Seismic Hazards and 

Land-Use Planning 

GEOLOGICAL SURVEY CIRCULAR 690 

Seismic Hazards and Land-Use Planning 

By D. R. Nichols and J. M. Buchanan-Banks 

G E 0 L 0 G I C A L S U R V E Y C I R C U L A R 690 

Washington 1974 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

First printing 1974 

Second printing 1974 

Third printing 1975 

Fourth printing 1980 

Fifth printing 1990 

Free on application to the Books & Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225 
CONTENTS 

Page 

Abstract-------------------------------------------- 1 

Introduction ---------------------------------------- 1 

Acknowledgments ---------------------------------- 1 

Seismic hazards and implications for land use ________ 2 

Surface faulting -------------------------------- 2 

Methods for assessing fault hazards __________ 5 

Implications for planning and land-use controls 6 

Ground shaking -------------------------------- 10 

Methods for assessing shaking hazards________ 13 

Implications for planning and land use________ 15 

Ground failure---------------------------------- 16 

Mechanisms of failure ---------------------- 18 

Results of ground failure -------------------- 18 

Page 

Seismic hazards and implications for land use-Con. 

Ground failure-Continued ----------------------

Methods for assessing ground failure hazards__ 20 

Implications for planning and land-use controls 20 

Tectonic deformation ---------------------------- 23 

Tsunami and seiche effects ----------------------

Methods for assessing wave and flooding hazards 

Implications for planning and land-use controls 

24 

26 

26 

Earth-science data needed to assess seismic hazards __ 28 

Principal sources of geologic and seismic data ________ 29 

Glossary ____________________________________________ 30 

References cited ------------------------------------ 32 

ILLUSTRATIONS 

Page 

FIGURE 1. Photograph of house damaged by reverse faulting, San Fernando earthquake__________________________ 3 

2. Map of recently active breaks along the San Andreas fault near Point Arena, Calif -------------------- 4 

3. Sketch of progressive lateral displacement along a single trace of the San Andreas fault________________ 5 

4. Map showing relation of branch and secondary faults to the main fault trace -------------------------- 6 

5. Graph of relationship of amount of displacement to length of surface rupture on the main fault trace____ 6 

6. Block diagrams of examples of some types of fault displacement and earth flexure -------------------- 7 

7. Photograph of curb displaced by fault creep on the Hayward fault ------------------------------------ 7 

8. Photograph of corral fence deformed and displaced 21 inches by creep along the San Andreas fault______ 8 

9. Map showing the location of USGS seismograph stations in central California ------------------------ 9 

10. Sketch showing example of minimum building setback easements along active fault traces in Portola Valley, 

Calif ---------------------------------------------------------------------------------------- 10 

11. Oblique aerial view of the approximate location of fault traces within a part of the Hayward fault zone__ 11 

12. Map showing schools, hospitals, and other public buildings on or near the traces of part of the Hayward fault 12 

13. Aerial photograph of San Francisco showing relationship of greatest damage in the 1906 earthquake to areas 

of former bay and marshlands------------------------------------------------------------------ 13 

14. Graph relating structural damage intensity for different height buildings to depth of soil -------------- 14 

15. Seismograph records showing the differences in amplification of energy with increased thickness of bay mud 16 

16-24. Photographs of: 

16. Unreinforced parapets which collapsed and caused severe damage during moderate Santa Rosa earthquake------------------------------------------------------------------------------------ 17 

17. Sand, liquefied during the 1973 Point Mugu earthquake, which fails to support the weight of a man 18 

18. The Juvenile Hall landslide generated by the 1971 San Fernando earthquake -------------------- 19 

19. Tilting and sinking of buildings, caused by liquefaction, during the 1964 Niigata, Japan, earthquake 

and residents salvaging belongings by carrying them down the exterior walls of apartment 

building --------------------------------------------------------------------------------- 20 

20. Lateral spreading of soft, surficial materials during the 1973 Point Mugu earthquake-------------- 20 

21. Ground cracks in flood-plain sediments from 1964 Alaskan earthquake____________________________ 21 

22. Ground lurching in tidal muds of Tomales Bay, Calif. from 1906 earthquake ---------------------- 21 

23. Sand volcanoes formed during the 1973 Point Mugu earthquake---------------------------------- 22 

24. Sand ridges formed by the 1964 Alaskan earthquake -------------------------------------------- 23 

25. Map showing landslide distribution in Mount Diablo area, California -------------------------------- 24 

26. Photograph of regional flooding of the Portage, Alaska, area due to tectonic land changes -------------- 25 

27. Photograph of tsunami damage from 1964 Alaskan earthquake -------------------------------------- 26 

28. Sketch map of Vaiont Reservoir, Italy, and flooded area from landslide-induced waves__________________ 27 

29. Photograph of destruction area from a giant wave caused by a rockslide in Lituya Bay, Alaska -------- 27 

III 
TABLE 

Page 

TABLE 1. Some economic costs resulting from development on unstable areas ------------------------------------ 23 

IV 
Seismic Hazards and land-Use Planning 

By D. R. Nichols and J. M. Buchanan-Banks 

ABSTRACT 

Basic earth-science data are necessary for a realistic assessment of seismic hazards and as a basis for limiting corrective 

land-use controls only to those areas of greatest hazard. For 

example, the location, character, and amount of likely displacement and activity of surface faulting can be predicted if 

detailed geologic maps and seismic data are available and are 

augmented by field studies at critical localities. Because few 

structures can withstand displacement of their foundations, 

they should be located off active fault traces, the distance varying with the character of faulting, the certainty with which 

fault traces are known, and the importance of the structure. 

Recreational activities and other nonoccupancy land uses 

should be considered for fault zone areas where land is under 

pressure for development; elsewhere, such areas should remain 

as open space. 

Two methods of predicting ground shaking effects have applications to land-use decisions: (1) Relative earthquake effects 

can be related to firmness of the ground and can be used in a 

gross way to allocate population density in the absence of more 

sophisticated analyses; and (2) intensity maps, based on, (a) 

damage from former earthquakes, or (b) a qualitative analyses 

of geologic units added to a design earthquake, can be helpful 

both for general and specific plans. Theoretical models are used 

with caution to predict ground motion for critical structures to 

be located at specific sites with unique foundation conditions. 

Fully adequate methods of assessing possible shaking remain 

to be developed. Where land-use decisions do not reflect likely 

ground shaking effects, stringent building codes are needed, 

particularly for important structures. 

Ground failure (landsliding, ground cracking and lurching, 

differential settlement, sand boils, and subsidence) commonly 

results from liquefaction, loss of soil strength, or compaction. 

Areas suspected of being most likely to fail should not be developed unless detailed site studies can demonstrate the hazard 

does not exist or can be overcome. Various methods can be used 

to reduce the high, long-term public costs that follow development of unstable ground. However, areas subject to tectonic 

deformation generally cannot be predicted nor can effects of 

such deformation be minimized. 

Large water waves, such as produced by tsunamis, seiches, 

and dam failure or overtopping, can be anticipated in many 

places. Their effects can be lessened by land-use regulations 

similar to flood-plain zoning, restrictions on location of critical 

structures, and appropriate warning systems. 

Many local, state, and federal government agencies, univer1 

sities, and private consultants may be able to assist planners by 

advising them of pertinent data and where those data can be 

obtained. Interpretation of the data for an evaluation of seismic 

risk commonly requires a team of planners, geologists, and soil 

and structural engineers. 

INTRODUCTION 

Urban planners and public officials in California and in many other parts of the United States 

have become increasingly concerned about the 

possible effects of future earthquakes and how to 

minimize damage and reduce loss of life. Interest 

in seismic hazards has increased further after the 

adoption in 1971 by the California legislature of 

an amendment to the State Planning Law that 

includes a uSeismic Safety Element" as amandatory element of the General Plan (Chapter 150, 

Section 65302 of the Government Code). This requirement, along with concerns for other geologic 

hazards and for conservation of natural resources, 

has focused the attention of planners on the contributions that geology and other earth sciences 

can make to the planning process. 

This report outlines those earthquake-induced 

geologic conditions that could be hazardous, the 

type of problems they may pose, how information 

can be obtained to assess the degree of hazard, and 

some possible implications to land use. The availability of earth-science information, of itself, does 

not insure that it will be used (Mader, 1972, p. 78). 

However, where it exists and the citizenry is 

aware and concerned, significant steps can and 

have been taken to amend land-use policies to 

reflect seismic and geologic conditions even without legislative encouragement (City of Hayward, 

Planning Commission Subcommittee on Land Use 

and Development Regulations, 1972). 

ACKNOWLEDGMENTS 

This report is modified from a draft report prepared by the senior author on behalf of the Land 
Use Planning Advisory Group to the California 

Joint Legislative Committee on Seismic Safety. 

The draft report was designed to provide 

guidelines for the preparation of a seismic safety 

element to city and county general plans. Both 

reports benefit greatly from the advice and 

comments of several members of the Land Use 

Planning Advisory Group, particularly those of its 

chairman, Mr. George G. Mader. Several city and 

county planners and earth-science consultants in 

the San Francisco Bay area also offered valuable 

suggestions. 

Except where noted, all photographs are from 

the files of the U.S. Geological Survey. 

SEISMIC HAZARDS AND IMPLICATIONS 

FOR LAND USE 

Earthquakes commonly give rise to various 

geologic processes that may cause severe damage 

to structures and death to people in them. These 

processes include surface faulting, ground shaking, associated ground failure, generation of large 

waves in bodies of water, and regional subsidence 

or downwarping. 

These seismic hazards vary widely from area to 

area, and the level of hazard depends on both 

geologic conditions and the extent and type ofland 

use. This section describes geologic conditions that 

may contribute to seismic (italicized words are 

defined in the glossary) hazard, how to determine 

their significance in a given area, the level of data 

desirable for land use decisions, and some possible 

implications for land use. 

SURFACE FAULTING 

The earth is laced with faults-planes or surfaces in earth materials along which failure has 

occurred and materials on opposite sides have 

moved relative to one another in response to the 

accumulation of stress. Most of these faults have 

not moved for hundreds of thousands or even millions of years and thus can be considered inactive. 

Others, however, show evidence of current activity 

or have moved recently enough to be considered 

active, that is, capable of displacement in the near 

future. Any fault movement beneath a building in 

excess of an inch or two could have catastrophic 

effects on the structure, depending upon design 

and construction and the shaking stresses the 

structure undergoes at the same time (fig. 1). 

Therefore, it is important to know not only which 

faults may move but how they may move. 

The definition of what constitutes an ((active 

2 

fault" may vary greatly according to the type of 

land use contemplated or to the importance of the 

structure. For example, the Atomic Energy Commission regards a fault as active or ucapable" with 

respect to nuclear reactor sites if it has moved uat 

or near the ground surface at least once in the past 

35,000 years," or umore than once in the past 

500,000 years" (Atomic Energy Commission, 

1971). A definition for purposes of town planning 

in New Zealand defines as active, any fault on 

which movement has taken place at least once in 

the last 20,000 years (Town and Country Planning 

Branch, Ministry of Works, 1965; originally published as 1,000 years by typographical error). 

Commonly, faults are regarded as active and of 

concern to land-use planning when there is evidence that they have moved during historic time 

or, through geologic evidence, there is a significant 

likelihood that they will move during the projected 

use of a particular structure or piece of land. Because geologic evidence may be lacking, obscure, 

or ambiguous as to specific times of past movement, geologists may be able to estimate relative 

degree of activity only after a regional analysis 

that may extend far beyond the locality up.der 

consideration. Such analysis may be based on historic evidence of fault movement, seismic activity 

(occurrence of small to moderate earthquakes 

along the fault trace even though not accompanied 

by obvious fault movement), displacement of recent earth layers (those deposited during the past 

10,000 years), and presence of geomorphically. 

young, fault-produced features (scarps, sag ponds, 

offset stream courses, and disruption of manmade 

features such as fences and curbs) (figs. 2, 3, 7, 8). 

Knowing that a particular fault is active, however, is only part of the problem. The other part is 

predicting the likely location of fault ruptures during the next significant earthquake. Geologists 

generally accept the premise that the next rupture 

will probably occur along the fault trace that ruptured last, especially if there is evidence of repeated earlier movements on the same fault trace 

(fig. 3 and Wallace, 1968a, p. 17). However, movement seldom is limited to a single fault surface 

throughout the lifetime of a fault system such as 

the San Andreas. In many places tens or even 

hundreds or thousands of individual fault surfaces 

make up the San Andreas in a zone varying in 

width from a few hundreds to many thousands of 

feet. Any individual fault surface may have ruptured at any time during the last 40 million years 
Figure 1.-House damaged by displacement along a thrust fault during the San Fernando earthquake, February 1971. 

or so that the fault has been active. It is speculated, 

however, that most of these surfaces probably 

have not moved in millions of years, and only infrequently may a new rupture surface develop or is 

fault movement transferred from one part of the 

fault zone to another. 

Faults that commonly produce significant displacement (more than several inches at a time) 

often have related branches that diverge from the 

main fault but usually have less movement along 

them (fig. 4). They may also have secondary faults 

that are not directly or obviously connected physically to the main fault trace. Secondary faults are 

usually nearby (within hundreds of feet of the 

main rupture), but they may extend as much as 

several miles away. As with branch faults, displacement along secondary faults is usually only a 

fraction of that along a main fault. 

The amount of displacement that can occur during a single earthquake can be related in a general 

way to the total length of a fault. The longer the 

3 

fault, the greater the potential for a great earthquake and the greater amount of displacement 

likely (fig. 5 and Albee and Smith, 1967, p. 432; 

Bonilla, 1970, fig. 3.16). The maximum displacement ever recorded during a single earthquake is 

about 42 feet of vertical displacement (Bonilla, 

1970). Horizontal movement of as much as 20 feet 

occurred along the San Andreas fault in 1906 

(Bonilla and Buchanan, 1970). 

In addition to the location and amount of displacement, the sense of movement is extremely 

important in estimating the amount and type of 

damage that might be produced. This was evidenced by the great damage over faults during the 

moderate (magnitude 6.6) San Fernando earthquake which produced a reverse or thrust fault 

movement (fig. 6a); movement occurs along a similar plane, but in an opposite direction on the normal (fig. 6b) Wasatch fault in Utah. Left-lateral 

movement(fig. 6c). and right-lateral movement, 

which is common to the San Andreas fault, proba-
12:f42'30" 

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SCALE 1 :48,000 

0 

B-lrom U.S. GoologiCIII Survey 

1:24,000 quldronglll, Point Arena, 

1982, Mollo P811 CrHk, 1982 

1 MILE 

1 KILOMETER 

FIGURE 2.-Map of recently active breaks along the San Andreas fault near Point Arena, Calif., illustrates kinds 

of fault-produced topographic features and the linearity of surface features which commonly result from faulting. (From 

Brown and Wolfe, 1970, sheet 1 of 2.) 

4 
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25' 

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0 150 METERS 

FIGURE 3.-Progressive lateral shifting in stream alinement due to repeated displacement along a single trace of the San 

Andreas fault. The major stream channel has been deflected 450 feet from A to B; earlier displacements are suggested 

by the beheaded stream segment at C, 1,200 feet from A. The small stream channel at D displays a series of offsetsrepresented by one deflection and three abandoned downstream segments-measuring 30, 70, 110, and 200 feet. (From 

Wallace, 1968a, fig. 8.) 

bly are less potentially damaging to most structures than normal or thrust faulting. 

Not all surface faulting need be rapid nor need it 

occur during major earthquakes. Imperceptibly 

slow movement, called "fault creep" (fig. 7), occurs 

along the Hayward, Calaveras, and some other 

faults and may be accompanied by microearthquakes. Similarly, not all deformation of the 

earth's surface produces fault displacements. 

Strains in the earth deform the rocks until their 

strength is exceeded and they rupture, producing 

the earthquake. Accompanying this bending, 

however, is a certain amount of plastic deformation (fig. 8). Both rupture and plastic deformation 

commonly occur along active fault zones and may 

be sufficient to damage or destroy structures over 

particularly strongly deformed rocks. Earthquakes deep within the earth may result from 

rupture of deeply buried rocks but without fault 

displacement at the ground surface, although the 

5 

surface rocks may be deformed(fig.6d). This may 

have occurred along a part of the NewportInglewood fault zone where movement along the 

fault during the last 10,000 years or so has merely 

caused a permanent flexuring or bending of the 

surface rocks (Castle, 1966). Recent surface displacement is not characteristic of faults in the 

Eastern United States. 

METHODS FOR ASSESSING FAULT HAZARDS 

The above discussion focuses on the kinds of 

problems that need to be assessed and gives a clue 

as to why specific, quantitative predictions on the 

exact location, nature, amount, and time of movement along a fault can seldom be provided. What 

the geologist can say and the degree of confidence 

behind the statements are based on the type and 

number of investigations that form the basis of the 

judgments, not only within the area of concern but 

also along an entire fault system. The following 
,---------------------~----------~~~ 

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FIGURE 4.-Map showing main fault traces (I), branch faults 

(II), and secondary faults (III). Dashed lines indicate uncertainty of specific fault locations. (From Bonilla, 1970, fig. 

3.4.) 

paragraphs list some of the principal data and the 

judgments they may allow. A later section (p. 

28-29) lists in greater detail the kinds of earthscience data needed ~nd their purpose. 

Background inform'at.ion of particular value includes: geologic maps (~scales of 1:24,000 to a 

maximum of 1:250,000), detailed geologic mapping of particular problem areas (at scales of 

1:6,000 or larger), long-term records from numerous, nearby seismograph stations (fig. 9), and topical studies of faulting, which may include interpretation of aerial photographs, examinations 

of trenches and bore holes, age dating of samples, 

and geophysical surveys. Lacking one or more of 

these categories of background studies may seriously limit the geologist's predictive capability. 

These studies should lead to knowledge about 

6 

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EXPLANATION 

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LENGTH OF SURFACE RUPTURE, IN MILES 

FIGURE 5.-Logarithmic plot relating maximum amount of 

surface displacement to the length of surface rupture on the 

main fault trace. Points record known historic surface faulting accompanying earthquakes in the continental United 

States and adjacent parts of Mexico. (From Bonilla, 1970, fig. 

3.17.) 

the location, total length, and width of the active 

fault zones and all the likely active traces. They 

should assess the sense of movement (horizontal or 

vertical) and the maximum amount expectable. 

The amount and nature of possible deformation 

should also be assessed within and adjacent to the 

fault zone. The character offaulting and deformation within each type of earth material at the surface should also be evaluated-do they break 

sharply along a single plane, do they shear over a 

wide zone, or is the movement absorbed by adjustments of individual grains with no definable 

fault trace? 

The data collected for an evaluation of hazard 

from surface rupture should be sufficient to allow 

the formulation of a design earthquake--that is, 

the maximum expectable earthquake magnitude, 

general depth of energy release, and general frequency of occurrence for each fault zone capable of 

generating an earthquake. 

IMPLICATIONS FOR PLANNING AND 

LAND-USE CONTROLS 

With the above information, the planner, in consultation with the geologists, seismologists, and 

engineers, can assess the consequences of surface 

rupture and deformation to different types of existing, planned, or possible land use (if uncontrolled 

or under existing regulations) in the areas subject 
Earth block before movement 

a. Thrust or reverse fault 

b. Normal fault 

c. Left·lateral fault 

d. Monoclinal fold caused by faulting at depth 

FIGURE 6.-Examples of some types of fault displacement and 

earth flexure . (Modified from Longwell and others, 1949.) 

7 

FIGURE 7 .-Curb displaced by fault creep on the Hayward fault. 

This type of movement is usually imperceptibly slow and 

generally is not accompanied by felt earthquakes. 

to ground displacement. Where these consequences suggest unacceptable levels of damage to 

property or loss of life, alternative land uses that 

would be compatible with fault rupture, and with 

adjacent and regional land uses, should be recommended. One alternative that might be considered 

would be to allow the planned use but to impose 

controls on the method of construction and its location so that an undue hazard would not occur. 

Implementation regulations might call for establishing a fault hazards easement (Mader and 

others, 1972) that would require a setback distance from the active fault traces (fig. 10). The 

amount of setback might differ with the type of 

faulting and deformation expected. It might also 

vary with respect to the character of individual 

faults and even segments of a single fault as well 

as with the knowledge or lack thereof of the fault 

zone and the structure or development being considered. Thus the more crit)cal the structure, the 

greater the likely setback limit. 
FIGURE 8.-Corral fence showing evidence of continuing deformation in a zone of the San Andreas fault, which results from 

strains that bend the rocks without significant earthquake activity. The distant portion of the fence has been offset about 

21 inches to the right of the near portion. (From Brown and Wallace, 1968, fig. 4.) 

In addition to adoption of a fault hazards easement, similar to a scenic easement, jurisdictions 

might consider adoption of "fault hazard zoning" 

or the broader "geologic hazard zoning," which 

would include such hazards as landslides and 

floods as well as faults. Such zoning might override 

conventional zoning, prohibit human occupancy, 

require a land use compatible with both the hazard 

and adjacent uses, or stipulate minimum site investigative and safety standards. Certainly, any 

development to be considered within, or immediately adjacent to, an active fault zone should 

require geologic studies to demonstrate that the 

proposed construction would conform to standards 

of community safety and that an undue hazard to 

life and property would not ensue. 

Alternatively, prohibition of all uses other than 

those essential to the public welfare (utility and 

8 

transportation facilities) could be considered in 

areas of extremely high hazard. Certain types of 

land use are completely compatible with the high 

level of hazard attendant to areas such as the San 

Andreas fault zone. Some of these include open 

space, recreation areas (including golf courses, 

nurseries, horseback riding, bike trails, and so on), 

cemeteries, freeways (but not interchanges), parking lots, and solid-waste disposal sites (under some 

conditions) (fig. 11). 

Where development already occurs within active fault zones, jurisdictions can adopt policies 

leading to the removal of critical engineering 

structures on the most accurately located active 

fault traces. Nonconforming building ordinances 

should be considered that could require eventual 

removal of structures in the greatest danger, starting with those that endanger the greatest number 
.-----------------------------------------------------------------------------------------------, 38·~· 

• 

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EXPLANATION 

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(Operated continuously during 

1econd quarter 1972.1 

Stations operated by other 

institutions 

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Monterey 

20 30 40 MILES 

0 10 20 30 40 Kl LOMETERS 

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12J"oo' 12o•oo' 

FIGURE 9.-Map showing the location of seismograph stations in a closely spared USGS instrument network in central 

California. These stations provide accurate data on the location, frequency, and size of earthquakes occurring within 

the area and aid in defining causative faults. 

9 
EXPLANATION 

0 500 FEET 

Fault trace location known I 11 ,, I I 0 150METEAS 

Fault trace location inferred 

FIGURE ·10. Example of minimum easements required for 

building setbacks from active fault traces by town ordinance 

in Portola Valley, Calif. All new building construction is 

prohibited within the 100-foot wide, lightly shaded zone (50 

feet on each side of the well-located portion of the San Andreas fault); structures with occupancies greater than single 

of lives-schools, hospitals, auditoriums, office 

buildings and apartment houses, followed by 

commercial buildings, and perhaps eventually by 

single-family residences (fig. 12). The nonconforming building ordinances might be based on either 

an arbitrary time schedule or the expected lifetime 

of the structures involved. Other innovative options for control of development include tax incentives and adoption of urban renewal policies that 

would encourage removal of hazardous structures 

and that would prohibit reconstruction in hazardous areas after earthquakes or other natural disasters (Diplock and Nichols, 1972). 

GROUND SHAKING 

Earthquake-generated ground shaking, in 

many instances, causes the most widespread 

earthquake damage. However, ground shakingwhat most people and structures react to during an 

earthquake-is one of the most difficult seismic 

hazards to predict and quantify. Data from past 

earthquakes have shown that the intensity of 

ground shaking can be several times larger on 

10 

family dwellings are required to be 125 feet from the fault 

trace (dark shading). Where location of the fault trace is less 

well known, the more conservative setbacks of 100 feet for 

single family residences and 175 feet for higher occupancies 

are required. (Modified from Mader and others, 1972, fig. 5.) 

sites underlain by thick deposits of saturated sediments than on bedrock. Consequently, the 

greatest losses, resulting solely from shaking, may 

occur where tall structures are built on thick, relatively soft, saturated sediments (fig. 13) and the 

least where they are built on firm bedrock (Wallace, 1968b, p. 67). 

In addition to the amplification effects of local 

geologic deposits, the amount of ground shaking at 

a particular site depends on (1) characteristics of 

the earthquake source (for example, magnitude, 

location, and area of causative fault surface) and 

(2) distance from the fault. To anticipate the severity of ground shaking likely to occur at a site, each 

of these factors must be taken into account. The 

extent of shaking damage is also dependent partly 

on the structural integrity of buildings before the 

earthquake. (See Page and others, 1972, for a discussion of ground motion values used in the seismic design of structures.) 

Characteristics of the earthquake source and 

distance can be crudely estimated from the seismic 

history of the area and detailed geologic mapping 
FIGURE ll.-View showing approximate location of fault traces within a part of the Hayward fault zone, some of which 

ruptured during the October 21, 1868 earthquake (Radbruch, 1967). The plant nursery, undeveloped open space, freeway, and cemetery are land uses most compatible with the hazards posed by this active fault. Other such uses might 

include drive-in theater, golf course, riding stable, and other recreational activities. 

11 
On trace 

Schools e 

Hospitals • 0 

122"00 

FIGURE 12.-Schools, hospitals, and other public buildings on or near traces of part of the Hayward fault. 

Ordinances declaring such buildings as nonconforming structures could lead to their eventual relocation 

to areas with less adverse geologic conditions, thereby reducing potential loss oflives and property. (From 

Alquist, 1971, p. 17.) 

12 
Figure 13.-Aerial photograph of San Francisco showing relationship of greatest damage in the 1906 earthquake 

(patterned) to areas of former bay and marshlands (landward edge shown by solid line). 

studies. The amount of data available for such 

estimates varies widely for different parts of the 

country, but in some areas (for example, the San 

Francisco Bay area) detailed research programs 

are providing data expressly for this purpose. With 

such estimates, it then becomes possible to ex13 

amine potential variations in shaking due to variations in local geologic conditions. 

METHODS FOR ASSESSING SHAKING HAZARDS 

Earth-science data bearing on possible effects of 

ground shaking are varied and often incomplete. 

Starting with a prediction of a design earthquake 
(see p. 6), an evaluation of shaking intensity can 

be made at the ground surface that reflects the 

effect of the local geology (rock, firm soil, and thick 

wet soil) on modifying the earthquake motion. One 

useful tool to assess potential building damage 

from knowledge of ground conditions is to relate 

the fundamental period of a building to the ground 

on which it rests. A damaging resonance commonly develops where the fundamental building 

period coincides with the natural period of the 

ground. In a very general way, the fundamental 

building period is related to its height or number of 

stories and that of the ground to its firmness, 

thickness, and degree of saturation. Taller buildings have a longer fundamental period (2 sec or 

more) and are subject to greater damage where 

they stand on ground with a long fundamental 

period (fig. 14). Conversely, 1- or 2-story buildings 

with a short fundamental period may be more vulnerable on firmer ground. 

100r----.----.----,----,-----,----,----, 

90 EXPLANATION 

1- o= buildings from 5 to 9 stories 

Z • • = buildings from 10 to 14 stories 

~ 80 b= buildings over 14 stories 

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Ideally, therefore, one means of expressing 

ground shaking is in terms of the likely response of 

specific building types-wood frame residences, 

single-story masonry structures, low-rise (3- to 

5-story), moderate-rise (6- to 15-story), and highrise (more than 15-story) buildings. Each of these 

building classes, in turn, can be translated into 

occupancy factors and generalized into land-use 

types. 

· Although we cannot presently predict when, 

where, or how great the next earthquake will be, 

several qualitative approaches can be used for 

planning purposes to anticipate where ground 

shaking will be most severe. Selection of any one 

approach depends upon the use to which it may be 

put, the money available, and recent improvements and sophistication in methodology. 

(1) Correlation of earthquake effects with the 

general firmness of rock and soil is an empirical 

technique based on examination of damage from 

numerous historic earthquakes. Because few 

earthquakes have occurred in areas where stringent building codes and modern construction 

standards are in effect, this correlation requires 

careful interpretation. Some examples of high 

shaking damage include areas of thick, soft sediments in downtown San Francisco, Santa Rosa, 

and San Jose during the 1906 San Francisco 

earthquake and parts of Caracas, Venezuela, during a 1967 earthquake. Areas of firmer soil and 

rock much nearer the epicenter during both earthquakes suffered considerably less damage. 

0 50 I 100 150 200 I 250 300 350 

Areas with relatively different shaking characteristics commonly can be determined from most 

good geologic maps that distinguish between different kinds of bedrock and unconsolidated deposits. Although such maps may not explicitly 

rank units by degree of firmness, give total sediment thickness, or assess degree of saturation, 

most geologists may be able to make such interpretations on the basis of a knowledge of the age 

of the geologic units and some additional engineering field and test data (Nichols and others, 1972). 

Any determination of the fundamental ground 

period requires knowledge of sediment thickness 

and measurements of the shear velocity of the 

geologic units. Maps prepared on this basis should 

only purport to serve as a general guide to relative 

ground shaking effects. 

I I 

I I 

I DEPTH OF SOIL, IN METERS 

I I 

I I 

0 0.4 0.6 0.8 1 .0 1.2 1.4 1.6 

FUNDAMENTAL PERIOD OF SOIL DEPOSIT,IN SECONDS 

FIGURE 14.-Structural damage intensity for different height 

buildings related to depth of soil and computed fundamental 

period of soil deposit. N = number of stories. Where the fundamental period of a soil deposit is short (between 0.6 and 0.8 

sec), the greatest damage will occur to buildings from five to 

nine stories tall. With longer soil periods, damage intensity 

to higher structures increases. (From Seed and others, 1972, 

fig. 12.) 

14 

(2) Intensity maps, based on the Modified Mercalli, or a similar intensity scale, have been made 

in many areas from damage studies of past earth-
quakes. In a general sense, intensity is a function 

of ground conditions and distance from the 

epicenter. Lower numbers on the scale indicate less 

severe shaking and are based on what people feel; 

intermediate numbers are assigned according to 

the type and amount of building damage sustained 

(without regard to age of construction), and higher 

numbers principally to secondary geologic effects 

(ground failure). 

Where intensity maps, based on previous earthquakes, do not exist or do not reflect the maximum 

expectable earthquake, they can be prepared 

using a recently developed method. Intensity increments, commensurate with local ground conditions, are added to a base intensity computed for a 

specified design earthquake. This technique has 

been used extensively in the Soviet Union 

(Barosh, 1969) and has been applied to the State of 

California (Evernden and others, 1972). 

Analyses based on (1) and (2) provide only general qualitative guidelines for ground shaking and 

earthquake-resistant design. They do not provide 

quantitative estimates of ground shaking for use 

in estimating engineering design parameters. Nor 

do they necessarily distinquish the effects on 

structures due solely to ground shaking from those 

due to ground failure. They can be made more 

useful, however, by applying empirical relations 

from parallel studies of ground motion characteristics determined from distant natural or 

manmade microseismic events (Borcherdt and 

others, 1972). Such studies provide a measure of 

amplification effects on different kinds of ground 

at low strain levels (fig. 15). Because the 

amplification effects from small ground motions 

are generally linear, while those from strong motion may be nonlinear, such measurements cannot 

be extrapolated directly to large earthquakes. 

Most soils and rocks have elastic properties up to 

certain levels of strain; beyond these levels, they 

deform plastically or rupture. Consequently, as 

the strain increases, the ground motion increases 

up to a point that varies from one ground condition 

to another. Strain increases that result from very 

large amounts of energy release, as in a great 

earthquake, probably are not matched by comparable increases in ground motion. Instead, the 

strain exceeds the-strength of the earth materials 

that yield, damping the motion. 

Theoretical nwdels to predict surface ground 

motion have existed for many years. Not until 

relatively recently, however, have enough observations been available from earthquakes and from 

in situ ground measurements to provide reliable 

data to use in the models and on which to base an 

evaluation of the validity of the models (Seed and 

Schnabel, 1972). Because theoretical modeling 

techniques require detailed knowledge of geologic 

and soil conditions and assumptions as to the 

character of the bedrock motion, their use has been 

fairly expensive and limited as a predictive tool to 

anticipate the effects at a single site--usually one 

to be occupied by a critical structure. These techniques are still in the developmental stage and 

have not yet won complete acceptance among the 

experts (Hudson, 1972, p. 41 and Newmark and 

others, 1972, p. 115-117). Increasing sophistication in analysis, along with expanding knowledge 

of earthquakes and their mechanism, may soon 

generate more widespread acceptance and 

perhaps eventually allow their application to general land-use proble_ms. 

In the meantime, the very broad generalized 

approach in characterizing the firmness of the 

ground appears to be adequate to assess the gross 

effects of ground shaking for general planning 

purposes. Where intensity maps representative of 

expectable earthquakes exist or can be prepared 

by modern techniques, they would be valuable for 

general plan purposes and for specific plans such 

as an urban renewal program or a large-scale redevelopment proposal. On the other hand, builders 

of proposed structures that are critical or that will 

have high occupancies might be required to have a 

dynamic analysis prepared of the structure and 

site as a means of assessing their safety and design. 

IMPLICATIONS FOR PLANNING AND LAND USE 

Seldom can a structure, without regard to its 

height, be declared inappropriate if it is carefully 

designed specifically for a given site. Nevertheless, as a broad planning tool, knowledge of expectable ground shaking effects, in combination with 

other considerations, could lead to low-density 

land uses in some areas. Elsewhere, such knowledge can lead to the adoption of building code 

provisions appropriate to areas with different 

ground shaking characteristics. For example, 

((geologicnazard zoning" might be applied to areas 

of very thick saturated sediments with high (long) 

fundamental ground periods equivalent to that of 

buildings likely to be in that zone, for example, 

high-rise structures. Ordinances might require 

15 
FEET I METERS 

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0 

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(J 

:t 

tOl-E 

65 19.8 

QI-N 

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52 15.8 

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22 6.7 TI-N 

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cr 

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100 120 140 160 180 

TIME, IN SECOOOS 

FIGURE 15.-Seismograph records from a single nuclear explosion show the differences in amplification of energy with 

increased thickness of bay mud. (From Borcherdt, 1970, fig. 5.) 

that increasingly detailed geologic, soil engineering, and structural engineering analyses be performed for buildings with the highest projected 

occupancies in areas of greatest expected shaking 

motion. Because, as discussed earlier, it is difficult 

to predict strong ground motion (strong motion) 

characteristics and their effects quantitatively, it 

is desirable to establish a legal and procedural 

framework that remains flexible enough to accomodate increasingly sophisticated methods of 

prediction. 

Other measures that are critical to a lessening of 

potentialloss.oflife include the adoption and strict 

enforcement of a hazardous building abatement 

ordinance and an ordinance to require removal of 

dangerous parapets. Because of the potential 

16 

economic impact, hazardous building abatement 

regulations might best be imposed gradually on a 

priority basis, selecting first those structures that 

are the most dangerous and with the highest occupancies, followed by buildings that constitute a 

lesser hazard and that have lower occupancies. 

Parapet ordinances, if enforced in urbanized 

areas, particularly where older high-rise structures may have poorly secured appendages (fig. 

16), have the potential of sharply reducing casualties and property damage during major earthquakes. 

GROUND FAILURE 

Earth materials in a natural condition tend to 

reach equilibrium over a long period of time. In 
FIGURE 16.-Unreinforced parapets, which collapsed during the moderate (magnitude 5.7) 1969 Santa Rosa earthquake, 

caused severe damage to persons and property. (From Alquist, 1971, p. 20.) 

geologically young and active areas such as 

California and Alaska, there are many regions 

where earth materials have not yet reached a 

natural state of stability. For example, most of the 

valleys and bay margins are underlain by recent 

loose materials that have not been compacted and 

hardened by long-term natural processes. Landslides are common on most of the hills and mountains as loose material moves downslope. In addition, many activities of man tend to make the 

earth materials less stable and hence to increase 

the chance of ground failure . Some of the natural 

17 

causes of instability are earthquakes, weak materials, stream and coastal erosion, and heavy rainfall. Human activities that contribute to instability include oversteepening of slopes by undercutting them or overloading them with artificial fill, 

extensive irrigation, poor drainage or even 

ground-water withdrawal, and removal of stabilizing vegetation. These causes of failure, which 

normally produce landslides and differential settlement, are augmented during earthquakes by 

strong ground motions that result in rapid 

changes in the state of earth materials. It is these 
changes, by means of liquefaction and loss of 

strength in fine-grained materials, that result in 

so many landslides during earthquakes as well as 

differential settlement, subsidence, ground cracking, ground lurching, and a variety of transient 

and permanent changes in the ground surface. 

MECHANISMS OF FAILURE 

Liquefaction is a common mechanism causing 

many types of ground failure . It occurs when the 

strength of saturated, loose, granular materials 

(silt, sand, or gravel) is dramatically reduced, such 

as may occur during an earthquake. The 

earthquake-induced deformation transforms a 

stable granular material into a fluidlike state in 

which the solid particles are virtually in suspension, similar to quicksand (fig. 17). The result, 

where the liquefied materials are in a broad buried 

layer, may be likened to the action of ball bearings 

in reducing friction in the movement of one material past another. The Juvenile Hall landslide during the 1971 San Fernando earthquake resulted 

from liquefaction of a shallow sand layer and involved an area almost a mile long and a failure 

surface that had a slope of only 21!2 percent (fig. 18 

and Youd, 1971, p. 107, 108). Where the liquefied 

granular layer is thick and occurs at the surface, 

structures may gradually sink downward. The 

Figure 17. - Sand, liquefied during the 1973 Point Mugu 

earthquake, fails to support the man. Loose, saturated, 

granular materials commonly are stable until an earthquake sharply reduces their strength. 

18 

tilting and sinking of buildings during the Niigata 

earthquake illustrate this phenomenon (fig. 19A, 

B). 

Loss of strength in fine-grained cohesive materials is another mechanism of ground or foundation failure and might manifest itself in squeezing 

or "lateral spreading" of soft, saturated clays (fig. 

20) such as San Francisco Bay mud. It can result in 

rapid or gradual loss of strength in the foundation 

materials so that structures built upon them 

gradually settle or break up as foundation soils 

move laterally by flowage. 

Other causes for loss of resistance include raising the ground water to reduce frictional resistance along a potential failure surface and removal 

of water or earth masses that may be serving as a 

buttress to prevent downslope movement. 

RESULTS OF GROUND FAILURE 

Although the basic causes of ground instability 

are simple in concept, the consequences are often 

complex and highly variable. They include 

numerous varieties of landslides, ground cracking, lurching, subsidence, and differential settlement. Moreover, these types of ground failure 

occur on a wide variety of ground conditions. 

Landslides, for example, do not require a steep 

slope on which to form, particularly during earthquakes. Many occur on slopes that are virtually 

flat, and the surface on which they fail may be very 

shallow (1 to 2 feet deep) or as much as hundreds of 

feet below the ground surface. The type of ground 

failure that develops in a given area is determined 

partly by the nature of the natural or manmade 

disturbance that occurs and partly by the topographic, geologic, hydrologic, and geotechnical 

characteristics of the ground. 

Ground cracking usually occurs in stiff surface 

materials and is associated with changes in surface topography or materials. For example, during 

the 1964 Alaskan earthquake, much of the ground 

cracking that occurred along river flood plains 

adjacent and parallel to stream channels and 

along road and railroad embankments resulted 

from differential movement owing either to liquefaction or to lateral spreading of a relatively 

soft, deeper layer under a stiffer surface layer (fig. 

21). Cracks may be only hairline or several feet 

wide and from a few feet to hundreds of feet long. 

Ground lurching may be both a transitory and 

permanent phenomenon. During earthquakes, 

soft saturated ground may be thrown into undulat-
FIGURE 18.-The Juvenile Hall landslide (outlined), generated by the 1971 San Fernando earthquake, involved an area 

almost a mile long. It resulted from liquefaction of a shallow sand layer and has a failure surface with a slope of only 

2'h percent. 

ing waves that may or may not remain when the 

ground motion ceases (fig. 22). The same or similar 

ground surface appearance may also result from 

permanent differential settlement of the ground, 

which can be caused by loss of soil strength or by 

liquefaction. Commonly, the water freed by liquefaction of buried and confined granular layers is 

forced to the ground surface, moving laterally toward steep slopes or vertically along the planes of 

weakness in the overlying layers. As the water 

moves toward the surface or free face, it often carries with it some of the sand. Thus, sand boils, 

sand volcanoes (fig. 23), sand ridges (fig. 24), and 

similar anomalous features attest to the occurrence of liquefaction. As sand and water are removed from the subsurface, the ground settles, 

often differentially because the sand and water are 

seldom removed evenly over broad areas. The resulting effects on buildings can be catastrophic. 

Subsidence of as much as several feet may occur 

over a broad area underlain by a thick sequence of 

sedimentary deposits. For example, after the 1906 

earthquake, a well casing was reported to have 

"risen" 2 feet out of the ground, when, in fact, the 

ground around it probably liquefied or compacted 

as a result of the shaking. Subsidence is likely to 

be greatest in areas where there has been withdrawal of fluids (ground water or oil) over a long 

period of time. Lesser amounts of subsidence can 

occur even where fluid withdrawal has not taken 

place, as in the Homer area of Alaska in 1964. 

Compaction effects may be predicted with some 

19 
FIGURE 19.-Niigata earthquake phenomena. A, Tilting and 

sinking of buildings caused by reduction of foundation support due to liquefaction of near-surface sand deposits during 

the 1964 Niigata, Japan, earthquake. (From Kawasumi, 

1968, pl. 7.)B, Residents salvaging furniture and personal 

possessions by carrying them down the exterior walls of 

apartment building tilted by liquefaction. (From Kawasumi, 

1968, pl. 7 .) 

degree of assurance over fairly broad areas (up to 1 

or 2 miles) and even on a site basis, especially 

when the cause may be liquefaction. 

METHODS FOR ASSESSING GROUND 

FAILURE HAZARDS 

Basic data on ground failure should include 

maps and data on areas most subject to landslides, 

liquefaction, and ground lurching or cracking as 

outlined on pages 28-29. These are areas that, 

because of steep slopes, saturated granular subsurface deposits, or weak or unstable ground conditions, might fail during major earthquakes. One 

or more maps showing the areal distribution of 

20 

FIGURE 20.-Lateral spreading of soft, surficial materials toward an exposed slope occurn'ld during the 1973 Point Mugu 

earthquake. 

slopes and each of these ground conditions is desirable, although not always possible. An absolute 

predictive capability is virtually impossible except 

for specific sites after careful exploration and 

analysis. 

IMPLICATIONS FOR PLANNING AND 

LAND-USE CONTROLS 

General land-use policy might be guided partly 

by knowledge of broad areas where instability is 

believed to be so pervasive that, along with other 

considerations, its preservation as open space or 

other nonoccupancy, may be indicated (fig. 25). On 

the other hand, except during earthquakes, such 

failures generally occur fairly slowly, may be preceded by indicators, and usually do not result in 

loss oflife, even though extensive or complete destruction of property is common. Therefore, the 

problem might be ignored. Alternatively, since 

ground failures can be life hazards during earthquakes, areas of known or likely low stability 

might be designated as geologic hazard zones. In 

such zones background studies (geologic and soil 

engineering reports) should be required to demonstrate that both static and dynamic hazardous 

conditions either do not exist or can be overcome 

by site preparation work or engineering design 

prior to approval of subdivision and site develop-
FIGURE 21.-Cracks in the active flood-plain sediments at the south end of bridge at Matanuska River, Alaska. An earthfili 

has been emplaced to substitute for a section of trestle damaged by shearing of wood piles at the ground. 

FIGURE 22.-Ground lurching on tidal flat at head of Tomales Bay, Calif., during the 1906 earthquake produced ridges and 

waves in tidal muds. 

21 
FIGURE 23.-Sand volcanoes in tidal flats produced by shaking of water-saturated sands during the 1973 Point Mugu earthquake. Using the birds for scale, the largest sand volcanoes are estimated to be several feet across. 

22 
FIGURE 24.-Ridges, formed by fluid injection of sand in ground 

cracks are exposed following the 1964 Alaskan earthquake. 

Shovel provides scale. 

ment applications. Although individual structures may be sited safely in such areas, roads, gas, 

water, and sewer lines can seldom be built without 

crossing unstable areas. Long-term costs in the 

form of public services may be great and generally 

must be borne by the entire community (table 1). 

Other solutions to instability problems that are 

being pursued include adoption of a program to 

allow tax deductions for property owners whose 

land is particularly susceptible to ground failure. 

Such a program might be designed to alleviate tax 

burdens on property where existing structures are 

being damaged and on unimproved land as long as 

it remains unimproved or until the owner can 

demonstrate that he has eliminated the hazardous 

conditions. For those relatively few developed 

areas where severe instability problems are 

known to exist and disaster merely awaits the 

TABLE 1.-Some economic costs resulting from development on 

unstable areas 1 

The economic loss as a consequence of development on these landslide deposits is already large, will continue to grow, and will probably become significantly greater if additional development is permitted without thorough engineering geology inves- tigations of the area. The estimated 1969-70 loss in market value for all houses in San Jose Highlands, for example, was $228,000, the loss for lots was $195,000, and the loss in valuation for specific landslide damage to certain houses was $61,520-a total loss of$484,520 (Santa Clara County Assessor's Office, written commun., Sept. 22, 1971). The cost data below, provided by the San Jose Department ofPublic Works (written commun., Sept. 28, 1971), reveal the variety and magnitude of expenses to a municipality when landslide activity takes place within a subdivision area. 

Actions taken by and financed by the City of San Jose in the San Jose Highlands area, 1968-71 

Soils study and consultant fees _________________ _ 

Soils study and consultant fees ------------------ Consultant for new road ------------------------ Construct 1,400 foot gravel-fill interception ditch (no water was apparently removed). Clean Hydraughers several times _____________ _ 

Construct dewatering wells (deactivated after 1 year, no apparent help). 

Above-ground flexible aluminum sanitary sewer __ 

Sewer photograph survey ---------------------- Replace sanitary sewer ------------------------ Aerial photography ---------------------------- Abandon 600 feet of only access road and build 4,000 feet of new access around landslide area 

Winter and spring road maintenance to remove ground swells and increasing 

grade due to downward creep 

1968 

1969 

1970 

1969 

1969 

1968 

1971 

1971 

1967 

1968 

1969 

1970 5 months of 1971 

$ 10,000 

10,000 

30,000 

15,000 

3,000 

25,000 

4,500 

3,000 

7,000 

2,000 

550,000 

0 9,000 

30,000 

32,000 

30,000 

Total __ __ _______ ____ _______ ___ _ ____ __ __ _______ _____ _________ $760,500 

Estimated value of city streets in San Jose Highlands 

(exclusive of new access road) ------------------------------------ $750,000 Estimated value of city utilities (street lights and sewers) 

in San Jose Highlands------------------------------------------- $300,000 

Landslide damage to gas lines in San Jose Highlands totaled $20,000 by late 1970 (Pacific Gas and Electric Co., written commun., Nov. 18, 1970). Landslide damage to water lines has become progressively worse according to the following figures pro- vided by the San Jose Highlands Water Company (written commun., Nov. 3, 1971): 

1967-68 

1968-69 

1969-70 

1970-71 l~ ~=~:E~r =================== =================== km (20 repairs}__ _____ ------------------------------- $5,816 

No information was obtained on the cost of landslide damage in the map area outside of the San Jose Highlands, but landslides were a substantial and presumably 

costly problem during and after construction of terminal facilities for the South Bay 

aqueduct (California Department of Water Resources, 1966). 

'Taken from Nilsen and Brabb, 1972. 

triggering action of an earthquake or an exceptionally wet winter, consideration should be given 

to the implementation of a hazardous building 

abatement ordinance or the initiation of nonconforming use procedures. 

TECTONIC DEFORMATION 

Earthquakes may produce major differential 

vertical and horizontal movements over broad 

parts of the earth's crust. For example, as a result 

of the 1964 Alaskan earthquake, between 70,000 

and 110,000 square miles of both the sea floor and 

land in southern Alaska were warped, elevating or 

depressing them as much as 6 feet; elevation 

changes locally exceeded 50 feet (fig. 26 and Hansen and others, 1966, p. 17). While the effect of 

compaction and tectonic subsidence may appear 

23 
37'52'30" 

SCALE 1:62 500 

0 2 3 4MILES 

0 2 3 4 KILOMETERS 

FIGURE 25.-Landslide distribution in Mount Diablo area, Contra Costa and Alameda Counties, Calif. Such maps, based 

largely on aerial photograph interpretation, are valuable in alerting public agencies to areas of known and possible 

low slope stability. Arrows show the direction of landslide movement. (From Nilsen, 1971.) 

the same locally, the mechanisms differ greatly, 

and the total area affected will be much greater 

where the cause is tectonic deformation. Tectonic 

land changes result from major movements in the 

earth's crust, and neither their location nor their 

magnitude is predictable. Therefore, there is little 

that can be done to minimize the effects of these 

changes before they occur. 

TSUNAMI AND SEICHE EFFECTS 

Tsunamis are large ocean waves generated by 

rapid changes in elevation oflarge masses of earth 

and ocean. They are commonly caused by vertical 

faulting beneath the ocean that rapidly moves a 

large volume of earth and water. Such rapid 

movement may generate huge waves of destructive force that can travel thousands of miles. Dur24 

ing the 1964 Alaskan earthquake, for example, 

faulting and crustal warping created tsunamis, or 

sea waves, tens offeet high that spread more than 

1,500 miles from the source area and caused devastation to many coastal communities within their 

reach (fig. 27). The effects of tsunamis can be 

greatly amplified by the configuration of the local 

shoreline and the sea bottom. Since a precise 

methodology does not exist to define these effects, 

it becomes important, through examination of the 

historic record, to determine if a particular section 

of the coastline has been subjected to tsunamis and 

to what elevation they have reached. It is also 

desirable to attempt to assess what amplifying 

effect a local coastal topographic configuration 

might have on uniquely directional incoming 

waves. 
FIGURE 26.-Flooding of the Portage area of Alaska was caused by regional subsidence and by tectonic land changes from 

the 1964 earthquake. 

Seismic seiches, or earthquake-generated 

standing waves, occur within enclosed or restricted bodies of water (lakes, reservoirs, bays, 

and rivers). They can be likened to the oscillations 

produced by the sloshing of water in a bowl or a 

bucket when it is shaken or jarred. Seiche waves 

generally have a low amplitude (less than a foot), 

but in shallow areas or where the water is constricted, wave runup can be as great as 20 or 30 

feet (McCulloch, 1966). Obviously, such high 

run ups can have a devastating effect on people and 

property within their reach; dams and reservoirs 

can be overtopped and large volumes of water released to inundate downstream development. 

Large water waves causing catastrophic inundation can also result during an earthquake from a 

dam failure or from large-scale landsliding into a 

reservoir or bay. The near failure of the Van Norman reservoir during the 1971 San Fernando 

earthquake required the evacuation of 80,000 

people that lived below it (Seed, 1972, p. 14). Although not the result of an earthquake, almost 

3,000 lives were lost in Italy in 1963 when a huge 

landslide (more than 312 million cubic yards of 

material) suddenly fell into Vaiont Reservoir, 

sending up a wall of water and rocks 850 feet above 

reservoir level opposite the slide area and waves of 

water about 330 feet above the crest of the dam 

(fig. 28 and Kiersch, 1964). Waves were more than 

230 feet high in the narrow valley as far as 1 mile 

downstream from the dam. Earthquake-generated 

landslides of this magnitude are possible hazards 

to dams or reservoirs. The 1958 Alaskan earthquake produced a massive rockfall that plunged 

into an inlet at the head of Lituya Bay, causing 

water to surge against the opposite wall of the 

inlet and to wash out trees up to 1, 720 feet above 

sea level (fig. 29 and Miller, 1960, p. 51). It is 

extremely fortunate that the bay was uninhabited 

and that no more than two fishermen died when 

25 
FIGURE 27.-Damage to shipping and structures at Kodiak from a tsunami generated by subsea faulting during the 1964 

Alaskan earthquake. 

their boat was destroyed as the wave passed out of 

the mouth of the bay. 

METHODS FOR ASSESSING WAVE AND 

FLOODING HAZARDS 

Assessing the hazards from tsunamis and 

seiches is very difficult and subject to varying interpretations because of very limited historical 

data and theoretical knowledge. Nevertheless, 

wave runup elevations could be predicted for most 

ocean and lake shorelines from examination of 

historic records. An attempt should be made to 

assess the amplifying effect of unique topographical coastal configurations even though the 

methodology may be very crude. Potential areas of 

26 

catastrophic inundation from dam and reservoir 

failure or from landslide-generated waves that 

overtop dam crests, on the other hand, can be 

mapped for all large bodies of water perched above 

populated areas. Recently passed legislation in 

California now requires the dam owners to prepare maps showing areas of potential inundation 

for use in disaster and land-use planning. 

IMPLICATIONS FOR PLANNING AND 

LAND-USE CONTROLS 

Stringent controls should be applied to all land 

use within areas subject to tsunami and seiche 

run up and in potential areas of inundation downstream from water-retaining structures that lie 

within active fault zones and landslide-prone 
N 

1 

( 

I 

o I 

I 

l 

I 

I 

lo 

I 

,-

1 

I 

0 2 MILE 

0 2 KILOMETER 

KEY 

0 

Cities and towns 

Reservoir and rivers 

FIGURE 28.-Sketch map of Vaiont Reservoir showing the 1963 landslide which created waves that overtopped the dam 

and caused flooding and destruction over large areas downstream. (Modified from Kiersch, 1964, fig. 1.) 

FIGURE 29.-A giant wave, generated at Lituya Bay, Alaska, on July 9, 1958 by a rockslide from the cliff (R) at the head 

of the bay, destroyed the forest over the light areas to a maximum altitude of 1,720 feet (D) and to a maximum distance 

of 3,600 feet inland from the high-tide shoreline at Fish Lake (F). 

areas. These controls might include any of the 

following: 

(1) Restrict land uses to those that are economically essential (for example, docks and 

warehouses) and warn owners, builders, and oc27 

cupants of the hazard. Prohibit siting of highoccupancy and critical structures (for example, 

schools, hospitals, police, and fire stations). 

(2) Place areas of potential inundation under 

flood-plain zoning, prohibiting all new construe-
tion and designating existing occupancies as nonconforming. 

(3) Where economically feasible and without encouraging a false sense of security, construct restraining or diversion structures to minimize potential inundation. 

( 4) Institute appropriate systems to warn of impending failure. 

(5) Adopt and implement evacuation plans. 

(6) Seek elimination of potentially hazardous 

dams or reservoirs. 

EARTH-SCIENCE DATA NEEDED TO 

ASSESS SEISMIC HAZARDS 

A rational formulation of land-use policies and 

of implementing regulations to minimize seismic 

hazards must rely on a broad base of earth-science 

information. Pertinent existing information, however, varies considerably from one locality to 

another. It should be recognized that the type, 

scope, and detail of geologic information needed 

will vary considerably in different areas depending on the complexity of the geology, the seismic 

history, type and distribution of existing and anticipated development, and the level of the planning effort. In a county where simple geologic relations and low seismic activity prevail, existing 

geologic mapping at a scale of 1:250,000 may be an 

adequate minimum informational level ifthe data 

are relatively recent and of high quality. In such 

instances compilation of existing information for 

analysis by planners in developing a comprehensive plan and its translation into model ordinances 

and land-use controls should require little additional data collection and should be relatively inexpensive. In areas of high seismicity and where 

complex geologic relations have not been resolved, 

however, an adequate comprehensive plan probably cannot be prepared without additional highly 

detailed (1:24,000 or larger scale) geologic, seismic, and engineering studies. Costs of these 

studies can vary considerably according to the 

amount of additional data needed, the number and 

type of disciplines involved, and the sophistication 

of interpretation provided. Consulting groups in 

the San Francisco Bay region in 1972-73 estimated costs for preparing seismic analyses as 

ranging between $2,000 and $20,000 for fairly 

simple geologic areas, where many data were available, on where the scope of interpretations was 

limited. In areas requiring much new detailed information, where the geology was complex, or 

where extensive, detailed analysis of the data was 

undertaken, these costs were estimated to range 

from $20,000 to $100,000 or more. These cost 

figures are offered as representative, and they may 

be exceeded under some circumstances. 

Because detailed studies or complex analyses 

may take 2 _years or more, interim policies based 

on a rapid geologic reconnaissance should guide 

development planning. These interim policies, 

since they would reflect unknown levels of risk, 

probably should be conservatively framed in areas 

of potential seismic hazard. 

The type and scope of earth-science studies 

likely to yield the most valuable data include: 

(1) Bibliographic research of geological and 

geophysical data, seismicity, historic earthquake 

records, including accounts of damage from shaking, faulting, and tsunamis. Such studies should 

include an evaluation of all existing published 

data. 

(2) Interpretation of remote sensing data, including conventional aerial photographs. Both the earliest and most recent photography at different 

scales should be examined. 

(3) Regional geologic maps, generally at a scale 

of 1:62,500 or larger. These commonly will have 

been prepared by the U.S. Geological Survey or 

state surveys. 

(4) Special-purpose detailed geologic maps of 

fault traces and zones, landslides, unconsolidated 

deposits subject to liquefaction, settlement, and 

subsidence (figs. 2 and 25). These may have been 

prepared only by private consultants for individual sites although the federal and state surveys 

have been preparing such maps for large areas in 

recent years. 

(5) Repeated geodetic measurements extending 

over long periods (decades) to detect possible horizontal and vertical land or sea changes. These are 

normally conducted only by public agencies toestablish mapping control and design of facilities. 

(6) Geophysical surveying to determine such 

things as depth to bedrock, seismic velocities, 

earth structure, magnetic properties of rocks, or 

shear wave properties. Surveying may have been 

conducted for research or design of specific 

facilities. 

(7) Measurements of fault creep and earth 

strain. Normally undertaken for research. 

(8) Seismometer arrays to determine seismic activity, fault location, type, and attitude, and likely 

hypocenter zones (fig. 9); conducted for research. 

28 
(9) Strong-motion instrumentation data from 

different geologic environs and representative 

buildings, collected for design and research. 

(10) Trenches across critical faults to determine 

location and type of displacement and to secure 

samples that might permit age dating of past 

movement to determine frequency of fault displacement. Trenches dug and examined both for 

research and site exploration. 

(11) Subsurface exploration to locate water 

levels and barriers and to obtain samples for determination of soil properties needed in computing 

ground response characteristics. Such data are 

largely collected by consultants as part of site exploration studies. 

(12) Detailed topographic maps and submarine 

profiles are needed to estimate slope stability, prepare possible inundation maps, and evaluate 

tsunami runup potential. Where available, these 

normally have been prepared by federal agencies 

but are being made increasingly for design oflarge 

coastal installations. 

(13) Empirical or theoretical modeling of ground 

response in typical geologic/soil environments. 

Such work has been done in universities, by consultants, and by government researchers in the 

United States and some other countries. 

(14) Preparation of relative risk maps. These 

have largely been prepared for specific, large land 

development projects. 

Although the above list encompasses the general range of studies needed for a comprehensive 

analysis of seismic hazards, it is not necessarily 

complete; in many areas, many of the data already 

may be available. 

PRINCIPAL SOURCES OF GEOLOGIC AND 

SEISMIC DATA 

Sources of information on geologic and seismic 

data that may be available for a given area include 

the following: 

(1) County or city departments of Building and 

Safety, Public Works, Building Inspectors, or 

Engineer's Office, especially if they contain a 

geologic staff, are a prime source of information. 

Although these offices are normally concerned 

with day-to-day problems of public works projects 

or in reviewing development and subdivision reports, they will probably have already compiled 

many available data, can evaluate their adequacy, 

identify significant gaps in data, and recommend 

the best means of obtaining additional data. 

(2) Geology departments of local colleges and 

universities are likely to be a good source for information on the local geology and seismology. For 

example, in California the Seismological Laboratory at the University of California at Berkeley 

and at the California Institute of Technology at 

Pasadena operate seismograph stations in various 

parts of the state and undertake extensive seismological research. They can provide invaluable 

data in some areas. Student theses often discuss 

areas near the school, and both faculty members 

and graduate students may undertake consulting 

work nearby. The staff of the department might be 

willing to reference primary data sources and to 

make a preliminary judgment on adequacy. In any 

event, they should be able to direct the inquirer to 

other sources for help. 

(3) Most states have a geological survey that 

may have a geologic mapping program underway 

and would be an excellent source for existing 

geologic data, or would be able to suggest the best 

method of obtaining additional data. In some instances, state surveys have entered into contracts 

with local governments to provide geologic maps 

and some interpretive maps. A few state surveys 

are developing a capability to conduct geophysical 

surveys and seismic studies and may undertake 

groun4-response analyses. 

(4) The U.S. Geological Survey has a nationwide 

program of geologic, hydrologic, and topographic 

mapping. Geologic and seismic research particularly applicable to an assessment of seismic 

hazards is concentrated largely in the San Francisco and Los Angeles areas and along the San 

Andreas and other major active faults in California and other western states. The U.S. Geological 

Survey is an excellent source for existing topographic, geologic, hydrologic, geophysical, and 

seismic data. Sources of additional data and possibly methods of interpretation and use may be suggested upon inquiry. 

Many of the functions that were formerly undertaken by the National Oceanic and Atmospheric 

Administration (NOAA) are now being carried out 

by the U.S. Geological Survey - a nationwide 

strong-motion instrument program, measurement 

of fault creep and crustal strain, operation of a 

worldwide seismograph network, and maintenance of an earthquake information center in 

Boulder, Colo. Two other critical activities- operation of a tsunami warning system and geodetic 

29 
surveying throughout the United States- continue to be conducted by NOAA. 

(5) The U.S. Army Corps of Engineers and U.S. 

Bureau of Reclamation conduct geologic studies of 

dams, reservoirs, and related areas. In addition, 

the Corps of Engineers conducts various studies of 

drainage basins, harbors, and coastal areas. Some 

of these studies may yield data useful in assessing 

seismic hazards. 

(6) Private consulting geologists and soil engineers are valuable, both as sources for existing 

data and as qualified consultants for the collection 

of new data and its analysis for seismic hazards. 

Their files often contain much relevant information (though generally not publicly available) obtained through work on a variety of construction 

projects - school and other public structures, 

streets and highways, utilities, and private developments. 

(7) In many states one or more agencies have 

·regulatory functions to require minimum standards of safety for major public structures including 

damage from earthquakes. These agencies commonly collect many valuable data or fund research 

projects. For example, in California, the Division 

of Safety of Dams in the Department of Water 

Resources has responsibility for approving the location and design and for the periodic inspection of 

all nonfederal dams more than 25 feet high or that 

can impound 50 acre-feet or more. The Office of 

Emergency Services, after consultation with the 

Department of Water Resources, is charged under 

a new state law to designate dams that require 

their owners to prepare maps of areas downstream 

that might be flooded upon failure of the dam. In 

addition, the geologic staff of the Department of 

Water Resources has conducted geologic and seismologic investigations along the route of most of 

California's major water projects. 

(8) Professional organizations, such as the Association of Engineering Geologists, the Earthquake Engineering Research Institute, and others 

also may be very helpful. They commonly organize 

symposia (Nichols and Campbell, 1971), publish 

informative booklets addressed to both the professional and planners (Grading Codes Advisory 

Board and Building Code Committee, 1973), and 

maintain lists of consultants. 

Small jurisdictions with few seismic hazards 

and without direct access to a staff of planners, 

geologists, and soil and structural engineers may 

find it necessary to contract for an evaluation of 

30 

seismic risk. But, whatever the size of the jurisdiction, agency, or developer, such an evaluation, if 

comprehensive and thoughtful, will probably be 

the product of a multidisciplinary team effort, 

whether prepared solely by consultants, by jurisdiction staff, or by a combination of both. 

GLOSSARY 

Amplification. The increase in earthquake 

ground motion that may occur to the principal 

components of seismic waves as they enter and 

pass through different earth materials. 

Bore hole. A hole drilled into the earth for exploratory purposes. 

Damping. A resistance to vibration that causes a 

progressive reduction of motion with time or 

distance. 

Epicenter. That point on the earth's surface directly above the point of origin of an earthquake. 

Free face. A sloping surface exposed to air or 

water such that there is little or no resistance to 

lateral movement of earth materials. 

Fundamental period. The longest period·(duration in time of one full cycle of oscillatory motion) for which a structure or soil column shows 

a response peak-commonly the period of maximum response. 

Geodetic measurements. Controls on location 

(vertical or horizontal) of positions on the earth's 

surface of a high order of accuracy, usually extended over large areas for surveying and mapping operations. 

Geophysical surveys. The use of one or more 

techniques of physical measurement to explore 

earth properties and processes. 

Hazardous building. Building considered unsafe 

owing to poor design, poor construction techniques or materials, defects in foundation conditions, or damage from any one of several possible 

causes. 

Hypocenter. That point along a fault within the 

earth where rupture begins and from which 

earthquake waves originate. 

Intensity. A subjective measure of the force of an 

earthquake at a particular place as determined 

by its effects on persons, structures, and earth 

materials. The principal scale used in the 

United States today is the Modified Mercalli, 

1956 version as defined below (modified from 

Richter, 1958, p. 137-138): 

I. Not felt. 
II. Felt by persons at rest, on upper floors, or 

favorably placed. 

III. Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration 

estimated. May not be recognized as an 

earthquake. 

IV. Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt 

like a heavy ball striking the walls. Standing automobiles rock. Windows, dishes, 

doors rattle. Wooden walls and frame may 

creak. 

V. Felt outdoors; direction estimated. Sleepers 

wakened. Liquids disturbed, some spilled. 

Small unstable objects displaced or upset. 

Doors swing. Shutters, pictures move. Pendulum clocks stop, start, change rate. 

VI. Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Windows, 

dishes, glassware broken. Knickknacks, 

books, etc., off shelves. Pictures off walls. 

Furniture moved or overturned. Weak plaster and masonry D1 cracked. 

VII. Difficult to stand. Noticed by drivers of automobiles. Hanging objects quiver. Furniture broken. Weak chimneys broken at roof 

line. Damage to masonry D, including 

cracks; fall of plaster, loose bricks, stones, 

tiles, and unbraced parapets. Small slides 

and caving in along sand or gravel banks. 

Large bells ring. 

VIII. Steering of automobiles affected. Damage 

to masonry C; partial collapse. Some damage to masonry B; none to masonry A. Fall 

of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame 

houses moved on foundations if not bolted 

down; loose panel walls thrown out. Decayed piling broken off. Branches broken 

from trees. Changes in flow or temperature 

of springs and wells. Cracks in wet ground 

and on steep slopes. 

IX. General panic. Masonry D destroyed; 

masonry C heavily damaged, sometimes 

with complete collapse; masonry B seriously damaged. General damage to foundations. Frame structures, if not bolted, 

shifted off foundations. Frames racked. 

Serious damage to reservoirs. Underground 

1See Uniform Building Code for specifications on quality of masonry construction. 

pipes broken. Conspicuous cracks in ground 

and liquefaction. 

X. Most masonry and frame structures destroyed with their foundations. Some wellbuilt wooden structures and bridges destroyed. Serious damage to dams, dikes, 

embankments. Large landslides. Water 

thrown on banks of canals, rivers, lakes, etc. 

Sand and mud shifted horizontally on 

beaches and flat land. Rails bent slightly. 

XI. Rails bent greatly. Underground pipelines 

completely out of service. 

XII. Damage nearly total. Large rock masses 

displaced. Lines of sight and level distorted. 

Objects thrown in the air. 

Left-lateral movement. A generally horizontal 

movement in which the block across the fault 

from the observer has moved to the left. 

Magnitude. The rating of a given earthquake is 

defined as the logarithm of the maximum amplitude on a seismogram written by an instrument of specified standard type calculated to be 

at a distance of 62 miles (100 km) from the epicenter. The zero of the scale is fixed arbitrarily. 

The scale is open ended but the largest known 

earthquake magnitudes are near 8%. Because 

the scale is logarithmic, every upward step of 1 

magnitude unit increases the recorded amplitude by 10. (After Richter, 1958, p. 17). 

Microearthquake. An earthquake having a 

magnitude of 2 or less on the Richter scale. 

Microseismic event. Earthquake or maninduced vibrations observable only with instruments. 

Modified Mercalli. See Intensity. 

Normal fault. A vertical to steeply inclined fault 

along which the block above the fault has moved 

downward relative to the block below. 

Plastic deformation. A permanent change, excluding rupture, in the shape of a solid. 

Remote sensing. The acquisition of information 

or measurement of some property of an object by 

a recording device that is not in physical or intimate contact with the object under study. The 

technique employs such devices as the camera, 

lasers, infrared and ultraviolet detectors, microwave and radio frequency receivers, and 

radar systems. 

Reverse fault. A steeply to slightly inclined fault 

in which the block above the fault has moved 

relatively upward or over the block below the 

fault. 

31 
Right-lateral movement. Generally horizontal 

movement in which the block across the fault 

from an observer has moved to the right. 

Right-normal fault. Horizontal movement in a 

right-lateral sense with accompanying normal 

fault movement. (See Right-lateral movement 

and Normal fault.) 

Sag pond. Enclosed depression, generally occupied by water, formed when movement along 

a fault has disturbed the surface or subsurface 

continuity of drainage. 

Sand boils. Turbid upward flow of water and some 

sand to the ground surface resulting from increased ground water pressures when saturated 

cohesionless materials are compacted by earthquake ground vibrations. 

Sand ridges. Low ridges of sand extruded along 

fissures caused by ground cracking and expulsion of water and sand by liquefaction. 

Sand volcano. A low, cone-shaped accumulation 

of sand produced by the upward expulsion of 

sand-laden water from compaction of saturated 

cohesionless materials subjected to earthquake 

ground vibrations. 

Scarp. A cliff or steep slope formed by a fault, 

generally by one side moving up relative to the 

other. 

Seismic. Pertaining to an earthquake or earth 

vibration, including those that are artifically 

induced. 

Seismograph. An instrument that scribes a permanent continuous record of earth vibrations. 

Seismometer. A device that detects vibrations of 

the earth, and whose physical constants are 

known sufficiently for calibration to permit calculation of actual ground motion from the 

seismograph. 

Shear. A mode of failure whereby two adjacent 

parts of a solid slide past one another parallel to 

the plane of failure. 

Shear wave. A distortional, secondary or transverse wave. 

Strain. The amount of any change in dimensions 

or shape of a body when subjected to deformation. 

Stress. In a solid, the force per unit area, acting on 

any designated plane within it. 

Strike-slip fault. Fault in which movement is 

principally horizontal. (See Right-lateral 

movement and Left-lateral movement.) 

Strong motion. Ground motion produced by a 

ustrong" earthquake or one capable of producing 

32 

damage to structures. The magnitude of such an 

earthquake may vary considerably according to 

the character of the earthquake. 

Thrust fault. See Reverse fault. 

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33