UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

CATALOG OF EARTHQUAKES IN SOUTHERN ALASKA

JULY-SEPTEMBER 1980

OPEN-FILE REPORT 83-15

T n ? s report is preliminary and has not been edited or reviewed for conformity

w i t h U.S. Geological Survey editorial standards.

Any use o f trade names and trademarks in this publication is for m

descriptive purposes only and does not constitute endorsement by the

U.S. Geological Survey.

Menlo Park , California

1983

CATALOG OF EARTHQUAKES I N SOUTHERN ALASKA JULY-SEPTEMBER 1980

K . A . Fogleman. C . D . Stephens. J . C . Lahr. J . A . Rogers. R . S . Canc i l l a . Roy Tam. S . M . Helton. J . A . Fre iberg . J . P . Meln ick

Page I n t r o d u c t i o n ............................................................ 1 Ins t r umen ta t i on ......................................................... 4 Data Process ing ......................................................... 7 V e l o c i t y Models ......................................................... 10 Magnitude ............................................................... 12 Ana l ys i s o f Q u a l i t y ..................................................... 13 U iscuss ion o f Ca ta log ................................................... 14 Acknowledgments ......................................................... 20 References .............................................................. 2 1

ILLUSTRATIONS

Page F i g u r e 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 ........................................ Block diagram o f t h e USGS te lemete red seismograph system ...... System response curves o f t y p i c a l USGS te lemete red

seismograph s t a t i o n s ........................................ 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 ......... Record o f s t a t i o n use ......................................... Map showing earthquake ep i cen te r s r epo r t ed i n t h e appendix .... Map o f ep i cen te r s f o r earthquakes w i t h magnitudes

g r e a t e r than 3.5 ............................................ Map showing l o c a t i o n o f c ross sec t i ons ........................ Cross sec t i ons 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 t h e appendix ......................................

TABLES

Page Table 1 S t a t i o n aa ta .................................................. 3

APPENDICES

Page Appendix Southern A laska earthquakes. t h i r d - q u a r t e r 1980 ................ 23

INTRODUCTION

The O f f i c e o f Earthquake S tud ies ( f o r m e r l y t h e N a t i o n a l Center f o r Earthquake Research) o f t h e U.S. Geo log ica l Survey (USGS) has ma in ta ined a program o f te lemete red se ismic r e c o r d i n g i n sou th - cen t ra l A1 aska s i n c e 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 da ta 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 h e a c t i v e se ismic zones o f southern Alaska, d e l i n e a t e s e i s m i c a l l y a c t i v e f a u l t s , assess se ismic r i s k , document p o t e n t i a l p remon i to ry earthquake phenomena, i n v e s t i g a t e c u r r e n t t e c t o n i c deformat ion, and s tudy t h e s t r u c t u r e and p h y s i c a l p r o p e r t i e s o f t h e c r u s t and upper mant le. A t a s k fundamental t o a l l o f these goa ls i s t h e r o u t i n e c a t a l o g i n g o f earthquake parameters f o r earthquakes l oca ted w i t h i n and ad jacen t t o t h e seismograph network.

The i n i t i a l network o f 10 s t a t i o n s , 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. I n subsequent summers a d d i t i o n s o r m o d i f i c a t i o n s t o t h e network were made. By t h e f a l l o f 1973, 26 s t a t i o n s extended f r om western Cook I n l e t t o eas te rn P r i n c e W i l l i a m Sound, and 4 s t a t i o n s were l oca ted t o t h e eas t between Cordova and Yakutat . A yea r 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 . T h i r t e e n o f these were p laced a long t h e eas te rn G u l f o f A laska w i t h suppor t from t h e Na t i ona l Oceanic and Atmospheric A d m i n i s t r a t i o n (NOAA) under t h e Oute r Con t i nen ta l S h e l f Environmental Assessment 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 of t h e o u t e r c o n t i n e n t a l s h e l f , a r e g i o n o f i n t e r e s t f o r o i l e x p l o r a t i o n . Dur ing t h e subsequent years t h e r e g i o n covered by t h e network has remained r e l 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 rumen- t a t i o n and i n s t a l l a t i o n o f t h e s t a t i o n s i n o r d e r t o make them more r e l i a b l e .

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 a re p l o t t e d i n F i g u r e 1 and l i s t e d i n Table 1 a long w i t h t h e a d d i t i o n a l s t a t i o n s f r om which read ings were obta ined. Each USGS s t a t i o n has a s i ng le , ver t ica l -component seismometer. The s t a t i o n s GLB, PNL, RDT, SKN, and VLZ a l s o have nor th -sou th - and eas t -wes t -o r ien ted h o r i z o n t a l seismometers. On September 22, 1980, s t a t i o n CYT was moved t o a new l o c a t i o n and i t s s t a t i o n code changed t o YKG.

T h i s earthquake c a t a l o g p resen ts o r i g i n t imes, f o c a l coo rd i na tes and magnitudes f o r 1,289 shocks o c c u r r i n g i n t h e t h i r d q u a r t e r o f 1980. Readings f r om a t o t a l o f 67 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 A laska Tsunami Warning Center (ATWC, f o r m e r l y Palmer Observatory) , 2 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 t h e U n i v e r s i t y o f A laska (U. of A.), and 4 s t a t i o n s operated i n southwest Yukon T e r r i t o r y by t h e E a r t h Phys ics Branch o f t h e Department o f Energy, Mines and Resources, Canada.

Earthquakes i n sou th - cen t ra l A laska 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 Na t i ona l Earthquake I n fo rma t i on Se rv i ce o f t h e USGS ana i t s predecessor s i nce t h e g r e a t A laska earthquake o f 1964 and a re pub l i shed i n t h e r e p o r t s " P r e l im ina ry De te rmina t ion o f Ep i cen te r s " (PDE) . I n c o n t r a s t , t h e shocks i n c l u d e d i n t h i s c a t a l o g a re as smal l as magnitude 1.0 and most are s m a l l e r 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 t h a t occur red i n sou th - cen t ra l A laska th rough 1975 have been t a b u l a t e d b y Meyers (1976).

Figure 1 . Map showing the locations of a1 1 USGS seismograph s ta t ions in southern Alaska and other s t a t ions used in the preparation o f this catalog. The symbols a r e as follows: so l id c i r c l e s , ve r t i ca l component USGS seismograph; c i r c l e s w i t h dots , three component USGS seismographs; open c i r c l e s , USGS s t a t i ons not reporting during t h i s quar ter ; diamonds, ATWC s t a t i ons ; t r i ang l e s , Univ . o f Alaska s t a t i ons ; squares, Dept. Energy, Mines and Resources, Canada. Quaternary volcanoes ( a f t e r King, 1969) a r e indicated by s t a r s .

Table 1. S t a t i o n Data

S TA CODE S T A T I O N NAME

L A T I T U D E LONGITUDE ELEV P D D L V l OLY2 D L V 3 TDLV M G N v n MOD KM SEC SEC SEC SEC AT I nz rnsr

ALC BAL BCP BGM BMR CF I CHX E l 6 CVA CVT DLV F BA

ALCAN BALDY

62 37.36 141 6.68 682 3 1.81 R.08 6.#0 1.88 1.80 USGS 61 2.17 142 28.67 1388 3 8.81 6.00 0.80 -8.19 1.68 162888 U S t S 69 57.20 139 38.18 396 3 S.01 8.88 8.88 -1.88 -0.27 76088 USGS 59 23.66 165 13.76 625 1 6.61 H.80 8.88 8.81 -1.27 76088 USCS 68 5 8 . 6 9 144 36.16 823 2 0.81 8.88 0.88 1.92 -6.27 38800 USGS 61 10.96 I47 45.99 3 2 8.81 0.88 0.80 8.08 6.08 76508 USGS 68 3.75 141 7.18 1067 3 8.01 1.80 6.88 -0.85 -0.27 38888 USGS 60 67.90 141 28.08 1654 3 6.81 8.88 0.80 -8.53 B.08 3886'8 USGS 6 1 32.79 145 44.96 98 2 6.01 0.80 8.80 8.80 -8.27 38888 USGS 68 4.47 142 24.68 323 3 H.81 8.80 6.80 8.67 -0.27 9581 USGS 68 22.28 137 3.98 738 3 8.81 U.81 1.88 2.37 0.01 EMRC 64 54.18 147 47.68 320 1 8.81 6,81 8.88 H.ll 8.88 ATWC

F I D F I D A L C O 60 43.73 146 35.79 488 2 8.81 8.81 8.88 N.80 -8.27 38808 USGS EKC GOLD KING CREEK 64 10.72 147 56.08 490 1 8.80 P.B8 8.88 8.08 1.88 UOFA GLB G I L A H I N A BUTTE 61 26.51 143 48.63 845 3 6.81 8.88 8.80 1.60 8.88 76015 USGS 6 L C GLACIER I S L A N D 68 53.44 147 4.38 3 2 0.11 8.08 8.80 6.88 -0.27 76088 USGS 6 V O GUYOT 68 0.78 141 20.29 183 3 8.81 1.85 8.80 -8.06 -8.27 38808 USCS H I N HINCHINBROOK I S L A N D 68 23.81 146 38,18 611 2 0.01 6.88 8.88 2.09 -8.27 38088 USGS HMT HAMILTON 60 20.19 144 15.64 6 2 0 3 8.81 0.80 1.88 -8.55 - # . Z f 76888 USES HON HARLEQUIN

I L IAMNA I N D I A N MOUNTAIN KOD I A K KLUANE LAKE K L U T l N A K I M B A L L PASS K N I K GLACIER KOIDERN R I V E R KAYAK I S L A N D MALASPINA GLACIER MOOSE PASS MONTAGUE ISLARD N l K I S H K A N I N I L C H I K PEDRO BAY P INNACLE PALMER OBSERVATORY ARCTIC VALLEY PEN1 NSULA PORTAGE

- --- USCS USGS ATVC ATVC

I L M I M A KDC KEY KL U KMP KNK KRY

EMRC USGS US6S . . .- US GS EMRC

KVK MLS MSP MTC N KA NNL P DB P I N PMR PMS PNL PR6

USES USGS USGS

0.88 -8.27 9 5 ~ 5 USGS 0.80 8.88 6688 USGS 0.80 8.08 34280 USGS 8.08 -8.27 384888 USGS -0.81 -8.27 76880 USGS 0.80 8.88 ATWC 8.88 1.88 ATVC -1.18 -0.27 76888 USGS 8 . n ~ a.nn ~ R ~ U U I IPCF

P WA PVL RDT R 1 U SAW SCM SGA

HOUSTON PORT WELLS REDOUBT R l O U

---- ATVC USGS USGS USGS USGS UOFA USGS

SAWMILL SHEEP MOUNTAIN SHERMAN GLACIER

S I T S I T K A SKL S K I L A K SKN SKWENTNA S L V SELDOVIA SPU SPURR SSN S U S I T N A

19 3 0.01 8,88 0.00 0.80 -8.27 -- - - -

ATVC - - - - 698 1 B.81 8.18 8.BB 8.88 0.88 76808 USGS 564 1 0.81 8.80 8.80 0.88 0.88 688688 USGS 91 1 8.01 8.80 8.18 0.08 0+85 73780 USGS

888 1 8.81 8.39 8.80 0.08 8.00 193888 USGS 1297 1 8.81 0.67 8.88 0.88 B.60 178500 USGS 385 3 8.81 0.88 8.08 8.79 -1.27 50508 USGS 2 9 9 3 8.81 0.00 0.01 2.14 -8.27 190B0 USGS 762 1 8.81 8.80 0.88 8.80 -8.27 Al'WC

SSP SUNSHINE P O I N T SUK SUCKLING H I L L S SVW SPARREVOHN SWD TOA T S 1 T T A VLZ VZ w WAX WHC WRG YAH VKG YKU

SEUARD TOLSONA TS I NA

. . . - USGS ATWC U56S ATVC USGS USGS USGS EMRC USGS USGS USGS ATUC

TATAL I NA VALDEZ .. ---- VALDEZ VEST WAXELL RIDGE WHITEHORSE WHITE R I V E R GL . . VAHTSE VAKATAGA VAKUTAT

Th is t a b l e l i s t s geographic coord ina tes and o t h e r p e r t i n e n t i n f o r m a t i o n o f a l l USGS seismograph s t a t i o n s i n southern Alaska and t he s t a t i o n s o f o t h e r i n s t i t u t i o n s used i n t h e p r e p a r a t i o n o f t h i s ca ta l og . P-MOD i s t h e number o f t h e P-wave v e l o c i t y model ass igned t o t h e s t a t i o n (see t e x t ) , where t h e numbers 1, 2, and 3 cor respond t o t h e western, c e n t r a l , and eas te rn models. D i s t h e t h i c kness o f t h e l o w - v e l o c i t y s u r f i c i a l sedimentary l a y e r i n k i l ome te r s ass igned i n t h e c a l c u l a t i o n o f t r a v e l t i m e s t o a g iven s t a t i o n . DLY1-3 a r e t h e s t a t i o n P-phase t r a v e l t i m e de lays i n seconds. TDLY i s t h e te lephone 1 i n e de lay i n seconds. The m a g n i f i c a t i o n (MAG) o f t h e v e r t i c a l seismograph component i s g iven a t 1 Hz. The i n s t i t u t i o n s (INST) o p e r a t i n g t h e s t a t i o n s o t h e r than t h e USGS a re t h e Alaska Tsunami Warnin Center (ATNC), t h e Geophysical I n s t i t u t e o f t h e U n i v e r s i t y o f Alaska 9 UOFA), and t h e Department o f Energy, Mines, and Resources, Canada (EfIRC). S t a t i o n CYT was r e l o c a t e d and i t s s t a t i o n code changed t o YKG.

INSTRUMENTATION

The i n s t r u m e n t a t i o n 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 l ock diagram i n F i g u r e 2. Data from each seismometer a re te lemete red t o t h e NOAA Alaska Tsunami Warning Center i n Palmer. The s tandard equipment a t each f i e l d s t a t i o n i nc l udes 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 o f an a m p l i f i e r and a v o l t a g e - c o n t r o l l e d o s c i 1 l a t o r ( V C O model NCER 202, o r A1VCO) and " a i r - c e l l " s to rage b a t t e r i e s (McGraw-Edison, Model ST-2-1000). The r e c e n t l y developed AlVCO u n i t s (Rogers and others , 1980) have been i n s t a l l e d a t n e a r l y a l l o f t h e USGS s t a t i o n s i n southern Alaska. These c r y s t a l - r e f e r e n c e d u n i t s have an automat ic ga in - rang ing c a p a b i l i t y and p rov i de d a i l y i n f o rma t i on on t h e g a i n s e t t i n g , geophone response, b a t t e r y vo l tage, s t a t i o n i d e n t i f i c a t i o n and temperature. Data a re te lemete red v i a a combinat ion o f leased te lephone c i r c u i t s (some o f which a re r e l ayed by s a t e l l i t e which i n t r oduces a -0.30 sec. t r ansm iss i on de lay ) and VHF (162-174 MHz) r a d i o l i n k s . The r a d i o equipment c o n s i s t s of low-power t r a n s m i t t e r s ( 100 mW) and r e c e i v e r s adapted f r om HT-200 Moto ro la h a n a i e - t a l k i e t r ansce i ve r s . Yagi antennae w i t h 9 db d i r e c t i o n a l g a i n (Scala, Model CAS-150) a re used. A t some s i t e s where AC power i s ava i l ab l e , base -s ta t i on r a d i o r e c e i v e r s (G.E. Model R46AP668) w i t h g r e a t e r s e n s i t i v i t y and r e l i a b i l i t y a re used. The c e n t r a l r e c o r d i n g f a c i l i t y i n co rpo ra tes a bank of d i s c r i m i n a t o r s (NCER J l O l o r Develco Model 6203), f o u r 16 m m - f i l m m u l t i - channel o s c i l l o g r a p h s (Teledyne Geotech Develocorder, Model 4000D), a 14-channel analog tape reco rde r (Be1 1 and Howel 1 Model VR3700B), and a t ime-code genera to r (Datum, Model 9100).

The p r i n c i p l e o f ope ra t i on i s as f o l l o w s : The seismometer t r a n s l a t e s movement o f t h e ground i n t o an e l e c t r i c a l vo l t age t h a t i s f e d i n t o t h e ampl i f ie r /VCO u n i t where t h e a m p l i f i e d vo l t age causes t h e f requency o f an audio-band o s c i l l a t o r t o f l u c t u a t e about i t s c e n t e r f requency. The f requency- modulated (FM) tone f r om t h e ampl i f ie r /VCO u n i t i s c a r r i e d d i r e c t l y by vo ice - grade te lephone c i r c u i t t o t h e r eco rd i ng s i t e o r a l t e r n a t e l y i s f e d th rough a VhF r a d i o l i n k on to a te lephone c i r c u i t . A t t h e r e c o r d i n g s i t e t h e FM se ismic s i g n a l i s demodulated by a d i s c r i m i n a t o r . The demodulated s i gna l , which i s s imp ly an a m p l i f i e d f o rm o f t h e i n i t i a l s i g n a l f r om t h e seismometer, i s recorded p h o t o g r a p h i c a l l y on a mu l t i channe l o s c i l l o g r a p h , t o g e t h e r w i t h t i m e marks f r om a c r y s t a l - c o n t r o l l e d chronometer. Twenty- four hours of da ta f o r 18 s t a t i o n s can be recorded on a s i n g l e 43 m-long r o l l o f 16-mm f i l m .

S i gna l s f r om more than one seismograph can be t r a n s m i t t e d on a s i n g l e te lephone c i r c u i t b y employing VCO u n i t s w i t h d i f f e r e n t c e n t e r f requenc ies . I n t h e s tandard c o n f i g u r a t i o n t h e r e i s a 340 Hz sepa ra t i on between c e n t e r f r equenc ies and a f i x e d bandwidth o f 250 Hz. Up t o e i g h t se ismic channels w i t h c e n t e r f requenc ies rang ing f rom 680 t o 3,060 Hz may be p laced on a s i n g l e vo ice-grade te lephone c i r c u i t .

F i g u r e 3 i l l u s t r a t e s t h e response c h a r a c t e r i s t i c s o f t h e e n t i r e se ismic system f r o m seismometer t o f i l m viewer. The response l e v e l a t each s t a t i o n i s ad jus ted i n s teps o f 6 d e c i b e l s so t h a t t h e ambient se ismic n o i s e produces a sma l l d e f l e c t i o n o f t h e t r a c e on t h e f i l m . As a r e s u l t , t h e a c t u a l response f o r an i n d i v i d u a l s t a t i o n may d i f f e r f r om t h a t of t h e t y p i c a l s t a t i o n by a f a c t o r o f 2, 4, 8, e t c . The m a g n i f i c a t i o n of t h e t y p i c a l s t a t i o n i s about b x 104 a t 1 Hz and 106 a t 10 Hz. The g a i n o f a s t a t i o n t h a t has an A l V C O u n i t i s a u t o m a t i c a l l y reduced by a f a c t o r o f 10 when t h e f l u c t u a t i o n s o f t h e FM s i g n a l exceed a p r e s e t t h resho ld .

F igu re 3. System response curves f o r typ i c a l USGS A1 aska seismographs t h a t incorpora te t h e A l V C O u n i t ( s o l i d curve) and the o l d e r VCO model NCER 202 u n i t ( do t ted cu rve ) .

The installation of a typical radio-linked station is shown in Figure 4. Degradation or interruption of data transmission due to inclement weather conditions is a major problem during the winter months. Some indication of the operational reliability of the USGS stations can be inferred from the plot of station use in Figure 5.

DATA PROCESSING

The 16-mm films (four per day) are mailed weekly from Palmer to Menlo Park where the seismic data are processed by the following multi-step routine:

1. Scanning. The scan film, which has 18 stations distributed throughout the network. i s scanned to identify and note times of all seismic events whether of iocal, regional, or teleseismic origin.

2. Timing. For the "well-recorded" local earthquakes identified in the scanning process, the following data are read from each station: P- and S-wave arrival times, direction of first motion, duration of signal in excess of a given threshold amplitude, and period and amplitude of maximum recorded signal. The criterion for choosing earthquakes to be timed is the duration of the signal, which i s related to the magnitude. The network is divided into three regions--western, central and eastern-- bounded approximately by longitudes 156O and 150" W., 150° and 145" W., and 145" ana 138" W., respectively. In the western and central regions, only events with signal durations longer than 80 s and 20 s, respectively, are timed. In the eastern region, a1 1 earthquakes which are recorded by at least three stations and for which at least four clear arrivals can be read are timed. These criteria were established to select from the large number of earthquakes recorded by the network those shocks that are of greatest interest to current research objectives.

Timing is done by projecting the seismic traces onto a table and digitizing the onsets of the P- and S-phases. The output from the digitizer, in the form of x-y data pairs on punched computer cards, is converted into phase data by computer using the program DIGIT3 (written by P. Ward and W. Ellsworth for use within the U.S. Geological Survey).

3. Initial computer processing. The phase data from the films are batch processed by computer using the program HYPOELLIPSE (Lahr, 1980) to obtain origin times, hypocenters, magnitudes and, if desired, first-motion plots for fault-plane solutions.

4. Analysis of initial computer results. Each hypocentral solution is checked for traveltime residuals greater than or equal to 0.75 seconds and for a poor spatial distribution of stations. Arrival times that produce large residuals are re-read. For shocks with a poor distribution of stations, readings from additional stations outside the USGS network are sought.

5. Final computer processing. The poor hypocentral solutions are rerun with corrections and the new solutions are checked for large residuals that might be due to remaining errors. Corrections are made as required before the final computer run is made.

.

F i g u r e 4 , Seismograph s t a t i o n s a t S u c k l i n g H i l l s (SUK) . Background: H igh g a i n seismograph s t a t i o n e n c l o s u r e and antenna mast. Foreground: K inernet r ics SMAl s t r o n g m o t i o n i n s t r u m e n t b o l t e d t o a c o n c r e t e s l a b poured w i t h i n a l a r g e c u l v e r t .

The earthquake l o c a t i o n s a re based on P and S a r r i v a l s . S a r r i v a l s a re impo r tan t f o r de te rmin ing ep i cen te r s o f shocks o u t s i d e t h e network and depths o f events i n t h e B e n i o f f zone beneath t h e network i n Cook I n l e t . Un fo r t una te l y , S cannot be read a t any s t a t i o n f o r some l a r g e events because t h e t r a c e s on t h e f i l m ove r l ap each o t h e r o r a re t o o f a i n t t o f o l l o w .

The HYPOELLIPSE computer program determines hypocenters by m in im i z i ng d i f f e r e n c e s between observed and computed t r a v e l t i m e s th rough an i t e r a t i v e least -squares scheme. I n many respec ts t h e program i s s i m i l a r t o HYPO71 (Lee and Lahr, 1972), which has been used i n t h e p r e p a r a t i o n o f ca ta l ogs of c e n t r a l C a l i f o r n i a earthquakes s i nce January 1969. An impo r tan t f e a t u r e a v a i l a b l e i n HYPOELLIPSE i s t h e c a l c u l a t i o n o f conf idence e l l i p s o i d s f o r each hypocenter. The e l l i p s o i d s p r o v i d e va luab le i n s i g h t i n t o t h e e f f e c t o f network geometry on p o s s i b l e hypocen t ra l e r r o r s .

VELOCITY MODELS

Our exper ience w i t h l o c a t i n g earthquakes i n southern A laska suggests t h a t s i g n i f i c a n t l a t e r a l v a r i a t i o n s a re p resen t i n t h e v e l o c i t y s t r u c t u r e across t h e network. Such v a r i a t i o n s m igh t be expected f r om t h e compl icated geology and t e c t o n i c s o f t h e r e g i o n (e.g., P l a f k e r , 1967). Very l i t t l e i n f o r m a t i o n i n t h e f o rm o f d i r e c t measurement i s a v a i l a b l e f o r t h e v e l o c i t y s t r u c t u r e i n southern Alaska. I n p rev i ous ca ta logs , o n l y two P-wave v e l o c i t y models c o n s i s t i n g o f h o r i z o n t a l l a y e r s o f cons tan t v e l o c i t y were used t o l o c a t e t h e earthquakes (e.g., Stephens and others , 1979). These v e l o c i t y models were d e r i v e d by m in im i z i ng t h e t r a v e l t i m e r e s i d u a l s f o r se l ec ted se t s o f earthquakes i n t h e Cook I n l e t r e g i o n (Model A o f Matumoto and Page, 1969) and near Valdez. The models proved adequate f o r l o c a t i n g earthquakes as f a r eas t as Kayak I s l and , b u t earthquakes l o c a t e d f a r t h e r t o t h e eas t o f t e n had l a r g e t r a v e l t i m e r e s i d u a l s a t nearby s t a t i o n s . An improved v e l o c i t y model f o r t h e r e g i o n eas t o f Kayak I s l a n d was developed by m i n i m i z i n g t h e t r a v e l t i m e r e s i d u a l s f o r a se l ec ted s e t o f a f te rshocks f r om t h e 1979 St. E l i a s earthquake t h a t occur red n o r t h o f I c y Bay (Stephens and o thers , 1980). A s i g n i f i c a n t d i f f e r e n c e between t h i s model and t h e e a r l i e r ones i s t h a t t h e new model c o n s i s t s o f a s i n g l e l a y e r o f l i n e a r l y i n c r e a s i n g v e l o c i t y over a ha l f -space o f cons tan t v e l o c i t y , wnereas t h e e a r l i e r models c o n s i s t o f severa l h o r i z o n t a l l a y e r s o f cons tan t v e l o c i t y .

I n t h e p r e p a r a t i o n o f t h i s ca ta log , t h e method o f ass i gn ing v e l o c i t y models t o c a l c u l a t e t h e o r e t i c a l t r a v e l t i m e s i s d i f f e r e n t f r om t h a t used i n some e a r l i e r ca ta logs . Prev ious ly , a s i n g l e v e l o c i t y model was used f o r a l l s t a t i o n s r e c o r d i n g a p a r t i c u l a r event, t h e cho ice o f t h e model depending on t h e r e g i o n i n which t h e shock occurred. I n t h e r e v i s e d procedure, a s i n g l e v e l o c i t y model i s assigned t o each s t a t i o n depending on t h e r e g i o n i n which the s t a t i o n i s l oca ted and i s used i n l o c a t i n g a l l events. Thus, a s t a t i o n i n t h e eas te rn r e g i o n w i l l use t h e eas te rn v e l o c i t y model t o c a l c u l a t e t r a v e l t i m e s from events t h a t occur i n t he western, c e n t r a l , and eas te rn p a r t s o f t h e network.

West o f l o n g i t u d e 148" 45' W. t h e v e l o c i t y model used i s as f o l l o w s :

Layer Depth (km) P v e l o c i t y (km/s)

0 - D D - 4 4 - 10

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

The th ickness , D, o f t h e f i r s t l a y e r i s a l lowed t o va ry between s t a t i o n s t o account f o r t h e presence o f t h i c k sec t i ons o f l o w - v e l o c i t y sediments beneath t h e s t a t i o n s NKA and NNL, which a re l oca ted i n t h e Cook I n l e t bas in . F o r these s t a t i o n s D i s 4 km. F o r a l l o t h e r s t a t i o n s D i s 0.01 km. It i s recognized t h a t a model comprised o f un i f o rm h o r i z o n t a l l a y e r s may be a poor r e p r e s e n t a t i o n o f t h e ac tua l v e l o c i t y s t r u c t u r e , p a r t i c u l a r l y i n t h e v i c i n i t y o f a subduc t ion zone (Mi t ronovas and Isacks, 1971; Jacob, 1972), a l though such a model does have t h e advantage o f s i m p l i f y i n g t h e computat ion o f t r a v e l t i m e s . I n o r d e r t o determine any b i a s t h a t m igh t r e s u l t from t h i s approximat ion, a s e t o f even ts i n t h e B e n i o f f zone below Cook I n l e t was r e l o c a t e d us i ng a r ay - t r a c i n g program o f E. R. Engdahl t h a t i n co rpo ra tes a more r e a l i s t i c , t h ree - d imensional v e l o c i t y model (Lahr, 1975). Hypocenter s h i f t s , appa ren t l y due t o t h e o v e r s i m p l i f i e d f l a t - l a y e r model, ranged f r om near ze ro a t a depth o f 60 km t o as g r e a t as 25 km a t t h e 160 km depth. The o f f s e t s were o r i e n t e d i n such a way t h a t t h e d i p o f t h e Ben io f f zone would appear t o be t o o g r e a t f o r l o c a t i o n s based on a f l a t - l a y e r e d model.

F o r earthquakes t h a t occur between l ong i t udes 148' 45 ' W. and 144' 30' W., t h e v e l o c i t y model used t o l o c a t e t h e events i s :

Layer Depth (km) P v e l o c i t y (km/s)

0.0 0.01

below 39

East o f l o n g i t u d e 144' 30' W. t h e P-wave v e l o c i t y o f t h e f i r s t l a y e r inc reases l i n e a r l y f r om 5.0 km/s a t t h e su r f ace t o 7.8 km/s a t 32 km depth, w n i l e t h e ha l f - space has a v e l o c i t y o f 8.2 km/s.

P-phase t r a v e l t i m e de lays a re a p p l i e d t o s t a t i o n s i n t h e network t h a t have c o n s i s t e n t and l a r g e r e s i d u a l s f o r t h e l o c a t i o n s o f l a r g e groups o f ea r t h - quakes. Each s t a t i o n has t h r e e de lays (DLY1, DLY2, and DLY3 o f Tab le 1 ) assigned t o i t t h a t correspond t o t h e western, c e n t r a l , and eas te rn r eg ions convered by t h e network. The p a r t i c u l a r de lay t h a t i s used t o l o c a t e an earthquake i s determined by t h e r e g i o n i n which t h e earthquake occurs. F o r example, a s t a t i o n near I c y Bay t h a t i s used t o l o c a t e an earthquake beneath Cook I n l e t w i l l be assigned a de lay DLY1, b u t t h e same s t a t i o n w i l l use DLY3 t o l o c a t e an earthquake t h a t occurs beneath I c y Bay. A d d i t i o n a l de lays a re app l i ed a t severa l s t a t i o n s t o c o r r e c t f o r a s a t e l l i t e l i n k i n t h e r e l a y o f

t h e s i g n a l . S-phase de lays a re determined by m u l t i p l y i n g t h e P-delay by 1.78, t h e P t o S v e l o c i t y r a t i o .

The i n i t i a l t r i a l depths f o r earthquakes which occur i n t h e western, c e n t r a l , and eas te rn p a r t s o f t h e network a re 75, 30, and 15 km, r e s p e c t i v e l y , and r e f l e c t a p rog ress i ve decrease i n t h e range o f depths o f earthquakes f rom west t o east .

MAGNITUDE

Magnitudes a re determined f r o m e i t h e r t h e s i g n a l d u r a t i o n o r t h e maximum t r a c e amp1 i tude. Eaton and o the rs ( 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 ampl i tudes recorded on s tandard h o r i z o n t a l Wood-Anderson t o r s i o n seismographs, by an amp l i tude magnitude based on maximum t r a c e ampl i tudes recorded on high-gain, h igh - f requency v e r t i c a l seismographs such as those operated i n t h e Alaskan network. The ampl i tude magnitude XMAG used i n t h i s c a t a l o g 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 express ion (Lee and Lahr, 1972)

XMAG = log10 A - 61 + ~ 2 1 o g l 0 ~ ~

where A i s t h e e q u i v a l e n 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 s tandard Wood-Anderson seismograph, D i s t h e hypocen t ra l d i s t a n c e i n k i l omete rs , and 61 and I32 a re constants . D i f f e r e n c e s i n t h e f requency response o f t h e two seismograph systems a re accounted f o r i n A. It i s assumed, however, t h a t t h e r e i s no sys temat i c d i f f e r e n c e between t h e maximum h o r i z o n t a l ground mot ion and t h e maximum v e r t i c a l mot ion. The terms -B1 + ~ ~ l o ~ ~ ~ ~ 2 approximate R i c h t e r ' s - loglOAo f u n c t i o n (R i ch te r , 1958, p. 342), which expresses t h e t r a c e amp l 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 i s tance .

F o r smal l , sha l l ow earthquakes i n c e n t r a l C a l i f o r n i a , Lee and o t h e r s (1972) express t h e d u r a t i o n magnitude FMAG a t a g i ven s t a t i o n by t h e r e l a t i o n

FMAG = -0.87 + 2.00 l o g l o T + 0.0035 DEL ( 2 )

where T i s t h e s i g n a l d u r a t i o n i n seconds f r om t h e P-wave onset t o t h e p o i n t where t h e peak-to-peak t r a c e ampl i tude on t h e Geotech Model 6585 f i l m v iewer f a l l s below 1 cm and DEL i s t h e e p i c e n t r a l d i s t a n c e i n k i l ome te r s .

Comparison o f XMAG and FMAG es t imates f rom equa t ions ( 1 ) and ( 2 ) f o r 77 Alaskan shocks i n t h e depth range 0 t o 150 krn and i n t h e magnitude range 1.5 t o 3.5 r e v e a l s a sys temat i c 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 i n c r e a s i n g 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 h e express ion f o r FMAG as f o l l o w s :

FMAG = -1.15 + 2.00 l o g l o T + 0.007 Z + 0.0035 DEL

where 7. i s t h e f o c a l depth i n k i l ome te r s .

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 c a t a l o g i s t h e FMAG es t imate . The XMAG va lue i s used o n l y where no FMAG can be determined.

ANALYSIS OF QUALITY

Two types o f e r r o r s e n t e r i n t o t h e de te rm ina t i on o f hypocenters: systemat ic e r r o r s l i m i t i n g t h e accuracy of hypocenters and random e r r o r s l i m i t i n g t h e p r e c i s i o n . Systemat ic e r r o r s a r i s e f r om an i n c o r r e c t v e l o c i t y model, m i s i d e n t i f i c a t i o n of phases, o r sys temat i c t i m i n g e r r o r s and can be eva lua ted th rough c o n t r o l l e d exper iments such as l o c a t i n g t h e coo rd i na tes of a known exp los ion . Random e r r o r s r e s u l t f rom random t i m i n g e r r o r s and a re es t imated f o r each earthquake th rough t h e use of s tandard s t a t i s t i c a l techniques.

F o r each earthquake, HYPOELLIPSE c a l c u l a t e s t h e l eng ths and o r i e n t a t i o n s o f t h e p r i n c i p a l axes o f t h e j o i n t conf idence e l l i p s o i d . The one-standard- a e v i a t i o n con f idence e l l i p s o i d descr ibes t h e r e g i o n o f space w i t h i n which one i s 68 pe rcen t c o n f i d e n t t h a t t h e hypocenter l i e s , assuming t h a t t h e o n l y source o f e r r o r i s random read ing e r r o r . The e l l i p s o i d i s a f u n c t i o n of t h e s t a t i o n geometry f o r each i n d i v i d u a l event, t h e v e l o c i t y model assumed and t h e s tandard d e v i a t i o n o f t h e random read ing e r r o r . The s tandard d e v i a t i o n determined f rom repeated read ings o f t h e same phases by f o u r se i smo log i s t s i s as sma l l as 0.01 t o 0.02 s f o r t h e most impu l s i ve a r r i v a l s and as l a r g e as 0.10 t o 0.20 s f o r emergent a r r i v a l s . The conf idence e l l i p s o i d s a re computed f o r a s tandard d e v i a t i o n o f 0.16 s and t h e r e f o r e l i k e l y overes t imate t h e 68 pe rcen t con f idence reg ions . The s tandard d e v i a t i o n of t h e r e s i d u a l s f o r an i n d i v i d u a l s o l u t i o n i s n o t used t o c a l c u l a t e t h e con f idence e l l i p s o i d because i t con ta i ns i n f o r m a t i o n n o t o n l y about random read ing e r r o r s b u t a l s o about t h e i n c o m p a t i b i l i t y o f t h e v e l o c i t y model t o t h e data. Thus, t h e con f idence e l l i p s o i d i s a measure o f t h e p r e c i s i o n o f t h e hypocen t ra l s o l u t i o n . I n a few extreme cases t h e va lue c a l c u l a t e d f o r one o f t h e e l l i p s o i d axes becomes very l a r g e corresponding t o a s p a t i a l d i r e c t i o n w i t h ve ry g r e a t u n c e r t a i n t y . I n these cases an upperbound l e n g t h o f 25 krn i s tabu la ted .

To f u l l y eva lua te t h e q u a l i t y o f a hypocenter one must cons ide r b o t h t h e con f idence e l l i p s o i d and t h e r o o t mean square (RMS) r e s i d u a l f o r t h e s o l u t i o n . The RMS r e s i d u a l r e f l e c t s b o t h sys temat i c and random e r r o r s , b u t t h e random e r r o r s a r e t y p i c a l l y much sma l le r . Hence t h e RMS r e s i d u a l i s p r i m a r i l y a measure o f t h e i n c o m p a t i b i l i t y o f t h e v e l o c i t y model, m i s i n t e r p r e t a t i o n o f phases, and sys temat i c t i m i n g e r r o r s . I n t e r p r e t a t i o n o f t h e RMS r e s i d u a l may depend upon t h e l o c a t i o n o f t h e earthquake. I n areas where t h e v e l o c i t y model i s i ncompa t i b l e w i t h t h e r e a l ea r th , RMS r e s i d u a l s cou ld be l a r g e and b e t r a y t h e i n c o m p a t i b i l i t y ; a l t e r n a t i v e l y , t h e RMS r e s i d u a l s c o u l d be sma l l and n o t r e f l e c t t h e e r r o r i n a bad hypocenter. Where the v e l o c i t y model i s compat ib le, however, a l a r g e RMS r e s i d u a l would i n d i c a t e p robab le m is read ings o f phases.

Other parameters p rov i ded by HYPOELLIPSE t h a t a re u s e f u l i n e v a l u a t i n g t h e qua1 i t y o f a hypocen t ra l s o l u t i o n are: GAP, t h e 1 a rges t az imutha l sepa ra t i on between s t a t i o n s measured f r om t h e ep i cen te r ; D3, t h e e p i c e n t r a l d i s t ance o f t h e t h i r a c l o s e s t s t a t i o n ; NP, t h e number o f P a r r i v a l s used i n t h e s o l u t i o n ; and NS, t h e number of S a r r i v a l s used i n t h e s o l u t i o n . I f GAP exceeds 180°, t h e earthquake l i e s o u t s i d e t h e network o f a v a i l a b l e s t a t i o n s and t h e s o l u t i o n i s g e n e r a l l y l ess r e l i a b l e than f o r events o c c u r r i n g i n s i d e t h e network.

DISCUSSION OF CATALOG

O r i g i n t imes, f o c a l coord inates, magnitudes, and r e l a t e d parameters f o r 1,289 earthquakes f r om July-September 1980 a re l i s t e d i n t h e Appendix. Ep icen te rs f o r these shocks a re p l o t t e d i n F i g u r e 6. I n F i g u r e 7, o n l y t h e earthquakes w i t h magnitudes g r e a t e r than 3.5 a re p l o t t e d . V e r t i c a l sec t i ons showing t h e depth d i s t r i b u t i o n o f a l l o f t h e shocks a re presented i n F i gu res 8 and 9.

We es t ima te t h a t t h i s c a t a l o g i s reasonably complete f o r shocks l a r g e r than magnitude 3.5 i n t h e western, 2.5 i n t h e c e n t r a l , and 2.0 i n t h e eas te rn r eg ions o f t h e area covered by t h e network. The minimum magnitude of t h e l i s t e d earthquakes i s 0.3 f o r c r u s t a l events (2130 km) and 3.3 f o r B e n i o f f zone events deeper than o r equal t o 100 km.

The p r e c i s i o n o f t h e hypocenters o r t h e r e l a t i v e accuracy o f t h e l o c a t i o n s o f ne i ghbo r i ng events i s represented b y t h e con f idence e l 1 i pso ids . The p r e c i s i o n o f ep icen te rs , expressed i n terms o f t h e maximum axes o f t h e p r o j e c t e d one- s tandard -dev ia t ion conf idence e l l i p s o i d s (ERH) , averages 5.2, 2.7, and 2.4 km, r e s p e c t i v e l y , i n t h e eastern, c e n t r a l , and western p a r t s o f t h e network. S i m i l a r l y , t h e p r e c i s i o n o f f o c a l depth (ERZ) averages about 5.4, 4.1, and 4.3 km, r e s p e c t i v e l y . The v a r i a t i o n i n t h e p r e c i s i o n o f hypocenter de te rm ina t i on across t h e network i s s t r o n g l y i n f l u e n c e d by d i f f e rences i n t h e s t a t i o n coverage i n t h e d i f f e r e n t reg ions .

The abso lu te accuracy o f t h e earthquake l o c a t i o n s i s d i f f i c u l t t o eva lua te i n t h e absence o f known exp los ions , Hypocenter b iases equal t o and l a r g e r than t h e dimensions o f t h e con f idence e l l i p s o i d s a re n o t u n l i k e l y f r om the over - s i m p l i f i e d v e l o c i t y model assumed i n t h e p r e p a r a t i o n o f t h i s ca ta log .

The dominant f e a t u r e i n t h e d i s t r i b u t i o n o f ep i cen te r s i s t h e l a r g e number o f a f tershocks f r om t h e 1979 St. E l i a s earthquake i n southeastern Alaska. A l l o f t h e a f t e r shocks w i t h b e t t e r c o n t r o l i n t h e s o l u t i o n were l oca ted a t depths l e s s than 30 km, which i s c o n s i s t e n t w i t h t h e depths found f o r a f t e r shocks i n t h e e a r l y p a r t o f t h e sequence (Stephens and others , 1980). It i s i n t e r e s t i n g t o no te t h a t t h e a f te rshocks p l o t t e d here appear t o f o rm s p a t i a l c l u s t e r s s i m i l a r t o those observed i n t h e e a r l y p a r t o f t h e sequence.

Over 10 earthquakes were l o c a t e d i n t h e r e g i o n o f t h e Wrangel l volcanoes n o r t h o f about 61' N. near t h e eas te rn p a r t o f t h e network ( F i g u r e 6 ) . S i m i l a r numbers o f events have been l oca ted near t h i s r e g i o n i n e a r l i e r q u a r t e r s o f data. Because t h e earthquakes occur red o u t s i d e o f t h e network t h e hypocenters a re g e n e r a l l y p o o r l y cons t ra ined . F o r t h i s reason i t i s n o t c l e a r whether t h e events a re o c c u r r i n g w i t h i n t h e c r u s t o r uppermost mant le, o r whether t h e may be assoc ia ted w i t h p a r t i c u l a r vo l can i c cen te rs .

W i t h i n t h e Yakataga se ismic gap, which i s l oca ted approx imate ly between Kayak I s l a n d and t h e western l i m i t o f t h e a f t e r shock zone o f t h e 1979 S t . E l i a s a f t e r shock zone, t h e p a t t e r n o f s e i s m i c i t y i s s i m i l a r t o t h a t observed i n e a r l i e r qua r t e r s . One i n t e r e s t i n g f e a t u r e i s an i nc rease i n t h e r a t e o f s e i s m i c i t y beg inn ing i n June 1980 i n t h e o f fshore area between l ong i t udes 146' 30' W. and 143Q 30' W. and n o r t h o f l a t i t u d e 59' N. Du r i ng t h e 4-month p e r i o d f r om June-September 1980 t h e month ly average number of shocks w i t h coda- d u r a t i o n magnitudes MLZ2 was e i g h t p e r month, as compared t o an average of about 1 1/2 p e r month f o r t h e p rev i ous 8-month per iod . Most o f t h e a c t i v i t y

DISTRNCE, K M

Figure 9. Vertical sections of hypocenters for t h e areas indicated i n Figure 8. Quaternary volcanoes are plotted a s so l id t r i ang l e s a t zero depth. All d is tances a r e i n kilometers. No vertical exaggeration.

18

was l o c a l i z e d about 50 km southwest o f Kayak I s l and . The l a r g e s t earthquake t o occur i n t h i s o f f s h o r e area i n almost 10 years was recorded on September 4, 1980. T h i s earthquake (MB=5.0, MS=5.4, PDE) was l oca ted about 60 km southeast o f Kayak I s l a n d and d i d n o t have any l o c a t a b l e af tershocks.

The s e i s m i c i t y throughout t h e remainder o f t h e network does n o t va ry markedly f rom t h a t descr ibed f o r p rev ious qua r te r s (Stephens and o thers , 1980; Fogleman and others , 1978; Lahr, and others , 1974). A we l l - de f i ned B e n i o f f zone d i p s t o t h e nor thwest beneath t h e Cook I n l e t r e g i o n (F igu re 9, sec t i ons G-J). The depth t o t h e t op o f t h i s zone v a r i e s f r om about 50 km beneath t h e western Kenai Peninsula t o about 115 beneath t h e a c t i v e volcanoes west o f Cook I n l e t . The d i p o f t h e B e n i o f f zone appears t o inc rease f r om no r theas t t o southwest, b u t t h e depth t o t h e se ismic zone beneath t h e a c t i v e volcanoes--Augustine, I l iamna, Redoubt and Spu r r - - i s n e a r l y cons tan t a t about 115 km.

A l l o f t h e se ismic a c t i v i t y i n t h e southern p a r t o f t h e network eas t o f l o n g i t u d e 146' W. occurs a t depths l e s s than about 35 km. The number o f l a r g e r magnitude earthquakes which occur i n t h e eas t i s cons ide rab l y sma l l e r than t h a t i n t h e western p a r t of t h e network ( F i g u r e 7) . Most o f t h e se ismic a c t i v i t y i n t h e eas te rn p a r t of t h e network appears t o be concent ra ted beneath I c y Bay and no r theas t o f Kayak I s l and .

The con ten ts o f t h e Hppendix may be ob ta ined i n forms amenable t o computer i n p u t (punched cards o r magnetic tape) by c o n t a c t i n g t h e authors.

ACKNOWLEDGEMENTS

We thank Rober t Eppley, Wayne Jorgensen, and t h e e n t i r e s t a f f o f t h e NOAA Tsunami Warning Center f o r t h e i r ass is tance i n ma in ta i n i ng ou r r e c o r d i n g equipment i n Palmer, Alaska, as w e l l as making t h e i r se ismic da ta a v a i l a b l e t o US.

We a l s o wish t o thank Hans Pulpan, o f t h e Geophysical I n s t i t u t e o f t h e U n i v e r s i t y of Alaska, f o r a coopera t i ve ope ra t i on o f southern Cook I n l e t seismograph s t a t i o n s .

We are indebted t o a l l o f those who have spent t i m e f a b r i c a t i n g , i n s t a l l i n g , and m a i n t a i n i n g t h e seismograph network i n Alaska, p a r t i c u l a r l y Greg Condrot te and W i l l i a n Wong.

B e t t y M c I n t i r e and the s t a f f o f t h e USGS Anchorage o f f i c e have been o f g r e a t ass is tance i n s o l v i n g l o g i s t i c problems, bo th i n t h e f i e l d and i n t h e o f f i c e .

Th i s c a t a l o g i s pa t t e rned a f t e r those prepared f o r c e n t r a l C a l i f o r n i a , and we g r a t e f u l l y acknowledge Drs. W. H. K. Lee and R. L. Wesson f o r development of many o f t h e procedures and techniques used here in .

T h i s work was supported j o i n t l y by t h e U.S. Geo log ica l Survey and by t h e Na t i ona l Oceanic and Atmospheric Admin is t ra t ion , under which a m u l t i - y e a r program responding t o needs o f pet ro leum development o f t h e Alaskan c o n t i n e n t a l she l f i s managed by t h e Outer Cont inen ta l She l f Environmental Assessment Program (OCSEAP) O f f i ce .

REFERENCES

Eaton, 3. P., O ' N e i l l , M. E:, and Murdock, J. N., 1970, A f te rshocks o f t h e 1966 Parkf ie ld-Cholame, C a l i f o r n i a , earthquake: a d e t a i l e d study, B u l l e t i n of t h e Se ismo log ica l S o c i e t y of America 60, p. 1151-1197.

Fogleman, K., Stephens, C., Lahr, J. C., Hel ton, S., and A l l an , M., 1978, Ca ta log of earthquakes i n southern Alaska, October-December 1977, U.S. Geo log ica l Survey Open-Fi le Report 78-1097, 28 p.

Jacob, K. H.? 1972, Global t e c t o n i c i m p l i c a t i o n s o f anomalous se ismic P t r a v e l t l m e s f r om t h e nuc lea r exp los i on Longshot, Journa l o f Geophysical Research 77, p. 2556-2573.

King, P. B., compi ler , 1969, Tec ton i c Map o f No r t h America, U.S, Geo log ica l Survey, sca le 1:5,000,000.

Lahr, J. C. ? 1975, D e t a i l e d se ismic i n v e s t i g a t i o n o f P a c i f i c - N o r t h American p l a t e interaction i n southern Alaska, Ph.D. d i s s e r t a t i o n , Columbia U n i v e r s i t y , 141 p.

Lahr, 3 . C., Engdahl, E. R., and Page, R. A., 1974, Loca t i ons and f o c a l mechanisms o f i n t e rmed ia te depth earthquakes below Cook I n l e t , Alaska, EOS 55, 349 p.

Lahr, 3. C., 1980, HYPOELLIPSE/MULTICS: A computer program f o r de te rm in i ng l o c a l earthquake hypocen t ra l parameters, magnitude, and f i r s t mot ion p a t t e r n , U.S. Geo log ica l Survey Open-Fi l e Repor t - 80-59, 59 p.

Lee, W. H. K.? and Lahr, J. C., 1972, HYP071: a computer program f o r deter rn in lng hypocenter, magnitude, and f i r s t mot ion p a t t e r n o f l o c a l earthquakes, U.S. Geo log ica l Survey Open-Fi le Report , 100 p .

Lee, h. H. K., Bennett , R. E., and Meagher, K. L.,1972, A method o f e s t i m a t i n g magnitude o f l o c a l earthquakes f r om s i g n a l du ra t i on , U.S. Geo log ica l Survey Open-Fi le Report, 28 p.

Matumoto, T., and Page, R. A., 1969, M ic roa f te rshocks f o l l o w i n g t h e Alaska earthquake o f 28 March 1964: "De te rmina t ion o f hypocenters and c r u s t a l v e l o c i t i e s i n t h e Kenai Peninsu la-Pr ince W i l l i a m Sound area," The P r i n c e W i l l i a m Sound, Alaska, Earthquake o f 1964 and Af tershocks, vo ls . 2B & C, U. S. Coast and Geodet ic Survey P u b l i c a t i o n 10-3, U.S. Government P r i n t i n g O f f i c e , Washington, D.C., p. 157-173.

Meyers, H., 1976, A h i s t o r i c a l summary o f earthquake e p i c e n t e r s i n and near Alaska, NOAA Techn ica l Memorandum EDS NGSDC-1, 57 p.

Mi t ronovas, W., and Isacks, B. L., 1971, Seismic v e l o c i t y anomalies i n t h e upper mant le beneath t h e Tonga-Kermadec i s l a n d arc , Journa l o f Geophysical Research 76, p. 7154-7180.

P l a f k e r , G., 1967, Geolog ic map o f t h e G u l f o f A laska T e r t i a r y Province, Alaska, U.S. Geo log ica l Survey Misce l laneous I n v e s t i g a t i o n s Map 1-84, sca le 1;500,000.

R i c h t e r , C. F., 1958, Elementary Seismology, W. H. Freeman and Co., San Franc isco, CA, 768 p.

Rogers, J. A., Maslak, S., and Lahr, J. C., 1980, A se ismic e l e c t r o n i c system w i t h automat ic c a l i b r a t i o n and c r y s t a l re fe rence , U.S. Geo log ica l Survey Open-Fi le Repor t 80-324, 130 p.

Stephens, C. D., and Lahr, J. C., 1981, Seismic s t u d i e s i n sou thern and south- eas te rn Alaska, i n W. L. Coonrad, ed., The Un i t ed S ta tes Geo log ica l Survey i n Alaska--Accomplishments d u r l n g 1980: U.S. Geo log ica l Survey C i r c u l a r ( i n p rep ) .

Stephens, C. D., Fogleman, K. A., Lahr, 3 . C., Hel ton, S. M., Canc i l l a , R. S . , Tam, Roy, and Fre iberg , 3. A., 1980, Cata log o f earthquakes i n southern Alaska, January-March 1980, U.S. Geo log ica l Survey Open-Fi le Repor t 80-1253, 55 p.

Stephens, C. D., Lahr, J. C., Foglernan, K. A., A l l an , M. A., and Hel ton, S. M., 1979, Cata log o f earthquakes i n southern Alaska, January- March 1978, U.S. Geo log ica l Survey Open-Fi le Repor t 79-718, 31 p.

Stephens, C. D.? Lahr, J. C., Fogleman, K. A., and Horner, R. B., 1980, The S t . E l i a s , Alaska, earthquake o f 28 February 1979: r e g i o n a l r eco rd i ng o f a f t e r shocks and sho r t - t e rm pre-earthquake s e i s m i c i t y , B u l l e t i n o f t h e Se ismo log ica l Society o f America 70, p. 1607-1633.

APPENDIX

Cataloq of Earthquakes

Earthquakes from southern Alaska are listed in chronological order. The following data are given for each event:

1. Origin time in Universal Time (UT): date, hour (HR) , minute (MN), and second (SEC). To convert to Alaska Standard Time (AST) subtract 10 hours.

2. Epicenter in degrees and minutes of north latitude (LAT N ) and west longitude (LONG W).

3. DEPTH, depth of focus in kilometers.

A letter code after the depth indicates as follows:

C - Solution was constrained based on EMRC source. O - Depth was constrained by a geophysicist. P - Solution was constrained based on PDE source. W - Station weighting modified (for events outside of network).

4. MAG, coda duration magnitude (FMAG) of the earthquake. A letter following the magnitude indicates a magnitude other than FMAG as follows:

A - Amp1 itude magnitude (XMAG), USGS. B - Body-wave magnitude (mb) , USGS National Earthquake Information

Service (NEIS). C - Local magnitude (ML), EMRC. ti - Local magnitude (ML), UOFA. H - Helicorder magnitude, an approximate magnitude calculated using

an empirical relationship between magnitudes determined from Develocorder records and corresponding coda durations or aniplitudes measured on Helicorder records.

P - Local magnitude (ML), Alaska Tsunami Warning Center. S - Surf ace-wave magnitude (MS), NEIS.

5. NP, number of P arrivals used in locating earthquake.

6. NS, number of S arrivals used in locating earthquake.

7. GAP, largest azimuthal separation in degrees between stations.

8. D3, epicentral distance in kilometers to the third closest station to the epicenter.

9. RMS, root-mean-square error in seconds o f the traveltime residuals:

where Ri is the observed minus computed arrival time o f the ith arrival, Wi i s the corresponding weight of the arrival, and t h e weights are normalized so that their sum equals N, the total number of arrivals used in the solution.

10. ERH, largest horizontal deviation in kilometers from the hypocenter within the one-standard-deviation confidence ellipsoid. This quantity is a measure of the epicentral precision for an event. Values of ERH t h a t exceed 25 km are tabulated as 25 km.

Projection of ellipsoid onto horizontal plane:

11. ERZ, largest vertical deviation in kilometers from the hypocenter within the one-standard-deviation confidence ellipsoid. This quantity is a measure of the depth precision for an event. Values of ERZ that exceed 25 km are tabulated as 25 km.

Projection o f ellipsoid onto vertical plane:

12. Q, q u a l i t y of t h e hypocenter. T h i s index i s a measure of t h e p r e c i s i o n of t h e hypocenter (see s e c t i o n Ana l ys i s of Q u a l i t y ) and i s c a l c u l a t e d f r om ERH and ERZ as f o l l o w s :

- Q - EKH ERZ

13. AZ1, DIP], and % I are t h e azimuth i n degrees ( c l ockw i se f r om n o r t h ) , d i p i n degrees, and s tandard e r r o r i n k i l o m e t e r s of t h e most n e a r l y h o r i z o n t a l o f t h e t h r e e p r i n c i p a l axes o f t h e one-s tandard-dev ia t ion e r r o r e l l i p s o i d . Values o f SE1 t h a t exceed 25 km a re t a b u l a t e d as 25 km.

14. AZ2, OIP2, and SE2 are def ined as above, bu t correspond t o t h e p r i n c i p a l a x i s o f i n t e r m e d i a t e d i p .

15. A23, DIP3, and SE3 a re d e f i n e d as above, b u t correspond t o t h e most n e a r l y v e r t i c a l p r i n c i p a l ax i s .

Magnitudes and f e l t r e p o r t s l i s t e d below an event were ob ta ined f r om t h e ~ r e l i n l i n a r ~ ~ e t e r m i n a t i o n o f Ep i cen te r s o f t h e USGS N a t i o n a l Earthquake In fo rmat i o n Se rv i ce ( N E I S ) , t h e Uepartment o f Enerq-y, Mines and Resources, Canada (LkRC), or t h e N O A A - A I ~ S ~ ~ ~ s u n a m i Warning center (ATWC) , The body-wave (rnb) and surface-wave (Ms) magnitudes a re those determined b y t h e NEIS.

n u n - * a m m l m- r nl -N- r IIN m g mm - rn m m m - **.a* hNr.*f. m m m m n ~ w n - B - r n N- Q n m r t n * c I n * m N I I- m m n m S 2 0 - m m m-mmm m19-N a9 -NN- 11 Nn -dm- rn NN N 2 N-d- n e m - - -(1 v - N N m

N o w m n m b w o m NN tu LIIN-r. c h m m m w UYI PI @ w m h m ~1 IC L - m - m m m m m + C m m m - W 3 m 1 - RN m m c N N - ~ Y N r * -A N 3 m m - m ~ m m c N--* N m n m - - d m ~ en N W Q I C - - ~ m~ t m - - m w m m m - n & N + -n t - - w ~ n * t m n + m ~ m - m r m - m m m ~ w m l - m m - m~ ~m m m = 8 - w ;; m m m m N m z z + I C -mmhCs WNrumm an-N -- Ild N N m d N N N - FI N N ~ N d

- ao q a m u e u m m n M n a a u m a n a m m a m q q p u u o m u m o m m m m m n u u m u q u m W INZ-r-mm~ UI- t m m m + ~ - h + w m m q 1 y: $ m m m m - ~ g x . . . . . . ' . . . . . . " . . . . . . . . . m - @ * m m m h m v m

e . . . . . . . . . w w ~ - n r m m r n t n - 2-*.IN m m n m N r r- - tn N N ~ N w N m-mm t m m m ~ NIO-NN I- - N N N d N

Yf"? N w n w . . . . . t n - m m n n r - n .- -- mrcmm- - w m r Y97N? Y ??? - - & P I - C C C

n b ~ n s m N N m -

* m m w m . . . . . ? ??YT d In NYI m a l m m m rr-• N a n f - 2 Q - - + t 2::: : .. 2: , , ,,,,

m y " ** m n m - m -

33 E2 G

ORIGIN T r n E CAT n Loac v 1986 HR MN SEC DE6 W I N DEC HIM

JUL 4 22 5 13 .7 59 5 1 . 0 141 14 .6

SOUTHERN ALASKA EARTHQUAKES, JULY - SEPTEMBER 1980 DEPTH )(A6 NP NS CAP 03 RHS ERH E R Z O A Z I D I P I S E l A Z 2 D I P 2 SEZ A 2 3 D l P 3 SE3

KH DEG Kt4 SEC KH KM DE6 DEG K M DEG OE6 KU DEC DEG KH 1 3 . 4 3.1 16 4 161 91 0 . 4 8 2 . 7 3.4 0 181 9 0 . 0 6 28 2 . 3 207 6 8 3 .7

3 . 6 ML EMRC 21.6 2 . 7 17 3 119 46 0 . 5 1 4 2 .4 A 1 2 1.4 275 I 6 0 .6 99 7 1 2 . 5 18 .5 1 . 8 7 2 162 82 0 . 1 s 5.B 3 . 0 8 88 27 1 . 0 193 27 5 .5 321 Sb 2 . 0 12.2 2 . 6 15 6 102 73 0 . 6 1 2 . 7 2 . 8 6 98 2 6 . 6 189 35 3 . 2 5 55 8 . 9

3 . 8 HL EURC I . A 4 3 172 127 0 . 2 1 7 . 2 2 . 6 C 137 2 7 . 2 106 2 1 8 .8 291 66 2.8

2.7 ML EMRC

7 . 5 2 . 1 13 7 84 7 1 0 . 5 7 2 .0 2 . 3 A 9 3 2 1 8 . 6 3 4 9 3 3 l . 8 2 1 8 4 9 2 . 9 2 .0 HL EWRC

5 8 . 6 3 . 2 11 5 143 183 0.10 3 . 1 2 5 , 0 D 3 8 1 1 . 6 3 0 0 1 3 . 1 I65 09 25.8 6 . 8 1.5 6 2 157 8 0 8 - 1 7 4 . 5 3 . 1 0 106 9 4 . 5 9 1 3 1 8 . 9 2 9 0 58 3.5

1 7 . 5 1.4A 1 3 182 67 8 . 2 8 13.8 8 . 4 D 3 6 13.1 94 18 2 . 6 242 7 8 8.5 4 1 . 0 3.5 19 1 117 47 B.25 2 . 8 2 . 5 0 281 1 1 .0 1 9 8 29 1.7 13 61 2 . 7

FELT AT PALMER

2.8 HL EWC 8.5 2.7 15 6 148 162 1 . 2 1 3.5 4 . 5 B 106 6 1 . 5 197 6 3 . 5 332 81 4 . 8

2.3 ML EMRC

ORIGIN TIME 1 9 8 8 HR MU SEC

JYL 8 12 17 12 .2 8 12 43 15 .7 8 15 59 4 . 2 8 16 2 8 37.8 0 28 1 12 .4

LAT N LONG U DEG WIN OE6 M I N 6 8 3 2 . 1 147 2 1 . 8 6 0 31.6 147 1 6 . 1 6 1 4 3 . 6 146 41 .2 6 1 4 9 . 1 147 5 4 . 3 6 1 3 4 . 1 149 5 0 . 8

SOUTHERN ALASKA EARTHOUAKES, JULY - SEP DEPTH MAG UP US GAP 03 RHS ERH

KM DEG KM SEC KM

TEMBER 1 9 8 8 ERZ U A21 D I P 1

KM D E 6 OEG 2 . 2 A 2 7 0 5 1 . 6 A 268 7 2 . 9 B 24 I 7 5 . 1 C 86 13 2 . 4 A 288 1

S E I A22 D I P 2 KH DEG OEC

0 . 7 179 18 8 . 7 L73 37 1.7 286 25 1.2 349 28 1.0 198 I 0

A23 D IP3 SE3 DEG DEE Kt4

15 71 2 .3 7 52 1 .8

145 59 3 . 3 198 59 5 . 8

24 8 0 2 . 4

22 .4 1 .B 3 3 219 1 1 s 8 . 3 3 1 8 . 8 1 5 . 2 1 .3 7 5 172 58 6 . 4 6 1 4 . 8

1 8 6 . 6 3 .0 23 4 188 147 8 . 6 2 2 . 5 10 .1 2.6 7 6 255 158 1.55 1 0 . 6

2 . 4 WL EMRC 5 8 . 7 2 . 1 11 1 0 94 66 8 . 2 9 1 . 8

11.3 2 . 8 16 9 1 6 8 6 3 8 . 5 2 2 . 0 31 .0 2 . 1 18 18 167 84 0 . 5 2 2 . 1

9 . 9 2 . 3 7 6 126 145 1 .26 8 . 8 2 . 1 ML EMRC

26 .6 3 . 7 25 1 101 122 0 . 3 2 3 . 0 53 2 6 . 5 145 7 . 1 4 .1 ML ATWC

6 0 1 3 . 2 148 59 .4

EMRC 2 . 3 11 5 7 1 43 8 .34 1 . 9 9 4 8 6 33 0 .44

1 .5 8 2 117 27 5 . 1 9 1 .4 7 1 148 47 0 . 1 8 2.1 17 8 98 18 8 . 6 6 EMRC 1.4 7 2 102 18 8 . 3 7 1 . 6 9 3 155 56 8 . 6 5

SOUTHERU ALASKA EARTHQUAKES, JULY - SEPTEMBER 1 9 8 6 ORICIU TIME LAT U LONG W DEPTH MA6 NP NS GAP 03 RMS ERH ERZ P A21 D I P 1 S E l A22 D I P 2

1381 HR UN SEC DEE MIN DEG MIN KM DEG KH SEC KH Kt4 D E 6 DEG KM DEG DEG J U L l I 1 3 2 5 4 5 . 3 5 9 5 7 . 0 1 4 8 5 7 . 6 8 . 9 1.5 8 5 123 35 0 . 7 0 1 . 2 l . 5 A 104 1 8 0 .5 12 14

11 14 2 0 10 .2 6 8 2 6 . 5 148 46 .4 0 . 5 1.3A 5 2 183 100 0 . 1 6 4 . 6 13 .8 D 261 8 2.3 316 0 1 1 1 7 P 5 6 . 3 6 6 1 7 . 9 1 4 0 1 6 . 0 11.2 2 . 5 17 6 80 60 0 . 7 9 1 . 9 2 . 9 8 9 1 1 8 . 9 0 28

SE2 A23 D I P 3 KM DE6 DEG

1.2 229 73 3 . 5 0 5 5 1 . 3 183 62

0 . 6 331 87

1 . 0 119 8 8

2 . 6 HL EMRC 1 1 2 0 2 0 5 8 . 3 6 0 3 7 . 0 1 4 1 4 2 . 7 9 . 3 2 . 1 16 8 6 1 65 8 . 8 5 0 . 8 2 . 0 A 2 2 3 1 8 . 8 133. 3

2 . 2 Ht EMRC 11 22 34 42 .2 6 8 1 3 . 9 141 5B.5 0 . 1 0 . 7 6 4 132 44 8 . 1 7 1 . 9 5 . 8 C 2 1 1 . 9 272 2

I 2 13 4 42 .8 6 0 9 . 9 136 44 .8 4.2 2 . 2 5 5 181 144 0 . 4 6 5 . 6 6 . 0 C 8 1 3 1 .4 327 17 2 . 2 ML EMRC

12 I 6 26 21 .6 6 1 4 1 . 0 146 13 .8 27 .2 2 . 0 16 5 98 62 8 . 6 5 1 . 2 1 . 3 A 2 7 2 24 S.9 I 6 7 31 I 2 2 8 33 49.6 61 2 7 . 1 146 3 3 . 5 1 4 . 0 2 .B 14 6 149 44 0 . 4 2 1 . 3 2 . 0 A 16 1 1 1.2 261 2 1 12 22 2 0 6.5 63 23 .4 147 12.8 42.6 3 .0 22 3 146 186 1 . 5 6 4 . 6 14 .6 D 174 3 1.6 265 14

3.1 ML A T W : 13 1 4 6 36.2 6 0 15.4 141 14 .5 14.1 1.2 4 3 197 1 8 6 0 .11 5.4 6 .4 C 107 2 l . B 15 37

I 3 1 63 38 .5 6 0 2 6 . 8 1 4 0 26 .4 1 .4 1 . 3 6 2 199 71 0 . 0 6 11 .6 18.9 D 9 1 5 1 . 6 I 8 4 3 8 13 2 6 3 7 . 2 6 8 1 7 . 9 145 6 . 3 2 9 . 3 2 . 2 2 8 4 132 47 0 . 5 8 1 . 4 1.3 A 1 1 8 19 8 . 7 2 t 4 35 13 3 4 9 2 4 . 1 6 0 4 6 . 9 1 1 3 4 4 . 2 23 .6 1 . 6 8 4 76 74 0 . 6 8 1 .9 5 . 9 C 356 2 1 . 0 87 11 13 4 54 49 .5 6 8 18 .7 141 5 . 8 13 .9 1 . 2 7 3 143 85 8 . M 9 . 5 6 . 9 C 94 25 1 . 0 214 35 13 5 2 6 2 1 . 5 5 9 5 9 . 1 1 5 2 4 3 . 2 95 .3 3 .7 2 4 2 68 86 1 . 5 9 2 . 0 2 . 4 A 8 1 2 2 . B 162 13

3 . 3 HL AWC

13 0 4 1 .7 6 1 3 3 . 0 1 4 6 2 4 . 3 3 5 . 0 2 .0 18 4 85 55 0 . 6 2 1.B 1 . 6 A 3 5 0 6 0 .9 261 2 1 13 11 1 5 4 4 . 7 6 2 2 7 . 1 1 4 8 5 1 . 8 31 .6 2 . 4 12 4 I 2 3 182 0 . 4 9 2 . 3 3 . 1 8 346 17 2 . 0 84 25 1 3 1 1 1 0 3 6 . 0 5 8 3 3 . 8 1 4 4 3 6 . 0 43 .6 3 .0 11 4 259 209 N . 4 0 5 . 8 2 4 . 9 D 275 3 3 . 1 184 4 I 3 17 24 3 2 . 1 6 0 4 . 3 141 21 .2 2 1 . 1 1 . 1 5 2 178 38 0 . 1 5 6 . 9 9 . 9 C 269 I 3 1 . 5 171 31 13 18 16 17.9 59 12.6 136 5 8 . 8 0.0 2 . 7 8 3 126 I 7 1 1 .54 5.6 6 . 6 C 3 t a 19 3 . 1 6I 24

2.6 ML EMRC

3 . 4 ML ATUC 15 4 22 10.6 6 1 19.0 1 5 8 4 i . 0 4 5 . 7 2 .1 14 7 7 1 76 0 . 3 9 1 . 9 2 . 3 A 89 13 0 . 9 108 33

ORIGIN TIME L A 1 II LONG W 191s HR UN SEC DEG HIU DEG WIN

JUL 14 7 49 37 .0 6 0 49 .4 146 5 1 . 0 16 9 22 57 .5 63 5 9 . 8 110 3 . 5 16 I # 23 3 2 . 2 6 0 38 .6 158 2 5 . a 15 1E 48 49 .6 6 0 11 .3 141 3 . 9 I S 11 26 3 1 . 3 6 0 6 . 9 141 6 . 6

SOUTHERN DEPTH MAG

Y U

ALASKA EARTHOUAKES. JULY - SEPTEMBER NP MS GAP D3 I H S ERH ERZ P

DEG KH SEC KH KM 3 2 15 5% 45 8 . 5 7 0 . 7 1 .2 A 17 5 149 274 0 . 7 9 9 .9 24.4 D 12 6 123 117 0 . 1 9 2 . 6 8 . 6 C 11 6 139 46 g.14 4 . 3 3 . 3 B

7 4 126 47 8 . 9 3 6 . 7 3 . 2 C

1 9 8 8 A21 D I P 1 DEG OEC

SEl M

0 . 7 9 .9 0 . 9 1.0 6 . 0

A22 DIP2 OEG DEC 2 6 1 16 190 12 156 4 183 35

94 22

AZ3 DEG D I P 3 DEC

7 1 7 4 19 78 23 74 I 9 54

387 64

2 . 6 1.6 15 1 1 114 29 0 . 8 8 0 . 9 1 . 3 A 18 11 0 . 9 111 14 8.6 2 5 1 72 9 .7 1.7 15 12 151 5 0 0 . 7 7 1 . 3 2 . 0 A 316 15 1 . 7 52 22 1 . 0 194 63

1 6 . 3 4 . 4 24 4 1 3 8 160 1 .43 3.8 1 2 . 9 0 345 5 2 . 4 01 7 1 .9 2 2 2 8 8 4 . 7 HL EMRC

11.7 2 . 5 2 5 12 73 44 8 .81 8 . 8 1 . 2 A 224 9 8 . 8 132 1E 0 . 7 355 76 3 0 . 0 3 .5 15 6 264 217 1 .22 13 .2 2 5 . 9 0 0 1 6 2 . 8 321 17 7.2 165 55

3 . 3 ML EMRC

- - - . . - - . . . . - 1 0 . 2 2 . 5 14 1 8 221 189 3 . 9 2 2 .1 2 . 8 B 181 2 1.B 273 36 1 . 0 80 5 1

2 . 0 2 .7 29 1 2 208 143 8 . 0 1 3 . 0 2 .1 8 206 23 4 . 1 314 37 2 . 1 9 1 4 4 1 . 9 1 .7 15 9 138 48 0 . 7 9 1 . 6 l . 0 A 112 1 0 .6 22 38 1 . 1 203 5 2 2 .3 2 . 1 26 I 4 7 0 32 8 . 0 4 1 . 1 l . 2 A 1H8 11 0 .5 0 39 8 . 8 211 4 9

2.6 ML EMRC

6 . 3 1.0 17 14 72 4 0 1 .05 1 . 5 L . 6 A 203 0 0 . 6 12 41 8 . 9 193 49 1.0 HL EMRC 1 4 3 . 1 4 .6 38 3 1 3 0 180 8 . 5 3 2 . 3 7 . 5 C 3 4 8 B 2 . 3 81 3 1.9 258 86 17 14 45 54 .1 63 9 . 2 I 5 0 35 .4

3 .4 ML ATUC 17 15 1B 3 4 . 3 59 56.8 141 1 . 9 I 7 I 6 3 2 20.3 6 8 31.2 142 5 3 . 6 17 16 46 33.2 6 1 4 9 . 7 149 48 .5

SOUTHERN DEPTH MAC

KM 3 . 7 8.8A 3.9 1.7 8 . 3 1.4 3.5 1 .9

ALASKA NP MS

EARTHQUAKES, JUL GAP 03 RMS DEG K H SEC 160 74 3.44 145 42 8.83

.Y - SEP ERN Kn

3.8 1. I 1.5 3.8 0 . 9

TEMSER 1980 ERZ P A21 O l P l

Kt4 DEG DEG A22 D I P 2 DEG OEG 95 I4

SE2 A23 D I P 3 KM DEG OE6

3.5 235 72

0 . 9 2 . 8 4 2 354 145 8.48 24.9 4.3 1.9 13 7 79 6 0 8 . 8 7 1.4

2.0 HL EMRC 9.2 1 . 6 8 2 15% 77 5.30 12.6 8 . 2 8.9 4 3 245 180 8.20 7.7 1.9 1.6 12 3 90 59 9.72 2.5

1.2 1.3 1.1 3 . 5 EHRC

1.3A 3.8 EMRC 1.7

1.5 2.5 EMRC 1.5 1.4 1.1

3.1 1.4 1.1 3.3 EMRC 3.4 EHRC

N W & * m g z N W P - N N q a w m

NQ-I.~ m c m ~ w -4-- - wm--m u RIUN m ~ q -tn m m ~ m - m-mm- n m m m - a m - m w a * w r - n ~ m m N m m h h f *& w N m t m m m -N N N N ~ - m - - N - m w - m m ~ N m N m

~ - u P * - N @ ( D N W C m t m z*= -Nmn

m m a c o 4 4 4 0 - o n m m m m u m u m m a m c a o m a q m qunac 4umcc -mm*- ra"v?Y I.??" "I-" m --be* . , . * a

yT""-**N LO-*"* . . - . , . . . . . . . . m r - - m - - ~ n * L O ~ N N m w ~ - * rn -t-- a t * -m N O ~ ~ N ANN--

N C - w o m m m u u W m N X I N f ? ? S P Y . Y Y **mmm L

~ m ~ b m m n I n w + m m - r m m l w m m m m m ~ t mmm 22 L O - m t m h m m - Q m - - m ~ ++-I- m a m * r ~ m - m ~ t m - m r N N ~ . . . . . . . . , . . . . . n ~ y w m r u m y y

b r r r m r e e r r mar- 4 i 4 i G i i i i G i i i d JJ ddrdJ ddiqw

m * m m N * T N N ~ t m m b - m m w + * n m r ~ n ~ m o n o m m r b m m r Q - - m rl c1 - d r r r -

a a u 7"-Nh m 7 l m N y y y m 3 w - q m 5 n - N m m ?Y"T YY"? ? ? ? ' E L . . . . . . , * . . . . . . . . NrrN" " I N d d -,",--YN N - N N - ,., N d N N 4 W . r "- c-*-- NNNNN

NI-ODI YIN YIN

m-mm- n I n N * m

a m z = z

m m n m m NNNNN

UI m w m - r N---

N m I B N N N

N Nnnn N NNNN

* h m & N - - - N N

NNNNN N N N W N

* I I nN t - d NNNN N NNNN N

--NNN NNNNN

mmm mm NNN NN

n n m n n NNNNN

SOUTHERU ALASKA EARTHQUAKES, JULY - SEPTEMBER 1905 Olt6IM T I M CAT N LORG W DEPTH MAG NP PIS GAP 03 RMS ERH ERZ 0 A21 D I P 1 SEl A22 D I P 2

198s HR MM S E C DEG M I K OEG MIN KM DE6 KM SEC KM KH DEG DEG KH DEG DEG JUL 23 15 37 2 5 . 5 6 5 12 .9 140 5 1 . 9 19 .8 2 . 6 2 1 0 01 36 8 . 5 4 1 . 7 1 . 8 A 284 8 0 . 8 21 41

7 - E ML FMRC

SE2 AZ3 D I P 3 KM OEG DEC

1 . 1 165 48

2.2 ML EMRC 2 4 2 44 3 6 . 6 59 8 . 2 14B 43.9 39.8 3 .0 2 8 4 236 155 8 . 3 5 7 . 5 6 . 5 C 180 2 7 .5 96 11 2 4 5 34 3 6 . 3 61 10.7 149 38.0 35.6 2 . 2 t 5 5 68 43 8 . 4 8 1 . 1 1 .4 A 132 4 1 . 0 223 6 24 6 5 9 4 1 . 6 6 5 0 . 4 1 3 6 4 4 . 7 2 3 . 8 2 . 7 1 8 6 104 142 1 .22 3 . 9 9 . 4 C 6 1 3 1 .4 332 14

2.7 ML EMRC

- - - . , - -. . . . - 24 9 5 8 3 9 . 8 6 1 5 0 . 8 1 4 9 3 1 . 7 3 4 . 0 2 . 3 17 6 163 63 8 . 3 7 1 . 8 t . 5 A 09 2 l . O 1 0 0 2 2 24 I 8 1 8 4 7 . 3 59 19 .7 137 3 1 . 7 1 . 9 2 . 6 1 2 5 127 127 5 . 9 0 4.9 6 .7 C 335 17 4 . 1 01 2 8

2 . 6 ML EHRC 24 10 23 5 7 . 0 59 1 2 . 5 138 5.8 1 8 . 1 1 .9 4 2 348 121 0 . 5 5 2 4 . 2 7 .6 D 209 15 2 5 . 8 114 2B

2 1 18 55 56.6 6 0 2 6 . 1 147 4 8 . 1 23 .7 2 . 8 23 7 79 64 0 . 4 1 1 . 6 1.9 A 275 13 S.7 7 28 2 4 1 5 3 9 1 5 . 7 6 8 1 1 . 6 1 4 8 5 0 . 9 1 3 . 9 2 . 3 15 6 83 6 1 5 . 2 3 1 . 9 2 , I A 85 1 8 . 7 3 5 4 4 1

2.4 ML EHRC 2 4 1 9 1 5 7 . 1 6 1 3 4 . 4 152 4 . 6 116.3 4 . 8 2 5 2 86 72 5 . 4 4 1 . 9 3 . 8 B 0 1 3 1 . 3 162 4

2 . 1 I11 A W - . - . . - . . . - - 2 1 19 1 8 38 .2 6 0 59.7 151 9.4 14 .9 1 .8 1 2 8 58 57 5 . 5 8 8 .8 2.B A 315 B B . 8 45 2 25 5 3 3 3 6 . 5 5 9 5 7 . 4 1 4 1 1 1 . 3 7 . 2 2 . 2 15 7 86 2 6 5 . 5 1 1 . 1 l . 0 A 199 2 1 .1 189 14

2 . 5 ML EHRC

4 . 1 1 .4 9 3 87 26 0 . 3 1 1 . 5 6 .9 2 . 3 9 5 72 63 0 . 2 3 1 .4

2 . 4 ML EHRC 43 .4 1.2A 1 0 6 131 5 1 5 . 4 1 1 . 9 29 .9 3.1 6 3 273 254 8 . 0 7 17 .5

2 . 6 ML EMRC 5.6 3 . 2 2 1 4 7 7 26 8 . 5 3 1.0

3 . 7 HL EMRC

4 . 6 0 . 9 5 2 138 20 8 . 1 3 2 . 7 6 . 3 2 . 1 17 7 53 51 8 . 3 3 1.0

2.3 HL EMRC 8 . 4 1 . 4 6 1 248 63 5 . 8 6 7 . 5

1 3 . 3 1 . 5 7 4 163 63 0 . 1 1 3 . 3

ORIGIN TIME 198. HR 1IH SEC

JUL 26 2 22 4 5 . 2 2 6 3 5 1 8.2 26 5 22 8 .1 26 6 56 9 .0 2 6 7 18 15 .8

LAT U DEG M l U 6 0 15 .3 6 8 14 .9 6 0 3 8 . 1 6 1 5 0 . 3 6 0 17.3

LON6 V DEE H I M

148 52 .4 140 50. L 143 3 2 . 7 147 42 .7 141 9 . 5

SOUTHERN DEPTH MA6

KH 16 .6 1 . 2 15 .4 1 . 7 14 .4 1 . 5 2 8 . 0 2 . 1

0 . 9 8 . 9

EARTHQUAKES, JULY - SEPTEMBER GAP 03 RMS ERH ERZ a DEG KH SEC KH Kt4 2B9 38 8 - 1 8 3 . 1 2 . 9 B 168 37 0 . 3 2 2 . 1 2 . 1 A 125 187 0 . 5 0 2 . 8 5.8 C 169 02 8 . 7 3 1 . 5 1 . 8 A 2H9 54 8 . 2 0 3 . 2 4 . 2 6

1 9 0 0 A21 D IP1 DEE DEG

06 9 276 6 163 5

01 0

S E l KM

8 . 9 0 . 7 1 . 6 8 . 6 8 . 9

A22 DIP2 DEG DEG 185 43

12 43 8 1 2 8

34-3 27 3 4 9 33

A13 D IP3 DEC DE6 347 46 1 8 8 46 267 68 186 61 192 55

26 9 15 1 0 . 0 68 16.4 140 47.8 13.8 1 . 6 11 5 164 4B 8 . 2 7 2 . 5 2 . 4 B 91 7 8 . 6 189 42 3 . 0 353 47 1.0 2 6 11 52 2 3 . 3 6 8 10.8 141 13.3 4 .9 8 . 7 5 4 285 40 0 . 1 7 2 . 6 3 . 0 6 96 4 8 3 38 1.7 191 52 3.6 2 6 1 2 2 1 1 . 6 63 5.1 1 4 9 2 8 . 5 8 8 . 6 4 . 4 36 2 113 167 8 . 6 9 2 . 1 9 . 9 C 261 1 1 . 6 335 2 1 . 9 142 74 9.5

3 . 6 YL ATVC -.- 2 6 1 2 2 4 2 3 . 1 6 1 3 8 . 1 1 4 9 5 2 . 2 3 6 . 2 1 . 6 7 5 111 46 8 . 3 9 1 . 8 1 . 2 A 2 0 6 2 3 1 . 9 183 27 0 . 7 3 3 0 5 3 1 .2 2 6 1 3 1 6 5 2 . 6 6 1 4 . 0 1 4 7 3 1 . 5 8 . 5 3.8 4 0 4 38 63 0 . 7 7 0 . 9 1 . 0 A 175 14 0 . 8 272 2 7 8 . 5 6 0 59 1.1

3.4 ML ATVC

26 15 1 4 45.5 6 1 15 .3 1 4 8 49.3 1 4 . 1 1 . 3 9 6 161 30 8 . 2 9 3 . 8 3.4 8 293 I # B.9 31 39 1 .4 191 1 9 4.3 2 6 I S 45 4 1 . 9 50 5 7 . 1 136 43 .2 2 5 . 4 2 . 0 6 4 278 I 9 9 8 . 7 5 15 .6 2 1 . 6 U E l 6 2 . 6 3 3 8 3 1 6 . 2 180 53 25.0

2 . 8 ML EMRC 2 6 1 7 2 8 1 8 . 9 6 8 1 3 . 3 141 2 .H 13 .9 1 . 5 5 4 199 59 S . 1 4 3 .7 2 . 4 B 9 1 7 1 . 1 184 25 4 . 8 346 64 1.9 2 6 2 B 1 9 1 5 . 5 5 9 5 7 . 4 141 7 . 7 2 . 9 1 . 1 8 4 99 29 8 . 1 5 1.1 2 . 7 6 96 7 1 .1 4 9 8 .6 223 78 2 . 7 2 6 2 B 2 2 5 1 . 9 6 1 4 6 . 5 149 5 . 4 12 .2 1.B 9 6 164 53 8 . 5 0 1 .5 2 . 1 A 3 5 8 2 1 1 . 2 261 26 8 . 8 128 58 2 . 4

3.4 ML ATVC 63 39 .4 152 45 .9 78 .4

3.5 ML ATVC 6 8 18.3 141 1 4 . 1 9 . 5

1.6 12 6 157 4 1 8 . 1 7 1.9 2 . 1 17 4 88 26 8 . 2 8 1.1 EMRC 2 . 1 18 5 9 0 26 8 . 4 0 1.1 EMRC 8 . 9 4 2 127 26 8 . 0 6 2 . 4 1 . 2 8 3 85 2 5 8 . 2 7 1 . 3

27 2 8 69 19 .8 6 5 56.3 147 38.B 6 . 8 1 . 9 2 3 5 08 52 0 . 6 4 H.3 1.2 A 266 I 3 8 . 6 173 13 1 . 9 4 0 71 1 . 3 2 7 2 1 5 2 5 . 1 5 9 4 5 . 6 1 3 8 5 9 . 9 15.B 1 . 5 4 3 228 8 1 S .23 10 .3 7 . 7 C 317 11 1 . 2 261 35 1B.B 62 42 3.0 20 1 1 5 3 . 5 5 3 5 7 . 5 1 4 1 7 . g 2 .4 1 . 7 6 4 166 138 8 . 3 5 3 .1 3 - 3 6 134 26 l . L 241 3 1 2 . 3 12 47 4 . 1 20 1 1 5 3 4 . 4 5 9 5 9 . 6 141 7 .7 7 . 9 3 . 8 2 0 4 15B 51 0 . 4 8 1 . 0 1 . 3 A 278 3 8 .8 8 15 1 . 9 169 75 1.2

3 .8 UL ATVC 3 .2 ML EHRC 20 2 9 58 .1 59 59 .1 141 8 - 2 5 . 3 1 . 8 12 3 151 5 1 8 . 2 7 2 . 2 2 . E A 100 1 8 8 . 8 9 1 1 2 . 7 209 47 1.3

2 . 1 ML EMRC 28 2 2 6 4 7 . 4 5 9 5 6 . 0 141 9 . 2 2 .6 1 . 5 5 4 168 05 0 . 3 7 5 . 4 6 . 8 C 221 11 2.4 124 31 1 . 0 328 57 9.5 28 2 29 2 5 . 1 6 8 1 2 . 5 148 5 2 . 3 1 9 . 8 3 . 1 25 3 63 67 0 . 6 2 1 . 8 1 . 9 A 289 8 l . O 27 43 1 .3 191 46 2.3

3.1 HL ATVC 3 . 3 ML EMRC 28 4 0 4 2 . S 6 1 2 6 . 4 1 4 9 5 2 . 3 4 6 . 1 2 .1 15 6 119 47 0 . 3 9 1 . 1 2 . 2 A 268 2 8 . 7 190 1 8 1.8 2 1 6 0 2 . 3 28 4 19 4 8 . 0 59 59 .4 141 8 . 8 6 . 7 1 . 7 13 3 80 26 0 . 3 8 1 . 2 1 . 3 A 194 2 1.1 184 24 0.6 2B8 66 1.4

OR1611 198. HR MU

JUL 2 8 18 53 28 23 26 29 2 26

TIME SEC

3 8 . 3 2 3 . 7 22 .3

41.1

5 9 . 9

5 8 . 3 1 1 . 0

55.6 23.3 16.4

LAT N DEC HIM 6 1 3 4 . 9 6# 12 .6 63 26 .8

3 . 6 0 5 3 . 1

6 8 9 . 8

6 s 3 . 7 6 0 l l . U

59 6 0 . U 59 5 9 . 7 6 1 4 8 . 0

LOW6 W DEC urn

150 0 . 1 140 4 3 . 7 153 15 .6

, 6 ML ATVC 138 3 3 . 1

SOU DEPTH

KH 4 3 . 1 17 .1 5 1 . 7

3 . 2 1 . 8 ML

7 . 1

I 1 .8 14 .5

2.4 Ut 2 . 9 3.6

29 .6

THERM MA6

2.1 2 . 3 4 . 1

1.8A EMRC 1 . 3

1.5 2.2 EMRC 1.7 1.3 2 . 1

ALASKA EARTHQUAKES. JULY - SEPTEMBER NP HS GAP 03 RMS ERH ERZ O

DE6 K M SEC KM KM 17 8 181 44 H . 3 9 I . 2 2 . 8 A 15 5 159 67 0 . 5 5 2 . 8 1 . 8 A 18 1 189 256 8 . 4 8 7 .3 25 .8 0

1989 A2 1 DEG 183 298 189

288

278

138 388

11 1 13

102

D IP1 DEG

1 7 2

26

5

6 16

16 3 1 I 1

S E I A22 D I P 2 KM DEG DEG

8 . 7 193 15 8 . 8 194 38 2 . 2 199 2

0 . 9 312 3 7

D I P 3 DEG

75 51 87

42

48

6 8 40

5 1 4 s 46

3 8 1 2 4 9 2 4 . 6 68 4 . 2 1 4 8 3 6 . 7 7.6 1 .9 1 3 6 113 4 1 8 . 5 2 1 .4 1 . 4 A 277 8 0 . 7 7 44 1 .1 187 46 1.6 2 . 4 ML EHRC

3 s 2 1 48 5 7 . 8 6 8 16.6 148 40.9 1 7 . 3 1 .6 9 5 163 46 8 . 6 4 2 . 1 2 .3 A 282 0 0 . 7 1E 4 8 1 .1 183 49 2 . 3 31 3 3 7 5 7 . 5 6 0 3 .7 1 4 8 3 0 . 7 10 .4 1 . 2 7 3 157 8 2 8 . 3 9 4 . 2 3 . 8 8 287 8 1 . 8 17 32 4 .9 197 50 1 . 8 31 5 13 42 .7 6 8 21 .7 I 4 8 40.4 8 . 6 1 . 7 13 7 75 5 0 8 . 6 3 1 . 2 1;5 A 112 1 B.6 2 1 38 1 .1 204 6B 1.6

1 . 8 HL EHRC 3 1 5 4 3 3 7 . 6 6 8 1 5 . 5 I 4 1 9 . 8 9 . 7 1 . 0 6 4 147 5 3 8 . 1 8 2 .5 3 - 8 0 277 B 1 . 0 7 29 1.5 187 61 4 .3

3 1 7 54 3 5 . 7 6 1 3 2 . 8 149 5 0 . 6 4 1 . 2 2.2 22 7 7 9 38 8 . 5 1 1 .1 2 . 3 A 118 4 8 . 7 2 0 8 5 1.1 341 84 2 .3 3 1 8 16 3 3 . 7 6 0 28 .0 148 3 9 . 3 2 . 7 1 .7 I2 6 176 7 1 0 . 9 6 1 .5 1.5 A 292 7 8 . 7 29 42 1 . 1 194 47 1.8 3 1 9 5 3 3 9 . 8 6 1 5 3 . 4 1 4 9 4 7 . 4 4 8 . 5 2.1 17 8 188 69 8 . 4 5 1 .7 2 . 1 A 291 8 8 . E 22 2 8 1.6 281 7 8 2 .2 31 11 59 23.4 59 23.3 152 13 .9 7 5 . 8 3 .2 28 6 131 94 S.56 1 . 9 2 . 9 0 347 # 1 .4 81 I0 1 . 8 257 79 2 .9

3 . 7 MB 3 . 0 ML ATVC 3 1 17 39 9 . 1 6 0 3 3 . 3 141 44 .7 9.9 1 . 7 13 7 151 63 8.65 f l .9 2 . 6 B 190 1 0 . 9 1#0 6 6.7 2E9 0 4 2 .7

3 .2 Mi ATUC 1 5 45 1 2 . 1 62 3 7 . 2 149 4 . 8 12 .8 2 . 5 14 6 132 116 8 - 5 6 3 . 1 4.2 0 16 18 2 . 3 277 27 1.3 136 57 4 . 8

2 . 0 ML EMRC 1 1 1 5 8 2 8 . 8 5 9 5 9 . 3 141 11 .6 8 . 4 8 . 9 5 1 113 23 8 . 2 8 3 . 2 7 . 9 C 1B2 9 2 . 8 I 9 4 11 2 . 8 334 76 8 .1

1 12 22 5 3 . 4 59 59 .5 141 1 4 . 9 1 . 9 1 .4 8 2 132 2 1 8.61 1 . 8 3.g B 101 1 8 1 . 7 88 17 1 .1 3 8 8 7U 3.2 1 1 4 3 9 1 5 . 5 6 8 1 2 . 1 153 13 .1 131.7 3 . 9 14 4 178 123 0 . 1 4 3 . 2 4 . 8 6 297 24 2 . 9 8 1 37 3.8 194 25 2.6

3 . 4 MC ATUC 1 17 48 49 .2 61 48 .7 149 4 8 . 1 42 .0 2 . 4 17 4 I 4 3 5 8 8 . 5 2 1 .4 2.4 A 189 3 1.1 199 3 1.4 334 86 2.4 1 2 3 7 1 6 . 5 5 9 3 7 . 5 1 4 8 4 1 . 7 33 .4 4 . 8 23 B 184 1%3 1.85 3 . 7 2 . 4 B 3 2 2 1.4 182 I 8 3 . 0 356 72 2 . 3

5 . 4 MB 5 .1 MS 5 . 7 MI. ATWC fELT I I V ) I W THE SEWARD AREA. ( 1 1 1 ) I # PARTS OF ANCHORAGE AND NORTH TO MATAUUSKA VALLEY

2 0 4 8 3 3 . 0 6 8 5 2 . 2 1 1 8 1 8 . 1 3 8 . 1 2.2 10 5 60 6 1 8 . 2 9 1 .1 1 . 6 A 261 6 8 . 9 165 7 1 . 1 29 79 1 . 6

SOUTHERN ALASKA EARTHQUAKES, J U L Y - SEPTEMBER 1983 ORICIW T I M L A T W LOUG V DEPTH HA6 HP US GAP 03 RMS ERH ERZ 0 A21 D I P 1 SEl A22 D I P 2 SE2 A13 D IP3 SE3

19BS HR HN SEC DEE WIN DEC HIM KH DE6 KM SEC KM KM DE6 DEC KM DEG DEG KM DEG DEE KM AUC 2 2 1 3 3 2 . 4 6 8 4 . 2 1 3 9 3 3 . 8 23 .8 1 .5 5 2 2ff4 46 0 . 4 6 7 . 5 3 . 0 C 216 4 7.5 124 16 1 . 1 3 2 0 73 3 . 8

2 4 1 2 1 9 . 3 6 8 1 5 . 2 141 7 . 2 5 . 2 1 . 3 8 4 147 5 1 0 . 1 3 2 . 5 3 . 5 0 85 6 B.O 352 29 l . O 106 6 0 4 . 8 2 7 36 9 . 9 59 3 9 . 8 137 3 . 8 5 . 2 2 . 5 4 3 355 205 0 . 4 4 2 5 . 0 1 9 . 2 D 227 4 2 5 . 8 133 4 2 2S.B 3 2 1 4B 12 .4

2 . 1 ML EHRC

6 0 1.6 149 16 .7 3 .1 HL A W C

6 1 43.9 146 14.7

43 .9 2 . 3 16 0 . 4 1 . 3 7

1 5 . 8 3 . 9 1s 3.8 HL EHRC

44 .2 2 . 1 1 3 18 .5 2 . 3 6

2 . 2 ML EMRC

14 .4 8 . 6 3 8 . 2 l . 2 A 5 9 . 0 1 .3 IB

29 .3 1 . 9 2 3 17.8 2 . 3 9

1 . 8 ML EMRC

1 . 3 7 1 138 9 1 8 . 2 3 1 6 . 5 4 . 7 0 4 . 1 2H 1 69 68 0 . 3 2 2 . 1 4 .3 8

F E L T (I111 Ill EAGLE RIVERfCHUGIAK 1.3A 1s 9 99 63 0 . 2 7 1 . 9 2 . 1 A

- - - . . - - . . . . - 4 2 2 1 0 3 4 . 9 6 8 1 -1 1 4 1 4 2 . 2 0 . 4 2 . 3 15 7 146 6B B.34 2 . 8 2 . 8 A 269 9 0 .6 7 43 2 . 4 173 46 1.5

2 . 5 HL EMRC

4 2 2 1 3 5 0 . 6 5 9 5 7 . 3 1 4 0 4 0 . 7 0 . 5 1 . 4 7 5 1 5 9 5 0 0 . 2 4 3.4 4 . 6 B 83 1 8 . 7 1 7 3 3 3 . 4 3 3 5 8 7 4 . 6

2 . 4 HL EMRC

Z U m h - t * n m m m - w N - t rzLmiLd . . * M y"" 1 P-f:? mUNO!m- .> . . . -ON?: . . . YTfT? W h

0 -NN -mm-m r n , ~ , ; =,m,m N m- -m - I - m n N m u r m a m w m m m * i d

YL m m t + --t- n u m w - m r n d ~ n m w n m m ~ u + m m L w O u m m m - h -I--& m m m h ~ - Q - m - m m u m m Q u ~ m m m m m - d - - - d m m m don++** $ r * * m rrr-r m m r r r r r r r m m X + r + + t r m t * *+rrr r m y n TI "---- ----- ---."- M - M - 4 * ---- - ----- ----- -- - M d

La t

. . . . ?"?? ?Y?=?Y ??""? X m m N h l m m m - N - A C m * I-*-- * m * - N - tob~ .m m t m t m m**- l- m u LO 0,- I- * * m m - t m - - - m o d w m - m - t m m - - - e r n ,n-r-r N+ LO- N t m

z E m - m m & dm&&- P m m m m N ~ Q - Q 2 e m m - 2 Q m Q - mmm-- UaWmmm $: - -C o m ' a m t n * W m Y u t o to*"** u m * u u u * m u ** ,a* *,nu,** ,mW,a,o&n u WID

OR16111 TIHE 198B UR MN SEC

AUC 13 9 8 4 2 . 1 13 11 49 5 8 . 1 13 13 3 5 8 . 4 13 13 53 32.1 1 3 14 11 2 8 . 3

LOHG V OEG HIM

141 11 .5 147 3 2 . 0

SOUTHERM ALASKA EARTHQUAKES. JULY - SEPTEMBER 1980 DEPTH HA6 I P WS GAP 03 I M S ERH ERZ P A21 D I P 1 S E l

KM OE6 KH SEC Kt4 KM DEG DE6 KH A22 D I P 2 D E 6 DEG 1BP 4 1

SE2 A23 DIP3 SE3 KH DEG OE6 KM

7.9 346 40 3.7 8 . 6 79 72 2 . 2 1 . 5 13 64 3 . 1 0 . 9 145 77 3.8 3 . 1 314 76 5.1

17.7 1 . 2 5 2 212 36 8 . 1 9 4 . 3 9 . 3 C 01 2 2 . 1 8 . 1 2.L 17 7 167 3 4 0 . 0 5 2 . 3 l . B A 2 0 0 2 8 . 6

2.5 ML EHRC 1.4 2 . 4 15 4 176 33 0 . 9 1 2 . 5 2 . 1 B 286 1N 8 . 6

2 . 5 ML EHRC 2 1 . 1 2.2 19 4 83 64 0 . 3 3 1 .4 3.3 0 172 6 1.3 1 1 . 0 1 . 3 6 4 161 7 4 0 . 4 1 7 . 9 5.4 C 207 13 8 . 0

1 .4 9 5 133 51 2 . 4 14 8 229 1 1 0 2 . 9 2 0 7 184 78 2 . 4 2 5 7 72 4 5 EHRC 2 . 1 2 1 9 46 3 9 EMRC

LAT 1 DEG MIN 6 5 1%. 5 61 49 .9 62 5 8 . 8 6 8 22 .4 6 8 20 .6

sou DEPTH

KM 2 9 . 6 48 .8 43 .4

1 . 5 8.0

THERW ALASKA EARTHQUAKES. JULY MA6 WP I S GAP 03 RMS

O E 6 KM SEC 2 . 2 24 11 127 66 8 . 4 1 2 . 3 17 11 157 57 8 . 3 5 3.1 14 0 131 I 5 8 8 . 8 6 1 . 3 0 3 155 95 0 . 4 8 1 . 5 6 4 217 6 9 8 . 2 4

- SEPTEMBER ERH ERZ O KH KM

1 . 2 1 . 6 A 3 . 8 2 .8 8 4 . 9 2 5 . 3 D 2 . 7 5 . 7 C 7 . 6 4 . 9 C

A21 D I P 1 DEG DEG 278 5

288 341 3 1

S E I KM

0 . 0 1 - 8 4.4 1.3 7 .6

A22 DIP2 DEE OE6

1# 21 197 39

81 1 354 2 8 278 7

A23 D IP3 S E 3 DEG DEG KM

18 22 43 9 .8 6 8 26 .1 147 33.5 25 .3 2 . 2 24 13 83 58 0 . 4 0 1 .0 1 . 5 A 2 7 8 7 8 .7 1 lb 1 . 0 145 78 1 . 6 1 8 2 2 5 1 2 5 . 2 6 2 5 9 . 8 1 5 8 3 8 . 7 5 7 . 8 4 . 4 11 1 120 171 0 . 3 6 2 . 6 1 7 . 2 0 293 3 2 .0 23 6 1 . 5 176 83 17.3

4 . 5 M0 4 .S HL ATVC FELT I 1 1 1 1 AT CURRY AND COLD CREEK 19 2 4 5 5 1 . 2 6 3 2 8 . 7 1 4 2 1 8 . 9 0 . 0 0 . 6 5 4 116 81 8 . 2 8 3 . 9 2 . 1 8 I38 25 4.2 25 39 0 . 9 251 4 8 1.5 19 3 3 2 1 4 . 8 63 7 . 8 158 6 . 1 89.4 3 . 9 12 4 120 172 0 . 3 2 9.6 2 3 . 1 0 305 8 2.1 38 19 4.6 193 69 2 4 . 6 19 0 19 3 4 . 4 5 9 46 .3 141 15 .4 2 .1 1 . 6 11 5 188 52 0 . 3 6 6 . 2 4 . 9 C 121 14 1.2 2 8 37 7.6 228 5 0 2.2

SOUTHERN A L A S U EARTHQUAKES, J U L Y - SEPTEMBER I 9 0 0 ORIEIM T I M E LAT M LONG W DEPTH MAC NP HS CAP 03 RHS ERH EAZ 9 A l l D I P 1 S E I A t 2 D I P 2

1986 H R H U SEC DEGHIM DEGMIN KM DE6 KM SEC Kt4 KW DEG DEG KH OE6 DE6 A U t 2 1 18 2 8 17 .9 61 5 4 . 8 149 34 .4 3 6 . 0 2 . 5 22 1 0 165 66 1 . 4 3 1 . 9 1 . 6 A 93 10 8 . 9 188 22

2 1 2 8 19 36 .6 59 35.4 138 46 .3 6 . 8 1 .0 4 3 251 63 3 .B9 4 . 9 6 . 0 C 353 2 1 8 . 0 93 23 22 1 43 5 0 . 3 61 32 .5 152 14 .6 138.5 4 .7 21 2 07 8 8 g . 2 6 1 . 9 2 . 6 0 182 13 1 . 5 276 10

4 . 3 Me 4.11 Ht ATW 22 4 3 8 4 6 . 0 61 27 .6 147 12 .3 27 .9 2 . 3 10 5 49 57 0 . 3 4 1 .1 2 . 2 A 23 0 1 . 1 123 0 22 6 5 7 0 . 7 6 0 3 9 . 1 1 5 5 4 0 . 2 15 .9 1 . 6 12 9 73 7 3 0 . 4 8 1 . 8 3 - 3 0 292 3 8 . 9 22 4

6 0 2 5 . 9 148 30.9 6 8 10 .6 140 5 5 . 7 6 8 7 . 6 149 48 .8

3,s H t ATVC 6 8 2 . 2 I 4 0 5 6 . 9 59 5 0 . 1 140 43 .3

6 8 2 8 . 1 141 1 7 . 1 6 8 19 .6 141 9 . 4 59 43 .1 138 20 .3 6 8 0 . 7 115 53 .1 6 8 9 . 6 153 13 .2

3.1 ML ATWC

6 0 2 3 . 9 141 14 .8 6 8 13 .2 141 8 . 2 6% 3 3 . 1 147 19 .9

3.4 HL ATWC 6 8 2 5 . 6 147 3 5 . 3

ORr6IM TIME 1 9 8 1 BR t4N SEC

AUC 25 3 22 15.1 25 4 42 51.1

LhT N LONG V DE6 HIN OE6 MIN 6 8 11 .4 148 5 7 . 9 6 8 42 .7 148 41 .2

SOU DEPTH

KM 8 . 1 0 . 9

85.1 1 4 . i

THERR MA6

ALASKA NP NS

18 3 7 5

19 1 9 2

EARTHQUAKES, JUI GAP 03 RHS D E G Kt! SEC 143 41 5 . 3 2 206 102 0 . 9 3

77 58 0 . 2 1 127 39 5 . 2 3

.Y - SEPTEMBER I 9 8 0 ERH E R Z Q A21 DFPl S E l A22 D I P 2

KM Kt4 DEG DEG KH DEG DEG 2 . 1 3 . 7 B 8 1 13 1 .4 335 13

1 3 . 5 1 1 . 3 D 138 I0 3 . 4 223. 2 0 2 . 2 2 . 8 B 18 1 0 1 . 6 114 32 6 . 5 4.4 C 275 8 1 .1 182 2 3 5 . 1 5 . 6 C 96 8 B . 9 0 38

A23 DIP3 SE3 DEG DEG KM 280 66 3 . 8

15 68 1 1 . 1 273 56 3.2

23 66 3 . 9 196 51 6 . 5 1 .1 8 . 8 7 4 135 53 0 . 4 9

31 .9 2 . 3 2 0 6 158 54 0 . 4 9 I H 3 . 7 3.3 16 2 74 89 0 . 1 2

9 . 4 1 . 3 1 0 1 98 54 8 - 1 8 9 . 4 1 . 8 A 5 2 141 5 7 8 . 8 9 9 . 8 1 . 9 2 2 7 02 30 0 . 5 7

2 6 . 2 2 - 5 2 5 4 138 68 0 . 6 6 8 . 1 1 .B 7 2 112 45 0 . 3 4

18 .9 8 .1A 8 5 87 69 8 . 5 9 12 .7 4 . 4 8 4 216 415 8 . 2 9

3 . 7 ML EMRC 11 .4 0 .7 7 4 127 55 0 . 6 1

2 8 . 1 3.0 9 2 139 I 7 4 8 . 3 1

4 . 8 0 .7A 5 3 199 99 8 . 3 8 1 5 . 8 1.1A 6 4 182 9 5 8 . 7 2

2 . 3 1 . 8 16 7 117 49 0 . 7 5 16 .8 2 . 0 1 0 3 143 85 0 . 1 9

4 3 . 2 2 . 1 9 4 581 78 P . 3 1 2 1 . 9 1.8A 8 6 77 52 8 . 3 5 6 8 . 0 2.6 10 3 126 69 8 . 2 7

0 . 4 1.5 12 4 78 59 1 .35 3 8 . 3 1.4A 18 5 L6B 62 8 . 1 8

2 4 . 9 1.3 4 3 286 99 8 . 4 3 7 . 9 1 .6 13 1 8 117 47 8 . 3 9 8.2 1 . 2 6 3 126 8 8 8 . 2 4

18 .8 1.5A 5 5 18.0 I 5 6 8 . 4 6 1 . 0 WL EMRC

42.8 1 . 0 A 15 11 92 29 8 . 3 3

L A T W LONG U D E t MIN DEG MlM 62 29 .6 151 14.8 5 8 43.8 158 3 3 . 8 6 1 11 .3 141 13.3 6 8 13 .2 148 46 .7 6U 51.8 1 5 8 2 2 . 5

SOUTHERN ALASKA EARTHQUAKES, JULY - SEPTEMBER 198% DEPTH MA6 NP NS GAP D3 RMS ERH E R Z P A21 D I P 1 SEl A Z Z D I P Z

KM OEC KM SEC Kn KM DEC DEG KM OEC DE6 8 5 . 1 3.6 17 5 194 110 0 . 3 0 4 . 2 7 . 5 C 114 1 5 3.6 28 16 18.3 1 .4 9 6 105 8 8 0 . 3 1 3 . 5 5 . 9 C 45 16 2 .8 3 1 0 f9 1 . 4 1.BA 6 2 133 113 8 . 3 0 5 . 8 7 . 9 C 95 2 1 .4 4 32

14 .9 1 .7 1# 5 134 73 8 .36 3 . 7 4 . 4 0 285 5 3 . 7 297 10 5 8 . 7 1.7 12 9 52 69 8 . 2 5 2 . 2 4 . 7 8 28 6 2 . 1 297 1 8

S E Z Kr4

1.7 1 . 1 3 . 0

A23 D I P 3 DEG DEG 245 60 173 65 180 50 1018 7 1 149 78

3 . 0 26 7 9 8 5 0 2 . 0 1 0 4 135 74 2 . 8 14 7 125 8 7 EMRC

I . 8 9 5 I28 7 8 1 . 7 6 4 148 Iff7 2 . 4 2 7 5 59 45 1.8A 7 2 145 0U 2 . 8 12 7 127 87 EWRC

ORIEIl TIME 196. HR MN SEC

SEP 6 3 23 24.1 5 5 43 7.8 5 5 46 14.8

4 . 5 ns 5 6 4 10.7 5 6 0 55.3

L A 1 M LON6 W DEG M I N OE6 M I N 61 23.1 15B 11.2 61 56.5 148 5.2 60 18.5 153 9.8

3.2 ML ATWC 65 9.5 148 57.6 68 14.9 141 25.4

SOUTHERN ALASKA EARTHOUAKES. JULY - SEPTEMBER 1988 DEPTH HAG N P NS GAP 03 RHS ERH ERZ P A21 D I P 1

KH DE6 Kt4 SEC KM Kt4 DEG DEG 44.0 2.0 12 8 7 6 37 0.27 1.8 2.9B 193 1 1 37.2 2.1 25 I4 168 62 0.52 2.2 1.1A 165 4

S E I KH 1.7 2 . 2 2.3

8.8 B.5

8.9 8.7 8.7 1.1

1.3

1.0

1.1

8.P I .d 3.7

0.0 1.8 1.5 0.9 0.7

1.2 0.7

1.2 l .B 7.8

5. a 8,s 1.2 1.4 3.1

0.9 8.5 1.2 8.8 8.9

1 .a 8.7 1.5 0.9 2.2

8.7

0.0 2.6 0.7 2.2

A22 D I P 2 DEG OEG 1BB 17 261 119 44 36

a 33 29 24

33B 27 336 9 141 11 135 22

25 14

135 4

I I6 22

33 16 42 27

292 13

5 35 81 35 272 4 10 38 18 27

207 23 16 I4

3 28 182 5 283 27

88 I t 304 7 355 21 356 29 192 25

193 40 3 34

264 24 36 17 270 19

201 38 185 39 349 19 5 27 81 39

I4 29

El7 41 359 17 261 3 81 42

SE2 A23 D I P 3 KM DEG DEG

0.1 2.1 21 13 BB 02 1.77 1 . 7 2.3 A 261 2 2.4 ML EMRC 8.2 3.B 28 5 77 88 1.67 1.5 2.3A 26 8

3.8 ML EMRC

0.7 1.1 5 2 215 62 8.25 3.9 7.8C 115 4 5.4 2.8 26 7 86 18 8.63 0.9 1.1 A 187 4

2 . 9 HL EHRC 15.1 1.2 4 4 218 45 B.BB 4.6 5.5 C 95 5 11.1 1.3 9 4 191 66 8.41 2.6 5.5 C 32 2 9.8 1.8 4 3 242 100 5.11 6.9 3.6 C 25 I 2

mrsxlr TtnE 198s HR MU SEC

SEP B 3 7 24 .6

L A 1 M LONG W D E t M I H DEG HIM

SOUTHERU ALASKA EARTHOVAKES. JULY - SEP DEPTH MAG UP NS GAP 03 RHS ERH

KM DEG KH SEC KH 35 .6 3 . 6 29 4 80 2 1 8 0 . 4 9 6 . 5

'TEMBER 1 9 0 0 ERZ 9 A21 DIP1

KM D E 6 DEG 5 . 2 C 24 5

SE1 A22 D I P 2 KM DEG DEG

2 . 1 2 9 8 36

SE2 A23 DIP3 SE3 KM DEE 0E6 KM

7 . 8 121 54 3.1 63 19 .6 151 15 .6 3.3 ML ATWC

6 1 3 . 8 1SB 3 5 . 2 6 1 39 .1 150 20 .8 60 9 . 9 139 4 5 . 7

3 1 . 0 1.7 7 4 119 63 B . 3 9 2 . 6 13.4 2 . 2 14 6 141 61 8 . 6 5 2 . 0 1 5 . 3 1.5 0 7 113 94 1 . 0 3 2 . 8

1 . 9 HL EMRC 37.9 1 . 9 1B 6 108 63 8 . 2 4 2 .1

183 .5 3.0 25 1 I S 1 92 0 .45 2 . 8 6 . 5 1 . 1 0 3 130 46 0 . 2 1 1 . 0

49.B 2 . 3 17 6 136 5 0 8 . 3 4 1 .4 1 5 . 6 2 .2 28 3 71 53 8 . 5 8 8 . 9 19.5 1.0 9 5 I 4 2 6 2 8 . 6 1 2 . 0

0 . 5 0 . 9 6 2 176 1 8 0 B . 1 6 9 . 6 2 . 0 8.9A 3 2 247 100 0 . 8 1 7 . 6

2 1 . 9 1 . 8 2 0 8 163 75 5 . 4 9 1 . 2 3 3 . 0 2.2 18 6 142 64 0 . 6 0 1.1 13 .2 1 .6 11 5 189 4 8 6.15 1.7

62 12.5 151 9 . 6 68 17.1 1 4 9 59 .2 6 1 36.8 ISB 2B.1 6 8 2 0 . 4 146 3 6 . 1 6 1 3 9 . 9 158 19 .9

9 3 110 46 8 . 1 3 3 8 2 4 1 73 8 . 4 1 FELT t I I 1 l AT ANCHORAGE 13 7 74 43 0 . 4 7 2 . 3

EMRC 0 . 9 A 4 . 4

6B 4 . 1 141 0 . 5 63 31.8 149 3 9 . 3

3.6 HL ATVC

2 1 . 3 1.8 18 1 0 . 8 0 .7A 4 0 . 9 2 . 0 5

2 . 1 ML EMRC 50.3 2 . 5 22 2 1 . 9 B . 9 3

16.4 1 .4 8 1 1 . 4 1.7 2 0 2 4 . 3 1 . 2 12 12 .8 1 . 9 13 1 1 . 0 2 . 4 26

2 - 5 ML EHRC

T I M E S EC

5 6 . 8 5 .7

2 1 . 3 40.9

42.6

L A T M LONG V DEC M I N DEG M I N 6 0 5 1 . 8 143 2 2 . 2 6 0 2 0 . 7 140 5 0 . 6 6 0 2 0 . 6 141 1 .4 6 0 3 2 . 7 141 44.4

3 .4 ML ATWC 6 8 4 8 . 5 149 5 7 . 0

61 5 4 . 5 149 5 5 . 0 2 . 6 MI. ATVC

6 0 7 . 5 152 5 8 . 3 3 . 3 MI. A T U C

61 6.5 149 22.7 61 41 .6 149 48.4 6% 7 .6 139 19.2

5 5 . 0 ATVC 5 8 . 3

3 . 3 MI. A T U C 61 6.5 149 22.7 61 41 .6 149 48.4 6% 7 .6 139 19.2

SOUTHERN 4LASKA EARTHQUAKES, JUL DEPTH MAG NP NS GAP D3 RMS

KM DEG KH SEC 16 .5 2.1 14 9 129 78 1 .1P 1 1 . 0 1.3 7 2 1 3 6 49 9 . 1 7 18.6 1.5 7 3 133 5 1 8 . 2 9 18 .1 2 . 9 15 7 63 64 5 . 4 2

2 .9 ML EMRC 4 0 . 2 1.8 12 4 06 5 1 8 . 2 1

.Y - SEPTEFIBER ERH ERZ P KH KM

1 . 9 3 . 6 B 2 .5 7 . 3 C 1 . 0 4 , P B 1.7 2 . 0 A

S E I hZ2 D I P 2 KM DEG DEG

1.9 97' 1 6

SEZ A13 D I P 3 KM OEG DE6

0 . 9 262 7 3

- r m m m y : w m w h m y - w m - d n m h ? ????: yy$ty :$? t~ m N N ' " ~ . . . . . . . . . . . . . . . . . . W Y " ' :??Y? w w b m ~ m ~ I - P - ~ - m m - - - m u m m b - - - m---- I-I 4 4 - - m m n n - m m ~ CI

~ - U N * - U J ~ - - w - - ~ - - m - ---a* w-m-m h h m m * ~ Q Q - m m + b - * ~ w - ~ m m m m m ~ u - ~ 7 - u ~ - m m q ~ m w m m m m m - - n m ~ n m m N w - m m n m b h m m 0 " N N-NN R-Ne'Jm R A N NN N Fl-N N N N N - m -mNc4-

e w w ~ T ~ ! m ~ m m n m - - m m n n w ~ e b m m f y y y y t ? m e m n * nnr m m ~ m m h - w * m m * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . d Y " " . . . . . . l w urn - - - b - m - m NI-NN ~ N N - N ~ r c - ~ Q*N-- --- - N ~ N N Q * mtNNN

d C1 rl s > ~ w u m r - - ~ m c b m m w d N I P m * m r - ~ r - w r n a ~ m b m m m n N N ~ n N w m w e m m n m m - 3 2 W l - m - N

M U ) . . . . . . . . . . . . . . . . . . . . . . . . . . UIINT~ DN*R? m ~ m m y m-mm- w - r * n mm- h - ~ n ~ m + - n ~ q m . . . . . . . . . - m q m m a I I I Q r n u a m m m Q b w m Q ? b m m h m b a h b m mmm i ti m e m u m m m m m e m

- 3 1 ~ w m m m t - m m r i - - B r r m - m b c ~ n r r N - r r r m m - c 2 N * o w n + c n r - w - - d d d N-d - - d d 4-

3z;mm mm-mm I C R - ~ mmmmm - b m UY t m w m m m c b m r - 2 q r n m - --N --+ WNN- m dc - -N - N-NN

SOUTHERI ALASKA EARTHQUAKES, JULY - SEP ORIGIU TIME L A 1 M LONG W DEPTH MA6 NP NS GAP D3 RMS ERH

I988 H R M N SEC DEGMIN DEGMIN KM OEG KM SEC KH SEP 25 7 59 4 8 . 8 6 8 1 1 . 9 I 4 1 1 4 . 5 1 6 . 8 1.B 0 2 115 56 8 . 1 4 9 . 8

25 0 7 46 .5 6 1 28 .9 149 5 3 . 0 3 9 . 4 3 . 2 32 8 6 0 43 8 . 3 0 1 . 1 2 -5 H i ATUC

'TEMBER 198% ERZ O A21 D I P 1

KH DEE DE6 6 . 7 C 319 17 2 . 1 A 08 4

SEI A22 DIP2 KH DE6 DEG

1 . 1 261 36 8 . 7 179. 0

SE2 A13 DIP3 KM OE6 DEG

9 . 8 74 41 1 .1 332 0 1

1.4 171 7 8 1 . B 133 8 0 1.1 101 5 1

2.3 ML EHRC 25 15 30 11 .5 6 1 58.6 147 2 4 . 3 3 1 . 3 2 . 3 27 17 167 6 6 B . 6 7 1.4 25 15 49 3 . 5 6 d 8 . 3 140 5 3 . 6 7 . 6 1.0 6 3 136 36 0 . 3 8 3 . 3 25 16 13 9 . 0 58 26 .2 141 16.6 14 .7 1 . 2 6 6 127 43 0 . 2 7 4 . 2 2 5 1 6 1 7 2 9 . 2 6 1 3 4 . 6 1 5 0 5 0 . 3 6 0 . 7 3 . 1 31 9 62 78 0 . 4 6 1 .4

2 6 2 8 1 6 4 2 . 6 6 1 3 7 . 2 1 4 9 5 8 . 0 42.1 1 .9 13 3 110 45 0 . 3 4 3 . 4 26 2 1 36 58.6 61 30 .5 147 5 . 9 26.1 1 . 9 19 11 73 65 3 . 6 8 1 . 0 27 3 5 2 12.3 6 8 10.3 141 1 . a 1 . 7 2 . 1 12 6 6 1 8 1 B.66 2 . 0

2 . 0 ML EMRC 27 4 46 32.5 6 0 28 .7 148 5 0 . 7 7.5 1 .3 8 3 136 49 8 . 4 4 1 .7 27 6 5 4 4 1 . 3 6 0 5 . 1 141 12 .7 1 1 . 5 1,5 7 2 198 5 3 0 . 3 7 7 . 8

2 7 7 3 S 3 7 . 5 59 10 .5 144 5 3 . 4 2 5 . 3 2 . 5 9 3 274 1 5 1 8 . 5 6 6 . 8 27 9 14 9 . 8 59 5 7 . 7 140 30 .4 6 . 4 2 . 1 13 6 168 49 0 . 3 9 1 . 9

1 . 9 HL EHRC 27 13 35 15 .5 6 1 3 8 . 0 I 4 9 4 8 . 8 3 7 . 0 2 . 1 10 5 143 44 N . 6 3 1 . 0 27 14 24 11 .4 6 1 1 3 . 1 $ 4 9 4 4 . 8 4 3 . 3 1.9 16 5 9 8 53 8.25 1.4 27 17 6 34 .5 6% 1 .4 141 1 1 . 4 8 . 1 1.B 8 2 94 40 8 . 4 5 1 .4

O R I G I N TlHE 198s HR MN SEC

SEP 27 22 5 0 2 . 9 28 8 43 4 . 0 28 2 21 26 .0 2 8 3 15 21.9 28 7 16 43 .5

L A T N LON6 W DEG nIn DEE U I M 6 8 10 .9 141 16 .5 62 7 .5 147 59.1 6 1 3 9 . 9 149 53 .5 6 1 5 8 . 3 149 5 6 . 2 6 1 5 3 . 1 I 5 0 17 .6

SOUTHERW ALASKA EARTHQUAKES, JULY - SEPTEMBER 198B DEPTH MAG BP I S GAP D3 RMS ERH ERZ 0 A21 D I P 1 S E I A22 D I P 2 SE2

KM DE6 KM SEC KM KM DEGDEG KU DEGDEG KU 3 . 2 1 . 8 12 5 183 57 8 . 4 5 1 . 3 1 .0 A 295 8 0 . 5 25 32 3 . 8

3 6 . 2 2 . 7 22 5 106 03 8 . 5 6 2 . 5 1 . 3 A 341 12 2.1 01 34 0 . 7 39.3 2 . 4 2 1 4 144 58 5.47 1 . 5 2 . 2 A 176 5 1.5 86 6 8.7 3 9 . 2 1.6 13 7 191 71 0 . 3 7 2 . 5 2 . 4 A 285 1 8 . 7 16 34 1.6 12.4 2 . 2 12 4 164 66 8 . 7 2 2 . 8 1 . 8 A 275 15 0 . 6 17 38 2 . 3

AZ3 D I P 3 DEG DE6 255 50 235 53 356 8 2 194 55 168 48

113.5 3 . 9 27 4 127 I 8 4 8 . 5 9 2 . 8 6 . 6 C 3 3 8 2 2.2 8 1 1 8 1.8 3 . 2 2 . 7 24 6 98 85 1 .59 1 . 7 2 . 1 A 8 1 2 1 .2 147 1 7 1.4

3 .0 HL EMRC