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A seismicity study of the Queen Charlotte Islands/Hecate Strait Region Bérubé, Joane 1985

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A SEISMI CITY STUDY OF THE QUEEN CHARLOTTE ISLANDS/HECATE STRAIT REGION by JOANE BERUBE B. Sc. (Honours), M c G i l l U n i v e r s i t y , 1982 A t h e s i s s u b m i t t e d i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r the degree of MASTER OF SCIENCE i n the F a c u l t y of Graduate S t u d i e s Department of Ge o p h y s i c s and Astronomy We ac c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d The U n i v e r s i t y of B r i t i s h Columbia June 1985 ®P © Joane Berube, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of ( f l Q O W y * > \ A The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) i i A b s t r a c t The Queen C h a r l o t t e I s l a n d s are l o c a t e d e a s t of the s e i s m i c a l l y a c t i v e Queen C h a r l o t t e t r a n s f o r m f a u l t zone which s e p a r a t e s the P a c i f i c and N o r t h American p l a t e s . The f a u l t zone i s the l o c u s of s i g n i f i c a n t s e i s m i c a c t i v i t y and i s d i s t i n g u i s h e d b a t h y m e t r i c a l l y by two s t e e p s c a r p s bounding a 15 t o 25 km wide t e r r a c e . To b e t t e r d e f i n e r e g i o n a l s e i s m i c i t y c h a r a c t e r i s t i c s , 16 p o r t a b l e seismographs and 6 ocean bottom seismographs were o p e r a t e d f o r 9 weeks and 5 days, r e s p e c t i v e l y , d u r i n g June t o August 1983. Three hundred and seventeen e v e n t s were d e t e c t e d ; 130 events t h a t were r e c o r d e d on 3 or more s t a t i o n s have been l o c a t e d . Twenty' events were i d e n t i f i e d as p o s s i b l e b l a s t s . N i n e t y - t w o of the l o c a t e d e a rthquakes l i e a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone, most w i t h i n the 1949, Ms = 8.1, e a r t h q u a k e r u p t u r e zone a l o n g the i n n e r s c a r p of the t e r r a c e . However, s e v e r a l earthquakes are l o c a t e d on the t e r r a c e and a few a r e a l i g n e d w i t h the o u t e r s c a r p where no a c t i v i t y has p r e v i o u s l y been observed. Most of the a c t i v i t y i s w e l l c o n s t r a i n e d t o be l e s s than 15 km i n depth. Two a r e a s of low s e i s m i c i t y were observed a l o n g the f a u l t zone. Only two e a r t h q u a k e s o c c u r r e d i n the documented s e i s m i c gap bound on the n o r t h by the 1949 r u p t u r e zone and on the s o u t h by the 1970 M = 7.0 e a r t h q u a k e . They were both a t -the s o u t h e r n t i p of the gap. A s i m i l a r r e g i o n of low a c t i v i t y was o b s e r v e d f o r the f a u l t a l o n g Graham I s l a n d . No major s e i s m i c i t y (M > 4.0) has been l o c a t e d i n t h i s r e g i o n s i n c e the 1949 e a r t h q u a k e . Composite f a u l t p l a n e mechanism s o l u t i o n s were d e t e r m i n e d f o r f i v e c l u s t e r s of e v e n t s a l o n g the f a u l t zone. E v e n t s t o the northwest of Graham I s l a n d are c o n s i s t e n t w i t h s t r i k e - s l i p motion a l o n g a f a u l t i n the d i r e c t i o n of the Queen C h a r l o t t e t r a n s f o r m f a u l t . The f o u r r e m a i n i n g c l u s t e r s were l o c a t e d a l o n g Moresby I s l a n d . The mechanisms f o r the s e are dominated by t h r u s t f a u l t i n g w i t h a component of c o m p r e s s i o n a l s t r e s s t r e n d i n g n o r t h - s o u t h . These events a r e i n t e r p r e t e d as the r e s u l t of o b l i q u e convergence between the P a c i f i c and N o r t h American p l a t e . S i g n i f i c a n t s e i s m i c i t y was l o c a t e d e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t zone. E i g h t e e n e a r t h q u a k e s , the l a r g e s t ML = 3.8, were l o c a t e d i n n o r t h e a s t e r n Graham I s l a n d and a d j a c e n t Hecate S t r a i t - Dixon E n t r a n c e a r e a . None c o u l d be a s s o c i a t e d w i t h known f a u l t s . The f o c a l depth of the s e e v e n t s i s w e l l c o n s t r a i n e d w i t h i n the c r u s t so they c o u l d not be a s s o c i a t e d w i t h a subducted p l a t e . A composite f a u l t p l a n e mechanism s o l u t i o n d e t e r m i n e d f o r some of these e a r t h q u a k e s i n d i c a t e s a t h r u s t i n g mechanism w i t h n o r t h - s o u t h t r e n d i n g c o m p r e s s i o n a l s t r e s s . One event w i t h a w e l l c o n s t r a i n e d s o l u t i o n a t a s h a l l o w f o c a l depth o c c u r r e d i n s o u t h e a s t e r n Hecate S t r a i t . T h i s event c o u l d be a s s o c i a t e d w i t h c r u s t a l l y p e r v a s i v e f a u l t s i d e n t i f i e d i n Hecate S t r a i t . A magnitude s c a l e based on the coda l e n g t h of the earthquake s i g n a l was d e t e r m i n e d . Magnitudes were c a l c u l a t e d f o r 265 of the e v e n t s r e c o r d e d d u r i n g the s t u d y . For the complete d a t a s e t a b - v a l u e of 0.55 ± 0.05 was d e t e r m i n e d . T h i s i v v a l u e i s s i g n i f i c a n t l y lower than v a l u e s from o t h e r s t u d i e s i n the Canadian C o r d i l l e r a , i n d i c a t i n g t h a t a g r e a t e r p e r c e n t a g e of the t o t a l number of e a r t h q u a k e s o c c u r s a t the h i g h e r magnitudes. However, the s h o r t p e r i o d of r e c o r d i n g and l a r g e magnitude s e i s m i c a c t i v i t y (4 e a r t h q u a k e s w i t h ML > 3.8 i n 9 weeks) might have b i a s e d the e s t i m a t e toward a low v a l u e . V Table of c o n t e n t s A b s t r a c t i i L i s t of T a b l e s y i i L i s t of F i g u r e s v i i i Acknowledgement x Chapter I INTRODUCTION: THE QUEEN CHARLOTTE ISLANDS REGION 1 1.1 T e c t o n i c H i s t o r y 1 1.2 P r e s e n t T e c t o n i c S e t t i n g 9 1 . 3 F a u l t s 15 1 . 4 S e i s m i c i t y 18 1.5 Purpose of t h i s Study 23 Chapter I I EXPERIMENT AND DATA 24 2.1 Experiment and In s t r u m e n t s 24 2.2 D i g i t a l Data 28 2 . 3 Ana l o g Data 31 2.3.1 Magnetic Tape R e c o r d i n g s 31 2.3.2 Paper R e c o r d i n g s 33 Chapter I I I HYPOCENTER LOCATIONS 35 3.1 I n t r o d u c t i o n 35 3.2 C r u s t a l S t r u c t u r e 36 3.3 Hypocenter L o c a t i o n s 41 3.3.1 I d e n t i f i c a t i o n and L o c a t i o n of B l a s t s 43 3.3.2 A c t i v i t y E a s t of the Queen C h a r l o t t e T r a n s f o r m F a u l t 45 3.3.3 A c t i v i t y a l o n g the N o r t h e r n Queen C h a r l o t t e T r a n s f o r m F a u l t 46 3.3.4 The S e i s m i c i t y a l o n g the Queen C h a r l o t t e T r a n s f o r m F a u l t 48 3.3.5 S e i s m i c Gaps 49 3.4 R e l o c a t i o n of Q u e s t i o n a b l e H y p o c e n t e r s 51 3.5 C o n c l u s i o n 54 Chapter IV EARTHQUAKE MAGNITUDES 56 Chapter V SEISMICITY RATES AND B-VALUE ..61 Chapter VI FAULT PLANE MECHANISM SOLUTIONS 69 6.1 I n t r o d u c t i o n 69 6.2 Ev e n t s E a s t of the Tra n s f o r m f a u l t 70 6.3 Ev e n t s i n the N o r t h e r n C l u s t e r 74 6.4 Ev e n t s a l o n g the Southern p a r t of the Queen C h a r l o t t e Transform F a u l t Zone 74 6.5 C o n c l u s i o n 77 v i Chapter V I I SUMMARY AND CONCLUSION 80 B i b l i o g r a p h y 83 Appendix A - ALL EVENTS IDENTIFIED ON RECORDING STATIONS DURING THE 1983 EXPERIMENT 86 Appendix B - SUMMARY OF THE HYPOELLIPSE SOLUTIONS FOR LOCATED EVENTS 94 Appendix C - MAGNITUDES EVALUATED FROM DATA RECORDED AT STATION BQP 98 v i i L i s t of t a b l e s I . Days of o p e r a t i o n of s e i s m i c s t a t i o n s 26 I I . S e i s m i c s t a t i o n l o c a t i o n s 27 I I I . R e l o c a t e d event 57 52 IV. R e l o c a t e d event 98. 53 V. Data used f o r c a l i b r a t i o n of the magnitude s c a l e ...58 V I . B - v a l u e s f o r e v e n t s grouped by r e g i o n s 66 V I 1 1 L i s t of f i g u r e s 1. T e c t o n i c h i s t o r y of the Queen C h a r l o t t e I s l a n d s r e g i o n . 3 2. Geology of the Queen C h a r l o t t e I s l a n d s 4 3. T e c t o n i c r e c o n s t r u c t i o n , L a t e C r e t a c e o u s t o E a r l y Miocene 6 4. I d e n t i f i e d f a u l t s i n the Queen C h a r l o t t e I s l a n d s r e g i o n . 7 5. Index map of the Queen C h a r l o t t e I s l a n d s 10 6. E f f e c t s of o b l i q u e s u b d u c t i o n i n the Queen C h a r l o t t e I s l a n d s r e g i o n 11 7. C r u s t a l s t r u c t u r e a c r o s s the t e r r a c e 13 8 . H i s t o r i c a l s e i s m i c i t y and f a u l t p l a n e mechanism s o l u t i o n s 2 0 9. H i s t o r i c a l s e i s m i c i t y ML > 4 21 10. S e i s m i c s t a t i o n s o p e r a t i n g d u r i n g the experiment 25 11. Sample of i n t e r n a l c l o c k d r i f t from a d i g i t a l s e i s m i c s t a t i o n ( M i c r o c o r d e r , PCM) 30 1 2 . C r u s t a l models used t o l o c a t e h y p o c e n t e r s 37 13. C r u s t a l s t r u c t u r e vs f o c a l depth 40 14. P o i s s o n ' s r a t i o 42 15. E a r t h q u a k e e p i c e n t e r l o c a t i o n s and magnitudes. t / n 16. True b l a s t l o c a t i o n s vs hypocenter b l a s t l o c a t i o n s . ..44 17. Depth c r o s s s e c t i o n of h y p o c e n t e r s 47 1 8 . Hypocenter l o c a t i o n s ; p r o j e c t i o n s of the s o l u t i o n s A ' i 4 e l l i p s o i d s on the s u r f a c e U - > - :'-> ^ s^e*M19. S e i s m i c gaps 50 u ' i x 20. C a l i b r a t i o n of s t a t i o n BQP f o r magnitude c a l c u l a t i o n . 59 21. S e l e c t e d magnitude d a t a s e t f o r e v a l u a t i o n of s e i s m i c r a t e s 62 22. Magnitude f r e q u e n c y d i s t r i b u t i o n 64 23. Maximum l i k e l i h o o d d e t e r m i n a t i o n of b - v a l u e 65 24. Magnitude - f r e q u e n c y of o c c u r r e n c e r e l a t i o n s c a l e d t o one year of r e c o r d i n g 68 25. L o c a t i o n of c l u s t e r s used t o g e n e r a t e the composite f a u l t p l a n e mechanism s o l u t i o n s 71 26. Composite f a u l t p l a n e mechanism s o l u t i o n f o r e v e n t s l o c a t e d i n l a n d 72 27. Composite f a u l t p l a n e mechanism s o l u t i o n f o r the n o r t h e r n c l u s t e r 73 28. Composite f a u l t p l a n e mechanism s o l u t i o n s i n c l u d i n g e v e n t s from a swarm 76 29. Composite f a u l t p l a n e mechanism s o l u t i o n s i n c l u d i n g e v e n t s a l o n g s o u t h e r n Queen C h a r l o t t e t r a n s f o r m f a u l t . 78 X Acknowledgement I w i s h t o exp r e s s my g r a t i t u d e t o Dr. R.M. E l l i s f o r h i s h e l p f u l g u idance and encouragement d u r i n g the p e r i o d of t h i s s t u d y . Many thanks t o Dr. G a r r y Rogers who p r o v i d e d u s e f u l d i r e c t i o n i n the development of t h i s t h e s i s . Thanks t o David Mackie f o r many e n l i g h t e n i n g d i s c u s s i o n s about a l l a s p e c t s of the p r o j e c t . A s p e c i a l thanks goes t o a l l who read my t h e s i s and improved i t : Dr. E l l i s , Dr. Rogers, Dr. Clowes and D a v i d M a c k i e . The data f o r t h i s study would have never been a c q u i r e d w i t h o u t the e x p e r t i s e and d e d i c a t i o n of Bob Meldrum who o r g a n i s e d and c o o r d i n a t e d the f i e l d program. I would a l s o w i s h t o thank everyone i n the G e o p h y s i c s and Astronomy Department, p a s t and p r e s e n t , who made my l i f e i n Vancouver so e n j o y a b l e . F i n a n c i a l s u p port f o r t h i s r e s e a r c h was p r o v i d e d from P a c i f i c G e o s c i e n c e C e n t e r , Department of Energy Mines and Res o u r c e s , t h r o u g h DSS c o n t r a c t numbers 06SB.23227-3-0605 and 06SB.23227-3-0878, by NSERC O p e r a t i n g Grant A2617, and from Chevron Canada Resources L i m i t e d . 1 I . INTRODUCTION: THE QUEEN CHARLOTTE ISLANDS REGION 1.1 T e c t o n i c H i s t o r y The west c o a s t of N o r t h America has been a t e c t o n i c a l l y a c t i v e boundary between the N o r t h American p l a t e and an o c e a n i c p l a t e s i n c e at l e a s t the E a r l y M e s o z o i c . C u r r e n t l y , the Queen C h a r l o t t e I s l a n d s a re s i t u a t e d i m m e d i a t e l y e a s t of the a c t i v e boundary between the N o r t h American and P a c i f i c p l a t e s . The h i s t o r y of the N o r t h American west c o a s t i s d i r e c t l y l i n k e d w i t h the s h a p i n g of the Queen C h a r l o t t e I s l a n d s r e g i o n ; i . e . i t s g e o l o g y , morphology and p r e s e n t t e c t o n i c s e t t i n g . T h i s s e c t i o n w i l l summarize v a r i o u s t e c t o n i c r e c o n s t r u c t i o n s proposed f o r the west c o a s t of N o r t h America t h a t a re r e l e v a n t t o the f o r m a t i o n of the Queen C h a r l o t t e I s l a n d s r e g i o n . . The west c o a s t of N o r t h America i s b e l i e v e d t o be formed of a number of a l l o c t h o n o u s t e r r a n e s . These t e r r a n e s were formed f a r from t h e i r p r e s e n t l o c a t i o n and a c c r e t e d t o the west c o a s t of N o r t h America as the p l a t e s on which they were l o c a t e d converged on the N o r t h American c o a s t ( e . g . Coney e t a l . , 1980). In the r e g i o n of the Queen C h a r l o t t e I s l a n d s two of the s e t e r r a n e s have been i d e n t i f i e d : the A l e x a n d e r t e r r a n e of P a l e o z o i c age, and, the W r a n g e l l i a t e r r a n e of Mesozoic age ( Y o r a t h and Chase, 1981). The A l e x a n d e r t e r r a n e has been i d e n t i f i e d i n p a r t s of s o u t h e a s t e r n A l a s k a and the Coast Mountains and i s b e l i e v e d t o form the n o r t h e a s t e r n end of the 2 Queen C h a r l o t t e I s l a n d s on Graham I s l a n d ( F i g u r e 1 ) . The W r a n g e l l i a t e r r a n e has been i d e n t i f i e d i n the remainder of the Queen C h a r l o t t e I s l a n d s , i n the Coast Mountains s o u t h e a s t of the I s l a n d s and on Vancouver I s l a n d . Rock f o r m a t i o n s b e l o n g i n g t o these two t e r r a n e s were d e s c r i b e d by S u t h e r l a n d Brown (1968). They were regrouped by Y o r a t h and Chase (1981) i n t o the a l l o c t h o n o u s assemblages ( F i g u r e 2 ) . The t e c t o n i c h i s t o r y of the Queen C h a r l o t t e I s l a n d s r e g i o n s t a r t s w i t h the f o r m a t i o n of the i s l a n d s i n E a r l y M e s o z o i c . P r e v i o u s t o t h i s time ( e a r l i e r than 140 my ago) the Queen C h a r l o t t e I s l a n d s as they e x i s t now were not y e t formed. The two a l l o c t h o n o u s t e r r a n e s of which the i s l a n d s are formed ( A l e x a n d e r and W r a n g e l l i a t e r r a n e s ) were c o n v e r g i n g toward each o t h e r ( F i g u r e 1) and c o l l i d e d a p p r o x i m a t e l y 140 my ago ( Y o r a t h and Chase, 1981). T h e i r s u t u r e l i e s presumably a l o n g the t r a c e of the S a n d s p i t f a u l t and t h r o u g h Hecate S t r a i t a l o n g R e n n e l l Sound f a u l t ( F i g u r e 1 ) . Some of the g e o l o g i c a l f o r m a t i o n s which date from the time of the c o l l i s i o n were d e s c r i b e d by S u t h e r l a n d Brown (1968). Y o r a t h and Chase regrouped them and l a b e l l e d them as the s u t u r e assemblages ( F i g u r e 2 ) . The r o c k s i n c l u d e d i n the s u t u r e assemblages show e v i d e n c e ( c o a r s e c o n g l o m e r a t e s and p l u t o n i s m ) f o r v i o l e n t t e c t o n i c a c t i v i t y such as c o l l i s i o n and/or s u b d u c t i o n a t t h a t t i m e . In L a t e C r e t a c e o u s time the two s u t u r e d t e r r a n e s presumably docked onto N o r t h America ( F i g u r e 1 ) . The west c o a s t of the Queen C h a r l o t t e I s l a n d s then became the l o c u s of the a c t i v e boundary between the N o r t h American p l a t e and the a d j a c e n t l-t o 3 K O cu rt-tr a n o> 3 fD i-J O D •^1 lO C fD fD O n-o 3 O to r t n o fD n - O O k£> 3 M i C O r O r t —• fD o c fD fD o 0) rt ro > 140 MILLION Y E A R S A G O W R A N G E L L I A M O V E S N O R T H W A R D P R O M T H E S O U T H E R N H E M I S P H E R E SOUTHEAST ALASKA -QUEEN CHARLOTTE ISLANDS 1 . VANCOUVER ISLAND 2 0 t o 1 7 m i l l i o n y e a r s a g o N o r t h A m e r i c a o v e r r i d e s t h e A n a h i m m a n t l e p l u m e ABOUT 140 MILLION YEARS A G O W R A N G E L L I A C O L L I D E S W I T H T H E A L E X A N D E R T E R R A N E a b o u t 1 7 m i l l i o n y e a r s a g o r i f t z o n e s a r e c r e a t e d t h e Q u e e n C h a r l o t t e I s l a n d s s t a r t m o v i n g n o r t h w a r d 90 TO 40 MILLION YEARS A G O C O M B I N E D W R A N G E L L I A A N D A L E X A N D E R T E R R A N E D O C K W I T H N O R T H A M E R I C A 3 . ».-.-, ' , v . >,x v : •.,£> - V < ^ i ^ c N O R T H Y,Z > j / ? ' - " ' - . ' A M E R I C A ' ; ; *__• n e x t 1 7 t o 2 m i l l i o n y e a r s a g o s u b s i d e n c e i n r i f t b a s i n s a c c u m u l a t i o n o f s e d i m e n t s F i g u r e 2 - G e o l o g y o f t h e Q u e e n C h a r l o t t e I s l a n d s . T h e f o u r a s s e m b l a g e s a r e r e g r o u p e d b y Y o r a t h a n d C h a s e , f r o m r o c k f o r m a t i o n s d e s c r i b e d b y S u t h e r l a n d B r o w n , 1 9 6 8 : ( 1 ) t h e a l l o c t h o n o u s a s s e m b l a g e s : A l e x a n d e r a n d W r a n g e l l i a t e r r a n e s . ( 2 ) t h e s u t u r e a s s e m b l a g e s : U p p e r J u r a s s i c p l u t o n s a n d L o w e r C r e t a c e o u s s e d i m e n t s . ( 3 ) t h e p o s t - s u t u r e a s s e m b l a g e s : M i d T e r t i a r y t o U p p e r C r e t a c e o u s s e d i m e n t s . ( 4 ) t h e r i f t a s s e m b l a g e s : M i d T e r t i a r y p l u t o n s , v o l c a n i c s a n d N e o g e n e s e d i m e n t s . 5 o c e a n i c p l a t e . At t h i s time the P a c i f i c p l a t e was not y e t a d j a c e n t to N o r t h America. E i t h e r the F a r a l l o n or the K u l a o c e a n i c p l a t e s were i n t e r a c t i n g a l o n g the boundary ( F i g u r e 3 ) . The c h a r a c t e r of the t e c t o n i c a c t i v i t y a l o n g the boundary, from L a t e Cretaceous t o E a r l y Miocene, i s not known. V a r i o u s s c e n a r i o s have been proposed (Ewing, 1980; R i d d i h o u g h , 1982b). These r e c o n s t r u c t i o n s i n c l u d e the f o l l o w i n g t e c t o n i c regimes: s t r i k e - s l i p , f u l l s u b d u c t i o n and o b l i q u e s u b d u c t i o n i n v a r i o u s s u c c e s s i o n s (e.g. F i g u r e 3 ) . In M i d d l e t o Upper Miocene, the P a c i f i c p l a t e became the a c t i v e o c e a n i c p l a t e a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t ( F i g u r e 4 ) . S i n c e then the c h a r a c t e r of the boundary has been d o m i n a n t l y s t r i k e - s l i p . From L a t e C r e t a c e o u s to E a r l y Miocene, however, the c o n f i g u r a t i o n of the Queen C h a r l o t t e I s l a n d s i s not b e l i e v e d t o have c h a n g e d ' ( Y o r a t h and Chase, 1981). The g e o l o g i c a l f o r m a t i o n s observed on the i s l a n d s dated from t h i s p e r i o d have been regrouped i n the p o s t -s u t u r e assemblages by Y o r a t h and Chase (1981) and a r e of s e d i m e n t a r y o r i g i n ( F i g u r e 2 ) . They c o n t a i n c l a s t s from the a l l o c t h o n o u s assemblages observed on the Queen C h a r l o t t e I s l a n d s and on the Coast M o u n t a i n s . The geology of the Queen C h a r l o t t e I s l a n d s i s marked by a major t e c t o n i c event t h a t o c c u r r e d i n E a r l y Miocene t i m e . M a s s i v e marine and non-marine v o l c a n i s m f o l l o w e d by a c c e l e r a t e d s e d i m e n t a t i o n of non-marine and marine o r i g i n o c c u r r e d around 20 my ago ( S u t h e r l a n d Brown, 1968). Y o r a t h and Chase (1981) have regrouped r o c k s of E a r l y Miocene age and younger as the r i f t assemblages ( F i g u r e 2 ) . 6 F i g u r e 3 - T e c t o n i c r e c o n s t r u c t i o n , L a t e C r e t a c e o u s t o E a r l y Miocene. A America p l a t e K K u l a p l a t e F F a r a l l o n p l a t e P P a c i f i c p l a t e The c h a r a c t e r of the boundary a l o n g the Queen C h a r l o t t e I s l a n d s changed from f u l l s u b d u c t i o n t o o b l i q u e s u b d u c t i o n t o f u l l s u b d u c t i o n a g a i n , u n t i l the P a c i f i c p l a t e became a d j a c e n t t o N o r t h America i n Mid-Miocene (not shown h e r e ) . Then the boundary became a t r a n s f o r m f a u l t . (from R i d d i h o u g h , 1982a). 7 F i g u r e 4 - I d e n t i f i e d f a u l t s i n the Queen C h a r l o t t e I s l a n d s r e g i o n . A d e s c r i p t i o n of each f a u l t i s i n c l u d e d i n s e c t i o n 1.3. The P a c i f i c p l a t e motion d i r e c t i o n w i t h r e s p e c t t o N o r t h America i s marked w i t h the arrow at the lower l e f t c o r n e r of the f i g u r e . Bathymetry c o n t o u r i n t e r v a l s a r e 20 m i n Hecate S t r a i t and 100 m on the t e r r a c e . 8 In E a r l y Miocene time the N o r t h American p l a t e s t a r t e d moving westward as a r e s u l t of the opening of the A t l a n t i c Ocean. The Anahim v o l c a n i c b e l t , o b s e r v e d from the west c o a s t of B r i t i s h Columbia to the A l b e r t a - B r i t i s h Columbia boundary, i s b e l i e v e d to have been formed as a r e s u l t of t h i s westward motion of the p l a t e over a hot spot or mantle plume, ( B e v i e r e t a l . , 1979). The e x t r a p o l a t i o n of the v e l o c i t y t r e n d of the Anahim v o l c a n i c b e l t p u t s the v o l c a n i c s o u r c e t h a t produced the b e l t i n Queen C h a r l o t t e Sound i n E a r l y Miocene ( F i g u r e 1). The plume i s b e l i e v e d t o have generated r i f t i n g by c r u s t a l t h i n n i n g ( Y o r a t h and Chase, 1981), the f o r m a t i o n of normal f a u l t s i n the c r u s t of Hecate S t r a i t , and the r e a c t i v a t i o n of major s t r i k e s l i p f a u l t s i n the area ( e . g . the S a n d s p i t , the Louscoone I n l e t and R e n n e l l Sound f a u l t s ( F i g u r e 4 ) ) . The passage of the hot spot was accompanied by marine and non-marine v o l c a n i s m a l o n g the r i f t and a l o n g the Louscoone I n l e t and S a n d s p i t f a u l t system. T h i s a c t i v i t y i s thought to have i n i t i a t e d the motion of the Queen C h a r l o t t e I s l a n d s northward toward t h e i r p r e s e n t p o s i t i o n ( F i g u r e 1). The L a t e O l i g o c e n e r i f t i n g i n Queen C h a r l o t t e Sound was f o l l o w e d i n E a r l y Miocene by s u b s i d e n c e of the r i f t b a s i n s ( Y o r a t h and Chase, 1981). M a r i n e sediments a l o n g w i t h t e r r i g e n o u s e l a s t i c s were d e p o s i t e d i n Hecate S t r a i t and Queen C h a r l o t t e Sound. Y o r a t h and Cameron (1982) suggest t h a t the T e r t i a r y sediments of the r i f t b a s i n s have s u s t a i n e d s u f f i c i e n t t h e r m a l metamorphism f o r the o r g a n i c m a t t e r t o be c o n v e r t e d t o l i q u i d h y d r o c a r b o n s . 9 1.2 P r e s e n t T e c t o n i c S e t t i n g For the purpose of s e i s m i c i t y s t u d i e s i t i s i m p o r t a n t t o understand as f u l l y as p o s s i b l e the contemporary t e c t o n i c regime i n the r e g i o n under e x a m i n a t i o n . The c h a r a c t e r of the p r e s e n t t e c t o n i c r e l a t i o n s h i p between the N o r t h American and P a c i f i c p l a t e s i n t e r a c t i n g i n the Queen C h a r l o t t e t r a n s f o r m f a u l t r e g i o n can be i n f e r r e d from v a r i o u s o b s e r v a t i o n s . F a u l t p l a n e s o l u t i o n s f o r major e a r t h q u a k e s a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t show p r e d o m i n a n t l y s t r i k e s l i p motion on two n e a r l y v e r t i c a l p l a n e s o r i e n t e d a p p r o x i m a t e l y p a r a l l e l and p e r p e n d i c u l a r t o the s t r i k e of the f a u l t (Wickens and Hodgson, 1967; Chandra, 1974; M i n s t e r e t a l . , 1974; Rogers, 1983). T h i s • w i l l be d i s c u s s e d i n more d e t a i l i n s e c t i o n 1.4. The p l a t e motion v e c t o r s have been o b t a i n e d from the i n v e r s i o n of s p r e a d i n g r a t e s , t r a n s f o r m f a u l t a z i m u t h s and earthquake s l i p v e c t o r s ( M i n s t e r and J o r d a n , 1978), and more l o c a l l y from f o c a l p l a n e mechanisms f o r e a r t h q u a k e s l o c a t e d i n A l a s k a (Perez and Jacob, 1980). The r e s u l t s show t h a t the t r a c e of the Queen C h a r l o t t e t r a n s f o r m f a u l t a l o n g n o r t h e r n Graham I s l a n d i s a l i g n e d w i t h the P a c i f i c ocean p l a t e motion w i t h r e s p e c t t o the N o r t h American p l a t e (5.5 cm/yr a t n o r t h 35° w e s t ) . A l o n g Moresby I s l a n d , however ( F i g u r e 5 ) , the f a u l t s t r i k e s from n o r t h 40° t o 50° west; i . e . t h e r e i s a m i s a l i g n m e n t of up t o 20° between the p l a t e motion and the t r e n d of the f a u l t ( F i g u r e 4 ) . Models suggest s u b d u c t i o n , a t a r a t e of 1.0 t o 2.0 cm/yr of the P a c i f i c p l a t e under the America p l a t e ( F i g u r e 6 ) . The more 10 F i g u r e 5 - Index map of the Queen C h a r l o t t e I s l a n d s . 11 F i g u r e 6 - E f f e c t s of o b l i q u e s u b d u c t i o n i n t h e Queen C h a r l o t t e I s l a n d s r e g i o n . The P a c i f i c p l a t e o b l i q u e l y c o n v e r g e s on N o r t h America at a r a t e of 55 mm/yr w i t h a s t r i k e s l i p component of 50 mm/yr and an o r t h o g o n a l convergence r a t e of 10 t o 20 mm/yr. The t r e n c h and a c c r e t i o n a r y wedge, t y p i c a l of s u b d u c t i o n zones a r e observed i n the Queen C h a r l o t t e I s l a n d s r e g i o n . I t i s b e l i e v e d t h a t the oc e a n i c p l a t e i s f r a c t u r e d a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t where the major p a r t of the motion o c c u r s . F o s s i l s of these f r a c t u r e s a r e subducted. The diagram a l s o i l l u s t r a t e s the f l e x u r e of the c o n t i n e n t a l l i t h o s p h e r e g e n e r a t e d by margin u n d e t h r u s t i n g . The Queen C h a r l o t t e I s l a n d s a r e u p l i f t e d and the Queen C h a r l o t t e B a s i n i s s y m p a t h e t i c a l l y d e p r e s s e d (from Y o r a t h and Hyndman, 1983). 12 convergent motion of the P a c i f i c p l a t e toward N o r t h America i s b e l i e v e d t o have s t a r t e d l e s s than 10 my ago as i n d i c a t e d by the change i n t r e n d of the Hawaiian seamount c h a i n (Cox and E n g e b r e t s o n , 1985). P h y s i o g r a p h i c and g e o p h y s i c a l e v i d e n c e support the h y p o t h e s i s of o b l i q u e s u b d u c t i o n under the Queen C h a r l o t t e I s l a n d s . The g r a v i t y and t o p o g r a p h i c p r o f i l e a c r o s s s o u t h e r n Moresby I s l a n d t o the m a i n l a n d i s c h a r a c t e r i z e d by a g r a v i t y h i g h and a t o p o g r a p h i c bulge 100 km seaward from the t r e n c h and a n o t h e r over the w e s t e r n p o r t i o n of the Queen C h a r l o t t e I s l a n d s ( S r i v a s t a v a et a l . , 1971). Anomalies of t h i s type i n the g r a v i t y and t o p o g r a p h i c p r o f i l e s a r e t y p i c a l l y a s s o c i a t e d w i t h s u b d u c t i o n zones ( F i g u r e 6 ) . The g r a v i t y p r o f i l e s a c r o s s the margin support the h y p o t h e s i s t h a t the t e r r a c e i s formed of an a c c r e t e d sedimentary wedge of low d e n s i t y ( S r i v a s t a v a et a l . , 1971). The a b r u p t d i s a p p e a r a n c e of the l i n e a r magnetic anomalies o b s e r v e d o f f the margin west of the Queen C h a r l o t t e t r a n s f o r m f a u l t s u g g ests t h a t the m a t e r i a l f o r m i n g the margin i s not o c e a n i c c r u s t or t h a t the o c e a n i c c r u s t i s b u r i e d under the t e r r a c e which i s " a s edimentary wedge ( S r i v a s t a v a et a l . , 1971; S r i v a s t a v a 1973). The a n a l y s i s of s e i s m i c r e f r a c t i o n p r o f i l e s (Horn et a l . , 1984; M a c k i e , 1985) c o n f i r m s t h a t the margin i s composed of low c r u s t a l v e l o c i t y m a t e r i a l w i t h h i g h v e l o c i t y g r a d i e n t s and i s d i s t i n c t from the m a t e r i a l on the Queen C h a r l o t t e I s l a n d s ( F i g u r e 7 ) . Heat f l o w measurements a c r o s s the margin cannot be e x p l a i n e d w i t h a s t e a d y s t a t e model f o r the c o n t a c t between the 13 C r u s t a l s t r u c t u r e d e r i v e d from r e f r a c t i o n d a t a i n . the Queen C h a r l o t t e I s l a n d s and t e r r a c e r e g i o n , from Horn e t a l . d 984). Note the low v e l o c i t y , h i g h g r a d i e n t s t r u c t u r e i n the t e r r a c e r e g i o n ( u n i t 6 and 7) d i s t i n c t from the Queen C h a r l o t t e I s l a n d s s t r u c t u r e . T h i s i s t y p i c a l f o r a s e d i m e n t a r y wedge. 14 o c e a n i c c r u s t and the c o n t i n e n t a l c r u s t a l o n g the Queen C h a r l o t t e I s l a n d s (Hyndman et a l , 1982). However, a s u b d u c t i n g p l a t e a c t i n g as a heat s i n k i n the Queen C h a r l o t t e t r a n s f o r m f a u l t r e g i o n c o u l d e x p l a i n the heat f l o w measurements. A t r e n c h can be observed on the bathymetry and on r e f l e c t i o n s e i s m i c p r o f i l e s seaward of the Queen C h a r l o t t e t e r r a c e (Chase and T i f f i n , 1972). The s e i s m i c p r o f i l e s i n d i c a t e t h a t the o c e a n i c basement d i p s landward and t h a t the t r e n c h i s m o s t l y i n f i l l e d w i t h f l a t l y i n g s e diments. L i t h o s p h e r i c f l e x u r e g e n e r a t e d by o b l i q u e u n d e r t h r u s t i n g was suggested as the cause of u p l i f t of the Queen C h a r l o t t e I s l a n d s r e g i o n and s u b s i d e n c e of the Queen C h a r l o t t e b a s i n ( F i g u r e 6 ) . Models f o r l i t h o s p h e r i c f l e x u r e by Y o r a t h and Hyndman (1983) were g e n e r a t e d f o r the Hecate S t r a i t r e g i o n . The sediment compaction d a t a from w e l l s i n Hecate S t r a i t show t h a t s u b s i d e n c e s t a r t e d about 6 my ago. The models were c o n s t r a i n e d by the g e o l o g y , e r o s i o n and s u b s i d e n c e r a t e s . A good f i t of the model w i t h the observed f l e x u r e was o b t a i n e d w i t h a 30° t h r u s t f a u l t a t a 10 mm/yr r a t e of o r t h o g o n a l convergence f o r a p e r i o d of 6 my ( F i g u r e 6 ) . The s e i s m i c i t y d a t a from p r e v i o u s s t u d i e s (Hyndman and E l l i s , 1981; Rogers, 1983) do not show any d i r e c t e v i d e n c e f o r s u b d u c t i o n under the Queen C h a r l o t t e I s l a n d s as no deep s e i s m i c i t y was r e c o r d e d e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t . However, the l i m i t a t i o n s of the p r e v i o u s s t u d i e s ( s t a t i o n d i s t r i b u t i o n s and s e n s i t i v i t i e s ) do not a l l o w any d e f i n i t i v e c o n c l u s i o n on the s e i s m i c p a t t e r n i n the Queen 1 5 C h a r l o t t e I s l a n d s r e g i o n except f o r the a c t i v i t y i n the Queen C h a r l o t t e t r a n s f o r m f a u l t zone. A more complete d i s c u s s i o n of th e s e i s m i c i t y d a t a i n the r e g i o n i s i n c l u d e d i n s e c t i o n 1.4. 1.3 F a u l t s A number of f a u l t s have been i d e n t i f i e d i n the Queen C h a r l o t t e I s l a n d s r e g i o n . Only the Queen C h a r l o t t e t r a n s f o r m f a u l t i s known t o be a c t i v e ( F i g u r e 4 ) . An o b j e c t i v e of t h i s s t u d y i s t o det e r m i n e from the d i s t r i b u t i o n of the s e i s m i c i t y w hich of the f a u l t s i d e n t i f i e d i n the Queen C h a r l o t t e I s l a n d s r e g i o n a r e s e i s m i c a l l y a c t i v e . The geology, the bathymetry, the g r a v i t y f i e l d map, and some r e f l e c t i o n s e i s m i c s e c t i o n s have been used t o t r a c e the S a n d s p i t , R e n n e l l Sound, Louscoone I n l e t , B e r e s f o r d , Langara and Queen C h a r l o t t e f a u l t s , and two f a u l t s i n s o u t h e r n Hecate S t r a i t ( S u t h e r l a n d Brown 1968; S r i v a s t a v a e t . a l 1971; Y o r a t h and Chase, 1981). The t e c t o n i c h i s t o r y and the p r e s e n t t e c t o n i c s e t t i n g d e s c r i b e d i n s e c t i o n s 1.1 and 1.2 a i d i n a s s e s s i n g the time of f o r m a t i o n and a c t i v e p e r i o d s of the i d e n t i f i e d f a u l t s . T h i s i n f o r m a t i o n a l s o h e l p s i n d e s c r i b i n g p a s t and p r e s e n t d i r e c t i o n of motion on the f a u l t s . A b r i e f d e s c r i p t i o n of each f a u l t f o l l o w s . The S a n d s p i t f a u l t i s t r a c e d from n o r t h e a s t e r n Moresby I s l a n d t o n o r t h w e s t e r n Graham I s l a n d . The n o r t h e r n s e c t i o n of the f a u l t on Graham I s l a n d i s not exposed; however, the g r a v i t y p r o f i l e s show a d e c r e a s e i n the f i e l d as one c r o s s e s t o the 16 southwest; t h i s f e a t u r e i s used t o i n f e r the t r a c e of the f a u l t . The f a u l t c o u l d have been r e a c t i v a t e d i n E a r l y Miocene time when the Anahim mantle plume was l o c a t e d i n Hecate S t r a i t ( s e c t i o n 1.1). The f a u l t a l s o e x h i b i t s g e o l o g i c a l and m o r p h o l o g i c a l e v i d e n c e f o r contemporary a c t i v i t y on i t s s o u t h e r n segment, such as o f f s e t c r e e k s , s m a l l s c a r p l e t s i n P l e i s t o c e n e s e d i m e n t s , sag ponds and l i n e a r sea c l i f f s , ( S u t h e r l a n d Brown, 1968). The R e n n e l l Sound-Louscoone I n l e t f a u l t system ( F i g u r e 4) was t r a c e d from g e o l o g i c a l e v i d e n c e by S u t h e r l a n d Brown (1968). R e l a t i v e d i s p l a c e m e n t s of 1500 t o 3000 m from C r e t a c e o u s t o T e r t i a r y i n age have been i d e n t i f i e d . There i s no e v i d e n c e f o r contemporary motion on the f a u l t s . The R e n n e l l Sound f a u l t e x tends through Hecate S t r a i t t o the m a i n l a n d as e v i d e n c e d by s i n g l e c h a n n e l s e i s m i c r e f l e c t i o n s e c t i o n s and g r a v i t y ( Y o r a t h and Chase, 1981). The s e i s m i c s e c t i o n s do not i n d i c a t e r e c e n t motion a l o n g the f a u l t i n Hecate S t r a i t as u n d i s t u r b e d sediments ar e seen o v e r l y i n g the f a u l t . The p a r t of the f a u l t e x t e n d i n g i n Hecate S t r a i t i s b e l i e v e d t o mark the s u t u r e zone between the W r a n g e l l i a t e r r a n e and the A l e x a n d e r t e r r a n e ( Y o r a t h and Chase, 1981). The S a n d s p i t f a u l t and Louscoone I n l e t f a u l t a r e b e l i e v e d t o have belonged t o the same system i n C r e t a c e o u s time ( Y o r a t h and Chase, 1981) w i t h a c t i v i t y a l o n g the R e n n e l l Sound f a u l t o f f s e t t i n g the two segments i n the T e r t i a r y ( Y o r a t h and Chase, 1981 ). To the s o u t h e a s t of Hecate S t r a i t two f a u l t s i d e n t i f i e d by Y o r a t h and Chase (1981) on r e f l e c t i o n p r o f i l e s a r e a s s o c i a t e d 17 w i t h a n o r t h e a s t e r l y d i r e c t e d b a t h y m e t r i c t r o u g h ( F i g u r e 4 ) . These are c r u s t a l l y p e r v a s i v e f a u l t s t h a t were formed i n E a r l y t o M i d d l e Miocene and are b e l i e v e d to bound an a r e a of r i f t i n g presumably g e n e r a t e d by the plume c a u s i n g the Anahim v o l c a n i c ( s e c t i o n 1.1). The B e r e s f o r d and Langara f a u l t s are l o c a t e d at the n o r t h w e s t e r n end of Graham I s l a n d ( F i g u r e 4 ) . Both f a u l t s t r e n d a t 90° from the main Queen C h a r l o t t e t r a n s f o r m f a u l t . The B e r e s f o r d f a u l t was t r a c e d on the b a s i s of g e o l o g i c a l e v i d e n c e on the i s l a n d and shows l e f t - l a t e r a l d i s p l a c e m e n t i n the L a t e C r e t a c e o u s ( S u t h e r l a n d Brown, 1968). The Langara f a u l t i s w e l l t r a c e d from the bathymetry, the g r a v i t y f i e l d map and marine r e f l e c t i o n s e i s m i c p r o f i l e s ( Y o r a t h and Chase, 1981). In t h e i r r e c o n s t r u c t i o n they propose t h a t l e f t - l a t e r a l motion a l o n g these f a u l t s i n L a t e T e r t i a r y r e s u l t e d i n the f i n a l c l o c k w i s e r o t a t i o n of the Queen C h a r l o t t e I s l a n d s i n t o t h e i r p r e s e n t p o s i t i o n . The Queen C h a r l o t t e t r a n s f o r m f a u l t p a r a l l e l s the west c o a s t of the Queen C h a r l o t t e I s l a n d s ( F i g u r e 4) and marks the boundary between the N o r t h American and P a c i f i c l i t h o s p h e r i c p l a t e s . The p r e s e n t t e c t o n i c r e l a t i o n s h i p between the two p l a t e s a l o n g the f a u l t has been d e s c r i b e d i n d e t a i l i n s e c t i o n 1.2. The bathymetry of the c o n t i n e n t a l s h e l f o f f the Queen C h a r l o t t e I s l a n d s i s c h a r a c t e r i z e d by two sharp d r o p s : from the west c o a s t of the Queen C h a r l o t t e I s l a n d s t o the s h o r t 30 km wide t e r r a c e (a drop of almost 2 km), and from the t e r r a c e t o the deep o c e a n i c t r o u g h (a drop of 1 km). Based on the p h y s i o g r a p h y i t i s not c l e a r which of the s c a r p s marks the 18 a c t i v e boundary between the P a c i f i c and American l i t h o s p h e r i c p l a t e s . P r e v i o u s s e i s m i c i t y s t u d i e s (Hyndman and E l l i s , 1 9 8 1 ; Rogers, 1983) a s s o c i a t e d the s e i s m i c a c t i v i t y w i t h the innermost s c a r p . 1 .4 S e i s m i c i t y The major s e i s m i c a c t i v i t y i n the Queen C h a r l o t t e I s l a n d s r e g i o n has been documented s i n c e the b e g i n n i n g of the 1900's as the f i r s t s e i s m i c s t a t i o n on Canada's west c o a s t was i n s t a l l e d i n 1898 i n V i c t o r i a ( M i l n e et a l . , 1978). However the f i r s t r e g i o n a l s t a t i o n on the Queen C h a r l o t t e I s l a n d s was not i n s t a l l e d u n t i l 1971 i n Queen C h a r l o t t e C i t y ( F i g u r e 5 ) . P r e s e n t l y , t h r e e r e g i o n a l s t a t i o n s o p e r a t e on the Queen C h a r l o t t e I s l a n d s : Cape St James ( S J B ) , S k i d e g a t e (SKB) and Tasu Sound (TSB) ( F i g u r e 5 ) . The s m a l l number of s t a t i o n s l i m i t s t h e a c c u r a c y of e p i c e n t e r l o c a t i o n s and p r e v e n t s the d e t e r m i n a t i o n of f o c a l d e p th w i t h s u f f i c i e n t a c c u r a c y t o a i d t e c t o n i c i n t e r p r e t a t i o n s . A l s o , the r e g i o n a l s t a t i o n s a r e r e c o r d e d a t a r a t e of 60 mm/min on paper and t h e i r s e n s i t i v i t y i s low i n o r d e r t o a v o i d s a t u r a t i o n by h i g h frequency ( > 10 Hz) manmade and low f r e q u e n c y ( 1-0.3 Hz) m i c r o s e i s m i c n o i s e . Thus o n l y e a r t h q u a k e s of ML > 2.0 a r e g e n e r a l l y r e c o r d e d on more than one r e g i o n a l s t a t i o n . A study of the h i s t o r i c a l s e i s m i c i t y of western B r i t i s h Columbia was done by Rogers (1983). In the Queen C h a r l o t t e I s l a n d s r e g i o n i t was not p o s s i b l e t o r e s o l v e the l o c a t i o n of 1 9 major earthquakes (magnitude g r e a t e r than 4) t o l e s s than ± 25 km. The best l o c a t i o n s are a l i g n e d w i t h the i n n e r s c a r p and the worst l o c a t e d e v e nts a r e w i t h i n ± 25 km of the i n n e r s c a r p . T h e r e f o r e t h e r e i s no i n d i c a t i o n , from the h i s t o r i c a l s e i s m i c i t y data s e t , t h a t a c t i v i t y o c c u r s o f f the i n n e r s c a r p ( F i g u r e s 8 and 9 ) . Two s m a l l e a r t h q u a k e s (M < 4) which had been l o c a t e d s i g n i f i c a n t l y e a s t of the Queen C h a r l o t t e t r a n s f o r m f a u l t were r e l o c a t e d by Rogers (1983) t o the n o r t h e a s t of Graham I s l a n d a l o n g Masset Sound ( F i g u r e 5 and 9 ) . F a u l t p l a n e mechanism s o l u t i o n s a r e w e l l c o n s t r a i n e d f o r two e a r t h q u a k e s (1949, 1970) i n t h i s r e g i o n (Rogers, 1983). The motion f o r the 1949 earthquake mechanism i s m a i n l y s t r i k e - s l i p w i t h a s m a l l t h r u s t component. The net h o r i z o n t a l motion d u r i n g t h i s e a r t h q uake i s s i g n i f i c a n t l y d i f f e r e n t (15°) from the l a t e s t P a c i f i c - A m e r i c a motions i n the r e g i o n but p a r a l l e l s the f a u l t i n t h i s a r e a . The m i s a l i g n m e n t would appear to i n d i c a t e t h a t some co m p r e s s i v e s t r e s s was not r e l e a s e d d u r i n g the 1949 e a r t h q u a k e , l e a v i n g s t r e s s t o be r e l e a s e d i n some o t h e r way. An a l t e r n a t i v e view p o i n t i s t o note t h a t the f i r s t motion f a u l t p l a n e mechanism s o l u t i o n s a r e o n l y i n d i c a t i v e of the c h a r a c t e r of the motion a t the onset of the r u p t u r e . B o s t w i c k (1984) found t h a t t h e r e was a l a r g e d i f f e r e n c e between the a f t e r s h o c k zone and the r u p t u r e l e n g t h d e r i v e d from the d i r e c t i v i t y f u n c t i o n and d i f f e r e n t i a l phases, i . e . the e f f e c t i v e r a d i a t i o n l e n g t h . T h i s s u g g e s t s t h a t the d i s p l a c e m e n t a l o n g the f a u l t was uneven. The f i r s t m otion mechanism would t h e r e f o r e not n e c e s s a r i l y r e p r e s e n t the c h a r a c t e r of the f a u l t i n g over the 20 F i g u r e 8 - H i s t o r i c a l s e i s m i c i t y and f a u l t p l a n e mechanism s o l u t i o n s . E p i c e n t e r s f o r e v e n t s of magnitude 5 and g r e a t e r (1900-1980) a r e shown as r e v i s e d by Rogers (1983). The s e i s m i c gap t o the s o u t h has not e x p e r i e n c e d any major e a r t h q u a k e i n a t l e a s t 80 y e a r s . The o n l y w e l l c o n s t r a i n e d f a u l t p l a n e mechanism s o l u t i o n s i n the Queen C h a r l o t t e I s l a n d s r e g i o n a r e i n c l u d e d . E p i c e n t e r s a r e e x p e c t e d t o be w i t h i n 25 km of the t r u e l o c a t i o n a t b e s t . The s c a t t e r about the i n n e r s c a r p i s not s i g n i f i c a n t . 21 F i g u r e 9 - H i s t o r i c a l s e i s m i c i t y ML > 4. A l l e p i c e n t e r s from the Canadian earthquake data f i l e f o r e vents w i t h magnitudes ML > 4 s i n c e 1965. Only a few were r e l o c a t e d by Rogers (1983), of which two a r e the e p i c e n t e r s w i t h M < 4 (open c i r c l e ) on n o r t h e a s t Moresby I s l a n d . E p i c e n t e r s a r e e x p e c t e d t o be w i t h i n 25 km of t r u e l o c a t i o n s (from Rogers, 1983). The s c a t t e r about the i n n e r s c a r p i s not s i g n i f i c a n t . 22 whole r u p t u r e zone. The c o m p r e s s i v e s t r e s s a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t t h a t one would expect t o be a s s o c i a t e d w i t h the 1949 earthquake might have been r e l e a s e d d u r i n g i t s r u p t u r e but would not have been i n d i c a t e d by the f i r s t motion mechanism s o l u t i o n . The 1970 earthquake shows a mechanism w i t h a c o m b i n a t i o n of s t r i k e - s l i p motion and t h r u s t f a u l t i n g . The h o r i z o n t a l motion d e s c r i b e d by the f a u l t p l a n e mechanism s o l u t i o n i s i n the d i r e c t i o n of the P a c i f i c Ocean p l a t e motion w i t h r e s p e c t t o N o r t h America (Rogers, 1983). The t h r u s t component i s c o n s i s t e n t w i t h the convergence of the two p l a t e s a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t . A s e i s m i c gap has been i d e n t i f i e d by Sykes (1971) s o u t h of the Queen C h a r l o t t e I s l a n d s ( F i g u r e 8 ) . I t i s bounded on the n o r t h by the 1949, Ms = 8.1, earthquake r u p t u r e zone d e l i n e a t e d by i t s s o u t h e r n a f t e r s h o c k s . The gap extends f o r 75 km and i s bounded on the s o u t h by the main shock of the 1970, M = 7.0, e a r t h q u a k e . A p a r t from an earthquake of M = 5.0 i n 1954, no s i g n i f i c a n t s e i s m i c i t y has been o b s e r v e d w i t h i n the boundary of the gap (Rogers, 1983). Some m i c r o e a r t h q u a k e s were l o c a t e d i n the gap d u r i n g a 10 day m i c r o e a r t h q u a k e survey (Hyndman and E l l i s , 1981). 23 1.5 Purpose of t h i s Study T h i s study was undertaken t o c l a r i f y the d i s t r i b u t i o n of the s e i s m i c a c t i v i t y i n the Queen C h a r l o t t e I s l a n d s r e g i o n and from t h i s t o p l a c e s t r o n g e r c o n s t r a i n t s on the t e c t o n i c p r o c e s s e s c u r r e n t l y o p e r a t i n g i n the r e g i o n . In orde r t o examine the c u r r e n t s e i s m i c i t y p a t t e r n , a 9-week m o n i t o r i n g experiment was undertaken i n c o l l a b o r a t i o n w i t h the P a c i f i c G e oscience C e n t r e d u r i n g June-August 1983. A d e s c r i p t i o n of the experiment and data c o l l e c t e d i s i n c l u d e d i n Chapter I I . S p e c i f i c a l l y the o b j e c t i v e s of t h i s study were t o determine whether: (1) s i g n i f i c a n t s e i s m i c i t y o c c u r s o f f the main Queen C h a r l o t t e t r a n s f o r m f a u l t zone and whether i t can be a s s o c i a t e d w i t h known f a u l t s ; (2) the proposed u n d e r t h r u s t i n g of the P a c i f i c p l a t e can be r e c o g n i z e d from the hypocenter d i s t r i b u t i o n and mechanism or a t l e a s t whether the s t r e s s p a t t e r n e x p e c t e d from the convergence of the P a c i f i c and N o r t h American p l a t e s i s observed; (3) t h e r e i s a r e c o g n i z a b l e d i f f e r e n c e i n the s e i s m i c i t y between the r u p t u r e zone of the 1949 earthquake and the s e i s m i c gap t o the s o u t h . The a n a l y s i s - i n t e r p r e t a t i o n s t e p s taken w i t h the e x t e n s i v e data s e t were: (1) d e t e r m i n a t i o n of h y p o c e n t e r s ( c h a p t e r I I I ) , (2) d e t e r m i n a t i o n of composite f o c a l mechanism s o l u t i o n s ( c h a p t e r I V ) , (3) d e t e r m i n a t i o n of a coda l e n g t h magnitude s c a l e and then the magnitudes ( c h a p t e r V ) , (4) d e t e r m i n a t i o n of s e i s m i c i t y r a t e s i n the Queen C h a r l o t t e I s l a n d s r e g i o n ( c h a p t e r V I ) . 24 I I . EXPERIMENT AND DATA 2.1 Experiment and I n s t r u m e n t s The d a t a f o r t h i s study were r e c o r d e d over a nine-week p e r i o d from mid-June t o l a t e - A u g u s t 1983. D u r i n g t h i s p e r i o d a t o t a l of 32 seismograph s i t e s on the Queen C h a r l o t t e I s l a n d s and mai n l a n d B r i t i s h Columbia ( F i g u r e 10), of which f o u r a r e r e g i o n a l s t a t i o n s from the Western Canada S e i s m i c Network, p r o v i d e d d a t a . D u r i n g the e x p e r i m e n t , 21 s i t e s were o c c u p i e d by 16 p o r t a b l e s e i s m i c r e c o r d e r s ; i . e . not a l l s t a t i o n s were o c c u p i e d s i m u l t a n e o u s l y (Table I ) . F u r t h e r , the v e r y wet c o n d i t i o n s and v i s i t s from bears r e n d e r e d some s t a t i o n s i n o p e r a b l e . S i x ocean bottom seismographs (OBSs) were d e p l o y e d f o r 7 days f o r a r e f r a c t i o n s u r v e y and a l i m i t e d amount of d a t a were o b t a i n e d on 3 systems. The l i s t of s e i s m i c s t a t i o n s i t e s used d u r i n g the experiment w i t h t h e i r l a t i t u d e , l o n g i t u d e and a l t i t u d e i s g i v e n i n T a b l e I I . A v a r i e t y of p o r t a b l e r e c o r d i n g i n s t r u m e n t s were used. D i g i t a l r e c o r d i n g s were o b t a i n e d from ten Teledyne Geotech MCR-600 M i c r o c o r d e r s and from t h r e e E a r t h P h y s i c s Branch EMR M a r k - I I Backpack systems, b o t h w i t h v e r t i c a l Mark P r o d u c t s L-4C seismometers. A n a l o g r e c o r d i n g s were o b t a i n e d from two Geotech 17373 FM tape r e c o r d e r s w i t h Geotech AS-330 a m p l i f i e r s r e c e i v i n g s i g n a l s from one v e r t i c a l and a l s o , sometimes, from one h o r i z o n t a l W i l l m o r e MK I I seismometers. The UBC OBSs which were (Jl F i g u r e 10 - S e i s m i c s t a t i o n s o p e r a t i n g d u r i n g the exper iment. The 21 l a n d s i t e s were o c c u p i e d by 1G p o r t a b l e seismographs d u r i n g t h e 1983 summer experiment. The 6 OBSs were de p l o y e d d u r i n g 7 days f o r a r e f r a c t i o n experiment. Only t h r e e (0W1, 0W2, 0E4) of the s i x r e c o r d e d e a r t h q u a k e s . Data from the f o u r r e g i o n a l s t a t i o n s a l s o were used. • s u o t ^ e ^ s xeuox69j U I O J J j a d e d a A T ^ i s u a s ^eaq = d SDUTpaooaj 6o-[eue ade^ oi^auBeui SHO = 0 B u t p j c o a j B O X B U B ade} Dx^au6eui = v jad e d pa^ouis = s j a d e d 5(ux = i e^ep i B 3 T . D T . P = w • s u o p e ^ s O T i u s i a s 30 uoi^eaado 30 sAerj. - I ST^ i^L H I P ! isnonb H i t ? t 3 N n r NO I I t X l U O J O S A U O arc c u a t t o a o i e u i OOE u i o i l a t m u t u i a t ' 1 1 1 1 1 1 1 1 1 1 1 1 1 1' d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d 99i d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d 9X9 d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d 8 r S d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d 9JO 9 9 9 9 S S 9 9 9 S S S S S 9 S S S S ' S S S 9 9 d H i W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W ' ' ' ' W W W W - " ' W W W W W H 1 w w w w w a s b b b f b b b b b d b b b b t i d b d b b b b d H b b b b d b b d o u b ' b b a b d b b b b b d b b b b b b d ' ' w w w w w w b S a • • • • I I I I I I ! I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Z U d 11111111111111111111111 • • t a d w w w w u w w w w w w w w w w w w w w w w w WId W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W O d o o o o o o o Z l \ 0 ooooooo I AO 0 0 0 0 0 0 0 f d O W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W w w w l w W W W W W W W W W W W b b b b b b b b b b b b W 0 " 1 I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I d d T w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w n • • w w w w w w w w w ' ' w w w w w wnr W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W b d b b b ' W 0 1 w w w w w w w w w w w w w w W 9 I 9 9 9 9 9 9 9 ' 9 9 d d O tititititititititititititititititititititititititititititja titititititititititibtitititititibdO w w w w w w w w w w w W W W W W W W W W 8 9 'wwwwwwwwwwww' w w w w w w w w w w w w w w w w W I O 9 9 9 9 9 9 9 9 9 9 S 9 9 9 9 9 9 9 9 9 9 9 9 S 9 9 9 9 9 9 S 9 S 9 S 9 9 S S 9 9 I I I I I I I I r I I I I I I I I I I d 0 8 w w W X 9 w w w w w w w w w w w w W I S 01 N 0 I i b i 9 92 27 S T A T I O N L A T T I T U D E L O N G I T U D E E L E V A T I O N I D D E G M I N D E G M I N M 0 E 4 5 3 N 3 0 . 9 2 1 3 0 W 4 2 9 3 - 1 6 2 OW1 5 2 N 4 8 . 0 4 1 3 2 W 2 9 . 5 3 - 9 3 1 OW2 5 2 N 5 3 . 0 0 1 3 2 W 2 0 . 9 8 - 4 6 0 B I M 5 2 N 2 5 . 6 6 13 1 W 2 0 . 7 4 8 B O P 5 3 N 14 . 5 6 1 3 2 W 0 9 . 2 1 2 5 D I M 5 2 N 5 6 . 2 9 1 3 2 W 12 . 4 1 3 G B M 5 2 N 2 3 7 7 1 3 1 W 3 0 . 2 5 4 G P A 5 3 N 0 7 . 3 4 13 1 W 4 7 . 0 8 8 0 G P P 5 3 N 0 7 . 7 7 13 1 W 4 8 . 19 5 0 I B M 5 3 N 0 1 . 6 2 1 3 2 W 19 . 0 2 4 I C M 5 2 N 17 . 9 8 1 3 1 w 0 9 . 4 2 3 J U M 5 3 N 3 9 . 2 1 1 3 2 w 17 . 1 1 7 5 L I M 5 2 N 4 2 . 9 0 13 1 w 3 4 . 7 9 7 L I P 5 4 N 1 5 . 3 9 1 3 3 w 0 3 . 3 1 2 5 L O M 5 2 N 1 1 . . 9 1 13 1 w 1 4 . 19 6 P C M 5 3 N 3 5 . . 5 3 1 3 2 w 5 2 . 4 2 12 P I M 5 2 N 2 1 . 2 8 13 1 w 19 . . 0 2 -> 4. P R 1 5 4 N 17 . 9 8 1 3 0 w 2 0 . 3 0 3 0 . P R 2 5 4 N 19 . 5 7 1 3 0 w 17 . 0 8 3 5 R S A 5 3 N 2 4 . 2 6 1 3 2 w 3 1 0 9 2 5 T H M 5 4 N 0 4 . 4 8 13 1 w 4 7 . 8 3 15 T H P 5 3 N 15 . 1 7 1 3 2 w 0 5 . 7 1 1 S R M 5 3 N 15 . 2 8 1 3 2 w 0 4 . 0 4 2 0 O F B 5 2 N 2 1 . 18 1 2 7 w 4 1 . 4 0 7 5 S J B 5 1 N 5 6 . 2 2 1 3 1 w 0 0 . 9 0 3 0 S K B 5 3 N 14 . 8 6 1 3 1 w 5 9 7 8 10 T S B 5 2 N 4 5 . 9 0 1 3 2 w 0 1 . 9 8 3 0 M I M 53 N 4 3 . 05 1 3 2 w 2 7 . 0 0 4 T a b l e I I - S e i s m i c s t a t i o n l o c a t i o n s . The l o c a t i o n s a r e shown on F i g u r e 10. 28 depl o y e d f o r a r e f r a c t i o n s u r v ey a l s o p r o v i d e d a n a l o g r e c o r d i n g s of s e v e r a l s e i s m i c events from two seismometers, one v e r t i c a l and one h o r i z o n t a l , and from a hydrophone. D a i l y paper seismographs were o b t a i n e d from f o u r drum r e c o r d e r s - a l l Sprengnether MEQ-800 s e i s m i c u n i t s o p e r a t e d w i t h v e r t i c a l Mark P r o d u c t s L-4C seismometers. The f o u r nearby r e g i o n a l s t a t i o n s a l s o p r o v i d e d paper seismograms. T a b l e I shows the p e r i o d of o p e r a t i o n f o r each s i t e and the type of i n s t r u m e n t i n use d u r i n g t h a t p e r i o d . 2.2 D i g i t a l Data The M i c r o c o r d e r s and Backpacks were o p e r a t e d i n event t r i g g e r mode and p r o v i d e d r e c o r d i n g s of e x c e l l e n t q u a l i t y . The d a t a on the M i c r o c o r d e r s were r e c o r d e d a t a r a t e of 150 samples/s and on the Backpacks a t 60 samples/s. The t r i g g e r i n g a l g o r i t h m used i s based on the v a r i a t i o n i n time of the r a t i o of a l o n g p e r i o d (60 s, the n o i s e ) t o a s h o r t p e r i o d (1 s, the s i g n a l ) average of the s e i s m i c s i g n a l . The t h r e s h o l d f o r the s i g n a l - t o - n o i s e r a t i o f o r t r i g g e r i n g was 12 db. The t r i g g e r i n g system a s s u r e s t h a t the q u a l i t y of the event r e c o r d e d i s e x c e l l e n t and m i n i m i z e s the number of f a l s e t r i g g e r s . N e v e r t h e l e s s i n s e v e r a l cases the d i g i t a l systems, t r i g g e r e d by n o i s e , q u i c k l y exhausted the c a p a c i t y of the c a s s e t t e t a p e . In o t h e r cases the P or S wave a r r i v a l s were l o s t because the a m p l i t u d e of the wave was not l a r g e enough t o cause t r i g g e r . A c c u r a t e t i m i n g f o r the M i c r o c o r d e r s was p r o v i d e d by 29 r e c o r d i n g the WWVB r a d i o time s i g n a l on one data c h a n n e l . When i t was not p o s s i b l e t o r e c o r d WWVB, the i n t e r n a l c l o c k r a t e d at each v i s i t t o the s i t e p r o v i d e d the t i m e . L i n e a r d r i f t of the c l o c k s was assumed between r a t i n g s . D r i f t r a t e s f o r s p e c i f i c i n s t r u m e n t - s i t e c o m b i n a t i o n s were a l s o e v a l u a t e d from the WWVB r a d i o time s i g n a l r e c o r d i n g s ( F i g u r e 11) and used t o improve the r e l i a b i l i t y of the time c o r r e c t i o n s . I t was found t h a t a l i n e a r d r i f t a p p r o x i m a t i o n f o r the M i c r o c o r d e r i n t e r n a l c l o c k s i s a good assumption ( F i g u r e 11). The d i g i t a l seismograms o b t a i n e d from the M i c r o c o r d e r data were p l o t t e d a t the r a t e of one second per i n c h w i t h maximum a m p l i t u d e of a p p r o x i m a t e l y four i n c h e s f o r the e v e n t s . The WWVB time s i g n a l was p l o t t e d p a r a l l e l t o the s e i s m i c s i g n a l when a v a i l a b l e . The r e a d i n g e r r o r f o r sharp a r r i v a l s on the M i c r o c o r d e r d a t a i s a t most ± 0.05 s when WWVB r a d i o time s i g n a l was r e c o r d e d and ± 0.10 s when the time c o r r e c t i o n s were determined from the c a l i b r a t i o n of the i n t e r n a l c l o c k a t s i t e v i s i t s . The Backpack d a t a p r o v i d e d as seismograms by the E a r t h P h y s i c s Branch'were p l o t t e d at a r a t e of one second per i n c h and w i t h maximum a m p l i t u d e of the s e i s m i c s i g n a l v a r y i n g from one h a l f i n c h t o s i x i n c h e s . No time c o r r e c t i o n s f o r the i n t e r n a l c l o c k accompanied the r e c o r d s . Based on p e r s o n a l f i e l d r a t i n g s d u r i n g the e x p e r i m e n t , I assumed t h a t the t i m i n g e r r o r s were of the o r d e r of ± 0.2 s. 30 UJ u> I I I 1 1 1 1 1 0 0 " ° 80 120 160 200 240 260 320 HOURS F i g u r e 11 - Sample of i n t e r n a l c l o c k d r i f t from a d i g i t a l s e i s m i c s t a t i o n ( M i c r o c o r d e r , PCM). T h i s p l o t was o b t a i n e d from i n t e r n a l c l o c k times r e c o r d e d when the WWVB r a d i o was r e c o r d e d on a M i c r o c o r d e r over a p e r i o d of 12 days. D e s p i t e the f a c t t h a t the M i c r o c o r d e r s were s u b m i t t e d t o adverse c o n d i t i o n s (changes i n temperature and v e r y wet c o n d i t i o n s ) t h e i r i n t e r n a l c l o c k d r i f t s were s u r p r i s i n g l y l i n e a r . 31 -2.3 Ana l o g Data 2.3.1 M a g n e t i c Tape R e c o r d i n g s The FM a n a l o g systems r e c o r d e d s e i s m i c d a t a c o n t i n u o u s l y and p r o v i d e d r e c o r d s of good t o e x c e l l e n t q u a l i t y . Because of the c o n t i n u o u s r e c o r d i n g i t i s p o s s i b l e t o i d e n t i f y h i g h e r f r e q u e n c y e v e n t s (5-10 Hz) t h a t a r e s m a l l e r i n a m p l i t u d e than the lower f r e q u e n c y n o i s e on which they are superimposed. H i g h f r e q u e n c y n o i s e was an i n t e r m i t t e n t problem a t both a n a l o g r e c o r d e r s i t e s (RSA, GPA, F i g u r e 10) as both s i t e s were l o c a t e d c l o s e t o roads near a r e a s of a c t i v e l o g g i n g . The s u r f and m i c r o s e i s m i c a c t i v i t y superimposed a low f r e q u e n c y n o i s e of 0.1 to 0.5 Hz, o f t e n w i t h a m p l i t u d e s much l a r g e r than s e i s m i c e v e n t s . S i x c h a n n e l s were a v a i l a b l e f o r r e c o r d i n g on the Geotech FM ana l o g systems. Two ch a n n e l s were used f o r the t i m i n g of the s e i s m i c s i g n a l , one f o r the i n t e r n a l c l o c k and one f o r the WWVB r a d i o t i m e s i g n a l . When the WWVB time s i g n a l r e c e p t i o n was poor, time c o r r e c t i o n s were e s t i m a t e d from the i n t e r n a l c l o c k r a t i n g s when the WWVB r e c e p t i o n was good. The f o u r r e m a i n i n g c h a n n e l s r e c o r d e d the s e i s m i c s i g n a l a t v a r i o u s g a i n l e v e l s t o a v o i d s a t u r a t i o n by l a r g e e v e n t s . For p a r t of the time one v e r t i c a l and one h o r i z o n t a l seismometer were used. The p l a y b a c k s from t h e FM a n a l o g r e c o r d i n g s were o b t a i n e d u s i n g a Bru s h 480 e i g h t c h a n n e l c h a r t r e c o r d e r . The d a t a were 32 p l a y e d back a t a speed of 5 mm/s w i t h maximum amp l i t u d e of 4 cm. The a r r i v a l time f o r sharp a r r i v a l s can be measured t o ± 0.2 s w i t h h i g h f r e q u e n c y n o i s e b e i n g the main sou r c e of e r r o r . More r e l i a b l e a r r i v a l t i m e s c o u l d be d e t e r m i n e d when both the v e r t i c a l and a h o r i z o n t a l seismometer were o p e r a t e d . For some events the S a r r i v a l s were much c l e a r e r on the h o r i z o n t a l component. When both P and S a r r i v a l s on the v e r t i c a l and the h o r i z o n t a l s e i s m i c s i g n a l were c l e a r , no c o n s i s t e n t d i s c r e p a n c y between the a r r i v a l t i m e s on the v e r t i c a l and the h o r i z o n t a l s e i s m i c t r a c e s was ob s e r v e d . T h i s i n d i c a t e s t h a t sharp P and S a r r i v a l s measured on the v e r t i c a l s i g n a l t r a c e o n l y c o r r e s p o n d e d to the t r u e a r r i v a l s . The OBSs r e c o r d e d c o n t i n u o u s l y on a n a l o g magnetic t a p e . The n o i s e l e v e l s on the OBSs were p a r t i c u l a r l y h i g h i n Hecate S t r a i t where they were de p l o y e d i n s h a l l o w water on u n c o n s o l i d a t e d sediments. N o i s e produced by the t i d e s and s h i p s was r e c o r d e d p e r i o d i c a l l y and g e n e r a l l y o b l i t e r a t e d the s i g n a l . Thus o n l y t h r e e of the 6 OBSs r e c o r d e d s e i s m i c e v e n t s . The p l a y b a c k s o b t a i n e d were p l o t t e d at a r a t e of 10 mm/s. The h o r i z o n t a l and v e r t i c a l geophones, a hydrophone and an i n t e r n a l time c h a n n e l were r e c o r d e d on f o u r p a r a l l e l t r a c k s . The time c o r r e c t i o n s were e v a l u a t e d by assuming a l i n e a r d r i f t of the i n t e r n a l c l o c k between the time of deployment and r e c o v e r y . Because the temperature a t the bottom of the sea i s n e a r l y c o n s t a n t , changes i n the d r i f t r a t e of the OBSs c l o c k s were not l i k e l y t o o c c u r . The time c o r r e c t i o n s o b t a i n e d are a c c u r a t e t o ± 0.01 s (M a c k i e , 1985). H i g h f r e q u e n c y n o i s e p r e v e n t s a c c u r a t e 33 p i c k s of s m a l l a m p l i t u d e a r r i v a l s . The a c c u r a c y of the r e a d i n g s i s e s t i m a t e d t o be ± 0.1 s. Because of the h i g h n o i s e l e v e l most phases c o u l d not be measured more a c c u r a t e l y then ± 0.5 s. F i l t e r i n g the data would not a p p r e c i a b l y improve the r e s u l t s o b t a i n e d from the few ev e n t s r e c o r d e d on the OBSs. 2.3.2 Paper R e c o r d i n g s The paper seismograms o b t a i n e d w i t h the MEQ-800 were of v a r i o u s forms and q u a l i t y . S t a t i o n s L I P , PR 1 and PR2 ( F i g u r e 10) were o p e r a t e d a t 60 mm/min u s i n g an ink system w i t h the same g a i n and f i l t e r s e t t i n g s ( g a i n : 84 db; f i l t e r : 0-10 Hz) . Time c a l i b r a t i o n was performed a t the b e g i n n i n g or the end of each r e c o r d u s i n g the s i g n a l from the WWV r a d i o superimposed on the i n t e r n a l c l o c k . The i n t e r n a l c l o c k was r e g u l a r l y s y n c h r o n i z e d t o the WWV time b r o a d c a s t . The n o i s e l e v e l a t the P r i n c e Rupert s t a t i o n s (PR1 and PR2) was low. At Langara I s l a n d - ( s t a t i o n L I P ) the n o i s e from ocean s w e l l a t tim e s c o m p l e t e l y o b l i t e r a t e d the s e i s m i c s i g n a l . These t h r e e s t a t i o n s (PR1, PR2, LI P ) p r o v i d e d a r r i v a l time d a t a of good t o poor q u a l i t y w i t h r e a d i n g e r r o r s from ± 0.50 s t o i 1.00 s or more when the r a t i n g of the s t a t i o n s ' i n t e r n a l c l o c k s was not performed a d e q u a t e l y . An MEQ-800 i n t e r m i t t e n t l y r e c o r d e d data a t Gray P o i n t ( s t a t i o n GPP) f o r a s h o r t p e r i o d at the b e g i n n i n g of the experiment u s i n g smoked paper and a r a t e of 60 mm/min. The s t a t i o n was q u i e t except f o r i n t e r m i t t e n t t r a f f i c . Time c o r r e c t i o n s were performed r e g u l a r l y a t each s i t e v i s i t . Even though the s t a t i o n was o p e r a t e d a t 60 mm/min (as f o r the ink 34 o p e r a t e d s t a t i o n s L I P , PR1 and PR2), the r e s o l u t i o n of the t r a c e on smoke paper reduces the a r r i v a l t i me e r r o r s t o l e s s then ± 0.5 s. Two MEQ-800's (BQP and THP) were o p e r a t e d a t 120 mm/min w i t h second marks from the i n t e r n a l c l o c k superimposed on the' s e i s m i c s i g n a l . The time c o r r e c t i o n s f o r these s t a t i o n s were performed r e g u l a r l y a t the b e g i n n i n g or the end of the d a i l y r e c o r d s . The c l o c k d r i f t was then c a l c u l a t e d and a c c u r a t e time c o r r e c t i o n s were made. The i n t e r n a l c l o c k s were s y n c h r o n i z e d t o WWV r e g u l a r l y . The s e i s m i c s i g n a l f o r the two s t a t i o n s was r e c o r d e d on smoked paper p r o v i d i n g a c l e a n and s h a r p r e c o r d i n g . F u r t h e r the n o i s e l e v e l a t BQP and THP was s i g n i f i c a n t l y reduced by the use of the r e c o r d i n g i n s t r u m e n t f i l t e r s . The a c c u r a c y of the time a r r i v a l s was ± 0.2 s f o r the two s t a t i o n s o p e r a t e d a t 120 mm/min. The d a t a from the r e g i o n a l s t a t i o n s was r e c o r d e d on heat s e n s i t i v e paper a t a r a t e of 60 mm/min. The apparent n o i s e l e v e l a t t h e s e s t a t i o n s was low but t h e i r s e n s i t i v i t y i s much lower then the p o r t a b l e s t a t i o n s . The a c c u r a c y of the phase a r r i v a l r e a d i n g s from the permanent s t a t i o n s i s a t best ± 0.5 s. 35 I I I . HYPOCENTER LOCATIONS 3•1 I n t r o d u c t i o n A t o t a l of 310 d i s t i n c t s e i s m i c e v e n t s were o b s e r v e d d u r i n g the 64 days of the experiment (APPENDIX A) as i d e n t i f i e d on drum r e c o r d i n g s or r e c o r d e d on a t l e a s t two of the d i g i t a l s t a t i o n s . From the complete d a t a s e t , 130 ev e n t s were l o c a t a b l e i n the Queen C h a r l o t t e I s l a n d s r e g i o n . Hypocenter l o c a t i o n s w i t h r e l i a b l e s o l u t i o n s c o u l d be o b t a i n e d f o r e v e n t s t h a t were r e c o r d e d on a t l e a s t t h r e e s t a t i o n s and had a t o t a l of a t l e a s t f i v e P or S a r r i v a l s c l e a r l y i d e n t i f i a b l e . Four P or S a r r i v a l s a t t h r e e s t a t i o n s ( i . e . t h r e e l i n e a r l y independent d a t a p o i n t s i n space and one i n time ) a r e needed t o e v a l u a t e an hypocenter l o c a t i o n ( l a t i t u d e , l o n g i t u d e , f o c a l depth and o r i g i n time) e x a c t l y . One e x t r a degree of freedom was needed t o a s s e s s the q u a l i t y of the s o l u t i o n . The 1978 v e r s i o n of the computer program HYPOELLIPSE ( L a h r , 1980) was used f o r l o c a t i o n . HYPOELLIPSE d e t e r m i n e s the hy p o c e n t e r s of l o c a l or near r e g i o n a l e a r t h q u a k e s by m i n i m i z i n g the r o o t mean squares (RMS) of the t r a v e l time r e s i d u a l s , a method f i r s t d e s c r i b e d by G e i g e r (1912). For each event l o c a t i o n the e l l i p s o i d which e n c l o s e s the one s t a n d a r d d e v i a t i o n volume i s p r o v i d e d by HYPOELLIPSE. T h i s p r o v i d e s a means t o a s s e s s the r e l i a b i l i t y of the l o c a t i o n a t the one s t a n d a r d d e v i a t i o n l e v e l . The method f o r s o l v i n g the r e g r e s s i o n 36 e q u a t i o n s and f i n d i n g the s t a n d a r d e r r o r e l l i p s o i d was d e v e l o p e d by Lahr (1978). The hypocenter s o l u t i o n s f o r the 130 s e i s m i c events from the HYPOELLIPSE program a r e g i v e n i n APPENDIX B. 3.2 C r u s t a l S t r u c t u r e The c r u s t a l s t r u c t u r e used i n the HYPOELLIPSE l o c a t i o n program was a m o d i f i e d s t r u c t u r e from two r e f r a c t i o n s t u d i e s , one by Johnson et a l . ( l 9 7 2 ) i n Dixon E n t r a n c e and the o t h e r by Horn et a l . (1984) a c r o s s the Queen C h a r l o t t e I s l a n d s near l a t i t u d e 52° 30'. One f e a t u r e of HYPOELLIPSE i s t h a t i t i s p o s s i b l e t o d e f i n e d i f f e r e n t o n e - d i m e n s i o n a l c r u s t a l s t r u c t u r e s f o r v a r i o u s groups of s t a t i o n s . Because of the r a p i d l y v a r y i n g c r u s t a l s t r u c t u r e i n the e a s t - w e s t d i r e c t i o n , t h i s f e a t u r e was used ( F i g u r e 12). The program e v a l u a t e s t r a v e l t i m e s by c a l c u l a t i n g f o r each s t a t i o n the time t h e a p p r o p r i a t e ray t a k e s t o t r a v e l from the hypocenter through the o n e - d i m e n s i o n a l l a y e r e d c r u s t a l s t r u c t u r e a s s i g n e d t o each s t a t i o n . The v e l o c i t i e s f o r the model l a y e r s are d e f i n e d by the v e l o c i t y at the t o p of each l a y e r and a v e r t i c a l l i n e a r g r a d i e n t throughout the t h i c k n e s s of the l a y e r . D i f f e r e n t c r u s t a l s t r u c t u r e s were a s s i g n e d t o d i f f e r e n t groups of s t a t i o n s . Most s t a t i o n s were a s s i g n e d a c r u s t a l s t r u c t u r e model w i t h v e l o c i t i e s and g r a d i e n t s d e r i v e d from Horn et a l . (1984), F i g u r e 7. The depth of the Moho f o r t h e s e s t a t i o n s was s e t t o 25 km i n agreement w i t h the model of Johnson et a l . (1972) f o r l o n g i t u d e s of 132° t o 133° west ( F i g u r e 12, 37 F i g u r e 12 - C r u s t a l models used t o l o c a t e h y p o c e n t e r s . The models used f o r the f o l l o w i n g groups of s t a t i o n s by HYPOELLIPSE were: • West Queen C h a r l o t t e I s l a n d s : L I P , 0W1, OW2, SJB • San C r i s t o v a l b a t h o l i t h : GBM, IBM • E a s t Queen C h a r l o t t e I s l a n d s : BIM, BQP, DIM, GPA, GPP, ICM, LIM, LOM, PLM, PIM, THP, SRM, JUM, THM. • M a i n l a n d : PR1, PR2, OFB, 0E4. The deep ocean c r u s t a l model was used t o r e l o c a t e e v e nts i n i t i a l l y l o c a t e d f a r t o the west of the Queen C h a r l o t t e I s l a n d s ( s e c t i o n 3.2). 38 e a s t Queen C h a r l o t t e I s l a n d s ) . Two s t a t i o n s were l o c a t e d on the San C r i s t o v a l B a t h o l i t h , a t Gowgaia Bay (GBM) and a t I n s k i p Beach (IBM) ( F i g u r e 5 ) . These were a s s i g n e d a c r u s t a l model w i t h h i g h e r than normal s u r f a c e v e l o c i t y which i s a p p r o p r i a t e f o r a g r a n i t i c b a t h o l i t h ( F i g u r e 12, San C r i s t o v a l B a t h o l i t h ) . A l s o , i t was found t h a t the s t r u c t u r e d e s c r i b e d p r e v i o u s l y ( e a s t Queen C h a r l o t t e I s l a n d s ) gave average r e s i d u a l s , between c a l c u l a t e d and o b s e r v e d t r a v e l t imes f o r s t a t i o n s IBM and GBM, t h a t were c o n s i s t e n t l y p o s i t i v e . T h i s i n d i c a t e s t h a t the c r u s t a l v e l o c i t i e s i n s t r u c t u r e 'east Queen C h a r l o t t e I s l a n d s ' were too slow f o r the two s t a t i o n s GBM and IBM. A f a s t e r s u r f a c e v e l o c i t y was a l s o needed f o r a r r i v a l s r e c o r d e d on the b a t h o l i t h d u r i n g a r e f r a c t i o n s u r v ey i n the a r e a (Horn et a l . 1984). The s t a t i o n s n e a r e s t t o the Queen C h a r l o t t e t r a n s f o r m f a u l t zone, on Langara I s l a n d ( L I P ) , a t Cape St James (SJB) and the two ocean bottom seismographs (OW1, 0W2) were a s s i g n e d a more o c e a n i c - l i k e s t r u c t u r e w i t h the Moho a t 15 km d e pth and c r u s t a l v e l o c i t y d e r i v e d from Horn et a l . (1984). A g a i n , more c o n s i s t e n t average s t a t i o n r e s i d u a l s were o b t a i n e d f o r these t h r e e s t a t i o n s when the 'west Queen C h a r l o t t e I s l a n d s ' c r u s t a l s t r u c t u r e was used. The s t a t i o n s l o c a t e d on the Coast Mountain range a t P r i n c e Rupert (PR1, PR2) and a t Ocean F a l l s (OFB) were a s s i g n e d the same upper c r u s t a l s t r u c t u r e as i n e a s t Queen C h a r l o t t e I s l a n d s ( F i g u r e 12) but the c o n t i n e n t a l c r u s t was extended t o 30 km d e p th i n agreement w i t h Johnson et a l . (1972). 39 The r e l a t i v e l y complex c r u s t a l s t r u c t u r e d e s c r i b e d i s j u s t i f i e d as they p r o v i d e the best r e s u l t s f o r the hy p o c e n t e r l o c a t i o n s . That i s , a l a r g e r number of e v e n t s were l o c a t e d w i t h l a r g e s t s t a n d a r d e r r o r of l e s s than ± 5 km, and the average r e s i d u a l s at each s t a t i o n s were c l o s e s t t o z e r o , when the c r u s t a l s t r u c t u r e s of F i g u r e 12 were used. The hypocenter l o c a t i o n s d i d not v a r y much by c h a n g i n g the c r u s t a l s t r u c t u r e w i t h i n r e a s o n a b l e l i m i t s . For w e l l c o n s t r a i n e d s o l u t i o n s , o b t a i n e d from an a z i m u t h a l d i s t r i b u t i o n of r e c o r d i n g s t a t i o n s w i t h l a r g e s t gap l e s s than 180°, t y p i c a l l y a d i f f e r e n c e of l e s s than 3 km i n f o c a l d e pth would be the most remarkable change i n the l o c a t i o n . A range of c r u s t a l s t r u c t u r e s was used to t e s t the r e l i a b i l i t y of the f o c a l depths f o r a s e t of w e l l l o c a t e d e v e n t s ( F i g u r e 13). The depth d i d not v a r y by more than ± 3 km a t the one s t a n d a r d d e v i a t i o n l e v e l f o r a range of a p p r o p r i a t e c r u s t a l s t r u c t u r e s . That i s , the s t a n d a r d d e v i a t i o n s i n the v e r t i c a l d i r e c t i o n f o r the s o l u t i o n s f o r the same event o b t a i n e d u s i n g d i f f e r e n t c r u s t a l s t r u c t u r e s , were a l l w i t h i n ± 3 km of each o t h e r . N e v e r t h e l e s s , the r e s i d u a l and/or c a l c u l a t e d e r r o r e l l i p s o i d s were s i g n i f i c a n t l y improved w i t h the c r u s t a l s t r u c t u r e - s t a t i o n arrangement d e s c r i b e d p r e v i o u s l y . P o i s s o n ' s r a t i o f o r the Queen C h a r l o t t e I s l a n d s r e g i o n can be d etermined by r e g r e s s i o n of the d i f f e r e n c e between S a r r i v a l s v e r s u s the d i f f e r e n c e of P a r r i v a l s f o r p a i r s of s t a t i o n s which r e c o r d e d the same event ( e q u a t i o n 3.2.1). 40 crustal structures F i g u r e 13 - C r u s t a l s t r u c t u r e vs f o c a l depth. Four e v e n t s w i t h w e l l c o n s t r a i n e d s o l u t i o n s were used to t e s t the e f f e c t of v a r y i n g c r u s t a l s t r u c t u r e on the f o c a l depth. The open c i r c l e s a r e w e l l c o n s t r a i n e d s o l u t i o n s and a r e r e p r e s e n t e d w i t h one s t a n d a r d d e v i a t i o n e r r o r b a r s , the b l a c k d o t s r e p r e s e n t p o o r l y c o n s t r a i n e d s o l u t i o n s . Event numbers a r e as In APPENDIX B. Event 55 was l o c a t e d e a s t of the main f a u l t , the t h r e e o t h e r e v e n t s were l o c a t e d ont the Queen C h a r l o t t e t r a n s f o r m f a u l t a l o n g Moresby I s l a n d . The s i x c r u s t a l s t r u c t u r e s a r e : • -1- a l a y e r over a h a l f space w i t h top l a y e r v e l o c i t y of 6.3 km/s f o r 30 km and the h a l f space v e l o c i t y of 8.0 km/s. • -2- a s i m i l a r s t r u c t u r e w i t h l a y e r v e l o c i t y of 5.8 km/s f o r 18 km and h a l f space v e l o c i t y of 7.9 km/s. • -3- from Mackie, 1985: two l a y e r s over a h a l f space w i t h l i n e a r v e l o c i t y g r a d i e n t : f i r s t l a y e r v e l o c i t y at the top G.O km, g r a d i e n t 0.02 km/s/km, t h i c k n e s s 10 km; second l a y e r v e l o c i t y at the top G.5 km/s, g r a d i e n t 0.06 km/s/km, t h i c k n e s s 8 km; h a l f space v e l o c i t y at the top 8.0 km/s, g r a d i e n t 0.006 km/s/km. • -4- o c e a n i c c r u s t a l model from F i g u r e 12. • -5- west Queen C h a r l o t t e I s l a n d s c r u s t a l model from F i g u r e 12. • -6- c o m b i n a t i o n of c r u s t a l models as on F i g u r e 12. Note t h a t the b e s t c o n s t r a i n e d f o c a l depths a re o b t a i n e d w i t h the c o m b i n a t i o n of c r u s t a l model (6) d e s c r i b e d i n s e c t i o n 3.2. 41 VP / VS = ( S 2 - S, ) / ( P 2 - P i ) (3.2.1) where VP and VS a r e the P and S wave v e l o c i t i e s , r e s p e c t i v e l y , and P,, S,, P 2 and S 2 a r e P and S a r r i v a l times f o r a p a i r of s t a t i o n s which r e c o r d e d the same ev e n t . The r a t i o of VP t o VS i s the same as the r a t i o of S wave a r r i v a l time d i f f e r e n c e s ( S 2 - S,) t o P wave a r r i v a l time d i f f e r e n c e s ( P 2 - P,) f o r r a y s t r a v e l i n g the same d i s t a n c e i n the same media. The r e g r e s s i o n method used was t h a t of York (1969). A l l w e l l r e c o r d e d P and S p a i r s of a r r i v a l s were used i n the r e g r e s s i o n y i e l d i n g a s e t of 757 s t a t i o n p a i r s ( F i g u r e 14). A v a l u e of 1.771 ± 0.003 f o r the r a t i o of P v e l o c i t y t o S v e l o c i t y was found. T h i s c o r r e s p o n d s to a P o i s s o n ' s r a t i o of a = 0.266 ± 0.001. T h i s r a t i o was used to o b t a i n the shear v e l o c i t y -model from the P v e l o c i t y models d e s c r i b e d above. 3.3 Hypocenter L o c a t i o n s The f i n a l 130 e p i c e n t e r l o c a t i o n s d e t e r m i n e d from the hypocenter program a r e shown on F i g u r e 15, i n back p o c k e t . A symbol s c a l e d a c c o r d i n g t o the magnitude of the event marks i t s l o c a t i o n . The magnitude s c a l e used i s d e s c r i b e d i n Chapter V. The summary of the f i n a l h y p ocenter s o l u t i o n s a r e g i v e n i n APPENDIX B. 42 S wave a r r i v a l time d i f f e r e n c e s vs P a r r i v a l time d i f f e r e n c e s f o r p a i r s of s t a t i o n s . The s l o p e g i v e s the P v e l o c i t y t o S v e l o c i t y r a t i o and thus P o i s s o n ' s r a t i o . 43 3.3.1 I d e n t i f i c a t i o n and L o c a t i o n of B l a s t s Twenty of the t o t a l number of e v e n t s l o c a t e d were i d e n t i f i e d as p o s s i b l e b l a s t s . T h e i r l o c a t i o n s a r e marked w i t h diamonds on F i g u r e 15. The p o s s i b l e b l a s t s were a l l r e c o r d e d d u r i n g working h o u r s ; they had low frequency S a r r i v a l s w i t h a m p l i t u d e s s m a l l e r than normal ; and the f i r s t m otions of the s e e v e n t s were c o m p r e s s i o n a l at a l l r e c o r d i n g s t a t i o n s . They a r e a l l l o c a t e d i n a r e a s of known l o g g i n g a c t i v i t y . The t r u e l o c a t i o n of two b l a s t s was p r o v i d e d by Crown F o r e s t I n d u s t r i e s L t d . The e p i c e n t e r l o c a t i o n s , found w i t h HYPOELLIPSE, l i e w i t h i n 1 km of the t r u e l o c a t i o n f o r the b e s t , and 5 km f o r the w o r s t , s o l u t i o n ( F i g u r e 16). The more p o o r l y l o c a t e d b l a s t was r e c o r d e d on 4 s t a t i o n s w i t h P and S a r r i v a l s r e c o r d e d a t each s t a t i o n . However, o n l y t h r e e s t a t i o n s were w i t h i n 40 km of the event. The b l a s t was l o c a t e d a t a depth of 2 km w i t h s t a n d a r d e r r o r of ± 4 km. The s o l u t i o n was l a b e l l e d as a q u a l i t y 'C by HYPOELLIPSE. T h i s c o r r e s p o n d s t o e v e n t s w i t h l a r g e s t s t a n d a r d e r r o r of l e s s then ± 5 km but g r e a t e r than ± 2.5 km. The b e t t e r l o c a t e d b l a s t was r e c o r d e d on 6 s t a t i o n s a l l w i t h i n a r a d i u s of 40 km from the event. A l t h o u g h the s o l u t i o n was v e r y w e l l c o n s t r a i n e d (a q u a l i t y 'A' event w i t h l a r g e s t s t a n d a r d e r r o r l e s s then ± 1.25 km), i t was l o c a t e d a t a depth of 9 km. T h i s c o u l d i n d i c a t e t h a t the c r u s t a l s t r u c t u r e used had s u r f a c e v e l o c i t i e s too f a s t or t h a t the r a t i o of P t o S v e l o c i t y f o r the s u r f a c e l a y e r was too h i g h . In f a c t , i t was found t h a t VP/VS f o r the p o s s i b l e b l a s t d a t a s e t was 44 F i g u r e 16 - True b l a s t l o c a t i o n s vs h y p o c e n t e r b l a s t l o c a t i o n s . The HYPOELLIPSE l o c a t i o n s a re r e p r e s e n t e d by the open symbols (A and B ) . The t r u e l o c a t i o n by the b l a c k symbols (A' and B ' ) . Event A o c c u r r e d on day 180 a t 21:08 U.T. and was r e c o r d e d on 4 s t a t i o n s . Event B o c c u r r e d on day 200 a t 18:56 U.T. and was r e c o r d e d on 6 s t a t i o n s . The q u a l i t y of the s o l u t i o n i s d i s c u s s e d i n s e c t i o n 3.3.1. A summary of the HYPOELLIPSE s o l u t i o n s i s g i v e n i n APPENDIX B (eve n t s 14 and 3 0 ) . 45 s i g n i f i c a n t l y lower (1.74 ± .01) than the v a l u e found f o r the complete d a t a s e t (1.771 + .003). Because we know t h a t the b l a s t s were d e t o n a t e d a t the s u r f a c e , t h i s lower P o i s s o n ' s r a t i o i s o n l y r e p r e s e n t a t i v e of the uppermost c r u s t . Most e v e n t s were l o c a t e d a t depths g r e a t e r then 5 km. ' The i n a p p r o p r i a t e s u r f a c e v e l o c i t y and/or P o i s s o n ' s r a t i o s h o u l d not a f f e c t e a r t h quake h y p o c e n t e r l o c a t i o n s s i g n i f i c a n t l y . The HYPOELLIPSE s o l u t i o n s f o r the two b l a s t s were used t o a s s e s s the r e l i a b i l i t y of the hy p o c e n t e r l o c a t i o n s and e r r o r e s t i m a t e s found w i t h the program HYPOELLIPSE. Based on t h e s e two examples, the HYPOELLIPSE s o l u t i o n s and e r r o r e s t i m a t e s seems t o be r e p r e s e n t a t i v e of the q u a l i t y of the h y p o c e n t e r l o c a t i o n s . 3.3.2 A c t i v i t y E a s t of t h e Queen C h a r l o t t e T r a n s f o r m F a u l t A number of e a r t h q u a k e s were l o c a t e d e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t r e g i o n . None were a s s o c i a t e d w i t h known f a u l t s except one l o c a t e d i n s o u t h e a s t e r n Hecate S t r a i t ( F i g u r e 15). E i g h t e e n e a r t h q u a k e s were l o c a t e d on n o r t h e a s t Graham I s l a n d . The l a r g e s t had a magnitude of 3.8 and was l o c a t e d a l o n g Masset Sound a t a f o c a l depth of 3 km. Four e v e n t s were l o c a t e d i n Dixon E n t r a n c e ( F i g u r e 5 ) . They a r e i d e n t i f i e d w i t h a D i n APPENDIX B (eve n t s 20, 27, 59, 119). The s t a t i o n s r e c o r d i n g t h e s e n o r t h e r n e v e n t s a r e d i s t r i b u t e d such t h a t they c o v e r a wedge of l e s s than 90° i n a z i m u t h . C o n s e q u e n t l y , the Dixon E n t r a n c e h y p o c e n t e r s c o u l d be 46 m i s l o c a t e d by more than ± 6 km i n h o r i z o n t a l d i r e c t i o n a t the one s t a n d a r d d e v i a t i o n l e v e l w i t h no c o n t r o l on the f o c a l d e p th of the e v e n t s . A l l the e a r t h q u a k e s e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t have f o c a l depths w i t h i n the c o n t i n e n t a l c r u s t ( F i g u r e 17). H a l f had w e l l c o n s t r a i n e d s o l u t i o n s f o r which s t a n d a r d e r r o r s were l e s s than ± 5 km. S i n c e c r u s t a l depth i n the a r e a extends t o 25 km (Jonhson e t a l . , 1972), the s o l u t i o n s c o n s t r a i n the hypocenter t o the c r u s t . T h e r e f o r e , none c o u l d be a s s o c i a t e d w i t h a s u b d u c t i n g s l a b . 3.3.3 A c t i v i t y a l o n g the No r t h e r n Queen C h a r l o t t e T r a n s f o r m  F a u l t The most a c t i v e s e c t i o n of t h e Queen C h a r l o t t e t r a n s f o r m f a u l t d u r i n g the experiment was t o the northwest of Graham I s l a n d ( F i g u r e 15). One earthquake of magnitude 5.1 (on day 212) and two o t h e r s of magnitude 4.1 and 3.8 (on day 221 and 225 r e s p e c t i v e l y ) were l o c a t e d t h e r e . The a c t i v i t y i n the c l u s t e r was r e c o r d e d from day 175 u n t i l t h e end of the e x p e r i m e n t , on day 236. A t o t a l of 30 f o r e s h o c k s and a f t e r s h o c k s were i d e n t i f i e d and l o c a t e d . The s t a t i o n s used t o l o c a t e e v e n t s i n the n o r t h e r n c l u s t e r span a wedge of l e s s than 90° i n a z i m u t h . Thus the h y p o c e n t e r s a r e not v e r y w e l l d e f i n e d . To improve the e p i c e n t e r l o c a t i o n , the depth of th e s e e v e n t s was f i x e d a t 5 km, the depth of the 'bes t ' h y p o c e n t e r l o c a t i o n s o l u t i o n , i . e . w i t h s m a l l e s t s t a n d a r d F i g u r e 17 - Depth c r o s s s e c t i o n of hypocenters. S e l e c t e d h y p o c e n t e r s on the Queen C h a r l o t t e t r a n s f o r m f a u l t zone and e a s t of the zone are p l o t t e d on the c r o s s s e c t i o n . A l l f o c a l depths of events e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t zone are w i t h i n the c r u s t . F o c a l d e pth f o r e v e n t s l o c a t e d a l o n g Moresby I s l a n d i n the Queen C h a r l o t t e t r a n s f o r m f a u l t zone are s h a l l o w e r than 25 km, and the bulk of the s e i s m i c i t y i s w e l l above 15 km. The open c i r c l e s w i t h e r r o r b a r s r e p r e s e n t w e l l c o n s t r a i n e d l o c a t i o n s . The e r r o r b a r s r e p r e s e n t one s t a n d a r d d e v i a t i o n as c a l c u l a t e d by the HYPOELLIPSE program. The b l a c k dots r e p r e s e n t f i x e d d e p t h or p o o r l y c o n s t r a i n e d s o l u t i o n s . 48 d e v i a t i o n s and l o w e s t r e s i d u a l s , o b t a i n e d w i t h a f r e e depth. The l a t i t u d e and l o n g i t u d e of the 'best' event was a l s o used as a s t a r t i n g s o l u t i o n f o r ev e n t s i n the c l u s t e r . Only s m a l l a d j u s t m e n t s were needed by HYPOELLIPSE t o f i n d the be s t s o l u t i o n f o r a s i n g l e e v e n t . The f i x e d d e pth and s t a r t i n g s o l u t i o n gave more c o n s i s t e n t hypocenter l o c a t i o n s f o r the main shocks, f o r e s h o c k s and a f t e r s h o c k s i n the c l u s t e r . A t i g h t group (25 km a c r o s s ) of 33 hyp o c e n t e r l o c a t i o n s was o b t a i n e d . 3.3.4 The S e i s m i c i t y a l o n g the Queen C h a r l o t t e T r a n s f o r m F a u l t The r e m a i n i n g s e i s m i c a c t i v i t y i s spread over the l e n g t h of the Queen C h a r l o t t e t r a n s f o r m f a u l t and the w i d t h of the t e r r a c e , a l t h o u g h most of i t o c c u r s a l o n g the i n n e r s c a r p of the. t e r r a c e . T h i s s c a r p i s b e l i e v e d t o be the t r a c e of the c u r r e n t a c t i v e boundary between the P a c i f i c p l a t e and the N o r t h American p l a t e . The s c a t t e r observed o f f the t r a c e of the f a u l t i s s i g n i f i c a n t . Even though most of the s e i s m i c i t y i s a l i g n e d w i t h the i n n e r s c a r p , some w e l l l o c a t e d events ( w i t h s m a l l s t a n d a r d e l l i p s o i d s and low r e s i d u a l s ) o c c u r on the s h e l f , and the s e i s m i c a c t i v i t y extends t o the t r a c e of the o u t e r s c a r p ( F i g u r e 18, i n back p o c k e t ) . An area of low s e i s m i c a c t i v i t y i s p r e s e n t s o u t h of the n o r t h e r n c l u s t e r f o r a l e n g t h of about 50 km (between l a t i t u d e 53° 20' and 54°) where the s e i s m i c r a t e i s much lower than a l o n g Moresby I s l a n d . The depths of the ev e n t s a l o n g the Queen C h a r l o t t e 49 t r a n s f o r m f a u l t extend t o 25 km. W e l l l o c a t e d e v e n t s w i t h v e r t i c a l s t a n d a r d e r r o r s of l e s s than ± 2 km do o c c u r a t depths of 20 km. However, the b u l k of the s e i s m i c i t y w i t h w e l l c o n s t r a i n e d h y p o c e n t e r l o c a t i o n s (+ 2 km maximum s t a n d a r d d e v i a t i o n ) l o c a t e w e l l above 15 km depth ( F i g u r e 17). 3.3.5 S e i s m i c Gaps Only two e a r t h q u a k e s were l o c a t e d i n the s e i s m i c gap a t the southern end of the a r e a of s t u d y ( F i g u r e 8 ) . The s e i s m i c a c t i v i t y i s s i g n i f i c a n t l y lower i n the gap than i t i s w i t h i n the r u p t u r e zone of the 1949 e a r t h q u a k e . Another s e i s m i c gap ( d e s c r i b e d i n s e c t i o n 3.5.4) was o b s e r v e d i n the d a t a . T h i s gap i s s i m i l a r i n l e n g t h and i n a c t i v i t y r a t e s to the s o u t h e r n gap and i t has not e x p e r i e n c e d any major s e i s m i c a c t i v i t y s i n c e the 1949 Ms =8.1 e a r t h q u a k e . However, i t i s d i f f i c u l t t o d i f f e r e n t i a t e between the e f f e c t of t h e s h o r t p e r i o d of r e c o r d i n g and the a c t u a l d i f f e r e n c e i n s e i s m i c r a t e s a l o n g the f a u l t . The two gaps i n our data may be a r t i f a c t s of the s h o r t r e c o r d i n g p e r i o d . N e v e r t h e l e s s , i t i s s i g n i f i c a n t t h a t the two gaps observed i n our data are a l i g n e d w i t h s e c t i o n s of low s e i s m i c i t y a l o n g the f a u l t s i n c e 1949 ( F i g u r e 19). 50 54°^ UJ 53 Q ZD H 5* 52 * • O o CO Iii :^ O) o _ • > POSSIBLE SEISMIC G A P f > > M A G N I T U D E < 4 > . 4 - 4 . 9 • 5 - 5.9 • 6 - 6.9 i > > > C N 4 1 SEISMIC GAP t> > i 1 1 • 1 • 1 1950 1960 1970 1980 T IME ( Y E A R S ) F i g u r e 19 - S e i s m i c gaps. The d i s t r i b u t i o n of t h e s e i s m i c a c t i v i t y a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone s i n c e the 1949 earthquake i s shown i n time (from Rogers (1983) w i t h the d a t a from t h i s e x p e r i m e n t added). A s e i s m i c gap t o the south was documented by Rogers (1983). D u r i n g t h i s experiment two s i m i l a r gaps were o b s e r v e d - one to the n o r t h marked as " p o s s i b l e s e i s m i c gap", and one t o the south where the s e i s m i c gap has a l r e a d y been i d e n t i f i e d . 51 3.4 R e l o c a t i o n of Q u e s t i o n a b l e Hypocenters Seven e v e n t s , l o c a t e d west of the o u t e r s c a r p of the c o n t i n e n t a l s h e l f , a t depths g r e a t e r than 25 km, and the s i n g l e event i n s o u t h e a s t e r n Hecate S t r a i t were examined i n d e t a i l . H y pocenters w i t h a f o c a l depth g r e a t e r than 25 km were r e l o c a t e d w i t h the depth f i x e d a t 15 km or 25 km. These 'deep' events were not l o c a t e d w i t h more a c c u r a c y than ± 5 km i n the v e r t i c a l d i r e c t i o n and t h e i r a z i m u t h a l gap f o r s t a t i o n d i s t r i b u t i o n was l a r g e r than 300°. The f i x e d depths a r e marked w i t h an a s t e r i s k i n APPENDIX B. The q u a l i t y of the hypocenter s o l u t i o n s was not s i g n i f i c a n t l y a f f e c t e d by f i x i n g the d e p t h s . That i s , the r e s i d u a l s between o b s e r v e d and c a l c u l a t e d P and S a r r i v a l s f o r the r e l o c a t e d s o l u t i o n s a r e w i t h i n the range of r e a d i n g e r r o r s f o r the d a t a . T h i s i n d i c a t e s t h a t the s o l u t i o n s at f i x e d depth are w i t h i n the l i m i t of r e l i a b i l i t y . F i v e e p i c e n t e r l o c a t i o n s ( l a t i t u d e and l o n g i t u d e ) were not a f f e c t e d by f i x i n g the d e p t h of the deep e v e n t s a t a s h a l l o w e r v a l u e . Two e p i c e n t e r s were however a f f e c t e d by f i x i n g the depth at 15 km (Table I I I and T a b l e I V ) . The two e v e n t s ( e v e n t s 57 and 98 of APPENDIX B ) which o r i g i n a l l y l o c a t e d a t depths g r e a t e r than 50 km on the o u t e r s c a r p of the Queen C h a r l o t t e t e r r a c e s h i f t e d even more t o the west of the t e r r a c e when r e l o c a t e d a t a f i x e d depth ( F i g u r e 15). Because t h e s e two e v e n t s were l o c a t e d s i g n i f i c a n t l y west of the Queen C h a r l o t t e I s l a n d s the p a t h of r a y s t r a v e l l i n g from the two event h y p o c e n t e r s t o the s t a t i o n s on the Queen C h a r l o t t e 52 Q U A L I T V s e A Z HOP I Z O N T AL 0 . 2 9 - 3 8 SE A 2 t . 9 0 • 1 2 8 . V E R T I C A L S E • 3 1 5 D A T E O R I G I N L A T L O N G 8 4 5 2 1 9 1 9 2 0 2 3 . 0 0 5 2 N 3 3 . 5 1 I 3 2 W 4 3 . 8 6 S E OF 0 R 1 G . O 2 3 0 D E P T H 5 8 . 5 4 M A G N O D 3 C A P M R M S O . 6 8 5 3 2 3 1 0 . 0 3 17 I T E R A T I O N S T O T A L E R H 1 . 9 E R Z 0 SOD A D J I N NR AVR AAR NM 3 . 1 0 C D 0 . 0 9 10 7 0 . 0 0 0 . 0 2 0 P - W A V E T R A V E L - T I M E D A T A AND D E L A Y S ( " S T A T I O N D A T A - ) ( • -S T N O I S T A Z M A I N P S E C P R M K » T C O R - 0 * T T O S - T T C A L - D E L A Y - E D L V = I P - R E 5 I P - W T T H I C S 5 E C K R M S T T O B T T C A L I § - R E 5 1 S - W T • ) V A R I ( S - W A V E T R A V E L - T I M E D A T A - - ) T S B 5 2 . 5 6 4 137 3 5 . 3 0 0 P - 1 - 0 . 1 0 1 2 . 2 0 1 2 . 1 4 D I M 5 5 I J O I 3 G 3 5 3 8 0 P D O B O P 8 5 5 2 7 1 2 3 3 8 . 7 0 0 P O O 1 C M 1 1 0 . 1 0 - 1 117 0 . 1 2 . 3 S 1 2 . 4 1 0 . 3 3 16 0 3 1 5 . 9 7 •O 8 0 Q U A L I T Y E V A L U A T I O N 0 . 0 1 0 . 0 5 O . 2 0 9 O 0 0 O . O l n 0 0 O 0 3 0 . 0 5 I . 2 5 7 O . 6 5 4 5 0 9 5 . 5 8 0 0 3 2 1 . 7 3 2 1 . 4 9 0 . 2 2 0 . 0 7 0 0 2 8 2 8 2 8 2 8 1 34 , 2 0 3 4 . 2 0 D I A G O N A L S I N O R D E R OF S T R E N G T H A V E OF F N [ l r o I N 1 S Z O 15 NE O . 19 SW O 3 5 F O 6 7 N SE NW O 7 2 0 . 8 1 0 8 1 N U M B E R 5 RMS M I N ORMS A V E D R M S O 0 3 O . 1 4 0 . 5 3 Q U A L 1 T Y C Q U A L I T Y = D SE A 7 H O R I Z O N T A L 0 . 6 5 - 2 B S E AZ V E R 1 I C A L SE = 6 . D A T E O R I G I N L A T L O N G D E P T H M A G NO 0 3 G A P M RMS E R H 8 4 5 2 1 9 1 9 3 0 2 3 . 9 0 5 2 N 3 0 . O 8 1 3 2 W 5 3 . 5 9 2 5 . 0 0 O . 6 1 5 0 3 2 8 I 0 . 3 7 1 6 S E OF 0 R 1 G • O 2 t 3 6 I T E R A T I O N S T O T A L E R Z Q SQO 6 . 7 0 C 0 A D J I N NR AVR AAR NM O 0 4 1 1 7 - 0 0 0 C . 3 0 0 - S T A T I O N D A T A - ) A I N ( P - WAVE T R A V E L - T I M E D A T A AND D E L A Y S - - ) V A R I (  S - W A V E T R A V E L - T I M E D A T A - - ) S T N D I S T A Z M P S E C P R M K * T C O R - O - T T O B - T T C A L - D E L A Y - E O L Y * P - R E S P - W T T H I C S S E C K R M S T T O B T T C A L S - R t S s - WT T S B 6 5 2 6 3 1 0 8 3 5 . 3 0 0 P - 3 - 0 10 1 1 . 3 0 1 0 . 9 6 0 . 0 0 1 0 . 3 3 0 . 1 5 4 0 . 4 4 . 8 3 3 2 0 . 8 3 1 9 . 4 1 1 4 1 0 I S A D I M 6 7 2 4 3 107 3 5 . 3 8 0 P D 0 0 . 1 1 . 4 8 1 1 . 2 4 0 . 0 . 0 0 0 . 2 3 2 . 7 7 2 0 . B O P 9 6 . 4 3 1 101 3 8 . 7 0 0 P D 0 0 . 3 3 1 5 . 1 3 15 . S 3 0 . 0 . 0 1 - 0 . 4 1 1 . 2 5 8 0 . 5 0 . 9 5 0 2 7 . 3 8 2 7 . 5 1 - 0 . ' 4 1 2 5 8 I C M 1 2 0 3 1 0 0 9 9 - 0 8 0 0 . O . O O 0 . 5 8 . 0 0 3 3 3 3 0 3 3 . 8 3 - 0 . 5 4 0 4 0 4 Q U A L I T Y E V A L U A T I O N D I A G O N A L S I N O R D E R OF S T R E N G T H A V E . OF END P O I N T S Z - O . O O NE O . 12 SW O . 19 E O . 2 2 S E 0 2 7 NW 0 . 2 7 N O . 37 N U M B E R 6 R M S O 3 7 M I N D R M S - 0 . 0 6 A V E D R M S 0 . 2 1 O U A L I T Y D SE AZ H O R I Z O N T A L 0 . 6 4 - 3 5 . O A T E O R I G I N L A T L O N G D E P T H MAC. NO 0 3 G A P M RMS 8 4 5 2 1 9 1 9 2 0 2 4 4 Q 5 2 N 3 3 3 0 1 3 2 W 3 B . 4 6 2 5 0 0 O 6 8 3 3 2 3 I 0 . 6 3 S E OF O R I G • 0 . 3 8 2 7 I T E R A T I O N S T O T A L SE AZ E R H 2 5 2 . 4 8 - 1 2 5 V E R T I C A L SE • 8 0 3 E R Z Q S O D A D J I N NR AVR AAR NM B O D D 0 0 . 0 2 11 7 O . O O 0 . 5 2 O - S T A T I O N OA T A - ) ( P - WAVE T R A V E L - T I ME DATA AND D E L A Y S - - ) V A R I (  S - W A V E T R A V E L - T I M E D A T A - - 1 S T N D 1 S 1 A Z M A I N P S E C P R M K T C 0 R - 0 - T T 0 8 - T T C A L - D E L A Y EDL Y * P - R E S P - W T T H I C S S E C K R M S T T O B T T C A L S - R t S S - WT T S B 4 7 . 3 6 0 1 1 3 3 5 . 3 0 O P - 1 - 0 . 1 0 1 0 . 8 0 9 . 9 0 0 . 0 . 0 1 0 8 9 0 . 3 5 2 0 . 4 4 8 3 3 2 0 . 3 3 1 7 . 5 2 2 7 9 0 1 17 D I M 5 1 . 7 3 4 1 1 1 3 5 . 3 8 O P D 0 0 . 1 0 . 9 8 1 0 . 5 5 0 . 0 . 0 0 0 4 3 2 . 1 1 4 0 . B O P 8 3 . 3 2 3 1 0 3 3 8 . 7 0 0 P D 0 0 . 3 3 1 4 . 6 3 1 5 . 3 4 0 . 0 0 1 - 0 . 7 2 1 . 1 3 0 0 . 5 0 . 9 5 0 2 6 . 8 8 2 7 . 1 7 - 0 . 3 1 1 1 3 0 I C M 1 0 4 . 9 1 0 5 1 0 0 - 0 . 8 C 0 . O . O O 0 5 8 0 0 1 3 2 . 8 0 3 3 . 13 - 0 . 3 3 1 1 5 6 Q U A L I T Y E V A L U A T I O N D I A G O N A L S I N O R O E R OF S T R E N G T H A V E . OF END P O I N T S Z - 0 . 0 1 NE O . O G s w 0 13 E 0 3 3 NW 0 . 4 9 S E 0 . 5 0 N 0 . 5 5 N U M B E R 6 RMS O 6 3 M I N D R M S - 0 10 A V E D R M S O 2 9 O U A L I T Y [1 T a b l e I I I R e l o c a t e d event 57. T h i s event was o r i g i n a l l y l o c a t e d deep, west of the o u t e r s c a r p of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone. I t was f i r s t l o c a t e d w i t h f r e e d e pth and the c r u s t a l s t r u c t u r e d e s c r i b e d i n s e c t i o n 3.4. The HYPOELLIPSE s o l u t i o n i s shown i n ( 1 ) . Then, i t was r e l o c a t e d at f i x e d depth (25 km) w i t h the same c r u s t a l s t r u c t u r e . The e p i c e n t e r s h i f t e d even f u r t h e r west of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone, ( 2 ) . T h i r d l y the event was r e l o c a t e d a t f i x e d f o c a l d e pth u s i n g a c r u s t a l s t r u c t u r e c o r r e s p o n d i n g to the v e l o c i t y s t r u c t u r e on the s h e l f (Horn et a l . , 1984). T h i s l a s t e p i c e n t e r i s the p r e f e r r e d s o l u t i o n f o r t h i s e v e n t . I t l i e s on the s h e l f at an a c c e p t a b l e depth of 25 km ( 3 ) . A l t h o u g h the q u a l i t y of the s o l u t i o n (QUALITY...) worsens f o r each r e l o c a t i o n , the f i n a l s o l u t i o n r e s i d u a l s (P-RES and S-RES) a r e s t i l l w i t h i n a r r i v a l time r e a d i n g e r r o r s f o r t h i s e v e n t . 53 HORIZONTAL VERTICAL QUALITY • B SE • 1.82 SE • 1_90 SF - 1 . 9 1 - J — — — ~ AZ • 3 3 . AZ • -57. DATE ORIGIN LAT LONG DEPTH MAG NO 03 GAP M RMS • 49209 2 1 3 6 .19.63 53N32.83 13JW 1.03 5 5 3B O 10105 352 1 0.09 St Of ORIG • 0.318 15 ITERATIONS TOTAL E RH 1 9 ERZ 0 SOO ADO IN NR AVR AAR NM t . 9 D C DO. 06 10 14 O. OO O 04 O (- STATION DATA -) ( P-WAVE TRAVEL-TIME DATA AND STN DIST AZM A IN PSEC PRMK•1 COR-0-TTOB-TTCAL-OELAY-EDLY• DELAYS --PCM HSA LIP MI M 80P THP CPA 76 . lOO 101 105 128 132 1 5 6 86 98 38 79 105 104 107 125 1 18 1 18 1 16 1 12 1 1 1 108 7.440PD3 6.700P*4 10.910P02 10.750PC0 14.890P*1 17 .81 17 .07 O.33 21.61 1 .02 22. 14 17 ,74 17.71 2 1 .56 22 .05 25 26 25.48 0. O O. 0. O. O. O. 0.00 O.OI 0.01 0.00 0.01 0.00 O 02 P-RES O 06 0.04 0.09 -0.24 -- ) VARI I - -P-WT IIIIC SSEC KRMS T T OB T1CAL S-WAVE TRAVEL-TIME DATA 0.248 0.0 0.273 0.516 14 89 20 95 18.10 2 1.61 26 . 86 36 95 33 8 I 1 25 . 26 25.27 3 31 32 30 89 4 28 47 30 83 3 31.98 31.97 3 37 . 56 37 . 54 2 38.34 38.38 2 44.18 44.36 •0 01 0.42 0.01 O.OI -0.04 -O. 22 • ) S-WT 6 4 3 4 0 241 0 0 1 .395 O. 137 O 258 O 186 QUALITY EVALUATION DIAGONALS IN ORDER OF STRENGTH AVE. OF END POINTS NE O. 12 SE 0. 18 NW 0 19 N 0 2 1 E 0.22 Z 0.26 SW 0 38 HORIZONTAL VERTICAL SE • 1.96 SE • 3 48 SE * 11.86 AZ • -56 AZ • 34 DATE ORIGIN LAT LONG DEPTH MAG NO 03 GAP M RMS ERH ERZ 0 SOD AOJ IN NR AVR AAR NM 845209 2136 49.52 53N25 74 134WII 35 25.00 0 10120 350 1 0.36 3 5 11.9 0 C 0 O 08 11 14 O 00 0.26 O SE OF ORIG • 0 . 3 2 1 6 ITERATIONS TflVAL (- STATION OATA - I ( P-WAVE TRAVEL-TIME DA 1 A AND OELAYS I VARI ( S-WAVE TRAVEL-TIME OATA - - I STN 01ST AZM AIN PSEC PRMK• 1C0R-0 •TTOB- TTCAL- DELAY - EDLY• P-RES P-WT TH1C SSEC KRMS TTOB TTCAL s - R f s " S- WT PCM 89 . 1 78 102 0. 0 0.00 0. 14 . 89 1 25 37 25 . IB 0 19 4 030 RSA 111.1 91 100 7.440P03 0. 17 .92 17.74 0. 0.01 0. 18 0.599 0 20. 95 3 3 1.43 30.88 0.54 0 599 LI P 118 5 39 100 6.700P»4 0. 17.18 18.70 O 0.01 0.0 0. 18 10 4 28.58 32.55 0 0 HIM 119.6 74 99 0. 0. 0.00 0. 2 1.61 3 32 .09 33.08 -0.99 0 793 BOP 137 .2 98 98 10.9I0PD2 0. 33 2 1.72 2 1 .64 0. O.OI 0.08 0.659 0. 26 . 86 3 37 .67 37 ,67 -0.01 0 330 THP 140.9 97 97 I0.750PC0 1 .02 22 . 35 22 . 19 0. 0.00 0.06 1 . 234 0 26.95 2 38 .45 38 .63 -0. 18 0 6 17 GPA 164 .0 101 96 14.890P*1 0. 25 .37 25.67 0. 0.02 -0.32 0. 690 0. 33 .8 1 2 44 . 29 44 .69 -0 43 0 460 QUALITY EVALUATION DIAGONALS IN OROER OF STRENGTH Z SE NW NE N E SW AVE. OF ENO POINTS O 03 O 08 O 09 O 15 0.18 O 35 O 39 HORIZONTAL VERTICAL QUALITY • D SE • 2.55 SE • 4.88 SE • 36.35 ~ ~ ~ " " ~ ~ " ~ AZ • -50 AZ . 40. DATE ORIGIN LAT LONG DEPTH 84S209 2136 50.40 5 3 N 2 1 7 3 133W55.33 15.00 SE OF OR IG • 0.484 7 ITERATIONS TOTAL MAG NO 03 GAP M RMS 0. 10105 347 I 0.60 ERH ERZ 0 SOD ADJ IN NR AVR AAR NM 4.9 36.4 0 0 0 0.02 11 14-0.00 0.42 0 (- STATION OATA -) ( P-WAVE TRAVEL-TIME DATA AND DELAYS STN OIST AZM AIN PSEC PRMK+TCOR-O'TTOB- TTCAL- DELAY -EOLY-PCM 74.2 69 97 0. 0. O.OO RSA 93.5 87 95 7 440PD3 0. 17.04 16.71 0. 0.01 MI M 105.3 67 95 0. 0. 0.00 L I P 114.8 29 94 6 700P*4 0. 16.30 20.07 0. 0.01 BOP 118.7 96 94 10 9I0PD2 0.33 20.84 20.68 0. 0.01 THP 122.4 95 94 10 750PCO 1 .02 21 .37 21 .28 0. 0.00 GPA 145 . 2 100 93 14 890P*1 0. 24 .49 24 . 88 0. 0.02 -) VARI ( P-WT THIC SSEC KRMS - S-WAVE TRAVEL-TIME DATA TTOB TTCAL (5-HE5 1 24 .49 24 . 18 30.55 29.59 31.21 32.89 27.70 35.54 36.79 36 63 37.57 37.68 43.41 44.07 ) 1 .69 O. 14 -O. 1 1 -0.70 S-WT 3.574 0.606 O. 777 0.0 0.356 0.67 1 0.544 QUALITY EVALUATION DIAGONALS IN ORDER OF STRENGTH AVE. OF ENO POINTS Z -0.00 NW 0.07 SE 0.08 NE O. 17 E O. 19 N O. 22 SW 0.24 NUMBER RMS MIN ORMS AVE ORMS OUALITY 10 0.60 -0.02 0.15 0 T a b l e -IV - R e l o c a t e d event &8. T h i s event was o r i g i n a l l y l o c a t e d deep, west of the o u t e r s c a r p of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone. I t was f i r s t l o c a t e d w i t h f r e e depth and the c r u s t a l s t r u c t u r e d e s c r i b e d i n s e c t i o n 3.4. The HYPOELLIPSE s o l u t i o n i s shown i n ( 1 ) . Then i t was r e l o c a t e d a t f i x e d depth (25 km) w i t h the same c r u s t a l s t r u c t u r e . The e p i c e n t e r s h i f t e d even f u r t h e r west of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone, ( 2 ) . T h i r d l y the event was r e l o c a t e d a t f i x e d f o c a l depth u s i n g a c r u s t a l s t r u c t u r e c o r r e s p o n d i n g to the v e l o c i t y s t r u c t u r e on the s h e l f (Horn et a l . , 1984). T h i s l a s t e p i c e n t e r i s the p r e f e r r e d s o l u t i o n f o r t h i s e v e n t . I t l i e s on the s h e l f a t an a c c e p t a b l e depth of 25 km ( 3 ) . A l t h o u g h the q u a l i t y of the s o l u t i o n (QUALITY...) worsens f o r each r e l o c a t i o n , the f i n a l s o l u t i o n r e s i d u a l s (P-RES and S-RES) a r e s t i l l w i t h i n a r r i v a l time r e a d i n g e r r o r s f o r t h i s e v e n t . 54 I s l a n d s would have been m a i n l y w i t h i n the v e l o c i t y c r u s t of the s h e l f . The use of a slow c r u s t a l v e l o c i t y s t r u c t u r e would t h e r e f o r e be more a p p r o p r i a t e t o l o c a t e these two e a r t h q u a k e s . The two events were r e l o c a t e d u s i n g a s t r u c t u r e w i t h slow c r u s t a l v e l o c i t i e s d e r i v e d from Horn e t a l . , (1984) ( F i g u r e 12, deep ocean). I t was p o s s i b l e t o f i n d w e l l - c o n s t r a i n e d s o l u t i o n s a t f i x e d s h a l l o w depth (25 km) f o r both e v e n t s . These s o l u t i o n s l o c a t e d a l o n g the o u t e r s c a r p of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone. A summary of the s o l u t i o n s f o r the t h r e e c a s e s f o r the two events i s g i v e n i n t a b l e I I I and IV and i n APPENDIX B : (1) the o r i g i n a l s o l u t i o n w i t h f r e e depth, (2) the r e l o c a t e d s o l u t i o n w i t h f i x e d depth a t 15 km and, (3) the f i n a l p r e f e r r e d s o l u t i o n r e l o c a t e d w i t h a low v e l o c i t y s t r u c t u r e and f i x e d d e p t h . The d e t a i l e d s o l u t i o n s f o r each event i n c l u d i n g r e s i d u a l s a t each s t a t i o n f o r the t h r e e c a s e s mentioned p r e v i o u s l y , are g i v e n i n Table I I I and Table IV. The o n l y event l o c a t e d t o the south of Hecate S t r a i t was a l s o examined c a r e f u l l y . The h y p o c e n t e r s o l u t i o n i s v e r y s t a b l e (event 33, APPENDIX B ) . The event i s b e l i e v e d t o have o c c u r r e d i n Hecate S t r a i t . No o t h e r a c t i v i t y i n s o u t h e a s t e r n Hecate S t r a i t was i d e n t i f i e d . 3.5 C o n c l u s i o n S i g n i f i c a n t s e i s m i c a c t i v i t y was r e c o r d e d e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t zone. None of the ear t h q u a k e s on n o r t h e r n Moresby I s l a n d c o u l d be a s s o c i a t e d w i t h known 55 f a u l t s . One event i s l o c a t e d i n Hecate S t r a i t p o s s i b l y on c r u s t a l l y p e r v a s i v e f a u l t s produced by r i f t i n g i n M i d d l e Miocene ( Y o r a t h and Chase, 1981). However, no o t h e r a c t i v i t y was r e c o r d e d i n t h i s a r e a . The a c t i v i t y e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t zone i s w e l l c o n s t r a i n e d t o f o c a l depths w i t h i n the c r u s t ; t h e r e i s no deep s e i s m i c i t y t h a t c o u l d be a s s o c i a t e d w i t h a s u b d u c t i n g s l a b . However, the l a r g e number of e a r t h q u a k e s e a s t of the Queen C h a r l o t t e t r a n s f o r m f a u l t c o u l d be a s s o c i a t e d w i t h s t r e s s g e n e r a t e d by the o b l i q u e convergent motion of the P a c i f i c p l a t e toward N o r t h A m e r i c a . The s e i s m i c a c t i v i t y a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone i s g e n e r a l l y a l i g n e d w i t h the i n n e r s c a r p of the t e r r a c e . The f o c a l depths are w e l l c o n s t r a i n e d t o be s h a l l o w e r than 25 km and the bulk of the a c t i v i t y i s above 15 km. There i s some s c a t t e r about the t r a c e of the i n n e r s c a r p throughout the w i d t h of the t e r r a c e . Three e v e n t s , not so w e l l c o n s t r a i n e d , a l i g n . w i t h the o u t e r s c a r p of the t e r r a c e . Two s e i s m i c gaps, a p p r o x i m a t e l y 60 km l o n g , were observed d u r i n g the e x p e r i m e n t . The s o u t h e r n gap has been documented by Rogers (1983) w i t h no s i g n i f i c a n t s e i s m i c i t y h a v i n g been observed f o r a t l e a s t 80 y e a r s . The n o r t h e r n gap l i e s w i t h i n the r u p t u r e zone of the 1949 Ms =8.1 earthquake w i t h no s i g n i f i c a n t s e i s m i c i t y r e c o r d e d s i n c e the 1949 earthquake ( F i g u r e 19). 56 IV. EARTHQUAKE MAGNITUDES A coda l e n g t h magnitude s c a l e was devel o p e d f o r the complete d a t a s e t by r e g r e s s i n g the magnitude of ev e n t s observed on the r e g i o n a l s t a t i o n s a g a i n s t the l o g a r i t h m of the coda l e n g t h a t s t a t i o n BQP. T h i s e n a b l e d d e t e r m i n a t i o n of l o c a l magnitude of the l o c a t e d e a r t h q u a k e s and a l l the events r e c o r d e d on s t a t i o n BQP. S t a t i o n BQP was chosen t o c a l i b r a t e the magnitude s c a l e and c a l c u l a t e the magnitude of most d e t e c t e d events because: (1) f o r the major p a r t of the experiment (from J u l y 4 t o August 24, 1983) s t a t i o n BQP was o p e r a t e d c o n t i n u o u s l y w i t h c o n s t a n t f i l t e r and g a i n s e t t i n g s ( T able I I ) , (2) due t o i t s h i g h s e n s i t i v i t y , low n o i s e l e v e l and c e n t r a l s i t e , BQP r e c o r d e d more events than any o t h e r s t a t i o n , and (3)' a l l the events r e c o r d e d on any s t a t i o n between J u l y 4 and August 24 were r e c o r d e d on BQP. The t e c h n i q u e of s i g n a l d u r a t i o n d e s c r i b e d by Lee et a l . (1972) was used t o c a l c u l a t e the magnitude of a l l the events r e c o r d e d d u r i n g the e x p e r i m e n t . E q u a t i o n 4.1 shows the r e l a t i o n s h i p between the s i g n a l d u r a t i o n or coda l e n g t h (F-P) and the magnitude s c a l e Mf. Mf = C, + C 2 l o g ( F - P ) (4.1) The two c o n s t a n t s C, and C 2 a r e s t a t i o n dependent. The coda l e n g t h , ( F - P ) , was de t e r m i n e d by measuring the l e n g t h i n time of the s i g n a l of an event from the time of f i r s t a r r i v a l (P) u n t i l the time a t which the s i g n a l c o u l d not be d i s t i n g u i s h e d above 57 the background n o i s e ( F ) . Twelve ea r t h q u a k e s f o r which the magnitudes (ML) were c a l c u l a t e d from permanent s t a t i o n r e c o r d i n g s by D r y s d a l e et a l . (1984a, b) were used t o d e r i v e the s t a t i o n dependent parameters i n 4.1 u s i n g the l i n e a r r e g r e s s i o n method of York (1969), (Table V F i g u r e 20). The r e s u l t s were C, = 4.96 ± 0.20 and C 2 = 3.80 ± 0.10 ( F i g u r e 2 0 ) , and were used t o c a l c u l a t e the magnitude of 265 e v e n t s f o r which s i g n a l d u r a t i o n v a l u e s from BQP were a v a i l a b l e (APPENDIX C ) . For the e a r l y p e r i o d of the experiment (June 23 t o J u l y 4, 1983) s t a t i o n BQP o p e r a t e d i n t e r m i t t e n t l y w i t h i n s t r u m e n t s e t t i n g s d i f f e r e n t from the l a t e r s e t t i n g s ( T a b l e I I ) . The d a t a r e c o r d e d on s t a t i o n BQP b e f o r e J u l y 4 w i l l be r e f e r r e d t o as 'BQP e a r l y ' . S i m i l a r l y the d a t a r e c o r d e d on s t a t i o n BQP a f t e r J u l y 4 w i l l be r e f e r e n c e d by 'BQP l a t e ' . I t i s not p o s s i b l e t o use the s i g n a l d u r a t i o n c o n s t a n t s C, and C 2 c a l i b r a t e d f o r s t a t i o n 'BQP l a t e ' t o c a l c u l a t e d i r e c t l y the magnitude of e a r l y e v e n t s . However as we s h a l l see, the two s t a t i o n s (GPP and 'BQP e a r l y ' ) can be used t o c a l c u l a t e the magnitude of the f i r s t t h i r t e e n l o c a t a b l e e v e n t s . Magnitudes (ML) c a l c u l a t e d by D r y s d a l e et a l . (1984a) were p r e f e r r e d over our magnitude e s t i m a t e s f o r e a r l y e v e n t s (APPENDIX B ) . Magnitudes f o r e v e n t s r e c o r d e d a t s t a t i o n GPP were c a l c u l a t e d u s i n g the v a l u e s of C, and C 2 from s t a t i o n 'BQP l a t e ' and found t o be c l o s e t o the D r y s d a l e e t a l . (1984a), magnitudes. T h i s i s t o be e x p e c t e d s i n c e the two s t a t i o n s (GPP and 1BQP l a t e ' ) had i d e n t i c a l i n s t r u m e n t s (MEQ-800 and Mark 5 8 BOP LOG(F-P ) BOP S.D. BOP MAG EPB MAG EPB S.D DAY HRMN 2 .00 2 3 1 1 . 88 1 . 90 1 . 89 2 .65 1.81 1 .90 2 . 37 2 . 28 1 . 96 1 . 96 0.03 0.02 0.03 0.03 0.03 0.01 0.04 0.03 0.01 0.01 0.02 0.02 2.6 3.8 2 . 2 2 . 3 2 . 2 5.1 1 .9 2.3 4 . 1 3 . 7 2.5 2 .5 2 . 7 4.0 2 . 2 2 2 5 1 2 4 , 3 2 2 . 6 0.2 0.2 0.2 0.3 O. 1 0.1 O. 1 O. 1 O. 1 0.2 0.3 6.1 187 187 204 208 2 12 2 12 2 15 2 19 22 1 225 228 2 29 0147 06 19 1 64 5 2049 0930 16 11 1344 0838 1747 2338 1 107 204 4 Table V - Data used f o r c a l i b r a t i o n of the magnitude s c a l e • S.D. I s the s t a n d a r d d e v i a t i o n . • BQP mag a r e the magnitudes of the e v e n t s e v a l u a t e d w i t h the c a l i b r a t e d magnitude s c a l e . • EPB mag i s the D r y s d a l e e t a l . (1984a, b) magnitude e s t imates. 59 F i g u r e 20 - C a l i b r a t i o n of s t a t i o n BQP f o r magnitude c a l c u l a t i o n . The data used f o r the r e g r e s s i o n a r e shown i n T a b l e V. The l i n e a r r e g r e s s i o n method of York (1969) i s used. 60 p r o d u c t s L-4C seismometer) w i t h s i m i l a r g a i n and f i l t e r s e t t i n g s . F u r t h e r , both were l o c a t e d on bedrock and were l e s s than 30 km a p a r t . A method t o e v a l u a t e the magnitude of e a r l y e v e n t s which were r e c o r d e d o n l y on 'BQP e a r l y ' was d e r i v e d . Four e v e n t s were r e c o r d e d a t both GPP and BQP d u r i n g the e a r l y p e r i o d of the e x p e r i m e n t . A c o r r e c t i o n f a c t o r (Cf) can be c a l c u l a t e d f o r 'BQP e a r l y ' u s i n g the d i f f e r e n c e between the average magnitudes of the t h r e e e v ents from b o t h s t a t i o n s (GPP and 'BQP e a r l y ' ) e s t i m a t e d w i t h C, and C 2 ( e q u a t i o n 4.2). Cf = ( Mf( GPP ) - Mf( 'BQP e a r l y 1 )) (4.2) T h i s c o r r e c t i o n f a c t o r (Cf = -0.4) i s used t o c a l c u l a t e magnitudes f o r e a r l y e v e n t s r e c o r d e d on BQP when GPP was not o p e r a t i n g (APPENDIX B ) . The s i g n a l d u r a t i o n s of s e i s m i c e v e n t s r e c o r d e d at s t a t i o n BQP were used t o c a l c u l a t e the magnitudes of 265 e v e n t s (APPENDIX C ) . The magnitudes range from -1.5 t o 5.1 w i t h e s t i m a t e d e r r o r s of ± 0.3. The d a t a s e t c o v e r s a l l e v e n t s l o c a t e d w i t h i n the boundary of the r e g i o n : from Louscoone I n l e t ( s t a t i o n L I P ) i n the n o r t h , t o Cape S t . James ( s t a t i o n SJB) i n the s o u th and P r i n c e Rupert ( s t a t i o n s PR1 and PR2) i n the e a s t ( F i g u r e 10). A l l the e v e n t s r e c o r d e d between J u l y 4 and August 24 on the s t a t i o n s mentioned above were r e c o r d e d at s t a t i o n BQP. 61 V. SEISMICITY RATES AND B-VALUE The s e i s m i c i t y r a t e and b - v a l u e i n the Queen C h a r l o t t e I s l a n d s r e g i o n d u r i n g t h i s experiment was d e t e r m i n e d by the method of maximum l i k e l i h o o d d e s c r i b e d by W e i c h e r t (1980). A magnitude d a t a s e t r e p r e s e n t a t i v e of the magnitude frequency d i s t r i b u t i o n i n the r e g i o n d u r i n g the experiment was s e l e c t e d from the complete s e t of magnitudes e v a l u a t e d from s t a t i o n 'BQP l a t e ' . The a c c e p t a b l e space w i t h i n which the magnitude d a t a s h o u l d l i e i n o r d e r t o r e p r e s e n t a d e q u a t e l y the magnitude frequency d i s t r i b u t i o n i n the Queen C h a r l o t t e I s l a n d s r e g i o n i s shown on F i g u r e 21 (a p l o t of d i s t a n c e (S-P) vs ma g n i t u d e ) . The da t a p o i n t s s h o u l d l i e w i t h i n the boundary r e p r e s e n t i n g : (1) the minimum magnitude of ev e n t s w i t h i n the b o u n d a r i e s of the r e g i o n but f a r from the r e c o r d i n g s t a t i o n , and (2) the maximum S-P v a l u e r e p r e s e n t i n g e v e nts t h a t o c c u r r e d i n the r e g i o n of i n t e r e s t . S m a l l magnitude e v e n t s o c c u r r i n g f a r from the s t a t i o n w i l l not be r e c o r d e d and thus w i l l m i s r e p r e s e n t the t r u e magnitude - f r e q u e n c y d i s t r i b u t i o n . F i g u r e 22 shows t h a t the magnitude f r e q u e n c y d i s t r i b u t i o n approaches a l i n e a r d i s t r i b u t i o n f o r events l a r g e r then 0.5. Thus a r e l i a b l e fa-v a l u e e s t i m a t e f o r the Queen C h a r l o t t e I s l a n d s r e g i o n s h o u l d be de t e r m i n e d u s i n g e v e nts w i t h magnitude l a r g e r then 0.5. A maximum v a l u e of 19.0 s f o r S-P r e c o r d e d a t BQP, c o r r e s p o n d i n g t o a p p r o x i m a t e l y 160 km, was used t o ensure t h a t the ev e n t s c o n s i d e r e d were i n the Queen C h a r l o t t e I s l a n d s r e g i o n . Of the 265 e v e n t s f o r which magnitudes were e v a l u a t e d , 172 had 62 6.0 F i g u r e 21 - S e l e c t e d magnitude d a t a s e t f o r e v a l u a t i o n of s e i s m i c r a t e s . The h a t c h e d r e g i o n c o r r e s p o n d s t o magnitudes c a l c u l a t e d from d a t a r e c o r d e d a t s t a t i o n BQP t h a t s h o u l d not be used t o e v a l u a t e the b - v a l u e and s e i s m i c i t y r a t e s f o r t h i s s t u d y . Only e v e n t s w i t h (S-P) v a l u e s > 19.0 and magnitude > 0.5 r e p r e s e n t a d e q u a t e l y th e magnitude-frequency d i s t r i b u t i o n i n the Queen C h a r l o t t e I s l a n d s r e g i o n . 0 63 magnitudes l a r g e r than 0.5 and S-P l e s s than 19.0 s e c . The magnitudes were grouped i n i n t e r v a l s of 0.6 u n i t s of magnitude. T h i s i n t e r v a l r e p r e s e n t s a c o n s e r v a t i v e e s t i m a t e of the e r r o r on the magnitude e v a l u a t e d i n t h i s study (Mf ± 0.3 ). T h i s i n t e r v a l a l s o reduces the s c a t t e r of the da t a p o i n t s about the b e s t f i t l i n e , p a r t i c u l a r l y a t the h i g h e r magnitude end of the r e l a t i o n s h i p , w i t h o u t u n d e r e s t i m a t i n g the a c c u r a c y of the magnitude s c a l e . An e s t i m a t e of the maximum p o s s i b l e earthquake s i z e a l o n g a f a u l t can be o b t a i n e d from the g e n e r a l r e l a t i o n between earthquake magnitudes and f a u l t a r e a g i v e n by Kanamori and Anderson, 1975. For the Queen C h a r l o t t e t r a n s f o r m f a u l t zone a maximum magnitude of w e l l over 8 would be e x p e c t e d . T h e r e f o r e , an a p r i o r i maximum magnitude of 9.0 was used t o dete r m i n e the b - v a l u e . However, t h i s maximum magnitude can be v a r i e d from 6.0 t o 10.0 w i t h o u t any s i g n i f i c a n t e f f e c t on the b-va l u e e s t i m a t e . A b - v a l u e of 0.61 ± 0.05 was dete r m i n e d f o r a l l the ev e n t s r e c o r d e d a t BQP between J u l y 4 and August 24 ( F i g u r e 2 3 ) . When p o s s i b l e b l a s t s were removed from the da t a s e t the b- v a l u e e s t i m a t e was 0.55 ± 0.05, a d i f f e r e n c e which i s not s i g n i f i c a n t a t the one s t a n d a r d d e v i a t i o n l e v e l . The b - v a l u e s e s t i m a t e d f o r eve n t s grouped by l o c a l r e g i o n s d i d not d i f f e r s i g n i f i c a n t l y from the r e g i o n a l g l o b a l b-value ( T a b l e V I ) . The b - v a l u e e s t i m a t e of 0.55 ± 0.05 i s s i g n i f i c a n t l y lower than the v a l u e of 0.71 ± 0.01 found by M i l n e e t a l . (1978) f o r eve n t s of magnitude between 4 and 8 i n the Queen C h a r l o t t e I s l a n d s r e g i o n . A low b-value means t h a t a l a r g e r f r a c t i o n of 64 • • V 5 -c o „ M=0.5 -2.0 0.0 1.0 2.0 M a g n i t u d e 3.0 4.0 5.0 F i g u r e 22 - Magnitude f r e q u e n c y d i s t r i b u t i o n . For e v e n t s w i t h magnitudes l a r g e r than 0.5 the magnitude-f r e q u e n c y d i s t r i b u t i o n approaches a l i n e a r r e l a t i o n s h i p . 65 i n M a g n i t u d e F i g u r e 23 - Maximum l i k e l i h o o d d e t e r m i n a t i o n of b - v a l u e . The events were regrouped i n i n t e r v a l s of ± 0.3 u n i t s of magnitude. A maximum p o s s i b l e magnitude f o r the Queen C h a r l o t t e I s l a n d s r e g i o n of 9.0 was used. 66 REGION B-VALUE +/- ST DEV A ( f o r 9 weeks) ALL EVENTS O.GO +/- 0 05 297 ALL EVENTS NO BLASTS 0.55 + /- 0 05 256 EVENTS ON FAULT, NO BLASTS 0.60 + /- O 05 237 NO EVENTS IN ML= 5.1 SERIES (N. OF MAIN FAULT) . 0.58 + /- 0 06 203 THE ML = 5.0 SERIES 0.72 + /- 0 07 205 EVENTS ON FAULT, NO EVENTS IN ML=5 1 SERIES. ... 0.65 + /- 0 07 185 EAST OF FAULT EVENTS 0.72 + /- 0 08 169 T a b l e VI - B-values f o r events grouped by r e g i o n s . B - v a l u e s were c a l c u l a t e d f o r events grouped by r e g i o n . No s i g n i f i c a n t d i f f e r e n c e e x i s t s a t the one s t a n d a r d d e v i a t i o n l e v e l . 67 the t o t a l number of e a r t h q u a k e s o c c u r s at the h i g h e r magnitudes. From M i l n e ' s e s t i m a t e , d e t e r m i n e d from data r e c o r d e d over a number of y e a r s , the e x p e c t e d number of e a r t h q u a k e s w i t h magnitude l a r g e r than 3.8 d u r i n g one y e a r , i s 10. D u r i n g the s h o r t r e c o r d i n g p e r i o d of 9 weeks, a s i x t h of a y e a r , 4 e v e n t s of magnitude l a r g e r than 3.8 were r e c o r d e d . I f the r a t e s o b s e r v e d d u r i n g the experiment are s c a l e d t o a one year p e r i o d , 23 events of magnitude l a r g e r than or e q u a l t o 3.8 would be r e c o r d e d . T h i s e f f e c t i s w e l l i l l u s t r a t e d on F i g u r e 24 i n which the d a t a s e t f o r t h i s s tudy was s c a l e d t o r e p r e s e n t a r e c o r d i n g p e r i o d of one year f o r comparison w i t h the M i l n e et a l . (1978) r e c u r r e n c e r e l a t i o n . The 4 l a r g e e v e nts r e c o r d e d d u r i n g the experiment might have b i a s e d the b - v a l u e e s t i m a t e toward a low v a l u e . 68 10.000.. Magnitude M F i g u r e 24 - Magnitude - f r e q u e n c y of o c c u r r e n c e r e l a t i o n s c a l e d t o one year of r e c o r d i n g . The r e l a t i o n d e r i v e d i n t h i s s tudy was s c a l e d t o a one year r e c o r d i n g p e r i o d . The magnitude f r e q u e n c y r e l a t i o n f o r the Queen C h a r l o t t e I s l a n d s r e g i o n c a l c u l a t e d by M i l n e et a l . (1978) i s g i v e n f o r c o m p a r i s o n . 69 V I . FAULT PLANE MECHANISM SOLUTIONS 6.1 I n t r o d u c t i o n I t was not p o s s i b l e t o f i n d w e l l - c o n s t r a i n e d f a u l t p l a n e mechanism s o l u t i o n s f o r s i n g l e e v e n t s due t o the poor d i s t r i b u t i o n of r e c o r d i n g s t a t i o n s . The s m a l l e s t a z i m u t h a l gap between s t a t i o n s i s 100° w i t h an average w e l l over 200° (APPENDIX B ) . The s e i s m i c s t a t i o n s were r e d i s t r i b u t e d d u r i n g the 9 weeks of the e x p e r i m e n t . T h e r e f o r e two e v e n t s g e n e r a t e d on an a c t i v e f a u l t from a s i m i l a r mechanism but d u r i n g d i f f e r e n t p e r i o d s of the experiment were r e c o r d e d on d i f f e r e n t s e t s of . s t a t i o n s . T h i s e f f e c t i v e l y expands the a z i m u t h a l d i s t r i b u t i o n s of f i r s t m otions r e c o r d e d from a p a r t i c u l a r l y a c t i v e a r e a . Assuming t h a t the o b s e r v e d f i r s t motions f o r a c l u s t e r of e v e n t s were g e n e r a t e d by s i m i l a r mechanisms, a w e l l c o n s t r a i n e d f a u l t p l a n e mechanism s o l u t i o n c o u l d be d e t e r m i n e d u s i n g a l l the ev e n t s i n the c l u s t e r . T h e r e f o r e composite f a u l t p l a n e , mechanism s o l u t i o n s f o r s i m i l a r e v e n t s w i t h a d j a c e n t h y p o c e n t e r s were g e n e r a t e d . The composite mechanisms were not c o n s t r a i n e d w e l l enough to p r o v i d e a c c e p t a b l e e s t i m a t e s of the d i p or t r e n d of a c t i v e f a u l t s . Changes i n c r u s t a l s t r u c t u r e d i d a f f e c t the d i s t r i b u t i o n s of f i r s t motions on the f a u l t p l a n e mechanism p l o t s . However, the g e n e r a l c h a r a c t e r of the r a d i a t i o n f i e l d was p r e s e r v e d . Thus c h a r a c t e r i s t i c s of the s t r e s s f i e l d 70 g e n e r a t i n g the observed mechanisms can be a s s e s s e d . F a u l t p l a n e mechanisms were d e r i v e d u s i n g the c r u s t a l s t r u c t u r e - s t a t i o n arrangement d e s c r i b e d i n Chapter I I I , s e c t i o n 3.2. S i x c l u s t e r s of e v e n ts were s e l e c t e d and the composite f a u l t p l a n e mechanism s o l u t i o n s determined f o r each ( F i g u r e 2 5 ) . The f i r s t motions f o r each event i n each group were p l o t t e d on an eq u a l area p r o j e c t i o n of the lower hemisphere of the r a d i a t i o n f i e l d . The f a u l t plane s o l u t i o n s were d e t e r m i n e d by f i t t i n g manually two p e r p e n d i c u l a r p l a n e s s e p a r a t i n g f i e l d s of compressions and d i l a t a t i o n s . 6.2 E v e n t s East of the Transform f a u l t The composite f a u l t p l a n e s o l u t i o n f o r earthquakes l o c a t e d e a s t of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone was d e t e r m i n e d u s i n g 10 e v e n t s ( F i g u r e 2 5 ) . I t was not p o s s i b l e t o f i n d a s o l u t i o n c o n s i s t e n t w i t h a l l the f i r s t m otions r e c o r d e d ( F i g u r e 26). However, a t h r u s t f a u l t mechanism f o r the c l u s t e r of e v e n t s i s most c o n s i s t e n t w i t h the d a t a . The a r r i v a l s (both compressions and d i l a t a t i o n s ) at the two P r i n c e Rupert s t a t i o n s (PR1 and PR2), t o the n o r t h of the e a r t h q u a k e s and the o t h e r c o m p r e s s i o n a l a r r i v a l s t h a t l i n e up w i t h the i n n e r boundary of a wedge of d i l a t a t i o n s , t o the s o u t h of the r a d i a t i o n f i e l d , c o n s t r a i n the mechanism t o t h r u s t f a u l t i n g ( F i g u r e 2 6 ) . A c o m p r e s s i o n a l s t r e s s t r e n d i n g n o r t h - s o u t h i s i n d i c a t e d by the f a u l t p l a n e mechanism s o l u t i o n . 71 F i g u r e 25 - L o c a t i o n of c l u s t e r s used t o g e n e r a t e the composite f a u l t p l a n e mechanism s o l u t i o n s . • (1) the n o r t h e r n c l u s t e r i n c l u d e s e v e n t s : 4, 5, 27, 34, 35, 37, 64, 70-73, 75, 77-79, 81, 86, 87, 9 1 , 95, 99, 100, 105-108, 111, 112, 117. T h e i r f o c a l depth was f i x e d a t 5 km. • (2) t h e c l u s t e r e a s t of t h e Queen C h a r l o t t e t r a n s f o r m f a u l t i n c l u d e s e v e n t s : 17-19, 22, 50, 51, 55, 56, 61, 63, 65, 110, 114, 119, 120, 128, 129. T h e i r average f o c a l depth i s 6 ± 5 km. • (3) the c l u s t e r on the Queen C h a r l o t t e t r a n s f o r m f a u l t t o the n o r t h of Moresby I s l a n d i n c l u d e s e v e n t s : f o r c l u s t e r a, 15, 23, 40, 41, 43, 60, and f o r c l u s t e r b, 10, 38, 39, 42, 44, 45. The average depth f o r c l u s t e r a i s 12 ± 5 km, and b, 9 ± 1 km. • (4) a: the next c l u s t e r t o the s o u t h i n c l u d e s e v e n t s : 2, 24, 31, 32, 97, 126. The average depth f o r these e v e n t s i s 17 + 3 km. (4) b. The s o u t h e r n c l u s t e r c o n t a i n s e v e n t s : 6, 7, 68, 83, 84, 104, 125. The average depth f o r these e v e n t s i s 15 ± 6 km. 72 F i g u r e 26 - Composite f a u l t p l a n e mechanism s o l u t i o n f o r e v e n t s l o c a t e d i n l a n d . The open c i r c l e s a r e d i l a t a t i o n s , the b l a c k symbols i n the ha t c h e d a r e a are c o m p r e s s i o n s . The p l o t i s an e q u a l a r e a p r o j e c t i o n of the lower hemisphere of the r a d i a t i o n f i e l d . The s o l u t i o n i s not c o n s i s t e n t w i t h a l l the a r r i v a l s . A t h r u s t mechanism produced by n o r t h - s o u t h t r e n d i n g compression i s however n e c e s s a r y t o accommodate t h e c o m p r e s s i o n a l a r r i v a l s i n the c e n t e r of the r a d i a t i o n f i e l d . 73 N i F i g u r e 27 - Composite f a u l t p l a n e mechanism s o l u t i o n f o r the n o r t h e r n c l u s t e r . The open c i r c l e s are d i l a t a t i o n s , the b l a c k symbols i n the hatched a r e a a r e c o m p r e s s i o n s . The p l o t i s an e q u a l area p r o j e c t i o n of the lower hemisphere of the r a d i a t i o n f i e l d . Superimposed on the data i s a s t r i k e - s l i p mechanism r e p r e s e n t i n g motion i n the d i r e c t i o n of the P a c i f i c p l a t e w i t h r e s p e c t t o the N o r t h American p l a t e . 74 6.3 Events i n the N o r t h e r n C l u s t e r The composite f a u l t plane s o l u t i o n f o r e v e n t s i n the n o r t h west c o r n e r of the area of s t u d y ( F i g u r e 25) was d e t e r m i n e d u s i n g a l l 33 events i n the a r e a . The f a u l t p l a n e mechanism s o l u t i o n i s not w e l l c o n s t r a i n e d by the f i r s t motion d i s t r i b u t i o n s . The p a t t e r n of f i r s t motion i s , however, g e n e r a l l y c o n s i s t e n t w i t h r i g h t l a t e r a l s t r i k e s l i p motion a l o n g a p l a n e t r e n d i n g a p p r o x i m a t e l y n o r t h 40° west ( F i g u r e 27) which i s c l o s e t o the P a c i f i c p l a t e motion r e l a t i v e t o N o r t h America and the t r e n d of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone i n the n o r t h e r n p a r t of the a r e a of s t u d y . 6.4 E v e n t s a l o n g the Southern p a r t of t h e Queen C h a r l o t t e  T r ansform F a u l t Zone I t was p o s s i b l e t o d e f i n e f o u r composite f a u l t p l a n e mechanism s o l u t i o n s a l o n g the s o u t h e r n Queen C h a r l o t t e t r a n s f o r m f a u l t zone ( F i g u r e 2 5 ) . The e v e n t s were s e l e c t e d from t h r e e c l u s t e r s of seven or more e v e n t s each. Two composite f a u l t p lane mechanism s o l u t i o n s were d e t e r m i n e d from the n o r t h e r n c l u s t e r . The two f a u l t p l a n e s o l u t i o n s d e r i v e d from e v e n t s a t l a t i t u d e 52° 50' on the i n n e r s c a r p of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone were d e t e r m i n e d from a t i g h t c l u s t e r of 12 events ( F i g u r e 25). E i g h t of t h e s e e v e n t s a r e p a r t of a swarm t h a t o c c u r r e d over a p e r i o d of l e s s then 24 hours on J u l y 24. 75 A l l t he events from the swarm a r e l o c a t e d w i t h i n 2 km of each o t h e r . The c l o s e s t s t a t i o n t o the swarm (DIM) r e c o r d e d both c o m p r e s s i o n s and d i l a t a t i o n s f o r e v e n t s t h a t were p a r t of the swarm ( F i g u r e 28 a and b ) . The f i r s t motions o b s e r v e d on s t a t i o n DIM e i t h e r o r i g i n a t e d on b o t h s i d e s of the f a u l t p l a n e or i t s a u x i l i a r y , or were g e n e r a t e d by two d i f f e r e n t mechanisms. I t was not p o s s i b l e t o f i n d a s o l u t i o n t h a t would i n c l u d e the co m p r e s s i o n s and the d i l a t a t i o n s r e c o r d e d a t s t a t i o n DIM and the o t h e r f i r s t m o t i o n s . The events were t h e r e f o r e s e p a r a t e d i n t o two groups i n which f i r s t m o t i o n s were c o n s i s t e n t w i t h one a n o t h e r . The f a u l t p l a n e mechanism s o l u t i o n s from the f i r s t group of e v e n t s was de t e r m i n e d u s i n g s i x e v e n t s of which 3 were p a r t of the swarm. I t was p o s s i b l e t o f i t o n l y t h r u s t mechanisms t o the d a t a ( f i g u r e 28 a ) . The f i e l d of d i l a t a t i o n s extends on both s i d e s of the r a d i a t i o n f i e l d c o v e r i n g 140° and 90° i n a z i m u t h . There are o n l y two s m a l l wedges' of the r a d i a t i o n f i e l d where co m p r e s s i o n a r e , or c o u l d be, o b s e r v e d . The mechanism i s not w e l l c o n s t r a i n e d and i t i s not p o s s i b l e t o a s s e s s the t r e n d or the d i p of the p o s s i b l e f a u l t p l a n e . The t h r u s t component, however, i s n e c e s s a r y t o g e n e r a t e the observed d i s t r i b u t i o n of f i r s t m o t i o n s . The comp r e s s i v e s t r e s s n e c e s s a r y t o g e n e r a t e the o b s e r v e d t h r u s t i n g i s o r i e n t e d n o r t h - s o u t h . The second group c o n t a i n i n g e v e n t s from the swarm i n c l u d e s the r e m a i n i n g 6 e v e n t s i n the northernmost c l u s t e r . F i v e e v e n t s of t h i s group were from the swarm. The composite f a u l t p l a n e mechanism ( F i g u r e 28 b) d e t e r m i n e d from t h i s group has an even 76 N (b) F i g u r e 28 - Composite f a u l t p l a n e mechanism s o l u t i o n s i n c l u d i n g e v e n t s from a swarm. The open c i r c l e s are d i l a t a t i o n s , the b l a c k symbols i n the hatched area are c o m p r e s s i o n s . The p l o t i s an e q u a l a r e a p r o j e c t i o n of the lower hemisphere of the r a d i a t i o n f i e l d . The c i r c l e d d ata i s from a r r i v a l s r e c o r d e d on s t a t i o n DIM f o r e v e n t s i n a s h o r t swarm ( s e c t i o n 7.4). I t was not p o s s i b l e t o accommodate a l l the a r r i v a l s r e c o r d e d a t DIM w i t h a s i n g l e f a u l t p l a n e mechanism s o l u t i o n . (a) shows dominant t h r u s t mechanism due t o n o r t h - s o u t h c o m p r e s s i o n . (b) shows v e r t i c a l f a u l t i n g . 77 l a r g e r d i s t r i b u t i o n of d i l a t a t i o n s than the p r e v i o u s group a n a l y z e d ; i t c o v e r s 170° of the n o r t h e a s t h a l f of the r a d i a t i o n f i e l d . Compressions were r e c o r d e d i n the s o u t h e a s t e r n h a l f of the r a d i a t i o n f i e l d . A n e a r l y v e r t i c a l f a u l t mechanism i s r e q u i r e d t o f i t the f i r s t motion d a t a . The f o r c e s g e n e r a t i n g the s t r e s s f i e l d observed i n t h i s f a u l t plane mechanism are d i f f i c u l t t o e x p l a i n . The next c l u s t e r of events f o r which a compos i t e f a u l t p l a n e mechanism s o l u t i o n was g e n e r a t e d i s l o c a t e d a l o n g the i n n e r s c a r p of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone a t l o n g i t u d e 132° ( F i g u r e 2 5 ) . Seven e v e n t s were used f o r t h i s s o l u t i o n ( F i g u r e 29 a ) . A n e a r l y v e r t i c a l f a u l t mechanism w i t h a s m a l l component of t h r u s t f a u l t i n g i s ob s e r v e d . The f i e l d of d i l a t a t i o n s extends over 150° to .the west of the r a d i a t i o n f i e l d . A s h a l l o w a n g l e a u x i l i a r y p l a n e d i p p i n g e a s t i s n e c e s s a r y t o accommodate the few d i l a t a t i o n s r e c o r d e d t o the south a t s h a l l o w emergent a n g l e s ( F i g u r e 29 a ) . A c l u s t e r of seven e v e n t s l o c a t e d s l i g h t l y s o u t h e a s t from the p r e v i o u s group a l s o p r o v i d e d d a t a t o generate a composite f a u l t p l a n e mechanism s o l u t i o n ( F i g u r e 2 5 ) . A w e l l c o n s t r a i n e d t h r u s t f a u l t i n g mechanism i s r e q u i r e d by the d a t a ( F i g u r e 29 b) 6.5 C o n c l u s i o n Three d i f f e r e n t s t r e s s f i e l d s were observed from the r a d i a t i o n f i e l d of events r e c o r d e d d u r i n g t h i s s t u d y . A s t r i k e s l i p mechanism was c o n s i s t e n t w i t h e v e n t s r e c o r d e d on the Queen C h a r l o t t e t r a n s f o r m f a u l t zone t o the northwest of Graham 78 N 1 (b) F i g u r e 29 - Composite f a u l t p l a n e mechanism s o l u t i o n s i n c l u d i n g e v e n t s a l o n g s o u t h e r n Queen C h a r l o t t e t r a n s f o r m f a u l t . The open c i r c l e s a r e d i l a t a t i o n s , t h e b l a c k symbols i n the h a t c h e d area a r e c o m p r e s s i o n s . The p l o t i s an e q u a l area p r o j e c t i o n of the lower hemisphere of the r a d i a t i o n f i e l d . F i g u r e a. shows dominant v e r t i c a l f a u l t i n g w i t h a s m a l l component of t h r u s t . F i g u r e b. shows t h r u s t mechanism a s s o c i a t e d w i t h compression i n the n o r t h - s o u t h d i r e c t i o n . 79 I s l a n d . Events l o c a t e d e a s t of the Queen C h a r l o t t e t r a n s f o r m f a u l t e x h i b i t t h r u s t mechanisms. A t h r u s t mechanism a l s o i s most c o n s i s t e n t w i t h s h a l l o w e v e nts a l o n g Moresby I s l a n d on the Queen C h a r l o t t e t r a n s f o r m f a u l t . The c o m p r e s s i v e s t r e s s e s g e n e r a t i n g the t h r u s t i n g mechanisms obse r v e d a r e g e n e r a l l y o r i e n t e d n o r t h - s o u t h . T h i s i s c o n s i s t e n t w i t h the d i r e c t i o n of convergence of the P a c i f i c p l a t e toward the N o r t h American p l a t e . A l s o t h r u s t f a u l t i n g mechanisms are commonly obse r v e d i n s h a l l o w earthquakes i n a r e a s of s u b d u c t i o n ( e . g . Perez and Jacob, 1980). One c l u s t e r a l o n g Moresby I s l a n d on the Queen C h a r l o t t e t r a n s f o r m f a u l t e x h i b i t v e r t i c a l f a u l t i n g . The f o r c e s g e n e r a t i n g the s t r e s s f i e l d o b served on t h e s e mechanisms a r e d i f f i c u l t t o e x p l a i n . 80 V I I . SUMMARY AND CONCLUSION The d i s t r i b u t i o n of s e i s m i c a c t i v i t y i s m a i n l y l o c a t e d on the Queen C h a r l o t t e t r a n s f o r m f a u l t zone a l o n g the i n n e r s c a r p of the t e r r a c e . A s i g n i f i c a n t s c a t t e r about the s c a r p i s o b s e r v e d and t h e a c t i v i t y e xtends t o the o u t e r s c a r p . The f o c a l depth of the e v e n t s a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone e x t e n d t o 25 km f o r w e l l l o c a t e d e v e n t s . However the b u l k of the a c t i v i t y i s l o c a t e d w e l l above 15 km. Two a r e a s w i t h lower s e i s m i c i t y r a t e s were o b s e r v e d i n the d a t a a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone ( F i g u r e 18). The n o r t h e r n area i s one which has not e x p e r i e n c e d a major earthquake s i n c e the 1949 Ms = 8.1 earthquake and the s o u t h e r n a r e a l i e s w i t h i n a documented s e i s m i c gap t h a t has not e x p e r i e n c e d a major s e i s m i c event f o r at l e a s t 80 y e a r s . The gaps obser v e d i n the data c o u l d however be a r t i f a c t s of the s h o r t r e c o r d i n g p e r i o d (9 weeks). F a u l t p l a n e mechanism s o l u t i o n s were d e t e r m i n e d f o r 5 c l u s t e r s a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone. The n o r t h e r n c l u s t e r s o l u t i o n i s c o n s i s t e n t w i t h r i g h t l a t e r a l s t r i k e - s l i p motion a l o n g a p l a n e t r e n d i n g i n the d i r e c t i o n of the P a c i f i c p l a t e motion w i t h r e s p e c t t o N o r t h A m e r i c a . T h i s i s t o be e x p e c t e d s i n c e , t o the n o r t h the P a c i f i c p l a t e motion and the Queen C h a r l o t t e t r a n s f o r m f a u l t zone are a l i g n e d . Three of the f o u r r e m a i n i n g c l u s t e r s t o t h e south of the f a u l t a l o n g Moresby I s l a n d e x h i b i t t h r u s t f a u l t mechanisms. The t h r u s t mechanisms a r e e v i d e n c e f o r convergence between the P a c i f i c and N o r t h American p l a t e s i n the s o u t h e r n Queen C h a r l o t t e I s l a n d s r e g i o n . The f i n a l c l u s t e r shows a v e r t i c a l f a u l t i n g . m e c h a n i s m 81 which i s d i f i c u l t t o e x p l a i n . S i g n i f i c a n t a c t i v i t y was l o c a t e d e a s t of the main Queen C h a r l o t t e t r a n s f o r m f a u l t zone, i n p a r t i c u l a r on the n o r t h e a s t of Graham I s l a n d . One event of magnitude 3.8 was l o c a t e d a l o n g Masset Sound ( f i g u r e 5 ) . None of these e v e n t s c o u l d be a s s o c i a t e d w i t h f a u l t s i d e n t i f i e d i n the a r e a . F o c a l depth f o r these e v e n t s are w e l l c o n s t r a i n e d w i t h i n the c r u s t ; none c o u l d be a s s o c i a t e d w i t h a s u b d u c t i n g s l a b . A composite f a u l t p l a n e mechanism s o l u t i o n was determined f o r the i n l a n d e v e n t s . The s o l u t i o n e x h i b i t s a t h r u s t mechanism w i t h n o r t h - s o u t h t r e n d i n g compression a x i s . The earthquakes a r e i n t e r p r e t e d as the r e s u l t of s t r a i n g e n e r a t e d by the convergence of the P a c i f i c and N o r t h American p l a t e s . I t s h o u l d be noted however, t h a t the s t r e s s f i e l d produced by pure s t r i k e s l i p motion (NW^SE) a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t would a l s o be accompanied by n o r t h - s o u t h t r e n d i n g c o m p r e s s i o n a l s t r e s s . One event was l o c a t e d i n Hecate S t r a i t t o the south of Moresby I s l a n d . The s o l u t i o n i s w e l l c o n s t r a i n e d (± 15 km) and c o u l d be a s s o c i a t e d w i t h c r u s t a l l y p e r v a s i v e f a u l t s suggested by Y o r a t h and Chase (1981) (see s e c t i o n 1.3). The magnitudes of a l l l o c a t e d e v e n t s and a l l events r e c o r d e d on s t a t i o n 'BQP l a t e ' were det e r m i n e d w i t h a coda l e n g t h s c a l e . These data was used t o c a l c u l a t e s e i s m i c i t y r a t e s and a b - v a l u e i n the Queen C h a r l o t t e I s l a n d s r e g i o n . The c a l c u l a t e d b v a l u e of 0.55 ± 0.05 i s . s i g n i f i c a n t l y lower than p r e v i o u s e s t i m a t e s (0.71 ± 0.01 from M i l n e e t a l . , 1978). T h i s low b - v a l u e c o u l d be an a r t i f a c t of the s h o r t r e c o r d i n g p e r i o d 82 and the f a c t t h a t 4 e v e n t s w i t h magnitude Mf > 3.5 were r e c o r d e d over a 9 week p e r i o d . A c c o r d i n g to M i l n e e t a l . ' s (1978) e s t i m a t e s d e t e r m i n e d from d a t a r e c o r d e d over a number of y e a r s , o n l y 2 e v e n t s of magnitude l a r g e r then 3.8 a r e e x p e c t e d t o be r e c o r d e d d u r i n g a 9 week p e r i o d i n the Queen C h a r l o t t e I s l a n d s r e g i o n . The c o n c l u s i o n s w i t h r e s p e c t t o the t h r e e main o b j e c t i v e s s t a t e d i n s e c t i o n 1.5 are as f o l l o w . (1) There i s s i g n i f i c a n t s e i s m i c a c t i v i t y e a s t of t h e main t r a n s f o r m f a u l t i n the Queen C h a r l o t t e I s l a n d s r e g i o n . However, none of the r e c o r d e d e v e n t s c o u l d be a s s o c i a t e d w i t h known f a u l t s except f o r one event i n Hecate S t r a i t . (2) A l l l o c a t e d e a r t h q u a k e s were w i t h i n the c r u s t . The f a u l t p l a n e mechanism s o l u t i o n f o r c l u s t e r s of. e v e n t s i n the a r e a are c o n s i s t e n t w i t h r i g h t - l a t e r a l s t r i k e - s l i p motion to the n o r t h of the Queen C h a r l o t t e t r a n s f o r m f a u l t ; they e x h i b i t dominant t h r u s t i n g f o r e v e n t s on the s o u t h e r n p a r t of the f a u l t and f o r e v e nts s i g n i f i c a n t l y e a s t of the f a u l t . These mechanisms a r e c o n s i s t e n t w i t h the convergent motion of the P a c i f i c p l a t e toward N o r t h . A m e r i c a , but they c o u l d a l s o be g e n e r a t e d from the s t r e s s f i e l d a s s o c i a t e d w i t h s t r i k e - s l i p motion a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t . (3) A s i g n i f i c a n t d i f f e r e n c e between the s e i s m i c r a t e s w i t h i n the documented gap t o the s o u t h of Graham I s l a n d and the r a t e s w i t h i n the 1949 e a r t h q u a k e r u p t u r e zone was o b s e r v e d i n the d a t a . The number of e v e n t s l o c a t e d w i t h i n the a f t e r s h o c k zone was v e r y l a r g e (92) i n c o m p a r i s o n w i t h o n l y two e v e n t s w i t h i n the s e i s m i c gap a t i t s s o u t h e r n end. 8 3 B i b l i o q r a p h y B e v i e r , M.L., R.L. Armstrong And J.G. Souther, (1979). Miocene p e r a l k a l i n e v o l c a n i s m i n w e s t - c e n t r a l B r i t i s h Columbia - i t s t e m p o r a l and p l a t e - t e c t o n i c s s e t t i n g . Geology, 7, 389-392. B o s t w i c k T.K., (1984). A Re-Examination of the August 22, 1949 Queen C h a r l o t t e E a r t h q u a k e . M. Sc. 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Canadian J o u r n a l of E a r t h S c i e n c e s , J_5, 1170-1193. M i n s t e r J.B., T.H. J o r d a n , P. M o l n a r , E. H a i n e s , (1974). N u m e r i c a l m o d e l l i n g of i n s t a n t a n e o u s p l a t e t e c t o n i c s . G e o p h y s i c a l J o u r n a l of the R o y a l A s t r o n o m i c a l S o c i e t y , 36, 541-576. M i n s t e r J.B., T.H. J o r d a n , (1978). P r e s e n t day p l a t e m o t i o n s . J o u r n a l of G e o p h y s i c a l R e s e a r c h , 8_3, 5331-5354. Perez O.J., K.H. Jacob, (1980). T e c t o n i c model and s e i s m i c p o t e n t i a l of the e a s t e r n G u l f of A l a s k a and Yakataga s e i s m i c gap. J o u r n a l of G e o p h y s i c a l R e s e a r c h , 85, 7132-7150. R i d d i h o u g h R.P., (1982a). One hundred m i l l i o n y e a r s of p l a t e t e c t o n i c s i n Western Canada. Geoscience Canada, 9, 28-34. 85 R i d d i h o u g h R.P., (1982b). Contemporary movements and t e c t o n i c s on Canada's west c o a s t . T e c t o n o p h y s i c s , 8_6, 319-341. Rogers G.C., (1983). S e i s m o t e c t o n i c s Of B r i t i s h Columbia. Ph. D. t h e s i s , U n i v e r s i t y of B r i t i s h C o lumbia, Department Of G e o p h y s i c s And Astronomy, 247 pp. S r i v a s t a v a S.P., (1973). I n t e r p r e t a i o n of g r a v i t y and magnetic measurements a c r o s s the c o n t i n e n t a l margin of B r i t i s h C olumbia, Canada. Canadian J o u r n a l of E a r t h S c i e n c e s , 10, 1664-1677. S r i v a s t a v a S.P, D.L. B a r r e t t , C.E. Keen, K.S. Manchester, K.G. S h i n , D.L. T i f f i n , R.L. Chase, A.G. Thomlinson, E. E. D a v i s , C.R.B. L i s t e r , (1971). P r e l i m i n a r y a n a l y s i s of g e o p h y s i c a l measurements n o r t h of the Juan de Fuca Ridge. Canadian J o u r n a l of E a r t h S c i e n c e s , 8, 1265-1281. S u t h e r l a n d Brown A., (1968). Geology of the Queen C h a r l o t t e I s l a n d s . B r i t i s h Columbia Department Of Mines And P e t r o l e u m R e s o u r c e s , B u l l e t i n 54, 226 pp. Sykes L.R., (1971). A f t e r s h o c k zones of g r e a t e a r t h q u a k e s , s e i s m i c i t y gaps and earthquake p r e d i c t i o n f o r A l a s k a and the A l e u t i a n s . J o u r n a l of G e o p h y s i c a l R e s e a r c h , 7_6' 8021-8041. W e i c h e r t D.H., (1980). E s t i m a t i o n of the e a r t h quake r e c u r e n c e parameters f o r unequal o b s e r v a t i o n p e r i o d s f o r d i f f e r e n t magnitudes. B u l l e t i n of the S e i s m o l o g i c a l S o c i e t y of A m erica, 70, 1337-1346. Wickens A . J . , J.H. Hodgson, (1967). Computer r e - e v a l u a t i o n of earthquake mechanism s o l u t i o n s 1922-1962. P u b l i c a t i o n of the Dominion O b s e r v a t o r y , Ottawa, 3_3, 1-560. Y o r a t h C.J., B.E.B Cameron, (1982). O i l on the West Coa s t . G e o s c i e n c e Canada, J J _ , 13-15. Y o r a t h C.J., R.D. Hyndman, (1983). S u bsidence and t h e r m a l h i s t o r y of the Queen C h a r l o t t e B a s i n . Canadian J o u r n a l of E a r t h S c i e n c e s , 20, 135-159. Y o r a t h C.J., R.L. Chase, (1981). T e c t o n i c h i s t o r y of the Queen C h a r l o t t e I s l a n d s and a d j a c e n t a r e a s - a model. Canadian J o u r n a l of E a r t h S c i e n c e s , J_8, 1717-1739. York D., (1969). L e a s t squares f i t t i n g of a s t r a i g h t l i n e . Canadian J o u r n a l Of P h y s i c s , 44, 1079-1086. 86 APPENDIX A - ALL EVENTS IDENTIFIED ON RECORDING STATIONS DURING THE 1983 EXPERIMENT 8 7 THP THM CO K * * CQ i/i * * * * CO -3 :» * SRM, j i * < ct IOC 10-IH l a s i u (ex ICM 13 lO J3 :D jo-in ILI. iO IS I O i s ICO i a ICS ici-lc; CO o BOI * * * * * * * * + * * + * * # * • * *- * * +-E CO * 1 CN cc r f CN CO r- CN O t-CN ro in CN CM CO in CN CO in in in CO ro CO CM ID CO 00 in in o CN CO CO in ID in CN O CO m in CO in oo CJ) r-CN in CN 00 in CO o CO in CO t— O CN CO in 0) in O in O v rr in T r- O CM CN CN ID ID t-CN CD O CN CN CM CN CN C N oo 0) CN r~ CN CN CM •CM r~ CO CN r-CN oo 0) o C N CO in ID ID 7-CM CO o * - r- O CO CO ro CD CM O -CM DAY co to CO ID CN r-CN CN co co r- r- CO r- CO 1-in in r~ r- m in ID r~ ID r-- to r~ ID I- ID t~-ID r-ID r- :ID .1- r-r» 0) r-CJ) O 00 O co CM 00 CO 00 in co ID CO ID oo ID CO ID CO 00 r-co r-00 t~ co r~ oo CO CO 0) co 0) co CO co 0) CO CT) oo CT) 00 O 0) O CD O CTS - O cn m %: l > - CM CO in ID t-00 CJ) O - CN CO tr in ID r- co 01 O CN :CM CM CM CO CN CM in CN ID CM t-CN CO CN o CN O CO CO CM CO CO CO •<T CO in CO ID CO t-co CO CO CT) CO o 1 1 CN ro •q-•3- in ID r-T co 0) o T in I 88 THP * * * + THM CC i — * * *- * * •» CO I/) * * ¥ + :•*.+. 0 0 l/l "* was < rv * •* * CM CT. * * : * : : ' * : * : * •: > • + C L Q. 12 O I D E <X T C t O t > — < CO CO O *- — » • CM > in in in o n in r- O CM — CM CM in in in nor*) CM CM CM CM CM CO CJ) CO I D r- co in in in co O O in co co O — — CM CM CO CO CO CO CO 0) O in in ip * * * * * * * * * • * * + * * :C0 in o I D t- in m CM f- O n I D I D * - CD CM f» I D 10 CO CN co CO CM o CM r- CM CM CM T - I D — CM. CM CM D CM ro *J CM ro ro *r CM »- in CM ro CM in CM ro •a- ro *- in CM; : — CN o a) O CM CO CM — 10 0) O CM CO CO f» co o — CM o O *T in r- co CO ro cc CO I D I D I D r-' CM CM CM CM *~ CM CM CM "*- CN •*- *~ — *~'. f in in in in I D r- co CO 0) CO O O O o o O o o O — , - — , - ro to ro ro ro ro :C0 CO CD CO CO CO CO CO CO CO 0) CO CO CO CO o O O o o o o o O O O o o O O O O O O O o o c o: CM CM CM CN CM CM CM CM CM I N CN CM CM CM CM CM CN CM CM CM CM CM CM CM: :CM co < J in co CO CO o CM ro <r in I D t- CO CO o CM ro in 10 r~ CO 0) O , - CM CO in IP t- co co o: : I D 10 10 10 I D CO I D I D r- r- r- r- r- r- r- r- oo co CO CO CO co 00 co CO co CO CO CO CO 0) CO 01 CO CO CO O: E V # D A Y H R M N 1 0 1 2 0 4 1 7 2 9 1 0 2 2 0 4 1 7 3 9 B 1 M B O P * * D I M * G B M G P A G P P I B M I C M + J U M L I M L I P L O M * M I M O F B 1 0 E 4 0 W 1 0 W 2 P C M P I M P R 1 P R 2 R S A * * S R M S J B S K B T 5 B * T H M T H P * 1 0 3 2 0 4 1 9 4 6 1 0 4 2 0 4 2 2 5 7 1 0 5 2 0 5 O O * * * * + * * * + * * + 1 0 6 2 0 5 2 2 1 3 1 0 7 2 0 6 5 4 5 1 0 8 2 0 6 9 2 9 * * * * * * * + * 1 0 9 2 0 6 2 1 3 1 1 0 2 0 7 1 4 4 1 1 1 2 0 7 5 0 * + * * + * * * * * 1 1 2 2 0 7 5 5 5 1 1 3 2 0 7 1 0 8 1 1 4 2 0 7 1 0 1 7 * * * * * * • 1 1 5 2 0 7 1 0 3 3 1 1 6 2 0 7 1 1 2 6 1 1 7 2 0 7 1 4 3 8 * * * * * * 1 1 8 2 0 7 1 5 3 1 1 9 2 0 7 1 6 4 1 1 2 0 2 0 7 1 8 2 0 * * * * * •* * 1 2 1 2 0 7 2 1 5 5 1 2 2 2 0 8 2 7 1 2 3 2 0 8 2 0 5 0 * * * * * * * * * * * * * * 1 2 4 2 0 8 2 2 9 1 2 5 2 0 9 1 2 2 6 1 2 6 2 0 9 1 6 7 * * * * 1 2 7 2 0 9 2 1 3 7 1 2 8 2 1 0 O 1 1 1 2 9 2 1 0 3 4 5 * * * * * 1 3 0 2 1 0 9 4 5 1 3 1 2 1 0 1 0 2 1 3 2 2 1 0 1 0 1 4 * * * * * * * * 1 3 3 2 1 0 1 0 2 5 1 3 4 2 1 0 1 1 5 1 3 5 2 1 0 1 1 1 9 * * * * 1 3 6 2 1 0 1 2 3 9 1 3 7 2 1 0 1 7 3 1 1 3 8 2 1 0 1 8 2 * + + 1 3 9 2 1 1 3 5 3 1 4 0 2 1 1 1 0 5 3 1 4 1 2 1 1 1 4 4 4 * * 1 4 2 2 1 1 1 4 5 3 1 4 3 2 1 1 1 4 5 6 1 4 4 2 1 1 1 5 0 * * * * * * 1 4 5 2 1 1 1 5 4 1 4 6 2 1 1 1 5 2 4 1 4 7 2 1 1 1 6 3 1 * * + * •* + * 1 4 8 2 1 1 1 8 1 8 1 4 9 2 1 1 2 1 3 7 1 5 0 2 1 1 2 2 1 7 * * * * * * * + *• * + * CO 90 i THP * ¥ ¥ ¥ ¥ \ ;* THM * TSB * * ¥ * ¥ * 1* * 03 l/l * * ¥ DO -3 l/l ¥ SRM cr ¥ ¥ + • * * * ¥ ¥ * + ¥ ¥ ¥ ¥ ¥ * ¥ * *• * * +• * : CN tx a ¥ * ¥ ¥ !X a. PIM! ¥ ¥ ¥ PCMI ¥ ¥ ¥ ¥ ¥ CN 3 D 3 D ^ UJ O OFB MIM ¥ * ¥ ¥ ¥ ¥ * * LOM It ¥ * * * * ¥ ¥ ¥ ¥ ¥ ¥ * * £ * * ¥ ¥ ¥ ¥ + * ¥ £ ZD -3 * * ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ * * -v I CM ¥ * ¥ * ¥ +• IBM GPP GPA * ¥ * * ¥ ¥ * +• £ CO o DIM * ¥ +• a o * * CO ¥' * ¥ * * * * * ¥ * * ¥ ¥ ¥ ¥ ¥ ¥ ¥ * ¥ ¥ ¥ ¥ ¥ ¥ :* ¥ ¥ * * * ¥ ¥ * BIM EV# DAY HR MN 151 211 23 9 152 212 7 33 * - CN in 0 * - •<? 01 CD CD 1 CN CN CN I CN CN CN :C0 in in in in co r- in r- r- cn 1 CN CN CN •CN CN CN llD t- CO | in in in 1 CO ^ CN ;in in TT O CO CN :CN CN 1 CN CN CO •CM CN CN CJ) O -1 in CO I D •rt rt CO in — :-7 in I D ; CO CO CO :CN CN CN iCN CO f iCD I D CD 1*- CO T-i co CM in :CD O ; co co co ICN CN CN :in I D t~-: ID CD CD CV f H CN - -.01 i- O ;*- CN ;co co T ;CM CN CN loo 01 O :CD CD t-: C D CN CO :n « <• JO O i» •CM CN CN i-r- CN CO •;r- r~ c-:r~ O CN ;CN CN Ir- r- 01 i^t in in |CN CN CN l^r m I D It- t» t-oo i-CO CO IO — CN 1 in in in ICN CN CN lr- CO 01 it- r- t-i t in ro *- in iro CD CD 1 in in in ICN CN CN lO CN ICO 00 C O iOl O CD :in -r-101 O CD 1 in in CD ICN CN CM Iro in CO CO C O i»- CO 01 CN IO CO 01 l l D CD CD ICM CN CM i<D r~ co 1 CO CO CO :c\ n O \*- n •<J) CN O • T- CN \\£> \S> r--!CN CN CN iO) O — 0) o CN CN O c\ m r- r-- r-CN CM CN CN CO T 0) 0) O) :<S> CD CO ;r- >> •CN (N CN \0 Oi CJ) CN CN * -^ .00 Ol — ;r- CO ICN CN CN Ico 01 O IOl 0) O CN i 91 CL I t -1 TSB + + * * * * CO l/l * * * * CO 1/5 * 1 to < l/> + * * * + * * > * *• *-*• * * * * CN c* Q-* * cr o-a o C L * CM 3 O ft ft ft i ft LU O CO Li. o * 'E s ! i • —1 Q-_ J * +• * * * * * * * * ;E j-J is ; D * * * * ;s j ( J * * * * E CO GPP l< • ia * ICS * * * # * # * * * *• * * +• * W90 DIM * * * ia io * * [co *• * * * * * * * * * * * * * * *• # * * :* * * * * * * # * * ¥ * *- + * + * # # * + BIM | Z cc — Is t 1 lor io cn II T O h LD — LD CO CO in co o ro CM :C~ CO 0) CO CO CO •CM ro CM •CM CM in m 03 CN CO 00 r - t*- r-* J if) iO CN > c3 n *- in : CO 0) CO O CM CM CO CM CM "tf 10 .CO CO • •»- CM CN •00 -r- CO . CD CO ^ ^ <x> r- co •3- r-;<g- m CM :C0 ^ CO cn o ;co co id) CO T-:<D CO O ;co ro ;ro o r-:CM ,o - t -:0) O *T •O *=r CN |Lf) CM CO i*T U> O "** CN :co o o) ; — ro :0) ro CO 10 T-in CM T 10 00 CO > CO CO co 0 0 0 ) 0 ) 0 ) CD CD CD O O O o O O O o o o T- , - y- »- , - , - , - CN CN :CN CM CN CN to ro ro CO ro CO CO CO 1 in in < CN CM CN CM CM CM CN •CM CM C J CN CN CN CN CN C J •CN C J CN C J C J CM :CN CM CM CM CN CN C J CN CN CN C J CM CM CM CN CN CN CM D CM C J CN CN CM CM CM CN CM CN CM CN CN CN CM CM CN CM C J CN CM CN CN CN CN C J : C N C J CN CN CM CM :CN CN CM C J CN CM CM CN CM CM CM CM CN CN C J CN CM CM , - CM CO t in 1 0 1^ CO 0 ) o , - O J CO *r in to r- co cn o , - CN CO ^ in CO :t - CO CJ) O _ CM ico ^ in CO r- CO O ) o , - CN CO in CD r~ CO 0 ) o > o o o O O O o O o T- •»- — CN CM CM CN CM C J C J :CN CN C J CO CO ro ! C 0 CO CO ro ro CO CO * T *r in LU CM CM CM CM CM CM CM CM CM CM CM CN CN CN CN CN CN ; C J CN CN CN CN CM CM CM CN :CN CN C J CN CN CN :CM CN CN CN CN C J CM CN CN CN CM CN CM CN CN CM CM CM 92 CL I 1 -s I * 1 -* 00 1/5 * 1 -* CO c n * * * * CO i/> s cc 1/1 < 1/5 •» CK * * * * CN or * CL * * + QC CL £ a *-£ a * CN 3 o 3 O r r UJ O i c a i n . * I O ! s ! £ S o _J * * CL _J * * * * * : : * * : * : : * * i s p * t # : * : * - 3 | 2 IBM GPP GPA * * +• * * + GBM * * * * I DIM 1 * * *-IBOP I * * * * * * + * * * * * * * * * * # * * * * * * * * * + * * * * BIM 1 ro ro 0) CO ro CO CO 00 CM O CM * r r o CM ID O CO r - CM in |CN in co CM CN CN ID o 1 co CN CN ;in ro CN CN CO t -CO in o CM CN in CM CN r o co CN in ro CO CN CO ID ro in •3- CD in 0 ) *T r- CN co CM HR CO CN CO CN in co o 1 in CO CM CO CO t - co *- CM :CN iCN CO 0) * r CO o CN CN 0) CO :C0 CN CN CM CM CM CN CO CN CO CM CO CN CM rt in in CD o CM O CM r o CM CO CN CO CM <- CN ID r - co CN DAY in CN CN in CN CN co CN CN CD CN CM LP CN CN LP CM CM CD CM CN LP CM CM CN CM t -CM CN r -CN CN r~ CN CM f -CN CM co CN CN CO CM CN CO CM CN co CM CN :C0 :CN iCM CO CM CN 01 CM CN 01 CM CM 01 CM CN 05 CM CM 01 CN CN o ro CM o CO CN : 0 :C0 •CN O CO CN O CO CM O CO CN O CO CN O ro CM O CO CN CO CN CM ro CM CN CO CN CN CO CN CN ro CN CM CO CN CN CO CM CN ro CM CN CO CM CN CO CM CN CO CM CO CO CM CO CO CM CO CO CM co ro CM ro CO CM ro CO CN l u j in CN CN in CN CO in CN *T in CM in in CM CD in CN r~ in CN CO in CN CD :in •CN o ID CM ID CN CM ID CM CO ID CN T ID CM m ID CM CD ID CN I -CD CN ico :ID ICM CO ID CN O r » CM r » CN CM r -CN CO t -CM •0-r -:CN in r » CN CD t -CN i t -i r -iCN CO f -CM 05 t -CM O CO CN co CN CM CO CN CO CO CN « T co CM in CO CM ID 00 CN t -oo CM CO CO CM 01 CO CN o 05 CN 05 CM CM CO CM CO 01 CN 05 CM in 05 CM ID 0 ) CN t -01 CM CO 01 CM 05 05 CM o o co THP THM TSB SKB SJB SRM RSA CM or a or a s. a PCM * ¥ * CM 3 O 0W1 0E4 OFB MIM LOM LIP I LIM * £ " 3 ¥ ¥ I CM IBM GPP < a (J I GBM I ¥ DIM" * [BOP] ¥ ¥ ¥ * * * +: ¥ BIM z £ IT) CO o co T CM CM CO CM GO T in CO CD CO ID CM CN CM •q- CJ) o CN CN O CD DAY rt CO CM CO CM :C0 ICN CO CM in CO CM in ICO ICN in ro CM in ro CM CD :CO ICN CD CO rM at *-> o H i CO CM O CO ICO :o ICO O CO in O CO 30G r-O CO co O CO lO) : 0 ICO o ro 94 APPENDIX B - SUMMARY OF THE HYPOELLIPSE SOLUTIONS FOR LOCATED EVENTS Codes i n column 5 are as f o l l o w : E = e a s t of the Queen C h a r l o t t e t r a n s f o r m f a u l t zone N = n o r t h e r n c l u s t e r F = a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t zone D = i n Di x o n E n t r a n c e * = p o s s i b l e b l a s t DEPTH, F i x e d depth s o l u t i o n s a r e marked w i t h an a s t e r i s k . FMAG i s the magnitude of the ev e n t s e v a l u a t e d as d e s c r i b e d i n Chapter V. When the v a l u e i s f o l l o w e d by: • a b l a n k , the magnitude was e v a l u a t e d u s i n g d a t a from 'BQP l a t e ' and the coda l e n g t h magnitude s c a l e d e s c r i b e d i n c h a p t e r V. • * , the magnitude (ML) i s taken from D r y s d a l e et a l . ( 1 9 8 4 a , b ) . • ' , the magnitude was e v a l u a t e d w i t h coda l e n g t h r e a d a t s t a t i o n GPP. • / , the magnitude was e v a l u a t e d u s i n g d a t a from 'BQP e a r l y ' and a c o r r e c t i o n f a c t o r . QUA r e p r e s e n t s the q u a l i t y of the s o l u t i o n based on the s i z e of the e r r o r e l l i p s o i d c a l c u l a t e d by HYPOELLIPSE. • A r e p r e s e n t s an event w i t h l a r g e s t s t a n d a r d d e v i a t i o n of + 1.25 km. • B r e p r e s e n t s an event w i t h l a r g e s t s t a n d a r d d e v i a t i o n of ± 2.5 km. • C r e p r e s e n t s an event w i t h l a r g e s t s t a n d a r d d e v i a t i o n of ± 5.0 km. • D r e p r e s e n t s an event w i t h s t a n d a r d d e v i a t i o n g r e a t e r than ± 5.0 km. #S i s the number of phases (P, S and S-P) used t o f i n d the hypocenter l o c a t i o n . GAP i s the l a r g e s t a z i m u t h a l gap between s t a t i o n s used t o l o c a t e the h y p o c e n t e r . D3 i s the d i s t a n c e ( i n km) t o the t h i r d c l o s e s t s t a t i o n , from which d a t a were used. S i z e and o r i e n t a t i o n of e r r o r e l l i p s o i d a r e : LGT i n me t r e s . AZI and DIP i n degre e s . S I Z E A N D O R I E N T A T I O N O F E R R O R E L I P S O I O E V # C Y R D A Y H R M N S E C . L A T M I N L O N M I N D E P T H F M A G O U A / * S R A P D 3 R M S A Z I 1 D I P 1 L O T 1 A Z I 2 D I P 2 L G T 2 L G T 3 1 F 8 4 1 7 2 1 4 3 2 3 5 1 6 5 2 N 3 4 4 5 1 3 1 W 4 3 4 0 1 9 3 2 * C 4 1 7 0 7 7 . 1 1 1 4 4 9 1 1 7 2 6 1 3 5 1 1 3 0 5 6 7 2 F 8 4 1 7 2 2 0 4 7 1 3 7 9 5 2 N 3 0 1 2 1 3 1 W 5 2 2 3 9 9 1 9 ' D 8 2 3 7 6 6 . 1 3 2 6 1 0 2 3 2 3 1 7 1 8 5 1 4 6 6 3 * 8 4 1 7 3 1 7 3 4 1 1 1 9 5 3 N 4 3 2 1 3 2 W 1 4 6 4 7 3 - 0 1 ' A 3 1 5 3 3 0 . 0 6 1 3 7 1 8 5 6 4 0 2 2 2 0 1 6 8 . 4 N 8 4 1 7 5 8 2 0 4 1 4 3 5 4 N 9 0 1 3 3 W 3 2 9 9 4 0 2 0 / D 4 3 4 6 1 3 7 . 0 6 8 1 7 4 3 8 1 4 9 2 8 2 1 3 9 9 0 0 5 N 8 4 1 7 5 2 0 2 0 5 0 7 2 5 4 N 1 1 8 1 3 3 W 4 6 5 0 1 0 0 1 9 / D 2 3 5 7 1 0 0 . 0 4 3 0 8 0 1 6 4 9 3 8 0 9 9 0 0 9 9 0 0 G F 8 4 1 7 G 8 4 1 2 7 9 5 2 N 2 1 7 4 1 3 1 W 3 8 5 2 1 8 6 1 9 ' C 9 2 0 6 3 3 . 1 7 3 1 9 1 2 1 2 4 2 6 1 3 9 3 0 5 6 2 3 7 F 8 4 1 7 G 1 2 4 5 3 5 1 8 5 2 N 2 1 5 1 3 1 W 3 6 8 4 1 9 6 0 5 ' A 5 2 2 8 3 1 . 0 9 1 4 7 1 2 7 6 2 6 1 4 4 1 1 6 1 9 7 8 * 8 4 1 7 G 2 1 3 3 5 4 5 3 N 2 8 6 3 1 3 2 W 1 9 6 0 1 0 9 / C 4 3 4 3 3 3 . 0 7 1 4 8 2 4 1 9 0 8 1 2 8 7 1 2 5 6 7 9 * 8 4 1 7 6 2 1 4 2 4 3 6 5 3 N 4 2 5 2 1 3 2 W 4 1 5 0 1 1 5 1 3 / A 3 2 2 3 6 3 . 0 7 2 6 1 3 1 0 3 3 6 7 5 1 5 0 1 0 F 8 4 1 7 6 2 2 4 6 2 3 4 1 5 2 N 5 2 7 5 1 3 2 W 2 5 9 9 1 1 5 0 4 / D 4 2 7 0 4 5 . 0 7 1 6 5 1 3 2 6 2 2 6 1 2 7 8 4 3 1 2 0 5 1 1 F 8 4 1 7 7 7 3 1 3 3 6 2 5 1 N 5 4 8 8 1 3 1 W 1 7 5 4 9 9 D 3 3 3 3 5 6 . 0 6 2 8 2 3 G 7 5 1 2 4 3 3 8 6 4 8 8 1 2 F 8 4 1 7 9 2 1 5 7 9 2 0 5 3 N 2 4 6 9 1 3 3 W 5 5 1 7 1 0 9 ' 0 4 2 8 6 6 5 . 0 8 8 1 1 1 1 6 0 1 6 3 1 6 6 2 1 8 3 7 1 3 * 8 4 1 8 0 1 7 2 0 2 8 8 8 5 3 N 3 9 7 1 3 2 W 1 6 4 2 9 4 0 2 ' A 3 1 6 9 3 2 . 0 6 1 4 0 2 5 4 3 3 5 2 9 1 4 7 5 1 4 * 8 4 1 8 0 2 1 8 5 5 3 5 3 N 4 5 7 1 3 2 W 1 3 4 1 1 5 0 5 / C 4 1 4 5 2 9 . 0 8 4 0 1 1 8 5 1 3 5 2 3 1 3 7 7 2 4 1 5 F 8 4 1 8 6 1 1 O 2 9 8 6 5 2 N 4 9 7 5 1 3 2 W 2 8 4 3 1 0 5 1 1 D 3 3 3 0 6 2 . 0 5 3 2 7 0 2 9 9 2 6 1 1 9 8 0 9 9 0 0 1 6 F 8 4 1 8 6 1 3 1 2 4 2 1 7 5 3 N 8 7 1 3 3 W 1 4 8 8 1 5 0 * 0 7 D 3 3 5 0 9 8 . 0 5 1 7 4 2 3 9 2 2 6 4 6 8 2 8 9 9 0 0 1 7 E 8 4 1 8 6 1 5 5 2 4 5 7 3 5 3 N 5 1 4 6 1 3 2 W 1 9 9 9 0 7 - 0 1 D 3 3 0 9 9 0 . 0 6 8 1 2 6 2 3 5 1 7 8 3 1 3 6 3 4 0 0 8 1 8 E 8 4 1 8 7 1 4 7 2 3 8 2 5 3 N 5 2 9 3 1 3 2 W 5 9 3 1 6 2 6 B 7 1 9 6 7 1 . 1 4 1 0 4 1 6 6 2 2 0 4 3 0 1 0 8 5 1 0 1 9 F 8 4 1 8 7 6 1 9 6 3 5 5 3 N 5 4 6 3 1 3 2 W 5 8 6 4 5 3 8 C 7 2 0 1 7 3 . 1 8 1 0 5 1 4 1 3 4 2 0 3 2 7 1 9 0 9 7 0 2 0 D 8 4 1 9 0 1 9 4 0 1 1 3 2 5 4 N 1 4 6 1 1 3 2 W 0 2 5 2 6 1 1 5 C 5 1 7 3 1 1 2 . 1 0 2 0 0 1 1 0 8 1 1 0 ' 6 8 6 8 2 6 2 1 * 8 4 1 9 0 2 1 5 4 3 7 7 0 5 3 N 2 5 1 7 1 3 2 W 3 1 9 2 3 8 - 0 9 D 3 2 4 4 3 8 . 0 6 1 2 2 2 3 1 2 1 4 4 3 1 7 0 0 7 2 2 2 F 8 4 1 9 1 O 4 0 2 4 3 5 3 N 5 5 9 9 1 3 2 W 7 2 8 8 3 1 3 C 9 1 2 8 6 4 . 1 7 2 2 0 5 6 0 1 2 9 1 2 1 1 6 9 1 9 2 3 F 8 4 1 9 1 4 4 5 5 2 1 2 5 2 N 4 9 5 9 1 3 2 W 2 2 7 3 2 1 9 2 3 + C 7 2 2 0 5 3 . 1 5 3 2 0 6 1 1 4 2 6 1 1 9 2 7 7 7 5 3 2 4 F 8 4 1 9 2 8 2 2 5 0 6 5 5 2 N 3 2 7 1 1 3 1 W 5 5 9 8 3 2 - 0 9 D 3 3 4 0 7 9 . 0 5 2 7 5 1 1 3 3 4 1 1 2 9 7 6 8 9 9 0 0 2 5 N 8 4 1 9 5 2 0 3 7 2 8 5 9 5 4 N 3 8 9 1 3 3 W 4 0 6 6 5 0 * 1 2 D 4 2 8 9 1 3 6 . 0 8 1 7 5 6 4 9 4 8 2 2 8 8 5 5 9 9 0 0 2 6 F 8 4 • 1 9 8 1 1 2 3 3 5 6 6 5 3 N 5 1 2 2 1 3 3 W 2 5 9 1 5 0 D 8 2 5 9 6 6 . 1 4 1 6 4 1 8 1 1 7 8 1 1 8 3 5 3 2 4 2 7 2 7 N 8 4 1 9 9 1 0 1 5 2 2 6 0 5 4 N 9 1 7 1 3 1 W 4 4 7 6 5 0 * - 0 1 D 3 2 2 6 1 0 5 . 0 6 2 6 1 2 3 5 2 1 3 8 3 3 1 1 4 7 3 7 7 3 2 8 * 8 4 2 0 0 1 4 5 0 6 1 5 3 N 4 0 7 0 1 3 2 W 3 5 9 1 1 8 - 0 9 A 3 2 5 2 5 6 . 0 6 1 9 6 2 4 1 4 2 9 8 2 5 4 9 8 4 2 9 I 8 4 2 0 0 9 2 1 4 7 8 5 5 3 N 5 6 5 1 3 2 W 2 8 6 4 8 7 1 5 A 7 2 0 3 5 2 . 1 5 1 4 9 1 6 8 2 6 1 1 5 1 0 3 2 4 6 3 0 * 8 4 2 0 0 1 8 5 6 3 3 3 5 5 3 N 4 4 4 1 3 2 W 1 5 8 3 8 7 0 8 A 6 1 7 0 2 3 . 1 1 3 5 4 8 3 6 2 6 1 2 1 1 0 0 2 2 7 3 1 F 8 4 2 0 0 2 0 6 7 1 0 5 2 N 2 9 9 3 1 3 1W 5 3 5 5 1 2 5 2 3 D 8 2 2 3 3 8 . 1 7 3 1 6 1 7 2 2 6 1 1 3 2 1 1 1 4 8 9 3 2 F 8 4 2 0 0 2 1 1 8 3 9 4 3 5 2 N 3 0 2 1 1 3 1 W 5 2 5 8 1 5 1 0 4 C 4 3 5 3 3 7 . 0 6 3 1 3 5 6 3 2 2 2 1 7 1 8 1 6 6 5 3 3 F 8 4 2 0 1 0 2 8 5 1 6 5 2 N 2 1 6 5 1 3 0 W 4 7 5 0 2 4 D 4 3 1 9 1 1 0 . 0 7 1 1 0 4 7 9 2 8 1 2 6 2 9 7 9 9 0 0 3 4 N 8 4 2 0 3 7 3 1 4 9 7 4 5 4 N 7 4 7 1 3 3 W 4 0 7 6 5 0 * 1 1 D 3 2 9 4 1 4 1 . 0 6 1 7 6 9 2 6 2 8 1 2 8 4 9 6 9 9 0 0 3 5 N 8 4 2 0 3 8 7 3 6 6 2 5 3 N 5 8 9 0 1 3 3 W 3 0 1 8 5 0 * - 0 9 D 3 2 6 9 1 2 1 . 0 6 1 7 4 3 2 0 0 8 3 3 4 4 8 4 9 9 0 0 3 6 F 8 4 2 0 3 8 4 1 5 2 3 1 5 2 N 3 3 7 6 1 3 1 W 5 9 2 6 8 5 0 2 B 3 3 4 7 7 6 . 0 6 2 8 1 1 5 5 1 1 1 1 6 7 2 8 8 3 7 N 8 4 2 0 3 1 8 2 3 4 9 3 5 3 N 5 3 6 1 1 3 3 W 2 5 1 8 5 0 * - 0 9 D 3 2 5 8 1 1 1 . 0 6 1 6 7 3 1 5 5 8 1 3 7 4 2 5 9 9 0 0 3 8 F 8 4 2 0 4 1 6 1 7 1 5 5 0 5 2 N 5 0 1 4 1 3 2 W 2 3 9 7 9 8 1 5 A 1 1 2 4 5 4 8 . 1 7 1 4 9 2 4 2 2 6 1 2 2 1 1 3 2 2 9 3 9 F 8 4 2 0 4 1 6 4 5 3 0 5 5 5 2 N 5 0 2 7 1 3 2 W 2 3 5 2 g 9 2 2 B 1 5 2 0 7 4 8 . 2 9 1 4 9 2 4 3 2 6 1 1 6 1 1 4 3 2 2 • 4 0 F 8 4 2 0 4 1 6 5 0 4 7 5 3 5 2 N 5 0 1 7 1 3 2 W 2 4 3 9 7 1 5 A 1 2 2 2 1 4 8 . 2 1 1 5 6 3 4 3 2 6 1 2 0 1 0 7 2 5 1 4 1 F 8 4 2 0 4 1 7 2 1 5 4 9 5 2 N 5 0 8 2 1 3 2 W 2 4 6 4 7 3 0 8 B 5 3 0 0 4 7 . 0 9 2 1 1 4 2 0 2 3 0 4 3 3 1 2 4 3 9 4 4 2 F 8 4 2 0 4 1 7 2 9 9 6 9 5 2 N 5 0 7 3 1 3 2 W 2 3 5 6 8 7 - 0 1 D 3 3 3 3 6 3 . 0 5 3 2 2 9 3 2 5 8 1 9 1 2 4 7 9 9 0 0 4 3 F 8 4 2 0 4 1 7 3 8 1 4 7 2 5 2 N 5 0 7 5 1 3 2 W 2 3 6 4 8 3 1 1 B 9 2 4 2 4 7 . 1 5 1 6 0 2 1 1 5 2 6 1 4 1 2 1 8 3 3 2 4 4 F 8 4 2 0 4 1 7 4 9 1 9 6 5 2 N 5 1 5 1 3 2 W 2 4 8 4 7 2 0 4 B 4 2 9 9 5 2 . 0 8 4 1 3 1 2 6 4 2 8 7 3 4 1 8 2 3 6 9 4 5 F 8 4 2 0 4 1 9 4 5 5 1 7 5 2 N 5 0 6 1 3 2 W 2 4 7 9 2 2 2 A 1 3 2 1 4 4 8 . 2 6 1 4 7 1 3 9 2 6 1 1 4 8 5 1 7 6 4 6 * 8 4 2 0 5 2 2 1 3 1 8 9 8 5 3 N 4 0 8 7 1 3 2 W 3 4 6 0 1 1 7 0 5 B 4 1 8 1 3 1 . 1 0 2 6 1 1 7 8 1 1 3 6 1 8 1 0 8 3 1 0 4 7 N 8 4 2 0 6 9 2 9 1 9 4 8 5 4 N 4 1 0 1 3 3 W 3 9 5 2 5 0 * - 0 9 D 3 2 8 8 1 3 5 . 0 6 1 7 7 6 1 4 8 8 3 3 0 2 5 6 9 9 0 0 4 8 F 8 4 2 0 6 2 1 3 2 5 6 3 5 2 N 4 3 9 4 1 3 2 W 1 9 8 2 5 0 2 4 C 1 2 2 1 8 5 6 . 2 4 3 2 0 4 1 1 8 2 6 1 2 7 3 0 4 8 1 3 4 9 * 8 4 2 0 7 1 4 4 6 7 4 5 3 N 3 3 7 4 1 3 2 W 2 4 6 7 5 0 0 7 B 6 1 4 8 3 1 . 1 2 2 6 1 0 1 0 5 1 7 1 4 6 5 3 5 0 VO S I Z E A N D O R I E N T A T I O N OF E R R O R E L I P S O I D E V / C C Y R D A Y HR M N S E C . L A T M I N L O N M I N D E P T H F M A G QUA #S G A P 0 3 R M S A Z I 1 D I P 1 L G T 1 A Z I 2 D I P 2 L G T 2 L G T 3 5 0 E 8 4 2 0 7 5 O 7 7 1 5 3 N 4 5 4 1 3 1 W 5 8 9 1 0 0 - 0 9 0 3 3 0 6 7 1 . 0 6 1 1 2 8 1 2 3 2 0 8 3 5 1 3 6 17 3 0 5 1 E 8 4 2 0 7 1 0 7 4 8 7 3 5 3 N 5 7 5 8 1 3 2 W 2 4 4 8 0 3 - 0 9 D 3 3 4 1 8 2 . 0 5 1 8 8 9 5 0 9 2 8 6 4 0 1 9 0 3 8 0 4 5 2 F 8 4 2 0 7 1 1 2 6 4 1 9 9 5 2 N 6 0 0 1 3 2 W 3 1 6 3 18 6 - 0 1 D 3 2 8 6 5 2 . 0 6 1 2 7 2 1 3 2 2 18 2 2 2 6 3 4 4 4 8 * 8 4 2 0 7 1 8 ? o 4 4 6 ? 5 3 N 4 6 7 1 3 2 W 1 6 1 5 6 5 - 0 9 C 4 2 5 4 3 3 . 0 8 2 9 9 3 1 6 8 2 0 8 17 3 4 6 9 1 1 5 4 F 8 4 2 0 7 2 1 5 4 1 5 5 1 5 3 N 1 5 3 1 3 2 W 4 4 2 3 1 0 6 1 7 D 8 2 3 8 5 0 . 1 5 3 1 6 0 9 3 2 6 1 1 5 5 E 8 4 2 0 8 2 0 4 9 4 0 9 8 5 3 N 4 2 5 4 1 3 2 W 7 5 5 7 3 2 3 A 1 1 1 0 1 4 6 . 2 2 1 9 7 4 4 7 1 0 7 8 5 0 2 0 8 5 6 E 8 4 2 0 9 1 6 6 17 8 4 5 3 N 4 2 8 6 1 3 2 W 7 6 1 1 0 0 - 0 9 D 3 3 0 4 7 0 . 0 6 2 8 2 0 2 8 5 1 2 0 4 4 7 9 9 0 0 5 7 F 8 4 2 0 9 2 1 3 6 4 8 9 0 5 3 N 3 2 8 3 1 3 4 W 1 0 9 5 5 4 1 5 D 1 0 3 5 2 1 0 5 . 0 9 2 0 3 1 6 6 6 1 1 3 2 4 5 8 9 9 0 0 8 4 2 0 9 2 1 3 6 4 9 5 2 5 3 N 2 5 7 4 1 3 4 W 1 1 3 5 2 5 0 * 1 5 D 1 0 3 5 0 1 2 0 . 3 6 5 8 E 8 4 2 1 0 0 1 0 5 9 9 1 5 3 N 5 5 1 1 3 2 W 6 4 4 5 5 1 1 C 6 2 3 8 6 3 . 1 1 1 1 9 5 1 3 2 2 1 1 19 1 7 3 5 9 D 8 4 2 1 0 3 4 4 5 2 9 7 5 4 N 4 5 2 9 1 3 2 W 3 3 6 3 5 5 1 6 D 3 3 4 2 1 0 0 . 0 6 9 5 1 8 9 5 1 8 6 2 4 2 8 1 9 9 0 0 8 4 ? 1 0 9 4 4 3 0 3 ? 5 2 N 5 0 17 1 3 2 W 2 3 4 0 1 3 6 1 3 C 9 2 4 4 5 0 . 1 5 3 3 0 0 5 5 2 6 1 8 1 9 0 8 0 0 6 1 E 8 4 2 I O 1 0 0 5 3 4 0 5 3 N 3 1 8 5 1 3 1 W 4 6 1 1 17 2 - 0 9 0 3 2 8 / 5 2 . 0 6 3 0 1 0 6 1 6 3 1 18 9 9 0 0 6 2 F 8 4 2 1 0 1 0 2 0 3 5 7 1 5 2 N 5 9 5 7 1 3 2 W 4 1 8 1 0 O - 0 9 D 3 3 2 2 6 2 . 0 5 3 0 0 0 5 3 6 3 0 0 9 17 9 9 0 0 F 8 4 2 1 0 1 0 1 4 a 3 9 5 3 N 4 9 4 2 1 3 2 W 2 4 1 1 8 9 0 8 A 5 2 0 3 6 7 . 1 0 2 0 5 3 1 5 4 2 9 5 1 1 9 7 1 4 5 6 4 N 8 4 2 1 0 1 2 3 7 4 9 3 9 5 4 N 1 2 3 3 1 3 3 W 4 9 4 0 5 0 * 1 3 U b 3 0 6 1 2 4 . 1 0 8 1 18 3 2 8 1 5 4 6 5 E 8 4 2 1 1 1 5 2 3 5 0 8 4 5 3 N 4 2 4 8 1 3 2 W 2 5 8 0 4 1 4 C 5 2 7 2 5 1 . 1 0 1 3 4 2 1 2 4 2 2 5 3 5 2 3 3 7 7 9 2 0 7 4 5 8 6 7 * 8 4 2 1 1 1 8 1 8 1 8 5 1 5 3 N 5 0 4 1 1 3 2 W 2 4 17 9 7 1 3 B 6 1 9 5 4 9 . 12 3 1 3 2 1 9 6 2 2 3 6 8 F 8 4 2 1 1 2 2 1 7 1 1 3 6 5 2 N 2 1 7 8 1 3 1 W 4 0 4 2 1 5 3 1 4 C 7 2 3 0 4 0 . 14 3 1 5 9 6 4 2 6 1 2 3 2 2 8 6 14 F 8 4 2 1 2 "9 3 0 3 6 2 6 5 2 N 3 3 5 3 1 3 2 W 1 18 9 9 2 2 D 1 0 2 1 8 5 3 . 2 1 1 4 6 1 6 6 8 1 2 1 4 9 1 3 3 6 7 0 N 8 4 2 1 2 1 6 1 1 2 8 2 5 4 N 7 5 9 1 3 3 W 4 8 5 9 5 0 * b 1 U 6 2 9 2 1 0 0 . 19 8 1 1 3 5 5 1 7 1 N 8 4 2 1 2 1 6 4 4 4 5 7 9 5 4 N 3 3 3 1 3 3 W 3 7 3 7 5 0 * 0 7 D 4 2 8 4 1 0 3 . 0 7 1 7 5 6 3 4 1 8 1 2 6 5 5 8 5 2 5 3 N 8 4 2 1 2 17 ? 5 6 9 6 5 4 N 1 0 2 1 3 3 W 4 3 4 3 5 0 * - 0 5 D 2 3 0 0 1 4 6 . 0 5 2 6 5 7 4 8 1 1 9 2 8 1 3 6 9 9 9 0 0 7 3 N 8 4 2 1 2 17 7 1 8 2 5 4 N 7 5 1 1 3 3 W 4 3 5 8 5 o * - 0 6 D 3 2 9 7 1 4 3 . 0 6 1 7 8 8 4 9 9 7 4 * 8 4 2 1 2 1 9 4 8 9 6 5 3 N 5 5 2 7 1 3 2 W 5 6 6 9 1 0 6 0 9 D 3 3 3 0 9 2 . 0 7 3 0 8 1 1 0 1 0 2 18 1 1 2 5 9 9 9 0 0 N 8 4 2 1 2 ? o •=57 4 3 2 4 5 4 N 6 9 5 1 3 3 W 4 1 3 0 5 0 * 1 4 D 4 2 9 4 1 0 6 . 0 8 1 7 3 1 2 2 1 6 8 1 2 9 4 2 1 5 1 4 8 7 6 F 8 4 2 1 3 9 3 1 3 3 1 5 5 3 N 14 9 6 1 3 2 W 5 0 7 8 1 0 3 1 3 U b 2 9 9 4 6 . 0 9 14 1 1 2 8 6 7 7 N 8 4 2 1 3 1 0 2 7 5 5 9 6 5 4 N 5 5 2 1 3 3 W 4 2 4 7 5 0 * 2 1 D 8 2 9 1 9 3 . 15 1 5 6 18 3 1 1 8 1 2 0 4 5 7 3 7 7 4 N 8 4 2 1 3 1 1 5 0 1 5 9 2 5 4 N 5 2 1 3 3 W 4 2 1 0 5 0 * 2 3 D 1 1 2 9 0 9 2 . 19 1 7 3 1 2 1 8 3 8 1 2 4 2 8 1 1 9 6 3 7 9 N 8 4 2 1 3 2 1 1 3 5 5 6 8 5 4 N 6 1 3 1 3 3 W 4 6 8 8 6 9 0 / U 4 2 9 / 1 14 . 0 7 8 2 7 6 4 2 8 0 * 8 4 2 14 0 4 3 0 3 6 5 3 N 3 7 4 4 1 3 2 W 3 5 2 9 1 5 3 0 5 B 5 1 4 2 2 0 . 1 0 2 6 1 9 9 9 1 3 9 1 2 1 2 5 3 6 3 N 8 4 2 1 4 7 1 8 2 3 1 9 5 4 N 6 7 1 1 3 3 W 3 9 3 3 5 0 * 1 6 D 6 2 9 1 9 1 . 1 0 1 7 5 1 0 2 0 0 8 1 2 7 3 5 5 2 6 9 8 8 2 F 8 4 2 1 5 1 1 3 8 14 7 6 5 1 N 5 7 4 7 1 3 1 W 3 1 19 1 2 - 0 b D 3 3 1 1 1 4 9 . 0 6 3 0 0 2 0 9 3 3 8 3 F 8 4 2 1 5 1 2 3 6 4 2 2 4 5 2 N 2 3 4 9 1 3 1 W 3 4 7 1 2 2 6 1 1 C 6 2 2 2 3 6 . 1 0 3 2 0 12 1 12 8 1 3 5 9 7 3 3 1 9 F 8 4 2 1 5 1 3 4 4 1 0 1 9 5 2 N 2 8 3 5 1 3 1W 5 1 9 1 13 5 1 9 D 9 2 2 9 4 0 . 1 5 3 2 0 2 9 3 2 6 1 1 5 3 1 2 1 5 7 4 8 5 F 8 4 2 1 5 1 9 5 9 5 2 3 4 5 2 N 4 0 1 2 1 3 2 W 1 3 9 8 8 b 1 1 U 4 3 1 6 6 4 . 0 7 1 2 4 1 1 0 5 8 6 N 8 4 2 1 6 1 0 O 5 5 2 2 5 4 N 5 1 0 1 3 3 W 3 9 6 9 5 0 * - 0 1 D 3 2 8 9 1 3 7 . 0 6 1 7 8 6 2 3 5 8 5 3 0 4 18 9 9 0 0 8 7 N 8 4 2 1 6 2 2 3 2 5 8 2 5 5 4 N 3 9 9 1 3 3 W 4 3 3 7 5 O 1 7 D 6 2 9 2 1 0 5 . 0 9 1 7 8 3 1 9 6 8 7 2 6 3 8 0 4 0 0 8 8 8 * 8 4 2 17 0 0 19 1 5 5 3 N 3 4 4 1 3 2 W 2 7 8 b 1 2 7 0 9 B b 1 7 2 18 . 1 0 2 7 1 8 0 3 6 6 8 9 F 8 4 2 1 7 0 2 9 1 8 3 0 5 2 N 3 3 7 6 1 3 2 W 1 2 6 1 1 2 1 7 D 1 0 2 8 0 4 4 . 18 3 1 5 1 1 3 9 2 6 1 8 3 0 0 2 1 2 0 F 8 4 2 17 3 2 1 1 0 14 5 2 N 5 1 5 1 3 2 W 3 6 18 0 5 1 8 C 5 2 6 2 6 2 . 0 9 3 2 1 7 1 10 8 1 3 4 2 0 3 1 1 4 8 9 1 N 8 4 2 17 6 1 6 7 3 1 5 4 N 5 8 3 1 3 3 W 3 6 1 1 b 0 * 1 0 U 3 2 8 7 1 0 5 . 0 7 1 8 2 5 5 0 8 9 2 F 8 4 2 17 9 3 4 4 4 14 5 2 N 3 5 4 4 1 3 2 W 9 6 1 1 1 - 0 9 D 3 3 2 3 9 4 . 0 6 3 3 7 7 2 5 1 2 6 1 2 4 2 9 4 1 3 2 7 9 3 * 8 4 2 17 1 9 4 2 2 4 0 5 3 N 3 7 7 2 1 3 2 W 3 5 5 7 14 0 - 0 9 B 3 2 3 5 5 2 . 0 6 1 8 7 1 5 6 7 2 8 1 17 2 6 6 3 0 4 9 4 F 8 4 2 1 8 1 4 1 1 9 5 5 5 2 N 3 7 7 1 1 3 1W 5 9 3 0 1 2 8 0 2 C 5 3 2 4 5 7 . 0 8 2 9 4 8 2 3 2 2 0 2 14 6 9 1 1 0 2 1 9 5 N 8 4 2 18 1 5 5 3 5 4 9 8 5 4 N 1 3 8 1 3 3 W 4 8 2 8 5 0 * 1 4 D 3 3 0 8 1 5 4 . 0 6 1 9 8 1 3 9 6 1 0 7 2 8 6 0 0 9 9 0 0 9 6 F 8 4 2 1 9 7 5 4 5 3 6 5 2 N 4 3 5 1 1 3 2 W 5 5 8 2 2 4 - 0 9 A 3 2 9 7 8 1 . 0 6 8 1 2 2 121 3 3 4 3 5 2 9 5 1 S I Z E A N D O R I E N T A T I O N OF E R R O R E L I P S O I D EV/f C Y R D A Y H R M N S E C . 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