GEOLOGICAL SURVEY CIRCULAR 797 

A Preliminary Study 

of the Santa Barbara, California, 

Earthquake of August 13, 1978 

and its Maior Aftershocks 

A Preliminary Study 

of the Santa Barbara, California, 

Earthquake of August 13, 1978 

and its Maior Aftershocks 

By W. H. K. Lee, C. E. Johnson, T. L. Henyey, and R. L. Yerkes 

GEOLOGICAL SURVEY CIRCULAR 

1978 

797 
United States Department of the Interior 

CECIL D. ANDRUS, Secretary 

Geological Survey 

H. William Menard, Director 

Library of Congress catalog-card No. 78-600153 

Free on appliCAtion to Branch of Distribution, U.S. Ge~l Survey, 1200 South lEads Str .. t, Arlington, VA 22202 
Abstract • 

Introduction 

CONTENTS 

Tectonic setting • • • • 

Data processing and analysis • 

Distribution of hypocenters 

Location of the main shock • • 

Focal nechanism of the nain shock 

Correlation • 

Conclusions • 

References cited • 

ILLUSTRATIONS 

Figure 1. Map showing locaticns of principal seisnograph 

stations am major e~ in Santa 

Page 

1 

1 

2 

3 

3 

5 

8 

9 

9 

• 10 

Page 

samara channel • 2 

2. Diagram sharing crustal structure nodels 5 

3. Map shCMing epicenters of Santa Ba:rbara 

earthquake and its major aftershocks • 8 

4. Diagram shcMing fault-plane solution of 

Santa Barl>ara earthquake • 9 

5. Cross section of area of figure 3 showing 

hypocenter distribution and faults . • 10 

TABLES 

Page 

Table 1. Coordinates and delays of principal seisnograph.ic stations used in the present study . • 4 

2. List of Santa Barbara earthquakes, August 

13-18' 1978. 0 0 • • • • 6 

3 o Criteria for the four quality grades of Q o 8 

III 

A Preliminary Study of the Santa Barbara, California, 

Earthquake of August 13, 1978 

and its Maior Aftershocks 

By W. H. K. Lee, C. E. Johnson, T. L. Henyey, and R. L. Yerkes 

ABSTRACT 

'Ihe M_r.5 .1 Santa Barbara earthquake of August 13, 1978 occurred at lat 34° 22.2'N., long 

119° 43. 0' 4 km south of Santa Barbara, Calif. 

at a depth of 12. 5 km in the northeast Santa 

Barbara Channel, part of the western Transverse 

Ranges gecnn:rphic-structural province. 'Ihis 

part of the province is characterized by 

seismically active, east-trenQing reverse faults 

and rates of coastal uplift that have averaged 

up to about 10 m/1000 years over the last 

45,000 years. 

No surface rupture was detected onshore. 

Subsurface rupture propagated northwest from 

the main shock tavard Goleta, 15 km west of 

Santa Bamara, where a maxinrum acceleration of 

0. 44 g was measured at ground level and extensive minor damage occurred; only minor injuries 

were reported. A fairly well- constrained faultplane solution of the main shock and distribution of the aftershocks indicate that leftreverse-oblique slip occurred on west-northwesttrending, north-dipping reverse faults ; inadequate dip control precludes good correlation 

with any one of several mapped faults. Had the 

earthquake been larger and rupture propagated 

to the southeast or a greater distance to the 

northwest, it could have posed a hazard to oilfield operations. The fault-plane solution and 

aftershock pattern closely fit the m:xlel of 

regional defo::rmation and the solution closely 

resembles those of five previously mapped events 

located within a 15-km radius. 

INTRODUCTION 

A m:xlerate-sized earthquake (Mr.. = 5 .1, an 

average fran five Wood-Anderson stations operated by the california Institute of Teclmology) 

occurred 4 k:m offshore of Santa Bal:bara, California at 3:54 p.m. local time (2254 GCT) on 

the 13th of August, 1978. Minor local damage 

occurred at the city of Santa Barbara; the 

carrpus of the University of California at Goleta 

15 k:m to the west suffered extensive minor damage. Hospitals treated scores of people for 

minor injuries; no major injuries were reported. 

'Ihis report sumnarizes the preli.minaJ:y results 

of our investigation of the main shock and the 

major aftershocks that occurred in the follcwing 

five days. 

'Ihe Santa Barbara Channel region i~ one of 

the nost active seismic areas of Ca1if01nia. 

'Ihe earliest recorded destructive earthc:'Jake, on Decerrber 21, 1812, heavily damaged several 

missions along the coast and had an estimated 

magnitude of 7. Since then, numerous ffi>ents 

have been felt and several damaging earthquakes 

have occurred. In particular, alnost tr~ entire 

business section of Santa Barbara was destroyed 

or rendered unsafe by the J1.me 29, 1925 earthquake of magnitude 6. 3. Santa Barbara c.lso was 

damaged by the June 30, 1941 earthquake of magnitude 6. 'lhese two eart:hiuakes are poorly 

located but are inferred to have occurred very 

near to the August 13, 1978 event (fig. 1). A 

list of significant earthquakes in the fanta 

BaiDara Channel area was prepared by Hamilton 

and others (1969) and later revised by Iee and 

Ellsworth (1975). 

With increasing population along tl',~ coast 

ani extensive petroleum developoont in the Santa 

Baxbara Channel, even m:xlerate-sized earthquakes 

may be hazardous. Lee and Ellsworth (1~75) 

argued that tectonic conditions in the C".hannel 

region are capable of generating an earthquake 

as large as magnitude 7 .. 5. In view of the continuing likelihood that a large earthquake will 

occur in the Santa Barbara Channel, a IliC'jor concern is the correlation of seismic data with 

recognized faults. 

AaknowZedgments.--we thank Larry Porter and 

Tom Wootton of the california Division of Mines 

and Geology and Gerry Brady of the U.S. Geological Survey for providing stJ::ong-notion data. We 

are grateful to Mari Gunn and Al Walter for 

qssistance in data processing, to Bob Burford 

and Gary Fuis for their stimulating discussions, 

and to Peter Leary, John M::Raney and DeJ-:-ek Monov 

for their tireless efforts in the speedy proc-
120°00' 119030' 119000' 

0 40 KILOMETERS I I 

EXPLANATION 

• Seismograph station 

1f Earthquake- Location and date * 1978 earthquake- Location of main shock 

----·· Fault- Dashed where approximately located; 

dotted where concealed 

Figure 1.--Locations of principal seisrrograph stations and major earthquakes in Santa Ba:t:bara 

Charmel. 

essing of the USC data. The USC Santa Barbara 

network is supported by the Conservation Division, U.S. Geological Survey. 

TECTONIC SETTING 

Santa Bal:bara Charm.el occupies the southwest quarter of the western Transverse Ranges, a gearorphic-structural province of southern 

California. Relative to adjoining terrain, 

the Transverse Ranges are unique in several 

inportant respects: the distinct east-west 

orientation, the type, age, and history of exposed basenent rocks, and the spectacular rates 

of corrpressi ve defonna.tion as indicated by the 

inposing reverse-fault-controlled IIDUntain 

fronts and the extrenely deep basins filled with 

young, intensely deformed secli.Irents (the Santa 

Baroara Channel-Ventura basin axis is coincident 

with the steepest known gravity gradient in 

California) . 

The western Transverse Ranges are botmded 

by major faults: the east-trending Santa Ynez 

2 

on the north, the southeast-trending San Gabriel 

on the east, and the east-trending Ar:acapa-Santa 

~nica on the south. Onshore segrrent.s of each 

of these faults juxtapose dissimilar baserrent 

rocks: the Santa Ynez fonns the south boundaJ::y 

of the central coast Franciscan, the San Gabriel 

fo:rms the southwest boundaJ::y of expos~ed Precambrian anorthosites of the western Sar Gabriel 

M:>untains, and the Malibu Coast-Sante: ~nica 

fonns the north boundary of the weste:~ Los 

Angeles basin-continental borderland Franciscan 

terrane .. 

'Ihe structure of the western Trc:nsverse 

Ranges is daninated by east-trending reverse 

faults; one of the best k:nown of these is the 

Red 1buntain fault. Well data, geolc :ric napping, 

and several congruent fault-plane solutions shew 

that the fault dips northward at about 60° , offsets strata as young as about 500 ,000 years, and 

has a :max:imurn stratigra:tfric separaticn of about 

7,500 m (Yeats and others, in press). 

A band of rroderate seismicity is associated 

with sarre of the east-trending revers~ faults 
within the western Transverse Ranges. '1hl.s 

result is based on a syste.ma.tic stu:ly of the 6-

year (1970-1975) record of seisrrographic stations operated by the u.s. Geological Survey, 

California Institute of Technology, University 

of Southern California, and California Departtrent of Water Resources (Lee and others, in 

press} • One or nore of about 200 fault-plane 

solutions derived from this 6-year record can be 

associated gearetrically with segments of the 

Red M:>untain, Pitas Point-Ventura, and San 

cayentano faults, and perhaps the Mid-<llannel 

fault and fault X (see fig. 3) o '!he solutions 

shaN generally near-horizontal P axes oriented 

at an average of N. 24 ° E. The inferred c:an- pressi ve stress is reflected in earthquakes of 

magnitude approximately 1 to 6.5 and reverse 

displacerrent on the east-trending faults; the 

average slip vector indicates approximately 

equal parts of vertical and left-lateral slip 

(Yerkes and lee, in press). 

All the evidence on the rate and sense of 

defonna.tion is :mutually consistent for indi vidual segments of the faults in the Santa Bal::bara 

Channel area: geologic data on the sense of 

latest displacement and arrount and sense of 

stratigraphic separation, geodetic data on tilting of coastal areas underlain by the faults, 

uplift of dated marine terrace deposits in such 

areas, and associated fault-plane solutions. 

'!he average rates of uplift (up to 10 m/1000 

years) , indicated by dating of deposits as young 

as 2, 500 years 1 show no slc:Mi.ng over the last 

45,000 years (Yerkes and Lee, in press) • 

'!he east-trending reverse faults that dominate the structure of the western Transverse 

Ranges may be viewed as slip surfaces between a 

series of north- to northeast-di:pping shingles 

along which many kilareters of north-south 

shortening and east-west extension occurred in 

latest Quaterna:cy time. '!he Santa Barbara earthquake of 13 August 19 78 and its aftershock pattern fit well with this nodel, and its faultplane solution neatly fits those of five previously mapped events within 15 km of it. 

DATA PROCESSING AND ANALYSIS 

'!he Santa Barbara earthquake and its aftershocks were well recorded by the California 

Institute of Teclmology (CIT) -u.s. Geological 

Survey (USffi) cooperative network in southern 

California and by seisnographic stations operated by University of Southern California (USC) , 

University of California at Santa Bal:bara (UC:SB), 

and California Depa.rt:nent of Water Resources 

(l~R) • It is very fortunate that the USC group 

established four stations (three in Santa Barbara Olannel) near the epicentral area one day 

before the earthquake o After the earthquake, 

additional stations were installed by usc, USGS, 

and others. 

In order to nake a study in a short time, 

we selected about 100 earthquakes (out of several 

hundred well-recorded ones) and processed IIDStly 

3 

data recorded at the critical stations (fig. 1). 

Initially, the data were processed ind£'1etldently 

at CIT, USGS, and USC. At CIT, the earthquakes 

were processed and analyzed in a routil1~ manner 

using a computer-assisted system desigiled by c. 

E .. Johnson. At USC, seismic data recorded on 

magnetic tapes were played back at a scue of 

1 an = 1 second and arrival times were read 

manually. CIT's Develocorder film reccr.dings of 

SYP station Cabout 30 km fran the epicenter} were 

scanned at the USGS. P-arri val, S-arrj val, and 

signal duration were neasured for events of duration 20 seconds or :rrore. Fran the scar list, 

arrival times for the larger aftershocks were 

read from Develocorder fil.ms that recorded the 

Santa Barl>ara Channel region stations. OVerall errors in the arrival tine data are gerP.rally 

less than 0 .1 second. · 

The data from these three sources were 

nerged and analyzed. We located the ecrthquakes 

using the HYP071 conputer program (Lee and Lahr, 

1975) . Initially, we used Healy's (19f 3) crustal structure nodel and station delays 'ill"nrked out 

for the Western Transverse Ranges by Le:~, Yerkes, 

and Simirenko (in press). This allCMeC' us to 

eliminate gross errors in arrival tin:es' quickly. 

We then selected 17 well-recorded eart:l1'1Uakes 

and derived a set of station oorrectiors using a 

crustal nodel (fig. 2) which approximates a tentative velocity profile in Santa Barbara Olannel 

obtained fran a geophysical survey usir') the 

seismic-reflection nethod. 

Station ooordinates and station de:lays are 

given in table 1. Finally, we relocate:-1 all 

earthquakes using this crustal nodel ard the 

station delays. Earthquakes were located on the 

basis of P-wave arrival tines.. '!he HYI"171 cx:mlputer program erploys Geiger's (1912) ~thod to 

detennine hypocenters by minimizing the: residuals between observed and calculated c:rri vals. 

Travel tines fran a trial hypocenter tc the 

stations and their Partial derivatives are cx:mputed on the assunption of a horizontal :multilayer nodel by a tedmique introduced t:' Eaton 

(1969). Earthquake magnitudes were estimated 

using the signal duration nethod (lee c:nd others, 

1972}. Hc:Mever, the present earthquake: magnitude 

estimates are very cn:rle and should :be calibrated 

against the local magni ttrle scale originally 

proposed by Richter in 1935 (Richter, 1958}. 

For exanple, magnitude estimated fran s-ignal 

duration for the main shock (table 2) is 4 .. 9, 

whereas the average Richter magnitude cf five 

'WCXXl-Anderson stations is 5 .1. 

DISTRIBUTION OF HYPOCENTERS 

A total of 71 earthquakes that occurred 

from 2254 GCT August 13 to 0718 GCT A~JSt 18, 

1978 are listed chronologically in table 2. 

Included are the origin time, location of hypocenter (epicenter and focal depth), magnitude, 

and nurrber of arrival tines used. In aildition, 

five parameters are listed as a neans of evaluating the quality of the hypocenter solution: 
Table 1.-- Coordinates and delays of prinaipaZ seismographia stations used in 

the present study 

Station Latitude (N) longitude (W) Elevation Delay 

code (m) (s) 

In 34° 18.72' 119° 33.68' -76 0.28 

occ 34° 18.57' 119° 39.35' -82 .34 

OCE 34° 22.00' 119° 37.35' -46 .04 

PKL 34° 26.84' 119° 36.98' 142 - .39 

Vl'R 34° 24.32' ugo 42.85' 122 0.00 

SBCC 34° 56.48' 120° 10.32' 610 .72 

SBCD 34° 22.12' 119° 20.63' 213 .04 

SBIC 34° 29.79' 119° 42.81' 1190 - .33 

SBIG 34° 6.57' 119° 3.85 1 415 - .77 

SBLP 34° 33.62 1 120° 24.03' 134 .29 

SBSC 33° 59.68' 119° 37.99' 457 - .59 

SBSM 34° 2.25' 120° 20.99' 172 - .19 

SBSN* 33° 14.70' 119° 30.40' 259 

CAM 34° 15.27' 119° L99' 271 .29 

ECF 34° 27.48' 119° 5.44 t 1005 .17 

KYP* 34° 6.10' 118° 52.77' 701 

PTD* 34° 0.25' 118° 48.37' 41 

SAD* 34° 4.88' 118° 39.90' 727 

SIP* 34° 12.26' 118° 46.92' 701 

SYP 34° 31.60 I 119° 58.70' 1305 .02 

*These stations are located more than 80 km from the Santa Barbara earthquakes 

and were not used in the earthquake location. 

( 1} the largest azimuthal separation between 

stations (a) , (2) epicentral distance to the 

nearest station (B), (3) root-mean-square error 

of the t.ine residuals, (4) standard error of the 

epicenter, and ( 5) standard error of the focal 

depth. On the basis of these paraneters, the 

general reliability of each earthquake solution 

is graded as either excellent (A), good (B), 

fair (C), or FXJOr (D). The criteria for these 

classifications are given in table 3. 

A brief discussion of the accuracy of hypocenter solution of earthquakes was given by Lee, 

Eaton, and Brabb (1971). To obtain a reliable 

epicenter, the largest azimuthal separation between stations (a) should be less than 180° , so 

that the earthquake epicenter is surrounded by 

stations. To d:>tain a reliable focal depth, 

epicentral distance to the nearest station (B) 

should be less than the focal depth, so that 

there is a direct ray-path. In addition, systerratic errors arise fran uncertainties in the 

crustal velocity nodel. These errors cannot be 

detemd.ned without controlled experiments, such 

4 

as calibrated eJq?losions in the focal region. 

OWing to the irregular distriliution o.f stations 

and occasional loss of data fran critical stations, the quality of hypocenter solu'::ions in 

table 2 varies. Although standard er.urs of 

epicenters and focal depth are given, they nust 

be interpreted with caution, especially for 

quality C and D solutions. These standard 

errors are conputed with respect to the assured 

crustal velocity m:rlel, which is not necessarily 

a good approxination to the real earth .. 

The epicenter distriliution (fig. 3) shaNS a 

linear trend of N. 60° W. with the main shock at 

the southeastern end. The d:i.rrension of the 

innediate aftershock area is approxim;..,tely 3 by 

12 km. The main shock was preceded four hours 

by a small earthquake located at the lower righthand corner of the area of figure 3. It is not 

clear to us whether this earthquake is related 

to the Santa Barbara earthquake. Howt1ver, it 

occurred in an area where a swann of earthquakes 

took place in March and April of 19 78. Inmediately after the main shock, seismic activity was 
concentrated 7 km nort:hwest of the main event. 

rater, a feN aftershocks occurred nearer to the 

main shock; only two aftershocks located southeast of the main shock occurred in the first 

five days. On August 16 a feN earthquakes 

occurred 10 km south of the epicenter; they 

appear to be associated with a different fault. 

LOCATION OF THE MAIN SHOCK 

Strong-notion 

station 

Santa Bal:bara 

Court House 

(USGS) 

Univ. calif. 

Santa Bal:bara 

North Hall 

(a:M;} 

Goleta Freefield (a:M;) 

Maximum catputed 

accel- Trigger S-P Difference 

eration tine tine 

0.2lg 1.9s 2.4s -0.5s 

0.44g 3.ls 3.0s +O.ls 

0.37g 3.3s 3.7s -0.4s 

We are fortunate that the Santa Bal:bara 

earthquakes were surrounded by seisnograph stations and especially that three stations were 

within 10 km of the earthquake epicenters (see 

fig. 1} • Hc:Mever, nost of the stations are 

located northeast of the earthquakes. To lessen 

the station-distribution bias, we enployed azimuthal weighting (Lee and Lahr, 1975}, ignored 

stations farther than 80 km fran the earthquake 

location, and also assigned greater weights to 

stations within 40 km of the earthquakes. 

'lbese ti..ne differences indicate that ou":" mainshock location and its error estilnates are 

reasonable. In addition, the station S~ (at 

P-WAVE VELOCITY, IN KilOMETERS PE'' SECOND 

02 3 4 6 8 9 

'lhe biggest uncertainty in eart:lquake location is due to our lack of knowledge of the 

crustal structure under the Santa Barbara 

Olannel region. Experinents with various 

crustal roodels indicate that the epicenter 

error may be as high as ±3 km and the focaldepth error ±5 krn. For a given crustal roodel, 

we also experinented with different subsets of 

arrival-ti..ne data for the main shock. '!he results showed that (1) epicentral locations do 

not differ nore than ±1 km if the earthquake is 

surrounded (naximJm azimuthal gap between stations less than 180°), and (2} focal depths do 

5 

not differ nore than ±2 km if there is a station 

within 10 km of the earthquake. 'Ihe relative ~ l'J 

location errors between different earthquakes ~ 

are srrall because we use station corrections ~ 

derived fran a set of better recorded earthquakes. 0 

In vieN of the above discussion, we suggest Q 

the follCMing main-shock paraneters: z 

Origin time= 22h 54m 52.4s (±0.1 s) 

Epicenter = 34° 22.2' N., 119° 43.0' W. 

(±2 km} 

Focal depth = 12 0 5 km ( ± 3 km) 

::i b:: 15 w 

0 

Magnitude = Mr. = 5 .1 (average of five CIT 2'J 

Wood-Anderson stations} 

'!be location para:rreter:s are also supported 

by the strong-notion data obtained fran both the 

USGS and the California Division of Mines and 

Geology ( a:M;) • 'Ihe tirre interval between s-wave 

arrival and the initiation of recording at the 

accelerareter (S-trigger tirre) is a mi.ni.mum esti- 25 

mate of the S-P interval because the recorder may 

not be triggered by the first P-wave arrival. 

I 

I 

I 

I 

I MODEL USED FOR I 

FAULT-PLANE ~: 

' SOLUTION .... ___ 1 

I 

I 

I 

I 

I 

I 

, I ___ , 

I 

If we adopt our main-shock location and a ratio 

of P-velocity to s-velocity of 1. 7, we obtain the 

follCMing differences between carputed S-P and 

observed S-trigger tirres: Figure 2 .-Crustal structure rrodels. 

5 
Table 2.--£ist of Santa Barbara earthquakes, August Z3-Z8, Z978 

[YFAR, IDN, DAY, HR., MN, SEC, origin time in Greenwich Civil Time (GCI') • IAT N 1 I..l:NG W, location of epicenter in 

degrees and minutes of north latitude and west longitude. DEPTH, depth of focus in k.il.areters. MAG, local magnitude <Mr) of the earthquake estimated fran signal durations .. NO, number of stations used in locating earthquake. GAP, largest azimuthal separation in degrees between stations .. r:MrN, epicentral distance in kilarreters 

to the nearest station. RM>, root-mean-square error of the time residuals: RMS = [E. (R .2/NO]\ where R. is the ~ ~ ~ 

observed seismic-wave arrival ti.Ire minus the cx::rnputed time at the i th station. Em, standard error of the epicenter in kilarreters: ERH =[SDX2 + SDY ]~. SDX and SDY are the standard errors in latitude arxl longitude, 

respectively, of the epicenter. When NO <5, ERH cannot be CX>ItpUted and is left blank. ERZ, standard error of 

the focal depth in kilaneters. When NO < 5, ERZ cannot be carrputed and is left blank. If ERZ ~ 20 km, it is also 

left blank. Q, solution quality of the hypaneter (table 3)] 

EVENT YFAR MJN DY HR. MN SEC IAT N LONG W DEPTH MAG NO GAP J:liiJIN RMS ERH ERZ Q 

1 1978 AUG 13 22 54 52.4 34-22.1 119-42.9 12.5 4.9 16 68 4.0 0.05 0.2 0.4 A 

2 13 23 1 0.7 34-24.2 119-46.3 12.9 2.4 11 98 5.3 0.03 0.3 0.2 B 

3 13 23 1 32.4 34-24.8 119-48.2 11.9 2. 1 8 228 8.2 0.10 2.2 0.8 c 

4 13 23 2 45.6 34-24.4 119-46.2 12.7 2.7 11 68 5.2 0.05 0.4 0.5 A 

5 13 23 4 13.9 34-23.8 119-45.7 12.0 ,.> a::- L..;:;J 5 193 4.5 0.00 0.2 0.1 c 

6 13 23 5 1.4 34--23. 1 119-47.6 9.1 2.4 10 128 7.7 0.06 0 t::• .;:J 0.5 B 

7 13 23 6 19.0 34-24.3 119-46.3 12.5 2. 1 14 68 5.3 0.05 0.3 0.6 A 

8 13 23 6 57.4 34-24.9 119-46.5 12.1 1.9 9 124 5.7 0.04 0.5 0.7 B 

0"1 9 13 23 7 30.1 34-24.6 119-46.6 12.2 2.7 13 70 5.8 0.03 0.2 0.4 A 

10 13 23 8 27.1 34-·24. 3 119-46.6 12.4 3. 1 13 69 11.7 0.05 0.2 1. 3 A 

11 13 23 9 20.9 34-24.7 119-·45. 9 12.1 ~L 5 8 122 4.7 0.04 0.5 0.6 B 

12 13 23 10 9.3 34-24.4 119-48.3 11.3 2.6 9 126 8.4 0.02 0.1 0.2 B 

13 13 23 11 1.7 34-24.3 119-46.4 12.8 3.3 12 123 5.5 0.02 0.1 0.3 B 

14 13 23 15 2.5 34-24.4 119-46.4 12.6 3.0 16 68 5.4 0.11 0.5 1. 1 A 

15 13 23 16 42.4 34-24.4 119-45.3 11.3 2. 1 11 70 3.8 0.05 0.3 0.3 A 

16 13 23 18 10.1 34-22.9 119-43.7 13.4 2.3 13 96 2.9 0.06 0.4 0.4 B 

17 13 23 18 32.0 34-25.5 119-36.2 0.3 2.1 6 96 10.4 0. 15 1.5 2.3 c 

18 13 23 18 56.9 34-23.5 119-44.9 13.1 2.9 12 97 3.4 0.03 0.2 0.3 B 

19 13 23 19 42.4 34-24.0 119-44.2 11.5 1.7 8 125 2. 1 0.10 1.3 0.7 B 

20 lr3 23 22 50.6 34-23.3 119-43.2 14.3 2. 1 8 115 2.0 0.02 0.2 0.2 B 

21 13 23 23 25.9 34-24.7 119-47.1 12.2 3.0 12 98 6.6 0.02 0.1 0.3 B 

22 13 23 23 53.8 34-24.0 119-44.7 12.5 2.9 9 146 2.9 0.01 0. 1 0.2 B 

23 13 23 30 46.8 34-24.8 119-49.0 10.7 2.0 12 81 9.5 0.05 0.3 0.4 A 

24 13 23 31 44.9 34-22.9 119-43.1 13.1 2.0 9 114 2.6 0.02 0.2 0.2 B 

25 13 23 34 26.5 34-24.6 119-47.2 13.6 2.3 9 75 6.7 0.04 0.3 0.5 A 

26 13 23 35 53.7 34-24.4 119-46.6 12.7 2.3 12 73 5.8 0.08 0.5 0.8 A 

27 13 23 40 2.5 34-24.8 119-47.5 10.6 2.6 13 75 11.7 0.08 0.4 0.7 B 

28 13 23 52 16.5 34-23.2 119-43.9 10.9 2.0 10 163 2.6 0.04 0.3 0.3 B 

29 13 23 54 52.3 34-24.7 119-48.9 11.2 2.9 15 70 9.4 0.04 0.2 0.3 A 

30 13 23 56 3.0 34-24.5 119-48.3 9.8 3.1 13 70 12.9 0.06 0.3 2.4 B 
-....J 

EVENT YEAR MJN DY HR MN SEC LAT N lONG W DEPTH MAG W GAP I:MIN RMS ERH ERZ Q 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

56 

57 

58 

59 

60 

61 

62 

63 

64 

65 

66 

67 

68 

69 

70 

71 

14 

14 

14 

14 

14 

0 14 

0 21 

0 36 

0 40 

1 2 

1.3 

13.5 

43.6 

10.9 

35.1 

14 

14 

14 

14 

14 

1 18 58.6 

1 24 4.1 

2 5 19.2 

2 28 56.9 

4 0 52.9 

14 

14 

14 

14 

14 

5 9 

5 22 

6 33 

7 1 

7 3 

14 7 45 

14 7 47 

14 8 46 

14 12 53 

14 16 7 

14 16 55 

14 17 25 

15 4 37 

15 6 25 

15 9 58 

15 15 52 

15 17 16 

16 0 39 

16 4 24 

16 5 31 

40.5 

42. 1 

26.8 

18.6 

15.3 

50.6 

54.7 

51.3 

42.0 

25. :5 

0.5 

56.4 

12.5 

56.8 

32.1 

45.5 

42.8 

33.8 

29.4 

6.0 

16 7 43 34.8 

16 8 57 56.7 

16 9 57 28.5 

16 10 43 37.4 

16 11 40 27.9 

1h 13 ~55 

17 2 58 

17 12 52 

18 1 55 

18 2 24 

11. h 

6.0 

8.0 

6.0 

21.8 

34-24.0 

34-24.8 

34-24.0 

34-24.2 

34-23.9 

34-24.6 

34-20.6 

34-23.7 

34-23.7 

34-23.6 

34-23.6 

34-23.4 

34-24.1 

34-24.6 

34-23.8 

34-24.5 

34-25.0 

34-24.2 

34-24.4 

34-·23. 9 

34-19.4 

34-·19. 4 

34-20.1 

34-20.1 

34-25.0 

34-23.1 

34-23.7 

34-23.8 

34-·21. 9 

34-15.8 

34-24.2 

34-19.7 

34-21.9 

34-23.8 

34-23.6 

34-24.6 

34-23.9 

34-·24. 4 

34-24.5 

34-24.6 

119-47.3 

119-48.8 

119-47.3 

119-46.6 

119-43.1 

119-47.6 

119-43.4 

119-46.8 

119-·45. 5 

119-44.6 

119-44.4 

119-43.2 

119-44.3 

119-45.1 

119-45.4 

119-48.3 

119-47.4 

119-47.4 

119-·46.5 

119-45.5 

119-49.7 

119-50.4 

119-50.6 

119-50.7 

119-47.1 

119-·48. 4 

119-44.6 

119-45.3 

119-·42. 6 

119-43.7 

119-46.8 

119-49.6 

119-42.5 

119-45.4 

119-45.7 

11°-48.3 

119-48.8 

119-46.3 

119-47.7 

119-46.4 

11.4 

11. 1 

12.4 

12.8 

14.1 

12.6 

9.8 

12.5 

13.3 

13.4 

13.5 

13.3 

13.5 

10.0 

13.2 

11.3 

13.9 

10.9 

13.5 

13.7 

14.5 

9.0 

6.9 

6.5 

11.8 

11. 1 

13.9 

12.3 

11.6 

7.7 

12.7 

8.0 

10.9 

12.8 

11.8 

11. ro:; 

13.8 

13.5 

12.0 

13.7 

18 7 18 51.4 34-24.1 119-46.0 12.6 

2.3 

2.9 

2.6 

2.3 

2.7 

2.2 

2.4 

1.9 

2.4 

2.4 

14 70 

13 127 

14 70 

10 99 

15 65 

15 

14 

13 

16 

16 

69 

72 

70 

68 

68 

;~.2 15 67 

2.7 13 133 

2.1 15 66 

2.4 14 67 

2.2. 14 68 

2.3 

2.0 

3.2 

2.4 

2.5 

2.3 

2.3 

2.4 

2.3 

2.3 

2.1 

2.3 

2.3 

2.3 

2.5 

2. 1 

2.3 

2.4 

2. 1 

2.8 

1 ? 

2.6 

2. 1 

2.1 

1.9 

14 70 

13 68 

13 70 

5 171 

13 68 

9 83 

9 95 

10 135 

11 95 

5 185 

6 194 

9 139 

8 98 

10 68 

11 92 

12 

11 

13 

11 

14 

75 

91 

68 

71 

69 

tro:; 71 

13 71 

5 170 

11 69 

6 169 

2.1 12 68 

6.9 0.03 

9.1 0.03 

6.8 0.04 

5.7 0.03 

0.9 0.03 

7.3 

6.9 

6.2 

4.2 

2.9 

2.7 

1.7 

2.2 

3 ~ .;;} 

4.0 

0.04 

0.06 

0.05 

0.02 

0.03 

0.02 

0.05 

0.04 

0.10 

0.03 

0.2 

0.2 

0.2 

0.2 

0.1 

0 "> . ' 

0.3 

0.3 

0. 1 

0.2 

0. 1 

0.3 

0.2 

0.5 

0.1 

0.2 A 

0.2 B 

0.6 A 

0.4 B 

0.2 A 

0.4 A 

0.2 A 

0.6 A 

0.2 A 

0.2 A 

0.2 A 

0.4 B 

0.3 A 

0.4 A 

0.2 A 

8.4 

7.2 

7.0 

5.6 

4. 1 

0.04 0.3 0.4 A 

0.01 0.1 0.1 A 

0.09 0.6 0.7 A 

0.25 11.2 10.0 D 

0.04 0.3 0.4 A 

13.9 

14.8 

14.2 

14.4 

6.7 

8.8 

3.0 

3.9 

4.4 

8.5 

0.08 

0.11 

0.05 

0.07 

0.06 

0.12 

0.02 

0.06 

0.06 

0.04 

6.1 0.05 

13.4 0.07 

4.5 0.06 

3.9 0.03 

4.6 0.04 

8.~ 0.01, 

9.1 0.14 

5.3 0.15 

7.5 0.04 

5.5 0.03 

0.8 

0.8 

0.3 

0.4 

0.2 

4.1 

0.3 

0.6 

0.4 

0.3 

0.3 

0.3 

0.4 

0.2 

0.2 

0.~ 

0.7 

6.4 

0.2 

0.5 

3.1 B 

1. 1 B 

0.4 B 

0.8 B 

0.0 c 

2.8 It 

0.3 B 

0.9 B 

0.3 A 

0.3 B 

0.6 A 

0.7 B 

0.3 A 

0.3 A 

0.2 A 

0.4 A 

1. 6 A 

5.7 It 

0.5 A 

0.8 B 

4.8 0.06 0.5 0.7 A 
Table 3.-Griteria for the four quality grades of Q 

[Q is based on both the nature of the station distribution with respect to the earthquake and the statistical 

measure of the solution. 'lhese two factors are eadl rated independently. Q is taken as the avercge of the 

ratings from the two scherres, for example, an A and a c yield a B, and two B t s yield a B. When t±e two ratings are only one level apart the lCMer one is used: for example, an A and a B yield a B] 

Solution quality Station distribution Statistical measures 

Q Epicenter Focal depth ID GAP IMIN RMS Em ERZ 

A Excellent--------Good---- > 5 90° ~ Depth or S km < 0.1S s < 1.0 km < 2.0 km 

B Good-------------Fair---- > 5 135° ~ 2 x depth or 10 km < 0.30 < 2.S < s.o 

c Fair-------------Poor---- > 5 180° ~SO km < o.so < s.o > s.o 

D Poor-------------Poor---- < 5 180° > SO km > o.so > 5.0 > s.o 

Santa BaJ::bara Musemn of Natural Histocy and 

operated by CIT) gives S-P ti.ne of 2.0 s fran 

its torsion and strong-notion instrurrents. If 

we include the SBC data and the above S-trigger 

tines as S-P intervals in our location of the 

IPain shock, the epicenter differs by about 1 km 

and the focal depth by about 2 km from our preferred location. 

FOCAL MECHANISM OF THE 

MAIN SHOCK 

119" 55' 119" 45' 

Fault-plane solutions of an eart'lquake can 

be detennined directly fran the first-notion 

pattern of P-waves provided that (1) the earthquake is well located, (2) the energe:"lt angles 

119" 35' 34'3o·r----------------------r----------------------r----------------------T--------------------~----------------------, 

EXPLANATION 

Magnitude 

o I.O~M<2.0 

0 2.0~ M< 3.0 

Q 3.0~M<4.0 

----?··Fault- Dashed where approximate; doled 

where concealed; queried where uncertain 

-----

-----.... 

0 

-- 0 8 

- -.... -- ··.;:, 

··· .. ~.f 

0 5 KILOMETERS 

A' 

-.. ·=-. ._!!R~~-~.: !_ARIDA FAUlT 

Santa Barbara •· • • ~ 

0 ~ 0 

~AIM SHOCK 

.............. RED MOUNTAIN ---------- ...._ 

......... 

0 ' ........... fAULT Y -- -- --!_I TAS_ !_OIIH FAULT 

-------+.-------- WELL #5 

.............. _o ..... ____ _ 

Figure 3.-EPicenters of Santa Baxbara earthquake and its major aftershocks. 

8 
of seismic waves to the stations are c:mput.ed 

cmrectl.y fran an adequate crustal IICdel, and 

(3) the true :polarity of the first P-notions is 

properly identified fran seisirograns. 'Ihe nodel 

we used to locate the eari:hJuakes approximates 

the travel tiires well, but it has too many 

arl>itrarily discrete layers. Consequently, it 

may give an erroneous first-notion pattern. 

'lherefore, we used a sinpler crustal mxlel (see 

fig. 2) for cntputing the first-notion pattern. 

Figure 4 sha-18 our fault-plane solution of the 

main shock. '!he two possible fault planes are 

(1) strike N. 66° w., dip 40° N., and (2) strike 

N. 22° w. , dip 60° s. The focal nechanism indicates reverse faulting with a minor strikeslip cxmponent. 'Ihe local geology and spatial 

distribution of the aftershocks d:>viously favor 

the N. 66 w. -40° N. fault plane, which has a 

minor left-lateral cxmponent. Our poor :Jmor,.rledge of the crustal structure precludes determination of the dip to better than ±10°. 'Ihe 

strike of the north-dipping fault plane is 

reasonably well constrained, but that of the 

south-dipping plane is poorly constrained. If, 

as in the present case, we intei:pret the crustal 

structure in tents of a sinple multilayer node!, 

then the dip of the fault plane is controlled by 

the first critical refraction angle of seismic 

rays to the intermadiate-distance stations. 

rnris in tum depends on the velocity contrast 

between the rocks in the focal area and those 

i.rmediately bela.r. 'Ihe fault dip (<I>) is determined approximately by: 

<1> = 90° - sin-1 (v1/v2 ) 

where v1 is the layer velocity containing the 

earthquake focus and v 2 is the velocity of the 

layer next bela.r. It is unlikely that the dip 

will be larger than 60° because that would require v2 to be nore than twice v1 , which is unlikely because v 2 cannot be greater than 8 km/s 

in the lCMer crust, and v1 is probably not less 

than 4 km/s at a depth of 12 km. 

CORRELATION 

In an atterpt to identify the fault or 

faults that generated the August 13, 1978 earthquake, we plotted a cross section of the earthquake hypocenters along line 'h-A' (fig. ~), 

which is perpendicular to the trend of the 

aftershock pattern. '!he result is shCMn in 

figure 5. 'Ihe present data are inadequate to 

m'liquely identify the generative fault. First, 

the fault may not be a uniformly dipping surface. 

Second, the hypocenters could be fitted to a 

surface dipping between 30° and 75° N. '1he 

fault-plane solution of the main shock suggests 

that faulting occurred on a plane dipping about 

40° N. but not greater than 60° N. ; if that 

plane is projected to the surface it can be 

correlated with fault X. However, geologic data 

in the eastern Santa Bai:bara Olannel indicate 

that sarre structural features south of well num9 

Figure 4.-Fault-plane solution of S~ta 

Ba.rl>ara earthquake. 

ber 5 (fig. 3) dip south. 'lbe Pitas Point fault 

dips steeply north near the surface and could be 

the generative fault if it dips nore gen+:ly at 

depth. 

CONCLUSIONS 

PreUmina.ry results on the Santa Barbara 

earthquake and its major aftershocks indicate 

that reverse faulting took place on a ncrthdipping fault at a depth of about 12 km and that 

the rupture propagated northwest torrlard Goleta. 

'!his is consistent with 0. 44g maximum ac~leration recorded by crM; in Goleta at North Hall, 

university of ca.lifon1ia at Santa Barbara; nost 

of the damage occurred in Goleta also. In addition, extension of the trend of the aftershock 

oottem westward intersects the shorelin~ at the 

nouth of Telecote Canyon; severe shaking there 

caused failure of a long segnent of 1:mSU'?lJ?Orted 

railroad fill and the resulting derail.:rre"'lt and 

wreck of a freight train about 7 minutes after 

the earthquake. 

The Santa Barbara earthquake was relatively 

small, and there was no onshore surface rupture .. 

The subsurface rupture progagated to the northwest. Had the earthquake been larger a"l.d rupture propagated to the southeast or a greater 

distance to the northwest, it could have posed 

a hazard to oilfield operations. It is interesting to note that the Jnne 30, 1941 Sa"l.ta 

Barbara earthquake was preceded by an eatthquake 

swann in Februai:'\.f of 1941. Similarly, t~ August 13, 1978 Santa Barbara earthquake w~ preceded by an earthquake swann located abo\lt 20 km 

taYard the southeast in March and April of 1978. 

Ten years before, the 1968 earthquake sw:n:m in 
1-

s ..... N :::> 1-~ ..... 

:::> ..... 

w ~ 

~ 1-

~ c( X ~ > • :r: -~ u 1- en 1- i ..... ..... 2 :::> ~ :::> 

.A ~ -< iL ~ A' ~ 

e 

IS' 34°20' 34°2fi' 

en 

"' w 

tw 

~ 5 

~ 

~ 8 

z 0 0 

' EXPLANATION :I: 0 1-

n.. 10 Magnitude w 

0 0 1.0 ~ M < 2.0 

0 2.0~ M < 3.0 

Q 3.0~M<4.0 

U " Main shock 

Figure 5 .. -cross section of area of figure 3, showing hypocenter distributions and faults. 

the Santa Barbara Chmnel was located in the 

sane general area as the March-April 1978 swann and included a magni tu:1e 5. 2 event (fig. ll 

(Sylvester and others, 1970}.. IJa.rever, this 

swarm was not follO!Ned by any larger earthquake. 

'lberefore, it is not clear that ea.rth}uake 

swanns are reliable precursors to larger earthquakes in the Santa Barbara Channel. 

REFERENCES CITED 

Allen, c. R., St. Amand, P., Richter, c. F., and 

Nor~t, J. M. , 1965, Relationship between 

seismicity and geologic structure in the 

southern california region: Seisnol. Soc. 

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

Eaton, J. P. , 1969 , Hypolayer-a carputer program for determining hypocenters of local 

earthquakes in an earth consisting of unifonn flat layers over a half-space: U.s. 

Geol. Survey q?en-file report, 155 p. 

Ellsworth, W. L., Cantbell, R. H., Hill, D. P., 

Page, R. A. , Alewine, R. w. , III, Hanks, 

T. C., Heaton, T. H., Hileman, J. A. , 

Kanartnri, H. , Minster, B. , and Whit.cx:nb, 

J. H. , 1973, Point Mugu, California, earthquake of 21 Februaey, 1973, and its aftershocks: Science, v. 182, p. 1127-1129. 

10 

Geiger, L. , 1912, PrOOabili ty nethod for the 

detel::mination of earthquake epi~.nters fran 

the arrival tine only (translate-1 fran 

Geiger•s 1910 Gernan article): Bull. St. 

IDuis Univ., v. 8, p. 56-71. 

Hamilton, R. M. , Yerkes, R. F., Browr , R. D., Jr., 

Burford, R. 0., and De Neyer, J. M., 1969, 

Seismicity and associated effects, Santa 

Bazbara region, pt. D of Geology, petroleum 

developnent, and seisnliCity of the Santa 

Ba.rl:>ara Olannel region, Califon1ia: u.s. 

Geol. Survey Prof. Paper 679, p. 47-68. 

Healy, J. H. , 1963, Crustal structure. along the 

ooast of california fran seisnrl..c refraction 

neasu:renents: J. Geophys. Res. , v. 68, p. 

5777-5787. 

Hileman, J. A., Allen, c. R., and Nordquist, J. 

M. , 1973, Seisnrl..city of the southem Califomia region: Contribution no. 2385, Div. 

of Geological and Planetary Sciences, California Institute of Technology. 

lee, W. H. K. , Bennett, R. E. , and .Me>"tgher, 

K. L., 1972, A nethod of estimating magnitude of local earthquakes frar signal 

duration: u.s. Geological S~r open-file 

report, 28 p. 

lee, W. H. K., Eaton, M. S., and BraJ:l'>, E. E., 

1971, '!he earthquake sequence ne::rr Danville, 
california, 1970: Seisnological Society of 

Anerica Bulletin, v. 61, p. 1771-1794. 

Lee, W. H. K., and Ellsworth, W. L., 1975, 

Earthquake activity in the Santa Bal:bara 

Olannel region, in Draft enviromrent ~ 

nent, Oil and gaS"developrent in the Santa 

Barbara Cll.armel outer oontinental shelf off 

california: U.s. Geological SUrvey, p. II80 - II-137. 

Lee, W. H. K., and Lahr, J. C., 1975, HYP071 

(Revised): A carputer program for determining hypocenter, magnitude, and first 

notion pattern of local earthquakes: U.S. 

Geological Survey Open-file Report 75-311, 

114 p. 

Lee, W. H. K., Yerkes, R. F., and Simirenko, M., 

(in press) , Recent eartb:Juake activity and 

focal nechaniSDB in the western Transverse 

Ranges, California: U.s. Geological Survey 

Circular 799A. 

Ridlter, C. F. , 19 58, Elenenta:cy seisnology: 

11 

San Francisco, W. H. Freedman and carpany, 

768 p. 

Stierman, D. J., and Ell.sworth, W. L., 1976, 

Aftershocks of the February 21, 1973 Point 

a:tgu, california earthquake: SeiSltl-:>logical 

Society of Anerica Bulletin, v. 66, no. 6, 

p. 1931-1952. 

Sylvester, A. G., Smith, s. W., and Sdlolz, c. H., 

1970, Farthquake swann in the Santa Barbara 

Cll.annel, california, 1968: Seisnological 

Society of Anerica Bulletin, v. 60, p. 1047-

1060. 

Yeats, R. S., Lee, W. H. K., and Yerkes, R. F., 

(in press) , Geology and seismicity of the 

eastern end of the Red lobuntain fault, 

Ventura Cotmty, california: u.s. G~logical Survey Professional Paper. 

Yerkes, R. F., and Lee, W. H. K., (in press), 

Late Quatema:ry defo:rnation in the western 

Transverse Ranges, california: U.s. Geological Survey Circular 799B. 

-k US GOVERNMENT PRINTING OFFICE 1978 689-035/48