THE SAN FERNANDO, CALIFORNIA, 

EARTHQUAKE OF FEBRUARY 9, 1971: 

A preliminary report published jointly by the U.S. Geological Survey 

and the National Oceanic and Atmospheric Administration 

U.S. DEPARTMENT OF THE INTERIOR U.S. DEPARTMENT OF COMMERCE 

THE SAN FERNANDO, CALIFORNIA, 

EARTHQUAKE OF FEBRUARY 9, 1971: 

A preliminary report published jointly by the U.S. Geological Survey 

and the National Oceanic and Atmospheric Administration 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 733 

Contributions from: 

California Division of Mines and Geology 

California Division of Oil and Gas 

California Institute of Technology 

Earthquake Engineering Research Institute 

H. J. Degenko/b and Associates, Engineers 

Lamont-Doherty Geological Observatory of Columbia University 

U.S. Deportment of Commerce, National Oceanic and Atmospheric Administration 

U.S. Department of the Interior, Geological Survey 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1971 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

UNITED STATES DEPARTMENT OF COMMERCE 

MAURICE H. ST ANS, Secretary 

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

Robert M. White, Administrator 

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

Washington, D.C. 20402 - Price $2.25 (paper cover) 
Lower Van Norman Dam in the Mission Hills, overlooking the heavily populated San Fernando Valley, was severely damaged and on the brink of catastrophic failure as a result of the San Fernando earthquake of February 9, 1971. 
THE SAN FERNANDO, 

CALIFORNIA, 

EARTHQUAKE 

FEBRUARY 9, 1971 
CONTENTS 

Page 

Introduction, by Arthur Grantz, U.S. Geological Survey ----·----------------------------------------------------··- 1 

An estimate of the damage, by Reuben Kachadoorian, U.S. Geological Survey ------------------------------------- 5 

Geologic setting and activity of faults in the San Fernando area, California, by Carl M. Wentworth and R. F. Yerkes, 

U.S. Geological Survey _______ -------------- ______ ------·---------------- _________ ---------------------------··- 6 

Main shock and larger aftershocks of the San Fernando earthquake, February 9 through March 1, 1971, by C. R. 

Allen, G. R. Engen, T. C. Hanks, J. M. Nordquist, and W. R. Thatcher, Seismological Laboratory, California Institute of Technology ----------------------------------- ----------------------------------------------------··- 17 

Precise locations of aftershocks of the San Fernando earthquake 2300 (GMT) February 10-1700 February 11, 

1971, by Thomas C. Hanks, Thomas H. Jordan, and J. Bernard Minster, Seismological Laboratory, California 

Institute of Technology _________________ ------------ __ -·------ __________ --------------------------------------- 21 

Aftershocks of the earthquake, by R. L. Wesson, W. H. K. Lee, and J. F. Gibbs, U.S. Geological Survey --------- 24 

Fault-plane solutions of the February 9, 1971, San Fernando earthquake and some aftershocks, by James H. Whitcomb, Seismological Laboratory, California Institute of Technology -------------------------------------------- 30 

Microearthquakes on the San Andreas fault and aftershocks of the San Fernando earthquake, by Christopher H. 

Scholz, Lamont-Doherty Geological Observatory of Columbia University -------------------------------------- 33 

Preliminary source parameter determination of the San Fernando earthquake, by Max Wyss, Lamont-Doherty Geological Observatory of Columbia University ________________________________________________________ :___________ 38 

Pattern of faulting and nature of fault movement in the San Fernando earthquake, by Barclay Kamb, L. T. Silver, 

M. J. Abrams, B. A. Carter, T. H. Jordan, and J. B. Minster, Division of Geological and Planetary Sciences, 

California Institute of Technology __ --------------------------------------------------------- _ ---------------- 41 

Surface faulting, by U.S. Geological Survey staff ----------·------------------------------------------------------ 55 

Strains and tilts associated with the San Fernando earthquake, by Pierre Jungels and Don L. Anderson, Seismological Laboratory, California Institute of Technology ---·------------------------------------------------------ 77 

Preliminary measurements of tectonic movement, by R. 0. Burford, R. 0. Castle, J. P. Church, W. T. Kinoshita, S. H. 

Kirby, R. T. Ruthven, and J. C. Savage, U.S. Geological Survey ---------------------------------------------- 80 

Repeated surveys of small scale figures established across surface fault ruptures following the earthquake, by John 

C. Lahr and Max Wyss, Lamont-Doherty Geological Observatory of Columbia University, and James A. Hileman, 

Seismological Laboratory, California Institute of Technology ------------------------------------------------- 86 

Instrumental monitoring of post-earthquake fault movements ( afterslip), by Robert D. Nason, Earthquake Mechanism Laboratory, National Oceanic and Atmospheric Administration ---------------------------------------- 89 

Preliminary results from recording aftershock ground motion on alluvial deposits, by Richard E. Warrick and William B. Joyner, U.S. Geological Survey -----------------·------------------------------------------------------ 91 

Shattered earth at Wallaby Street, Sylmar, by Robert D. Nason, Earthquake Mechanism Laboratory, National 

Oceanic and Atmospheric Administration --------------·------------------------------------------------------ 97 

Seismically triggered landslides in the area above the San Fernando Valley, by Douglas M. Morton, California Division of Mines and Geology ----------------------------·------------------------------------------------------ 99 

Landsliding in the vicinity of the Van Norman Lakes, by T. L. Youd, U.S. Geological Survey _____________ .:________ 105 

Ground failure on the San Fernando surface away from obviously tectonic rupture zones, by Robert V. Sharp, U.S. 

Geological Survey --------------------------------------·-------------------~---------------------------------- 110 

Methane seep off Malibu Point following the San Fernando earthquake, by H. Edward Clifton, H. Gary Greene, 

George W. Moore, and R. Lawrence Phillips, U.S. Geological Survey ----------------------------------------- 112 

Oil and gas seepages and damage to oil field facilities related to the earthquake, by California Division of Oil and 

Gas ---------------------------------------------------·------------------------------------------------------ 117 

Water-resources aspects, by A. O.Waananen and W. R. Moyle, Jr., U.S. Geological Survey ------------------------ 119 

Damage to constructed works associated with soil movements and foundation failures, by T. L. Youd and H. W. 

Olsen, U.S. Geological Survey ___ -----------------------·------------------------- ____________ ----------------- 126 

Preliminary structural lessons from the earthquake, by Henry J. Degenkolb, H. J. Degenkolb and Associates, Engineers --------------------------------------------------·------------------------------------------------------ 133 

v 
VI CONTENTS 

THE FOLLOWING TECHNICAL REPORTS ARE FROM THE NATIONAL OCEANIC AND ATMOSPHERIC 

ADMINISTRATION, EARTHQUAKE ENGINEERING RESEARCH INSTITUTE 

A preliminary report of near-field seismic monitoring of the San Fernando earthquake aftershock series, by A. F. 

Espinosa, E. R. Engdahl, A. C. Tarr, and S. Brockman, National Ocean Survey, National Oceanic and AtmosPage 

pheric Administration _________________ -----------------·- ___________________________ -------------------------- 135 

Preliminary fault-plane solution for the San Fernando earthquake, by W. Dillinger and A. F. Espinosa, National 

Ocean Survey, National Oceanic and Atmospheric Administration ------------------------------------------- 142 

Some observations of the San Fernando, California, earthquake with a laser strain meter, by Jon Berger, Institute 

of 9eophysics and Planetary Physics, University of California, San Diego ----------------------------------- 150 

Preliminary report on felt area and intensity, by Nina H. Scott, National Ocean Survey, National Oceanic and 

Atmospheric Administration _______________________________ ---------------------------- _____________ _ _________ 153 

Ground motion amplification and vibration measurements, by Kenneth King, National Ocean Survey, National 

Oceanic and Atmospheric Administration --------------·------------------------------------------------------ 155 

Magnetic field survey of the San Fernando earthquake epicentral area, by J. E. O'Donnell and H. E. Kaufman, 

National Ocean Survey, National Oceanic and Atmospheric Administration ---------------------------------- 157 

Crustal-movement surveys and preearthquake strain analysis, by C. A. Whitten, National Ocean Survey, National 

Oceanic and Atmospheric Administration ---------------------------------------------------------------------- 161 

Preliminary strong-motion results from the San Fernando earthquake of February 9, Hi71, by R. P. Maley and W. 

K. Cloud, National Ocean Survey, National Oceanic and Atmospheric Administration ------------------------ 163 

Evidence of record' vertical accelerations at Kagel Canyon during the earthquake, by B. J. Morrill, National Ocean 

Survey, National Oceanic and Atmospheric Administration --------------------------------------------------- 177 

Introduction to the engineering study, by the Earthquake Engineering Research Institute Committee _____________ 182 

Soils and foundations, by L. LeRoy Crandall, L. LeRoy Crandall and Associates ---------------------------------- 186 

Damage to the Olive View Hospital buildings, by the Earthquake Engineering Research Institute Committee _______ 188 

Damage to the Los Angeles County Juvenile Facilities, Sylmar, by James H. Thompson, Wilson and Thompson, ConsuUing Structural Engineers --------------------------------------------------------------------------------- 191 

Damage to the Pacoima Memorial Lutheran Hospital, by William F. Ropp, Daniel, Mann, Johnson, and Mendenhall, 

Architects and Engineers ____________ --------------- _________________ ------------------ ____________ __________ 193 

Damage to the Holy Cross Hospital, by S. B. Barnes, S. B. Barnes and Associates -------------------------------- 195 

Damage to the Indian Hills Medical Building, by James H. Thompson, Wilson and Thompson, Consulting Structural 

Engineers, and James J. Kesler, Karotis and Kesler ----·------------------------------------------------------ 198 

Damage to the Union Bank building, by Paul Greenfield, Erkel-Greenfield and Associates --------------------------· 200 

Damage to the San Fernando Industrial Tract, by Earthquake Engineering Research Institute Committee ---------· 201 

Damage to the Sylmar Industrial Tract, by Earthquake Engineering Research Institute Committee ----------------· 203 

Damage to a market, Glenoaks and Hubbard, San Fernando, by Walter Dickey, Consulting Structural Engineer ____ 204 

Damage to a market, 13570 Eldridge, Los Angeles, by Earthquake Engineering Research Institute Committee _______ 206 

Damage to two store buildings in the North Oaks Shopping Center, and one building in the Valencia Shopping Center, by James J. Kesler, Karotis and Kesler ------------------------------------------------------------------ 207 

Damage to public school buildings, by J. F. Meehan, California Office of Architecture and Construction _____________ 209 

Damage to other buildings, by Walter Brugger, Research Engineer, Los Angeles City Division of Buildings and 

Safety _____________________________________________ ......... - _ __ _ _ _ _ _ _ _ __ _ __ _ _ _ _ __ _ __ _ ___ __ _ __ _ __ _ __ _ ___ _ _ __ ____ _ _ 213 

Damage to building equipment and contents, by J. Marx Ayres, Ayres, Cohen, and Hayakawa --------------------- 220 

Damage to water supply systems, by C. Martin .Duke, University of California at Los Angeles --------------------- 225 

Damage to transportation systems, by J. F. Meehan, California Office of Architecture and Construction ------------- 241 

Damage to energy and communications systems, by D. F. Moran, Consulting Structural Engineer ------------------- 245 

Sociological aspects of the earthquake, by Earthquake Engineering Research Institute Committee ------------------ 251 

Preliminary conclusions and recommendations based on engineering studies, by Earthquake Engineering Research 

Institute Committee _________ -------------------------------- ______________________ ---------------------------- 253 

Cooperating organizations ---------------------------------------------------------------------------------------- 254 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

INTRODUCTION 

By ARTHUR GRANTZ 

U.S. GEOLOGICAL SURVEY 

The violent tremors that shook the San Fernando 

area (see fig. 1) at about 6 o'clock on the morning 

of February 9, 1971, are a painful reminder that 

earthquakes and the violent distortions and displacements of the earth's surface which commonly 

accompany them are a natural and permanent part 

of the environment in sizeable areas of the United 

States. The tremors also warn us that we must· 

improve our ability to recognize those places where 

such potentially destructive distortions ·and displacements are likely to occur before we plan new 

cities or design buildings and structures in these 

areas. They also warn us that we must reexamine the 

criteria by which we judge the safety of older 

buildings and structures and the design of some 

types of new buildings and structures in the earthquake-prone regions. The reminder, however, cost 

64 people their lives and created physical losses 

estimated at more than one-half billion dollars. The 

total loss may approach $1 billion when all the· 

direct and indirect costs are tallied. If the earthquake had struck during the working day, when 

public buildings, businesses, and highways are 

crowded, the loss of life and the incidence of major 

injuries would have been greater. Had the Lower 

Van Norman Lake Dam, which was close to collapse when the earthquake ended, actually failed, the 

San Fernando earthquake might have become infamous as the deadliest in United States history. 

It must be emphasized that the toll at and near 

San Fernando was exacted by an earthquake of 

only moderate size-as judged by its rating of 6.6 

on the Richter magnitude scale. By comparison, the 

great San Francisco earthquake of 1906, which has 

been assigned a Richter magnitude of 8.3, radiated 

perhaps a few hundred times more energy and 

inflicted severe damage over a much greater area. 

If an earthquake like that of 1906 were to strike 

in or near one of coastal California's major population centers it is likely that the casualties and 

physical loss suffered at San Fernando would be 

exceeded manyfold. 

On the other side of the ledger, many earth 

scientists and engineers are now convinced that the 

body of knowledge concerning earthquakes and 

their effects is at last sufficiently large and sophisticated that we can learn from this earthquake some 

important and very practical lessons by which we 

can alleviate and perhaps even forestall the damage 

that some types of earthquake will inevitably 

threaten. To this end, an impressive number of 

researchers and practitioners in the earth and 

engineering sciences immediately turned their attention to the San Fernando earthquake and its 

geologic, seismologic, and engineering effects. 

A prompt response to the earthquake was critical, 

for both the public officials and the private persons 

who had to cope with the destruction had a great 

and immediate need for reliable information about 

the earthquake and its effects. In addition, past experience had shown that (1) monitoring of aftershocks and continuing distortions of the earth's 

surface must begin promptly because these phenomena die out quickly, (2) the field evidence 

from which the nature of earthquakes and their 

damaging geologic effects must be deduced. is rap-
2 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

10 0 10 20 30 40 KILOMETERS 

~~~~~~====~~~====~ 

10 0 10 20 MILES 

8=~~==~~~~~======== 

FIGURE 1.-lndex map showing earthquake epicenter. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 3 

idly destroyed by even emergency repairs or heavy 

precipitation, and (3) hazardous geologic and engineering situations must be quickly identified and 

brought to the attention of public and private 

officials. Thus, although the San Fernando earthquake occurred at 6 :00 a.m. local time, investigators from throughout California were in the 

stricken areas the same morning, and by the next 

day dozens of investigators were analyzing the engineering failures and were mapping and describing 

the surface fault ruptures, vertical and horizontalshifts in the land surface, landslides, and soil and 

foundation failures that caused much of the damage 

at San Fernando. Dozens of sensitive instruments 

were installed promptly to study the aftershocks 

and their effects on various kinds of geologic foundation materials and to monitor postearthquake 

fault movements and continuing distortions of the 

land surface. Fortunately for seismologists the epicenter fell within the permanent seismograph network of the Seismological Laboratory of the California Institute of Technology, and the character 

and location of the main shock and also of the early 

aftershocks were well determined even before . the 

California Institute of Technology net was supplemented by the emplacement of portable seismometers from other institutions. 

Damage in the San Fernando and Sylmar areas of 

Los Angeles County was severe because the epicenter lay only about 14 km (9 miles) north of 

the center of San Fernando and because the fault 

which broke to produce the earthquake was a thrust 

that extended beneath these communities from the 

epicenter and intersected and ruptured the surface 

of the ground in heavily ,built-up areas within them. 

Earthquakes have been associated with thrust faults 

before in California but not as commonly as with 

strike-slip faults of the San Andreas type. Accordingly, comparative studies of the seismic and geologic character, secondary geologic effects, and patterns of damage produced by these two types of 

earthquakes will receive careful attention. Examples of such comparisons are the relative widths 

of the zones of broken ground along the two types 

of fault ruptures and the relation of Richter magnitude and modified Mercalli intensity for the two 

types of earthquakes. 

Relative uplift and warping of the land surface 

above the wedge of rocks overlying the northward-dipping thrust fault was a prominent feature 

of this earthquake, and one which the geologic 

record testifies has occurred repeatedly in the past. 

This indicates clearly that the San Fernando earthquake is not an isolated "freak" event, but one 

which we must presume will recur in the future. It 

is accordingly important that the recurrence interval and any relationship that may exist between 

the patterns of uplift and the patterns of damage 

will, it is hoped, be important aspects of the continuing studies of the earthquake. 

The question of whether or not the location of the 

ruptures produced by the thrust fault zone where it 

emerged at the surface could have been predicted 

receives considerable attention in this report. 

Clearly, much of the damage could have been prevented had these zones been delineated, and zoned 

for open space or parks, before the San FernandoSylmar area was urbanized. It is encouraging for 

the future that many investigators feel confident 

that, armed with the knowledge gained at San 

Fernando, they can identify and delineate other 

similarly active thrust faults in this region and 

elsewhere in the Western United States. 

Probably the most significant and certainly the 

most surprising body of data recorded during the 

earthquake is a unique collection of strong-motion 

accelerograms reported by Maley and Cloud in this 

report. These writers report that the ground accelerations produced by this moderate magnitude (6.6) 

earthquake " ... were the highest ever recorded, 

that is, in the 0.5- to 0.75-g range with several highfrequency peaks to 1 g." These records will surely 

lead to a careful reassessment of earthquake-resistant design criteria because they indicate ground 

accelerations several times greater than those commonly assumed in building criteria for seismic 

regions. They will also provoke intensive study of 

the relation of these surprisingly high accelerations 

to local geologic or topographic conditions at the 

recording sites as well as to the charact~ristics of 

the earthquake and its associated thrust faulting. 

The field and laboratory investigations of the· 

earthquake were characterized, and materially aided 

from the very beginning, by unusually free interchange of information among the participating 

scientists and engineers. As a result, a preliminary 

understanding of the earthquake and its geologic 

and engineering consequences evolved and could 

be disseminated very quickly. This interchange was 

particularly gratifying to the participating investigators because it was apparent that ~ truly full and 

useful understanding of either the scientific or the 

engineering implications of the earthquake and 

its effects will require the integration of insights 

from many disciplines. 

The present report is a preliminary evaluation of 
4 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

data gathered by many groups of investigators during the first 3 weeks after the earthquake. A list of 

cooperating organizations is given at the end of 

the report. Though many of the papers are written 

for the specialist, most will be very useful to the 

general reader and to public officials wanting to 

learn about the earthquake and its effects. The 

report is published jointly by the Geological Survey 

of the U.S. Department of the Interior and the National Oceanic and Atmospheric Agency of the U.S. 

Department of Commerce in the conviction that 

early publication of these necessarily preliminary 

results will meet the following important and immediate needs : 

-It will provide early geologic and engineerguidance to private citizens and public officials engaged in reconstructing the damaged 

areas. 

-It will alert private citizens and public officials to possibly dangerous geologic and engineering situations, such a~ landslide hazards, that were created by the earthquake. 

-It will foster the early exchange of preliminary data and ideas among the many investigators studying the earthquake, particularly 

between workers in different disciplines and 

between scientists and engineers, to the end 

that knowledge of the utmost possible practical value to society will result. 

-It will help to disseminate the preliminary 

results of the earthquake investigations and 

provide information on investigations in progress to the scientific and engineering communities. This should encourage the participation of additional investigators who might 

improve our understanding of the earthquake 

and its effects, and who might suggest additional measures that could be taken to reduce 

the risk posed by future earthquakes. 

-It will inform the public about an event that 

directly affected hundreds of thousands of 

people and could be a preview of future 

events affecting millions. 

-It will focus the attention of public officials 

works and on some of the measures by which 

the hazards from future earthquakes might 

be reduced. 

Rapid publication of preliminary results, while 

it meets many immediate needs, also inevitably results in some duplication, some lapses in data, and 

even a measure of disagreement among the various 

contributing investigators. Indeed, this report will 

serve to alert the participating investigators and 

others to the existence of these gaps and disagreements at an earlier stage than is usually possible, 

and we suspect that the final body of knowledge concerning the earthquake will be expedited and greatly 

improved thereby. Most of the investigations reported in preliminary form in this report are continuing, and most of the present papers will be 

followed by more complete accounts in the months 

and years ahead. 

Readers of this report will find the following U.S. 

Geological Survey 7%' topographic quadrangle 

maps useful for geographic details of the San Fernando area: Oat Mountain, San Fernando, and Sunland, Calif. 

Published geologic source maps include the following-others are indicated in the reference 

citations: 

California Division of Mines and Geology, 1969, Geologic map 

of California, Los Angeles sheet: scale 1 : 250,000. 

Oakeshott, G. B., 1958, Geology and mineral deposits of San 

Fernando quadrangle, Los Angeles County, California: 

Calif. Div. Mines and Geology Bull. 172. 

It would have been desirable to have used a single 

system of measurement units throughout this report, preferably metric. However, in the interest of 

timely publication of this report, conversion to a 

single system was impractical, especially as considerable redrafting of the illustrations would have 

been involved. To assist in making comparisons, the 

following table of equivalent metric and English 

units of length is provided: 

1 millimeter (mm) = 0.039 inch 

1 centimeter (em) =0.39 inch 

1 meter (m) =3.28 feet 

1 kilometer (km) = 0.62 miles 

and planners, while the memory of the earth- ____1 inch=25.4 mm or 2.54 em 

quake is still fresh, on the multiplicity of 1 foot= 0.305 m 

ways in which earthquakes can destroy man's 1 mile= 1.609 km 
AN ESTIMATE OF THE DAMAGE 

By REUBEN KACHADOORIAN 

U.S. GEOLOGICAL SURVEY 

The San Fernando earthquake of February 9, 1971 

lasted about 60 seconds. Within this brief span of 

time 64 persons lost their lives, and the Los Angeles 

area suffered damage estimated at $553 million 

(table 1). This estimate does not include the cost of 

TABLE 1.-Estimate of damage 

l Data supplied by the city of Los Angeles, city of San Fernando, county of Los Angeles~ Los Angeles Unified School District, Corps of Engineers. Los Angeles Flood Control System, State of California, and region 7 of the Office of Emergency Preparedness] 

Structure Number damaged 

Schools ...... ............................... 180 

Hospitals ---·-···---·········-···· 4 

Residential Homes : .................................... 21,761 l 

Apartment houses ......... ...... 102 Mobile homes ........................................ 1,707 Commercial buildings ........ 542 Miscellaneous structures ........................... 250 Highways and roads ..... . ........................................................ . Dams .... . .......................... . .................................. .. Other public structures ......... . ................................................. . Utilities ....... ____ .................................. _ ............................................ . Personal property ................................... . 

Total ........... .. 

Amount 

$22,500,000 

50,000,000 

179,500,000 

27,500,000 

36,500,000 

145,000,000 

42,000,000 

50,000,000 

553,000,000 

emergency services, loss of employment, and loss of 

revenue from taxes and change in the tax base. The 

impact of the earthquake upon the economy of the 

Los Angeles area may reach three-quarters of a billion dollars when the damage analysis is completed 

and all factors are taken into consideration. The private sector suffered $253 million of the $553 million; 

the remaining $300 million damage was to publicly 

owned structures. 

A total of 180 schools were damaged; of these, 35 

received major structural damage and 18 had to be 

vacated. In the Los Angeles Unified School District, 

which includes the schools in the city of San Fernando, 131 of 617 schools received minor to major 

damage. The remaining 49 schools were not in the 

Los Angeles Unified School District. These schools 

received more than $1,000 damage each and were as 

far away as Whittier, about 40 miles southeast of 

San Fernando. 

Two hospitals, the $34 million Olive View, only recently constructed, and the $15 million Veterans, sustained major damage and partial collapse. Reportedly, both facilities will have to be replaced. The Veterans Hospital was constructed during the 1920's 

prior to the establishment of earthquake codes in the 

State of California. 

A total of 21,761 single family dwellings were 

damaged. Of these, 465 were declared unsafe. In 

addition, there were 62 apartment houses and 372 

commercial structures so severely damaged that they 

were also declared unsafe. 

Damage to highways and roads consisted of $22.5 

million to the State Freeway system and $5 million to 

city and county roads. The chief damage to the 

freeway was the collapse of five overpasses and damage to an additional seven. 

Five dams were damaged-the Upper and Lower 

Van Norman Dams, Pacoima Dam, Lopez Dam, and 

Hansen Dam. The Lower Van Norman Dam was 

damaged so severely that the estimated cost of replacement is $34 million. The gravity-arch Pacoima 

Dam suffered about $1.5 million damage at its abutments. Minor damage occurred at Lopez and Hansen 

Dams. 

Public structures damaged, exclusive of dams, 

highways, and hospitals, include those owned by the 

city of Los Angeles, city of San Fernando, county of 

Los Angeles, State of California, and the Federal 

Government. About $73 million damage was done to 

structures owned by the city of Los Angeles. 

Damage to utilities included $14 million to water, 

sewer, electrical and telephone facilities, and $28. 

million to the Sylmar electrical converter station. 

5 
GEOLOGIC SETTING AND ACTIVITY OF FAULTS IN THE SAN FERNANDO AREA, CALIFORNIA 

By CARL M. WENTWORTH and R. F. YERKES 

U.S. GEOLOGICAL SURVEY 

With a section on 

SEISMOLOGICAL ENVIRONMENT 

By CLARENCE R. ALLEN 

SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY 

The faulting associated with the San Fernando 

earthquake of February 9, 1971, occurred in the 

Transverse Ranges structural province, a region 

noted for its strong and relatively young tectonic 

deformation. This is, however, the first example of 

historic surface faulting within the interior of that 

province. 

The Transverse Ranges structural province 

trends eastward across southern California (across 

the center of fig. 1) and constitutes a region of late 

Cenozoic north-south shortening that lies athwart 

the northwesterly regional trend of the dominant 

San Andreas fault system. In the past 30 million 

years the San Andreas fault, master fault of the system, has undergone about 200 km of right-lateral 

strike slip in southern California (Crowell, 1962). 

During historic time, surface faulting in southern 

California has largely been confined to this and related right-lateral strike slip faults in the San Andreas system. Notable exceptions are the historic 

ruptures of the east- and northeast-trending White 

Wolf and possibly Big Pine faults, and now the 

1971 San Fernando faulting, all of which have displayed at least some component of left-lateral strike 

slip (fig:. 1). 

The Transverse Ranges province consists of numerous east-trending mountain ranges and valleys 

typified by late Cenozoic structural deformation and 

strike slip, reverse, and thrust faults of ~imilar 

trend (Bailey and Jahns, 1954; Jennings and 

Strand, 1969). The most spectacular development of 

the structure of this province is in the Ventura 

Basin, where an immense Cenozoic syncline that includes a thickness of 1,500 m of marine Pleistocene 

6 

sediments has both limbs overturned and overridden 

by thrusts (Bailey and Jahns, 1954, p. 92-96). 

Very young deformation in the Transverse Ranges 

is not restricted to the Ventura Basin, however, and 

late Quaternary faulting is known to occur from 

near Point Conception eastward to the San Andreas 

fault. 

The February 9, 1971, faulting broke the ground 

surface near the north margin of the San Fernando 

Valley opposite the "great bend" in the San Andreas fault south of the San Joaquin Valley (fig. 1). 

The geometry of the crustal blocks in this region is 

such that the Transverse Ranges structural block 

southwest of the San Andreas fault is constrained 

and compressed against the bend as the block moves 

northwestward along the fault. During the past 5 to 

10 million years' this compressive deformation has 

thrust the mountain blocks up over adjacent valleys 

to the south. The movement has occurred along 

north-dipping reverse or thrust-fault systems such 

as the Sierra Madre and Santa Susana, which trend 

west and northwest along the southern margins of 

the mountain blocks. The most impressive product 

of this uplift is the bold southern front of the San 

Gabriel Mountains, which stands some 1,500 m 

above the San Fernando and Los Angeles areas to 

the south. Additional horizontal shortening and 

uplift of one of the blocks occurred along the ruptures that accompanied the San Fernando earthquake. 

Although segments of the surface traces of many 

of the Transverse Ranges faults have been mapped 

and interpreted in the context of regional structural 

history, the abundant but relatively unobtrusive evi-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 7 

N 

1 

EXPLANATION 

Historically and recently 

active faults 

Possible extensions of historically and 

recently active faults, and related 

inactive faults 

Inferred extensions of active or related 

inactive faults beneath surficial deposits 

~ 

or the sea floor 

Fauft segments with surface or postulated 

submarine slip during historical earth -

quakes Or with continuous or intermittent 

aseismic fault slippage 120" ll8" 

\ 

\ 

A v E 

50 100 M ILES 

UNDERWATER CONTOURS IN fEET 

' ' 

R 

~ 

T 

\ 

\ 

I 

\ 

114" 

.... 

) 

/ 34" 

MAJOR HISTORICALLY AND RECENTLY ACTIVE FAULTS OF THE SOUTHERN CALIFORNIA REGION 

FIGURE 1.-Major historically and recently active faults of the southern California region. 

dence of their recent geologic activity has not been 

widely recognized or appreciated. Study of the 1971 

San Fernando faulting should reinforce our confidence in using this geologic data to evaluate the future behavior of faults. 

SEISMOLOGICAL ENVIRONMENT 

In the years prior to 1971, the area of the San 

Fernando earthquake had been one of low to moderate seismic activity-not unlike that of many other 

parts of California. Indeed, the 1934-63 strainrelease maps (Allen and others, 1965) indicated that 

the northern San Fernando Valley was seismically 

less active than most other parts of the greater Los 

Angeles area. Certainly there was nothing in the 

very recent seismic history to suggest that this 

area, more than any other area, was particularly 

likely to experience a magnitude 6.6 earthquake. It 

must be kept in mind, however, that an earthquake 

of at least this magnitude occurs somewhere in the 

southern California region on the average of about 

once every 4 years (Allen and others, 1965), and in 

this sense the earthquake itself was no great surprise. An earthquake of about this same magnitude 

occurred in 1968 in the Borrego Mountain area 220 

km southeast of Los Angeles, but damage was small 

because-unlike the 1971 event-it occurred in a remote location. 

Between 1934 and .1971, which is the interval 

during which epicentral locations of southern California earthquakes have been listed by the California Institute of Technology, only about 10 earthquakes of magnitude 3.0 and greater occurred 

within the area that corresponds to the epicentral 

region of the San Fernando earthquake. None of 

these was large, although a few were felt locally, 

such as the magnitude 4.0 shock of August 30, 1964, 

that was centered under southern San Fernando. 

Previous to 1934, two shocks are of special interest: 

the magnitude 5.2 earthquake of August 30, 1930, 

was probably much closer to San Fernando than the 

original assignment of the epicenter location in 

Santa Monica Bay suggests, and it is particularly 

noteworthy because it caused some minor damage to 
8 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 
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solida.ted g ravel , sand , s!lr , and t:lay 

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co mmonly uverl<::lin hy suil 

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Stream terrace deposits 

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Faults Thrust fault 

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dott ed where concealed. queri ed where doubtful 

Tectonic ruptures ------ associated with earthquake 

of February 9, 1971 

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11 ental, soft, poorly to well-cunsu lldat ed 

sed iments; upper part conglomerate and voars e -

g ra ined sa ndston e , mudston e , and t uff: Iuwe r 

part poorl y sort ed co nglom erate with interbedded 

coar~e-grained sandstone, siltstone, and mudsrone, coar se basal vo nglume r ate co nsists of 

angular fragments of underlying basem e nt 

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UNCONFORMITY 

C0EJIHlli4 

Saugus Formation 

OT s. llOrth and cast part of map : s lightly to 

muduratu ly consolidated t:Darse -gr a in cd sand· 

stone, conglumerate. and mudston ~ 

Os . southwe st part of m ap : s lightly .:on solid a ted 

t.:ung l-omerare and cu arse -~ ai ned sand:sr urJ e 

T sr, Sunshine R anch Memb er, of Pliocene age, in 

west part of map ; siltsto ne with interbedded 

.._:;; andston e and conglomerate. locall y interfingers 

wi th uppe r part of P ico Formation 

Pico 

-

Formation .\1arine , soft siltstone. mudstone , and fine-gr ained 

sandston e with interbedd e d coarse -grained sa ndstone and resist ant pebble conglom e r ate; upper 

part int erfinger s with Saugu ~ Formation and 

.lower part with T owsley Formation 

r:: mP:!:·)~~~l Towsley Formation Soft s iltston e and mudstone with inte rb edde d mod erate ly indurated, sand stone and conglomerate ; basa l c onglomerate in west center of map is well ind ura te d and contains boulders and blocks of lac ally-derived baseme~t ro cks. upper pa rt interfingers 

with Pi co Format ion in northwest part of map 

C.u 

... Q.J Q.J { ~ . S .S Modelo Formation 

::0: Silts ton e , soft mudstone, and silicl!ous shale, 

minor int e rbedded ."i:Jndston e 

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UNCONFORMITY 

Topanga • Formation 

Sands : oJJ e a nd cobble -bould er conglom e r ate , poorly 

sorted . m as siv e . commonly well indurated 

UNCONFORMITY 

Volcanic • rocks 

Ba saltic flows . tuff brec cia s . and flow brec c.:ias , 

h a rd and dense to soft. v es i c ular. and amygdaloidal 

Undifferentiated lower Tertiary and Upper 

Cretaceous rocks 

Chi efly sandstone, s iltston e, and p e bble co n -

g lomerate commonl y referred to Martinez and 

Chico Form ations;commonly well i ndurated and 

resistant. C rops out in Simi Hill s in west part 

of map and slivers along San Gabriel fault 

UNCONFORMITY 

Basement complex 

Ign eo us aud meta-igneo us roc ks , commonly d ense 

and cry stalline . North of San Gabriel fault . 

c.: fl ie fl y gab bro. ano rtho sit e, and granodior ite , 

south of Sa n G abri e l fault. chiefly granodiorite 

and diorit e gneiss 

fer: 

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Geology comp 1led by R . F . Yerke s and 

C. . Wentworth, 197 1 

FIGURE 2.-Generalized geologic map of the San Fernando area, Los Angeles County, Calif. (Van Norman Lakes are called San Fernando Lakes on this map 

base.) 

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10 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

both Chatsworth Dam and Lower Van Norman 

Dam. Of much greater significance in terms of its 

similarity to the recent San Fernando earthquake is 

the so-called Pico Canyon earthquake of 1893; Pico 

Canyon is only 5 km west of Newhall, which was 

very heavily shaken by both the 1893 and the 1971 

events. Townley and Allen's (1939) description suggests a magnitude of about 6, inasmuch as the 

shock was described as heavy in Mojave, Ventura, 

and San Bernardino, and was felt in San Diego. 

Numerous landslides and fissures were reported in 

the Newhall area, and aftershocks continued for 

some time. The contemporary report that "landslides from every peak in sight came tumbling down 

with huge boulders; the mountains appeared as if 

myriads of volcanoes had burst forth" might well 

have applied to the 1971 event in addition. It seems 

probable that the 1893 earthquake originated 

slightly west of the 1971 epicenter, but it certainly 

indicates that moderate earthquakes of this size are 

no stranger to the region. 

STRATIGRAPHY 

The San Fernando Valley is in the southeastern 

part of the Ventura Basin area, and its sedimentary 

rocks are similar to those described in the northwest by Winterer and Durham (1962). Oakeshott 

(1958) provides a description of the units at the 

north side of the valley, in the area of the---main 

shock, aftershocks, and surface faulting that accompanied the earthquake. 

In the central Transverse Ranges the crystalline 

basement rocks are overlain with great unconformity by Cretaceous and younger sedimentary rocks 

many thousands of meters thick. The San Fernando 

Valley itself (figs. 2, 3) is an asymmetric synclinorium developed chiefly in Miocene and younger rocks 

that have been deformed by late Cenozoic folding 

and faulting, especially at the northern margin by 

thrusting along the Santa Susana fault and its eastward equivalents. Based on a gravity-density model, 

Corbato (1963) estimates that approximately 4,500 

m of sedimentary rocks are present in the central 

part of the valley. 

None of the late Cenozoic sedimentary rocks are 

particularly hard, and the Saugus Formation especially is only partially indurated and difficult to distinguish from alluvium in drill holes. 

Precambrian to Cretaceous crystalline rocks of 

the basement complex are exposed in the San Gabriel Mountains in the northeast part of the map 

area and in the Verdugo Mountains in the southeast 

corner. These dense metamorphic and igneous rocks 

118'30' 

2 

+ 12 

118 '22'30" 

+ 

3 

34' 

22' 

30" 

FIGURE 3.-Index to geologic map sources. 1, Winterer and 

Durham (1962); 2, R. B. Saul, 1970, California Division of 

Mines and Geology, work in progress; 3, Oakeshott (1958); 

4, T. W. Dibblee, Jr., unpublished data; 5, Bishop (1950); 

6, R. B. Saul, 1968, California Division of Mines and Geology, work in progress; 7, Merifield (1958); 8, Metropolitan 

Water District, 1968, unpublished geologic map L-1078; 

9, Metropolitan Water District, 1968, unpublished geologic 

map B-20262; 10, Metropolitan Water District, 1968, unpublished geologic map L-1084; 11, Metropolitan Water 

District, 1968, unpublished ge~logic map L-1079 ; 12, R. F. 

Yerkes and C. W. Wentworth, generalized from California 

State Water Rights Board (1962), Corbato (1963), and 

Holmes (1919); 13, Johnston (1938); 14, C. W. Jennings 

and R. B. Saul, 1969, California Division of Mines and 

Geology, unpublished data. The unpublished maps of the 

Metropolitan Water District of Southern California are on 

file with the California Division of Mines and Geology. 

constitute the terrane on which .the sedimentary sequence was deposited. Cretaceous and lower Tertiary sedimentary strata are only exposed locally 

along the Santa Susana and San Gabriel faults, although to the west and south of figure 2 they crop 

out extensively. Within the map area south of the 

San Gabriel fault, the oldest sedimentary rocks 

overlying the basement are the middle Miocene 

Topanga Formation, which includes about 300 m of 

conglomerate, marine sandstone, and volcanic rocks. 

As much as 1,500 m of marine upper Miocene 

Modelo Formation is exposed along the foothills of 

the San Gabriel and Verdugo Mountains, in the 

Mission Hills, and in the Santa Susana Mountains. 

The Modelo is overlain by, and locally interfingers 

with, the Towsley Formation of late Miocene-early 

Pliocene age. The Towsley ranges in thickness from 

zero where it is overlapped by the Pico Formation 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 11 

just south of the San Gabriel fault zone to about 

750 m in the east and west central parts of the map 

area. 

The Pico grades upward and laterally into the late 

Pliocene-early Pleistocene Saugus Formation, a 

shallow marine to brackish-water unit that rims the 

north side of the San Fernando Valley. The Saugus 

Formation thickens westward from essentially zero 

at Big Tujunga Canyon to about 1,950 m at Lopez 

Canyon east of Pacoima Wash. An exploratory well 

drilled north of the Olive View fault and about llf2 

km west of Olive View Sanitorium penetrated a 

minimum stratigraphic thickness of 1,200 m of Saugus Formation, and the California State Water 

Rights Board report (1962, v. I., p. 52) states that 

the formation exceeds 1,800 m in thickness in the 

syncline near Sylmar. 

The "middle Pleistocene" Pacoima Formation of 

Oakeshott (1958) has been combined with the Saugus Formation on the map (fig. 2). This deformed 

fanglomerate-breccia unit is exposed north of Sylmar, where it unconformably overlies the Saugus 

and is unconformably truncated by stream-terrace 

and alluvial deposits. 

Uplifted erosional remnants of stream-terrace 

gravel and sand are widely distributed in the San 

Fernando area, but only a few are shown on the 

generalized map. No direct evidence for the age 

of these deposits is available, although a late Pleistocene age is inferred on the basis of their stratigraphic position, lack of deformation, and unconformable relations with the underlying Saugus 

Formation. Oakeshott (1958) was able to distinguish five stages of terrace formation along Pacoima Wash and two in the Lopez-Kagel Canyon 

area 6% km northeast of San Fernando. Some of 

the late Quaternar-y history .. of the mountain blocks 

can be obtained from such geomorphic features. 

UNCONSOLIDATED SEDIMENTS 

The relatively flat surface of San Fernando Valley is underlain by unconsolidated sand, gravel, and 

finer sediment ranging in thickness from zero at the 

valley edges to greater than 200 m in the east-central part of the valley near the south margin of 

figure 2. In the Sylmar area, alluvium is perhaps 6 

m thick, except along Pacoima Wash (California 

State Water Rights Board, 1962). 

Sediment west of Van Norman Lakes and along 

the southern part of the valley has been supplied by 

streams draining areas of sedimentary rocks, with 

the result that alluvium in these areas consists predominantly of clay. In contrast, larger streams at 

the north margin of the valley east of the Lakes 

drain crystalline rocks of high relief and have produced deposits of coarser materials with abundant 

gravel. 

Additional information concerning the alluvial 

deposits in San Fernando Valley is available from 

California State Water Rights Board (1962): plate 

6 (v. I) of that report shows contours on the base 

of the valley fill, or water-bearing sediments, and 

plate 30 shows ground-water contours as of 1958. 

The agricultural soil map of Holmes (1919) is also 

useful. 

EVIDENCE FOR LATE QUATERNARY FAULTING 

A number of faults in the San Fernando area follow prominent topographic breaks at the boundaries 

between the alluvial valleys and the adjacent hills 

and mountains. This relationship, combined with 

stratigraphic evidence, indicates that these faults 

were active in late Quaternary time and that they 

followed the general tectonic patterns established in 

late Tertiary time. The immediately available evidence concerning the late Quaternary history of 

these faults is cited in a following section on structure. This evidence is critical to the evaluation of 

possible future movements on these faults. 

Unfortunately, the geologic record of the late 

Quaternary, which is the past few hundred thousand years of earth history, is incomplete and difficult to interpret. Few of the alluvial deposits that 

constitute the sole stratigraphic record of late Quaternary time in the San Fernando area are even approximately dated at present, and their stratigraphic relations are poorly known and difficult to 

decipher. Topographic features produced by faulting of the ground surface· constitute the only other 

direct record of .late Quaternary , faulting but are 

often difficult to interpret. Most can form in more 

than one way, and their durability in various geologic and climatic situations, although relatively 

short in geologic time, is poorly understood. 

Where late Quaternary faults are buried or ob-

~cured by alluvium, subsurface information is 

needed to evaluate their history. Particularly useful 

are data on the effects of such faults on the movement of ground water. These effects are essentially 

of two kinds: (1) clayey gouge seams can form 

along such faults, even in alluvium, and partly or 

completely block passage of water across them, or (2) 

faulting can also produce a step in the bedrock surface beneath the alluvium, which will impose a barrier to ground-water movements if the general 

direction of such movement is toward the upthrown 

block or the development of a ground-water cascade 
12 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

if the direction is opposite. Although such steps 

could be formed by erosion or faulting prior to burial by alluvium, well-defined steps of significant 

length are more likely to form by postalluvium 

faulting. Erosion of a channel through a faultgouge barrier could also result in the formation of a 

ground-water cascade. All hydrologic evidence cited 

in the following pages comes from a valuable study 

of ground water in the San Fernando Valley by the 

California State Water Rights Board (1962). 

The age of the San Fernando Valley alluvium 

that is involved in faulting is unknown in detail. 

These deposits, however, are sufficiently young that 

it is prudent to consider any fault that has an observable effect on the movement of shallow ground 

water in the San Fernando Valley to have been active in late Quaternary time. 

STRUCTURE 

The structure of the San Fernando Valley area is 

dominated by two intersecting regional fault systems: the northwest-trending San Andreas system 

of right-lateral strike-slip faults, which includes the 

San Gabriel fault, and the east-trending system of 

north-dipping reverse and thrust faults along which 

much of the uplift of individual ranges has been accomplished. Among the latter are the Santa SusanaSierra Madre trend and faults within the San Fernando Valley. 

Although the older geologic history of the San 

Fernando Valley area is dominated by the San Gabriel fault zone, the present-day structure of the 

northern margin of the valley has been greatly 

modified by overthrusting on the north-dipping reverse faults. Uplift along these faults has created 

the large residual gravity gradients mapped by Corbato (1963, map 3) and are shown in figure 4 of 

this report. All of the foregoing fault trends exhibit 

evidence of late Quaternary displacement. 

SAN GABRIEL FAULT 

The San Gabriel fault resembles the San Andreas 

in many ways. It consists of a zone of imbricate 

steeply north-dipping faults and is characterized by 

deflected drainage courses, strike valleys, notched 

ridges, and largely dissimilar geology on opposite 

sides (Oakeshott, 1958). 

The work of Crowell ( 1950, 1952, and 1962) indicates that the fault absorbed about 30 km of right 

strike slip and locally as much as 4.3 km of dip slip 

during Pliocene time. Oakeshott ( 1958) cites evidence for 2.5 to 6.5 km of right slip along the fault 

zone in late Pliocene-Quaternary time and shows 

the "middle Pleistocene" Pacoima Formation to be 

EXP LANATION 

Basement co mpte>~ 

Fault 

Dolled w/r ere corH:e all'd 

Thrust rault 

DO Large r es 1dual gravrty grad re nt 

Boundary of small re srdua l 

gravrtv c hange 

FIGURE 4.-Structure map of the San Fernando Valley area 

modified from Corbato (1963, fig. 7). 

offset in an area northwest of figure 2. Late Quaternary stream-terrace deposits appear to be unaffected by the San Gabriel fault, although none lies 

completely across the fault zone. The displacement 

of Pleistocene deposits and deflected drainages 

along the fault warrant attention to the possibility 

of renewed movement along this fault. 

SANTA SUSANA FAULT 

The Santa Susana is a long east-trending fault 

zone characterized by low-angle thrusting, a sinuous 

trace, and a gentle north dip. Estimates of horizontal shortening and vertical separation across it 

range upward from 2.4 km (Hazzard, 1944; Oakeshott, 1958). 

In the Santa Susana Mountains at the west side 

of figure 2, the fault consists of two parallel strands 

about 0.5 km apart. The northern strand is entirely 

within Tertiary rocks, whereas the southern strand 

forms a thrust contact on which Miocene strata on 

the north overrode Quaternary terrace deposits on 

the south (Bishop, 1950, p. 93-94). 

More recent work east of Bishop's area by R. B. 

Saul (fig. 3) suggests that landsliding might account for some of Bishop's observations. In any 

case, late Quaternary faulting has occurred on the 

south face of the Santa Susana Mountains because 

the west-trending Devonshire fault of Bishop 

(1950) moved both during and after accumulation 

of the terrace deposits. 

The two western traces of the Santa Susana fault 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 13 

merge northwest of Sylmar and continue eastward 

to form a series of northeast-trending faults along 

which rocks of the basement complex have been 

thrust over sedimentary units as young as the Pliocene-Pleistocene Saugus Formation and the "middle Pleistocene" Pacoima Formation. The terrace 

deposits, however, do not appear to be affected 

( Oakeshott, 1958). 

GRANADA HILLS-MISSION HILLS TREND 

This trend of faults is a l4rgely buried system of 

east-trending range-front faults along which the 

southeastern Santa Susana Mountains and the Mission Hills have been uplifted. 

Existence of the Granada Hills fault is based on 

the straight south margin of the adjacent mountains, which suggests that the inferred fault had 

late Quaternary displacement. 

The existence of the Mission Hills fault was postulated by Oakeshott (1958, p. 94, pls. 1 and 2) on 

the basis of topography, a geologic section in a test 

well, and analogy with faults in the mountains north 

of Sylmar. 

The San Fernando fault zone, as used in this report, is defined as the zone of tectonic surface rupture of the 1971 San Fernando earthquake. It consists of the Mission Wells, Sylmar, and Tujunga 

fault segments and other scattered minor faults. 

The Mission Wells and Sylmar segments extend 

generally eastward from the Granada Hills-Mission 

Hills trend and closely coincide with the surface 

trace of a known impediment to southward movement of ground water. This ground-water anomaly 

is shown in figure 2 as a northeast- and east-trending queried fault crossing the neck in the alluvial 

sm·face south of Sylmar. It is marked by a 15-m 

difference in ground-water levels, higher on the 

north, with ground-water cascades flowing southward through alluviated erosional notches at its 

east and west ends. Ground water north of the 

anomaly occurs in confined aquifers in steeply 

north-dipping Saugus strata that are truncated and 

covered by a thin veneer of alluvium; south of the 

anomaly ground water is unconfined and occurs in 

coarse alluvial gravels. 

The California State Water Rights Board report 

(1962) relates the Sylmar ground-water anomaly to 

impermeable strata in the north-dipping Towsley 

( = Repetto in their report) and Saugus Formations. The trace of the ground-water anomaly, however, is at an oblique angle to the strike of beds in 

the Saugus-Towsley; this angle suggests that a 

structural discontinuity such as a fault could more 

reasonably explain it. 

The ground-water anomaly is here concluded to 

be the product of a reverse fault that has raised 

north·ward-dipping Saugus Formation in the Little 

Tujunga syncline against alluvial gravels on the 

south, with progressive erosional planation maintaining only a thin veneer of alluvium over the Saugus strata in the rising northern fault block. Gouge 

along such a fault could account for the impediment 

to ground-water flow, and vertical displacement 

along it could account for the different thicknesses 

of alluvium north and south of the ground-water 

anomaly. Together, these factors could produce the 

resultant differences in ground-water habit across 

the anomaly. M. M. Clark has observed a rather 

subtle south-facing topographic escarpment, on aerial photographs taken in 1952, that extends nearly 

continuously along the approximate trace of the 

ground-water anomaly and which is thought to be a 

result of the latest movements on the fault postulated to have caused the anomaly. (See the section 

on "Surface faulting" by the U.S. Geological Survey 

staff in this report.) 

The zone of faulting that approximately follows 

the base of the western San Gabriel Mountains eastward from San Fernando along the north side of 

Tujunga Valley is called the Tujunga segment of 

the San Fernando fault zone in this report. 1 Kamb 

and others (this report) note that the Tujunga 

fault segment as thus defined differs from that of 

Hill ( 1930) for a postulated fault in the central alluvia ted part of the Tujunga Valley and suggest 

that the older definition by Hill be dropped. 

A number of unnamed fault traces had been 

mapped along the Tujunga fault segment prior to 

the new 1971 surface ruptures. One of these faults 

just west of Oliver Canyon dips northward 60° and 

thrusts Miocene strata southward over upper Pleistocene terrace deposits (Oakeshott, 1958). At the 

mouth of Little Tujunga Canyon a ground-water 

cascade of perhaps 30 m, which suggests late Quaternary displacement, is nearly coincident with the 

site of a 1971 rupture. 

VERDUGO FAULT 

The Verdugo fault lies at the southwest foot of 

the Verdugo Mountains (fig. 2, and Jennings and 

Strand, 1969) and is probably responsible for the 

1,000 m of relief between the mountain crest and 

the base of the alluvial fill to the south. This conclu1 R .. J. Proctor of the Los Angeles Metrovolitan Water District reports 

that tectonic ruptures associated with ihe February n earthquake roughlv 

follow a north-dipping thrust fault which he had previously mapped and which he has named Lakeview fault. The scarps in Schwartz and Oliver 

Canyons coincide with this fault, which would be synonomous with the 

Tujunga fault segment as used in this revort. 
14 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

sion is supported by the steep residual gravity gradient found by Corbato (1963, map 3; fig. 4 of this 

paper) to extend along this trend from Burbank to 

west of the Pacoima Hills. The steep southwest face 

of the mountains, the presence of faulted streamterrace deposits north of Burbank (California State 

·water Rights Board report, v.ll., p. A- 23) and a 

ground-water cascade at the mouth of Verdugo 

Wash led Wentworth, Ziony, and Buchanan (1970, 

pl. 1) to conclude that the southeastern end of the 

Verdugo fault had undergone late Quaternary displacement. Between the Verdugo Mountains and the 

Pacoima Hills, clayey gouge seams have been 

formed by fault movement in the alluvial fill along 

the trend of the Verdugo fault, and the resultant 

ground-water impediment has been used as the 

trace for the fault in figure 2. Topographic and 

gravity evidence for the Verdugo fault are lacking 

between the Pacoima Hills and the Mission Hills. 

Limited information indiCates, however, that 

ground-water levels northeast of a reasonable extension of the fault are more than 60 m higher than 

southwest of it and therefore that a major groundwater cascade occurs there. 

NORTHRIDGE HILLS FAULT 

The Northridge Hills fault trends southeastward from the southeastern Santa Susana 

Mountains across the valley floor along the south 

side of the Northridge Hills. The eastward extent of 

the fault is unknown, although its easternmost topographic expression appears almost halfway across 

the valley. The fault forms a distinct though discontinuous topographic feature along its mapped 

length in the valley and is inferred to displace older 

late Quaternary deposits (Qt in fig. 2) and to raise 

Saugus Formation into low hills along its central 

part. Late Quaternary displacement on the Northridge Hills fault may be considerable, for cross sections in the California State Water Rights Board 

report (1962) show the base of the alluvium to be 

faulted downward by as much as about 300m on its 

southwest side. 

CHATSWORTH FAULT 

Corbato (1963, map 3; and fig. 4 of this paper) 

shows a steep gravity gradient extending northeastward across the west end of the San Fernando Valley, which coincides in position with the northeastward trend of faults that juxtapose upper Miocene 

Modelo Formation against Cretaceous rocks at and 

southwest of Chatsworth Reservoir (Jennings and 

Strand, 1969). The bedrock surface beneath the valley alluvium has been dropped down on the southeast side to produce a 25-m ground-water cascade 

within the a11uvium. Additional evidence of late 

Quaternary displacement may exist in the form of 

faulted terrace deposits at the northeast end of 

Chatsworth Reservoir (Conrad, 1949). 

ACTIVITY OF FAULTS 

A fault is active if, because of its present tectonic 

setting, it can undergo movement from time to time 

in the immediate geologic future. This active state 

exists independently of the geologists' ability to recognize it. A number of characteristics have been 

u.sed to identify active faults, such as historic 

seismicity or surface faulting, crustal strain, geologically recent displacement inferred from topography or stratigraphy, or physical connection with a 

known active fault. Not enough is known, however, 

of the behavior of faults to assure successful discrimination of all active faults by such characteristics. 

Of the faults discussed above, only the San Andreas fault and the San Fernando fault zone are 

known to be active on the basis of earthquakes or 

historic surface faulting, and the San Fernando 

fault was discovered to be active only when it ruptured the ground surface on February 9, 1971. It is 

evident, however, that more faults in the San Fernando Va1ley area may be active today than are 

now recognized. Study of the topographic and stratigraphic records of the past histories of these 

faults, in concert with studies of earthquake activity and crustal strain, can lead to important insights into their possible activity. 

Agreement does not currently exist on the length 

of fault history that should be used in evaluating 

the future behavior of faults. The commonly used 

cutoff of 10,000 years (beginning of Holocene time) 

seems too short in the light of surface faulting in 

1952 along the White Wolf fault, which was not 

previously recogni·zed as an active fault and exhibited no obvious evidence of late Quaternary activity 

other than defining a steep mountain front ( Oakeshott, 1955; Dibblee, 1955). The White Wolf experience, combined with the likelihood that only some 

fraction of the past movements of a fault will actually be evident in the geologic record, led Wentworth, Ziony, and Buchanan (1970) to suggest (p. 

13 and 15) that faults with evidence of Holocene 

displacement probably should be considered active 

for most purposes and that it may be desirable to 

consider faults with late Quaternary displacement 

as active, at least for land uses 1·equiring relatively 

high safety factors. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 15 

The addition of the 1971 San Fernando event to 

the experience of the 1952 White Wolf event 

strengthens the conclusion that, in the absence of 

proof to the contrary, demonstrated late Quaternary 

movement should be considered evidence that a 

fault is probably active. Thus, we would tentatively 

conclude that all the faults described above that 

have had late Quaternary displacement are probably 

active. Further work will be required to test and 

corroborate the conclusions of late Quaternary displacement and to evaluate the movement rates and 

characteristics of these faults. 

In view of the foregoing, the location of the 1971 

San Fernando faulting should not have come as a 

complete surprise because preearthquake information was sufficient to suggest the existence of faults 

having late Quaternary displacement along or near 

the positions of the main traces of the February 

1971 ruptures. It would not, however, have been 

possible to predict, on the basis of present knowledge, that the next surface faulting in Southern 

California, or even in the San Fernando area, would 

occur either where or when it did. 

CONCLUSIONS 

The San Fernando Valley area is underlain by a 

depositional basin that dates from Miocene time and 

is bordered by pre-Cenozoic crystalline basement 

rocks. The basement rocks are unconformably overlain by an Upper Cretaceous-Cenozoic sequence of 

clastic sedimentary rocks that has been deformed by 

north-south compression, producing east-west folds 

and causing thrust faulting during late Cenozoic 

time along the southern margins of the mountain 

ranges. The thrust faulting-and the February 

1971 rupturing-are continuations of long-established tectonic processes that have resulted in uplift 

of the mountainous parts of the Transverse Ranges. 

The faulting of February 9, 1971, near San Fernando occurred on faults not previously recognizedas active, although sufficient evidence was available 

to suggest that there had been movements along 

their main traces in late Quaternary time. The topographic and stratigraphic record of late Quaternary 

fault movements, including their effect on groundwater flow, must be given greater scrutiny, because 

late Quaternary displacement appears to be a sufficient criterion for probable activity of a fault in 

this area. Numerous faults in the San Fernando 

Valley area exhibit some evidence of late Quaternary displacement and in the light of the San Fernando faulting should be considered probably active 

until investigated in detail with both geologic and 

geophysical techniques. 

REFERENCES CITED 

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: Seismol. Soc. 

America Bull, v. 55, p. 753-797. 

Bailey, T. L. and Jahns, R. H., 1954, Geology of the Transverse Range Province, southern California, in Jahns, 

R. H., ed., Geology of southern California: California 

Div. Mines and Geology Bull. 170, p. 83-106. 

Bishop, W. C., 1950, Geology of the southern flank of Santa 

Susana Mountains, county line to Limekiln Canyon, Los 

Angeles County, California: Los Angeles, California Univ. 

M.A. thesis. 

California State Water Rights Board, 1962, The city of Los 

Angeles vs. City of San Fernando: California State Water 

Rights Board, Report of Referee, No. 650079, v. I, 258 p., 

36 pls.; v. II, various pages. 

Conrad, S. D., 1949, Geology of the eastern portion of the 

Simi Hills, Los Angeles and Ventura Counties, California: 

Los Angeles, California Univ. M.A. thesis. 

Corbato, C. E., 1963, Bouguer gravity anomalies of the San 

Fernando Valley, California: California Univ. Pubs. Geol. 

Sci., v. 46, no. 1, p. 1-32. 

Crowell, J. C., 1950, Geology of Hungry Valley area, southern 

California: Am. Assoc. Petroleum Geologists Bull., v. 34, 

p. 1623-1646. 

---1952, Probable large lateral displacement on San 

Gabriel fault, southern California: Am. Assoc. Petroleum 

Geologists Bull., v. 36, no. 10, p. 2026-2035. 

---1962, Displacement along the San Andreas fault, California: Geol. Soc. America Spec. Paper 71, 61 p. 

Dibblee, T. W., Jr., 1955, Geology of the southeastern margin 

of the San Joaquin Valley, California, in Oakeshott, G. B., 

ed., Earthquakes in Kern County, California, during 1952: 

California Div. Mines and Geology Bull. 171, p. 23-34. 

Hazzard, J. C., 1944, Some features of Santa Susana thrust, 

vicinity of Aliso Canyon field, Los Angeles County, California [abs.]: Am. Assoc. Petroleum Geologists Bull., v. 

28,no. 12,p. 1780-1781. 

Hill, M. L., 1930, Structure of the San Gabriel Mts. north of 

Los Angeles, California: California Univ. Pubs. Geol. Sci., 

v. 19,no.6,p. 137-170. 

Holmes, L. C., 1919, Soil survey of the San Fernando Valley 

.area, California, i?J. Field operations.of the Bureau-of Soils 

1915: U.S. Dept. Agriculture, Bur. Soils, 17th rept., pl. 

63, scale 1:62,500. 

Jennings, C. W., and Strand, R. G., 1969, Geologic map of 

California, Olaf P. Jenkins edition, Los Angeles sheet: 

California Div. Mines and Geology, scale 1:250,000. 

Johnston, R. L., 1938, The geology of a portion of the western 

Verdugo Mountains: Los Angeles, California Univ. M.A. 

thesis. 

Merifield, P. M., 1958, Geology of a portion of the southwestern San Gabriel Mountains, San Fernando and Oat 

Mountain quadrangles, Los Angeles County, California: 

Los Angeles, Califm:nia Univ. M.A. thesis. 

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 Div. Mines and Geology Bull. 171, p. 15-22. 
16 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

---1958, Geology and mineral deposits of San Fernando 

quadrangle, Los Angeles County, California: California 

Div. Mines and Geology Bull. 172, 147 p., map scale 

1:62,500. 

Townley, S. D., and Allen, M. W., 1939, Descriptive catalog 

of earthquakes of the Pacific Coast of the United States, 

1769 to 1928: Seismol. Soc. America Bull., v. 29, p. 1-297. 

Wentworth, C. M., Ziony, .J. I., and Buchanan, J. M., 1970, 

Preliminary geologic environmental map of the greater 

Los Angeles area, California: U.S. Atomic Energy Comm., 

TID-25363, 41 p., map scale 1 :250,000. 

Winterer, E. L., and Durham, D. L., 1962, Geology of southeastern Ventura basin, Los Angeles County, California: 

U.S. Geol. Survey Prof. Paper 334-H, p. 275-366, map 

scale 1 :24,000. 
MAIN SHOCK AND LARGER AFTERSHOCKS OF THE SAN FERNANDO EARTHQUAKE, 

FEBRUARY 9 THROUGH MARCH 1, 1971 l 

By C. R. ALLEN, G. R. ENGEN, T. C. HANKS, J. M. NORDQUIST, and W. R. THATCHER 

SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY 

The purpose of this paper is to summarize the 

seismological information on the main shock of the 

San Fernando earthquake and its aftershocks that 

occurred within the subsequent three weeks, from 

February 9 through March 1, 1971. These preliminary data are based on records of the permanent 

stations of the California Institute of Technology 

seismographic array, with supplemental information from the U.S. Geological Survey station at 

Point Mugu and the California Department of 

Water Resources stations at Pyramid and Cedar 

Springs (both telemetered to Pasadena). During the 

first few hours of activity, these were the only 

nearby stations that were in operation, but portable 

seismographic units that were installed by various 

groups in the ensuing days will eventually allow 

much better hypocentral determinations for the 

late aftershocks than are presented in this preliminary report. 

The main shock has tentatively been assigned the 

following parameters: 

Magnitude (ML) __ 6.6 

Origin time _______ 14 :00:41.6, 9 F ebruary 1971 

(GMT) 

Location __________ 34' 24.0' N., 118' 23.7' W. 

Depth ------------13.0 km 

It should be emphasized that the hypocenter of the 

main shock represents only the point of initial rupture. Breaking presumably then propagated southward and upward from this point at about 45 °, reaching the ground surface in the Sylmar-San 

Fernando area (fig. 1). It is not surprising that the 

principal geologic and engineering effects were observed some distance south of the epicenter, where 

the fault plane was shallower and the fault displacement presumably was greater. 

Station readings used in locating the main shock 

are given in table 1; all of these 11 stations are less 

than 200 km from the epicenter. The fact that three 

1 Contribution No. 1990, Division of Geological and Planetary Sciences, 

California Institute of Technology, Pasadena, California. 

.JY' ·o 3.0-3.4 -.., 

t "' 0 0 • 3.5-3.9 ~ ~ 

• 4.0 - 4.4 5 JO km • 4.5 -5.1 

Main Shock Acton 

5 

\Soug~s • 

• • • Newhall Q . • . .... 

• . •• • • • f ault trac. es •' .. • • :<~ .. .. 

FIGURE 1.-Index map of study area, showing epicenters of 

the main shock and aftershocks of magnitude 3.0 and 

greater of the San Fernando earthquake for the first 3 

weeks of activity, February 9 through March 1, 1971. 

stations were within 40 km of the epicenter gives us 

reasonable confidence in the solution, although individual station corrections derived from accurately 

located aftershocks-and hopefully calibration explosions- will later be used to refine the hypocentrallocation. The x, y, and z standard errors for the 

tentative location of the main shock are 1.2, 2.0, and 

2.5 km, respectively. The magnitude is based solely 

on the strong-motion (4X) record from Pasadena 

and will undoubtedly be modified when the more 

distant stations are considered; in the meantime it 

agrees well with the assignment of 6.5 by Berkeley 

17 
18 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

TABLE 1.-P-wave arrival times for the main shock at stations 

used in computing the hypocenter 

[DWR, California Department of Water Resources; USGS, U.S. Geological Survey [ 

Station 

symbol 

PAS 

PYR 

MWC 

SBLG 

CSP 

RVR 

ISA 

SYP 

CLC 

GSC 

PLM 

Station name 

Pasadena ___________ --_-_----_--- __ Pyramid (DWR) _______ --- ____ ---- _ 

Mount Wilson ____ ---------------- Pt. Mugu (USGS) _________________ _ Cedar Springs (DWR) _____________ _ Riverside _________________________ _ Isabella __________________________ _ 

Santa Ynez Park __________________ _ China Lake ______________ ---_---- __ 

Goldstone ______ ------------------- Palomar __________________________ _ 

Time 

h m s 

14:00:48.1 

14:00:48.0 

14:00:48.3 

14:00:53.0 

14:00:57.1 

14:00:58.5 

14:01:04.5 

14:01:05.0 

14:01:07.8 

14:01:08.5 

14:01:09.2 

Distance km 

37.1 

39.5 

39.5 

70.8 

97.0 

105.0 

140.2 

146.2 

173.0 

176.3 

183.3 

(Bruce Bolt, personal commun.) and the range of 

6.3 to 6.7 reported by the National Ocean Survey 

(Leonard Murphy, personal commun.). 

There were no foreshocks or other obvious precursory activity, and a careful examination of the 

Mt. Wilson records indicates that no shocks exceeding magnitude 1.5 had occurred in the area in the 

preceding 8 days. No shock exceeding magnitude 2.5 

had been identified in the area during the preceding 

4 months, and it appears that the most recent identifiable event within the area of subsequent activity 

was a shock of magnitude 2.6 that occurred north 

of Sylmar (fig. 1) on September 28, 1970. In the 

years prior to 1971, the area of the San Fernando 

earthquake had been one of low to moderate seismic 

activity-not unlike that of many other parts of 

southern California (Allen and others, 1965). The 

only major historic shock originating within this 

specific area was the so-called Pico Canyon earthquake of 1893 (Townley and Allen, 1939), which 

was probably in the magnitude-6 range but clearly 

was not as large as the 1971 event. The San· Fernando earthquake of 1971 again emphasizes the fallacy of assuming, for a given area, that the largest 

shock -experienced in the past is necessarily :typical 

of the largest shock to be expected in the future. 

Table 2 is a preliminary list of all shocks of the 

San Fernando series of magnitude 3.0 and greater 

that occurred through March 1, 1971. The list, 

which includes some 200 events, is felt to be relatively complete following the first hour of activity, 

during which many small events cannot be discerned because of the frequent occurrence of larger 

shocks. Considerable use has been made of the 4X 

and 100X strong-motion instruments at Pasadena, 

Riverside, and Santa Barbara in studying shocks of 

the first hour, and we feel that most larger events 

have been recognized. With the exception 9f the 

main shock, locations of most of the earthquakes 

listed in table 2 have been determined with depths 

restricted to 8.0 km, which appears to be a reasonable average on the basis of the more accurate determinations using portable stations (Hanks and others, this report). None of the locations in table 2 

has made use of portable stations; the objective has 

TABLE 2.-Shocks of the San Fernando series of magnitude 3.0 and 

greater, February 9 through March 1, 1971 

[Magnitude assignment..:;, in particular, are very tentative. Depths are restricted to 8.0 km, except for the main shock, which is at 13.0 kmj 

Date Time (GMT) ML 

Feb 9 1400 41.6 6.6 1401 5.1 1402 4.4 1402 4.3 1403 4.5 1404 4.3 1406 4.2 1407 4.5 1408 3.9 1409 3.9 1410 21.5 5.1 1413 3.6 1416 4.2 1419 4.4 1422 3.6 1425 3.8 1426 06.9 3.7 1428 3.6 1429 05.2 3.6 1429 3.7 1431 3.7 1432 3.1 1434 3.6 1434 5.1 1439 4.0 1440 4.1 

1441 3.4 1443 3.5 1443 46.7 4.7 1448 3.4 1450 3.9 1452 44.4 3.5 1455 3.7 1457 24.3 3.6 1500 3.2 1503 07.1 3.6 1506 3.3 1510 01.1 4.1 1521 06.6 3.7 1521 3.9 1526 00.7 3.0 1528 25.8 3.7 1530 37.8 3. 7 1535 41.5 3.6 1538 29.7 4.2 1545 58.0 3.6 1548 04.6 3.2 1551 00.9 3.6 1557 3.3 1558 20.7 5.1 1601 45.0 3.3 1614 3.9 1619. 26.0 ,4 •. 3 1621 3.4 1625 3.0 1626 3.2 1627 3.2 1628 41.8 3.3 1628 3.4 1629 3.4 1632 3.8 1633 3.3 1638 3.6 1639 3.8 1641 3.1 1641 3.6 1647 03.7 3.5 1703 47.6 3.6 1704 3.5 1705 3.1 1714 3.1 1719 15.7 3.1 1722 3.2 1739 3.6 1802 3.4 1827 3.5 1829 24.6 3.5 1857 02.4 4.0 1941 3.4 1941 3.5 2011 34.3 3.4 2017 3.5 2027 3.4 2030 3.1 

2037 3.5 2038 3.5 

Lat (N.) 

34'21. 7' 

34'24.0' 

34'21. 8' 

34'18. 5' 

34'19. 7' 

34'20. 8' 

34'18 .0' 

34'23.7' 

34'13.9' 

34'14. 9' 34°14.1' 

34'22.9' 

34'22. 5' 34'21. 0' 34'18.9' 

34'19. 7' 34'16.1' 

34'20.1' 

34'17.1' 

. 34°16 .l' 

34'22.5' 

34°20.6' 

34'18 .8' 

34°23 .6' 

34'20.2' 

34'20. 7' 

34°25 .3' 

Long (W.) 

118'23. 7' 

118'27 .5' 

118'24.6' 

118'27 .2' 

118'24. 3' 

118'29 .4' 

118'28.6' 

118'24. 5' 118'30. 5' 

J.J.s"2i:s• 

118°27 .0' 118'21. 6' 118'23.4' 

118°28.1' 

118'26 .2' 118'19. 7' 118'29 .4' 

118°19 .8' 118'15.3' 

iiil":i5:7' 

118'20. 6' 

118°29 .3' 118'29.6' 

118'26 .5' 

118°29 .0' 118'17 .3' 

118°19 .1' 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 19 

TABLE 2.-Shocks of the San Fernando series of magnitude 3.0 and 

greater, February 9 through March 1, 1971-Continued 

Date 

Feb. 10 

Feb. 11 

Feb. 12 

Feb. 13 

Feb. 14 

Feb. 15 

Feb. 16 

Feb. 17 

Feb. 18 

Feb. 19 

Feb.20 

Feb. 21 

Time (GMT) 

2043 24.9 2046 11.9 2053 34.2 2056 02.1 2128 

2129 08.1 2248 37.3 2344 

0013 55.1 0016 

0107 

0116 12.0 0138 15.6 0228 

0230 13.5 0312 11.9 0314 

0402 

0410 11.6 0415 

0416 

0506 35.8 0518 07.0 0533 

0541 41.7 0624 49.8 0654 33.0 0700 45.3 0714 57.4 0727 03.2 0736 

0830 

0923 

0933 24.3 1000 06.3 1129 25.2 1131 34.5 1145 53.1 1153 

1210 

1227 

1242 19.1 1349 53.6 1435 26.5 1511 25.5 1522 10.7 1548 11.3 1738 54.9 1854 41.5 1906 06.0 2342 28.5 0030 01.0 0343 11.9 0407 17.0 0733 59.5 0924 38.8 1132 56.3 1421 20.6 1643 31.8 1935 08.2 2328 21.1 2335 47.8 0809 31.3 0920 53.8 0952 20.7 1502 43.7 1622 44.6 0256 

0645 55.6 2230 18.9 0338 39.9 0732 54.3 1208 

1344 49.2 1753 58.9 0110 50.4 0804 49.7 0846 54.8 1303 42.3 2333 12.0 0437 04.4 0708 26.0 1439 19.1 1654 39.3 1008 06.2 1015 40.5 0921 52.8 1545 22.5 2209 41.2 0245 11.2 0807 57.1 0808 

0809 27.4 2315 57.9 0242 12.0 0550 52.3 0715 11.5 0743 03.1 1050 

3.4 

3.5 

3.4 

3.1 

3.4 

3.4 

3.7 

3.1 

3.1 

3.3 

3.3 

3.0 

4.0 

3.3 

3.5 

4.0 

3.3 

3.2 

3.3 

3.5 

3.4 

4.6 

4.6 

3.4 

3.1 

3.3 

3.3 

3.2 

3.4 

4.1 

3.3 

3.4 

3.2 

3.2 

3.6 

3.4 

3.5 

3.5 

3.2 

3.5 

3.2 

3.1 

4.2 

3.8 

3.0 

3.2 

3.5 

4.3 

4.1 

3.4 

3.3 

3.4 

3.3 

3.2 

3.1 

3.2 

3.1 

3.3 

3.4 

3.5 

3.1 

3.5 

3.0 

3.1 

3.2 

3.5 

3.6 

3.0 

3.2 

3.0 

3.2 

3.0 

3.1 

3.6 

3.2 

3.3 

3.9 

3.5 

3.3 

3.0 

3.5 

3.4 

3.2 

3.0 

3.0 

3.3 

3.1 

3.1 

3.0 

3.4 

3.4 

3.7 

3.3 

3.3 

3.2 

4.0 

3.9 

3.5 

3.0 

Lat (N.) 

34"21.3' 

34°23. 6' 34°24. 7' 34°23 .6' 

34°20.1' 

34°21.1' 

34°18. 8' 

34°19 .4' 34°16.3' 

34°19.6' 

34°20. 5' 

34°22.1' 

34°22 .4' 34°24 .3' 

34°19 .3' 34°22.1' 

34°22. 2' 34°15.8' 

34°18.1' 

34°21.1' 

34°17.3' 

34°25.6' 

·34°26. 0' 34°21.6' 

34°20 .0' 

34°18.4' 

34°22.8' 

34°20. 7' 34°24.8' 

34°23.0' 

34°18. 7' 34°22 .4' 34°23.4' 

34°21.9' 

34°22 .0' 34°22. 5' 34°24. 9' 34°21.0' 

34°27. 9' 34°21. 4' 34°20.3' 

34°18.2' 

34°13. 6' 34°26.0' 

34°27. 5' 34°18. 5' 34°23. 5' 34°25. 0' 34°17 .4' 34°25. 8' 34°25.2' 

34°18 .6' 34°26. 4' 34°19. 2' 34°10. 8' 

34°15.7' 

34°18 .3' 34°21.2' 

34°27 .1' 34°23 .8' 34°24 .2' 34°17.1' 

34°14 .1' 34°22 .3' 34°18 .2' 34°24. 8' 34°21.3' 

34°20.0' 

34°20. 0' 34°24 .0' 34°22 .6' 34°17 .4' 34°27 .0' 

34"26.0' 

34°15. 7' 34°13 .9' 34°22 .2' 34°22. 5' 34°22. 8' 

Long (W.) 

118°28.1' 

118°26.4' 

118°23.9' 

118°20 .1' 

118°27 .0' 118°28.4' 

118°18 .4' 

118°19 .0' 118°30.2' 

118°29. 2' 118°18. 7' 

118°27 .6' 

118°20.8' 

118°25 .0' 

118°18 .4' 118°21.9' 

118°26. 7' 118°19 .1' 118°26. 7' 118°26.5' 

118°15.9' 

118°27 .3' 118°25. 2' 118°26. 9' 118°28. 7' 

118°17. 5' 118°25.5' 

118°28. 9' 118°25.0' 

118°30 .2' 118°17.1' 

118°22.3' 

118°27 .1' 118°19 .1' 118°21. 0' 118°20. 7' 118°21. 7' 118°28.6' 

118°28.2' 

118°22.6' 

118°16 .3' 118°19. 7' 118°30. 7' 118°24 .1' 118°26.6' 

118°23 .1' 118°18. 7' 118°26. 6' 118°30.0' 

118°21.8' 

118°25. 9' 

118°32.2' 

118°24.4' 

118°25.2' 

118°13 .3' 

118°31.0' 

118°17 .3' 118°28.3' 

118°25.3' 

118°26.8' 

118°26.9' 

118°34. 0' 118°32. 8' 118°28.4' 

118°18. 5' 118°24. 9' 

118°27. 8' 118°18. 7' 118°21. 5' 11s•2o.6' 

118°26. 7' 118°30.1' 

118°19. 6' 

118°26. 2' 118°32 .3' 118°33 .9' 118°28.1' 

118"26. 7' 118"26.5' 

TABLE 2.-Shocks of the San Fernando series of magnitude 3.0 and 

greater, February 9 through March 1, 1971-Continued 

Date 

Feb. 22 Feb. 23 Feb. 24 

Feb.25 

Feb. 26 

Feb. 28 Mar.1 

Time (GMT) 

1406 05.1 1813 13.0 0624 43.8 0531 38.0 1518 01.4 1604 14.8 1127 33.2 1425 51.8 1554 06.1 2027 58.5 0210 24.9 0333 01.0 2122 34.9 2251 34.7 0428 20.9 3.3 

3.0 

3.0 

3.0 

3.0 

3.5 

3.1 

3.2 

3.0 

3.4 

3.0 

3.3 

3.3 

3.0 

3.3 

Lat (N.) 

34°22.6' 

34°15.6' 

34°16 .9' 34°21. 5' 34°27 .6' 34°24.6' 

34°22.9' 

34°25.0' 

34°20.2' 

34°17 .0' 34°23.2' 

34°21.4' 

34°25.5' 

34°17 .8' 34°21.3' 

Long (W.) 

U8°27 .6' ll8°19 .3' 118°19 .4' ll8"21.0' 

118°25.5' 

ll8°26.5' 

118"27 .8' 118°27. 9' 118°19 .5' 118°22. 7' 118°13. 7' 118°26.2' 

118°27 .1' 118°18.1' 

118°27 .2' 

simply been to get a rapid and homogeneous listing. 

Nevertheless, comparison of those epicentral locations in table 2 for which we have also obtained independent solutions based on the portable stations 

(Hanks and others, this report) suggests that most 

are accurate to within 2 km. 

All the shocks in table 2 for which epicentral locations have been determined are shown in figure 1, 

which also shows their relationship to geographic 

features and to the traces of surficial fault movement 

associated with the earthquake (after Kamb and 

others, this report). The greatest concentration of 

aftershock activity lies roughly in the shape of an 

inverted U which has remarkable symmetry both 

with respect to the epicenter of the main shock and 

to the pattern of surface faulting. There appears to 

have been more aftershock activity on the southwest-trending west flank of the pattern, but the 

consistent outline is nevertheless striking; of particular note is the relative absence of aftershocks in 

the area just north of the surficial fault traces, 

where much of the heaviest shaking took place. It is 

interesting that the location of Pacoima Dam, 

where the extraordinary strong-motion record of 

the main shock was written (Maley and Cloud, this 

report; Housner and Hudson, 1971), is very nearly 

in the center of this aftershock-void area. 

It is tempting to suggest that the aftershocks delineate the boundary of slippage on the north-dipping thrust fault, with the aftershocks concentrated 

in the areas of postearthquake stress concentration 

at the edge of the slippage. Since there is no stress 

concentration at the surface trace, few aftershocks 

would be expected here. The segment that slipped 

would then be visualized as a north-dipping thrust 

plate with the shape of an inverted U, extending 

north from the surface trace down to the hypocentral area 12 km north. The principal difficulty with 

this interpretation is that aftershock depths and 

focal mechanisms obtained to date do not portray 
20 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

such a simple picture; instead, the aftershocks seem 

to fall into three distinct groups, each with its own 

characteristic depths and focal mechanisms (Hanks 

and others, this report; Whitcomb, this report). 

Much work remains to be done to synthesize the aftershock pattern and determine its tectonic significance. We nevertheless feel at this time that the aftershock epicenters of figure 1 do indeed tend to 

delineate the boundaries of the thrust displacement 

that caused the San Fernando earthquake, although 

many of the shocks of the western limb evidently 

represent deeper strike-slip events whose relationship to the main thrust fault is very complex. 

Operation of the Caltech seismographic array has 

been made possible over the years by contributions 

by the Earthquake Research Affiliates, a group of 

industrial sponsors whose help is particularly appreciated at times such as this. We also appreciate 

the generosity and the spirit of free communication 

that has typified all the groups and individuals investigating this earthquake. 

REFERENCES 

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: Seismol. 

Soc. America Bull., v. 55, p. 753-797. 

Housner, G. W., and Hudson, E. E., 1971, Preliminary report 

on the engineering aspects of the San Fernando, California, earthquake of February 9, 1971: Seismol. Soc. 

America Bull. (In press.) 

Townley, S. D., and Allen, M. W., 1939, Descriptive catalog 

of earthquakes of the Pacific Coast of the United States, 

1769 to 1928: Seismol. Soc. America Bull., v. 29, p. 

1-297. 
PRECISE LOCATIONS OF AFTERSHOCKS OF THE SAN FERNANDO EARTHQUAKE 2300 

(GMT) FEBRUARY 10-1700 FEBRUARY 11, 1971 1 

By THOMAS C. HANKS, THOMAS H. JORDAN, and J. BERNARD MINSTER 

SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY 

Forty-seven aftershocks of the San Fernando 

earthquake have been located using six portable 

seismograph units operated by the California Institute of Technology, a portable seismograph operated by the University of California, San Diego, 

and permanent stations at Pyramid (California Department of Water Resources) and Mount Wilson 

(Cal tech). The locations of the seven portable units 

are shown in figure 1; station coordinates are listed 

in table 1. Both P- and S-wave readings have been 

the input data for an iterative, least-squares, halfspace hypocentral location program similar to that 

described by Flinn ( 1960) . A P-wave velocity of 

5.58 kmps (kilometer per second) and an S-wave 

velocity of 3.26 kmps have been used for the hypocentral determinations given in figure 1. 

TABLE I.- Location of stations used in hypocenter determinations 

[CIT, California Institute of Technology; UCSD, University of California, San Diego; CDWR, California Department of Water Resources] 

Station Agency 

Mt. Wilson ________ CIT 

Bouquet Canyon ___ CIT 

Brown's Canyon ___ CIT 

Indian Canyon _____ CIT 

Soledad Canyon ____ CIT 

Iron Canyon ____ ___ CIT 

Golden Oak Ranch _ CIT 

Little Tujunga_____ UCSD 

Pyramid __________ CDWR 

North 

lat 

34°13.4' 

33.5' 

17 . 6' 

25.2' 

26.1' 

23.3' 

23.8' 

17 .7' 

34.1' 

West long 

118°03 0 5' 

25.5' 

35.4' 

16.2' 

21. 7' 

23.9' 

28.3' 

21.6' 

44. 5' 

Alt 

(m) 

1,730 

890 

412 

884 

575 

588 

482 

396 

1,240 

These aftershocks represent a reasonably complete sample of the locatable events occurring between 33 and 51 hours after the main shock. Most 

of these events have magnitudes in the range 1 < 

ML < 3; nine of them have M ~ 3. The epicentral 

distribution of these aftershocks (fig. 1) does not 

differ significantly from the general epicentral pattern of 120 larger aftershocks occurring up to 3 

weeks after the main shock (Allen and others, this 

report) . An exception to this is the absence of loca1. Contribution No. 1994, California Institute of Technology, Division of 

Geological and Planetary Sciences, Pasadena, California 

A' 

t \0·--"""""~_;,10. km 

Costo1c 

Brown's 

Canyon 

• 

• Bouquet Reser,voir "' 

~ 

Canyon 

FIGURE I.-Distribution of aftershocks of the San Fernando 

earthquake, in the time interval 2300 (GMT) February 

10-1700 February 11, 1971. The larger open square is the 

main-shock epicenter; the three smaller squar es are 

epicenters for three events ML > 4.5. Solid triangles locate 

the portable seismograph stations. Numbered solid circles 

a re aftershock locations with the depth (km) as indicated. 

Open circles with an interior line are shallow aftershocks 

(h < 5 km). Roman numerals denote groupings of aftershocks: I = epicentral group, II = Chatsworth segment, 

III = eastern group. Fault traces after the section by 

Kamb and others in this report. 

tions during the 18 hour sample considered here in 

the area 1-8 km (kilometer) north of Sunland. 

Generally, we believe that enough earthquakes have 

been located to sample reasonably well the aftershock region defined by the larger events. There IS 

21 
22 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

no reason at this point to suspect that this 18-hour 

interval is anomalous. On the basis of their hypocentral locations, we have classified members of this 

sequence of aftershocks into three groups: the epicentral group, the Chatsworth segment, and the 

eastern group (fig. 1). We discuss the location characteristics for each group below. 

THE EPICENTRAL GROUP 

This group of 19 aftershocks is a cluster centered 

3 km north of the main-shock epicenter (determined by Allen and others, this report, as 34 °24.0' 

N, 118°23.7' W). Depths of these events range from 

6 to 13 km, excluding one event at 5 km and one 

shallow event (h < 5 km). A typical location in 

this group is based on seven P- and three S-wave 

readings; the RMS (root mean square) travel-time 

residual is in general less than 0.2 sec. We consider 

the epicenters to be determined within 1 km and the 

depths to be determined within 1-2 km. 

THE CHATSWORTH SEGMENT 

This group of aftershocks lies within a linear 

zone extending southwest from the vicinity of the 

main shock to Chatsworth. The number of arrival 

times used and the RMS residuals computed are 

similar to those of the epicentral group. However, 

station proximity and azimuthal coverage are not so 

favorable as for the former group. We consider 

these epicenters to be determined within 1 km and 

the depths within 2 km. The depth range (7-11 

km) of these events is narrower than that of the 

epicentral group, but this may only reflect the small 

number of locations. To our knowledge, there are no 

surficial tectonic features along this zone. 

THE EASTERN GROUP 

This group of aftershocks consists of 15 located 

events. All these have depths less than 8 km, and 10 

are shallow (h < 5 km). More precise depth determinations for the shallow events have not been assigned because of inadequate control; the nearest 

stations are no closer than 5-10 km. The RMS residuals for events of this group are generally between 0.2 sec and 0.3 sec. An RMS residual of 0.23 

sec for a typical event located at the surface increases only slightly (to 0.25 sec) if the aftershock 

is relocated at a depth of 5 km. Relocation of depths 

deeper than 5 km causes the RMS residual to increase rapidly, to 0.35 sec at 6 km and 0.53 sec at 8 

km. The larger RMS residuals for these shallow 

events may reflect anomalous near-surface velocity 

structure, anomalous station residuals for rays 

traveling nearly horizontally, or both. Calibration of 

the array by an explosion in this area is necessary 

if hypocentral locations in this region are to be improved, especially for the shallower aftershocks. Six 

of the shallow events have ML > 3. Thus, strain release in the aftershock zone is dominated by these 

shallow events during this period of time. 

A fourth area of interest can be defined by the 

relative absence of aftershocks occurring within it. 

It is north of the observed surface-fault breakage 

and interior to the three groups discussed previously. Only four aftershocks are located in this region. This could reflect the limited time sample considered. All events in this region have local 

magnitudes less than 2, and they represent less than 

10 percent of the data. 

DISCUSSION 

Recognizing the limitations imposed by the short 

time sample of aftershock occurrence discussed and 

the small number of events located, we believe that 

three groups of aftershocks can be tentatively identified on the basis of their hypocentral characteristics. These groupings can also be characterized by 

the type of focal-mechanism solution occurring 

within each. We will attempt a preliminary interpretation of these groupings and their relationship 

to each other, the observed surface faulting, and the 

main shock. 

The deepest hypocenters of the epicentral group, 

with the exception of one event at 13 km depth, 

roughly define a plane which dips at 32° to the 

north. The strike of this plane is approximately 

east-west, which is consistent with fault-plane solutions for the main shock (Whitcomb, this report). 

The plane interesects the surface in the vicinity of 

observed ground breakage along the Sylmar and 

Tujunga fault segments (Kamb and others and U.S. 

Geological Survey staff, this report). 

Recognizing the thrust characteristics of the surface faulting, the main shock, and aftershocks of the 

epicentral group, we will refer to this plane as the 

thrust plane, where the appellation is a matter of 

reference and interpretation. The tentative hypocenter of the main shock falls below this plane 

(Allen and others, this report), but its depth determination is probably reliable to only -+- 4 km. 

Focal mechanisms of aftershocks in this region 

are similar to that for the main shock (Whitcomb, 

this report). The shallower events of the epicentral 

group probably reflect readjustment of the upper 

thrust plate to the main-shock dislocation. 

Events of the Chatsworth segment differ significantly from aftershocks of the epicentral group. 
THE SAN FERNANDO, CALIFORNIA, EAR~HQUAKE OF FEBRUARY 9, 1971 23 

First, their epicenters define a linear seismic zone. 

Second, all hypocenters fall below the thrust plane. 

Third, the depth determinations for these events 

are relatively uniform. Fourth, fault-plane solutions 

for aftershocks in the Chatsworth segment are consistent with left-lateral strike-slip displacement in a 

direction parallel to the alignment of epicenters 

(Whitcomb, this report). While the amount of data 

in this group is limited, we feel that aftershocks of 

the Chatsworth segment reflect tectonic accommodation different from, although not unrelated to, that 

occurring in the region of the epicentral group. 

Aftershocks of the eastern group constitute a 

third grouping, on the basis of the preponderance 

of shallow-depth determinations and the almost random orientation of compressional and tensional axes 

of fault-place solutions for aftershocks in this region (Whitcomb, this report). All the hypocenters 

of the eastern group aftershocks fall above the 

thrust plane defined by the epicentral group. It is 

not easy to relate this diffuse zone of shallow activity to the epicentral group, despite their proximity. 

It is tempting to interpret these three groups of 

aftershocks as defining the boundaries of the upper 

thrust plate on the north ( eipicentral group), the 

west-northwest (Chatsworth segment), and the 

east-northeast (eastern group) . The south boundary 

is defined by the observed surface-fault breakage 

and zones of severe structural damage. The base of 

the upper thrust plate is defined by the thrust 

plane. However, this interpretation does not satisfy 

salient features of the aftershock sequence. 

We have noted that all aftershocks of the Chatsworth segment lie below the thrust plane. We interpret this activity as defining northwest margin 

of the lower thrust plate. Displacement along this 

margin is left lateral as inferred from the faultplane solutions. The absence of events along the 

Chatsworth segment above the thrust plane and the 

absence of surficial tectonic features along the zone 

suggest that the upper thrust plate remained competent across this demarcation. In contrast to the 

Chatsworth segment, the diffuse shallow activity of 

the eastern group does not define such an obvious 

boundary. Also Whitcomb has observed no consistent pattern in the fault-plane solutions for shocks in 

this region. Whether this constitutes a tectonic 

boundary is questionable. As yet we can offer no 

satisfactory explanation for the shallow activity of 

the eastern group. 

ACKNOWLEDGMENTS 

Geoffrey Davies provided an invaluable service by 

programming the hypocentral location program for 

the PDP-10. We gratefully acknowledge the efforts 

of J. Leonard Blayney, David Johnson, John Romo, 

Herrmann Spetzler, and Daniel Tanner in accomplishing a rapid emplacement of the portable seismograph units of the California Institute of Technology. James Brune made the University of 

California, San Diego records from Little Tujunga 

Canyon available to us. The tectonic interpretation 

presented in this work was developed in collaboration with James Whitcomb. 

REFERENCE 

Flinn, E. A., 1960, Local earthquake location with an electronic computer: Seismol. Soc. America Bull., v. 50, p. 

457-470. 
AFTERSHOCKS OF THE EARTHQUAKE 

By R. L. WESSON, W. H. K. LEE_, and J. F. GIBBS 

U.S. GEOLOGICAL SURVEY 

Twenty-six hours after the San Fernando earthquake of February 9, 1971, teams from the U.S. 

Geological Survey were in the field in the epicentral 

area, establishing a network of 19 portable seismograph stations. The installation of this network was 

coordinated with other groups through the Seismological Laboratory of the California Institute of 

Technology. The purpose of studying the aftershock 

sequence is to determine the dynamics of the tectonic 

environment in the vicinity of the San Fernando 

earthquake and, if possible, to delineate the surfaces at depth along which movement occurred during and after the earthquake and to determine the 

nature of that movement. If this aftershock sequence follows the pattern of other sequences from 

earthquakes of a similar magnitude, as the present 

(March 1971) data suggest, the aftershocks may be 

expected to continue for more than 2 months. 

This paper describes a preliminary analysis of 

40 hours of recording from 0000 GMT, February 12, 

to 1600 GMT, February 13. A short-time sample 

such as this cannot give any detail of the temporal 

variation of activity, but by careful study of the 

earthquakes recorded in this period, we hope to obtain a picture of the spatial distribution of activity. 

The equipment, field operations, and data processing 

techniques are the same as those described by Eaton, 

O'Neill, and Murdock (1970). The seismometer output is recorded in the field on magnetic tape. The 

tape can later be played back slowly to give a conventional seismogram or at high speed for selected 

time periods. 

The network is presently composed of 19 portable 

stations. The locations and recording histories of 

these stations are listed in table 1. During the time 

interval under discussion, a minimum of eight and 

a maximum of 14 portable stations were operational. 

Locations of these portable stations relative to the 

24 

main shock are indicated in figure 1. Readings from 

the portable network were supplemented for some 

of the larger events by readings from permanent 

regional networks: California Institute of Technology (four events), California Department of 

Water Resources (four events) the University of 

Southern California (15 events) and the U.S. Geological Survey telemeter station near Point Mugu. 

DATA ANALYSIS 

Events were selected for timing and location by 

two methods. In the first case, high-speed playbacks 

were obtained for all earthquakes with signal duration longer than 25 seconds at the U.S. Geological 

Survey telemeter station near Laguna Peak 

( SBLG), some 70 km west of the active region. This 

duration corresponds to a local magnitude, ML, of 

approximately 2.1. All these events were timed and 

located as were a few smaller events which happened to occur during the playback intervals. This 

process yielded 62 events. Secondly, to obtain a 

sample of the spatial distribution of smaller shocks, 

nine tapes were played back at high speed continuously for a 2Vt hour period from 0545 GMT to 

0800 GMT February 12. All events that were 

thought to be locatable were timed. A total of 102 

different events were located with local magnitudes 

as low as 0. Of course many of the smaller events 

could not be timed at all the stations, resulting in 

locations of lower quality. 

The crustal velocity model used in computing the 

hypocenters is listed in table 2. It is a smoothed 

version of the model obtained by Healy (1963) on 

a reversed seismic refraction line from Santa Monica Bay to Camp Roberts. The velocity model was 

smoothed to avoid large velocity discontinuities 

which complicate focal depth determinations. The 

U.S. Geological Survey intends to conduct a seis-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 25 

mic refraction experiment to determine with preciseness the crustal velocity structure in the San 

Gabriel Mountains-San Fernando Valley region before the portable stations are removed. To make 

a first-order correction for lateral-velocity variations, the average arrival time residuals from the 

location of the 62 larger events were incorporated 

as station corrections. All 164 earthquakes were 

then located with the corrected model. This process 

tends to improve relative locations but does not 

correct for systematic bias. The quality of the resulting locations is described in table 3. The bases 

of the quality ratings are detailed in table 4. The 

locations were accomplished using the HYP071 

computer program written by W. H. K. Lee. 

DISTRIBUTION OF HYPOCENTERS 

The epicenters and focal depths of all the aftershocks with quality A, B, and C were plotted with 

the observed surface ground breakage in figure 2. 

The epicenters occupy a large inverted U-shaped 

area north of the surface breakage. The maximum 

focal depths generally increase toward the north 

from 5-7 km below the zone of ground breakage to 

12-15 km at the northern limit of the activity. It 

is possible that there is a systematic error in the 

focal-depth estimates. 

A projection of all these hypocenters onto a northstriking plane is shown in figure 3. The maximum focal depth along the section suggests the 

lower boundary of a wedge or slab-shaped area 

of activity dipping 30° to 40° to the north. The 

upper boundary is less clearly defined. The apparent 

alinement of hypocenters at 5 km depth is an artifact of the location computation and requires special comment. The program HYP071 does not follow a straight-forward least-squares procedure, 

rather it utilizes a stepwise multiple-regression 

scheme described by Draper and Smith (1966). At 

each step in the iteration, the program examines 

the change in each variable for its statistical significance. If a change in a variable, say depth, is not 

statistically significant, the variable is eliminated 

from the regression for that step and remains unchanged. This means, in terms of the alinement of 

hypocenters at 5 km, (fig. 3) that no change in 

focal depth from the initial trial value of 5 km was 

statistically significant for the given set of arrivaltime observations. Actually, many of the events 

shown at 5 km are probably more shallow, but there 

were no stations close enough to establish good 

control. 

FOCAL MECHANISM SOLUTIONS 

The line segments plotted at a few of the hypocenters in figure 3 indicate the apparent dip in the 

north-south plane of the approximately east-trending nodal plane resulting from preliminary focal 

mechanism determinations. During the last 16 hours 

of the sample interval, clear first motions were available for several earthquakes at as many as 16 stations. In several cases these readings were adequate 

to indicate a tentative fault-plane solution. Several 

types of mechanisms were observed. Solutions indicating thrust faulting were obtained at several different locations in the active region, although other 

types of solutions were also tentatively indicated. 

In particular, solutions for two shocks on the western limb of the U and two shocks on the northeastern edge indicated strike-slip faulting. Two solutions near the northern limit indicated normal 

faulting. 

The generally dipping aftershock activity and the 

tentative results from aftershock focal-mechanism 

solutions are in general agreement with a faultplane solution for the main shock determined from 

first-motions of P waves at both near-in and distant 

stations. First motions from 73 stations were used. 

The sources are National Ocean Survey (54), U.S. 

Geological Survey (8), California Institute of Technology (7), California Department of Water Resources (3), and University of Southern California 

(1). Ray paths to the near-in stations were computed using a local velocity model. The rest were 

computed using the P-velocity table of Herrin 

( 1968). The solution is shown in figure 4. 

The best fitting nodal planes are: 

Nodal plane Slip direction 

Strike Dip Trend Plunge 

Fault plane ____ N. 108° E. 50° N. N. 56° E. 43° 

Auxiliary plane_ N. 146° E. 46° sw. 

The plane listed first is similar in strike and dip 

to fault surfaces mapped in the San Fernando area. 

The surface defined by the aftershocks is also similar in strike, but it dips at a more gentle angle 

to the north. The sense of movement is reverse and 

left lateral with a ratio of dip slip to strike slip of 

about 2. This is similar to the displacements observed in the field along well-exposed fault surfaces. 

MAGNITUDES 

The relationship of areal distribution to magnitude is shown in figure 5. The larger shocks are 
26 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

concentrated around the periphery of the inverted 

U, while with few exceptions only smaller shocks 

occur in the interior. This concentration of large 

shocks on the periphery of the zone of activity is 

supported by the locations of the aftershocks magnitude 3.0 and above through February 23 obtained by 

the California Institute of Technology ( 1971). 

Therefore, this is not a bias in our time sample, but 

a true areal variation. 

DISCUSSION AND WORK IN PROGRESS 

It is hazardous at this point to speculate on the 

eventual conclusions of this study. The faulting associated with the San Fernando earthquake and its 

aftershocks is quite complex. We expect to locate 

several hundred more events to refine the spatial 

distribution of activity and to establish any temporal variations. Preliminary results suggest that 

focal-mechanism solutions will be extremely helpful in deciphering the complex pattern of faulting. 

Despite the hazards, observations obtained thus 

far provide a firm basis for a working hypothesis. 

The inverted U-shaped pattern of activity, particularly the concentration of relatively large events on 

the periphery, and the ground breakage to the south 

seem to define the areal extent of a thrust sheet 

clearly. The distribution of focal depths and the 

nature of the focal-mechanism solutions indicate 

the principal plane along which slippage took place. 

This aftershock sequence provides a rare opportunity to study the three-dimensional character of 

a thrust sheet and the associated faulting. 

ACKNOWLEDGMENTS 

The authors wish to acknowledge the cooperation 

of the Seismological Laboratory of the California 

Institute of Technology, the California Department 

of Water Resources, the National Ocean Survey, and 

Professor Leon Teng of the University of Southern 

California. Ed Criley, John Coakley, and Steven 

Gallenthine of the U.S. Geological Survey installed 

and continue to operate the portable network. This 

research was carried out while one of the authors 

(R. L. W.) was pursuing an NRC-USGS Post-Doctoral Research Associateship. 

REFERENCES 

California Institute of Technology, Division of Geological and 

Planetary Sciences, 1971, Preliminary Seismological and 

Geological Studies of the San Fernando, California, 

Earthquake of February 9, 1971, Seismol. Soc. America 

Bulletin. In press. 

Draper, N. R., and Smith, H., 1966, Applied regression analysis: New York, John Wiley & Sons, 407 p. 

Eaton, J. P., O'Neill, M. E., and Murdock, J. N., 1970, Detailed study of the aftershocks of the 1966 Parkfield· 

Cholame, California, earthquake: Seismol. Soc. America 

Bull., v. 60, p. 1151-1197. 

Healy, J. H., 1963, Crustal structure along the coast of California from seismic-refraction measurements: Jour. 

Geophys. Res., v. 68, p. 5777-5787. 

Herrin, E., ed., 1968, Special number-1968 Seismological 

tables for P phases: Seismol. Soc. America Bull., v. 58, 

no. 4, p. 1196-1219. 

TABLE 1.-Portable station list--San Fernando earthquake, February 1971 

Station 

code 

VAN 

OIL 

AGD 

BRD 

DOC 

GRO 

GRG 

DUB 

MAY 

CHL 

JOS 

NIL 

TRP 

sus 

TRC 

PIC 

QAL 

SPL 

ewe 

OAK 

HAS 

Location Latitude 

West of Van Norman Lake ------------------ 34°17.66' 

Placenita Oil Field -------------------------- 34°23.78' 

Agua Dulce Canyon -------------------------- 34 °26.65' 

Bear Divide ---------------------------------- 34 o 21.60' 

Doane Canyon -------------------------------- 34 o 17.16' 

Griffith Park Observatory -------------------- 34°07.08' 

Griffith Park-Girls Camp ---------------------- 34 °07.65' 

Dubois Farm -------------------------------- 34°17.10' 

May Canyon-Sylmar -------------------------- 34°19.78' 

Charley Peak-Castaic ------------------------ 34 o 31.00' 

Josephine Peak Road ------------------------- 34 °16.67' 

Niles Ranch-Aliso Canyon -------------------- 34°24.91' 

Trippet Ranch-Topanga ---------------------- 34°05.43' 

White Oaks Park-Santa Susanna ------------- 34°17.34' 

Trail Canyon off Big Tujunga Canyon ________ 34°18.94' 

Pico Canyon, west of Newhall ---------------- 34°22.42' 

Quail Spring --------------------------------- 34°23.85' 

Near Sierra Pelona Lookout, south of 

Bouquet Reservoir -------------------------- 34°33.76' 

Cold Water Canyon -------------------------- 34o 7.80' 

Oak Spring- ---------------------------------- 34°27.44' 

Haskell Canyon ------------------------------ 34°30.20' 

Longitude 

118°29.42' 

118°29.39' 

118°19.98' 

118°23.85' 

118°18.88' 

118°17.95' 

118°18.75' 

118°22.83' 

118°25.73' 

118°34.94' 

118°08.59' 

118°07.31' 

118°35.11' 

118°39.75' 

118° 15.67' 

118°37.12' 

118°17.14' 

118°21.34' 

118°24.25' 

118°23.44' 

118°28.75' 

Elevation 

(m) 

358 

588 

622 

863 

530 

344 

244 

384 

497 

631 

1335 

1150 

421 

378 

945 

532 

1237 

1454 

307 

529 

716 

Date and time of installation 

(PST) 

2/10 

2/10 

2/11 

2/11 

2/10 

In 2/11 

out 2/13 

2/13 

2/11 

2/11 

In 2/10 

out 2/16 

2/12 

2/12 

2/12 

2/12 

2/12 

2/15 

2/14 

2/14 

2/14 

2/26 

.-.2/16 

15 23 

15 30 

13 05 

19 00 

17 00 

17 05 

11 10 

21 45 

10 05 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 27 

TABLE 2.-Smoothed crustal model 

Velocity 

(km/sec) 

3.2 

3.6 

4.0 

4.4 

4.7 

5.1 

5.4 

5.6 

5.8 

5.9 

6.0 

6.4 

6.8 

8.2 

Depth 

(km) 

0.0 

.5 

1.0 

1.5 

2.0 

2.5 

3.0 

3.5 

4.0 

4.5 

5.0 

14.5 

15.0 

32.0 

TABLE 3.-Quality of locations 

Quality 

(Q) Number of locations 

A ----------------------------------------------------- 5 

B ----------------------------------------------------- 54 

c ----------------------------------------------------- 70 

D ----------------------------------------------------- 35 

Total _____________________________ ________ ______ _ 164 

TABLE 4.-Bases of the quality ratings 

Q Epicenter Focal depth 

A__ __________________ Excellent_ ____ ----------- -----_ Good 

B ___________________ _ Good---------------- ---------- Fair 

C ______________ ______ Fair - - ---------------------- --- Poor 

D ____________________ Poor--------------------------- Poor 

Q is based on both the nature of the station distribution with 

respect to the earthquake and the statistical measure of 

the solution. These two factors are each rated independently according to the following scheme: 

Station distribution 

NO 

A ________ >6 

B ________ 56 

c ________ 26 

D ______ __ Others 

Statistical m,easures 

RMS (sec) 

A __ ______ < 0.15 

B ________ < 0.30 c ___ __ ___ < o.5o 

D ________ Others 

GAP 

< 90 ° 

<135° 

~180 ° 

ERH (km ) 

<LO 

<:"2.5 

<:"5.0 

DMIN 

<DEPTH or 5 km 

<:2 X DEPTH or 10 km 

~50 km 

ERZ (km) 

<2.0 

~5.0 

Q is taken as the average of the ratings from the two schemes, that is, an A and a C yield a B, and two B's yield a B. When the two ratings are only one level apart the lower one is used, that is, an A and a B yield a B. 

CHL .. 

0 10 

Epic enter of 

OIL *Ma i;A:hoc:ABRIEL 

• BRO 

MT NS 

FIGURE I.-Location of portable seismograph stations used 

for preliminary analysis. 

CD 

w 

U1 

0 

CD 

w 

;n 

0 

34 32 .5 

0 

5 

34 12 . 5 

10 KM . 6 

R 

7[ 

c II c .. 3R7 75 55 ~SR ~ 9 5 o9 5 5 B 

S7ffl-AEIJ 5 6 

~ 5 55 ~4 7 

,- B 5 

0 

2 R 65 ... 9 

5 9 

5 8 -==--.. - t / 

--

34 32.5 

.. 

0 5 

0 

9R 

4 7 

~ 54 

5 B 55 .. 5 6 

... 55 

2. 

aJ 

;n 

0 

34 12.5 

FIGURE 2.-Epicenters and focal depths of all A, B and C 

quality shocks. The symbols 0-9 and A-E indicate focal 

depths of 0 through 15 kilometers. Also indicated is the 

surface ground breakage. The maximum depths of the 

shocks generally increase to the north. 
~ 

~ 

:c 

~ 

a.. 

w 

0 

s DISTANCE . KM . 

0 I I I I 'r/;_ ;;(~ I I I y I I I I <?. I I I I I ':' I I I I I y I I 

OF GROUND BREAKAGE 

+ 

+ 

+ + + 

+ + 

+ + ++ + ++ ..... + + + + + ........... + 

+ 

.. .. + ""- + 

\ + + 

+ 

+ + 

+ 

.. "'- + + 

+ + 

MAIN 

+ + 

+ ~++-+++ + ...... .. + 

+ 

+ 

+ 

+ 

+ ...... ...... + 

+ + + 

+ .. + 

.... 

+ .... + + + 

+"' 

+ 

+ :<-.. , + + 

+ 

SHOCK + ~ 

+ 

+ 

+ 

FIGURE 3.-Projection of all A, B and C quality hypocenters the trace of ground breakage and the hypocenter of the 

onto a north-striking vertical plane. Line segments indi- main shock as located by the California Institute of Techcate apparent dips in this plane of nodal planes from nology (1971). The origin of the horizontal coordinates is 

fault-plane solutions discussed in text. Also indicated are 34 °22.5'. 

"' 

N 

I'V 

00 

>-3 

l:I1 

tr:1 

Ul 

> 

z 

"%j 

tr:1 

;:o 

z 

> z 

tJ 

0 

("} 

> t-' 

..... 

"%j 

0 

;:o 

z 

..... 

> 

tr:1 

> ;:o 

>-3 

l:I1 

/:) 

d 

> 

~ 

tr:1 

0 

"%j 

>zj 

trl 

t!:l 

;:o 

d 

> 

;:o 

><! 

~ 

...... 

~ 

-'l 

...... 
THE SAN F ERNANDO, CALIFORNIA, EARTH QUAKE OF FEBRUARY 9, 1971 29 

N 

0 

••••• 

• •• I 

... •,, 

w ' + •• • I 

T MAXIMUM TENSIONAL 

AXIS S 

C MAXIMUM COMPRESSIONAL 

AXIS 

_- SLIP DIRECTION 

~· 

• 

• 

• 

• • 

STRIKE 

N146°E 

DIP 

4s•sw 

so•N 

e COMPRESSION 

o DILATATION 

F rGURE 4.-F ault-plane solution from P-wave first motions of 

the main shock of the San Fernando earthquake. The plot 

is an equal area projection of the lower focal hemisphere. 

CIJ 

w 

Ul 

0 

CIJ 

w 

Ul 

0 

34 32 . 5 

0 

2 

34 12. 5 

5 

2 

1' 2 

2 

34 32 . 5 

10 KM. 

' 

2 1 

l 

0 

20 

34 12 . 5 

CIJ 

Ul 

0 

CIJ 

Ul 

0 

FrGURE 5.-Magnitudes of a ll located shocks. The larger 

shocks are concentrated on the periphery of the act ive 

zone. 
FAULT-PLANE SOLUTIONS OF THE FEBRUARY 9, 1971, SAN FERNANDO EARTHQUAKE 

AND SOME AFTERSHOCKS 1 

By JAMES H. WHITCOMB 

SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY 

This paper presents a preliminary look at the 

focal mechanisms of the February 9, 1971, San Fernando earthquake and 22 of the larger aftershocks 

during the first 3 days following the earthquake. 

(See table 1.) The location of the event was most 

advantageous for deriving first motions due to its 

occurrence in the midst of the seismic network of 

the California Institute of Technology in southern 

California. The only focal-sphere "hole" lay to the 

southwest in the Pacific Ocean, but fortunately this 

has not greatly limited the solution. 

TABLE 1.-Aftershocks recorded during first 3 days following the 

February 9, 1971, San Fernando earthquake 

/Focal-mechanism solutions are presented in figure 2. Depths are from Hanks and others, this report] 

Aftershock 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

Date 

Feb. 9, 1971 ____ do _____ _ ____ do _____ _ 

____ do _____ _ 

Feb. 10, 1971 ____ do _____ _ 

____ do _____ _ ____ do _____ _ ____ do _____ _ ____ do _____ _ 

____ do _____ _ ____ do _____ _ ____ do _____ _ 

____ do _____ _ 

Feb. 11, 1971 ____ do _____ _ ____ do _____ _ ____ do _____ _ 

____ do _____ _ ____ do _____ _ 

____ do _____ _ ____ do _____ _ 

Origin time 

Hr 

15 

15 

15 

16 

01 

03 

05 

05 

07 

13 

14 

17 

18 

23 

00 

04 

07 

09 

11 

14 

19 

23 

Min 

10 

38 

58 

19 

38 

12 

06 

18 

27 

49 

35 

38 

54 

42 

30 

07 

33 

24 

32 

21 

35 

35 

4.1 

4.2 

5.1 

4.3 

4.0 

4.0 

4.6 

4.6 

4.1 

4.2 

3.8 

4.3 

4.1 

3.3 

3.4 

3.2 

3.1 

3.2 

3.1 

3.3 

3.5 

3.5 

Depth 

km 

<5 

<5 

11 

13 

<5 

<5 

<5 

The aftershocks were chosen mainly on the basis 

of magnitude and the availability of locations at the 

time this paper was written. All fault-plane solutions were constructed independently of each other 

1 Contribution No. 1991, Division of Geological Sciences, California Institute of Technology, Pasadena, California 91109. 

30 

without reference to their epicentral location. Only 

stations received by California Institute of Technology have been used thus far for the aftershocks. 

This limits the resolution of the dip of nodal planes 

somewhat, but it has been possible to determine 

quite well the general type and orientation of the 

focal mechanisms for most of the shocks above 

magnitude ML=3.0. 

MAIN EVENT 

Figure 1 shows the fault-plane solution calculated 

from P-wave first motions plotted on the lower 

focal hemisphere. With the assumption of a doublecouple mechanism, the two thrust planes derived 

have the following parameters: Strike = N. 26° W., 

dip = 44° SW. and strike = N. 64° W., dip = 52° 

NE. The latter is the preferred fault-plane choice 

based on the observed surface faulting. The northeast-dipping plane is well defined by a nodal line 

projecting through central California, Oregon, and 

Washington and by the dilatation at LASA. The 

strike of the secondary plane is fairly well defined 

by close-in stations. However, these stations, which 

_ plot near the rim of the projection, are expected to 

have more variability because they are most affected by lateral crustal-velocity discontinuities. 

Thus, the secondary plane, and in turn the slip-vector azimuth, are subject to the most error. The slip 

vector in the fault plane is shown in figure 1 and 

defines movement with a plunge of 45° and a rake 

of 64 o. The ratio of throw or vertical motion to 

strike-slip is predicted to be about 1.6 to 1. A 

projection down the calculated fault plane from the 

observed surface faulting towards the epicenter 

yields a focal depth of about 15 km (kilometer) for 

the initiation of the main shock. 

AFTERSHOCKS 

Judging from their position with respect to the 

main epicenter and the observed surface faulting, 

most of the aftershocks seem to bound a thrust 

block along lines striking southwest and southeast 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

N 

31 

w 

c 

~-· • ~L~SA '{\.r;,\'::,'+-

e•e .. • '- \'? 

e • I ~ PLUNGE • 45' 

" ., RAKE·64' 

• • •• + '· .. e 

• 

• 

0 DIP·44'SW 

~OS1RI<E ,26'W 

T TENSIONAL AXIS 

C COMPRESSIONAL AXIS 

e CO MPR ESSION 

0 DILATATION 

E 

" NODAL CHARA CTER ~ NOT DEFINITE 

FIGURE 1.-Focal-mechanism solution for main shock of the 

February 9, 1971, San Fernando earthquake. Equal-area 

projection of P-wave first motions on lower focal hemisphere. Take-off angles were calculated using a crustal 

model with the CIT208 P-wave velocity model and a focal 

depth of 14 km. Readings were made by the author for 

southern California stations and were provided by various 

sources for the remaining stations. A complete listing of 

all readings is available on request. 

from the main epicenter (Allen and others, this report). Figure 2 shows schematic diagrams of the 

focal-mechanism solutions (lower hemisphere) for 

the 22 aftershocks done thus far and given in table 

1. Note that only six of the 22 aftershock faultplane solutions have thrust mechanisms like the 

main shock and that three of these are separated 

from the main groups of aftershocks. Event 17 is 

northwest of the main epicenter and has a focal 

depth of about 13 km (Hanks and others, this report). Event 18 is east of the epicenter and has a 

shallow focal depth ( <5 km). Event 22 is south of 

the main epicenter and presumably lies in the main 

thrust plane near the observed surface faulting. The 

remaining three thrust solutions, events 3, 7, and 

20, are in the southeast-trending line of aftershocks. 

Let us consider the hypothesis that the aftershock 

activity is a continuation of failure along the edges 

of the thrust plane associated with the main shock 

and with the same sense of motion-that is, a 

thrust plane dipping north-northeast. Events 3, 7, 

and 20 agree with this hypothesis. The last of these 

is about 10 km from the main epicenter and gives a 

Main Shock 

QualitY.. of Fault Plane Solution : 

oo 

Good Fair 

~Compression 

0--oilototion 

Poor 0 5 

34°30' 

34°15' 

./(' 

I 

10 km 

FIGURE 2.-Focal-mechanism solutions of 22 aftershocks of 

the February 9, 1971, San Fernando earthquake. The 

schematic solutions are on equal-area projections of the 

lower focal hemisphere. For a listing of the events see 

table 1. 

shallow focus ( < 5 km, Hanks and others, this report) which would be expected. The southwest line 

of aftershocks, however, does not have a thrust 

focal mechanism in the events studied thus far. All 

the remaining solutions in figure 2 do not have 

more than small thrust components. 

Now let us consider only motion of an overthrust 

block bounded by strike-slip faults along the two 

lines of aftershocks which strike southeast and 

southwest from the main shock. The edges of the 

overthrust block should then have right-lateral slippage along the southwest line and left-lateral slippage along the southeast line. There is only one solution in figure 2 that fits this picture; it is event 14 

on the southeast line of aftershocks. A depth 

estimate for event 14 indicates a shallow ( < 5 km) 

focus (Hanks and others, this report) which is compatible with this hypothesis. The southwest line 

shows no solutions that are right-lateral, which is 

not compatible with the hypothesis that strike-slip 
32 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

faults bound the upper thrust block. This does not 

preclude the possibility, however, that further investigation will find solutions of this type. 

Another model to be considered would have the 

lower thrust block bounded by southwest- and 

southeast-trending strike-slip faults along the lines 

of aftershocks, with the upper thrust block immobilized by the crust to the north. By this hypothesis, 

the lower thrust block would have slipped along 

these strike-slip faults, resulting in left-lateral motion along the southwest line and right-lateral motion along the southeast line of aftershocks. The 

southeast line has only one solution, event 6, which 

is compatible with right-lateral strike-slip motion. 

Significantly, on the southwest line, all the solutions 

in figure 2 (except anomalous event 4) are compatible with left-lateral strike-slip on a nearly vertical 

southwest-striking fault plane. The only focal depth 

thus far determined for this group is 11 km for 

event 16 (Hanks and others, this report). These observations present a strong case for the hypothesis 

that the southwest-striking line of aftershocks represents motion of the lower thrust block against a 

block to the northwest along a left-lateral strike-slip 

fault. This mechanism also provides a convenient 

~xplanation for the aftershocks that extend more 

than 10 km southwest of the observed traces of surface faulting. 

Three solutions near the southeast line of aftershocks show normal faulting with north or northeast-trending tension axes, events 12, 15, and 19. 

The last two have shallow focal depths ( < 5 km, 

Hanks and others, this report). These events may 

represent a local response to release of compressive 

stress in the upper thrust block by the main earthquake. This agrees with both the calculated and the 

observed response of the strain field to the main 

event in this direction (Junkels and Anderson, this 

report). 

CONCLUSIONS 

The overall tectonic picture of the main event and 

subsequent motions, based on the fault plane solutions obtained thus far, can be represented by a 

main thrust-fault plane striking N. 64 o W., dipping 

about 52° to the northeast and having a left-lateral 

strike slip component. The upper thrust block is 

probably stuck to the crustal material to the northwest but is breaking up in a complicated pattern 

along the southeast aftershock zone. The lower underthrust block is actively slipping with left-lateral 

motion against the block to the northwest along a 

nearly vertical strike-slip fault which extends from 

the main-shock focus southwest along that aftershock zone to a point that lies at least 10 km south 

of the observed surface faulting. 

The apparent asymmetry of the types of failure 

around the symmetrical aftershock pattern is probably due to the direction of the axis of maximum 

compression. Instead of a north-south compression 

symmetrical with the aftershock pattern and with 

the major strike-slip faults of the region, the axis 

of compression derived for the main shock trends 

northeast-southwest. This direction would favor a 

preexisting southwest-trending strike-slip fault and 

increase the normal stress on a southeast-trending 

strike-slip fault. This normal stress would promote 

complex failure, rather than simple strike-slip 

offset, on the southeast-trending fault zone after the 

thrust movement associated with the main shock. 

ACKNOWLEDGMENTS 

The first-motion data that was promptly provided 

by individuals and organizations too numerous to 

mention here is greatly appreciated. This work was 

aided by many discussions with Don Anderson, 

Clarence Allen, Peter Molnar, Thomas Hanks, Bernard Minster, and Thomas Jordan. 
MICROEARTHQUAKES ON THE SAN ANDREAS FAULT AND AFTERSHOCKS OF THE 

SAN FERNANDO EARTHQUAKE 1 

By CHRISTOPHER H. SCHOLZ 

LAMONT-DOHERTY GEOLOGICAL OBSERVATORY OF COLUMBIA UNIVERSITY 

Summary 

Within 36 hours of the San Fernando earthquake, four 

portable microearthquake stations were installed along the 

nearby San Andreas fault. The purpose of the study was to 

determine if the San Fernando earthquake produced an increase in microearthquake activity along that section of the 

fault. Instruments were located at a total of five sites evenly 

spaced from Gorman to Valyermo and operated for 4¥2 

days at high magnification. Thousands of aftershocks were 

recorded, but only 16 events could be identified from S-P 

times as possibly originating from the San Andreas fault. 

To date, only two of these have been positively identified as 

local to the San Andreas. Even if all events are proved on 

further study to be local to the San Andreas, the rate of 

about one event per day at each site is not a significant increase over the activity observed in 1966 by J. N. Brune and 

C. R. Allen. 

For the first 120 hours following the main shock, aftershock activity decayed exponentially with an exponent near 

-1, as is normal. The aftershock epicentral distribution was 

determined statistically from S-P time distributions at several stations. Most aftershocks fell within an area 25 km 

(kilometers) wide directly to the southwest of the main 

shock. The most intense activity occurred in a 5- to 10-kmwide band trending 15 km southwest from the main shock, 

with a secondary parallel zone of high activity 10 km to 

the southeast. First motions from the majority of aftershocks 

are consistent with thrust faulting with a left-lateral component on an east-west fault, similar to that observed from 

surface ruptures. This mechanism is compatible with the 

strain accumulation field in this region. 

INTRODUCTION 

The San Andreas fault zone lies approximately 20 

km (kilometers) north of the epicenter of the San 

Fernando earthquake. That part of the San Andreas 

has not had a major earthquake since 1857 and 

therefore may be a likely site of high stress and 

possibly the site of the next great California earthquake (Allen and others, 1965). It therefore seemed 

~ribution 1630. Lamont-Doherty Geological Observatory. 

important to monitor that region to determine if 

seismic activity had increased there as a result of 

the nearby San Fernando earthquake. This possibility did not seem unlikely because an earthquake of 

similar size, the Borrego Mountain earthquake of 

1968, produced movement on faults as distant as 70 

km from the epicenter (Allen and others, 1968). 

MICROEARTHQUAKES ON THE SAN ANDREAS FAULT 

On February 9, 1971, immediately after the San 

Fernando earthquake, efforts were initiated at the 

Lamont-Doherty Geological Observatory to prepare 

four portable high-gain microearthquake systems 

for this study. In spite of difficulties due to emergency restrictions around the epicentral region, 

three of these instruments were installed early the 

following day. The fourth station was installed 2 

days later. These stations are shown on the map 

(fig. 1) and pertinent data are given in table 1. 

The network was operated for 4Yz days. On February 12, station LSV was pulled out and reinstalled 

at site BRC. All stations were within a few kilometers of the San Andreas fault, and the site distribution gave complete coverage along the 100-kmlong segment from Gorman to Valyermo. The instruments were run at high gain (106 at 20 hertzes). 

Thousands of aftershocks were recorded at each 

site. The records were carefully searched for events 

with anomalously low S-P times, and correlation between stations was attempted for such events. Of 

these, more than two-thirds were rejected as aftershocks not originating from the San Andreas region. 

To date, only 16 events have been recognized as 

possibly local to the San Andreas fault. These are 

listed in the table opposite the closest station and are 

grouped in three categories. The two events in category A were well recorded at two or more stations 

33 
34 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

MOJAVE N 

45' DESERT 

0 10 Ml 

15' 

0 10 KM 

45' 30' 15' 

FIGURE 1.-Map of epicentral and adjoining regions, showing major faults. The triangles are temporary seismograph stations installed for this study. The crosshatched area gives the approximate distribution of aftershocks, and the heavy 

lines, surface ruptures of the San Fernando earthquake. Epicenter of main shock and area of aftershocks are from 

the section by Allen and others. 

TABLE !.-Aftershocks originating from the San Andreas fault region during a 4 112-day period following the San Fernando earthquake 

Station North West Date and time (GMT) Recording (fig. 1) latitude longitude installed hours Events Rate of events per 1 1966 

A B c day this study 

GOR _______ 34° 46.9' 118° 48.0' 2/10/71: 1200 hours 101 2 1 0.7 2.0 

LSV • ______ 34° 36.4' 118° 19.5' 2/10/71: 2100 49 2 1.0 .0 

SWM ______ 34° 42.1' 118° 32.1' 2/10/71: 1800 95 2 3 1.2 .0 

MER _______ 34° 29.8' 118° 02.4' 2/12/71: 1600 57 2 4 2.5 1.0 

BRC _______ 34° 23.0' 117° 46.3' 2/12/71: 2300 48 .0 5.0 

1 Rates measured by Brune and Allen (1967). 2 Pulled out February 12, installed at site BRC. 

A. Well recorded at two or more stations. B. Well recorded at one station. C. Doubtful. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 35 

and can definitely be considered local to the San 

Andreas fault. They occurred 4 minutes apart on 

February 13. The events in category B were well 

recorded at one station and are considered likely 

local events. Those listed under C are considered 

doubtful. 

The resulting rates of seismic activity for the 

several sites ranged from 0 to 2.5 events per day. 

These are listed in the table with comparable rates 

measured in 1966 by Brune and Allen (1967). Three 

of the sites had slightly higher rates of activity 

than in 1966, but two were less active. One wonders, 

of course, how reproducible such low rates should 

be. Brune and Allen's four sites in the Carrizo Plains 

northwest of the present study area were reoccupied 

in 1968 with results that agreed completely with the 

earlier study (C. H. Scholz, unpub. data). On the 

other hand, a magnitude 3.4 earthquake on February 28, 1969, near Palmdale produced a considerable 

number of very local aftershocks (Max Wyss, unpub. data). Thus, in view of these uncertainties, 

plus the possibility that a number of the class C 

shocks noted above were misinterpreted aftershocks, 

it seems clear that no significant increase in seismic 

activity occurred on the San Andreas fault as a result of the San Fernando earthquake. 

During the course of this work, numerous roads 

that cross the San Andreas fault trace were examined for possible cracking due to fault slip. No such 

cracking was observed. 

AFTERSHOCKS OF THE EARTHQUAKE 

As noted above, thousands of aftershocks were recorded at each site. Although the stations were not 

installed for optimum study of the aftershock sequence, it was of interest to see how useful a few 

rapidly installed portable stations could be in determining the characteristics of the sequence. 

In figure 2 is shown the decay of activity recorded 

at SWM. The sequence obeys an exponential decay 

law. The solid line, for guidance, has a slope of -1, 

which is a normal decay rate for aftershock sequences. As can be observed, the actual decay rate is 

very close to this. 

The spacial distribution of aftershocks was determined statistically by reading S-P times for a large 

number of uncorrelated events at several sites. Histograms of S-P times were then constructed for each 

site, giving the distribution of aftershocks with distance from site. Concentric rings corresponding to 

different S-P times could then be drawn on a map. 

Such rings from two stations intersect to define two 

alternative regions within which the relative activa:: 

:::> 

0 

I 

a:: 

w 

[l. 

en 

1-

• 

• 

~ 10 

> 

w • 

• • 

• 

• • • 

HOURS 

FIGURE 2.-Decay curve for aftershocks recorded at 

station SWM. 

• 

ity can be determined, provided that it can be assumed that the aftershocks originated beneath one 

of the two alternative regions. Comparison of the 

area of aftershocks in figures 1 and 3 indicates that 

this is indeed a reasonable assumption. 

A map of the aftershock zone shown in figure 3 

was constructed as noted above, using 200 events 

from stations GOR. and MER. About 80 percent of 

our aftershocks occurred within both alternative regions, one of which corresponds with the area of 

aftershocks delineated in figure 1. The activity 

within each subregion of figure 3 is given as the 

percentage of the total number of aftershocks expected, on a statistical basis, to lie within that subregion. 

The aftershocks appear to have been concentrated 

in a zone 25 km wide directly to the southwest of the 

main shock and north of the zone of surface faulting. The most intense activity formed a band 5-10 

km wide trending 15 km southwest from the epicenter of the main shock. A secondary trend of activity parallels the most intense zone 10 km to the 

southeast. 

First motions are dominantly up at stations GOR 

and SWM and down at LSV, MER, and BRC. These 

motions are consistent with thrust faulting with a 

left-lateral strike-slip component on an east-west 
36 T HE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

34 ° 30' 

PERCENT TOTAL 

AFTERSHOCKS 

7 

6 ~ 

~~ 

5 \ 

4 ' \ 

3 \ 

2 \ 

' I I 1 I I 

----· ......,.... FAULTING ~ 

• ' MAIN SHOCK ~ 

,, 

,, 

' ' ~ 

, > 

0 5 MI LES 

0 5 KILO METERS 

1 18° 30' 118°15' 

FIGURE 3.-Statistical distribution of aftershocks inferred from S-P time distributions at two stations ( GOR and MER) . 

striking, north-dipping fault, that is, the motions 

are consistent with the evidence from surface rupturing. There appear to be enough exceptions, however, to suggest that a significant number of aftershocks have different mechanisms. 

DISCUSSION 

The San Fernando earthquake apparently occurred on one of the east-west-trending thrust faults 

of the Transverse Ranges, and involved thrusting to 

the south with some left-lateral movement. This 

seems to agree with the general state of stress for 

that region. Disregarding the poorly described 1857 

earthquake, the only other major earthquake in the 

region of the east-west bend in the San Andreas 

fault system was the 1952 Kern County earthquake, 

which also involved thrust faulting with a leftlateral component. Both of these earthquakes thus 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 37 

had slip vectors nearly perpendicular to the San 

Andreas fault. This agrees with geodetic evidence 

(Scholz and Fitch, 1969; Miller and others, 1969) 

which shows that strain accumulating in that region 

is nearly uniaxial compression perpendicular to the 

San Andreas fault. 

The above also suggests that high shear stress is 

not now building up on that segment of the 'san 

Andreas. A lack of high shear stress now would 

explain why that region was unaffected by the San 

Fernando earthquake. 

ACKNOWLEDGMENTS 

I thank Max Wyss and John Lahr for their assistance in the fieldwork, and the enthusiastic group 

of colleagues and students who helped get us into 

the field quickly. This project was supported by the 

National Science Foundation under grant GA 22709. 

REFERENCES 

Allen, C. R., St. Amand, Pierre, Richter, C. F., and Nordquist, J. M., 1965, Relationship between seismicity and 

geologic structure in the Southern California region: 

Seismol. Soc. America Bull., v. 55, p. 753-797. 

Allen, C. R., Grantz, Arthur, Brune, J. N., Clark, M., Sharp, 

R. V., Theodore, T., Wolfe, E., and Wyss, Max, 1968, 

The Borrego Mountain, California earthquake of 9 April 

1968, A preliminary report: Seismol. Soc. America Bull., 

v. 58, p. 1183-1186. 

Brune, J. N., and Allen, C. R., 1967, A microearthquake survey of the San Andreas fault system in Southern California: Seismol. Soc. America Bull., v. 57, p. 277-296. 

Miller, R. W., Pope, A. J., Stettner, H. S., David, J. L., 1969, 

Crustal movements investigations-triangulations, TaftMojave area: U.S. Coast and Geod. Survey Operations 

Data Rept. DR-6, 85 p. 

Scholz, C. H., and Fitch, T., 1969, Strain accumulation along 

the San Andreas fault: Jour. Geophys. Research, v. 74, 

p. 6649-6666. 
PRELIMINARY SOURCE PARAMETER DETERMINATION OF THE SAN FERNANDO 

EARTHQUAKE 1 

By MAX WYSS 

LAMONT-DOHERTY GEOLOGICAL OBSERVATORY OF COLUMBIA UNIVERSITY 

Abstract 

The seismic moment (1.5 • 102

" dyne em) and the source 

dimensions (8< r<21 km) of the San Fernando, Calif., earthquake are estimated from teleseismically recorded P-waves 

and compared with the same parameters obtained from field 

observations. From the combined teleseismic and field data 

the dislocation (100 em) and stress-drop (30 bars) ar~ estimated. 

INTRODUCTION 

The purpose of this paper is to supplement and 

improve by the use of teleseismic data the preliminary source-parameter estimates based on field 

observations. 

Based on dislocation theory, the strength of a seismic source, the seismic moment M 0 , can be estimated 

from the long period part of displacement spectra. 

To obtain the moment from P-waves, the theoretical 

results of Keilis-Borok (1959) and Ben-Menahem et 

al. (1968) were used. For surface waves the tabulated excitation functions of Ben-Menahem et al. 

(1970), which are based on earlier results by BenMenahem and Harkrider (1964), were used. 

A second basic source parameter that can be estimated from body-wave spectra is the source dimension r. It has been recognized by several authors 

that the peak/corner frequency of the seismic spectrum must be a function of the source dimension 

(e.g., Kasahara, 1957, Berckhemer and Jacob, 1968; 

Archambeau, 1968). In the test case of the Borrego 

Mountain, Calif., earthquake, which produced a welldocumented surface rupture and. aftershock zone 

(Alle11 et al., 1968), it was found that the recent 

theory by ·Brune (1970) best predicted the source 

dimensions r from body-w~ve spectra. Brune's 

(1970) relation between corner frequency fa and 

the source area A is 

1 Contribution No. 1642, Lamont-Doherty Geological Observatory. 

l.P tt2 1.la 

A= or r= (1) tr fo 2 ... fo 

where a is the P-wave velocity. 

Aki (1966) showed that the moment Mo was related to the product of fault area A times average 

dislocation across it D 

Mo=11A D (2) 

where 11 is the shear modulus. Combining the seismic 

moment and the source area, both determined from 

body wave spectra, with equation (2) one obtains 

the dislocation at the source D. Using the appropriate equation, one then can estimate the stress drop 

Acr from the ratio of D to r (Brune, 1970). 

Since the moment determination is based on spectral amplitude, the error at any one station can be 

considerable. However, if several stations are used 

the errors are estimated not to exceed a factor of 

two. The determination of the corner frequency, and 

hence the source dimensions, can be reduced in accuracy by focusing effects due to a radiating source. 

However, if several stations at different azimuths 

are used, these effects will average out and the error 

of the final result for r will probably not exceed a 

factor of 2. In computing D and Acr from M 0 and A, 

somewhat larger errors could result. Particularly, 

the stress-drop critically depends on the estimated 

source dimension. 

The accuracies with which the moment and source 

dimensions are determined from body-wave spectra 

are comparable to the accuracies of source parameters obtained from surface fracture observations. 

The fault-area estimate based on the aftershock distribution is more reliable than that based on teleseismic analysis. However, the relation of surface fractures to the area that ruptured during an earthquake 

is not always clear. In the present case, the San 

38 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 39 

Fernando earthquake, the tectonic surface rupture 

seems to be shorter than the extent of aftershock 

activity, and the main zone of aftershocks appears 

not to be parallel to the surface break (Abrams et 

al., 1971). In such cases the accuracy of the source 

dimension and dislocation estimate based on teleseismic data and on field observations may be approximately the same. The moment determination from 

teleseismic data is considered superior to the field 

estimates because in the -latter case the moment is 

obtained from the basic measurements by equation 

(2). 

DATA 

The seismic moment was computed from P-wave 

displacement spectra of four WWS stations and two 

high-gain instruments operated by Lamont-Doherty 

Geological Observatory. The moments together with 

the uncorrected long-period spectral amplitudes 

(T>20 sec) are given in table 1. For the moment 

determination the amplitudes were corrected for 

attenuation, geometrical spreading and the effect of 

the free surface at the receiver (Ben-Menahem et 

al., 1965). Both moment determinations based on 

the radiation pattern by W. H. K. Lee et al. (written 

commun., 1971) (USGS) and Abrams et al. (1971) 

(CIT) are given in table 1. Because of the more 

consistent results, the CIT solution is preferred. The 

USGS solution puts College, Alaska, on a node, 

which is inconsistent with our data. The average 

moment based on P-wave and the CIT fault-plane 

solution is 1.3 · 1026 dyne em. 

The Rayleigh wave spectra from Stuttgart and 

Uppsala, at a period of 50 sec, furnished a moment 

o-f 0.8 · 10 26 dyne em and 3 · 102 '; dyne em, respectively. In this computation the tables published by 

Ben-Menahem et al. (1970) were used. The average 

moment obtained from surface waves is 1.9 · 1026 

dyne em. 

The preliminary corner/peak frequency fo is also 

given in table 1. For four stations an upper and a 

lower bound of f 0 was given. In the average the 

corner /peak frequency was found to be approximately 0.1 Hz. 

The area outlined as possible fault area by the 

aftershocks was estimated from the aftershock data 

given by Abrams et al. (1971). The aftershocks 

occurred over an area of approximately 460 km2 • 

The average displacement as estimated from the 

surface rupture may be taken as 1. m (Abrams et 

al., 1971). These values for the source parameters 

are compared with the values obtained from P-wave 

analysis in table 2. 

DISCUSSION AND CONCLUSIONS 

The three independent moment determinations 

(P-wave, Rayleigh wave, field data) are in excellent agreement. Giving the three methods equal 

weight, the average moment of the San Fernando 

earthquake is 1.5 · 10zn dyne em. 

The rupture area (source dimension) inferred 

from the P-wave spectra as compared with the 

aftershock area appears to be an overestimate when 

Brune's (1970) relation is used and an underestimate when Berckhemer and Jacob's (1968) results 

are used. Unlike the case of the Borrego Mountain 

earthquake, these preliminary data suggest that the 

method of Berckhemer and Jacob (1968) gives results which agree better than Brune's with the field 

observations (table 2). It appears that data from 

more azimuths are needed in order to decide which 

body-wave method, if any, furnishes the right source 

area for a thrust fault like the San Fernando earthquake. Preliminary limits for the radius of this 

earthquake are 21>r>8 km. 

Values for the average dislocation D are also 

given in table 2. They range from 31 to 220 em. 

Because it is uncertain which equation should be 

used to compute the rupture area, the stress-drop 

is obtained from the moment and the dimensions of 

the aftershocks, rather than from body-wave spectra 

TABJ"E !.-Spectral data 

Station 

Umea_________ (UME) -------- Stuttgart_____ (STU)--------- Weston_______ (WES) _______ _ Georgetown___ ( GEO) ________ _ Uppsa}a ______________________ _ 

Clipper mine 1 (near COL) ---- Ogdensburg (OGD) -----------

1 Murphy (1971). 

Distance 

(deg) 

76.8 

85.0 

37.0 

33.3 

78. 

35.3 

35.0 

Long period Azimuth amplitude 

(deg) (10-2 em sec) 

18 0.58 

32 .8 

63 1.8 

70 2.4 

339 1.3 

66 .7 

Corner Moment frequency (10 2 6 dyne em) 

(Hz) USGS CIT 

0.1 1.2 0.72 

.07- .2 1.2 .86 

.08 1.6 1.6 

.06- .08 2.0 2.1 

.1 

7.7 1.5 

1.0 1.0 
40 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

TABLE 2.-Source pa?'ameters 

Source Moment radius (10 2 • dyne em) (km) 

P-Wave: (Brune) __________ 1.3 21 

( Berckhemer & 1.3 8 

Jacob). 

Field Observations ----- 1.4 12 

Area 

(km 2 ) 

1,400 

180 

460 

Displacement 

(em) 

31 

240 

100 

alone. Using the average moment of 1.5 · 1026 dyne 

em and Starr's (1928) equation for stress-drop on 

dip-slip faults, we obtain approximately AD-=30 bars. 

This preliminary result suggests that the San 

Fernando earthquake was another low stress-drop 

event. This supports the idea that stress-drop decreases with decreasing magnitude (King and 

Knopoff, 1968; Wyss, 1970). If the strength of the 

earth's crust is assumed to be on the order of 100 

bars (Chinnery, 1964), the San Fernando earthquake relieved only approximately 30 per cent of 

the total stress that may have accumulated in the 

source region. This result suggests that the San 

Fernando area may not be considered immune to 

further earthquakes. However, it may take a very 

long time to accumulate the additional 30 bars necessary for another earthquake of the same size as the 

one on February 9, 1971. 

ACKNOWLEDGMENTS 

I wish to thank Mr. Modgling from the Environmental Data Service, NOAA, Dr. R. Schick, and 

Dr. M. Bath for furnishing data from their stations. 

Drs. P. Molnar, C. Scholz and B. !sacks critically 

read the manuscript and made helpful comments. 

This study was supported by the National Science 

Foundation NSF Grant GA-22709. 

REFERENCES 

Abrams, M., Allen, C., Anderson, D., Berkey, N., Carey, D., 

Carter, B., Davies, G., Engen, G., Foley, M., Hanks, T., 

Heimberger, D., Hileman, J., Jordan, T., Jungels, P., 

Kamb, B., Liu, H., Minster, B., Nordquist, J., Penrose, 

B., Silver, L., Smith, R., Thatcher, W., Thomsen, L., 

Whitcomb, J., and Wood, S., 1971, Preliminary seismological and geological studies of the San Fernando, California earthquake of February 9, 1971: Seismol. Soc. 

America Bull. [In press.] 

Allen, C. R., Grantz, A., Brune, J. N., Clark, M. M., Sharp, R. 

V., Theodore, 'I'. G., Wolfe, E. W., Wyss, M., 1968. The 

Borrego Mountain, California, earthquake of April 9, 

1968. A preliminary report: Seismol. Soc. America Bull., 

v. 58, p. 1183-1186. 

Aki, K., 1966, Generation and propagation of G waves from 

the Niigata earthquake of June 16, 1964, Part 2. Estimation of earthquake moment, released energy, and 

stress-strain drop from the G wave spectrum: Earthquake Res. Inst. Bull., v. 44, p. 73. 

Archambeau, C. B., 1968, General theory of elastodynamic 

source fields: Rev. Geophysics, v. 6, p. 241. 

Ben-Menahem, A., and Harkrider, D., 1964, Radiation patterns of seimsic surface waves from buried dipolar point 

sources in a flat stratified earth: Jour. Geophys. Research, v. 69, p. 2605-2620. 

---Smith, S. W., and Teng, T-L., 1965, A procedure for 

source studies from spectrums of long-period seismic 

body waves: Seismol. Soc. America Bull., v. 55, p. 203-

235. 

---Rosenman, M., and Harkrider, D. G., 1970, Fast evaluation of source parameters from isolated surface wave 

signals: Part 1. Universal tables, Seismol. Soc. America 

Bull., v. 60, p. 1337. 

Berckhemer, H., and Jacob, K. H., 1968, Investigation of the 

dynamical process in earthquake foci by analyzing the 

pulse shape of body waves: Final Scientific Report, 

AF61 (052) -801. 

Brune, J. N ., 1970, Tectonic stress and the spectra of seismic 

shear waves from earthquakes: Jour. Geophys. Research, v. 75, p. 4997. 

Chinnery, M. A., 1964, The strength of the earth's crust 

under horizontal shear stress: Jour. Geophys. Research, 

v. 69, p. 2085. 

Kasahara, K., 1957, The nature of seismic origins as inferred from seismological and geodetic observations: 

Earthquake Res. Inst. Bull., v. 35, p. 473. 

Keylis-Borok, V. I., 1959, On estimation of the displacement 

in an earthquake source and of source dimensions : 

Amali. Geofisica, v. 12, p. 205. 

King, Chi-yu, and Knopoff, L., 1968, Stress drop in earthquake, Seismol. Soc. America Bull., v. 58, p. 249. 

Murphy, A. J., 1971, High-gain, long-period seismograph station, Installation Report, Fairbanks, Alaska: ARPA 

Scientific Report. [In press.] 

Starr, A. T., 1928, Slip in a crystal and rupture in a solid 

due to shear: Cambridge Philos. Soc. Proc., v. 24, p. 

489-500. 

Wyss, M., 1970, Observation and interpretation of tectonic 

strain release mechanisms: California Inst. Technology, 

unpub. Ph. D. thesis. 
PATTERN OF FAULTING AND NATURE OF FAULT MOVEMENT 

IN THE SAN FERNANDO EARTHQUAKE 1 

By BARCLAY KAMB, L. T. SILVER, M. J. ABRAMS, B. A. CARTER, T. H. JORDAN, and J. B. MINSTER 

DIVISION OF GEOLOGICAL AND PLANETARY SCIENCES, CALIFORNIA INSTITUTE OF TECHNOLOGY 

PURPOSE AND SCOPE 

In an effort to understand the mechanism of the 

February 9, 1971, San Fernando earthquake in relation to seismic observations and regional geology, 

we have gathered information on the occurrence 

and amount of ground displacement by surface 

faulting. Most of the field data were obtained 

within the first 4 days after the earthquake, because 

we wished to describe the fault features as much as 

possible in their pristine state. Systematic observations were made only in the area generally east of 

Sylmar and Olive View Hospital, that is, in the 

eastern part of the area strongly affected by the 

earthquake, where manifestations of surface· faulting were particularly well developed. While our description of faulting is therefore limited to this area 

and while there doubtless are fault features that we 

have missed in the area studied, our results are presented here as a contribution to the general body of 

knowledge about the earthquake. 

AREA STUDIED 

Figure 1 shows the area of detailed study, and, in 

summary form, the results obtained. The geology of 

the area has been described by Oakeshott (1958). 

The San Gabriel Mountains, forming a steep escarpment at the northern edge of the area, are underlain by crystalline rocks thrust southward toward 

the San Fernando Valley along the north-dipping 

Hospital Fault, whose roughly east-west trace lies 

near the foot of the escarpment, about 0.7 km north 

of Veterans Hospital. The alluviated San Fernando 

Valley to the south is underlain by Tertiary sediments. These are exposed only at isolated places 

near the mountain front, being elsewhere deeply 

buried by Quaternary alluvium. East of Pacoima 

Wash, however, an area of foothills intervenes be1 Contribution No. 1995, California Institute of Technology, Division of 

Geological and Planetary Sciences, Pasadena, California. Important contributions to the collection of field data for this report were made by 

N. Berkey, D. Carey, M. Foley, T. Hanks, D. Heimberger, H. Liu, B. 

Penrose, R. Smith, L. Thomsen, and S. Wood. 

tween the mountain front (here marked by the 

Lopez Fault, the apparent eastward continuation of 

the Hospital Fault) and the alluviated valley into 

which empties Big Tujunga Wash. These foothills, 

with relief of 90-180 m, are underlain by Tertiary 

sediments which, in the southern part of the hills, 

dip uniformly northward at about 65°. 

In reconnaissance fashion we have searched for 

surface faulting in the San Gabriel Mountains 

northward from the area of figure 1 to Soledad 

Canyon, in the vicinity of the epcienter of the main 

shock. 

FAULT PATTERN 

Fault displacements of the ground surface that 

occurred in the earthquake are shown in figure 1, in 

as much detail as is possible at the map scale. 

Faulting extends almost continuously over a distance of 10 km from south of Sylmar eastward to 

the mouth of Little Tujunga Canyon, with small 

discontinuous manifestations continuing at least another 2 km farther east. This zone of faulting is 

here called the San Fernando fault zone. Its overall 

trend in the area studied is N. 72° W. 

Some 2 km east of the easternmost fault feature 

shown in figure 1, there occurs a 1.0 m left-lateral 

offset of Oro Vista Avenue where it crosses Big Tujunga Wash. That this is not an isolated tectonic 

feature is shown by a number of indications of surface faulting in the intervening area (Perry Ehlig, 

personal commun.), which we have not studied. The 

San Fernando fault zone thus continues about 2 km 

beyond the eastern edge of figure 1. The total length 

of the zone of fault movement so defined is at least 

12 km, and is comparable to the distance from the 

surface ruptures to the epicenter of the main shock, 

which lies about 13 km north of the mouth of Lopez 

Canyon (C. R. Allen, personal commun.). 

Although the fault breaks that we studied die out 

westward as indicated in figure 1, other isolated 

manifestations of tectonic faulting, including the re41 
42 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

0 

N 

. ,9ooc 

··· .... ... .... .. , . • . 

J lD 

0 ~ "" r<l 

0 2 

Fault scarp, showing dip of fault plane. 

Zone of distributed surface deformation, 

~ Lateral component of fault slip, in inches. 

Vertical offset, in inches, • on upthrown side. 

Horizontal shortening across foul! trace, in inches . 

KILOMETERS 

118° 26' 25' 24' 23' 22' 21' 20' 

FIGURE 1.-Surface faulting in a portion of the area affected by the San F ernando earthquake. Base map from U.S. Geological 

Sur vey San F ernando and Sunland quadrangles, 1:24,000 original scale. 

ported Mission Wells fault segment, may well be 

present west of the area of figure 1. 

The fault breaks in the area studied can be conveniently placed in five groups: 1. A zone of breakage extending approximately westward from Pacoima Wash toward Sylmar, and here called the 

Sylmar fault segment. (See fig. 1.) 2. A fault line 

along the southern edge of the foothills, from Pacoima Wash eastward almost continuously to Little 

Tujunga Canyon and discontinuously farther eastward into the Big Tujunga; this is called the Tujunga fault segment. 3. A group of short faults 

within the foothills some 0.3-0.9 km north of the 

Tujunga segment, and trending subparallel to it. 4. 

A complex group of short breaks in the area between the west end of the Tujunga segment and the 

east end of the Sylmar segment. 5. A short fault just 

west of the mouth of Pacoima Canyon, which we 

will here call the Veterans fault, since it lies about 

1 km east of Veterans Hospital (fig. 1). In the terminology used here and by the U.S. Geological Survey (this report), the Sylmar and Tujunga segments are a part of the San Fernando fault zone, 

which includes also the Mi8sion Wells segment farther west. Fault groups 3 and 4 are also part of this 

zone, but the fault in group 5 is a separate feature. 

The different groups of faults (with exception of 

group 5) have in common a generally east-west 

strike, northward dip, and combined thrust and 

left-lateral displacement. They differ in their relationships to the underlying bedrock, in the types of 

surface rupture produced, and in detailed features 

of attitude and displacement. The displacements 

along the Sylmar fault segment are generally larger 

than those in the other groups. The Sylmar segment 

reaches the surface in alluvium, and displacements 

along it tend to be distributed somewhat diffusely 

over a zone about 50 m wide, with few scarps, 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 43 

"mole tracks," or other linear features of surface 

disruption that would allow discrete fault breaks to 

be traced continuously for distances of hundreds of 

meters. No direct observations of the fault attitude 

were possible. The Tujunga fault segment is for the 

most part a single clean break, forming a well-defined fault scarp that follows closely the topographic break at the base of the foothills. The scarp 

probably cuts bedrock near the surface over most of 

its -length, but clean bedrock is rarely exposed in it 

because of its proximity to the bedrock-alluvium 

contact and because of a thick soil mantle derived 

by mass wasting from the slopes above. As judged 

from the trace where it crosses canyon mouths (for 

observations see fig. 1), the fault dips 20°-25° to 

the north and is a thrust. The faults of group 3 

clearly cut and are controlled by the sedimentary 

rocks of the foothills. Where well exposed, the 

faults are seen to parallel bedding in the sediments 

and to dip about 65° N. They may be classified as 

bedding-plane reverse faults. The faults of group 3 

have distinctly less lateral continuity than the Tujunga segment. The Veterans fault (group 5) is 

similar in having short lateral extent, and in being 

parallel to bedding in the enclosing Tertiary ( Saugus) sediments. It dips about 60° N. Although it is 

a small fault, it is especially significant because it is 

the only definite tectonic displacement found in the 

zone along the foot of the San Gabriel Mountain escarpment, where the greatest recognized intensity 

of ground shaking occurred. Group 4 consists of a 

complex collection of breaks of various kinds, which 

do not fit the simple pattern of the other groups. 

IDENTIFICATION OF TECTONIC FAULTING 

The lines plotted in figure 1 represent either actual fault scarps or else zones of surface disruption 

that are definite and continuous enough to be considered the result of ground displacement by faulting. We avoid hypothetical interpolation between or 

extrapolation beyond observed features of surface 

faulting, even though in some examples, particularly along the Tujunga segment, the alinement of 

separate scarps is so good that movement along a 

single continuous fault surface at depth is clearly 

indicated. 

We endeavor to omit from figure 1 any scarps or 

fissures caused by compaction of artificial or alluvial fill or by the motion of landslide blocks. In 

the Sylmar fault segment, there is relatively little 

possiblity of landslide motion because of the low relief; but in the foothill areas to the east, as well as 

in the San Gabriel Mountains to the north, very 

widespread landsliding took place during the earthquake. Numerous headwall fissures of landslide 

blocks, up to hundreds of meters in extent, are recognizable from their pattern and location on the affected slopes. A few of the scarps plotted in the 

foothill area of figure 1 have some attributes of 

such fissures but are retained in figure 1 because 

landslide blocks bounded by them are not recognizable as such and would have to be unexpectedly 

large. An example is the prominent scarp, about 1 

m high located near lat 34°16.8', long 118°20.9'. 

(fig. 1). If this scarp, which is accompanied by an 

extension crack about 1.2 m wide, were the head of 

a large landslide block, there should be a prominent 

toe somewhere lower on the slope, but none is 

found . .It is possible that such scarps are in part 

tectonic in origin and have been accentuated and 

modified by down-slope movement, so that they take 

on some attributes of landslide fissures. 

Scarps of the Tujunga segment have an attitude 

and sense of displacement appropriate to landslide 

toes and are consistently located near the base of 

the foothill front, where the toes of landslides on 

the steep south-facing slope of the foothills could be 

expected. However, the uniform northward dip of 

bedding in this area tends to inhibit landslide motion on these slopes. Recognizable landslides are 

relatively rare on the south-facing slopes, whereas 

they are abundant on eastward- and especially westward-facing slopes in the canyons that cut southward through the foothills. If the scarps along the 

southern foot of the hills were primarily toes of 

landslide blocks, one could expect that headwall fissures would be most prominent on the hill slopes 

above places where the scarps at the foot were largest. In fact, an inverse relationship is observed. The 

most prominent potential headwall fissure (at long 

118°20.9', fig. 1) is at a place where there is no 

scarp at the foot of the hills, and few indications of 

ground disruption there. 

The scarp of the Tujunga fault segment is shown 

definitely to be tectonic in origin where it crosses 

the 0.5-km-wide mouth of Little Tujunga Canyon. 

In this locality there is no high ground to the north 

within 0.5 km of the scarp, and hence no source 

area for a landslide block of reasonable dimensions. 

It is possible that in other places the scarps of 

the Tujunga fault segment contain some contribution from landsliding or general downslope motion 

along the front of the hills, but for the reasons 

given we believe that the displacements seen in 

these scarps are primarily tectonic in origin. 
44 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FAULT DISPLACEMENT 

Figure 1 shows the slip, in inches, that occurred 

across the observed fault lines. In measurements repeated at given localities on different days, we 

found no change in displacement, and we therefore 

believe that essentially all the displacement occurred during the main earthquake. 

In figure 1 the slip is given in terms of its vertical, lateral, and transverse components. Where the 

f ault break has the more common form of a ramp 

several meters wide and where the ground surface 

is rough and irregular, the accuracy is as poor as 

+ 5 inches or worse. The lateral slip component (horizontal component parallel to the fault strike) is 

measurable where preexisting straight features 

such as fences or curbs cross the fault line. In favorable situations the measurement is accurate to a 

fraction of an inch, but it is uncertain by 5 inches 

or more when the offset is distributed over many 

meters. Large errors arise if pre-existing jogs in 

streets or fence lines are not taken into account. 

The transverse slip component (horizontal component perpendicular to the fault strike) manifests itself either as extension or compression across the 

fault zone. Longitudinal shortening of street or 

sidewalk pavement is a very common feature of the 

San Fernando earthquake. Its usual form is a brittle 

failure of the pavement along a fracture perpendicular to the street or sidewalk and an overriding of 

the pavement from one side (the upthrown side, if 

any) over that on the other. In this situation the 

compression can be measured to an accuracy of 

about 1 inch. Compressional overthrusting along 

fault scarps in unpaved ground is also very common, and the amount of shortening can sometimes 

be determined to an accuracy of about 5 inches, 

particularly where turf overrides turf. Overall, the 

accuracy of the slip values given in figure 1 is + 5 

inches, although many values are more reliable than 

this. 

The largest slip component in the San Fernando 

earthquake is left lateral and occurs near the middle of the Sylmar segment, where it reaches about 

1.6 m ( 64 in). Left-lateral slip of up to 0.8 m (32 

in) occurs in fault groups 2 and 3 but is not as consistently present as in the Sylmar segment. Vertical 

displacement, north side up, is shown by almost all 

faults. The maximum uplifts are comparable in 

fault groups 1 to 3 and amount to 0.8-0.9 m 

(30-34 in.). North-south compression across the 

generally east-trending faults is also a consistent 

feature. Transverse compressions of up to 0.8 m (30 

in) are typical of fault groups 1 and 2, with a maximum of 1.1 m ( 42 in) recorded in Little Tujunga 

Canyon. Displacements are generally smaller in 

groups 4 and 5 than in 1 to 3. 

The data in figure 1 indicate that the overall 

fault-displacement in the San Fernando earthquake 

involved nearly equal amounts of north-south compression, vertical uplift (north side up), and leftlateral slip and hence may be described as a thrusting of a northern block to the southwest over a 

southern block, along a fault surface dipping about 

45 ° north. 

A more detailed assessment of the fault motion is 

provided in table 1, which gives the displacement 

vector for faults of groups 1 to 3 at 13 locations 

where the slip components are relatively well determined. The vectors in table 1 are obtained from the 

slip components in figure 1 and are expressed in 

terms of the motion of the southern block relative 

to the northern. The directions of these vectors are 

plotted stereographically in figure 2. The grouping 

of the points in figure 2 reveals that in the central 

part of the San Fernando fault zone, from long 

118°23' to 25.8', the displacement vectors tend to 

N 

0 0 • 0 

0 

• • 0 

• • • • 

10. 

• 

w + E 

down 

s 

FIGURE 2.-Stereographic plot of fault displacement vectors 

at the localities listed in table 1. Vectors r epresent motion 

of south side of fault with respect to north side, and are 

plotted on the lower hemisphere. Solid circles refer to 

localities in the central part of the San Fernando fault 

zone, between longitude 118° 23' and 118° 25.8', open circles 

to localities outside this interval. The triangle is the plunge 

of slickensides at locality 13 in table 1. The great circle 

represents a fa ult plane striking N. 72° W. and dipping 

45 o north. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 45 

cluster about a plunge of 35° toward N. 60° E., 

whereas toward the ends of the zone the plunge azimuth swings northward. This behavior suggests 

that mechanical constraints require the lateral slip 

component to die out more rapidly toward the ends 

of the fault zone than the transverse component 

does. Relative to the overall S. 72° E. trend of the 

zone, the N. 60° E. plunge azimuth makes an angle 

of about 45°, implying equal components of lateral 

slip and transverse compression. 

TABLE I.-Magnitude and direction of fault displacements 

Location 

No. Fault 

group -------------------------- Street(s) Long 

118° 

1 1 Glenoaks-Lucas ___________________ 26.2' 

2 1 Phillippi-Chivers _________________ 25.9' 

3 1 Gridley __________________________ 25.8' 

4 1 Fernmont-Cometa ________________ "25.6' 

5 1 Adelphia-Harding _________________ 25.4' 

6 1 Freeway 210 _____________________ 25.1' 

7 1 Chippewa-Newton ________________ 24.8' 

8 2 Foothill (hospital) ________________ 24.5' 

9 2 Lopez Canyon ____________________ 24.0' 

10 2 Little Tujunga (lower) ____________ 22.2' 

11 2 0.25 km east of No. 10 ____________ 22 .1' 

12 3 Little Tujunga (upper) ____________ 22.1' 

13 3 Lopez Canyon-Bailey _____________ 24.0' 

The total fault displacements indicated in table 1 

range from 0.8 to 1.9 m (31-74 in). The largest 

displacements are near the middle of the Sylmar 

fault segment. If we sum the displacements across 

faults of groups 2 and 3 in Lopez Canyon or in Little Tujunga Canyon, we see that the aggregate displacement across the Sylmar-Tujunga fault segments is as large or somewhat larger in the foothill 

area than it is farther west, amounting to about 2 

m. The maximum aggregate uplift across the zone, 

calculated along a traverse in Lopez Canyon, is 

about 1.9 m (74 in), north side up. 

The relative magnitudes of the vertical and transverse slip components provide a measure of the dip 

of the fault planes. Dips inferred on this basis are 

given in table 1 and are compared with dips measured directly on the fault planes at two locations 

where this was possible. The agreement is not close 

but suggests that individual inferred dip values are 

reliable to ± 20°. A similarly low reliability is implied by the scatter of the inferred dip values in 

table 1, if the actual fault planes of the zone have a 

nearly constant dip. At the level of accuracy of the 

inferred dip values in table 1, there is no clear distinction between overall fault-plane dips for groups 

1 and 2, but there is a suggestion that faults of 

group 3 dip somewhat more steeply than those of 

group 2, in agreement with the available surface observations of fault attitude. 

The average of the dip values in table 1 (omitting 

Nos. 1 and 2) is 42° north and may provide a measFault slip vector 

(motion of south side relative Dip of fault plane to north side) 

Length Azimuth Plunge Inferred Observed 

in. m 

30 0.8 N. 13° W. 12° N. 13° NW. 

52 1.3 N. 7o E. 13° N. 15° NW. 

72 1.8 N. 57° E. 9o NE. ? 

74 1.9 N. 67° E. 24° NE. 48° N. 

53 1.3 N. 82° E. 35° E. 79° N. 

34 .9 N. 27° E. 9° NE. 12° N. 

38 1.0 N. 49° E. 18° NE. 27° N. 

42 1.1 N. 53° E. 45° NE. 45° NE. 

38 1.0 N.61°E. 32° NE. 45° N. 25° N. 

46 1.2 N. 10° E. 23° N. 23° N. 

31 .8 N. 2° W. 29° N. 31 oNE. 

31 .8 N. 60 E. 49° N. 49° N. 

53 1.3 N. 62° E. 40° NE. 53° N. 64° N. 

ure of the overall dip of the master fault plane at 

depth. This dip is consistent with the observed hypocentral depth of 13 km for the main shock, in relation to the epicenter location about 13 km north 

of the zone of surface faulting (C. R. Allen, personal 

commun.). 

DETAILED FEATURES OF THE SYLMAR 

FAULT SEGMENT 

The representation of the Sylmar fault segment 

in figure 1 is based on the detailed observations of 

surface deformation shown in figure 3. The zone of 

fault movement is outlined by fractures in the paving of streets, sidewalks, and driveways. As indicated by the heavy solid lines in figure 3, with very 

few exceptions these fractures run either transverse 

to the streets or parallel to them along their margins. Because of this control of fracture orientation 

by the street pattern, the individual fractures do 

not generally give direct expression of the fault displacement in the Sylmar segment. Owing to the distributed character of the deformation, its effects in 

unpaved ground are generally too diffuse to be 

traced continuously. However, major structural 

damage to buildings is confined to the immediate 

zone of surface deformation outlined by the distribution of street fractures, even in places where deformation of unpaved ground adjacent to buildings 

is so diffuse as to be not clearly recognizable as the 

result of fault displacement. The zones of deformation indicated by the lighter lines in figure 3 were 
46 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

EXPLANATION 

25~ t Lateral displacement across interval shown, in inches. 

33-++- Horizontal shortening over interval shown, in inches. 

+- ~ Horizontal extension over interval shown. 

'-t Group of cable spools, with arrow showing ground 

A'-'> displacement under spools . 

0 . 2 .4 .6 kilometer 

FIGURE 3.-Surface faults and street offsets in the Sylmar fault segment and in the area between the Sylmar and Tujunga 

segments. The Tujunga fault scarp terminates in the southeast corner of the map. Base map derived from aerial 

photography. 

traced from one street crossing to the next by locating evidences of major structural damage to buildings in the intervening unpaved areas. 

Most of the displacement figures given in figure 3 

represent offsets across individual streets. Lateral 

components are in all such cases measured perpendicular to the street line, and longitudinal components (horizontal compression or extension) are 

parallel to the street line. Lateral and vertical displacements are generally distributed more or less 

diffusely over intervals of up to 50 m, and the figures given represent cumulative offset across the intervals marked by the arrow symbols. Longitudinal 

displacements, almost invariably compressional, are 

localized at individual fractures (overthrusts) or 

pressure ridges in the pavement; typically, several 

of these cross the street within the zone of fault deformation. Because of an apparent dynamic sliding 

of large, rigid pavement slabs during the earthquake, extensional cracks are occasionally found adjacent to compressional overthrusts crossing the 

same street. The best example of this is on Gridley 

Street between Chivers and Phillippi A venues. The 

longitudinal displacements given in figure 3 are the 

-net cumulative amounts over the intervals shown by 

the arrows, with any compensating extension taken 

into consideration. 

To obtain displacements across the Sylmar fault 

segment from the street offset data in figure 3, 

some interpretation is necessary. In principle, the 

three perpendicular components of offset (vertical, 

longitudinal, transverse) across a single street completely determine the slip vector, which is obtainable by vectorial addition of these components. If the 

fault displacement is faithfully registered across 

each street crossed by the zone and if the south side 

moved as a rigid block with respect to the north 

side, then it follows that in a network of perpendicular streets the lateral offset across one street 

should in principle be equal to the longitudinal 

offset along nearly perpendicular streets nearby, the 

longitudinal offset being compressional or extensional as required by the sense of lateral offset and 

the trend of the fault with respect to the streets. 

When this rule is tested against the street offset 

data of figure 3, it is found to be poorly satisfied. 

Examples of violation of the rule are found near intersections of the following streets: Chippewa and 

Gladstone, Harding and Adelphia, Cometa and 

Fernmont, Knox and Gridley, Gridley and Phillippi. 

The last of these is striking: the 21-inch left-lateral 

offset on Gridley between Knox and Phillippi requires 21 inches of longitudinal extension on Phillippi where the fault zone crosses it, but instead of 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 47 

this, 33 inches of longitudinal compression is observed. 

On some streets the lack of any recorded lateral 

offset, to correspond with longitudinal compression 

on perpendicular streets, may be simply a detection 

difficulty, if the original street alinement was not 

linear enough to allow observation of a distributed 

lateral offset. Inconsistent observations of longitudinal displacement may be due to the occasional operation of some mechanism of pavement sliding that 

distributes the longitudinal offset so widely as to be 

undetectable or that transfers it to seemingly inappropriate locations. Thus the 72-inch longitudinal 

compression on Gridley is more appropriate to a location near Knox than to its observed position between Phillippi and Chivers. The lack of longitudinal offsets on either Fernmont or Cometa near their 

intersection, in spite of the definite lateral offsets on 

these streets, argues clearly for some mechanism 

whereby the expected longitudinal displacements 

are redistributed elsewhere or masked. 

To arrive at displacements across the Sylmar 

fault segment in the face of the problems discussed 

above, we adopt a somewhat arbitrary procedure. 

For each location listed in table 1, we select from 

figure 3 the street-offset observations considered 

representative, restricting the choice to streets in 

the immediate vicinity and ignoring any offsets that 

conflict in the sense discussed above. Where observations are compatible on adjacent streets, they are 

averaged. The selections are listed in table 2 in a 

format that shows also which offset observations 

are ignored at each location. Consistent with the 

previous discussion, the selections are made from 

the point of view that observed offsets are more significant than a lack of confirmatory offset observations on adjacent streets. Hence, the selections in 

table 2 give larger fault displacements than would 

be obtained if the offset observations on all streets 

crossed by the fault zone were simply averaged. 

The fault vectors obtained in this way for the 

Sylmar fault segment are listed in table 1. The horizontal slip components shown along the Sylmar segment in figure 1 are obtained by projecting the vectors of table 1 onto the strike and the dip lines of 

the fault. 

The street-offset data along the Sylmar fault segment in figure 3 show certain regularities that bear 

on the fault displacements derived in table 1. Lateral offsets are consistently left lateral, and on 

northwest-trending streets they are consistently 

larger than on northeast-trending streets. By itself 

this implies that across the generally east-trending 

TABLE 2.-Selection of representative street offsets for determinations 

of displacement on the Sylmar fault segment 

Loeation Offsets selected ( +) 

No. Streets 

Vertical Transverse Longitudinal 

1 Glenoaks ____________ _ + Lucas _______________ _ VVarren + _____________ _ 7th _________________ _ + + 2 Chivers _____________ _ + Phillippi_ ___________ _ + + Knox _______________ _ Gridley + _____________ _ 3 Gridley _____________ _ Knox _______________ _ + + 

+ Phillippi_ ___________ _ 4 Fernmont_ __________ _ + Cometa ____________ _ 8th _________________ _ + + 

+ 5 Harding ____________ _ + Adelphia ____________ _ + + FoothilL ___________ _ Bromont + ____________ _ 

6 Freeway 210 _________ _ Maclay + + + _____________ _ 

7 Chippewa ___________ _ Newton + + _____________ _ 

MacNeiL + ___________ _ HunnewelL _________ _ + 

fault zone there is some north-south compression in 

addition to left-lateral slip, but the lateral slip exceeds 

the transverse compression. This agrees with the 

displacement vectors found at locations 3 to 5 and 

at 7. If it were generally true, then longitudinal 

extension would be expected on northwest-trending 

streets crossing the fault, but, instead, these streets 

show only longitudinal compression. '('here are, 

however, indications of northwest extension in two 

areas of tension cracks, one between Foothill Boulevard and the 210 Freeway and the other between 

Glenoaks Boulevard and Lucas Street (figure 3). 

Both of these areas lie slightly northeast of the zone 

of fault deformation as indicated by breaks in 

street pavement. Indications of compression along 

northwest-trending streets oare·generally, weak along 

the fault line east of Gridley Street, and in this portion we may conclude that, on balancing the indications from lateral and longitudinal street offsets, 

the overall fault displacement must have carried the 

south side approximately northeast relative to the 

north side and the lateral and transverse slip components on the west-trending fault must be approximately equal. 

Near Gridley Street (long. 118°25.8'), the trend 

of the Sylmar fault segment swings rather abruptly 

from west to southwest. West of the bend, prominent longitudinal compressions on northwest-trending streets are found, which cause the indicated displacements to swing toward the north (locations 1 

and 2, table 1). The approximate equality of longi-
48 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

tudinal and transverse displacements across the No. 8 (table 1), where the fault reaches Foothill 

fault is thus preserved west of the bend, but this re- Boulevard and turns northwest (long :1)8°24.6'). 

quires that the rock masses north and south of the The general lack of left-lateral offsets recorded elsefault moved in a manner quite different from rigid where may be due in part to the scarcity of linear 

blocks. features crossing the fault line. However, at the 

TUJUNGA FAULT SEGMENT 

Because this fault is generally marked by a scarp 

or as a sharply localized zone of surface displacement, 

the components of slip across it can be measured directly, without the complications discussed above 

for the Sylmar segment. However, since the scarp 

traverses an unpaved and irregular ground surface 

over most of its length, the individual slip measurements cannot generally be made with the accuracy 

attainable along the Sylmar segment. 

The fault scarp is most prominent at its western 

end and near Little Tujunga Canyon. Its· detailed 

continuity is interrupted in several places between 

Lopez and Little Tujunga Canyons. The largest 

such interruption is at long 118°22.8'. Traced from 

the west, the scarp here decreases in height and 

separates into several small parallel scarps or fissures, which gradually become more diffuse and are 

replaced by parallel "mole tracks" in a zone about 

15 m wide; finally this zone disappears in plowed 

fields. 

Five-tenths km east of Little Tujunga Wash, the 

scarp enters an area of residential subdivision and 

becomes obscure. However, the line of faulting 

clearly extends 1 km farther east, as indicated by 

a1ined breaks in street pavement and. in water 

mains. The displacement here is generally small 

(about 0.2 m of north-south compression, with little 

detectable vertical and no lateral movement), and 

there is relatively-little~major structural damage to 

houses along the fault line. Farther east the surface 

effects of faulting die out entirely, except for two 

broken water mains and some small north-south 

compressions in driveway pavement near long 

118°20.4'. 

Although the displacement on the Tujunga fault 

segment dies out toward the east edge of figure 1, 

substantial displacement reappears farther east, as 

mentioned earlier, along the segment of the fault in 

Big Tujunga Wash, where left-lateral slip of as 

much as 1.0 m is observed. This segment of the 

fault has a due-east trend and appears to turn toward the northeast near its eastern end, where it 

crosses Oro Vista A venue. 

Left-lateral displacement across the Tujunga 

fault segment is definite at Lopez Canyon, and a 

similar displacement vector is indicated at location 

Little Tujunga road there is definitely no lateral 

offset, and in an orange grove 250 m to the east 

there is a definite right-lateral offset of 25 em. 

FAULTS OF GROUP 3 

The sharp, 0.8-m-high scarp in Lopez Canyon at 

lat 34°17.8', 0.9 km north of the Tujunga fault segment, is one of the more striking fault features produced in the earthquake. It will be called here the 

Oak Hill fault scarp because it passes near Oak Hill 

School. Where the scarp cuts bedrock (Tertiary sediments) in the canyon bottom, it exposes the slickensided fault surface, dipping 64 o N., in agreement 

with the dip indicated by the trace of the scarp on 

the west wall of the canyon. The plunges of slickensides, projected onto a vertical plane parallel to the 

fault strike, are in the range 40° to 55° E, indicating on the average about equal amounts of vertical 

and left-lateral offset across the fault. The average 

slickenside plunge vector is plotted as a triangle in 

figure 2. 

The amount of clay gouge exposed in the fault 

scarp indicates that previous movements have occurred on the Oak Hill fault, but does not reveal 

their age. 

Where the Oak Hill fault passes into alluvium in 

the canyon bottom, its scarp becomes diffuse. Although it reappears in the bedrock of the canyon 

walls, the scarp rapidly decreases in height as 

traced both east and west, and it disappears within 

250 m of the canyon bottom on both sides. This behavior is peculiar, in view .of-the initial prominence 

of the fault scarp and the general absence of alluvial fill that might obscure its lateral continuation. Other scarps of group 3 are similarly restricted in their lateral extent. We believe that this 

is a real effect, although landsliding could in places 

obscure the faults and although our search was not 

thorough enough to rule out additional fault segments in some of the more remote parts of the 

foothill area. 

The location, alinement, and displacement (table 

1, location No. 13) of the Oak Hill fault might suggest that it represents an eastward continuation of 

the Sylmar segment, but there is definitely no 

connection between these two segments in terms of 

scarps or other recognizable features of surface 

faulting that formed in the San Fernando earthquake. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 49 

Lateral motion on group 3 scarps shows an inconstancy similar to that of group 2. Although the Oak 

Hill scarp 100m west of Lopez Canyon Road shows 

an 0.8-m left-lateral displacement, the road itself is 

displaced right-laterally by 0.1 m along the same 

line. Small left-lateral displacements appear at several isolated places in the group 3 zone, including 

the northern scarp cutting the highway in Little 

Tujunga Canyon, but there are also examples of 

fault breaks with no lateral offset, such as the one 

in Lopez Canyon 300 m south of the Oak Hill scarp. 

The northern fault break in Little Tujunga Canyon cannot be traced continuously eastward, and 

the only evidence of eastward continuatior::t is an 

alinement of small scarps with reversed sense of 

vertical displacement (south side up), at long 

118°21.8'. The prominent scarp at long 118°20.9' 

lies on a continuation of the suggested S. 70° E. 

trend, but we found no evidence of fault continuity 

over the intervening distance of 1 km. 

On the west side of Little Tujunga Wash, there is 

evidence, discovered by J. L. Smith (personal commun.), that the base of old terrace gravels is offset 

vertically 2.5 m, north side up, along the northern 

fault break. Since the displacement during the San 

Fernando earthquake was only about 0.6 m, this 

shows that previous displacements have occurred on 

this fault in Quaternary time. 

Traced westward, the northern break in Little 

Tujunga canyon follows a number of discontinuous 

small scarps as far as long 118°22.7'. Its trend over 

this interval is due west and suggests that it might 

join the Tujunga fault segment farther west. Similar behavior is suggested for the rupture at long 

118°22.9', lat 34 °17 .4'. 

If the dip observed for faults of group 3 (about 

65° N) continues beneath the surface, these faults 

will meet the more shallowly-dipping Tujunga fault 

segment at depth. Since the 65° dip at the surface 

is controlled by bedding, it seems likely that at 

depth the faults will swing around into a tectonically-controlled orientation with an approximately 45° 

dip, as inferred for the fault zone as a whole. Thus, 

the faults of group 3 will tend to merge with the 

Tujunga fault segment at depth. 

From their limited lateral extent and their relationship to the Tujunga fault segment, it appears 

that the faults of group 3 are secondary effects produced by fractures that splayed off from the main 

thrust fault and up into the overriding block. The 

tendency for secondary fracturing to affect the 

upper block is reflected also in the relatively shallow focal depths of the aftershocks, by comparison 

with the main shock (C. R. Allen, personal commun.). However, there is no evidence that any of 

the scarps of group 3 were formed during one of 

the aftershocks. Although the above interpretation 

identifies the Tuj~nga fault segment as the surface 

trace of the master thrust, it should be noted that 

the displacement across the zone of group 3 faults 

is comparable to that across the Tujunga fault segment itself. West of Pacoima Wash, the role of the 

master break is assumed by the Sylmar fault segment, but here there is no secondary faulting in the 

upper block, unless the Veterans fault is of this 

type. 

FAULTS OF GROUP 4 

These faults, shown in detail in figure 3, occupy 

the area between the eastern end of the Sylmar 

fault segment (northeast corner of fig. 3) and the 

western end of the Tujunga segment (southeast 

corner of fig. 3). They represent the mechanical 

connection between these two major fault segments 

during the earthquake. Viewed in general terms, the 

line of surface displacement along the Tujunga 

fault segment turns northward around the southwest corner of the foothill area and follows the 

western edge of the foothills north to the trace of 

the Sylmar fault segment, which then carries the 

displacement westward. In detail, however, this 

northward connection is complex. Instead of a single clear break, there is a maze of small ruptures. 

As shown in figure 3, the scarp of the Tujunga 

fault segment disappears shortly after turning 

northward at Foothill Boulevard. On its projected 

trend to the north is an area of three city blocks 

southeast of Arroyo Street in which numerous small 

pavement ruptures indicate ground deformation. 

The fractures here are almost exclusively perpendicular or parallel to the streets, showing again, as 

in the Sylmar zone, that the paveinerit largely controls the individual fractures. 

The style of deformation in this area is remarkable: there is little lateral or vertical displacement, 

but fractures of both northeast and northwest orientation show consistent shortening, which indicates a net loss of surface area. The aggregate compression (given in fig. 1) is, however, greater in the 

northeast direction than in the northwest, which is 

consistent with the relative motion indicated elsewhere for the blocks between which the deformed 

area lies. 

In the northeast part of this area is a small scarp 

(maximum height 0.4 m, or 15 in.) that extends irregularly northeast, ignoring the street pattern, for 
50 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

about 200 m. Landsliding from the nearby west-facing hill slope might be responsible for this scarp, 

but its configuration is not clearly that of a landslide toe, and the abundant other evidences of tectonic deformation in the immediate area make the 

appearance of a fault scarp plausible. 

Although there are some small indications of surface deformation farther north, the main line of 

displacement appears to proceed westward across 

Arroyo Street to the roughly westward-trending 

fault scarp of maximum height 0.6 m (24 in.) that 

lies southwest of Gladstone Street. We shall refer to 

this feature as the Power Line scarp because it 

crosses a Southern California Edison Co. transmission line right of way at this point. It displaces a 

northwest-trending freeway fence line by 0.9 m (36 

in.) left-laterally. From the Power Line scarp, the 

line of displacement goes northward to the Pacoima 

flood-control channel, following a north-trending 

break that shows definite right-lateral displacement 

where it crosses the freeway fence line. How the 

further connection northward to the Sylmar fault 

segment is made remains undetermined. 

Some unique evidence as to ground displacements 

in the vicinity of the Power Line scarp is provided 

by an array of 173 large cable spools, each weighing 

about 6 tons, which stood in neat rows in the transmission-line right of way as outlined by the dotted 

rectangles in figure 3. The spools stood on their 

rims, like wheels, with the spool axes oriented 

northeast. The rims had pressed down as much as 

10 em into the sandy soil. Although the spools were 

oriented so as to roll northwest-southeast, during 

the earthquake very few of them rolled. Instead, 

most of them shifted 10-20 em sideways, gouging 

out a track in the soil. The sideways (NE-SW) motions are plotted in figure 4, in a format which 

shows schematically both the displacement of each 

spool and also the position of the spool in the entire 

array. Figure 4 shows that some of the spools did 

not move and that some oscillated back and forth, 

but many moved in a consistent pattern to one side 

or the other. As a whole, the spools outlined in 

group A moved consistently toward the southwest, 

and those in group C moved toward the northeast, 

while those in group B showed no preferred direction of motion and represent a transition group between A and C. The actual positions of these groups 

on the ground are shown in figure 3. 

The ground suface had little or no lateral slope in 

the area of the reels, and there was no consistent 

difference in lateral slope between groups A and C; 

hence, we believe that the reversal in response from 

Fault scarp~! 

! ............ , 

Group A j ~ (···\······ : : I 

. . . . . . . . . . . 

: : 

............. 

B 

···············=\···· 

scarp 

c 

40 20 ~ 20 40cm 

--- SW I I I I I I I I NE --

FIGURE 4.-Displacements of cable reels that moved in the 

earthquake. Fine lines represent rows of reels in their approximate original position on the ground, but foreshortened 

in the NW-SE direction. Heavy lines represent the amount 

of sideward displacement of individual reels northeastward 

or southwestward from their original positions, according 

to the scale at bottom. The actual position on the ground of 

the groups of reels, as outlined with dotted lines, is shown 

in figure 3. The location of the Power Line fault scarp 

is shown schematically in relation to the rows of reels. 

group A to group C reflects a reversal in the sense 

of ground motion in the earthquake. Such a reversal 

is consistent with the geologic evidence that an important line of fault offset passed through the spool 

array. The Power Line scarp cut obliquely through 

the array, following a northwest trend along one of 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 51 

the rows of reels for about 75 m before turning 

westward and out of the array, as shown schematically in :figure 4. Although the reels that stood on or 

very near the scarp (which was here only 10 to 20 

em high) showed no preferred displacement, suggesting that the fault was a nodal line in the displacement field, the complete pattern of displacements in figure 4 indicates that the line of reversal 

in ground motion passed through the array along a 

roughly north-south line and did not follow the 

scarp. 

The mechanics of the response of a 6-ton spool to 

the ground motion of an earthquake is a matter of 

some complexity that we must leave for future investigation. The simplest possible assumption is 

that the spools tended to remain stationary in space 

during the initial large ground displacement that 

occurred as nearby faults slipped. In this case the 

displacement pattern in figure 4 indicate's that the 

west side of the nodal line, containing reel group A, 

moved northeast, and the east side southwest. The 

indicated type of displacement and fault orientation 

are the same as seen in the north-trending, rightlateral fault that lies northwest of the Power Line 

fault, as mentioned previously. We cannot explain 

the discrepancy between the fault pattern inferred 

from the reels and the pattern of fault displacement 

actually found on the ground surface in this area. 

Nevertheless, the fact that most of the reels moved 

sideways toward the northeast or southwest, 

whereas mechanically they could much more easily 

have rolled northwest or southeast, is strong evidence for a northeast-southwest polarization of the 

ground motion and a corresponding direction of 

fault displacement. 

Although the faults of group 4 show, in aggregate, displacements comparable to those of the Tujunga fault segment at its western end, the detailed 

surface path by which the rupture on the Tujunga 

fault segment connected with the Sylmar zone was 

complex and remains obscure, as the preceeding discussion shows. 

VETERANS FAULT 

Because of its position 1 km east of Veterans 

Hospital (fig. 1), which was severely damaged in 

the earthquake, this fault has special importance. 

It lies at the east end of a zone along the base of 

the San Gabriel Mountain escarpment, where the 

greatest structural damage to buildings occurred. 

Within this zone, the Veterans fault is the only feature of ground disruption that has a direct tectonic 

origin, as far as we have been able to find. It is also 

the only tectonic feature produced during the San 

Fernando earthquake outside of the San Fernando 

fault zone, within the area studied by us. 

The Veterans fault forms a low scarp, with maximum vertical offset of about 20 em, extending for 

350 m along a generally east-west trend. Some extension to the east beyond the visible scarp is indicated by a broken sewer pipe, but the scarp definitely does not cross Pacoima Wash or cut the 

paved road east of the wash. A southwestward extension of about 250 m beyond the recognizable 

scarp is defined by a zone of major structural damage to houses, but this zone cannot be traced to, or 

toward, the wing of the Veterans Hospital that collapsed in the earthquake. 

The fault is clearly exposed cutting bedrock at 

several places. The fault plane dips consistently 

northward at about 61 o. It is parallel to bedding in 

sediments of the Saugus formation (Plio-Pleistocene) , which lie immediately north of the fault. 

Along the fault these sediments are brought into 

thrust contact with old (uplifted) Quaternary fan 

gravels. The total thrust displacement of Saugus 

over fan gravel amounts to at least 5 m, much 

larger than the displacement in the earthquake. 

This indicates a prior history of displacement on 

the fault in Quaternary (and possibly Holocene) 

time. 

There was no detectable lateral component of displacement on the fault as a result of the earthquake. 

The comparatively steep dip of the Veterans 

fault, and its relation to the underlying Tertiary 

sediments, is similar to the situation in faults of 

group 3 and by analogy suggests a relationship with 

the Sylmar fault segment. However, because of the 

proximity of the Veterans fault to the San Gabriel 

Mountain front and its accompanying thrusts, a mechanical connection with these important faults 

seems more likely. 

RECONNAISSANCE SURVEY OF THE 

EPICENTRAL AREA 

Previously mapped faults in crystalline rocks of 

the epicentral area between the north edge of figure 

1 and Soledad Canyon, at the northern foot of the 

San Gabriel Mountains, were examined for indications of displacement in the earthquake. Where possible, the actual fault planes were examined. In 

most cases the faults could be located to within 10 

m or better, so that even a small amount of displacement could have been recognized if present. 

The traverses for this purpose, which were made 

during the first 7 days following the earthquake, 
52 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

also permitted a reconnaissance search for movements on previously unmapped faults. 

The San Gabriel fault was examined near Bear 

Divide (long 118°23.8' W., lat 34°21.5'N.) and near 

Dillon Divide (long 118°21.1' W., lat 34°20.8'N.) and 

showed no evidence of displacement in either location. 

In the area of the epicenter of the main shock 

near Soledad Canyon, three sets of faults can be 

distinguished, from oldest to youngest: ( 1) mostly 

east-west trending, probably right-lateral faults, 

with large vertical displacements (includes the Soledad fault) ; (2) left-lateral faults in a set trending 

about N. 35° E. and a slightly younger set trending 

about N. 55° E. with large displacements; (3) 

northwest-trending faults with small vertical and 

right-lateral displacements. All these are high-angle 

faults, with the exception of the Soledad fault, 

which dips at low angles to the north. None of these 

faults show evidence of Holocene activity, although 

all experienced movement in late Cenozoic time. The 

following faults of these sets were examined and 

showed no evidence of displacement: the Soledad 

fault at several places in Soledad Canyon in the vicinity of the originally located position of the epicenter near the mouth of Agua Dulce Canyon; 

north-northeast-trending fault which bounds part of 

the northwestern San Gabriel Mountains in upper 

Iron Canyon (long 118°23.8' W., lat 34°23.6' N.); 

the northeast-trending Magic Mountain fault in 

lower Sand Canyon (long 118°23.9' W., lat 

34°22.8' N.) and Indian Canyon (long 118°16.3' W. 

lat 34°25.7' N.; and a northeast-trending fault in Bear 

Canyon (long 118°23.8' W., lat 34°22.2' N.), that is 

probably related to the Magic Mountain fault. 

A small crack (2 em wide and 15 m long) trends 

N. 55° E. along the trace of the Pole Canyon fault 

at long 118°23.0' W., lat 34°25.0' N. It cuts thin 

soil covering bedrock ·along the crest of a small 

ridge. It shows no horizontal offset, and might have 

been produced by differential settling of gravels on 

one side of the fault. The Pole Canyon fault showed 

no other evidence of movement at this location. In 

Soledad Canyon at long 118°21.4' W., lat 34°25.7' 

N., a zone of cracks in unconsolidated alluvium 

crosses the concealed trace of the Pole Canyon 

fault, which here trends N. 75° E. This zone is 2 to 

3 m wide and about 300m long, trends about N. 5o 

E. and consists of several tension cracks up to 4 

inches wide. The cracks parallel the axis of the canyon and were probably caused by settling and compaction of the alluvium. 

Several faults in Soledad Canyon near Ravenna 

(approx. long 118°14' W., lat 34°27' N.) were examined and show no evidence of breakage. However, there are cracks in road fill and asphalt in 

this area, which are noteworthy in that no comparable cracks occur along the Soledad Canyon highway for at least 10 miles to the west. 

North of Pacoima reservoir, at lat 118°23.6' W., 

long 34°21.2' N. cracks were observed along several 

preexisting faults of unknown age and displacement. On the average, these faults strike N. 60° W. 

and dip 40° SW. Two examples showed dip-slip displacement of 1-2 em, down to the southwest. This 

displacement could represent the movement of either tectonic or large landslide blocks downward toward the San Fernando basin. In view of the abundant other evidence of landsliding in the mountain 

area, the cracks in question cannot by themselves be 

taken as positive evidence of fault movement. 

RELATION OF SURFACE FAULTING TO 

BEDROCK GEOLOGY 

The overall fault motion that occurred during the 

San Fernando earthquake-combined left-lateral 

slip and thrusting across a north-dipping surfaceis the type of motion expected in the Transverse 

Range structural province, on the basis of geological and seismological experience (Allen and others, 

1965, p. 758). Faults along the southern edge of the 

San Gabriel Mountains have generally been interpreted as thrusts with predominantly dip-slip movement (Bailey and Jahns, 1954, p. 103), but faults 

elsewhere in the Transverse Range province, in particular the Malibu Coast fault and east-west faults 

of the Channel Islands, show definite left-lateral 

displacement (Lamar, 1961; Barbat, 1958; Kew, 

1927; Rand, 1931). 

The faults that actually moved during the earthquake, shown in figure 1, do not correspond closely 

with bedrock faults shown in recently published 

geologic maps (Oakeshoot, 1958; Jennings and 

Strang, 1969). However, an unnamed fault identical 

in surface trace with the Tujunga fault segment as 

defined here was indicated by Miller (1934) in a 

geologic map of the western San Gabriel Mountains. 

This fault was probably identified by Miller on the 

basis of the sharp topographic break at the south 

edge of the foothills. Miller represented the fault as 

turning abruptly northward at the southwestern 

corner of the foothill area, essentially at the point 

where the scarp of the Tujunga fault segment of 

the San Fernando earthquake turns northward toward the complex of group 4 faults described above. 

Although he did not individually discuss the partie-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 53 

ular fault in question, Miller (1934, p. 78) interpreted faults of this type as steeply northwarddipping reverse faults, which is in accord with our 

observations, except for the relatively shallow dip 

(about 25°) found here for the Tujunga fault segment. 

The Tujunga fault segment as defined here is not 

the same as the Tujunga fault shown on the map of 

Hill (1930). Hill's fault, which was marked with a 

queried line, has a nearly east-west trend and lies 1.3 

km south of the Tujunga fault segment as recognized here at the mouth of Little Tujunga Canyon. 

In defining the Tujunga in the way done here, we 

are proposing that the older definition introduced 

by Hill (1930) be dropped. 

Near the south edge of the Little Tujunga foothills at long 118°20.9', a short thrust fault dipping 

60° N., and carrying Modelo (Miocene) sediments 

over Quaternary terrace gravels is identified by 

Oakeshott ( 1958, pl. 1). The fault is shown as extending with a N. 85° E. trace for a distance of 

about 0.8 km. If plotted on figure 1, it would pass 

just south of the observed scarp at long 118°20.9', 

but with a distinctly different trend. No displacement was observed on this fault in the San Fernando earthquake. Its attitude and sense of movement are the same as observed for faults of group 

3, and like these, it would joint the Tujunga fault 

segment if traced westward, according to the 

mapped trace shown by Oakeshott (1958). Its main 

significance is in establishing the prior occurrence 

of reverse faulting near the southern edge of the 

foothills. 

No fault corresponding to the prominent Oak Hill 

scarp was recognized by Oakeshott (1958). The 

upper fault break in Little Tujunga Canyon would, 

if traced_ somewhat farther east th~l). shown, in. 

figure 1, connect approximately with a fault of uncertain displacement and attitude shown by Oakeshott (1958). Further investigation is required to 

establish whether this bedrock fault does in fact 

connect with the fault that produced the scarp in 

Little Tujunga Canyon. As noted earlier, there is 

now evidence that both this fault and the Oak Hill 

scarp had a history of movement prior to the San 

Fernando earthquake. 

Although published geologic maps do not show a 

fault along the trace of the Sylmar fault segment, it 

appears possible that this segment represents a 

northeastward continuation of the Mission Hills 

thrust, which was recognized by Oakeshott (1958) 

primarily from well data. If the southwest-trending 

western portion of the Sylmar fault segment is prolonged 1.6 km southwest, it connects approximately 

with the surface trace of the Mission Hills thrust as 

plotted by Oakeshott. Since the plotted trace of the 

thrust in this area was not based on specific geological control and was therefore marked with queries, 

the connection of the two fault segments is only hypothetical. Nevertheless, the Mission Hills thrust 

provides a reasonable example of the type of geologic and tectonic structure that probably underlies 

the trace of the San Fernando fault zone. 

The Sierra Madre fault zone, a zone of major reverse faults and thrusts along which the crystalline 

basement rocks of the San Gabriel Mountains have 

been uplifted and thrust southward over Cenozoic 

sediments, is the most prominent tectonic element 

in the immediate vicinity of the region affected by 

the San Fernando earthquake. It extends east-west 

along the base of the mountain front near the north 

edge of figure 1. In that area, the main thrust contact between basement rocks and sediments is locally designated the Hospital Fault (Oakeshott, 

1958). In view of the high intensity of ground shaking along the foot of the escarpment, as testified by 

the destruction at Olive View and Veterans Hospitals, and in view of the large thrust component of 

the overall fault motion that occurred, it would be 

reasonable to expect motion on the Hospital fault or 

other thrusts of the Sierra Madre zone. The only indication of such motion found by us is the small 

feature here called the Veterans fault. This fault 

Jies 0.5 km south of the basement-sedimentary contact, which represents the major structural break 

and the probable trace of the Hospital fault, if it 

extends this far east (although it is not so shown 

by Oakeshott, 1958). The Veterans fault can be considered a part of the Sierra Madre fault zone, on 

the basis of. its location near the basement contact, 

its attitude, and its sense of movement. Although 

the movement of the Veterans fault is thus a definite indication of activity on the Sierra Madre fault 

zone in the San Fernando earthquake, the fault feature involved was only a minor one and the extent 

and amount of displacement were small compared 

to what occurred to the south along the San Fernando fault zone. In a wider sense, however, the 

San Fernando fault zone can be considered an integral part of the same system of Transverse Range 

faults that includes the Sierra Madre fault zone, 

and in fact the two zones probably join when traced 

eastward to the vicinity of Sunland, about 5 km 

east of figure 1. 

Geologic cross sections drawn from the San Fernando Valley northward across the San Gabriel 
54 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

Mountains (Oakeshott, 1958) show faults of the 

Sierra Madre zone as dipping generally at angles of 

60° and steeper northward. Although these relatively steep dips agree with the attitudes of faults 

of groups 3 and 5, they conflict with the previously 

discussed general indication that the active fault 

plane as a whole dips about 45° N. 

CONCLUSIONS 

The San Fernando earthquake was caused by 

movement on northward-dipping thrust faults that 

conform to a consistent pattern of such faulting in 

the Transverse Ranges. Almost all the fault movement in the area studied can be explained in terms 

of a single master fracture at depth, striking N. 72° 

W. and dipping about 45° toward the north. The individual fault segments that moved at the surface, 

forming collectively the San Fernando fault zone, 

strike more nearly east-west and bear an en echelon 

relation to the inferred master fracture. Although 

there are local divergences in displacements of individual faults, the overall fault motion was a thrusting of the north side approximately southwestward 

over the south side, with approximately equal 

amounts of vertical uplift, north-south compression, 

and left-lateral slip. This motion combines the types 

of displacement known to be characteristic of major 

faults of the Transverse Range province. The overall displacement was about 2 m. 

Fault movement did not occur near the surface in 

the vicinity of the epicenter of the main shock. A 

reasonable model of the fault movement in the 

earthquake is initiation of fracture at a depth of 

about 13 km under the epicenter, followed by propagation of the fracture southward to the ground surface along a plane dipping about 45° N. 

At the surface, only a small amount of localized 

fault movement took place along the Sierra Madre 

fault zone, ·the major tectonic feature in the immediate vicinity of the area most affected by the earthquake, and the most obvious candidate for movement of the type observed. Most of the fracturing 

reached the surface about 4 km farther south, along 

faults that are minor by comparison (the San Fernando zone). These faults nevertheless fit the general pattern of faulting' set by the major faults, and 

they probably join the Sierra Madre fault zone a 

short distance to the east. 

The tectonic model of the earthquake suggests 

that thrusts related to the Sierra Madre zone, which 

bound the San Gabriel range on the south, pass at 

depth entirely beneath the range to the north. Thus, 

they ,are not simply marginal reverse faults, as they 

are usually visualized. This model may apply to 

major Transverse Range thrusts generally. 

None of the faults that moved in the San Fernando earthquake had been clearly identified in adyance as active faults. There is now evidence that at 

least some of them had a prior history of movement. The Tujunga fault segment could have been 

suspected on the basis of its associated foothill topography. The Sylmar fault segment could have 

been recognized, if at all, only by subsurface investigations. 

ACKNOWLEDGMENTS 

We are grateful to the U.S. Geological Survey 

and to Woodward-Lundgren and Associates for 

supplying large-scale aerial photographs of the 

earthquake area, which helped materially in the 

mapping. We also wish to acknowledge the contributions to the collection of the field data made by 

the students and associates whose names are cited 

in the initial footnote. The material available for 

this report has been significantly improved by the 

generous exchange of information among many scientists studying the earthquake, whose names cannot be individually acknowledged here. 

REFERENCES 

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: Seismol. Soc. 

America Bull. 55, 753. 

Bailey, T. L. and Jahns, R. H., 1954, Geology of the Transverse Range Province, Southern California: California 

Div. Mines Bull. 170, chap. II, p. 83. 

Barbat, W. F., 1958, Los Angeles basin area, California, in 

Weeks, L. G., ed., Habitat of Oil: Tulsa, Okla., Am. Assoc. 

Petroleum Geologists p. 62. 

Hill, M. L., 1930, Structure of the San Gabriel Mts. north of 

Los Angeles, Calif.: California Univ. Pubs. v. Geol. Sci. 

19, No.6. p. 137-170. 

Jennings, C. W., and Strand, R. G. eds., 1969, Los Angeles 

sheet, Geologic map of California: California Div. Mines 

and Geology Map Sheet. 

Kew, W. S. W., 1927, Geological sketch of Santa Rosa Island, 

Santa Barbara County, Calif.: Geol. Soc. America Bull. 

38, 645. 

Lamar, D. L., 1961 Structural evolution of the northern margin of the Los Angeles basin: Ph.D. Thesis, University of 

California, Los Angeles, 142 p. 

Miller, W. J., 1934, Geology of the western San Gabrial 

Mountains of California: California Univ. Pubs., Los 

Angeles Math. Phys. Sci., v. 1, p. 114. 

Oakeshott, G. B., 1958, Geology and mineral deposits of the 

San Fernando quadrangle: California Div. Mines and 

Geology Bull. 172. 

Rand, W. W., 1931, Preliminary report of the geology of 

Santa Cruz Island, Santa Barbara County, Calif.: Calif. 

Div. Mines, Rept. State Mineralogist 27, 214. 
SURFACE FAULTING 

By U.S. GEOLOGICAL SURVEY STAFF 1 

Tectonic movements associated with the February 

9, 1971, San Fernando earthquake produced a zone 

of surface breakage which partly follows the boundary between the San Gabriel Mountains and the San 

Fernando-Tujunga Valleys, and partly transects the 

northern salient of the San Fernando Valley. This 

latter zone of tectonic ruptures was specifically associated with some· of the most extreme damage 

caused by the earthquake anywhere in the epicentral region. 

The zone of surface breakage trends roughly 

east-west, is about 15 km long, and is slightly concave towards the south. A notable discontinuity occurs near the middle of the arc where the western 

half is offset about 1 km north of the eastern half. 

The sense of movement along the breaks is complex. 

Almost all scarps are south facing, with the mountain block up relative to the valley block. Most of 

the larger scarps consistently show a left-lateral 

sense of motion, but a broadly defined zone of 

smaller scarps and cracks, which parallels in part 

the main zone of breakage, shows right-lateral 

offsets. Within the entire 15 km length of the surface breakage, the maximum vertical offset measured on a single scarp is about 1 m, the maximum 

lateral offset about 1 m, and the maximum shortening (thrust component) about 0.9 m. 

Almost all aftershocks recorded during the first 

weeks following the earthquake were located north 

of the main line of tectonic surface ruptures (fig. 1, 

and Wesson and others, this report). The aftershocks form a diffuse, but relatively well defined 

zone that dips about 40° to the north, which is 

about 15° less steep than the dip of the fault plane 

as measured at the surface. The calculated dip of 

the fault using the depth to the hypocenter and the 

distance between the epicenter and the tectonic 

ground breakage is about 45°, using data available 

on March 1, 1971. This is about 10° shallower than 

1 M. G. Bonilla, J. M. Buchanan, R. 0. Castle, M. M. Clark, V. A. Frizzell, 

R. M. Gulliver, F. K. Miller, J.P. Pinkerton, D. C. Ross, R. V. Sharp, R. F. 

Yerkes, and J. I. Ziony. 

the most reliable dips measured at the surface. 

Surface ruptures generated during the earthquake fall into two principal groups: tectonic and 

nontectonic. Although the two are vastly different 

in origin, they are commonly difficult to distinguish 

from one another in the field. Only scarps interpreted to be tectonic are shown in figure 2. 

Surface ruptures that are known or suspected to 

be tectonic breaks created during the earthquake 

extend discontinuously from the San Diego Freeway 

just south of Lower Van Norman Lake to Big Tujunga Canyon. No such ruptures were found between the San Diego Freeway and the Osceola 

Street School or in the area from just east of San 

Fernando Road to just west of the intersection of 

Glenoaks Boulevard and Hubbard Street. The zone 

of breakage bends to the south about 0.4 km south 

of Lopez Dam, but some breaks may be continuous 

through the low hills into Lopez Canyon to the east. 

From the Foothill Nursing Home, eastward along 

the front of the mountains, the surface faulting is 

generally well defined, but locally discontinuous, to 

a point just east of Little Tujunga Canyon. East of 

this point, for a distance of about 2 km, no obvious 

surface faulting is found along the front of the 

range. About 0.3 km east of the Lakeview Terrace 

Sanitarium, surface breakage again is in evidence, 

·with only· a· few interruptions; to a point about 0.3 

km into Big Tujunga Canyon. About 0.4 km farther 

up the canyon, a 0.3 km scarp marks the eastern 

limit of surface ruptures. From approximately 

Lopez Canyon east to Little Tujunga Canyon, discontinuous, usually smaller, breaks occur north of 

the relatively through-going line of breaks along the 

front of the range. Two of these breaks are found 

in Lopez Canyon, two in Bartholomaus Canyon, 

four small breaks cross Kagel Canyon, and single 

breaks intersect Little . Tujunga, Oliver, and 

Schwartz Canyons. A relatively short, presumably 

lectonic rupture characterized by a small southfacing scarp was recognized just east of the U.S. 

Veterans Hospital; it has no apparent continuity 

55 
56 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

0 5 MILES 

0 5 KILOMETERS 

FIGURE 1.-Sketch map showing the relation of the surface faulting to the epicenter and the location of aftershocks. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 57 

with the main zone of breakage to the south. 

The concentration of ruptures in some areas and 

their absence in others, and the apparent discontinuity near the middle of the breaks, allow a natural 

division into three segments. For convenience these 

segments are named as follows: (1) The surface 

faulting from the San Diego Freeway to just east 

of San Fernando Road is referred to as the Mission 

Wells segment of the San Fernando fault zone. (2) 

The ruptures from the intersection of Hubbard 

Street and Glenoaks Boulevard to the Foothill Nursing Home are referred to as the Sylmar segment of 

the San Fernando fault zone. ( 3) Some of the 

breakage that roughly follows the mountain front 

east of the nursing home is referred to as the Tujunga segment of the San Fernando fault zone. 

Oakeshott (1958, p. 92) grouped several faults 

within the range front in the Sierra Madre fault 

zone; this zone extends from the northeastern end 

of the Santa Susana fault to the western end of the 

Rowley fault zone. Only the easternmost 0.3 km of 

the Tujunga segment of the February 9, 1971, surface faulting coincides with any of the faults shown 

on his geologic map, although the scarp formed east 

of the Veterans Hospital, identified provisionally as 

tectonic, may be part of the Sierra Madre zone. 

Oakeshott (1958, pl. 1) shows several faults in the 

Miocene and Pliocene sedimentary rocks in the 

foothills north of the Tujunga segment as mapped 

in figure 1 of this paper; but no movement was 

noted along them after the earthquake. Even 

though no movement occurred along any of the 

known faults composing the Sierra Madre fault 

zone, its importance should not be minimized. It is 

one of the major tectonic zones along which uplift 

of the San Gabriel Mountains has occurred ( Oakeshott, 1958, p. 105), and the surface faulting of 

February 9 may be part of the same system. 

DESCRIPTION OF SURFACE FAULTING 

The tectonic ground breakage of February 9 is 

described segment by segment from west to east. 

MISSION WELLS SEGMENT OF THE SAN FERNANDO 

FAULT ZONE 

Near the Mission Wells historical monument, 1.5 

km east of Lower Van Norman Lake, a small 

south-facing scarp 0.05-0.25 m in height trends 

about N. 60° E. (fig. 2). Surface cracks showing 

left-lateral offsets extend from just southwest of the 

northwest corner of Osceola Street School to about 

one block east of San Fernando Road. Cracks were 

also found in the concrete pavement of the Golden 

State Freeway along the strike of this zone, but 

these may have been caused by landslides. This segment has no surficial expression between the San 

Diego Freeway and the Osceola Street School, nor 

from a point about one block east of San Fernando 

Road to the intersection of Hubbard Street and 

Glenoaks Boulevard. 

SYLMAR SEGMENT OF THE SAN FERNANDO 

FAULT ZONE 

The Sylmar segment is a well-defined zone of tectonic fractures that extends eastward from the 

heavily damaged shopping center at the south corner of the intersection of Hubbard Street and Glenoaks Boulevard to the range front immediately 

south of Lopez Dam. Cumulative displacement 

across the central part of this zone consists of leftlateral, vertical, and horizontal-shortening components as great as 1.9 m, 1.39 m, and 0.6 m, respectively (fig. 3 and table 1). The maximum 

components of displacement across any individual 

break in the zone, however, are about half of these 

values, and they are far less across most breaks. 

This zone generally ranges from about 75 to more 

than 200 m in width, but virtually all the lateral 

movement and shortening caused by thrusting, together with about one-half of the vertical displacement, are concentrated in a narrow band along the 

southern border of the zone (fig. 2). The remainder 

of the vertical displacement is distributed across 

many small normal (extension) faults and a few 

small thrust faults that occupy the remainder of the 

zone and show minor left- or right-lateral displacement. Thus, the zone of fractures is divided into a 

narrow southern zone of shearing and thrusting 

and a wider northern zone of extension; vertical 

displacement occurs in both. This distribution of 

displacement is well shown by ruptured utility pipes 

beneath streets and by sidewalks, curbs, and streets 

(figs.4and5). 

The· extension or compression of sidewalks and 

curbs with respect to the underlying ground provides a basis for estimating surface distortion. For 

example, all the northwest-southeast trending 

streets (Foothill, Eighth, Glenoaks) showed net extension across the fault zone, whereas the northeast-trending streets were shortened (fig. 6). Unfortunately, the large number of measurements 

required (commonly more than 100 in a block 400 

m long) together with various uncertainties limits 

the accuracy of the determinations of net change 

across the fault zone to about ± 0.1 m. Our estimates were further hampered by street-repair 

crews, who swiftly removed sections of splintered 

or buckled sidewalks and curbs. 
58 

I tao 

) 

I 

THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

27 '30" 

.. ~ 

,""'.I 

-.,.~·· Pio"neer 

,}1~{11or1al Cerrl 

' --- -BM~_60_ I .~ ·~\ 

' 

\j 

,j· ·, 

FIGURE 2.-Map showing tectonic ruptures formed during the San Fernando earthquake of February 9, 1971. 

Figure 2 continues on following pages. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 2.-Continued. 

Tectonic rupture, showing dip 

Quened where tectomc ongw IS doubtful; 

where surface expression Is poor 

Boundaries of ·;o:n:e: d~niii:nl~ main tectonic 

ruptures in Sylmar segment of San Fernando 

fault zone 

0.30C 

Magnitude of shortemng across 

ruptures or other compressional 

m 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 shorteillli;at tectonic ruptures 

or component of shortening on features 

other than surface ruptures 

.40 

---1....Q.. 

u 

component of rei ative 

Dot or 0 on downthrown side of rupture, U on 

upthrown side. Magnitude of vertiCal 

59 
60 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

0 1 MILE 

0 .5 1 KILOMETER 

FIGURE 2.-Continued. See preceding pages for explanation. 

Few fractures of the ground surface can be 

traced across streets, houses, and yards. Owing to 

their rigidity, streets (including curbs and sidewalks) tend to bridge the shear zone; this rigidity 

commonly allows compression to be transmitted to 

buckles and overthrusts in streets, curbs, and sidewalks as much as 100 m from the zone of ground 

breakage. On the other hand, extension is usually 

expressed in the overlying sidewalks and curbs at 

the closest construction joint (generally within a 

few meters) and in asphalt pavement by tensile 

failures normal to the length of the street (fig. 7) 

and apparently within a few tens of meters of the 

underlying ground extension. Houses commonly 

hide faults that pass beneath them unless displacement is large enough (about 50-100 mm) to visibly 

affect the house. Many fractures that are obvious on 

bare ground are completely hidden by cultivation or 

planting. However, the small number of fractures 

that have displacements greater than 0.1 or 0.2 m, 

such as those that cross Bromont Street and the 

street just west of it, generally maintain continuity 

across these features (fig. 8). The net result of 

these effects is that the shear zone is revealed, if 

not sharply bounded, by obvious left-lateral offset of 

each street that it crosses (fig. 9), whereas the zone 

of extension is marked by normal faults and extension fractures across each street within the zone. 

The southern boundary of the zone of fractures is 

sharp, whereas the northern boundary is not. Obvious ground fractures cease a few tens of meters 

beyond the southern boundary of shearing and 

thrusting, whereas the zone of extension fractures 

has a diffuse boundary, marked by a gradual reduc-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 61 

0 1 MILE 

0 .5 1 Kl LOM ETER 

FIGURE 2.-Continued. 

tion in the number of fractures and displacement 

across them. The northern boundary of the zone of 

extension shown in figure 2 roughly limits the area 

in which extension fractures are evident across bare 

ground. 

The sharply defined main strand of the Sylmar 

fault segment changes northward into a broad area 

broken by numerous, relatively closely spaced faults 

which almost uniformly display small right-lateral 

offsets. The dimensions of the area showing fractures of this kind are about 1.8 km in the east-west 

direction, somewhat less than the length of the 

main part of the Sylmar fault segment, and about 

1.3 km from north to south. The faults share the 

east-west trend of the left-lateral zone and generally show slight extensional gaping as well as 

right-lateral displacement. Where present, the sense 

of vertical components of movement is usually down 

on the north, or opposite to the direction of vertical 

offset in the belt of apparent right slip within the 

zone of the Sylmar fault segment. The right-lateral 

faults are usually simple, nearly linear fractures in 

the ground but have somewhat more complex traces 

where they break pavements, sidewalks, and concrete slabs of houses. Spacing of the faults ranges 

from a minimum of about 20 m to a maximum of 

about 100 m. Residents in the area state that many 

of the fractures showed only slight offsets immediately after the earthquake and that they continued 

to move for several days thereafter. 

One of the most complex sectors of surface rupturing occurs northeast of San Fernando Airport in 

the area of apparent discontinuity between the Sylmar and Tujunga segments of the San Fernando 
62 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

N 

---

F=0.55m 

0=2.0m 

---

-~J ;:,::::"" 

--}Zone of shearing 

and thrusting 

0> 

~~---=-~:::.:.:..--3 

0 2 METERS 

0 2 4 6 FEET 

VECTOR SCALE 

FIGURE 3.-Slip vectors along an assumed fault plane crossing Orange Grove Avenue and Eighth Street. Derived from postearthquake changes (A, B, and C) in Orange Grove Avenue and Eighth Street (fig. 4). Vectors represent the movement of 

one end of each street with respect to the other end. Values are summarized in table 1. A, change in length of street; 

B, left-lateral displacement of street; C, vertical displacement of street; D, horizontal displacement of ground; E, strike slip; 

F, horizontal shortening ; G, dip slip; H, net slip; J, dip of fault plane. 

TABLE I.- Summary of measurements shown in figures 3 and 4 

A. Change in length of street_ _ B. Left-lateral displacement of street __________ _______ _ 

C. Vertical displacement of 

street __________ _______ _ 

D. Horizontal displacement of 

ground _______________ _ E. Strike slip _______________ _ 

F. Horizontal shortening ____ _ G. Dip slip ______ ____ __ _____ _ H. Net slip _______ __ _______ _ 

I. Strike of fault plane ______ _ J. Dip of fault plane __ ___ ___ _ 

Orange Grove from 8th t o 7th St. in meters and (ft) or degrees 

-1.9 ( -6.2) 

.7 (2.3) 

-1.39 (-4.6) 

2.0 (6.6) 

1.9 (6.2) 

.55 (1.8) 

1.5 (4.9) 

2.4 (7.9) 

N. 85° E. 

69° 

8th St., from Orange Grove to Harding in meters and (ft) or degrees 

0.64 (2.1) 

1.9 (6.2) 

2.0 (6.6) 

.6 (2) 

.6 (2) 

N. 85° E. 

fault zone. The complexity involves not only geometric irregularity of the fault strands but also loss of 

demonstrable continuity of the fault traces and possible variation in the sense of the lateral component 

of displacement. 

Between Maclay A venue and Pacoima Wash, the 

sense of horizontal separation on the Sylmar segment reverses from left- to right-lateral. The northern or northeastern side, however, is consistently 

the relatively upthrown block. On the first street 

southeast of Maclay A venue, the break shows about 

0.12 m of left-lateral separation of curbs; but one 

block farther southeast, no lateral separation is visible on curb lines, suggesting (from the angular relationship of the fault trace and street) a small 

left-lateral component of slip. One block farther 

east, curbs are separated right-laterally about 0.3 

m, reflecting either a yet smaller left-lateral component combined with the vertical component of 

offset, or possibly a small right-lateral component of 

movement. Immediately east of Pacoima Wash, the 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 63 

ORANGE GROVE AVENI)( 

~one of shearono-,-zone of extension• 

1------Net shortenong of ground------1~-t---Net extension- of ground 

1-------0\lerall shortening 1.9 m--- -----l 

A 

0 20 40 60 80 100 METERS 

0 100 200 300 FEET 

B 

_, 

.. 

FIGURE 4.-Changes in level, length, and horizontal alinement 

along Orange Grove Avenue between Seventh and Eighth 

Streets, city of San Fernando. A. Changes in length and 

alinement (plan view). Left-lateral displacement of the 

street from the original alinement was measured by sighting along the northeast curb February 19, 1971. Change 

in length of the street was measured February 20, 1971, 

by R. T. Ruthven, U.S. Geological Survey. Localization of 

horizontal movement was determined by measuring compression and extension of curbs and sidewalks on both 

sides of Orange Grove A venue. This figure shows that most 

of the shearing and thrusting is concentrated in the shearthrust zone near the southern boundary of the break zone. 

B. Changes in elevation relative to leveling done in January 1962. The elevation of the intersection of Orange Grove 

Avenue and Seventh Street is assumed to have remained 

unchanged. Measured February 15, 1971, by R. E. Munn, 

Engineering Department, city of San Fernando. This profile shows that vertical displacement is distributed across 

the entire zone of breakage. 

Sylmar segment of the fault displaces an originally 

linear north-south fence about 1.0 m in a left-lateral 

direction. Because the trace of the ground rupture 

is almost exactly perpendicular to the fence line, 

there is no ambiguity as to the sense of the lateral 

component of offset at that point. 

Eastward from the northern point of the spreading basin next to Pacoima Wash, the trace of the 

Sylmar segment of the fault curves abruptly to a 

southward trend and becomes approximately coincident with the base of the steep mountain front. 

The trace is visible only for a short distance at that 

location; however, despite the near absence of surficial breakage along the base of the slope southward 

to the reentrant canyons at the Burns ranchhouse, 

damaged water pipes excavated after the eetrthquake indicate at least 0.43 m of east-west shortening of the ground surface about 0.4 km northwest 

of the ranchhouse. The mountain block, furtherFIGURE 5.-Shortened section of gas pipe taken from the 

shear"thrust zone across Glenoaks Boulevard. This piece 

was shortened more than 0.1 m ( 4 in.) ; at least one other 

shortened section of the same pipe was removed from 

another place in this shear zone. Immediately north of the 

shear zone across Glenoaks Boulevard, but still in the fault 

zone, this pipe and adjacent water pipes were each broken 

in several places by extension of the ground combined with 

downward movement to the south. Despite the shortening 

in the shear zone shown by this photograph, the net change 

in the length of Glenoaks Boulevard and the pipes buried 

beneath it was an extension of 0.6 m between Hubbard and 

Orange Grove Avenues (measured February 20, 1971, by 

R. T. Ruthven). 

FIGURE 6.-Shortened sidewalk. The slab resting on top of 

this sidewalk on the southeast side of Orange Grove Avenue 

near Phillippi Street has been thrust from left to right. 

Thrusting between Phillippi and Knox Streets shortened 

Orange Grove about 1.3 m (about 4 ft) and ejected the 

slab. The two corners at the ends of the block yielded 

little, forcing the sidewalk to buckle at this point. 

more, rose at least a few centimeters relative to the 

alluvial flat at that point. No obvious disturbance or 

cracking of the ground surface was evident at the 

shortened pipelines, raising the possibility that a 
64 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 7.-Graben across Eighth Street in the zone of extension fractures. Foundering of the down-dropped block is 

exaggerated by the presence of a large (about 5 x 6 m 

cross section) flood-control conduit beneath Eighth Street. 

This conduit was severely damaged in the fault zone. The 

condition of the tie bars in the construction joint in the 

sidewalk in the foreground indicates at least one cycle of 

opening and closing of the sidewalk slabs with movement 

greater than the length of the exposed bars. 

similarly imperceptible compression zone may 

continue southward to the vicinity of the San Fernando Ranger Station. 

Near the San Fernando Ranger Station, the sidewalks and pavements at the southeast ends of two 

cui-de-sacs that run northwest-southeast were broken and shifted to the northwest; asphalt parking 

lots were disrupted; and two buildings were jammed 

together (fig. 10), causing severe structural damage 

to at least one of them. Their orientation indicates a 

strong component of northwest-southeast shortening. One of the cui-de-sacs, Montero A venue, was 

shortened in a northwest-southeast direction by 1.07 

m (the difference between the length measured by 

steel tape on February 14 and the length given in 

official records) . A monument originally set on the 

projection of the centerline, and about 20 m southFIGURE 8.-Shear-thrust zone at Cometa Avenue (parallel to 

and northeast of Eighth Street). The two larger thrust 

faults (A and B) account for most of the strike slip and 

shortening of the shear-thrust zone, which is less than about 

10 m wide at this location. The overthrust driveway and 

adjoining street span the shear-thrust zone and indicate 

roughly 1 m of shortening. The curb at the right is offset 

nearly 2 m left-laterally across these two breaks. Vertical 

displacement is about 0.5 m. The closest house has broken 

free of its foundation and shifted nearly 0.5 m to the right 

(north). 

east of the end of the street, was shifted about 0.2 

m southwest of the centerline. The shortening buckled the sidewalk and flattened the circle at the end 

of the street and produced crescent-shaped openings 

between the curb and the sidewalk (figs. 11 and 

12). The form of the ruptures both in the streets 

and in vacant lots indicates strong compression in 

the northwest-southeast direction and uplift of the 

southeast side, possibly combined with a minor 

right-slip component. Numerous landslide scarps up 

to 1 m high cut the flanks and ridges of the hill immediately to the east. Their presence suggests the 

possibility that settling and spreading of the bedded 

and jointed rock that constitutes the hill may have 

forced out a wedge of alluvium at the base of the 

hill, produced most of the compressional effects, and 

masked whatever tectonic displacements may have 

occurred. 

The west end of the Tujunga fault segment may 

connect with the Sylmar segment along a hidden 

zone of compression near the base of the mountain 

slope in the vicinity of the San Fernando Ranger 

Station. It is furthermore possible that the Sylmar 

segment branches, and the eastern strand extends 

into the mountains along the line of the northernmost mapped faulting in Lopez Canyon. Demonstration of such a connection is not possible, however, 

because of the extensive landslides on the hill east 

of Burns Ranch. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 65 

FIGURE 9.-Left-lateral offset of the northeast side of Knox 

Street in the shear-thrust zone. Underthrusting of adjacent 

turf by both curb and sidewalk in the zone of offset indicates that they bridge a narrower shear zone in the ground. 

TUJUNGA SEGMENT OF THE SAN FERNANDO 

FAULT ZONE 

The Tujunga segment extends along the front of 

the hills on the north side of Tujunga valley in a 

discontinuous fashion from the vicinity of the 

Foothill Nursing Home, which lies on the northeast 

side of Foothill Boulevard, eastward into Big Tujunga Canyon.' 

In front of the nursing home the curb is raised 

about 1 m above the street level (fig. 13) . A transverse component of movement, shown by about 0.9 

m of shortening, was measured along a fence trending N. 50° E. on the east side of the nursing home. 

East of the nursing home, a low, but well-defined 

fault trace continues with only a few interruptions 

to the mouth of Lopez Canyon. Where the surface 

ruptures transect the lower slopes of the hills just 

1 R. J. Proctor of the Los Angeles Metropolitan Water District reports 

that tectonic ruptures associated with the February 9 earthquake roughly 

follow a north-dipping thrust fault, which h e had previously mapped and 

which he has named the Lakeview fault. The scarps in Schwartz and Oliver 

Canyons coincide with this fault, which would be synon ymous with the 

Tujunga fault segment as used in this volume. 

east of the nursing home, the scarps are low, but 

well defined. A conspicuous zone of tension cracks 

about 2-3 m wide formed about 10 m upslope from 

the base of the scarps. On the west side of Lopez 

Canyon, the scarp, which is about 0.85 m in height 

(fig. 14), is a hummocky, multistranded bulge at the 

leading edge of the overriding northern block. In a 

trailer park immediately west of Lopez Canyon, the 

fault appears to follow a shallow-dipping plane in 

Tertiary marine deposits. About 0.4 km west of 

Lopez Canyon and for approximately 200 m along 

strike, the fault plane has a rather uniform dip of 

about 55° N. Just east of the canyon, the fault zone 

is defined by many subparallel imbricate breaks. 

Eastward from Lopez Canyon the fault zone is 

made up of many en echelon segments. About 0.8 

km east of the mouth of the canyon, the dip of the 

fault appears to lessen to about 15° N., but tectonic 

scarps are difficult to distinguish from the toes of 

landslides in this area. At the mouth of Bartholomaus Canyon, the scarp is about 0.25 m high, up on 

the north side, and shows about 0.1 m left-lateral 

offset of the streambank. The frontal scarp is about 

0.60 m high and well exposed in Little Tujunga 

Canyon (fig. 15). East of this canyon for about 1.5 

km, the zone is marked by compressional buckles 

and lacks developed scarps. 

A gap of 2.2 km, within which no tectonic breaks 

have been found along the range front, separates 

the breaks near Little Tujunga Canyon from a 

well-defined south-facing scarp on the north side of 

Big Tujunga Creek, about 0.4 km east of the Lakeview Terrace Sanitarium. The scarp is 150 m long 

and 0.35 m high, but it cannot be traced continFIGURE 10.-Detail of interpenetration of two buildings caused 

by ground rupture. Edges of asphalt paving, outlined in 

lower left corner of photograph, overlap by 0.49 m. Near 

southeast end of Gladstone Avenue, near San Fernando 

Ranger Station. 
66 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

uously across the creek. The southeast end of this 

ground breakage is connected by a few discontinuous scarps to a well-developed line of surface rupture that is continuously traceable for about 0.9 km 

to the east. This line of ruptures is developed 

mostly in unconsolidated stream sediments which 

have been extensively churned by earth moving 

equipment, and the appearance and height of the 

fault scarp here varies considerably along strike. 

Several measurements of scarp height are shown in 

figure 2. About 1.5 km east of the Lakeview Terrace 

Sanitarium, this break cuts interlayered thin-bedded 

siltstone and conglomerate exposed on the north 

edge of Big Tujunga Wash. The fault plane here 

strikes about N. 70° W, and dips 55-60° N. Slickensides, which may or may not be related to the 

most recent movement, are developed in a thin zone 

of fault gouge and dip straight down the fault 

plane. The gouge indicates that the February 9 

movement at this point occurred along a preexisting 

fault. 

A few meters east of the faulted bedrock, the 

scarp, which is again in the stream sediments, becomes indistinct and cannot be distinguished from 

ridges formed by earth-moving equipment. Two disconnected scarps, each about 150-200 m long, continue en echelon to the east (fig. 2). The more easterly of these offsets the extension of Oro Vista 

Avenue about 0.3 m in a left-lateral sense. The 

height of this scarp is about 0.5 m, in the stream 

FIGURE H.-Oblique aerial photograph of ground breakage on Montero Avenue near San Fernando Ranger Station. Note 

thrusting in open ground, compression of sidewalk and asphalt street, and crescent shaped openings near curbs (arrows). 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 67 

FIGURE 12.-Detail of compression of sidewalk and asphalt 

street. The compr essed sidewalk at left shortened 0.3 m. 

Note tree tilting southeast. 

bottom below this street. About 0.4 km east of this 

break lies the scarp which marks the eastern end of 

the tectonic breakage. This scarp is 0.3 km long and 

strikes N. 75° E. Part of it is developed in thinbedded siltstone and with the siltstone dips 62° N. 

Movement was up on the north, about 0.4 m. Four 

cracks that cross Mount Gleason Avenue about 0.7 

km farther east show both left-. and right-lateral 

displacements up to 0.02, m, and are probably not 

tectonic breaks. 

SURFACE FAULTING IN THE MOUNTAINS NORTH 

OF THE TUJUNGA SEGMENT 

In addition to the fault trace at the mouth of 

Lopez Canyon, other February 9 traces cross the 

canyon 0.6 km and 0.9 km north of its mouth. The 

northernmost of these occurred on an existing fault 

that was marked by gouge and shearing in the adjacent rock, but the earlier faulting apparently was 

not expressed in the n1odern topography. VVhere 

this trace extends westward from Lopez Canyon 

Road, it crosses a flat artificially graded surface underlain partly by bedrock and partly by alluvium 

(fig. 16). Figure 17 shows in plan and profile the 

very different expression of the fault in the two 

media. A distinct fault scarp about 1 m high 

formed in the bedrock (fig. 18), whereas a gentle 

monocline developed in the alluvium. The bedrock 

here consists of bedded friable sandstone, conglomerate, and thin shale, and it has about the same attitude (strike N. 80° VV., dip 70° N.) on both sides 

of the fault. The fault strikes N. 80° VV. and dips 

65° N. at the surface (fig. 19), and this attitude 

continues to a depth of at least 10 m, where the 

fault was penetrated by a 36-inch borehole, visible 

FIGURE 13.-Scarp formed near curb in front of Foothill 

Nursing Home. Scarp is about 1 m high here but is more 

subdued where it developed in unconsolidated sandy soil 

on either side of the nursing home. View looks northwest 

on Foothill Boulevard. 

FIGURE 14.-Scarp in trailer court just west of the mouth of 

Lopez Canyon. Buckling of wood guardrail indicates considerable shortening, but the amount of shortening could 

not be precisely measured because guardrail posts on upper 

part of scarp detached from the ground. Height of scarp 

is about 0.85 m. View towards northeast. Mouth of Lopez 

Canyon in background. 

in figure 16, drilled to install wire extensometer. 

The gentle monocline that marks the fault in the 

alluvium is some 30-35 m wide (profile B-B' in 

fig. 17). Although the difference in height across the 

monocline is about the same as across the scarp, it 

would be difficult to identify this as a structural 

warp from the profile alone. Between 836 and 839 
68 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 15.- Scarp in orange grove in Little Tujung a Canyon. 

Scarp is about 0.4 m high her e, a nd about 0.6 m high in 

canyon bottom 80 m to west. View looks north. 

on profile B-B', the monocline is marked by a series of weakly developed pressure ridges trending 

east-southeast and tension fractures trending 

north-northeast. Some of the fractures show minor 

left-lateral displacement. Between S36 and S38, the 

monocline is characterized by generally east- or 

east-northeast-trending tension fractures that display small vertical movements (down on the south). 

These movements are accompanied by small leftlateral displacements between S36 and S37 and by 

small right-lateral displacements between S37 and 

S38. 

Three linear features that were used to calculate 

the fault displacement in Lopez Canyon are marked 

I, II, and III in figure 17. These features, which 

were probably made by a bulldozer, consist of two 

ridges (I and II) and the edge of a shallow cut 

(III) . The reverse-slip and left lateral slip components calculated from the field measurements are, 

respectively, 1.05 m and 0.80 m for I; 1.26 m and 

0.85 m for II; and 0.88 m and 0.70 m for III. The 

average values of the components are about 1.05 m 

FIGURE 16.-0blique aerial photograph of fault scarp 0.9 km north of mouth of Lopez Canyon. Note gradation to monoclines 

at each end of scarp. Drill rig is setting casing in borehole that confirmed 65° dip of fault. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 69 

reverse slip and 0.80 m left-lateral slip, or 1.32 m 

oblique (net) slip. 

Near the east end of the scarp, slickensides in the 

gouge are inclined 58° from the horizontal (fig. 20) 

which indicates a somewhat lower ratio (0.635) of 

strike slip to dip slip than was obtained from the 

displaced bulldozer features (0.76). It is uncertain, 

however, whether these slickensides formed on February 9 or during an earlier movement on the same 

fault plane. Both indicate that this was a left-reverse oblique fault according to the classification of 

Bonilla and Buchanan (1970, p 7-9). 

\ 

B 

About 0.6 km north of the mouth of Lopez Canyon, a small scarp bulges up the pavement of the 

Lopez Canyon Road, with the north side elevated 

about 0.2 m. A roadcut alongside the break exposes 

disturbed and somewhat slumped sandstone and 

siltstone, but no positive evidence or prior move5 0 5 10 15 20 25 METERS l!ll! l I l I I I 

31 A 553 5 1 Post-f aulting profile 

<J) 3o ·--.L-~--~;2 ,5 35 

A' 

31 

a:: 29 ----------- )~----.:!.3 54 ~ 28 Approximate pre-faulting T, F It 

1 :.__ _____ ...:; -------....:::..:.:.:: 

~ 27 profile ,~ au Pane I 

30 

525 29 

28 

27 

6~-----------------------------~ 26 

B' 

31 538 / Post-faul ting profile iQ 30 ------L ____ . 37 

31 

30 

~29 ~--------.5~3=6~~====~-----539 w 28 Approximate pre-faulting profile7 ------.........::=l- ~27~------- --------------------------~ 

5 40 29 

28 

27 

0 5 10 METERS 

FIGURE 17.- Plan and profiles of trace of fault 0.9 km north of mouth of Lopez Canyon, based on planetable mapping. For 

location see figure 2. Elevations on profiles referred to local assumed datum. Numbers preceded by S are field survey 

stations. See t ext for details. 
70 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 18.-Fault scarp in bedrock, Lopez Canyon. Note fault surface dipping under scarp, debris from collapsed hanging 

wall of fault, and thin layer of unconsolidated material over bedrock. Large divisions on horizontal rod are 12 inches 

(0.3 m). 

FIGURE 19.-Detail of dipping fault plane shown in figure 18, showing sloughing gouge; photographs mounted as a stereoscopic pair. The scale in the lower right, which is 170 mm long, is also shown at the same spot in figure 18. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 71 

ment such as a gouge zone or structural truncation 

of bedding is visible. About 110 m due west of this 

scarp, however, a northward-dipping fault surface is 

visible on a steep face cut in similar sedimentary 

rocks. Although preearthquake reference lines are 

not present across this break, a thrust movement of 

a few centimeters, possibly with a minor left-lateral 

component of slip is evident. In contrast to the cut 

at the road, the offset here appears to have occurred 

along a preexisting fault, as shown by gouge and 

the slight structural discordance of the underlying 

beds at the fault. The offset apparently dies out 

westward within the upper part of the cut, and no 

tectonic rupturing was found on a projected line at 

any point higher on the hill. Whether this fault 

joins the scarp to the ,east of Lopez Canyon Road is 

uncertain. Pavement and soil in the intervening sector are located on fill and are strongly fractured. 

This breakage, however, is probably nontectonic, 

and the continuity of the two offsets is in doubt. 

Thirteen fractures exhibiting right-lateral offset 

break Lopez Canyon Road between 0.27 km and 

0.53 km north of the Tujunga segment of the San 

Fernando fault zone. The net right-lateral offset 

across these breaks is about 0.5 m, of which about 

half is concentrated in a narrow zone at its southern edge. Although the breaks cannot be traced either west or east, it is likely that they are of tectonic origin. They appear to be similar to breaks 

within the broad zone of right-lateral rupturing immediately north of the Sylmar segment. 

Another well-developed south-facing scarp lies 

about 0.4 km up Little Tujunga Canyon from the 

frontal scarp. This upper scarp is a hummocky 

bulge similar to those at the range front. It dies out 

about 0.3 km east of Little Tujunga Road, but it 

continues westward almost to Kagel Canyon. Just 

west of Little Tujunga Canyon, the scarp is 0.45 m 

high. Several small scarps cross Kagel Canyon, but 

cannot be traced for any distance outside the canyon. A small south-facing scarp extends westward 

from the bottom of Bartholomaus Canyon but cannot be traced east of it. Although the scarp is little 

more than a buckle in the bottom of the canyon, on 

the ridge 0.3 km to the west, it is about 0.30 m high 

and displays about 0.58 m of left-lateral offset. 

Prominent scarps of probable tectonic origin 

cross the bottoms of Oliver and Schwartz canyons 

about 0.4 km north of their mouths. The scarp in 

Oliver Canyon is about 0.9 m high and that in 

Schwartz Canyon about 0.3 m. Although both are 

probably parts of longer structural features, they 

cannot be traced with confidence outside of the canyons through the extensive landslides which mantle 

the surrounding hillsides. 

SCARP EAST OF THE VETERANS HOSPITAL 

Although extensive damage to man-made structures occurred along a zone extending from Upper 

Van Norman Lake to the head of Pacoima Wash, 

there is only one scarp in this zone interpreted to be 

of possible tectonic origin. This scarp is about 300 

FIGURE 20.-Detail of fault plane showing slickensides inclined 58° from horizontal; photographs mounted as a stereoscopic 

pair. Note apparent change of inclination of the striations over this length. Vertical groove near compass is artificial. 

These slickensides may have been produced by a fault movement previous to the one on February 9. 
72 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

m long ann is expressed as a small nearly east-west 

surface rupture. It is between the U.S. Veterans 

Hospital and Pacoima Wash and is well exposed in 

cuts and fills of a partly developed housing tract 

near Rajah Street (fig. 2). In the banks of cuts, the 

slip surface dips generally northward between 36° 

and 48°, parallel to bedding of sandstone and conglomeratic sandstone of the Pacoima Formation 

(included in Saugus Formation on the geologic map 

in the paper by Wentworth and Yerkes, this report). Displacement is apparently directly updip, 

and the maximum relative uplift of the northern 

slide is about 0.18 m. Westward the strike of the 

break gradually swings toward the southwest. A 

line joining the western end of ,the continuous fracture to a short scarp with vertical offset observed 

on Hubbard Street would have a southwesterly 

trend. Although the rupture has the appearance of 

a tectonic fracture, it conceivably could represent 

the bulged toe of an unexpectedly large landslide 

whose upslope limits have not been recognized. 

The projection of the fault, is it continues along 

its last observed trend, passes well south of the Veterans Hospital. Although no further tectonic breaks 

were recognized west of the scarp, this does not 

preclude the possibility that the zone from west of 

Juvenile Hall to the Veterans Hospital was tectonically active during the earthquake. For example, 

left-lateral deformation may have occurred across 

the zone near the Juvenile Hall, as a postearthquake 

resurvey of San Fernando Road showed a small 

left-lateral and southward shift of a point due west 

of the Juvenile Hall with respect to a point at the 

corner of Roxford Street and San Fernando Road 

(Youd, this report). 

COMPARISON OF RUPTURE DIMENSIONS TO 

MAGNITUDE OF THE EARTHQUAKE 

Comparison of the maximum surface displacement and length of the February 9 faulting with 

other reverse-oblique-slip faulting is difficult because only about six examples of historic surface 

faulting of this sense are recorded in the world Iitei·ature; furthermore, the data for this type of fault 

do not show a consistent relation between earthquake magnitude and fault displacement or length. 

Compared with historic surface faulting of all 

types, however, the February 9 faulting has a 

greater displacement and a smaller fault length 

than would be expected to accompany a magnitude 

6.6 earthquake. Empirical data on all types of historic surface faulting treated as one group (Bonilla 

and Buchanan, 1970, figs. 2 and 3, set 1-140) indicate 

that the surface faulting accompanying a magnitude 6.6 earthquake is likely to have a maximum 

surface displacement of 0.8 m and a surface length 

of about 20 km, in contrast to the 2.4 m displacement and about 15 km length of the February· 9 

faulting. 

PREEARTHQUAKE TOPOGRAPHIC EXPRESSION 

OF THE SAN FERNANDO FAULT ZONE 

The San Fernando earthquake of 1971 shares 

many topographic similarities with the Arvin-Tehachapi earthquakes of 1952 (Oakeshott, 1955). 

Movements during both earthquakes combined 

thrusting with left-lateral strike slip, and both involved faults that were not widely considered, on 

topographic evidence, to be presently active. 

Most of the 1971 breakage along the San Fernando fault zone followed scarps created by previous faulting. The Tujunga segment followed an 

obvious scarp along a range front, as recognized 

some time ago by Miller (1928 and 1934). Inspection of preearthquake vertical aerial photographs 

(1 :24,000 scale from 1952 and 1:90,000 scale from 

1964) reveals that the Mission Wells and Sylmar 

segments also followed a single, nearly continuous 

scarp, but this scarp becomes almost undetectable in 

its central part. Neither the Tujunga nor the Mission 

Wells-Sylmar scarps, however, could have been positively identified as scarps of presently active faults 

without supporting stratigraphic evidence. 

The land forms created in the zone of breakage 

of a reverse fault contrast strongly with those that 

mark the most recently active traces of strike-slip 

faults such as the San Andreas, San Jacinto, and 

Garlock for example, Ross, 1969; Clark, 1970; 

Sharp, 1970; Vedder and Wallance, 1970. Thus although the scarp followed by the surface ruptures 

along the Tujunga segment is straight, in detail it 

lacks the striking continuity and abundant scarps 

across alluvium associated with known active 

strike-slip faults that follow range fronts. It also 

lacks the extensive, and in some places linear, 

scarps that characterize geologically young normal 

faults such as those along the eastern base of the 

Sierra Nevada (for example, Shelton, 1966, fig. 

342). The geomorphic criteria of these other active 

faults indicate that the Tujunga segment might well 

be classified as less recently active than it evidently 

is. 

The eastern end of the Sylmar segment follows 

the face of a prominent south-facing scarp that is 

6-10 m high, but it diverges from this scarp to the 

west, near the Foothill Freeway. Farther west, the 

fault follows an increasingly wide and less well· de-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 73 

fined scarp as far as Orange Grove Avenue, where 

the scarp becomes nearly indistinguishable from 

local variations in the regional slope. A distinct increase in slope occurs, however, where Glenoaks 

Boulevard crosses the fault zone, and the 1:90,000-

scale aerial photographs show a broad (about 

i00-300 m wide) but definite south-facing scarp 

continuing westward to Mission Wells. There the 

scarp again becomes prominent along the Mission 

Wells segment of the 1971 breaks. The course of the 

Mission Wells segment farther west into the hills 

surrounding Lower Van Norman Lake follows no 

prominent topographic trend. These scarps and 

changes in slope along and between the Sylmar and 

Mission Wells segments are almost certainly tectonic, but they could not have been so identified before the earthquake without other corroborating 

geologic evidence as similar landforms could have 

been produced by other processes. 

Thus, in marked contrast to many of the active 

strike-slip and normal faults of California, the active traces of the San Fernando fault cannot be 

identified by topography alone. Rather, topography 

along this thrust fault could serve to confirm identifications made from subsurface or other evidence. 

Were the fault identified by other evidence, however, the topography would indicate the sense of 

displacement across the fault. Where the scarps are 

distinct, the topography could also serve to define 

the position and character of displacement of the 

fault more closely. 

If the San Fernando fault zone has a record of 

activity comparable to that of active normal and 

strike-slip faults in California, the generally poor 

topographic expression must be related to the nature of the surface ruptures and movements associated with thrusting. As shown in figure 2, displacement over most of the Sylmar segment extended 

across a wide zone, creating a broad, gentle scarp. 

Eastward from about Eighth Street, however, where 

displacement in 1971 was concentrated into a progressively more narrow zone, the old scarp becomes 

correspondingly narrower and steeper. This relation 

between width of the 1971 zone of breaks and the 

prominence of the old scarp suggests that previous 

movement on the Sylmar segment resembled that of 

1971. If the present zone of breakage follows the 

course of prior recent movements on the Tujunga 

segment, much of the detailed topographic expression of these recent movements along the narrower 

zone of breakage of that segment probably was 

masked or destroyed by associated landsliding at 

the time of each earthquake. 

The dip of a range-front reverse fault creates sinuous, rather than straight scarps or zones of surface breakage. The fault trace therefore lacks linear 

continuity, an important clue in the recognition of 

topography created by active strike-slip faults. 

Thrus!ing in alluvium or poorly consolidated sediments also seems to shatter the upthrown block 

more than do either strike-slip or normal faulting, 

presumably leading to more rapid destruction of the 

newly formed scarp. 

COULD THE LOCATION OF THE FAULT SCARPS 

OF FEBRUARY 9, 1971, HAVE BEEN PREDICTED? 

The recognition of active reverse faults has been 

shown above to be usually much more difficult than 

the recognition of active strike-slip and normal 

faults. As the recognition of such faults in seismic 

regions is critical to safe development, it is clearly 

important to ask whether a geologic investigation 

could have determined the location and youthfulness 

of the fault zone in which the surface ruptures of 

February 9 formed. The answer is yes. 

Wentworth and Yerkes (this report) show that 

previous subsurface investigations revealed a 

groundwater anomaly along the trend of the Sylmar 

and Mission Wells segments of the San Fernando 

Fault that could reasonably have been interpreted 

as a very young fault. This interpretation would 

have been supported by the scarps discussed above; 

moreover, trenches across the fault zone would very 

probably have revealed lines of previous fault 

breakage. Similarly, subsurface investigations at 

critical locations along the Tujunga segment might 

have reinforced the limited data from surface features as to the recency of movement along the 

range front. For example, the newly exposed scarp 

in upper Lopez Canyon described in this paper contained abundant gouge of earlier episodes of movement, and the ground-water cascade further south 

in the canyon (Wentworth and Yerkes, this report) 

also suggests recent movement. 

RELATION OF SURFACE FAULTING TO DAMAGE TO 

BUILDINGS 

The Sylmar segment of the San Fernando fault is 

a zone of concentrated major damage to buildings. 

This fact is indicated by figure 21, which shows the 

location of buildings in parts of San Fernando and 

Los Angeles that were posted as unsafe as of Feb:. 

ruary 24-March 1, 1971. Not only is there a 

greater concentration of such buildings within the 

mapped fault zone than in any other comparable 

area in the figure, but east of Seventh Street the 
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FIGURE 21.-Relation of surface faulting to the location of damaged buildings posted as unsafe (black squares) by officials of the cities of Los Angeles and 

San Fernando. From preliminary lists supplied by the Los Angeles Department of Building and Safety on February 24, 1971, and by the San Fernando 

Department of Building and Planning on February 24 and March 1, 1971. The lists were not necessarily complete and were subject to daily additions 

and deletions at the time they were sent. Many unsafe commercial buildings in the vicinity of San Fernando Road in San Fernando were not plotted 

because no street address was supplied. Most houses plotted along the Sylmar segment west of Foothill Boulevard are within 25 m of their correct position; elsewhere in San Fernando most houses are plotted within 50 m of their correct position; most of those on the remainder of the map are within 200 

II!- of their correct position. Surface fault traces are from figure 2. 

-:J 

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.-,3 

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trl 

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THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 75 

pattern of posted buildings closely conforms to the 

narrowing limits of the zone of breaks. Many additional buildings in the fault zone suffered severe 

structural damage, but were not classified as unsafe. 

Table 2 compares the number of posted, damaged, 

and undamaged houses within the mapped fault 

zone between Seventh and Eighth Streets in San 

Fernando to the same categories of houses in bands 

of roughly comparable width adjacent to each side 

of the fault zone. The table shows some important 

differences between these zones. For example, 30 

percent of the houses within the fault zone were 

posted as unsafe, as compared with only 5 percent 

of those on either side. Eighty percent of the houses 

in the fault zone suffered moderate or worse damage, but only 30 percent of those immediately beyond experienced such damage. 

TABLE 2.-Summary of dam.age to houses in San Fernando 

along the Sylmar segment of the San Fernando fault zone 

between Seventh and Eighth Streets 1 

Type of damage 

Total number of houses in zone __ Undamaged or minor damage __ _ Moderate to severe structural 

damage3 -------------- _-- __ Posted as unsafe _____________ _ 

Total, moderate damage or worse ____________________ _ 

Within fault zone Within zones of com- shown in figure 1 parab1e width on each side of the fault zone z 

Number of houses 

94 

21 

43 

30 

73 

Percentage 

of houses 

in this 

zone 

100 

20 

50 

30 

80 

Number of houses 

161 

110 

42 

9 

51 

Percentage 

of houses 

in this 

zone 

100 

70 

25 

5 

30 

1 From preliminary house-by-house descriptions supplied by the San Fernando Department of Building and Planning, Feb. 24 and Mar. 1, 1971. 2 Rounded to reflect uncertainties in the descriptions of damage. :1 For example, cracked or broken foundation, house shifted. on foundation. 

The increased damage to houses in the break zone 

apparently resulted from the large horizontal and 

vertical displacements across ground fractures in 

this area (Youd and Olsen, this report). In contrast, the area north of the Sylmar segment and 

east of Foothill Boulevard has widespread surface 

fractures that show only small displacements. Significantly, this area was not associated with extraordinary damage to buildings, apparently in part 

because ground displacements were not sufficiently 

large. 

Concentrations of "unsafe" houses shown in 

figure 21 beyond the limits of significant faulting 

may result from such causes as locally amplified 

seismic shaking, local surficial ground movement, 

undiscovered tectonic movement, or design and construction. 

ABSENCE OF MOVEMENT ALONG KNOWN FAULTS 

IN THE EPICENTRAL REGION 

Several faults in the epicentral region of the San 

Fernando earthquake were checked to determine if 

any movement occurred along them. No evidence of 

movement or cracks that might be related to tectonic movements were found. The following faults 

were examined: 

1. Santa Susana thrust. 

2. Mission Hills thrust where it is crossed by 

Woodley A venue. 

3. San Gabriel fault in Big Tujunga Canyon. 

4. San Gabriel fault where it is crossed by Little 

Tujunga Road. 

5. Unnamed fault trending west-northwest through 

downtown Sunland and Tujunga. This fault is 

entirely subsurface in the sections checked. 

6. Park fault south of Foothill Boulevard and east 

of Green Verdugo Reservoir. 

7. Hospital fault due north of U.S. Veterans Hospital (eastern extension of Santa Susana Fault 

on geologic map in paper by Wentworth and 

Yerkes, this report). 

8. Northridge Hills fault at Balboa Boulevard. 

TECTONIC AND ENGINEERING IMPLICATIONS 

To recapitulate, mapping of the tectonic fracture 

zones .shows that faulting associated with the San 

Fernando earthquake was characterized by left-reverse oblique slip of up to 2.4 m, along an approximately east-striking fault system that dips north 

about 55° at the surface. The sense of movement 

determined from surface measurements accords 

closely with that deduced from fault-plane solutions for the main shock. (See Whitcomb; Dillinger 

and Espinosa, this report.) Detailed mapping has 

also shown that the zone of tectonic fractures is defined on the south by a conspicuous major break or . 

narrow shear zone; we identify virtually no tectonic 

fractures south of this boundary. The northern 

boundary of the breakage zone, however, is diffuse. 

The gross relationship between earthquake damage and surface faulting is demonstrated by the remarkable concentration of major damage within the 

zone of surface breaks along the Sylmar segment. 

The gross relationship between damage and deformation in the thrust plate above the faults with 

surface breakage is shown, but more equivocally, by 

the great predominance of major damage in the 

upper plate. The occurrence of major damage along 

the mountain front between and beyond the Olive 

View and U.S. Veterans Hospitals suggests the possibility of faulting in that area. Tectonic fractures 

here could easily be masked by the abundant land-
76 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

slides; nevertheless, we have direct evidence of only 

one relatively short break along this zone that could 

be interpreted as tectonic. 

REFERENCES 

Bonilla, M. G., and Buchanan, J. M., 1970, Interim report on 

worldwide historic surface faulting: U.S. Geol. Survey 

open-file report. 

Clark, M. M., 1970, Some characteristics of the most recently 

active traces of the Garlock fault [abs.]: Geol. Soc. 

America Abs. with programs, v. 2, no. 2, p. 82. 

Miller, W. J., 1928, Geomorphology of the southwestern San 

Gabriel Mountains of California: Calif. Univ. Pubs. Geol. 

Sci., v. 17, p. 193-240. 

---1934, Geology of the western San Gabriel Mountains of 

California: Calif. Univ. Los Angeles Pubs. Math and 

Physical Sci., v. 1, p. 1-114. 

Oakeshott, G. B., ed., 1955, Earthquakes in Kern County, 

California, during 1952: Calif. Div. Mines Bull. 171, 283 p. 

---1958, Geology and mineral deposits of San Fernando 

quadrangle, Los Angeles Co., Calif.: Calif. Div. Mines 

Bull. 172, 147 p. 

Ross, D. C., 1969, Recently active breaks along the San 

Andreas Fault between Tejon Pass and Cajon Pass, 

southern California: U.S. Geol. Survey Misc. Geol. Inv. 

Map I-553, scale 1:24,000. 

Sharp, R. V., 1970, Map showing recently active breaks along 

the San Jacinto fault zone between San Bernardino area 

and Borrego Valley, California: U.S. Geol. Survey openfile map, scale 1:24,000. 

Shelton, J. S., 1966, Geology Illustrated: San Francisco, W. H. 

Freeman and Co., 434 p. 

Vedder, J. G., and Wallace, R. E., 1970, Map showing recently 

active breaks along the San Andreas and related faults 

between Cholame Valley and Tejon Pass, California: U.S. 

Geol. Survey Misc. Geol. Inv. Map I-574, scale 1:24,000. 
STRAINS AND TILTS ASSOCIATED WITH THE SAN FERNANDO EARTHQUAKE 1 

By PIERRE JUNGELS and DON L. ANDERSON 

SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY 

The San Fernando earthquake of February 9, 

1971, M= 6.6, was well recorded on the quartzstrain seismometers and mercury tiltmeters at the Isabella facility of California Institute of TechnolN.E. DIRECT STRAIN 

---; 1----

1 hr. 

FIGURE 1.-Strain seismogram for theN. 51.7° E. component at Isabella from 0100 February 9 (left side of record) to 0100 

February 10, 1971 (PST.). Note the "permanent" offset on the record at the superimposed very large amplitude deflections that mark the main shock at approximately 0601 February 9, 1971 (PST.). The vertical offsets, or steps, in the 

seismogram following (to the right of) the main shock are the result of automatic recentering of the trace. 

'Contribution No. 1989, Division of Geological and Planetary Sciences, 

California Institute of Technology, Pasadena, California. 

77 
78 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

ogy. The facility is located 147 km (kilometers) 

north of the epicenter. Figure 1 shows the strain 

seismogram for the N. 51.7° E . component of strain 

from 0100 February 9 to 0100 February 10, 1971 

(PST). The seismic waves from the main shock, 

which occurred at approximately 0601 on February 

9 (PST), and aftershocks are superimposed on tidal 

strains. The "permanent" offset on this record corresponds to a net dilatation, or lengthening, of 

4.19 X10-9 • This represents a change in the static 

strain field that is associated with the earthquake. 

The permanent offsets on the four instruments 

are: 

N. 51.7° E. strain - ---------- - 4.19 X 10- 9 , 

N. 51.7° E. tilt - -------------< 7 x 10- 3/L radians, 

N. 38.3° W. strain - - --------- 13.6 x 10- 9 , 

N. 38.3 ° W. tilt ______ _____ __ 0.1/L radians. 

The UCSD (University of California at San 

Diego) strain meter, southeast of the epicenter and 

oriented N. 45° E., exhibited an offset of 

+ 1.6 X 10-9, corresponding to a release of tension 

(J. Berger, personal commun.). 

Two strain meters installed near the Nevada Test 

Site 380 km to the northeast of the epicenter exhibit offsets of the order of - 3 X10-10, both dilatational. 

From the fault-plane solution for the main shock, 

and from the field observations of surface faulting, 

Isabella should be in a compressional strain release 

quadrant, and the UCSD station should be in a tensional release quadrant. Both components of strain 

at Isabella and those of the Nevada Test Site exhibit tensional offsets, that is, release of compression. The UCSD strain meter indicates tensional release although we do not know, of course, if the net 

strain is tensional. 

Both the fault-plane solution and the field observations of surface faulting indicate that overthrusting and left-lateral motion were associated with the 

faulting. The dip of the fault plane is 45° NE. at 

the surface and 52° NE. at the hypocenter. Unfortunately, solutions for the strain field associated 

with a dipping fault have not been published. Crude 

estimates of the expected strain field can be obt ained by combining theoretical strains for strikeslip and dip-slip motion. For this purpose we use 

the graphs in Press (1965). Taking a fault length 

of 20 km, a fault depth of 10 km, a vertical movement of 11fs m (meters), and a horizontal movement of 1 m, we calculate for Isabella (147 km 

north of epicenter): 

N. 51.7° E. strain _____ _____ -12 X 10-9, 

N. 38.3° W. strain __________ - 10 X 10-9 ; 

for the UCSD strain meter, +1.4 X10-9 ; and for 

the Nevada Test Site we get an areal dilation of approximately -3 X 10-10 • This good agreement certainly provides us with the motivation to do the 

complete calculation. The results will be reported in 

a later paper. 

\ 

\ 

\ 

119° 

\ 

\ 

118° 

ISABELLA 

I 

-136xi0- 9 

N38.3 ow 

117" 

TENSIONAL\ COMPRESSIONAL 

RELEASE RELEASE 35o 

I ,;:;.""~ 

\ "-"" 0 

0 1: . ~"" .,~'" ~ -f.r_ J'..v. \ ""~""~" . .-o.~ "* / '"~ ......... r{<- . / , -z ~ \ / . ' / 

COMPRESSION-:·.·-......: ·'. ¥-··. ~~ ... · Eplcel nter 

RELEASE ., ~'-....- /1 \ 'b PASADENA 

/ ' " '-..... 52°NE 

/ ----

.;Y' 

1 

C' 

0 C' 

0 

--Fault traces "? 

Ma1n aftershocks zone 

50 100 km 

33° 

STRAIN FIELD CHANGE , 

SAN FERNANDO EARTHQUAKE 

February 9, 1971 \ 

FIGURE 2.-Strain field changes associated with the San 

F erna ndo earthquake. 

The theoretical tilts for the vertical fault are an 

order of magnitude greater than observed, and this 

probably is where the inadequacies of the model are 

most important. 

The principal aftershocks mainly line up along 

the compression release axis and along the southeast nodal axis. It will be interesting to see if these 

two groups have different focal mechanisms. 

The strike of the original break, as inferred from 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 79 

the fault-plane solution, is closely parallel to the 

closest segment of the San Andreas fault some 30 

km to the northeast. A simple calculation shows 

that the San Fernando earthquake decreased the 

elastic compressional stress across the San Andreas 

fault by 2 X 10-s, which corresponds to a tensional 

stress of approximately 1 bar. Tension and shear 

strains calculated along the San Andreas are both 

about 5 X 10-7

, or a fraction of a bar. 

As can be seen from figure 1, the earthquake occurred very close to the time of maximum tidal 

compressional strains. (A total lunar eclipse, associated with maximum tidal tension, occurred some 18 

hours later.) Larger tidal compressions occurred 

during prior tidal cycles, 24 and 48 hours earlier. 

ACKNOWLEDGMENTS 

We acknowledge helpful conversations with Clarence R. Allen, James H. Whitcomb, David Harkrider, and Charles Archambeau. Auxiliary data was 

kindly provided by John M. Nordquist, Whitcomb, 

and John Berger. The Isabella facility is due to the 

efforts of Hugo Benioff, Stewart Smith, and William Gile. The station is supported by grants from 

the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air 

Force Office of Scientific Research under contract 

Nos. F44620-69-C-0067 and AFOSR-70-1954. 

The Earthquake Research Affiliates, a private group 

of sponsors, has contributed greatly to our program 

in earthquake research. 

REFERENCE 

Press, Frank, 1965, Displacements, strains and tilts at teleseismic distances: Jour. Geophys. Research v. 70, p. 

2395-2412. 
PRELIMINARY MEASUREMENTS OF TECTONIC MOVEMENT 

By R. 0. BURFORD, R. 0. CASTLE, J. P. CHURCH, W. T. KINOSHITA, 

S. H. KIRBY, R. T. RUTHVEN, and J. C. SAVAGE 

U.S. GEOLOGICAL SURVEY 

Instrumental measurements within an area surrounding the tectonic surface disturbance were 

begun almost immediately following the San Fernando earthquake of February 9, 1971. These measurements were designed to: (1) show such elevation 

and length changes as may have occurred at or 

about the time of the main shock, and (2) provide 

information on rate and amount of continuing tectonic movements (aftercreep), should any occur. A 

variety of measurement techniques were utilized for 

both preearthquake and postearthquake observations, including conventional leveling, triangulation, 

trilateration, vertical angle readings, and special instrumentation of the surface breaks. 

PREEARTHQUAKE AND POSTEARTHQUAKE 

COMPARISONS 

Results of comparisons between preearthquake 

and postearthquake measurements are summarized 

in figure 1. The general distribution of the tectonic 

surface fractures mapped during the postearthquake field investigation is also shown. 

Preearthquake vertical control is generally good 

south of the frontal scarp of the San Gabriel Mountains; it extends into the mountains locally, notably 

along the Southern Pacific Railroad and up Lopez, 

Kagel, and Little Tujunga Canyons. Postearthquake 

level circuits were selected to determine the elevation changes across the zones of tectonic rupture 

discovered in reconnaissance of the area during the 

2 or 3 days following the earthquake. Several assumptions exclusive of those associated with instrumental precision and surveying procedures are built 

into the elevation determinations leading to the 

vertical movements shown in figure 1. 

1. Preexisting circuits of temporally separated levelings have been connected locally in order to 

provide a basis for the postearthquake comparisons. It has been assumed, in other words, 

that the connecting bench mark (s) remained 

80 

stable between those levelings preceding the 

earthquake. 

2. The elevation changes reported in figure 1 are in 

most cases based on a comparison between 

earlier adjusted elevations and postearthquake 

observed elevations. Owing to the relatively 

short circuits utilized in these comparisons, it 

is unlikely that the values given in figure 1 

would be more than slightly modified if the 

comparisons had been between observed values only. 

3. All the elevation changes shown in figure 1 

are related to an arbitrarily selected separate 

control point within each one of the disconnected circuits. 

Preexisting horizontal control has not yet been 

researched in detail; hence, we are limited at present to only a few meaningful comparisons. The 

triangulation networks of the National Ocean Survey and the Los Angeles County Department of 

County Engineer should provide a firm basis for the 

recognition of any regional length changes. Furthermore, survey traverses carried out in connection with freeway or other highway construction 

can be expected to provide fairly good local control. 

However, except for those areas in which horizontal 

changes have been dramatically large, remaining 

preearthquake horizontal control generally affords 

an inadequate basis for the recognition of significant earth movements. 

Approximate length changes determined along 

several streets in the City of San Fernando depend 

on postearthquake resection of street intersections. 

The control points to which the 1938 surveying is 

referred have not been recovered; therefore, it is 

unlikely that these length changes are accurate to 

better than .±0.1 m (meter). Length changes along 

those lines comprising the regional network represented in figure 1 are based on comparisons between 

preearthquake triangulated distances and 1971 geo-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 81 

dimeter measurements ; changes over these distances 

are considered accurate to +-0.1 m, for lines up to 

10 km (kilometers) long. 

INTERPRETATION OF ELEVATION CHANGES 

Level circuit 1 was deliberately routed through 

the unbroken area between the Mission Wells and 

Sylmar segments of the San Fernando fault zone. 

The elevation changes shown here are, nevertheless, 

compatible with those inferred from direct observations to the east and west of this circuit, where examination of the fractures indicates that the northern block was thrust upward and to the south 

relative to the s·outhern block. That a substantial elevation change occurred between the northern and 

southern bench marks simply testifies to the existence of faulting that for reasons unexplained has 

not yet propagated to the surface. 

Circuit 2 was so designed as to extend from a 

point well south of the zone of surface rupturing to 

a point at least a short distance beyond the base of 

the San Gabriel Mountains. This circuit was extended northward across the area of c~mcentrated 

structural damage at the base of the San Gabriel 

Mountains in order to detect any earthquake-associated vertical uplift or faulting otherwise obscured 

by numerous landslides on the foothill slopes. The 

results indicate that there was no additional faulting along the base of the San Gabriel Mountains. A 

conclusion drawn from the elevation changes along 

circuit 2 is that the general uplift from south to 

north can be separated into three zones of distinct 

character: ( 1) northward tilt of the southern block 

between the railroad and the line of surface fractures, (2) pronounced upward arching of the leading edge of the upper plate with a peak uplift about 

1/2 km north of the fracture zone, and (3) northward tilt of the northern block between the point of 

maximum uplift and the north end of the level line. 

The character of elevation changes along level circuit 2 is consistent in general with an elastic rebound model based on a reverse-slip or thrust interpretation of the observed phenomena. The lack of 

detail in preearthquake and postearthquake comparisons along level circuit 2 is a hindrance to a definite interpretation regarding elastic rebound, but a 

pattern consistent with the proposed rebound is 

more completely developed in the leveling along circuit 3. 

The leveling network identified as circuit 3 in 

figure 1 is the most extensive and comprehensive of 

the circuits developed thus far in our operations. 

All the circuit 3 field elevations determined after 

the earthquake were related to a single bench mark 

(City of Los Angeles BM 5-M-22) at the corner of 

Foothill Boulevard and Eldridge A venue. The vertical changes at recovered bench marks were entered 

on the map before closure errors on extended loops 

could be checked and distributed. 

An area enclosed by the leveling loop . through 

Kagel and Lopez Canyons contains the largest vertical displacements thus far docu11fented. A profile of 

vertical displacement was constructed by projection 

of bench-mark data onto the line indicated in figure 

1. Approximate locations for each even 112-m elevation change were determined by interpolation along 

the profile line, and the results are shown in figure 

2. 

Comparison of the elevation changes among the 

five or six bench marks clearly south of the fracture 

zone indicates a relatively slight northward tilt of 

the southern block compared to the prominent 

north'ward tilt of the upper (north) block from the 

point of maximum uplift up to Pacoima Reservoir. 

The leading edge of the upper plate was sharply 

arched or buckled in a similar manner to the upper 

plate north of the break in San Fernando. The 

south-facing flank of the upward warp contains at 

least three locally prominent but apparently discontinuous scarps. Total accumulated displacement 

across the known scarps accounts for only about 1.5 

m of the uplift; the remaining 0.8 m could be distributed among smaller scarps or perhaps could be 

more smoothly distributed as a flexure in surface 

material overlying a cleaner break at some unknown depth. 

The preliminary results of releveling are thought 

to be reasonably consistent with an elastic rebound 

model based on dislocation theory as presented by 

Savage and Hastie ( 1969). Although their work 

was an attempt to model a dip-slip (normal) fault 

with a right-lateral component, the resulting displacement values can be altered to predict the surface movements associated with a reverse or thrust 

fault with a left-lateral component. by reversing all 

the signs and displacement vectors. The model thus 

altered suggests that the upper plate (north block) 

should rise near the leading edge by an amount approximately twice the amount of downdrop on the 

lower plate near the fault break. The apparent lack 

of complete agreement between the prelirqinary results of the releveiing and the dislocation model 

might well be. duet~ (1) the complex nature of the 

faulting indicated by the presence of several surface 

breaks, and (2) the r~lative nature of the pr~liminary data. 
82 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

0 

0 

2 MILES 

2 KILOMETERS 

FIGURE 1.-Map ~howing elevation and length changes in meters derived through comparison of preearthquake and postearthquake measurements. Elevation changes along each of the three identified circuits are relative to arbitrarily 

selected control points to the south of main fracture zone. Based on unpublished data of the Geological Survey, Los 

Angeles County Department of County Engineer, Los Angeles County Flood Control District, City of Los Angeles 

Bureau of Engineering, and City of San Fernando. 

A tentative tie between circuits 2 and 3, based on 

leveling underway by the Bureau of Engineering of 

the City of Los Angeles, indicates that the elevation 

changes along circuit 2 should be corrected by 

+ 0.057 m in order to compare them with changes 

recognized along circuit 3. 

INTERPRETATION OF LENGTH CHANGES 

Changes in horizontal lengths were measured on 

two different scales: a trilateration survey across 

the area of greatest damage involving lines of about 

5 km length and a short traverse across the fault 

break in the City of San Fernando (near the corner 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 83 

EXPLANATION 

-- .--

[

+ 0 .032 mJ [+ 1.829 mJ 

1960 1960/63 

Level circuit showing locations of selected 

bench marks . (Change in elevation and date 

of original leveling shown in brackets) . 

[

+0.6m] ~ 

1938 ----------- __... __... ....... Line of horizontal measurement. (Change in 

length and date of original measurement shown 

in brackets; see Table I for long lines). 

A through E 

Approximate locations of creep arrays. 

Approximate location of major tectonic 

fracture generated during earthquake. 

FIGURE !.-Continued. 

of Borden and Orange Grove) involving lines 

shorter than 0.5 km. Both surveys showed significant changes between preearthquake and postearthquake data. The trilateration survey also indicated 

+3 

that measurable movement occurred after February 

9, 1971. 

A preliminary trilateration network consisting of 

stations PACOIMA L1, PACOIMA E2 ECC, SYLMAR F8, and MAYS 2 (designated L1, E2, F8, and 

MAYS, respectively, in fig. 1) was surveyed on February 11, 1971, with a Geodolite. A helicopter was 

flown along the line of sight at the time of observation to determine the refractivity. An expanded network consisting of 12 stations, including reobservation of the preliminary network, was surveyed by 

the same procedure 2 weeks later. At the present 

time, data are available to discuss only the preliminary network and one additional station (PACOIMA #2, designated No. 2 in fig. 1). Table 1 

TABLE 1.- Difference between preearthquake and postearthquake 

measurements 

Length of line (met ers) 

Line Preearth- Postearth- quake quake 

PACOIMA Ll- PACOIMA #2 .. ____ __ _ 3,229.33 

PACOIMA E2 ECC .. 5,141.72 SYLMAR F8 _____ __ __ _ 6,708.64 

PACOIMA E2 ECC- PACOIMA #2.... 5, 728.76 SYLMAR F8 ____ 5,354.90 

3,229.28 

5,139.69 

6, 707.12 5, 728.57 5,354.94 

Change 

in length 

(meters) 

-0.05 

-2.03 

-1.52 

-0.19 

+0.04 

shows the line lengths determined before and after 

the earthquake. A mean date for the preearthquake 

surveys would be about 1935; thus, the changes in 

table 1 may include some strain accumulated in the 

36-year period between surveys. The accuracy of 

the preearthquake data is probably accurate to 

0.007 m. The uncertainty in the change of length is 

therefore of the order of 0.10 m. The simplest interfl) 

QJ ... 

_ l Lopez Canyon 

/ " I 

upper scarp 

~ QJ 2 

0 't + ::::J ~ 0 

I c +-

fl) 

o c +I 

a.. 0 

_,.....-...¥ ._1 Lower scarp at 

_... ___..-- __.. : /_., J bose of hills 

.... - ( ~-. ...... I ...... 

1:~ M l 

1-. +- 0 0 +- > 

QJ 

~~ w 0 f---+----------------· 

11~ \ ___ _ _!_ ...... . ...... I 

0 <l 

(0 

m 

N 

-I 0 2 Km 

= :=---==-==----:::== = 

s 

FIGURE 2.-Profile of interpolated relative vertical displacement along a line crossing the zone of surface breaks between 

Hansen Lake and Kagel Mountain. See figure 1 for location of profile line. 
84 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

pretation of the data in table 1 is that stations P ACOlMA #2, PACOIMA E2 ECC, and SYLMAR F8 

have remained approximately fixed relative to one 

another (presumably lying south or west of the limits of the northern fault block), but P A COlMA L1 

has moved 2.0 m to the west relative to those stations. This would suggest that PACOIMA L1 lies on 

the northern fault block. Superficially, it would appear to indicate pure left-lateral strike slip on the 

fault. However, dislocation models (for example, see 

Savage and Hastie, 1969) show that the motion 

near the toe of the hanging block of an oblique-slip 

fault of moderate dip is essentially parallel to the 

strike. Thus, the trilateration data are apparently 

consistent with reverse oblique slip (say 2 m reverse slip and 2 m left slip) on a fault plane dipping 50° to 60° N. 

The resurvey of the preliminary trilateration network was undertaken to detect evidence for 

·continued movement associated with either aftershocks or creep on the primary fault. The pertinent 

data are displayed in table 2. The uncertainty in 

TABLE 2.-Postearthquake length changes 

Length of line (meters) Line Feb. 11 Feb. 23 

PACOIMA L1-SYLMAR F8 .......... 6,707.12 MAYS 2 .............. 4,510.51 PACOIMA E2 ECC-SYLMAR FS.... 5,354.94 MAYS 2 ________ 5,453.75 

PACOIMA LL .. 5,139.69 

6, 707.07 4,510.47 

5,354.96 

5, 453.75 5,139. 65 

Change 

in length 

(meters) 

-0.05 

-.04 

+.02 

0.00 

-.04 

each distance measurement is about 0.007 m, so that 

the uncertainty in the change in length is about 

0.01 m. As can be seen from the table, additional 

movement has occurred in the 12-day interval between surveys. 

Finally, a short traverse was carried across the 

fault break in the city of San Fernando to determine the displacement on the fault. Horizontal displacements were measured by changes in distances 

between street intersections. As can be seen in 

figure 1, a shortening o{l.9 m was observed in the 

northeast direction and a lengthening of about 0.4 

m was observed in the northwest direction. Together these measurements imply a horizontal component of slip of about 2.0 m in the direction S. 57° 

W. Leveling data through this area suggest relative 

uplift of the northern block by about 1.3 m. Thus, 

the indicated fault movement is about 1.7 m left-slip 

and 1.7 m reverse-slip on a fault dipping about 50° 

N. 

MEASUREMENTS FOR DETECTION OF 

CONTINUING MOVEMENTS 

Tightly controlled creep arrays have been established in northern San Fernando, in Lopez Canyon, 

north of Pacoima Memorial Hospital, and in Little 

Tujunga Canyon. (See fig. 1.) In addition, selected 

segments of level circuits 1, 2, and 3 are being monitored for continuing vertical movements. Observations at each of the creep arrays include horizontal 

and vertical angle readings from a central point 

with a Wild T-3 theodolite, heights of instrument 

and targets measured to +0.5 mm (millimeter), and 

indirect determination of two lengths per array by 

angle readings on subtense bars. All the lines along 

which these measurements were completed are between about 50 and 200 m in length. In general, two 

lines in each array cross a zone of surface breakage, and the remaining two are situated on the 

same side of the break as the instrument station. 

The postearthquake movements detected thus far 

are mostly random. Some of these small displacements (on the order of a few millimeters) are definitely above the observational noise but might be 

associated with unstable marks or with continued 

landsliding or slumping of surface material. 

VERTICAL WIRE EXTENSOMETER INSTALLATION 

AND PRELIMINARY RESULTS 

A vertical exploratory hole was drilled through 

the buried surface of the prominent fault break in 

Lopez Canyon on February 19, 1971 (fig. 1, site C). 

The exposed slip surface of the fault on the hanging-wall scarp strikes about N. 81° W. and dips 65° 

N. Based on these data, the 3-foot (0.9-m) diameter 

hole was centered 4.6 m north of the projected lip 

of the bedrock scarp and was drilled to a depth of 

11.3 m. The south edge of the hole intersects the 

buried fault-gouge layer at about 9.3 m below the 

surface. Following the emplacement of casing down 

to an 8. 7 m depth, side-wall samples at 15-cm ( centimeter) intervals below the casing were obtained, 

and slickensided gouge material abundant in the 

8.90- to 9.35-m depth interval was examined. One 

slip surface in the gouge material which was exposed during sampling yielded a strike of N. 80° W. 

and a dip of 50° to 55° N. 

Following examination and sampling in the hole, 

two invar wires were anchored to the bottom of the 

hole and were coupled to displacement-measuring 

devices at the top. One device is purely mechanical. 

It records with 10:1 amplification and +0.02 mm 

resolution on a paper chart from which time can be 

read to about+ 10 minutes. To date, the mechanical 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 85 

recorder has operated continuously since 18:10 P.s.t. 

on February 19, 1971. Movement transmitted by the 

second wire is sensed by a precision electronic displacement transducer. Displacement signals are 

generated by movement of a ferrite core within the 

barrel of a linear variable differential transformer 

(LVDT). The LVDT output is recorded continuously on a portable strip-chart recorder. Optimum 

resolution for this system is about -+-0.001 mm, and 

time can be read with resolution varying between 

+1 and ±5 minutes depending on the chart-drive 

speed selected. The electronic system has produced 

about 75 percent complete coverage since the starting time given above. Sources of noise on both records are thought to be essentially limited to thermal expansion and contraction of the instrument 

table and steel support legs, aside from slight frictional drag in the mechanical system and thermallyinduced drift in the various electronic components of the second system. The current maximum 

amplitude of the diurnal thermal drift on the sensitive displacement record does not exceed 0.005 mm. 

The results obtained thus far suggest that slight 

downward movements of the hanging-wall block 

have occurred during certain of the larger aftershocks; these movements have produced a net lowering of the scarp by about 0.13 mm. These results 

are summarized in table 3. Two of the negative 

TABLE 3.-Vertical displacement episodes and net drift at Lopez 

Canyon extensometer site, February 1971 

lPacific standard times. Displacement: negative entry denotes contraction] 

Day Time Displacement '• Comments 

(±10 min) (mm) X10-• 

20_-- ----- 04:00 +0.04 +3.3 21:45 -0.09 -7.5 Mag. 4.0 aftershock at 21:51. 23:15 -0.08 -6.7 Mag. 3.9 aftershock at 23:15. 2L _______ 08:00 +0.04 +3.3 14:00 +0.05 +4.2 22 ________ 10:00 +0.03 +2.5 

19_-- ----- 18:10\ to -0.13 -10.8 Net negative drift on 23 ________ 12:00J mechanical record. 

(vertical contraction) events occurred as sharp 

steps of slightly less than 0.1 m:in each on the mechanical record, and these were approximately coincident with the aftershocks of February 20 at 21:51 

and 23:15 P.s.t. Several episodes of vertical extension (lengthening of the hole or upward movement 

of the hanging-wall block) were recorded on both 

instruments, but these show no obvious correlation 

with known aftershocks. The positive events are 

characterized by gradual onset of displacement over 

time intervals of about 1 hour; thus, they closely resemble episodic creep events recorded on certain 

strike-slip faults. 

STRAIN MEASUREMENTS PROGRAM OF THE 

CALIFORNIA DIVISION OF MINES AND GEOLOGY 

Twelve geodimeter lines within the State of California strain-monitoring network between Gorman 

and San Bernardino were remeasured within a few 

weeks following the San Fernando earthquake. 

Comparison of postearthquake lengths with those 

measured during the period 1963-66 shows that all 

lines examined are now longer, irrespective of their 

orientation. Preliminary appraisal of the changes 

suggests that areal dilation of about +2 to +3 

parts per million occurred in a region surrounding 

the San Andreas fault and containing Gorman and 

Cajon Pass. The length changes do not suggest lateral slip on known faults or any significant shear, 

although a slight shear component might be detected following more rigorous analysis of the data 

(Roger Greensfelder, personal commun., 1971). 

CONCLUSIONS 

This brief summary of the preliminary results of 

instrumental observations shows that the moderate 

magnitude San Fernando earthquake has been associated with surprisingly large, if areally restricted, 

permanent crustal movements. Because the preexisting control is generally very good in the area of 

surface disturbance, the San Fernando earthquake 

may provide an almost unprecedented opportunity 

for detailed documentation of the tectonically induced surface movements associated with a failure 

along a reverse or thrust fault. The results of an 

expended study will doubtless contribute significantly to a much greater understanding of the general problems concerning surface expression of 

deep-seated tectonic processes. 

REFERENCE 

Savage, J. C., and Hastie, L. M., 1969, A dislocation model for 

the Fairview Peak, Nevada earthquake: Seismol. Soc. Am. 

Bull. 59 (5), p. 1937-1948. 
REPEATED SURVEYS OF SMALL SCALE FIGURES ESTABLISHED ACROSS SURFACE 

FAULT RUPTURES FOLLOWING THE EARTHQUAKE 1 

By JoHN C. LAHR and MAX WYSS 

LAMONT-DOHERTY GEOLOGICAL OBSERVATORY OF COLUMBIA UNIVERSITY 

AND 

JAMES A. HILEMAN 

SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY 

ABSTRACT 

Starting 36 hours after the February 9, 1971, San 

Fernando earthquake, four small-scale geodetic figures wereestablished across the zone of surface-fault ruptures associated with the San Fernando earthquake. Each figure 

consists of one or two theodolite stations and about three 

reference points on each side of the fault. Two of the figures 

indicated no more than 2 millimeters of displacement. The 

data at the Middle Ranch figure, which spans the fault at the 

mouth of Little Tujunga Canyon, show that a small additional 

thrust with 2 mm uplift and 6 mm of compression may have 

occurred between two and four days after the main event. 

The displacements at the Aztec figure in Sylmar are consistent with left-lateral shear in the zone of the figure and 

range from 4 to 20 mm. 

INTRODUCTION 

Two recent California earthquakes with surface 

rupture were followed by substantial additional displacement across the related fault trace. During the 

2 years following the Parkfield earthquake of June 

28, 1966, a total of approximately 25-centimeter displacement was accumulated at an exponentially decaying rate (Smith and Wyss, 1968). Most of this 

displacement was aseismic (Scholz and others, 

1969) . During the days. immediately following the 

main shock, the creep rate was so high that it was 

difficult to tell how much, if any, surface displacement was associated with the earthquake itself. In 

any event, the creep displacement was equal to, or 

exceeded, the initial offset (Smith and Wyss, 1968), 

In the case of the Borrego Mountain earthquake 

of April 9, 1968, aftermovements were much less 

obvious. This earthquake produced two main 

branches of surface rupture which were offset in 

echelon (Allen and others, 1968). A small-scale geodetic network was established across the northern 

1 Contribution No. 1631 Lamont-Doherty Geological Observatory; Contribution No. 1992, California Institute of Technology, Division of Geological 

and Planetary Sciences, Pasadena, California 

86 

branch by Wyss only 12 hours after the earthquake. 

The position measurements across the fault were 

repeated at a rate of once per hour. However, no 

movement could be detected. A half year later, local 

residents suggested that the southern part of the 

fault was still active. Inspection of the fault trace 

indicated that additional displacement of the order 

of the initial offset on that part of the fault had accumulated. 

It is evident that even the most basic questions 

concerning dislocations following an earthquake 

with surface breakage are still to be answered. Indeed it is not known whether aftercreep is the norm 

or the exception. Before one can understand the 

mechanism of aftercreep, one needs to know some 

of the basic properties of the phenomenon. Both the 

Parkfield and the Borrego Mou.ntain surface traces 

lacked the extensive and dense network of measurements needed to determine the extent and propagation of creep events. 

This study of small-scale geodetic networks 

across the surface trace of the faulting that accompanied the San Fernando earthquake of February 9, 

1971, was undertaken with the hope of determining 

the extent of aftercreep at as many localities as 

possible. On February 10, 36 hours after the main 

shock, the first small-scale geodetic network has 

been installed across the fault trace. On February 

11, three more networks were established. 

DATA 

The locations of the survey stations are given in 

table 1. The first three stations straddle the fault 

break that lies along the base of the foothills and is 

informally named the "Tujunga fault segment." 

(See maps showing tectonic ruptures in papers by 

Kamb and others and by U.S. Geological Survey 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 87 

TABLE I.-Location of surveys 

Date Date Station North lat West long established last measured (1971) (1971) 

Middle Ranch ___ 34°16'56" 118°22'13" Feb. 11 Feb. 25 Lopez __________ 17'15" 24'00". 11 24 FoothilL __ • ____ 17'18" 24'31" 10 13 Aztec ____ ·----- 17'58" 26'21" 11 Mar. 1 

staff, this report.) The fourth station, Aztec, is 

somewhat west of the western end of the "Sylmar 

fault segment." This break appeared to stop or to 

branch out near the intersection of Hubbard Street 

and Glenoaks Boulevard in Sylmar. The Aztec station was set up beyond what appeared to be the end 

of the break in order to see whether the fault trace 

might propagate westward. 

In establishing these stations, speed was considered to be of prime importance, because an exponential decay of possible creep as observed at Parkfield (Smith and Wyss, 1966) could be expected. 

Further it was felt that the number of stations was 

more important than accuracy at each station. Both 

at Parkfield and at Borrego Mountain, the accumulated creep displacement was large, but the number 

of stations deployed along the . fault to record the 

displacement was insufficient. 

For these reasons the theodolite stations consisted 

of 1-meter steel rods driven into the ground, while 

the other nearby points were nails in trees or telephone poles. More distant points were structures 

such as water towers or houses. 

A Wild T-2 theodolite was used at station Lopez 

and for some of the later measurements at stations 

Aztec and Middle Ranch. All other measurements 

were made with a Kern DKM-3 theodolite. 

The three figures at the base of the foothills were 

chosen in areas with as little relief as possible so 

that secondary slumping would not affect the measurements. Two of the figures, Lopez and Middle 

Ranch, are at·the mouths-of canyons and consist of 

one theodolite station and a number of points on 

both sides of the fault trace. At Lopez, two surveys 

indicated no more than 2 mm of lateral motion or 

compression across the Tujunga fault segment. 

At the Middle Ranch figure, the changes in three 

angles which cross the fault zone are consistent 

with 6 mm of north-south compression and no lateral motion across the Tujunga fault segment. A 

conservative estimate of the error in this measurement is plus or minus 3 mm. This displacement occurred between February 11 and 13 and was combined with 2 plus or minus 1 mm uplift of the 

targets north of the fault. 

The Foothill figure is at the western end of the 

Tujunga fault segment, just before the break turns 

north. It consists of two theodolite stations, three 

reference points on the south side of the fault and 

two points on the north side. The data indicate that 

no more than 2 mm of vertical, lateral, or compressive movement occurred across the fault zone at the 

Foothill station. 

Between Pacoima Wash and Foothill Boulevard, 

the Sylmar fault segment trends east-west. Farther 

to the west it continues for 2 km as a zone curving 

to the south. The Aztec figure is somewhat to the 

north of the end of this zone over ground that experienced little apparent offset during the earthquake. 

The figure is set up in a field free from hardtop, 

and at the time of installation, no cracks, pressure 

ridges, or fault scarps could be detected. It was 

hoped that further lateral offset would extend with 

less curvature and pass through this figure. The 

network consists of two theodolite stations, three 

points within 200 m, and a distant water tower. 

Changes have been observed in all three short lines 

that are consistent with left-lateral motion both 

northeast and southwest of the theodolite stations. 

Between February 13 and March 1, a line to a garage on the southwest indicated about 2 em of left 

lateral displacement, while a more distant telephone 

pole at the same azimuth indicated only 5 mm displacement. A telephone pole to the northeast showed 

4 mm left lateral displacement. A conservative estimate of the errors is plus or minus 3 mm. This 

error estimate is rather large because some of the 

observed angles changed in an erratic fashion. We 

believe that these changes, however, could be real. 

In the field it was evident that streets and sidewalks 

acted as stress guides over long distances. The telephone poles could have been coupled to the pavement, which may react in a complex manner to 

ground deformation. 

DISCUSSION 

Very little displacement occurred along the prodominant trace of the faulting that accompanied the 

San Fernando earthquake in the period from 1% to 

14 days after the main event. A number of explanations for the absence of much fault creep are possible. The creep after the Borrego Mountain and 

Parkfield earthquakes may have been exceptional, 

and many earthquakes may not produce significant 

creep. Only observations after future earthquakes 

can resolve this question. Perhaps the mechanism of 

aftermovements is more effective for strike-slip displacement than for thrusting. The aftershocks may 

have occurred predominantly within the upper block 

rather than on the thrust plane (California Institute 
88 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

of Technology, 1971). This would in turn imply that 

the deformations occuring after the main event 

were within the upper block and would not result in 

additional significant displacement on the initial 

fault plane. Finally, it is possible that aftercreep 

has occurred at other locations or will occur in the 

future. 

ACKNOWLEDGMENTS 

We thank L. Sykes and B. !sacks for critically 

reading the manuscript. Ralph Gillman, Chris 

Scholz, and Peter Molnar helped establish and survey the figures. Our thanks also go to B. Kamb and 

to all those at the Seismological Laboratory, California Institute of Technology, for their aid in 

quickly locating the zones of surface faulting. This 

project was supported by the National Science 

Foundation under grant GA 22709 and by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air 

Force Cambridge Research Laboratory under contract F 19628-68-C-0341. 

REFERENCES 

Allen, C. R., Grantz, A., Brune, J. N., Clark, M. M., Sharp, 

R. V., Theodore, T. G., Wolfe, E. W. and Wyss, M., 1968, 

The Borrego Mountain, California, earthquake of 9 April 

1968: A preliminary report: Seimol. Soc. America Bull., v. 

58, p, 1183-1186. 

California Institute of Technology, Division of Geological 

and Planetary Sciences, 1971, Preliminary seismological 

and geological studies of the San Fernando, California, 

earthquake of 9 February 1971: Seismol. Soc. America 

Bull. (In press.) 

Scholz, C. H., Wyss, M., and Smith, S. W., 1969, Seismic and 

aseismic slip on the San Andreas fault: Jour. Geophys. 

Research, v. 74, p, 2049-2069. 

Smith, S. W., and Wyss, M., 1968, Displacement on the San 

Andreas Fault subsequent to the 1966 Parkfield earthquake: Scismol. Soc. America Bull., v. 58, p. 1955-1973. 
INSTRUMENTAL MONITORING OF POSTEARTHQUAKE FAULT MOVEMENTS 

By ROBERT D. NASON 

EARTHQUAKE MECHANISM LABORATORY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

With many earthquake sequences it has been 

noted that surface movement continues on a fault 

for many days and even months. This shows a gradually increasing offset, but at a steadily decreasing 

rate, at the fault in the days following the main 

earthquake. The continuing postearthquake fault 

movement can be called "afterslip" in analogy to 

aftershocks. 

Afterslip was well observed following the June 

1966 earthquake at Parkfield, Calif. (Wallace and 

Roth, 1967; Smith and Wyss, 1968; Scholz and 

others, 1969), and has been noted from historic 

data for at least five other California earthquakes 

(Nason, 1969) . But afterslip has apparently not occurred following some other earthquakes. The total 

number of known examples is small. 

The cause of afterslip or its absence is not known, 

though there are several theories (Scholz and others, 

1969; Nason, 1969). The relationship between afterslip and aftershocks is also unclear. But it is likely 

that the study of afterslip will provide many clues 

for better understanding of earthquake mechanism 

and aftershocks. It is even possible that the study 

of afterslip may help in estimating the probability 

of large damaging aftershocks following an earthquake. 

The Earthquake Mechanism Laboratory of the 

National Oceanic and Atmospheric Administration 

has prepared a special program for the instrumental monitoring of afterslip following major earthquakes. The first instrumental installation was at 

Ocotillo Wells, Calif., immediately after the Borrego 

Mountain earthquake of April 1968. The prime objectives of the program are: (1) is afterslip occurring with a particular earthquake sequence; (2) if 

so, what are the time and spacial characteristics of 

the afterslip; and (3) how does the afterslip relate 

to the earthquake aftershocks. 

SAN FERNANDO EARTHQUAKE MONITORING 

Early field reports by many investigators indicated that sizeable transverse movement had occurred on faults in the northern part of the San 

Fernando Valley. We are particularly indebted to 

the geologists from the California Institute of Technology and the U.S. Geological Survey for these 

early reports. The thrust movement on the northdipping faults caused both uplift and compression 

at the fault traces which approached 1 meter at 

many places. (See other sections in this report.) 

Twelve creepmeters (instruments designed to 

monitor the slippage on faults) were immediately 

assembled and taken to the earthquake area the day 

after the earthquake; six were specially designed to 

measure horizontal (strike-slip) fault movement 

and six were designed to measure vertical (dip-slip) 

FIGURE 1.-Design of dip-slip (beam-tilt) creepmeter: (A) 

trench cut into upper wall of fault scarp, (B) % -inch 

threaded rods driven into ground, (C) beam of rectangular 

cross section, with slotted holes, securely fastened to rightside rod, (D) precise 20-second spirit level, mounted, (E) 

nut on threaded rod to raise or lower end of beam until 

level, (F) machinists dial gauge, reading to 0.01 mm, to 

measure amount of raising of beam in any releveling, and 

(G) mark on beam to indicate any change of horizontal 

distance between threaded rods. 

89 
90 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 2.-Location of fault monitoring sites. 

fault movement (fig. 1). Five of the dip-slip creepmeters were installed on the thrust faults (their 

first us,e in afterslip studies). The five instruments 

were installed at (1) Little Tujunga Canyon (site 

LT, fig. 2), (2) Foothill Nursing Home (site FN), 

(3) Maclay Street (site MC), (4) Bromont Street 

(site BM), and (5) Rajah and Tucker Streets (site 

RJ). In addition, small fault monitoring patterns 

of survey marks were established at Kagel Canyon 

(site KG), Rajah Street (site RJ), and Olive View 

(site OV). 

The initial results indicate that there has been 

no change (no afterslip) at any of these sites. 

ACKNOWLEDGMENTS 

The author thanks the many geologists of the 

California Institute of Technology, U.S. Geological 

Survey, and the California Division of Mines and 

Geology for information on the location of the fault 

traces, and David Polanshek of San Francisco State 

College for assistance with the instrument installation. 

REFERENCES 

Nason, R. D., 1969, Continuing fault movement after earthquakes: Am. Geophys. Union Trans., v. 50, no. 1, p. 252. 

Wallace, R. E., and Roth, E. F ., 1967, Rates and patterns 

of progressive deformation, in The Parkfield-Cholame, 

Calif., earthquakes of June-August 1966-Surface geologic effects, water-resources aspects, and preliminary 

seismic data: U.S. Geol. Survey Prof. Paper 579, p. 

23-37. 

Scholz, C. H., Wyss, Max, and Smith, S. W., 1969, Seismic 

and aseismic slip on the San Andreas fault: Jour. 

Geophys. Research, v. 74, no. 8, p. 2049-2069. 

Smith, S. W., and Wyss, Max, 1968, Displacement on the 

San Andreas fault subsequent to the 1966 Parkfield 

earthquake: Seismol. Soc. America Bull., v. 58, no. 6, 

p. 1955-1973. 
PRELIMINARY RESULTS FROM RECORDING AFTERSHOCK GROUND MOTION ON 

ALLUVIAL DEPOSITS 

By RICHARD E. WARRICK and WILLIAM B. JOYNER 

U. S. GEOLOGICAL SURVEY 

Six sensitive accelerographs were installed to record aftershocks from the San Fernando earthquake 

of February 9, 1971, to determine the relative 

ground response in different geologic environments. 

Sites were located on the Quaternary alluvium covering the San Fernando Valley and on both sedimentary and crystalline bedrock in the nearby hills. Several recordings were obtained through February 22, 

the last date records were collected before this report. All the usable recordings were from sites on 

alluvium; however, the instruments are still in place 

so future events may be recorded at both bedrock 

and alluvial sites. 

The instruments are Kinemetrics type SMA-1 

strong motion accelerographs equipped with vertical 

triggers and employing sensors designed for full 

scale deflection at 1;4, g. These instruments have been 

modified by H. Mills, of the U.S. Geological Survey, 

National Center for Earthquake Research, to allow 

the recording of radio time signals from National 

Bureau of Standards station WWVB. The recording 

of any 1-minute segment of the radio time-signal 

permits identification of the day, hour, minute, and 

second of a seismic event. The complete station consists of the accelerograph, radio receiver with antenna, and a storage battery. The motion sensors are 

set for approximately 0.6 critical damping. Sensitivities and resonant frequencies of the instrument 

are listed in table 1. 

The recordings were made in two phases. During 

the first phase, February 10-13, the emphasis was on 

fast deployment, and the instruments were not 

bolted down. They were placed on existing concrete 

slabs embedded in the ground, except for station 

LA-6, where the instrument was placed on a scraped 

surface of outcropping granite. During the second 

phase, which began on February 18 and is continuTABLE I.-Instrument characteristics 

Instru- Station assignment Com .. Average resonant Average ment Phase I Phase II ponent frequency (Hz) sensitivity 

Feb., 10-13 Feb., 19-22 

163 ... LA-2 ............ LA-5A ........ 

171 ....... LA-3 ...... .. LA-2A 

173 LA-4... ......... LA-7 

176 .... LA-5 ........ LA-3 

177...... . LA-6 ............ LA-8 

178.......... LA-L ........ LA-6 

L..... . ....... 11.8 V ..................... 11.1 T ....................... 13.5 L ..................... 14.1 V ...................... 13.2 T ........................ 13.4 L ....................... 14.9 V..... . .. 11.9 T ....................... 13.5 L. ...................... 13.5 V ................... 13.6 T ....................... 12.6 L........ .. ......... 13.5 v ..................... 13.8 T.. ...................... 13.0 L ........................ 13.4 V ...................... 13.0 T ........................ 13.2 

(em per g) 

7.8 

8.4 

5.8 

6.6 

6.4 

5.8 

5.8 

7.7 

6.6 

6.2 

6.1 

6.9 

6.4 

6.2 

7.3 

6.7 

7.0 

6.8 

ing, some changes of location were made, including 

adding a third bedrock station, and all the instruments were secured in place with bolts. Tilt calibrations were made on the instruments between the two 

recording phases. 

The index map (fig. 1) shows recording sites and 

the epicenters of two events selected for illustration. 

The times of operation and the data quality at the 

various stations are diagrammed in figure 2. The 

coordinates of the recording sites and brief geologic 

descriptions based on Oakeshott's (1958) map and 

our own field observations are given in table 2. The 

available subsurface geologic information has not 

yet been compiled, but maps and sections published 

by the California State Water Rights Board (1962) 

suggest that the valley sites are characterized by 

Quaternary alluvium up to 100 feet thick overlying 

Pleistocene or Pliocene sediments. 

The two best recorded events occurred on February 21 at 0550 and 0715 GMT (figs. 3 and 4). The 

preliminary analysis of these records is limited to 

a simple reading of the period and peak amplitude 

91 
92 

Lower 

Van 

Norman 

Lake 

THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

Feb. 21 

055~ 

+ 

Olive View 

Hospital + 

Feb. 21 

071~ 

+ 

0 2 

+ 

V. A. Hospital 

.. 6 

+ 

34° 24' 

Q) 

0 

N 

N 

km 

Lake 

FIGURE 1.-Index map of recording stations and two selected epicenters. The thin line indicates the approximate contact 

between the recent alluvium and older material along the northern part of the San Fernando Valley (Oakeshott, 

1958). Stations are indicated by triangles. Epicenters are indicated by circles and crosses. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 93 

Feb. 

10 

.. J 

19 '-

20 rl 

21 -

22 

si 

3 

0 

Recording Stations 

4II 5IT I ' 

.L 

I~ 3 

0 ~ 

~ ~ ~ 0 

2A 

0 

4 

4 

FIGURE 2.-Instrument operation and data-quality chart. The 

short horizontal lines note beginning and end of recording 

intervals. The numerals to the left of the recording interval 

bar give the number of events recorded in that interval. 

The left vertical line of the bar refers to data quality: 

solid when good, broken when questionable for any reason. 

The right side line refers to timing signals: solid when 

good, broken when absent or unreadable. The time scale 

shows the beginning of each day in Greenwich mean time. 

of the maximum pulse recorded on any component. 

These data are given in tables 3 and 4 along with 

preliminary determinations of epicenter location and 

magnitude furnished by Wayne Thatcher of the California Institute of Technology. 

Station LA-2A recorded somewhat greater amplitudes than the other stations and, from the visual 

appearance of the record, shows a somewhat greater 

emphasis on low frequencies. Further analysis will 

be required to determine the significance of these 

characteristics. Station LA-3 recorded lower ampliTABLE 2.- Station descriptions 

Station North 

latitude 

LA-1 _ _ __ ____ 34 o 19.50' 

LA-lA ............ 34 o 19.63' 

LA-2 --·---··--·--- 34 o 18.53' LA-2A.-------- --- 34 o 18.53' 

LA-3 ·--·-·--······· 34°17.13' LA-4 _ ...... 34 o 19.49' 

LA-5 ----- -------- 34°19.81' 

LA-5A .... ....... 34 o 19.85' 

LA-6 .............. 34 o 20.22' LA-7 ............... 34°19.01' 

LA-8 ---- 34 o 17 .53' 

West longitude 

118°24.93' 

118°24.87' 

118 °26.82' 118 °26.82' 118°26.39' 

118°26.87' 

118°27.04' 

118°27.02' 

118 °25.00' 118°25.87' 

118 '24.19' 

Geologic unit ( Oakeshott. 1958) 

Quaternary alluvium (at edge of alluvial basin). Do. Quaternary a1luvium. Do. 

Do. Quaternary alluvium (at edge of alluvial basin). Sandstone of the Lower Pliocene Repetto Formation. A local deposit of alluvial material at the foot of a hill composed of sandstone of the Lower Pliocene Repetto Formation. 

Gran itic rock. Quaternary alluvium. Interbedded conglomerate and sand- stone of the Lower Pliocene Re- petto Formation. 

tudes, which may be due to the greater distances 

from the epicenters. With the exception of station 

LA-3, there is no obvious relation between distance 

from epicenters and amplitude or frequency content. 

Consistently higher ground accelerations were 

recorded for the 0715 event compared to the 0550 

event even though the magnitudes and distances from 

epicenters for the two events are very nearly the 

same. This difference may be related to the nature 

of the source function or it may reflect uncertainty 

in the preliminary determinations of magnitude. 

A more detailed analysis of the recordings is 

planned. The recording units will be left in place for 

as long as there is a significant chance for additional 

TABLE 3.-- Event on Februar,y 21, 1971 (0550 GMT) 

[Origin time: 05:50:52.5. Location: 34°22.2' 118°28.1'. Focal depth: Constrained to 8 km. Magnitude (ML) 4.0. Data from California Institute of Technology] 

Station Epicentral Azimuth, Maximum Approximate Direction 

distance station to component period (sec) 

(km) epicenter of acceleration (g) 

LA-2A ··········· 7.1 N. 16 ° w_ 0.08 0.25 E 

LA-3- ............ 9.7 N. 15' w. .05 .14 N 

LA-5A --- 4.7 N. 21° w. .08 .15 N 

LA-7 _ ............ 6.8 N. 30° w. .06 .16? s 

TABLE 4.-E1.> ent on F'ebruary 21, 1971 (0715 GMT) 

[Origin time: 07:15 :ll.5. Location: 34°22.5', ll8'26.7'. Focal depth: Con- strained to 8 km. Magnitude (Mr) : 3.9 Data from California Institute of 

Technology] 

Epicentral Azimuth, Maximum Approximate Direction 

distance station to component period (sec) 

(km) epicenter of acceleraStation tion (g) 

LA-2A ........... 7.3 N . 2' E. 0.15 0.24 w LA-3 ...... ....... 9.9 N. 2' w. .06 .22 E 

LA-5A ..... .. .... 4.9 N. 6' E. .10 .20 N 

LA-7 - .......... 6.5 N. 11' w. .12 .14 s 
94 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

LA- 5A 

52-0550 ~--------------------------

w 

. _____ ....._ ____ _ -------~-- · _· --·-·~ .· 

LA- 7 s 

52-0550 

UP 

E 

LA-2A 

52-0550 

w 

LA- 3 N 

52-0550 

w 

FIGURE 3.-Accelcrograms of Feb. 21, 0550 event. The vertical capped bar indicates the 1/4g deflection as determined by tilt 

calibration. The direction symbol and arrow shows the sense of ground motion for deflections in the direction of the 

arrow. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 95 

LA-5A 

52-0715 

UP 

w 

. __ ,..---_,-~ _,--_ ----- - - ------_,--

LA-7 

52-0715 

E 

LA-2A N 

52-0715 UP 

I w 

. -- - ·----

LA- 3 N 

52-0715 

w 

FIGURE 4.-Accelerograms of Feb. 21, 0715 event. The vertical capped bar indicates the 1/ 4g deflection as determined by tilt 

calibration. The direction symbol and arrow shows the sense of ground motion for deflections in the direction of the 

arrow. 
96 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

events to yield data for comparing the response of 

bedrock and alluvial sites. 

ACKNOWLEDGMENTS 

We wish to express appreciation to the staffs of 

the U.S. Veterans Hospital and the Olive View Hospital and to the officers and men of the Los Angeles 

Fire Department, Station 91, and the San Fernando 

Fire Department, for their generous cooperation at 

a difficult time and for giving permission to install 

the recording instruments. Mr. Edward Arneson, 

President of the California Camellia Gardens, and 

Mrs. Hanna, manager of the trailer court on Lopez 

Canyon Road, gave permission to install instruments. We are indebted to Edward Roth, of the U.S. 

Geological Survey, who set up and maintained the 

instruments during the second phase of field operation and to Kinemetrics, Inc., of San Gabriel, which 

assisted with supplies and emergency repairs to the 

recorder. 

REFERENCES 

California State Water Rights Board, 1962, The city of 

Los Angeles vs. city of San Fernando: California State 

Water Rights Board, Report of Referee, No. 650079, v. 

I, 258 p., 36 pis. 

Oakeshott, G. B., 1958, Geology and mineral deposits of- San 

Fernando quadrangle, Los Angeles County, California: 

California Div. Mines and Geology Bull. 172, 14 7 p. 
SHATTERED EARTH AT WALLABY STREET, SYLMAR 

By ROBERT D. NASON 

EARTHQUAKE MECHANISM LABORATORY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

One of the most fascinating effects of the earthquake's shaking is found at a small area of "shattered earth" near Wallaby and Rajah Streets. This 

site is in the northeasternmost corner of Sylmar, 

and only 1 mile from the strong-motion instrument, 

which showed high seismic accelerations at Pacoima 

Reservoir. The shattered earth is on the narrow flat 

top of a low ridge parallel to Wallaby Street and 

north of Rajah Street. The ridge-top is about 20 

feet higher than Wallaby Street and about 60 feet 

higher than a stream canyon to the east. (See approximate cross section, fig. 1.) The ridge-top consists of 10 feet of uplifted unconsolidated terrace 

W4LLABY ST. 

STREAM 

CANYON 

FIGURE I.- Approximate northeast-southwest section across 

ridge with shattered-earth effects alongside Wallaby Street, 

Sylmar. XXX's indicate location of shattered earth. 

deposits, which overlies consolidated Late Cenozoic 

shale and sandstone. The flat top is about 15 feet 

wide. 

For 200 feet along flat ground at the top of the 

ridge, the soil was thoroughly broken and overturned by shaking during the earthquake, giving an 

impression of well-plowed land (figs. 2, 3, 4). Soil 

clods are shattered and overturned such that 90 

percent of the surface is fresh mineral soil. The 

FIGURE 2.- View of shattered earth on fiat ridge-top, looking 

southeast. Wallaby Street on right. 

FIGURE 3.-Detail of shattered earth, with 6-inch folding rule 

for scale. Fine-grained material has been partially consolidated by a postearthquake rainstorm. 

other 10 percent consists of the grassy tops of 

detached soil clods. Much of the soil has been pul97 
98 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 4.-View of fractured ground immediately southeast 

of shattered earth, which is on the ridge-top in upper 

right. Collapsed frames of uncompleted houses on far side 

of Wall a by Street. 

veriz,ed into particles of sand-grain size. The surface 

was soft enough so that one would sink about 3 

inches into the loose soil when the site was first observed 4 days after the earthquake. The soil had 

undoubtedly been hardpacked like nearby areas before the earthquake. A 30-inch-deep trench and 

probings with a stick showed that the soil is loose 

to a depth of 1 to 2 feet, becoming gradationally 

harder like the original soil with increased depth. 

No discontinuities or layers were evident in the 

trench. 

The tossed-earth effect is confined to the 15-footwide flat top of the ridge for a length of 200 feet. 

To the north and south the ridge-top is wider, and 

the tossed-earth effect does not occur. The south end 

of the shattered-earth area is well defined with a 

transition from the thoroughly shattered earth to 

unshattered earth in a boundary only 10 feet wide. 

South of the boundary the flat ridge-top is crossed 

by many open fractures up to 1 inch wide and several feet apart, which might represent incipient 

shattering, but there is no overturning of dirt. 

Boulders on the ground outside of the tossed-earth 

area are somewhat dislodged but not shifted in any 

unusual manner. There are no boulders for special 

study in the tossed-earth area. The surrounding local countryside was searched, but no other region of 

tossed-earth effects was found. 

The special features of this site are ( 1) the 

tossed-earth phenomenon of overturned soil, which 

may indicate a seismic shaking exceeding 1.0 g; the 

pulverization of the soil may mean that the high 

acceleration occurred over many wave cycles; (2) 

the localized nature of the shaking, with the tossedearth effect occurring in an area only 200 feet long 

by 15 feet wide and a southern boundary only 10 

feet wide; ( 3) the restriction of the tossed-earth 

phenomenon to the top of the ridge where the ridge 

is narrowest, with no significant slope failures on 

the sides of the ridge line. The very localized nature 

of the high acceleration indicated by the tossed-earth 

may result from unknown effects of constructive interference of seismic waves arriving along different 

paths and possible focusing or concentration of seismic wave energy at the narrowed-down ridge-top. 

This suggests that seismic wave interference effects 

are probably very important to the detailed distribution of strong shaking and earthquake damage. 

A local resident living on Tucker Street reports that 

the strong shaking lasted through many cycles. This 

agrees with the inference of many wave cycles because of the pulverized nature of the broken soil. 

The fact that the soil was thoroughly overturned is 

an indication of the strength of the shaking. It 

would appear that possible seismic wave interference and focusing patterns may be very important 

to the local distribution of strong seismic shaking 

and related damage. 

ACKNOWLEDGMENTS 

The author thanks John Pfluke and Glenn Converse of the National Oceanic and Atmospheric Administration Earthquake Mechanism Laboratory for 

their assistance in the field. 
SEISMICALLY TRIGGERED LANDSLIDES IN THE AREA ABOVE THE 

SAN FERNANDO VALLEY 

By DOUGLAS M. MORTON 

CALIFORNIA DIVISION OF MINES AND GEOLOGY 

Interpretation of aerial photographs taken a few 

days after the San Fernando earthquake indicates 

that the earthquake triggered more than 1,000 landslides in a 250 km~ (square kilometer) area in the 

hilly and mountainous terrain north of the San 

Fernando Valley. The gross distribution of the 

slides was controlled primarily by the intensity of 

ground shaking, but important local variations in 

the density of landslides reflect variations in the 

character and structural history of local geologic 

formations. The earthquake also produced some 

areas of highly fractured rock, especially along ridge 

tops, that are likely to give rise to abundant landslides if they receive sufficient moisture. 

This report summarizes a preliminary photointerpretive investigation of landslides triggered by 

the earthquake. The investigation used black-andwhite aerial photographs taken for the U.S. Geological Survey on February 9, 1971 (American Aerial 

Surveys, Inc., scale 1: 10,000), and color photographs taken on February 18, 1971 (U.S. Air Force, 

scale~ 1: 20,000). Photographic coverage was adequate for the area of interest (see fig. 1) with the 

exception of the northeast part, where cloud cover 

largely obscured the ground. 

Landsliding was a direct and immediate response 

to the ground shaking of the earthquake, although 

some rock falls continued for several days along 

steep canyon walls (for example, Pacoima and Little 

Tujunga Canyons). Some of these rock falls may 

have been triggered by aftershocks. The landslides 

are concentrated south-southwest of the epicenter of 

the main shock, adjacent to the area of tectonic 

rupture at the surface, and within the area of principal aftershocks. 

Approximately 1,000 landslides, ranging in length 

from about 15 to more than 300 m (meters) were 

mapped from the aerial photographs. Only a few 

were verified in the field. Rock falls, soil falls, 

debris slides and avalanches, and slumps were the 

principal types of landslides triggered by the earthquake. Surficial (~ 0.2 to 1 m thick) debris slides 

(fig. 3) and avalanches were probably the most 

widespread and common types of failure and were 

especially pronounced in areas underlain by sedimentary rocks. Rock falls were common on steepwalled canyon faces cut in well-fractured basement 

rock, but also occurred in sedimentary rock where 

a particularly resistant bed cropped out on oversteepened slopes. Soil falls occurred mainly at the 

free face of recent stream terrace deposits along 

major drainages. Slumping (fig. 2) was found 

largely on reactivated, preexisting ( preearthquake) 

slumps. 

Landslide distribution was controlled primarily 

by the intensity of ground shaking, for most slides 

occurred in the area of surface rupture. Local variation in landslide density reflected the character of 

local rock units, degree of fracturing and faulting, 

and the existence of preexisting landslide deposits. 

Physiography controlled the density of landslides 

only in areas of extreme topographic steepness. 

The relationship of landsliding to the intensity of 

shaking is particularly clear in the westward-striking Pico, Modelo, Towsley, and Saugus Formations 

west of San Fernando Valley. There, the number of 

landslides decreases markedly along strike westward 

from the valley, away from the area of aftershocks 

and most intense tectonic rupturing. 

Landslide distribution controlled by rock type is 

best seen in the vicinity of Lopez and Bartholomaus 

Canyons (fig. 4B). Here, numerous landslides 

formed on outcrops of the Modelo and Towsley Formations, while relatively few formed on the immediately adjacent Saugus Formation. Free faces of 

stream terrace deposits were also especially slide 

99 
0 2 4 6 MILES 

0 2 4 6 KILOMETERS 

FIGURE 1.-Seismically triggered landslides in the San Fernando Valley area. 

..... 

0 

0 

>-3 

::I1 

t':j 

Ul 

> z 

"%j 

t':j 

~ 

z 

> z 

tj 

.0 

0 

> t" 

...... 

"%j 

0 

~ 

F 

t':j 

> 

~ 

>-3 

::I1 

!:) 

c::: 

> 

::>::: 

t':j 

0 

"%j 

"%j 

t':j 

l:d 

~ 

c::: 

> 

~ 

~ 

·"' 

..... 

"' -'I 

..... 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 101 

prone, giving rise to small soil falls over a considerably larger area than that of figure 1. Numerous 

rock falls also occurred where highly fractured basement rock is exposed on steep slopes, especially 

along the major drainages-Pacoima, Little Tujunga, and Big Tujunga Canyons. Rock falls at the 

mouth of Pacoima Canyon (fig. 4A) covered sizable 

areas, but apparently consisted only of surficial 

material. 

Previously weakened rock showed a common tendency to fail. A number of old landslides were reactivated, as shown by fresh scarps from 0.25 to about 

1 m high. Some small old scarps failed as debris 

slides. Parts of other large old slides failed as a 

number of small discrete new slides generally concentrated along the toe of the·old slide (for example, 

in Pacoima Canyon, fig. 4A). Some landslides were 

localized by crushed rock along fault zones. Thus, 

the San Gabriel fault zone was the locus of a narrow band of landslides north of Placerita Canyon 

(fig. 5) 0 

Landslides were also common in ·excavations, and 

many roads were blocked by failures in cut slopes. 

Innumerable minor rock falls occurred in roadcuts 

in the area of figure 1, and extended eastward 

throughout most of the San Gabriel Mountains. 

Large rotational or complex landslides, which are 

characteristic of the San Gabriel and Santa Susana 

Mountains, did not form during the San Fernando 

earthquake. Apparently, such slides form under different circumstances-for instance, seismic shaking 

at times when the ground is saturated by prolonged 

or heavy rain, or by seismic shaking with longer 

period vibrations or of longer duration than the 

San Fernando earthquake. One possible incipient, 

large complex failure may be represented by features south and east of the San Fernando Ranger 

Station, which lies between the west end of the 

Tujunga segment and the east end of the Sylmar 

segment of the San Fernando fault zone. Northward, compressional surface deformation in the 

valley margin there may represent relatively largescale landsliding related to numerous fractures 

which extend over an area 0.2 to 0.5 km wide in the 

hills above the ranger station (fig. 4B). 

FIGURE 2.-Slump-type failure, east of Little Tujunga 

Canyon. 

Widespread ground fracturing throughout much 

of the area of figure 1 is closely related to landsliding. This fracturing appears to be most pronounced 

along ridge tops, where, given sufficient rainfall, the 

highly fractured surficial materials may give rise to 

abundant debris slides and flows. These materials 

may now conceivably have the potential for generating as many (or even more) landslides as were triggered during the earthquake. 
102 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Failure in roadcut, Balboa Boulevard, with small debris slide in ravine to the right of roadcut. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

34°20' 

A 

B 

FIGURE 4.-A, Landslides in lower Pacoima Canyon area, San Fernando quadrangle, showing topographic control of some landslides and landsliding within older landslide deposits. B, Landslides 

in the Lopez Canyon area, San Fernando quadrangle, showing lithologic control of landslide distribution. See figure 5 for explanation of symbols. 

103 
104 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

EXPLANATION 

~ Seismically triggered landslides. DirectiOn of 

movement in larger slides 1ndicated by arrows 

~~ Alluvial depos1ts 

Stream 

~ terrace deposits 

I Os I OTs I Tsr I 

Saugus Formation 

Pica 

~ Formation 

l 

~ ll:: ~ w 

1-

<>: 

::::J J 0 

>-

0:: 

<>: 

r0:: 

w 

1-

Approximate contact 

Approximate fault 

20 

-'-

Strike and dip of beds 

Towsley 

~ Formation 

~n] Modelo Formation 

GJ Mint Canyon Formation 

c:J 

Topanga Formation 

8 Basement complex 

Geology from compilation by Yerkes and Wentworth, this report 

0 

L 

118"27'30" 

1 MILE 

D 0 o 

.............. 

N 

1 

-- ................ 

·· .. ·· . 

>-

0::: 

«: 

1-

0::: 

w 

1-

z: 

}~ u 

0 ON 

r-0 (j) 

w 

::;; 0:: 

0... 

FIGURE 5.-Landslides in the Placerita Canyon area, Mint Canyon quadrangle, 

showing localization of landslides along the San Gabriel fault. 
LANDSLIDING IN THE VICINITY OF THE VAN NORMAN LAKES 

By T. L. Youo 

U.S. GEOLOGICAL SURVEY 

This section focuses on the Van Norman Lakes 

area because the earthquake triggered a large number of landslides there and because some of these 

slides moved down very gentle slopes. An additional 

reason is the large amount of damage which occurred there. 

The geology of the area has been described by 

Oakeshott (1958), Merifield (1958), and Wentworth 

and Yerkes (this report). The following information is from their reports. The Van Norman Lakes 

lie in a valley eroded in north-dipping strata of the 

Saugus and Modelo Formations. The lakes are impounded at their south ends by dams constructed 

across this valley. Both lakes are bounded on the 

southeast and southwest by slightly consolidated 

sandstones and mudstones of Pliocene and Pleistocene age. The rest of the lakeshore area is covered 

by recent alluvium. The principal structural features in the area are the Mission Hills thrust located south of the Mission Hills, the Olive View 

fault, which cuts northeastward across the area just 

north of the upper lake, and the Mission Hills syncline, which generally parallels the Olive View fault. 

(See fig. 1.) 

Because of the reservoirs and a confined aquifer 

in the Little Tujunga syncline, the water table in 

the general area is at a relatively high level and intersects the surface at several locations. At the time 

of the earthquake, the water table was probably not 

more than a few meters below the surface at any 

point in the alluvial areas surrounding the lakes. 

The soils in the area have been mapped by the 

Soil Conservation Service (U.S. Department of Agriculture, 1915). Sandy loams, commonly with components of gravel and silt, have formed on the alluvium. Clay loams and rough ground are the common 

soil types on the upland hills. 

LANDSLIDES 

A large number of landslides formed in the 

vicinity of the Van Norman Lakes in response to 

the February 9 earthquake. The most significant 

ruptures generated by these movements are plotted 

in figure 1. Only the slides in recent alluvium are 

discussed here. Siides in bedrock areas, including 

some in the subject area, are described by Morton 

(this report); and slope failures in constructed fills, 

including the nearly disastrous slump in the Lower 

Van Norman Dam, are described by Y oud and 

Olsen (this report). 

Extensive slumping occurred in the alluvium 

around the margins of both the Lower and the 

Upper Van Norman Lakes. In some places a nearly 

continuous line of scarps formed. The scarp on the 

west shore of the lower lake is more than 1 km (kilometer) long. Sand boils commonly formed below 

these scarps (fig. 1). 

A recently filled and graded area west of the 

upper lake was broken up by numerous fissures, 

which generally tended to parallel the shoreline and 

the contour of the previous surface, shown by the 

contours on the map in figure 1. This area is considered here because of the likelihood that failure in 

the alluvium below the fill is reponsible for the sliding. Extensional and vertical displacements in the 

fill indicate movement toward the reservoir either 

in the form of block glides or in slightly rotated 

slumps. Sand boils erupted in the southern part of 

this fracture zone some 180 m (meters) from the 

lake and several meters above the water level at the 

time of the shock. 

Many fissures formed in the area west of that described in the previous paragraph. Of those observed, the most notable were in a schoolyard in the 

mouth of Bee Canyon, nearly 1 km from the upper 

lake. These fissures were characterized by vertical 

displacements of as much as 50 mm (millimeters) 

and continuous lengths of perhaps 100 m. They 

seemingly formed the head of a landslide which had 

moved down the very mild slope (about 1.5° or 2.5 

percent) eastward toward the upper lake. 

The most damaging slide in the vicinity of the 

lakes formed a tonguelike feature (in plan) extend105 
106 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

34°17'30" 

0 KILOMETER 

FIGURE 1.-Map of Van Norman Lakes vicinity, showing surficial ruptures associated with landslides activated by the 

earthquake. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 107 

EXPLANATION 

Sma ll s urf ace c rac k 

Large surface c rack 

120 

V ert ical di spl aceme nt. in mi II imet ers 

95 

Horizont al d ispl ac ement . in mi llimet ers 

Sand boi I 

........... 

Struc tura l feature 

Geology from Meri field, 1958 and 

Ook eshott, 1958 

FIGURE !.-Continued. 

ing northeastward from the upper lake for a distance of 1.2 km. Located on or crossing this slide, 

hereafter called the Juvenile Hall slide (fig. 2), are 

a major part of the San Fernando Valley Juvenile 

Hall, trunk lines of the Southern Pacific Railroad, 

San Fernando Boulevard, Interstate Highway 5, the 

Sylmar electrical converter station, and several 

pipelines and canals. (See Youd and Olsen, this report). Earthquake damage to these facilities will 

likely exceed $30 million. 

The available evidence indicates that the displacements associated with this feature are of landslide 

rather than tectonic origin. The evidence includes: 

( 1) the tonguelike shape of the feature and the fact 

that the rupture pattern did not extend beyond the 

bounds of the feature; (2) fissures with right-lateral displacements formed on the north margin, fisFIGURE 2.-0blique photograph of San F ernando Valley Juvenile Hall area 

and approximate boundaries of the Juvenile Hall slide. View t o east. 
108 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

sures with an almost equal amount of left-lateral 

displacement formed on the south margin, and almost purely extensional cracks formed at the head; 

(3) Survey data generously supplied by the City of 

Los Angeles (L. D. Paulsen, Bureau of Engineering, city of Los Angeles, Oral Commun., Feb. 26, 

1971) show that movements of the feature relative 

to the adjacent ground exceeded relative movements 

between survey points on opposite sides of the feature. 

Resurvey of San Fernando Boulevard revealed 

that the distance across the slide from the survey 

point at the Interstate 5 overpass to a point near 

Olden Street had shortened 43 mm. Relative to the 

Roxford Street intersection with San Fernando 

Boulevard (southeast of the slide), the survey 

points near the Interstate 5 overpass (northwest of 

the slide) had moved south 300 mm and west 210 

mm. These relative movements are considerably less 

than the total downslope movements of the slide, 

which ranged from 0.5 to 1.0 m (based on visual observation and cumulative measurements of displacements across fissures). Thus, it appears unlikely 

that the feature mapped as the Juvenile Hall slide 

had a tectonic origin, even though the southwest 

movement of the Interstate 5 overpass with respect 

to the Roxford Street intersection could have been 

produced by left-lateral tectonic displacement on a 

northeast trending fault or fault zone through the 

area of the slide. 

The surface on which movement occurred has a 

very gently slope; it averages about 1.5° (2.5 percent) over its entire length assuming that the toe of 

the slide is at the shoreline of Upper Van Norman 

Lake. The maximum slope was about go (5 percent) 

near the head. Surprisingly, the average slope between the Juvenile Hall and the converter station, 

which appeared to be the minimum, was only 0.9° 

(1.5 percent). 

Numerous sand boils erupted on the lake floor, 

presumably near the toe of the slide. These were exposed after the water level was lowered. Sand boils 

were also found at the following locations: Behind 

the converter station near the base of the graded 

fill, in a field south of Juvenile Hall (fig. 3), and 

along the north edge of the railroad grade in front 

of the Juvenile Hall Administration Building. 

During the earthquake, the crest of the Upper 

Van Norman Dam subsided a maximum of 0.9 m 

and shifted downstream a maximum of 1.5 m with 

respect to its abutments (W. F. Hansen, Los Angeles Department of Water and Power, oral commun., 

FIGURE 3.-Sand boils on Juvenile Hall slide. A damaged part 

of the Juvenile Hall is in the background. 

Feb. 23, 1971). In light of this it would appear that 

a low-gradient slide, similar to the one described 

above, may have cut through the valley floor beneath the dam and caused these movements. 

EXPLANATION OF SLIDES ON 

LOW-GRADIENT SLOPES 

The most reasonable explanation for slippage of 

the Juvenile Hall slide on a slope of such low gradient is that the underlying soils were partially or 

completely liquefied during the earthquake. The 

many sand boils observed on or near the slide are 

evidence that this occurred. 

In addition to causing sand boils, the increased 

pore water pressures associated with the liquefied 

condition would reduce the shear strength of the 

subsurface soils. This strength would have to be reduced to a value less than the tangential component 

of the lithostatic stress for movement to occur on 

slides such as the Juvenile Hall slide, which is presumed to be very long compared with its depth. 

This reduction in strength can readily be explained 

by increased pore water pressure and the shear 

strength relationship for granular soils: 

T = (un - u) tan</> (1) 

where T is the shear strength of the soil, u is the 

pore water pressure, <Tn is the normal stress on the 

failure plane (essentially the lithostatic pressure for 

low-gradient slopes), and cp is the angle of internal 

friction of the soil. Thus, if the pore water pressure 

under the Juvenile Hall slide increased to a value 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 109 

approching the lithostatic pressure during the 

shock, the soil strength would have been reduced to 

nearly zero, allowing the movement to occur. The 

field evidence indicates that this probably was the 

case. 

It is also probable that movements on many, if 

not all, of the other slides in the alluvium surrounding the Van Norman Lakes were directly attributable to increased pore water pressures generated by 

the earthquake. 

REFERENCES CITED 

Merifield, P. M., 1958, Geology of a portion of the southwestern San Gabriel Mountains, San Fernando and Oat 

Mountain quadrangles, Los Angeles County, California: 

Los Angeles, California Univ. M.A. thesis (unpub.) 

Oakeshott, G. B., 1958, Geology and mineral deposits of San 

Fernando quadrangle, Los Angeles County, California: 

California Div. Mines and Geology Bull. 172, 147 p., 5 pis. 

U.S. Department of Agriculture, 1915, Soil map, California, 

San Fernando Valley sheet: Soil Conservation Service, 

Washington, D.C. 
GROUND FAILURE ON THE SAN FERNANDO SURFACE AWAY FROM OBVIOUSLY 

TETONIC RUPTURE ZONES 

By ROBERT V. SHARP 

U.S. GEOLOGICAL SURVEY 

The earthquake of February 9 produced widespread ground fracturing in the form of cracking, 

thrusting, and slumping across much of the surface 

on which the communities of San Fernando and 

Sylmar are built. The relatively smooth and flat surface, here termed the "San Fernanao surface," is outlined in the generalized ground-rupture map by the 

U.S. Geological Survey staff. Fracturing on the San 

Fernando surface is particularly evident in pavements and sidewalks. The nature of displacement on 

many fractures hints at possible deeply rooted tectonic influence; yet most offsets can be explained 

satisfactorily by surficial slippage not involving tectonism. In view of previously published literature on 

the geologic evidence for faults projecting under the 

San Fernando surface from the neighboring mountainous area, fracturing was investigated throughout 

the surface to determine whether it reflected renewed tectonic movement along generally concealed 

faults. 

Examination of the affected region revealed no 

definite tectonic zones other than those described 

elsewhere in this volume. Particular effort was made 

to identify persistent patterns or alinements of fracture zones that might be expected along throughgoing faults. Despite the negative evidence, however, 

it is conceivable that tectonic movement did alter the 

form of the San Fernando surface in a subtle way at 

unrecognized locations. Geodetic remeasurement of 

the horizontal and vertical positions of established 

points on the surface is now in progress. Detailed 

data of this kind will provide the critical evidence for 

or against tectonic dislocation outside of the San 

Fernando fault zone. The fracturing in the fault zone 

itself is described in accompanying sections by Kamb 

and others and by U.S. Geological Survey staff. 

Where fractures resulting from landsliding, slumpno 

ing, and lurching are developed near or within a zone 

of tectonic rupture, it is sometimes difficult to determine the origin of individual fractures. However, 

many fractures are readily attributable to nontectonic processes because of their localized distribution, 

orientation with respect to natural or artificial topographic features and constructed works, and the 

sense and pattern of the offset along them. Tectonic 

fractures are primarily recognized by their continuity and map pattern, pattern of displacement, and indifference to the position of overlying constructed 

works. 

Three kinds of ground failure by fracturing were 

recognized outside of the major zone of tectonic 

movement on the San Fernando surface-ground 

breaks evident in both soil and overlying constructed 

works, cracks restricted to soil near built structures, 

and cracks in pavements and other thin structures 

resting on unaffected substrate. These all displace 

the ground surface in a manner that can be related 

to minor topographic features or constructed works, 

and they appear not to be related to through-going 

fracture systems. Nontectonic fractures were not 

mapped and are not illustrated in this preliminary 

report. 

Ground breaks involving both constructed works 

and the underlying soil occurred on large and small 

scale. The larger failures of this type, such as the 

landslide under the San Fernando Valley Juvenile 

Hall, are discussed in the section by Y oud. Smallscale failures and fractures that break both the 

soil and overlying works appear to be related chiefly 

to artificial cut or fill slopes on the ground surface. 

Parallelism between the free face and scarps developed at the upslope end of the fill indicate failure 

by small-scale downslope movement. 

Failures in soil alongside structures or large fills 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 111 

are a common result of shaking on the San Fernando 

surface. Both extensional cracks and compressional 

zones indicated by small-scale thrust faults have 

been produced by vibration and lurching of houses, 

concrete walls, curbs, sidewalks, and other heavy objects imbedded in the ground. Many of these fractures do not extend into even small structures, such 

as driveways, that may lie above them. In every case, 

the distribution of fracturing of this type is restricted to the immediate location of structures or 

larger fills, and consequently cannot be considered to 

be tectonic. 

The most easily seen evidence for apparent ground 

breakage outside of known tectonic zones is the fracturing, thrusting, and buckling of pavements, curbs, 

and sidewalks. However, only in exceptional cases do 

the breaks extend across the adjoining ground surface as far as a meter, and most terminate at the 

edge of the slabs of pavement. The evidence thus indicates that fractures in pavement for the most part 

do not reflect displacement in the ground and hence 

are nontectonic. Even vertical offsets in pavement 

usually do not extend into the surrounding soil, suggesting that compaction of the roadbed or perhaps of 

fill over buried pipelines has occurred. At the time of 

strong shaking, slabs of pavement (including curbs 

and sidewalks) commonly decoupled from the underlying soil and were translated downslope along the 

lengths of the streets. Slight rotational effects resuiting from small differences in the amount of 

translation of one side of such slabs relative to the 

other side are shown by lateral offsets at many of the 

open extensional cracks that broke pavements during 

the earthquake. 

Distinguishing the various types of displacement 

produced by shaking from truly tectonic movement 

ultimately rests on whether there has been any net 

extension, shortening, or changes in elevation. The 

observation that compression may be transmitted 

along a street for several blocks before the appearance of overthrusts or buckled up blocks of pavement 

complicates the problem of locating minor ground 

displacements of possible tectonic origin. Attempts at 

quickly determining dimensional changes along 

streets by tabulating extensional openings and compressional overlaps have shown that errors which are 

comparable to the size of the offsets being sought are 

possible. In addition to the imprecision in measuring 

fractures, permanent dimensional changes in the 

form of compressional shortening and possibly tensile elongation of pavement and sidewalk slabs are 

known to have occurred. Other dimensional changes 

were presumably caused by myriad fractures that 

escaped detection because of their extremely small 

size. Apparently only relatively large offsets can be 

detected and roughly estimated by measuring fractures in sidewalks and pavement and that small but 

real tectonic offsets could easily be overlooked. 
METHANE SEEP OFF MALIBU POINT FOLLOWING THE SAN FERNANDO EARTHQUAKE 

By H. EDWARD CLIFTON, H. GARY GREENE, GEORGE W. MOORE, and R. LAWRENCE PHILLIPS 

U.S. GEOLOGICAL SURVEY 

At approximately 8 o'clock on the morning of the 

San Fernando earthquake, February 9, 1971, observers on the pier in Kellers Shelter near Malibu Point, 

Calif. (fig. 1), noticed a large volume of gas escaping 

from the ocean surface about 500 m (meters) from 

the shoreline. The seep probably began with the 

earthquake at about 6: 00 a.m. but was unnoticed for 

2 hours because coastal fog restricted the visibility 

around Malibu Point. The seep occurred in a linear 

zone that was oriented approximately east-west, 

parallel to the general trend of geologic structure in 

this area (Schoellhamer and Yerkes, 1961). Malibu 

Point lies approximately 50 km (kilometers) southwest of the earthquake epicenter, and some houses in 

the vicinity of the Point suffered minor structural 

damage during the earthquake. The probable coincidence of the seep with the San Fernando earthquake and the similarity of its trend to that of local 

faults (fig. 1) raised the possibility that the earthquake had triggered secondary faulting near Malibu . 

Point. 

To evaluate the geological significance of the seep, 

personnel of the U.S. Geological Survey conducted a 

brief investigation. The day after the earthquake 

George W. Moore visited the site and, with the aid of 

local diver Bill Farell, obtained samples of the gas for 

analysis. The following day the other authors of this 

section used scubas to investigate the sea floor at the 

seep and to collect additional samples of the gas. A 

surveying team from the Department of the Los 

Angeles County Engineer located the position and 

the trend of the seep by triangulation from onshore 

beach marks to marker buoys emplaced by the diving 

team. 

We wish to acknowledge the generous assistance 

of Mr. Sam Miller, Regional Engineer, Department of 

the Los Angeles County Engineer. We also wish to 

thank Lt. Ted Davis and Mr. Roger Smith, Los Angeles County Lifeguard Patrol, who provided support 

for the diving operation. 

112 

SETTING 

The seep occurred in 6-8 m of water east of Malibu 

Point, 400-500 m from the mouth of Malibu Creek. 

The area around Malibu Point appears to be at least 

in part a deltaic deposit at the mouth of the creek. 

Outcrops of bedrock occur, however, at the southernmost tip of the Point, and abundant boulders near 

the shoreline suggest that bedrock lies close to sea 

level on the east side of the Point. 

Malibu Point lies on the south side of the Santa 

Monica Mountains. The rocks underlying the vicinity 

of the Point consist of marine shale, mudstone, siltstone, and sandstone of middle and late Miocene age 

(R. F. Yerkes, written commun., 1971). These strata 

lie in or near the east-trending Malibu Coast deformation zone, which includes the Malibu Coast fault 

(fig. 1). This zone is characterized by north-oversouth compressive deformation and contains a number of north-dipping faults (R. F. Yerkes and C. M. 

Wentworth, unpub. data, 1965). 

The sea floor in Kellers Shelter slopes evenly and 

gently seaward to a distance of about 6 km from the 

shore, where it abruptly increases in slope (U.S. 

Coast and Geodetic Survey Sheet 5101). In the vicinity of the seep, 400-500 m from the shore, the sea 

floor is nearly flat and an unknown thickness of relatively young sediment overlies the bedrock. 

DESCRIPTION 

Gas bubbles broke the ocean's surface in a zone 

approximately 12 m wide by 120m long and oriented 

N. 78°E. (fig. 1). Two days after the earthquake the 

gas bubbles ranged in diameter from 0.5 to 2 em 

(centimeters) at the surface and were escaping into 

the atmosphere at a rate of about 1-5 bubbles per 

second; some strings of bubbles were discontinuous. 

Eyewitnesses reported that a much greater volume 

of gas was escaping on the day of the earthquake and 

that a second zone of bubbles was present trending 

shoreward at an acute angle from the major seep. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 113 

The sea floor in the vicinity of the seep is composed of fine to very fine brown sand that contains 

abundant organic debris. Irregular sand ripples 1-4 

em high cover most of the floor. During the diving 

observations, the ripples were inactive and currents 

generated by the waves transported only fine organic 

matter. A few millimeters to several centimeters below the surface of the floor, the sediment is very 

cohesive and is black and fetid. Approximately 10 

em beneath the surface of the floor, the sand coarsens to medium grain size and is better sorted. 

The gas emanated from small holes and craters in 

the sea floor. The smallest holes were only several 

millimeters in diameter, whereas the largest craters 

were up to 40 em across and 10-15 em deep. The 

craters were lined or rimmed with dark sand derived 

from the subsurface. Generally, a greater volume of 

gas issued from the larger craters, although some of 

the large craters seemed to be totally inactive. All 

the craters were sharply defined and showed no evidence of modification by waves or bottom currents. 

Many of the craters contained large amounts of grass 

and other organic detritus. The gas commonly emanated around tubes of an unidentified burrowing 

organism. 

Many of the emanation sites seemed to be locally 

clustered and lay a few centimeters to 1 or 2 meters 

apart; outside such clusters the emanations occurred 

several meters apart. Some of the emanations occurred several meters apart. Some of the emanation clusters showed a linear trend approximately 

parallel to the general trend of the seep. Ripples 

within the clusters tended to be less pronounced than 

they were elsewhere, and detrital organic material, 

particularly grass, seemed to be more abundant in 

the areas of greatest emanation. 

No ruptures or dislocations of the sea floor were 

observed during the dive. The cohesiveness of the 

sediment in Kellers Shelter probably is sufficient to 

preserve the expression of such features. Moreover, 

the state of preservation of the craters suggests that 

little or no sediment was transported by wave activity during the two days that elapsed between the 

earthquake and the time of underwater observation 

of t!he seep. Therefore, scarps or fissures that formed 

on the sea floor would probably have been discernible had they existed. An anchor chain lying on the 

sediment surface crossed one of the clusters of craters at an angle to the trend of the seep; this chain 

was lying in a shallow scour groove that was nowhere dislocated along its extent. The absence of 

dislocation precludes lateral faulting of the sediment, 

at least along the extent of the anchor chain. 

Three box cores were taken through the uppermost 

17 em of sediment in one of the clusters of craters to 

look for possible earthquake disturbance of internal 

sedimentary structures. None of the cores was taken 

directly over an active gas emanation. X-ray radiographs of the cores identify a layer 5-6 em thick at 

the top of the core consisting of finely cross-stratified 

sand. Within this layer no evidence exists of breakage or other disruption attributable to the San Fernando earthquake. 

COMPOSITION OF THE GAS 

The gas was sampled by inverting glass containers, filled with water, oyer bubble outlets., After the 

gas displaced the water, the containers were capped. 

The bubble outlets that were sampled were located 

in the center of small craters on the ocean floor at a 

depth of about 10 m. Precaution was taken to release 

pressure from the sample container on ascent to the 

surface. 

Mass-spectrometer analysis by Motoaki Sato, U.S. 

Geological Survey, Washington, D. C., shows the 

sample of gas collected for Moore to have the following composition: 

Volume percent 

(with water) 

Methane --------------- 90.0 

Nitrogen -------------- 4.4 

Water ----------------- 3.6 

Carbon dioxide _________ 1.2 

Oxygen ____ ------------ .75 

Argon ----------------- .08 

Volume percent 

(without water) 

93.3 

4.6 

1.2 

.8 

.1 

The ratio of nitrogen to argon is virtually that of air, 

but the ratio of nitrogen to oxygen is not. Oxygen is 

apparently deficient, whereas carbon dioxide is added 

(Motoaki Sato, written commun., 1971). Other samples . of gas are being processed for radiometric 

dating. 

DISCUSSION 

Two possible origins exist for the methane that 

seeped from the sea floor near Malibu Point. Either 

the gas developed from decaying organic material in 

the marine sediment above the Miocene bedrock, or 

it formed and was trapped in the bedrock until its 

release following the earthquake. Presently, data are 

insufficient to eliminate either possibility. The composition of the gas suggests that it is marsh gas. 

Gas from the oil fields in the Los Angeles basin con-
114 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

118°42' 

I 

34.01'40" I 

0 

PACIFIC OCEAN 

0 

0 .5 

-Gas seep N zone 

Malibu Pt. 

~~ !b? I 

1 MILE 

1 KILOMETER 

FIGURE 1.-Location of the gas seep that began off Malibu Point on F ebruary 9, 1971, and its relation to local geologic 

features. Geology modified from R. F. Yerkes (written commun., 1971) . 

tains about 9 percent ethane and 1 percent propane, 

both of which would have been detected in the seep 

gas had they been present. It is not known whether 

the sediment cover in Kellers Shelter contains sufficient organic material to generate the volume of 

methane that escaped in the seep. The bedrock exposures at sea level at Malibu Point and in adjacent 

sea cliffs suggest that the sediment thickness at the 

seep is not very great. No accurate data on thickness 

are available; the nearby pier is sufficiently old that 

no records remain of the depth to bedrock under its 

pilings (Sam Miller, oral commun., 1971). 

If the gas originated in the unconsolidated sediment, three possible explanations for the seep exist: 

(1) compaction within an ancient linear channel incised into the bedrock, (2) release in a line controlled 

by bedding in the underlying Miocene strata, and (3) 

release in a line controlled by a fracture in the bedrock. If the gas originated within the Miocene strata, 

the seep could only have formed along a fracture in 

the bedrock. No dislocation or displacement of bedrock is necessarily implicit in either of the two possible explanations that postulate a fracture in the 

bedrock. 

The orientation of the seep is consistent with all 

the foregoing possibilities. If it were alined along an 

ancient channel in the bedrock, it would imply that 

the channel was cut parallel to the slope contours. 

Such an orientation of a deeply eroded channel seems 

somewhat unlikely, but would not be impossible for 

short distances. 'I'he orientation is nearly parallel to 

bedding in the rocks exposed at Malibu Point and 

also parallel to the trend of faults mapped in this 

area (fig. 1). The eyewitness account of a second line 

of gas seepage extending shoreward at an acute 

angle from the primary seep suggests that the flow 

of gas is at least partly controlled by fractures in the 

bedrock. 

The westward projection of the seep extends into 

a cove lying between two patches of abundant boulders. This cove could be interpreted as a channel cut 

in the past by Malibu Creek, as a less resistant stratigraphic layer in the bedrock, or as a sheared zone 

of faulting in the bedrock. The location of the cove 

along the projection of the seep therefore provides 

little evidence concerning the origin of the seep. 

The roads leading out to Malibu Point and the alluvium on the delta of Malibu Creek were examined 
J{ 

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THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

EXPLANATION 

SURFICIAL DEPOSITS 

Artificial fill 

Chiefly fill for roadways; locally includes cut 

surfaces 

Oal I Qalp I Of I Ob I Od Ols I 

Alluvial, colluvial, fan, beach, dune, landslide, debris, and undifferentiated surficial 

deposits: 

Oal, alluvial sand, gravel, and silt; subrounded 

boulders locally exceed 5 feet, thickness locally 

exceeds 100 feet in Malibu Canyon 

Oalp, alluvial and mudflow deposits underlying 

flood plains incised to depths as great as 25 

feet 

Of, fan deposits in tributaries and below steep 

slopes along coast; thickness locally as great 

as 100 teet, but commonly less than 10 feet 

Ob, beach deposits; fine- to medium-grained 

sand, rounded pebble gravel locally at base, 

thickness less than 25 feet 

Od, dune deposits; fine- to medium-grained loose 

sand; thickness locally exceeds 50 feet 

Ols, landslide deposits; may include both bedrock 

and surficial materials 

FhtmJ 

Terrace deposits 

Q) 

c:: 

<I> 

(.) 

0 

ii 

.... 

<I> 

Q, 

Q, 

~.I{ ;a!:5 

"0 

BEDROCK UNITS 

AREA SOUTH OF MALl BU COAST FAULT 

Monterey Shale 

Marine shale and siltstone 

il{ ::;: .. 

sandstone 

.;,. .. ~~.~~~/ ..... ~. ~" AREA NORTH OF MALl BU COAST FAULT 

l>3vrl 

Middle and upper Topanga Formation of 

Durrell ( 1954) (Upper plate of Malibu Bowl 

fault) 

Ttv, volcanic rocks; andesitic and basaltic flows 

and flow breccias; locally includes mudflow 

breccia, pillow breccia 

Ttvr, volcanic rocks of Ramera Canyon area; 

andesitic and basaltic breccias, tuff breccias, 

flows(?), and minor volcanic sandstone 

<li ,3.!:! ~~{ Vaqueros ~ FormatiOn 

~ !:!; UndiVIded sequences of chiefly manne sandstone, 

Ost, stream terrace deposits; interbedded gravel, 

sand, and silt, thickness locally as great as 

100 feet 

Otm, marine terrace deposits; sand, silty sand, 

and gravel; sand, friable, well sorted, fine to 

medium grained, as thick as 20 teet 

g <li'"g ~ siltstone, and pebbly sandstone 

1~~~ <:.>"0 H~{ t:>..~il:: Nonmanne sandstone, Sesp~ ;:rm~tion pebbly sandstone, and 

~ § :§- ~ mudstone 

MAP SYMBOLS 

Bedding 

Contact or mapped horizon 

·Long dash where approximately located, short 

dash where inferred 

25 

-'-

Strike and. dip of· beds 

_,_ 30 

Approximate strike and dip of beds determined from indirect evidence 

25 

Strike and dip of indistinct layering in 

volcanic rocks 

65 

Strike and dip of joint 

Faults 

Fault symbols; long dash where approximately 

located, short dash where inferred, dotted where 

concealed, queried where doubtful; x. igneous 

rock intruded along fault 

65 u ~"*"-----·? 

High-angle fault, showing dip; 

u, upthrown side; o, downthrown side 

Low-angle fault, sawteeth on upper plate 

Relative displacement not determined 

40 .... ...1... ..... _._ 

Malibu Coast fault, showing dip 

Boxes on upper. plate of reve.rs~ fault 

Folds 

~ 

60 

Axis of complex fold, showing direction and 

amount of plunge, and dip of axial surface 

25 

-E-L30 +-3--'---

Minor anticline Minor syncline 

Showing plunge and dip of axial surface 

Landslides 

Most landslides are complex; symbol may include 

more than one type and stage of movement; may 

include both bedrock and surficial materials 

Landslide 

Arrows show general' direction of movement; 

queried where origin of feature doubtful 

>-

a:: 

<:( 

1-

0: 

w 

1-

115 
116 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

for fresh fractures that might be associated with the 

methane seep. Only one fresh joint or crack was 

found. This crack occurs in hard-packed alluvium on 

the west side of Malibu Creek well off the projection 

of the seep. No offset across the crack could be detected. 

CONCLUSIONS 

The methane gas that seeped from the sea floor 

following the San Fernando earthquake may have 

originated from the decay of organic material in 

Holocene or Pleistocene sediment, or it may be much 

older, having formed in the Miocene bedrock underlying this area. Radioisotope analysis of the gas, currently in progress, may establish its age and origin. 

The trend and location of the seep may be controlled by either ancient channels incised in the bedrock, structural attitude of the underlying strata, or 

fractures through these strata. 'Ilhe report of a second line of gas seepage shortly after the earthquake 

suggests that fractures are at least in part responsible. If the age of the gas proves to be pre-Pleistocene, seeping of the gas along fractures in the bedrock would be indicated. 

Regardless of its origin, the seep was not accompanied by active faulting on the sea floor. No detectable rupture or dislocation of the sediment surface 

occurred along the seep as a result of tJhe San Fernando earthquake. 

REFERENCE 

Schoellhamer, J. E. and Yerkes, R. F., 1961, Preliminary 

geologic map of the coastal part of the Malibu Beach 

quadrangle: U.S. Geol. Survey open-file rept. 
OIL AND GAS SEEPAGES AND DAMAGE TO OIL FIELD FACILITIES RELATED 

TO THE EARTHQUAKE 

By CALIFORNIA DIVISION OF OIL AND GAS 

OIL AND GAS SEEP AGES 

SALT LAKE FIELD 

Four oil and gas seepages have been reported 

within a 1-mile radius of the famous Rancho La 

Brea tar deposits following the earthquake of February 9. Historically, this area, like many other 

areas in Southern California, has been known for 

its high incidence of oil and gas seepages. 

This area also marks the location of many oil 

wells that were abandoned between 1920 and 1935. 

The exact relationship between the earthquake and 

the seeps is not known at this early date; however, 

there is a joint study under way by members of the 

oil and gas industr y to determine the full nature of 

this phenomenon. The California Division of Oil and 

Gas is actively involved in this project. 

MALIBU OFFSHORE 

On February 9, 1971, bubbles of gas were discovered rising to the surface of the ocean approximately 200 yards off Malibu Pier. (See figure 1 of 

this report and also the map in the section by Clifton 

and others.) Lt. Ted Davis of the Los Angeles County 

118°42' 118°40'10" 

34°02'30" .----------------=~--------------------------~------ ----------~---------------, 

•• .. ·\\ 

0 

PACIFIC OCEAN 

II 

\ 

'\ 

II 

• 

' 

line of seeps 

noted on Feb. 9, 

, 1971 but not on 

Line ' < Feb. 10, 1971 

of seeps ,..--'1-

...-- ...-- \lnitialseep 

Malibu Pt 

APPROX IM ATE MEAN 

DECLINATI ON, 1971 

reported on 

Feb. 9 . 1971 

34 oo 1 '40" '--------------------------------------------------------------------------------' 

0 MILE 

0 .5 KILO METER 

FIGURE !.-Location of gas seeps off Malibu Point. 

117 
118 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

Lifeguard Patrol stated that the bubbles had appeared shortly after the earthquake. 

On February 10 the seep was seen to consist of 

a series of small individual seeps occurring along a 

line extending at least 800 feet from a point 200 

yards slightly southwest of the end of Malibu Pier, 

and approximately 600 yards northeasterly from 

Malibu Point. 

Lt. Davis stated that another line of seeps was 

noted on February 9, originating at the easterly end 

of the previously noted seep line and extending 

northwesterly some 300 feet. However, by February 

10 bubble activity along this line had declined to 

the point that it was no longer visible. 

Scuba divers reported that the seeps appeared to 

emanate from the sea floor as individual columns of 

bubbles occurring along the previously described 

line. Plastic bags placed over individual seeps required about 20 minutes to recover approximately 

three-quarters of a cubic foot of gas. 

In the opinion of those who were present on February 9, the seep activity had declined approximately 75 percent by February 10. 

An analysis of the gas is presented in the section 

by Clifton and others. 

DAMAGE TO OIL FIELD FACILITIES 

Despite the severity of the earthquake of February 9, relatively little damage was sustained by 

facilities in the nearby oil and gas fields. 

Division engineers making field checks after the 

earthquake reported minor damage to tanks, roads, 

and a few wells. Line breakage occurred in several 

fields; however, where breaks did occur, only minor 

spillage was noted. 

Several fields lost electrical power and immediately shut down, but most of them were again operating normally within a matter of hours. 

The Newhall Refining Co., Inc., refinery, 2 miles 

southeast of the town of Newhall and approximately 

11 miles southwest of the earthquake's epicenter, 

was forced to shut down temporarily because of 

damage to storage tanks and pipelines. Estimated 

repair costs range from $8,000 to $12,000. The refinery is a 5,500-barrels-per-day unit that produces 

asphalt, road oils, and jet fuel. 

A note of interest was the report that the Cascade 

field showed an increase in gas production after the 

quake. 
WATER-RESOURCES ASPECTS 

By A. 0. W AANANEN and W. R. MOYLE, JR. 

U.S. GEOLOGICAL SURVEY 

Damage to hydraulic structures constituted the 

major impact of the San Fernando earthquake of 

February 9, 1971, on the water resources and the 

water supplies of the area principally affected by 

the seismic shocks. The effects on the water resources of the region included noticeable fluctuations 

in the stages of streams and reservoirs and water 

levels in wells, the roiling of water in water-supply 

systems, short-term changes in the flow of streams, 

and short-term changes in ground-water levels. The 

major damage was caused by the principal M6.6 

shock that occurred at 0601 hours February 9. The 

full effect or effects of any additional damage that 

may have resulted from the lesser shocks have not 

been appraised in this preliminary account. 

A normal and expected effect of earthquakes of 

magnitude 5.0 or greater is the development of hydroseisms-seismically induced fluctuations of water levels in wells, streams, lakes, ponds, and reservoirs. They are a common response of water bodies 

to seismic shock. Hydroseisms resulting from moderate and greater shocks have been recorded at 

streamflow measurement stations and ground-water 

observation wells over wide areas and have been 

reported by many investigators. The impact of the 

Alaska earthquake of March 27, 1964, for example, 

as reporte·d· by Vorhis···(1967) ·was recorded afsites · 

far distant from the epicenter. 

Hydroseisms caused by the San Fernando earthquake on February 9 were recorded at gaging stations and observation wells over a wide area in California, and in Arizona and Nevada. The area extends more than 500 km (kilometers) from the epicenter near San Fernando, about 40 km northwest 

of Los Angeles. Responses were recorded as far 

north as Fresno, in the middle Salinas River basin, 

near the Mexican border in California, and as far 

east as Phoenix, Ariz. Selected sites in California 

that are indicative of the areal extent of the seismic 

shock effects are shown in figure 1. The data were 

obtained at gaging stations and observation wells 

operated by the U.S. Geological Survey and by state, 

county, and local agencies. The cooperation of these 

agencies in making the data available is gratefully 

acknowledged. 

Fluctuations recorded at selected gaging stations 

are listed in table 1 ; the location of the stations is 

shown in figure 1. Similar fluctuations were indicated by the charts for many stations in the San 

Fernando Valley, Santa Clara River basin, and adjacent basins; most of the records indicate response 

only to the principal shock. 

TABLE !.-Fluctuations in water level recorded at gaging 

stations, February 9, 1971 

Site 

(fig. 1) 

Stream or reservoir and station Fluctuations recorded 

as double amplitude 

(mm) 

Net 

change, 

rise (+l or fall (-) 

(mm) 

L __ San Antonio Reservoir near Bradley_ 60 0 

2 ___ Santa Margarita Lake near Pozo____ 6 0 

3 ___ Arroyo Grande at Arroyo Grande___ 21 0 

4 ___ Santa Ynez River near Lompoc_____ 24 +3 

5 ___ Sandyland Bridge at slough at 

Carpinteria --------------------- 113 0 

6 ___ Matilija Reservoir at Matilija 

Hot Springs --------------------- 54 0 

7 ___ Sespe Creek near Fillmore__________ 34 +6 

s ___ Los Angeles River below Sepulveda 

Dam ---------------------------- 225 0 

·9 __ c.Arroyo Seco-near ·Pasadena--~~----- 67 +24 

10 ___ San Gabriel River below Santa Fe 

Dam, near Baldwin Park _________ 100 +6 

1L __ Deep Creek near Hesperia__________ 12 0 

12 ___ Mojave River at Afton______________ 6 0 

13 ___ Santa Ana River diversion near 

Mentone ------------------------ 9 0 

14 ___ Santa Ana River below Prado Dam_ 46 0 

15 ___ San Jacinto River near San Jacinto_ 8 0 

16 ___ San Luis Rey River near Oceanside_ 9 0 

17 ___ Sweetwater River near Descanso____ 3 0 

Parts of recorder charts showing hydroseisms on 

February 9 at three selected gaging stations are reproduced in figure 2. The record for Los Angeles 

River below Sepulveda Dam (site 8) shows the effects of the principal shock and at least two of the 

lesser shocks. The record also indicates the effect 

119 
120 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

118" 116" 

·:: ,, : ;',1 Ill E.._R " ' \.:' o ''A I '·' 

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0 

EXPLANATION 

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Gag1ng stat1on 

.19 

I 

l1 

Water level observation well i ' 

0 

I : 

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Compact1 on -recorder site 

I ' 

Approximate epicenter ; i 

50 MILES i 

I' 100 KILOMETERS i• 1 

L__L __ L_~--~~ ! 

----v.:--?\~ 

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33'----i--------------,~------------~--------------+-----~~~---+~--------~~~~S=~~~--t-H Sen Ctem~t• I eftd -.. , I -... r 

I 

' __ '··. ...... I 

120' 

FIGURE 1.-Selected gaging stations, observation wells, and compaction-recorder sites that showed effects of the San Fernando earthquake, February 9, 1971. Gaging stations and observation wells are listed in tables 1 and 2, respectively. 

of the release of water from Lower Van Norman 

Lake to Bull Creek and subsequent discharge to the 

Los Angeles River. 

Change in streamflow--a common response of the 

water regimen to earthquakes--is indicated by the 

records for Arroyo Seco near Pasadena (site 9) and 

San Gabriel River below Santa Fe Dam, near Baldwin Park (site 10), though the changes are minor. 

The effect of the sequence of shocks that followed 

the principal seismic shock is shown by the Arroyo 

Seco record, and the discharge increased from 5.4 

cfs (cubic feet per second), or 0.15 cubic meters 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 121 

IJl 

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Los Angeles River at 

Sepulveda Dam. Calif.(site 8) 

~-0.05 L_ ______ _L ________ L_ ______ _L ______ ~ 

(:J 0.4 .-------~--------,--------.--------, 

0.25 ~-------L--------~------~------~ 

.--------,-~---------~-------,-1-------. 

San Gabriel River below Santa Fe Dam, 

near Baldwin Park, Cal if.(site 10) 

-

3 I I I .0 L_ ______ ...J..... ________ L_ ______ _L ______ ~ 

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0~ 

z w Well at site 22. near Palmdale, Calif. :3t;:; ::< :S:z o_ 

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FEBRUARY 9. 1971 

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Well at site 23. Long Beach, Calif. 

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14.4 

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Well at site 27, 

Long Beach, Cal if. 

rr1-

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9 10 

FEBRUARY 1971 

-

-

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11 

FIGURE 2.-Fluctuations recorded at selected gaging stations and observation wells in response to the San Fernando earthquake. 
122 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

per second to 6.6 cfs (0.19 cubic meters per second). 

The San Gabriel River record reflects a minor increase in discharge. Gaging stations in the vicinity 

of the epicenter of the earthquake have not been 

accessible because of landslides and road damage; 

thus, the seismic effects on water flows in Pacoima 

Creek have not been determined. 

The records for reservoirs such as San Antonio 

Reservoir near Bradley (site 1), Santa Margarita 

Lake near Pozo (site 2), and Matilija Reservoir at 

Matilija Hot Springs (site 6), though reflecting the 

principal seismic shock, do not show significant periodic water-level fluctuations (seiches). Santa Margarita Lake (Salinas Reservoir) previously had 

shown seiche-caused water-level fluctuations in response to the Alaskan earthquake of March 27, 1964, 

and the Borrego Mountain, Calif., earthquake of 

April 9, 1968. 

Seiches, however, may be the most common surface-water effect attributable to the San Fernando 

earthquake. Countless swimming pools in the San 

Fernando Valley and in widespread adjacent areas 

in southern California were subjected to seiches and 

sloshing water. Many lost a substantial pa·rt of their 

contents through sloshing and spill. Pools as far 

away as Cypress, 30 km southeast of Los Angeles 

and 70 km southeast of the epicenter, were lowered 

as much as 30 em (centimeters) by spill. 

Abrupt and pronounced fluctuations of water 

levels in wells in response to the seismic shocks February 9, 1971, were shown by many recorders on 

observation wells. The records for several we11s also 

demonstrated some postearthquake changes in water 

levels as a result of the shock. Compaction recorders 

in Fresno, Kings, and Tulare Counties showed movements at the approximate time of the principal 

shock. 

Hydroseismic data for selected wells are given in 

table 2; the location of the wells is shown in figure 

1. The wells listed are identified by both a site number and a well number. The well numbers indicate 

the location of wells according to the rectangular 

system for the subdivision of public lands. The numbers identify the township, range, section, location 

within the section, serial number of well in the section, and the baseline and meridian in accord with 

the standard practices in California and Arizona. 

Parts of recorder charts showing fluctuations and 

water-level changes in response to the principal seismic shock at three observation wells are reproduced 

in figure 2. The records for the two Long Beach 

wells (sites 23 and 27) illustrate contrary effects, 

but records for other wells in the Long Beach area 

TABl~E 2.-Fluctuations of water level in observation wells, 

February 9, 1971 

Site 

(fig. 1) 

Well County Area Depth of of well below 

land 

surface 

(meters) 

18 ........ 18S/19E-20P1 M ...... Kings ............ Lemoore......... 55.23 19 ...... 24S/26E-34F1 M ...... Tulare ............ Richgrove...... 62.40 20 ........ 32S/28E-20Q1 M ...... Kern ............... Conner. ........ 48.04 21.. ... 32S/13E-30K14 M .... San Luis Arroyo· 

Obispo.......... Grande.......... 9.24 22 ........ 6N/10W-20P1 S ....... Los Angeles ... Palmdale........ 53.5 23 ........ 4S/13W-12K1 S .............. do ............. Long Beach... 37.82 24 ....... .4S/12W-5H2 S ................ do ..................... do............. 13.20 25 .... .4S/12W-21Ll S ................ do ................... do ............. 17.13 26 ....... .4S/12W-24M4 S ............... do ..................... do............. 13.82 27 ...... ..4S/12W-24M4 S ............... do ..................... do............. 14.87 28 ........ 6S/10W-6P S .......... Orange ........... Huntington 

Beach............ 1.5 29 ..... 3S/1W-1N1 S ............ Riverside ........ Beaumont ....... 107.8 B-2-9-7abb G ............. Maricopa, Harquahala Ariz............... Plains........... 92.7 B-2-2-24cbb2 G ............... do ............ McMicken...... 117.4 

1 In some wells, water levels changed in one direction only. 

Double Net ampli~ change tude rise ( +) 

(mm)' or 

24 

152 

140 

6 

76 

174 

920 

380 

1070 

590 

244 

85 

107 

30 

fall (-) 

(mm) 

-24 

-143 

-125 

-6 

-9 

-174 

+46 

-122 

+340 

+150 

-15 0 

-107 0 

(sites 24, 25, 26, and others) show effects that correspond with one or the other of these examples. 

The water-level rise of 1.07 m (meter) in the well 

at site 26, near Long Beach, was the greatest change 

observed; subsequently the level declined 0.74 m in 

2 hours and an additional 0.24 m in the next 24 

hours. The trace was quite similar to that for the 

well at site 27 (fig. 2). The well at site 22, near 

Palmdale, demonstrates a direct response to the 

principal shock and is representative of the records 

at many observation wells. 

The most dramatic water-related effects of the 

seismic shocks were on hydraulic structures such as 

dams, reservoirs, water tanks, water mains, pipelines, and sewer facilities. Many incidents of destruction, rupture or other damage, and associated 

loss of water-supply services occurred in the San 

Fernando Valley and adjacent areas. 

· The-van Norman Lakes (fig: 3), a series of· reservoirs at the head of the San Fernando Valley, suffered severe damage. The lakes are part of the Los 

Angeles Aqueduct water-supply system and provide 

part of the water supply to the local area. 

The earthfill dams on both the Upper and the 

Lower Van Norman Lakes (sites A and B, fig. 3) 

were severely damaged by the earthquake. The dam 

at the upper lake moved about 2 m downstream and 

the crest slumped substantially. The dam on Lower 

Van Norman Lake, initially completed in 1918, was 

fractured, the crest slumped, and a large part of the 

upstream concrete facing of the dam slid into the 

reservoir. (See section by Youd and Olsen.) One of 

the two intake towers was destroyed. Fortunately the 

dam was not breached. At the time of the earthquake 

Lower Van Norman Lake (capacity, 20,500 acre-ft) 
~ 

118.22'30" 

0 1 2 MILES 

0 2 KILOMETERS 

FIGURE 3.-Map showing location of hydraulic structures damaged by the San Fernando earthquake and of impediments to ground-water flow. 

1-:3 

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124 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

was being filled and contained about 11,000 acrefeet of water at a level 7.6 m below the spillway 

crest. A water-surface surge of 0.6 m was recorded 

at the time of the principal shock. The surge probably was caused by the shock, the destruction of the 

dam facing, and landslides near the spillway. 

Prompt opening of the available discharge facilities at Lower Van Norman Dam started lake-lowering. operations necessary to reduce the hazard of 

breaching the dam; by February 15 the levels had 

been lowered more than' 6 m. The record for Los 

Angeles River below Sepulveda Dam (fig. 2), at a 

point 15 km downstream from Lower Van Norman 

Dam, illustrates the manner in which water discharged from Lower Van Norman Lake reached the 

Los Angeles River on February 9. Effective operations at the dam were expedited by prompt decisions 

by local authorities. The speedy evacuation of residents from the area downstream from Lower Van 

Norman Lake was based on the awareness of personnel of the city of Los Angeles of the potential extent 

of flooding if the dam were breached. 

Other facilities of the Los Angeles Department 

of Water and Power also suffered heavy damage. 

Many water mains in the Sylmar and San Fernando 

areas were ruptured by the seismic shocks. The damage was particularly heavy along Foothill Boulevard 

(fig. 3) in the vicinity of the San Fernando fault. 

Damage to water-distribution facilities becomes evident readily through reduction or interruption of 

water serviee. Damage to sewer lines and systems 

is less obvious, however, and may not become evident for many months. Damage to two aqueducts cut 

off water service to nearly 10,000 homes in Los 

Angeles for a short period. Because of the damage 

to the Van Norman Lakes, the Los Angeles water 

supplies normally transported by the Los Angeles 

Aqueduct through the lakes were diverted to other 

reservoirs in the system after February 9. 

In the city of San Fernando, damage to water 

wells interrupted water service to about 17,000 residents. Tanker trucks were put into service to supply 

basic needs pending the restoration of water-supply 

and distribution facilities. 

Many water tanks were destroyed by the earthquake. Elevated tanks appeared to be particularly 

susceptible to damage. A short northwest-trending 

break of uncertain origin north of the Olive View 

Hospital at Sylmar passed under and apparently 

caused rupture of a large steel water tank (site C, 

fig. 3). An elevated water tank at a trailer park in 

Lopez Canyon (site D, fig. 3) was destroyed; in the 

process the tank was moved about 30 m northwest 

from its pad. The top and sides of a steel aboveground tank near the mouth of Lopez Canyon (site 

E, fig. 3) were severely battered by wave motion in 

the tank. An elevated fiberglass tank near the northwest shore of Lower Van Norman Lake (site F, 

fig. 3) literally exploded when it struck the ground, 

as shown by the shredding of the fibers. In contrast, 

a concrete tank set in the ground near the Sylmar 

Post Office (site G, fig. 3) was not damaged. 

Studies of the ground-water resources of the upper San Fernando Valley by state, county, and local 

agencies, particularly by the California State Water 

Rights Board (1962) and the Los Angeles Department of Water and Power have indicated the presence of several impediments or barriers to groundwater flow. Two of these impediments are indicated 

in figure 3. The east-west impediment passing 

through the city of San Fernando closely parallels 

the San Fernando fault, the zone of ground rupture 

from the February 9 earthquake. This barrier marks 

the boundary between the Sylmar and San Fernando 

hydrologic subareas of the upper Los Angeles River 

valley-fill area. The investigations have indicated 

confined ground-water conditions in the Sylmar 

subarea. 

Review of water-level altitudes in the Sylmar and 

adjacent San Fernando subareas in 1938, 1944, 1958, 

and 1970 indicates that changes in ground-water 

levels have not been great, generally less than 6 m, 

north of the San Fernando barrier and east of the 

northwest-trending barrier. Water levels on opposite 

sides of the barrier south of San Fernando, however, 

are markedly different, with the levels southwest of 

the barrier as much as 80-90 m lower. 

Postearthquake data are being obtained by the 

Los Angeles Department of Water and Power as 

part of the regular monitoring program. These data 

should provide information significant to assessing 

the effects of the earthquake on the barriers and on 

ground-water flow. In the immediate postearthquake 

period, water-level rises could be expected in some 

areas following cessation of pumping as a result of 

power interruption and damage to wells and distribution facilities. 

The quality of water in distribution systems was 

affected temporarily by the extensive disruption of 

the facilities, mains, and pipelines caused by the 

seismic shock combined with the rupture and damage to the mains. The sediment content of the water 

supplies remained high for a time following restoration of services. 

Facilities of the California Water Project, notably 

the nearly complete Castaic Dam and powerplant, 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 125 

near the epicenter of the earthquake, as well as the 

California Aqueduct and tunnels through the Tehachapi Mountains, experienced no damage from the 

shocks. 

REFERENCES 

California State Water Rights Board, 1962, Report of referee, city of Los Angeles vs. city of San Fernando, California Superior Court, County of Los Angeles, No. 

650079: Calif. State Water Rights Board, v. 1, 258 p. 

Vorhis, R. C., 1967, Hydrologic effects of the earthquake of 

March 27, 1964, outside Alaska: U.S. Geol. Survey Prof. 

Paper 544-C, 54 p. 
DAMAGE TO CONSTRUCTED WORKS, ASSOCIATED WITH SOIL MOVEMENTS AND 

FOUNDATION FAILURES 

By .T. L. YOUD and H. W. OLSEN 

U.S. GEOLOGICAL SURVEY 

This report describes earthquake damage to dams 

and canals, transportation routes, utilities, and 

buildings in the northern San Fernando Valley that 

was caused by, or associated with, various types of 

soil movements and foundation failures. Because 

our reconnaissance was relatively brief and limited 

in scope, the information presented here is a preliminary and partial account of these types of 

damage. 

DAMS AND CANALS 

The February 9 earthquake severely damaged the 

Upper and Lower Van Norman Dams. The latter 

appeared to have been on the brink of failure, which 

would have created catastrophic inundation of the 

heavily populated area below. Eighty thousand people were forced to abandon their homes for 4 days 

while the water level in the reservoir was lowered 

to a level which would preclude flooding in case of 

further damage to the dam during strong aftershocks. On brief visits to the other major dams in 

the strongly shaken area, we observed only minor 

to negligible damage. 

In the vicinity of the Van Norman Lakes, sections of several canals were badly damaged and 

rendered unusable until major repairs could be 

made. Several flood-control dikes also suffered 

slumping, but because they were not impounding 

water at the time of the shock, their failure presented no immediate hazard. The hydrologic effects 

of the shock and the disruption of water-distribution services and related facilities are discussed by 

W aananen in this report. 

The principal damage to the Lower Van Norman 

Dam was a massive upstream slope failure which 

dislodged a major segment of the earthfill embankment and deposited it on the reservoir floor (fig 1) . 

126 

FIGURE 1.-Scarp of upstream slope failure in the Lower Van 

Norman Lake Dam. 

The slide carried with it the upstream concrete 

lining and crest of the dam and moved along a rup-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 127 

ture surface which intersected the downstream face 

of the dam at an elevation only 1.5 meters above 

water level (John R. Teerink, Deputy Director, 

California Department of Water Resources; statement presented to the Special Investigations subcommittee of the House Committee on Public Works, 

in Los Angeles, Calif., on Feb. 24, 1971) . 

The Upper Van Norman Dam, immediately above 

the lower lake, subsided about 0.9 meter and shifted 

downstream about 1.5 meters during the shock (W. 

F. Hansen, Los Angeles Department of Water and 

Power, oral commun.). Extensive cracking and 

slumping disrupted the upstream concrete lining 

of this dam, and the downstream slope of the embankment also was cracked. The concrete lining 

around the Upper Van Norman Lake was cracked 

extensively near the high-water line. 

Both the Upper and the Lower Van Norman 

Dams were constructed by the hydraulic-fill process. 

The lower dam was built in 1918 and enlarged several times since then. (Statement by J. R. Teerink 

cited above.) The upper dam was built in 1921. The 

FIGURE 2.-Canal damage caused by the Juvenile Hall slide. 
128 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

materials in the lower dam, exposed by the slope 

failure, are sandy in composition and distinctly 

layered. 

A safety inspection of the Lower Van Norman 

Dam in 1964 led to an agreement between the State 

of California and the City of Los Angeles Department of Water and Power that the reservoir operations would be restricted so that the water level was 

maintained nearly 10 feet below normal. (Statement 

by J. R. Teerink cited above.) Because the quake 

reduced the height of the dam substantially below 

the previous normal water level, it is indeed fortunate that this additional margin of safety had 

been required. 

The massive slope failure in the Lower Van Norman Dam may have been caused by seismically induced inertia forces alone or in concert with lique-

_f~ctjon _of __ the _ell_!bankment materi_a!s, tecto_n_ic d~~ ____ _ FI.G_URE il.-Collapsed structures at the Foothill and Golden 

formation, or foundation soil failures. Tectonic de- State Freeway interchange. 

formation is considered because of the surface rupturing discovered on the Mission Hills segment of 

the San Fernando fault zone near the east abutment 

of the dam and because of the possibility that undetected movements may have extended into the vicinity of the dam. Foundation soil movements are considered because of the numerous slides observed in 

the reaches above the dam (Youd, this report). 

Possible causes for the subsidence and downstream movement of the Upper Van Norman Dam 

include seismic compaction, lateral spreading of the 

embankment, and foundation movements associated 

with the landslides described by Youd (this report). 

Damage to the canals in the vicinity of the Van 

Norman Lakes was generally in the form of cracked 

and broken concrete linings and displaced canal 

banks. In nearly all places this damage was related to slumping of the canal banks or displacement of the canal structure by an underlying landslide. For example, the lining of the canal between 

the Sylmar electrical-converter station and Interstate 5 was severely disrupted in the section located 

on the Juv,enile Hall slide (Youd, this report), but 

suffered only minor damage beyond this area (fig. 

2). 

TRANSPORTATION ROUTES 

Earthquake damage blocked several major transportation routes through the northern San Fernando 

Valley and severely disrupted many others. Interstate Highway 5 was blocked in both directions by 

collapsed bridges, as were also the main lines of the 

Southern Pacific Railroad, at the Foothill Interchange complex (fig. 3). A number of other highway bridges also collapsed or were damaged beyond 

use. Slope failures, subsidence at bridge approaches, 

and buckled and displaced pavements left other 

sections of freeway, main roads, and city streets 

disrupted in varying degrees. 

Tectonic displacements in the San Fernando fault 

zone were responsible for a large part of the pavement damage caused by the earthquake. Wherever 

structures such as roadways, curbs, and walks 

crossed zones of tectonic disturbance, they were 

cracked, buckled, or displaced. In some locations 

these disruptions blocked the streets; in others, 

where the magnitude of the tectonic displacement 

was less or spread over a wider zone, the pavement 

was cracked and distorted but posed only slight 

hindranc·e to traffic. 

Thrust faulting was particularly destructive to 

pavements, leaving them fractured and vertically 

displaced at all places where fault ruptures were 

observed to cross them. Compression over finite 

zones, apparently caused by the thrust faulting, 

spectacularly buckled rigid pavement sections at 

vulnerable points and pushed walks over curbs at 

street intersections. Extensional cracks were common in the zones of tectonic rupture but were generally small enough to cause little hindrance to 

traffic; however, they will have to be repaired to 

protect the road base from water intrusion. Similar 

types of pavement damage were also produced by 

small gravitational downslope ground movements 

outside of the zones of tectonic rupture. 

Landslides also caused severe highway damage. 

For example, in Weldon Canyon just north of the 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 129 

heavily damaged Foothill interchange, a section of 

Foothill Boulevard located on a cut in the mountain side slipped down and blocked both northbound 

lanes of Interstate 5. Another landslide in a fill near 

the east shore of the Lower Van Norman Lake disrupted the southbound lanes of Interstate 5. The 

pavement was badly broken here by the landslide, 

and cracks extended into the fill to considerable 

depths-one fissure 4 meters deep was found in the 

embankment slope. Emergency repairs were made, 

and the grade was reopened to traffic within hours 

after the earthquake. 

Where the Juvenile Hall slide crossed the Southern Pacific Railroad, San Fernando Boulevard, and 

Interstate 5, the rail and roadway embankments 

subsided appreciably in places and were laterally 

displaced generally more than 0.5 meter (fig. 4). 

FIGURE 4.-Lateral and vertical displacement of the Southern 

Pacific Railroad on the Juvenile Hall slide. The lateral 

displacement of the rail exceeded that of the underlying 

embankment. 

Substantial repairs had to be made to both the highways and to the railroad before normal traffic could 

resume. 

Subsidence of the approaches to highway bridges 

was very common in the northern San Fernando 

Valley and probably resulted from seismic compaction or lateral spreading of the highway fills or 

underlying soils. Compaction and (or) lateral 

spreading also caused considerable differential subsidence in highway grades where fill sections adjoined cut sections. Examples of this type of damage were found in the Interstate 5 grade east of the 

Van Norman Lakes. 

Seismic shaking rather than tectonic ground 

movement, landslides, or local bearing-capacity failures appeared to be the primary causes of the bridge 

damage we observed. 

UTILITIES 

Extensive damage was inflicted upon the telephone, power, gas, water, and sewer systems in the 

northern San Fernando Valley communities of Sylmar, San Fernando, and Pacoima. Buried pipelines 

were particularly hard hit where breaks, probably 

numbering in the thousands, disrupted essential 

services. Above-ground facilities also were damaged. 

It took at least 2 weeks to restore essential gas and 

water services throughout the area, even with the 

aid of temporary emergency measures. 

The Sylmar electrical converter station was hard 

hit, with damage estimated at $28 million. This 

facility is particularly important because it ties 

southern California to the Bonneville electrical 

power system, and is the facility that converts the 

power from direct current to alternating current. 

The damage to this facility consisted mainly of overturned and broken elecrical equipment and ruptured underground conduits (fig. 5). Return of the 

FIGURE 5.-0verturned equipment at the Sylmar electrical 

converter station. 

cfacility to full service will probably take at least a 

year. 

A power-generating plant north of the converter 

facility was also heavily damaged and will likewise 

be out of service for some time. Substantial but less 

serious damage was sustained by substations, transmission poles and towers, and powerlines throughout the heavily shaken area. 
130 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

The extensive damage to underground pipelines 

was due in large part to the location, size, and distributed nature of the surface ruptures generated 

by the tectonic movements in the San Fernando 

fault zone. The largest fault displacements had both 

thrust and left-lateral components. Nearly every 

pipeline crossing such ruptures was either fractured 

or badly distorted. Sketches illustrating thrust and 

left-lateral movements and their effects on pipelines 

and buildings are diagramed in figure 6. Zones of 

(A) Thrust displacement 

(C) Lett-lateral dilplacement 

c.-..-> 

-

(B) V~rtical dilpl&cement 

~ .._ 

''"·"'"''~ " ~ '· ·~ """~ - (D) Extensional displacement 

(E) Localized differential displacements 

FIGURE 6.-Basic types of ground ruptures and associated 

pipeline and building damage in the northern San F ernando Valley. 

extensional cracking and zones of compression were 

associated with the tectonic ruptures. Extensional 

displacements were frequently large enough to pull 

apart or fracture pipelines. Displacements of this 

type are diagramed in figure 6D. In the compressed 

zones, many pipes were buckled and telescoped or 

thrust into manholes, commonly with relative displacements of as much as several tenths of a meter 

(illustrated in the section of "Surface faulting," by 

U.S. Geological Survey staff, this report). 

Landslides and minor downslope gravitational 

movements also contributed substantially to pipeline damage. The associated differential horizontal 

and vertical displacements commonly marked locations of pipeline breaks. For example, several breaks 

were found along the margins of, at the head of, and 

in an area upslope from the Juvenile Hall slide. 

Lateral, vertical, and extensional pipe offsets were 

observed in these breaks, and the observed offsets 

were invariably consistent with the observed surface 

ground movements. 

In the area upslope from the head of the Juvenile 

Hall slide, several extensional cracks, as much as 

30 mm wide, were found in the vicinity of the pipeline breaks. These fissures indicate downslope movements similar to those discussed by Sharp (this 

report) and are probably expressions of a poorly 

delineated landslide. 

The Sylmar electrical converter station sits 

astride the lower parts of the Juvenile Hall slide. 

Although this slide apparently caused no significant 

structural damage, many fissures were found within 

the surrounding graded yard. These fissures may 

have played an important part in the subsurface 

damage to the station. 

Some pipeline breaks occurred in areas where no 

ground fractures were detected. Yield or fatigue 

fractures were detected. Yield or fatigue fractures 

could have caused these ruptures. 

A common secondary effect of gasline and waterline breaks was disruption of the overlying surface, 

either by erosion from leaking water or in the form 

of a crater blown out by the pressurized gas. In a 

few places the gas was ignited, leading to spectacular fires. 

Damage to overhead utilities, including telephone 

and power transmission lines, consisted of tightened 

and in some places broken wires, sagging lines, and 

downed or leaning poles. Shortening or lengthening 

of the distance between poles or towers by tectonic 

or landslide movements and disturbance of the pole 

foundations by surface rupturing appeared to be the 

principal causes of this type of damage. 

BUILDINGS 

Damage to buildings, ranging from minor cracking to total collapse, occurred throughout the Los 

Angeles area. But damage in the northern San Fer-
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 131 

nando Valley communities of Pacoima, San Fernando, and Sylmar was by far the most severe and 

widespread. Major damage occurred to buildings of 

all types in these communities, including single- and 

multiple-family dwellings, light-commercial and industrial buildings, schools, and hospitals. There 

were no high-rise buildings in these communities. 

The hospitals were among the tallest buildings in 

the area, and their partial collaps·e produced most 

of the deaths and injuries, and the most dramatic 

damage of the earthquake. Part of the damage, including the collapses at the Olive View and Veterans 

Administration Hospitals, occurred in areas w_here 

no significant soil or foundation failures were 

evident. 

A substantial part of the building damage observed in our reconnaissance was directly related to 

ground rupture beneath structures. Sketches of the 

basic types of ground ruptures observed, and simplified diagrams depicting the types of damage inflicted to buildings located athwart these ruptures, 

are illustrated in figure 6. 

Almost all buildings overlying thrust faults, with 

or without accompanying lateral displacements, suffered severely. Figure 6A illustrates the type of distress such displacements induced in overlying structures. A house wrecked by a thrust fault is shown in 

figure 7. Commonly, buildings undercut by such rupFIGURE 7.-House damaged by thrust-fault displacement. 

tures were thrust horizontally, in some places being 

forced against adjacent buildings. (See photograph 

in section on "Surface faulting," by U.S. Geological 

Survey staff, this report.) 

As previously mentioned, extensional cracks, accompanied to some degree by vertical and horizontal 

components of fault displacement, were common 

throughout the San Fernando fault zone. Similar 

cracks were also formed on slopes by weakly developed landslide movements. Where cracks of this 

character passed beneath light buildings, their 

foundations often fractured in tension, which in 

turn opened up cracks in the overlying structures 

(fig. 6D). An example of this type of damage was 

observed in a house on Tucker A venue east of Rajah 

Street in the area sloping down toward Pacoima 

Wash. Downhill displacement of no more than a few 

tenths of a meter opened up a crack which broke 

through the street and walks, passed beneath the 

house (fig. 8), and continued on down the slope 

FIGURE 8.-House damaged by tension crack. 

behind. The slab foundation of the house was fractured by tension cracks as was the house itself. 

Damage was severe, and the house was designated 

as unsafe. Weakening of this house by foundation 

failure probably made the house more vulnerable 

to additional shaking damage. 

The San Fernando Valley Juvenile Hall was severely damaged where it was underlain by the 

Juvenile Hall slide. The ground in the slide zone 

was ruptured in a complex manner, having components of vertical (fig. 6B), lateral (fig. 6C), and 

extensional (fig. 6D) displacement. In one part of 

the area, it appeared that the foundation and underlying soil had fractured into blocks which moved 

relative to one another in a manner illustrated by 

figure 6E. This behavior suggests that blocks of soil 

were temporarily supported by an underlying liquefied or partially liquefied layer. Evidence for this 

is the existence of sand boils nearby and the very 

low gradient down which the landslide moved. 
132 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

SUMMARY 

Soil movements and foundation failures were associated with much of the damage to structures in 

the northern San Fernando Valley. Tectonic movements of various kinds, including compressional 

(thrust), vertical, lateral, and extensional displacements, were particularly damaging to underground 

utilities and all types of overlying structures. Landslide movements on nearly level ground inflicted 

extensive damage to pipelines, canals, and light 

buildings such as the Juvenile Hall but caused little 

damage to heavier structures on massive foundations such as the principal building at the Sylmar 

electrical converter station. Small landslide movements in hilly areas generated minor cracks and 

displacements that caused heavy damage to overlying single-family dwellings. Massive landslides on 

steep natural slopes and constructed embankments 

blocked major highways at several locations, and 

nearly breached the Lower Van Norman Dam. 
PRELIMINARY STRUCTURAL LESSONS FROM THE EARTHQUAKE 

By HENRY J. DEGENKOLB 

H. J. DEGENKOLB AND ASSOCIATES, ENGINEERS 

It is always risky to try to anticipate lessons from 

a disaster before all of the data, studies, and research are available. In this particular earthquake 

there are certain complicating factors that may 

emphasize this fact. However, this very statement 

emphasizes one or two factors that greatly influence the structural engineer's attitude when approaching a structural design problem. 

First and foremost, it is very clear that the 

ground motions and stability of the foundation 

greatly affect the performance of the structure situated thereon. It is clearly evident that certain 

structures situated within a very narrow band of 

great ground disturbance in this earthquake were 

affected much more than those outside of this band. 

There is a band, for example, going diagonally 

through the San Fernando Juvenile Hall, the Boy's 

Market at Glenoaks and Hagar, and certain industrial areas north of the San Fernando Airport where 

buildings of identical or similar construction were 

damaged much more than structures only 50 or 100 

feet away. Some way must be found to locate precisely these areas of great ground deformation so 

that the structural engineer can either avoid these 

areas or provide suitable foundations so that the 

buildings can perform as a unit. 

Secondly, there may be ground or rock configurations that will shake the superimposed structure to 

a greater intensity than anticipated from past 

records. 

It is reported that the closest strong motion record of this earthquake, taken at or near the summit 

of a fractured rock formation, indicated ground 

accelerations of more than 100 percent g horizontal 

and 70 percent g vertical. For 12 seconds, the recurring motions were recorded at about 50 percent 

g. This would indicate that ground motions for even 

a moderate earthquake may be much greater than 

assumed by many engineers and that the required 

strength or ductility may be much greater than 

anticipated by many engineers and the current 

building codes. The very fact that such strong 

ground motions continued for such a long time 

would indicate that structural materials may have 

to undergo many more cycles of stress in the plastic 

range than many previous tests and research studies 

have assumed. While it may be argued that such 

conditions are highly unusual, many buildings, 

dams, bridges, towers, and so forth, may be and 

are located on these unusual sites and may be subjected to these extreme motions. At the very least, 

some method must be devised to recognize those 

unusual sites that are subject to such large forces 

for so long a time. It is interesting to note that these 

high concentrations of force, motion, or energy are 

on some form of rock rather than on saturated alluvium. They occurred with a smaller earthquake 

than the previous (El Centro 1940) maximum record on alluvium. I 

If it can be assumed that the damage caused by 

ground vibration as compared to ground permanent 

deformation would be typical or representative of 

the anticipated design earthquake, certain rather 

disturbing observations can be made even at this 

preliminary stage. However, these observations must 

be accepted with great caution, since at present 

there is no clear way of differentiating damage due 

to vibration from damage caused by permanent 

ground deformations. 

Observation 1 concerns light industrial or warehouse structures using tilt-up concrete or reinforced 

masonry walls with plywood diaphragm roofs. Many 

walls pulled away from diaphragms at forces approximating or exceeding 100 percent g. It is not 

enough to rely on the plywood nailing to attach the 

walls to the roof diaphragm. The main framing 

members-girder, beams, and joists-must be anchored substantially to the walls in addition to the 

plywood nailing. Many roofs failed when the nails 

133 
134 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

pulled out of the diaphragms even though the plywood sheet splices were staggered. 

Observation 2 concerns the horizontal reinforcing 

in reinforced concrete block walls. The 1952 Kern 

County ,earthquakes showed that horizontal reinforcing should not be concentrated only at foundations and bond beams but must be distributed 

throughout the height of the wall. Over the years 

this uniform distribution has been minimized to the 

point where only prefabricated wire ties are used at 

about 24 inches center to center vertically. Various 

failures in this last earthquake strongly indicate 

that this is not sufficient and that more substantial 

reinforcement is required, especially in stack bond 

construction. 

Observation 3 concerns the use of frame action 

concrete framing (bending of beams and columns) 

to resist major earthquake forces. The October 1, 

1969, Santa Rosa earthquake gave a preview of trouble to come when very well designed structures had 

large deformations causing much nonstructural 

damage in a comparatively small (Richter 5.6) 

earthquake and caused spalling in 80 percent of the 

columns. With the present somewhat larger (but not 

major or great) earthquake, the example of the 

Olive View Sanitarium main building and the 

smaller two-story building to the north, should give 

engineers and code-writing authorities nightmares. 

Even though the building remained standing, all but 

one of the exits were unusable, and the emergency 

power equipment was inoperative owing to building 

failure. A slightly longer earthquake with the same 

amplitude of motion or magnitude of accelerations 

would probably have caused collapse of the main 

structure with a greater loss of life. Some more stable 

method of framing must be devised. 

Observation 4 concerns the use of nationally acceptable specifications for the use of structural materials. Most specifications are designed to yield 

certain minimum specified or reliable strengths. 

Strength alone is not enough in earthquake-prone 

areas. Both strength and ductility are required. 

Present specifications for concrete buildings in particular (probably also for other materials) permit 

details of steel reinforcing that are not appropriate 

in seismic areas although they are accepted in present building codes. Most California engineers use 

more column ties than required by national standards. The lack of sufficient column ties was probably 

a cause of much column disintegration as exhibited 

in this earthquake. Building codes must be reexamined to improve requirements relating to hooks, 

bonding, column ties, through reinforcing, bar laps, 

and other items. 

Observation 5 concerns electrical and mechanical 

equipment. Some transformers, boilers, pumps, and 

panels were displaced and rendered unusable. Emergency power supplies in some cases were inoperative 

because of building failures. In future designs, it 

will be necessary to consider the effects of earthquakes on the equipment to a greater extent than at 

present. Equipment must be more adequately braced 

and anchored. 
CONTRIBUTIONS FROM NATIONAL OCEANIC AND ATMOSPHERIC· ADMINIS'TRATION, 

EARTHQUAKE ENGINEERING RESEARCH INSTITUTE 

A PRELIMINARY REPORT OF NEAR-FIELD SEISMIC MONITORING OF THE SAN FERNANDO 

EARTHQUAKE AFTERSHOCK SERIES 

By A. F. ESPINOSA, E. R. ENGDAHL, A. C. TARR, and S. BROCKMAN 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

Two seismological field parties from the National 

Oceanic and Atmospheric Administration, National 

Ocean Survey, were dispatched to southern California immediately following the San Fernando 

earthquake of February 9, 1971 to monitor aftershock activity in the immediate vicinity of and near 

the epicenter. During the early morning hours of 

February 10, a four-man team from the Special 

Projects Party at Las Vegas, Nev., installed a continuously recording tripartite array (fig. 2) centered 

on, and at distances of 5 to 10 km from, the provisional epicenter. The total number of Special Projects Party stations was increased to 28 at the end 

of the first week. A three-man team from the Albuquerque Seismological Center installed five self-contained units between 20 and 35 km from the 

epicenter. 

The instrumentation of the tripartite array consisted of two systems-a short-period vertical seismometer recording on .smoked paper, and highergain, multilevel, three-component seismometers recording on magnetic tape. The near-field instrumentation consisted of self-contained, short-period seismometers recording on magnetic tape. 

The locale of the Sen Fernando earthquake is 

shown in figure 1. Figure 2 is a topographic map 

centered on the section of the San Gabriel Mountains 

in which the tripartite array was deployed. The locations of the three stations were: 

SCF 34°26.0' N. 

SGM ...... 34°22.9' N. 

SHC ...... 34°30.4' N. 

118°17.3' w. 

118°23.0' w. 

118°21.7' w. 

These stations were in operation 24 hours after the 

main shock. A sample smoked-paper seismogram is 

shown in figure 3. 

Of the hundreds of aftershocks detected by these 

instruments, most were in the 2.0 to 3.0 magnitude 

range, many were larger than magnitude 3.0, and 

some were as small as magnitude 1.0. Aftershocks 

with magnitudes larger than about 3.0 show clipped 

amplitudes on the smoked-paper records. On the 

basis of the frequency of aftershocks, the zone of 

activity appears to be closest to station SCF. (See 

fig. 4.) Figure 5 depicts the decay of aftershock 

occurrence at station SCF; the frequency of occurrence falls quite rapidly from a maximum of 45 

events per hour on February 10, and 15 events per 

hour on February 11, to 6 events per hour on February 15. On the basis of S-P times at station SCF, 

the aftershocks occurred over a range of 5 to 45 km 

from this station with a mode of about 15 km. Variations in signal character were clearly evident and 

wave frequencies ranged from 10 to 25 Hz. Variability in the sense of first motion at SCF is indicative either of the areal extent of the aftershock 

zone or of a change in the focal mechanism itself for 

individual aftershocks, or both. 

Station LSM, at Little Skull Mountain, Nev., is a 

sensitive installation about 318 km from the aftershock zone; this station was capable of monitoring 

the principal aftershocks in the series. Operating 

gain at LSM is 2 million at 10 Hz, and 220,000 at 

1.0 Hz. Figure 6 depicts the hourly counts of aftershock detection, which fell from 20 per hour at the 

beginning of the sequence to 4 per hour at 2400 

GMT, February 10, 1971; a cumulative count for the 

period was 292 events. 

The cooperation of the following individuals is 

acknowledged: W. K. Cloud, J. Hoffman, K. King, 

L. M. Murphy, J. Peterson, and C. Stepp of the 

National Ocean Survey, and C. Allen of the California Institute of Technology. 

135 
136 

1 go 

THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

'-

SAN FERNANDO 

~ , ....... 

lOS ANGElES 

SCAlE 

0 10 20 KM. 

FIGURE 1.-Index map of part of Los Angeles County, showing some of the major fault systems in the epicentral area, 

place names, and the epicenter of the main shock (star). 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

. ::-:J\1:,' 

Y----~:.!; t'}!__..~.I;.,-!~:+:::::=:==== .. =,.=, .. =,':' . -: l. ·:: r~.c~ ~ :~ : ~ ~ Sn.6 M-<.1 rit1 ---- ?.:"\ __ ... ~. \) ,\ 

.. ~ 

"' 

... "' 

0 

0 

0 

0 

~ 

137 

FIGURE 2.-A topographic map of San Fernando and the San Gabriel Mountains, showing the epicenter location (star). 

SCF, SGM, and SHC are the recording sites of the NOAA/ NOS station locations. 
138 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Smoked-paper seismogram from station SCF. In stallation was at 0800 GMT, February 10, 1971. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

OSCF 

4001-

0 

.. 

:c 300 1- C> 

.... "" 

.... 

... 

~ ""' 

C> t::.SGM ::r:: 0 ., 

.... 

C> 

"" .... 

... 200 1- ~ 

= t::. 0 0 z 

0 

0 t::. t::. 

100 ~ 

I I I I 

9 10 11 12 13 14 

FEBRUARY 

0 

0' 0 

0 

t::. t::. 

I I 

15 16 

1971 • 

0SCF 

!::. SGM 

OSHC 

0SHC 

I I 

17 18 

-

-

-

-

I 

19 20 

FIGURE 4.-Number of aftershocks per day, as a function of 

time, for the near-field stations SCF, SGM, and SHC. 

139 
140 

55 

a: 

::::t 

Q 

:z: 

a: 

w.l 

A.. 

en 

:.::: 

(,) 

Q 

:z: 

en 

... 

Q 

a: 

w.l 

GD 

:IE 

::::t 

:z: 

10 

THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

SCF 

12 

FIGURE 5.-Hourly frequency of aftershocks detected at station SCF, as a function of time (GMT). 

= CD 

= 

..... 

V) 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 141 

25r-------------------------------------------------------------------~ 

LSM(~~318 KM) 

AFTERSHOCKS PER HOUR 

FIGURE 6.- Hourly frequency of occurrence of aftershocks, as a function of time (GMT), for station LSM, Nevada. Instrument gain at 1.0 Hz is 220,000, and at 10 Hz is approximately 2 million. Distance to the seismically active area is about 

318 km. 
PRELIMINARY FAULT-PLANE SOLUTION FOR THE SAN FERNANDO EARTHQUAKE 

By W. DILLINGER and A. F. ESPINOSA 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

The February 9, 1971, San Fernando earthquake, 

Richter magnitude 6.6, caused extensive damage 

in the Los Angeles and San Fernando areas. The 

National Ocean Survey (NOS) requested recordings for the main event from the Worldwide Network of Standard Seismographs (WWNSS) in order 

to evaluate the focal mechanism. 

The preliminary hypocenter parameters for this 

earthquake, as reported to the NOS by California 

Institute of Technology, are: 

Origin time: 14: 00: 41.5 GMT. 

Epicenter: 34°24.0' N. 118°23.7' W. 

Depth: 13 km. 

A preliminary set of focal-mechanism solutions 

from P-waves recorded on short- and long-period 

seismograph systems is presented herein. In table 

1 are listed the observed data covering an epicentral 

distance range from 0.3° to 134.7°. The azimuths 

in this table and all directions presented in this 

paper are measured clockwise, north through east. 

The last seven entries in this table are for PKP 

readings. The sense of motion is listed as read on 

the short-period (SP) and long-period (LP) recordings, and as reported by the NEIC of NOS. A 

quality-grading control is listed next to the SP and 

(or) LP sense of motion as read by NOS personnel; 

for instance: G =good, F =fair, P =poor, etc. The 

132 short-period observations are used for the shortperiod solution and are plotted in an equal-area 

projection in figure 1. In the long-period solution, 

47 observations are used, and are plotted in figure 

3. Figures 1 through 4 represent the lower hemisphere of the focal sphere. 

The procedure for finding the best fitting focal 

planes is incremental. Two orthogonal planes are 

incrementally rotated through three orthogonal 

angles to sample the focal sphere completely. For 

142 

each position of the planes the numl;>er of observations in agreement with that orientation is computed as the score. The orientation of the planes 

which gives the highest score is selected as the best 

solution. These score values are then plotted at the 

positions of the poles of the planes and are contoured to show the approximate limits of the solution. A paper discussing these procedures was presented at the annual meeting of the Seismological 

Society of America in April 1969. (Focal Mechanism Determinations Using P- and S-Wave Data, 

by S. T. Harding, W. H. Dillinger, and A. J. Pope.) 

The contours in figures 2 and 4 represent bounds 

on the poles of the planes. The contours that parallel the B plane limit the movement of the pole of 

the A plane. The contours in the vicinity of the A 

plane bound the pole of the B plane. If the limitation in accuracy caused by the incremental process 

is considered, ·then any pole that falls within a 

given contour may be selected and will give a solution which has a score represented by that contour. However, pairs of poles must be selected to 

give orthogonal planes. The edge of the contoured 

regions must be considered to be approximate owing 

to the incremental sampling. In the solutions presented here the increment used was 5°. 

As can be seen from the solution diagrams; figures 2 and 4, the B plane is well determined by the 

P-wave data shown here, whereas the A plane is 

not. In figure 2 the inner contours represent solutions from the short-period data which have 90 percent of the observations in agreement, and the outer 

contours represent solutions with 88 percent agreement. These show that the pole and the strike of the 

A plane can vary over a range of about 60°. The 

dip of the A plane can vary over about 15° but 

not independently of the strike, as the pole of this 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 143 

plane is confined to a narrow band shown by the 

contours parallel to the other plane. 

Figures 3 and 4 show the P-wave fault-plane 

solution using 47 long-period observations. The solutions from these data for planes A and B are 

listed in table 2; however, they are only good representative samples and do not include all the possible solutions. The region of acceptable solutions is 

shown by the contours in figure 4. The inner contours show the approximate boundaries for solutions with 47 consistent observations. The outer contour is the approximate boundary for solutions 

which give 46 consistent observations from a total 

of 47. 

Inspection of the long-period data and of the contours plotted for that solution shows that a plane 

striking 90° and dipping southward will also satisfy 

the data with all stations consistent. 

The short-period data yield two solutions with 

119 consistent observations from a total of 132. 

These results are as follows: 

A plane B plane 

Dip Dip Strike Dip direction Strike Dip direction degrees degrees degrees degrees degrees degrees 

120.0 40.0 210.0 120.0 50.0 30.0 

90.48 43.96 180.48 120.0 50.0 30.0 

The above discussion and the accompanying diagrams clearly show the limits of the solutions and 

the possible alternate solutions. The long- and shortperiod data available are generally in good agre~­

ment. 

The direction of maximum shear obtained from 

geodetic surveys indicates an east-west direction 

near the Santa Susanna Fault and the Van Norman 

Reservoir. The maximum shear near Newhall has 

a northwest direction, which is close to the San 

Gabriel Fault. (See section by C. A. Whitten, this 

volume.) The B plane discussed in this paper is well 

determined and generally agrees with the strike 

directions of the San Gabriel Fault and the direction 

of maximum shear noted above. If an east-west 

plane is selected from those possible solutions given 

by our data, then it will be in agreement with the 

maximum shear direction in the vicinity of the Reservoir geodetic control station. 

A tentative interpretation of the information currently available in our offices would seem to favor 

the preliminary short-period P-wave solutions, with 

an east-west strike and a plane dipping toward the 

south. This preferred solution is consistent with the 

long-period P-wave data and is shown pictorially 

in figure 5. However, the contours in figures 2 and 

4 indicate that many interpretations are possible, 

and, indeed, the advantage of the contours is to 

show the various interpretations which will fit the 

data. 

The results presented in this short note are subject to additional interpretation as further information becomes available and as the S-wave data 

are incorporated in the final fault-plane analysis. 

ACKNOWLEDGMENTS 

We are grateful to the Canadian, WWNSS, and 

the directors of the cooperating seismological stations who made their seismograms available for 

this study. The following also gave support for this 

report: L. M. Murphy, S. T. Algermissen, W. V. 

Person, E. R. Engdahl, G. J. Dunphy, R. Hansen, 

R. Robertson, and the Operating Branch of NOAA 

Computing Division. 

TABLE !.-Observed data 

Sense of motion Delta 

STA SP LP NEIC degrees 

MWC 

PAS 

BLG 

ISA 

SYP 

GSC C 

LAC C G 

PLM 

PKF 

PRI 

BTY 

MCV 

SMN 

CPX C G 

BCN D G 

GLA 

SLD 

TNP D 

TPH 

JAS D 

MHC 

MNV D G 

MDC 

BRK 

OLC 

KNB D G 

NRR D 

REN D 

EUR 

MMA C F 

ORV C PF 

BMN D 

GCA D PF 

MIN 

EKO D 

TUC C G 

ELK D G 

DUG D VG D VG 

FHC 

UBO D G D G 

ALQ C G 

BMO D VG 

COR 

c .3 

D .3 

D .6 

D 1.3 

c 1.3 

D 1.6 

c 1.6 

c 1.6 

c 2.2 

D 2.6 

c 2.8 

D 2.9 

c 3.0 

3.1 

3.3 

c 3.3 

D 3.5 

3.8 

c 3.8 

D 3.9 

c 4.0 

D 4.0 

c 4.5 

c 4.7 

c 5.1 

5.2 

5.3 

5.3 

c 5.4 

c 5.4 

c 5.7 

6.1 

6.1 

c 6.5 

6.7 

6.7 

D 6.8 

c 7.3 

c 7.7 

9.2 

9.8 

10.5 

D 10.9 

Azimuth 

degrees 

121.1 

143.0 

243.5 

356.7 

276.4 

54.6 

89.4 

128.6 

312.4 

313.8 

27.5 

40.3 

25.2 

36.1 

60.4 

113.2 

320.1 

14.0 

14.0 

335.5 

319.0 

2.6 

321.6 

319.0 

316.9 

58.3 

347.7 

347.9 

20.1 

97.0 

335.1 

8.4 

63.0 

337.6 

17.1 

105.9 

20.6 

35.8 

326.9 

47.2 

83.4 

4.2 

341.0 

Focal 

angle 

degrees 

96.33 

96.33 

88.7 

56.7 

56.8 

56.7 

56.7 

56.7 

56.6 

56.7 

56.6 

56.5 

56.5 

56.5 

56.1 

56.1 

56.1 

56.1 

56.4 

56.1 

56.1 

56.4 

56.1 

56.0 

55.5 

55.5 

55.5 

55.5 

55.5 

55.5 

55.5 

55.7 

55.7 

55.5 

55.4 

55.4 

55.3 

55.0 

54.7 

53.9 

53.6 

53.2 

53.0 
144 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

TABLE !.-Observed data-continued TABLE !.-Observed data-continued 

·----

Sense of motion Focal Sense of motion Focal Delta Azimuth angle Delta Azimuth angle STA SP LP NEIC degrees degrees degrees STA SP LP NEIC degrees degrees degrees 

GOL D p D VG D 11.7 59.2 52.5 NOR c 57.9 9.7 23.8 

DEN D p D VG 11.9 59.3 52.1 KTG c 60.1 22.7 23.5 

NEW c ? D VG 13.9 3.5 50.3 ARE c 67.4 130.6 21.6 

HHM D 14.3 11.8 50.1 PNS c 69.2 128.1 21.0 

NTI c ? 14.3 3.8 50.1 LPB c 69.6 128.0 20.8 

VIC D p D G 14.6 346.6 49.9 TRO c 71.7 14.4 20.4 

LAO D 15.4 33.2 49.7 KEV c VG c VG 73.1 11.9 19.9 

JCT c G c G 16.2 98.8 48.2 VAL c VG c VG 73.6 37.8 19.9 

SES c G D G c 16.9 16.3 47.5 SOD c p 75.2 13.2 19.5 

DAL c p D VG c 18.1 88.8 47.7 CPP c 76.4 137.1 19.1 

FAY c 19.8 78.1 40.6 KJN c F c VG 78.2 14.4 18.7 

FSJ c 20.5 350.1 37.5 UPP c 79.3 20.8 18.4 

SLM c G c VG 23.0 71.1 34.9 NUR c G c VG 80.7 17.5 17.9 

DBQ c VG c VG 23.1 61.2 35.0 PEL c 80.7 141.0 17.9 

FFC c G c VG 23.4 24.4 34.5 DBN c 80.8 31.3 17.9 

OXF c 23.9 81.4 34.5 COP c G c G c 81.0 25.7 17.8 

NOL c p 24.3 92.6 34.8 PTO c G c VG 81.0 46.0 17.8 

CHI c G 25.2 63.6 33.5 ucc c G c G 81.3 32.6 17.7 

LHC D G c VG 25.7 48.2 33.3 KRL c 84.4 31.9 17.0 

SHA c p c G 25.7 89.7 33.1 TOL c 84.4 44.7 17.0 

CPO c F 26.8 77.9 32.4 BUH c 84.6 32.3 16.9 

MLF c p 27.6 70.1 32.1 GRF c 85.1 30.1 17.0 

ATL c F c G 28.2 82.2 31.7 PRU c 86.2 28.2 16.7 

YKC c G c VG 28.2 3.8 31.7 FUR D 86.3 31.0 16.7 

FCC c G c G 29.2 26.0 31.9 KHC c 86.5 29.2 16.6 

CLE c F c VP 29.8 65.2 31.5 IFR c 87.9 50.1 16.1 

BLA c G c G 30.8 73.6 30.9 HNR c VG c VG c 88.5 257.6 16.2 

MRG c 31.0 68.8 30.9 TRI c 89.3 31.3 16.0 

SCB c VG 31.6 61.0 30.9 CMP c 94.1 24.9 15.6 

KDC D F 32.7 326.1 30.5 ESA c 96.1 262.4 15.4 

BLC c 32.9 17.7 30.5 ANP c 97.9 307.6 15.2 

LPS c 33.1 119.9 30.7 ATH c 99.9 29.5 15.7 

wsc c G 33.2 69.7 30.7 DAR c p 114.0 271.1 6.2 

GEO c c 33.3 69.9 30.6 ASP c 117.0 258.7 6.3 

PMR c c G 33.5 333.7 30.5 BNG D 124.1 55.2 6.3 

OTT c G c VG c 34.2 58.2 30.3 POO c 126.1 345.5 6.2 

GWC c 34.9 40.6 30.0 KLG c 130.1 256.5 6.3 

INK c 35.0 350.7 30.1 MEK D 130.9 262.8 6.3 

COL c G 35.3 338.7 29.8 MUN D 134.7 257.0 6.3 

MNT c 35.6 58.1 29.7 

HVO c 35.9 255.0 29.6 

KIP c G c PF 37.1 260.1 29.4 

BNH c 37.3 59.7 29.4 

WES c c G 37.4 63.4 29.4 TABLE 2.-P-wave fault plane solutions long period data SFA c G c VG c 37.6 55.6 29.4 

GMA c 40.1 333.8 28.9 

SCH c VG c 40.9 43.8 28.6 

MBC c 41.9 359.6 28.6 A B RES c G c VG c 42.0 9.1 28.6 

FBC c G c G c 42.2 30.4 28.7 

BHP c F c G c 43.7 116.1 28.2 Direction Direction 

BEC c G 44.5 76.8 28.3 Strike Dip maximum Strike Dip maximum 

ADK c 44.7 311.4 28.1 degrees degrees dip degrees degrees degrees dip degrees 

SJG c G c G c 49.1 95.4 26.9 

STJ c G c G c 49.9 53.8 26.6 120.0 40.0 210.0 120.0 50.0 30.0 

QUI c 50.8 124.1 26.2 160.0 50.0 250.0 118.07 48.44 28.07 

ALE c G c G c 51.8 7.9 26.3 180.0 60.0 270.0 116.57 52.24 26.57 

CAR c 52.5 104.2 26.0 145.0 45.0 235.0 117.76 48:36 27.76 

MDZ c 52.5 104.0 26.0 152.55 51.13 242.55 120.0 50.0 30.0 

CUM c 54.4 102.1 25.3 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 145 

CALIFORNIA 1971 FEB 9 1400 41.7 34.39N 11B.39W 16KM 

P WAVE FIRST MOTIONS 

N 

COHPRESSION l!l 

DILRTRTION X 

X 

X X 

X X X lllx 

iljl!l tll: X l!ll!l X X 

l!l l!l X!l # X X 

~l!l l!l X 

l!l l!l l!l 

l!l l!l l!l l!l X ~!!I l!l X X X l!l X l!l l!l X l!l \.1!1 l!l 

l!l 

l!l~~ l!ll!l ltl II!JI!l l!l l!l l!l l!l 

l!l l!l l!l 

l!ll!l 

l!l 

l!l l!l 

l!l l!lJ l!l l!l l!l 

' l!l l!ll!l e l!l l!l l!l 

l!l 

l!l 

FIGURE 1.-P-wave sense of motion for the San Fernando earthquake short-period data. 
146 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

CALIFORNIA 1971 FEB 9 1400 41.7 34.39N 118.39W 16KM 

P WAVE SOLUTION 

N 

B 

A 

FIGURE 2.-Lower hemisphere of focal sphere. Fault plane solution from P-wave short-period observations. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

CALIFORNIA 1971 FEB 9 

P WAVE FIRST MOTIONS 

DILATATION X 

1400 41.7 34.39N 

X 

[!] 

X 

[!]l!l 

[!] [!] 

118.39W 

N 

X 

[!] 

[!] 

[!] 

16KM 

X 

[!] 

[!] 

[!] 

[!] 

X 

X 

[!] 

[!] 

1!1 

[!] 

FIGURE 3.-P-wave sense of motion, long-period observations. 

[!] 

[!] [!] 

[!] 

147 
148 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

CALIFORNIA 1971 FEB 9 1400 41-7 34.39N 118.39H 16KM 

P HAVE SOLUTION 

N 

8 

A 

FIGURE 4.-Lower hemisphere of focal sphere. Fault plane solution from P-wave long-period observations. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

SAN FERNANDO EARTHQUAKE PRELIMINARY FAULT PLANE SOLUTION 

FIGURE 5.-Perspective view of epicenter location and preliminary fault planes. 

149 
SOME OBSERVATIONS OF THE SAN FERNANDO, CALIFORNIA 

EARTHQUAKE WITH A LASER STRAIN METER 

By JON BERGER 

INSTITUTE OF GEOPHYSICS AND PLANETARY PHYSICS, UNIVERSITY OF CALIFORNIA, SAN DIEGO 

A digital interferometeric laser strain meter has 

been operating on the surface at the Camp Elliott 

Geophysical Observatory of the University of California, San Diego, for the past 18 months. The 

device has a least count strain (LCS) of 4x 10-10, 

a frequency response that is flat from DC to 1 mHz 

0 

0 

d 

V> 

r0 

0 

0 

0 

(D 

0 

0 

d 

V> 

"" 

0 

0 

d 

0 

"' 

0 

0 

d 

"' 

Go """0 -'d .,., 

I 

0 

0 

d 

0 

"' I 

0 

0 

d 

"' "" I 

0 

0 

d 

0 

'f 

0 

0 

d 

"' 

\9000.00 79080.00 79160.00 792~0. 00 79320. 00 79~00. 00 79~80. 00 79560.00 796~0. 00 79720.00 79800.00 79880.00 

TIME. IN SECONDS 

FIGURE 1 .-A section of the record from the San Fernando earthquake. Strain is measured in units of least 

150 

79960.00 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 151 

and a dynamic range of better than 105 (i.e., it will 

accommodate relative motion of the two ends of 

a few centimeters). The estimated long-term stability is better than ± 1 LCS/ month. These features make this instrument useful for recording 

both secular strain rates and seismic events. 

The output from the digital fringe counter is 

recorded at one sample/ second on magnetic tape. 

Figure 1 shows a section of the record from the 

San Fernando earthquake. The peak dynamic 

strains recorded were 6 x 10- 7 , which occurred at a 

period of 8.6 seconds. The angle from the strainmeter direction to the epicenter is approximately 

82°, and hence the sensitivity is near a minimum 

for both longitudinal and transverse waves. 

In figure 2, 6 hours of data around the earthquake time have been lowpassed through a zero 

phase shift digital filter with a cut-off frequency 

of 2 X 10- 3 Hz. The general concave appearance of 

data is due to the earth's tide. A clearly apparent 

offset occurred at the time of the earthquake in 

the source of compression and of a magnitude of 

1.6 x 10- 9 • Further examination of data from an 

extended period revealed a change in the secular 

strain rate from 4X 10- 9 / day to 8 X 10-9 /day at the 

time of the earthquake ± 8 hours. Changes in the 

secular strain rate of this magnitude, not coincident with earthquakes, have been observed before 

but such a sudden change is not normal. 

800~0. 00 80120.00 80200.00 80280.00 80360.00 80~~0. 00 80520.00 80600.00 80680.00 80760.00 808~0. 00 A0920. 00 ~ 1000.00 

TIME, IN SECONDS 

count strain (LCS). One LCS equals 4Xl0-'

0

• Time is referred arbitrarily to the beginning of magnetic tape. 
152 

0 

0 

.A 

N 

0 

0 

lf) 

. 

0 

0 

d 

0 

0 

lf) 

. 

........ 0 C/) 0 

u • _l0 

01 

:3 

0 0 _J 0 

~ I 

0 

0 

d 

I 

0 

0 

. lf) 

I 

0 

0 

d 

N 

I 

0 

0 

.A 

THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

4 LCS 

NL---~--~--~---L--~---J----~--~--~--~---L--~---J----L---~--~--~---L--~--~--~ 

1

720.99 7'W.99 760.99 780.99 800.99 820.99 8~0.99 860,99 880.99 

TIME, IN SECONDS 

FIGURE 2.-A 6-hour section of the record has been lowpassed to reveal the strain offset. 

900.99 920.99 

•10 2 
PRELIMINARY REPORT ON FELT AREA AND INTENSITY 

By NINA H. SCOTT 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

This earthquake, the most destructive to occur in 

southern California since the Long Beach earthquake of March 10, 1933, was felt over approximately 80,000 square miles of California, Nevada, 

and Arizona; one observer at Beryl, Utah, reported 

the shock was slightly felt there (fig. 1). 

The felt area was determined principally from the 

earthquake questionnaire card (Form NOS-680) 

canvass conducted by the National Ocean Survey. 

To date (March 4, 1971), 2,068 cards have been distributed-784 were distributed to postmasters and 

1,284 to various other persons, including several 

hundred to structural engineers. To date, 1,860 reports have been received, and numerous requests for 

this form are being received daily. 

A maximum intensity of VIII-XI has been assigned tentatively to a small area in the foothills of 

northern San Fernando Valley. This assignment is 

based on the catastrophic damage to the Sylmar 

Veterans Hospital, the Olive View Hospital, and 

the Holy Cross Hospital. Other effects in this high 

intensity zone were major damage to the Van 

Norman Dam, severe damage to water and power 

facilities, collapse of freeway overpasses, major 

ground ruptures, and bending of railroad tracks. 

A report received from Robert E. Noel, reservoir 

keeper, Van Norman Dam, stated: "My wife and 

child were already up. She heard the quake coming. 

I was asleep. I tried to get out of bed but couldn't 

until the worst was over. I made a quick check of 

the family and a quick check of the house, then 

dressed and went to check the dam. We live on the 

reservoir at the bottom of the dam on the west end. 

When I got to the main road going to the top of the 

dam, I could see, through the dust, an irregularity 

of the crest of the structure below, looking to the 

top. I drove to the top of the dam and around the 

west abutment and saw the damage to the face. It 

was hard to believe what I saw." 

Outside of the intensity VII zone (as shown in 

fig. 1), only slight to moderate damage was reported, principally cracked or fallen plaster and 

broken windows. 

Nearly all observers remarked on the long duration of the earthquake. 

The following reports are of interest regarding 

the direction of motion : 

Fire Station No. 7 4 in Kagel Canyon.-"This 

building was moved approximately 12 inches off, 

foundation and had to rise over sill at least 41/2 

inches to settle down without damaging the 

shingles." 

Bear Divide Range1· Station (NWV,.sec. 7, R. 14 

W., Route 4, Box 303, Saugus) .-"A great up-anddown motion, changing to north-south motion." 

13706 N. Kagel Canyon Road (in area of Fire 

Station No. 7 4) .-"My husband was awake and was 

thrown from north to south. Furniture was overturned from north to south, east-west, and west-east. 

Refrigerator was out of position from south to 

north about 18 inches. Kitchen cabinets were almost 

emptied both from north and south. Most violent 

action, from final position of furniture, seemed to 

be from east to west." 

Valencia (just northwest of Newhall) .-"Sensation was a violent rotary motion." 

153 
37' 

J>• 

)J• 

II 

J'l• 

JJ• 

P.· 

NEVADA 

II+'• 

I 

I 

I 

I 

IIJ• 

~ry'UTAH 

I •' 

,. 

' ' "' ~ '{e\\ 1>-le'b 

~,i-'\'>0 le' 

I .. · : 

1-------------In' 

/:1~. 

J• .t· o't 

• ... ;.~ 'r ~ 

7 

0 ¥• fa.kersfield 

v $ r.tt.r ( 

~ 

..n 

~ 

0 

J' 

. .I !•Wh .... rRid .. 

0 

0 

~ 

"'?~ 

~. 

Sen'-- C.t.lln• l.,.nd~AY8ton 

PRELIMINARY DRAFT OF INTENSITY AND AREA AFFECTED 

BY THE 

SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF 

FEBRUARY 9, 1971, 06:00:45' PST 

Dot without number = not felt 

·~ 

" 

l. ... if 

II f' 

'· 

I '"' 

.r.aoron 

' .. , ' '\. f•l•throp "\,. Well .. • 

' ' 

"'"' ' .,. 

' "' ', ; 

v " ' . ' , -- . ' 

,, ., 

S:'flt(,r -~-"" ,, • J' 

o¥ 

.fueern• v.uey 

'Boor City 

J 

""-, ~;nomen 

.~t( ARIZONA 

~. ', 

.. t t 

r: , 

• f Dnert Center ) 

Blyt~,t 

'-Y 

.. Soft~ !{' ., c;t';v.. ~\ I-IV ,. ""'\ 

~. ,5'' ··~ __ .; .-_'! "" __ l' l•vumo £L.:---- t( -- . 

. M E X I C 0 ~~'---

.. 

'~- "'' /IS'' //If. 1!3' 

FIGURE 1.-Preliminary draft of intensity and area affected by the San Fernando, California, earthquake of February 9, 

1971, 06:00:45 PST. 

,,. 

Jf' 

3'{' 

JJ' 

32.' 

"""" 01 

..,.. 

8 

::r1 

t<j 

en 

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> 

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0 

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,..... 

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-:] 

,..... 
GROUND-MOTION AMPLIFICATION AND VIBRATION MEASUREMENTS 

By KENNETH KING 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

The Las Vegas Special Projects Party of NOS, 

in cooperation with the Atomic Energy Commission, installed and operated seismic instruments 

in California in the vicinity of the main epicenter 

of the San Fernando earthquake. The locations of 

the stations for the following programs are given 

in table 1. 

BUILDING AND FREE FIELD SEISMIC MEASUREMENTS (PROGRAM NO. 1) 

Several locations were instrumented with threecomponent velocity systems for seismic comparisons of aftershocks. The Van Norman Dam was 

instrumented to compare to an instrumented free 

field location, which was 100 yards from the Dam. 

The damaged Veterans Hospital was instrumented 

to compare with a free field station on bedrock 

in Loop Canyon. Ground plants were made near 

several schools to add to the Loop Canyon comparison. The stations recorded for approximately 

2 days. 

BANK OF CALIFORNIA PROGRAM (PROGRAM NO. 2) 

The NOAA/NOS maintains three accelerographs in the Bank of California. The Special Projects Party installed additional three-component 

seismic systems near those three locations inside 

the building, plus one in the free field to study 

the building amplification and response characteristics to motion induced by aftershocks following 

the San Fernando earthquake. The seismic systems used were broad band and velocity sensitive systems and were recorded on magnetic tape. 

The four systems operated for about 5 days. The 

data have not yet been inspected or evaluated. 

P A COlMA DAM COMPARISON (PROGRAM NO. 3) 

The National Ocean Survey maintains an accelerograph station at the Pacoima Dam which 

recorded a high-level acceleration on the main San 

Fernando earthquake. To check the validity of the 

resulting strong-motion record, the NOS instrumented the accelograph location, the crest of the 

Dam, and a free field location in bedrock approximately 250 yards from the Dam with three-component velocity sensing systems. The stations recorded approximately 30 aftershocks that will be 

used for amplification and attenuation studies. 

GROUND MOTION AMPLIFICATION (PROGRAM NOS. 

4 AND 5) 

The National Ocean Survey fielded two programs to study the seismic effects in the ground 

motion amplification study. Industrial and cultural 

seismic noise forced low-gain recordings which 

resulted in a limited number of recorded aftershocks. However, many events were recorded and 

can be used for the study. The portable seismic 

stations used on the programs consisted of three 

velocity sensing transducers, two horizontal and 

one vertical, which record broad spectrum from 

0.1 to 30 Hz on magnetic tape. 

Program No. 4 consisted of 23 three-component 

seismic stations located on a grid in the San Fernando Valley. Most stations were located in ground 

plants; a few were colocated at a preexisting seismic station, and one station was colocated with 

a Geological Survey seismic station. The stations 

recorded simultaneously for approximately 4 days. 

Program No. 5 consisted of a similar network of 

23 seismic stations located in the area of Glendale, 

Calif. The stations recorded for approximately 4 

days. 

BUILDING VIBRATION PROGRAM (PROGRAM NO. 6) 

The Las Vegas Field Party measured the major 

structural periods of several buildings in the 

greater Los Angeles area. Data of induced and 

natural seismic disturbances in the horizontal 

planes of the high-rise structures were recorded 

155 
156 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

by temporarily installing velocity sensitive transducers at the uppermost accelerograph location in 

each of the buildings. The horizontal transducers 

were oriented to the short or minor and long or 

major axes of the building. The transducer/amplifier system is of the L-7 type, which has an essentially flat velocity response from 0.1 Hz to 100 

Hz. The recording procedure was to record several 

minutes of ambient seismic background and then 

supplement this data with several short records 

of induced background. The induced force consisted of inertia created by a man swaying his 

body in synchronization with the building's natural 

period. The force was applied parallel to both 

major and minor horizontal axes of the building. 

The personnel who shifted their weight closed a 

contact, indicated on each seismogram at the stoppage of input. The refined method used has been 

developed through experience in Reno, Nev., Salt 

Lake City, Utah, and Las Vegas, Nev. 

Phase I consisted of a quick test in 68 buildings. 

Phase II is a recheck and retest of buildings that 

gave questionable seismograms in Phase I. The 

seismograms were processed and scaled for preliminary information. The operation averaged six 

buildings per day. The following personnel recorded, scaled, and compiled data: Kenneth W. 

King, geophysicist; Louise Wuollet, geophysicist; 

John West, technician; and Eugene Sember a, technician. 

TABLE I.-Station locations 

l Recorded on magnetic tape] 

Station identification 

Progran~ 1 

Van Norman Dam (on the dam) .................. . Van Norman Dam (free field) ......................... . Sylmar V. A. Hospital Chapel 

Sylmar Loop Canyon ........................... . Alameney High School .......................... . Gridley Street School ............ . 

Time on (P.s.t.) 

16 Feb 2100 16 Feb 2230 17 Feb 1320 17 Feb 1500 17 Feb 1345 17 Feb 1600 

Time off (P.s.t.) 

18 Feb 1300 18 Feb 1415 22 Feb 0900 22 Feb 1000 19 Feb 1200 22 Feb 1100 

TABLE 1.-Station locations-Continued 

Station identification 

Program. 2 

Bank of California (roof) ....................... . Do (7th floor) .................................. . Do (basement) ..... . Do (free field) ........... ............. . ..... . San Fernando Junior High ........................ . Gridley Street School ................. . Sylmar V. A. Hospital Chapel 

Sylmar Loop Canyon .... 

Program ."1 

Pacoima Dam (crest accelograph location, 

Time on (P.s.t.) 

18 Feb 1900 18 Feb 1700 18 Feb 1600 18 Feb 1500 19 Feb 1300 22 Feb 1100 22 Feb 1000 22 Feb 1100 

(free Held) ...... ............................ .. .... 24 Feb 

Progrant 4 (San Fernando Grid) 

Time off (P.s.t.) 

22 Feb 0200 22 Feb 2200 22 Feb 11301 23 Feb 1000 23 Feb 1000 23 Feb 1000 1 

27 Feb 1000 1 

27 Feb 1000 1 

Still running 

Golden State Freeway ............ ..... 26 Feb 2 Mar 

Olive View Hospital .................... --······do. . ................. Do. V. A. Hospital ············-·- .......................... ··---... do. . ................. Do. Van Norman Lake (Upper) ....................... do .................. Do. Eldorado Avenue School ................................ . .. do. . ................. Do. 

Gridley School ....................... ························--···· _ ...... do. ·-················Do. Olive Vi,;ta ......................................... . ............ do .. __ ........................ Do. Lo\ver Van Norman Dam ........ ___ .do ........................... Do. Alameney School ....................................................... do .......................... Do. Vaugan Street School ................... . ...... -....... do ............................ Do. 

Pacoima Lutheran Hospital ·······-····----·... _ .... do ............................ Do. Mission Hills Shopping Genter ............................... do ............................ Do. Mary Emaculate School . . ... do ......... -.................. Do. Jessup Park ........ .... ... ............. . ...... do ........................... Do. Holiday Inn .......... .. . ............................... do ............................ Do. Laurel High School ...... do ......... _ .................. Do. 

Sylvan Park School ·······················-······do ............................ Do. Bel Air Presbyterian Church .. do ............................ Do. Fire Station No. 108 ................................................ do ............................ Do. Walter Reed Junior High School ......................... do ............................ Do. Rank of California ... ...... ............ . .... do ............................ Do. Arminta Street School ···-·· .......................... do ............................ Do. 

Hubbard Street School ... ·····-················ --...... do ............................ Do. 

Program .5 (Glendale Grid) 

31, Dunsmore Street School ···············- 5 Mar 8 Mar 32, 3428 Prospect ............................ . .... -...... do ........................... Do. 33, Radio Tower "Free Field" ..................... . .... do ........................... Do. 34, Casa Odobe de Son Rafael .......... do ............................ Do. 35, Ool urn bus School ............................................ _ ...... do .......... _ ................. Do. 36, Edison School ..... do ............................ Do. 37, Atwater School ..... ........................ . .... do ........................... Do. 38, Verdugo Park ······-·· ..... do ............................ Do. 39, Nibley Park ............ ................ ......... . .... do_ ........................... Do. 40, Wilson Junior High School .................... . -·· .... do ........................... Do. 41, Municipal Services Building .............................. do ............................ Do. 42. Glendale High School ........................................ do ............................ Do. 43, Verdugo Recreation Center ................................. do ............................ Do. 44, Scholl Canyon Park .............................................. do ........................... Do. 45, Griffith Manor Park ........................................... do ............................ Do. 46, Griffith Park Headquarters ... . .......... do .......................... Do. 47, Brand Park ..... . ........ do ............................ Do. 48, Roosevelt Park ····-········· .............. do ............................ Do. 

1 Also used in Program 5. 
MAGNETIC FIELD SURVEY OF THE SAN FERNANDO EARTHQUAKE EPICENTRAL AREA 

By J. E. O'DONNELL and H. E. KAUFMANN 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

SEISMOMAGNETIC EFFECT 

Recently the Japanese (Rikitake, 1968) and the 

Russians (Golovkov, 1969) have reported on conducting magnetic repeat field surveys in seismic 

areas in order to investigate the seismomagnetic 

effect. Their work suggests large changes in the 

magnetic field which could ·be related to earthquakes. Briener and Kovach (1968) have reported 

on work in the United States that consists of continuous monitoring of the magnetic field rather 

than running repeat magnetic surveys. They have 

an array of five rubidium magnetometers which 

have been operating in a differential mode, for the 

past few years, along a short portion of the San 

Andreas fault. Their work indicates that only very 

small changes (a few gammas) have been detected 

that could be correlated with creep and occasional 

small ·earthquakes along the San Andreas fault. 

The San Fernando earthquake presented an opportunity in the United States to initiate an attempt 

to measure the seismomagnetic effect by magnetic 

field repeat surveys. A magnetic survey was made of 

the epicentral area between February 23 and March 

4, 1971. A second survey will be necessary to detect 

any change, since we have no reports of the area 

being surveyed before the earthquake. A similar 

study was made by Kato (1940) when he conducted 

a magnetic field survey after a Japanese earthquake 

and then repeated it a year later. He found over a 

100-gamma change, which he attributed primarily 

to the seismic activity in the area. 

DESCRIPTION OF FIELD SURVEY 

Thirty-two stations were established in the epicentral area, along with a base station which continuously monitored the magnetic field changes. The 

base station records were us·ed to remove the diurnal 

and temporal variations from the survey. The recordings were made with a Schonstedt HMS-1 fluxgate magnetometer with a special sensor mount to 

allow alignment of the sensor in the total field direction. An ELSEC proton precession magnetometer 

( ± 1.2 gamma) was used to take absolute measurements at this position during the survey, in order 

to establish a true base control. A 1-gamma drift per 

day was found at the base station, which could be 

due either to magnetometer drift or tilting of the 

sensor. The sensitivity and chart speed of this system were 0.9 gamma per mm and 1.2 minutes per 

mm, respectively. The sensitivity was computed 

from recorded calibration pulses obtained from energizing a calibration coil on the sensor. 

The repeat stations were located on existing survey markers such as bench, triangulation, and reference markers whenever possible. These markers 

and other geographic positions were obtained from 

U.S. Geological Survey 7%' topographic maps. The 

technique for making the measurements consisted 

of placing the sensor 60 inches above the marker on 

a tripod and observing five readings. The readings 

were repeated also at the four cardinal points located 20 feet from the marker. These cardinal-point 

values give an indication of the magnetic gradient 

in the vicinity of the marker. In some cases, artificial magnetic anomalies, such as metal stakes and 

pipes, were noted in the station description. In a 

few cases, some of the cardinal points were not suitable for measurement. A file of complete station 

descriptions is being maintained at the Fredericksburg Geomagnetic Center. The observed and reduced 

data are presented in table 1, along with the gradient data, which indicate the better stations to be 

used for repeat work. 

DISCUSSION OF DATA 

The Sand Canyon station was occupied on three 

occasions during the survey, while Reynier Canyon 

and Sunland were occupied twice. The largest ob157 
158 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

TABLE I.-Magnetic total field survey data for epicentral area of San Fernando earthquake of February 9, 1971 

Diurtlal and Base Station Month Observed temporal station Corrected name and and U.T. value variation drift Corrected gradient Remarks location day (gammas) correction correction value values 

Sand Canyon Fire Station 2-24 17: 04 49942 +8 +1 49951 499578 Los Angeles County 

(long 118°24'48.0" W., 49959W Fire Station 

lat 34 °23'05.4" N.) ·------- 49894N No. 123. 

3-3 21: 44 49901 +56 +8 49965 499868 

49980W 

49912N 

3-4 18: 26 49930 +27 +9 49966 499848 

49975W 

49914N 

Dillon Divide 2-24 18: 56 50333 +25 +1 50359 504088 Former Forest 

(long 118°20'5.0" W., 59287W Service monulat 34°20'37.5" N.) ·------- 50202N ment, 1945. 

50383E 

Dillon Ranch 19: 58 49784 +53 +1 49838 50140S U.S.G.S. 

(long 118°21'25.0" W., 50022W bench mark. 

lat 34°20'50.0" N.) ·------- 49948N 

49594E 

Indian Springs 21: 09 49962 +52 +1 50015 49952S U.S.G.S. 

(long 118°20'14.5" W., 50013W bench mark. 

lat 34 °19'21.0" N.) ·------- 50120N R68 1929. 

49999E 

Reese 2-24 22: 23 50131 +59 +1 50191 502698 Forest Service 

(long 118°20'10.5" W., 50230N marker 1940? 

lat 34°19'11.0" N.). -----· 50249E 

Camp No. 9 2-25 17: 44 50827 +28 +2 50857 508088 Measurements 

(long 118°23'43.5" W., 50807W taken during lOy 

lat 34°21'31.0" N.). -----· 50913N bay activity of 20 

50840E · min duration. 

Little Tujunga Heli-pad 19: 31 50233 +39 +2 50274 503238 

(long 118°21'34.5" W., 50228W 

lat 34°17'45.0" N.). -----· 50277N 

Reynier Canyon 21: 43 50011 +65 +2 50078 49967S U.S.G.S. 

(long 118°25'04.5" W., 49962W bench mark 

lat 34°23'01.5" N.). -----· 49968N R8 1929. 

50017E 

3-1 16: 58 50051 +15 +6 50072 499708 

49965W 

49970N 

50015E 

Placerita 2-25 22: 55 50002 +43 +2 50047 50004E U.S.G.8. 

(long 118°29'24.0" W., triangulation lat 34°23'46.5" N.). _____ station 

Port 19: 50 49970 +36 +3 50009 500018 Los Angeles County 

(long 118°19'44.0" W., 50009W Port (reference 

lat 34°23'11.0" N.). _____ 50010N mark No.2. 

50006E 

Magic 20: 36 50029 +44 +3 50076 496378 U.8.C.&G.S. 

(long 118°19'03.0" W., 49514W triangulation 

lat 34°23'11.0" N.). _____ 49372N station 1958. 

Sensor 8 in. 

above marker. 

Cub 21: 45 49943 +42 +3 49989 500848 Forest Service 

(long 118°17'57.0" W., 49870W marker 1945. 

lat 34°23'28.5" N.). -----· 49995N 

50196E 

Pacoima 2-27 17: 41 50274 +22 +4 50300 50046S Pacoima triangu-

(long 118°24'20.0" W., 50041W lation marker 

lat 34°17'33'5" N.). -----· 50034N 1935 RE 2177. 

50023E 

Sunland 2-27 18: 30 50237 +33 +4 50274 50207S Forest Service 

(long 118°22'51.0" W., 50260W reference 

lat 34°16'43.5" N.). -----· 50212N marker No. 2. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 159 

TABLE !.-Magnetic total field survey data for epicentral area of San Fernando earthquake of February 9, 1971-Continued 

Diurnal and Base Station Month Observed temporal station Corrected name and and U.T. value variation drift Corrected gradient Remarks location day (gammas) correction correction value values 

3-1 20: 44 50229 +46 +6 50281 50212S 

50261W 

50213N 

Pacoima E2 20: 03 50304 +53 +4 50361 50239S Los Angeles County 

(long 118•27'40.0" W., 50215W control survey 

!at 34•17'22.5" N.). -----· 50184N mark 2177. 

50190E 

Garfield 2-28 18: 43 50812 +31 +5 50848 50784S Forest Service 

(long 118•20'59.0" W., 50854W Garfield 4622 

!at 34•22'02.0" N.). ______ 50969N 4622 1945. Sensor 

50857E 10 in. above 

marker. 

Trial Cyn. Dl 19: 47 +48 +5 49894S Los Angeles County 

(long 118.16'15.0" W., 49899W Trial Cyn. D1, 

lat34.23' 45.5" N.). ------ 49900N 1962 steel post 

49907E by marker. 

Indian 2-28 20: 23 50201 +50 +5 50256 50250S Forest Service 

(long 118 • 15' 19.0" W ., 50281W indian 1945 

lat 34•23'39.5" N.). _____ 50245N marker. 

50249E 

Camp Ground 1 21: 32 49669 +42 +5 42716 49560S 

(long 118.16'32.0" W., 49477W 

!at 34.22'30.0" N.). _____ 49451N 

49600E 

Santa Clara Divide 22: 23 49779 +35 +5 49819 49725S 

(long 118.17'06.5" W., 49854W 

lat 34•23'44.0" N.). _____ 49852N 

49767E 

Indian Canyon head 23: 00 50079 +30 +5 50114 50124S 

(long 118.16'12.0" W., 50151W 

lat 34 •25'04.0" N.). -----· 50101N 

50145E 

Soledad Camp 23: 31 49979 +27 +5 50011 500238 

(long 118.16'39.0" W., 50022W 

!at 34•26'17.0" N.). -----· 50038N 

50010E 

Aqua Dulce Bridge 24: 04 50118 +23 +5 50146 501488 

(long 118.20'07.5" W., 50123W 

!at 34•26'18.0" N.). -----· 50147N 

50143E 

Stone quarry 2-28 24: 46 50094 +20 +5 50119 50039S U.S.C.&G.8. 

(long 118•20' 42.5" w ., 50073W bench mark 

!at 34.26'02.0" N.). ______ 49868N Q486 1955. 

50098E 

Placerita Canyon State Park 17: 33 50200 +18 +6 50224 50375S 

(long 118•28'11.0" W., 50212W 

!at 34•24' 40.0" N.). ______ 50202N 

50228E 

Mint Canyon 18: 41 50407 +25 +6 50438 50093S 

(long 118•25'08.5" W., 50092W 

!at 34 •27' 50.5" N.). ______ 50088N 

50090E 

Vasquez Rocks 23: 30 50321 +14 +6 50341 50339S 

(long 118•19'16.5" W., 50338W 

!at 34.29'20.0" N.). ______ 50323N 

50350E 

May 3-2 19: 38 51101 +33 +7 51141 512768 U.8.G.S. marker. 

(long 118.25'44.0" W., 50818W 

lat 34 •21'08.0" N.). ______ 50890N 

51301E 

Fernando 1 3-2 21: 00 51121 +47 +7 51175 50841S Los Angeles County 

(long 118.25'03.5" W., 50818W survey marker 

!at 34.21'11.0" N.). -----· 50738N 1955. 

50869E 
160 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

TABLE I.-Magnetic total field survey data for epicentral area of San Fernando earthquake of February 9, 1971-Continued 

Diurnal and Base Station Month Observed name and and U.T. value location day (gammas) 

Norman Reservoir 24: 08 50089 

(long 118°29'15.0" W., 

!at 34°17'30.0" N.). ------

Big Tujunga 3-3 18: 50 49840 

(long 118°15'16.0" W., 

!at 34 o 18' 49.5" N.). ------

North Ball Park 19: 54 49859 

(long 118°17'30.0" W., 

!at 34°16'57.0" N.). ------

Silver Star Lane 2-23 to 

(long 118°24'43.0" W., 

!at 34 °23'05.5" N.). ------ 3-4 

served difference (14 gammas) at the Sand Canyon 

station is larger than the minimum error of 6 gammas involved in the magnetic reduction of the data. 

Two other possible errors not included in the reduction are the conductivity anomaly effect (Schmucker, 1970; and Elvert and others, 1970) and artificial magnetic gradients. The conductivity effect, we 

feel, would be negligible, since the magnetic activity 

recorded at the base station indicated only slight 

activity during a few measurements. The diurnal 

was less than 50 gammas but should be essentially 

uniform over the small area surveyed. The most 

likely source of error is in attempting to relocate 

the same position in a high magnetic gradient. The 

cardinal points at a station were not reoccupied 

precisely, while the center position was not off by 

more than 3 inches. Since a torroidal-wound sensor 

was used, with the ELSEC, it allowed measurements 

in a high gradient. It would be possible to have a 

high gradient 5 feet away (distance of sensor from 

ground), but to drop off substantially at 20 feet if 

temporal station Corrected 

variatiorl drift Corrected gradient Remarks correction correction value values 

+16 +7 50102 501158 U.S.C.&G.S. 

50107W triangulation 

50105N reservoir 1932. 

50131E 

+33 +8 49881 49786S U.S.G.S. marker 

49759W R 79 1929. 

49680N 

49649E 

+61 +8 49928 49869W 

49877N 

49911E 

Base station con- tinuous recording 

directly east of 

Los Angeles fire 

station 123. 

the source were very localized. Consequently, we do 

not feel the Sand Canyon differences are of any significance at this time. 

REFERENCES 

Briener, S., and Kovach, R. L., 1968, Local magnetic events 

associated with displacement along the San Andreas 

fault (California): Tectonophysics, v. 6, no. 1, p. 69-73. 

Elvers, D., Perkins, D., and Holbrook, R., 1970, A survey of 

anomalous geomagnetic variations in Puerto Rico: Operational Data Rept. C&GS DR 9, U.S. Department of 

Commerce, 1-44. 

Golovkov, V. P., 1969, Anomalous geomagnetic field variations 

in a seismically active region: Geomagnetism and Aeronomy, v. 9, no. 6, p. 912-913. 

Kato, Y., 1940, Investigation of the changes in the earth's 

magnetic field accompanying earthquake or volcanic 

eruptions: Tohoku Univ. Sci. Rept., ser. 1, v. 29, no. 3, 

p. 315-326. 

Rikitake, T., 1968, Geomagnetism and earthquake prediction: 

Tectonophysics, v. 6, no. 1, p. 59-68. 

Schmucker, U., 1970, an introduction to induction anomalies. 

Jour. Geomagnetism and Geoelectricity, v. 22, no. 1-2, 

p. 9-33. 
CRUSTAL-MOVEMENT SURVEYS AND PREEARTHQUAKE STRAIN ANALYSIS 

By C. A. WHITTEN 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

The geodetic party assigned to California for 

monitoring crustal movement, and especially for 

repeating the fault-crossing surveys to detect fault 

slippage, had been working in the Los Angeles area 

for a few days immediately preceding the San 

Fernando earthquake. Recent preearthquake remeasurements of three of these fault-crossing surveys along the San Gabriel and San Andreas faults 

indicated no slippage. This seven-man party, with 

a few additional geodetic technicians, was assigned 

the task of reobserving the networks of geodetic 

control in the San Fernando region and the San 

Gabriel Mountains. Some of this control, which consists of triangulation and leveling, had been established by the Los Angeles County Engineer's Office. 

Personnel from that office are also engaged in reobserving portions of these networks. These cooperative efforts are fully coordinated by Ira H. 

Alexander, Division Engineer from Los Angeles, 

and Captain L. S. Baker, Chief, Geodesy Division of 

the National Ocean Survey. Several weeks will be 

required to complete the field surveys, reduce the 

measurements, and analyze the results. 

The epicenters of the earthquake and major aftershocks are very near the southern end of one of the 

older arcs of triangulation established in 1932 as 

part of a broad program for detecting crustal deformation in California. This arc extended from San 

Fernando to Bakersfield in a dog-leg fashion with 

the axis of the arc perpendicular to the San Gabriel, 

San Andreas, and Garlock faults. This special survey was repeated in 1952 and again in 1962. The 

analyses of the resurveys in those years did not indicate any slippage along those major faults. 

However, following the earthquake of February 

9, the data from the extreme southern end of these 

three surveys were reanalyzed. Components of maximum shear were computed for the triangles in the 

network and the results are shown in figure 1. One 

of the triangles, with one of its vertices at the Van 

Norman Reservoir and the other two in the Mission 

Hills, shows an accumulation of strain of 41 X 10-6 

units in the 30 years from 1932 to 1962. The direction of maximum shear for the triangles covering 

the general area of the Santa Susana fault is eastwest. The direction of maximum shear for the triangles further north, near Newhall, and closer to the 

San Gabriel fault is northwest-southeast. In both 

cases, the direction of shear indicates right-lateral 

movement. · 

These components of shear, when considered colhictively, provide some basis for interpretation of 

rates of accumulation of strain prior to the earthquake. However, it must be emphasized that the 

units are expressed in parts per million and are derived from conventional triangulation which could 

not be expected to be more accurate than 10 parts 

per million. Further, considering that the results 

depend upon comparisons of two surveys, the computed values may have an uncertainty of the order 

of 15 parts per million. The postearthquake program 

of reobservation includes the use of a laser geodime"" 

ter. Thus, any additional resurveys in the future 

would provide information with uncertainties not 

exceeding one or two parts per million. 

161 
162 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

YUCCA 

TOWSLEY 

SAN FERNANDO 

6 

1932 to 1963 

y x 1o-6 

0 20 40 

SAUGUS 

NEWHALL 

EDISON 

CORNER 8 Miles 

0 1 2 

FIGURE I.-Components of shear. 

41 x 1o-6 

32 

16-22 

11 

3 

Von Norman 

3 

N 
PRELIMINARY STRONG-MOTION RESULTS FROM THE SAN FERNANDO EARTHQUAKE OF 

FEBRUARY 9, 1971 

By R. P. MALEY and W. K. CLOUD 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

More than 250 strong-motion accelerographs were 

triggered in southern California by the magnitude 

6.fi San Fernando earthquake of February 9, 1971. 

More than 200 of these are located in the Los Angeles area, primarily as a dire.ct result of the inclusion in the building .. codes of L<:>s Angeles and 

neighboring cities of a seismograph section requiring the installation of three accelerographs in building-s six stories and taller. In, addition, approximately 120 seismoscope records · were obtained 

within the strongly shaken area ; these are almost 

equally divided between those located at damsites 

and those located on different geologic formations. 

Most of the strong-motion instruments are privately 

owned but are maintained by the Seismological Field 

Survey unit of NOAA's National Ocean Survey as 

part of a cooperative network. 

The collection of records has nearly been completed; concurrently, the production of archival 

copies of the accelerograms and digitization of the 

important records are being done at the Jet Propulsion Laboratory in Pasadena. As record processing 

is completed, reproductions of the originals are being posted in the vibration laboratory at Thomas 

Engineering on the California Institute of Technology campus for public inspection. Detailed anallysis of the strong-motion data is just beginning, 

although preliminary raw scaling of maximum accelerations is well underway. A sampling of those 

results has been included in this report. 

PRELIMINARY STRONG-MOTION DATA 

The locations of accelerographs outside the Los 

Angeles area are shown in figure 1. The individual 

stations are listed in table 1, which includes a selection of maximum ground-level accelerations recorded between 15 and 85 miles from the epicenter. 

Note that the spread of peak values measured at 

four sites in the Lake Hughes array, 15 to 19 miles 

distant, varies by a factor of more than two, ranging from 0.16 to 0.37 g, perhaps a consequence of 

the variation of rock types. The maximum accelerations of slightly less than 0.4 g observed at one Lake 

Hughes site and nearby Castaic are considerably 

larger than the ground-level records obtained at 

equivalent distances in the San Fernando Valley 

south of the epicenter. 

The distribution of accelerographs in the Los 

Angeles area is shown in figure 2. At Pacoima Dam, 

5 miles south of the epicenter, the earthquake accelerations were the highest ever recorded, i.e., in 

the 0.5 to 0.75-g range with several high-frequency 

peaks to 1 g (fig. 3). The initiation of strongest 

shaking began 1 to 2 seconds after instrumental 

triggering and lasted for approximately 12 seconds. 

The accelerograph, owned by the Los Angeles 

County Flood Control District, is located on a small 

ledge above the east abutment of the concrete arch 

dam situated in the deep narrow Pacoima Canyon 

above the Sylmar district of Los Angeles. Rock at 

the site is a gneissic granite-diorite complex, with 

prominent jointing trends parallel to the canyon. 

Figure 4A shows the relative location of the instrument housing and the massive spalling of bedrock 

that occurred below the station during th€ earthquake. In addition, some cracking, displacement, and 

subsequent tilting of the rock adjacent to the instrument housing were observed following the shock 

(fig. 4B). Tilting of the ledge was evidenced by a 

permanent displacement of the horizontal-triggering pendulum on the accelerograph, which caused 

aH the paper to run off during the first 15 to 20 

minutes following the earthquake. 

A representative pattern of the maximum ground163 
164 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

level accelerations measured in the Los Angeles area 

is listed in table 2, with the specific station locations 

keyed to the map of the metropolitan area (fig. 2). 

The largest values ( >0.2 g) are generally observed 

at the stations nearest the epicenter, i.e., in the San 

Fernando Valley and at Pasadena. Dropoff of peak 

values, to 0.10 to 0.15 g, is noted in the high-rise 

area of central Los Angeles and along the Wilshire 

strip, although there are some deviations in this 

general trend. Ground records from the extended 

Los Angeles basin generally show about 10 seconds 

of higher-frequency strong shaking, followed by 

several cycles of longer-period waves in the 2-second 

period range. 

Records were obtained in the upper levels of more 

than 60 buildings, six to 42 stories in height, ranging from 13 to 53 miles from the epicenter. These 

instruments are maintained by the Seismological 

Field Survey in cooperation with building owners in 

the cities that have incorporated the mandatory accelerograph provisions within the building code. 

Representative maximum accelerations recorded at 

the top level of a cross-section of structures are 

contained in table 3. Peak values in excess of 0.4 g 

were recorded as distant as downtown Los Angeles, 

nominally 26 miles, although the vast majority of 

measurements were in the 0.2- to 0.4-g range. From 

the sample thus far available, it is noted that taller 

structures (greater than 15 stories) tend to fall on 

the middle and lower end of this range, with the 

exception of identical twin towers (not included in 

table 3) located in central Los Angeles. The highest 

top-floor accelerations are approximately two to 

three times those measured at the ground level in 

the same structure. 

Within a few days after the earthquake, five temporary accelerographs were installed at the following locations: Lower Van Norman Dam in San Fernando Valley, Pacoima Dam, the U.S. Forest Service Station in Soledad Canyon, the Los Angeles 

County Fire Station in San Canyon, and Acton. A 

number of aftershocks have triggered these instruments as well as several others at original stations, 

but the results are not yet available. 

Excellent seismoscope records were obtained 

throughout Los Angeles and in adjacent strongly 

shaken areas to the north and northwest. Among 

these is a unique record from a Los Angeles Department of Water Power seismoscope originally 

located on the crest of Lower Van Norman earthfill 

dam. During the earthquake, this section of the crest 

partially failed and the instrument slid down into 

the lake. Undaunted by the apparent loss of the record, B. J. Morrill of the Seismological Field Survey 

pursued the recovery of the instrument in the belief 

a usable record could be obtained. When the lake 

level was lowered as a safety measure, the seismoscope was sighted and eventually appeared above 

water where it was retrieved by Morrill. Fortunately, the smoked glass plate was still in place, 

providing a record of the earthquake and the simultaneous dam failure (fig. 5). A second record was 

also recovered from the west abutment of Lower 

Van Norman Dam. 

Another fine set of seismoscope records was obtained at Santa Felicia Dam, 22 miles northwest of 

the epicenter, where six instruments owned by the 

United Water Conservation District are located on 

the crest, east, and west abutments and below the 

toe of the dam. Large, strongly polarized amplitudes 

at an angle of approximately 40° to the axis of the 

dam were recorded at the two crest stations. When 

this prominent alignment was projected to the 

southeast on a map, the line fell substantially south 

of the instrumental epicenter. 

SUMMARY 

More than 250 accelerograph records and 100 

seismoscope records on the San Fernando earthquake were obtained from the cooperative network 

maintained by the Seismological Field Survey unit 

of NOAA's National Ocean Survey. All records have 

been collected and are now being quickly scaled and 

duplicated; shortly they will be digitized prior to 

more comprehensive analysis. 

Maximum ground accelerations were observed at 

Castaic and Lake Hughes, where values were slightly 

less than 0.4 g, and at Pacoima Dam, where there 

were a few peaks in the 1-g range, the highest ever 

recorded. Evaluation of the latter record may prove 

to be difficult because of facturing of rock adjacent 

to the station during the earthquake. Ground accelerations in the Los Angeles area were predominantly 

<0.2 g, except in the San Fernando Valley and 

Pasadena, while on the top floors of taller buildings 

maximum values occasionally exceeded 0.4 g but 

more often were in the 0.2- to 0.4-g range. 

Five temporary accelerograph stations were established after the main shock between 1 and 10 

miles from the earthquake epicenter. These included 

Pacoima Dam and Lower Van Norman Dam. 

Among the significant seismoscope records obtained were two from Lower Van Norman Dam, including one from the crest that had slid into the lake 

during the earthquake, and a second set of six records from Santa Felicia Dam, located 22 miles 

northwestof the epicenter. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 165 

This earthquake has provided the largest collection of significant strong-motion data ever obtained 

and should prove to be of unprecedented value to 

the engineers, earth scientists, and public officials 

concerned with the problem of seismic hazards. 

TABLE 1.-StTong-motion accelerographs in southern California (exclusive of Los Angeles) with selected maximum 

ground-level accelerations 

Sampled 

maximum 

Acceleration Number of (fraction of Location instruments gravity) 

1. Point Concepcion 1 

2. Cachuma Dam .............. 2 3. Santa Barbara ................. 2 4. Port Hueneme 1 

5. Santa Felicia Dam ......... 2 6. Castaic ...................... 1 

7. Lake Hughes array ...... 4 8. Fairmont Reservoir ................ 1 9. Palmdale ............ ....................... I 

10. Pearblossom 1 

11. Wrightwood 2 

12. Cedar Springs 2 

13. Devils Canyon .................... 2 

14. San Bernardino 1 15. Lorna Linda .......................... 1 

16. Colton ...... .. ... ................. 1 

17. Desert Hot Springs 1 

I 8. Puddingstone Dam ...... 1 

19. San Antonio Dam .............. 1 20. Carbon Canyon Dam 1 

21. Whittier Narrows 1 22. Santa Ana 1 

23. Costa Mesa ..................... 1 

24. Perris ... ... ............... 1 25. San Onofre 1 

26. Hemet ......... ........................ 1 

27. Anza ........ _........ 1 

28. Borrego Springs ..... 1 29. Superstition Mountain ............ 1 30. El Centro-Imperial .................. 4 

31. San Diego .................. 3 

32. San .Juan Capistrano .... 1 33. Fullerton (building) 3 

34. Orange (building) 3 

35. Gorman 1 36. Fort Tejon .......... 1 

37. Grapevine .... 1 38. Wheeler Ridge .... 1 

Total number of instruments ..... 56 

0.03 

.39 

.16-.37 

.13 

.15 

.04 

.08 

.10 

.02 

.04 

Distance 

from epicenter 

(miles) 

49 

18 

15-19 

20 

28 

65 

39 

33 

85 

45 

TABLE 2.-Strong-motion accelerographs in the Los Angeles 

area with selected maximum ground level-accelerations 

Location Number of instruments 

1. 111 N. Hope .... 3 

2. 445 S. Figueroa 3 

3. 533 S. Fremont ..... 3 

4. 611 W. Sixth ............................ 3 

5. 250 E. First 3 6. 646 S. Olive .............................. 3 

7. 808 S. Olive 3 8. 420 S. Grand ............. 3 

9. Santa Anita Dam .............. 1 10. Cal Tech: Atheneaum and Millikan Library, Pasadena 11. Jet Propulsion Lab., Pasadena ................................ 2 12. 633 E. Broadway, Glendale.... 1 

13. 1640 Marengo ....... .............. 3 

14. 48I4 Lorna Vista, Vernon 1 15. 3663 S. Hoover ................ 3 

16. 3407 W. Sixth ......... 3 

17. 3470 Wilshire ............ 3 18. 3710 Wilshire ..... 3 19. 4867 Sunset ................. 3 

20. 4680 Wilshire 3 

21. !025 N. Highland ... 3 

Sampled 

maximum 

Acceleration 

(fraction of gravity) 

.14 

.13 

.22 

.27 

.12 

Distance 

from 

epicenter 

(miles) 

26 

26 

23 

22 

TABLE 2-Continued 

Location 

Number of instruments 

22. 7080 Hollywood ... 23. 120 N. Robertson 24. 1901 Ave. of Stars ......... . 25. 9·15 Tiverton ................... . 26. UCLA Eng. bldg .... . 27. 16055 Ventura ...... . 28. 8244 Orion ............. . 29. Pacoima Dam ............. . 30. Terminal Island, Long 3 

3 

3 

3 

1 ..... 3 

3 

I 

Beach ..................................... . 31. 215 W. Broadway, Long Beach ..................... 1 32. 2011 Zonal ... 3 

33. Pasadena Scismol. Lab............ 1 34. 3345 Wilshire 3 

35. 750 Garland ........................ 3 

36. 3440 University 3 37. 5260 Century ............................ 3 38. 984I Airport Blvd..... 3 

39. 15433 Ventura 3 

40. 8639 Lincoln .............................. 3 

41. 6424 Sunset 3 42. 6464 Sunset .............................. 3 

43. 3838 Lankershim 3 44. 3411 Wilshire 3 

45. 800 W. First .......................... 3 

46. 222 Figueroa ....................... ...... 3 

47. 11661 San Vicente .................... 3 

48. 1900 Ave. of Stars 3 

49. 234 Figueroa 3 

50. 3550 Wilshire ....... 3 

51. 2070 Century Park East ........ 3 52. Griffith Park ........ ........... 1 53. Long Beach State College ...... 1 

54. 1150 s. Hill ............ 3 

55. 1625 W. Olympic ................... 3 

56. Palos Verdes Estates .... ... 1 

57. 900 S. Fremont, Alhambra 3 

58. I5I07 Vanower 3 

59. 16661 Ventura 3 

60. 15910 Ventura ... 3 

61. 15250 Ventura 3 

62. 15724 Ventura 3 

GR. 1760 N. Orchid 3 

64. 930 Hi!gard ......... ..... 3 

65. 435 N. Oakhurst, Beverly Hills ..................................... . 66. 4fi0 Roxbury, Beverly Hills .. . 67. 9100 Wilshire, Heverly Hills 68. 9450 Wilshire, Beverly Hills ... . 69. 5900 Wilshire, Beverly Hills ... . 70. 6200 Wilshire, Beverly Hills 71. 1177 Beverly Drive 72. 1880 Century Park East 73. 1800 Century Park East 74. Century City Ground ........... . 75. 1888 Century Park East ....... . 76. 2500 Wilshire ........ . 

3 

3 

3 

3 

3 

3 

3 

3 

3 

1 

6 

3 77. 616 S. Norman die ······· 3 

Total number of instruments ········ 209 

1. Several high·frequency peaks to 1 g. 

Sampled 

maximum 

Acceleration 

(fraction of gravity) 

.11 

.17 

······:28' (vertical) 

l .5-. 75 

.03 

.04 

.18 

.18 

.12 

.04 

.23 

.09 

.13 

.10 

Distance 

from 

epicenter 

(miles) 

21 

25 

13 

5 

45 

31 

18 

21 

27 

43 

18 

24 

25 

24 

TABLE 3.-Representative maximum accelerations recorded 

on the top floors of Los Angeles area buildings 

l All stations are in Los Angeles unless otherwise noted] 

Maximum Distance from acceleration epicenter Floor (fraction of 

Station (miles) level gravity) 

8244 Orion 13 8 (roof 0.39 

15107 Van owen 15 8 (roof) .38 

15250 Ventura 18 13 (roof) .26 

3838 Lankershim 18 21 (penthouse) .23 

Millikan Library-CIT, Pasadena 23 10 (roof) .34 

1880 Century Park East 25 17 (penthouse) .27 

4680 Wilshire 25 6 .30 

1640 Marengo ................... 26 8 (roof) .43 

611 w. Sixth 26 42 (penthouse) .18 

250 E. First .................. 26 17 (roof) .21v 

8639 Lincoln 30 12 .12 

4000 w. chav~-~~~--·o·~~-~g~ 53 19 .08 
166 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

TABLE 4.-Seismoscopes in southern California 

Location Site 

Altadena _________________ Devils Gate Reservoir (crest). 

Devils Gate Reservoir (left bank). 

1972 Skyview Drive (residence). Arcadia __________________ Santa Anita Reservoir. 

Arrowhead _______________ U.S. Forest Service station. 

Azusa ___________________ . Cogswell Reservoir (crest). 

Cogswell Reservoir (right bank). 

San Gabriel Reservoir (crest)_ 

San Gabriel Reservoir (left bank). B.everly HilJs ____________ .Lower Franklin Canyon (west 

abutment). 

Lower Franklin Canyon (main 

dam, crest). Burbank _________________ Burbank High School. 

Castaic_ __________________ North Station. 

· Old Ridge Routes. 

Cedar Springs ____________ Strong-motion station. 

Exterior. 

Claremont_ _______________ Live Oak Reservoir (crest). 

Live Oak Reservoir (left bank). 

Thompson Creek Reservoir (crest). 

Thompson Creek Reservoir (left 

bank). Encino ___________________ Encino Reservoir (crest). 

Encino Reservoir (tower). 

Encino Reservoir (west abutment). El Centro ________________ Jmperial Valley Irrigation District, 

strong-motion station. 

El Centro High School. 

El Centro steamplant. 

El Centro waterworks. 

El Segundo _______________ Hyperian treatment plant. 

Eagle,R<ick _______________ Eagle Rock Reservoir (west abutment). 

Eagle Rock Reservoir (main dam, 

crest). Fairmount_ ______________ Fairmount Reservoir (south abutment). 

Fairmont Reservoir (main dam, 

crest). Glendale _________________ Herbert Hoover High School. 

Glendora _________________ Big· Dalton Reservoir (crest). 

Big Dalton Reservoir (left bank). Goleta (2) _______________ .Two ____________ ------ _____ _ 

Hollywood _______________ Hollywood Reservoir (west abutment). 

Hollywood Reservoir (main dam, 

crest). La Jo!la __________________ Boquet Canyon Reservoir (west 

abutment). 

Boquet Canyon Reservoir (main 

dam, crest). Lake Hughes _____________ Array No. 2. 

Array No. 3. 

Array No. 4. 

Array No. 4A. 

Array No. 5. 

Array No. 7. 

Array No. 8. 

Array No. 9. 

Array No. 11. 

Array No. 12. 

Long Beach ______________ Municipal Bldg., strong-motion site· 

San Pedro High School. 

Terminal Island, strong-motion 

site. 

Los Angeles--------------Baldwin Hills Reservoir (east 

abutment). 

E. Los "Angeles Jr.. College. 

Hancock Park. 

Taylor Residence. 

Colton, strong-motion site. 

Hollywood, strong-motion site. 

Tauxe Residence. 

Edison Bldg., strong-motion site. 

Location 

TABLE 4.-Continued 

Site 

Vernon, strong-motion site. 

Leeds Residence. 

UCLA, strong-motion site. 

Duke Residence. 

San Marino City Hall. 

W. Los Angeles Public Library. 

Van Nuys High School. 

Southgate High School. 

Elysian Heights School. 

Playa Del Rey School. 

Windsor Hills School. 

Museum School Admin. Bldg. 

Huntington Park City Hall. 

Narbonne High School. 

Monrovia _________________ Sawpit Canyon Reservoir (right 

bank). 

Sawpit Canyon Reservoir (crest). 

Mount Wilson ____________ Cal Tech Seismograph Station. 

Olancha __________________ Haiwee Reservoir (east abutment). 

Haiwee Reservoir (main dam, 

crest). Pacoima __________________ Pacoima Dam. 

Pasadena ________________ Eaton Wash Reservoir (base). 

Eaton Wash Reservoir (crest). 

Gilman Residence. 

Millikan Library, CIT. 

Motta Residence. 

Muir High School. 

Washington Jr. High School. 

Seismological Laboratory. 

San Raphael School. 

Garfield School. 

Hale School. 

Cal Tech, strong-motion site. 

Pearblossom _____________ .Pear blossom pumping plant. Perris ____________________ Strong-motion station. 

Riverside ________________ Cal Tech Seismograph Station. 

San Bernardino __________ . Post Office, strong-motion site. 

Devils Canyon Site No. I. 

Devils Canyon Site No. 2. 

Devils Canyon Site No. 4. 

Devils Canyon Site No. 5. 

Devils Canyon Site No. 6. 

Devils Canyon Site No. 7. 

San Dimas _______________ Puddingstone Reservoir. 

San Dimas Reservoir (crest). 

San Dimas Reservoir (left bank). 

Puddingstone Reservoir, strongmotion site. 

San Fernando ____________ Lower San Fernando Reservoir 

(east abutment). 

Lower San Fernando Reservoir 

(main dam, crest). 

San Marino ______________ l155 Shenadoah Rd. (residence). 

Santa Ana _______________ Strong-motion site. 

Santa Barbara ___________ Strong-motion station. 

University of California. 

Museum. 

Santa Felicia Dam ________ Toe of dam. 

Outlet works. 

Right abutment. 

Right crest. 

Dam crest. 

Left abutment. 

Saugus __________________ Dry Canyon (east abutment). 

Dry Canyon (main dam, crest). 

Sunland __________________ Big Tujunga Reservoir (crest). 

Big Tujunga Reservoir (left 

bank). 

Table Mountain __________ Tiltmeter station. 

Westwood ________________ Lower Stone Canyon Reservoir 

(east abutment). 

Lower Stone Canyon Reservoir 

(main dam, crest). 
.2 

Santa Barbara 

.o..., ('/~ 

/(' 

N 

~ 

0 

(' ~ NEWPORT-INGLEWOOD 

Af FAULT 

"" 

0 20 40 60 

MILES --··-··-··.-··--··-·· MEXICO 

., 

( 

.\. 

\.. 

\ 

t., 

) 

~ 

( 

/ 

. "' ( ~ 

J~~ );; 

,..,· "' ~ 

i 

'--') 

I 

.J 

FIGURE !.-Location of strong-motion accelerographs in southern California maintained by the NOS-NOAA as part of the cooperative network 

(February 1971). 

>-3 

::r1 

t:::l 

U1 

> z 

"%j 

t:::l 

~ 

z 

> 

z 

I:) 

0 

0 

> 

t"' 

-

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0 

~ 

z 

> 

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> 

~ 

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> 

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t:::l 

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q 

> 

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~ 

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..... 

<0 

_, 

..... 

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cr;, 

-:] 
168 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

PACOIMA DAM 

.,. 

e ss 

PASADENA Q 

N 

L 

0 10 

MILES 

FIGURE 2.-Location of strong-motion accelerographs in the Los Angeles area maintained by the NOS-NOAA as 

part of the cooperative network (February 1971). 
( 

,j 

' \, /1.04g 

I . 

FIGURE 3.-Accelerograph record from the abutment of Pacoima Dam, a cooperative station with the Los Angeles County Flood Control District. 

>-3 

i:I1 

M 

ifl 

> 

z 

"l:j 

M 

~ 

z 

> 

z 

t:j 

0 

() 

> 

t-< 

...... 

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0 

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z 

> 

M 

> 

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> p::: 

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0 

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M 

l:d 

~ 

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> 

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>-< 

,;o 

..... 

<D 

-'l 

..... 

O'l """ 

<:0 
170 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 4.-Accelerograph site on the east abutment of Pacoima Dam. The instrument is located in the small silolike 

structure. Note (A) the massive spalling of bedrock and (B) the cracking and displacement adjacent to the accelerograph housing. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 5.-Seismoscope record from Lower Van Norman Dam, a cooperative station with the 

Los Angeles Department of Water and Power. Arrow points north. 

171 
s 74° w 

S = 7 .55 cm f g 

DOWN 

S = 7 .62 cm / g 

S 16° E 

S = 7.60 cm / g 

..... 

-.:) 

~ 

o-,3 

::r: 

~ 

U1 

> z 

~ 

~ 

~ 

z 

> 

z 

t:1 

0 

0 

> t"' 

...... 

~ 

0 

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z 

:; 

~ 

> 

~ 

o-,3 

::r: 

10 

~ 

> 

~ 

~ 

0 

~ 

~ 

~ 

~ 

~ 

~ 

--------------------------~ NATIONAL OCEAN SURVEY - NOAA 

SEISMOLOGICAL FIELD SURVEY 

PACOIMA DAM 

AR-240 S/ N 179 

EARTHQUAKE OF 9 FEB 1971 0600 PST 

FIGURE 6.-Accelerograph record, Pacoima Dam. 

~ 

<D 

...... 

<D 

...:] 

...... 
N 21 ° E 

S = 8.1 cm/ g 

DOWN 

S = 7.9 cm/ g 

N 69° W 

S = 7.6 cm/ g 

-~~~A~~ ~ --- lillt~ t.".l 

~ 

z 

> 

z 

0 

0 

C1 

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z 

...... 

> 

t.".l 

> 

~ 

>-3 

_- ! 

~ 

t.".l 

to 

~ 

C1 

> 

~ 

><: 

_;D 

----------------------------------------~ NATIONAL OCEAN SURVEY - NOAA 

SEISMOLOGICAL FIELD SURVEY 

CASTAIC, OLD RIDGE ROUTE 

AR-240 S/ N 124 

EARTHQUAKE OF 9 FEB 1971 0600 PST 

FIGURE 7.-Accelerograph record, Castaic, Old Ridge Routes. 

~ 

~ 

1-' 

-.1 

c.:> 
NORTH 

S = 7.6 cm / g 

DOWN 

S = 7.6 cm / g 

WEST 

S = 7.6 cm / g 

~ 

-l 

~ 

>-3 

::1:1 

t<,j 

r:n 

> z 

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'=' 0 

0 

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> ---·---------------------------------------------------~ NATIONAL OCEAN SURVEY - NOAA ><: 

SEISMOLOGICAL FIELD SURVEY 

LOS ANGELES, 8244 ORION BLVD , 8th FLOOR 

AR-240 S/ N 199 

EARTHQUAKE OF 9 FEB 1971 0600 PST 

FIGURE 8.-Accelerograph record, U>s Angeles, 8244 Orion, eighth floor. 

<:> 

""" <:> 

...::] 

""" 
NORTH 

S = 7 .6 cmf g 

DOWN 

S = 7.6 cm f g 

WEST 

S = 7.6 cm f g 

>-3 

::z:: 

t.".1 

- ~ z 

> 

z 

tj 

9 

0 

- ~ .?> 

t.".1 

-~~~~ > 

.:;.::: t.".1 

0 

"%j 

"%j 

t.".1 

t!i 

::0 

q 

--------------------------------------------------- > 

NATIONAL OCEAN SURVEY - NOAA 

SEISMOLOGICAL FIELD SURVEY 

LOS ANGELES, 8244 ORION BLVD. , 4th FLOOR 

AR-240 S/ N 210 

EARTHQUAKE OF 9 FEB 1971 0600 PST 

FIGURE 9.-Accelerograph record, Los Angeles, 8244 Orion, fourth floor. 

::0 

>< 

~'-0 

..... 

'-0 

-'1 

..... 

,_. 

-J 

01 
II 

...... 

-J 

en 

>-3 

::r: 

t".l 

U1 

~~R:~ 9 -~~~~A~~~ ~, r Z 

DOWN 

S = 7 .6 cm / g 

WEST 

S = 7.6 cm f g 

> z 

l:j 

0 

C1 

> 

-

IZ 

~ 

.> 

t".l 

> 

~ 

>-3 

::r: 

- ~ ---- p:: 

t".l 

0 

>:rj 

>:rj 

t".l 

td 

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q 

---------------------------------------------------------> NATIONAL OCEAN SURVEY - NOAA ~ 

SEISMOLOGICAL FIELD SURVEY ><: 

LOS ANGELES, 8244 ORION BLVD., 1st FLOOR ~ 

AR-240 S/ N 190 ~ 

EARTHQUAKE OF 9 FEB 1971 0600 PST ;::l 

FIGURE 10.-Accelerograph record, Los Angeles, 8244 Orion, first floor. 
EVIDENCE OF RECORD VERTICAL ACCELERATIONS A'T KAGEL CANYON 

DURING THE EARTHQUAKE 

By B. J. MORRILL 

NATIONAL OCEAN SURVEY, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

The earthquake of February 9, 1971, which caused 

great damage in the foothills of the northern part of 

San Fernando Valley and which was felt throughout the greater part of southern California, produced evidence of vertical accelerations far in excess 

of any ever recorded instrumentally. The largest 

vertical accelerations recorded by a strong-motion 

seismograph during this quake were in the range 

of 0.5 to 0.75 g at Pacoima Dam, some 2.75 miles 

north-northwest of the Kagel Canyon Fire Station. 

Pacoima Dam is 5 miles and the Fire Station is 8 

miles from the epicenter. The particular evidence 

was noted at the Los Angeles County Fire Station 

No. 74, 12587 North Dexter Park Road (Kagel 

Canyon), San Fernando, and it suggests that the 

vertical acceleration exceeded that of gravity and 

may have equaled or exceeded that of the great 

Assam earthquake of June 12, 1897 (Oldham, 1897) 

in very local situations such as described here. The 

questionnaire card shown in figure 1 indicates that 

the motion was extremely violent. 

Firemen were resting in the wood-frame quarters 

building shown in figure 2. Mr. J. White, duty fireman, stated that he was tossed out of bed onto the 

floor, and the bed landed on top of him. Every object 

in the building was upset. Even the handset of a 

standard wall phone came off its hook. Loud cracking and thunderlike noises added to the general 

confusion. The building was shifted off its foundation. Outside, rocks were thrown off the ground, 

and large cracks appeared in both soil and rock. The 

rear view of the quarters building in figure 3 shows 

one of the many ground cracks that appeared 

throughout the area. The surface of a hill adjacent 

to the building exhibited the "shattered earth" effect 

reported (see section by R. Nason, this report) a few 

miles to the west. A nearby rock roadcut appeared 

to have exploded, and the adjacent road was offset in 

many places (figs. 4 through 6). 

A 20-ton fire truck enclosed in the garage (figs. 7 

and 8) moved 6 to 8 feet fore and aft, 2 to 3 feet 

sideways without leaving visible skid marks on the 

garage floor. The truck was in gear, and the brakes 

were set. Damage to the truck was a bent rear step, 

broken windshield, shattered red light, and siren 

broken off. Also, a ladder and a hook were broken. 

Marks which appear to have been made by the right 

rear tire were found on the door frame (fig. 9) 3 

feet above the floor, while the metal fender was not 

damaged. The fender extends several inches out beyond the upper portion of the tire. Four feet above 

the floor the hose rack was broken by the rear 

step of the truck. The step was bent up while the 

hose rack was broken downward. The rear of the 

garage was pushed outward 6 to 8 inches, and the 

final position of the truck was about 4 feet out the 

front of the garage, with the garage door resting 

on the cab. 

Figure 10 sho~s the northwest corner of the quarters building. Note 'that the bottom row of shingles 

is undisturbed. Thes.e shingles prior to the quake 

overlapped the foundation 4% inches. Figures 11 

and 12 show a plan and an elevation view of figure 

10 with appropriate measurements taken shortly 

after the quake. 

Figures 10, 11, and 12 suggest that the building 

accelerated upward, with respect to the ground, at a 

rate of at least 1 g for about 0.1 second; that is, if 

one assumes only 1 g and the given distance. 

There is other evidence of catastrophic accelerations in the immediate area of the earthquake, of 

ground cracking and faulting. In Soledad Canyon, 

champagne glasses were broken at the base of the 

stems without unusual horizontal displacement. In 

177 
178 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

U.S. DEPARTI.IENT OF COI.II.IERCE 

NOS FORM 680 111·70) 

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

NATIONAL OCEAN SURVEY OMB No. 41·R0013 

Approval Expires June 30, 1975 EARTHQUAKE REPORT 

1. An earthquake was felt QO; nor felt 0 Time_~:::::,.:~=--- 0601 !\.M. 

Om of shock February 9' 1971 ______ P.M. 

If feh, please supply information below (Underline appMpriate words ur fill spaces.) 

If not felt, please sign and return card, which requires no postage. 

a. City, County, Stare, and Township _L_ !L Count~, Qa lif, 

w Ran~e, ,Section, Quarre.r Section, or Coordinates R-3N-14H. Sec. 32 ~ 

~ b. Ground: ;:::) 

zo @gravelly, Joost", comp~cr, marshy, filled in, or 0:%: 

- .... sloping, sreep, or 1-a:: 

~~ 

gw c. II inside, type ol construction d. Ouol ity of construction 

...J(,!) 

a::~ ;:::)0:: Wood, brick, s(one, or wood fram~ New.(';ld, well buil7)r,onrly budr, or ____ 

0;:::) 

>-O e. Ho. of floors f. Observer's g. Activity when earthquake occurred: h. II outsid.e, you, 

N in building floor Walkin~:.G;!"ri~lying down, others were: 

Single 1st ,leeping Quiet, auive 

zz a. Felt by: 

og Very few, several, many, all (in your home~n commun~ ., .... b. Awakened: ~--~ 

U...J No one, few, many, all (in your home>(In communiryi) W;:::) 

~Q. c. Frightened: ~0 

WQ. No one, few, many, all (in your home{n communiij}general panic 

,.; 

0 

w., a. Rattling of windows, doors, dishes, etc. A 11 of above prior to shoe 

t-o 

""z ...J;:::) b. Creoking of building (Describd Loud-snapping wo «"' Loud -similar to Jet .. c. Earth noises: Faint, moderate, loud 

a. Outsidot: 

w (1) Trees and bushes <haken, vehicles rocked, ere. Yes 

(,!) 

-c (2) Ground cracked; landslides; water diMurbed. etc. .1'\11 of these ~ 

~ (3) Chimneys, tombstones, elevated warrr tanks, etc., cracked, twisted, 

0 overturned A 11 of thee.e 

0 

z (4) Other effects 

"" "' b. Buildinvs: 

1-

u (I) Hanging objects swung moderately,~ Direction East to West 

1.1.1 

~ 

~ (2) Small objects shifted, overturned, fell S 

w (3) Furniture shifted, overturned, broken Yes _. (4) Plaster cracked, broken, fell Yes "" u (5) Windows cracked Yes ;;; 

>- (6) Structural elements of brick, wood, or Wood 

:I: 

Q. Damage slight, moderate, great Grea :C 

.,; 

Additional infor ... tion will be appreciated. Use apace on ,.verao aide. 

FIGURE 1.-Earthquake report questionnaire indicates violent motion felt in Kagel Canyon. 

k 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 179 

many places transformers were lifted out of their 

brackets. Seismoscope records in some locations 

showed interruptions in their traces, which suggest 

that the styli left the smoke glass plates. Figure 13 

shows one of these records. 

ACKNOWLEDGMENTS 

The patience and cooperation of the people of 

FIGURE 2.- Quarters building of Los Angeles County Fire 

Station No. 74 (Kagel Canyon). 

FIGURE 3.-Rear view of figure 2, showing one of the many 

ground cracks in the area. 

Kagel Canyon so soon after their disaster is very 

much appreciated. 

Members of the Earthquake Mechanism Laboratory, NOAA, headed by Dr. Don Tocher, reviewed 

the manuscript. 

REFERENCE 

Oldham, R. D., 1897, Report on the Great Earthquake of 

June 12, 1897: India Geol. Survey Mem. v. 29 [1899]. 

FIGURE 4.-Tossed-earth effect noted at top of rock hill beside 

quarters building. 

FIGURE 5.-Typical road cracking and offsets in immediate 

area. 
180 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 6.-Highway cracks and offsets. Rocks in face of road 

cut shattered with explosive intensity. 

FIGURE 7.-Twenty-ton fire truck, located in garage at left, 

was moved several feet forward, backward, and sideways, 

without leaving visible skid marks on floor. 

FIGURE 8.-Front view of fire truck shows broken windshield, 

damaged red light, and siren 

FIGURE 9.-Damage to garage interior. Rubber marks on 

door frame appear to have been made by rear tire of truck. 

FIGURE 10.-Northwest corner of quarters building showing 

shingles which overlapped foundation. Shingles on opposite 

side of building also undamaged. 
THE SAN FERNANDO, CALIF'ORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 181 

~---- ;;u • .. -----~ 

FIGURE 11.-Plan view of quarters building, northwest corner. 

/ ~rovYI cl •, 

"' l 

FIGURE 12.-Elevation view of quarters building, northwest 

corner. 

FIGURE 13.-Burbank High School seismoscope record. Vertical motion lifted stylus arm and interrupted trace. 
PRELIMINARY REPORT OF AN ENGINEERING STUDY 

This preliminary report on the engineering 

study of the San Fernando earthquake was prepared by the Earthquake Engineering Research 

Institute (EERI) under contract with the National 

Oceanic and Atmospheric Administration of the 

Department of Commerce. The EERI is a nonprofit 

organization composed of engineers and scientists 

from many earthquake-related disciplines. The membership is by invitation and is drawn from government, university, and private professional practice. The members of the EERI Committee are 

D. F. Moran, Chairman, Clarence Allen, W. A. 

Brugger, L. LeRoy Crandall, H. J. Degenkolb, 

C. M. Duke, J. F. Meehan, C. W. Pinkham, and 

Robert E. Wallace. Karl V. Steinbrugge provides 

liaison between the National Oceanic and Atmospheric Administration and the Earthquake Engineering Research Institute. A list of cooperating 

organizations is given at the end of the report. 

INTRODUCTION TO 'THE ENGINEERING STUDY 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

The San Fernando earthquake of February 9, 

1971, is very significant for several reasons. 

Despite the moderate magnitude of 6.6, damage 

to structures, utilities, and transportation systems 

was severe over a small area. We must consider this 

earthquake as another warning. As in Long Beach 

(1933) and Alaska (1964), the off-hours timing 

(6: 01 a.m.) was fortunate, and the resulting loss 

of life and injuries were only a small fraction of 

what might have resulted had the earthquake occurred 1 or 2 hours later. 

The collapse of structures at the Olive View 

Hospital and the freeway bridges, combined with 

severe damage to roads and freeways, would have 

resulted in a large loss of life and many injuries. 

(See figs. 1 and 2 for maps of the area.) Collapse 

of old, unreinforced masonry walls would have 

caused additional deaths and injuries. Even so, 

45 persons were killed by collapse of a portion of 

the Veterans Hospital in Sylmar. 

We must learn important lessons from this 

earthquake which we can apply to improvement of 

our building codes, emergency procedures, and 

182 

transportation facilities. We may not be so fortunate when the next earthquake occurs. 

This shock is also significant because of the 200 

records that were made by strong-motion instruments. In about each of 50 tall buildings three 

instruments were installed and operating, generally one in the basement or ground floor, one about 

midheight, and one on the roof. Records of all of 

these and other instruments will provide us with a 

wealth of data for evaluation of performance of 

all types of structures. This is easily the most 

instrumentally important earthquake which has 

ever occurred. 

The earthquake also provided the first real test 

of earthquake-resistive construction as it is practiced in California. 

Many structures failed the test. The three major 

multistory buildings in the area were hospitals, 

and all had to be evacuated owing to severe structural damage. Several freeway-bridge collapses 

caused closing of three major freeways and one 

railway north of Los Angeles. 

Residential and apartment damage was heavy, 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 183 

~1M> jUS. 

SA/J FERNANDO VALLEY AREA 

SCALE /!J /JILES 

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IJOAA/ EE R! 

SAN FER/JA/JDO EARTHQUAr.E IIJVESTIGATION COMMITTEE 

AAARCH 1971 

FIGURE 1.-San Fernando area. 
184 THE SAN F ERNANDO, CALIF ORNIA, EARTHQUAKE OF F EBRUARY 9, 1971 

SAN ~~RNANOO 

VALLI!'Y 

LOS ANGE.LES ARE.A 

SCALE IN MILES 

0 1 13,5678 

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VALL£Y Fl<wy 

PACOIMA DAM 

SAIJ FER1JAt.JDO EARTI-IQUAKf mVESTIGATION COMMITTE£ 

MM~CU 197 1 

VINCENT 

FIGURE 2.-Los Angeles area. 

'/NO FI<WY 

WEST COYINA 

ORANGI! COONT'Y 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 185 

even to newer types. Undoubtedly, ground lurching, settling, and cracking contributed to the damage. 

Detailed studies of perhaps 50 structures including buildings, bridges, dams, and dwellings will be 

be made. 

Analysis of structures will be correlated with 

instrumental records. Included will be several 

high-rise structures which produced records. 

The economic loss for this shock is estimated at 

one billion dollars, with about one-half for private 

and the other half for public properties. 

Extensive studies must be made to determine the 

relative effects on damage of ground movements 

such as lurching, settling, cracking, and compression as compared with the effects. of ground vibration. 

The exact cause of damage to many structures 

may never be clearly known. There are strong evidences of severe vertical accelerations which could 

contribute to increased damage. 

This preliminary report is necessarily brief and 

limited to descriptions of what was there and what 

happened to it. Many facts about damage and 

detailed statistical data are not available at this 

time. It is too early to reach conclusions and make 

significant recommendations. 

The committee is _convinced that the importance 

of this earthquake justifies a major investigation. 

We must learn as much as possible from this moderate quake before the next disastrous temblor 

comes. 

We wish to acknowledge the valuable contributions of the various subcommittees and organizations. We are particularly grateful for the section 

on buildings which was provided by members of 

the Structural Engineers Association of California. Many structural engineers examined damaged structures and provided reports thereon as a 

service to their profession. 

All organizations and agencies contacted have 

responded willingly and offered the committee 

their data, reports, and photographs for use in its 

investigation. 
SOILS AND FOUNDATIONS 

By L. LEROY CRANDALL 

L. LEROY CRANDALL AND AsSOCIATES 

With few exceptions, the buildings in the area of 

the greatest damage are underlain by a varying 

thickness of recent alluvial deposits. In the San 

Fernando portion of the San Fernando Valley, these 

alluvial deposits are relatively granular, consisting 

primarily of sands and silts. It is apparent that the 

bedrock motions during the earthquake were amplified several-fold, resulting in much larger groundsurface accelerations and amplitudes than might 

otherwise be expected from an earthquake of magnitude 6.6. 

Although the surface accelerations were large, 

the greatest damage to structures and utilities may 

have been caused by ruptures and fractures in the 

earth's surface. Measurements of the permanent 

earth displacements are only in the preliminary 

stages as yet, but it is apparent that lateral and 

vertical offsets of several feet have occurred along 

some of the ruptures in the alluvial soils. The rupturing seems to occur in an east-west direction in 

several belts extending across the· northern San 

Fernando Valley. Ruptures have also been observed 

in the hills to the north and east, but very few 

buildings are located on the relatively steep hillsides. Highways and transmission lines in those 

areas, however, suffered severe damage, particularly the bridge structures of the freeways. The 

cause of the extensive ground rupturing is one of 

186 

the important aspects of the earthquake yet to be 

determined. While many believe the rupturing is 

a result of tectonic movements in the bedrock, there 

is the possibility that the permanent surface displacement resulted from extreme ground shaking. 

Most buildings in the area are supported on conventional spread footings, although some of the 

taller structures are on drilled cast-in-place friction 

piles. Except where actual ground rupturing occurred beneath a building, the foundations of the 

buildings appear to have functioned satisfactorily. 

This observation is based on very limited investigation, however, and much study remains to be done 

before definite conclusions can be drawn. There is 

no doubt, however, that severe damage occurred to 

all buildings which were subjected to significant 

ground rupturing. Much thought needs to be given 

to methods of minimizing the effects of such permanent ground displacements, although it is doubtful 

that anything can be done to prevent serious structural damage in such cases. In passing, great praise 

should be given to the structural engineers whose 

buildings, for the most part, refused to collapse 

even though rent asunder by deformations of several 

feet. The fact that many of the buildings are standing at all should be heartening to those who occupy 

the structures and whose lives would be in jeopardy 

in less well-designed and less well-built structures. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 187 

FIGURE 1.-Earthslide, afternoon of February 9, 1971, near 

intersection of Routes 5 and 14. J. F. Meehan, OAC photograph. 

FIGURE 2.-Surface expression of movement 2% feet vertically, Lopez Canyon and Foothill Boulevard, J. F. Meehan, 

OAC photograph. 

FIGURE 3.-Foothill Boulevard, east of Arroyo. Compression 

ridge in street, J. F. Meehan, OAC photograph. 

FIGURE 4.-Sidewalk, San Fernando Industrial Park. J. F. 

Meehan, OAC Photograph. 
DAMAGE TO THE OLIVE VIEW HOSPITAL BUILDINGS 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

The Olive View Hospital is a new facility owned 

by the County of Los Angeles. There are five structures in the complex; a large five-story medicaltreatment and care facility, a two-story psychiatric 

unit, power plant, assembly building, and small 

parking shelter (fig. 1). 

Foundations are reinforced concrete, spread type. 

The medical-care facility is a five-story reinforcedconcrete structure over a basement area larger than 

the building above. Concrete is hardrock. The basement-floor level is at grade on the south and east 

sides but is buried at the north and west sides. The 

basement areas which extend beyond the structure 

above have dirt and planting supported on the basement-roof areas. 

The plan is roughly cross shaped with four structurally-separated stair towers and recreation areas, 

located at the ends of each wing. Towers are supported over larger basement areas except for the 

tower located on the north side. 

Construction is reinforced concrete. Generally, 

floor and roof are fiat slabs with drop panels at columns. The lateral-force bracing system consists of 

reinforced-concrete shear walls for the top four 

stories and moment-resisting frames for the lower 

story and basement. 

Ground breakage occurring in this area consisted 

of cracks in ground and paving and also compression 

ridges. An eyewitness describes the first and last 

movements as strongly vertical. 

Areas of the basement collapsed, mainly outside of 

the structure supported above. Some perimeter basement columns punched through the slabs supporting 

earth and planting above (fig. 2). All towers except 

the north tower fell away from the main building 

and rested on their sides. The north tower is leaning 

but still standing. The collapsed towers pushed into 

the basement below and tore away vertically adjacent to the main building in some cases. 

The main building suffered severe damage to the 

first-story columns above the basement and is leaning about 1% feet to the north in the first story 

(fig. 3). Damage to the upper four floors is only 

188 

moderate. Most first-story columns are square with 

round, spirally wrapped cores except for those at the 

corners, which are "L" shaped and tied. At the exterior walls, number 18 reinforcing bars extend from 

the basement columns up about 5 or 6 feet into the 

corners of the spirally wrapped columns above (fig. 

4). These bars generally broke out of the corners. 

The round column cores were badly crushed, but 

concrete remained inside the spirals. Corner columns were badly fractured (fig. 5), many ties were 

broken, and some concrete fell from inside the vertical bars. 

The assembly building is a one-story reinforcedconcrete structure located just north of the medical 

care building (fig. 6). This structure is leaning about 

18 inches toward the north (fig. 7). 

The psychiatric unit was a two-story reinforced 

concrete structure. Floors and roof are pan-joist 

construction. Concrete above grade is lightweight. 

Lateral-force resisting system is by frame action for 

both floors. Columns are tied. 

Columns in the first story failed (fig. 8), and the 

second floor is resting on the grade slab. Columns 

are badly shattered with broken ties, and much of 

the concrete is displaced from inside reinforcing 

bars. Direction of failure seems to be in a south and 

east direction (fig. 9) . 

The power station suffered severe damage to contents. Boilers were shifted as much as 4 feet. Piping 

and electrical and mechanical equipment were badly 

damaged (fig. 10). Steel flat-bar bracing in the 

north wall was stretched and broken (fig. 11). However, the reinforced-masonry shear wall at the south 

side was only slightly cracked. 

The one-story parking shelter has a reinforcedconcrete roof slab supported on columns. There are 

no walls. Columns failed, generally at the top, and 

the roof fell on several vehicles (fig. 12). 

A special committee of members of the Structural 

Engineers Association of Southern California, with 

Wiiiiam T. Wheeler as chairman, has been appointed 

to study damage to this hospital facility for the 

County of Los Angeles. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 189 

FIGURE 1.-0live View Hospital. Medical Care Building on 

right, Assembly Building in center, and Psychiatric Unit 

at left. 

FIGURE 2.-0live View. South side of Medical Care Building. 

Columns punched through basement roof slab. 

FIGURE 3.-0live View, Medical Care Facility, north wall. 

Note shattered concrete in corner column. 

FIGURE 4.-0live View, Medical Care Facility. Spirallywrapped column with number 18 corner bars. 

FIGURE 5.-0live View Medical Care Building. Corner column, 

first story. 

FIGURE 6.-0live View Medical Care Building. First-and 

second-story columns. 
190 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 7.-0live View Assembly Building. 

FIGURE 8.-0live View Psychiatric Unit. Second floor rests 

on tables and chairs. 

FIGURE 9.-0live View Hospital. Overturned concrete benches. 

Psychiatric Unit in background. 

FIGURE 10.-0live View Power Building. Bent pipe hanger. 

FIGURE 11.-0live View Power Building. Flat-bar bracing 

broken in north wall. 

FIGURE 12.-0live View Parking Shelter. 
DAMAGE TO THE LOS ANGELES COUNTY JUVENILE FACILITIES, SYLMAR 

By JAMES H. THOMPSON 

WILSON AND THOMPSON, CONSULTING STRUCTURAL ENGINEERS 

The Juvenile Hall facilities comprise many oneand two-story buildings constructed of concrete 

floors and roofs with concrete frame or reinforced 

masonry bearing walls and in some cases nonbearing walls. Design is based on a modern building 

code with earthquake-resistive requirements. 

The area was subjected to very heavy ground 

movement. Fissures opened that measured 18 to 24 

inches wide at the top with a depth of 4 to 5 feet 

(fig. 1). Lateral differential movement occurred, 

causing pavement to rupture and slide as much as 

1 to 2 feet over adjacent pavement. Vertical movement occurred, causing heaving up of large areas 

several feet high and depressions in other areas. 

Generally, movement was very large, resulting in 

permanent ground displacements and extensive damFIGURE !.-Juvenile Hall. Ground crack opening in girls dormitory. J. F. Meehan, photograph. 

age to the building construction. 

Damage to buildings was very heavy and extensive (fig. 2). Virtually every building received significant structural damage, except the gymnasium 

and one or two other buildings. 

A portion of the two-story administration building 

(concrete frame) collapsed completely in the first 

story (fig: 3). Other one-story buildings have either 

collapsed or are nearing collapse. Many masonry 

walls were cracked and shattered or experienced 

heavy displacement (fig. 4). Hammering effects between adjacent buildings is evident in many places 

and caused significant structural damage a long 

interface lines. 

Preliminary estimates indicate that few, if any, 

of the damaged buildings can be saved. 

FIGURE 2.-Juvenile Hall. Detail of wall failure. J. F. Meehan, 

OAC photograph. 

191 
192 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Juvenile Hall. Cracks in pavement extend under collapsed administration building. 

J. F. Meehan, OAC photograph. 

FIGURE 4.-Juvenile Hall. Cantilevered walls leaning. J. F. Meehan, OAC Photograph. 

i41 
DAMAGE TO THE PACOIMA MEMORIAL LUTHERAN HOSPITAL 

(11600 Eldridge A venue, Pafoima) 

By WILLIAM F. RoPP 

DANIEL, MANN, JOHNSON, AND MENDENHALL, ARCHITECTS AND ENGINEERS 

The building is composed of three sections isolated from each other by separation joints (fig. 1). 

The south section is one story in height, the north 

section is two and three stories in height, and the 

center section, or Nursing Tower, is four full stories 

in height with a mechanical penthouse. 

The building is reinforced concrete and reinforced 

masonry. The floor and roof structures are reinforced concrete pan-joisted slabs supported by reinforced concrete beams. Shear walls for the south 

and center sections are reinforced concrete, while 

several of the shear walls for the north and south 

sections are reinforced brick masonry. 

The building is supported by a foundation consisting of drilled concrete piles in clusters approximately 40 feet in length. 

Damage to the building caused by the earthquake 

was massive. It is evident that the structure experienced sufficient seismic forces to cause actual 

uplift (fig. 2). The east end wall of the center 

section (fig. 3), which is a major horizontal loadresisting element of the structure, was cracked 

sufficiently to render it ineffective for further usage. 

The west end wall of the center section, also a 

major horizontal load resisting element, was badly 

cracked, though not as badly as the east wall. Some 

south wall piers of the center section, which act 

as both vertical and horizontal load resisting elements, are badly cracked near the second-floor level. 

Floor slabs of the second and third floors have 

sustained large diagonal cracks near the juncture 

with the end walls. This was caused by large horizontal forces being delivered to the end shear walls. 

There is evidence of vertical misalignment of 

floor slabs which occurred during the rocking and 

apparent uplift of the structure. 

A severe diagonal crack has occurred in the west 

wall of the cafeteria located in the south section 

(fig. 4). 

This structure, built in 1959, was designed to, and 

did, comply with the requirements of the Los 

Angeles City Building Code in force at that time. 

The design and construction of the building was 

checked and approved by the Los Angeles Department of Building and Safety. In accordance with the 

requirements of the Building Code, the structure 

was designed to resist equivalent horizontal forces 

of approximately 10 percent of gravity. There is 

substantial evidence that the actual horizontal-force 

magnitude experienced was several times that 

amount. 

The feasibility of restoration of the building has 

been considered. The north and south sections of 

the building could be restored with confidence, as 

the damage appears to be light. Restoration of the 

Nursing Tower, the four-story building, could entail 

the following: 

1. Removal and replacement of the damaged east 

shear wall. This would require shoring of adjacent structure until replacement was complete. 

2. Removal and replacement of west shear wall. 

3. Removal and replacement of damaged wall piers 

on south wall. 

4. Realignment of vertically displaced floor slabs. 

5. Removal and replacement of damaged floor slabs 

at ends of building. 

6. Exposure and repair, if required, of drilled pile 

footings at perimeter of tower. 

7. Exposure and repair, if required, of interior 

bearing walls and columns. 

8. Exposure and repair, if required, of interior 

block walls. 

193 
194 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

9. Replacement of slabs, floor finish, and ceilings 

removed for above noted exposure. 

10. Restoration of wall finish, tile, door frames, 

ceilings, and other finish damaged during the 

earthquake. 

11. Restoration of mechanical and electrical sysFIGURE !.-Pacoima Memorial Lutheran Hospital. New addition in rear. J. F. Meehan, OAC photograph. 

FIGURE 2.-Pacoima Memorial Lutheran Hospital ground 

cracks at north wall. Building raised about five inches 

relative to ground. D. F. Moran photograph. 

terns disturbed during rehabilitation. 

12. The possible construction of additional shearresisting elements. 

The Department of Building and Safety will require that restoration include the bringing of the 

structure up to 1971 code requirements, including 

that for earthquake protection. 

FIGURE 3.-Pacoima Memorial Lutheran Hospital, east shear 

wall diagonal cracks. White lines are patching before 

ake. D. F. Moran 

FIGURE 4.-Pacoima Memorial Lutheran Hospital cracked 

brick wall at west side of south section. 
DAMAGE TO THE HOLY CROSS HOSPITAL 

(15031 Rinaldi, Granada Hills) 

By S. B. BARNES 

S. B. BARNES AND ASSOCIATES 

This hospital is a 10-year old seven-story building walls failed above the third floor. Beam failures 

containing about 162 two-bed rooms plus necessary occurred at both the· third and the fourth floors 

support units including administration, pathology, where they spanned in a direction of 90° to the line 

radiology, maternity, operating, kitchen, cafeteria, of the shear walls. Floor diaphragms near this 

and laundry facilities. The basic seven-story tower region sustained severe diagonal cracking at the 

has plan dimensions of about 89 x 184 feet, and its second through fourth floors. Overturning moments 

longitudinal axis extends approximately in an east- in each of this pair of shear walls caused much spallwest direction (fig. 1). There is a three-story north ing and crushing of concrete within the depth of 

wing and a one-story south wing (fig. 2). The wings the third-floor framing. 

are attached to the basic tower area. There is a Distress in the transverse shear walls at the east 

basement under a portion of the tower area. end of the tower is also apparent (fig. 4). One of 

The framing system consists of lightweight con- these walls which connects to the easterly· corner 

crete pan joist and beam floors supported by stone column of the tower and extends fromthe third floor 

concrete columns and bearing walls. Foundations to the tower roof has severe diagonal cracking in 

are drilled cast-in-place friction. piles. Plans call for the third and fourth stories. Crushing and spalling 

. ,·.the. ultimate compressive st~ength to be 3,000 psi of the fourth-floor pour intrustc)n has· occ'urred at 

for the lightweight concrete and 5,000 psi for the Jhe:~0r-ner, column resulting in column failure just 

stone concrete in the tower area. Resistan:ce:'to' . above the floor pour as well (fig. 5). 

lateral loads is prcNidea,;oy···a bo~ system consisting Architectural columns of 16 x 32 inches spaced 

of the floor and roof diaphragms supported by the at 23-foot centers along the south and north sides 

concrete shear walls. of the tower have severe diagonal cracking and 

Damage to the structure was severe below the spalling within the third and fourth stories. Spansixth floor. The most severe damage occurred in the drel beams connecting these columns have medium 

second to fourth stories where shear walls under- intensity cracking, including horizontal cracks along 

went considerable diagonal cracking and some the pour lines at the tops of floor slabs. 

columns and beams failed (fig. 3). Horizontal cracks The third-floor diaphragm of the north wing has 

at pour lines are apparent in all shear walls. From pulled away from the floor of the basic tower area. 

the fourth floor downward, lateral loads due to the A crack about one-eighth of an inch wide extends 

mass of the north wing appear to have contributed the full width of the floor along the north edge 

to the severity of damage in the second to fourth of the tower area. There are no second-story shear 

stories. walls in this north wing extending in a north to 

At the south end of the tower area is a pair of south direction. Second-story columns in the north 

transverse shear walls interconnected by spandrel wing have cracked and spalled as a result of motion 

beams at floor lines and extending up from the in the south to north direction. 

second floor to the roof of the tower. The floor Longitudinal walls in the core area of the tower 

diaphragms at the third and fourth floors almost have cracked severely in the first to fourth stories. 

completely separated from this pair of shear walls. Of particular interest here are the lintels over doors, 

Columns on the same line as the pair of shear where concrete has cracked in an "X" pattern and, 

195 
196 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

in some cases, complete crushing has occurred. The 

diagonal cracking of lintels extends from the 

corners of openings to the soffit of the floor slab 

above, causing separation of the concrete slab from 

the stems of the joist in the local areas near the 

lintels. 

Vl 

LJJ 

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PLAN 

Further study and detailed evaluation of failures 

in this building should yield much information concerning mechanisms of failure, effects of various 

structural details, and effects of construction 

methods upon the response of a building of this 

type to earthquake loading. 

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S. B. BARNES & ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 

2 236 IE VU LY IO UL IVAID • LOS ANOILES , CA LifORN IA 90057 • :U2 · 23U 

FIGURE 1.-Plan dimensions of seven-story tower, Holy Cross hospital. t · 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 197 

FIGURE 2.-Holy Cross Hospital right. Indian Hills Medical 

Center l~ft. 

FIGURE 3.-Holy Cross Hospital, west wall. J. F. Meehan OAC 

photograph. 

FIGURE 4.-Holy Cross Hospital, east wall. J. F. Meehan OAC 

photograph. 

FIGURE 5.-Holy Cross Hospital, southeast corner column. 

J. F. Meehan OAC photograph. 
DAMAGE TO THE INDIAN HILLS MEDICAL BUILDING 

(14935 Rinaldi, Granada Hills) 

By JAMES H. THOMPSON 

WILSON AND THOMPSON, CONSULTING STRUCTURAL ENGINEERS 

AND 

JAMES KESLER 

KAROTIS AND KESLER 

The medical building is a six-story reinforced 

concrete structure, 64 feet by 172 feet in plan witt 

a 17- by 85-foot projection on the south side. Firststory height is 17 feet 6 inches, and the stories 

above are 13 feet 3 inches high. It has a reinforced 

concrete pile foundation and a light steel frame 

penthouse (fig. 1). 

The building utilizes "frames in walls" for its 

lateral force bracing system; concrete beams and 

columns carry vertical loads elsewhere. Seismic deFIGURE 1.-lndian Hills Medical Center. Note horizontal 

crack in center shear wall. J. F. Meehan, OAC Photograph. 

198 

sign is based on the 1966 Los Angeles City Building 

Code (K=l.O). 

Shear walls parallel to each of the main axes of 

the building had multiple diagonal cracks (fig. 2), 

and the concrete spalled along the vertical edges of 

the walls at the second, third, and fourth floors. 

Vertical reinforcing buckled in some instances. 

Cracks also occurred at the beam and column connections (fig. 3). The ceilings, stairways, elevators, 

and mechanical equipment supports in the penthouse also suffered damage. 

FIGURE 2.-Indian Hills Medical Center. Cracks in north wall. 

J. F. Meehan, OAC photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 199 

FIGURE 3.-lndian Hills Medical Center. Northwest corner. J. J. Kesler, photograph. 
DAMAGE 'TO THE UNION BANK BUILDING 

(Northeast corner of Sepulveda and Ventura, Sh~rman Oaks) 

By PAUL GREENFIELD 

ERKEL-GREENFIELD AND ASSOCIATES 

The subject structure is 13 stories high over a 

two-level subterranean garage. The building above 

grade has floor-to-floor dimensions of 11 feet 

9 inches, the first to second floor being 23 feet 

6 inches. Total height of building is 164 feet 6 inches. 

The longitudinal dimension (east-west) is seven 

bays at 27 feet 0 inch or 193 feet 0 inch. Transverse 

dimension (north-south) is two bays at 36 feet 

0 inch or 72 feet 0 inch. 

The mechanical penthouse is composed of light 

steel, framing, steel stud walls, and tufcor, zonolite 

concrete roof. 

The building is composed of reinforced concrete 

columns, girders, and beams; a 41;2-inch one-way 

concrete slab spans 12 feet 8 inches between eastwest intermediate beams. All interior columns are 

36 inches square while exterior columns are 24 X 36 

inches. The 36-inch dimension is in the transverse 

direction. The four-corner columns are architecturally shaped 36 inches square having a 12-inch 

square corner notch which is the corner farthest 

removed from the center of the building. The 

remaining end-wall columns are 24 X 36 inches. 

Typical spandrel girders are 18 X 41 inches, the 

second floor spandrel girders being 18 X 56 inches. The 

interior longitudinal girder is 24 X 32 inches, while 

the transverse frame girders are 24 X 33 inches. 

The foundations consist of drilled cast-in-place 

friction piles. 

Structural damage was limited principally to the 

four-corner columns. These columns are considerably stiffer than other exterior columns owing to an 

200 

architectural configuration. The damage consisted 

of diagonal cracks at the second-floor joint. The 

southwest corner column cracked also at approximately 5 feet above ground level. The second-floor 

spandrel beam showed slight vertical hairline cracks 

above the colunms. A short concrete shear wall 

below grade indicated a diagonal hairline crack. 

This shear wall is between the ground floor and two 

sublevels. 

Nonstructural damage was noted as follows: 

1. The elevators were out of commission. 

2. Several doors in the 2d, 3d, 4th, and 5th floors 

were slightly jammed, indicating some partition 

movement. 

3. Considerable areas of ceiling tile over the second 

floor fell. 

4. One dry-wall partition at the east end of the 

building buckled and showed horizontal movement. 

5. Some steel stairlandings pulled away from their 

supports but were still functional. 

6. Five large panes of glass in the first floor cracked 

or broke. 

7. Marble veneer in the first-floor lobby cracked and 

fell away from the walls and had to be replaced. 

The upper floors showed the least damage, and 

the penthouse showed no damage. The mechanical 

equipment in the penthouse was intact and securely 

mounted. 

The building was designed under the 1964 Los 

Angeles City Code as a 100-percent frame using a 

K value of 0.67. 
DAMAGE TO THE SAN FERNANDO INDUSTRIAL TRACT 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

The San Fernando industrial tract is located east 

of the intersection of Foothill Boulevard and Arroyo 

Street in the City of Los Angeles. Construction is 

one story and of moderate area with mostly tilt-up 

concrete walls. There are a few reinforced-masonry 

walls. Roofs are generally plywood sheathing. 

A path of severe ground movement traverses the 

site consisting of compression ridges, cracks, and 

lurching. One reinforced-concrete block structure 

located at 12685 Foothill evidently suffered damage 

as a result of cracks extending directly under the 

building. The side walls were bowed outward. 

A majority of the structures in this tract were 

posted as unsafe by the Los Angeles City Building 

Department. 

Two apparently identical tilt-up structures are 

located about 100 feet apart at 12863 and 12885 

Foothill. The one at 12885 suffered fracturing of 

the front-wall columns in the sash opening. Similar 

columns in the other building were only slightly 

cracked. 

A reinforced-brick wall structure located at 12836 

West Arroyo Street suffered collapse of the south 

wall (fig. 1) and the south-end bay of roof framing. 

The plywood sheathing was three-eighths of an 

inch thick, and most nails in the ledger pulled 

through the plywood in some cases (fig. 2). Some 

nails pulled out of the ledgers. Brick pilasters were 

spalled at beam seats (fig. 3) . 

The roof construction in this tract is typical of 

many structures in southern and other parts of 

California. This system is sometimes called "panelized." The plywood sheathing is supported on 2 X 4-

inch joists at 2 feet on center. These are supported 

on 4-inch-thick purlins spanning 20 to 25 feet. Main 

roof beams are glued laminated wood on tapered 

steel beams. 

Attachment to walls is by a 4-inch-thick ledger 

bolted to the wall. The plywood sheathing is nailed 

to the tops of the ledgers, and the purlins and joists 

are supported on the ledgers by metal joist hangers. 

Most plywood diaphragm failures seemed to be 

by tension, causing nails to pull out of plywood or 

out of supporting ledgers and joists. The ledgers 

split horizontally along the bolt line, in some cases. 

The east wall collapsed in a reinforced-concrete 

block structure at 12424 Gladstone. Plywood sheathing was one-half of an inch thick. 

At 12460 Gladstone, a portion of the west wall 

collapsed (fig. 4). Walls are reinforced-concrete 

tilt-up construction. Roof sheathing is %-inch plywood. Other walls were leaning out and cracked, 

and the east end roof bay collapsed. An interior 

portion of the roof also fell in this structure. This 

structure has a dock-height floor. 

201 
202 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 1.-12836 West Arroyo. South wall collapse. J. F. 

Meehan, OAC photograph. 

FIGURE 2.-12836 West Arroyo. Ledger on walls. Nails pulled 

through plywood sheathing. J. F. Meehan, OAC photograph. 

FIGURE 3.-12836 West Arroyo. Damaged pilaster. J. F. 

Meehan, OAC photograph. 

FIGURE 4.-San Fernando Industrial Tract. 12460 Gladstone. 

Collapsed front wall. J. F. Meehan, OAC photograph. 
DAMAGE TO THE SYLMAR INDUSTRIAL TRACT 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

In a large industrial building tract located in 

the city of Los Angeles just north of the city of 

San Fernando, a majority of the structures were 

posted as unsafe. Most of the construction is one 

story with precast concrete tilt-up walls and panelized plywood roofs. Some reinforced hollow concrete block walls were observed. 

There was considerable evidence of ground 

movement in this area such as cracking and compression ridges. 

Numerous failures occurred in the plywood roof 

systems. These were mostly direct tension failures, 

either at the exterior walls or in the general roof 

area. Severe wall damage and collapses resulted in 

many cases. 

One new structure which had not been occupied 

was located at 12950 Bradley Avenue in this tract. 

Most of the glass on the west (front) wall was broken. 

The roof framing and sheathing was pulled away 

from the front wall but did not collapse. The 

east-end roof ba,y._.,_collapsed, and the east wall was 

cracked and leanin.g toward the east slightly. 

Another tilt-up located at 12880 Br~dley suffered collapse of the east-end roof bay and also 

wall collapse at the northwest corner. 

A reinforced-concrete-block building wall collapsed at 12874 Bradley. 

These and many other buildings in this tract 

deserve more careful analysis and evaluation of 

performance. This general type of construction is 

widely used in southern and other areas of California. 

Loss of life and .,;1n]uries could have resulted 

from collapses of these structures had the shock 

occurred 1 or 2 hours later. 

203 
DAMAGE TO A MARKET, GLENOAKS AND HUBBARD, SAN FERNANDO 

By WALTER DICKEY 

CONSULTING STRUCTURAL ENGINEER 

This building was the westerly building of the 

complex at Glenoaks and Hubbard. It was about 

150 by 180 feet square. The roof consisted of 

plywood paneled system on purlins carried by 

glued-laminated beams on pipe columns. Several 

cracks went through the floor slab of the building, 

showing a meandering cracking or slippage. These 

were not only quite open cracks but had differentials of elevation of as much as 6 or 8 inches. 

The west end of the north wall and the west 

wall were open, on columns. The south wall had 

been a reinforced grouted brick wall, but at the 

time of inspection it had been removed because 

of having pulled away from the roof diaphragm 

system (figs. 1 and 2) . It is possible that there 

had been considerable rotation of this rather 

eccentrically stiff building. 

In addition, the easterly wall support had been 

FIGURE 1.-Market, Hubbard and Glenoaks. J. F. Meehan, 

OAS photograph. 

204 

lost as the glued-laminated beams had pulled off 

their supporting pilasters. 

The southerly wall of the dock-height area had 

obviously been moved considerably to the south 

as shown by the tilted wall of the stairway (fig. 3). 

The easterly wall had a crack right adjacent to 

it and had separated from an abutting wall toward 

its northerly end (fig. 4). It had also pulled away 

from the glued-laminated beams of this particular easterly wall, pulling off the anchors which 

had relatively small ties. 

The large ceiling area had been rigidly attached 

to the exterior and, during the shake, had dislodged the fixtures which fell down on whatever 

was beneath. 

The failure of the ties had probably been due 

to the great amount of ground movement, slippage, 

and cracking through the area. 

FIGURE 2.-Market. East wall. J. F. Meehan, OAC photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Market. This portion of building moved southerly 

tilting the dock wall and fracturing the landing. Note the 

random cracks in paving in the background. Walter Dickey 

photograph. 

FIGURE 4.-Market. Separation of intersecting walls where 

crack passed through building. Walter Dickey photograph. 

205 
DAMAGE TO A MARKET, 13570 ELDRIDGE, LOS ANGELES 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

This market building was posted unsafe and has 

been vacated. It is a one-story reinforced-concrete 

building built with precast concrete tilt-up walls. 

Roof is plywood sheathing supported on inverted 

tapered steel girders. 

A reinforced brick shear wall at the southwest 

corner was shattered. A canopy along the west 

side is supported on pipe columns on the outside 

but evidently was dropped several inches where it 

206 

.)oms the main building. Most of the glass along 

the west side was broken. 

A building located at 1132 Pico Street in the 

city of San Fernando has reinforced-concrete rigid 

frames supported concrete roof slabs and precast 

concrete walls. This structure was posted unsafe. 

The north wall panels broke loose from the frames 

and were leaning out. Some were shored. 
DAMAGE TO TWO STORE BUILDINGS IN THE NORTH OAKS SHOPPING CENTER 

AND ONE BUILDING IN THE VALENCIA SHOPPING CENTER 

By JAMES J. KESLER 

KAROTIS AND KESLER 

Department store-North Oaks Shopping Center (19419 Soledad Canyon Road).-The building 

is one story with brick exterior walls, glued-laminated beams, and panelized wood roof (fig. 1). 

The rear wall of the building separated from 

the roof by about 9 inches in one area, and the 

adjacent roof section collapsed (fig. 2). Other sections of roof along the side walls also collapsed, 

and purlins were pulled out of their supports. 

Building material store-North Oaks Shopping 

Center (1D~07 Soledad Canyon Road).-The building is one story with brick exterior walls, interior 

columns, and wood roof construction. 

Brick piers spalled at connection to wood beams 

along front wall (fig. 3). Interior partitions 

cracked. Several main beams were pulled out from 

the masonry at their support along the front wall 

(fig. 4). Ledgers along masonry walls were pulled 

out, and parts of the roof structure collapsed. 

Cracks occurred in the paving of a nearby parking lot (fig. 5). 

Store building-Valencia Shopping Center 

(24200 Lyons Avenue).-The building is a onestory brick masonry and wood roof construction. 

Masonry walls appear to be continuous on three 

sides of the building, but are reduced to relatively short walls on each side of the large glassed 

opening at the front. A large sign projects above 

the roof at one end of one of the short walls. 

Large sections of the suspended ceiling collapsed; almost all the glass in the front wall broke. 

The brick walls at the front (fig. 6) spalled at 

ceiling level, and additional spalling occurred near 

ceiling level at the sign support. 

FIGURE 1.-North Oaks Shopping Center, 19419 Soledad 

Canyon Road. 

207 
208 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 2.-North Oaks. Roof collapse. 19419 Soledad Canyon 

Road. 

FIGURE 3.-North Oaks Shopping Center, 19407 Soledad 

Canyon Road. Front wall columns. 

FIGURE 4.-North Oaks, Market. T-bar ceiling damage. 

FIGURE 5.-Crack in paving. North Oaks Shopping Center. 

FIGURE 6.-Store building, 24200 Lyons Avenue. Damage to 

front shear wall. 
DAMAGE TO PUBLIC SCHOOl~ BUILDINGS 

By J. F. MEEHAN 

CALIFORNIA OFFICE OF ARCHITECTURE AND CONSTRUCTION 

The author traveled to the epicentral area, which Prior to 1967 there were no statutes on the siting 

was then given as 34°26.4' N. and 118°19.6' W. This requirements of public schools with reference to 

is about 11/:.l miles from the Agua Dulce Elementary geologic hazards. In 1967, geologic siting requireSchool constructed in 1966. The observed damage ments were added to the statutes but applied only 

to this school consisted of the fall of several plastic to new school sites. 

light diffusers from the fluorescent tube light fix- This earthquake tested a large number of pretures and some light "cosmetic" damage . (fig. 1). Field Act school buildings and an immense number 

No other damage was observed. This building is of of post-Field Act school buildings in the entire 

reinforced grouted brick masonry walls and wood affected area. 

frame roof with a plywood roof diaphragm. This ........... The unrehabilitated pre-Field Act school buildings 

building was sited in cut, and there was no ground which received a modest amount of vibration were 

cracking observed in the school grounds. damaged as expected. It is the intent of the Los 

The Field Act was placed in the statutes by the Angeles City School Board to demolish such preCalifornia State Legislature about 6 weeks after Field Act school buildings. Several pre-Field Act 

the 1933 Long Beach earthquake. This act places school buildings in the area were rehabilitated to 

the construction of public school buildings under the meet the requirements of the Field Act and were 

supervision of the State for the protection of life not damaged to any significance. The plaster cracks 

and property. Basically, it requires a California- will be repaired and the buildings will continue in 

licensed architect or structural engineer to prepare use. 

plans and supervise construction of public school There were several thousand post-Field Act school 

buildings, the construction to be continuously in- buildings in the stricken area. Most of these suffered 

spected by an inspector acceptable to the architect, no damage of any kind. In areas where the site destructural engineer and State; it requires the archi- veloped surface cracking, the building, too, develtect, structural engineer, inspector, and contractor oped comparable distress. Where the vibrations 

to provide affidavits certifying that all work is in were strong, nonstructural damage occurred, usually 

conformance with the approved plans and specifica- in the form of damaged ceilings and light fixtures. 

tions; false statements on such certificates is a Three buildings have been found to have suffered 

felony. The act provides other conditions, and the vibrational damage in the structure. The damage 

complete act can be found in Sections 15451 through to these three buildings will be described. 

15465 of the California Education Code. 

In 1967, the State Legislature required all public 

school buildings built prior to the enactment of the 

Field Act in 1933 to be examined for safety by 

June 30, 1970, and provided that if such buildings 

were found to be unsafe, they could not be used for 

public school use after June 30, 1975, unless they 

were rehabilitated to meet the requirements of the 

Field Act. The law absolved school board members 

of personal liability if steps were taken to alleviate 

the hazards. 

STRUCTURAL VIBRATIONAL DAMAGE-FIELD ACT 

APPROVED 

Clark Jr. High School, Glendale School District.-

This site is located about 15 miles south of the epicenter. One of the buildings on this site is a partial 

three-story building of reinforced gypsum concrete 

on structural steel roof framing. The second floor 

is of reinforced concrete framing. The roof was 

laterally supported by reinforced grouted brick masonry construction exterior shear walls, and a steel 

209 
210 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

X brace was placed at the center of the roof.,dia- -came displaced and produced considerable piping 

phragm to resist the transverse Jatera1 force shear damage. 

for this double-loaded corridor classroom wing. 

Roofing contained diagonal bulges at the shear 

walls, indicating possible cracks in the reinforced 

gypsum concrete diaphragm. Several reinforced 

grouted brick masonry shear walls contained hairline diagonal cracks. The flat bar diagonal X brace 

buckled sufficiently to warp the steel studs and thus 

damaged the gypsum lath fastened to the steel studs 

with sheet metal clips (fig. 2). Many light fixtures 

became displaced. 

Crescenta Valley High School, La Cre.~centa.­

This site is located about 16 miles south of the epicenter and about a mile from the Clark Junior High 

School. A double-loaded corridor classroom wing on 

this site, of three-story reinforced concrete construction, suffered structural damage. Two first-floor wall 

piers about 3 feet wide and 4 feet high in the administration portion were rather heavily X cracked. 

A horizontal construction joint between the wall and 

footing of the administration portion was exposed. 

The roof diaphragm contained light cracks under 

the roof overhang perpendicular to the wall approximately midway between the end walls. This is indicative of typical bending tension cracks of the roof diaphragm at midspan. Bolts were sheared off the floor 

beams of a third-floor walkway bridge between this 

classroom wing and an adjacent wing; however, the 

walkway was not damaged. The first floor was diagonally cracked across the building, which could have 

been the result of ground surficial damage. There 

was also considerable nonstructural damage in this 

wing. About 50 percent of the light fixtures on the 

third floor were damaged-many fell to the floor. 

Two such fixtures on the second floor were damaged. 

Several fusible link louvers over the classroom doorways fell to the floor. Furniture was overturned on 

the third floor. All third-floor map racks, hooked to 

eye-bolts in the walls, became dislodged and fell to 

the floor. Wall plaster in the administration office 

was cracked, and a piece of plaster 15 inches by 3 

feet fell from the ceiling in the storage room. 

PatTick HenTy Junio1' High School, Gmnada Hills 

Ar·ea of Los Angeles.-This site is located about 16 

miles southwest of the epicenter and had structural 

damage due to vibration. The four columns were 

damaged under the roof beams of a four-column 

reinforced-concrete two-story bridgeway between 

two classroom wings. 

DAMAGE DUE TO SURF ACE GROUND MOVEMENT 

Several public school sites experienced damage 

when the ground cracking progressed through the 

school buildings. It is expected that building damage 

will result from such foundation activity or ground 

surface expression of the faulting, and the building 

codes do not and cannot provide for this. 

Van Gogh School.-It was originally reported that 

the Van Gogh School (fig. 3), located west of the 

Upper Van Norman Reservoir and about 16 miles 

from the epicenter, would be demolished. However, 

this site is now under investigation by engineering 

geologists, and the extent of the structural damage 

is being investigated by structural engineers. 

Sylma:r High School.-This site, about 15 miles 

southwest of the epicenter, contained evidence of 

considerable ground surface expression of the fault 

(fig. 4) 

San Fernando Valley J·uvenile Hall.-This site, 

about 14 miles southwest of the epicenter, also contained evidence of considerable ground surface expressions of the fault. Several school buildings at 

this site were built under supervision provided by 

the Field Act. 

Soledad Canyon School.-This school is located in 

Solemint, about 8 miles from the epicenter, and in 

the vicinity of Newhall. The reinforced grouted 

brick masonry walls were cracked about a foot 

around each end of the diagonal roof member. Note 

the typical diagonal cracks in the playground paving 

area. Such cracking was found throughout the 

No chemicals in the laboratory were lost because school site. Extensive damage occurred to the T-bar 

of a suggestion made and accomplished during a ceiling construction and light fixtures in the multirecent fire and panic safety check made at the _.s.jte· .. ·-·purpose buildings (fig. 5). 

last year .. All she.lves i~ the c~~mistr.y~labo~atory Hanby School.-This school site is located in 

were. eqm~ped With 4-mch rmlmgs to retam the Honpy about 12 miles from the epicenter and had 

chemicals m the event of an earthquake. ground surface cracking throughout the site. One 

Glass was broken at a stairway exit in the girls' such .crack passed through one of the buildings and 

gymnasium. produced a 1%-inch vertical displacement in the 

The pedestals under the swimming pool filters be- floor slab and cracked the roof concrete bond beam. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 211 

NONSTRUCTURAL VIBRATIONAL DAMAGE 

Innumerable school buildings suffered nonstructural damage. The greatest single class of damage 

found in Field Act approved buildings was to the 

ceilings and light fixtures. The most common ceiling 

damage was of T-bar ceilings with lay-in panels. 

The damage always occurred at the perimeter of the 

ceiling where it adjoins the walls and partitions. 

Damage was frequently found within the central 

portion of the ceiling at the intersections of the Tbars and around the light fixtures. 

At the Edison School and Bret Hart School in 

Burbank, T-bar ceilings were installed under the 

1970-adopted ceiling requirements of the Schoolhouse Section of the Office of Architecture and Construction. No damage of any kind was observed to 

these ceilings. This new regulation requires that all 

ceilings must resist a lateral load of 1 pound per 

square foot or 20 percent of the weight of the 

ceiling. 

Ceiling ventilating grilles fell to the floor at 

many sites throughout the area. Such grilles are 

frequently set in the ceiling with little or no anchorage connection. 

Expansion joints provided at covered passage or 

arcade roof junctions with buildings frequently 

pounded together, causing ceiling plaster spalling. 

PRE-FIELD ACT SCHOOL BUILDINGS 

Morningside Elementary.-This site is located in 

San Fernando about 12 miles from the epicenter. 

There were two pre-Field Act classroom buildings 

of two-story construction on this site. One such 

building is a reinforced concrete building and was 

rehabilitated to meet the requirements of the Field 

Act and suffered no damage. The other, a brick 

masonry building, suffered damage to such an extent 

that it will be demolished. 

Adult Education Center, Burbank.-This preField Act school building is located about 19 miles 

from the epicenter. 

Administration Center, Glendale.-This pre-Field 

Act school building about 21 miles from the epicenter was in the process of being rehabilitated. 

The entry brickwork was shaken from the building 

at the entry (fig. 6). 

CONCLUSIONS 

Although the investigation of the performance of 

public school buildings is incomplete at this time, 

there are several conclusions which can be drawn: 

1. T-bar ceilings require engineering considerations 

to resist the dynamic forces of earthquakes. 

2. All parts, including the anchorage, of light fixtures require engineering considerations to resist the dynamic forces of earthquakes. 

3. All overhead objects such as grilles and fixtures, 

require particular attention to details and positive mechanical anchorage to prevent displacement during earthquakes. 

4. Strong-motion earthquake records show the 

lateral loads experienced in many structures 

greatly exceed those required by present codes. 

Consideration will be given to this information 

as it applies to low, intermediate, and high 

buildings. 

FIGURE 1.- Agua Dulce School, about 11h miles from epicenter. Plastic lenses from several light fixtures fell to floor. 

J. F. Meehan, OAC photograph. 

FIGURE 2.-Clark Junior High School. Steel flat bar diagonal 

bracing buckled and damaged plastere<\ partitions. J. F. 

Meehan, OAC photograph. 
212 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Van Gogh School. Damage at junction of foundation and wood stud wall. J. F. Meehan, OAC photograph. 

FIGURE 4.-Sylmar High School. Arcade roof joints pounded. 

J. F. Meehan, OAC photograph. 

FIGURE 5.-Soledad Canyon School, T-bar ceiling, and light 

fixtures. J. F. Meehan, photograph. 

FIGURE 6.-Administration Center, Glendale. This pre-Field 

Act School was being rehabilitated. Brick work over the 

entry fell. J. F. Meehan, OAC photograph. 
DAMAGE TO OTHER BUILDINGS 

By WALTER BRUGGER 

RESEARCH ENGINEER, Los ANGELES CITY DIVISION OF BUILDINGS AND SAFETY 

DWELLINGS 

There were over 700 dwellings evacuated and 

declared unsafe and an additional 8,000 received 

varying degrees of damage (figs. 1 and 2). 

A dwelling in the vicinity of Cometa and Fernmont was shaken off the foundation and moved 

approximately 2 feet forward (fig. 3). This building was in very close proximity to an earth fracture which has been identified as the Sylmar segment of the San Fernando fault. The damage to 

the rear stoop indicates a high intensity of ground 

motion in that area. 

Many buildings that were slightly damaged lost 

fireplaces (fig. 4). 

Numerous masonry garden walls fell over in the 

area (fig. 5). 

APARTMENT HOUSES 

There were approximately 60 apartment buildings evacuated and declared unsafe, which constituted 1,100 dwelling units. An additional 63 

received damage in varying degrees (fig. 6). 

OLD BRICK BUILDINGS-PARAPET REP AIR PROGRAM 

In 1949 the city of Los Angeles initiated a parapet repair program for unreinforced masonry 

buildings. At the present time the program is approximately 85 percent complete. 

Preliminary reports indicate that the parapets 

which were repaired under this program generally 

withstood the earthquake in good shape. 

Many unreinforced masonry buildings were 

damaged in downtown Los Angeles (figs. 7 and 8). 

A large number of buildings of this type were also 

damaged in the city of San Fernando and the 

Sylmar section of the city of Los Angeles; however, the exact number is unknown at this time. 

VETERANS HOSPITAL 

An old hospital building at the Veterans Administration completely collapsed caqsing 45 deaths 

(fig. 9). This building had a skeleton concrete 

frame, concrete floors, and unreinforced hollow tile 

filler walls. The building which was five or six 

stories in height is reported to have been constructed before 1930. 

TRAILER PARKS 

Numerous house trailers fell off their supports 

(fig. 10). 

GASOLINE STATIONS 

Generally, gasoline stations performed well. At 

one modern station a decorative masonry chimney 

fell (fig. 11), and large rocks on the roof of 

canopies were thrown off (fig. 12). 

213 
214 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

L : .. 

FIGURE 1.-Almetz Street, between VA Hospital and Olive View. Los Angeles City Department of Building and Safety 

photograph. 

FIGURE 2.-0lder dwelling in the vicinity of 8th Street and Fernmont in San Fernando. Los Angeles City Department of 

Building and Safety photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 215 

FIGURE 3.-Dwelling in the vicinity of Cometa and Fernmont, San Fernando. Building was shaken off foundation and moved 

2 feet forward. Los Angeles City Department of Building and Safety photograph. 

FIGURE 4.-Typical masonry fireplace damage. Los Angeles City Department of Building and Safety photograph. 
216 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 5.-Typical concrete block masonry garden walls thrown down. Los Angeles City Department of Building and Safety 

photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 217 

FIGURE 6.-Rear of apartment at Foothill Boulevard and Harding. Los Angeles City Department of Building and Safety 

photograph. 

FIGURE 7.-Midnight Mission in downtown Los Angeles. Los Angeles City Department of Building and Safety photograph. 
218 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 8.-Near 4th Street and Alameda, Los Angeles. Los Angeles City Department of Building and Safety photograph. 

FIGURE 9.-Veterans Hospital rescue operations. Los Angeles City Department of Building and Safety photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 219 

FIGURE 10.-House trailer off supports. J. F. Meehan, OAC photograph. 

FIGURE 11.-Gasoline station, collapsed masonry chimney. FIGURE 12.-Gasoline station. Rocks shaken off canopies. J. F. 

Foothill and Van Nuys Boulevard. D. F. Moran, photograph. Meehan, OAC photograph. 
DAMAGE TO BUILDING EQUIPMENT AND CONTENTS 

By J. MARX A!YRES 

-d 

AYRES, COHEN, AND HAYAKAWA 

We must modify our design philosophy that a 

building is safe if it survives an earthquake without damage to the structural system. The structural frame may absorb the earthquake forces 

without failures, but the movement of the building 

induces significant secondary damage to nonstructural elements. 

A building is not safe if, during an earthquake, 

light fixtures and ceilings fall, elevators do not 

operate, emergency generators do not come on, 

loose objects block exits, and broken glass falls into 

the street. A building is not properly designed if 

an owner sustains huge losses due to nonstructural 

damage. The lessons learned by detailed studies of 

damage sustained by these earthquake-tested buildings must be carefully documented and widely disseminated. 

The nonstructural damage observed to date appeared to follow that recorded in Anchorage, 

Alaska, during the March 27, 1964, earthquake. 

Elevators.-Traction elevators were damaged 

when motor generator sets mounted on unrestrained vibration~isolation bases "walked 

around" the machinery rooms, and control panels 

fell over (fig. 1). Guide rails for counterweights 

were deformed, freeing the counterweights to 

swing about in the hoistways, resulting in snarled 

cables and in some instances, damaged cabs (fig. 

2). 

Light Fixtures.-Pendant-mounted light fixtures 

fell when supports tore loose at ceilings or the 

sheet-metal back of fixtures deformed (fig. 3). 

Lines of recessed fluorescent fixtures dropped from 

plaster ceilings. 

Ceilings.-Ceiling tile was battered at perimeter 

walls as. nonrestrained ceilings and light fixtures 

220 

moved (fig. 4). Restrained fire-sprinkler p1pmg 

and exposed heads tore ceiling tile as the unrestrained ceilings moved. Tile fell from perimeter 

runner strips that moved with the adjacent walls 

or partitions (fig. 5). At the Los Angeles County 

Courts Building, perimeter tile was damaged in 

most of the court rooms and corridors. 

Glass.-Resilient rubber mounts in glass panels 

prevented excessive glass breakage (fig. 6). 

Tightly mounted glass panels failed. 

Facades.-Excessive cracking of structural 

frame caused exterior plaster to fall. 

Emergency Powe1·.-Heavy emergency generators resting on unrestrained vibration-isolation 

spring mounts moved horizontally and fell to the 

floor, rupturing connections (fig. 7). 

Mechanical Systems.-Pump motors were 

thrown from their pedestal mounts (fig. 8), and 

water chillers were torn from their tube bundles 

because they were_ not properly secured and tied together and to the floor (fig. 9). Heavy tanks not 

secured to floors shifted, and improperly designed 

legs collapsed (fig. 10). Central-station air-conditioning systems mounted on large unrestrained 

vibration-isolation springs shifted off their mounts 

(fig. 11). Large steam boilers shifted 31;2 feet (fig. 

12), damaging stacks, pipes, control panels and adjacent walls, because the boilers were not properly 

secured to the rloor (figs. 13 and 14). 

Storage Racks and Loose Objects.-Markets 

found their aisles filled with materials thrown from 

shelves. Library books were thrown to the floor 

(fig. 15), and in some instances, the book racks 

collapsed. Loose objects and carts blocked exits (fig. 

16). 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 221 

FIGURE I.-Holy Cross Hospital. Elevator machinery-room 

generator sets were thrown off their mounts, and control 

panels were damaged. J. M. Ayres, photograph. 

FIGURE 2.-Holy Cross Hospital. Elevator counterweights 

slipped out of their guide rails. J. M. Ayres, photograph. 

FIGURE 3.-0live View Power Plant. Light-fixture pendant 

mounts failed. J. M. Ayres, photograph. 

FIGURE 4.-0live View Hospital. Light fixtures slipped from 

support brackets as plaster ceiling moved. J. M. Ayres, 

photograph. 

FIGURE 5.-Holy Cross Chapel. Marble veneer fell from wall. 

J. M. Ayres, photograph. 
222 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 6.-0live View Hospital. Glass light in rubber mount FIGURE 8.-0live View Power Plant. Condenser water-pump 

did not fail even though excessive frame deformation broke motors were thrown from their pedestal mounts. J. M. 

three adjacent lites. J . M. Ayres, photograph. Ayres, photograph. 

FIGURE 7.-0live View Hospital. Emergency generators moved 

off of their vibration-isolation spring mounts. J. M. Ayres, 

photograph. 

FIGURE 9.-0iive View Power Plant. Water chillers were torn 

from their adjacent tube bundles. J. M. Ayres, photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 223 

FIGURE 10.-0live View Power Plant. Water softeners collapsed when screwed pipe legs failed. J. M. Ayres, 

photograph. 

FIGURE 11.-0live View Hospital. Large central-station airconditioning systems moved off their vibration-isolation 

spring mounts. J. M. Ayres, photograph. 

FIGURE 12.-0live View Power Plant. Boilers shifted 3% feet. 

J. M. Ayres, photograph. 

FIGURE 13.-0live View Power Plant. Boiler control panels 

tilted and held up by tubing and conduits. J. M. Ayres, 

photograph. 
224 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 14.-0live View Power Plant. Roof-mounted coolingtower intake louver damaged by racking, and adjacent 

boiler stacks twisted when boilers moved. J. M. Ayres, 

photograph. 

FIGURE 15.-Sylmar Elementary School. Books thrown from 

shelves. J. M. Ayres, photograph. 

FIGURE 16.-0live View Hospital. Corridor blocked by overturned carts. J. M. Ayres, photograph. 
DAMAGE TO WATER SUPPLY SYSTEMS 

By C. MARTIN DUKE 

UNIVERSITY OF CALIFORNIA AT Los ANGELES 

The earthquake of February 9, 1971, did extensive damage to water-supply systems and their 

components. Most of this damage occurred in and 

around the most heavily shaken area, which included Sylmar, San Fernando, the Van Norman 

Reservoirs, and the Jensen Filtration Plant. Types 

of damage ranged from major dam failures to 

breakage of house connections for water and sewage, and included trunkline breaks, aqueduct and 

tunnel damage, and structural failures in a major 

filtration plant. 

Strong-motion accelerographs and seismoscopes 

functioned at several dams. 

STATEWIDE WATER SYSTEMS 

Mr. Lawrence B. James, Chief Geologist of the 

California Department of Water Resources, reported on March 4 that there was no damage to 

any of the California Water Plant facilities, which 

extend from northern California across the Tehachapi Mountains, Antelope Valley, and to the vicinity of San Bernardino. Precise leveling is underway to assess possible changes in grade along the 

aqueduct. 

Mr. Philip West, engineering geologist of the 

Southern California Edison Co., reported on 

March 4 that there had been no damage of any 

sort to the company's hydropower facilities, which 

are in the Sierra Nevada and San Bernardino 

Mountains. 

FLOOD CONTROL FACILITIES 

About $2,500,000 damage was done to Los Angeles County Flood Control District facilities. 

About half of this amount was due to breakage of 

reinforced concrete open channel and underground 

box channels (fig. 1) which appeared to be associated with surface fault displacement of major 

ground cracking. In one case, such breakage extended for the length of a city block. 

Pacoima Dam, built in 1938 as a 370-foot-high 

concrete arch structure, is of interest because of 

the extremely large accelerations measured at one 

abutment, and because of rockslides in the earthquake near the west abutment which may require 

remedial measures (fig. 2). Water level behind the 

dam was quite low at the time of the ·earthquake. 

International Engineering Co. of San Francisco 

has been asked to study this case. The following 

summary was provided on March 8 by Orner D. 

Hall, Assistant Chief Deputy Engineer : 

No damage occurred to District flood control structures 

outside the San Fernando-Sylmar area, except for minor 

damage at a limited number of locations. 

The thrust of the earthquake caused substantial damage 

to portions of Wilson Canyon Channel, Mansfield Avenue 

Storm Drain, Pacoima Wash, Lopez Canyon Channel, and 

Storm Drain Bond Issue Project No. 256, Glenoaks Boulevard Drain, all in the San Fernando-Sylmar area. Damage occurred to other structures in the same area. Rubble 

channel side slopes cracked and small sections of concrete 

channel inverts were ruptured. There were some separations 

of concrete tox c:ulverts; many drain joints will need to 

be resealed; catch basins were damaged; there was extensive spalling of concrete; concrete channel walls were displaced; and in one case, a reinforced concrete box structure 

failed. 

Relatively minor damage occurred at the debris basins 

and a debris disposal area in the Sylmar area. Wilson, 

Schoolhouse, Stetson, Hog, and Sombrero Debris Basins will 

require repairs, and we are proceeding to make repairs as 

required. 

The only major District dam in the Sylmar area is Pacoima Dam. We have inspected it very carefully following 

the earthquake. Although massive rockslides occurred in the 

vicinity of the dam, and trails, roads, wate~-lines, and buildings in the camp area were damaged, there was no apparent structural damage to the1 dam. However, in view of our 

dam safety program, we are proceeding with a more detailed evaluation of the e~ects that the earthquake may 

have produced structurally/ to the dam. 

225 
226 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

Col. Robert J. Malley, Los Angeles District Engineer of the Corps of Engineers, reported on March 

3 an absence of damage to the District's 11 dams 

and 20 debris basins, with one exception. This was 

the Lopez Debris Basin, north of Hansen Dam, 

which had serious damage. Hansen Dam was undamaged. 

METROPOLITAN WATER DISTRICT OF SOUTHERN 

CALIFORNIA 

The following nine paragraphs are quoted from 

a statement made on approximately February 16 by 

Mr. Henry J. Mills, General Manager of the district. 

Of special interest are the nearly completed Jensen 

Filtration Plant, Balboa Inlet Tunnel, San Fernando 

Tunnel, extensive ground cracking near the filtration plant, and the wash water tank. 

The Metropolitan Water District's vast operating system 

of aqueducts, pumping plants, reservoirs, and treatment 

plants furnishing Colorado River water to Southern California came through the earthquake of February 9, 1971, with 

relatively little damage and there was no interruption of 

flow in any of its delivery lines. The 250-mile Colorado River 

Aqueduct with its five pumping plants continued to deliver 

a billion gallons of Colorado River water a day and the 

nearly 500 miles of distribution pipelines and tunnels continued to furnish water throughout Southern California to 

the District's 211 member agencies. 

The Santa Monica Feeder and the Orange County Feeder 

each had one minor joint separation, both of which were 

repaired with no interruption of service. The L.A. Headquarters Building suffered superficial (non-structural) concrete and plaster damage along with a few broken windows. 

Certain earth slope an:d drainage system damage occurred 

on District property in the vicinity of the earthquake epicenter. This brief summation of damages reflects how relatively unscathed the District's existing facilities survived 

the major earthquake. 

On the day of the earthquake the Metropolitan Water 

District had completed or had under construction about 500 

million dollars worth of new facilities to be used for the 

distribution of State Project water when it becomes available next year from the California Aqueduct, also under 

construction. Most of these facilities, which have not yet 

been accepted by District, escaped serious damage with the 

exception of the 45 million dollar Joseph Jensen Filtration 

Plant and its inlet tunnel, which are located in the Sylmar 

area where the worst damage occurred. The main shock had 

a magnitude of 6.6 on the Richter Scale about 13 miles to 

the northeast of the Jensen Plant, and the acceleration at 

the ground surface of the plant was on the order of 0.4 g. 

Lateral earth movement of a foot or more occurred at the 

plant site. 

The construction of the J enser;t plant was about 85 percent 

complete on the ninth of February and all concrete work 

was completed. Damage to portions of the plant was extensive and the District's engineering staff, together with consultants George .Hqusner, the ·firm of Converse, Davis and 

Associates, and H. B. Seed, are still in the process of assessing the damage and determinitJg the cost and method of 

repairs. The finished water re~ervoir, a covered concrete 

structure approximately 500 feet square, was most severely 

damaged (figs. 3 and 4). About 300 feet of the concrete 

effluent box conduit between the filter beds and the reservoir is also severely damaged, and the chemical building 

and the influent conduit where it connects to the main control building received moderate to heavy damage. The 1%, 

million gallon steel wash water tank (fig. 5) was half full 

of water, and while it was damaged sufficiently to pull its 

foundation bolts out of its concrete foundation, it did not 

lose any water. Minor damage occurred at other places 

such as in the mixing basins and to the traveling bridges 

with their sludge removal equipment. 

The rest of the plant shows surprisingly little damage, 

including the main control building, the settling basins, 

filters, wash water reclamation units and chemical storage 

area. There is minor damage at some construction joints and 

some structures show indications of movement, but on the 

whole the major portion of the plant is in good condition. 

The Balboa Inlet Tunnel, 14 feet in diameter, which will 

bring the water from the Foothill Feeder at Magazine Canyon to the Jensen Plant, received some damage about 1,500 

feet in from its downstream portal. For a distance of about 

100 feet at the fault crossing, the tunnel lining is badly 

damaged (Fig. 6). Other tunnels and pipelines along the 

Foothill Feeder and the Sepulveda Feeder leading from 

the Jensen Plant to the Palos Verdes Reservoir apparently 

escaped any serious damage. The San Fernando Tunnel, 18 

feet in diameter and 29,000 feet in length, extending from 

Magazine Canyon to Pacoima Wash, was about two thirds 

excavated, being driven from the, east portal. There was 

some vertical displacement along this tunnel and minor 

damage to the tunnel supports. District surveyors are presently checking the tunnel for line and grade. 

One of the District's primary activities during the aftermath of the earthquake was to assist the City of San Fernando in restoring water service to many of its 17,000 residents. In cooperation with Calleguas MWD and the cities 

of Pasadena, Burbank, and Long Beach, District crews 

worked around the clock for several days making temporary 

service installations and initiating pipeline repairs so that 

the City of San Fernando could again meet water demands 

in most of its service area. The Corps of Engineers has now 

taken over the responsibility of permanently restoring the 

City's system. 

It will be some time before the total extent of the earthquake damage is known, as well as what steps will be necessary to repair the damage. It appears, however, from all 

information presently available, that the Metropolitan Water 

District should be able to accept, treat, and deliver State 

Project water not later than the summer of 1972. 

Mr. Munson Dowd, Chief Design Engineer, on 

March 3 reaffirmed the foregoing statement and 

added that the San Fernando Tunnel had experienced a 6 V:2-foot vertical displacement between its 

portal and a point 4 V2 miles into the tunnel. 

LOS ANGELES DEPARTMENT OF WATER AND 

POWER 

Most dramatic of the department's water system damage was the failure of two old hydraulicfill earth dams. The larger of these, Lower San 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 227 

Fernando Dam, was in danger of imminent sudden 

release of the waters of Lower Van Norman Reservoir into a downstream residential area of 80,000 

people. Immediate and effective action of the Department, with the aid of several other agencies, 

prevented such a disaster. The actions included reservoir drainage and reinforcement and evacuation 

of the imperiled area. The dams will be discussed in 

more detail below. 

Also damaged were the First and Second Owens 

River Aqueducts. The First Aqueduct, the larger 

of the two, was restored to working order within 

2 days. The Second, completed in 1970, was damaged in its Saugus pipeline portion between Terminal Hill and Magazine Canyon, but should be returned to service within a month. The damage consisted of buckling of the pipe and movement of its 

supports. 

Water service to the Granada Hills, Porter Ranch, 

Sylmar, and other high-elevation areas in the San 

Fernando Valley was interrupted when the Susana, 

Granada, and Maclay trunklines were broken in 

many places by permanent differential ground displacements (fig. 7). On the Granada line, most of 

the 10 or 12 breaks were in the Jensen Filtration 

Plant area. 

The wood roof collapsed at the small Maclay Reservoir, on the Maclay High Line, and cracking occurred at the sides and corners of the basin. Rapid 

repairs are under way. 

Table 1 provides a summary of the damages to 

the water system facilities of the department. The 

two dams constitute the greatest loss, followed by 

the Saugus pipeline and the trunklines. 

The failed dams were constructed in approximately 1915 by the hydraulic-fill method. This involves sluicing earth and rock from the reservoir 

bottom and nearby hills into a pond in the dam 

area and draining off the excess water. In contradistinction, modern good practice calls for careful 

placing of all earth materials, with compaction by 

sheepsfoot or pneumatic rollers under controlled 

moisture content and density. 

Upper San Fernando Dam, retaining Upper Van 

Norman Reservoir, had a crest elevation of 1,218 

feet (U.S. Geol. Survey), a spillway elevation of 

1,210 feet, and a maximum dam height of about 

60 feet. Side slopes were approximately 2.4 :1 on 

the upstream face, with a slope-berm-slope configuration averaging approximately 4:1 on the downstream face (fig. 8). At the time of the earthquake, 

the lake was full to the spillway level. 

TABLE !.-Estimated tota[ costs of temporary a·ncl pennanent 

restoration of fcuilities dama.ged in earthquake of Febr1ta?"Y 9, 1971 

[Los Angeles Department of Water and Power. Effective Feb. 14, 1971, 

approximately. Preliminary and subject to revision] 

Immediate Permanent repairs Reconstruction Total 

Deadman siphon _______ $20,000 

Cascades -------------- 45,000 

Various First Aqueduct 

locations ------------- High-speed channel ___ _ Bypass channel _______ _ 

Saugus pipeline 

100,000 

57,256 

75,200 

(Terminal Hill) _____ 100,000 

First Aqueduct penstock 80,000 

Terminal pad and 

structure ____________ 95,000 

Powerhouse bypass ____ 84,000 

Tujunga trunkline ____ _ Granada trunkline ____ _ 

Susana trunkline 

Maclay High Line _____ _ 

Susana-Tujunga 

150,000 

50,000 

50,000 

connector ____________ 12,000 

Stone Canyon line 

blowoff -------------- Upper Van Norman 

6,000 

Bypass -------------- 40,000 

Lower Van Norman 

Bypass drain ________ 6,000 

Olden street line _______ 37,500 

Chatsworth high line 

connections ----------- 30,000 

Van Norman pumping 

station suction line __ 45,000 

Maclay Reservoir 25,000 

Upper Van N onnan Reservoir ____________ 100,000 

Lower Van Norman 

Reservoir ------------ 350,000 

Van Norman Bypass Reservoir ____________ 30,000 

Second Upper Van 

Norman Reservoir 

Bypass line _________ _ 

Sesnon Inlet-Outlet line_ 40,000 

Granada Hills inletoutlet line ----------- 15,000 

Alta Vista inlet-outlet 

line ----------------- 15,000 

Various pumping 

stations ------------- 11,000 

Turbidity control at 

reservoirs ------------ 119,458 

Ducommun yard buildings ___________ _ 

Tank trucks -----··----- Distribution mains and 

1,000 

3,000 

trunk lines ---------- 1,150,000 

Meters and service 

connections ---------- 645,000 

Operation of source and pumping facilities 30,000 

Lost water -------------5,875,000 

TOTAL ________ $9,492,414 

225,045 

262,520 

1,810,300 

257,000 

---- --·-"·---· 

1,543,000 

769,000 

500,000 

8,000,000 

$20,000 

45,000 

100,000 

282,301 

337,720 

1,910,300 

337,000 

95,000 

84,000 

1,543,000 

150,000 

50,000 

819,000 

12,000 

6,000 

40,000 

6,000 

37,500 

30,000 

45,000 

525,000 

8,100,000 

25,000,000 25,350,000 

30,000 

500,000 

235,000 

13,000 

500,000 

275,000 

28,000 

15,000 

11,000 

119,458 

1,000 

3,000 

1,398,000 

645,000 

30,000 

5,875,000 

$39,114,865 $48,855,279 

The failure mechanism appears to have been a 

downstream sliding on a curved surface, extending 

under the dam to or beyond the downstream toe, 

from an area of extensive longitudinal cracking 

on the upstream face. The dam crest displaced 
228 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

about 3 feet downward and about 5 feet horizontally downstream. Other phenomena are consistent 

with this hypothesis, including longitudinal cracks 

on the upper part of the downstream face and joint 

separations and compressions located, respectively, 

in the upstream and downstream portions of the 

outlet tunnel. The sink hole seems due to such a 

joint separation. Continued operation of this dam, 

at a sharply lowered water surface elevation, is essential for water-supply purposes, and the department is proceeding with interim repairs pending 

reconstruction in the near future. 

Lower San Fernando Dam was a much larger 

structure than the upper dam. Its crest elevation 

was 1,143 feet (U.S. Geol. Survey), with maximum 

water-surface elevation not allowed to exceed 1,135 

feet, and a maximum dam height of about 142 feet. 

The dam rests on some 35 feet of alluvium overlying 

bedrock. Side slopes were 2.5:1 upstream, with a 

slope-berm-slope arrangement having an average 

slope of about 4:1 downstream. At the time of the 

earthquake, the water-surface elevation was 1,109.4 

feet. 

The failure mechanism of the lower dam appears 

to have been a sliding of the top of the dam into 

the reservoir on a curved surface extending upstream from a zone of major longitudinal cracking that appeared on the upper (2.5 :1) slope of 

the downstream face (figs. 9, 10, and 11). This 

hypothesis is supported by soundings taken in the 

reservoir to establish the top of the sliding mass 

and by an absence of cracking or other deformation below the downstream berm. 

Residents of the 12-square-mile evacuated corridor between the San Diego Freeway and Balboa 

Street were permitted to return at 4 p.m. on Friday, 

February 12. This action was taken based on the 

judgment of officials that the Lower Van Norman 

water surface had been sufficiently lowered (by 13 

feet) to reduce to an acceptable level the hazard 

due to a major aftershock. Water had been discharged at its maximum rate since minutes after 

the earthquake. The Corps of Engineers added 

about 10 percent to the rate by means of 11 pumps. 

The lower dam has been taken out of circulation 

and essentially emptied. Plans for removal and reconstruction are indefinite at this point. The Department of Water and Power, the Department of 

Water Resources, and Prof. H. B. Seed will perform a major investigation of the failure. 

Several cases of damage to large water-storage 

tanks have occurred. One is the Sesnon Tank of 

LADWP in Granada Hills which developed a donutlike wrinkle in its top third. A tank at Olive View 

developed such a wrinkle at its bottom. A MWD 

tank near the Jensen plant pulled out its anchor 

bolts but did not lose its water. 

Appreciation is expressed to Mr. Robert V. Phillips, Chief Engineer of Water Works and Assistant 

Manager of the Los Angeles Department of Water 

and Power, for authorizing access to the water system damage data given herein. 

CITY OF SAN FERNANDO WATER SUPPLY 

San Fernando, with a population of 17,000, had 

its water-supply system devastated by the earthquake. The sole supply was from wells north of the 

city. Whether the wells themselves were ruptured 

by ground cracking is not yet known, but the delivery conduit from the well field was shattered. 

The distribution system was so fractured by ground 

cracking, as well as by the violent shaking, as to 

require practically a completely new water system 

for the city (fig. 12). 

All the city's reservoirs were leaking, two of 

them not being repairable. A new 3-million-gallon 

reservoir is being planned. 

Besides the water-supply problem, San Fernando 

had massive damage to the sewage system, gas 

system, street paving, street lighting, homes, and 

small businesses. 

Emergency assistance to the populace was provided by the city with extensive support of the 

Metropolitan Water District, the Cities of Pasadena, Burbank, and Long Beach, the Corps of Engineers, Salvation Army, and the Red Cross, among 

others. The Calleguas Water System and some Los 

Angeles water were connected into the San Fernando fire hydrants, with fire hose and 10-inch 

pipelines run down street gutters. Some 250 portable toilets were set up. The MWD reported the 

repair of some 45 leaks found upon repressuring 

the water system. The Corps of Engineers has now 

taken over the overall utilities reconstruction task, 

and has contracted with Morrison-Knudson Corp. 

CONCLUSIONS 

Detailed analyses must be made of the behavior 

of the following structures: 

Lower San Fernando Dam 

Upper San Fernando Dam 

Jensen Filtration Plant 

Saugus Pipeline 

San Fernando Tunnel 

Pacoima Dam 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 229 

Flood Control District Box Culvert 

Lopez Debris Basin 

Balboa Inlet Tunnel 

LADWP Granada Trunk Line 

Sesnon Water Tank 

MWD Wash Water Tank 

A case study should be made of the San Fernando 

water, sewage, gas, and street systems. Another case 

study should be made of the sociological aspects of 

the evacuation below Lower San Fernando Dam. 

Many of the above structures and systems were 

designed in accordance with the criteria and procedures of modern good practice. However, instrumental records obtained a few miles from the zone 

of heaviest damage appear to contain more severe 

ground motions than those that have been used as 

a basis for design up to now. Furthermore, widespread surface fault breaking and ground cracking, 

such as obviously played a major role in much of the 

damage here, has not in the past been incorporated 

systematically into the design of most structures. 

The explanation for much of the damage to hydraulic structures designed according to modern 

good practice should evolve in context with the 

studies now being undertaken. 

WILSON CANYON CHANNEL 

STATION 45+10+. 

FIGURE 1.-Inside of Box Culvert at Wilson Canyon Channel. Los Angeles County Flood Control District photograph. 
230 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 2.-Rockslides at west abutment of Pacoima Dam. LACFCD photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Metropolitan Water District, Joseph Jensen Filtration Plant, Interior of finished water reservoir. MWD 

photographs. 

231 
232 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 4.-Metropolitan Water District, Joseph Jensen Filtration Plant. Looking north along the east perimeter of the finished water reservoir showing cracks in the compacted fill adjacent to the reservoir. MWD photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 233 

FIGURE 5.-1,750,000 gallon wash water tank, Jensen Filtration Plant. J. F. Meehan, OAC photograph. 
234 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 6.-Metropolitan Water District, Balboa Inlet Tunnel. View from inside the tunnel approximately 1600 feet from the 

south portal showing damage to the tunnel lining. MWD photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 235 

FIGURE 7.-Water trunk line break under repair. DWP photograph. 
236 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 8.-Looking downstream from the berm of Upper San F ernando Dam. Sink hole in foreground. DWP photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 237 

FIGURE 9.-Lower San Fernando Dam. February 9, 1971. DWP photograph by Max Gould. 
238 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 10.-Lower San Fernando Dam, near east abutment, February 9, 1971. DWP photograph by Max Gould. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 239 

FIGURE 11.-Lower San Fernando Dam, lowest point in dam after failure. February 9, 1971. DWP photograph by Max Gould. 
240 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 12.-Residential water meter exhibiting leakage. DWP photograph by Roy Collins. 

!Ia! 
DAMAGE TO TRANSPORTATION SYSTEMS 

By J. F. MEEHAN 

CALIFORNIA OFFICE OF ARCHITECTURE AND CONSTRUCTION 

HIGHWAYS AND BRIDGES 

Structural damage which resulted from the earthquake of February 9 centered in an area north of 

San Fernando which includes the Route 5/210 Interchange (fig. 1) and the Route 5/14 Interchange (fig. 

-2). 

Most of the major damage was within the general area of the two interchanges, which are about a 

mile apart along Route 5. 

Five structures must be entirely replaced. Three 

of these structures totally collapsed during the 

earthquake. The other two partially collapsed and 

were so badly shattered as to require the removal 

of the entire structure (fig. 3). 

In addition, at the 5/14 Interchange, two spans of 

a nine-span bridge collapsed. Also, at the crossing of 

the Los Angeles Aqueduct and Route 5, a portion of 

the structure which carries the aqueduct channel 

under Foothill Boulevard collapsed and must be 

replaced. 

In addition to these structures \\-11ich will require 

total or partial replacement, almost all the remaining structures in the general vicinity of the interchanges (possibly including as many as 70 structures) sustained some degree of damage (fig. 4). 

Many of these structures will require extensive 

repair. 

The total estimated cost of all structure damage 

resulting from the earthquake is $9.5 million. 

The opening of Route 5 through the interchange 

area will require the construction of one temporary 

bridge over San Fernando Road and the Southern 

Pacific tracks to detour Route 5 traffic around the 

site of the San Fernando Road Overhead, which partially collapsed and must be entirely removed. 

A preliminary investigation by our engineering 

geologists indicates that movement occurred on the 

Santa Susana thrust fault, which passes through 

the interchange areas. 

In general, the footings at the 5/210 Interchange 

are on piles in about 40 feet of granular alluvial 

material which overlays harder material in this 

area while the footings at the 5/14 Interchange consist 'of drilled caissons in rock. According to the 

geologists, this accounts for the greater movement 

at the 5/210 Interchange resulting in greater 

damage to the structures (figs. 5 and 6) . 

Some of the preliminary recommendations for 

improved performance in bridge structures during 

an earthquake that have been proposed by the 

Bridge Study Team are1. Use anchored ties or spirals. 

2. Use added ties at tops and bottoms of 

columns. 

3. Use intermediate crossties in large columns. 

4. Use 135° hooks on column hoops and crossties. 

5. Prohibit splices in reinforcement at maximum moment locations. 

It is proposed to anchor columns more effectively 

into footings by1. Putting column bar hooks under the bottom 

mat. 

2. Putting top mat and stirrups in footing slabs. 

Numerous slides in the San Gabriel Mountains 

blocked several highways. Many streets were damaged by water and gas leaking from ruptured pipes. 

Some were damaged by ground cracks and compression ridges. 

RAILROADS 

The railroad line adjacent to San Fernando Road 

was closed by collapse of freeway structures at the 

intersection of Routes 5 and 210. Rails were also 

bent just west of the Juvenile facility (fig. 7). 

HARBORS 

Los Angeles and Long Beach reported that the 

harbor areas did not suffer any significant damage. 

241 
242 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE I.-Interchange at Route 5/ 210. Looking west. Overpass and bridge collapses. California Division of Highways 

photograph. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 243 

FIGURE 2.-Interchange at Routes 5/14. Looking north. Overpasses under construction collapsed. California Division of 

Highways photograph. 
244 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-Freeway overpass collapse. At interchange of 

Routes 5/210. J. F. Meehan, OAC photograph. 

FIGURE 4.-Freeway compression, about 27 inches. South of 

interchange of Routes 5/210. J . F. Meehan, photograph. 

FIGURE 5.-Freeway overpass collapse. Routes 5/210. Column 

bores pulled from footing. J. F. Meehan, OAC photograph. 

FIGURE 6.-Freeway Interchange 5/210. Column movement in 

soil. J. F. Meehan, OAC photograph. 

FIGURE 7.-Railroad west of Juvenile Facility. J. F. Meehan, 

OAC photograph. 

''! 
DAMAGE TO ENERGY AND COMMUNICATION SYSTEMS 

By D. F. MORAN 

CONSULTING STRUCURAL ENGINEER 

ELECTRICAL 

GENERATING FACILITIES 

The Los Angeles Department of Water and Power 

Valley Steam Plant is located in the San Fernando 

Valley, about 6 miles south of the epicentral area. 

There are four steam electric-generating units with 

four 250-foot-high concrete stacks. 

Boilers are hung from and enclosed by braced 

steel frames. Boilers are anchored laterally to the 

steel frames. The boilers must expand laterally and 

downward owing to operating temperatures and 

pressures. The lateral anchorages between the boiler 

frame and the supporting steel fn,me must then 

allow these movements but resist lateral forces due 

to earthquakes. Two systems are used in this plant. 

These are link and sliding type. 

The electric-generating units are supported on 

heavy reinforced-concrete portal-frame-type pedestals which are very rigid to prevent excessive 

deflections. 

The entire plant was designed for lateral forces 

equivalent to 20 percent of gravity. 

The only damage in the plant was a broken lightning rod insulator on one of the large transformers. 

There were evidences of heavy lateral forces at the 

bracing connections between the boilers and steel 

frames. Some of the large piping moved and mashed 

the insulation at supports. The oil-storage tanks 

and stacks did not suffer damage. No evidence of 

damage to the electrical generator has been detected. 

A small 50-year-old hydroelectric plant is located 

just northeast of the Upper Van Norman Reservoir 

and is powered by the Owens Valley aqueduct. The 

earthquake caused the aqueduct pipe to fracture at 

the scroll case of the turbine. This caused severe 

undermining of the structure. However, structural 

damage to this old reinforced-concrete structure was 

only moderate. 

TRANSMISSION LINES 

There were no reported failures of completed 

large electrical transmission lines or towers as a 

result of this earthquake. Ground cracks occurred 

near some towers in the San Gabriel Mountains. 

Two towers under construction were reported to 

have fallen. 

TERMINALS 

Sylmar Converter Station 

There was extensive damage to this station where 

the 800,000 volt d.c. line from the Pacific Northwest 

terminates. The loss of the Pacific Intertie, which 

was dedicated in September 1970, means power 

from the Northwest-around 525,000 kilowattswill not be available this summer· when peak demands for power occur. However, power from 

steamplants in the area is sufficient to meet the 

present electrical demands, while other sources of 

power Jo help meet the peak summer load are now 

being obtained by negotiation. 

Damage to this plant was in excess of $28 million and involves mainly electrical equipment and 

underground conduit. Evidences of severe ground 

movement in this area exist. There are many cracks 

and separations of concrete walls in the yard area. 

The building has a steel frame with metal deck 

roof and walls. A partial basement occurs under the 

service area. A structural separation divides the 

valve bay to the north from the service area to the 

south. This separation stops at the first floor, where 

the separate steel columns above rest on commonreinforced-concrete columns. 

The steel frames have vertical "X" bracing to 

resist earthquake forces. The steel frame and bracing performed well. 

Damage occurred in the basement in the vicinity 

of the separation joint. 

245 
246 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

Two large, 50-foot-high steel-framed radioshielded areas adjoin the main building on the east 

and west sides. These frames are covered with wire 

mesh and have horizontal and vertical steel "X" 

bracing. Loading of these frames is small, consisting 

of conductors and insulators. 

Numerous braces were buckled and stretched or 

broken. Many columns are bent and some lean. 

Ground cracks occur in these areas, and there is 

evidence of stretching of the ground. There may 

also be some differential vertical movements. It is 

estimated that these structures could resist more 

than 50 percent gravity owing to their light weight 

and wind-design loads. It is felt that the majority of 

this damage is due to ground lurching and settlement in these areas. 

Severe damage to electrical equipment occurred in 

the valve bays. 

Outdoor electrical equipment was heavily damaged. Most· of this equipment was supported on 

insulators which failed during the earthquake (fig. 

1). Some heavy pieces of equipment overturned 

owing to failure of their anchorage to foundation 

pads (fig. 2). Extensive damage was caused by 

swinging of heavy conductors which broke supporting insulators. 

Anchorages of very large (200 ton) transformers 

performed well. 

Olive Switching Station 

This station is located about 1 mile southeast 

of the converter station. Severe damage was suffered 

by the electrical equipment in this yard (fig. 3). 

Insulator-supported equipment collapsed and 

several large transformers fell over. 

The Vincent Intertie Station 

The Vincent Intertie Station has some equipment similar to the Sylmar Converter Station but 

suffered only minor damage. 

Distributing Stations 

Two modern distributing stations in the SylmarGranada Hills area suffered damage to the cantilevered walls surrounding the plants, but electrical 

equipment performed well. 

One distributing station in Sylmar has 20-foot reinforced-concrete-block cantilever walls. These walls 

were designed for 20 percent gravity. Vertical concrete-block pilasters supported on drilled concrete 

piles support these walls. The performance of these 

walls was good considering the probable severity 

of ground motion. Many of the pilasters were 

cracked and spalled near their bases, and walls were 

leaning both in and out 1 to 2 feet at the top. However, none collapsed. 

Another station in Granada Hills had precast-concrete cantilevered walls supported by vertical steel 

beams. These were designed for 20 percent of 

gravity. Many of the steel columns were bent, and 

some ruptured in the webs. Concrete-panel-to-steelcolumn connections failed in some cases, but no 

panels fell down. 

Several old distributing stations in downtown Los 

Angeles suffered cracks in their unreinforced brick 

walls. 

Oistribution Systems 

Many pole transformers were thrown down in 

the Sylmar area. Insulators and crossarms were 

broken, and wires and poles were knocked down. 

Cables sheared off in underground ducts. 

By Friday, February 12, all feeders were restored, 

downed transformers were replaced, and all power 

to customers was back in service. 

Careful studies must be made of the performance 

of electrical equipment. Designs must be developed 

by structural engineers working together. Full-scale 

tests of some equipment under simulated earthquake loading would be desirable. 

GAS 

The Southern California Gas Co. reports that, in 

general, the distribution piping system withstood 

the stresses of the earthquake remarkably well. This 

is borne out by the fact that in many areas where 

buildings obtained appreciable damage, the system 

remained intact. 

The major transmission lines from out-of-State, 

30 inches in diameter or more, did not suffer any 

apparent damage. Service to the great majority of 

the company's 3.1 million customers was little 

affected. 

The only area where the distribution piping 

system was seriously damaged occurred within a 

11- to 12-square-mile area in the northeast section 

of San Fernando Valley, including Sylmar and the 

city of San Fernando. This region suffered widespread damage to all types of buildings and underground structures, as well as utility services. The 

somewhat diagonal area is bounded by the Golden 

State Freeway on the west, the Pacoima Wash on 

the south, and the San Gabriel Mountains on the 

north. 
THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 247 

The transmission system handling the deliveries 

of California gas from the San Joaquin Valley to the 

Los Angeles basin was damaged to the extent that 

four lines had to be shut down in the San Fernando 

area. Damage to the four lines, which range from 

12 to 26 inches in diameter, occurred between Newhall and San Fernando and resulted in the loss of 

supply to the distribution system in the SylmarSan Fernando area. 

The distribution system in this hard-hit area consists principally of a network of 2-, 3-, and 4-inch 

welded steel mains serving approximately 17,000 

customers. The violent earth movement there 

pulled, compressed, and twisted the piping system, 

resulting in: broken mains, valves, and service 

risers. Approximately 450 breaks have been discovered. 

There were two or three gas fires within streets 

at broken lines. We are not aware of any specific 

damage to buildings due to fires associated with gas. 

In general, all utility facilities were out of serv-

' ice in the critical San Fernando area-gas, electric, 

water, telephone, and sewer. 

Damage to the remainder of the company's distribution system was confined to isolated fractures 

or pipe separations that did not result in serious 

impairment of service to customers. 

Repairs to the damaged gas mains in San 

Fernando area were commenced almost immediately 

after the earthquake. Gas service to customers was 

restored commencing Sunday, February 14, and 

completed for the most part by Saturday, February 

20th. 

TELEPHONE SYSTEMS 

The General Telephone Co. reports that all the 

telephone equipment in the Sylmar central office 

was totally destroyed by the earthquake. Damage to 

the building and equipment is estimated at $4.5 

million. The 9,500 customers in Sylmar were completely without telephone service. 

Around-the-clock work began at once to rebuild 

the central office. On February 27, just 18 days after 

the earthquake enough equipment was installed t6 

place more than 1,000 Sylmar customers back in 

service. 

Attention must be given to the anchorage and 

bracing of critical telephone equipment. 
248 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 1.-Sylmar Converter Station collapsed condenser banks. DWP photograph. 
f n-

;/ 

THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 2.-Sylmar Converter Station air switches. DWP photograph. 

249 
250 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

FIGURE 3.-0live Switching Station overturned transformers. DWP photograph 

~''4'! 
SOCIOLOGICAL ASPECTS OF 'THE EARTHQUAKE 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

In general, emergency measures worked well in 

this earthquake. Many fires were started but were 

quickly extinguished by the fire departments. Some 

fires in streets due to ruptured gaslines burned for 

some time. 

Efficient action by the police department, aided by 

television and radio announcements, resulted in the 

orderly evacuation of some 80,000 persons below the 

threatened Lower Van Norman Dam. Police then 

patroled the vacated area to prevent looting. 

Emergency actions to rescue persons trapped in 

the collapse at the Veterans Hospital in Sylmar were 

initiated shortly after the shock, following a delay 

due to communication difficulties. The U.S. Corps of 

Engineers provided heavy equipment and fire departments were on the scene. 

Prison labor helped in the rescue effort, which 

went on for some 100 hours. Many persons were 

trapped between collapsed concrete floor slabs which 

were stacked directly on top of each other. The 

rescue work was slow and painstaking- for this 

reason. 

Traffic lanes on the damaged freeway systems 

were opened to thru traffic within a few days. 

Numerous pavement cracks and settled abutment 

fills at bridges had to be filled in with asphalt, and 

bypasses were built around the overpass collapse 

areas. 

Emergency evacuation of patients from the four 

damaged hospitals in the area was orderly. Patients 

were carried down stairways because elevators were 

inoperative. 

About 80 inmates of the Los Angeles County 

Juvenile facility in Sylmar escaped when a part of 

a wall collapsed. All inmates were later evacuated 

from this heavily damaged facility. 

Many areas were without power, water, gas, and 

telephone service for several days after the earthquake. Restoration of these utilities is a slow and 

expensive process, particularly when facilities are 

underground. In the city of San Fernando, a 

temporary water system was installed above grade. 

Red Cross and Salvation Army units were effective in mass care actions. 

In all cases, repair crews are working around the 

clock to restore services. 

A severe water shortage was alleviated somewhat 

by providing large tanker trucks in shopping-center 

parking lots. Some grocery stores which suffered 

heavy damage held food sales in their parking lots. 

All residents were requested to turn off their 

gas supply to prevent leakage and possible explosion. 

Severe damage to telephone-exchange equipmnt 

will result in impaired service in the heavily hit 

area for several months. 

Total damage to sewer and storm-drain facilities 

is not known at this time. 

The local building departments quickly sent inspection teams into the field to check structures for 

safe occupancy. Numerous structures were posted as 

unsafe after a cursory examination disclosed some 

damage. Later, crews were sent around to make 

more complete checks and specify to the owners what 

the extent of damage actually was. 

Repair of damage is proceeding rapidly, particularly in commercial and industrial construction. In 

one case it was observed that an occupant of an industrial building had erected a temporary wood wall 

to replace a collapsed wall and was proceeding with 

"business as usual," although his structure was 

posted as "unsafe" by the Building Department. 

The loss of life associated with this earthquake 

is 63. Nine of these deaths were as a result of heart 

attacks, and 45 died as a result of the collapse at the 

Veterans Hospital. One person was killed in the 

collapse at the Olive View Hospital. One person 

died owing to partial collapse of the old Midnight 

Mission in downtown Los Angeles. Two persons were 

killed in a truck under a freeway overpass collapse. 

251 
252 THE SAN FERNANDO, CALIFORNIA, EARTHQUAKE OF FEBRUARY 9, 1971 

Over 1,000 persons were injured; many by broken 

glass. 

It should be pointed out that the loss of life and 

injuries would have been much greater had the 

shock occurred even 1 hour later, when many 

persons would have been traveling to work on 

crowded freeways and would have been occupying 

areas of buildings which collapsed. 

Total restoration costs have been estimated at $1 

billion. About one-half of this is for public and the 

other for private damage. The U.S. Corps of Engineers is proceeding with restoration work in the 

city of San Fernando and other areas. They will be 

rebuilding public facilities, as requested, to fully 

conform to current codes. 

The amount of loss covered by insurance is small, 

probably less than $50 million with very little of 

this on dwellings. 

Many dwellings are total losses, and this is a serious blow to the owner who already has a large 

mortgage and must borrow more money to rebuild. 

Some owners have abandoned their heavily damaged 

homes. 

The overall effect of this earthquake on employment is not known at this time. Certainly it will provide many jobs in the construction industry, but 

some manufacturing and service jobs may be curtailed during the rebuilding program. 

Severe psychological traumas to individuals have 

been reported. 
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS BASED ON ENGINEERING STUDIES 

By EARTHQUAKE ENGINEERING RESEARCH INSTITUTE COMMITTEE 

The committee has arrived at the following preliminary conclusions and recommendations: 

1. The hazard of non-earthquake-resistive construction was reemphasized. Old structures, particularly unreinforced masonry bearing wall type with 

weak mortar, performed poorly. Collapse of nonearthquake-resistive skeleton concrete frame buildings with unreinforced hollow tile walls at the 

Veterans Hospital resulted in the greatest single loss 

of life. 

2. Modern high-rise construction survived this 

shock well. However, most were not fully tested 

owing to their distance from the epicenter. We must 

learn as much as possible from correlation of strongmotion records with design criteria. 

3. Surprisingly large ground motions were recorded. They exceeded, at some places, the El Centro 

and Taft records which have guided earthquakeresistive design for 30 years. The high vertical accelerations recorded on instruments and reported by 

witnesses probably contributed to increased damage 

to structures. 

4. Reassessment of some design criteria and 

methods are indicated for bridges, overpasses, buildings, and earth dams containing hydraulic fills. Particular attention should be focused on the poor 

behavior of many one-story industrial and commercial structures, since they comprise the majority 

of construction, other than residences. Plywood 

diaphragms must be studied and tested. Reinforcing 

and joinery details must be improved. 

5. Desirability of designing important. buildings 

for differential foundation movements must be considered. Also, overall increased seismic safety of important structures such as hospitals, utilities, and 

those housing emergency operations must be 

examined. 

6. Greater caution is required relative to building 

in the zones of larger faults, and effort is required 

to map the fault locations better and to understand 

their degree of activity. Ground movements such as 

lurching, settling, cracking, and compression in 

many areas undoubtedly contributed significantly to 

damage to structures in these areas. 

7. Confidence increased in California publicschool design criteria and methods. However, nonearthquake-resistive school buildings performed 

poorly. 

8. This is the most important earthquake in history from the standpoint of instrumental data and 

real testing of earthquake-resistive construction. 

9. Modern one-story wood-frame and stucco dwellings performed reasonably well considering the high 

ground accelerations and movements. However, reconsideration of code provisions and enforcement is 

indicated, particularly for two-story construction 

and masonry chimneys. 

10. New efforts are needed to safeguard important electrical, mechanical, and communication equipment. New design criteria and methods must be developed. 

11. Greater attention to the hazard of broken 

glass is needed. 

12. Disaster-relief activities were effective but 

should be improved relative to organization and 

communication. 

13. The Earthquake Engineering Research Institute is convinced that this important earthquake 

must be the subject of a major investigation and 

report. 

253 
254 

COOPERATING ORGANIZATIONS 

American Society of Civil Engineers-Los Angeles Section 

California Department of Aeronautics 

California Department of Navigation and Ocean Development 

California Department of Water Resources 

California Division of Highways 

California Division of Mines and Geology 

California Institute of Technology 

General Telephone Company 

International Conference of Building Officials 

Lamont-Doherty Geological Observatory of Columbia University 

Long Beach Harbor Department 

Los Angeles City Building Department 

Los Angeles City Engineer 

Los Angeles City Fire Department 

Los Angeles City Police Department 

Los Angeles County Engineers Office 

Los Angeles County Flood Control District 

Los Angeles County Road Department 

Los Angeles Department of Airports 

Los Angeles Department of Water and Power 

Los Angeles Harbor Department 

Metropolitan Water District of Southern California 

Pacific Telephone Company 

Southern California Edison Company 

Southern California Gas Company 

Southern Pacific Railroad 

Structural Engineers Association of California 

U.S. Army Corps of Engineers 

U.S. Atomic Energy Commission 

U.S. Bureau of Public Roads 

U.S. Office of Emergency Preparedness 

University of California, Los Angeles, Berkeley, and Davis 

~1tf4 ! ;, U, S. GOVERNMENT PRINTING OFFICE : 1971 0 - 420-813