthquake 

epicenter map of California, 1900 through 1974: California Division of Mines and Geology Map Sheet 39, scale 1:1,000,000. 

Richter, C. F., 1935, An instrumental earthquake magnitude scale: 

Bulletin of the Seismological Society of America, v. 25, no. 1, 

p. 1-32. 

___ 1958, Elementary seismology: San Francisco, Calif., W. H. 

Freeman, 768 p. 

__ 1970, Magnitude of the Inglewood, California, earthquake of 

June 21, 1920: Bulletin of the Seismological Society of America, v. 

60,no.2,p.647-B49. 

Richter, C. F., Allen, C. R., and Nordquist, J. M., 1958, The Desert Hot 

Springs earthquakes and their tectonic environment: Bulletin of the 

Seismological Society of America, v. 48, no. 4, p. 315-337. 

Rodgers, D. A., 1973, Isoseismal map for the 10 March 1933 Long Beach 

earthquake: California Geology, v. 26, no. 3, cover. 

Sanders, C., McNally, K., and Kanamori, H., 1981, The state of stress 

near the Anza seismic gap, San Jacinto fault zone, southern California, in Brown, A. R., and Ruff, R. W., eds., Geology of the San 

Jacinto Mountains: South Coast Geological Society Annual Field 

Trip Guidebook 9, p. 61-B7. 

Scott, N. H., 1973, Felt area and intensity of San Fernando earthquake, 

in Murphy, L. M., ed., San Fernando, California, earthquake of 

February 9, 1971, v. 3, Geological and geophysical studies: Washington, D.C., National Oceanic and Atmospheric Administration, 

p.23-48. 

Stover, C. W .. and von Hake, C. A., eds., 1980, United States earthquakes, 1978: Washington, D.C., U.S. Geological Survey and National Oceanic and Atmospheric Administration, 112 p. 

Strand, C. L., 1980, Pre-1900 earthquakes of Baja California and San 

Diego County: San Diego, Calif., San Diego State University, unpublished M.Sc. thesis, 316 p. 

Taber, Stephen, 1920, The Inglewood earthquake in southern California, June 21, 1920: Bulletin of the Seismological Society of 

America, v. 10, no. 3, p. 129-145. 
Teng, T. L., 1979, Earthquake hazard research in the Los Angeles basin 

and its offshore area: Menlo Park, Calif., technical report to U.S. 

Geological Survey under contract 14--08-0001-16704, 191 p. 

Thatcher, Wayne, 1979, Systematic inversion of geodetic data in central California: Journal of Geophysical Research, v. 84, no. 5, 

p. 2283-2295. 

Thatcher, Wayne, Hileman, J. A., and Hanks, T. C., 1975, Seismic slip 

distribution along the San Jacinto fault zone, southern California, 

and its implications: Geological Society of America Bulletin, v. 86, 

no.8,p. 114G-1146. 

Toppozada, T. R., and Parke, D. L., 1975, Isoseismal map for the 29 

June, Hi25, Santa Barbara earthquake: California Geology, v. 28, 

no. 6, p. 132 (scale approximately 1:4,300,000). 

__ 1982, Areas damaged by California earthquakes, 190Q-1949: 

California Division of Mines and Geology Open-File Report 82-17 

SAC,65p. 

Toppozada, T. R., Parke, D. L., and Higgins, C. T., 1978, Seismicity of 

California 190Q-1931: California Division of Mines and Geology 

Special Report 135, 39 p. 

Toppozada, T. R., Real, C. R., and Parke, D. L., 1981, Preparation of 

isoseismal maps and summaries of reported effects for pre-1900 

California earthquakes: California Division of Mines and Geology 

Open-File Report 81-11 SAC, 182 p. 

Townley, S. D., 1918, The San Jacinto earthquake of April 21, 1918: 

Bulletin of the Seismological Society of America, v. 8, nos. 2 and 3, 

p. 45-62. 

von Hake, C. A., and Cloud, W. K., eels., 1971, United States earthquakes 1969: Washington, D.C., National Oceanic and Atmospheric Administration, 80 p. 

Whitcomb, j. H., Allen, C. R., Garmany, J. D., and Hileman, j. A., 1973, 

San Fernando earthquake series, 1971-Focal mechanisms and 

tectonics: Reviews of Geophysics and Space Physics, v. 11, no. 3, 

p. 693-730. 

Wood, H. 0., 1937, The Terwilliger Valley earthquake of March 25, 

1937: Bulletin of the Seismological Society of America, v. 27, no. 4, 

p. 305-312. 

Wood, H. 0., and Richter, C. F., 1931, Recent earthquakes near Whittier, California: Bulletin of the Seismological Society of America, v. 

21,no.3,p. 183-203. 

Woodward-Clyde Consultants, 1979, Report of the evaluation of maximum earthquake and site ground motion parameters associated 

with the Offshore Zone of Deformation San Onofre Nuclear 

Generating Station: Los Angeles, Calif., report prepared for 

Southern California Edison Company, 56 p., 11 figs., 10 apps. 

Yeats, R. S., 1981, Quaternary flake tectonics of the California 

Transverse Ranges: Geology, v. 9, no. 1, p. 1&-20. 

Yerkes, R. F., Greene, H. G., Tinsley, J. C., and Lajoie, K. R., 1981, 

Seismotectonic setting of the Santa Barbara Channel area, southern California: U.S. Geological Survey Map Miscellaneous Field 

Studies Map MF-1169, scale 1:250,000, 25-p. text. 

Evaluating Earthquake and Surface-Faulting Potential 

Allen, C. R., 1957, San Andreas fault in San Gorgonio Pass, southern 

California: Geological Society of America Bulletin, v. 68, 

p. 315-350. 

___ 1975, Geological criteria for evaluating seismicity: Geological 

Society of America Bulletin, v. 86, p. 1041-1057. 

Allen, C. R., Wyss, M., Brune, j. N., Grantz, A., and Wallace, R. E., 1972, 

Displacements on the Imperial, Superstition Hills, and San 

Andreas faults triggered by the Borrego Mountain earthquake, in 

The Borrego Mountain earthquake of April9, 1968: U.S. Geological 

Survey Professional Paper 787, p. 87-104. 

Allen, C. R., Hanks, T. C., and Whitcomb, J. H., 1975, Seismological 

studies of the San Fernando earthquake and their tectonic implications, in Oakeshott, G. B., eel., San Fernando, California, earthquake of 9 February 1971: California Division of Mines and 

Geology Bulletin 196, p. 257-262. 

Anderson, j. G., 1979, Estimating the seismicity from geological structure for seismic-risk studies: Bulletin of the Seismological Society 

of America, v. 69, no. 1, p. 135-158. 

Barnett, D. M., and Freund, L. B., 1975, An estimate of strike-slip fault 

friction stress and fault depth from surface displacement data: 

Bulletin of the Seismological Society of America, v. 65, no. 5, 

p. 1259-1266. 

Barnhart, j. T., and Slosson, j. E., 1973, The Northridge Hills and 

associated faults-A zone of high seismic probability, in Moran, 

D. E., Slosson, J. E., Stone, R. 0., and Yelverton, G. A., eels., 

Geology, seismicity, and environmental impact: Los Angeles, Calif., 

Association of Engineering Geologists, p. 253-256. 

Barrows, A. G., 1974, A review of the geology and earthquake history of 

the Newport-Inglewood structural zone, southern California: California Division of Mines and Geology Special Report 114, 115 p. 

__ 1975, Surface effects and related geology of the San Fernando 

earthquake in the foothill region between Little Tujunga and 

Wilson Canyons, in Oakeshott, G. B., eel., San Fernando, California,, 

earthquake of 9 February 1971: California Division of Mines and 

Geology Bulletin 196, p. 97-117. 

__ 1979, Geology and fault activity of the Valyermo segment of the 

San Andreas fault zone, Los Angeles County, California: California 

Division of Mines and Geology Open-File Report 79-1 LA, 49 p. 

___ 1980, Geologic map of the San Andreas fault zone and adjoining 

terrane, juniper Hills and vicinity, Los Angeles County, California: 

California Division of Mines and Geology Open-File Report 8Q-2 

LA, scale 1:9,600. 

Barrows, A. G., Kahle, J. E., and Beeby, D. J., 1976, Geology and fault activity of the Palmdale segment of the San Andreas fault zone, Los 

Angeles County, California: California Division of Mines and 

Geology Open-File Report 76-6 LA, 30 p. 

__ 1985, Earthquake hazards and tectonic history of the San 

Andreas fault zone, Los Angeles County, California: California 

Division of Mines and Geology Open-File Report 85-10 LA, 250 p. 

Beeby, D. )., 1979, Geology and fault activity of the Lake Hughes segment of the San Andreas fault zone, Los Angeles County, California: California Division of Mines and Geology Open-File Report 

79-2 LA, 35 p. 

Blair, M. L., and Spangle, W. E., 1979, Seismic safety and land-use planning-Seleeted example from California: U.S. Geological Survey 

Professional Paper941-B, 81 p. 

Bonilla, M. G., 1970, Surface faulting and related effects, in Wiegel, 

R. 1., eel., Earthquake engineering: Englewood Cliffs, N.J., PrenticeHall, p. 47-74. 

___ 1973, Trench exposures across surface fault ruptures 

associated with the San Fernando earthquake, in Murphy, L. M., 

ed., San Fernando, California, earthquake of February 9, 1971, v. 

3, Geological and geophysical studies: Washington, D.C., National 

Oceanic and Atmospheric Administration, p. 173-182. 

References Cited 473 
___ 1982, Evaluation of potential surface faulting and other tectonic 

deformation: U.S. Geological Survey Open-File Report 82-732, 

88p. 

Bonilla, M. G., and Buchanan, J. M., 1970, Interim report on worldwide 

historic surface faulting: U.S. Geological Survey Open-File Report, 

32p. 

Bonilla, M.G., Mark, R. K., and Lienkaemper, J. J., 1984, Statistical relations among earthquake magnitude, surface rupture length, and 

surface fault displacement: Bulletin of the Seismological Society of 

America, v. 74, no. 6, p. 2379--2411. 

Boore, D. M., 1977, The motion of the ground in earthquakes: Scientific 

American, v. 237, no. 6, p. 68-78. 

Bravinder, K. M., 1942, Los Angeles basin earthquake of October 21, 

1941, and its effect on certain producing wells in Dominguez field, 

Los Angeles County, California: American Association of Petroleum Geologists Bulletin. v. 26, p. 388--399. 

Bryant, M. E., and Fife, D. L., 1982 [1984], The Peralta Hills fault, 

a Transverse Ranges structure in the northern Peninsular Ranges, 

southern California, in Fife, D. L., and Minch, J. A., eds., Geology 

and mineral wealth of the California Transverse Ranges: Santa 

Ana, Calif., South Coast Geological Society, p. 403--409. 

Bryant, W. A., 1978, The Raymond Hill fault-An urban geological in- . 

vestigation: California Geology, v. 31, no. 6, p. 127-142. 

Buchanan-Banks, J. M., Pampeyan, E. H., Wagner, H. C., and 

McCulloch, D. S., 1978, Preliminary map showing recency of faulting in coastal south-central California: U.S. Geological Survey Miscellaneous Field Studies Map MF-910, scale 1:250,000. 

Buika, J. A., and Teng, T., 1979, A seismicity study for portions of the 

Los Angeles basin, Santa Monica basin, and Santa Monica Mountains, California: Menlo Park, Calif., technical report to U.S. Geological Survey under contract 14--08--0001-16704, 134 p. 

Bull, W. B., Menges, C. M., and McFadden, L. D., 1979, Stream terraces 

of the San Gabriel Mountains, California: Menlo Park, Calif., 

technical report to U.S. Geological Survey under contract 

14--08--001--G-394, 140 p. 

Burford, R. 0., 1972, Continued slip on the Coyote Creek fault after the 

Borrego Mountain earthquake, in The Borrego Mountain earthquake of April 9, 1968: U.S. Geological Survey Professional Paper 

787, p. 105-111. 

Burford, R. 0., and Harsh, P. W., 1980, Slip on the San Andreas fault in 

central California from alinement array surveys: Bulletin of the 

Seismological Society of America, v. 70, no. 4, p. 1233-1261. 

California Department of Water Resources, 1966, Santa Ana Gap 

salinity barrier, Orange County: California Department of Water 

Resources Bulletin 147-1, 178 p. 

___ 1968, Sea-water intrusion, Balsa-Sunset area, Orange County: 

California Department of Water Resources Bulletin 63-2, 167 p. 

___ 1970, Meeting water demands in the Chino-Riverside area, Appendix A-Water supply: California Department of Water 

Resources Bulletin 104-3, 108 p. 

Castle, R. 0., 1966, Preliminary study of the geology of two proposed 

sites for a nuclear-powered desalting plant near Sunset Beach and 

Pelican Point, Orange County, California: U.S. Geological Survey 

open-file report to the U.S. Atomic Energy Commission, 73 p. 

Castle, R. 0., and Yerkes, R. F., 1976, Recent surface movements in the 

Baldwin H.ills, Los Angeles County, California: U.S. Geological 

Survey Professional Paper 882, 125 p. 

Cemen, I., 1977, Geology of the Sespe-Piru Creek area, Ventura County, 

California: Athens, Ohio, Ohio University, unpublished M.Sci. 

thesis, 68 p. 

Chinnery, M. A., 1965, The vertical displacements associated with 

transcurrent faulting: Journal of Geophysical Research, v. 70, no. 

18, p. 4627--4632. 

474 Earthquake Hazards in the Los Angeles Region 

Chung, D. H., and Bernreuter, D. L., 1981, Regional relationships among 

earthquake magnitude scales: Reviews of Geophysics and Space 

Physics, v. 19, no. 4, p. 644-663. 

Church, J. P., Castle, R. 0., Clark, M. M., and Morton, D. M., 1974, Continuing crustal deformation in the western Mojave Desert [abs.]: 

Geological Society of America Abstracts with Programs, v. 6, no. 7, 

p. 687. 

Clark, M. M., 1972, Surface rupture along the Coyote Creek fault, in 

The Borrego Mountain earthquake of April9, 1968: U.S. Geological 

Survey Professional Paper 787, p. 55-86. 

Clark, M. M., Grantz, A., and Rubin, M., 1972, Holocene activity of the 

Coyote Creek fault as recorded in sediments of Lake Cahuilla, in 

The Borrego Mountain earthquake of April9, 1968: U.S. Geological 

Survey Professional Paper 787, p. 112-130. 

Clark, M. M., Lienkaemper, J. J., Harwood, D. S., Lajoie, K. R., Matti, 

J. C., Perkins, J. A., Rymer, M. J., Sarna-Wojcicki, A. M., Sharp, 

R. V., Sims, J. D., Tinsley, J. C., III, and Ziony, J. I., 1984, 

Preliminary slip-rate table and map of late-Quaternary faults of 

California: U.S. Geological Survey Open-File Report 84-106, 5 

sheets, scale 1:1,000,000. 

Cluff, L. S., 1978, Geologic considerations for seismic microzonation, in 

International Conference on Microzonation for Safer Construc;:tion 

Research and Application, 2d, San Francisco, Calif., 1978, Proceedings: v. 1, p. 135-152. 

Corbett, E. J., and Johnson, C. E., 1982, The Santa Barbara, California, 

earthquake of 13 August 1978: Bulletin of the Seismological Society of America, v. 72, no. 6, p. 2201-2226. 

Corbett, E. J., and Piper, K. A., 1981, Santa Barbara Island, California, 

earthquake, September 4, 1981 [abs.]: EOS, Transactions of the 

American Geophysical Union, v. 62, no. 45, p. 958. 

Cotton, W. R., Ehlig, P., and Seward, A. E., 1983, Holocene activity of 

the San Gabriel fault, Valencia, California [abs.]: Association of 

Engineering Geologists Annual Meeting, 26th, San Diego, Calif., 

1983, Abstracts and Programs, p. 60. 

Cramer, C. H., and Harrington, J. M., 1984, Seismicity and tectonics 

of the eastern San Gabriel Mountains area, San Bernardino and 

Los Angeles counties, California, in Cramer, C. H., Harrington, 

j. M., Chase, G. W., and Bennett, j. H., Microearthquake, geophysical, and geodetic surveys for earthquake hazards evaluation, eastem San Gabriel Mountains and upper Pomona Valley areas, San 

Bernardino County, California: California Division of Mines and 

Geology Open-File Report 84--23 SAC, p. 5-22. 

_in press, Seismicity and tectonics of the Cucamonga fault and 

the eastern San Gabriel Mountains, San Bernardino County, California, in Recent reverse faulting in the Transverse Ranges, California: U.S. Geological Survey Professional Paper 1339. 

Crippen, R. E., Luyendyk, B. P., and Hajic, E. j., 1982, High resolution 

structural mapping in the Santa Barbara Channel [abs.]: Geological Society of America Abstracts with Programs, v. 14, no. 4, 

p.157. 

Crook, R., Jr., Proctor, R. j., and Lindvall, C. E., 1983, Seismicity of the 

Santa Monica and Hollywood faults determined by trenching: 

Menlo Park, Calif., technical report to U.S. Geological Survey 

under contract 14--08--0001-20523, 26 p. 

Crook, R., Jr., Allen, C. R., Kamb, B., Payne, C. M., and Proctor, R. J., in 

press, Quaternary geology and seismic hazard of the Sierra Madre 

and associated faults, western San Gabriel Mountains, California, 

in Recent reverse faulting in the Transverse Ranges, California: 

U.S. Geological Survey Professional Paper 1339. 

Darrow, A. C., and Fischer, P. J., 1983, Activity and earthquake potential of the Palos Verdes fault: Menlo Park, Calif., technical report 

to U.S. Geological Survey under contract 14--08--0001-19786,90 p. 
Darrow, A. C., and Sylvester, A. G., 1983, Activity of the central reach 

of the Santa Ynez fault: Menlo Park, Calif., technical report to U.S. 

Geological Survey under contract 14-08--0001-19787,28 p. 

Davis, T., and Duebendorfer, E., 1982, Surficial structure and geomorphology of the western "Big Bend" San Andreas.fault, in Cooper, 

J.D., compiler, Neotectonics in southern California: Geological 

Society of America Annual Meeting, Cordilleran Section, 78th, 

Anaheim, Calif., 1982, Guidebook, p. 79--106. 

Dibblee, T. W., Jr., 1966, Geology of the central Santa Ynez Mountains, 

Santa Barbara County, California: California Division of Mines and 

Geology Bulletin 186, 99 p. 

Durham, D. L., and Yerkes, R. F., 1964, Geology and oil resources of the 

eastern Puente Hills area, southern California: U.S. Geological 

Survey Professional Paper 420-B, 62 p. 

Fett, J.D., Hamilton, D. H., and Fleming, F. A., 1967, Continuing surface 

displacements along the Casa Lorna and San Jacinto faults in San 

Jacinto Valley, Riverside County, California: Engineering Geology, 

v. 4, no. 1, p. 22-32. 

Fife, D. L., Hoffman, R. A., Bryant, M. E., Rushing, R. J., Ruff, R. W., Santareangelo, A. A., and Unruh, M. E., 1980, The Peralta Hills thrust 

fault, southern California [abs.]: Geological Society of America 

Abstracts with Programs, v. 12, no. 3, p. 106. 

Freund, L. B., and Barnett, D. M., 1976, Two-<limensional analysis of 

surface deformation due to dip-slip faulting: Bulletin of the 

Seismological Society of America, v. 66, no. 3, p. 667--£75. 

Gardner, D. A., 1982, Seismic/ground rupture hazards associated with 

the Camarillo fault, in Cooper, j. D., compiler, Neotectonics in 

southern California: Geological Society of America Annual Meeting, Cordilleran Section, 78th, Anaheim, Calif., 1982, Guidebook, 

p. 59--£0. 

Gilluly, J., and Grant, U. S., 1949, Subsidence in the Long Beach Harbor 

area, California: Geological Society of America Bulletin, v. 60, 

p. 461-530. 

Given, D. D., 1981, Seismicity of the San jacinto fault zone, in Brown, 

A. R., and Ruff, R. W., eds., Geology of the San Jacinto Mountains: 

South Coast Geological Society Annual Field Trip Guidebook 9, 

p. 55--£0. 

Green, S. M., 1983, Seismotectonic study of the San Andreas, Mission Creek, and Banning fault system: Los Angeles, Calif., University of California, unpublished M.Sci. thesis, 52 p .. 

Greene, H. G., Wolf, S. C., and BJorn, K. G., 1978, The marine geology of 

the easterrl. Santa Barbara Channel with particular emphasis on 

the ground water basins offshore from the Oxnard Plain, California: U.S. Geological Survey Open-File Report 78-305, 104 p. 

Guptill, P. D., and Heath, E. G., 1981, Surface faulting along the 

Newport-Inglewood zone of deformation: California Geology, v. 34, 

no. 7, p. 142-148. 

Guptill, P., Collins, D., Sugiura, R., and Birkhahn, P., 1979, Quaternary 

deformation along the Llano fault, southern Antelope Valley, 

California [abs.]: Geological Society of American Abstracts with 

Programs, v. 11, no. 3, p. 81. 

Hadley, D., and Combs, J., 1974, Microearthquake distribution and 

mechanisms of faulting in the Fontana-San Bernardino area of 

southern California: Bulletin of the Seismological Society of 

America, v. 64, no. B5, p. 1477-1499. 

Hanks, T. C., and Kanamori, H., 1979, A moment magnitude scale: Jour·· 

nal of Geophysical Research, v. 84, no. B5, p. 2348-2350. 

Hanks, T. C., Thatcher, W., and Hileman, j. A., 1975, Seismic moments 

of the larger earthquakes of the southern California region, 

1890-1973: Geological Society of America Bulletin, v. 86, 

p. 1131-1139. 

Hannan, D. L., Lung, R., and Leighton, F. B., 1979, Geologic investigation 

of recency of fault activity by surface trenching on the Whittier 

fault, California: Menlo Park, Calif., technical report to U.S. Geological Survey under contract 14-08--0001-16821, CEL-2024, 

43p. 

Hanson, D. W., 1981, Surface and subsurface geology of the Simi Valley 

area, Ventura County, California: Corvallis, Oreg., Oregon State 

University, unpublished M.Sci. thesis, 95 p. 

Hart, E. W., 1980, Fault-rupture haZard zones in California: California 

Division of Mines and Geology Special Publication 42, 25 p. 

Hart, E. W., Bortugno, E. J., and Smith, T. C., 1977, Summary 

report-Fault evaluation program, 1976 area (western Transverse Ranges): California Division of Mines and Geology Open-File 

Report 77-8 SF, 8 p. 

Hart, E. W., Smith, D. P., and Smith, T. C., 1978, Summary 

report-Fault evaluation program, 1977 area (Los Angeles basin 

region): California Division of Mines and Geology Open-File Report 

78-10 SF, 8 p. 

Hart, E. W., Smith, D. P., and Saul, R. B., 1979, Summary report-Fault 

evaluation program, 1978 area (Peninsula Ranges-Salton Trough 

region): California Division of Mines and Geology Open-File Report 

79-10SF, lOp. 

Hays, W. W., 1980, Procedures for estimating earthquake ground motions: U.S. Geological Survey Professional Paper 1114, 77 p. 

Heath, E. G., Jensen, D. E., and Lukesh, D. W., 1982, Style and age of 

deformation on the Chino fault, in Cooper, J. D., compiler, Neotectonics in southern California: Geological Society of America 

Annual Meeting, Cordilleran Section, 78th, Anaheim, Calif., 1982, 

Guidebook, p. 123-134. 

Herd, D. G., 1979, Neotectonic framework of central coastal California 

and its implications to microzonation of the San Francisco Bay 

region, in Brabb, E. E., ed., Progress on seismic zonation in the San 

Francisco Bay region: U.S. Geological Survey Circular 807, 

p. 3-12. 

Hileman, J. A., and Hanks, T. C., 1975, Seismicity along the San 

Andreas fault, southern California, in Crowell, J. C., ed., San Andreas fault in southern California: California Division of Mines and 

Geology Special Report 118, p. 28-39. 

Hileman, J. A., Allen, C. R., and Nordquist, J. M., 1973, Seismicity of the 

southern California region, 1 January 1932 to 31 December 1972: 

Pasadena, Calif., California Institute of Technology Seismological 

Laboratory, 487 p. 

Hill, R. L., 1979, Potrero Canyon fault and University High School 

escarpment, in Field guide to selected engineering geologic 

features, Santa Monica Mountains, Association of Engineering 

Geologists, Southern California Section, Guidebook to May 19, 

1979, field trip: Los Angeles, Calif., p. 83-103. 

Hill, R. L., Sprotte, E. C., Bennett, J. H., Real, C. R., and Slade, R. C., 

1979, Location and activity of the Santa Monica fault, Beverly 

Hills-Hollywood area, California, in Earthquake hazards 

associated with faults in the greater Los Angeles metropolitan 

area, Los Angeles County, California, including faults in the Santa 

Monica-Raymond, Verdugo-Eagle Rock, and Benedict Canyon 

fault zones: California Division of Mines and Geology Open-File 

Report 79-16 LA, p. B1-B43. 

jackson, P. A., and Yeats, R. S., 1982, Structural evolution of Carpinteria basin, western Transverse Ranges, California: American 

Association of Petroleum Geologists Bulletin, v. 66, no. 7, 

p. 805-829. 

Jakes, M. C. K., 1979, Surface and subsurface geology of the Camarillo 

and Los Posas Hills area, Ventura County, California: Corvallis, 

Oreg., Oregon State University, unpublished M.Sci. thesis, 116 p. 

Jungels, P. H., and Frazier, G. A., 1973, Finite element analysis of the 

residual displacements for an earthquake rupture-Source 

parameters for the San Fernando earthquake: journal of Geophysical Research, v. 78, no. 23, p. 5062-5083. 

References Cited 475 
Junger, A., 1976, Offshore structure between Santa Cruz and Santa 

Rosa Islands, in Howell, D. G., ed., Aspects of the geologic history 

of the California Continental Borderland: American Association of 

Petroleum Geologists, Pacific Section, Miscellaneous Publication 

24, p. 418-426. 

__ 1979, Maps and seismic profiles showing geologic structure of 

the northern Channel Islands platform, California Continental 

Borderland: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-991, scale 1:250,000. 

Junger, A., and Wagner, H. C., 1977, Geology of the Santa Monica and 

San Pedro basins, California Continental Borderland: U.S. Geological Survey Miscellaneous Field Studies Map MF -820, scale 

1:250,000. 

Kahle, J. E., 1975, Surface effects and related geology of the Lakeview 

fault segment of the San Fernando fault zone, in Oakeshott, G. B., 

ed., San Fernando, California, earthquake of 9 February 1971: 

California Division of Mines and Geology Bulletin 196, p. 119--136. 

___ 1979, Geology and fault activity of the San Andreas fault zone 

between Quail Lake and Three Points, Los Angeles County, California: California Division of Mines and Geology Open-File Report 

79--3 LA, 42 p. 

Kahle, J. E., and Barrows, A. G., 1980, Fault activity of the Three Points 

and Pine Canyon segments, San Andreas fault zone, Los Angeles 

County, California: California Division of Mines and Geology OpenFile Report 8G-13 LA, 38 p. I 

Kahle, J. E., Smith, D. P., and Beeby, D. J., 1977, Geology of the Leona 

Valley segment of the San Andreas fault zone, Los Angeles County, 

California: California Division of Mines and Geology Open-File 

Report 77-2 LA, 167 p. 

Kamb, B., Silver, L. :r., Abrams, M. J., Carter, B. A., Jordan, T. H., and 

Minster, J. B., 1971, Pattern of faulting and nature of fault movement in the San Fernando earthquake, in The San Fernando, 

California, earthquake of February 9, 1971: U.S. Geological Survey 

Professional Paper 733, p. 41-54. 

Kanamori, H., and Regan, J., 1982, Long-period surface waves, in The 

Imperial Valley, California, earthquake of October 15, 1979: U.S. 

Geological Survey Professional Paper 1254, p. 55-58. 

Keaton, J. R., 1978, Geomorphic evidence for late Quaternary displacement along the Santa Ynez fault zone, Blue Canyon, eastern Santa 

Barbara County, California [abs.]: Geological Society of America 

Abstracts with Programs, v. 10, no. 3, p. 111. 

Keller, E. A., Johnson, D. 1., Clark, M. N., and Rockwell, T. K., 1980, 

Tectonic geomorphology and earthquake hazard, north flank, central Ventura basin, California: Menlo Park, Calif., technical report 

to U.S. Geological Survey under contract 14--08--0001-17678, 

178p. 

Keller, E. A., Rockwell, T. K., Clark, M. N., Dembroff, G. R., and Johnson, 

D. L., 1982, Tectonic geomorphology of the Ventura, Ojai, and Santa Paula areas, western Transverse Ranges, California: in Cooper, · 

J. D., compiler, Neotectonics in southern California: Geological 

Society of America Annual Meeting, Cordilleran Section, 78th, 

Anaheim, Calif., 1982, Guidebook, p. 25-42. 

Kennedy, M. P., 1977, Recency and character of faulting along the 

Elsinore fault zone in southern Riverside County, California: 

California Division of Mines and Geology Special Report 131, 12 p. 

Kern, J. P., 1977, Origin and history of upper Pleistocene marine terraces, San Diego, California: Geological Society of America 

Bulletin, v. 88, p. 1553-1566. 

Kew, W. S. W., 1927, Geologic sketch of Santa Rosa Island, Santa Barbara County, California: Geological Society of America Bulletin, v. 

38, p. 645-653. 

Knuepfer, P. L., Coppersmith, K. J., and Cluff, L. S., 1981, A framework 

for classifying faults based on their relative degree of activity 

[abs.]: Earthquake Notes, v. 52, no. 1, p. 7G-71. 

476 Earthquake Hazards in the Los Angeles Region 

Kowalewsky, D. B., 1978, Indications of Holocene activity along 

branches of the Mission Hills fault west of Balboa Boulevard, in 

Geologic guide and engineering geology case histories, Los Angeles 

metropolitan area: Association of Engineering Geologists, Annual 

California Section Conference, 1st, Los Angeles, Calif., 1978, 

Guidebook, p. 53-63. 

Lajoie, K. R., Kern, J. P., Wehmiller, J. F .. Kennedy, G. 1., Mathieson, 

S. A., Sarna-Wojcicki, A. M., Yerkes, R. F., and McCrory, P. F., 

1979, Quaternary marine terrace shorelines and crustal deformation, San Diego to Santa Barbara, California, in Abbott, P. L., ed., 

Geologic excursions in the southern California area: San Diego, 

Calif., San Diego State University, Department of Geological 

Sciences, p. 3-15. 

Lamar, D. L., 1972, Microseismicity and recent tectonic activity in the 

Whittier fault area: Menlo Park, Calif., technical report to U.S. 

Geological Survey under contract 14-0!Hl0001-12288, 40 p. 

__ 1973, Microseismicity of the Whittier fault, California, in 

Guidebook to the Tertiary geology of eastern Orange and Los 

Angeles Counties, California: South Coast Geological Society Field 

Trip Guidebook, p. 61-66. 

Lamar, D. L., and Scrivner, P. J., 1983, Annotated bibliography of 

engineering geology reports prepared to satisfy the Alquist-Priolo 

Special Studies Zones Act in southern California, pt. III, in Lamar, 

D. L., Smith, J. L., LaViolette, J. W., Custis, K., and Scrivner, P., 

eds., 1983, Application of private site-specific data to regional 

evaluation of earthquake and faulting potential in southern California: U.S. Geological Survey Open-File Report 83-834, 105 p. 

Lamar, D. L., and Swanson, S. C., 1981, Study of seismic activity by 

selective trenching along the Elsinore fault zone, southern California: Menlo Park, Calif., technical report to U.S. Geological Survey 

under contract 14-0!Hl001-19144, 35 p. 

Lamar, D. L., Merifield, P. M., and Proctor, R. J., 1973, Earthquake 

recurrence intervals on major faults in southern California, in 

Moran, D. E., Slosson, J. E., Stone, R. 0., and Yelverton, C. A., eds., 

Geology, seismicity, and environmental impact: Los Angeles, Calif., 

Association of Engineering Geologists, p. 265-276. 

Langenkamp, D., and Combs, J., 1974, Microearthquake study of the 

Elsinore fault zone, southern California: Bulletin of the Seismological Society of America, v. 64, no. 1, p. 187-203. 

Lee, W. H. K., and Stewart, S. W., 1981, Principles and applications of 

microearthquake networks: Advances in Geophysics, supp. 2, 

p. 153-163. 

Lee, W. H. K., Johnson, C. E., Henyey, T. L., and Yerkes, R. F., 1978, A 

preliminary study of the Santa Barbara, California, earthquake of 

August 13, 1978, and its major aftershocks: U.S. Geological Survey 

Circular 797, 11 p. 

Lee, W. H. K., Yerkes, R. F., and Simirenko, M., 1979, Recent earthquake activity and focal mechanisms in the western Transverse 

Ranges, California: U.S. Geological Survey Circular 799--A, 37 p. 

Leighton, F. B., Lung, R., and Cann, L. R., 1977, Geologic investigation by 

surface trenching of active faulting on the Santa Susana fault, Los 

Angeles and Ventura Counties, California: Menlo Park, Calif., technical report to U.S. Geological Survey under contract 14--08--

0001-15863, CEL-288, 63 p. 

Lindh, A. G., 1983, A preliminary assessment of long-term probabilities 

for large earthquakes along selected fault segments of the San 

Andreas fault system: U.S. Geological Survey Open-File Report 

83-63, 15p. 

LNG Seismic Review Panel, 1981, Seismic safety review of the proposed 

liquefied natural gas facility, Little Cojo Bay, Santa Barbara County, California: San Francisco, Calif., California State Public 

Utilities Commission, 33 p. 

Lofgren, B. E., 1976, Land subsidence and aquifer-system compaction in 

the San Jacinto Valley, Riverside County, California-A progress 
report: U.S. Geological Survey Journal of Research, v. 4, _no. 1, 

p. 9-18. 

Lung, R., and Weick, R. J., 1978, Exploratory trenching of the Santa 

Susana fault in Los Angeles and Ventura Counties, California, in 

Geologic guide and engineering geology case histories, Los Angeles 

metropolitan area: Association of Engineering Geologists, Annual 

California Section Conference, 1st, Los Angeles, Calif., 1978, 

Guidebook, p. 73-80. 

McGill, J. T., 1981, Recent movement on the Potrero Canyon fault, 

Pacific Palisades area, Los Angeles, in Geological Survey research 

1980: U.S. Geological Survey Professional Paper 1175, p. 258-259. 

___ 1982, Preliminary geologic map of the Pacific Palisades area, 

City of Los Angeles, California: U.S. Geological Survey Open-File 

Report 82-194, scale 1:4,800, 15-p. text. 

Mark, R. K., and Bonilla, M. G., 1977, Regression analysis of earthquake 

magnitude and surface fault length using the 1970 data of Bonilla 

and Buchanan: U.S. Geological Survey Open-File Report 77-614, 

8p. 

Martner, S. T., 1948, The Dominguez Hills, California, earthquake of 

June 18, 1944: Bulletin of the Seismological Society of America, v. 

38,p.105-119. 

Matsuda, T., 1975, Magnitude and recurrence interval of earthquakes 

from a fault:. Zisin, ser. 2, v. 28, p. 269-283. (In Japanese with 

English abstract.) 

___ 1977, Estimation of future destructive earthquakes from active 

faults on land in Japan: Journal of Physics of the Earth, v. 25; 

suppl., p. S251-S260. 

Matti, J. C., and Morton, D. M., 1982, Geologic history of the Banning 

fault zone, southern California [abs.]: Geological Society of 

America Abstracts with Programs, v. 14, no. 4, p. 184. 

Matti, J. C., Morton, D. M., Tinsley, J. C., and McFadden, L. D., in 

press, The Cucamonga fault zone, pt. 2, History of faulting on the 

Day Canyon and East Etiwanda Canyon alluvial fans, in Recent 

reverse faulting in the Transverse Ranges, California: U.S. 

Geological Survey Professional Paper 1339. 

Matti, J. C., Tinsley, J. C., Morton, D. M., and McFadden, L. D., 1982, 

Holocene faulting history as recorded by alluvial stratigraphy 

within the Cucamonga fault zone-A preliminary view, in Tinsley, 

J. C., Matti, J. C., and McFadden, L. D., eds., Late Quaternary 

pedogenesis and alluvial chronologies of the Los Angeles and San 

Gabriel Mountains areas, southern California: Geological Society 

of America Annual Meeting, Cordilleran Section, 78th, Anaheim, 

Calif., 1982, Guidebook 12, p. 29-44. 

Meisling, K. E., 1984, Neotectonics of the north frontal fault system of 

the San Bernardino Mountains, southern California: Pasadena, 

·calif., California Institute of Technology, unpublished Ph.D. thesis, 

394p. 

Meisling, K. E., and Weldon, R. J., 1982a, Slip rate, offset, and history of 

the Cleghorn fault, western San Bernardino Mountains, southern 

California [abs.]: Geological Society of America Abstracts with 

Programs, v. 14, no. 4, p. 215. 

___ 1982b, The late-Cenozoic structure and stratigraphy of the 

western San Bernardino Mountains, in Geologic excursions in the 

Transverse Ranges: Geological Society of America Annual Meeting, Cordilleran Section, 78th, Anaheim, Calif., 1982, Guidebook, 

p. 75-81. 

Mezger, L., and Weldon, R. J., 1983, Tectonic implications of the 

Quaternary history of lower Lytle Creek, southeast San Gabriel 

Mountains [abs.]: Geological Society of America Abstracts with 

Programs,v. 15,no.5,p.418. 

Miller, F. K., 1979, Geologic map of the San Bernardino North 

quadrangle, California: U.S. Geological Survey Open-File Report 

79-770, scale 1:24,000. 

_in press, Reverse fault system bounding the north side of the San 

Bernardino Mountains, in Recent reverse faulting in the Transverse Ranges, California: U.S. Geological Survey Professional 

Paper 1339. 

Miller, F. K., and Morton, D. M., 1980, Potassium-argon geochronology 

of the eastern Transverse Ranges and southern Mojave Desert, 

southern California: U.S. Geological Survey Professional Paper 

1152, 30p. 

Millman, D. E., 1985, Neotectonics of part of the northern Elsinore 

fault zone in the Temescal Valley area, western Riverside County, 

California: San Diego, Calif., San Diego State University unpublished M.Sci. thesis. 

Molnar, P., 1979, Earthquake recurrence intervals and plate tectonics: 

Bulletin of the Seismological Society of America, v. 69, no. 1, 

p. 115-133. 

Morton, D. M., 1973, Geology of parts of the Azusa and Mount Wilson 

quadrangles, San Gabriel Mountains, Los Angeles County, California: California Division of Mines and Geology Special Report 105, 

21p . 

. ___ 1975, Synopsis of the geology of the eastern San Gabriel Mountains, southern California, in Crowell, J. C., ed., San Andreas fault 

in southern California: California Division of Mines and Geology 

Special Report 118, p. 170-176. 

___ 1976, Generalized fault map of southwestern San Bernardino 

County (west half), plates 2A and 2B, in Fife, D. L., Rodgers, D. A., 

Chase, G. W., Chapman, R. H., and Sprotte, E. C., 3ds., Geologic 

hazards in southwestern San Bernardino County, California: 

California Division of Mines and Geology Special Report 113, 40 p. 

___ 1978, Ground fissuring in part of the San Jacinto Valley, southern 

California [abs.]: Geological Society of America Abstracts with 

Programs, v. 10, no. 3, p. 138. 

Morton, D. M., and Matti, J. C., in press, The Cucamonga fault zone, 

pt. 1, Geologic setting and history of Quaternary faulting, in Recent 

reverse faulting in the Transverse Ranges, California: U.S. 

Geological Survey Professional Paper 1339. 

Morton, D. M., and Miller, F. K., 1975, Geology of the San Andreas fault 

zone north of San Bernardino between Cajon Canyon and Santa 

Ana Wash, in Crowell, J. C., ed., San Andreas fault in southern 

California: California Division of Mines and Geology Special 

Report 118, p. 136-;146. 

Morton, D. M., Miller, F. K., and Smith, C. C., 1980, Photoreconnaissance maps showing young-looking fault features in the 

_southern Mojave Desert, California: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1051, scales 1:24,000 to 

1:62,500,7 sheets. 

Morton, D. M., Matti, J. C., and Tinsley, J. C., 1982, Quaternary history 

of the Cucamonga fault zone, southern California [abs.]: Geological 

Society of America Abstracts with Programs, v. 14, no. 4, p. 218. 

Morton, P. K., Miller, R. V., and Fife, D. L., 1973, Preliminary geoenvironmental maps of Orange County, California: California Division of Mines and Geology Preliminary Report 15, 4 pis., scale 

1:48,000. 

Nardin, T. R., 1981, Seismic stratigraphy of Santa Monica and San 

Pedro basins, California Continental Borderland-Late Neogene 

history of sedimentation and tectonics: Los Angeles, Calif., University of Southern California, unpublished Ph.D. thesis, 270 p. 

Nardin, T. R., and Henyey, T. L., 1978, Pliocene-Pleistocene 

diastrophism of Santa Monica and San Pedro shelves, California 

Continental Borderland: American Association of Petroleum Geologists Bulletin, v. 62, no. 2, p. 247-272. 

Nelligan, F. M., 1978, Geology of the Newhall area of the eastern Ventura and western Soledad basins, Los Angeles County, California: 

Corvallis, Oreg., Oregon State University, unpublished M.Sci. 

thesis, 117 p. 

Nuttli, 0. W., and Hermann, R. B., 1982, Earthquake magnitude scales: 

Proceedings of the American Society of Civil Engineers, Journal of 

the Geotechnical Engineering Division, v. 108, no. GT5, p. 783-786. 

References Cited 477 
Olson, D. J., 1982, Surface and subsurface geology of the Santa Barbara-Goleta metropolitan area, Santa Barbara County, California: 

Menlo Park, Calif., technical report to U.S. Geological Survey 

under contract 14-08-0001-19173, 71 p. 

Pampeyan, E. H., 1979, Preliminary map showing recency of faulting in 

coastal north-central California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1070, scale 1:250,000. 

Patterson, R. H., 1979, Tectonic geomorphology and neotectonics of the 

Santa Cruz Island fault, Santa Barbara County, California: Santa 

Barbara, Calif., University of California, unpublished M.Sci. thesis, 

141p. 

Pechmann, J. C., in press, Tectonic implications of small earthquakes in 

the central Transverse Ranges, California, in Recent reverse faulting in the Transverse Ranges, California: U.S. Geological Survey 

Professional Paper 1339. 

Pinault, C. T., and Rockwell, T. K., 1984, Rate3 and sense of Holocene 

faulting on the southern Elsinore fault: Further constraints on the 

distribution of dextral shear between the Pacific and North American plates [abs.]: Geological Society of America Abstracts with 

Programs, v. 16, no. 6, p. 624. 

Poland, J. F., and Piper, A. M., 1956, Ground water geology of the 

coastal zone, Long Beach-Santa Ana area, California: U.S. Geological Survey Water-Supply Paper 1109, 126 p. 

Poland, J. F., Garrett, A. A., and Sinnott, A., 1959, Geology, hydrology, 

and chemical character of ground waters in the Torrance-Santa 

Monica area, California: U.S. Geological Survey Water-Supply 

Paper 1461, 425 p. 

Ponti, D. J., and Burke, D. B., 1980, Map showing Quaternary geology of 

the eastern Antelope Valley and vicinity, California: U.S. Geological Survey Open-File Report 80-1064, scale 1:62,500. 

Proctor, R. J., 1962, Geologic features of a section across the Casa Lorna 

fault, exposed in an aqueduct trench near San Jacinto, California: 

Geol,ogical Society of America Bulletin, v. 73, p. 1293-1296. 

___ 1974, New localities for fault creep in southern CaliforniaRaymond and Casa Lorna faults [abs.]: Geological Society of America Abstracts with Programs, v. 6, no. 3, p. 238. 

Raleigh, C. B., Sieh, K., Sykes, L. R., and Anderson, D. L., 1982, 

Forecasting southern California earthquakes: Science, v. 217, no. 

4565,p.1097-1104. 

Rasmussen, G. S., 1981, Nature of surface rupture and recurrence interval, Casa Lorna fault, in Brown, A. R., and Ruff, R. W., eds., 

Geology of the San Jacinto Mountains: South Coast Geological 

Society Annual Field Trip Guidebook 9, p. 48-54. 

___ 1982a, Geologic features and rate of movement along the south 

branch of the San Andreas fault, San Bernardino, California, in 

Cooper, J. D., compiler, Neotectonics in southern California: 

Geological Society of America Annual Meeting, Cordilleran Section, 78th, Anaheim, Calif., 1982, Guidebook, p. 109--114. 

___ 1982b, Historic earthquakes along the San Jacinto fault zone, 

San Jacinto, California: in Cooper, J. D., compiler, Neotectonics in 

southern California: Geological Society of America Annual Meeting, Cordilleran Section, 78th, Anaheim, Calif., 1982, Guidebook, 

p. 115-121. 

Real, C. R., in press, Seismicity and tectonics of the Santa 

Monica-Hollywood-Raymond Hill fault and northern Los Angeles 

basin, Los Angeles County, California, in Recent reverse faulting in 

the Transverse Ranges, California: U.S. Geological Survey Professional Paper 1339. 

Research Group for Active Faults of Japan, 1980, Active faults in Japan, 

sheet maps and inventories: Tokyo, University of Tokyo Press, 

363 p. (In Japanese with English summary.) 

Richter, C. F., 1935, An instrumental earthquake magnitude scale: 

Bulletin of the Seismological Society of America, v. 25, no. 1, 

D.1-32. 

478 Earthquake Hazards in the Los Angeles Region 

___ 1958, Elementary seismology: San Francisco, Calif., W. H. 

Freeman, 768 p. 

Ricketts, E. W., and Whaley, K. R., 1975, Structure and stratigraphy of 

the Oak Ridge fault-Santa Susana fault intersection, Ventura 

Basin, California: Athens, Ohio, Ohio University, unpublished 

M.Sci. thesis, 81 p. 

Rieser, R. B., 1976, Structural study of the Oak Ridge fault between 

South Mountains and Wiley Canyon, Ventura County, California: 

Athens, Ohio, Ohio University, unpublished M.Sci. thesis, 93 p. 

Rockwell, T. K., 1982, Style, rates, and recency of deformation along the 

San Cayetano fault, western Transverse Ranges, California [abs.]: 

Geological Society of America Abstracts with Programs, v. 14, no. 

4,p. 228. 

___ 1983, Soil chronology, geology, and neotectonics of the north central Ventura basin, California: Santa Barbara, Calif., University of 

California, unpublished Ph.D. thesis, 424 p. 

Rockwell, T. K., Keller, E. A., Clark, M. N., and Johnson, D. L., 1984, 

Chronology and rates of faulting of Ventura River terraces, California: Geological Society of America Bulletin, v. 95, no. 12, 

p. 1466-1474. 

Rockwell, T. K., Lamar, D. L., McElwain, R. S., and Millman, D. E., 

1985, Late Holocene recurrent faulting on the Glen Ivy North 

strand of the Elsinore fault, southern California [abs.]: Geological 

Society of America Abstracts with Programs, Cordilleran Section, 

v. 17, no. 6, p. 404. 

Ross, D. C., 1969, Map showing recently active breaks along the San 

Andreas fault between Tejon Pass and Cajon Pass, southern California: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-553, scale 1:24,000. 

Rust, D. J., 1982, Radiocarbon dates for the most recent large 

prehistoric earthquake and for late Holocene slip rates, San Andreas fault in part of the Transverse Ranges north of Los Angeles 

[abs.]: Geological Society of America Abstracts with Programs, v. 

14, no. 4, p. 229. 

Sanders, C. 0., and Kanamori, H., 1984, A seismotectonic analysis of 

the Anza seismic gap, San Jacinto fault zone, southern California: 

Journal of Geophysical Research, v. 89, no. B7, p. 5873-5890. 

Sarna-Wojcicki, A. M., Williams, K. M., and Yerkes, R. F., 1976, 

Geology of the Ventura fault, Ventura County, California: U.S. 

Geological Survey Miscellaneous Field Studies Map MF-781, scale 

"1:6,000. 

Sarna-Wojcicki, A. M., Bowman, H. R., Meyer, C. E., Russell, P. C., 

Woodward, M. J., McCoy, G., Rowe, J. J., Jr., Baedecker, P. A., 

Asaro, F., and Michael, H., 1984, Chemical analyses, correlations, 

and ages of upper Pliocene and Pleistocene ash layers of eastcentral and southern California: U.S. Geological Survey Professional Paper 1293, 40 p. 

Sarna-Wojcicki, A. M., Lajoie, K. R., and Yerkes, R. F., in press, Recurrent Holocene displacement on the Javon Canyon fault-A comparison of fault movement history with calculated average recurrence 

intervals, in Recent reverse faulting in the Transverse Ranges, 

California: U.S. Geological Survey Professional Paper 1339. 

Saul, R. B., 1975, Geology of the southeast slope of the Santa Susana 

Mountains and geologic effects of the San Fernando earthquake, in 

Oakeshott, G. B., ed., San Fernando, California, earthquake of 9 

February 1971: California Division of Mines and Geology Bulletin 

196, p. 53-70. 

Savage, J. C., Burford, R. 0., and Kinoshita, W. T., 1975, Earth 

movements from geodetic measurements, in Oakeshott, G. B., ed., 

San Fernando, California, earthquake of 9 February 1971: California Division of Mines and Geology Bulletin 196, p. 175-186. 

Schlueter, J. C., 1976, Geology of the upper Ojai-Timber Canyon area, 

Ventura County, California: Athens, Ohio, Ohio University, unpublished M.Sci. thesis, 76 p. 
Schoellhamer, J. E., Vedder, J. G., Yerkes, R. F., and Kinney, D. M., 1981, 

Geology of the northern Santa Ana Mountains, California: U.S. 

Geological Survey Professional Paper 42(}.-D, 119 p. 

Scholz, C. H., 1982, Scaling laws for large earthquakes-Consequences 

for physical models: Bulletin of the Seismological Society of 

America, v. 72, no. 1, p.l-14. 

Schubert, C., and Crowell, J. C., 1980, Neotectonic map of the San 

Andreas fault between Valyermo and Wrightwood, California: 

Menlo Park, Calif., technical report to U.S. Geological Survey 

under contract 14-{)8-{)001-17676, 20 p. 

Schwartz, D. P., and Coppersmith, K. J., 1984, Fault behavior and 

characteristic earthquakes: Examples from the Wasatch and San 

Andreas fault zones: Journal of Geophysical Research, v. 89, no. 

B7, p. 5681-5698. 

Sharp, R. V., 1967, San Jacinto fault zone in the Peninsula Ranges of 

southern California: Geological Society of America Bulletin, v. 78, 

p. 705-730. 

__ 1972, Map showing recently active breaks along the San Jacinto 

fault zone between the San Bernardino area and Borrego Valley, 

California: U.S. Geological Survey Miscellaneous Investigations 

Map I-675, scale 1:24,000. 

__ 1975, Displacement on tectonic ruptures, in Oakeshott, G. B., ed., 

San Fernando, California, earthquake of 9 February 1971: California Division of Mines and Geology Bulletin 196, p. 187-194. 

__ 1981a, Displacements on tectonic ruptures in the San Fernando 

earthquake of February 9, 1971-Discussion and some implications: U.S. Geological Survey Open-File Report 81-668, 14 p. 

__ 1981b, Variable rates of late Quaternary strike slip on the San 

Jacinto fault zone, southern California: Journal of Geophysical 

Research,v.86,no.B3,p.1754-1762. 

Sharp, R. V., and Clark, M. M., 1972, Geologic evidence of previous 

faulting near the 1968 rupture on the Coyote Creek fault, in The 

Borrego Mountain earthquake of April 9, 1968: U.S. Geological 

Survey Professional Paper 787, p. 131-140. 

Sharp, R. V., Lienkaemper, J. J., Bonilla, M. G., Burke, D. B., Cox, B. F., 

Herd, D. G., Miller, D. M., Morton, D. M., Ponti, D. J., Rymer, M. J., 

Tinsley, J. C., Yount, J. C., Kahle, J. E., Hart, E. W., and Sieh, K. E., 

1982, Surface faulting in central Imperial Valley, in The Imperial 

Valley, California, earthquake of October 15, 1979: U.S. Geological 

Survey Professional Paper 1254, p. 119-143. 

Shields, K. E., 1978, Faults along the northwestern margin of the San 

Fernando Valley, Los Angeles County, California, in Geologic guide 

and engineering geology case histories, Los Angeles metropolitan 

area: Association of Engineering Geologists, Annual California 

Section Conference, 1st, Los Angeles, Calif., 1978, Guidebook, 

p. 44-52. 

Sieh, K. E., 1978a, Slip along the San Andreas fault associated with the 

great 1857 earthquake: Bulletin of the Seismological Society of 

America, v. 68, p. 1421-1448. 

__ 1978b, Central California foreshocks of the great 1857 earthquake: Bulletin of the Seismological Society of America, v. 68, 

p. 1731-1749. 

__ 1978c, Prehistoric large earthquakes produced by slip on the San 

Andreas fault at Pallett Creek, California: Journal of Geophysical 

Research, v. 83, no. 8, p. 3907-3939. 

__ 1981, A review of geological evidence for recurrence times of . 

large earthquakes, in Simpson, D. W., and Richards, P. G., eds., 

Earthquake prediction-An international review: American Geophysical Union Maurice Ewing Series, no. 4, p. 181-207. 

__ 1984, Lateral offsets and revised dates of large prehistoric 

earthquakes at Pallett Creek, southern California: Journal of Geophysical Research, v. 89, no. B9, p. 7641-7670. 

Sieh, K. E., and Jahns, R. E., 1984, Holocene activity of the San Andreas 

fault at Wallace Creek, California: Geological Society of America 

Bulletin, v. 95, p. 883-896. 

Simila, G. W., Eliades, P. G., Hagan, J. D., and Adams, H. G., 1982, 

Microearthquake activity in the Santa Susana Mountains and Simi 

Hills, San Fernando Valley [abs.]: Earthquake Notes, v. 53, no. 1, 

p.84. 

Slemmons, D. B., 1977, State-of-the-art for assessing earthquake 

hazards in the United States; faults and earthquake magnitude: 

U.S. Army Corps of Engineers Waterways Experiment Station 

Miscellaneous Paper 5-3-73-1, Report 6, 166 p. 

Stanley, K. 0., 1966, The structural history of the Clearwater fault, 

northwest Los Angeles County, California: Los Angeles, Calif., U niversity of California, unpublished M.A. thesis, 73 p. 

Stein, R. S., and King, G. C. P., 1984, Seismic potential revealed by 

surface folding: 1983 Coalinga, California, earthquake: Science, v. 

224, p. 869-872. 

Stein, R. S., and Thatcher, W., 1981, Seismic and aseismic deformation 

associated with the 1952 Kern County, California, earthquake and 

relationship to the Quaternary history of the White Wolf fault: 

Journal of Geophysical Research, v. 86, no. B6, p. 4913-4928. 

Stitt, L. T., 1983, Geology, seismic hazard, and ground-rupture hazard 

of the San Gabriel and Holser faults, eastern Ventura and western 

Soledad basins, California: Menlo Park, Calif., technical report to 

U.S. Geological Survey under contract 14-DB-0001-19138, 26 p. 

Thatcher, W., Hileman, J. A., and Hanks, T. C., 1975, Seismic slip 

distribution along the San Jacinto fault zone, southern California, 

and its implications: Geological Society of America Bulletin, v. 86, 

p. 114(}.-1146. 

U.S. Geological Survey Staff, 1971, Surface faulting, in The San Fernando, California, earthquake of February 9, 1971: U.S. Geological 

Survey Professional Paper 733, p. 55-76. 

Upson, J. E., 1951, Geology and ground-water resources of the southcoast basins of Santa Barbara County, California, with u section on 

Surface-water resources, by H. G. Thomasson, Jr.: U.S. Geological 

Survey Water-Supply Paper 1108, 144 p. 

Wallace, R. E., 1977, Profiles and ages of young fault scarps, northcentral Nevada: Geological Society of America Bulletin, v. 88, 

p. 1267-1281. 

__ 1981, Active faults, paleoseismology, and earthquake hazards in 

the western United States, in Simpson, D. W., and Richards, P. G., 

eds., Earthquake prediction-An international review: American 

Geophysical Union Maurice Ewing Series, no. 4, p. 209-216. 

__ 1982, Fault-scarp analysis in paleoseismicity [abs.]: EOS, Transactions of the American Geophysical Union, v. 63, no. 18, p. 435. 

Weber, F. H., Jr., 1975, Surface effects and related geology of the San 

Fernando earthquake in the Sylmar area, in Oakeshott, G. B., ed., 

San Fernando, California, earthquake of 9 February 1981: California Division of Mines and Geology Bulletin 196, p. 71-96. 

__ 1977, Seismic hazards related to geologic factors, Elsinore and 

Chino fault zones, northwestern Riverside County, California: 

California Division of Mines and Geology Open-File Report 77-4 

LA,96p. 

__ 1978, Geologic and geomorphic investigation of the San Gabriel 

fault zone, Los Angeles and Ventura Counties, California: Menlo 

Park, Calif., technical report to U.S. Geological Survey under contract 14-{)8-{)001-16600, 78 p. 

__ 1980,' Geological features related to character and recency of 

movement along faults, north-central Los Angeles County, California, in Weber, F. H., Jr., Bennett, J. H., Chapman, R. H., Chase, 

G. W., and Saul, R. B., eds., Earthquake hazards associated with 

the Verdugo-Eagle Rock and Benedict Canyon fault zones, Los 

Angeles County, California: California Division of Mines and 

Geology Open-File Report 8(}.-10 LA, p. B 1-B 116. 

__ 1982, Geology and geomorphology along the San Gabriel fault 

zone, Los Angeles and Ventura Cdunties, California: California 

Division of Mines and Geology Open-File Report 82-2 LA, 157 p. 

References Cited 479 
Weber, F. H., Jr., and Kiessling, E. W., 1975, General features of seismic 

hazards of Ventura County, California, in Seismic hazards of Ventura County, California: California Division of Mines and Geology 

Open-File Report 76-5 LA, p. 8-217. 

Weldon, R. J., and Sieh, K. E., 1981, Offset rate and possible timing of 

recent earthquakes on the San Andreas fault in Cajon Pass, California [abs.]: EOS, Transactions of the American Geophysical 

Union, v. 62, no. 45, p. 1048. 

Wentworth, C. M., Ziony, J. I., and Buchanan, J. M., 1970, Preliminary 

environmental map of the greater Los Angeles area, California: 

Springfield, Va., National Technical Information Service 

TID-25363, 41 p., 1:250,000 scale. (Available in microfiche only.) 

Wesnousky, S. G., Scholz, C. H., and Shimazaki, K., 1982, Deformation 

of an island arc: Rates of moment release and crustal shortening in 

intraplate Japan determined from seismicity and Quaternary fault 

data: Journal of Geophysical Research, v. 87, no. 8, p. 6829-6852. 

Wesnousky, S. G., Scholz, C. H., Shimazaki, K., and Matsuda, T., 1984, 

Integration of geological and seismological data for the analysis of 

seismic hazard: A case study of Japan: Bulletin of the Seismological 

Society of America, v. 74, no. 2, p. 687-708. 

Wesson, R. L., Page, R. A., Boore, D. M., and Yerkes, R. F., 1974, Expectable earthquakes and their ground motions in the Van Norman 

reservoirs area, in The Van Norman reservoirs area, northern San 

Fernando Valley, California: U.S. Geological Survey Circular 

691-B, p. B1-B9. 

Wesson, R. L., Helley, E. J., Lajoie, K. R., and Wentworth, C. M., 1975, 

Faults and future earthquakes, in Borcherdt, R. D., ed., Studies for 

seismic zonation of the San Francisco Bay region: U.S. Geological 

Survey Professional Paper 941-A, p. A5-A30. 

Woodring, W. P., Bramlette, M. N., and Kew, W. S. W., 1946, Geology 

and paleontology of Palos Verdes Hills, California: U.S. Geological 

Survey Professional Paper 207, 145 p. 

Woodward-Clyde Consultants, 1979, Report on the evaluation of maximum earthquake and site ground motion parameters associated 

with the Offshore Zone of Deformation, San Onofre Nuclear 

Generating Station: Los Angeles, Calif., report prepared for 

Southern California Edison, 56 p., 11 figs., 10 apps. 

Wyss, M., 1979, Estimating maximum expectable magnitude of earthquakes from fault dimensions: Geology, v. 7, p. 336-340. 

Yeats, R. S., 1977, High rates of vertical crustal movement near Ventura, California: Science, v. 196, p. 295-298. 

___ 1982, Low-shake faults of the Ventura basin, California, in 

Cooper, J. D., compiler, Neotectonics in southern California: Geological Society of America Annual Meeting, Cordilleran Section, 

78th, Anaheim, Calif., 1982, Guidebook, p. 3-23. 

___ 1983, Large-scale Quaternary detachments in Ventura basin, 

southern California: Journal of Geophysical Research, v. 88, no. 1, 

p. 569--583. 

Yeats, R. S., and Olson, D. J., 1984, Alternate fault model for the Santa 

Barbara, California, earthquake of 13 August 1978: Bulletin of the 

Seismological Society of America, v. 74, no. 5, p. 1545-1553. 

Yeats, R. S., Lant, K. J., and Shields, K. E., 1977, Subsurface geology of 

the Santa Susana fault in the aftershock area downstep of the 

1971 San Fernando earthquake: Menlo Park, Calif., technical 

report to U.S. Geological Survey under contract 14--08--0001-

15271,23 p. 

Yeats, R. S., Clark, M. N., Keller, E. A., and Rockwell, T. K., 1981, Active 

fault hazard in southern California-Ground rupture versus seismic shaking: Geological Society of America Bulletin, v. 92, 

p. 189--196. 

480 Earthquake Hazards in the Los Angeles Region 

Yeats, R. S., Keller, E. A., Rockwell, T. K., Lajoie, K. R., Sarna-Wojcicki, 

A.M., and Yerkes, R. F., 1982, Field trip number 3-Neotectonics 

of the Ventura Basin-Road log, in Cooper, J. D., compiler, Neotectonics in southern California: Geological S_ociety of America Annual Meeting, Cordilleran Section, 78th, Anaheim, Calif., 1982, 

Guidebook, p. 61-76. 

Yeats, R. S., Lee, W. H. K., and Yerkes, R. F., in press, Geology and 

seismicity of the eastern Red Mountain fault, Ventura County, California, in Recent reverse faulting in the Transverse Ranges, California: U.S. Geological Survey Professional Paper 1339. 

Yerkes, R. F., 1972, Geology and oil resources of the western Puente 

Hills area, southern California: U.S. Geological Survey Professional Paper 420-C, 60 p. 

Yerkes, R. F., and Lee, W. H. K., 1979a, Faults, fault activity, 

epicenters, focal depths, and focal mechanisms, 1970-75 earthquakes, western Transverse Ranges, California: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-1032, 2 sheets, scale 

1:250,000. 

___ 1979b, Late Quaternary deformation in the western Transverse 

Ranges, California: U.S. Geological Survey Circular 799--B, 10 p. 

Yerkes, R. F., and Wentworth, C. M., 1965, Structure, Quaternary 

history, and general geology of the Corral Canyon area, Los 

Angeles County, California: U.S. Geological Survey Open-File 

Report 864, 215 p. 

Yerkes, R. F., McCulloh, T. H., Schoellhamer, J. E., and Vedder, J. G., 

1965, Geology of the Los Angeles basin, California-An introduction: U.S. Geological Survey Professional Paper 420-A, 57 p. 

Yerkes, R. F., Gorsline, D. S., and Rusnak, G. A., 1967, Origin of Redondo submarine canyon, southern California, in Geological Survey 

research 1967: U.S. Geological Survey Professional Paper 575-C, 

p. C97-C105. 

Yerkes, R. F., Bonilla, M.G., Youd, T. L., and Sims, J.D., 1974, Geologic 

environment of the Van Norman reservoirs area, in The Van Norman reservoirs area, northern San Fernando Valley, California: 

U.S. Geological Survey Circular 691-A, p. A1-A35. 

Yerkes, R. F., Greene, H. G., Tinsley, J. C., and Lajoie, K. R., 1981, 

Seismotectonic setting of the Santa Barbara Channel area, southern California: U.S. Geological Survey Miscellaneous Studies Map 

MF-1169, scale 1:250,000. 

Yerkes, R. F., Ellsworth, W. L., and Tinsley, J. C., 1983, Triggered 

reverse fault and earthquake due to crustal unloading, northwest 

Traverse Ranges, California: Geology, v. 11, p. 287-291. 

Yerkes, R. F., McGarr, A. F., Wentworth, C. M., and Walter, A. W., 

1984, Abnormally high fluid pressures near the Coast RangesGreat Valley boundary, California, may aid northeast-directed 

thrusting responsible for the 1983 Coalinga earthquake [abs.]: 

EOS, Transactions of the American Geophysical Union, v. 65, no. 

45, p. 995. 

Youd, T. L., Yerkes, R. F., and Clark, M. M., 1978, San Fernando 

faulting damage and its effect on land use, in American Society of 

Civil Engineers Specialty Conference on Earthquake Engineering 

and Soil Dynamics, Pasadena, Calif., 1978, Proceedings: v. 2, 

p. 1111-1125. 

Ziony, J. I., Wentworth, C. M., and Buchanan, J. M., 1973, Recency of 

faulting: A widely applicable criterion for assessing the activity of 

faults: World Conference on Earthquake Engineering, 5th, Rome 

1973,Proceedings,v.2,p.1680-1683. 

Ziony, J. I., Wentworth, C. M., Buchanan-Banks, J. M., and Wagner, 

H. C., 1974, Preliminary map showing recency of faulting in 

coastal southern California: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-585, scale 1:250,000. 
Predicting Earthquake Ground Motion: An Introduction 

Apse!. R. J., Frazier, G. A., Jurkevics, A., and Fried, J. C., 1981, 

Ground motion prediction for the Los Angeles Basin from a major 

San Andreas earthquake: U.S. Geological Survey Open-File Report 

81-276, 217 p. 

Blume, J. A., Scholl, R. E., Somerville, M. R., and Honda, K. K., 1980, 

Damage prediction of an earthquake in southern California: U.S. 

Geological Survey Open-File Report 80-1145,83 p. 

Borcherdt, R. D., 1970, Effects of local geology on ground motion near 

San Francisco Bay: Bulletin of the Seismological Society of 

America, v. 60, p. 29-61. 

___ ed., 1975, Studies for seismic zonation of the San Francisco Bay 

region: U.S. Geological Survey Professional Paper941-A, 102 p. 

Borcherdt, R. D., and Gibbs, J. F., 1976, Effects of local geological conditions in the San Francisco Bay region on ground motions and the 

intensities of the 1906 earthquake: Bulletin of the Seismological 

Society of America, v. 66, p. 467-500. 

Borcherdt, R. D., Gibbs, J. F., and Lajoie, K. R., 1975a, Maps showing 

maximum earthquake intensity predicted in the southern San 

Francisco Bay region, California, for large earthquakes on the San 

Andreas and Hayward faults: U.S. Geological Survey Miscellaneous Field Studies Map MF-709, scale 1:125,000, 11-p. text. 

Borcherdt, R. D., Brabb, E. E., Joyner, W. B., Helley, E. J., Lajoie, 

K. R., Page, R. A., Wesson, R. L., and Youd, T. L., 1975b, Predicted 

geologic effects of a postulated earthquake, in Borcherdt, R. D., 

ed., Studies for seismic zonation of the San Francisco Bay region: 

U.S. Geological Survey Professional Paper 941-A, p. A88-A96. 

Borcherdt, R. D., Joyner, W. B., Warrick, R. E., and Gibbs, J. F., 1975c, 

Response of local geologic units to ground shaking, in Borcherdt, 

R. D., ed., Studies for seismic zonation of the San Francisco Bay 

region: U.S. Geological Survey Professional Paper 941-A, 

p.A52-A67. 

Borcherdt, R. D., Gibbs, J. F., and Fumal. T. E., 1979, Progress on ground 

motion predictions for the San Francisco Bay region, in Brabb, 

E. E., ed., Progress on seismic zonation in the San Francisco Bay 

region: U.S. Geological Survey Circular 807, p. 13-25. 

Davis, J. F., Bennett, J. H., Borchardt, G. A., Kahle, J. E., Rice, S. J., and 

Silva, M. A., 1982a, Earthquake planning scenario for a magnitude 

8.3 earthquake on the San Andreas fault in southern California: 

California Division of Mines and Geology Special Publication 60, 

128p. 

___ 1982b, Earthquake planning scenario for a magnitude 8.3 earthquake on the San Andreas fault in the San Francisco Bay area: 

California Division of Mines and Geology Special Publication 61, 

160p. 

Evernden, J. F., 1975, Seismic intensities, "size" of earthquakes and 

related parameters: Bulletin of the Seismological Society , of 

America, v. 65, p. 1287-1313. 

Evernden, J. F., Hibbard, R. R., and Schneider, J. F., 1973, Interpretation 

of seismic intensity data: Bulletin of the Seismological Society of 

America, v. 63, p. 399-422. 

Evernden, J. F., Kohler, W. M., and Clow, G. D., 1981, Seismic intensities 

of earthquakes of conterminous United States-Their prediction 

and interpretation: U.S. Geological Survey Professional Paper 

1223,56 p. 

Fumal, T. E., 1978, Correlations between seismic wave velocities and 

physical properties of near-surface geologic materials in the southern San Francisco Bay region, California: U.S. Geological Survey 

Open-File Report 78-1067, 52 p., 1 pl. 

Fumal, T. E., Gibbs, J. F., and Roth, E. F., 1981, In-situ measurements of 

seismic velocity at 22 locations in the Los Angeles, California, 

region: U.S. Geological Survey Open-File Report 82-833, 140 p. 

___ 1982, In-situ measurements of seismic velocity at 10 strong motion accelerograph stations in central California: U.S. Geological 

Survey Open-File Report 82-407, 78 p. 

___ 1984, In-situ measurements of seismic velocity at 16 locations in 

the Los Angeles region: U.S. Geological Survey Open-File Report 

84-681, 18 p., 65 figs., 32 tables. 

Gibbs, J. F., Fumal, T.' E., and Borcherdt, R. D., 1975, In-situ 

measurements of seismic velocities at 12 locations in the San Francisco Bay region: U.S. Geological Survey Open-File Report 75-564, 

20 p., 44 figs., 24 tables. 

___ 1976, In-situ measurements of seismic velocities in the San Francisco Bay region, pt. II: U.S. Geological Survey Open-File Report 

7&-731, 145 p., 88 figs., 46 tables. 

Gibbs, J. F., Fumal, T. E., Borcherdt, R. D., and Roth, E. F., 1977, In-situ 

measurements of seismic velocities in the San Francisco Bay 

region, pt. Ill: U.S. Geological Survey Open-File Report 77-850, 145 

p., 46 pls., 87 figs. 

Gibbs, J, F., Fumal. T. E., and Roth, E. F. 1980, In-situ measurements of 

seismic velocities at 27 locations in the Los Angeles, California, 

region: U.S. Geological Survey Open-File Report 80-378, 169 p. 

Hays, W. W., 1980, Procedures for estimating earthquake ground motions: U.S. Geological Survey Professional Paper 1114, 77 p. 

Kanai, K., 1952, Relation between the nature of the surface layer and 

the amplitudes of earthquake motions: Bulletin of the Earthquake 

Research Institute, University of Tokyo, v. 30, p. 31-37. 

Kockelman, W. J., 1975, Use of U.S. Geological Survey earth-science 

products by city planning agencies in the San Francisco Bay 

region, California: U.S. Geological Survey Open-File Report 

75-276, 110 p. 

__ -_1979, Use of U.S. Geological Survey earth-science products by 

-- - --selected regional agencies in the San Francisco Bay region, California: U.S. Geological Survey Open-File Report 79-221, 173 p. 

___ 1980, Examples of the use of earth-science information by decisionmakers in the San Francisco Bay region, California: U.S. Geological Survey Open-File Report 80-124, 88 p. 

Kockelman, W. J., and Brabb, E. E., 1979, Examples of seismic zonation 

in the San Francisco Bay region, in Brabb, E. E., ed., Progress on 

seismic zonation in the San Francisco Bay region: U.S. Geological 

Survey Circular 807, p. 73-84. 

Lajoie, K. R., and Helley, E. J., 1975, Differentiation of sedimentary 

deposits for purposes of seismic zonation, in Borcherdt, R. D., ed., 

Studies for seismic zonation of the San Francisco Bay region: U.S. 

Geological Survey Professional Paper 941-A, p. A39-A51. 

Page, R. A., Boore, D. M., and Dieterich, J. H., 1975, Estimation of bedrock motion at the ground surface, in Borcherdt, R. D., ed., Studies 

for seismic zonation of the San Francisco Bay region: U.S. Geological Survey Professional Paper 941-A, p. A31-A38. 

Rogers, A. M., Covington, P. A., Borcherdt, R. D., and Tinsley, J. C., 

1980, Comparative ground response studies in Los Angeles using 

NTS nuclear explosions and San Fernando earthquake data, in 

Proceedings of Conference XIII: Evaluation of regional seismic 

hazards and risk: U.S. Geological Survey Open-File Report 81-437, 

p. 143-161. 

Rogers, A. M., Borcherdt, R. D., Covington, P. A., and Perkins, D. M., 

1984, A comparative ground response study near Los Angeles 

using recordings of Nevada tests and the 1971 San Fernando 

References Cited 481 
earthquake: Bulletin of the Seismological Society of America, v. 74, 

no. 5, p. 1925--1949. 

Richter, C. F., 1958, Elementary seismology: San Francisco, W. H. 

Freeman, 768 p. 

Wood, H. 0., 1908, Distribution of apparent intensity in San Francisco, 

in The California earthquake of April 18, 1906, report of the State 

Earthquake Investigation Commission: Carnegie Institute of Washington Publication 87, p. 220--245. 

Mapping Quaternary Sedimentary Deposits for Areal Variations 

in Shaking Response 

Birkeland, P. W., 1984, Soils and geomorphology: New York, Oxford 

University Press, 372 p. 

Borcherdt, R. D., 1970, Effect of local geology on ground motion near 

San Francisco Bay: Bulletin of the Seismological Society of 

America, v. 60, p. 29--61. 

Borcherdt, R. D., and Gibbs, J. F., 1976, Effects of local geologic conditions in the San Francisco Bay region on ground motions and the intensities of the 1906 earthquake: Bulletin of the Seismological 

Society of America, v. 66, p. 467-500. 

Borcherdt, R. D., Joyner, W. B., Warrick, R. E., and Gibbs, J. F., 1975, 

Response of local geologic units to ground shaking, in Borcherdt, 

R. D., ed., Studies for seismic zonation of the San Francisco Bay 

region: U.S. Geological Survey Professional Paper 941-A, 

p.A52-A67. 

California Water Rights Board, 1962, Report of referee, City of San 

Fernando, California Superior Court, County of Los Angeles no. 

650079: v. 1, 258 p. 

Campbell, K. W., 1976, A note on the distribution of earthquake damage 

in Long Beach, 1933: Bulletin of the Seismological Society of 

. America, v. 66, p. 1001-1006. 

Cox, B. F., and Morton, D. M., 1978, Generalized map of surficial 

materials in northwestern Riverside and southwestern San Bernardino Counties, California: U.S. Geological Survey Open-File 

Report 78--978, scale 1:125,000. 

Eckis, R., 1928, Alluvial fans of the Cucamonga district, southern 

California: Journal of Geology, v. 36, no. 3, p. 224-247. 

___ 1934, South Coastal basin investigation, geology and groundwater storage capacity of valley fill: California Department of 

Water Resources Bulletin 45, 279 p. 

Eckmann, E. C., and Zinn, C. D., 1917, Soil survey of the Pasadena area, 

California: Washington, D.C., U.S. Department of Agriculture, 

Bureau of Soils, sdile 1:62,500. 

Fumal, T. E., 1978, Correlations between seismic wave velocities and 

physical properties of near-surface geologic materials in the southern San Francisco Bay region: Santa Cruz, Calif., University of 

California, unpublished M.Sci. thesis, 113 p. 

Gutenberg, B., 1957, Effects of ground on earthquake motion: Bulletin of 

the Seismological Society of America, v. 47, p. 221-250. 

Hastorf, C. A., and Tinsley, J. C., 1981, Maps and index of radiocarbon 

dated samples from southern California: U. S. Geological Survey 

Miscellaneous Field Studies Map MF-1296, scales 1:125,000 and 

1:500,000. 

Holmes, L. c.: Eckmann, E. C., Harrington, G. L., Guernsey, J. E., and 

Zinn, C. J., 1915, Soil map of California, San Fernando Valley 

sheet: Washington, D.C., U.S. Department of Agriculture, Bureau 

of Soils, scale 1:62,500. 

Jennings, C. W., 1962, Geologic map of California, Long Beach sheet: 

Sacramento, Calif., California Division of Mines and Geology, scale 

1:250,000. 

Jennings, C. W., and Strand, R. G., 1969, Geologic map of California, Los 

Angeles sheet: Sacramento, Calif., California Division of Mines and 

Geology, scale 1:250,000. 

Jenny, H., 1941, Factors of soil formation: New York, McGraw-Hill, 

281p. 

482 Earthquake Hazards in the los Angeles Region 

___ 1961, Derivation of state factor equations of soils and 

ecosystems: Soil Science Society of America Proceedings, v. 61, 

p. 385--388. 

Kanai, K., 1952, Relation between the nature of the surficial layer and 

the amplitude of earthquake motion: Bulletin of the Earthquake 

Research Institute, University of Tokyo, v. 30, pt. 1, p. 31-37. 

Knecht, A. A., 1971, Soil survey of the western Riverside area, California: U.S. Department of Agriculture Soil Conservation Service and 

U.S. Department of Interior Bureau of Indian Affairs, in cooperation with the University of California Agriculture Experiment Station, scale 1:15,840. 

Lajoie, K. R., and Helley, E. J., 1975, Classification and mapping of 

Quaternary sediment for purposes of seismic zonation, in Borcherdt, R. D., ed., Studies for seismic zonation of the San Francisco 

Bay region: U.S. Geological Survey Professional Paper 941-A, 

p.A39-A51. 

Lamar, D. L., 1970, Geology of the Elysian Park-Repetto Hills area, Los 

Angeles County, California: California Division of Mines and 

Geology Special Report 101, 45 p. 

Lawson, A. C., and others, 1908, The California earthquake of April 18, 

1906, in Atlas: Washington, D.C., Carnegie Institute of Washington,643 p. 

McFadden, L. D., 1982, The impacts of temporal and spatial climatic 

changes on alluvial soils genesis in southern California: Tucson, 

Ariz., University of Arizona, unpublished Ph.D. dissection, 430 p. 

McFadden, L. D., and Tinsley, J. C., 1982, Soil-profile development in 

xeric climates: A summary, in Tinsley, J. C., Matti, J. C., and 

McFadden, L. D., eds., Late Quaternary pedogenesis and alluvial 

chronologies of the Los Angeles and San Gabriel Mountains areas, 

southern California, and Holocene faulting and alluvial 

stratigraphy within the Cucamonga fault zone-A preliminary 

view: Geological Society of America Annual Meeting, Cordilleran 

Section, 78th, Anaheim, Calif., 1982, Guidebook 12, p. 15-19. 

McFadden, L. D., Tinsley, J. C., and Hendricks, D., 1980, A preliminary 

soil chronosequence for the tectonically and climatically controlled 

terraces and alluvial fans of the San Gabriel Mountains and the 

Los Angeles basin, California [abs.]: Geological Society of America 

Abstracts with Programs, v. 12, no. 3, p. 119. 

McCoy, G., and Sarna-Wojcicki, A. M., 1978, Preliminary map showing 

surficial materials of the Ventura-Oxnard Plain area, California: 

U.S. Geological Survey Open-File Report 78-1065, scale 1:125,000. 

Medvedev, J. V., 1962, Engineering seismology: Moscow, Academia 

Nauk Press. (English translation by Israel Program for Scientific 

Translations. Available from National Technical Information Service, Springfield, Va.) 

Milne, J., 1908, Seismology, 2d edition: London, K. Paul, Trench, 

Trubner, and Co., 320 p. 

Munsell Soil Color Charts, 1975: Baltimore, Md., Kollmorgen Corporation, Macbeth Division. 

Nelson, J. W., Pendleton, R. L., Dunn,). E., Strahan, A. T., and Watson, 

E. B., 1915, Soil survey of the Riverside area, California: Washington, D.C., U.S, Department of Agriculture, Bureau of Soils, scale 

1:62,500. . 

Nelson, J. W., Zinn, C. J., Strahorn, A. T., Watson, E. B., and Dunn, J. E., 

1916, Soil survey of the Los Angeles area, California: Washington, 
D.C., U.S. Department of Agriculture, Bureau of Soils, scale 

1:62,500. 

Poland, ). F., 1959, Hydrology of the Long Beach-Santa Ana area, 

California: U.S. Geological Survey Water-Supply Paper 1471, 

257p. 

Rabey, D. E., 1977, Soil survey of Los Angeles County, California, west 

San Fernando Valley area): West Los Angeles County Resource 

Conservation District, in cooperation with the U.S. Department of 

Agriculture Soil Conservation Service and the University of 

California Agriculture Experiment Station, unedited interim 

report, scale 1:24,000. 

Rogers, A. M., Tinsley, ). C., Hays, W. W., and King, K. W., 1979, 

Evaluation of the relation between near-surface geologic units and 

ground response in the vicinity of Long Beach, California: Bulletin 

of the Seismological Society of America, v. 61, p. 1603-1622. 

Rogers, T. H., 1965, Geologic map of California, Santa Ana sheet: 

Sacramento, Calif., California Division of Mines and Geology, scale 

1:250,000. 

__ 1969, Geologic map of California, San Bernardino sheet: 

Sacramento, Calif., California Division of Mines and Geology, scale 

1:250,000. 

Schumm, S. A., 1977, The fluvial system: New York, John Wiley, 338 p. 

Sail Conservation Survey Staff, 1969, Unpublished soil survey of the 

San Bernardino area, California: Redlands, Calif., U.S. Department 

of Agriculture, Soil Conservation Service, scale 1:24,000. 

Soil Survey Staff, 1975, Soil taxonomy, a basic system of soil classification for making and interpreting soil surveys: U.S. Department of 

Agriculture Handbook 436, 754 p. 

Thomas, R. G., Landry, J. J., and Turney, R. J., 1961, Planned utilization 

of the ground water basins of the coastal plain of Los Angeles 

County-Appendix A, Ground water geology: California Department of Water Resources Bulletin 104, 181 p. 

Yerkes, R. F., 1965, Geology of the Los Angeles basin-An introduction: 

U.S. Geological Survey Professional Paper 42~A. 57 p. 

Wood, H. 0., 1933, Preliniinary report on the Long Beach earthquake: 

Bulletin of the Seismological Society of America, v. 23, p. 42-56. 

Mapping Shear-Wave Velocities of Near-Surface Geologic Materials 

Bazarra, A. R. S., 1967, Use of the SPT for estimating settlements of 

shallow foundations on sand: Urbana, Ill., University of Illinois, unpublished Ph.D. thesis, 381 p. 

Blackerby, B. A., 1965, The Conejo volcanics in the Malibu Lake area of 

the western Santa Monica Mountains, Los Angeles County, California: Los Angeles, Calif., University of California, unpublished Ph.D. 

thesis, 194 p. 

Borcherdt, R. D., Gibbs, J. F., and Fumal, T. E., 1979, Progress on ground 

motion predictions for the San Francisco Bay region, California, in 

Brabb, E. E., ed., Progress on seismic zonation in the San Francisco 

Bay region: U.S. Geological Survey Circular 807, p. 13-25. 

California Department of Water Resources, 1970, Meeting water 

demands in the Chino-Riverside area-Appendix A, Water supply: California Department of Water Resources Bulletin 104-3, 

108p. 

California Division of Mines and Geology, 1976, Geologic hazards in 

southwestern San Bernardino County, California: California Division of Mines and Geology Special Report 113, 40 p. 

Cox, B. F., and Morton, D. M., 1978, Generalized map of surficial 

materials in northwestern Riverside and southwestern San Bernardino Counties, California: U.S. Geological Survey Open-File 

Report 78--978, scale 1:125,000. 

Dibblee, T. W., Jr., 1964, Geologic map of the San Gorgonio Mountain 

quadrangle, San Bernardino and Riverside Counties, California: 

U.S. Geological Survey Miscellaneous Geologic Investigations Map 

I-431, scale 1:62,500. 

Durrell, Cordell, 1954, Geology of the Santa Monica Mountains, Los 

Angeles and Ventura Counties: California Division of Mines and 

Geology Bulletin 170, map sheet 8, scale 1:125,000. 

Ellen, S. D., Wentworth, C. M., Brabb, E. E., and Pampeyan, E. H., 1972, 

Description of geologic units, San Mateo County, California, in 

Brabb, E. E., and Pampeyan, E. H., Preliminary geologic map of 

San Mateo County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-328, scale 1:62,500, 1~p. text. 

Frick, C., 1921, Extinct vertebrate fauna of the badlands of Bautista 

Creek and San Timoteo Canyon, southern California: University of 

California Publications, Bulletin of the Department of Geology, v. 

12,no.5,p.277-424. 

Fumal, T. E., 1978, Correlations between seismic wave velocities and 

physical properties of near-surface geologic materials in the southern San Francisco Bay region: Santa Cruz, Calif., University of 

California, unpublished M.Sci. thesis, 113 p. 

Fumal, T. E., Gibbs, J. F., and Roth, E. F., 1981, In-situ measurements of 

seismic velocity at 19 locations in the Los Angeles, California, 

region: U.S. Geological Survey Open-File Report 81-399, 123 p. 

___ 1982, In-situ measurements of seismic velocity at 22 locations in 

the Los Angeles, California, region: U.S. Geological Survey OpenFile Report 82-833, 140 p. 

___ 1984, In-situ measurements of seismic velocity at 16 locations in 

the Los Angeles, California, region: U.S. Geological Survey OpenFile Report 84-681, 109 p. 

Gibbs, J. F., Fumal, T. E., and Borcherdt, R. D., 1975, In-situ 

measurements of seismic velocities at 12 locations in the San Francisco Bay region: U.S. Geological Survey Open-File Report 75-564, 

20p. 

___ 1976, In-situ measurements of seismic velocities in the San Francisco Bay region, pt. II: U.S. Geological Survey Open-File Report 

76--731, 145 p. 

Gibbs, J. F., Fumal, T. E., Borcherdt, R. D., and Roth, E. F., 1977, In-situ 

measurements of seismic velocities in the San Francisco Bay 

region, pt. III: U.S. Geological Survey Open-File Report 77-850, 

145p. 

Gibbs, J. F., Fumal, T. E., and Roth, E. F., 1980, In-situ measurements of 

seismic velocity at 27 locations in the Los Angeles, California, 

region: U.S. Geological Survey Open-File Report 8~378, 169 p. 

Hardin B. 0., and Black, W. L., 1968, Vibration modulus of normally 

consolidated clay: Proceedings of the American Society of Civil 

Engineers, journal of the Soil Mechanics and Foundations Division, 

v. 94, no. SM2, p. 353-369. 

Hardin, B. 0., and Drenevich, V. P., 1972, Shear modulus and damping 

in soils: Measurement and parameter effects: Proceedings of the 

American Society of Civil Engineers, journal of the Soil Mechanics 

and Foundations Division, v. 98, no. SM6, p. 603-624. 

Hardin, B. 0., and Richart, F. E., 1963, Elastic wave velocities in 

granular soils: Proceedings of the American Society of Civil Engineers, journal of the Soil Mechanics and Foundations Division, v. 

89, no. SM1, p. 33-65. 

Joyner, W. B., Warrick, R. E., and Fumal, T. E., 1981, The effect of 

Quaternary alluvium on strong ground motion in the Coyote Lake, 

California, earthquake of 1979: Bulletin of the Seismological Society of America, v. 71, p. 1333-1349. 

Kobayashi, N., 1959, A method of determining the underground structure by means of SH waves: Zisin, ser. 2, v. 12, p. 19-24. 

References Cited 483 
Lajoie, K. R., and Helley, E. J., 1975, Differentiation of sedimentary 

deposits for seismic-zonation purposes, in Borchardt, R. D., Studies 

for seismic zonation of the San Francisco Bay region: U. S. Geological Survey Professional Paper 941-A, p. A39-A51. 

Meade, R. H., 1968, Compaction of sediments underlying areas of land 

subsidence in central California: U.S. Geological Survey Professional Paper 497-D, 39 p. 

Neuerburg, G. J., 1953, Geology of the Griffith Park area, Los Angeles 

County, California: California Division of Mines and Geology Special Report 33, 29 p. 

Ponti, D. J., and Burke, D. B., 1980, Map showing Quaternary geology of . 

the eastern Antelope Valley and vicinity, California: U.S. Geological Survey Open-File Report 80-1064, scale 1:62,500. 

Ponti, D. J., Burke, D. B., and Hedel, C. W., 1981, Map showing Quaternary geology of the central Antelope Valley and vicinity, California: U.S. Geological Survey Open-File Report 81-737, scale 

1:62,500. 

Schmertman, J. H., 1978, Use of the SPT to measure dynamic soil properties-Yes, but ... !, in Dynamic geotechnical testing: American 

Society for Testing and Materials Special Technical Publication 

654, p. 341-355. 

Seed, H. B., Idriss, I. M., and Aarango, 1., 1983, Evaluation of liquefaction potential using field performance data: Journal of Geotechnical Engineering, v. 109, no. 3, p. 458-482. 

Predicting Seismic Intensities 

Algermissen, S. T., and Steinbrugge, K. V., 1979, Earthquake losses to 

buildings in the San Francisco Bay area, in Brabb, E. E., ed., Progress on seismic zonation in the San Francisco Bay region: U.S. 

Geological Survey Circular 807, p. 61-72. 

Archambeau, C. B., 1968, General theory of elastodynamic source 

fields: Reviews of Geophysics, v. 16, p. 241-288. 

Archambeau, C. B., and Minster, J. B., 1978, Dynamics in prestressed 

media with moving phase boundaries: A continuous theory of 

failure in solids: Geophysical Journal of the Royal Astronomical 

Society, v. 52, p. 65-96. 

Bancroft, H. H., 1885, History of California, 1801-1824, v. 2, in The 

works of Hubert Howe Bancroft, v. 19: San Francisco, A. L. Bancroft, 795 p. 

Blume, J. A., 1981,. What is needed to significantly advance the state of 

the art in earthquake-resistant design, in Proceedings of Conference XIII, Evaluation of regional hazards and risk: U.S. Geological 

Survey Open-File Report 81-437, p. 11-12. 

Blume, J. A., Scholl, R. E., Sommerville, M. R., and Honda, K. R., 1980, 

Damage prediction of an earthquake in southern California: U.S. 

Geological Survey Open-File Report 80-1145, 83 p. 

Borchardt, R. D., 1970, Effects of local geology on ground motion near 

San Francisco Bay: Bulletin of the Seismological Society of 

America, v. 60, p. 29-61. 

California Division of Mines and Geology, [1958-1969), Geologic atlas of 

California, Olaf P. Jenkins edition: Sacramento, Calif., 27 map 

sheets, 1:250,000 scale. 

Davis, J. F., Bennett, J. H., Borchardt, G. A., Kahle, J. E., Rice, S. J., and 

Silva, M. A., 1982a, Earthquake planning scenario for a magnitude 

8.3 earthquake on the San Andreas fault in southern California: 

California Division of Mines and Geology Special Publication 

60,160p. 

__ 1982b, Earthquake planning scenario for a magnitude 8.3 earthquake on the San Andreas fault in the San Francisco Bay area: 

California Division of Mines and Geology Special Publication 61, 

160p. 

484 Earthquake Hazards in the Los Angeles Region 

Soil Survey Staff, 1951, Soil survey manual: U.S. Department of 

Agriculture Handbook 18, 503 p. 

Stokoe, K. H., II, and Richart, F. E., 1973, In-situ and laboratory shear 

wave velocities: International Conference on Soil Mechanics and 

Foundation Engineering, 8th, Moscow 1973, Proceedings, v. 1, p. 2, 

403-409. 

Terzaghi, K., and Peck, R. B., 1967, Soil mechanics in engineering practice, 2d ed.: New York, John Wiley, 729 p. 

Walsh, J. B., and Brace, W. F., 1966, Elasticity of rock: A review of 

some recent theoretical studies: Felsmechanik und Ingenieurgeologie, v. 4, p. 283-297. 

Warrick, R. E., 1974, Seismic investigation of a San Francisco Bay mud 

site: Bulletin of the Seismological Society of America, v. 64, p. 

375-385. 

Wentworth, C. M., Ellen, Stephen, Frizzel, V. A., and Schlocker, J., 1985, 

Map of hillside materials and descriptions of their engineering 

characteristics, San Mateo County, California: U.S. Geological 

Survey Miscellaneous Investigations Map I-1257-D, scale 

1:62,500. 

Wentworth, C. M., Ziony, J. 1., and Buchanan, J. M., 1970, Preliminary 

geologic environmental map of the greater Los Angeles area, California: Springfield, Va., National Technical Information Service 

TDI-25363, 41 p., 1:250,000 scale. (Available in microfiche only.) 

Evernden, J. F., 1975a, Further studies on seismic discrimination: 

Bulletin of the Seismological Society of America, v. 65, p. 359--391. 

___ 1975b, Seismic intensities, 'size' of earthquakes, and related 

phenomena: Bulletin of the Seismological Society of America, v. 65, 

p. 1287-1315. 

___ 1982, Comments on seismological input to microzonation maps: 

International Earthquake Microzonation Conference, 3d, Seattle, 

Wash., 1982, Proceedings, v. III, p.1170-1204. 

___ 1983, Intensities in eastern Asia: Chinese Geophysics, v. 2, no. 2, 

p. 405-438. [Published by the American Geophysical Union.) 

Evernden, J. F., and Archambeau, C. B., in press, Seismological aspects 

of monitoring a Comprehensive Test Ban Treaty, in Technical 

means of verification of compliance with arms control treaties: 

New York, Pergamon/Brasserys. 

Evernden, J. F., Hibbard, R. R., and Schneider, J. F., 1973, Interpretation 

of seismic intensity data: Bulletin of the Seismological Society of 

America, v. 63, p. 399-422. 

Evernden, J. F., Kohler, W. M., and Claw, G. D., 1981, Seismic intensities 

of earthquakes of conterminous United States-Their prediction 

and interpretation: U.S. Geological Survey Professional Paper 

1223,56 p. 

Federal Emergency Management Agency, 1980, An assessment of the 

consequences and preparations for a catastrophic California 

earthquake: Findings and actions taken: Washington, D.C., 59 p. 

Freeman, J. R., 1932, Earthquake damage and earthquake insurance: 

New York, McGraw-Hill, 904 p. 

Friedman, D. G., 1969, Computer simulation of earthquake hazards: 

California Office of Emergency Preparedness, Proceedings of Conference on Geologic Hazards and Public Problems, p. 153-181. 

___ 1975, Computer simulation in natural hazard assessment: 

Boulder, Colo., University of Colorado Monograph NSF-RAE-75--002, Institute of Behavioral Sciences, 192 p. 

Gulliver, R. M., in press, Estimation of homeless caseload for disaster 

assistance due to an earthquake: San Francisco, Calif., Federal 

Emergency Management Agency, Region IX. 
Hanks, T. C., 1979, b values and w-'Y seismic source models: Implications for tectonic stress variations along active crustal fault zones 

and the estimation of high-frequency strong ground motion: Journal 

of Geophysical Resea~ch, v. 84, p. 2235-2242. 

Hanks, T. C., and Johnson, D. A., 1976, Geophysical assessments of peak 

accelerations: Bulletin of the Seismological Society of America, v. 

66, p. 959-968. 

Hanks, T. C., and McGuire, R. K., 1981, The character of highfrequency ground motion: Bulletin of the Seismological Society of 

America, v. 71, p. 2071-2095. 

Helley, E. J., Lajoie, K. R., Spangle, W. E., and Blair, M. L., 1979, 

Flatland deposits of the San Francisco Bay region-Their geology 

and engineering properties, and their importance to comprehensive planning: U.S. Geological Survey Professional Paper 943,88 p. 

Joyner, W. B., and Boore, D. M., 1981, Peak horizontal acceleration and 

velocity from strong-motion records including records from the 

1979 Imperial Valley, California, earthquake: Bulletin of the 

Seismological Society of America, v. 71, p. 2011-2038. 

Kustu, 0., 1981, A survey of low-rise damage from the August 6, 1979, 

Coyote Lake (Gilroy, California) earthquake: Menlo Park, Calif., 

technical report to U.S. Geological Survey under contract 

14-08-0001-107310,49 p. 

Lomnitz, ·c., 1981, Environmental siting of nuclear power plants: International Association ofEngineering Geology Bulletin 23, p. 26-36. 

Maley, R. P., and Cloud, W. K., 1973, Strong-motion accelerograph 

records, in Murphy, L. M., ed., San Fernando, California, earthquake of February 9, 1971, v. 3, Geology and geophysics: 

Washington, D.C., U.S. Department of Commerce, p. 325-348. 

Medvedev, S. V., 1962, Engineering seismology: Moscow, Akademia 

Nauk Press. (Translated into English by the Israel Program for 

Scientific Translations. Available from National Technical Information Service, Springfield, Va.) 

___ 1976, Seismic zoning of the U.S.S.R.: Moscow, Akademia Nauk 

Press. (Translated into English by the Israel Program for Scientific 

Translations. i}vailable from the National Technical Information 

Service, Springfield, Va.) 

Minster, J. B., 1973, Elastodynamics of failure in a continuum: 

Pasadena, Calif., California Institute of Technology, unpublished 

Ph.D. thesis. 

Richter, C. F., 1958, Seismic regionalization: Bulletin of the 

Seismological Society of America, v. 49, p. 123-162. 

___ 1972, Seismic regionalization or zoning: Revision: International 

Conference on Microzonation, 1st, Seattle, Wash., 1972, Proceedings, v. I, p. 267-282. 

Rojahn, C., and Mark, P. N., 1982, An analysis of strong-motion data 

from a severely damaged structure-The Imperial County Services 

Building, in The Imperial Valley earthquake of October 15, 1979: 

U.S. Geological Survey Professional Paper 1254, p. 357-375. 

Scott, N. H., 1973, Felt area and intensity of San Fernando earthquake, 

in Murphy, L. M., ed., San Fernando earthquake of February 9, 

1971, v. 3, Geology and geophysics: Washington, D.C., U.S. Department of Commerce, p. 23--48. 

Smolka, A., and Berz, G., 1981, Methods of hazard mapping-Requirements of the insurance industry: International Association of Engineering Geology Bulletin 23, p. 21-24. 

Steinbrugge, K. V., and Schader, E. E., 1973, Earthquake damage and 

related statistics, in Murphy, L. M., ed., San Fernando earthquake 

of February 9, 1971, v. 1, pt. B: Washington, D.C., U.S. Department 

of Commerce, p. 691-724. 

Trifunac, M. D., and Brady, A. G., 1975, A study on the correlation of 

seismic intensity scales with the peaks of recorded ground motion: 

Bulletin of the Seismological Society of America, v. 65, p. 139-162. 

Tucker, B. E., and Brune, J. N., 1973, Seismograms, S-wave spectra and 

source parameters for aftershocks of San Fernando earthquake, in 

Murphy, L. M., ed., San Fernando earthquake of February 9, 1971, 

v. 3, Geology and geophysics: Washington, D.C., U.S. Department 

of Commerce, p. 69-122. 

U.S. Geological Survey, 1981, Scenarios of possible earthquakes affecting major California population centers, with estimates of intensity and ground shaking: U.S. Geological Survey Open-File 

Report 81-115, 36 p. 

U.S. Geological Survey Staff, 1982, Seismic zonation. of the Los Angeles 

region-A progress report: International Earthquake Microzonation Conference, 3d, Seattle, Wash., 1982, Proceedings, v. 1, 

p.157-172. 

Predictive Mapping of Earthquake Ground Motion 

Aki, K., and Richards, P. G., 1980, Quantitative seismology, v. 1: San 

Francisco, Calif., W. H. Freeman, 557 p. 

Algermissen, S. T., and Perkins, D. M., 1976, A probabilistic estimate of 

maximum acceleration in rock in the contiguous United States: 

U.S. Geological Survey Open-File Report 76--416, 45 p. 

Allen, C. R., 1975, Geological criteria for evaluating seismicity: 

Geological Society of America Bulletin, v. 86, p. 1041-1057. 

Allen, C. R., Hanks, T. C., and Whitcomb, J. H., 1973, San Fernando 

earthquake-Seismological studies and their tectonic implications, 

in Murphy, L. M., ed., San Fernando, California, earthquake of 

February 9, 1971, v. 3, Geological and geophysical studies: 

Washington, D.C., National Oceanic and Atmospheric Administration, p. 13-21. 

Anderson, J. G., and Luco, J. E., 1983, Consequences of slip rate constraints on earthquake occurrence relations: Bulletin of the 

Seismological Society of America, v. 73, p. 471--496. 

Applied Technology Council, 1978, Tentative provisions for the development of seismic regulations for buildings: Applied Technology 

Council Publication 3-Q6, 505 p. 

Bonilla, M. G., 1967, Historic surface faulting in continental United 

States and adjacent parts of Mexico: U.S. Geological Survey OpenFile Report 67-23, 36 p. 

Bonilla, M. G., Mark, R. K., and Lienkaemper, J. J., 1984, Statistical relations among earthquake magnitude, surface rupture length, and 

surface fault displacement: Bulletin of the Seismological Society of 

America, v. 74, p. 2379-2411. 

Boore, D. M., and Joyner, W. B., 1982, The empirical prediction of 

ground motion: Bulletin of the Seismological Society of America, 

v. 72, p. S269-S286. 

Brady, A. G., Perez, V., and Mark, P. N., 1980, The Imperial Valley 

earthquake, October 15, 1979--Digitization and processing of accelerograph records: U.S. Geological Survey Open-File Report 

8~703, 311 p. 

Brune, J. N., 1968, Seismic moment, seismicity, and rate of slip along 

major fault zones: Journal of Geophysical Research, v. 73, 

p. 777-784. 

Bullen, K. E., 1965, An introduction to the theory of seismology: Cambridge, Cambridge University Press, 381 p. 

References Cited 485 
Campbell, K. W., 1981, Near-source attenuation of peak horizontal 

acceleration: Bulletin of the Seismological Society of America, 

v.71,p.2039-2070. 

Chavez, D., Gonzales, J., Reyes, A., Medina, M., Duarte, C., Brune, J. N., 

Vernon, F. L., III, Simons, R., Hutton, L. K., German, P. T., and 

Johnson, C. E., 1982, Main-shock location and magnitude determination using combined U.S. and Mexican data, in The Imperial 

Valley, California, earthquake of October 15, 1979: U.S. Geological 

Survey Professional Paper 1254, p. 51-54. 

Cornell, C. A., 1968, Engineering seismic risk analysis: Bulletin of the 

Seismological Society of America, v. 58, p. 1583-1606. 

Der Kiureghian, A., and Ang, A. H. S., 1977, A fault-rupture model for 

seismic risk analysis: Bulletin of the Seismological Society of 

America,v.67,p.1173-1194. 

Dunbar, W. S., Boore, D. M., and Thatcher, W., 1980, Pre-, co-, and 

post-seismic strain changes associated with the 1952 ML = 7.2 

Kern County, California, earthquake: Bulletin of the Seismological 

Society of America, v. 70, p. 1893-1905. 

Eaton, J.P., O'Neill, M. E., and Murdock, J. N., 1970, Aftershocks of the 

1966 Parkfield-Cholame, California, earthquake-A detailed 

study: Bulletin of the Seismological Society of America, v. 60, 

p. 1151-1197. 

Gutenberg B., and Richter C. F., 1954, Seismicity of the Earth and 

associated phenomena: Princeton, N.J., Princeton University Press, 

310p. 

Hamilton, R. M., 1972, Aftershocks of the Borrego Mountain earthquake from April 12 to June 12, 1968, in The Borrego Mountain 

earthquake of April 9, 1968: U.S. Geological Survey Professional 

Paper 787, p. 31-54. 

Hanks, T. C., and Kanamori, H., 1979, A moment magnitude scale: Journal o.fGeophysical Research, v. 84, p. 2348-2350. 

Hanks, T. C., and Wyss, M., 1972, The use of body-wave spectra in the 

determination of seismic-source parameters: Bulletin of the 

Seismological Society of America, v. 62, p. 561-568. 

Hanks, T. C., Hileman, J. A., and Thatcher, W., 1975, Seismic moments 

of the larger earthquakes of the southern California region: 

Geological Society of America Bulletin, v. 86, p. 1131-1139. 

Ishimoto, M., and Iida, K., 1939, Observations sur les seismes 

enregistJ.es par le microsismographe construit dernierement: 

Bulletin of the Earthquake Research Institute, University of Tokyo, 

v. 17, p. 443-478. (In Japanese with summary in French.) 

Joyner, W. B., and Boore, D. M., 1981, Peak horizontal acceleration and 

velocity from strong-motion records including records from the 

1979 Imperial Valley, California, earthquake: Bulletin of the 

Seismological Society of America, v. 71, p. 2011-2038. 

___ 1982a, Estimation of response-spectral values as functions of 

magnitude, distance, and site conditions: U.S. Geological Survey 

Open-File Report 82-881, 14 p. 

___ 1982b, Prediction of earthquake response spectra: U.S. 

Geological Survey Open-File Report 82-977, 16 p. 

Joyner, W. B., Warrick, R. E., and Fumal, T. E., 1981, The effect of 

Quaternary alluvium on strong ground motion in the Coyote Lake, 

California, earthquake of 1979: Bulletin of the Seismological Society of America, v. 71, p. 1333-1349. 

Lahr, J. C., and Stephens, C. D., 1982, Alaska seismic zone: Possible example of non-linear magnitude distribution for faults [abs.]: Earthquake Notes, v. 53, p. 66. 

Lindh, A. G., and Boore, D. M., 1981, Control of rupture by fault 

geometry during the 1966 Parkfield earthquake: Bulletin of the 

Seismological Society of America, v. 71, p. 95-116. 

486 Earthquake Hazards in the los Angeles Region 

McGuire, R. K., 1974, Seismic structural response risk analysis, incorporating peak response regressions on earthquake magnitude and 

distance: Cambridge, Mass., Research Report R74-51, Massachusetts Institute of Technology, Department of Civil Engineering, 

371 p. 

___ 1978, FRISK: Computer program for seismic risk analysis using 

faults as earthquake sources: U.S. Geological Survey Open-File 

Report 78-1007, 71 p. 

McGuire, R. K., and Shedlock, K. M., 1981, Statistical uncertainties in 

hazard evaluations in the United States: Bulletin of the Seismological Society of America, v. 71, p. 1287-1308. 

Molnar, P., 1979, Earthquake recurrence intervals and plate tectonics: 

Bulletin of the Seismological Society of America, v. 69, p. 115-133. 

Newmark, N. M., and Hall, W. J., 1969, Seismic design criteria for 

nuclear reactor facilities: World Conference on Earthquake Engineering, 4th, Santiago, Chile, 1969, Proceedings, v. 2, 

p. B4-37-B4-50. 

Scholz, C. H., 1982, Scaling laws for large earthquakes: Consequences 

for physical models: Bulletin of the Seismological Society of 

America, v. 72, p. 1-14. 

Schwartz, D. P., Coppersmith, K. J., Swan, F. H., III, Somerville, P., 

and Savage, W. U., 1981, "Characteristic" earthquakes on intraplate normal faults [abs.]: Earthquake Notes, v. 52, p. 71. 

Sharp, R. V., Lienkaemper, J. J., Bonilla, M. G., Burke, D. B., Fox, B. F., 

Herd, D. G., Miller, D. M., Morton, D. M., Ponti, D. J., Rymer, M. J., 

Tinsley, J. C., Yount, J. C., Kahle, J. E., Hart, E. W., and Sieh, K. E., 

1982, Surface faulting in the central Imperial Valley, in The Imperial Valley, California, earthquake of October 15, 1979: U.S. 

Geological Survey Professional Paper 1254, p. 119-143. 

Singh, S. K., Astiz, L., and Havskov, J., 1981, Seismic gaps and recurrence periods of large earthquakes along the Mexican subduction 

zone: A reexamination: Bulletin of the Seismological Society of 

America, v. 71, p. 827-843. 

Slemmons, D. B., 1977, State-of-the-art for assessing earthquake 

hazards in the United States: Faults and earthquake magnitude: 

U.S. Army Corps of Engineers Waterways Experiment Station Miscellaneous Paper S-3-71-1, Report 6, 129 p. 

Swanger, H. J., and Boore, D. M., 1978, Simulation of strong-motion 

displacements using surface-wave modal superposition: Bulletin of 

the Seismological Society of America, v. 68, p. 907-922. 

Sykes, L. R., and Quittmeyer, R. C., 1981, Repeat times of great earthquake along simple plate boundaries, in Simpson, D. W., and 

Richards, P. G., eds., Earthquake prediction-An international 

review: American Geophysical Union Maurice Ewing Series, no. 4, 

p. 217-247. 

Thatcher, W., 1975, Strain accumulation and release mechanism of the 

1906 San Francisco earthquake: Journal of Geophysical Research, 

v.80,p.4862-4872. 

Trifunac, M. D., and Anderson, J. G., 1978, Preliminary empirical 

models for scaling pseudo-relative velocity spectra, appendix A, in 

Methods for prediction of strong earthquake ground motion: U.S. 

Nuclear Regulatory Commission Report NUREG/CR-0689, 565 p. 

Tsai, Y. B., and Aki, K., 1969, Simultaneous determination of the seismic 

moment and attenuation of seismic surface waves: Bulletin of the 

Seismological Society of America, v. 59, p. 275-287. 

U.S. Atomic Energy Commission, 1973, Design response spectra for 

seismic design of nuclear power plants: Washington, D.C., Regulatory guide 1.60, 6 p. 

Wesnousky, S. G., Scholz, C. H., Shimazaki, K., and Matsuda, T., 1983, 

Earthquake frequency distribution and the mechanics of faulting: 

Journal of Geophysical Research, v. 88, p. 9331-9340. 
Predicting Relative Ground Response 

Aki, K., 1969, Analysis of the seismic coda of local earthquakes as scattered waves: Journal of Geophysical Research, v. 74, p. 615-631. 

Algermissen, S. T., Rinehart, W. A., and Stepp, J. C., 1972, A technique 

for seismic zoning: Economic considerations, in International Conference on Microzonation for Safer Construction, 1st, Seattle, 

Wash., 1978, Proceedings: p. 943-956. 

Anderberg, M. R., 1973, Cluster analysis for applications, in Probability 

and mathematical statistics, v. 19: New York, Academic, 359 p. 

Barosh, P. J., 1969, Use of seismic intensity data to predict the effects of 

earthquakes and underground nuclear explosion in various 

geologic settings: U.S. Geological Survey Bulletin 1279,93 p. 

Boore, D. M., 1972, A note on the effect of simple topography on seismic 

SH waves: Bulletin of the Seismological Society of America, v. 62, 

p. 275-284. 

Borcherdt, R. D., 1970, Effects of local geology on ground motion near 

San Francisco Bay: Bulletin of the Seismological Society of 

America, v. 60, p. 29--61. 

Borcherdt, R. D., and Gibbs, J. F., 1976, Effects of local geologic conditions in the San Francisco Bay region on ground motions and the intensities of the 1906 earthquake: Bulletin of the Seismological 

Society of America, v. 66, p. 467-500. 

Borcherdt, R. D., Joyner, W. B., Warrick, R. E., and Gibbs, J. F., 1975, 

Response of local geologic units to ground shaking, in Studies for 

seismic zonation of the San Francisco Bay region: U.S. Geological 

Survey Professional Paper 941-A, p. A52-A67. 

California Department of Water Resources, 1966, San Gabriel Valley, 

Appendix A-Geohydrology: California Department of Water Resources Bulletin 104-2, 229 p. 

California Water Rights Board, 1961, Report of referee, City of Los 

Angeles vs. the City of San Fernando, Superior Court of the State of 

California case no. 650048: Sacramento, Calif., 258 p., apps. 

Campbell, K. W., 1976, A note on the distribution of earthquake damage 

in Long Beach, 1933: Bulletin of the Seismological Society of 

America, v. 66, p. 1001-1006. 

Chiaruttini, C., and Siro, 1., 1981, The correlation of peak ground 

horizontal acceleration with magnitude, distance, and seismic intensity for Friuli and Ancona, Italy, and the Alpide Belt: Bulletin of 

the Seismological Society of America, v. 71, p. 1993-2009. 

Cooley, W. W., and Lohnes, P.R., 1971, Multivariate data analysis: New 

York, John Wiley, 364 p. 

Drake, L. H., and Mal, A. K., 1972, Love and Rayleigh waves in the San 

Fernando Valley: Bulletin of the Seismological Society of America, 

v.62,p. 1673-1690. 

Dutcher, L. C., and Garrett, A. A., 1963, Geologic and hydrologic 

features of the San Bernardino area, California: U.S. Geological 

Survey Water-Supply Paper 1419, 114 p. 

Earthquake Engineering Research Laboratory, 1969--1975, Strongmotion earthquake accelerograms, VI, pts. A-Y: Pasadena, Calif., 

California Institute of Technology, v. 2. 

Espinosa, A. F., and Algermissen, S. T., 1972, A study of soil amplification factors in earthquake damage areas, Caracas, Venezuela: National Oceanic and Atmospheric Administration Technical Report 

ERL 28Q--ESL 31, 201 p. 

Esteva, L., 1977, Microzoning: Models and reality, in World Conference 

on Earthquake Engineering, 6th, New Delhi, 1977, Proceedings: 

p. 27-43. 

Fumal, T. E., 1978, Correlations between seismic wave velocities and 

physical properties of near-surface geologic materials in the southern San Francisco Bay region: Santa Cruz, Calif., University of 

California, unpublished M.Sci. thesis, 113 p. 

F1.1J11al, T. E., Gibbs, J. F., and Roth, E. F., 1981, In-situ measurements of 

seismic velocity at 19 locations in the Los Angeles, California, 

region: U.S. Geological Survey Open-File Report 81-399, 121 p. 

___ 1982, In-situ measurements of seismic velocity at 22 locations in 

the Los Angeles, California, region: U.S. Geological Survey OpenFile Report 82-833, 138 p. 

___ 1984, In-situ measurements of seismic velocity at 16 locations in 

the Los Angeles, California, region: U.S. Geological Survey OpenFile Report 84-681, 109 p. 

Gibbs, J. F., Fumal, T. E., and Roth, E. F., 1980, In-situ measurements of 

seismic velocity at 27 locations in the Los Angeles, California, 

region: U.S. Geoiogical Survey Open-File Report 8Q--378, 167 p. 

Gutenberg, B., 1957, Effects of ground on earthquake motion: Bulletin of 

the Seismological Society of America, v. 47, p. 221-250. 

Hanks, T. C., 1975, Strong ground motion of the San Fernando, Calif., 

earthquake: Ground displacement: Bulletin of the Seismological 

Society of America, v. 65, p. 193-225. 

Hanks, T. C., and McGuire, R. K., 1981, The character of highfrequency strong ground motion: Bulletin of the Seismological 

Society of America, v. 21, p. 2071-2095. 

Hardin, B. 0., and Drnevich, V. P., 1972, Shear modulus and damping in 

soils: Measurement and parameter effects: Proceedings of the 

American Society of Civil Engineers, Journal of the Soil Mechanics 

and Foundations Division, v. 98, p. 603-624. 

Hartigan, J. A., 1975, Clustering algorithms: New York, John Wiley, 

351 p. 

Hays, W. W., and Algermissen, S. T., 1982, Problems in the construction of a map to zone the earthquake ground shaking hazard, in International Earthquake Microzonation Conference, 3d, Seattle, 

Wash., 1982, Proceedings: p. 145-156. 

Hays, W. W., and King, K. W., 1982, Zoning of the earthquake ground 

shaking hazard along the Wasatch Fault zone, Utah, in International Earthquake Microzonation Conference, 3d, Seattle, Wash., 

1982, Proceedings: p. 1307-1318. 

Howell, B. F., and Schultz, T. R., 1975, Attenuation of Modified Mercalli 

intensity with distance from the epicenter: Bulletin of the 

Seismological Society of America, v. 65, p. 651-666. 

Hudson, J. A., and Douglas, A., 1975, Rayleigh wave spectra and group 

velocity minima, and the resonance of P waves in layered structures: Geophysical Journal of the Royal Astronomical Society, v. 42, 

p. 175-188. 

IMSL, 1982, IMSL computer programs: Houston, Tex. 

Johnson, C. E., 1979, I, Cedar-An approach to the computer automation of short-period local seismic networks; II, Seismotectonics of 

the Imperial Valley of southern California: Pasadena, Calif., 

California Institute of Technology, unpublished Ph.D. thesis, 332 p. 

Joyner, W. B., and Boore, D. M., 1981, Peak horizontal accelerations 

and velocity from strong motion records including records from the 

1979 Imperial Valley, California, earthquake: Bulletin of the 

Seismological Society of America, v. 71, p. 2011-2038. 

Joyner, W. B., and Chen, A. T. F., 1975, Calculation of nonlinear ground 

response in earthquakes: Bulletin of the Seismological Society of 

America, v. 65, p. 1315-1336. 

Joyner, W. B., Warrick, R. E., and Fumal, T. E., 1981, The effect of 

Quaternary alluvium on strong ground motion in the Coyote Lake, 

California, earthquake of 1979: Bulletin of the Seismological Society of America, v. 71, p. 1333-1349. 

Kanai, K., 1952, Relation between the nature of surface layer and the 

amplitude of earthquake motion: Bulletin of the Earthquake 

Research Institute, University of Tokyo, v. 30, p. 31-37. 

References Cited 487 
1 Kanai, K., and Yoshizawa, S., 1958, The amplitude and the period of 

earthquake motions: Bulletin of the Earthquake Research Institute, 

University of Tokyo, v. 36, p. 275-293. 

Kanai, K., Takahasi, R., and Kawasumi, H., 1956, Seismic 

characteristics of ground, in World Conference on Earthquake 

Engineering, 1st, Berkeley, Calif., 1956, Proceedings: p. 31-1-

31-16. 

King, K. W., 1982, A study of surface and subsurface ground motions at 

Calico Hills, Nevada, Test Site: U.S. Geological Survey Open-File 

Report 82-1044, 19 p. 

Lastrico, R., 1970, Effects of site and propagation path on recorded 

strong earthquake motions: Los Angeles, Calif., University of 

California, unpublished Ph.D thesis, 205 p. 

Lawson, A. C., and others, 1908, The California earthquake of April 18, 

1906, in Carnegie Institute of Washington Atlas: Washington, D.C., 

2v., 643p. 

McCulloh, T. H., 1957, Simple Bouguer gravity and generalized geologic 

map of the northwestern part of the Los Angeles basin, California: 

U.S. Geological Survey Geophysical Investigations Map GP-149, 

scale 1:48,000. 

___ 1960, Gravity variations and the geology of the Los Angeles basin 

of California, in Short papers in the geological sciences: U.S. 

Geological Survey Professional Paper 40G-B, p. B32Q-B325. 

McEvilly, T. V., and Johnson, L. R., 1980, The role of anelasticity in 

earthquake ground motion: U.S. Geological Survey Open-File 

Report 8Q-912, 36 p. 

McFadden, L. D., and Tinsley, J. C., 1982, Soil profile development in 

xeric climates; a summary, in Tinsley, J. C., and others, eds., 

Guidebook; Late Quaternary pedogenesis and alluvial chronologies 

of the Los Angeles and San Gabriel Mountains, southern California, and Holocene faulting and alluvial stratigraphy within the 

Cucamonga fault zone: Boulder, Colo., Geological Society of 

America, p. 15-19. 

Medvedev, J. V., 1962, Engineering seismology: Moscow, Academia 

Nauk. (Translated into English by Israel Program for Scientific 

Translations, Jerusalem, 1965, 260 p.) 

Milne, J., 1898, Seismology, 1st ed.: London, Kegan Paul, Trench, 

Triiber, 320 p. 

Minakami, T., and Sakuma, S., 1948, The earthquake-motions on 

various formations of the earth's surface, pt. I, Observations at 

Koti City: Bulletin of the Earthquake Research Institute, University 

of Tokyo, v. 26, p. 61-66. 

Morrison, D. G., 1969, On the interpretation of discriminant analysis: 

Journal of Marketing Research, v. 6, p. 156-163. 

___ 1974, Discriminant analysis, in Ferber, R., ed., Handbook of 

marketing research: New York, McGraw-Hill, 1344 p. 

Mosteller, F., and Tukey, J. W., 1977, Data analysis and regression: 

Reading, Mass., Addison-Wesley, 588 p. 

Mueller, C. S., D. M. Boore, and R. L. Porcella, 1982, Detailed study of 

site amplification at El Centro strong-motion array station no. 6, in 

International Earthquake Microzonation Conference, 3d, Seattle, 

Wash., 1982, Proceedings, v. 1: p. 413-424. 

Murphy, J. R., and Hewlett, R. A., 1975, Analysis of seismic response in 

the city of Las Vegas, Nevada: A preliminary microzonation: 

Bulletin of the Seismological Society of America, v. 65, 

p. 1575-1597. 

Murphy, J. R., Weaver, N. L., and Lamers, G. B., 1970, Effects of local 

geology on the amplitudes of seismic waves, in U.S. Atomic Energy 

Commission Report NV0-1163-205: Springfield, Va., National 

Technical Information Service, 3 v. 

Murphy, J. R., Weaver, N. L., and Davis, A. H., 1971, Amplification of 

seismic body waves by low-veloCity surface layers: Bulletin of the 

Seismological Society of America, v. 61, p. 109-145. 

Nie, N. H., Hull, C. H., Jenkins, J. G., Steinbrenner, K., and Bent, D. H., 

488 Earthquake Hazards in the Los Angeles Region 

1975, SPSS statistical package for the social sciences: New York, 

McGraw-Hill, 675 p. 

Nuclear Regulatory Commission, 1980, Geotechnical data from accelerograph stations investigated during the period 1975-1979, in 

U.S. Nuclear Regulatory Commission Report NUREG/CR-1643 R6, 

RA: Springfield, Va., National Technical Information Service, 

150p. 

Ooba, S., 1957, Study of the relation between subsoil conditions and the 

distribution of the damage percentage of wooden dwelling houses 

in the province of Totomi in the case of the Tonankai earthquake of 

December 7, 1944: Bulletin of the Earthquake Research Institute, 

University of Tokyo, v. 36, p. 201-295. 

Poland, J. F .. 1959, Hydrology of tbP. Long Beach-Santa Ana area, 

California: U.S. Geological Survey Water-Supply Paper 1471, 257 p. 

Poland, J. F., Garrett, A. A., and Sinnot, A., 1959, Geology, hydrology, 

and chemical character of ground water in the Torrance-Santa 

Monica area, California: U.S. Geological Survey Water-!)upply 

Paper 1461, 425 p. 

Poland, J. F., Piper, A. M., and others, 1956, Ground-water geology of 

the coastal zone, Long Beach-Santa Ana area, California: U.S. 

Geological Survey Water-Supply Paper 1109, 162 p. 

Porcella, R. L., and Matthiesim, R. B., 1979, Preliminary summary of the 

U.S. Geological Survey strong-motion records from the Oct. 15, 

1979, Imperial Valley earthquake: U.S. Geological Survey OpenFile Report 79-1654,41 p. 

Rogers, A. M., and Hays, W. W., 1978, Preliminary evaluation of site 

transfer functions developed from earthquake and nuclear explosions, in International Conference on Microzonation, 2d, San Francisco, Calif., 1978, Proceedings, v. 2: p. 753-764. 

Rogers, A. M., Katz, L. J., and Bennett, T. J., 1974, Topographic effects 

on ground motion for incident P waves: A model study: Bulletin of 

the Seismological Society of America, v. 64, p. 437-456. 

Rogers, A. M., Tinsley, J. C., Hays, W. W., and King, K. W., 1979, 

Evaluation of the relation between near-surface geological units 

and ground response in the vicinity of Long Beach, California: 

Bulletin of the Seismological Society of America, v. 61, 

p. 1603-1622. 

Rogers, A. M., Covington, P. A., Park, R. B., Borcherdt, R. D., and 

Perkins, D. M., 1980, Nuclear event time histories and computed 

site transfer functions for locations in the Los Angeles region: U.S. 

Geological Survey Open-File Report 8Q-1173, 207 p. 

Rogers, A. M., Borcherdt, R. D., Covington, P. A., and Perkins, D. M., 

1984, A comparative ground response study near Los Angeles 

using recordings from Nevada nuclear tests and the 1971 San Fernando earthquake: Bulletin of the Seismological Society of 

America, v. 74, p. 1925-1949. 

Seed, H. B., and Idriss, I. M., 1970, Soil moduli and damping factors for 

dynamic response analysis: Berkeley, Calif., Report EERC 7Q-10, 

Earthquake Engineering Research Center, University of California, 

15p. 

Thomas, R. G., Landry, J. J., and Turney, R. J., 1961, Planned utilization 

of the groundwater basins of the coastal plain of Los Angeles County, California, Appendix A-Groundwater geology: California 

Department of Water Resources Bulletin 104, 181 p. 

Turner, E., and Stokoe, K. H .• 1982, Static and dynamic properties of 

clayey soils subjected to 1979 Imperial Valley earthquake: Austin, 

Tex., Engineering Report GR 82-26, Geotechnical Engineering 

Center, University of Texas, 208 p. 

Velleman, P., and Hoaglin, D., 1981, ABC's of EDA: Belmont, Calif., Duxbury Press, 354 p. 

Wood, H. D., 1933, Preliminary report on the Long Beach earthquake: 

Bulletin of the Seismological Society of America, v. 23, p. 42-56. 

Yerkes, R. F., McCulloh, T. H., Schoellhamer, J. E., and Vedder, J. G., 

1965, Geology of the Los Angeles basin, California-An introduction: U.S. Geological Survey Professional Paper 42Q-A, 57 p. 
Predicting Earthquake Ground-Motion Time-Histories 

Aki, K., 1967, Scaling law of seismic spectrum: Journal of Geophysical 

Research, v. 72, p. 1217-1231. 

__ 1979, Characterization of barriers on an earthquake fault: Journal of Geophysical Research, v. 84, p. 614CHl148. 

Aki, K., and Chouet, B., 1975, Origin of coda waves: Source, attenuation, and scattering effects: Journal of Geophysical Research, v. 80, 

p. 3322-3342. 

Aki, K., Bouchon, M., Chouet, B., and Das, S., 1977, Quantitative prediction of strong motion for a potential earthquake fault: Annali 

Geofisica, v. 30, p. 341-368. 

Alekseev, A. S., and Mikhailenko, B. G., 1980, The solution of dynamic 

problems of elastic wave propagation in inhomogeneous media by 

a combination of partial separation of variables and finitedifference methods: Journal of Geophysics, v. 48, p. 161-172. 

Andrews, D. J., 1981, A stochastic fault model, 2, Time-dependent case: 

Journal of Geophysical Research, v. 86, p. 10821-10834. 

Apse!, R. J., and Luco, J. E., 1983, On the Green's functions for a layered 

half-space, pt. II: Bulletin of the Seismological Society of America, 

v. 73, p. 931-952. 

Apse!, R. J., Frazier, G. A., Jurkevics, A., and Fried, J. C., 1981, Ground 

motion prediction for the Los Angeles basin from a major San Andreas earthquake: U.S. Geological Survey Open-File Report 

81-276, 217 p. 

Archuleta, R. J., 1984, A faulting model for the 1979 Imperial Valley 

earthquake: Journal of Geophysical Research, v. 89, p. 4559-4585. 

Archuleta, R. J., and Day, S. M., 1980, Dynamic rupture in a layered 

medium: The 1966 Parkfield earthquake: Bulletin of the Seismological Society of America, v. 70, p. 671-689. 

Archuleta, R. J., and Frazier, G. A., 1978, Three-dimensional numerical 

simulations and dynamic faulting in a half-space: Bulletin of the 

Seismological Society of America, v. 68, p. 573-598. 

Ben-Menahem, A., 1961, Radiation of seismic surface waves from finite 

moving sources: Bulletin of the Seismological Society of America, v. 

51, p. 401-435. 

Bernard, P., and Madariaga, R., 1984, A new asymptotic method for the 

modeling of neaor-field accelerograms: Bulletin of the Seismological 

Society of America, v. 74, p. 539--558. 

Biehler, S., Kovach, R. L., and Allen, C. R., 1964, Geophysical 

framework of the northern end of the Gulf of California structural 

province, in Van Andel, T. H., and Shor, G. G., Jr., eds., Marine 

geology of the Gulf of California: American Association of 

Petroleum Geologists Memoir 3, p. 126--143. 

Boatwright, J., 1981, Quasi-dynamic models of simple earthquakes: Application to an aftershock of the 1975 Oroville, California, earthquake: Bulletin of the Seismological Society of America, v. 71, 

p. 69--94. 

Boatwright, J., and Boore, D. M., 1982, Analysis of the ground accelerations radiated by the 1980 Livermore earthquakes for directivity 

and dynamic source characteristics: Bulletin of the Seismological 

Society of America, v. 72, p. 1843-1866. 

Boore, D. M., 1972, Finite difference methods for seismic wave propagation in heterogeneous materials, in Bolt, B. A., ed., Methods of 

computational physics, 11: New York, Academic, p. 1-37. 

Boore, D. M., and Joyner, W. B., 1978, The influence of rupture incoherence on seismic directivity: Bulletin of the Seismological 

Society of America, v. 68, p. 283-300. 

Bouchon, M., 1978, A dynamic source model for the San Fernando 

earthquake: Bulletin of the Seismological Society of America, v. 68, 

p. 1555-1576. 

__ 1979, Predictability of ground displacement and velocity near an 

earthquake fault: An example: The Parkfield earthquake of 1966: 

Journal of Geophysical Research, v. 84, p. 6149--6156. 

__ 1980, Calculation of complete seismograms for an explosive 

source in a layered medium: Geophysics, v. 45, p. 197-203. 

__ 1982, The rupture mechanism of the Coyote Lake earthquake of 

August 1979 inferred from near-field data: Bulletin of the Seismological Society of America, v. 72, p. 745-758. 

Bracewell, R., 1965, The Fourier transform and its application: New 

York, McGraw-Hill, p. 24-35. 

Burdick, L. J., and Orcutt, J. A., 1979, A comparison of the generalized 

ray and reflectivity methods of waveform synthesis: Geophysical 

Journal of the Royal Astronomical Society, v. 46, p. 87-108. 

Cerveny, V., 1983, Synthetic body wave seismograms for laterally varying layered structures by the Gaussian beam method: Geophysical 

Journal of the Royal Astronomical Society, v. 73, p. 389-426. 

Cormier, V. F., 1980, The synthesis of complete seismograms in an earth 

model specified by radially inhomogeneous layers: Bulletin of the 

Seismological Society of America, v. 70, p. 691-716. 

Cormier, V. F., and Spudich, P., 1984, Amplification of ground motion 

and waveform complexity in fault zones: Examples from the San 

Andreas and Calaveras faults: Geophysical Journal of the Royal 

Astronomical Society, v. 79, p. 135-152. 

Das, S., and Aki, K., 1977a, A numerical study of two-dimensional spontaneous rupture propagation: Geophysical Journal of the Royal 

Astronomical Society, v.•50, p. 643-668. 

__ 1977b, Fault plane with barriers: A versatile earthquake model: 

Journal of Geophysical Research, v. 82, p. 5658--5670. 

Day, S. M., 1982, Three-dimensional simulation of spontaneous rupture: 

The effect of nonuniform prestress: Bulletin of the Seismological 

Society of America, v. 72, p. 1881-1902. 

Fuis, G. S., Mooney, W. D., Healy, J. H., McMechan, G. A., and Lutter, 

W. J., 1982, Crustal structure of the Imperial Valley region, in The 

Imperial Valley earthquake of October 15, 1979: U.S. Geological 

Survey Professional Paper 1254, p. 25-49. 

Geller, R. J., 1976, Scaling relations for earthquake 'Source parameters 

and magnitudes: Bulletin of the Seismological Society of America, 

v.66,p. 1501-1523. 

Hamilton, E. L., 1978, Sound velocity-density relations in sea-floor 

sediments and rocks: Acoustical Society of America Journal, v. 63, 

p. 366--377. 

__ 1979, Vr/V. and Poisson's ratios in marine sediments and rocks: 

Acoustical Society of America Journal, v. 66, p. 1093-1011. 

Hartzell, S. H., 1978, Earthquake aftershocks as Green's functions: 

Geophysical Research Letters, v. 5, p. 1-4. 

__ 1982, Simulation of ground accelerations for the May, 1980, 

Mammoth Lakes, California, earthquakes: Bulletin of the Seismological Society of America, v. 72, p. 2381-2388. 

Hartzell, S. H., and Heaton, T. H., 1983, Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of 

the 1979 Imperial Valley, California, earthquake: Bulletin of the 

Seismological Society of America, v. 73, p. 1553-1584. 

Hartzell, S. H., and Heimberger, D. V., 1982, Strong motion modeling of 

the Imperial Valley earthquake of 1979: Bulletin of the Seismological Society of America, v. 72, p. 571-596. 

Harvey, D. J., 1981, Seismogram synthesis using normal mode superposition: The locked mode approximation: Geophysical Journal of 

the Royal Astronomical Society, v. 66, p. 37-69. 

Haskell, N. A., 1964, Total energy and energy spectral density of elastic 

wave radiation from propagating faults: Bulletin of the Seismological Society of America, v. 84, p. 614CHl148. 

__ 1966, Total energy and energy spectral density of elastic wave 

radiation from propagating faults, pt. II, A statistical source model: 

Bulletin of the Seismological Society of America, v. 56, p. 125-140. 

References Cited 489 
Heaton, T. H., 1982, The San Fernando earthquake: A double event?: 

Bulletin of the Seismological Society of America, v. 72, 

p. 2037-2062. 

Heaton, T. H., and Heimberger, D. V., 1979, Generalized ray models of 

the San Fernando earthquake: Bulletin of the Seismological Society 

of America, v. 69, p. 1311-1341. 

Heimberger, D. V., 1968, The crust mantle transition in the Bering Sea: 

Bulletin of the Seismological Society of America, v. 58, p. 179-214. 

Heimberger, D. V., and Harkrider, D. G., 1978, Modeling earthquakes 

with generalized ray theory, in Miklowitz, )., and Achenbach, J. D., 

eds., Modern problems in elastic wave propagation: New York, 

John Wiley, p. 499-518. 

Hemnann, R. B., 1979, SH-wave generation by dislocation sources-A 

numerical study: Bulletin of the Seismological Society of America, 

v. 69, p. 1-15. 

Hong, T. L., and Heimberger, D. V., 1978, Glorified optics and wave 

propagation in non-planar structures: Bulletin of the Seismological 

Society of America, v. 68, p. 1313-1330. 

lrikura, K., 1983, Semi-empirical estimation of strong ground motions 

during large earthquakes: Bulletin of the Disaster Prevention Research Institute, v. 33, p. 63-104. 

Kanamori, H., 1979, A semi-empirical approach to prediction of longperiod ground motions from great earthquakes: Bulletin of the 

Seismological Society of America, v. 69, p. 1654-1670. 

Kennett, B. L. N., 1980, Seismic waves in a stratified half-space, II, 

Theoretical seismograms: Geophysical journal of the Royal 

Astronomical Society, v. 61, p. 1-10. 

Kennett, B. L. N., and Illingworth, M. R., 1981, Seismic waves in a 

stratified half-space, III, Piecewise smooth models: Geophysical 

journal of the Royal Astronomical Society, v. 66, p. 633-675. 

Kind, R., 1978, The reflectivity method for a buried source: journal of 

Geophysics, v. 44, p. 603-612. 

Kostrov, B. V., 1964, Self-similar problems of propagation of shear 

cracks: Journal of Applied Mathematics and Mechanics, v. 28, 

p. 1077-1087. 

Liu, H.-L., and Heaton, T. H., 1984, Array analysis of the ground 

velocities in the 1971 San Fernando, California, earthquake: 

Bulletin of the Seismological Society of America, v. 74, p. 1951-

1968. 

Liu, H.-L., and Heimberger, D. V., 1983, The near-source ground motion 

of the August 6, 1979, Coyote Lake, California, earthquake: 

Bulletin of the Seismological Society of America, v. 73, p. 201-218. 

Madariaga, R., 1983, High frequency radiation from dynamic earthquake fault models: Annales Geophysicae, v. 1, p. 17-23. 

McMechan, G. A., and Mooney, W. D., 1980, Asymptotic ray theory and 

synthetic seismograms for laterally varying structures: Theory and 

Evaluating Liquefaction Potential 

Agnew, D. C., and Sieh, K. E., 1978, A documentary study of the felt effects of the great California earthquake of 1857: Bulletin of the 

Seismological Society of America, v. 68, p. 1717-1729. 

Algermissen, S. T., Perkins, D. M., Thenhaus, P. C., Hanson, S. L., and 

Bender, B. L., 1982, Probabilistic estimates of maximum acceleration and velocity in rock in the contiguous United States: U.S. 

Geological Survey Open-File Report 82-1033, 107 p., 6 oversize 

sheets. 

Barrows, A. G., 1974, A review of the geology and earthquake history of 

the Newport-Inglewood structural zone, southern California: 

California Division of Mines and Geology Special Report 114, 

115p. 

490 Earthquake Hazards in the Los Angeles Region 

application to the Imperial Valley, California, earthquake: Bulletin 

of the Seismological Society of America, v. 70, p. 2021-2035. 

Mikumo, T., and Miyatake, T., 1978, Dynamical rupture process on 

a three-dimensional fault with non-uniform frictions and near-field 

seismic waves: Geophysical Journal of the Royal Astronomical 

Society, v. 54, p. 417-438. 

Mooney, W. D., and Luetgert, J. M., 1982, A seismic refraction survey of 

the Santa Clara Valley and southern Santa Cruz Mountains, westcentral California: Bulletin of the Seismological Society of 

America, v. 72, p. 901-910. 

Nowack, R., and Aki, K., 1984, The 2-D Gaussian beam synthetic 

method: Testing and application: Journal of Geophysical Research, 

v.89,p.7797-7819. 

Olson, A. H., and Apse!, R. J., 1982, Finite faults and inverse theory with 

applications to the 1979 Imperial Valley earthquake: Bulletin of the 

Seismological Society of America, v. 72, p. 1969-2002. 

Olson, A. H., Orcutt, J. A., and Frazier, G. A., 1984, The discrete 

wavenumber/finite element method for synthetic seismograms: 

Geophysical Journal of the Royal Astronomical Society, v. 77, 

p. 421-460. 

Papageorgiou, A. S., and Aki, K., 1983, A specific barrier model for the 

quantitative description of inhomogeneous faulting and the prediction of strong ground motion, pt. II, Applications of the model: 

Bulletin of the Seismological Society of America, v. 73, p. 953-978. 

Rial, J. A., 1984, Caustics and focusing produced by sedimentary basins: 

Applications of catastrophy theory to earthquake seismology: 

Geophysical Journal of the Royal Astronomical Society, v. 79, 

p. 923-938. 

Spudich, P., and Ascher, U., 1983, Calculation of complete theoretical 

seismograms in vertically varying media using collocation methods: 

Geophysical Journal of the Royal Astronomical Society, v. 75, 

p. 101-124. 

Spudich, P., and Cranswick, E., 1984, Direct observation of rupture 

propagation during the 1979 Imperial Valley, California, earthquake using a short-baseline accelerometer array: Bulletin of the 

Seismological Society of America, v. 74, p. 2083-2114. 

Spudich, P., and Frazer, L. N., 1984, Use of ray theory to calculate highfrequency radiation from earthquake sources having spatially 

variable rupture velocity and stress drop: Bulletin of the Seismological Society of America, v. 74, p. 2061-2082. 

Spudich, P., and Orcutt, )., 1982, Estimation of earthquake ground motion relevant to the triggering of marine mass movements, in Saxov, 

S., and Nieuwenhuis, J. K., eds., Marine slides and other mass 

movements: New York, Plenum, p. 219-232. 

Wiggins, R. A., and Heimberger, D. V., 1974, Synthetic seismogram 

computation by expansion in generalized rays: Geophysical journal 

of the Royal Astronomical Society, v. 37, p. 73-90. 

Bates, R. L., and jackson, J. A., eds., 1980, Glossary of geology, 2d ed.: 

Falls Church, Va., American Geological Institute, p. 465. 

Bonilla, M.G., Mark, R. K., and Lienkaemper, J. J., 1984, Statistical relations among earthquake magnitude, surface rupture length, and 

surface fault displacement: Bulletin of the Seismological Society of 

America, v. 74, no. 6, p. 2379-2412. 

Buwalda, ). P., 1940, Geology of the Raymond basin: Report to the 

Pasadena Water Depa-rtment, 131 p. 

California Department of Water Resources, 1961, Planned utilization of 

the ground water basins of the coastal plain of Los Angeles County-Appendix A, Ground water geology: California Department of 

Water Resources Bulletin 104, 181 p. 
__ 1966, Planned utilizations of ground water basins, San Gabriel 

Valley-Appendix A, Geohydrology: California Department of 

Water Resources Bulletin 104-2, 229 p. 

California Water Rights Board, 1962, Report of referee, City of San Fernando, California Superior Court, County of Los Angeles no. 

650079: v. 1, 258 p. 

Carson, S. E., and Matti, J. C., 1982, Contour map showing minimum 

depth to ground water, upper Santa Ana River valley, California, 

1973-1979: U.S. Geological Survey Open-File Report 82-1128, 

49p. 

Chen, A. T. F., 1984, Petal: Penetration testing and liquefaction, an interactive computer program: U.S. Geological Survey Open-File 

Report 84-290, 23 p. 

Conkling, H., 1927, San Gabriel investigation: California Division of 

Water Resources Bulletin 5, 640 p. 

Cox, B. F., and Morton, D. M., 1978, Generalized map of surficial 

materials in northwestern Riverside and southwestern San 

Bernardino Counties, California: U.S. Geological Survey Open-File 

Report 78-978, scale 1:125,000. 

Crook, R. J., Jr., Allen, C. R., Kamb, B., Payne, C. M., and Proctor, R. J., 

1979, Quaternary geology and seismic hazard of the Sierra Madre 

and associated faults: Menlo Park, Calif., annual technical report 

submitted to U.S. Geological Survey under contract 14-08-

0001-15258, 117 p. 

Durham, D. L., and Yerkes, R. F., 1964, Geology and oil resources of the 

eastern Puente Hills area, southern California: U.S. Geological 

Survey Professional Paper 420-B, 62 p. 

Dutcher, L. C., and Garrett, A. A., 1963, Geologic and hydrologic 

features of the San Bernardino area, California-With special 

reference to the underflow across the San Jacinto fault: U.S. Geological Survey Water-Supply Paper 1419, 114 p. 

Eckis, R., 1934, Geology and ground water storage capacity of valley fill: 

California Division of Water Resources Bulletin 45,279 p. 

Gutenberg, B., and Richter, C. F., 1941, Seismicity of the earth: 

Geological Society of America Special Paper 34, p. 1-333. 

Hansen, W. R., 1965, Effects of the earthquake of March 27, 1964, 

at Anchorage, Alaska: U.S. Geological Survey Professional Paper 

542-A,68p. 

King, E. J., Tinsley, J. C., and Preston, R. J., 1981, Maps showing historic 

flooding in the San Fernando Valley, California, 1934-1956: U.S. 

Geological Survey Open-File Report 81-153, 7 pis., 1:24,000 scale. 

McCoy, G., and Sarna-Wojcicki, A. M., 1978, Preliminary map showing 

surficial materials of the Ventura-Oxnard Plain area, California: 

U.S. Geological Survey Open-File Report 78-1065, scale 1:125,000. 

McCulloch, D. S., and Bonilla, M. G., 1970, Effects of the earthquake of 

March 27, 1964, on the Alaska Railroad: U.S. Geological Survey 

Professional Paper 543-A, 41 p. 

McFadden, L. D., 1982, The impacts of temporal and spatial climatic 

changes on alluvial soils genesis in southern California: Tucson, 

Ariz., University of Arizona, unpublished Ph.D. thesis, 430 p. 

McFadden, L. D., and Tinsley, J. C., 1982, Soil profile development in 

xeric climates, in Tinsley, J. C., Matti, J. C., and McFadden, L. D., 

eds., Late Quaternary pedogenesis and alluvial chronologies of the 

Los Angeles and San Gabriel Mountains areas, southern California, and Holocene faulting and alluvial stratigraphy within the 

Cucamonga fault zone: A preliminary view: Geological Society of 

America Annual Meeting, Cordilleran Section, 78th, Anaheim, 

Calif., 1982, Guidebook 12, 45 p. 

Mendenhall, W. C., 1905a, Development of underground waters in the 

central coastal plain region of southern California: U.S. Geological 

Survey Water-Supply Paper 138, 160 p. 

__ 1905b, Development of underground waters in the western 

coastal plain region of southern California: U.S. Geological Survey 

Water-Supply Paper 139, 103 p. 

__ 1908, Ground waters and irrigation enterprises in the Foothill 

Belt, southern California: U.S. Geological Survey Water-Supply 

Paper 219, 180 p. 

Munsell Soil Color Charts, 1975, 1975 edition: Baltimore, Md., 

Kollmorgen Corporation, Macbeth Division. 

Poland, J. F., 1959, Hydrology of the Long Beach-Santa Ana area, 

California: U.S. Geological Survey Water-Supply Paper 1471, 

257p. 

Poland, J. F., Piper, A. M., and others, 1956, Ground water geology of 

the coastal zone, Long Beach-Santa Ana area, California: U.S. 

Geological Survey Water-Supply Paper 1109, 162 p. 

Poland, J. F., Garrett, A. A., and Sinnott, A., 1959, Geology, hydrology, 

and chemical character of ground waters in the Torrance-Santa 

Monica area, California: U.S. Geological Survey Water-Supply 

Paper 1461,423 p. 

Randell, D. H., 1983, Liquefaction potential in coastal areas in and 

around Long Beach, California: Long Beach, Calif., California State 

University, unpublished M.Sci. thesis, 250 p. 

Richter, C. F., 1958, Elementary seismology: San Francisco, W. H. 

Freeman, p. 359. 

Rigby, J. K., and Hamblin, W. K., 1972, Recognition of ancient sedimentary environments: Society of Economic Paleontologists and 

Mineralogists Special Publication 16, 340 p. 

Rogers, T. H., 1965, Geologic map of California, Santa Ana sheet: San 

Francisco, Calif., California Division of Mines and Geology, scale 

1:250,000. 

Roth, R. A., and Kavazanjian, E., Jr., 1984, Liquefaction susceptibility 

mapping for San Francisco, California: Association of Engineering 

Geologists Bulletin, v. 21, no. 4, p. 459-478. 

Seed, H. B., and Alonso, J.-L., 1973, Effects of soil-saturated interaction 

in the Caracas earthquake of 1967, in Earthquake engineering 

research at Berkeley: Berkeley, Calif., Report 72-23, University of 

California, College of Engineering Earthquake Engineering 

Research Center, p. 47-50. 

Seed, H. B., and Idriss, I. M., 1967, Analysis of soil liquefaction: Niigata 

earthquake: Proceedings of the American Society of Civil Engineers, Journal of the Soil Mechanics and Foundations Division, 

v. 93, no SM3, p. 83-108. 

___ 1971, Simplified procedure for evaluating soil liquefaction potential: Proceedings of the American Society of Civil Engineers, Journal of the Soil Mechanics and Foundations Division, v. 97, no. SM9, 

p. 1249-1273. 

Seed, H. B., Lee, K. L., Idriss, I. M., and Makdisi, F. I., 1975, The slides 

in the San Fernando Dams during the earthquake of February 9, 

1971: Proceedings of the American Society of Civil Engineers, Journal of the Geotechnical Division, v. 101, no, GT7, p. 651-688. 

Seed, H. B., Idriss, I. M., and Arango, Ignacio, 1983, Evaluation of 

liquefaction potential using field performance data: American 

Society of Civil Engineers Journal of Geotechnical Engineering, 

v. 109, no. 3, p. 458-482. 

Sherburne, R. W., Fuller, D. R., Cole, J. W., Greenwood, R. B., Mumm, 

H. A., and Real, C. R., 1981, Classification and mapping of Quaternary sedimentary deposits for purposes of seismic zonation, south 

coastal Los Angeles basin, Orange County, California: California 

Division of Mines and Geology Open-File Report 81-10 LA, 245 p., 

8 pis., scale 1:48,000. 

Sprotte, E. C., and Johnson, J. A., 1976, Investigation of potential differential settlement and potential liquefaction of Holocene 

sediments due to seismically induced ground shaking, Oxnard 

Plain area, Ventura County, California, in Seismic hazards study of 

Ventura County, California: California Division of Mines and 

Geology Open-File Report 76-5 LA, p. 219-254. 

Sprotte, E. C., Fuller, D. M., Greenwood, R. B., Mumm, H. A., Real, C. R., 

and Sherburne, R. W., 1980, Classification and mapping of Quaternary sedimentary deposits for purposes of seismic zonation, south 

coastal Los Angeles basin, Orange County, California: California 

References Cited 491 
Division of Mines and Geology Open-File Report 8G-19 LA, 267 p., 

17 pls., scale 1:48,000. 

Thenhaus, P. C., Perkins, D. M., Ziony, J. I., and Algermissen, S. T., 

1980, Probabilistic estimates of maximum seismic horizontal 

ground motion on rock in coastal California and the adjacent outer 

continental shelf: U.S. Geological Survey Open-File Report 8G-924, 

36p. 

Tinsley, J. C., and Youd, T. L., 1979, Application of historic flood records 

to mapping of liquefaction susceptibility in urban areas-An 

example from the San Fernando Valley, California: Geological Society of America Abstracts with Programs, v. 11, p. 132. 

Troxell, H. C., 1942, Floods of March 1938 in southern California: U.S. 

Geological Survey Water Supply Paper 844, 399 p. 

Troxell, H. C., and Peterson, J. Q., 1937, Floods in La Canada Valley, 

California, January 1, 1934: U.S. Geological Survey Water-Supply 

Paper 796-C, 98 p. 

Weber, F. H., Jr., and Kiessling, E. W., 1976, General features of seismic 

hazards of Ventura County, California, in Seismic hazards study of 

Ventura County, California: California Division of Mines and 

Geology Open-File Report 76-5 LA, p. 8-218. 

Yerkes, R. F., 1972, Geology and oil resources of the western Puente 

Hills area, southern California: U.S. Geological Survey Professional Paper 42o-G, 63 p. 

Yerkes, R. F., McCulloh, T. H., Schoellhamer, J. E., and Vedder, J. G., 

1965, Geology of the Los Angeles basin-An introduction: U.S. 

Geological Survey Professional Paper 42G-A, 57 p. 

Youd, T. L., 1971, Landsliding in the vicinity of the Van Norman Lakes, 

in The San Fernando, California, earthquake of February 9, 1971: 

U.S. Geological Survey Professional Paper 733, p. 105-109. 

__ 1973, Liquefaction, flow, and associated ground failure: U.S. 

Geological Survey Circular 688, 12 p. 

__ 1978a, Major cause of earthquake damage is ground failure: 

Civil Engineering, v. 48, no. 4, p. 47-51. 

__ 1978b, Mapping liquefaction-induced ground failure potential: 

Proceedings of the American Society of Civil Engineers, Journal of 

the Geotechnical Engineering Division, v. 104, no GT4, p. 433-446. 

__ 1980, Ground failure displacement and earthquake damage to 

buildings: American Society of Civil Engineers Conference on Civil 

Engineering and Nuclear Power, 2d, Knoxville, Tenn., 1980, v. 2, 

p. Hl-2-7-6-26. 

Youd, T. L., and Hoose, S. N., 1977, Liquefaction susceptibility and 

geologic setting: World Conference on Earthquake Engineering, 

6th, New Delhi 1977, Proceedings, v. 3, p. 2189-2194. 

Youd, T. L., and Perkins, D. M., 1978, Mapping liquefaction-induced 

ground failure potential: Proceedings of the American Society of 

Civil Engineers, Journal of the Geotechnical Engineering Division, 

v. 104, no. GT4, p. 433-446. 

Youd, T. L., and Wieczorek, G. F., 1982, Liquefaction and secondary 

ground failure, in The Imperial Valley, California, earthquake of 

October 15, 1979: U.S. Geological Survey Professional Paper 1254, 

p. 223-246. 

__ 1984, Liquefaction during the 1981 and previous earthquakes 

near Westmorland, California: U.S. Geological Survey Open-File 

Report 84-680, 36 p. 

Youd, T. L., Nichols, D. R., Helley, E. J., and Lajoie, K. R., 1975, 

Liquefaction potential, in Studies for seismic zonation of the San 

Francisco Bay region: U.S. Geological Survey Professional Paper 

941-A, p. A68-A74. 

Youd, T. L., Tinsley, J. C., Perkins, D. M., King, E. J., and Preston, R. F., 

1978, Liquefaction potential map of San Fernando Valley, California: International Conference on Microzonation for Safer Construction-Research and Applications, 2d, San Francisco 1978, 

Proceedings, v. 1, p. 267-278. 

Zielbauer, E. J., Burnham, W. L., and Keene, A. G., 1961, Coastal basins 

barrier and replenishment investigation, Alamitos Barrier Project 

geologic investigation: Los Angeles County Flood Control District, 

28p. 

Zielbauer, E. J., Kues, H. A., Burnham, W. L., and Keene, A. G., 1962, 

Coastal basins barrier and replenishment investigation, Dominguez 

Gap Barrier Project geologic investigation: Los Angeles County 

Flood Control District, 29 p. 

Predicting Areal Limits of Earthquake-Induced Landsliding 

Arias, A., 1970, A measure of earthquake intensity, in Hansen, R. J., ed., 

Seismic design for nuclear power plants: Cambridge, Mass., MIT 

Press, p. 438-483. 

Barrows, A. G., 1973, Earthquakes along the Newport-Inglewood structural zone: California Geology, v. 26, p. 60-68. 

Buwalda, J. P., and St. Amand, Pierre, 1955, Geological effects of the 

Arvin-Tehachapi earthquake, in Oakeshott, G. B., ed., Earthquakes 

in Kern County, California, during 1952: California Division of 

Mines and Geology Bulletin 171, p. 41-56. 

California Division of Highways, 1975, Highway damage in the San Fernando earthquake, in Oakeshott, G. B., ed., San Fernando, California, earthquake of February 9, 1971: California Division of Mines 

and Geology Bulletin 196, p. 369-379. 

Campbell, R. H., 1975, Soil slips, debris flows, and rainstorms in the 

Santa Monica Mountains and vicinity, southern California: U.S. 

Geological Survey Professional Paper 851, 51 p. 

Clark, B. R., Leighton, F. B., Cann, L. R., and Gaffey, J. T., 1979, Surficial 

landslides triggered by seismic shaking, San Fernando earthquake 

of 1971: Menlo Park, Calif., final technical report to U.S. Geological 

Survey under contract 14-08-001-16810, 42 p. 

492 Earthquake Hazards in the Los Angeles Region 

Coffman, J. L., and von Hake, 1973, United States earthquakes 1971: 

Washington, D.C., National Oceanic and Atmospheric Administration, 176 p. 

Dobry, R., Idriss, I. M., and Ng, E., 1978, Duration characteristics of 

horizontal components of strong-motion earthquake records: 

Bulletin of the Seismological Society of America, v. 68, 

p. 1487-1520. 

Fallgren, R. B., and Smith, J. L., 1973, Ground displacement at San Fernando Valley Juvenile Hall during San Fernando earthquake, in 

Murphy, L. M., ed., San Fernando, California, earthquake of 

February 9, 1971, v. 3, Geological and geophysical studies: 

Washington, D.C., National Oceanic and Atmospheric Administration, p. 189-196. 

Field, M. E., and Hall, R. K., 1982, Sonographs of submarine sediment 

failure caused by the 1980 earthquake off northern California: 

Geo-Marine Letters, v. 2, p. 135-141. 

Goodman, R. E., and Seed, H. B., 1966, Earthquake-induced 

displacements in sand embankments: Proceedings of the American 

Society of Civil Engineers, Journal of the Soil Mechanics and 

Foundations Division, v. 92, no. SM2, p. 125-146. 
Hanks, T. C., and Kanamori, H., 1979, A moment magnitude scale: Journal of Geophysical Research, v. 84, no. B5, p. 2348-2350. 

Hanks, T. C., and McGuire, R. K., 1981, The character of highfrequency strong ground motion: Bulletin of the Seismological 

Society of America, v. 71, p. 2071-2095. 

Harp, E. L., Keefer, D. K., and Wilson, R. C., 1980, A comparison of artificial and natural slope failures, the Santa Barbara earthquake 

of August 13, 1978: California Geology, v. 33, p. 102-105. 

Harp, E. L., Wilson, R. C., and Wieczorek, G. F., 1981, Landslides from 

the February 4, 1976, Guatemala earthquake: U.S. Geological 

Survey Professional Paper 1204-A, 35 p. 

Joyner, W. B., and Boore, D. M., 1981, Peak horizontal acceleration and 

velocity from strong-motion records including records from the 

1979 Imperial Valley, California, earthquake: Bulletin of the Seismological Society of America, v. 71, p. 2011-2038. 

Kachadoorian, R., 1971, An estimate of the damage, in The San Fernando, California, earthquake of February 9, 1971: U.S. Geological 

Survey Professional Paper 733, .p. ey. 

Kanamori, H., 1977, The energy release in great earthquakes: Journal 

of Geophysical Research, v. 82, no. 20, p. 2981-2987. 

Keefer, D. K., 1984a, Rock avalanches caused by earthquakes-Source 

characteristics: Science, v. 223, no. 4642, p. 1288-1290. 

___ 1984b, Landslides caused by earthquakes: Geological Society of 

America Bulletin, v. 95, no. 4, p. 406-421. 

Keefer, D. K., and Tannaci, N. E., 1981, Bibliography on landslides, soil 

liquefaction, and related ground failures in selected historic earthquakes: U.S. Geological Survey Open-File Report 81-572, 39 p. 

Keefer, D. K., Wieczorek, G. F., Harp, E. L., and Tuel, D. H., 1978, 

Preliminary assessment of seismically induced landslide 

susceptibility, in International Conference on Microzonation, 2d, 

San Francisco, Calif., 1978, Proceedings, v. 1: p. 279-290. 

Kobayashi, Y., 1981, Causes of fatalities in recent earthquakes in 

Japan: Journal of Disaster Science, v. 3, p. 15-22 .. 

Kuribayashi, E., and Tatsuoka, F., 1975, Brief review of liquefaction during earthquakes in Japan: Soils and Foundations, v. 

15,no.4,p.81-92. 

__ 1977, History of earthquake-induced soil liquefaction in Japan: 

Ministry of Construction of Japan, Public Works Research Institute 

Bulletin, v. 31, 26 p. 

Lee, W. H. K., Johnson, C. E., Henyey, T. L., and Yerkes, R. F., 1978, A 

preliminary study of the Santa Barbara earthquake of August 13, 

1978, and its major aftershocks: U.S. Geological Survey Circular 

797,11 p. 

Lindh, A. G., and Boore, D. M., 1981, Control of rupture by fault 

geometry during the 1966 Parkfield earthquake: Bulletin of the 

Seismological of America, v. 71, p. 95-116. 

Maher, T. J., 1933, Abstract of reports received regarding the earthquake which occurred in southern California on March 10, 1933: 

San Francisco, Calif., U.S. Coast and Geodetic Survey, 64 p. 

Miller, R. K., and Felszeghy, S. F., 1978, Engineering features of the 

Santa Barbara earthquake of August 13, 1978: Berkeley, Calif., 

Special Report UCSB-ME-78-2, Earthquake Engineering 

Research Institute, unpaginated. 

Morton, D. M., 197J, Seismically triggered landslides in the area above 

the San Fernando Valley, in The San Fernando, California, earthquake of February 9, 1971: U.S. Geological Survey Professional 

Paper 733, p. 99-104. 

___ 1975, Seismically triggered landslides in the area above the San 

Fernando Valley, in Oakeshott, G. B., ed., San Fernando, California, earthquake of February 9, 1971: California Division of Mines 

and Geology Bulletin 196, p. 145-154. 

Neumann, Frank, 1935, United States earthquakes, 1933: Washington, 

D.C., U.S. Coast and Geodetic Survey, p. 9-162. 

Newmark, N. M., 1965, Effects of earthquakes on dams and embankments: Geotechnique, v. 15, no. 2, p. 139-160. 

Oakeshott, G. B., 1955, The Kern County earthquakes in California's 

geologic history, in Oakeshott, G. B., ed., Earthquakes in Kern 

County, California, during 1952: California Division of Mines and 

Geology Bulletin 171, p. 15-22. 

__ 1973, 40 years ago ... The Long Beach-Compton earthquake 

of March 10, 1933: California Geology, v. 26, p. 55-59. 

Perry, 0. W., 1955, Highway damage resulting from the Kern County 

earthquakes, with a section on Bridge earthquake report, ArvinTehachapi earthquake, by Stewart Mitchell, in Oakeshott, G. B., 

ed., Earthquakes in Kern County, California, during 1952: California Division of Mines and Geology Bulletin 171, p. 227-234. 

Plafker, G., Erickson, G. E., and Fernandez.Concha, J., Jr., 1971, 

Geological aspects of the May 31, 1970, Peru earthquake: Bulletin 

of the Seismological Society of America, v. 61, p. 543-578. 

Seed, H. B., Lee, K. L., Idriss, I. M., and Makdisi, F. I., 1975, The slides 

in the San Fernando dams during the earthquake of February 9, 

1971: Proceedings of the American Society of Civil Engineers, Journal of the Geotechnical Engineering Division, v. 101, no. GT7, 

p. 651--688. 

Steinbrugge, K. V., and Moran, D. F., 1954, An engineering study of the 

southern California earthquake of July 21, 1952, and its aftershocks: Bulletin of the Seismological.Society of America, v. 44, 

p. 201-337. 

Vanmarcke, E. H., and Lai, S. P., 1980, Strong-motion duration and RMS 

amplitude of earthquake records: Bulletin of the Seismological 

Society of America, v. 70, p. 1293-1307. 

Varnes, D. J., 1978, Slope movement types and processes, in Schuster, 

R. L., and Krizek, R. J., eds., Landslides-Analysis and control: National Academy of Sciences Transportation Research Board 

Special Report 176, p. 12-33. 

Warne, A. H., 1955, Ground fracture patterns in the southern San Joaquin Valley resulting from the Arvin-Tehachapi earthquake, in 

Oakeshott, G. B., ed., Earthquakes in Kern County, California, during 1952: California Department of Mines and Geology Bulletin 

171, p. 57-66. 

Wieczorek, G. F., Wilson, R. C., and Harp, E. L., 1985, Map of slope 

stability during earthquakes in San Mateo' County, California: U.S. 

Geological Survey Miscellaneous Investigations Map I-1257-E, 

scale 1:62,500. 

Wilson, R. C., and Keefer, D. K., 1983, Dynamic analysis of a slope 

failure from the 1979 Coyote Lake, California, earthquake: Bulletin 

of the Seismological Society of America, v. 73, p. 863-877. 

Wood, H. 0., 1933, Preliminary report on the Long Beach earthquake: 

Bulletin of the Seismological Society of America, v. 23, p. 42-56. 

Yen, B. C., and Trotter, J. R., 1978, Shallow slides due to 1971 San Fernando earthquake: American Society of Civil Engineers, Proceedings of the Specialty Conference on Earthquake Engineering and 

Soil Dynamics, v. 2, p. 1076-1096. 

Yerkes, R. F., 1973, Effects of San Fernando earthquake as related to 

geology, in Murphy, L. M., ed., San Fernando, California, earthquake of February 9, 1971, v. 3, Geological and geophysical 

studies: Washington, D.C., National Oceanic and Atmospheric Administration, p. 137-154. 

Yerkes, R. F., and Campbell, R. H., 1980, Geologic map of east-central 

Santa Monica Mountains, Los Angeles County, California: U.S. 

Geological Survey Miscellaneous Investigations Map I-1146, scale 

1:24,000. 

Youd, T. L., 1971, Landsliding in the vicinity of the Van Norman Lakes, 

in The San Fernando, California, earthquake of February 9, 1971: 

U.S. Geological Survey Professional Paper 733, p. 105-109. 

___ 1977, Discussion of "Brief review of liquefaction during earthquakes in Japan," by E. Kuribayshi and F. Tatsuoka, 1975: Soils 

and Foundations, v. 17, no. 1, p. 82-85. 

___ 1980, Ground failure displacement and earthquake damage to 

buildings: American Society of Civil Engineers, Proceedings of the 

References Cited 493 
Specialty Conference on Civil Engineering and Nuclear Power, v. 2, 

p. 7-6-1-Hl-26. 

Youd, T. L., and Hoose, S. N., 1978, Historic ground failures in northern 

California triggered by earthquakes: U.S. Geological Survey Professional Paper 993, 177 p. 

Youd, T. L., and Olsen, H. W., 1971, Damage to constructed works 

associated with soil movements and foundation failures, in The 

San Fernando, California, earthquake of February 9, 1971: U.S. 

Geological Survey Professional Paper 733, p. 126-132. 

Youd, T. L., and Perkins, D. M., 1978, Mapping liquefaction-induced 

ground failure potential: Proceedings of the American Society of 

Civil Engineers, Journal of the Geotechnical Engineering Division, 

v. 104, no. GT4, p. 433-446. 

Identifying Potentially Active Faults and Unstable Slopes Offshore 

Baddley, E. R., 1954, Geology of the South Mountain oil field, Ventura 

County, in Johns, R. H., ed., Geology of southern California: California Division of Mines Bulletin 170, map sheet 29. 

Barrows, A. G., 1974, A review of the geology and earthquake history of 

the Newport-Inglewood structural zone, southern California: 

California Division of Mines and Geology Special Report 114, 

155 p. 

Bernard, B. B., Brooks, J. M., and Sackett, W. M., 1976, Natural gas 

seepage in the Gulf of Mexico: Earth and Planetary Science 

Letters, v. 31, p. 48-54. 

Campbell, R. H., and Yerkes, R. F., 1976, Cenozoic evolution of the Los 

Angeles basin area-Relation to plate tectonics, in Howell, D. G., 

ed., Aspects of the geologic history of the California continental 

borderland: American Association of Petroleum Geologists (Pacific 

Section) Miscellaneous Publication 24, p. 541-558. 

Clarke, S. H., Greene, H. G., Field, M. E., and Lee, W. H. K., 1983, 

Reconnaissance geology and geologic hazards of selected areas of 

the southern California continental borderland: U.S. Geological 

Survey Open-File Report 83-62, 78 p. 

Clarke, S. H., Greene, H. G., Kennedy, M. P., and Vedder, J. G., 1985, 

Geologic map of the inner-southern California continental margin, 

in Greene, H. G., and Kennedy, M.P., eds., Geologic map series of 

the California continental margin: Sacramento, California Division 

of Mines and Geology, pl. 1A, scale 1:250,000. 

Claypool, G. E., and Kaplan, I. R., 1974, The origin of methane in marine 

sediments, in Kaplan, I. R., ed., Natural gases in marine sediments: 

New York, Plenum, p. 94-129. 

Clifton, H. E., Greene, H. G., Moore, G. W., and Phillips, R. L., 1971, 

Methane seep off Malibu Point following the San Fernando earthquake, in The San Fernando, California, earthquake of February 9, 

1971: U.S. Geological Survey Professional Paper 733, p. 112-116. 

Corbett, E. J., and Piper, K. A., 1981, Santa Barbara Island, California, 

earthquake, September 4, 1981 [abs.]: EOS, Transactions of the 

American Geophysical Union, v. 62, no. 45, p. 958. 

Dames and Moore and MESA• (Marine Environmental Science 

Associates), 1983, Activity and earthquake potential of the Palos 

Verdes fault: Menlo Park, Calif., final technical report to U.S. 

Geological Survey under contract 14-08-0001-19786, 90 p. 

Dobrin, M. B., 1976, Introduction to geophysical prospecting: New York, 

McGraw-Hill, 630 p. 

Dott, R. G., Jr., 1963, Dynamics of subaqueous gravity depositional 

processes: Bulletin of the American Association of Petroleum 

Geologists, v. 47, no. 1, p. 104-128. 

Edwards, B. D., 1982, Geologic hazards in Santa Monica Basin: U.S. 

Geological Survey Administrative Report AA851-IA1-22, submitted to Bureau of Land Management (Los Angeles), 23 p. 

Edwards, B. D., Field, M. E., and Clukey, E. C., 1980, Geological and 

geotechnical analyses of a submarine slump, California 

borderland: Annual Offshore Technology Conference, 12th, 

Houston, Tex., 1980, Proceedings, p. 399-410. 

Emery, K. 0., 1960, The sea off southern California: New York, John 

Wiley,366p. 

494 Earthquake Hazards in the los Angeles Region 

Field, M. E., and Edwards, B. D., 1980, Slopes of the southern California 

continental borderland: A regime of mass transport, in Field, M. E., 

Bouma, A. H., Colburn, I. P., Douglas, R. G., and Ingle, J. C., eds., 

Quaternary depositional environments of the Pacific coast: Society 

of Economic Paleontologists and Mineralogists (Pacific Section), 

Pacific Coast Paleogeography Symposium 4, Los Angeles, Calif., 

1980, p. 169-184. 

Field, M. E., Gardner, J. V., Jennings, A. E., and Edwards, B. D., 1982, 

Earthquake-induced sediment failures on a 0.25° slope, Klamath 

River delta, California: Geology, v. 10, p. 542-546. 

Fischer, P. J., 1972, Geologic evolution and Quaternary geology of the 

Santa Barbara basin, California: Los Angeles, Calif., University of 

Southern California, unpublished Ph.D. thesis, 337 p. 

Fischer, P. J., and Stevenson, A. J., 1973, Natural hydrocarbon seeps 

along the northern shelf of the Santa Barbara Basin, California: 

Annual Offshore Technology Conference, 5th, Houston, Tex., 1973, 

Proceedings, p. 159-169. 

Greene, H. G., and Kennedy, M. P., 1981, Review of offshore seismic 

reflection profiles in the vicinity of the Cristianitos fault, San 

Onofre, California, in Safety evaluation report (geology and 

seismology) related to the operation of San Onofre Nuclear 

Generating Station, units 2 and 3: Washington, D.C., Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, 

p. F-3-F-23. 

Greene, H. G., Lee, W. H. K., McCulloch, D. S., and Brabb, E. E., 1973, 

Faults and earthquakes in the Monterey Bay region, California: 

U.S. Geological Survey Miscellaneous Field Investigation Map 

MF-518, 4 sheets, scale 1:200,000. 

Greene, H. G., Clarke, S. H., Field, M. E., Linker, F. I., and Wagner, 

H. C., 1975, Preliminary report on the environmental geology of 

selected areas of the southern California borderland: U.S. 

Geological Survey Open-File Report 75-596, 70 p., 16 pis. 

Greene, H. G., Wolf, S. C., and Blom, K. G., 1978, The marine geology of 

the eastern Santa Barbara channel with particular emphasis on 

the groundwater basins offshore from the Oxnard Plain, southern 

California: U.S. Geological Survey Open-File Report 78-305, 

104 p., 13 pis. 

Greene, H. G., Bailey, K. A., Clarke, S. H., Ziony, J. 1., and Kennedy, 

M. P., 1979, Implications of fault patterns of the inner California 

continental borderland between San Pedro and San Diego, in Abbott, P. L., and Elliott, W. J., eds., Earthquakes and other perils, San 

Diego region: Geological Society of America Annual Meeting, 92d, 

San Diego, Calif., 1979, Field trip guidebook, p. 21-27. 

Hall, R. W., and Ensiminger, H. R., eds., 1979, Potential geologic 

hazards and constraints for blocks in proposed mid-Atlantic OCS 

oil and gas l~ase sale 49: U.S. Geological Survey Open-File Report 

79-264, 176 p., 12 figs., 1 pl. 

Hampton, M. A., and Bouma, A. H., 1977, Slope instability near the 

shelf break, western Gulf of Alaska: Marine Geotechnology, v. 2, 

p. 309-322. 
Haner, B. E., and Gorsline, D. S., 1978, Processes and morphology of 

continental slope between Santa Monica and Dume submarine 

canyons, southern California: Marine Geology, v. 28, p. 77-87. 

Harding, T. P., 1973, Newport-Inglewood trend, California-An example of wrenching style of deformation: Bulletin of the American 

Association of Petroleum Geologists, v. 57, no. 1, p. 97-116. 

Heezen, B. C., and Drake, C. L., 1964, Grand Banks slump: Bulletin of 

the American Association of Petroleum Geologists, v. 48, no. 2, 

p. 221-225. 

Hileman, J. A., Allan, C. R., and Nordquist, J. M., 1973, Seismicity of the 

southern California region, 1 January 1932 to 31 December 1972: 

California Institute of Technology Division of Geology and 

Planetary Sciences Contribution 2385, 404 p. 

Hill, M. L., 1971, Newport-Inglewood zone and Mesozoic subduction, 

California: Geological Society of America Bulletin, v. 82, no. 10, 

p. 2957-2962. 

Jennings, C. W., 1973, State of California preliminary fault and geologic 

map: California Division of Mines and Geology Preliminary Report 

13, scale 1:750,000. 

___ 1977, Geologic map of California: California Division of Mines 

and Geology Geologic Data Map Series, scale 1:750,000. 

Junger, Arne, 1976, Offshore structure between Santa Cruz and Santa 

Rosa Islands, in Howell, D. G., ed., Aspects of the geologic history 

of the California continental borderland: American Association of 

Petroleum Geologists (Pacific Section) Miscellaneous Publication 

24, p. 418-426. 

___ 1979, Maps and seismic profiles showing geologic structure of 

the northern Channel Islands platform, California continental 

borderland: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-991, Hl-p. text, 5 sheets. 

Junger, Arne, and Wagner, H. C., 1977, Geology of the Santa Monica 

and San Pedro basins, California continental borderland: U.S. 

Geological Survey Miscellaneous Field Studies Map MF-820, scale 

1:250,000. 

Kennedy, M. P., Greene, H. G., and Clarke, S. H., in press, Atlas of 

geologic features, stratigraphy, and bibliography from the California continental margin: California Division of Mines and Geology 

Bulletin. 

Lee, W. H. K., Johnson, C. E., Henyey, T. L., and Yerkes, R. L., 1978, A 

preliminary study of the Santa Barbara, California, earthquake of 

August 13, 1978, and its major aftershocks: U.S. Geological Survey 

Circular 797, 11 p. 

Lee, W. H. K., Yerkes, R. F., and Simirenko, M., 1979, Recent earthquake activity and focal mechanisms in the western Transverse 

Ranges, California: U.S. Geological Survey Circular 799-A, 37 p. 

Legg, M., and Kennedy, M. P., 1979, Faulting offshore San Diego and 

northern Baja California, in Abbott, P. L., and Elliott, W. J., eds., 

Earthquakes and other perils, San Diego region: Geological Society 

of America Annual Meeting, 92d, San Diego, Calif., 1979, Fieldtrip 

guidebook, p. 29-46. 

Lewis, K. B., 1971, Slumping on a continental slope inclined at 1°-4°: 

Sedimentology, v. 16, p. 97-110. 

Luyendyk, B. P., Hajic, E. J., Crippen, R. E., and Simonett, D. S., 1983, 

Side-scan sonar and high-resolution reflection maps of the Santa 

Barbara Channel seafloor: Santa Barbara, Calif., California Sea 

Grant College Program Report T -CSGCP-006, Department of Geological Sciences, Department of Geography, and Marine Sciences 

Institute, University of California, 17 p., 7 sheets. 

Malouta, D. N., Gorsline, D. S., and Thornton, S. E., 1981, Processes and 

rates of recent (Holocene) basin filling in an active transform 

margin: Santa Monica basin, California continental borderland: 

Journal of Sedimentary Petrology, v. 51, p. 1077-1095. 

McCulloh, T. H., 1960, Gravity variations and the geology of the Los 

Angeles basin of California: U.S. Geological Survey Professional 

Paper 400-B, p. B320-B325. 

Moody, J. D., and Hill, M. J., 1956, Wrench fault tectonics: Geological 

Society of America Bulletin, v. 67, p. 1207-1246. 

Moore, D. G., 1961, Submarine slumps: Journal of Sedimentary 

Petrology, v. 31, p. 343-357. 

___ 1969, Reflection profiling studies of the California continental 

borderland: Structure and Quaternary turbidite basins: Geological 

Society of America Special Paper 107, 142 p. 

Nardin, T. R., 1981, Seismic stratigraphy of Santa Monica and San 

Pedro basins, California continental borderland: Late Neogene 

history of sedimentation and tectonics: Los Angeles, Calif., University of Southern California, unpublished Ph.D. dissertation, 270 p. 

Nardin, T. R., and Henyey, T. L., 1978, Plio-Pleistocene diastrophism of 

Santa Monica and San Pedro shelves, California continental 

borderland: Bulletin of the American Association of Petroleum 

Geologists, v. 62, no. 2, p. 247-272. 

Nelson, C. H., Kvenvolden, K. A., and Clukey, E. C., 1978, Thermogenic 

gases in near surface sediments of Norton Sound, Alaska, in Annual Offshore Technology Conference, 10th, Houston, Tex., 1978, 

Proceedings: p. 2623-2633. 

Ogle, B. A., and Hacker, R. N., 1969, Cross section, coastal area, Ventura County, in Geology and oil fields of coastal areas, Ventura and 

Los Angeles basins, California: American Association of Petroleum 

Geologists, Society of Exploration Geophysicists, and Society of 

Economic Paleontologists and Mineralogists (Pacific Sections) Annual Meeting, 44th, Los Angeles, Calif., 1969, Fieldtrip guidebook. 

Patterson, R. H., 1979, Tectonic geomorphology and neotectonics of the 

Santa Cruz Island fault, Santa Barbara County, California: Santa 

Barbara, University of California, unpublished M.Sci. thesis, 141 p. 

Prior, D. B., and Coleman, J. M., 1977, Disintegrating retrogressive landslides on very-low-angle subaqueous slopes, Mississippi delta: 

Marine Geotechnology, v. 3, p. 37-60. 

Richmond, W. C., Cummings, L. J., Hamlin, S., and Nagaty, M. E., 1981, 

Geological hazards and constraints in the area of proposed OCS oil 

and gas lease sale 48, southern California: U.S. Geological Survey 

Open-File Report 81-307, 37 p. 

Sangrey, D. A., 1977, Marine geotechnology-State of the art: Marine 

Geotechnology, v. 2, p. 45-80. 

Sarna-Wojcicki, A. M., Williams, K. M., and Yerkes, R. F., 1976, 

Geology of the Ventura fault, Ventura County, California: U.S. 

Geological Survey Miscellaneous Field Studies Map MF-781, scale 

1:6,000. 

Schoellhamer, J. E., and Woodford, A. 0., 1951, The floor of the Los 

Angeles basin, Los Angeles, Orange, and San Bernardino Counties, 

California: U.S. Geological Survey Oil and Gas Investigation Map 

OM-117, 2 sheets. 

Seed, H. B., Murarka, R., Lysmer, J., and Idriss, I. M., 1975, Relationships between maximum acceleration, maximum velocity, distance 

from source, and local site conditions for moderately strong earthquakes: Bulletin of the Seismological Society of America, v. 66, no. 

4, p. 1323-1342. 

Seines, P. B., 1982, Geotechnical problems in offshore earthquake 

engineering: Norwegian Geotechnical Institute Publication 140, 

p. 1-27. 

Stein, R. S., and King, G. C. P., 1984, Seismic potential revealed by 

surface folding: 1983 Coalinga, California, earthquake: Science, v. 

224, p. 869-872. 

Teng, Ta-liang, and Henyey, T. L., 1975, Microearthquake monitoring in 

the city of Long Beach area for the year 1974: Los Angeles, Calif., 

Technical Report 75-2, University of Southern California Geophysical Laboratory, 50 p. 

Thornton, S. E., 1981, Holocene stratigraphy and sedimentary processes in Santa Barbara basin: Influence of tectonics, ocean circulation, climate and mass movement: Los Angeles, Calif., University of 

Southern California, unpublished Ph.D. thesis, 351 p. 

References Cited 495 
U.S. Coast and Geodetic Survey, 1967a, Santa Barbara-Huntington 

Beach: U.S. Coast and Geodetic Survey Bathymetric Map 

1206N-15, scale 1:250,000. 

__ 1967b, Huntington Beach-Punta Sal Si Pudes: U.S. Coast and 

Geodetic Survey Bathymetric Map 1206N-16, scale 1:250,000. 

U.S. Nuclear Regulatory Commission, 1981, Safety evaluation report 

related to the operation of San Onofre Nuclear Generating Station, 

units 2 and 3: Washington, D.C., Office of Nuclear Reactor Regulation, NUREG-0712, dockets 5Q--361, 5Q--362, 106 p. 

Vedder, J. G., Beyer, L. A., Junger, Arne, Moore, C. W., Roberts, A. E., 

Taylor, J. C., and Wagner, H. C., 1974, Preliminary report on the 

geology of the continental borderland of southern California: U.S. 

Geological Survey Miscellaneous Field Studies Map MF--624, 34-p. 

text, 9 sheets. 

Vedder, J. G., Greene, H. G., Clarke, S. H., and Kennedy, M. P., 1985, 

Geologic map of the mid-southern California continental margin, in 

Greene, H. G., and Kennedy, M. P., eds., Geologic map series of the 

California continental margin: California Division of Mines and 

Geology, pl. 2A, scale 1:250,000. 

Weaver, D. W., Doerner, D. P., and Nolf, B., 1969, Geology of the 

northern Channel Islands, California: American Association of 

Petroleum Geologists and Society of Economic Paleontologists and 

Mineralogists (Pacific Sections) Special Publication, 200 p. 

Wilcox, R. E., Harding, T. P., and Seely, D. R., 1973, Basic wrench tectonics: Bulletin of the American Association of Petroleum 

Geologists, v. 57, no. 1, p. 74-96. 

Evaluating Tsunami Potential 

Abe, K., 1973, Tsunami and mechanism of great earthquakes: Physics 

of the Earth and Planetary Interiors, v. 7, p. 143-153. 

__ 1975, Reliable estimation of the seismic moment of large earthquakes: Journal of Physics of the Earth, v. 23, p. 381-390. 

__ 1979, Size of great earthquakes of 1837-1974 inferred from 

tsunami data: Journal of Geophysical Research, v. 84, no. B4, 

p. 1561-1568. 

Agnew, D. C., 1979, Tsunami history of San Diego, in Abbott, P. L., and 

Elliott, W. J., eds., Earthquakes and other perils, San Diego region: 

San Diego, Ealif., San Diego Association of Geologists, p. 117-122. 

Alfors, J. T., Burnett, J. L., and Gay, T. E., Jr., 1973, Urban geology 

master plan for California: California Division of Mines and 

Geology Bulletin 198, 112 p. 

Auffret, G. A., Auzende, J. M., Gennesseaux, M., Monti, S., Pastouret, 

L., Pautot, G., and Vanney, J. R., 1982, Recent mass wasting processes on the Provincial Margin (western Mediterranean), in Saxov, 

S., and Nieuwahuis, J. K., eds., Marine slides and other mass 

movements: New York, Plenum, p. 53-58. 

Beavan, J., Hauksson, E., McNutt, S. R., Bilham, R., and Jacob, K. H., 

1983a, Tilt and seismicity changes in the Shuman seismic gap: 

Science, v. 222, p. 322-325. 

Beavan, J., Bilham, R., and Hurst, K., 1983b, Coherent tilt signals 

observed in the Shumagin Islands seismic gap [abs.): EOS, Transactions of the American Geophysical Union, v. 64, no. 18, p. 258. 

Ben-Menahem, A., 1961, Radiation of seismic-surface waves from finite 

moving sources: Bulletin of the Seismological Society of America, v. 

51, p. 401-435. 

Bernard, E. N., and Goulet, R., 1981, Tsunami research opportunities: 

Washington, D.C., National Science Foundation, 50 p. 

Bernard, E. N., Lander, J. F., and Hebenstreit, G. T., 1982, Feasibility 

study on mitigating tsunami hazards in the Pacific: National 

496 Earthquake Hazards in the Los Angeles Region 

Wilkinson, G. R., 1971, California offshore oil and gas seeps: California 

Oil Fields-Summary of Operations, v. 57, no. 1, p. 5-28. 

Woodring, W. P., Bramlette, M. N., and Kew, W. S. W., 1946, Geology 

and paleontology of Palos Verdes Hills, California: U.S. Geological 

Survey Professional Paper 207, 145 p. 

Yerkes, R. F., and Lee, W. H. K., 1979a, Faults, fault activity, 

epicenters, focal depths, focal mechanisms, 197Q--75 earthquakes, 

western Transverse Ranges, California: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1032, 2 sheets, scale 

1:250,000. 

__ 1979b, Late Quaternary deformation in the western Transverse 

Ranges, California: U.S. Geological Survey Circular 799-B, 10 p. 

Yerkes, R. F., McCulloh, T. H., Schoellhamer, J. E., and Vedder, J. G., 

1965, Geology of the Los Angeles basin, California-An introduction: U.S. Geological Survey Professional Paper 42Q--A, 57 p. 

Yerkes, R. F., Gorsline, D. S., and Rusnak, G. A., 1967, Origin of Redondo submarine canyon, southern California, in Geological survey 

research 1967: U.S. Geological Survey Professional Paper 575-C, 

p. C97-C105. 

Yerkes, R. F., Greene, H. G., Tinsley, J. C., and Lajoie, K. R., 1981, 

Seismotectonic setting of the Santa Barbara Channel area, southern California: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-1169, 25-p. text, 1 sheet. 

Ziony, J. 1., Wentworth, C. M., Buchanan-Banks, J. M., and Wagner, 

H. C., 1974, Preliminary map showing recency of faulting in 

coastal southern California: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-585, 3 sheets, scale 1:250,000. 

Oceanic and Atmospheric Administration Technical Memorandum ERL PMEL-37, 43 p. 

Bertero, V. V., Corley, W. G., and others, 1985, Damage survey of the 

Nihon-Kai-Chubu, Japan, earthquake of May 26, 1983: Earthquake 

Spectra, v. 1, no. 2, p. 319--352. 

Blackford, M. E., 1981, Tsunami potential of seismic gaps in the 

Aleutian-Alaska arc [abs.): EOS, Transactions of the American 

Geophysical Union, v. 62, no. 45, p. 945. 

Bonilla, M. G., Mark, R. K., and Lienkaemper, J. J., 1984, Statistical 

relations among earthquake magnitude, surface rupture length, 

and surface fault displacement: Bulletin of the Seismological Society of America, v. 74, p. 2379--2411. 

Brandsma, M., Divoky, D., and Hwang, L. S., 1978, Circumpacific variation of computed tsunami features, in Tsunami symposium: 

Ottawa, Canada, Marine Sciences Directorate, Department of 

Fisheries and Environment Manuscript Report Series 48, 

p. 132-151. 

Brune, J. N., Nafe, J. E., and Oliver, J. E., 1960, A simplified method for 

the analysis and synthesis of dispersed wave trains: Journal of Geophysical Research, v. 65, no. 1, p. 287-304. 

Burford, R. 0., Castle, R. 0., Church, J.P., Kinoshita, W. F., Kirby, S. H., 

Ruthven, R. T., and Savage, J. C., 1971, Preliminary measurements 

of tectonic movements of February 9, 1971: U.S. Geological Survey 

Professional Paper 773, p. 8Q--85. 

Butler, H. L., 1978, Numerical simulation of Coos Bay-South Slough 

complex: U.S. Army Corps of Engineers Waterways Experimental 

Station Technical Report H-78-22, 31 p. 

Byerly, P., 1930, The California earthquakes of November 4, 1927: 

Bulletin of the Seismological Society of America, v. 20, p. 53--66. 

Cassidy, A., 1862, Miscellaneous notes on the tide gauge & tidal observations at San Diego-California 1853-1854: San Diego, Calif., 

Serra Museum Library, unpublished papers. 
Cooper, A., 1971, Structure of the continental shelf west of San Francisco, California: U.S. Geological Survey Open-File Report, 65 p. 

Coulter, H. W., and Migliaccio, R. R., 1966, Effects of the earthquake of 

March 27, 1964-Effects on communities-Valdez, Alaska: U.S. 

Geological Survey Professional Paper 542-C, p. C1-C36. 

Curray, J. R., and Nason, R. D., 1967, San Andreas fault north of Point 

Arena, California: Geological Society of America Bulletin, v. 78, no. 

3, p. 413-418. 

Darrow, A. C., and Fischer, P. J., 1983, Activity and earthquake potential of the Palos Verdes fault zone: Menlo Park, Calif., technical report to U.S. Geological Survey under contract 14-08-0001-19786, 

90p. 

Davidson, D. D., and Whalin, R. W., 1974, Potential landslide-generated 

water waves, Libby Dam and Lake Koocanusa, Montana: U.S. 

Army Corps of Engineers Waterways Experiment Station Technical Report H-74-15, 33 p. 

Davies, J., Sykes, L., House, L., and Jacob, K., 1981, Shumagin seismic 

gap, Alaska Peninsula: History of great earthquakes, tectonic setting, and evidence for high seismic potential: Journal of Geophysical Research, v. 86, no. B5, p. 3821-3855. 

Eaton, J. P., 1984, Focal mechanisms of near-shore earthquakes between Santa Barbara and Monterey, California: U.S. Geological 

Survey Open-File Report 84-477, 6 p. 

Eaton, J. P., Richer, D. H., and Ault, W. J., 1961, The tsunami of May 23, 

1960, on the island of Hawaii: Bulletin of the Seismological Society 

of America, v. 51, p. 135-157. 

Edgers, L., and Karlsrud, K., 1982, Soil flows generated by submarine 

slides-Case studies and consequences: Norwegian Technical 

Institute Publication 143, p. 1-10. 

Edwards, B. D., Field, M. E., and Clukey, E. C., 1980, Geological and 

geotechnical analysis of a submarine slump, California 

borderland: Offshore Technology Conference, 12th, Houston, Tex., 

1980, Proceedings, p. 399-410. 

Federal Emergency Management Agency, 1982, Flood insurance study, 

city of Huntington Beach, California, Orange County: San Francisco, Calif., FEMA Region IX, 28 p. 

Field, M. E., and Edwards, B. D., 1980, Slopes of the southern California 

continental borderland: A regime of mass transport, in Field, M. E., 

Bouma, A. H., Colburn, I. P., Douglas, R. G., and Ingle J. C., eds., 

Proceedings of the Quaternary depositional environments of the 

Pacific Coast: Pacific Coast Paleogeography Symposium No. 4: Los 

Angeles, Calif., Society of Economic Paleontologists and 

Mineralogists, Pacific Section, p. 169-184. 

Field, M. E., Gardner, J. V., Jennings, A. E., and Edwards, B. D., 1982, 

Earthquake-induced sediment failures on a 0.25 slope, Klamath 

River delta, California: Geology, v. 10, p. 542-546. 

Fukao, Y., 1979, Tsunami earthquakes and subduction processes near 

deep-sea trenches: Journal of Geophysical Research, v. 84, no. B5, 

p. 2303-2314. 

Fumumoto, A. S., 1969, Ionospheric recording of Rayleigh waves for 

estimating source mechanisms, in Adams, W. M., Tsunamis in the 

Pacific Ocean: Honolulu, Hawaii, East-West Center Press, 

p.119-134. 

Furneaux, R., 1964, Krakatoa: Englewood Cliffs, N.J., Prentice-Hall, 

224p. 

Galanopoulos, A. G., and Bacon, E., 1969, Atlantis, the truth behind the 

legend: New York, Bobbs-Merrill, 216 p. 

Garcia, A. W., 1976, Effect of source orientation and location in the 

Peru-Chile trench on tsunami amplitude along the Pacific coast of 

the continental United States: U.S. Army Corps of Engineers 

Waterways Experiment Station Research Report H-76--2, 20 p. 

Garcia, A. W., and Houston, J. R., 1975, Type 16 flood insurance 

study-Tsunami predictions for Monterey and San Francisco Bays 

and Puget Sound: U.S. Army Corps of Engineers Waterways Experiment Station Technical Report H-75-17, 21 p. 

Garcia, W. J., 1972, A study of water waves generated by tectonic 

displacements: Berkeley, Calif., Technical Report HEL 16--9, University of California, Berkeley, Hydraulic Engineering Laboratory, 

114p. 

Gawthrop, H. W., 1975, Seismicity of the central California coastal 

region: U.S. Geological Survey Open-File Report 75-134, 87 p. 

___ 1978a, The 1927 Lompoc, California earthquake: Bulletin of the 

Seismological Society of America, v. 68, p. 1705-1716. 

___ 1978b, Seismicity and tectonics of central California coastal 

region, in Silver, E. A., and Normark, W. R., eds., San GregoriaHosgri fault zone, California: California Division of Mines and 

Geology Special Report 137, p. 45-56. 

Gennesseaux, A. M., Mauffret, A., and Pautot, G., 1980, Les glissements 

sous-marins de Ia pente continentale nicoise et Ia rupture de cables 

en mer Ligure (Mediterranee occidentale): Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences, v. 290, ser. 

D. p. 959-962. 

Grantz, A., Plafker, G., and Kachadoorian, R., 1964, Alaska's Good 

Friday earthquake, March 27, 1964, a preliminary geologic evaluation: U.S. Geological Survey Circular 491, 35 p. 

Greene; H. G., Clarke, S. H., Field, M. E., Linker, F. 1., and Wagner, 

H. C., 1975, Preliminary report on the environmental geology of selected areas of the southern California borderland: U.S. Geological 

Survey Open-File Report 75-596, 70 p., 16 pis. 

Hampton, M. A., 1972, The role of subaqueous debris flow in generating 

turbidity currents: Journal of Sedimentary Petrology, v. 42, 

p. 775-793. 

Hanks, T. C., 1979, The Lompoc, California earthquake (Novemb-er 4, 

1927; M = 7.3) and its aftershocks: Bulletin of the Seismological 

Society of America, v. 69, p. 451-462. 

Hanks, T. C., and Kanamori, H., 1979, A moment magnitude scale: 

Journal of Geophysical Research, v. 84, no. B5, p. 2348--2350. 

Hauksson, E., 1983, Regular or precursory seismicity, 1973-1983, in the 

Shumagin seismic gap, Alaska [abs]: EOS, Transactions of the 

American Geophysical Union, v. 64, no. 18, p. 258. 

Heath, E., 1748, A full account of the late dreadful earthquake at Port 

Royal in Jamaica, in A true and particular rel.ation of the dreadful 

earthquake which happen'd at Lima ••• 1746: London, printed for 

T. Osborne in Grays's Inn, p. 327-341. 

Heaton, T. H., and Kanamori, H., 1984, Seismic potential associated 

with subduction in the northwestern United States: Bulletin of the 

Seismological Society of America, v. 74, no. 3, p. 933-941. 

Heezen, B. C., and Ewing, M., 1952, Turbidity currents and submarine 

slumps and the Grand Banks earthquake: American Journal of 

Science, v. 250, p. 849-873. 

Hellmuth, A., Sievers, C., Villegas, C. G., and Barros, G., 1963, The 

seismic sea wave of 22 May 1960 along the Chilean coast: Bulletin 

of the Seismological Society of America, v. 53, p. 1125-1190. 

Hisamoto, S., and Murayama, C., 1962, Drawing the wave fronts of the 

Chilean tsunami of May 23, 1960: Quarterly Journal of Seismology, 

v. 26, p. 1-8. 

Hokubei Mainichi (North American Daily), 1983, An account of the 

Akita earthquake: June 2, 1983. 

Holden, E. S., 1898, A catalogue of earthquakes on the Pacific coast: 

Smithsonian Miscellaneous Collections, v. 37, no. E, 253 p. 

Hoskins, E. G., and Griffiths, J. R., 1971, Hydrocarbon potential of 

northern and central California offshore, in Cram, I. H., ed., Future 

petroleum provinces of the United States-Their petroleum potential: American Association of Petroleum Geologists Memoir 15, 

p. 212-228. 

House, L., and Boatwright, J., 1980, Investigation of two high stress drop 

earthquakes in the Shumagin seismic gap, Alaska: Journal of 

Geophysical Research, v. 85, no. B12, p. 7151-7165. 

House, L. S., Sykes, L. R., Davies, J. N., and Jacob, K. H., 1981, Identification of a possible seismic gap near Unalaska Island, Eastern 

References Cited 497 
Aleutians, Alaska, in Simpson, D. W., and Richards, P. G., eds., 

Earthquake prediction: An international review: American Geophysical Union, Maurice Ewing Series, no. 4, p. 81-92. 

Houston, j. R., 1979, Tsunamis, seiches, and landslide-induced water 

waves: State-of-the-art for assessing earthquake hazards in the 

United States: U.S. Army Corps of Engineers Waterways Experiment Station Miscellaneous Paper S-73-1, 88 p. 

___ 1980, Type 19 flood in~urance study: Tsunami predictions for 

southern California: U.S. Army Corps of Engineers Waterways Experiment Station Technical Report HL-8D-18, 172 p. 

Houston, j. R., and Butler, H. L., 1979, A numerical model for tsunami 

inundation: U.S. Army Corps of Engineers Experimental Waterways Station Technical Report HL-79-2, 54 p. 

Houston, J. R., and Garcia, A. W., 1974, Type 16 flood insurance study: 

Tsunami predictions for Pacific coastal communities: U.S. Army 

Corps of Engineers Waterways Experiment Station Technical 

Report H-74-3, 10 p. 

___ 1978, Type 16 flood insurance study: Tsunami predictions for the 

west coast of the United States: U.S. Army Corps of Engineers 

Waterways Experiment Station Technical Report H-78-26, 38 p. 

Houston, j. R., Whalin, R. W., Garcia, A. W., and Butler, H. L., 1975, Effect of source orientation and location in the Aleutian Trench on 

tsunami amplitude along the Pacific coast of the continental United 

States: U.S. Army Corps of Engineers Waterways Experiment Station Research Report H-75-4, 22 p. 

Hove, K., Seines, P. B., and Bungum, H., 1982, Seaquakes: A potential 

threat to offshore structures: Norwegian Technical Institute Publication 143, p. 1-10. 

Hwang, L. S., Butler, H. L., and Divoky, D., 1972, Tsunami model: 

Generation and open sea characteristics: Bulletin of the Seismological Society of America, v. 62, p. 1529-1596. 

Hwang, L. S., and Lee, K. Y., 1979, Tsunamis, Proceedings of the National Science Foundation Workshop: Pasadena, Calif., Tetra 

Tech, Inc., 328 p. 

!ida, K., 1963a, Magnitude, energy, and generation mechanisms of 

tsunamis and a catalog of earthquakes associated with tsunamis, 

in Proceedings of the 1oth Pacific Science Congress Symposium: 

International Union of Geodesy and Geophysics Monograph 24, 

p. 7-18. 

___ 1963b, On the estimation of tsunami energy, in Proceedings of 

the 1oth Pacific Science Congress Symposium: International Union 

of Geodesy and Geophysics Monograph 24, p. 167-173. 

___ 1970, The generation of tsunamis and the focal mechanisms of 

earthquakes, in Adams, W. M., ed., Tsunamis in the Pacific Ocean: 

Honolulu, Hawaii, East-West Center Press, p. 3-18. 

!ida, K., Cox, D. C., and Pararas-Carayannis, G., 1967a, Preliminary 

catalog of tsunamis occurring in the Pacific Ocean: Hawaii Institute of Geophysics Data Report 5, 265 p. 

___ 1967b, Bibliography to the preliminary catalog of tsunamis occurring in the Pacific Ocean: Hawaii Institute of Geophysics Data 

Report 6, 27 p. 

Imamura, A., 1949, List of tsunamis in japan [in japanese): journal of 

the Seismological Society of japan, v. 2, p. 23-28 

jacob, K. H., 1983, Aleutian seismic gaps: High probability for great 

Shumagin earthquake in next 10 years [abs.]: EOS, Transactions of 

the American Geophysical Union, v. 64, no. 18, p. 258. 

japan Times, 1983, Quake, tsunami kill 32 in Tohoku, Hokka'ido: May 

27, no. 30,305, p. 1. 

Junger, A., and Wagner, H. C., 1977, Geology of the Santa Monica and 

San Pedro basins, California Continental Borderland: U.S. Geological Survey Miscellaneous Field Studies Map MF-820, 10-p. text, 

scale 1:250,000. 

Kachadoorian, R., 1965, Effects of the earthquake of March 27, 1964, at 

Whittier, Alaska: U.S. Geological Survey Professional Paper 

542-B,p.B1-B21. 

498 Earthquake Hazards in the Los Angeles Region 

Kachadoorian, R., and Plafker, G., 1967, Effects of the earthquake of 

March 27, 1964, on the communities of Kodiak and the nearby 

islands: U.S. Geological Survey Professional Paper 542-F, 41 p. 

Kajiura, K., 1979, Tsunami generation, in Hwang, L., and Lee, Y. K., 

eds., Tsunamis, Proceedings of the National Science Foundation 

Workshop: Pasadena, Calif., Tetra Tech, Inc., p. 15-36. 

Kanamori, H., 1972, Mechanism of tsunami earthquakes: Physics of the 

Earth and Planetary Interiors, v. 5, p. 346--359. 

___ 1977, The energy release in great earthquakes: journal of 

Geophysical Research, v. 82, no. 20, p. 2981-2987. 

Kanamori, H., and Given, j. W., 1982, Use of long-period surface waves 

for rapid determination of earthquake source parameters: Physics 

of the Earth and Planetary Interiors, v. 30, p. 26Q-268. 

Kelleher, j. A., 1970, Space-time seismicity of the Alaska-Aleutian 

seismic zone: journal of Geophysical Reseach, v. 75, no. 29, 

p. 5745-5756. 

___ 1972, Rupture zones of large South American earthquakes and 

some predictions: journal of Geophysical Research, v. 77, no. 11, 

p. 2087-2103. 

___ 1979, Summary map of tsunami source area, in Hwang, L., and 

Lee, Y. K., eds., Tsunami, Proceedings of the National Science 

Foundation Workshop: Pasadena, Calif., Tetra Tech, Inc., p. 12. 

Kelleher, j., Savino, j., Rowlett, H., and McCann, W., 1974, Why and 

where great thrust earthquakes occur along island arcs: journal of 

Geophysical Research, v. 79, no. 32, p. 4889-4899. 

Keulegan, G. G., Harrison, )., and Mathews, M. j., 1969, Theoretics in 

design of the proposed Crescent City Harbor tsunami model: U.S. 

Army Corps of Engineers Technical Report H-69-9, 68 p. 

Kuenen, Ph. H., 1950, Turbidity currents of high density: International 

Geologic Congress, 18th, London 1948, Report, pt. 8, p. 44-52. 

Kobayashi, Y., 1981, Causes of fatalities in recent earthquakes in 

japan: journal of Disaster Science, v. 3, p. 15-22. 

Lawson, A. C., and others, 1908, The California earthquake of April 18, 

1906--Report of the State Earthquake Investigation Commission: 

Washington, D.C., Carnegie Institute of Washington, v. 1, 451 p. 

Lee, W. H. K., and Ellsworth, W. L., 1975, Earthquake activity in the 

Santa Barbara Channel region, in Draft environmental statement, 

oil and gas development in the Santa Barbara Channel outer continental shelf off California: Menlo Park, Calif., U.S. Geological 

Survey, p. II-BD-Il-137. 

Lee, W. H. K., johnson, C. E., Henyey, T. L., and Yerkes, R. L., 1978, A 

preliminary study of the Santa Barbara, California, earthquake of 

August 13, 1978, and its major aftershocks: U.S. Geological Survey 

Circular 797, 11 p. 

Lee, Y. K., Wu, F. H., Wier, W., Parnicky, P., and DeMers, D., 1982, 

Methodology for computing coastal flood statistics in southern 

California: Pasadena, Calif., Report TC-3205, Tetra Tech, Inc., 

75p. 

Leendertse, j. j., 1967, Aspects of a computational model for long-period 

water-wave propagation: Santa Monica, Calif., Memorandum 

RM-5294-PR, Rand Corporation, 179 p. 

Lemke, R. W., 1967, Effects of the earthquake of March 27, 1964, at 

Seward, Alaska: U.S. Geological Survey Professional Paper 542-E, 

p. E1-E43. 

Lindh, A., Motooka, C., Ball, S., and Dollar, R., 1981, Current seismicity 

of the central California coastal region from Point Buchan to Point 

Piedras Blancas-A preliminary report: U.S. Geological Survey 

Open-File Report 81-44, 14 p. 

Link, M. C., 1960, Exploring the drowned city of Port Royal: National 

Geographic Magazine, no. 117, p. 151-183. 

Lockridge, P. A., and Smith, R. H., 1984, Tsunamis in the Pacific basin: 

National Oceanic and Atmospheric Administration, National 

Geographic Data Center, scale 1:17,000,000. 
Magoon, 0. T., 1965, Structural damage by tsunamis: American Society 

of Civil Engineers Specialty Conference on Coastal Engineering, 

Santa Barbara, Calif., 1965, Proceedings, p. 35--68. 

Marine Advisors, 1965, Examination of tsunami potential at the San 

Onofre nuclear generating station: La Jolla, Calif., Report A-163, 

59p. 

McCann, W. R., Nishenko, S. P., Sykes, L. R., and Krause, J., 1979, 

Seismic gaps and plate tectonics: Seismic potential for major 

boundaries: Pure and Applied Geophysics, v. 117, no. 4, 

p. 1082-1147. 

McCulloch, D. S., 1966, Slide-induced waves, seiching, and ground fracturing caused by the earthquake of March 27, 1964, at Kenai Lake, 

Alaska: U.S. Geological Survey Professional Paper 543-A, 

p. A1-A41. 

McCulloch, D. S., Greene, H. G., Heston, K. S., and Rubin, D. M., 1980, A 

summary of the geology and geologic hazards in proposed Lease 

Sale 53, central California outer continental shelf: U.S. Geological 

Survey Open File-Report 8D-1095, 76 p. 

McCulloch, W. S., and Pitts, W., 1948, The statistical organization of 

nervous activity: Biometrics, v. 4, p. 91-99. 

McKean, K., and Mohs, M., 1983, Tracking the killer waves: Discover, 

v. 4, no. 8, p. 18-24. 

McLellan, H. S., 1965, Elements of physical oceanography: New York, 

Pergamon, 151 p. 

Miller, D. J., 1960, Giant waves at Lituya Bay, Alaska: U.S. Geological 

Survey Professional Paper 354-C, p. C51-C83. 

Miller, G. R., Munk, W. H., and Snodgrass, F. E., 1962, Long-period 

waves over California's continental borderland, pt. II, Tsunamis: 

Journal of Marine Research, v. 20, p. 31-41. 

Montessus de Ballore, F. de, 1907, The science seismology-Earthquakes [in French): Paris, Armand Colin, 579 p. 

Murty, T. S., 1977, Seismic sea waves; tsunamis: Bulletin of the 

Fisheries Research Board of Canada 198, 337 p. 

___ 1979, Submarine slide-generated water waves in Kitimat Inlet, 

British Columbia: Journal of Geophysical Research, v. 84, no. C12, 

p. 7777-7779. 

Magi, K., 1969, Some features of recent seismic activity in and near 

Japan [2): Bulletin of the Earthquake Research Institute, University 

of Tokyo, v. 46, p. 1225-1236. 

Ohtke, M., Matumoto, T., and Latham, G.V., 1977, Seismicity gap near 

Oaxaca, southern Mexico, as a possible precursor to a large earthquake: Pure and Applied Geophysics, v. 115, p. 375-385. 

Osamu, T., 1984, A report on the 1983 Nihonkai.Chubu earthquake: 

Shizuoka, Japan, Tokai University, 64 p. 

Pararas.Carayannis, G., Dong, B., and Farmer, R., 1982, Annotated 

tsunami bibliography 1962-1976: Prepared by National Oceanic 

and Atmospheric Administration International Tsunami Information Center for the Nuclear Regulatory Commission, Paper 

NUREG/CR-2840, 532 p. 

Plafker, G., 1972, Alaskan earthquake of 1964 and Chilean earthquake 

of 1960: Implications for arc tectonics: Journal of Geophysical 

Research, v. 77, no. 5, p. 901-925. 

___ 1978, Closing comment, in Proceedings of Conference VI: 

Methodology for identifying seismic gaps and soon-to-break gaps: 

U.S. Geological Survey Open-File Report 78-943, p. 918. 

Plafker, G., Kachadoorian, R., Eckel, E. B., and Mayo, L. P., 1969, Effects of the earthquake of March 27, 1964, at various communities: 

U.S. Geological Survey Professional Paper 542-G, p. G1-G50. 

Preuss, )., 1982, Application of microzonation concept to land management in tsunami hazard zones: International Earthquake Microzonation Conference, 3d, Seattle, Wash., 1982, Proceedings, v. 11, 

p. 717-728. 

Prins, J. E., 1958, Characteristics of waves generated by a local disturbance: EOS, Transactions of the American Geophysical Union, 

v.39,no.5,p.865-874. 

Prior, D. B., Bornhold, B. D., Coleman, J. M., and Bryant, W. R., 1982, 

Morphology of a submarine slide, Kitimat Arm, British Columbia: 

Geology, v. 10, p. 588-592. 

Raichlen, F., 1979, Bay and harbor response to tsunamis, in Hwang, L., 

and Lee, Y. K., eds., Tsunamis, Proceedings of the National Science 

Foundation Workshop: Pasadena, Calif., Tetra Tech, Inc., 

p. 188-221. 

Raney, D. C., and Butler, H. L., 1975, A numerical model for predicting 

the effects of landslide-generated water waves: U.S. Army Corps 

of Engineers Water Ways Experiment Station Research Report 

H-75-1,24p. 

Saint-Amand, P., 1961, Los Terremotos De Mayo-Chile 1960: China 

Lake, Calif., Technical Article 14, NOTS TP2701, U.S .. Naval Ordnance Test Station, Michelson Laboratories, 39 p. 

San Francisco Examiner, 1979, Tidal wave kills ten on Riviera: October 

17, 115th year, no. 235, p. 18. 

Savage, J. C., and Prescott, W. H., 1978, Geodetic control and the 1927 

Lompoc, California, earthquake: Bulletin of the Seismological Society of America, v. 68, p. 1699--1703. 

Schwab, W. C., and Lee, H. )., 1983, Geotechnical analysis of submarine 

landslides in glacial marin!'! sediment, northeast Gulf of Alaska, in 

Molnia, B. F., ed., Glacial-marine sedimentation: New York, 

Plenum, p. 145-184. 

Shepard, F. P., 1933, Depth changes in Sagami Bay during the great 

Japanese earthquake: Journal of Geology, v. 41, p. 527-536. 

___ 1948, Submarine geology: New York, Harper, 348 p. 

Shepard, F. P., McDonald, G. A., and Cox, D. C., 1950, The tsunami of 

April!, 1946: University of California Scripps Institution of Oceanography Bulletin, v. 5, p. 391-528. 

Slingerland, R. L., and Voight, B., 1979, Occurrences, properties, and 

predictive models of landslide-generated water waves, in Voight, 

B., ed., Rockslides and avalanches, v. 2: New York, Elsevier, 

p. 317-397. 

Smith, S. W., 1975, Aftershocks of the 1927 Lompoc earthquake: 

Berkeley, Calif., TERA Technical Report, 18 p. 

Soloviev, S. L., 1970, Recurrence of tsunamis in the Pacific, in Adams, 

W. M., ed., Tsunamis in the Pacific Ocean: Honolulu, Hawaii, EastWest Center Press, p. 149--163. 

Spaeth, M. G., and Berkman, S. C., 1967, The tsunami of March 28, 

1964, as recorded at tide stations: U.S. Coast and Geodetic Survey 

Technical Bulletin 33, 86 p. 

Spudich, P., and Orcutt, J., 1982, Estimation of earthquake ground motions relevent to the triggering of marine mass movements, in 

Saxov, S., and Nieuwauhuis, J. K., eds., Marine slides and other 

mass movements: New York, Plenum, p. 219-231. 

Striem, H. L., and Miloh, T., 1975, Tsunamis induced by submarine 

slumpings off the coast of Israel: Tel Aviv, Israel, Israel Atomic 

Energy Commission, 23 p. 

Sykes, L. R., 1971, Aftershock zones of great earthquakes, seismicity 

gaps, earthquake prediction for Alaska and the Aleutians: Journal 

of Geophysical Research, v. 76, no. 23, p. 8021-8041. 

Sykes, L. R., Kisslinger, J. B., House, L., Davies, J. N., and Jacobs, K. H., 

1981, Rupture zones and repeat times of great earthquakes along 

the Alaskan-Aleutian arc, 1784-1980, in Simpson, D. W., and 

Richards, P. G., eds., Earthquake prediction: An international 

review: American Geophysical Union Maurice Ewing Series, no. 4, 

p. 73-80. 

Takahasi, R., 1963, On some model experiments on tsunami generation: 

Proceedings of the 1oth Pacific Science Congress Symposium: 

International Union of Geodesy and Geophysics Monograph 24, 

p. 245-248. 

The Volcano Letter, 1931, Hawaiian Volcano Observatory, National 

Park, Hawaii: February 13, no. 321, p. 1. 

Thenhaus, P. C., Perkins., D. M., Ziony, J. 1., and Algermissen, S. T., 

1980, Probabilistic estimates of maximum seismic horizontal 

References Cited 499 
ground motion on rock in coastal California and the adjacent outer 

continental shelf: U.S. Geological Survey Open-File Report 8G-924, 

69p. 

Toppozada, T. R., Real, C. R., and Parke, D. L., 1981, Preparation of 

isoseismal maps and summary of reported effects for pre-1900 

California earthquakes: California Division of Mines and Geology 

Open-File Report 81-11 SAC, 182 p. 

Townley, S. D., and Allen, M. W., 1939, Descriptive catalog of earthquakes of the Pacific Coast of the United States, 1769 to 1928: 

Bulletin of the Seismological Society of America, v. 29, p. 1-297. 

Tuck, E. 0., 1979, Models for predicting tsunami propagation, in 

Hwang, L., and Lee, Y. K., eds., Tsunamis, Proceedings of the National Science Foundation Workshop: Pasadena, Calif., Tetra 

Tech, Inc., p. 43-104. 

Tudor, W. J., 1964, Tsunami damage at Kodiak, Alaska and Crescent 

City, California, from Alaska earthquake of 27 March 1964: Port 

Hueneme, Calif., Technical Note N-622, U.S. Naval Civil Engineering Laboratory, 128 p. 

Van Darn, W. G., 1964, Source mechanism of the tsunami of March 28, 

1964, in Alaska, in Conference of Coastal Engineers, 9th, Lisbon 

1964, Proceedings: New York, American Society of Civil Engineers, 

p. 16&-190. 

__ 1970, Tsunami response at Wake Island: A model study: Journal 

of Marine Research, v. 28, p. 33&-344. 

__ 1979a, Instrumentation and observations, in Hwang, L., and Lee, 

Y. K., eds., Tsunamis, Proceedings of the National Science Foundation Workshop: Pasadena, Calif., Tetra Tech, Inc., p. 281-295. 

__ 1979b, Theoretical aspects of tsunamis along the San Diego 

coastline, in Abbot, P. L., and Elliot, W. J., Earthquakes and other 

perils, San Diego region: San Diego, Calif., San Diego Association 

of Geologists, p. 115-116. 

Wagner, H. C., 1974, Marine geology between Cape San Martin and 

Point Sal, south-central California offshore--A preliminary report: 

U.S. Geological Survey Open-File Report 74-252, 17 p. 

Ward, S. N., 1979, Ringing P waves and submarine faulting: Journal of 

Geophysical Research, v. 84, no. B6, p. 3057-3062. 

Wiegel, R. L., 1955, Laboratory studies of gravity waves generated by 

the movement of a submerged body: EOS, Transactions of the 

American Geophysical Union, v. 36, p. 759-774. 

__ 1969, Seismic sea waves, in Olson, R. A., and Wallace, M. M., 

eds., Geologic hazards and public problems, State of California Office of Emergency Preparedness Conference, San Francisco, Calif., 

1969, Proceedings: p. 53-75. 

__ 1970, Tsunamis, in Wiegel, R. L., ed., Earthquake engineering: 

Englewood Cliffs, N.J., Prentice-Hall, p. 253-306. 

Wiegel, R. L., Noda, E. K., Kube, E. M., Gee, D. M., and Tornberg, G. F., 

1970, Water waves generated by landslides in reservoirs: Proceedings of the American Society of Civil Engineers, Journal of the 

Waterways and Harbors Division, v. 96, no. WW2, p. 307-334. 

Wilson, B. W., 1971, Tsunami-responses of San Pedro Bay and shelf, 

California: Proceedings of the American Society of Civil Engineers, 

Journal of the Waterways and Harbors Division, v. 97, no. WW2, 

p. 239-258. 

Wilson, B. W., and Tprum, A., 1968, The tsunami of the Alaskan earthquake, 1964: Coastal Engineering Research Center Technical 

Memorandum 25, 50 p. 

Wood, H. 0., 1916, California earthquakes-A synthetic study of 

recorded shocks: Bulletin of the Seismological Society of America, 

v. 6, p. 55-180. 

__ 1933, Preliminary report on the Long Beach earthquake: Bulletin 

of the Seismological Society of America, v. 23, p. 43-56. 

Wood, H. 0., Heck, N.H., and Eppley, R. A., 1966, Earthquake history of 

the United States, pt. 2, Stronger earthquakes of California and 

western Nevada (revised through 1963): U.S. Coast and Geodetic 

Survey [Publication ]41-1, 48 p. 

Woodward-Clyde, Inc., 1979, Report of the evaluation of maximum 

earthquake and site ground motion parameters associated with the 

offshore zone of deformation, San Onofre nuclear generating station: Rosemead, Calif., report prepared for Southern California 

Edison, 13 p. 

Wu, T. Y., 1979, On tsunami propagation-Evaluation of existing 

models, in Hwang, L., and Lee, Y. K., eds., Tsunamis, Proceedings 

of the National Science Foundation Workshop: Pasadena, Calif., 

Tetra Tech, Inc., p. 11G-143. 

Yeh, H.-C., 1975, Mechanism of the 1927 Lompoc earthquake from surface wave analysis: Seattle, Wash., University of Washington, 

unpublished M.Sci. thesis, 91 p. 

Yerkes, R. F., and Lee, W. H. K., 1979, Faults, fault activity, epicenters, 

focal depths, focal mechanisms, 197G-75 earthquakes, western 

Transverse Ranges, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1032, 2 sheets, scale 1:250,000. 

Yerkes, R. F., Greene, H. G., Tinsley, J. C., and Lajoie, K. R., 1981, 

Seismotectonic setting of Santa Barbara Channel area, southern 

California: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-1169, 25-p. text, 1 sheet, scale 1:250,000. 

Predicted Geologic and Seismologic Effects of a Postulated Magnitude 6.5 

Earthquake Along the Northern Part of the Newport-Inglewood Zone 

Andrews, D. J., 1976, Rupture velocity of plane shear cracks: Journal of 

Geophysical Research, v. 81, p. 5679-5687. 

Archuleta, R. J., 1984, A faulting model for the 1979 Imperial Valley 

earthquake: Journal of Geophysical Research, v. 89, p. 4559-4585. 

Archuleta, R. J., and Frazier, G. A., 1978, Three-dimensional numerical 

simulations of dynamic faulting in a half-space: Bulletin of the 

Seismological Society of America, v. 68, p. 541-572. 

Asada, A., Kawakami, R., and Yanagiasawa, E., 1980, Geological and 

soil mechanical studies on damage to housing sites by the 

Miyagiken.Qki earthquake, 1978: World Conference on Earthquake Engineering, 7th, Istanbul 1980, Proceedings, v. 3, 

Geotechnical aspects, p. 219-226. 

500 Earthquake Hazards in the Los Angeles Region 

Barrows, A. G., 1974, A review of the geology and earthquake history of 

the Newport-Inglewood structural zone, southern California: 

California Divison of Mines and Geology Special Report 114, 115 p. 

Boore, D. M., and Joyner, W. B., 1978, The influence of rupture incoherence on seismic directivity: Bulletin of the Seismological 

Society of America, v. 68, p. 283-300. 

Bravinder, K. M., 1942, Los Angeles basin earthquake of October 21, 

1941, and its effect on certain producing wells in Dominguez field, 

Los Angeles County, California: Bulletin of the American Association of Petroleum Geologists, v. 26, p. 388-399. 

California Department of Water Resources, 1961, Planned utilization of 

the ground water basins of the coastal plain of Los Angeles County, 
Appendix A, Ground water geology: California Department of 

Water Resources Bulletin 104, 181 p. 

___ 1966, Planned utilization of ground water b·asins, San Gabriel 

Valley, Appendix A, Geohydrology: California Department of 

Water Resources Bulletin 104-2, 229 p. 

California Division of Highways, 1975, Highway damage in the San Fernando earthquake, in Oakeshott, G. B., ed., San Fernando, California, earthquake of 9 February 1971: California Division of Mines 

and Geology Bulletin 196, p. 369-379. 

California Division of Mines and Geology (1958-1969), Geologic atlas of 

California, Olaf P. Jenkins edition: Sacramento, Calif., 27 sheets, 

scale 1:250,000. 

California Water Rights Board, 1962, Report of referee, City of San Fernando: California Superior Court, County of Los Angeles no. 

650079, v. 1, 258 p. 

Campbell, R. H., 1975, Soil slips, debris flows, and rainstorms in the 

Santa Monica Mountains and vicinity, southern California: U.S. 

Geological Survey Professional Paper 851, 51 p. 

Castle, R. 0., and Yerkes, R. F., 1976, Recent surface movements in the 

Baldwin Hills, Los Angeles County, California: U.S. Geological 

Survey Professional Paper 882, 125 p. 

Durrell, C., 1954, Geology of the Santa Monica Mountains, Los Angeles 

and Ventura Counties: California Division of Mines and Geology 

Bulletin 170, map sheet 8, scale 1:125,000. 

Ehlig, P. L., 1982, Mechanics of the Abalone Cove landslide, including 

the role of ground water in landslide stability and a model for 

development of large landslides in the Palos Verdes Hills, in 

Cooper, J. D., compiler, Landslides and landslide abatement, Palos 

Verdes peninsula, southern California: Geological Society of 

America Annual Meeting (Cordilleran Section), 78th, Anaheim, 

Calif., 1982, Guidebook, p. 57-66. 

Evernden, J. F., Kohler, W. M., and Claw, G. D., 1981, Seismic intensities 

of earthquake of conterminous United States-Their prediction 

and interpretation: U.S. Geological Survey Professional Paper 

1223,56 p. 

Geller, R. J., 1976, Scaling relations for earthquake source parameters 

and magnitudes: Bulletin of the Seismological Society of America, 

v.66,p.1501-1523. 

Gilluly, J., and Grant, U.S., 1949, Subsidence in the Long Beach Harbor 

area, California: Geological Society of America Bulletin, v. 60, 

p. 461-530. 

Guptill, P. D., and Heath, E. G., 1981, Surface faulting along the 

Newport-Inglewood zone of deformation: California Geology, v. 34, 

p. 142-148. 

Hanks, T. C., and Kanamori, H., 1979, A moment magnitude scale: Journal of Geophysical Research, v. 84, p. 2348-2350. 

Harding, T. P., 1973, Newport-Inglewood trend, California-An example of wrenching style of deformation: Bulletin of the American 

Association of Petroleum Geologists, v. 57, p. 97-116. 

Harp, E. L., Keefer, D. K., and Wilson, R. C., 1980, A comparison of artificial and natural slope failures-The Santa Barbara earthquake 

of August 13, 1978: California Geology, v. 33, p. 102-105. 

Harp, E. L., Wilson, R. C., and Wieczorek, G. F., 1981, Landslides from 

the February 4, 1976, Guatemala earthquake: U.S. Geological 

Survey Professional Paper 1204-A, 35 p. 

Hartzell, S. H., and Heaton, T. H., 1983, Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of 

the 1979 Imperial Valley, California, earthquake: Bulletin of the 

Seismological Society of America, v. 73, p. 1553-1583. 

Hartzell, S. H., and Heimberger, D. V., 1982, Strong motion modeling of 

the Imperial Valley earthquake of 1979: Bulletin of the Seismological Society of America, v. 72, p. 571-596. 

Hill, R. L., Sprotte, E. C., Bennett, J. H., Chapman, R. H., Chase, G. W., 

Real, C. R., and Barchart, G., 1977, Santa Monica Raymond Hill 

fault zone study Los Angeles County, California: Menlo Park, Calif., 

final technical report to U.S. Geological Survey under contract 

14-080001-15858. 

Keefer, D. K., 1984, Landslides caused by earthquakes: Geological 

Society of America Bulletin, v. 95, no. 4, p. 406-421. 

Martner, S. T., 1948, The Dominguez Hills, California, earthquake of 

June 18, 1944: Bulletin of the Seismological Society of America, v. 

38, p. 105-119. 

McCulloh, T. H., 1960, Gravity variations and the geology of the Los 

Angeles basin of California, in Geological Survey research 

1960-Short papers in the geological sciences: U.S. Geological 

Survey Professional Paper 400--B, p. B320-B325. 

McGill, J. T., 1982, Preliminary geologic map of the Pacific Palisades 

area, city of Los Angeles, California: U.S. Geological Survey OpenFile Report 82-194, 15 p., 2 pls. 

Morton, D. M., 1971, Seismically triggered landslides in the area above 

the San Fernando Valley, in The San Fernando, California, earthquake of February 9, 1971: U.S. Geological Survey Professional 

Paper 733, p. 99-104. 

Olson, A. H., and Apsel, R. J., 1982, Finite faults and inverse theory with 

applications to the 1979 Imperial Valley earthquake: Bulletin of the 

Seismological Society of America, v. 72, p. 1969-2002. 

Olson, A. H., Orcutt, J. A., and Frazier, G. A., 1984, The discrete 

wavenumber/finite element method for synthetic seismograms: 

Geophysical Journal of the Royal Astronomical Society, v. 77, 

p. 421-460. 

Teng, T. L., Real, C. R., and Henyey, T. L., 1973, Microearthquakes and 

water flooding in Los Angeles: Bulletin of the Seismological Society 

of America, v. 63, p. 859-875. 

Toppozada, T. R., and Parke, D. L., 1982, Areas damaged by California 

earthquakes, 1900--1949: California Division of Mines and Geology 

Open-File Report 82-17 SAC, 65 p. 

Waananen, A. 0., and Moyle, W. R., Jr., 1971, Water-resource aspects, 

in The San Fernando, California, earthquake of February 9, 1971: 

U.S. Geological Survey Professional Paper 733, p. 119-125. 

__ 1972, Water-resource effects, in The Borrego Mountain earthquake of April 9, i968: U.S. Geological Survey Professional Paper 

787, p. 183-189. 

Weber, F. H., Jr., 1979, General features of landsliding and debris 

flooding in southern California, in Landslides in the Los Angeles 

region, California-Effects of February-March 1978 rains: California Division of Mines and Geology Open-File Report 79-4 LA, 

p. 15-47. 

__ 1980, Landsliding and flooding in southern California during the 

winter of 1979-80: California Division of Mines and Geology OpenFile Report 80--3 LA, 69 p. 

__ ed., 1982, Slope stability and geology of the Baldwin Hills, Los 

Angeles County, California: California Division of Mines and Geology Special Report 152, 93 p. 

Wentworth, C. M., Ziony, J. 1., and Buchanan, J. M., 1970, Preliminary 

geologic environmental map of the greater Los Angeles area, 

California: Springfield, Va., National Technical Information Service TID-25363, 41 p., 1:250,000 scale. (Available in microfiche 

only.) 

Woodward-Clyde Consultants, 1979, Report on the evaluation of maximum earthquake and site ground motion parameters associated 

with the Offshore Zone of Deformation, San Onofre Nuclear 

Generating Station: Los Angeles, Calif., report prepared for 

Southern California Edison, 56 p. 

Yeats, R. S., 1973, Newport-Inglewood fault zone, Los Angeles basin, 

California: Bulletin of the American Association of Petroleum 

Geologists, v. 57, p. 117-135. 

Yen, B. C., and Trotter, J. R., 1978, Shallow slides due to 1971 San Fernando earthquake, in Earthquake engineering and soil dynamics: 

References Cited 501 
Proceedings of the American Society of Civil Engineers 

Geotechnical Engineering Division Specialty Conference, v. 2, 

p. 1076-1096. 

Yerkes, R. F., and Campbell, R. H., 1980, Geologic map of east-central 

Santa Monica Mountains, Los Angeles County, California: U.S. 

Geological Survey Miscellaneous Investigations Map I-1146, scale 

1:24,000. 

Yerkes, R. F., McCulloh, T. H., Schoellhamer, J. E., and Vedder, J. G., 

1965, Geology of the Los Angeles basin, California-An introduction: U.S. Geological Survey Professional Paper 420-A, 57 p. 

Youd, T. L., 1980, Ground failure displacement and earthquake damage 

to buildings: American Society of Civil Engineers Conference on 

Civil Engineering and Nuclear Power, 2d, Knoxville, Tenn., 1980, v. 

2, p. 7-6-2-7.{).26. 

Youd, T. L., and Perkins, D. M., 1978, Mapping liquefaction-induced 

ground failure potential: Proceedings of the American Society of 

Civil Engineers, Journal of the Geotechnical Engineering Division, 

v. 104, no. GT 4, p. 433-446. 

Youd, T. L., and Wieczorek, G. F., 1982, Liquefaction and secondary 

ground failure, in The Imperial Valley earthquake of October 15, 

1979: U.S. Geological Survey Professional Paper 1244, p. 223-246. 

Using Earth-Science Information for Earthquake Hazard Reduction 

Algermissen, S. T., Hopper, M. G., Campbell, Kenneth, Rinehart, W. A., 

Perkins, D. M., Steinbrugge, K. V., Lagorio, H. J., Moran, D. F., 

Cluff, L. S., Degenkolb, H. J., Duke, C. M., Gates, G. 0., Jacobson, 

D. W., Olson, R. A., and Allen, C. R., 1973, A study of earthquake 

losses in the Los Angeles, California, area: Boulder, Colo., National 

Oceanic and Atmospheric Administration Environmental Research 

Laboratories, report prepared for the Federal Disaster Assistance 

Administration, 331 p. 

Algermissen, S. T., Perkins, D. M., Thenhaus, P. C., Hanson, S. L., an!l 

Bender, B. L., 1982, Probabilistic estimates of maximum acceleration and velocity in rock in the contiguous United States: U.S. 

Geological Survey Open-File Report 82-1033, 107 p. 

American Institute of Architects Research Corporation, 1975, Architects and engineers: Washington, D.C., 94 p. 

Association of Engineering Geologists, 1973, Guidelines to 

geologic/seismic reports: California Division of Mines and Geology 

Note37, 2 p. 

Barrows, A. G., Kahle, J. E., and Beeby, D. J., 197~. Geology and fault activity of the Palmdale segment of the San Andreas fault zone, Los 

Angeles County, California: California Division of Mines and 

Geology Open-File Report 76-6 LA, 30 p. 

Blair, M. L., and Spangle, W. E., 1979, Seismic safety and land-use planning-Selected examples from California: U.S. Geological Survey 

Professional Paper 941-B, 82 p. · 

Blume, J. A., Scholl, R. E., Somerville, M. R., and Honda, K. K., 1978, 

Damage prediction of an earthquake in southern California: Menlo 

Park, Calif., final technical report to U.S. Geological Survey under 

contract 14--06-0001-15889,83 p. 

Bonilla, M. G., 1970, Surface faulting and related effects, in Weigel, 

R. L., ed., Earthquake engineering: Englewood Cliffs, N.J., PrenticeHall, p. 47-74. 

Brown, R. D., Jr., and Kockelman, W. J., 1983, Geologic principles for 

prudent land-use-A decisionmaker's guide for the San Francisco 

Bay region: U.S. Geological Survey Professional Paper 946, 97 p. 

California Assembly Select Committee on Landslide Prevention, 1980, A 

report based on committee hearing, Sacramento, California, April 

18, 1980: Sacramento, Calif., California State Assembly Publications,22p. 

California Association of Realtors, 1977, Disclosure of geologic hazards: 

Los Angeles, Calif., 43 p. 

___ 1978, Special studies zone and flood hazard disclosure-Standard form SSD-FHD-11: Los Angeles, Calif., 1 p. 

___ 1981, Real estate purchase contract and receipt for 

deposit-Standard form D-11-1, -2: Los Angeles, Calif., 2 p. 

California Legislature, 1971, Local planning laws, as amended: Sec. 

65300 and following, West's annotated California government 

code. 

502 Earthquake Hazards in the Los Angeles Region 

___ 1972, Alquist-Priolo Special Studies Zones Act, as amended, in 

California public resources code: Sec. 2621 and following, West's 

annotated California government code. 

California Building Safety Board Geotechnical Subcommittee, 1975, 

Recommended guidelines for determining the maximum credible 

and the maximum probable earthquakes: California Division of 

Mines and Geology Note 43, 1 p. 

California Department of Insurance, 1982, California earthquake zoning and probable maximum loss program-An estimate of potential insured earthquake loss from analysis of data sumbitted by 

property and casualty companies in California: Sacramento, Calif., 

41p. 

California Department of Water Resources, 1981, Earthquake inspection, in Earthquake safety and response plan: Castaic, Calif., sec. 

8.0, p. 142-168. 

California Division· of Highways, 1972, After quake disaster. .. the 

hard road back: Highway News Bulletin, District 7, Los Angeles, 

Spring 1972, 7 p. 

California Division of Mines and Geology, [1958-1969], Geologic atlas 

of California, Olaf P. Jenkins edition: Sacramento, Calif., 27 map 

sheets, 1:250,000 scale. 

___ 1975, Recommended guidelines for geologic reports on offshore 

operations and facilities: Note 47, 2 p. 

___ 1979, Ritter Ridge quadrangle: Sacramento, Calif., Special 

Studies Zones Map, scale 1:24,000. 

California Education Code, 1933, as amended: Sec. 39140 and following, 81130 and following, 39210 and following, 81160 and following; 39002, 81003 and following, West's annotated California education code. 

California Office of Planning and Research, 1980, General plan 

guidelines (revised Dec. 17, 1982): Sacramento, Calif., 348 p. 

California Public Utilities Commission, 1979, Rules governing design, 

construction, testing, maintenance, and operation of utility gas 

gathering, transmission, and distribution piping systems, pt. III, 

Liquefied natural gas facilities safety standards of general order 

no. 112-D: San Francisco, Calif., p. III-B-7-III-B-30, app. B. 

California Seismic Safety Commission Hazardous Buildings Committee, 

1979, Hazardous buildings-Local programs to improve life safety 

(revised February 1980): Sacramento, Calif., 158 p. 

Clark, M. M., Grantz, Arthur, and Rubin, Meyer, 1972, Holocene activity of Coyote Creek fault as recorded in sediments of Lake Cahuilla: 

U.S. Geological Survey Professional Paper 787, p.112-130. 

Conway, B. J., Fong, P. T., Hawkins, G. H., and Ostrom, D. K., 1978, 

Seismic design guidelines for substation facilities: Transactions on 

Power, Apparatus, and Systems, v. PAS-97, no. 3, p. 703-713. 

Davis, J. F., Bennett, J. H., Borchardt, G. A., Kahle, J. E., Rice, S. J., and 

Silva, M. A., 1982, Earthquake planning scenario for a magnitude 
8.3 earthquake on the San Andreas fault in southern California: 

California Division of Mines and Geology Special Publication 60, 

128p. 

Dibblee, T. W., Jr., 1950, Geology of southwestern Santa Barbara County, California: California Division of Mines and Geology Bulletin 

150,95 p. 

___ 1966, Geology of the Central Santa Ynez Mountains, Santa Barbara County, California: California Division of Mines and Geology 

Bulletin 186, 99 p. 

___ 1973, Stratigraphy of the southern Coast Ranges near the San 

Andreas fault from Cholame to Maricopa, California: U.S. Geological Survey Professional Paper 764, 45 p. 

Dunne, R. G., ed., 1978, Consensus report of the Task Force on Earthquake Prediction; City of Los Angeles: Los Angeles, Calif., 47 p. 

Eberhart-Axten and Associates, Inc., 1980, Fault investigation and 

evaluation of surface rupture, 128-acre site, Leona Valley, California: Anaheim, Calif., 12 p. 

Envirocom Corporation, 1974, Safety and seismic safety elements, comprehensive general plan, City of Simi Valley: Sherman Oaks, Calif., 

69p. 

Evenson, R. E., and Miller, G. A., 1963, Geology and ground-water 

features of Point Arguello Naval Missile Facility, Santa Barbara 

County, California: U.S. Geological Survey Water-Supply Paper 

1619-F, 35 p. 

Evernden, J. F., Kohler, W. M., and Glow, G. D., 1981, Seismic intensities 

of earthquakes of conterminous United States-Their prediction 

and interpretation: U.S. Geological Survey Professional Paper 

1223,56 p. 

Federal Emergency Management Agency, 1980, An assessment of the 

consequences and preparations for a catastrophic California 

earthquake; findings and actions taken: Prepared from analyses 

carried out by the National Security Council ad hoc committee on 

assessment of consequences and preparations for a major California earthquake, M&R-2, January 1981: Washinglon, D.C., 59 p. 

Fife, D. L., Rodgers, D. A., Chase, G. W., Chapman, R. H., Sprotte, E. C., 

and Morton, D. M., 1976, Geologic hazards in southwestern San 

Bernardino County, California: California Division of Mines and 

Geology Special Report 113, 40 p. 

Gates, J. H., 1976, California's seismic design criteria for bridges: Proceedings of the American Society of Civil Engineers, Journal of the 

Structural Division, v. 102, no. ST-12, p. 2301-2313. 

Greensfelder, R. W., 1972, Maximum credible bedrock acceleration 

from earthquakes in California: California Division of Mines and 

Geology Map Sheet 23, scale 1:2,000,000. (Revised August 1974; 

modified by California Department of Transportation Office of 

Structures, October 1974.] 

___ 1973, A map of maximum expected bedrock accleration from 

earthquakes in California: Sacramento, Calif., report accompanying California Division of Mines and Geology Map Sheet 23, 19 p. 

Hamilton, R. M., Yerkes, R. F., Brown, R. D., Jr., Burford, R. 0., and 

DeNoyer, J. M., 1969, Seismicity and associated effects, Santa Barbara region, in Geology, petroleum development, and seismicity of 

the Santa Barbara channel region, California: U.S. Geological 

Survey Profes~ional Paper 679--D, p. 47-68. 

Hart, E. W., 1980, Fault-rupture hazard zones in California: California 

Division of Mines and Geology Special Publication 42, 25 p. 

Hart, E. W., Bortugno, E. J., and Smith, T. C., 1977, Summary report; 

fault evaluation program, 1976 area (western Transverse Ranges]: 

California Division of Mines and Geology Open-File Report 78-10 

SF,13 p. 

Hart, E. W., Smith, D. P., and Smith, T. C., 1978, Summary report; fault 

evaluation program, 1977 area (Los Angeles basin region]: California Division of Mines and Geology Open-File Report 78-10 SF, 16 p. 

Hart, E. W., Smith, D. P., and Saul, R. B., 1979, Summary report; fault 

evaluation program, 1978 area (Peninsular Ranges-Salton Trough 

region]: California Division of Mines and Geology Open-File Report 

79-10 SF, 17 p. 

Hays, W. W., 1980, Procedures for estimating earthquake ground motions: U.S. Geological Survey Professional Paper 1114, 77 p. 

Hoffman, Richard, Meunier, Gary, and Kibbee, joel, 1983, A database 

and pilot study design for the southern California region: Los 

Angeles, Calif., Southern California Association of Governments, 

11p. 

International Conference of Building Officials, 1979, Uniform building 

code: Whittier, Calif., 734 p. 

Jansen, R. B., Dukleth, G. W., and Barrett, K. G., 1976, Problems of 

hydraulic fill dams, in International Congress on Large Dams, Mexico City 1976, Proceedings: Q.14, R.16, p. 337-364. 

Kockelman, W. J., 1975, Use of U.S. Geological Survey earth-science 

products by city planning agencies in the San Francisco Bay 

region, California: U.S. Geological Survey Open-File Report 

75-276, 110 p. 

___ 1976, Use of U.S. Geological Survey earth-science products by 

county planning agencies in the San Francisco Bay region, California: U.S. Geological Survey Open-File Report 76-547, 186 p. 

___ 1979, Use of U.S. Geological Survey earth-science products by 

selected regional agencies in the San Francisco Bay region, 

California: U.S. Geological Survey Open-File Report 79--221, 173 p. 

___ 1980, Examples of the use of earth-science information by decisionmakers in the San Francisco Bay region, California: U.S. Geological Survey Open-File Report 80-124, 88 p. 

Kockelman, W. J., and Brabb, E. E., 1978, Examples of seismic zonation 

in the San Francisco Bay region, in Brabb, E. E., ed., 1979, Progress 

on seismic zonation in the San Francisco Bay region: U.S. 

Geological Survey Circular 807, p. 73-84. 

Lamar, D. L., Merifield, P. M., and Proctor, R. J., 1973, Earthquake 

recurrence intervals on major faults in southern California, in 

Geology, seismicity, and environmental impact: Los Angeles, Calif., 

Association of Engineering Geologists, p. 265-276. 

LNG Seismic Review Panel, 1981, Seismic safety review of the proposed 

liquefied natural gas facility, Little Cojo Bay, Santa Barbara County, California: Report prepared for the California State Public 

Utilities Commission, 33 p. 

Los Angeles City Council, 1981, Ordinance no. 154,807 relative to earthquake hazard reduction in existing buildings: Los Angeles 

Municipal Code, ch. IX, art. 1, div. 68,. sec. 91.6801 and following. 

Los Angeles City Office of the Mayor, 1980, Emergency operations 

organization, earthquake prediction response plan (2d draft]: City 

of Los Angeles Civil Defense and Disaster Board, 172 p. 

Los Angeles City Planning Department, 1979, Draft environmental impact report on earthquake hazard reduction in existing buildings 

constructed before 1934 in the City of Los Angeles (amended September 1980]: Environmental Review Section EIR 583-78-CW, 

36 p., 3 exhibits, 2 apps. 

___ 1980, Final environmental impact report on earthquake hazard 

reduction in existing buildings constructed before 1934 in the City 

of Los Angeles: Environmental Review Section EIR 583-78-CW, 

84p. 

Los Angeles County Department of County Engineer, 1977, Engineering 

geologic report, Skyline south easement (south segment], county 

water works district no. 29-Malibu: Los Angeles, Calif., Engineering Geology Section, 10 p. 

Los Angeles County Department of County Engineer-Facilities, 1979, 

Preliminary geologic study, Kanan Dume Road cut failure, stations 

132 to 136, March 1979: Los Angeles, Calif., Environmental 

Development Division, 5 p. 

Los Angeles County Department of Regional Planning, undated, Content 

and format for environmental impact reports-Geotechnical 

hazards: Los Angeles, Calif., 3 p. 

___ 1974, Seismic safety element: Los Angeles, Calif., 170 p. 

References Cited 503 
__ 1980, General plan: Los Angeles, Calif., 435 p. 

Los Angeles Comity Sheriffs Department, undated, Computer-assisted 

communication system: Los Angeles, Calif., 8 p. 

Los Angeles Department of City Planning, 1974, Seismic safety plan; a 

portion of the general plan of the City of Los Angeles; adopted by 

the Los Angeles City Council, September 10, 1975: Los Angeles, 

Calif., file no. 74-3401, 14 p. 

Los Angeles Earthquake Safety Study Committee, 1978, Division 

58-Earthquake hazard reduction in existing buildings: Preliminary draft as approv~ by the Earthquake Safety Study Committee, November 9, 1978: Los Angeles, Calif., 13 p. 

Los Angeles Unified School District, 1975, Emergency procedures: Los 

Angeles, Calif., Student Auxiliary Services Branch, p. 30-35. 

Mancarti, G. D., 1981, New concepts in earthquake retrofitting of 

highway bridges: Paper presented at Northwest Bridge Engineers 

Conference, Boise, Ida., 1981, 22 p. 

Metropolitan Water District of Southern California Earthquake Committee, 1978, Emergency response plan-General procedures (revised August 1981): Los Angeles, Calif., 34 P~ 8 apps. 

Muir, K. S., 1968, Ground-water reconnaissance of the Santa BarbaraMontecito area, Santa Barbara County, California: U.S. Geological 

Survey Water-Supply Paper 1859-A, 28 p. 

Orange County Environmental Management Agency, 1975, Safety element, amended October 1977: Santa Ana, Calif., 67 p. 

Ostrom, D. K., 1976, The need for a seismic design guide: Journal of Environmental Sciences, v. 19, no. 2, p. 28--33. 

Pate, M.-E., and Shah, H. C., 198o; Public policy issues-Earthquake 

engineering: Bulletin of the Seismological Society of America, v. 70, 

no.5,p.1955-1968. 

Portohi Valley Town Council, 1973, Zoning regulations: Ordinance no. 

1967-80, sec. 6209.2. 

Richter, C. F., 1958, Elementary seismology: San Francisco, W. H. 

Freeman, 768 p. 

Riverside County Planning Department, 1978, Seismic safety/safety 

plan elements-Policy report: Riverside, Calif., 51 p. 

Robinson, G. D., and Spieker, A. M., eds., 1978, "Nature to be commanded ... ": U.S. Geological Survey Professional Paper 950, 95 p. 

San Bernardino County Planning Department, 1979, Consolidated 

general plan and implementation system: San Bernardino, Calif., 

141p. 

San Diego County Environmental Development Agency, 1975, Seismic 

safety element; San Diego County general plan, pt. V: San Diego, 

Calif.,14p. 

San Fernando Valley Board of Realtors, Inc., 1976, Realtor report: Van 

Nuys, Calif., v. 56, no. 20, 9 p. 

Santa Ana City Council, 1981, Seismic safety ordinance: Ordinance no. 

NS-1518 as amended by ordinance no. NS-1598, art. XI, sec. 

8--2000 and following. 

Santa Barbara County Planning Department, 1979, Seismic safety and 

safety element: Santa Barbara, Calif., 207 p. 

Sarna-Wojcicki, A. M., Williams, K. M., and Yerkes, R. F;, 1976, 

GtlQlogy of the Ventura fault, Ventura County, California: U.S. 

Geological Survey Miscellaneous Field Studies Map MF-781, scale 

1:6,000. 

Seed, H. B., and Schnabel, P. B., 1972, Accelerations in rock for earthquakes in the Western United States: Berkeley, Calif., Report 72-2, 

University of California Earthquake Engineering Research Center, 

15p. 

Sharp, R. V., 1972, Map showing recently active breaks along the San 

Jacinto fault zone between the San Bernardino area and Borrego 

Valley, California: U.S. Geological Survey Miscellaneous Geologic 

Investigations Map I-675, scale 1:24,000. 

Southern California Association of Governments, 1982, Executive summary of draft environmental impact report on Draft SCAG-82 

growth forecast policy: Los Angeles, Calif., 36 p. 

504 Earthquake Hazards in the Los Angeles Region 

Southern California Earthquake Preparedness Project and California 

State Seismic Safety Commission, 1981, Work program: Van Nuys, 

Calif., 28 p. 

Southern California Earthquake Preparedness Project and Environmental Volunteers, Inc., 1983, Hands on earthquake learning 

package-Instructor's guide: Van Nuys, Calif., 104 p. 

Spangle and Associates, Inc., Degenkolb, and Associates, and Earth 

Sciences Associates, 1980, Land use planning after earthquakes: 

Portola Valley, Calif., 158 p. 

___ 1981, Research program for pre-earthquake planning, 

1981-1983: Portola Valley, Calif., National Science Foundation, 

Project CEE 8024724, 19 p. 

Sunset Magazine, 1982, Getting ready for a big quake: Menlo Park, 

Calif., Lane Publishing Company, March, p. 104-111. 

Thenhaus, P. C., Perkins, D. M., Ziony, J. I., and Algermissen, S. T., 

1980, Probabilistic estimates of maximum seismic horizontal 

ground motion on rock in coastal California and the adjacent outer 

continental shelf: U.S. Geological Survey Open-File Report 80-924, 

69p. 

United Nations, 1976, Guidelines for disaster prevention, v. 2, Building 

measures for minimizing the impact of disasters: Geneva, Office of 

the United Nations Disaster Relief Coordinator, 59 p. 

University of California Center for Planning and Development 

Research, 1982, An earthquake advisor's handbook for woodframe houses: Berkeley, Calif., College of Environmental Design, 

90p. 

Upson, J. E., 1951, Geology and ground-water resources of the south 

coast basins of Santa Barbara County, California: U.S. Geological 

Survey Water-Supply Paper 1108, 144 p. 

U.S. Department of Housing and Urban Development, 1980, The home 

builder's guide for earthquake design: Office of Policy Development and Research Guideline 6, 57 p. 

U.S. Geological Survey, 1981, Scenarios of possible earthquakes affecting major California population centers, with estimates of intensity 

and ground shaking: U.S. Geological Survey Open-File Report 

81-115, 36p. 

U.S. Nuclear Regulatory Commission, 1981, NRC staffs proposed findings of fact and conclusions of law in the form of a proposed initial 

decision before the Atomic Safety and Licensing Board in the matter of Southern California Edison Company, et al.: Washington, 

D.C., docket nos. 50-361 OL, 50-362 OL, 112 p. 

Ventura County Department of Public Works, 1974, Recommended 

guidelines for preparing engineering geologic reports: California 

Division of Mines and Geology Note 44, 2 p. 

Ventura County Environmental Resources Agency, 1974, Seismic safety 

and safety element of the general plan: Ventura, Calif., 303 p. 

Wallace, R. E., 1970, Earthquake recurrence intervals on the San 

Andreas fault: Geological Society of America Bulletin, v. 81, 

p. 2875-2890. 

Weber, F. H., Jr., 1977, Seismic hazards related to geologic factors, 

Elsinore and Chino fault zones, northwestern Riverside County, 

California: California Division of Mines and Geology Open-File 

Report 77-4 LA, 96 p. 

Weber, F. H., Jr., Kiessling, E. W., Sprotte, E. C., Johnson, J. A., Sherburne, R. W., and Cleveland, G. B., 1975, Seismic hazards study of 

V~tura County: California Division of Mines and Geology OpenFile Report 78--5 LA, 396 p. 

Wiggins, J. H., Jr., and Moran, D. F., 1971, Earthquake safety in the city 

of Long Beach based on the concept of "balanced risk": Redondo 

Beach, Calif., J. H. Wiggins, 128 p. 

Woodring, W. P., and Bramlette, M. N., 1950, Geology and paleontology 

of the Santa Maria Dist..fi~t. California: U.S. Geological Survey Professional Paper 222, 185 p. 
Woodward-Gizienski and Associates and F. Beach Leighton and 

Associates, 1974, Seismic safety study for the city of San Diego: 

San Diego, Calif., 41 p. 

Woodward-McNeill and Associates, 1975, Draft seismic safety element: 

Orange, Calif., 167 p: 

Worts, G. F., Jr., 1951, Geology and ground-water resources of the 

Santa Maria Valley area, California: U.S. Geological Survey 

Water-Supply Paper 1000, 169 p. 

Youd, T. L., Tinsley, J. C., Perkins, D. M., King, E. J., and Preston, R. F., 

1979, Liquefaction potential map of San Fernando Valley, California, in Brabb, E. E., ed., 1979, Progress on seismic zonation in the 

San Francisco Bay region: U.S. Geological Survey Circular 807, 

p. 37-48. 

<>U.S. GOVERNMENT PRINTING OFFICE: 1985-461-436Y20010 

Youd, T. L., Yerkes, R. F., and Clark, M. M., 1978, San Fernando 

faulting damage and its effect on land use, in Speciality Conference on Earthquake Enginering and Soil Dynamics, Proceedings: 

Pasadena, Calif., American Society of Civil Engineers, 

p. 1111-1125. 

Ziony, J. I., Wentworth, C. M., and Buchanan, J. M., 1973, Recency of 

faulting; a widely applicable criterion for assessing the activity of 

faults: World Conference on Earthquake Engineering, 5th, Rome 

1973, v. 2, p. 168Q-1691. 

Ziony, J. I., Wentworth, C. M., Buchanan-Banks, J. M., and Wagner, 

H. C., 1974, Preliminary map showing recency of faulting in 

coastal southern California: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-585, scale 1:250,000, 8-p. text. 

References Cited 505