CIRC 914 

STRONG-MOTION 

PROGRAM REPORT, 

JANUARY-DECEMBER 1981 

* WESTMORLAND, CALIFORNIA, 

EARTHQUAKE OF APRIL 26, 1981 

e ACCELEROGRAPH STATION 

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UNITE~~ !E.§_-----

------MEXICO 

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GEOLOGICAL SURVEY CIRCULAR 914 

Strong-Motion 

Program Report, 

January - December 1981 

GEOLOGICAL SURVEY CIRCULAR 914 

1983 
United States Department of the Interior 

JAMES G. WATT, Secretory 

Geological Survey 

Dallas L. Peck, Director 

Library of Congress catalog-card No. 83-600616 

Free on application to Branch of Distribution, U.S. Geological Survey 

604 South Pickett Street, Alexandria, VA 22304 
PREFACE 

This Strong-Motion Program report gives preliminary information on the 

nature and availability of strong-motion data recorded by the U.S. Geological 

Survey {USGS). The program is operated by the USGS in cooperation with 

numerous Federal, State, and local agencies and private organizations. Major 

objectives of the program are to record both strong ground motion and the 

response of various types of engineered structures during earthquakes and to 

disseminate this information and data to the international 

earthquake-engineering research and design community. 

This report contains a summary of the accelerograms recovered from the 

USGS National Strong-Motion Network during the year 1981. A brief summary of 

USGS strong-motion data recorded during the Westmorland, California, 

earthquake of April 26, 1981, and a revision of strong-motion data recorded 

during the Livermore, California, earthquakes of January 24 and 26, 1980, are 

included along with summaries of recent strong-motion reports, notes on the 

availability of digitized data, and additional general information related to 

the USGS and to other strong-motion programs. The data summary in table 1 

contains information on those accelerograms recovered {although not 

necessarily recorded} during 1981. 

iii 

Ronald L. Porcella, Editor 

U.S. Geological Survey, Mail Stop 77 

Menlo Park, California 94025 
Preface - - - - - - - - -

1981 strong-motion records -

CONTENTS 

Page 

- iii 

______ l 

The Westmorland, California, earthquake of April 26, 1981 - - - - -

Revised strong-motion data, part III - - - - - - - -

1 

4 

Summaries of recent strong-motion reports - - - - 7 

Availability of strong-motion information and data - - - - - - 8 

Data sources - - - - - - - - ~ - - - - - - - - - - - - - - - - - - - - - - 10 

ILLUSTRATIONS 

Figure - Location map, Westmorland earthquake - - - - 2 

2 - Accelerograms, Westmorland earthquake - 3 

TABLES 

Table 1 - Summary of 1981 accelerograms - - - - - - - - - - - - - - - - - 11 

2 - Livermore earthquake of January 24, revised accelerograph data - 5 

3- Livermore earthquake of January 26, revised accelerograph data- 6 
STRONG-MOTION PROGRAM 

REPORT, JANUARY-DECEMBER 

1981 

1981 STRONG-MOTION RECORDS 

By J. C. Switzer 

Duri~ 1981 there were 125 records recovered 

from the USGS National Strong-Motion Network, 

. compared with a yearly average of 227 records for the 

period 197 2 to 1980 inclusive. The most significant 

record set obtained in 1981 was recorded during the 

magnitude 5.6 earthquake on April 26 near Westmorland in the Imperial Valley, California. This 

earthquake triggered accelerographs at 24 USGS 

stations in the region and produced significant ground 

accelerations at the Brawley, Salton Sea, Parachute 

Test, and Superstition Mountain stations (see the 

following report). 

The USGS Hawaii strong-motion network 

produced 25 records during 1981; this brings the total 

number of accelerograph records to more than 100 

since the network was first established in February 

1973. Two strong-motion stations on Mauna Loa and 

Mauna Kea were triggered and produced the first 

records from those stations since their installations in 

1979 and 1980, respectively. The most significant 

acceleration was recorded at the Molokai Airport 

station during a magnitude 5.5 earthquake on March 5, 

1981; the maximum horizontal acceleration was 0.19 g 

with a strong duration (acceleration greater than 

0.10 g) of 0.3 second (see table 1, end of report). 

Many of the additional records recovered in 1981 

(table 1) are related to small-magnitude earthquakes 

near Bear Valley, in central California, and near 

Anchorage, in south-central Alaska. 

THE WESTMORlAND, CAliFORNIA, 

EARTHQUAKE OF APRil 26, 1981 

[The following report has been abstracted from Maley, 

R. P., and Etheredge, E. C., 1982, Strong-motion data 

from the Westmorland, California, earthquake of April 

26, 1981: U.S. Geological Survey Open-File Report 

81-114 9, 18 p.] 

A magnitude 5.6 earthquake occurred 8 km 

northwest of Westmorland, California, on April 26, 

1981, triggeri~ U.S. Geological Survey (USGS) 

strong-motion accelerographs at 24 of the 30 stations 

located in the Imperial Valley region. The earthquake 

triggered all instruments less than 2 8 km from the 

epicenter with the nearest record from Salton Sea, 9 

km north of the epicenter (fig. 1). In addition to the 

1 

network operated by the USGS, the State of California 

Division of Mines and Geology (CDMG) obtained 

records from stations located at West morland, Niland, 

and in El Centro adjacent to the former site of the 

Imperial County Services Building (McJunkin and 

Kaliakin, 1981). Data were recorded by both the USGS 

and CDMG networks from ground-level accelerographs 

(ground stations, not necessarily free-field stations) 

located in one-story buildings or in small fiberglass 

instrument shelters. Most recorders were equipped 

with WWVB radio receivers, but due to either poor 

signal or receiver-timer problems, real time was 

impressed on only half of the records • 

Table 1 provides a summary of the accelerograph 

data for the 24 USGS stations. Maximum 

accelerations exceeded 0.10 g at four stations (fig. 2); 

Salton Sea 0.22 g (9 km), Brawley 0.18 g (17 km), 

Parachute Test 0.23 g (20 km), and Superstition 

Mountain 0.11 g (24 km). The first three stations are 

located on alluvium while the Superstition Mountain 

station is on granite. Although maximum 

accelerations are essentially equivalent at Salton Sea, 

Brawley, and Parachute Test, the level of motion is 

significantly higher and the duration longer at Salton 

Sea, with pulses exceeding 0.10 g for more than 

6 seconds (fig. 2). The maximum accelerations in El 

Centro and along the El Centro array were generally 

0.02 to 0.06 g. This earthquake was the second time 

the entire El Centro array was triggered by a single 

event, the first being the October 15, 1979, Imperial 

Valley earthquake ( Porcella and Matthiesen, 1979). 

McJunkin and Kaliakin (1981) reported the 

following accelerations for the CDMG instrumentation 

located in Imperial Valley: Westmorland, 7 km, 0.49 g 

horizontal and 0.80 g (spike) vertical; Niland, 19 km, 

0.19 g horizontal and 0.13 g vertical; and El Centro, 35 

km, less than 0.05 g. All CDMG instruments are 

located on alluvium. 

S-wave minus trigger times (S-t), such as those 

shown in table 1, have been reported for numerous earthquakes over the past several years. The 

instruments are usually triggered during one of the 

first P-wave arrivals, but this is not always true, 

particularly when P-waves are small and lack a strong 

impulsive character. For example, during the 

Westmorland earthquake, El Centro 6 had an S-t 

interval of from 0.8 to 1.1 seconds larger (triggered 

earlier) than El Centro 1, 2, and 3 at nearly equivalent 

distances. In other instances, no S-t exists when 

instruments were triggered during later arrivals. For 

instance, trigger times obtained from the WWVB code 

at El Centro 7 and 8 are, respectively, 4 and 3 seconds 

later than station 6 although they are at essentially 

equal distances. The instrument at station 6 is housed 

in a small fiberglass shelter located 1.2 km east of the 

Imperial fault while station 7 is a large corrugated 
0 

Station 3 0 

25 

EXPLANATION 

ACCELEROGRAPH STATION 

• Triggered 

o Not Triggered 

• Inoperative * Epicenter 

50 KILOMETERS 

RIVERSIDE ----------------~MPERIAL---

I 

oi....J 0<: 

IJ.lolle3 ZQ.. 

<::E v:ll1 

Superstition 

Mountain 

• • El Centro Array 

Station 1 

Figure 1.- Strong-motion stations in the Imperial Valley 

region during the Westmorland earthquake of 

April 26, 1981. 

steel-frame building with concrete slab floor 0. 7 km 

west of the fault. The April 26 records from station 6 

show lower frequency (::: 8 Hz), higher amplitude 

vertical motion while station 7 has higher frequency 

( :::20 Hz), lower amplitude vertical motion. These 

same characteristics were noted on aftershock 

recordings of the October 15, 1979, earthquake. Late 

triggerings could be attributed to a number of 

variables: site re!!ponse and the effects of 

transmission path and source mechanism, structural 

modification of base shaking, and response 

characteristic of vertical starters, which have a peak 

sensitivity at 4 Hz falling off rapidly above 10 Hz. 

Thus, depending upon the frequency and the level of 

ground motion, at least for smaller events, 

strong-motion instruments may or may not trigger 

within a few tenths of a second of first P-wave 

arrivals. The relatively long triggering delays 

* Use of product names or trademarks is for 

descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey. 

2 

observed at stations 7 and 8 (3+ and 4+ seconds) would 

exceed the standard 2.5-second pre-event memory 

(PEM) used by the USGS in digital strong-motion 

systems. Similar delays were observed at station 9, 

where three accelerographs are installed: a 

Kinemetrics* SMA-1, a Kinemetrics* DSA-1 digital 

recorder with PEM, and a standard U.S. Coast and 

Geodetic Survey (C and GS) strong-motion 

accelerograph, each triggered independently by 

Kinemetrics* VS-1 vertical starters. An analog 

playback of the DSA-1 vertical component reveals 

there was ground motion occurring at the site at the 

beginning of the 2.5 seconds of recorded pre-event 

data. Acceleration levels were below the nominal 

0.01-g triggering level for the first 1.6 seconds while 

the following 0. 9 second shows acceleration pulses 

that reach and just slightly exceed 0.01 g. Two 

percent of g is not attained until 3.2 seconds into the 

recording. Although the instruments are not 

interconnected, relative triggering times can be 

determined by comparing the same phase arrivals on 

identical components. This comparison indicates the 

SMA-1 and the C and GS accelerograph triggered 
approximately 2.8 to 3.0 seconds after the PEM data 

was being recorded. The trigger delay after ground 

accelerations nominally reached 0.01 g was a little 

more than 1 second in each instance. If smaller 

earthquake recordings are of sufficient seismological 

and/or engineeri~ interest an additional 2.5-second 

PEM could be incorporated in the existing digital 

systems. 

SALTON SEA 

BRAWLEY 

S-wave (S) 0.18 g 

Numerous foreshocks and aftershocks of 

magnitude 3 to 4 events (Caltech Seismological 

Laboratory) were recorded at Salton Sea on April 26 

and 27 (also reported by McJunkin and Kaliakin 1981, 

for CDMG's Westmorland station). Maximum 

----~~vt~tJ~/'~t..r~N·~~NJit''',(V'I"'vo.,./{V',f"'<Mf'""""-~~"""'"""------------

::.~p;;;;;,f\.tf'v'""'·.JwJ'J'.v'v~~~,t"vv<fvV'v'o~._.....,~~~~.--r'._..~-~~~-­

trigger (t) 

PARACHUTE TEST 

0.23 g 

SUPERSTITION MTN 

-~~r[v..~-J·~~J"'-'-'""""'"""""""""'"""""-.IV"".,.._..._"""-_____ ~--~-------

o.11 9 ---------------------------

--~:;rt~~f"/V".'IJM;.~I.,J"'-,.f\l'w"".·.r..r/'-f'•-v--.,....___~,____~~-------------------

10 SEC 

-.~--_-_-_ -_ -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ -_-_-_ -_-_-_ -_-_-

Figure 2.- USGS accelerograms greater than 0.10 g from the Westmorland 

earthquake of April 26, 1981 (from Maley and Etheredge, 1981). 

3 
accelerations equalled or exceeded 0. 05 g during four 

of those earthquakes; the largest 0.11 g, was recorded 

5 1/2 hours after the main shock. Fourteen of the 

aftershocks and one foreshock occurred during the 

instruments normal run time thus allowing the 

determination of S-wave minus P-wave times (S-P) and 

comparison with S-t times. The foreshock S-P was 2.3 

seconds compared to S-t's of 1.9 to 2.2 seconds. The 

aftershock S-P's within the first 30 minutes of the 

main shock ranged from 2. 2 to 2. 8 seconds compared 

to S-t's of 2.3 to 2.5 seconds. This suggests the trigger 

delay was a few tenths of a second at Salton Sea, 

perhaps no larger than 0.4 second. Five hours after 

the main earthquake, S-P's suddenly decreased to 1.3 

to 1.5 seconds for all nine measurable shocks while 

S-t's ranged from 1.1 to 1.3 seconds, again indicating a 

few tenths of second trigger delay. The later 

aftershocks, at least those recorded by strong-motion 

instruments, had migrated nearer to the recording 

station compared to the main event and the closely 

following aftershocks. Relatively local seismicity has 

been observed during previous earthquake sequences. 

For instance, seven shocks recorded at Salton Sea 

within two weeks after the magnitude 6.4 October 15, 

1979, earthquake had small S-t times of 0.9 to 1.6 

seconds, and in one instance an S-P of 1.2 seconds, 

(Porcella and Matthiesen, 1980}, indicating a relatively 

near-source area. The epicenter of the 1979 

earthquake was 66 km from the Salton Sea station. 

References: 

McJunkin, R. D., and Kaliakin, N. A., 1981, Strongmotion records recovered from the Westmorland, 

California earthquake of 26 April 1981: 

California Division of Mines and Geology Report 

81-5.1, 11 p. 

Porcella, R. L., and Matthiesen, R. B., 1979, Preliminary summary of the U.S. Geological Survey 

strollt-motion records from the October 15, 1979 

Imperial Valley earthquake: U.S. Geological 

Survey Open File Report 79-1654, 41 p. 

Porcella, R. L., and Matthiesen, R. B., 1980, Strongmotion data summary, Imperial Valley earthquake 

of October 15, 1979 and aftershocks, in Seismic 

Engineering Program Report, September 

December 1979: U.S. Geological Survey Circular 

818-C, p. 3-60. 

REVISED STRONG-MOTION DATA, PART Ill 

By R. L. Porcella 

One of the primary objectives of the National 

Strong-Motion Network operated by the U.S. 

Geological Survey is to disseminate data from ground 

sites and structures that have been subjected to strong 

motion during earthquakes. These data are published 

initially as preliminary peak acceleration and strong 

duration values for each component on the recording 

(see Porcella and Matthiesen, 1979, for example) and 

later, after digitization and processillt, as uncorrected 

acceleration; corrected acceleration, velocity, and 

displacement; and response spectra (see Brady and 

others, 1980, for example). Although the 

peak-acceleration value is not directly related to 

4 

frequency content or duration of strong shaking, the 

value is readily obtained from an accelerogram and 

thus is widely used as a general indicator of the 

severity of strong shaking in studies of the attenuation 

characteristics of horizontal ground motion for 

varying earthquake magnitudes, source mechanisms, 

source-site distances, and recording-site conditions 

(Porcella, 1983). 

A recent increase in real time strong-motion data 

at both far- and near-source distances has resulted in 

numerous requests from the seismological community 

for more detailed lists of both the recorded 

peak-acceleration values and source-site distances in 

order to utilize better these data in studies of ground 

motion attenuation. Tables 2 and 3 are revised lists of 

both U.S. Geological Survey and California Division of 

Mines and Geology data from the Livermore, 

California, earthquakes of January 24 and 26, 1980; 

the peak-horizontal ground acceleration recorded at 

each site has been rescaled to 0.001 g and is listed 

together with the corresponding source-site distance. 

References: 

Brady, A. G., Perez, V., and Mork, P. N ., 1980, The 

Imperial Valley earthquake, digitization and 

processing of accelerograph records: U.S. 

Geological Survey Open-File Report 8Q-703, 309 p. 

Porcella, R. L., 1983, Revised strong-motion data, in 

Seismic Engineering Program Report, May-August 

1980: U.S. Geological Survey Circular 854-B, 

p. 4-8. 

Porcella, R. L., and Matthiesen, R. B., 1979, Preliminary summary of the U.S. Geological Survey 

strollt-motion records from the October 15, 1979 

Imperial Valley Earthquake: U.S. Geological 

Survey Open-File Report 79-1654, 41 p. 
Table 2.- Revised COMG and USGS ground-motion data from the 

Livermore earthquake of January 24, 1980 

Strong-motion Station Peak Horizontal 

Name, Owner, Coordinates D1stance Ground Acceleration 

and USGS Number (km) (g) 

Delta Pump Plant, 37.80 N 11.5 0.120 

COWR, 1030 121.62 w 

San Ramon, 37.729N 16.2 .154 

CDMG, 1418 121.928W 

San Ramon, 37.78 N 17.2 .052 

CDMG, 1383 121.98 w 

Livermore Hospital, 37 .625N 19.7 . 175 

VA, 1226 121.762W 

De 1 V a 11 e (toe ) , 37.617N 20.7 .261 

CDWR, 1265 121.746W 

Antioch School, 38.015N 21.2 .045 

CDMG, 1308 121.813W 

Walnut Creek, 37.906N 25.2 .032 

CDMG, 1530 l22.064W 

Pleasant Hi 11, 37.946N 26.9 .033 

CDMG, 1510 122.060W 

Tracy Water Plant, 37.77 N 28.8 .086 

CDMG, 1298 121.42 w 

Hayward, 37.655N 29.9 .048 

CDMG, 1524 l22.056W 

Oakland, 37.742N 32.6 .016 

CDMG, 1457 122.148W 

Fremont, 37. 530N 33.3 .056 

CDMG, 1299 121.919W 

Caldecott Tunnel, 37.857N 37.5 .020 

CDMG, 1525 122.214W 

Briones Dam Abut., 37.91 N 37.7 .016 

CDMG, 1416 122.21 w 

APEEL Array 3E, 37.66 N 40.5 .065 

CDMG, 1219 122.06 w 

El Cerrito, 37.897N 44.9 .005 

CDMG, 1419 122.298W 

Halls Valley, 37.338N 50.6 .093 

CDMG, 1422 121.744W 

San Jose, 37.338N 52.3 .023 

CDMG, 1507 121.888W 

San Jose, 37.338N 52.4 .011 

CDMG, 1506 121.893W 

Redwood City, 37.45 N 59.1 .011 

CDMG, 1468 122.27 w 

South San Francisco, 37 .660N 59.4 .017 

CDMG, 1466 l22.439W 

Saratoga, 37.27 N 62.8 .018 

CDMG, 1460 122.01 w 

Capitola, 36.974N 93.3 .023 

CDMG, 1376 l21.952W 

5 
Table 3.- Revised CDMG and USGS ground-motion data from the 

Livermore aftershock of January 26, 1980 

Stron9-motion Station Peak Horizontal 

Name, Owner, Coordinates Distance Ground Acceleration 

and USGS Number (km} {g) 

Fagundes Ranch, 37.753N 9.9 0.259 

CDMG, (Temp.) l21.772W 

Morgan Park, 37.819N 13.5 .267 

CDMG, (Temp.) l21.795W 

Delta Pump Plant, 37.80 N 14.3 .071 

CDWR, 1030 121.62 w 

Livermore Hospital, 37.625N 16.2 .059 

VA, 1226 l21.762W 

De 1 V a 11 e ( toe ) , 37.617N 16.8 .047 

CDWR, 1265 l21.746W 

San Ramon, 37.729N 19.9 .275 

CDMG, 1418 l21.928W 

San Ramon, 37.78 N 24.2 .058 

CDMG, 1383 121.98 w 

Antioch, 37.970N 28.0 .026 

CDMG, (Temp.) l21.829W 

Fremont, 37. 530N 30.4 .039 

CDMG, 1299 121.919W 

Hayward, 37.655N 31.9 .059 

CDMG, 1524 122.056W 

Antioch School, 38.015N 32.2 .112 

CDMG, 1308 l21.813W 

Walnut Creek, 37.906N 35.9 .057 

CDMG, 1530 122.064W 

Pleasant Hill, 37.946N 38.1 .035 

CDMG, 1510 122.060W 

Oakland, 37.742N 38.3 .026 

CDMG, 1457 l22.148W 

APEEL Array 3E, 37.66 N 38.9 .065 

CDMG, 1219 122.06 w 

Briones Dam Abut., 37.91 N 47.6 .044 

CDMG, 1416 122.21 w 

San Jose, 37.338N 47.7 .006 

CDMG, 1507 121.888W 

San Jose, 37.338N 47.8 .005 

CDMG, 1506 l21.893W 

Oakland, 37.81 N 49.1 .026 

CDMG, 1456 122.27 w 

El Cerrito, 37.897N 54.0 .010 

CDMG, 1419 l22.298W 

Saratoga, 37.27 N 58.6 .012 

CDMG, 1460 122.01 w 

Redwood City, 37.45 N 58.7 .003 

CDMG, 1468 122.27 w 

South San Francisco, 37.660N 64.0 .012 

CDMG, 1466 l22.439W 

6 
SUMMARIES OF RECENT 

STRONG-MOTION REPORTS * 

SOIL-FOUNDATION INTERACTION 

AND DIFFERENTIAL GROUND MOTIONS 

By G. N. Bycroft 

Differential ground motions due to horizontally 

propagating surface waves are of importance in 

determining the stresses and displacements developed 

in extended structures such as large mat foundations 

for nuclear power stations, dams, bridges and 

pipelines. A general method is developed for 

determining the motion of a large rigid mat foundation 

subjected to travelling surface waves and observations 

made on the relative displacements of individual 

foundations and their importance in bridge failure. 

Reference: Journal of Earthquake Engineering and 

Structural Dynamics, v. 8 p. 397-404. 

IN-SITU MEASUREMENTS OF SEISMIC 

VELOCITIES AT 19 LOCATIONS IN THE 

LOS ANGELES, CALIFORNIA, REGION 

By T. E. Fumal, J. F. Gibbs, 

and E. F. Roth 

Studies conducted in the San Francisco Bay region 

have shown that average shear-wave velocity can be 

related to quantitative estimates of ground motion 

such as amplification from nuclear explosions and 

earthquake intensity. Furthermore, when certain 

physical properties of the geologic materials such as 

texture, hardness, and fracture spacing are described 

during geologic mapping, a method can be used to 

predict shear-wave velocity from descriptions of 

geologic units. By measuring shear-wave velocities in 

representative geologic units, regional maps depicting 

the earthquake hazard can be compiled. 

These studies are presently being extended to the 

Los Angeles Basin and the Oxnard-Ventura areas. To 

date, shear and compressional waves have been 

measured in boreholes at 46 locations. A previous 

report summarized seismic and geologic data at sites 

1-27. This report presents the data for sites 28-46. 

At each location seismic travel times are measured in 

drill holes, normally at 2.5 m intervals to a depth of 30 

m. Geologic logs are compiled from drill cuttings, 

undisturbed samples, and penetrometer samples. The 

data provide a detailed comparison of geologic and 

seismic characteristics and parameters for estimating 

strong earthquake ground motions quantitatively at 

each of the sites. 

Reference: U.S. Geological Survey Open-File Report, 

81-399, 121 p. (see section "Data Sources"). 

* Inclusion of strong-motion information sources is 

intended as a service to our readers and does not 

imply endorsement of these reports by the U.S. 

Geological Survey. 

7 

U.S. STRONG-MOTION 

EARTHQUAKE INSTRUMENTATION 

Edited by W. D. I wan 

The U.S. National Workshop on Strong-Motion 

Earthquake Instrumentation was held April 12-14, 

1981, on the campus of Westmont College in Santa 

Barbara, California. The workshop was organized by a 

steering committee appointed by the Earthquake 

Engineering Research Institute and the Universities 

Council for Earthquake Engineering Research. 

The objectives of the workshop were to ( 1) review 

existing strong-motion instrumentation programs in 

the U.S., (2) develop a unified strategy for the 

deployment of strong-motion instruments both in the 

free-field and in buildings, and (3) formulate a plan for 

the coordination of existing strong-motion programs, 

the on-going installation and operation of instruments, 

and the management of strong-motion data. To 

achieve these objectives, the workshop was organized 

into a number of working committees covering the 

major areas to be addressed. This volume is the 

product of the combined efforts of those in attendance. 

Reference: Earthquake Engineering Research Institute 

(see section "Data Sources") and Universities 

Council for Earthquake Engineering Research, 

55 p. and append. 

STRONG-MOTION DATA 

FROM THE WESTMORLAND, CALIFORNIA, 

EARTHQUAKE OF APRIL 26,1981 

By R. P. Maley and E. C. Etheredge 

A moderate earthquake occurred 8 km northwest 

of Westmorland, California, at 1209 (UTC) on April 26, 

1981, triggering U.S. Geological Survey (USGS) 

strong-motion accelerographs at 24 of 30 stations 

located in the Imperial Valley region. The earthquake 

triggered all instruments less than 28 km from the 

epicenter with the nearest record from Salton Sea, 9 

km north of the epicenter. In addition to the network 

operated by the Survey, the State of California 

Division of Mines and Geology (CDMG) obtained 

records from stations located at Westmorland, Niland, 

and in El Centro adjacent to the former site of the 

Imperial County Services Building. Data were 

recorded by both the USGS and CDMG networks from 

ground-level accelerographs (ground stations, not 

necessarily free-field stations) located in one-story 

buildings or in small fiberglass instrument shelters. 

Most recorders were equipped with WWVB radio 

receivers, but due to either poor signal or 

receiver-timer problems, real time was impressed on 

only half of the records. 

Reference: U.S. Geological Survey Open-File Report 

81-1149, 18 p. (see section "Data Sources"). 
AVAILABILITY OF STRONG-MOTION 

INFORMATION AND DATA 

U.S. GEOLOGICAL SURVEY 

STRONG-MOTION NETWORK DATA 

By April Converse 

De~riptions of strong-motion accelerograph 

records and the circumstances in which they were recorded are available to ·anyone involved in 

earthquake engineering through the computer-based 

Strong-Motion Information Retrieval System (SMIRS). 

SMIRS provides ready access to information about 

strong-motion records and the level of processing and 

analysis that has been performed on them. 

Information about earthquakes that generated 

recorded motion and about the sites at which the 

motion was recorded is also provided. 

With an ordinary phone line and a keyboard 

terminal, a SMIRS user may review the information 

free of charge. Once accessed, SMIRS will offer a 

general introduction and will tell the user how to 

request more detailed instructions. The user also will 

be given an opportunity to request a copy of the 

printed user's manual. 

SMIRS resides in one of the U.S. Geological 

Survey computers in Denver, Colorado. It can be 

accessed by telephoning the computer center directly 

or by telephoning a local node in the TYMNET 

telecommunications network. The direct-dial 

telephone numbers for the Denver computer center 

are: 

(303) 232-0058 for 300 baud modems such 

as those included in the TI 

Silent 700 terminals, 

(303) 232-5309 for 1200 baud modems such 

as the VADIC modems, 

(303) 232-2248 for 1200 baud BELL 212a 

modems. 

The TYMNET telecommunications network can be 

used to access SMIRS without incurring a 

long-distance telephone charge to Denver. TYMNET 

Corporation maintains local telephone numbers in 

many cities in the United States and in several foreign 

countries. TYMNET phone numbers can be obtained 

from TYMNET Corporation's Western Customer 

Service at (800) 323-7389 or TYMNET Customer 

Support Group at (800) 366-0149. 

Take the following steps to connect your terminal 

to SMIRS. 

1) Set the switches, keys, or buttons on the terminal 

that allow a choice of operating modes: 

transmission speed= 300 baud (30 characters 

per second) or 1200 baud; 

on line; 

lower case ASCII characters; and 

full duplex (if you are going to dial a 

TYMNET number) or 

half duplex (if you are going to dial 

Denver directly). 

2) Plug in and turn on the terminal; turn on the 

8 

3) 

4) 

5) 

6) 

7) 

Sa) 

modem too if it is a separate device. Notice 

whether the modem uses an acoustic coupler or whether the modem is directly connected to a telephone. An acoustic coupler will have a cradle 

into which a telephone handset can be inserted. 

Look for a label or diagram on an acoustic coupler 

that will show you in which direction the 

telephone cord should go. A direct-connect 

modem will have a switch that can be set for 

voice or data transmission. 

Telephone the USGS computer center in Denver 

or telephone the TYMNET number nearest you; 

wait for a high-pitched tone. 

Place the telephone handset in the cradle on the 

acoustic coupler or set the direct-connect switch 

to "data." Wait for the "carrier detect" light to 

turn on; this indicates that the terminal is 

receiving a signal from the computer or from the 

TYMNET equipment. 

If you telephoned the Denver computer center 

directly, skip this section, but if you telephoned a 

TYMNET number, the TYMNET prompts (shown 

underlined here) and your responses (shown in 

italics here) should proceed as follows: 

please type your terminal identifier e 

please log in: gsbc1234: 2361 :sandstone <CR> 

The <CR> symbol represents the carriage-return 

key. 

The "gsbcl234" is what TYMNET refers to as a 

user name, the "2361" is a location identifier for 

the USGS computer center, and the "sandstone" is 

a password. Note that the "sandstone" will not be 

printed at your terminal while you type. 

Do not be alarmed if the first prompt comes at an 

odd speed. 

TYMNET will now connect your terminal to a 

computer selecting device in Denver. If the 

computer selector is operating, "GSD N is online" 

will be printed at your terminal. 

Type the carriage return key. The computer 

selecting device will ask you to "enter class", to 

which you should answer "mult": 

enter class rrrult <CR> 

The selecting device will answer with several 

lines, something like "CONNECTING TO 

DENVER MULTICS" and "class mult start". 

Type the line-feed key. The MULTICS computer 

will respond with several lines that will tell you 

which computer you have accessed, how many 

other users are connected, and so forth. 

If your terminal will transmit both upper and 

lowercase characters, type: 

enter <your _name> SMIRS <CR> 

The <CR> represents the carriage-return key and 

<your name> is your own name typed without any 

embedded blanks. It is good practice for you to 
choose a version of your name that will probably 

be unique, and to use that version of your name 

every time you log onto SMIRS. That way, any 

messages sent to you through SMIRS will not be 

received by the wrong user. 

Note that the word "enter" is in lower case and 

"SMIRS" is in upper case. 

8b) If your terminal has only uppercase characters, 

type: 

MAP <CR> 

ENTER <YOUR NAME> \S\M\I\R \S <CR> 

The "MAP" statement instructs the computer to 

interpret all the alphabetic characters you will 

subsequently type as though they were in 

lowercase, except those characters that follow a left slant ( \). 

9) From now on, SMIRS will prompt you whenever it 

expects you to type something. All the prompt 

lines begin and end with two dashes; answer by 

typing a question mark if you do not know what is 

expected of you. 

Do not be concerned if the computer does not 

respond immediately after you enter SMIRS. The 

response time may improve in the future, but it will 

always be fastest during nonworking hours (Denver 

time). 

CALIFORNIA DIVISION OF MINES 

AND GEOLOGY STRONG-MOTION DATA 

Processed strong-motion data from selected 

earthquakes are available from the California Division 

of Mines and Geology (CDMG). The data have been 

prepared by the interim CDMG strong-motion data 

processing system. This system is composed of a 

series of programs that have been developed by the 

California Institute of Technology, the USGS, and the 

CDMG, with special emphasis on the handling of 

long-duration film records from multiple-channel 

central recording instruments. 

The data are grouped by phase: 

Phase I Uncorrected accelerations, 

Phase II Corrected accelerations, velocities, 

and displacements, 

Phase III Response spectra. 

Each phase contains three-channel subgroups 

arranged by station. At the present time, data from 

the following earthquakes have been processed: 

Santa Barbara earthquake of August 13, 1978 

Station 

UCSB Goleta 

U CSB North Hall 

Freitas Building 

Channels 

3 

9 

9 

Imperial Valley earthquake of October 15, 1979 

El Centro free-field 3 

9 

Imperial County Services Bldg. 13 

The data are available on standard nine-track 

tapes, along with a microfiche copy of the tape 

contents. Interested parties should contact the CDMG 

Office of Strong-Motion Studies (see section "Data 

Sources"). 

It is the policy of the CDMG to make all 

strong-motion record data promptly available to the 

public in a manner consistent with good data 

management. Requests for copies of records, personal 

access to record or data files, and copies of data files 

should be made to the Chief, Office of Strong-Motion 

Studies (OSMS), and should specify identity and 

medium of materials to be provided or reviewed. 

Desired access or delivery dates should be specific. 

When a request for copies of materials or personal 

access to files is received, OSMS staff will provide the 

requested material or will set an appointment time for 

personal review of files; the requestor will be notified 

immediately of any significant delay or other problems 

that prevent meeting the request. Charges for 

copying or other processing of materials will be based 

on the actual cost of producing and delivering the 

items, and OSMS will retain control of originals and 

master copies of all items. 

FOREIGN STRONG-MOTION DATA 

Because of the long history of close cooperation 

between the United States and the Central and South 

American strong-motion programs, much of the data 

from those programs are available from the same 

sources as the United States data (see below). 

Information about strong-motion data from the 

Western Hemisphere will be included in the 

Strong-Motion Information Retrieval System operated 

by the USGS. 

The USGS does not attempt to obtain first-class 

copies of records from those foreign organizations 

that prepare data reports comparable to those 

prepared by the USGS. Abstracts of the data reports 

from such organizations are presented in this Seismic 

Engineering Program Report series, and through 

informal arrangements, copies of the data and records 

are made available. 

NOAA WORLDWIDE STRONG-MOTION DATA 

A worldwide collection of strong-motion 

seismograms for dissemination to the scientific and 

engineering community is available from World Data 

Center A for Solid Earth Geophysics, National 

Geophysical Data Center (N GDC). Countries 

contributing to the strong-motion data base include 

Australia, Italy, Japan, New Zealand, Rumania, 

U.S.S.R., and Yugoslavia. The USGS has furnished 

records from its network of cooperative strong-motion 

stations, including those in Central and South America. 

Copies of strong-motion records are available on 35-mm film, on 70-mm film chips, as paper copies, and 

as digitized data on punched cards or magnetic tape. 

A list of most records can be obtained from the World 

Data Center A publication "Catalog of Seismograms 

and Strong-motion Records," Report SE-6. This 

catalog can be ordered from NGDC (NOAA) for $3.00 
(see section "Data Sources"). 

The most significant strong-motion records 

recorded in the United States and Latin America 

between 1931 and 1971 have been copied on seven 

reels of 35-mm film (xl2 reduction) and 70-mm film 

chips (approximately x8 reduction). The film chips are 

available for $1.50 per chip; longer records are 

continued on additional chips. The 35-mm film copies 

can be purchased for $30 per reel, the complete set of 

reels for $180. There is a minimum charge of $10 per 

order. Check with the National Geophysical Data 

Center for current prices before placing an order. 

Japan and Australia have supplied magnetic tapes 

of digitized data from stations located in the western 

Pacific Ocean (the Japanese Islands, New Guinea, and 

New Britain). A series of 400 United States 

strong-motion records (1933-71) were digitized by the 

California Institute of Technology and are now 

available on six magnetic tapes. The USGS is 

digitizing post-1971 records from its network; they 

have generated 15 tapes of strong-motion records 

recorded from 1967 to 1981 in the United States, 

Chile, Nicaragua, San Salvador, and Mexico. 

Other digitized data include punched cards 

containing strong-motion records from the March 4, 

1977, earthquake in Rumania (recorded in Bucharest); 

the Gazli earthquake of May 17, 1976, in Uzbek, 

U.S.S.R.; and three earthquakes in the New Madrid 

seismic zone (located in midcontinental United States) 

in 1975 and 1976. 

Recent acquisitions include a magnetic tape of 

strong-motion records triggered by a swarm of 

earthquakes that occurred in northern Italy near the 

town of Friuli in 1976; these were compiled by the 

National Commission for Nuclear Energy and have 

been given to the center for distribution. Other data 

include records obtained from California earthquakes 

near Santa Barbara in August 1978, Gilroy in August 

1979, El Centro in October 1979, and Livermore in 

January 1980. 

A table listing all digitized strong-motion records 

available on magnetic tape may be obtained free of 

charge from NOAA. Digitized strong-motion records 

may be purchased either in punched card format 

(including all three instrument components) or in tape 

format. 

Checks or money orders should be made payable 

to "Commerce/NOAA/NGDC"; inquiries should be 

addressed to NOAA (see section "Data Sources"). 

OAT A SOURCES 

For reports or information regarding 

strong-motion records and data, address inquiries to 

the appropriate agency listed below: 

1. Branch of Distribution 

U.S. Geological Survey 

604 s. Pickett Street 

Alexandria, VA 2 2304 

2. Earthquake Engineering 

Research Institute 

2620 Telegraph A venue 

Berkeley, CA 94704 

(804) 756-6141 

(FTS) 756-6141 

(415) 848-0972 

3. 

4. 

5. 

6. 

7. 

8. 

10 

National Geq:>hysical (303) 497-6764 

Data Center (FTS) 320-6764 

NOAA, Code E/GC11 

32 5 Broadway Street 

Boulder, CO 80303 

National Technical (703) 487-4650 

Information Service (FTS) 737-4650 

5285 Port Royal Road 

U.S. Dept. of Commerce 

Springfield, VA 2 2161 

NISEE/Computer Applications (415) 642-5113 

519 Davis Hall, UC Berkeley 

Berkeley, CA 94720. 

Office of Strong-Motion (916) 322-3105 

Studies (FTS) 552-3105 

California Division of 

Mines and Geology 

2811 "0" Street 

Sacramento, CA 95816 

Open-File Services Section (303) 234-5888 

Branch of Distribution (FTS) 234-5888 

U.S. Geological Survey 

Box 25425, Federal Center 

Denver, CO 80225 

National Strong-Motion 

Program (415) 323-8111 

U.S. Geological Survey ext 2881 

345 Middlefield Road, MS 77 (FTS) 467-2881 

Menlo Park, CA 94025. 
Table 1 • - Summary of U.S. acceZerograph records recovered during 1981 

Event 

14 February 1981 

0609 UTC 

Washington 

46.35N, l22.24W 

Magnitude 5.5 

28 September 1980-

5 March 1981 

Hawaii 

Epicenters and 

magnitudes unknown 

5 March 1981 

1409 UTC 

Hawaii 

2l.02N, 156.99W 

Magnitude 5.5 

10 March 1981 

2356 UTC 

Cent. California 

36.86N, l21.67W 

Magnitude 3.4 

Station name 

(owner)1 

Station 

coord. 

S-t2 OirectionJ Max accl4 Ouration5 

(s) (i) (s) 

Mud Mountain Dam 

Crest 

(ACOE) 

Honokaa, Hawaii 

Fire Station 

(USGS) 

47.14° N * 

121.93° w 

20.080° N * 

155.465° w 

Note: Four additional records** recovered. 

Hawaii Nat•l Park, HI 19.329° N * 

Wahaula Util. Center 155.031° W 

(USGS) 

Note: Two additional records** recovered. 

Mauna Loa, Hawaii 

NOAA Observatory 

(USGS) 

19.539° N 4.7 

155.580° w 

Note: Two additional records** recovered. 

Pahala, Hawaii 

Kau Hospital 

(USGS) 

Note: One additional 

Waiohinu, Hawaii 

Kau Baseyard 

(USGS) 

Molokai Airport 

Fire Station 

(USGS) 

Watsonville Array #1 

Anzar Road 

(USGS) 

19.20° N * 

155.47° w 

record** recovered. 

19.070° N * 

155.615° w 

21.158° N 2.9 

157.096° w 

36.885° N * 

121.589° w 

150° 

Up 

060° 

** 

** 

** 

0.06 

.05 

.09 

.03 

.04 

.07 

** 

.19 0.3 

.07 

• 13 2-peaks 

** 

See footnotes at end of table. 

11 
Table 1 • - Summary of U.S. accelerograph records recovered during 1981 - continued 

Event Station name Station S-t2 Direction3 Max accl 4 Duration5 

(owner )1 coord. (s) (g) (s) 

2 April 1981 Denver Regency Inn 37.771° N 2.1 ** 

1610 UTC Basement 104.992° w 

Colorado {USGS) 

39.91N, 104.96W 

Magnitude 3.8 

26 April 1981 El Centro Station 32.960° N 2.0 230° 0.05 

1209 UTC Borchard Ranch 115.319° w Up .02 

So. California (USGS) 140° .06 

33.13N, ll5.65W 

Magnitude 5.6 El Centro Station 2 32.916° N 2.4 ** 

Keystone Road 115.366° w 

(USGS)t 

El Centro Station 3 32.894° N 2.5 ** 

Pine Union School 115.380° w 

(USGS)t 

El Centro Station 4 32.864° N * ** 

Anderson Road 115.432° w 

(USGS)t 

El Centro Station 5 32.855° N 0.3 230° .05 

James Road 115.466° w Up .02 

(USGS) 140 .05 

El Centro Station 6 32.839° N 3.2 230° .05 

Huston Road 115.487° w Up .03 

(USGS) 140° .05 

El Centro Station 7 32.829° N * 230° .04 

Imperial Valley Coll. 115.504 ° w Up .02 

(USGS) 140° .04 

El Centro Station 8 32.811° N 1.3 230° .05 

Cruickshank Road 115.532° w Up .06 

(USGS)t 140° .06 

El Centro Station 9 32.794° N 2.8 ** 

Commercial Avenue 115.549° w 

(USGS)t (film record) 

El Centro Station 9 32.794 N * ** 

Commercial Avenue 115.549 w 

(USGS)t (paper record) 

See footnotes at end of table. 

12 
Table 1 • - Summary of U.S. acceZerograph records recovered during 1981 - continued 

Event Station name Station S-t2 Direction.? Max accl4 DurationS 

(owner)l coord. (s) (g) (s) 

26 Apri 1 1981 El Centro Station 10 32.780° N 2.4 ** 

1209 UTC Community Hospital 115.567° w 

-continued- (USGS)t 

El Centro Station 11 32.752° N 1.8 ** 

McCabe School 115.594° w 

(USGS)t 

E1 Centro Station 12 32.718° N 4.2 ** 

Brockman Road 115.637° w 

(USGS)t 

El Centro Station 13 32.709° N 2.9 ** 

Strobel Residence 115.683° w 

(USGS) 

El Centro Diff. Array 32.796° N 1.5 360° 0.06 

Dogwood Road 115.535° w Up .02 

(USGS) (film record) 270° .08 

Calexico Fire Station 32.669° N 5.5 ** 

Fifth Street 115.492° w 

(USGS) 

Holtville 32.812° N 3.1 ** 

Post Office 115.377° w 

(USGS) 

Plaster City 32.79° N * ** 

Storehouse 115.86° w 

(USGS)t 

Salton Sea 33.18° N 2.3 315° .19 5.5 

Wildlife Refuge 115.62° w Up .22 4.5 

(USGS) 225° .20 6.2 

Note: Five pre-event** and five post-event records** recovered 

at Salton Sea Wildlife Refuge. 

Brawley 32.988° N 3.0 315° • 17 0.6 

Municipal Airport 115.509° w Up • 10 1-peak 

(USGS) 225° • 16 2.8 

Superstition Mtn. 32.955° N 2.1 135° .11 2-peaks 

USN Camera Site 115.823° w Up .05 

(USGS) 045° .08 

See footnotes at end of table. 

13 
Table 1 . - Summary of U.S. accelerograph records recovered during 1981 - continued 

Event Station name Station S-t2 Direction3 Max accl4 Duration5 

(owner)l coord. (s) (gJ ( s) 

26 Apri 1 1981 Parachute Test Site 32.93° N 3.1 315° 0.16 1.6 

1209 UTC Imler Road 115.70° w Up .13 3.9 

-continued- (USGS) 225° .23 2.4 

Co ache 11 a Can a 1 33.64° N 7.5 ** 

Station 1 116.08° w 

(USGS) 

Oc ot i 11 o We 11 s 33.14 ° N * ** 

Burro Bend Cafe 116.13° w 

(USGS) 

Borrego Air Ranch 33.19° N * ** 

Borrego Springs 116.28° w 

(USGS) 

5 May 1981 Anchorage 61.220° N * ** 

2128 UTC Westward Hotel 149.892° w 

Southern A 1 ask a (USGS) 61.66N, 149.66W 

Magnitude 4.4 

8 June 1981 Bear Valley Sta. 5 37.673° N * ** 

0309 UTC Callens Ranch 121.195° w 

Central California (USGS) 

36.75N, 121.36W 

Magnitude 4.2 Bear Valley Sta. 12 36.658° N 3.5 ** 

Williams Ranch 121.249° w 

(USGS) 

Hall i ster 36.85° N 2.9 ** 

City Hall Annex 121.40° w 

(USGS) 

28 January 1980- Hayward City Hall 37.68° N * 

25 June 1981 (CHY) 122.08° w 

Central California 

Epicenter and Sixth floor ** 

magnitude unknown 

Eleventh floor ** 

14 October 1980- Bear Valley Sta. 10 36.532° N 1.6 ** 

25 June 1981 Webb Residence 121.143° w 

Central California (USGS) 

Epicenters and 

magnitudes unknown Note: Five additional records** recovered. 

See footnotes at end of table. 

14 
Table 1 • - Summary of U.S. accelerograph records recovered during 1981 - continued 

Event 

26 June 1981 

0143 UTC 

Central California 

36.56N, 121.24W 

Magnitude 3.0 

2 July 1981 

0923 UTC 

Central California 

Epicenter and 

magnitude unknown 

25 July 1981 

2148 UTC 

Central California 

36.55°N, 121.07°W 

Magnitude 3.0 

11 February 1981-

28 July 1981 

So. California 

Epicenters and 

magnitude unknown 

14 August 1981 

1249 UTC 

Central California 

36.77N, 121.29W 

Magnitude 4.2 

2 February 1981-

1 September 1981 

No. California 

Epicenters and 

magnitudes unknown 

Station name Station S-t2 Direction3 Max accl4 

(owner)1 coord. (s) (g) 

Bear Valley Sta. 10 36.532° N 1.6 310° 0.07 

Webb Residence 121.143° w Up .03 

(USGS) 220° .05 

Bear Valley Sta. 10 36.532° N 1.4 ** 

Webb Residence 121.143° w 

(USGS) 

Bear Valley Sta. 14 36.569° N * ** 

Upper Butts Ranch 121.043° w 

(USGS) 

Bear V a 11 ey S t a. 11 36.608° N * ** 

Wilkinson Ranch 121 .109° w 

(USGS) 

Diemer Filter Plant 33.91° N 0.3 

(MWD) 117.82° w 

Basement ** 

Reservoir roof ** 

Note: Two additional records** recovered at reservoir roof. 

Bear Valley Sta. 12 36.658° N 3.7 

Williams Ranch 121.249° W 

(USGS) 

Palo Alto VA Hospital 37.40° N 

Building 1 122.14° W 

(VA) 

Basement 

** 

** 

Roof ** 

Duration5 

(s) 

Note: Two each additional records** recovered at basement and roof. 

See footnotes at end of table. 

15 
Table 1 • - Summary of U.S. acceZerograph records recovered during 1981 - continued 

Event 

25 March 1981-

9 September 1981 

Central California 

Epicenter and 

magnitude unknown 

11 September 1981 

0502 UTC 

SE Alaska 

60.07N, 139.57W 

Magnitude 4.1 

14 September 1981 

0819 UTC 

Central California 

36.66N, 121.33W 

Magnitude 3.1 

6 October 1980-

16 September 1981 

Southern Hawaii 

Epicenters and 

magnitudes unknown 

3 March 1981-

17 September 1981 

Southern Hawaii 

Epicenters and 

magnitudes unknown 

Station name 

(owner)l 

Station S-t2 Direction3 Max acc14 Duration5 

SAGO Central 

Harris Ranch 

(USGS) 

Bane as Point 

(USGS) 

Bear Valley Sta. 12 

Williams Ranch 

(USGS) 

coord. ( s) 

36.76° N * 

121.45° w 

59.953° N * 

139.635° w 

36.658° N 1.9 

121.249° w 

Mauna Kea, Hawaii 19.752° N * 

State Park Center 155.530° W 

(USGS) 

Note: Three additional records** recovered. 

Hawaii Nat'l Park, HI 19.423° N * 

Volcano Observatory 155.291° W 

{USGS) 

Note: Two additonal records** recovered. 

Hawaii Nat'l Park, HI 19.329° N 1.2 

Wahaula Uti1. Center 155.031° W 

(USGS) 

Note: One additional record** recovered. 

Mauna Loa, Hawaii 

NOAA Observatory 

(USGS) 

19.539° N 2.1 

155.580° w 

(g) (s) 

** 

0.06 

.02 

.05 

** 

** 

** 

** 

** 

See footnotes at end of table. 

16 
Table 1 • - Summary of U.S.acceZerograph records recovered during 1981 - continued 

Event 

17 September 1981 

0018 UTC 

SE Alaska 

60.03N, l39.39W 

Magnitude 4.3 

21 May 1981-

19 September 1981 

Centra 1 A 1 ask a 

Epicenters and 

magnitudes unknown 

Station name 

(owner)1 

Bancas Point 

(USGS) 

Anchorage 

New Federal Bldg. 

(USGS) 

Basement 

Anchorage 

A 1 ask a Hospita 1 

(USGS) 

Ground floor 

Fourth floor 

Seventh floor 

Anchorage 

Westward Hote 1 

(USGS) 

Basement 

Roof 

Station 

coord. 

S-t2 Oirection3 Max accl4 

(s) (B) 

59.953° N * 

139.635° w 

61.216° N 9.5 

149.883° w 

61.21° N * 

149.82° w 

61.220° N 9.4 

149.892° w 

0.05 

.01 

.05 

** 

** 

** 

** 

** 

** 

Ouration5 

(s) 

Note: Two each additional records** recovered at basement and roof. 

15 September 1981-

27 September 1981 

Central California 

Epicenter and 

magnitude unknown 

Tal-keetna 

FAA-VOR Bldg. 

(USGS) 

Bear Valley Sta. 12 

Williams Ranch 

(USGS) 

See footnotes at end of table. 

62.30° N * 

150.10° W 

36.658° N 1.9 

121.249° w 

17 

** 

** 
Table 1 • - Summary of U.S. acceZerograph records recovered during 1981 - continued 

Event Station name Station S-t2 Direction.3' Max acc1 4 Duration5 

(owner)l coord. (s) (g) (s) 

28 September 1981 Bear Valley Sta. 12 36.658° N 3.8 ** 

0734 UTC Williams Ranch 121.249° w 

Central California (USGS) 

36.79N, 121.59W 

Magnitude 3.9 

30 September 1981 Lake Success Dam 36.061° N 0.8 

1153 UTC (ACOE) 118.920° w 

Eastern California 

37 .59N, 118.89W Downstream ** 

Magnitude 5.9 

Left abutment ** 

Left crest ** 

Right abutment ** 

Right crest ** 

Slope ** 

1 October 1981 Bear Valley Sta. 10 36.532° N 1.6 ** 

1922 UTC Webb Residence 121.143° w 

Central California (USGS) Epicenter and 

magnitude unknown 

24 August 1979- San Francisco 37.795° N * 

6 October 1981 Transamerica Bldg. 122.401° w 

Central California (TA) 

Epicenter and 

magnitude unknown Sub-basement ** 

24th floor ** 

49th floor ** 

58th floor ** 

Note: One additional record** recovered at 58th floor. 

See footnotes at end of table. 

18 
Table l • - Summary of U.S. acceZerograph records recovered during 1981 - continued 

Event Station name Station S-t2 Direction.3 Max acc1 4 Duration5 

(owner)1 

8 October 1981 Pinyon,Flat Observ. 

2020 UTC (USGS) 

Southern California 

Epicenter and 

magnitude unknown 

20 October 1981 Pinyon Flat Observ. 

1241 UTC (USGS) 

Southern California 

33.52N, ll6.45W 

Magnitude 3.0 

22 September 1981- Hollister 

27 October 1981 City Ha 11 Annex 

Central California (USGS) 

Epicenter and 

magnitude unknown 

10 June 1981- Terminus Dam 

10 December 1981 Crest 

Central California (ACOE) Epicenter and 

magnitude unknown 

1station owner code: 

ACOE - U.S. Army Corps of Engineers. 

CHY - City of Hayward. 

coord. (s) 

33.61° N * 

116.46° w 

33.61° N * 

116.46° w 

36.85° N 3.0 

121.40° w 

36.41° N * 

119.00° w 

MWD -Metropolitan Water District of Southern California. 

USGS - U.S. Geological Survey. 

VA - Veterans Administration. 

TA - Transamerica Building. 

(g_) 

** 

** 

** 

** 

t - WWVB time code not legible or instrument not equipped with a radio receiver; 

correlation of accelerogram with event may be questionable. 

2S-wave arrival minus trigger time (S- t) interval. 

* S-t time is questionable or cannot be determined. 

(s) 

3 Direction of case acceleration for upward trace deflection on accelerogram. Horizontal 

components are listed as azimuth in degrees clockwise from north. Vertical components 

are listed as "up" or "down." 

4Peak acceleration recorded at ground level on one vertical and two orthogonal horizontal 

components unless otherwise noted. 

** Denotes maximum acceleration is less than 0.05 ~ at ground level or less than 

0.10 ~at non-ground-level stations. 

5Duration between first and last peaks of acceleration greater than 0.10 ~· 

19 
GPO 787-042/11: