UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

CATALOG OF EARTHQUAKES IN SOUTHERN ALASKA

JANUARY-MARCH 1978

OPEN-FILE REPORT 79-718

This report is preliminary and has not been edited or reviewed for conformity

with Geological Survey standards and nomenclature

Menlo Park, California

1979

Cover map: Top of the World Map, Na t~ona l Geographic Society, 1965 -

CATALOG OF EARTHQUAKES I N SOUTHERN ALASKA JANUARY-MARCH 1978

C. D. Stephens, J. C. Lahr, K. A. Fogleman M. A. A l lan, and S. M. Hel ton

CONTENTS

Page I n t r o d u c t i o n ......................................................... 2 Ins t rumenta t ion ....................................................... 2 Data Processing ................................................. 6 Magnitude . . .... . .. .. . . . ... .... . . . . . . .. . . . . .. . . . . . . . . . . . . . . , . . . . 11 Analys is o f Qua1 i t y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Discussion o f Catalog ................................................ 17 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . , . . . . . 19

ILLUSTRATIONS

F igure 1 Map showing p r i n c i p a l seismograph s t a t i o n s used i n l o c a t i n g earthquakes 3

2 Block diagram o f the USGS telemetered seismograph system ......................... 5

3 System response o f a t y p i c a l USGS telemetered seismograph s t a t i o n . . . . . . . . . . . . . . . . . . . 7

4 P i c t u r e o f a t y p i c a l seismograph s t a t i o n i n s t a l l a t i o n ....................... 8

5 Map ' showing earthquake ep icenters repo r ted i n t h e appendix . . . . . . . . . . . . . . . . . . . . 13

6 Map o f epicenters f o r earthquakes w i t h magnitudes greater than 3.5 ............................ 14

7 Map showing l o c a t i o n of cross sect ions ...................... 15 8 Cross sec t i on showing d i s t r i b u t i o n

o f earthquake hypocenters l i s t e d i n the appendix ....... 16

TABLES

Table 1 S ta t i on data ............................................... 4

APPENDICES

Appendix A. Southern Alaska earthquakes, f i r s t quar te r 1978 .......... 20

Appendix B. L i s t o f earthquakes occur r ing ou ts ide o f t h e USGS seismic network dur ing the f i r s t qua r te r o f 1978 ................. 31

Any use of trade namw and trademarks in thin publication iu for descriptive purposes only and does not constitute pndors~ment by the TJ.S. Geological Survey.

INTRODUCTION

The Nat iona l Center f o r Earthquake Research of t h e U.S. Geologica l Survey (USGS) began a program o f te lemetered seismic reco rd ing i n sou th-cent ra l Alaska i n 1971. The p r i n c i p a l o b j e c t i v e s o f t h i s program have been t o use ,

data recorded by t h i s network t o p r e c i s e l y l o c a t e earthquakes i n t he a c t i v e seismic zones of southern A1 aska, t o de l i nea te seismi c a l l y a c t i v e f a u l t s , t o assess seismic r i s k , t o document p o t e n t i a1 premoni tory earthquake phenomena, t o i n v e s t i g a t e cu r ren t t e c t o n i c deformation, and t o s tudy t h e s t r u c t u r e and phys ica l p rope r t i es o f the c r u s t and upper mantle. A t ask fundamental t o a l l o f these goals i s t h e r o u t i n e ca ta log ing o f earthquake parameters f o r earthquakes l oca ted w i t h i n and adjacent t o t h e seismograph network.

The i n i t i a l network o f 10 s ta t i ons , 7 around Cook I n l e t and 3 near Valdez, was i n s t a l l e d i n 1971. Each sumner s ince then add i t ions o r mod i f i ca t i ons t o t h e network have been made. By t h e F a l l o f 1973, 26 s t a t i o n s extended from western Cook I n l e t t o eastern Pr ince W i l l i a m Sound, and 4 s t a t i o n s were l oca ted between Cordova and Yakutat. A year l a t e r 20 a d d i t i o n a l s t a t i o n s were i n s t a l l e d . Th i r teen o f these were p laced along t h e eastern G u l f o f Alaska w i t h suppor t from t h e Nat iona l Oceanic and Atmospheric Admin i s t ra t i on (NOAA) under t h e Outer Cont inenta l She l f Environmental Program t o i n v e s t i g a t e t h e s e i s m i c i t y o f t h e ou ter con t i nen ta l s h e l f (OCS) reg ion o f i n t e r e s t f o r o i 1 exp lo ra t i on . Dur ing t h e subsequent years the r e g i o n covered by t h e network has remained r e 1 a t i v e l y f i x e d w h i l e e f f o r t has been made t o improve t h e ins t rumenta t ion and i n s t a l l a t i o n o f the s t a t i o n s i n order t o make them more r e l i a b l e .

This earthquake ca ta log presents o r i g i n t imes, f o c a l coord inates and magnitudes f o r 384 shocks occu r r i ng i n t h e f i r s t qua r te r o f 1978. Readings from a t o t a l o f 62 s t a t i o n s were used t o l o c a t e t h e shocks, i n c l u d i n g 11 s t a t i o n s operated by t h e NOAA A1 aska Tsunami Warning Center ( f o rmer l y Palmer

' Observatory), and 5 s t a t i o n s operated by t h e Geophysical I n s t i t u t e o f the U n i v e r s i t y o f A1 aska (U. of A.).

Earthquakes i n sou th-cent ra l Alaska as smal l as magnitude 3.0 have been r o u t i n e l y l oca ted by t h e Nat iona l Earthquake In fo rma t i on Serv ice of t h e USGS and i t s predecessor s ince t h e great Alaska earthquake o f 1964 and pub l i shed i n t h e r e p o r t s "Pre l im inary Determinat ion o f Epi centers" (PDE) . I n con t ras t t h e shocks inc luded i n t h i s ca ta log are as smal l as magnitude 1.0 and most are smal ler than magnitude 3.0. Data f o r t h e l a r g e r h i s t o r i c earthquakes i n sou th-cent ra l Alaska have been tabu la ted by Meyers (1976).

The l o c a t i o n s o f t h e s t a t i o n s o f t h e USGS seismograph network are p l o t t e d i n F igu re 1 and l i s t e d i n Table 1 along w i t h t he a d d i t i o n a l s t a t i o n s from which readings were obtained. The USGS s t a t i o n s have s ing le , v e r t i cal-component seismometers except f o r GLB, PNL, RDT, SKN, and VLZ which a l so have two h o r i z o n t a l se i smometers.

INSTRUMENTATION

The ins t rumenta t ion i n t h e USGS seismograph network i s i l l u s t r a t e d i n t h e b lock diagram i n F igu re 2. Data f rom each seismometer are te lemetered t o a cen t ra l r eco rd ing p o i n t a t t h e NOAA Alaska Tsunami Warning Center. The standard equipment a t each f i e l d s t a t i o n inc ludes a v e r t i c a l seismometer w i t h a n a t u r a l f requency o f 1.0 Hz (Mark Products, Model L-4), a package c o n s i s t i n g

Table 1. Station Data C F I S M I C S T A T I O N S U T I L I Z E D D U R I N G J A N U A R Y - M A R C H 1 9 7 8

S T A C O D C

*..-- A U K O A L E C S P I G [+ L R C D A C F I C H X C K K C O L c v n F I D G I L G L P G L C G L M G Y O HF:T H 0 Pr I L M I M A K ti C K L U K P P K N K K Y K L V Y PICK M I D M L S M S P h i Y A F A X P 1 I1 PMR P M S P N L P U G F W A P W L R O T R I U S A W S G A S K L S K N S L V

S P U S S N S S P S U K S V W SW D T O A T S I S T A V L z v Z W U A X WFG Y A H Y K G

S T A T I O N N A K E

------------ A b G U S T I N E I S . B A L t 0 Y U A h C A S P O I N T 0 1 6 M O l 1 t : T I I I h P L A t K R A P I D S C A P F D O U G L A S C O L L E G E F I C F D C H A I X H I L L S C H E k O K C O L L E G k C O R t r O V A F I D A L G O t 1 L F " O R F G I L A H I N A B U T T E ( > L A C I E R I S . G I L M O H f D O R C G U Y O T H I L L S F IT . H A V I L T O t J H A R L C Q U I t J L A k E I L I A M N A I N D I A N M O U N T A I N K O D I A K K L U T I N A K I C P A L L P A S : K N l K Y A Y A k I S . L E V Y M C K L N L E Y P C P K M I D D L K T O N I S . M A L A S P I N P 1 1 0 0 S t P A S S I 4 1 r I S H K A PAX'@!\ ' F I N N A C L E P A L P I E R O R S E P V A T O R Y A R C T I C V A L L E Y P E N I N S U L A P O R T A G E I I O U S T O P I P O R T * E L L S R k D O U B T R l O U S A k M I L L S W E R F I A I I G L A C I E R S K I L A K S K V E N T I r A S E L D O V I A S P U R K S U S I T N A S U t l S H I N E P C I N T S U C K L I t l G H I L L S S P A R H E V O H N S E W A R D T O L S O t J A ' I S I N A T A T A L I N I , V A L D E Z V A L D E Z W E S T W A X E L L R I D G f L H I T E n l u r R G L C R Y A H T S E Y A K A T A G F

L A T N D F G W I N

------- 59 20.10 61 2.17 59 56.90 59 23.34 63 3F.10 5 E 57.32 61 10.96 6 0 4.00 59 57.58 6 4 54.00 60 32.79 60 43.73 64 58.50 61 26.51 6 0 53.44 64 59.23 6 0 8.78 6 0 20.19 59 27.10 6 0 10.92 66 4.11 57 44.87 61 29.57 61 30.78 61 24.75 S o 52.10 6L 1Z.00 6 3 43.96 59 25.67 59 45.80 6 0 29.35 60 44.58 62 58.25 6 0 5.80 61 35.53 61 14.68 59 40.12 6 0 51.87 61 39.05 6 0 51.56 60 34.43 59 52.70 61 48.49 6 0 30.07 60 30.86 61 58.82 5 9 78.28 61 10.90 61 27.83 6 0 10.80 6 0 4 - 6 0 61 6.49 6 0 6.72 62 6.29 61 13.57 62 55.80 t l 7.89 61 3.54 6 0 27.OC 6 0 2 . 2 7 6F 21.80 6 0 4 - 2 0

LON: W D E G n I N ..------- 153 25.66 142 20.67 1 3 9 37.01-1 155 13.02 145 50.70 153 31.77 1 4 7 45.99 141 7.10 154 13.99 147 47.60 145 44.96 146 35.79 1 4 7 29.70 1 4 3 48.63 147 4.35 1 4 7 23.33 141 28.29 144 15.64 158 52.62 152 48.97 153 40.72 1 5 2 29.50 145 55.21 145 1.09 148 27.34 144 31.39 149 15.20 14R 56.10 1 4 6 2 0 . 3 4 140 9.00 149 21.64 1 5 1 14.28 145 28.1 1 140 15 .40 1 4 9 7.85 149 33.63 1 3 9 23.82 149 1 - 4 2 1 4 9 52.72 148 20.09 1 5 2 24.37 141 13.70 1 4 8 19 .98 145 12.42 150 12.91 151 31.78 151 34.83 1 5 2 3.26 1 5 0 44.60 142 50.30 143 47.00 155 37.30 149 26.9h 146 10.34 145 20.24 156 1.32 146 19.92 146 33.24 1L2 51.10 142 1.9c 1 4 1 44.70 1 L 2 25.33

E L E V R

---- 2 9 3

1 3 0 0 1 0

5 6 7 8 0 9 3 8 6

2 7 9 3 7 3 2 3 2 0

9 0 4 8 8 3 5 0 8 4 5

3 8 2 0 1 8 3 6 2 0 372 5 5 0

1 3 8 0 1 3 .

1 0 1 2 1 1 4 3

595 3 7 5 2 3 C 61 0

3 7 2

1 5 0 1 0 0

113C 9 7 5 1 0 0 7 1 6

T D L Y S E C ----

0.00 0.00 0.30 0.00 o.nn 0.00 0.00 0.30 0.00 0.00 0.30 0.30 0.0 0 0.00 0.50 0.00 0.30 0.30 0.30 0.00 0.00 0.00 0.00 0.30 0.00 0.30 0.00 0.00 0.30 0.30 0.00 0.08 0.00 0.3n 0.00 0.00 0.30 0.00 0.00 0.00 0.00 0.30 O.OO 0.30 0.00 0.00 0.00 0.00 0.00 0.30 0.30 n. o o 0.00 0.00 0.30 0.00 0.3 0 0.30 0.30 G.30 0.30 0.30

M A G B 1HZ

---*

U O F A U S G S U S G S U S G S N O A A U S G S L t S G S U S G S U S G S U S G S U S G S U S G S N O A P U S G S U S G S 110 F A U S G S U S G S U S G S U S G S N O A A N O A A U S G S U S G S U S G S I !SGS LIO F A U O F A NO A A U S G S U S G S U S G S 110 F A U S G S N O A A N O A 4 U S G S I I S G S N O A A U S G S U S G S L l S G S U S G S U S G S U S G S U S G S U S G S U S G S U S G S U S G S U S G S N O A P U S G S N O A A U S G S N O A A U S 6 5 U S G 5 I I S G S U S t S U S G S 1 1 5 6 5

This table l i s t s geographic coordinates and other pertinent information for s ta t ions used in the preparation of t h i s catalog. D i s the thickness of the low-velocity surf ic ial sedimentary layer, in kilometers, assigned in the calculation of travel-times to a given s tat ion. DELAY i s the s ta t ion P-phase travel-time delay in seconds. TDLY i s the telephone l ine delay in seconds. The magnification (MAG) of the vertical seismograph component i s given a t 1 Hz, The ins t i tu t ions (INST) operating the s tat ions a re the NOAA Alaska Tsunami Warning Center and the Geophysical Ins t i tu te os the University.of A1 as ka (UOFA) .

of a pre-amp1 i f i e r and a vo1 tage-control 1 ed osci 11 ator (VCO model NCER 202) and a i r -ce l l storage ba t te r ies (McGraw-Edison, Model ST-2-1000). Data are t e lme te r ed via a leased telephone c i r c u i t or a VHF (162-174 MHz) radio l ink feeding a telephone c i r cu i t . The radio l ink i s provided by a low-power transmitter (100 m w ) and receiver adapted from a HT-200 Motorola handie-talkie transceiver and two Yagi antennae with 9 db directional gain (Scala, Model CAS-150). The central recording f aci 1 i t y incorporates a bank of discriminators ( N C E R JlOl or Develco Model 6203), a 16 mm-film multi-channel osci 11 ograph (Teledyne Geotech Devel ocorder , Model 4000D), a time-code

9 enerator (Datum, Model 9100) and a radio receiver f o r WWV time s ignals Specific Products SR7R).

The pr inciple of operation i s as follows: The seismometer t rans la tes movement of the ground into an e l ec t r i c a l voltage t ha t i s fed in to t he ampl if ier/VCO unit where the ampl i f ied voltage causes the frequency of an audio-band osc i l l ator t o f luc tua te about i t s center frequency. The frequency-modulated (FM) tone from the ampl i f ier/VCO unit i s carr ied d i r ec t l y by voice-grade telephone c i r c u i t t o the recording s i t e or a l t e rna te ly i s fed through a V H F radio l ink onto a telephone c i r c u i t . A t the recording s i t e , the FM seismic signal i s demodulated by a discriminator. The demodul ated s ignal , which i s simply an amplified form of the i n i t i a l signal from the seismometer, i s recorded photographically on a mu1 t i channel osci 1 lograph, together w i t h time marks from a crystal-controlled chronometer. Each day i s recorded on a s ingle 142-foot r o l l of f i lm.

Signals from more than one seismograph can be transmitted on a s ing le telephone c i r c u i t by employing VCO units with d i f fe ren t center frequencies. In the standard configuration there i s a 340 Hz separation between center frequencies and a f ixed bandwidth of 250 Hz. Up t o e ight seismic channels w i t h center frequencies ranging from 680 t o 3060 Hz may be placed on a s ing le voice-grade telephone c i r c u i t .

Figure 3 i l l u s t r a t e s the response charac te r i s t i cs of the e n t i r e seismic system from seismometer t o f i lm viewer. The response level a t each s t a t i on i s adjusted i n s teps of 6 decibels so t ha t the ambient seismic noise produces a small deflection of the t race on t he film. As a r e s u l t , the actual response fo r an individual s ta t ion may d i f f e r from tha t of the typical s t a t i on by a fac tor of 2, 4, 8, e tc . The magnification of t he typical s t a t ion i s about 6 x lo4 a t 1 Hz and 106 a t 10 Hz.

The i n s t a l l a t i on of a typical radio-linked s t a t i on i s shown in Figure 4. Degradation or interruption of data transmission due t o inclement weather conditions is a major problem during the winter months.

DATA PROCESSING

The 16 mn f i lms (four per day) a re mailed weekly t o Menlo Park where the seismic data are processed by the following mu1 t i s t e p routine:

1. Scanning. The scan fi lm, which has 18 s ta t ions dis t r ibuted throughout the network i s scanned t o iden t i fy and note times of a l l seismic events whether of local , regional , or te leseismic or igin .

2. Timing. For the "we1 1-recorded" local earthquakes iden t i f i ed in the

FREQUENCY

Figure 3. Response curve for a typical USGS seismograph system.

.c C -6-

.Q u m != L +Jar v, I + 0 a,

Em E m a 5 L 07 E- *r 0 .F w s u m .F a, w v r ?I 3 ra 0 s

F C c a,

u w c r .r L E a m rd

In order t o determine any bias that might r e s u l t from t h i s approximation, a s e t of events in the Benioff zone below Cook In l e t was relocated using a ray-tracing program of E. R. Engdahl tha t incorporates a more r e a l i s t i c , three-dimensional velocity model (Lahr, 1975). Hypocenter s h i f t s , apparently due t o the oversimplified f l at-1 ayer model, ranged from near zero a t a depth of 60 km t o as great as 25 km a t the 160 km depth. The of f se t s were oriented in such a way tha t the dip of the Benioff zone would appear t o be too great in the f la t - layered model.

Two dif ferent P-wave velocity models are used t o locate the earthquakes. West of 149"W the velocity model used i s based on Model A of Matumoto and Page (1969) derived fo r the eastern Kenai Peninsula-Prince William Sound region. The velocity model i s specif ied as follows:

Layer 1 2 3 4 5 6 7 8 9

10

Depth ( k m ) 0 - D D - 4 4 - 10

10 - 15 15 - 20 20 - 25 25 - 33 33 - 47 47 - 65 below 64

P velocity (km/sec) * --

The thickness of the f i r s t layer i s allowed t o vary between s ta t ions t o account fo r the presence of thick sections of low-velocity sediments beneath the s t a t i ons NKA and N N L , which are located in the Cook In le t basin. For these s ta t ions D i s 4 km. For a l l other s ta t ions 0 i s 0.01 km. For earthquakes t ha t occurred eas t of 14g0, the velocity model used t o locate t he events i s one t ha t was developed by minimizing the travel-t ime res iduals f o r a group of earthquakes near Valdez. The model i s specified by:

Layer Depth ( k m ) 1 0 2 0.01 3 20 4 below 32

P velocity (km/sec) 2.75

A value of 1.78 f o r the velocity r a t i o between P and S i s assumed f o r both models. The i n i t i a1 t r i a1 depth fo r earthquakes which occur west of 149"W i s 75 km. East of 149"W t h i s value i s 15 km because the seismicity i n t h i s par t of the net occurs a t shallow depths.

Travel-time delays were applied t o s ta t ions i n the network t ha t had consistent and large res iduals f o r t he locations of a large group of earthquakes. Additional del ays were appl ied a t several s t a t i ons t o correct 1

fo r a s a t e l l i t e l ink in the re lay of the signal . The P-phase delays are 4 l i s t e d in Table 1 and a re added t o the calculated P-phase travel-times a t each 1 s ta t ion . For S-phases the delay i s mult iplied by 1.78, the P t o S velocity I

r a t i o .

MAGNITUDE

Magnitudes are determined f rom e i t h e r t he s i g n a l du ra t i on o r t he maximum t r a c e amplitude. Eaton and o thers (1970) approximate t h e R i c h t e r l o c a l magnitude, whose d e f i n i t i o n i s t i e d t o maximum t r a c e amplitudes recorded on standard h o r i z o n t a l Wood-Anderson t o r s i o n seismographs, by an ampl i tude magnitude based on maximum t r a c e amplitudes recorded on high-gain, h igh- frequency ve r t ' ca l seismographs such as those operated i n t h e Alaskan network. The amp1 i t u d e magnitude XMAG used i n t h i s ca ta log i s based on t h e work o f Eaton and h i s co-workers and i s g iven by t h e expression (Lee and Lahr, 1972)

XMAG = loglO A - B1 + B210g10D 2

(1)

where A i s t h e equ iva len t maximum t r a c e ampl i tude i n m i l l i m e t e r s on a standard Wood-Anderson seismograph, D i s t he hypocentra l d is tance i n k i lometers , and B1 and B2 are constants. D i f fe rences i n t h e frequency response o f t h e two seismograph systems are accounted f o r i n A; however, i t i s assumed t h a t t he re i s no systematic d i f f e rence between the maximum h o r i z o n t a l ground motion and t h e maximum v e r t i c a l motion. The terms

-B1 + B2 logl0D 2

approximate R i c h t e r ' s -logl0A0

f u n c t i o n (Richter , 1958, p. 342) , which expresses the t r a c e ampl i tude f o r an earthquake o f magnitude zero as a f u n c t i o n o f e p i c e n t r a l d is tance. For smal l l o c a l earthquakes i n c e n t r a l Ca l i f o rn ia , B1 = 3.38 and B2 = 1.50 f o r = 200 t o 600 km.

F o r small, shal low earthquakes i n c e n t r a l Ca l i f o rn ia , Lee and others (1972) express the du ra t i on magnitude FMAG a t a g iven s t a t i o n by the r e l a t i o n

FMAG = -0.87 + 2.00 loglor t 0.0035A (2)

where , i s t h e s igna l du ra t i on i n seconds from the P-wave onset t o t h e p o i n t where the peak-to-peak t r a c e ampl i tude on the Geotech Model 6585 f i l m v iewer f a l l s below 1 cm and A i s t h e e p i c e n t r a l d is tance i n k i lometers .

Comparison o f XMAG and FMAG est imates f rom equat ions (1) and (2 ) f o r 77 Alaskan shocks i n t h e depth range 0 t o 150 km and i n t h e magnitude range 1.5 t o 3.5 revea ls a systematic l i n e a r decrease o f FMAG r e l a t i v e t o XMAG w i t h inc reas ing f o c a l depth. To remove t h i s discrepancy, a l i n e a r dependence on depth i s added t o t he expression f o r FMAG as fo l lows:

FMAG = -1.15 + 2.00 logl0, + 0.0071 t 0.0035A

where z i s t he f o c a l depth i n k i lometers .

For earthquakes l a r g e r than magnitude 3.0, FMAG values may be compared t o mb magnitudes l i s t e d i n t h e PDE repo r t s . The average and standard dev ia t i ons f o r 47 events i n the magnitude range 3.0 t o 5.5 are 0.02 and 0.44 respec t i ve l y ; hence t h e two measures are compatible.

The magnitude p r e f e r e n t i a l l y assigned t o each earthquake i n t h i s ca ta log i s t h e FMAG est imate. The XMAG va lue i s used o n l y where no FMAG can be determined.

11

'I- L L

F igu re 7. Map showing the area inc luded i n each o f the cross sec t ions o f Figure 8. D i r e c t i o n of v iew f o r sec t ions A-E i s N 60° E, f o r sec t i on F i s N 40' E, and f o r sec t ions G-J i s N 20° E.

ACKNOWLEDGEMENTS

We thank Robert Eppley, Wayne Jorgensen and the e n t i r e s t a f f of the NOAA Tsunami Warning Center f o r t h e i r assistance in maintaining our recording equipment in Palmer, Alaska, as well as making t h e i r seismic data avai lable t o US.

We also wish t o thank Jurgen Kienle of the Geophysical I n s t i t u t e of the University of A1 aska f o r a cooperative operation of southern Cook In le t seismograph s ta t ions .

We are indebted t o a l l of those who have spent time fabr ica t ing , ins ta l 1 ing, and maintaining the seismograph network i n A1 aska, part icul arly John Roger, Marion Salsman, Tom Walker and Tom Cleese.

Betty McIntire and the s t a f f of the USGS Anchorage of f ice has been of great assistance in solving l o g i s t i c problems, both in the f i e l d and i n the off ice .

This catalog i s patterned a f t e r those prepared f o r central California and we gra te fu l ly acknowledge Drs. W. H. K. Lee and R. L. Wesson f o r development of many of the procedures and techniques used herein.

This study was supported j o in t l y by the U. S. Geological Survey and by the National Oceanic and Atmospheric Administration, under which a multi-year program responding t o needs of petroleum development of t he A1 askan continental shelf i s managed by the Outer Continental Shelf Environmental Assessment Program (OCSEAP) Office.

REFERENCES

Eaton, J. P . , M. E. O'Neill, and J. N . Murdock (1970). Aftershocks of the 1966 Parkfield-Cholme, Cal i fornia , earthquake: a deta i led study, - Bull. Seism. Soc. Am. 60, 1151-1197.

Foglman, K . , C . Stephens, J. C . Lahr, M . Allan, and S. Helton (1978). Catalo

Survey, Open-File Report 78-1097, 28 p. -9 of earthquakes in southern Alaska, October-December 1977, U.S. Geologica

Jacob, K. H. (1972). Global tec tonic implications of anomalous seismic P traveltimes from the nuclear explosion Longshot, J. Geophys. Res. 77, 2556-2573.

Lahr, J. C. (1975). Detailed seismic investigation of Pacif ic-North American p la te in teract ion i n southern A1 aska, Ph.D. d i s se r ta t ion , Columbia University, 141 p.

Lahr, J. C., E. R. Engdahl, and R . A. Page (1974). Locations and focal mechanisms of i ntennedi ate depth earthquakes be1 ow Cook In1 e t , A1 aska, EOS 55 349. - -9

Lahr, J. C., (unpubl ished computer program). HYPOELLIPSE: A computer program f o r determining local earthquake hypocentral parameters, magnitude, and f i r s t motion pat tern .

Lahr, J. C., R, A. Page, and J. A. Thomas (1974). Catalog of earthquakes i n south centra l Alaska, Apri 1-June 1972, U. S. Geological Survey, Open-Fi l e Report, 35 p .

Lee, W . H. K . , and J. C. Lahr (1972). HYP071: a computer program f o r determining hypocenter, magnitude, and f i r s t motion pat tern of local earthquakes, U. S. Geolog

Lee, W. H. K . , R. E. Bennett, estimating magnitude of G e o l o ~ ~ c a l Survey, Open-t i 1e Keport, 28 p.

Matumoto, T., and R. A. Page (1969). Microaftershocks following the Alaska earthquake of 28 March 1964: "Determination of hypocenters and crustal veloci t ies in the Kenai Peninsula-Prince William Sound area", The Prince William Sound, Alaska, Earthquake of 1964 and Aftershocks, vol. 2B & C , U. 5 . Coast and Geodetic Survey Pub1 ication 10-3, U.S. Govt. Printing Office, Washington, 157-173.

Meyers, H. (1976). A h i s to r ica l sumnary of earthquake epicenters in and near A1 aska, NOAA Techni cal Memorandum EDS NGSDC-1.

Mitronovas, W . , and B. L. Isacks (1971). Seismic velocity anomalies in the upper mantle beneath the Tonga-Kermadec island arc. J. Geophys. Res. 76, 71 54-7180.

Richter, C . F. (1958). Elementary Seismology, W . H. Freeman and Co., 768 pp.

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REMARKS

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P THE MAGNITUDE O F T H I S EARTHQUAKE COULD NOT R E DETERMINED BECAUSE T H E COOAS OVERLAPPED W I T H THOSE O F T H E P R E V I O U S EVENT.

A D D I T I O N A L SOLITHEAN A L A S K A E A R T H Q U A K E S , J A N - M A R 1 9 7 8

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