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Earthquake swarm on the Queen Charlotte Islands fracture zone Wetmiller, Robert Joseph 1969

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AN EARTHQUAKE SWARM ON THE QUEEN CHARLOTTE ISLANDS FRACTURE ZONE by ROBERT JOSEPH WETMILLER B.Sc.  University  A THESIS SUBMITTED  o f M a n i t o b a , 1967  IN PARTIAL  THE REQUIREMENTS  OF  FOR THE DEGREE OF  MASTER OF i n the  FULFILMENT  SCIENCE  Department of  GEOPHYSICS  We a c c e p t required  \his  thesis  as c o n f o r m i n g t o  standard  THE UNIVERSITY OF BRITISH COLUMBIA August,  1969  the  In p r e s e n t i n g  this thesis  in 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  an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , the  L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e  I further agree that permission f o r s c h o l a r l y p u r p o s e s may by h i s r e p r e s e n t a t i v e s .  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a Date  J u l y 31,  1969  Columbia  thesis or  publication  g a i n s h a l l n o t be a l l o w e d w i t h o u t  GEOPHYSICS  that  Study.  Department  It i s u n d e r s t o o d t h a t c o p y i n g o r  permission.  Department of  and  copying of this  be g r a n t e d b y t h e Head o f my  o f t h i s thes.is f o r f i n a n c i a l written  for extensive  I agree  for  my  i  ABSTRACT  An e a r t h q u a k e rise  system i n  data  are  western August  in  the n o r t h e a s t  the  form of  27 t o  September  stations  as  and 19 o f  an a r r a y  respect  to  this  1,  two  array.  5-day  area.  This  period.  lines  magnitude-frequency  following T T  These  p  n  Sn  travel  greater  than  the  station  to  properties  Five considered  located  the  swarm i s  180 km f r o m  swarm p l u s  c a n t h u s be  estimated.  British  on  the  arrivals  of the  i n western  with  in  the  the  C o l u m b i a show  relationships:  = ( S . 5 1 ± 0 . 3 8 ) '•+ A / ( 7 . 6 9 ± 0 . 0 3 ) (10.16±1.25)  =  times  are  + A/(4.45±0.03)  consistent with  a crust  on V a n c o u v e r  Island  50 km t h i c k . for  tectonic  events  in  features  the  swarm a r e  i n the  associated  northeast  E x p l o r e r T r e n c h and t h e Queen C h a r l o t t e  Pacific Island  Zone. The e v e n t s  time  Columbia are  r e c o r d e d 217 d i s t i n c t  time-distance  w i t h two d i s t i n c t  Fracture  British  relationship  The e p i c e n t e r s  Ocean - t h e  investigation.  I s l a n d about  The Pn and Sn a r r i v a l s the  of  The c l o s e s t  Statistical  from  The  period  l a r g e r magnitude events  station  ocean  "  i n western the  the  considered.  C o l u m b i a , c o v e r i n g the  n o r t h e r n end o f Vancouver  source  Ocean i s  1967.  follows  seismograph  Pacific  standard seismograph records  p o r t i o n of B r i t i s h  The s t u d y  the  swarm o c c u r r i n g on a segment o f  and t h e  in  polarity  the of  swarm show a non-random d i s t r i b u t i o n the  first  arrival  varies  with  station  in  and w i t h e v e n t .  These  involving  release  strain  facts  suggest  a generating  by movement on a f a u l t  c o u p l e d w i t h some s o r t  o f t r i g g e r i n g mechanism.  frequency  is  relationship  Log for  2.0  1 Q  < M  N = (4.07±0.50)  L  < 4.0.  characteristic volcanic  determined  of  The v a l u e  earthquake  reconciled  the  The m a g n i t u d e -  L  slope  (-1.10)  generated  in  the  p a r a d o x c o n c e r n i n g the  idea of  as  is  a result  of  ridge  crustal  by d i a p i r i c  material  off-setting  s o u r c e mechanism  " T h e New G l o b a l T e c t o n i c s "  extension across  the  swarms  faults  as  (1.10±0.20)M for  or  activity. The a p p a r e n t  of  -  process  crests  fracture  (involving intrusions)  zones w i l l  generation  is  that of  and t r a n s f o r m  occuj: t o g e t h e r .  new faulting  ACKNOWLEDGEMENTS  I  wish  to  in supervising suggestions  thank the  Professor  research,  and h e l p  D e p a r t m e n t who made The t o p i c was Astrophysical  and a l l life  Observatory,  Miss Judy For  the  portions  of  W.  Victoria,  Research  Research  M. E l l i s in  research  C o u n c i l Post  C o u n c i l Grant  I  G. Milne  B.  patience  for  the  his  Geophysics  C ,  computing at  t y p i n g was  Dominion facilities  the  done by  McLauchlin. received  Graduate No.  o f the  Department  C o l u m b i a and t h e  this  R.  for his  interesting.  Computer S c i e n c e  British  Clarke  other people  C o p e l a n d and M i s s M a r i a n n e  a National National  of  C.  Professor  s u g g e s t e d by D r .  were p r o v i d e d by t h e University  so  G . K.  assistance  Scholarship  67-4327 o f D r .  from  and a  G . K.  C.  Clark  iv  T A B L E , O F CONTENTS Page 1.  INTRODUCTION 1.1 1.2 1.3 1.4 1.5 1.6  2.  5.  OF ARRIVAL  TIMES  Estimating Epicenters Model Events E p i c e n t e r s i n the N o r t h e a s t P a c i f i c Model P e r t u r b a t i o n s  the  13 18 28  Ocean  31 38 52 56 62  4.1  Time R e l a t i o n s  4.2  Magnitude Determinations  Swarm  63 66  CONCLUSIONS  71  BIBLIOGRAPHY  75  APPENDIX A O r i g i n Time f r o m P and S A r r i v a l s APPENDIX B Test of Location Procedure APPENDIX C The E a r t h q u a k e  11 12  31  THE EARTHQUAKE SWARM AT PHC of  1 6 7 9  13  The New G l o b a l T e c t o n i c s The N o r t h e a s t P a c i f i c Ocean W e s t e r n B r i t i s h C o l u m b i a and V a n c o u v e r I s l a n d  INTERPRETATION 3.1 3.2 3.3 3.4  4.  The E a r t h q u a k e Swarm: Summary o f A v a i l a b l e Data Earthquake.Swarms The S o u r c e A r e a E s t i m a t e s of E p i c e n t e r s T r a v e l T i m e s and C r u s t a l S t r u c t u r e o f Vancouver Island Purpose o f T h e s i s  CONTINENTAL MARGIN TECTONICS 2.1 2.2 2.3  3.  1  Swarm a t  PHC  '  77 77 81 81 83 83  V  L I S T OF FIGURES  FIGURE NO.  Page  1.1-1  Area  1.1-2  Epicenters  for  Calculated  by USCGS  2.1- 1  Block  of  Diagram  Ideas o f  2.2- 1  Study  and S e i s m o g r a p h 14 E v e n t s  the  Illustrating  some o f  for  Northeast  Pacific  Summary D i a g r a m o f M a g n e t i c N o r t h e a s t P a c i f i c Ocean  2.2- 4  Bottom Topography f o r N o r t h e a s t  3.1- 1 3.2- 1 3.2-2  Tertiary British  Portions  Tectonics  Columbia of  the  PHC  on the  15  Ocean  and  Anomalies  21  in  Pacific  Insular  the Ocean  Belt  of  2 8 , 1967  (a)  Model f o r  in  (b)  Standard  Events  Crust  Columbia  Crustal  of  the  Model f o r  Earth  3.2-4  Epicenters  3.2-5  E p i c e n t e r s f o r 19 E v e n t s o f t h e Swarm C a l c u l a t e d i n Terms o f a R e g i o n a l M o d e l the E a r t h ' s C r u s t  Function  19 E v e n t s  o f O r i g i n Time  of  the  Swarm as  40 43  Regional  E p i c e n t e r s f o r 19 E v e n t s o f t h e Swarm C a l c u l a t e d i n Terms o f a R e g i o n a l M o d e l the E a r t h ' s Crust for  24  35 British  the  23  30  T r a v e l Times f o r Pn and Sn i n W e s t e r n C o l u m b i a u s i n g USCGS E p i c e n t e r s Western B r i t i s h  20  Ocean  Vertical-Component  Seismogram f o r August  Seismic 3.2-3  the  F a u l t P l a n e S o l u t i o n s , M a j o r F a u l t s and Bottom Topography f o r N o r t h e r n C o a s t a l California  2.2-3  2.3- 1  Swarm as  " T h e New G l o b a l T e c t o n i c s "  Seismicity  2 4  Western North America 2.2-2  in  Stations  43 of a  of  47 49  51  vi T r a v e l T i m e s f o r Pn and Sn i n W e s t e r n B r i t i s h Columbia Assuming A l l E v e n t s had a V o c a l D e p t h o f 10 km E p i c e n t e r s P l u s 90% C o n f i d e n c e E l l i p s e s f o r 8 Well Defined Events Using a Standard C r u s t a l Model E p i c e n t e r s P l u s 90% C o n f i d e n c e E l l i p s e s f o r 8 Well Defined Events Using a Regional C r u s t a l Model H i s t o g r a m Showing Number o f E v e n t s T h r e e Hour P e r i o d s  for  H i s t o g r a m Showing Number o f T h r e e Hour P e r i o d s f o r which N Events Occurred Richter  and Body Wave M a g n i t u d e  Magnitude-Frequency Estimation  Determinations  Relationship  o f O r i g i n Time f r o m S-P  Interval  vii  LIST'OF  TABLES  TABLE NO.  Page  1.1-1  USCGS P r e l i m i n a r y  Determination of  Epicenters 3.1- 1 3.2- 1  .  3  P and S E v e n t s Estimates  34  of L a t i t u d e ,  Time by L e a s t  3.2- 2  Estimates  3.3- 1  Estimate  A-l  O r i g i n Time f r o m S-P  Least  Least  of  Squares  Squares of  Latitude  Latitude  Squares  for  L o n g i t u d e and O r i g i n Procedure  and L o n g i t u d e . b y  and L o n g i t u d e by  2 Models  Interval  46 50 57 80  INTRODUCTION  1.  1.1  The E a r t h q u a k e In  the  Summary o f A v a i l a b l e  swarm o f  at  least  occurred  in  the  0 6 . 2 2 . 5 0 U. 217 e v e n t s  eastern  of  the  larger  stations  of  the U n i t e d S t a t e s  magnitudes centers  of  the  except  in  Figure depths  epicentral  2 c a s e s where  epicenters  all  side,  average  with  fall  in  Determination  given  for  results  i n Table  all  events  estimates values  of  5.2  Island  1.1-1).  for  1.1-1  (USCGS)  Epicenters  locations and t h e  of  events  with  end o f  the  shallow;  and  epi-  area,  roughly  129.7°W.  f r o m 3.1  magnitude o c c u r r i n g near  to  the  to  24 and 18 km a r e  50.2°N,  range  are  were r e s t r a i n e d  an i r r e g u l a r  on P wave a m p l i t u d e s )  depths  33 km,  given.  The  70 km on a The m a g n i t u d e s  5.1,  w i t h the  the b e g i n n i n g  2  and  swarm.  This  seismic  seismograph s t a t i o n s PHC, A L B , V I C , VIC,  (Figure  to  1.1-2.  (based  (PHC,  2.7  C o a s t and G e o d e t i c S u r v e y s  co-ordinates  largest  range  were r e c o r d e d by s e i s m o g r a p h  Preliminary  is  1st,  earthquake  of Vancouver  Islands  A summary o f . t h e i r  focal  USCGS in  events  the events  plotted The  for  their  period.  Ocean w e s t  Queen C h a r l o t t e  the  that  on A u g u s t 2 7 , an  the magnitude  Pacific  of  and r e p o r t e d i n  T.  in  Fourteen  for  Data  6-day p e r i o d f r o m A u g u s t 2 7 t h t o S e p t e m b e r  1967, b e g i n n i n g at  and s o u t h e a s t  Swarm:  FSJ,  activity  in western  VAN, FSJ, PNT)  was  also  r e c o r d e d by  and c e n t r a l  PNT and M I C .  were e q u i p p e d w i t h  Four  7 Canadian  British of  Columbia,  these  stations  conventional  Willmore  F I G U R E 1.1-1: P H Y S I O G R A P H Y AND LAND FORMS OF B R I T I S H COLUMBIA, SOURCE A R E A FOR E A R T H QUAKES I S O U T L I N E D . SEISMOGRAPH S T A T I O N S USED IN T H I S STUDY ARE MARKED BY A S T E R I S K S  7—-  N/LANDFORM UNITS OF BRITISH COLUMBIA  COASTAL SYSTEM fI „')^, CoO atvae'ltTM ruuofh uY nS a tn E A S T E R N S TiEMAm I[ 1flaky V o u n a t m t Roty Mouna tni Trench 1  N ITERO IR SVSFcfM [[""]ISP Un i* o u h t e nd Northern ^ M PotautcnuiainirniAe raa* GalR EATttihPLA N IStui and Cuctls I 1P ni* M f  TABLE USCGS  EVENT NUMBER AUGUST  AUGUST  27, 2 4 5 7 28 10 11 32 13 0 0 17 19 21  SEPTEMBER 1 0  PRELIMINARY  LATITUDE ( D E G . N)  1.1-1  DETERMINATION  LONGITUDE ( D E G . W)  ORIGIN H/M/S  OF  TIME  EPICENTERS  DEPTH (KM)  MAGNITUDE  1967 50.30 50.22 50 . 15 50.19  129.87 129.87 129.83 129.70  12/56/36.7 13/34/52.6 15/18/45. 1 18/29/07.4  33 24 33 33  4.0 5.1 3.8 4.1  50.19 50.10 50.34 50.13 50.23 50.24 50.30 50.41 50.40  129.48 129.09 129.73 129.55 129.60 129.78 130.08 129.55 129.84  11/32/10.5 11/41/20.6 11/45/34.6 12/39/18.1 12/59/03.2 12/59/04.4 13/49/42.1 15/07/11.7 16/20/06.6  33 33 33 33 33 36 18 33 33  3.7 3.8 3.7 4.1 4.0 4.0 4.6 4.5 5.1  5 0 . 60  129.51  14/11/25.4  33  4.6  -  4  FIGURE  1.1-2:  E P I C E N T E R S F O R 1*4 E V E N T S I N T H E S W A R M C A L C U L A T E D BY U S C G S . SOLID TRIANGLES LARGER MAGNITUDE EVENTS. DEPTH IS C O N S T R A I N E D T O 33 KM  AS ARE  5 Seismographs, while  the  recording  remaining  3 components  stations  with vertical-component records  are  in  magnifications  the in  PHC r e c o r d e d stations VAN 1 9 ,  recorded FSJ  left the  this  (Pn)  an o r d e r  interior  of  of  their  of  arrivals within  of  the  These  to  60 mm/min, w i t h  ALB  The r e c o r d s  All  records  Island  (Figure  from This  and 2 on  first  are  which  arrivals  with  f o r which  stations  19,  were  1.1-1),  identified  common e v e n t s  3 7 , VIC  available.  f o r which  c o u l d be  other  f r o m MIC  and t h e  Columbia  all  some first  located  source. of  arrival  using dividers  consistent  seconds.  (Sn)  were made f r o m the  Observatory, are  British  All  period.  less;  3 on V a n c o u v e r  8 common e v e n t s  Measurements amplitudes  2.  c o u l d be p i c k e d .  850 km o f  one-second  equipped  only.  scaled  and so were n o t  and 11 a d d i t i o n a l  alone  at  poor q u a l i t y , lost  and s e c o n d a r r i v a l s  confidence,  records,  short-periods,  were  instruments  o f magnitude  5 stations,  plateau  a total  and  t h e most e v e n t s , . 2 1 7 , w h i l e  p e r i o d were  an " a r r a y "  recorded  20 K r a n g e  3 3 , PNT 2 2 , and MIC  not used because VAN f o r  chart  long-  VAN and MIC)  short-period  form o f the  (ALB,  at  original  and m e t r i c  ±0.5 seconds  limits  times,  and t h e  S-P  times  and P and S  records  of  scale.  The t i m e s  times  s h o u l d be r e g a r d e d  as  the  for  S to  the  901  Dominion for  P  ±2.0 confidence  level. The r e c o r d i n g Pacific of  Ocean r e p r e s e n t s  interesting  What was  of  its  questions.  relationship  an e a r t h q u a k e  swarm  an uncommon e v e n t Where d i d t h e to  the  in  the  and r a i s e d  activity  tectonics  northeast  of  the  take  a number place?  region?  What  special  relationship  do e a r t h q u a k e  Tectonics"?  about  differs  earthquake  the  small  region of  this  1.2  occurrence  Earthquake  vulcanism; of  great  the  the  o f magma a t  Whitham,  Piche,  A swarm  - b o t h terms  lack  of  des-  within  a  a main s h o c k .  be u s e d i n  in  However,  this  of  paper.  in  recent  a c c o m p a n i e d by  tracing the  the path  N.W.T.,  tectonic  of  recent  1968).  The l a c k  in  (1958)  than  the  1 Q  the  the  area.  a main s h o c k ,  swarm a r e  of v o l c a n i c  the v a l u e b,  of b larger  of  in  swarms.  also  of  is  an  was  but  c o u l d have b e e n c a u s e d by  vulcanism  of  it  origin,  There  swarms  o f magma  investigation  o f Mould Bay,  were o f  release  areas  usually  sometimes  earthquakes  characteristics  It  are  the v i c i n i t y  Log  swarms.  the  occur  eruptions  g i v e n by R i c h t e r  Values  Global  general  number o f e a r t h q u a k e s - in  swarms  and t e r m i n a t i o n  is  some  d e p t h c o u l d n o t be e l i m i n a t e d .  evidence  diagnostic  series  t e r m swarm w i l l  strain  geologic  ship  a large  surface.  swarm i n  appropriate  general  New  Swarms  volcanic  concluded that  initiation  "the  c a n be c o n s i d e r e d .  - aftershock  numbers o f e v e n t s ,  earthquake  ment  the  earthquake  from depth t o  the  of  question f i r s t ,  s p a c e and t i m e  criterion  Most  last  swarms  from a f o r e s h o c k  cribe  By  to  '  To b e g i n w i t h t h e facts  swarms b e a r  that  moveno  (Smith, and s u d d e n  thought  A l s o u s e d as  frequency-magnitude  to  be  a  relation-  as N = a - b M  1.0 a r e  (1.2-1)  L  more c h a r a c t e r i s t i c  has b e e n s u g g e s t e d t h a t  earthquake  of  swarms  volcanic are  7 a s s o c i a t e d w i t h the Oliver,  and S y k e s ,  and v o l c a n i c ridge  of  crests 1968),  activity.  off-setting thought  t o be  seismicity  1.3  in  zones  lated  two d i f f e r e n t  respect  the  along  1969).  processes  oceanic ridges part  the  This  is  generating  Oliver of  of  of  t h e much has  A "New  the  the  earth's  the  recently  faults)  earth's  stimu-  Tectonics"  1968)  crust  faults  larger  Global  and S y k e s ,  and t r a n s f o r m  blocks  and t r a n s f o r m  which  tectonics.  which  aseismic nature,  are  to  explain  (oceanic in  crust  1965b))  rises,  terms  of  moving  least  developed .ridge-type a faster  1967),  interest  (formerly  and t h e  Queen  The Cobb R i s e p a r a l l e l s  from r o u g h l y (at  of p a r t i c u l a r  (McManus,  (Wilson,  Zone.  coasts  spreading at  Francis,  steeper  areas.  Ocean i s  arcs,  Cobb R i s e  Island Fracture  poorly  occurring  median  the  with  other.  J u a n de F u c a R i d g e  Washington  J . G.  different  features  o f major  to each  are  of  (Isacks,  Two f e a t u r e s thesis  a l o n g the  •  in global  and i s l a n d  faulting  a significantly  those  of such features  tectonic  interactions  of  Pacific  has b e e n p r o p o s e d  trenches  (Isacks,  Area  pattern  interest  the major  (T.  the  the n o r t h e a s t  world-wide  system  occurring  have  than  result  The a r r a n g e m e n t in  Ridge  the  The S o u r c e  ocean r i s e  Earthquakes  relation  fracture  the  and c h a r a c t e r i z e d by n o r m a l  the M i d - A t l a n t i c  magnitude-frequency  of  rate  over  500 km a t the  last  topography, than o t h e r  the  sea. half  of  the  Charlotte Oregon  and  relatively  century) that the  this  named  Its  suggest  parts  in  and  it  ocean  is rise  8 system.  It  activity,  is  the  interpreted and on t h e also  terminated Blanco  as  a dextral joining  Fracture  a dextral  n o r t h by t h e  a seismic  feature  Cobb R i s e  USCGS,  place  129.6°W.  On t h e  this  is  area  northwest. latitude  to  Trench,  for  area  bathymetric  but  1967)  in in  of  ridge-ridge Fracture  1968),  a zone o f  Zone,  interpreted  type,  (Wilson,  the  swarm,  as  as  1965b)  the v i c i n i t y  located  of  fracture  "probable  crustal  associated with a feature on t h e  by  50.2°N, (1963) ,  zone  trending  considered to extend  abuts  type,  Trench.  a large  not  seismic  1968),  map c o m p i l e d by McManus  is  trending northeast,  the  Islands  ridge-arc  events  source  The Cobb R i s e o  the  of high  and. S y k e s , of  and S y k e s ,  the A l e u t i a n  mapped as p a r t  50 N;  (McManus,  the  fault  Queen C h a r l o t t e  of  an a r e a  (Tobin  transform  transform fault  the  s o u t h by  Zone  (Tobin  The e p i c e n t e r s the  on the  to  topography"  called fracture  the  Explorer  zone a t  this  latitude. This  feature  crest  by W i l s o n ,  field  anomalies  None o f (Tobin the  the  also  (1965b) in  the  in  suggests  tonics,  especially  in  the  Queen C h a r l o t t e  the  The b r o a d , s c o p e Ocean,  as  the p e r i o d  of  d e t e r m i n e d by t h e  additional  Fracture tectonics two  of  total  magnetic  and Mason  complexities the  (1961) .  1954-1965,  o f b o t h the b e t t e r  r e g i o n between  Islands  of  ridge  a r e a has b e e n a s s o c i a t e d  The s c a t t e r  epicenters  a possible  as p r e s e n t e d by R a f f  this  located  as  distribution  recorded for  1968)  Trench.  interpreted  from the  area  seismicity  and S y k e s ,  Explorer  was  with  and p o o r e r in  Explorer  the  tec-  Trench  and  Zone. in  the n o r t h e a s t  independent  studies  of  Pacific seismicity  and e a r t h q u a k e Lomnitz  mechanisms o f T o b i n and S y k e s ,  and M c E v i l l y ,  movement  from the  Charlotte  (1968),  East  Pacific  Island Fracture  consistent spreading  idea of  from r i d g e  crests  swarm w i t h  this  Estimates  of  in  of  by a l l o w i n g and o r i g i n which  times  free time  the  equations  in  the  are  cessing. sense  Different  basic  against  are  s u c h as  represented  by  on  the  estimated.  commonly e s t i m a t e d  the  reduction of  latitude,  sum o f  the  the  parameters.  unknown  2 sources  at  various of  of  the  of  of  arrival  stations  an e v e n t  This  simultaneous  errors  in  this  times  reading error  are  for  errors  given  depth  variables  for  One  specific f o r pro-,  a "random p r o c e s s " i n  the  other  an  Along with  sources:  the  observer.  same r e c o r d w i l l  a given event. of  times,  technique  method.  and c o l l e c t e d  is  a  non-linear  must be r e c o g n i z e d and r e c o r d e d by  same t i m e  free  by  "errors"  longitude,  squared e r r o r s .  a set  the  floor  (1965b) .  standard expected a r r i v a l  experienced observers  always p i c k  can be  involving  p r o c e s s by w h i c h  it  is  depends g r e a t l y  and c h o o s i n g t h o s e v a l u e s  The a r r i v a l  that  earthquakes  s o l u t i o n of  read  Queen  and o c e a n  activity  environment  the  lateral  The m o t i o n  faulting  seismic  Bolt,  right  south to  the n o r t h .  epicenters  variables  There are involves  the  as p r o p o s e d by W i l s o n the  squares  minimize the  requires  events  for  least  read a r r i v a l  consistent  and  Epicenters  Epicenters technique  the  in  in  transform  tectonic  c o n f i d e n c e w i t h which  1.4  of  one o f  Rise  Zone  w i t h the  The a s s o c i a t i o n the  is  (1968)  not  this  instrumental  10 variations, bine  noise  to g i v e  bution  in  the  factors arrival  time  actual  of  an e v e n t  lies  w i t h the  times  of bias  in epicenter  arrive  On a w o r l d - w i d e  at  special  models  c a n be g e n e r a t e d , b u t  sort  average  for  arrival  The s o u r c e p a r a m e t e r s  average  model f o r  procedures;  times  calculated  model assumed. the  For  upper  are  areas  explosions,  has become a p p a r e n t  whole type  used s i n c e  earth,  topography.  recent  years  travel  time  the  location  of  advent  for  (Herrin  Report  The p r o b l e m o f critical  in western  Ocean because areas.  of  those which travel  the  is  earth  times  an  and  large  Jeffreys-Builen  seconds  late  over  the  from areas  with  trench-  been p a r t i a l l y  remedied  in  r e v i s e d new s t a n d a r d  world  et  eliminated;  al,  1968)  location  but not  procedures,  north  (Seismic  #133) . a model f o r  the  crust  N o r t h A m e r i c a and the  the^ c r u s t  "best  certainly  technology  the  some  interest.  anomalous  that  have  problems,  l o n g s h o t was p l a c e d up t o 60 km t o o f a r  and w e s t by s t a n d a r d e a r t h q u a k e Data L a b o r a t o r y  represent  area  source  Tables  all  the  earthquakes  adoption of  tables  the  specific  of nuclear  T h i s p r o b l e m has  by t h e  wide  of  1 9 4 0 , were s e v e r a l  and b i a s e d  for  prothe  for  then only  100 km o f  Since  Tables,  they  over  inapplicable. it  the  compare  basis, Jeffreys-Bullen  interpolation  the  com-  distri-  location  a " b e s t " value  been used w i t h  fit"  of which  a probability  " s t a n d a r d " model u s e d t o  and h e n c e  parameters.  of  - all  time.  The s e c o n d s o u r c e cedures  and t i m e m i s c o u n t s  and u p p e r m a n t l e  is  especially  northeast is  Pacific  anomalous  in  these  11 1.5  Travel In  of  Times the  98 s h o t s large  of  is  therefore  center  of  the  On t h e Savage  for  (1965)  Washington give  the  T h i s would  for  southeast  of  7.67  and t r a n s f o r m  oceanic  nate  for that  crustal  some  one lack  The c r u s t  of  50 km t h i c k  of  7.8  or  Chibis  of  7.7  30 o r  the  near  Island  in  crustal  the upper mantle  p r o b l e m , the  both features  Pacific  in this  pertinent the  is  especially  critical  to  the model chosen f o r  source  since the  existence  the  makes  (1965), depths.  in  the  use  region unwise.  i n depth  of  of It  is  area  in  l o c a t i o n procedure area  low.  crust.  crustal  a normal  concerning this  occur  active  information  source  vicinity  w i t h anomalous  the  exists  35 km  western  and C o l l i v e r  r a p i d changes  and  km/sec.  c a n be e x p e c t e d t o be a b n o r m a l l y  crust  of  thickness  of Vancouver  that  faults,  little  structure  crustal  anomalous:  the n o r t h e a s t  very  in  C o l u m b i a , White  km/sec and n o r m a l  indicate  Coupled with t h i s  model  least  of B r i t i s h  Dehlinger,  and s e i s m i c v e l o c i t i e s  in  surveys  representing  t h a n 400 km.  t o be a t  plateau  values  Island is  sections,  less  P-wave v e l o c i t i e s  Pn v e l o c i t i e s  ridges  The d a t a ,  Observatory  t o n s , were d i s t i n g u i s h e d by t h e  interpreted  and O r e g o n ,  of Vancouver  1960 t h e D o m i n i o n  Island.  give  to  Island  300 p o u n d s o f e x p l o s i v e s p l u s  distances  interior  and u p p e r m a n t l e Immediately  1,500  o f Vancouver  seismic refraction  Island.  approximately  explosion of  earth the  out e x t e n s i v e  of Vancouver  Pn a r r i v a l s  Structure  p e r i o d from 1953 t o  Canada c a r r i e d  the v i c i n i t y  of  and C r u s t a l  unfortuthe  case. is  This  sensitive  12 1.6  Purpose This  in (1)  of  Thesis  thesis  was u n d e r t a k e n w i t h t h e  To examine an e a r t h q u a k e  swarm i n  special  (a)  The S o u r c e  Area.  (b)  The S o u r c e  Mechanism.  To o b t a i n British (a)  (b)  light  reference  Columbia,  aims  regional  velocities  the v i c i n i t y  scale.  "New  to:  in  western  under  f o r Pn and Sn waves  o f Vancouver  the p o s s i b i l i t y  continental  the  Island.  Upper m a n t l e  To a s s e s s  of  particularly:  Depth to M o h o r o v i C i c d i s c o n t i n u i t y  in  the  the  i n f o r m a t i o n on t h e u p p e r m a n t l e  Vancouver  (3)  three  mind.  Global T e c t o n i c s " with  (2)  following  of  Island.  locating  margin of western  seismic  events  N o r t h A m e r i c a on a  off  2.  This have  chapter  appeared  seismology  CONTINENTAL MARGIN TECTONICS  in  provide larger  of  "a point pattern  of view"  of view"  is  that  B.  s u g g e s t e d by F. hypothesis  expansion or interest  in  d e c a d e by  contraction these  the  discovery patterns  of  roles  and t r a n s f o r m  faults,  complicated facet  of  of the  the p r o p e r t i e s  represents  of  each o t h e r . first  a  the  earth's  This  concept  theories  and A . W e g e n e r ,  earth  of  continen-  the  con-  through g e o l o g i c time.  has b e e n s t i m u l a t e d the  d i s t r i b u t i o n of  The New G l o b a l  blocks  p r o p o s e d by V e n i n g M e i n e s z , and i d e a s  theories  and f i n a l l y  large  the  of  in  dynamic n a t u r e  the  ocean r i s e  the  system,  by t h e n a t u r e  of  transform  of New  past  of ocean  ocean f l o o r magnetic  trenches  the  anomaly  faulting.  Tectonics  " T h e New G l o b a l T e c t o n i c s " 1968)  the  to  Taylor  r e c o g n i t i o n of  the world-wide  which  c a n be more p r o p e r l y u n d e r s t o o d .  tal  2.1  trenches,  from which  forms:  cell  those papers  o c e a n f l o o r i n g s p r e a d i n g , and t h e  has b e e n p r o p o s e d i n many  vection  and  Columbia.  c a n and do move w i t h r e s p e c t  drift  which  dealing with tectonics  and p a r t i c u l a r l y  t h a t p r o c e s s by r i d g e s ,  The " p o i n t crust  10 y e a r s  scale  British  The c o n c e p t in  b o r r o w e d f r o m many p u b l i c a t i o n s  the p a s t  on a l a r g e  concern western  played  is  an a t t e m p t  to view  (Isacks, large  and g e o p h y s i c a l phenomena, p a r t i c u l a r l y  Oliver,  and  segments o f  seismicity  and  Sykes,  geological tectonics,  14 in  a single  coherent  of  r e c o n c i l i n g very  framework.  It  many d i v e r s e  has  the  problems  remarkable  ability  i n g e o l o g y and g e o -  physics. The u p p e r p o r t i o n s several  hundreds  layers;  the  prising  the  o f km, a r e  lithosphere,  The l i t h o s p h e r e  of  is  crust  of  stresses  limited values.  is  two  or  three  significant values,  in  but w i l l the  resist  shear  the  in  is  stresses.  seismology.  particularly the  layers  (Figure  It  The n e a r  strongly  relatively respect  to each It  at  the  stable,  is  trenches,  asthenosphere,  stress  of  by f l o w i n g .  thickness  limited  The  and a g a i n  final can  seismic  waves, between  asthenosphere-  throughout  divided  low-velocity  The b o u n d a r i e s  the  risen  t o the  into  a few  blocks which  geologic  time.  large,  c a n move  with  other.  the motions of  on the: s u r f a c e ridges  shear  attenuates  laterally-rigid  edges w h i c h p r o d u c e s  structures  is  shear  c o n s i d e r e d t o have no  shear waves.  lithosphere  the  possess  2.1-1).  possibly gradational;  surface  can r e s i s t  corresponds roughly  m e s o s p h e r i c b o u n d a r y has p e r h a p s  com-  considered to  it  resist  of uncertain  high-frequency  are  that  and i s  cannot  three  and t h e m e s o s p h e r e . .  The s e c o n d l a y e r ,  it  The a s t h e n o s p h e r e layer  and i s  accommodate t h e s t r e s s e s  mesosphere,  as much as  one h u n d r e d km t h i c k ,  sense  h u n d r e d km t h i c k ,  "strength";  layer,  of  and u p p e r m a n t l e ,  "strength"  perhaps  asthenosphere  order  significant of  earth,  c o n s i d e r e d t o be made o f  the  the  the  and m a j o r  these  blocks  the major  of  the  tectonically  earth  transform  and t h e  - these  faults.  are The  interactions active the  oceanic  distribution  15  F I G U R E 2.1-1: B L O C K D I A G R A M I L L U S T R A T I N G S C H E M A T I C A L L Y T H E C O N F I G U R A T I O N S AND ROLES OF T H E L I T H O S P H E R E , A S T H E N O S P H E R E , A N D M E S O S P H E R E I N A V E R S I O N O F T H E NEW G L O B A L T E C T O N I C S IN WHICH THE L I T H O S P H E R E , A LAYER OF STRENGTH, PLAYS A KEY ROLE. A R R O W S ON L I T H O S P H E R E I N D I C A T E R E L A T I V E MOVEMENTS OF ADJOINING BLOCKS. ARROWS I N A S T H E N O S P H E R E R E P R E S E N T P O S S I B L E C O M P E N S A T I N G FLOW I N R E S P O N S E T O DOWNWARD M O V E M E N T O F S E G M E N T S O F L I T H O S P H E R E . ONE A R C - T O - A R C TRANSFORM F A U L T A P P E A R S AT L E F T BETWEEN O P P O S I T E L Y FACING ZONES OF CONVERGENCE ( I S L A N D A R C S ) , TWO R I D G E - T O - R I D G E T R A N S F O R M F A U L T S A L O N G O C E A N R I D G E A T CENTER, SIMPLE ARC STRUCTURE AT RIGHT. (FROM ISACKS, O L I V E R AND S Y K E S 1968)  16 of  these  structures  around the magnetic  earth  different  of  stress  new c r u s t a l  material,  developed are  lithospheric  block  recognized,  stable  tectonic  rises  as  type  two b l o c k s  involved  in  crust  generally  is  slide  of  more c o m p l i c a t e d t h a n on o c e a n i c The m e c h a n i s m w h i c h  one,  set  uncertain.  In  representing  results  the  density  the  the  active  and one w i t h surface  an  in  types  role. type  of  lithosphere  Oceanic-type crust  in  zones crusts  energy needed f o r  lines  heat  in  is  adjust the  material  active lying  places,  these this. a  lower  as b e s t  Gravitational certain  on  containing  away f r o m t h e  blocks  density  of thought  element,  lithosphere  plunging,  are  on c o n t i n e n t a l  the  asthenosphere.  lithosphere  the  m a r g i n s , by no means  two  carry  higher  shear  crust.  lithospheric  a relatively  lower  in  the  second theory  relatively  the  c e l l s , which  and t o w h i c h the  is  of  of  The  lithosphere  earth's  rises  generates  There are  asthenosphere  of convection  mantle, can.  the  the  continental of  zones of  nature  crust  an i m p o r t a n t  is  In  of  o c e a n i c m a r g i n s , but  compression.  is  are  by one a n o t h e r .  active  The d e v e l o p m e n t  a  zones o f c o m p r e s s i o n and  Two t y p e s  underthrust  from  symptomatic o f  c o m p l i c a t e d by t h e  play  as d e d u c e d  e x t e n s i o n and g e n e r a t i o n  of  activities  is  a continental-type  interactions  activity  well.  and t r a n s f o r m f a u l t s  The d i v i s i o n  continental  are  zones o f  blocks with t e c t o n i c a l l y  follows  the b l o c k s  structures  involved.  crust.  tectonic  remarkably  trenches  are  further  one w i t h  zones o f  motion o f  sea agree  field;  interactions  oceanic  at  the  underthrusting,  stresses  and t h e  anomalies Each  as p r i n c i p a l  they  element, over  the  instability into  the  17 asthenosphere. and t h e  The a s t h e n o s p h e r e  downthrust  lithosphere  asthenospheric material  tectonics,  but  elements.  In  significance, limb  of  trenches  representing  feature,  faulting,  both cases, of  In  strain  faults  release  from a t e c t o n i c  point  somehow c o r r e l a t e d can then  imagine  instance,  the  which  are  present  earth's If  volcanic swarms  trenches  are  the  while  strain of  rises  release their  If  role  of  in  ancient  surface swarms  activity,  it.  trenches  they  are  a primary  the  continent  for  the  view o c e a n i c  ridges  lessen  are  and,  one  for  second p o i n t  geology.  plates,  feature,  of South America -  From t h e alone  important  upper m a n t l e ,  global  to  In  is  rises  in  lithospheric  own.  the  own s t r e s s e s ,  of  by  faulting.  their  the  a  representing  them g e n e r a t i n g  to  are  elements,  in  so p r e v a l e n t  second p o i n t  rising  cells  look  same and  to convection  the  tectonic  falling  stresses,  on t h e  by b e i n g b o r n u n d e r n e a t h  strains the  second,  of  on t h e  have t h e  the  secondary  by w r e n c h  of view.  r i p p i n g apart  v i e w , we must forces  are  into  same p a t t e r n  d e v e l o p i n g no s t r e s s e s  transform  flowing,  continue.  they p l a c e  zones o f  by  converted  and r i s e s  the  representing  but  the  respectively  The e m p h a s i s p l a c e d  Africa  in  the emphasis  first,  this  t h e p r o c e s s may  e l e m e n t , which produce the  secondary  zones  the  in  to  gradually  result  a convection c e l l .  primary  normal  differ  is  so t h a t  Both p r o c e s s e s w i l l  adjusts  of  disruptive In  fact,  from  extensional  allowing  extension  of  occur. volcanic  then  it  to o c c u r a l o n g the  events,  or at  w o u l d be n a t u r a l oceanic  ridge  least to  triggered  expect  system, since  by  earthquake ridge  18 crests  are  zones o f  vulcanism.  Most e a r t h q u a k e  aftershock generally commonly  diapiric  sequences, small  lack  - less  ascribed  as  ridge  system,  larger  zones  rather  fracture may be the  strain,  of  ridge  the  move p a s t  crustal  material  strains  without  rupture  The N o r t h e a s t  The i n t e r a c t i o n s  to  earthquake idea  of  type  while  strain It  can r e s i s t  overall  except  features.  of  two  shear litho-  crests  faulting  may be t h a t  in  are  and  normal  larger  shearing  strains.  Ocean  of  the  Pacific  so i t  of  marked by t h e arcs  Ocean l i t h o s p h e r i c  lithospheric  the  b l o c k as  responsible  will  framework  margins  The i s l a n d  as  by n o r m a l  also  developed  ridge  relatively  than d i l a t i o n a l  tectonic  one,, are  the  the  but  release  forces  It  oceanic  that  patterns  zones o f  frictional  material.  swarm s t u d i e d h e r e ,  The c o n t i n e n t a l cases  are  is  fracture  the c r e s t s ,  e a c h o t h e r were u l t i m a t e l y  the  from the  than  and t h e N o r t h A m e r i c a n c o n t i n e n t relative  on t h e  strength  each o t h e r ,  Pacific  swarms.  suggests  stress  are  a main e v e n t  This  of extensional  oceanic  of  crests.  different  o f new c r u s t a l  magnitudes  occurring  t e n d t o be  Transform f a u l t s  release  generation  2.2  events  widespread  from f o r e s h o c k -  of v o l c a n i c  earthquakes  d e v e l o p e d , p e r h a p s , by  spheric plates zones  the  due t o  areas.  event;  Such a l a c k  5.  z o n e s have g r e a t e r  in part  two  a "major"  for  o f magma and  as d i s t i n c t  a characteristic  that  than  swarms,  than  may a l s o be n o t e d the  intrusions  of  be w i s e the  they  move  the  t o have  a good  area.  Pacific  development  and t r e n c h e s  for  block  of  Ocean, i n of the  active  all trench-  western  19 Pacific  (Kurile,  Bonin,  Kermadec t r e n c h e s ) active  features  greatest  free  trenches  is  air  also  Island chain, this  on t h e  gravity  is  of Mexico to  type  topography  features  in  the western  or n e a r off  the  the  the give  conclusions  w i t h the  the  have  the  the  deepest  vulcanism,  America.  and  the  large  of  Aleutian  The s o l e  exception  of N o r t h A m e r i c a , from  A l a s k a , where t h e u s u a l a series  were  first  of  ridge  about United  recognized in  one-third States  of  some h i n t  the as  from t h i s  the  trench-  crests  and by t h e  of  and  of  the  of  seismic of  magnetic  Alaska) (Figures  epicenters  Focal the  the activity  and O r e g o n  mechanism  zones.  The  have  lately  investigation of  of  the bathymetry  anomalies  of  associated  crests.  Northeast  Pacific  (Seismological  and N o r t h e r n  zones.  i n c r e a s e d knowledge study  terms  earthquake  the n a t u r e  line  the  California  tectonic to  of  (exclusive  The d i s t r i b u t i o n o f  strike  drawn  ridge  McEvilly,  tectonically  they  of Japan,  Two p a p e r s , by T o b i n and S y k e s of  and  The d e v e l o p m e n t  coast  of northern  b e e n c o n f i r m e d by t h e area,  and C e n t r a l  area;  coasts  and 2 . 2 - 2 ) .  delineates  the  earth;  seismicity,  coasts  r e p l a c e d by  of  solutions  the  the western  seismicity  2.2-1  t h e most  and e x t e n s i v e  south-central  is  the  Tonga,  faults.  These  occurs  of  anomalies.  seen o f f  Gulf  transform  flow  Marianas,  criterion  the h i g h e s t  and S o u t h  pattern  any  surface  high heat  negative  to  a r e by  ocean d e p t h s ,  earthquakes,  Phillipine,  Ocean, 1968), Evidence  (Seismicity and B o l t ,  and T e c t o n i c s  Lomnitz  on t h e T e c t o n i c s  of  C a l i f o r n i a and t h e M e n d o c i n o E s c a r p m e n t ,  and  Central 1968),  20  120°  FIGURE  2.2-1:  115'  S E I S M I C I T Y FOR NORTHEAST P A C I F I C OCEAN AND W E S T E R N N O R T H A M E R I C A N O R T H O F 40°N F O R T H E P E R I O D 195^-1963. ( F R O M T O B I N A N D S Y K E S 1967)  21  FIGURE 2.2-2:  FAULT PLANE SOLUTIONS, MAJOR FAULTS AND OCEAN BOTTOM TOPOGRAPHY FOR NORTHERN COASTAL CALIFORNIA AND OFFSHORE. (FROM BOLT, LOMNITZ AND MCEVILLY 1 9 6 8 )  22 discuss  the  Faults,  Oceanic  Vancouver crests  s e i s m o l o g i c a l evidence Ridges  Island,  of  and M a g n e t i c  1965b)  McManus  (Physiography  Pacific  O c e a n , 1967) zones  in  of has  terms  is  that  operating  ment on t h e  s o u t h and c e n t r a l that  is,  respect  the to  Survey o f f  the  ridge  from t h e s e rises  coast  California)  the is  and d e s t r o y e d  area  the  ridge  as  West  1961)  Coast  and  Northeast  crests  and  Cobb  investigations faults  of North America. San A n d r e a s  consistently  Ocean b a s i n  along the  three  and t r a n s f o r m  is  Fault  The moveSystem  and G o r d a R i s e s  by  -  with  New o c e a n i c  a l o n g the A l e u t i a n  of  right-lateral  moving n o r t h w e s t  the North American c o n t i n e n t .  being generated intrusions  reached  (including  Pacific  the  of  topography.  the w e s t e r n  system  of  Cobb and G o r d a R i s e s ,  a system of oceanic off  in  (Transform  Southwest  50°N L a t i t u d e ,  identified of  The c o n c l u s i o n s suggests  the  to  Wilson  existence  anomalies  and Mason ( M a g n e t i c  North America 40°N L a t i t u d e  fracture  Anomalies  proposed the  and a c c o m p a n y i n g m a g n e t i c  r e p o r t e d by R a f f  available.  crust  is  diapiric  T r e n c h by  underthrusting. There by  is  some d o u b t  the  feature  named t h e  Wilson  (1965b)  as  magnetic "probably  associated 1963 of  crestal"  crest  in  ( T o b i n and S y k e s , does n o t  terms - at  of  in  terms  of  played  in  It  interpreted  by McManus  for  1968)(Figures that  was  the  topography, but  least  suggest  role  Trench.  and i d e n t i f i e d  seismicity  seismicity  the  Explorer  a ridge  anomalies,  about  this  the  by  associated  (1967)  as  has n o t had  t h e p e r i o d f r o m 1954 2.2-3  process  and 2 . 2 - 4 ) .  Explorer  any through  The  Trench is  lack not  23  FIGURE  2.2-3:  S U P E R P O S E D ON R A F F A N D M A S O N ' S S U M M A R Y D I A G R A M OF THE MAGNETIC ANOMALIES IN THE NORTHEAST P A C I F I C O C E A N ARE ARROWS WHICH I N D I C A T E T H E A X E S O F 3 S H O R T R I D G E L E N G T H S AND S T R A I G H T L I N E S WHICH I N D I C A T E FAULTS O F F - S E T T I N G THE ANOMALY P A T T E R N . ( A F T E R V I N E AND W I L S O N 1966)  24  -OUATSINO  _  5TIRN1 SEAVQONT  t,  CANTON  %1  / $ * }(/,'••'••"' r  \'  ;  J  PiiJL REVERE  .  .CUC'JKIUSH C-j CANYON ^6^, £ ^ CRCWTHEB A  !  •«AYS CANYON  ^•SUIOE CANTON  WASHINGTON  "'WILL A PA  CANTON  •-STGNEWALL  BANK  A^TCK '  CALIFORNIA  DEPTH IN FATHOMS 0  SEAMCUNT, UNJTATEO DEPTH  J  7  ="\. \ "ToGE " -.OI.PMOEHJX f|lCG£ ' i a s i ^  .  ""ESCANABA RiDGE ESCANASA TROUGH  CCWPILFD BY D. A. V; MAhUS tEPAhTWEST C CCEAr.OGRSPMT UNIVERSITY C* WASHt«iGT0H,'  l€HJ-'  J  i  ' TRINIDAD CANTON  ' EEL CANYON BEAR VALLEf ''MENDOCINO CANYON  \VENOOClMO " OG€ ( f  FIGURE  2.2-H:  I JK3  BOTTOM TOPOGRAPHY FORNORTHEAST P A C I F I C OCEAN FROM MCMANUS 1 9 6 7 . S O U R C E A R E A F O R E A R T H Q U A K E SWARM O U T L I N E D I N U P P E R L E F T - H A N D C O R N E R  25 actively  spreading.  quake was  located  off-setting Pacific along of  the  shows  ridge  crest  the  on t h e  fracture  Rise  the  In  crest  zones.  crest  "New  crests)  suggests  of  but  zone.  Global T e c t o n i c s " , of  topography of  strength  and low  spreading  The o c c u r r e n c e intersection  of  Island Fracture Explorer  are  it  is,  though p o s s i b l y ( s t r a i n being the  in  to  the  time,  three  the  point  hand,  of  ridge  lithosphere)  other  low  off-set  (on  which  well-developed  Trench would suggest  swarm i n  the  T r e n c h w i t h t h e Queen the  ways t o  on t h e  crustal  area  of  the  Charlotte  question of  the n a t u r e  explain  general  of  Explorer  at  the  Trench.  First;  lack  the  feature,  active  spreading  released  at  by o t h e r  Cobb R i s e ) . least  over  has  Explorer  Trench, either  The p r e s e n t  the  has  areas  ceased  of  the  system  Queen C h a r l o t t e  Second, s e i s m i c i t y a ten year  taken p l a c e  r e c o r d e d , but  one t i m e ,  period.  is  not  which,  - notably  Island  Third,  of  and most  i n d e e d , an a s e i s m i c n o n - a c t i v e  activity  o r was  at  East t o be  from the  thin  On t h e  the  seismicity  an e a r t h q u a k e  Explorer  southern e x t e n s i o n of  Zone  of  the  rates.  Zone r a i s e s  activity  obvious,  of  earth-  away f r o m  seismicity  fact,  one  Trench. There  seismic  the  of  crest  for  (or  Explorer  only  concentrate  In  strength  the  the  lack  suggests high spreading r a t e s . crestal  to  time  Cobb R i s e ,  tendency  itself  lack  the  Most o f  a similar  by a f r a c t u r e  view of  same p e r i o d o f  Fracture  stationary seismic  b u t has n o t b e e n a s s o c i a t e d w i t h because  it  inaccurately pattern  of  was  t o o weak t o be r e c o r d e d ,  located  tectonic  the  away f r o m t h e  elements  in  the  feature. north-  26 east  Pacific  M i o c e n e Age  Ocean i s  (25 m i l l i o n y e a r s )  Tertiary  Ages  the  Pacific  East  (10  thought  t o have  ment o f  the  (Isacks, (or  was  slip  Rise  Baja  (Menard,  and S y k e s ,  displacement  length,  series  present  are  e x c e p t where  of  The G u l f  Mexico  resulted  right-lateral System,  is  by move-  away f r o m c e n t r a l  of  to  of C a l i f o r n i a  25 m i l l i o n y e a r s  ocean  long,  across  generally  they  Rises.  commonly a s c r i b e d  Fault  floor  parallel the  C l a r i o n , C l i p p e r t o n and o t h e r at  assigns  in  in  strike-  the  past  1961) .  of  east-west  (1967)  T h i s movement has  San A n d r e a s  (Hamilton,  the  roughly  features  are  past  1968).  McManus  Cobb and G o r d a  1964).  the  A Pre-Cenozoic pattern  Murray,  the  some 350 m i l e s  on t h e  100 m i l l i o n y e a r s  trending  to  C a l i f o r n i a Peninsula  product of)  r e p r e s e n t e d by  recent.  - 70 m i l l i o n y e a r s )  developed in  Oliver the  relatively  spreading  fracture  Pacific  - the  fracture  is  zones Mendocino,  zones.  These  a s e i s m i c a l o n g most o f  intersect  portions  of  their  an a c t i v e  rise  system. Of p a r t i c u l a r  interest  the Mendocino F r a c t u r e coast  and a c t s  as  seismic a c t i v i t y Rise  and t h e  1968)  as  System, the  the  Zone where  California  an e x t e n s i o n o f  Pacific  Charlotte  it  eastern-most approaches  out  the  the  coast  (Tobin  is  activity  interpreted on t h e  to sea near  California  the and  San A n d r e a s  Cape M e n d o c i n o .  with respect San A n d r e a s ,  of  Gorda R i s e .  between  m o t i o n on t h e  Island Fault  of  portion  Mendocino Escarpment  b a s i n northwest  (right-lateral  the  southern terminus  on t h e  which passes  is  Gorda Sykes,  Fault Motion  to North America Blanco  Zones and e x t e n s i o n a c r o s s  and Queen the  The  East  of  27 Pacific,  G o r d a , and Cobb R i s e s )  some s o r t  of normal p r e s s u r e . a c r o s s  The r e s u l t rotation  of  of  this  the  Gorda  the  Fracture  Zone This  Explorer the  of  the  rises  of  Explorer itself  the  simple  this  the  w i t h the  tectonic East  north.  oceanic was  to  the  of  the  Fracture  system  Pacific  a r e a between  off  so t h a t  the  system to  simplification Queen  of  Charlotte  of  one  the Trench  Island Fracture in  south to  the  extending  Aleutian  to  Zone  geometrically  would then a l s o  with respect  Trench.  a  transform fault  Such a p r o c e s s may e x p l a i n Explorer  the  crest.  Zone w o u l d r e s u l t  the  If  c o m p l i c a t e d by  and t h e E x p l o r e r  The Cobb and G o r d a R i s e s  on t h e  crust  Queen C h a r l o t t e  a n d w o u l d move n o r t h w e s t  activity  was  the  Island.  The b a s i n e a s t  ridge  in  Blanco  unstable with respect  - a ridge-arc Rise  Fault  Cobb R i s e w o u l d r e p r e s e n t  sheared  off"  1968).  o f the  The e x t e n s i o n o f  t o be an a c t i v e  American c o n t i n e n t . of  the  continuing process.  San A n d r e a s  extinct,  San A n d r e a s  to j o i n  the T e r t i a r y  Trench)  T r e n c h w o u l d be  cease  from the  the  spreading, a progressive  southward  The j o i n i n g  in  in in  Explorer of  clockwise  w o u l d be a " s h e a r i n g  L o m n i t z and M c E v i l l y ,  system would ensue.  Island Fault  to  the b a s i n  z o n e s o f weakness  t h e new d i r e c t i o n  aspect  force  T r e n c h and t h e n o r t h e r n e n d o f V a n c o u v e r  (including  the  this  may h a v e b e e n t h e h i s t o r y  development  older  of  across  (Bolt,  a  Zone.  Basin.  G o r d a B a s i n by an e x t e n s i o n o f  System n o r t h w e s t  without  the Mendocino F r a c t u r e  p r e s s u r e would b e , m e c h a n i c a l l y  A second r e s u l t of  c a n n o t be a c c o m p l i s h e d  the  Trench be  North  the p r e s e n t  lack  28 2.3  Western  British  The p r e s e n t expressed in  the  of  along  extension  a northwest seismic  of the  the  pattern  activity  Washington  day t e c t o n i c s  Local  along  ridges  the  northeast  and wrench  variations  an e a s t - w e s t  - but of  these  the  in  this  trend  of  Islands  Columbia suggests  that  s h o u l d be a p p a r e n t  in  the  recent  as  of  the  along  of  the  Oregon  a consequence  Basin  Block  The p r o x i m i t y ' o f  Zone t o  influence  the  one  exist  on a p o r t i o n  Pacific  Block.  Fracture the  the  is  faulting  pattern  c a n be e x p l a i n e d  contact  Pacific  and t r a n s f o r m f a u l t s  trend  North American C o n t i n e n t a l  Queen C h a r l o t t e  in  Island  and a zone o f c o m p r e s s i o n a l o n g  Coast  geometry  of  a northeast  trend.  Mendocino Scarp  C o l u m b i a and V a n c o u v e r  coast  of  the  British  right-lateral  geological history  and  movement  of  the  region. The g e o l o g i c h i s t o r y Columbia and the  (Sutherland-Brown, Queen C h a r l o t t e  with periods  the  1968),  and the  undergone a long faulting  periods  the  To t h e  of  deposition  strong the  this  Early  belt  lies  North American C o r d i l l e r a which  and e x t e n s i v e  of  metamorphism.  now t h e w e s t e r n  portion  physiography  this  a r e a may have  This  is  thought  i n what  is  The M e s o z o i c  r e s e m b l e d the  irregular,  has  compression, f o l d i n g ,  system o p e r a t i n g  of North America.  Asia with  east  Island  of  Especially  and c o m p l i c a t e d h i s t o r y  of Southeast  British  i n c l u d i n g Vancouver  alternates  Late T e r t i a r y .  a mesozoic trench  of  of  t h e M i d and L a t e J u r a s s i c ,  be a p r o d u c t o f  coast  insular belt  o f v u l c a n i s m and p l u t o n i s m .  Canadian p o r t i o n of  thrust  the  Islands,  plutonism occurred during Cretaceous  of  deeply  present  embayed  day  to  29 continental system  crust  (White,  Late J u r a s s i c  of  1968).  Early  folding  Tertiary  and w r e n c h  vulcanism  on t h e  occurred in the  the  (McManus, faulting  down m o t i o n '  influence which  of  Olympic Mountains Islands  the  nearby  of  is  Straights  o f J u a n de F u c a where  where across  the  coastline  and o f f s h o r e  the  shows  the  islands.  At  of  tectonic  Cobb R i s e line the  the  the  coast  paralleling  coastline  environment.  Intense  occurred,  the  fault  faults  show  Fracture  zone l i e s of  to  fjordic  o f J u a n de  the Zone  to  reflects  the w e s t . the  of  the  the  topoFuca  extension  undergoes a t r a n s i t i o n  i n each case  block  immediately  r e p l a c e d by  Cobb R i s e  large  common  with the nature  latitude is  On  2.3-1).  development the  deformation  Washington.  Islands  fault  roughly  extensive  and n o r m a l e a s t  (Figure  feature  from  From t h e A l a s k a n P a n h a n d l e  t h e w r e n c h m o t i o n on t h e  continuous nature  impressive.  this  the  witnessed  w i t h the  These  Queen C h a r l o t t e  coastline  graphy  wrench  during  Island with  eruptions  \  The c o r r e l a t i o n  period  o f northwest  1968).  \  dates  island.  became a c t i v e  developed contemporaneously  offshore  This  subareal  right-lateral  i  tectonics  the  arc  ago).  on V a n c o u v e r  (Sutherland-Brown,  of  of  island  became e m e r g e n t  1968).  southern t i p  of  an o f f s h o r e  150 m i l l i o n y e a r s  t r e n d i n g northwest  characteristics  with  day p a t t e r n  Queen C h a r l o t t e  faults  relief  The c o a s t l i n e  (roughly  The p r e s e n t the  low  to  a The  prevailing  i3r OIXON  ENTRANCE  2>C-L  \  ^  !  '  rp^?  53-  V''C..\M o\ \  L E G E N D  \  ,  IS L A U D S  %  Tertiory Post-Tectonic  \'^XgbV  of T e r , i o r  Plutons  ore  chiefly  ) ' °i  e  plutons on V a n c o u v e r  Post-Tectonic Syntectonic  c3  Oo  plu'ons  plutons. chiefly  Plutons of unknown type  52-  Island  of  and  Jurassic age  age V/////A  Foults K-A  oge  in m i l l i o n y e a r s  SOUND On  Vancouver  are  Pre-Nanaimo  Islond  Post-Tectonic  Plutons  Group  FIGURE 3.3-1: TERTIARY TECTONICS ON THE INSULAR BELT OF B R I T I S H COLUMBIA SHOWING MAJOR FAULTS AND PLUTONS. CFROM A. SUTHERLAND-BROWN  1966)  Stole  Mi'es  5 a n Juon I 126*  o  31  3.  INTERPRETATION  The P and S a r r i v a l s distances Canada, highly  by t h e  d e p e n d e n t on t h e  to estimate and the mates  epicenters  are  model o f  for  the  available  refers  event  times  f r o m PHC, A L B , V I C ,  i n the  of  time  t a k e n by t h e  an e v e n t  The e p i c e n t e r  of  is  the  to  USCGS  an a r r a y  account.  the  this  These  they  in  of  5 arrival at  the  use  fact  esti-  records  different  same s e q u e n c e o f The a r r i v a l  ascending order  and r e f e r r e d  then  an e v e n t  earthquake  type  times  at  PHC t a k e n  a negative  is  as o r i g i n .  an a r r a y  from the  in  space  c a n be  to  a  of time  origin the  epicenter  to  PHC.  longitude,  in  sec  which  a function of  the  epicenter,  and t i m e .  c a n be v i e w e d  of event  times  The  of 4 numbers;  used.  arrival  number r e p r e s e n t i n g  to t r a v e l  in  5 stations  i n d e g r e e s , d e p t h i n km and o r i g i n t i m e  the  takes  and c o n s i d e r a  earthquake  FSJ  Pn e n e r g y  An e v e n t , - T , If  into  which  and PNT.  Pn a r r i v a l  time  E.  to  swarm showed t h e  arranged  a x i s w i t h the  locate  An a t t e m p t has b e e n made  t h e USCGS e s t i m a t e s ;  a single  Every  latitude  events  are  Epicenters  g e n e r a t e d by  are  of s e i s m i c events  of  earth.  An " e v e n t " seconds  times  recorded a r r i v a l s the  regional  the Dominion O b s e r v a t o r y  l o c a l geology.  independent of  Estimating  events  travel  o c e a n i c o r i g i n of  w h i c h were n o t  3.1  the  TIMES  were r e c o r d e d w i t h i n  seismographs of  r e g i o n s where  OF ARRIVAL  as  i d e n t i f i e d , whether  it  is  a P  or  32 S event, value  event  o f E chosen which  event. the  a reference  This  of  the  event  must  to e x i s t  include  Ideally random e r r o r , sources  is  was  in  the  at  set  to  the  observed  of equations  in  (1968). of  4 equations;  the  the  stations.  should e x i s t ,  epicentral of  least  4 different  data  but because  from  estimates  a  several  can o n l y  be  confidence.  of e p i c e n t e r s  terms  arrival  must be a t  solution  degree  and Freedman  refracted  there  1968),  a certain  generated  event  and a  (3.1-1)  introduced into  The e s t i m a t i o n Herrin,  reference  solution of  arrivals  (Freedman,  quoted to  c a n be g e n e r a t e d  CT(E)  a unique  R,  type  E. T  For a s o l u t i o n  that  fits.the  represents  4 unknowns  of  is  For t h i s  study  the  Tucker,  reference  event  g e o l o g i c a l model  assuming  along a continuous upper mantle w i t h  constant  velocities  of propagation.  calculated  directly  in  a plausible  d i s c u s s e d by  Arrival  terms  of  times  this  (and  derivatives)  were  m o d e l as a f u n c t i o n  of  the  random e r r o r  the  epicenter. With the of  equations  introduction  of  We assume t h e  of  assumptions  valid  arrival  + R  set  (3.1-2)  d i s t r i b u t i o n o f R t o be u n b o u n d e d , c e n t e r e d  and i n d e p e n d e n t  are  vector  becomes T = CT(E)  stations  the  are  the  individual only  if  stations  well  u s e d and d e p e n d on t h e  times. Freedman  involved.  defined events  at  zero  These  and g o o d  method u s e d t o c o l l e c t  the  . (1968)  suggests  that  errors  involved  in  reading  33 the  arrival  times  o f P phases  on s t a n d a r d i n s t r u m e n t s  arising  from: (1)  Miscounts  (2)  Misidentifications  (3)  Instrumental  errors, (4) all  other  For  in  errors  effects  this  study  instrument  - residual  were  the of  the  sharp  and t h o u g h S e v e n t s that  p r o b l e m at  2 stations,  (Table  the  3.1-1)  classes  basis  remaining  reduced to ments.  The f i n a l  same  charts  S events  of  of normal  an a r r a y well  already  of quality., for  three  in  a small  largely  though  defined,  the  they  had t h e  times  use  error  times  of  over  The o u t p u t  is  harder  a p e r i o d of  f r o m the  rather  difficult  into  (Figure  were p i c k e d by c o p y i n g t h e  Error a  3.1-1).  records,  (2)  factor  s h o u l d be instru-  to e v a l u a t e . t h r e e months  seismographs,  unfortunate  events  two  standard, high quality  (4),  a  show a  b u t may be (3)  not  and.8 S  8 g o o d and 11 f a i r .  Error  the  added  N o i s e was  19 P e v e n t s  8 good P e v e n t s  and  though o f t e n  in motion.  The  area  eliminates  s t u d y were d i v i d e d apriori  factor,  data  clock  distributions.  and a r r i v a l  stations.  one mm/sec, i s the  phase  t h a t would-remain even  11 P and 8 S e v e n t s .  individual.  scaled  retrieval  read  as  and PNT,  a minimum by t h e  r e c o r d s were the  VIC  these  s h o u l d be e l i m i n a t e d the  error  were commonly s h a r p  t r a c e was  chosen f o r  on t h e  o f the  response  were u s u a l l y  difficulty  arrival  of paper speed,  a mixture  stations  P events  at  first  grouping of epicenters  (1).  scatter  the  hours  eliminated  error  greater  seconds, minutes,  - variations  a p p r o x i m a t e d w e l l by  consideration  in  of  - missing  errors  variations  Reading  c a n be  - multiples  as  it  The by  paper-  makes  The 8 g o o d P  cutting  out  the  and  TABLE P AND  P  EVENT IMBER  DATE M/D/Y  2 4 7 13 17 19 20 21 89  08/27/67 08/27/67 08/27/67 08/28/67 08/28/67 0 8 / 2 8/6 7 08/28/67 08/28/67 STANDARD  12/57/02. 13/35/19. 18/29/32. 12/39/U2. 13/50/10. 15/07/36. 15/26/17. 16/20/31. P EVENT  1 6 10 11 12 14 18 22  08/27/67 08/27/67 08/28/67 08/28/67 08/28/67 08/27/67 08/28/67 08/28/67 08/28/67 08/29/67 08/28/67  08/35/08 17/40/41 11/32/33 11/41/40 12/27/19 12/44/19 14/44/03 17/22/21 19/04/52 11/45/58 12/23/33  EVENTS  2h  32 33 S  EVENTS  2 k  7  13 17 19 20 21 89  P ARRIVAL H/M/S  8/27/67 12/57/02. 8/27/67 13/35/19. 8/27/67 18/29/32. 8/28/67 12/39/42. 8/28/67 13/50/10. 8/28/67 15/07/36. 8/28/67 15/26/17. 8/28/67 16/20/31. STANDARD S EVENT  2 9 5 0 0 0 0 5  2 9 5 0 0 0 0 5  3.1-1 S  EVENTS  A R R I V A L R E F E R R E D TO PHC ALB VIC PHC FSJ  PNT  0 0 0 0 0 0 0 0 0  26. 26. 25. 25. 25. 22. 25. 26. 25.  2 2 2 0 4 8 2 6 3  43. 42. 41. 41. 45. 40. 42. 44. 42.  2 2 4 6 0 8 2 0 5  54. 54. 54. 54. 53. 54. 54. 53. 54.  0 2 6 4 2 2 0 8 0  71. 73. 72. 71. 75. 70. 73. 74. 72.  8 4 8 6 2 0 2 8 7  0. "0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0  26. 26. 27. 24. 28. 23. 29. 27. 25. 27. 29.  0 0 0 0 0 0 0 0 0 0 0  42. 41. 42. 35. 42. 45. 47. 48. 35. 43. 46.  0 0 0 0 0 0 0 0 0 0 0  56. 54. 55. 54. 54. 54. 54. 55. 53. 55. 55.  0 0 0 0 0 0 0 0 0 0 0  62. 71. 76. 73. 78. 73. 78. 72. 75. 78. 72.  0 0 0 0 0 0 0 0 0 0 0  69. 67. 66. 68. 67. 64. 66. 69. 67.  8 4 2 0 8 6 8 4 7  97. 98. 89. 95. 95. 95. 98. 98. 96.  8 0 6 6 6 2 4 2 2  113. 114. 115. 117. 116. 116. 116. 118. 116.  4 0 4 2 0 4 4 4 1  150. 149. 145. 146. .149. 149. 148. 154. 149.  4 4 0 4 0 0 4 4 2  0. 0. 0. 0. 0, 0. 0. 0. 0.  22. 22. 22. 22. 21. 22. 22. 22. 22.  8 0 2 4 6 8 0 0 4  35  FIGURE  3.1-1:  P O R T I O N S OF THE PHC V E R T I C A L - C O M P O N E N T SEISMOGRAM F O R A U G U S T 28, 1967. T I M E MARKS ARE AT ONE M I N U T E I N T E R V A L S . N O T E O P P O S I T E P O L A R I T Y FOR F I R S T B R E A K S ON TWO L A R G E S T E V E N T S ( E V E N T S 20  AND  21)  36 traces  and a l i g n i n g  same a r r i v a l remaining  them t o g e t h e r  for  w o u l d be c o n s i s t e n t l y  11 P e v e n t s  seem u n r e a s o n a b l e ,  are  then,  picked  somewhat to  each  less  assume  station, for  each  so t h a t  the  event.  consistent.  It  The  does  a normal d i s t r i b u t i o n  for  not R,  2 (R~N(0,a  I)),  at  least  The c r i t e r i o n principle. derived  With the  by  this  for  the  8 good  chosen f o r  events.  best  fit  is  assumption of normality  method a r e  equivalent  the  least  on R,  squares  estimates  t o maximum l i k e l i h o o d  estimates. We c h o o s e E = E so t h a t R'R where  R'  is  the  transpose  the  product  = (T-CT)'(T-CT) of  |^  R.  = minimum  (3.1-3)  Thus  (R'R)  |g = CR'-I^R) |g = 0  (3.1-4)  or [(T-CT)'|ECT]£ CT i s latitude).  For  refracted  a single  arrivals, CI\  where E^  a quadratic  = E  function layer  CT has  o f E^  crust  the  of  and E^  = /C  V  Q  1  2  3  (E -S )2 1  1  0  2  0  + A/Vi  (E -S )2 2  = velocity  i n basement  Cj,  = no.  C2 = n o . =  crust  2  in  = (longitude,  0  C  = velocity  S  6  +  2  km/sec  latitude)  km/sec of  station  o f km/degree  longitude  of  latitude  km/degree  s i n - ^ / V ^  (longitude  thickness  < H and A  (3.1-5)  Q  H,  and  assuming  form  + (2H-E )cose /V  4  =  (3.1-6)  37 This  is just  the standard  assumed t h a t earth  f o r the d i s t a n c e s  approximation i s Equation  arrivals;  in this  study  is  a  flat  enough. a set of 4 non-linear  o f E.  To s o l v e  Reduction.  this  equations  A linear  s e t we u s e t h e t e c h n i q u e  approximation to CT, repre-  s e n t e d b y C T * , i s t a k e n b y e x p a n d i n g CT i n a power some s u i t a b l e  it  A  t h e 4 unknowns  o f Gauss-Newton  accurate  encountered  3.1-5 r e p r e s e n t s  1  in  form f o r r e f r a c t e d  point E  Q  series  about  .  Thus CT*(E) is  = CT(E ) o  a good a p p r o x i m a t i o n o n l y The  g^rCTlg  9 ^2  1  ^3  1  3  "  P T  ^  if  tE^Z  li-  P T  -  (3.1-7)  o  (E-E )  is  Q  i s a 4 x 5 matrix with  o  VE^2  aTJj^l  + | ^ C T | g (E-E )•  JE 4 x  Li  II  II  <»  "  small. elements  W S X  LL  II  "  1 4  evaluated  at the p o i n t  -rir C T . be c o n t i n u o u s ^k J Substituting  Q  It  i s required that  the f u n c t i o n s  functions, C T * f o r CT i n 3.1-5 g i v e s  I E C T I E IECTIE O  E .  (  O  g  " o' E  "  I ^ I E O R  V- ^ 1  O  where R  Q  = T - CT(E ) Q  (3.1-9)  38 To s i m p l i f y  the  notation  let  X = |wCT|'  (3.1-10)  ' o  Equation  3.1-8 _  which E  Q  (X'X)(E-E ) for  convergence E  Where t h e considered  this  following  the  The p r o c e s s  (X'X)X«R _ k  k is  the  study  is  is  using E  for  obtained. (3.1-12)  1  iterations.  4 iterations  A maximum o f  repeated  accuracy  number o f  3 or  is  2  For  events  were n o r m a l l y  10 i t e r a t i o n s  assumption R-N(0,a I)  was  valid  required  used i n  t h e n E^  any  has  case.  the  properties:  (1)  E^  (2)  An u n b i a s e d e s t i m a t e  - N[E,o (X'X)  ],  z  a (3) ^ •  (3.1-11)  Q  a sufficient  *  subscript in  E.  to  =  k  convergence. If  = X'R  q  c a n be s o l v e d  until  for  becomes  2  P[EJ-t k a/2 1  where E of  o  is  the  /a X. . ij 2  1  1  < EJ*  epicenter  is  2  = lR' . (I-X(X'X)- )R _ k  true  k  < gj+t k a/2 /  0  1  /a X..] ij  = 1 - a  2  J  th where is  j  Student's  3.2  Model  superscript "t"  Distribution  CT.  and h e n c e have  United  j  (Graybill,  For  consideration  regional  travel States"  times  is  distances  s t a n d a r d models  been suggested  correct  the  element  of E  and  1961).  Events  A serious event,  indicates  for  (Herrin  et  the  . . . "but  is  not  form o f  standard  the  travel  reference time  u p p e r h u n d r e d km o f  al,  t h r o u g h the  the  1968)  upper  intended  which  mantle to  the  "should beneath  represent  relations, earth,  give the  the  central actual  39 velocity the  structure  earth."  beneath t h i s  (Herrin,  For  this  A is  patible  al,  model, T  where  et  Pn  7  ,  4  or  i n d e e d any o t h e r p a r t  1  times  +  A  / 8  0  for  Pn a r r i v a l s  (3.2-1) relation  a s i m p l e g e o l o g i c a l model c o n s i s t i n g o f  15 and 25 km t h i c k w i t h P wave v e l o c i t i e s resting  are  9  m e a s u r e d i n km ( A < 1000 k m ) . T h i s  with  of  1968).  travel =  area  6.0  on a basement w i t h P wave v e l o c i t y  is 2  com-  layers,  and 6.75 k m / s e c ,  8.049 km/sec.  (Figure  3.2-2(b)) . For western swarm  British  (USCGS e p i c e n t e r s )  Columbia, using  the  travel  times  10 e v e n t s  from  f o r Pn and Sn  the  arrivals  are T T  p  n  g  n  = (2.58±1.56)  + A/(7.63±0.03)  (3.2-2)  = (9.61±1.97)  A/(4.46±0.03)  (3.2-3)  where  135 < A < 750 km ( F i g u r e s  great  deal  of  scatter  is  due t o t h e  If  we c o n s i d e r t h e  the  delay  about  in  the  USCGS  scatter the  that  linear  suggests that  but  a large  assigned to  the  events  marked by t r i a n g l e s  times  so t h a t  and 1 . 1 - 2 ) .  sec),  events  4 and 21 i n  The f a c t show a s i m p l e  two  arrival  25 km a p a r t ,  as b i a s  =4.0  o r i g i n times  between  The e p i c e n t e r s  (RMS  3.2-1  is  consistently  Figure  1.1-2  a part  of  There part  horizon is  of  by t h e  a this  USCGS.  in Figure  about  3.2-1  8 seconds.  as r e p o r t e d by USCGS  the  delay  must be  are  assigned  estimates. the  5 arrival  relation  to  the events  times  of  an i n d i v i d u a l  distance with can be t h o u g h t  taken  t o be t h e  event  a s m a l l degree of  in  s i m p l e wave r e f r a c t e d . a l o n g a c o n t i n u o u s h o r i z o n .  refracting  is  terms  of  of  The  Mohorovicic discontinuity -  4 + +  F I G U R E 3-2-1: T R A V E L T I M E S FOR P n AND S n IN WESTERN B R I T I S H COLUMBIA U S I N G USCGS E P I C E N T E R S . TRIANGLES INDICATE EVENTS 4 AND 21  +  As +A  t  i °-°  10.0  1  1  1  20.0  30.0  40.0  1  SO.O  1 60.0  EPICENTRAL DISTANCE (KM] IX10  i 1  —  70 0  )'  so.o  — I — 90.0  -1 100.0  this  is  the  first  evidence  that  this  discontinuity  d e f i n e d by e x p l o s i o n s e i s m o l b g y e x i s t s Vancouver  km/sec)  et  al  is  the  not  area  (1965).  velocity  in  this  an u n u s u a l v a l u e  for  value.  Also  favourably  to  because  or t h i n n i n g  t h e USCGS  the  in  of  of  profile  recent  7.67  km/sec  and O r e g o n by  interpreting  profile  layers  epicenters  regions  the v a l u e  Washington  s h o u l d be t a k e n  case,  interfaces  is  Dehlinger  the  apparent  unreversed  can g r e a t l y  were e s t i m a t e d  and  affect  its  assuming normal  and s o can be e x p e c t e d t o be b i a s e d . Once i t  u n d e r s t o o d as hence  was  realized  simple  a reference  this  model the  (1)  The v e l o c i t y  event  (3)  The n a t u r e  source  of  arrivals  u n d e r the  refraction  from o c e a n i c the  time  of events  oceanic  c o u l d be  a g e o l o g i c a l model  p o i n t s were t a k e n  profiles  The t r a n s i t i o n  the  c o u l d be c o n s t r u c t e d .  following  (2)  that  refracted  deduced from independent  In  into  5 receiving  and  constructing  account: stations  as  surveys.  crust  crust  to  in  continental  the  vicinity  crust. of  the  area. T h i s was  variable taken  of  s u g g e s t e d by t h e  of western  Care  dipping  crust  the v i c i n i t y  Pn wave v e l o c i t y  t e c t o n i s m and compares found f o r  classically  Island.  The a p p a r e n t (7.63  in  as  accomplished using  depth to basement.  from Tseng  Continental  (1968) , and W h i t e  b a s e m e n t u n d e r V a n c o u v e r I s l a n d was interior  of B r i t i s h  t o be 20 km t h i c k .  a four-layer  Columbia at A transition  crustal  and Savage set  35 km. crust  at  profiles  were  (1965).  Depth  50 km and i n  the  Oceanic was  model w i t h  crust  introduced  was  to  taken  between  42 the  oceanic  section  is  Snell's  Law  crust given  in Figure  located  account  the  geometry  of western  the  if  epicenters  the  for  British in  the  taken  lateral  arrival  only  vicinity  in  this  so t h a t  for  The p r e s e n c e area  suggests  epicenters  7.67  an a t t e m p t  Columbia.  information  limitation.  as  variations  m o d e l d i f f i c u l t , -and l a c k  geophysical  ocean r i s e cated,  but  section  model r e p r e s e n t s  a smooth f u n c t i o n  serious  directly  source  in  area.  terms  of  epicenters  could  times  freely  so  dictated.  were c o n s i d e r e d t o be e v e r y w h e r e homogeneous and  As s u c h ,  other  crust,  transition  made t o  ambitious  the  t h e m o d e l were c h o s e n s o t h a t  and t h e basement v e l o c i t y  attempt  be  of  on o c e a n i c  move o n t o t h e  tropic  calculated  in  obeying  k  model.  The l a y e r s  A composite  Model events  f r o m any p o i n t  C T . were a l s o  The p a r a m e t e r s were  Island crust.  3„2-2(a).  c o u l d be g e n e r a t e d  The f u n c t i o n s this  and t h e V a n c o u v e r  of  the of  the  in  this  figure.  t o accommodate  refraction oceanic  the  l o c a t e d on t h i s  that  epicenter  a major  that  km/sec w i t h no  The c o n s t r a i n t of  iso-  CT(E)  makes  profiles  section  is  a more or  a  transform fault  geometry  is  more  model c a n be  the  and  compli-  expected  t o be b i a s e d . This USCGS  is  estimates,  exactly but  the  on a d i f f e r e n t  effect  of  the  regional bias  tation  of  the  arrival  When t h e variables, to  assume  same c r i t i c i s m made e a r l i e r scale.  any v a l u e ,  is  the  hoped t h a t  has b e e n r e d u c e d f r o m the  the  interpre-  times.  l o c a t i o n p r o c e d u r e was  latitude,  It  of  longitude, f o r which  first  initiated  d e p t h and o r i g i n travel  the  t i m e were  t i m e s w o u l d be  four free  generated  FOCAL  REGION  PHC  A  A  5.0 6.0  5.0  ALB  5.9^  VIC  A  FSJ  A  5.0  6.0 6.6  PNT  A  6.1  4.7  v  5.9  6.6  7.1  7.67 50 km  i—  7.67  ESTIMATED P VELOCITY (KM/SEC)  50 km  6.0  6.75 (b)  8.049 FIGURE  3.2-2:  (a)  COMPOSITE  (b)  STANDARD  S E C T I O N FOR CRUST  OF T H EEARTH  CRUSTAL MODEL FOR REGIONAL  IN WESTERN  SEISMIC EVENTS  BRITISH  COLUMBIA  AFTER HERRIN  E T A L 1968  44 to  the  5 stations.  made i t  impossible to separate  i n depth of the  focus  division  iteration  of  the  time  not  use o f  in  procedure  origin  time.  In  layers  a smooth f u n c t i o n o f  the u n d e s i r a b l e m a t h e m a t i c a l  with depth,  it  was  The v a l u e  of  10 km (as  opposed to  c h o s e n t o be c o n s i s t e n t w i t h t h e seismic activity the  San A n d r e a s  Lomnitz the  in  the  Fault  and M c E v i l l y ,  and b e c a u s e  swarm m i g h t be a v o l c a n i c This  represents  The number o f f r o m one t o plane  at  two by  a depth of  increase meters,  degrees  the  distributed  constraining  p r e c i s i o n of  (latitude,  freedom i n  10 km.  longitude  the  step  was  the along  (Bolt,  suspicion  in  the  that  interpretation.  t h e m o d e l has b e e n epicenters  estimates and o r i g i n  among 3 v a r i a b l e s  USCGS) all  20 km  o f the  The i m m e d i a t e the  duration.  event.  an i m p o r t a n t  of  associated  (earthquakes  seldom deeper than  1968))  of  depth  procedure  the  nature  system  the  qualities  10 km f o r  shallow  the  Either  33 km u s e d by t h e  ocean r i d g e  are  that  iteration  of  changes  addition  meant  and b e c a u s e  at  arrivals  dependence  depth.  had t o be removed f r o m the  removed and s e t  first  Mathematically  and t h e i r  t o blow u p .  distinct  only  corresponding to  independent  model i n t o  f u n c t i o n CT was origin  were n o t  the  effects  from changes  two v a r i a b l e s  caused the  or  Unfortunately,  instead  result  of  the  time)  of  to  increased  a horizontal of  this  remaining as  4, while  the  RMS  is  to  parais  decreasing  the  accuracy. Real but  in  light  ocean r i d g e  differences of  the  system  in  depths  of  f o c u s u n d o u b t e d l y do  exist,  shallow  nature  of  the  the  it  seismicity  w o u l d seem r e a s o n a b l e  to  along  suppose t h a t  these  45 differences poor  are s m a l l .  station  from  this  s h a l l o w e r than  station  be  distribution  the  second.  it  location was  Estimates  were  There  the  however.  origin  consequence  times  recording  and  origin  highly To  advanced  stations  correlated  t i m e was  initial  starting  a normal  gave  figures and  and  bias  an  not  this  10  sec.  The  point  and  less  around  one  and T a b l e  on  T h i s was  dependent  on  which  3.2-1). epi-  the model taken  and  t o be  a  placed a l l Thus l o n g i t u d e  variables,  into  of  sec.  a s s o c i a t e d w i t h the  introduced a bias  independent  could  distribution)  o f the s o u r c e .  strictly  time  commonly  d i s t r i b u t i o n which  side  was  the assumptions  3.2-3  difficulties  one  center of  origin  e v e n t s was  (Figure  station on  t i m e , though  remove t h i s  times  about  the  with  three i t e r a t i o n s .  They were p l a c e d i r r e g u l a r l y  o f the p o o r  the  i n about  successful  were s e r i o u s  Shocks  procedure  l o n g i t u d e and  of the  justified.  position  t h e maximum  small.  the l o c a t i o n  ( b a s e d on  arrival  the  southwest).  f o r the b e t t e r  p r o c e d u r e was  based  centers  times  independent  the v a r i a n c e o f the The  ( t o the  arrival  v a l u e s were  one  i n the  be moved away f r o m  restrained  standard deviation  than  will  Estimates of latitude,  o b t a i n e d from  final  in errors  s o u r c e s h o u l d be  10 km  Once d e p t h was workable.  result  depth, coupled with  o f c o r r e s p o n d i n g magnitude so t h a t  amount o f e r r o r  the  in focal  distribution, will  of epicenters  focus  Errors  were  the e s t i m a t e s .  method o f e s t i m a t i n g  origin  required. It  c a n be  n o t e d , however, t h a t  swarm c o n s i d e r e d as independent  o f the  a whole, origin  form  time  the e p i c e n t e r s  a definite  assumed  of  the  p a t t e r n which  f o r t h e swarm  (each  is event  TABLE 3.2-1 ESTIMATES OF LATITUDE, LONGITUDE AND ORIGIN TIME BY LEAST SQUARES PROCEDURE EVENT NUMBER  LATITUDE (DEG. N)  S.D.  LONGITUDE (DEG. W) S.D. .  2 4 7 13 17 19 20 21 89  50. 13 49. 97 49. 88 49. 94 50. 17 49. 86 49. 95 50. 12 50. 00  0.06 0.11 0.10 0.02 0.2 9 0. 18 0.12 0.17 0.07  130. 19 130. 85 130. 85 130. 55 130. 68 130. 45 130. 87 130. 70 130. 66  0.26 0.48 0.43 0.08 1.30 0.73 0.52 0.77 0.31  1 6 10 11 12 14 18 22 24 32 33  50.57 49. 92 49. 88 48. 67 49.80 50. 17 50. 38 50.44 48.31 49. 92 50. 43  0.15 0.15 0.39 1. 03 0.67 0. 38 0. 31 0. 15 1.95 0.56 0.07  126.84 130.75 131.32 134.53 132.25 130.01 130.37 128.92 136.41 131.45 129.11  0.23 0.63 1. 69 3.48 2.91 1.61 1.44 - 0.73 6.44 2.43 0.23  S.D.  = STANDARD DEVIATION  ORIGIN TIME (SEC) S.D.  ESTIMATE S.D. T (SEC)  -32. 70 2. 17 4.20 -38.16 -38.72 , 3.79 0.-69 -36.39 -35.90 11.02 6.30 -36.68 -38.61 4.55 -36.02 6.5 6 -39.63 2.70  0.42 0. 68 0. 60 0.12 1.93 1.08 0.73 1. 14 0.46  -11.66 -38.22 -41.42 -77.33 -49.11 -31.26 -31.38 -21.82 -95.06 -41.82 -27.19  2.76 0.90 2. 18 2.39 3.17 2. 63 2.25 1.71 3.35 3.09 1.10  1.41 5.48 14.99 34.79 26. 39 13.03 11.63 5.85 66.00 21.59 0.67  ON  47  FIGURE  3  .  2  -  3  :  E P I C E N T E R S FOR E V E N T S O F T H E SWARM C A L C U L A T E D IN TERMS OF A R E G I O N A L MODEL OF THE EARTH'S C R U S T . SOLID TRIANGLES INDICATE BETTER DEFINED LOCATIONS. D E P T H I S C O N S T R A I N E D T O 1 0 KM 1 9  48 considered to (Figure events  take  3.2-4).  but  west  trend  Islands  in  the  an e a r t h q u a k e  is  Zone.  this  not  assumption i s  time  regional distances  B o t h P and S f o l l o w  Ratio  is  two c o n d i t i o n s  the  constant  are  the  same p a t h  both s a t i s f i e d  For  the  8 good P and S e v e n t s ,  5 stations.  paths  For  origin  in  idea  of  a north-  Charlotte times  without  is changing  for  an e a r t h q u a k e  occur-  are  not  ray  path.  from s o u r c e for  local  to  receiver.  events  if  the  too c o m p l i c a t e d . o r i g i n t i m e s were  r e m a i n i n g 11 o n l y PHC was  calculated used.  A). o r i g i n t i m e s were  of  the  constrained  to  times,  and F i g u r e  is  the  If  variables.  Queen  southwest  along the  travel  S-P  the  following assumptions:  the  the  the  is  b o t h P and S a r r i v a l s  geometry o f  centers  apparent  of e a r l i e r to the  if  T h i s method i m p l i e s  (2)  (Appendix  is  c a n be c a l c u l a t e d  Poisson's  all  t o bunch  i n c o m p a t i b l e w i t h the  The e f f e c t  (1)  using  station)  c a n be e x p e c t e d t o be  associated with  of e p i c e n t e r s  first  appreciably.  An o r i g i n  These  reach the  The p a t t e r n w h i c h  trend  t o move t h e p a t t e r n  recorded.  to  s p a c e more t h a n t h e y  swarm.  Fracture  ring within  of  assumption i s  - this  the p a t t e r n  same t i m e  The e f f e c t  together  reality,  the  c a l c u l a t e d by t h i s  method t h e  swarm c o u l d be e s t i m a t e d  again.  10 km and o r i g i n t i m e  the value  so t h a t  The p a t t e r n 3.2-5);  longitude in this  and l a t i t u d e case  the n o r t h w e s t  and by c o n s i d e r i n g o n l y  the  evident.  trend  The n o r t h e a s t  to  is  trend  less is  8 good e v e n t s is  epi-  D e p t h was calculated  were t h e distinct  partially a northeast  only (Table  from free 3.2-2  obscured, trend  is  a s s o c i a t e d w i t h the E x p l o r e r T r e n c h .  49  FIGURE  3.2-4:  E P I C E N T E R S F O R 19 E V E N T S I N T H E S W A R M . A S A F U N C T I O N OF O R I G I N T I M E . THE 3 CLUSTERS ' FROM L E F T TO R I G H T A R E FOR V A L U E S OF O R I G I N TIME OF -35, -30 AND -25 SEC  TABLE 3.2-2 ESTIMATES OF LATITUDE AND LONGITUDE BY LEAST SQUARES ORIGIN TIME FROM S-P INTERVAL EVENT NUMBER 2 4  LATITUDE (DEG. N)  S. D.  LONGITUDE (DEG. W) S. D.  ORIGIN TIME (SEC) S. D.  ESTIMATE S.D. T (SEC)  13 17 19 20 21 89  50. 21 50.16 50. Ok 50. 05 50.28 50.05 50. 13 50.29 50. Ik  0. 05 0. 09 0. 07 0. Ok 0. 15 0. 10 0. 09 0. 11 0. 07  129.81 129.91 130.00 130.04 130.13 129.54 130.00 129.76 129.96  0. 04 0. 07 0. 06 0. 03 0. 11 0. 09 0. 07 0. 09 0. 05  -29.60 -30.20 -32.20 -3 2.10 -32.30 -29.10 -31.2 0 -28.20 -30.90  4. 63 3. 5 8 3. 48 2. 05 5. 81 3. 40 3. 03 1. 99 1. 28  0. 62 1.24 1.01 0.5 7 2.03 1.50 1.20 1.50 0.90  1 6 10 11 12 14 18 22 24 32 33  49.94 50. 11 50. 13 49. 91 50.27 50.20 50.40 50. 31 49. 99 50.18 50. 29  0.42 0.10 0. 19 0. 31 0.29 0. 19 0.17 0. 18 0. 40 0.25 0.12  129.72 129.82 130.07 129.63 129.86 129.84 130.22 130.01 129.70 130.12 129.98  0. 34 0.08 0. 14 0.26 0.23 0. 15 0.13 0.14 0. 32 0.19 0.09  -31.20 -30.40 -30.70 -30.20 -28.50 -29.90 -30.20 -29.90 -30.20 -30.40 -29.60  0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  6.06 1.35 2.53 4. 42 3. 93 2.64 2.25 2.42 5.67 3.38 1.57  7  S.D. = STANDARD DEVIATION  O  51  FIGURE 3.2-5:  EPICENTERS FOR 19 EVENTS IN THE SWARM CALCULATED IN TERMS OF A REGIONAL MODEL FOR THE CRUST OF THE EARTH. SOLID TRIANGLES ARE BETTER DEFINED•LOCATIONS. DEPTH IS CONSTRAINED TO 10 KM  52 The v a l i d i t y bution the  of epicenters  fracture  zone,  s m a l l e r magnitude northeast of  the  of  trend,  origin  However,  the  procedure  two t r e n d s  may be a r g u e d .  is  primarily  along  times  of  the  trench,  the  larger  distribution  more s e n s i t i v e (northwest  trend)  the  coastline  (northeast  trend).  of  to  10 km w i l l  events  possible  that  o c c u r r e d at  the  the  no e v i d e n c e  function  of  for T T  3.3  p  n  g  n  the  times  = (5.51±0.38) = (10.16±1.25)  Epicenters  in  the  How s i g n i f i c a n t The f a c t quakes  that  are  set  quakes which  are  is  deeper  interpretation defined  the  events.  location parallel  the  constraint in  to  to of  focal  depths  it  entirely  trench  could  have  but with d i f f e r i n g  focal  depths  25 k m ) .  There  focal  of  depths that  of the  is  epicenters  a consistent  Pn and Sn i n w e s t e r n  Pacific  epicenters  available,  are ( F i g u r e  3.2-6): (3.2-4) (3.2-5)  Ocean are  (except  limits  a  British  + A/(4.45±0.03)  Northeast  as  path.  + A/(7.69±0.03)  than  The  a l o n g the  no i n f o r m a t i o n on d e p t h  shallow)  for  Thus,  of epicenters  these  along  trend.  sort  for  of  in epicenters  Moreover  lying  any  trend,  changes p e r p e n d i c u l a r  interpretation  traced  final  a result  such that  than  a spread of  from the  time  is  distri-  defined events.  any d i f f e r e n c e s  same e p i c e n t e r  The t r a v e l Columbia  in  the  locations  magnitude w e l l  a northwest  6 events  ( t h i s would r e q u i r e is  result  s h o w i n g up as  is  to changes  coastline  in  The n o r t h w e s t  b a s e d on t h e  the  depths  evident  and h e n c e more p o o r l y  station  is  the  the  is  open t o  that  all  findings.  10 km, and t h e r e f o r e  take  question. earthEarthless  time  + F I G U R E 3.2-6: TRAVEL TIMES FOR P n AND S n IN WESTERN B R I T I S H C O L U M B I A ASSUMING A L L EVENTS HAVE A F O C A L D E P T H O F 10 K M  +  +  +  '  4 f  0.0  10.0  20.0  30.0 0  40.0  50.0  EPICENTRfll DISTANCE  60.0  (KM) "(X10  70.0  J  )  BO.O  100.0  54 than normal  t o reach the s t a t i o n s , w i l l  be l o c a t e d  coast, w h i l e earthquakes  s h a l l o w e r t h a n 10 km w i l l  farther  The s i m p l e model chosen  crust, will  from that  have  the coast. o f two l a y e r s  an e f f e c t .  crust  will  mean t h a t  There  seems t o be no r e l e v a n t  a more a m b i t i o u s m o d e l . a serious stations and  effect. used  though  station  origin  minimum  array,  view  t o o much  have  defined  This  raises  located  on t h e o c e a n ' s  on t h e  reduced to a  seem w i s e  epicenter  the l e a s t  the r e l a t i o n  procedure.  Such  squares p r i n c i p l e o f the e p i c e n t e r  as d e f i n e d  - i t may  floor.  a comparison  E p i c e n t e r s at  by a s e c o n d t h e same d a t a  only  demonstrates  A more r e l i a b l e  to a ridge  be  the a r r i v a l s  study u s i n g  works.  not to  of estimating  c a n n o t be c o n f i r m e d e x c e p t p e r h a p s  location  fault,  i t would  t h e whole p r o b l e m  and  form  procedure.  e v e n t s , n o t t o o f a r from  c o n d i t i o n s under which  d e t e r m i n e d by an i n d e p e n d e n t  is  have  time  effect  seems t o have b e e n  location  that  also  i n d e p e n d e n t l y , the  an u n d e s i r a b l e  o f these d i f f i c u l t i e s  epicenters  usually  same  justify  and s m a l l number o f  c o n f i d e n c e i n an i n d i v i d u a l  were r e c o r d e d .  sea  still  problem  a p r o d u c t o f the s p e c i a l  seismic  will  t o g e t h e r by t h e i t e r a t i o n  For well  this  to  (see Appendix B ) . In  put  may  are b i a s e d .  to determine o r i g i n  times are c a l c u l a t e d  epicenters.  station  distribution  o f earthquakes  distribution  calculated the  The p o o r  and v e l o c i t i e s  available  distribution  h e r e made i t i m p o s s i b l e  longitude  Even  The s t a t i o n  be mapped  model by t h e r e a l  the estimates f o r epicenters information  to the  f o r the oceanic  with constant thickness  Any d e p a r t u r e f r o m t h i s  closer  check,  or trench or trans-  independently of seismology.  I f more  precision  than  this  is  attempted,  must be c o n s i d e r e d . If use  of  the  the  recording  for  for  a typical  Pacific,  United  say  d i s t r i b u t e d on a l l  very  accurate  on t h e  Blanco  graph s t a t i o n s  in western  be n o t e d  the  (1)  If  of  focus  (2)  first  If  ( H e r r i n et  estimation  Fracture  arrivals  only  longitude  are  and o r i g i n  procedure,  In  addition  to  these  compares w i t h t h e g e o l o g y o f new s t a n d a r d P t a b l e s this  may n o t  data  is  the  crust  variations  for  events  teleseismic Since  are  and  of e p i c e n t e r s . in  the  the  seismic  source  area However,  the  east seismo-  following points  no i n f o r m a t i o n  are  of  may  about  depth  of  two p o i n t s the  the  United  since  only  source  originating  same  be b i a s e d t o o  epicenter the  source  States  typical  will  oceanic  be  area  (assuming  teleseismic  However,  far  used.  a small portion of  area. in  the  distribution  geology of  central  in  the  events the  ray  significant  trenches  do  exist,  s t u d y was  to  deter-  distances.  one o f  effect  station  For  the  calculated  epicenter w i l l  used).  be so c r u c i a l  in  mine t h e  the  then  Z o n e , and r e c o r d e d by  used,  time  then the  a c c o r d i n g t o how w e l l  at  of  area  epicenter:  w e s t by an amount d e p e n d i n g on the  even  model  c a n be e x p e c t e d .  iteration  biased  the  1968)  occurring  North America,  estimated  al,  sides  low m a g n i t u d e e a r t h q u a k e  about  of  S t a t e s were a s e i s m i c  new s t a n d a r d P t a b l e s  would allow  limitations  <  central  stations  the  the  objectives  of  the model used i n  locating  estimating  p r o c e d u r e was made f l e x i b l e  wide range  of models.  Any l a y e r e d  this  epicenters,  enough t o  the  accommodate a  g e o l o g i c a l m o d e l c o u l d be  56 translated  into  located with If  respect  times,  and t o  inflate  relation  Figure  the  to  is  t o move e p i c e n t e r s  T h i s example p o i n t s  in using epicenters  calculated  errors  squared, with respect  to  values  Model  3.4  The  without  basic is  In  particular  at  a particular  fitting  (Figure  that  it  closer  us  to  station to  instance, events  basic  some m o d e l .  is  not  change  3 . 3 - 1 and used  in  uncertainty The  sum o f  The w o r t h  the  attached  the model h a s .  it  is  strictly  to is  residual  the  a large  whether  are  and p o s i t i v e  c h o s e n by t h e  is  least  arrivals  any s i g n i f i c a n t  model a r e  a certain  the  valid  number o f  bias  farther  each  vari-  present at  stations.  squares p r i n c i p l e ,  station  considered  is  consistently negative at  zero.  on t h e m o d e l u s e d .  generated at  standard c r u s t a l that  at  of  occurring.  the r e s i d u a l s  evident  true,  judgments  for  the model are if  the d i s t r i b u t i o n  s y m m e t r i c and c e n t e r e d  indicates  The r e s i d u a l s  stations  zero value  southwest  are  those which minimize the  t o make c e r t a i n  the average  3.3-1),  the model.  Figure  local  independent checks.  a s s u m p t i o n made a b o u t  with respect For  to the  same s t a t i o n s  out the  the  Perturbations  enough and a l l o w s  by  only  the  a s s u m p t i o n , though perhaps not  ations  events  generally  3.3-1,  d e p e n d on how much v a l i d i t y  reading errors This  (Table  T h i s assumes t h a t  values  the  and  t i m e s were u s e d i n s t e a d o f  epicenters  are  Law  model.  c o n f i d e n c e e l l i p s e s , but  between  both cases .  obeying S n e l l ' s  this  result  the  3.3-2).  involved  times  standard t r a v e l  travel  the  travel  in  the Since  only  the  the  TABLE ESTIMATE  STANDARD CRUSTAL  BRITISH  L A T I T U D E AND L O N G I T U D E BY L E A S T O R I G I N T I M E FROM S-P INTERVAL  LATITUDE ( D E G . N)  2 4 7 13 17 .19 20 21  5 0 . 16 50.12 50.00 50.01 50.22 50.01 50.09 50.26 CRUSTAL  S . D. 0. 0. 0. 0. 0. 0. 0. 0.  09 16 16 12 26 11 17 20  LONGITUDE ( D E G . W) 130.07 130.16 130.34 130.29 130.51 129.79 130.25 130.01  S . D. 0. 0. 0. 0. 0. 0. 0. 0.  07 12 12 09 19 09 13 15  ORIGIN (SEC) -29.60 -30.20 - 3 2 . 20, -32.10 -32.30 -29.10 -31.20 -28.20  TIME S . D.  ESTIMATE S.D. T ( S E C )  4. 3. 3. 2. 5. 3. 3. 1.  1.26 2.17 2.15 1.52 3.56 1.53 2.26 2.71  63 58 48 05 81 40 03 99  MODEL  EVENT NUMBER  LATITUDE ( D E G . N)  S.D.  2 4 7 13 17 19 20 21  50.21 50.16 50.04 50.05 50.28 50.05 50.13 50.29  0.05 0.09 0.07 0.04 0.15 0.10 0.09 0.11  S.D.  SQUARES  MODEL  EVENT NUMBER  COLUMBIA  OF  3.3-1  = STANDARD  LONGITUDE ( D E G . W) 129.81 129.91 130.00 130.04 130.13 129.54 130.00 129.76  DEVIATION  S.D. 0.04 0.07 0.06 0.03 0.11 0.09 0.07 0.09  ORIGIN (SEC) -29.60 -30.20 -32.20 -32.10 -32.30 -29.10 -31.20 -28.20  TIME S.D. 4.63 3.58 3.48 2.05 5.81 3.40 3.03 1.99  ESTIMATE S.D. T ( S E C ) 0.62 1.24 1.01 0.57 2.03 1.50 1.20 1.50  58  PHC FIGURE  3.3-1:  ALB VIC F S J  PNT  E P I C E N T E R S P L U S 90% C O N F I D E N C E E L L I P S E S F O R 8 WELL DEFINED EVENTS USING THE STANDARD C R U S T A L M O D E L A D O P T E D BY H E R R I N E T A L 1968. AVERAGE R E S I D U A L S IN S E C AT THE.5 S T A T I O N S A R E SHOWN I N H I S T O G R A M UNDERNEATH  59  -2  — PHC  FIGURE  3-3-2:  ALB V I C F 5 J  PNT  E P I C E N T E R S P L U S 90% C O N F I D E N C E E L L I P S E S F O R 8 WELL D E F I N E D EVENTS USING A REGIONAL CRUSTAL MODEL. AVERAGE RESIDUALS AT THE 5 S T A T I O N S A R E SHOWN I N H I S T O G R A M UNDERNEATH  60 relative cant.  value  Since  of the  residuals  between  positive  residuals  indicate  would suggest case  8.05 km/sec)  thinning  towards For  the  with  respect  50 km f o r  the  too high or  the  farther  for  Arrivals to  Because  Again,  ray  only  of  the r e l a t i v e  crust  is  difference (1968) near  the  being thicker If terms  of this  the  in that  them.  the  and ALB  the  c r u s t mantle is  crust  the  residual  between  a major  are  structure  crust  the  on t h e  the b i a s  case  to  the  epicenters  Care  of in  the  case,  variations layer).  significant, In  the  this  case  island,  line  the  that the  with Tseng's  discontinuity  upper c r u s t  on t h e  exists north  south.  i n the  be s u c h as  not  PHC  independent,  and PHC i n d i c a t e s  is  at  in  boundary  bottom  stations.  This  island;  the  is  northern part  10 km.  given  independent of  3 stations  (particularly  study,  and l a t e  local  the  is  are  c a u s e d by  of  this  this  as  true  this  5 stations  a t VIC  these  in  interpreted  model w i l l  away f r o m P H C ,  calculate  is  to  crust  i n each  in  than the  this  s t r e s s e d here  of  crust  different  being roughly  center  the  b o t h ALB and VIC  suggestion that  the  (in  is  difference  thicker  the model  this  station  the  between  the  This pattern  paths  absolute value  one s e c d e l a y the  can be  thickness the  early  stations. the  residuals  the  at  t h e m o d e l , w h i c h has  all  signifi-  stations.  8 events are  of  is  arrivals,  alternatively  f i n a l model adopted f o r  azimuth from s o u r c e to  these  to  is  stations  late  t h e basement v e l o c i t y  residual  3.3-2.  depth.  in  the  average  Figure  at  that  the  epicenters  calculated  t o move t h e e s t i m a t e d southwest.  are  functions  s h o u l d be t a k e n  in  It of  in  points  s h o u l d be t h e model u s e d  interpreting  travel  61 times  generated  from such e p i c e n t e r s  The r e a s o n i n g  is  (A.  1947) .  A.  Milne,  circular,  the p r e y  in is  terms the  of  ever  a new elusive  model. "woozle"  62  4.  THE EARTHQUAKE SWARM AT PHC  The s u s p i c i o n e x i s t s s o u r c e mechanism i s Since  this  a region of  occurred  ultimately  any e a r t h q u a k e  in  first  the p a s t .  ocean  h a n d , but  seamounts  the  suggests  All  location  that  previous  terms  of  right-lateral  The two mechanisms the  are  wrench  not  complicated nature  of  o f the  volcanic  seismicity  Islands  source  the  source  area,  area  has  area  Fracture  has Zone  motion a l o n g the northwest  i n c o m p a t i b l e , however, the  activity  activity in  the  activity.  f l o o r no v o l c a n i c  b e e n a s s o c i a t e d w i t h t h e Queen C h a r l o t t e in  swarm t h a t  connected with v o l c a n i c  swarm o c c u r r e d on t h e  c o u l d be o b s e r v e d in  for  trend.  and i n v i e w  of  both probably play  a  role. The s e i s m o g r a p h s t a t i o n than  200 km f r o m t h e  distinct  arrivals  (to  movement g r e a t e r  than  For  the  each  arrival  (Appendix  source  at  P o r t H a r d y was  and r e c o r d e d a l a r g e  be c l a s s i f i e d  as  an a r r i v a l  the  of  the  thickness  f o l l o w i n g parameters  trace were  located number  less  of  entailed  trace  - roughly  1 mm).  estimated:  C)  (1)  Arrival  time  Pn.  (2)  Sn-Pn  (3)  Pn a m p l i t u d e ,  three  components.  (4)  Sn  three  components.  time.  ampltidue,  The e s t i m a t i o n  of  a m p l i t u d e s was  trace  movement was  of  such h i g h  often  indistinct.  Some  idea of  somewhat frequency the  subjective, and t h e  relative  since  arrivals  energy  the were  involved  in  63 each event  4.1  was  h o p e d t o be o b t a i n e d .  Time R e l a t i o n s All  refer  times  of  the  refer  Swgrm  to  arrival  t o b o d y wave m a g n i t u d e s  times  (except  The swarm c o n s i s t e d o f a t  sisting August trace  of  141 a r r i v a l s ,  28. was  number o f  For  in v i r t u a l l y events  o f up t o  suggests  for  3-hour p e r i o d s three  bursts  12 h o u r s .  some s o r t  of  to  A u g u s t 28  the  A histogram for  the  Figure  4.1-1.  s e p a r a t e d by  the  - aftershock  T.  in  activity of  con-  decay  of  inactive  the  sequence.  bursts  Two  occur at  1 5 : 2 6 and 1 6 : 2 0  28 c o i n c i d i n g w i t h t h e peak  activity  on A u g u s t 2 8 .  in  greater  than 4.0 p r e c e e d these  A magnitude  in  an 18-hour p e r i o d .  were c o n f i n e d t o  48 e v e n t  with a large  occurred at  amount o f  the  Almost a l l first  two  the  swarm a r e  larger  the  than  larger activity.  13:35 August 2 7 , u n c o r r e l a t e d  secondary a c t i v i t y .  not  of  40 h o u r s o f  The h i s t o g r a m s h o w i n g  t h e number o f h o u r s w i t h a g i v e n number o f e v e n t s of  Nine  a 4-hour p e r i o d , 2 shocks w i t h magnitudes g r e a t e r  magnitude events  (Figure  a 132  and 4 . 7  4.0 occur a f t e r  events  over  a 2 7 - h o u r p e r i o d on  given  The n a t u r e  foreshock  shocks w i t h magnitudes events  of  noted).  1 1 : 4 5 U.  is  magnitudes  The main a c t i v i t y ,  continuous motion.  shocks w i t h magnitudes 4.9 August  restricted  All  217 e v e n t s  T.  5 hours b e g i n n i n g at  The d i a g r a m r e v e a l s periods  was  PHC.  where  least  h o u r p e r i o d , b e g i n n i n g a t . 6 . 2 2 . 5 0 U.  at  shows  randomly d i s t r i b u t e d i n  that  the  time  4.1-2) . The use o f  azimuths,  plus  the  only  5 stations  fact  that  the  over  first  a l i m i t e d range arrivals  f o r most  of events  (13)^^(17) 4 8 -  40  —  UJ > UJ 32—  b_ O  or 24—  UJ CD  16—  6  12 AUG.  FIGURE  18 27  4.1-1:  0  6  12  AUG.  18 28  0  6  12 AUG.  18 29  0  6  12 AUG.  18 30  H I S T O G R A M SHOWING NUMBER O F E V E N T S FOR T H R E E HOUR L A R G E R M A G N I T U D E E V E N T S A R E I N D I C A T E D BY NUMBERS  0  6  12 AUG.  PERIODS.  18 31  0  6  12 SEPT.  18 I  UJ.  20-  2 '6o  ri  or LU •L  Li_  I2H  o  a en or  ZD  POISSON  DISTRIBUTION  4H  0  n  J  8  20  12  NUMBER FIGURE  4.1-2:  H I S T O G R A M SHOWING NUMBER  24  OF  28  32  36  44  48  EVENTS  O F T H R E E HOUR P E R I O D S  FOR WHICH N EVENTS  OCCURRED  66 were commonly i n d e f i n i t e , polarity  of  the  first  made f a u l t  arrivals  arrivals  PHC were o f t e n  of  the  No e v e n t  same s e n s e  than  defined  an h o u r ,  to give  but  not  a pattern  The d i s t r i b u t i o n of  the  for  polarity  some o f  4.2  of  the  Magnitude  first  events  of  down t o  2.7.  records  the  recorded  once w i t h i n were w e l l  and  a period  enough  in  time p l u s  suggests  the  variability  a tectonic  mechanism  swarm.  f r o m PHC a l l o w e d  Richter  calculation  represented  on t h e  USCGS was of  3.7.  magnitudes  t h e minimum amount  of  s e i s m o g r a m s f r o m PHC.  m a g n i t u d e s , M^, i^ere d e f i n e d f r o m  the  formula M  where A ,  L  = log  1 0  A - log  e x p r e s s e d i n mm i s  1 0  A  (4.2-1)  o  t h e mean o f t h e maximum t r a c e  f r o m z e r o , w h i c h w o u l d have b e e n r e c o r d e d by  standard h o r i z o n t a l and l o g A is "10 O  torsion  a distance  n r i  was  a d d i t i o n , PHC  VIC  3.1-1).  of events  T h i s magnitude  Standard  tude  In  general  which  5 stations ;  m a g n i t u d e r e p o r t e d by t h e  t r a c e movement d e t e c t a b l e  usual  all  the  Determinations  The s m a l l e s t The u s e  c o u l d be f o u n d  enough a r r i v a l s  arrivals  in  The f o l l o w i n g  arrivals,  (Figure  b a s e d on  at  opposite p o l a r i t i e s .  b o t h c o m p r e s s i o n a l and d i l a t i o n a l less  solutions  unreliable.  comments may be made, h o w e v e r . generated  plane  used c o r r e s p o n d i n g to  (Figure  4.2-1).  maximum t r a c e  seismometers  factor.  in  this  correspond in  orthogonally  this  an e p i c e n t r a l  No v a r i a t i o n  amplitudes  For  a pair  case  distance  figure all  is  cases  ampliof  orientated,  l o g , A ^ = -3.5 °10 O n  of  190-200 km  considered. to the  Sn  The arrival.  67  m • ( 4.1 ± 0.1) + ( I.I ± 0.3) M  L  » 3.5 +  Log  m' » 1.8 + 0.8 tr*  - 0.11  O  MAGNITUDE  | 0  M  A  L  UNITS  2  FROM  USCGS  Log  | 0  A  68 The m a g n i f i c a t i o n on t h e period  is  40  h o r i z o n t a l s e i s m o m e t e r s o f PHC a t  relation  between  m = (4.1±0.1) An e s t i m a t e ,  o f m g i v e n by t h i s  . compared t o the  The d i f f e r e n c e magnitude PHC i s  + (1 . l ± 0 . 3 ) L o g  i m p l i e d between  m = 0 . 1 7 + 1.1  = 1.7  1 Q  was  the  M  an  linear.  A  (4.2-2)  the  standard  ±0.3 u n i t s and m was  (Figure  4.2-1).  then (4.2-3)  g i v e n by R i c h t e r  (1958) (4.2-4)  L  or  of  events  L  either  small events  abnormally  relationship  + 0.8  suggests that for  Using  M  standard r e l a t i o n m'  at  The r e l a t i o n  f o r m u l a was  terms  10 l a r g e r  b a s e d on n o r m a l d i s t r i b u t i o n s , o f  The r e l a t i o n  the  also defined in  the magnitude o f  r e p o r t e d by t h e USCGS and l o g ^ A .  deviation  sec  K.  A b o d y wave m a g n i t u d e , m, was empirical  0.8  t h e USCGS  that  the  is  underestimating  amplitude of  arrivals  large.  Richter  (Figure  magnitudes the m a g n i t u d e - f r e q u e n c y  4.2-2)  for  the range o f magnitudes 2.0  to  4 . 0 becomes log The v a l u e is  sensitive  to  1 0  for  N = (4.07±0.50) the  slope of  For earthquakes  eruptions,  values at  up t o  of  quakes w i t h R i c h t e r so t h a t  the  directly  the  in  this  10 km b u t  still  these  magnitudes  results  values less  are than  must be e x t r a p o l a t e d .  For  with  for  range  in  1959).  (Minakami,  derived  -1.10,  volcanic  associated  the  case  earthquakes  associated with  - 1 . 1 8 has b e e n r e p o r t e d  s h o u l d be n o t e d t h a t  here,  line,  (4.2-5)  -4 have b e e n f o u n d ( S u z u k i ,  depths to  vulcanism a value It  the  t h e mechanism g e n e r a t i n g  question.  earthquakes  - (1.10±0.20)  I960).  micro-earth-  considered  Log  | 0  N  « (4.1 ± 0.5) - (I.I  ±  0.2)  M  L  2 ,cr  C>  « 0.04  NOT  USED  IN  RICHTER FIGURE  4.2-2:  FINAL  SOLUTION  MAGNITUDE  MAGNITUDE-FREQUENCY I N T H E SWARM  (M )  RELATIONSHIP  L  F O R 217 E V E N T S  70 For to  2.4)  (1968) that  a micro-earthquake  r e c o r d e d at reports  the  MBC i n  a value  swarm was  for  swarm  (magnitude  the  Northwest  the  slope of  generated  as  range  Territories, -0.68.  a result  He  from  -1.1  Whitham  concludes  o f movement a l o n g  a  fault. For -1.10,  is  activity  the  suggestive on a f a u l t .  suggestion that quakes have the  swarm d i s c u s s e d h e r e of volcanic This  off-setting  in  slope  than  fracture  ridge those  zones.  value  activity line  crests for  for  rather  with T. J .  the m a g n i t u d e - f r e q u e n c y  a s s o c i a t e d w i t h the  a steeper  is  the  the  than G.  the  earthquakes  tectonic  Francis  relationships of  slope,  for  earth-  Mid-Atlantic associated  (1969)  Ridge with  71  5..  In tectonics from the  the p a s t of  the  Gulf  sistently  of  zones,  continental California  force.  trend,  Pacific  associate zones:  force  the  the  two  in  time  seismograph s t a t i o n s tectonic  along  frequency that  swarm. the  played  is  a part.  extension  of  of  and t h e  In  to  the  the  accept the  ridges  on a of  continent. one r e a l i z a t i o n of  Zone,  larger  of  events  tectonic  a zone  material. of  first  of  epicenters  at  distriat  that  a  fault, of  T r e n c h , and t h e  recorded the  The  arrivals  on a  larger magnitude  PHC s u g g e s t  swarm.  t h a t b o t h mechanisms "New  tectonic  Columbia suggest  the  Explorer  217 e v e n t s  2  determined  by movement of  trending  o f movement  to the is  con-  E x p l o r e r T r e n c h , a zone  British  The l o c a t i o n  fact,  across  terms  o f new c r u s t a l  release  is  faulting  19 e p i c e n t e r s  mechanism g e n e r a t e d  easy  in  Island Fracture  in western  trend of  relation  a volcanic It  that  the  of  and t h e p o l a r i t y  mechanism, s t r a i n  generated  t r e n d and w r e n c h  the  America  a northwest  independently  faulting,  North  r e p r e s e n t e d by  with respect  Queen C h a r l o t t e strike  of  that  Islands  swarm p r e s e n t e d h e r e  swarm w i t h  b u t i o n of events  is  and c a n be t h o u g h t  e x t e n s i o n and g e n e r a t i o n  events  the A l e u t i a n  The d i s t r i b u t i o n  right-lateral of  margin o f western to  Basin northwest  pattern.  has become e v i d e n t  a manifestation This  The e a r t h q u a k e this  it  e x t e n s i o n on a n o r t h e a s t  northwest the  CONCLUSIONS  few y e a r s  e x p r e s s e d as  right - lateral  ;  c o u l d have  Global Tectonics"  and t r a n s f o r m f a u l t i n g  predicts along  fracture  72 zones w i l l  be c o n t i n u o u s .  Trench occurred f i r s t , on b o t h s i d e s  of  the  oceanic  regions  a poor s t a t i o n the  earth.  western  in  of bias  conditions. in  For  reality.  For good q u a l i t y  the  depth  source  is  between times  the  present  the  in  any  of  zones  "The  located  f r o m two  an u n r e a l i s t i c the  Pacific of  times  sources:  of  for  its  shallow  own  seismic  Ocean and r e c o r d e d  d e p t h and o r i g i n  west than  are  represents  they  times  are  in  for  desirable, the  in  Bias  i n d e p e n d e n t methods  of events  in  model  light  low m a g n i t u d e  farther  range  presented  individual  represents  5 stations  and r e c o r d e d by  with  typical  realistically  epicenters  The a r r i v a l s ,  epicentral  a case  arise  considered in  results,  and o r i g i n  epicenters  at  along f a u l t  as  geology  of  area.  For bias  and u s e o f  epicenters  a model which  Explorer  standard l o c a t i o n procedure.  moves  estimating  on t h e  epicenters  Problems  the n o r t h e a s t  generally  as  represents  North America, poor estimates  the  activity  i n earthquake  unavoidable.  may o c c u r when u s i n g t h e  well  This  c a s e must be  occurring  case  action.  distribution  Each  particular activity  is  this  f o l l o w e d by a d j u s t m e n t s  trench.  New G l o b a l T e c t o n i c s " Some d e g r e e  In  paper, but  differences  u s e d and h e n c e  5 stations  this  estimate,  real  Pn and S n ,  175 t o  in  is  the in  a degree relation  the  arrival  tectonically  g e n e r a t e d by e v e n t s  i n western  British  750 km showed a s i m p l e  of  significant.  in  the  Columbia i n linear  swarm  the  relation  distance T  p n  T~  = (5.51±0.38) = (10.16ll.25)  + A/(7.69±0.03) + A/(4 . 4 5 1 0 . 0 3 )  (5-1) (5-2)  , where  7  A is  3  epicentral  suggested that  the  distance  arrivals  travelling  wave r e f r a c t e d  underlying  the  the  crust  crusts, the in  in  was  crust  this  travel lated into  of  this  times. in  the  thicker southern  Mohorovic'ic  British  the  area.  the  epicenters  the model,  parameters  of  under Vancouver  differences on t h e  the  for  times  type for  generated observed  events  were  was  calcu-  introduced depth to  the  I s l a n d c o u l d n o t be c a l c u l a t e d ,  but  were e v i d e n t ;  n o r t h e r n end o f  the  the  crust  appears  I s l a n d than  on t h e  t o be  10 km  central  or  part. recommendations  for  further  studies  follow  from  conclusions.  mechanisms g e n e r a t e d  events  in  the  two  swarm.  distinct  T h i s may be  by  first  motion s t u d i e s  of  the  8 l a r g e r magnitude  of  these  (numbers  7,  13,  20 and 21)  Explorer  faulting  Fracture  2,  4,  are  trending plane.  were a s s o c i a t e d w i t h t h e  faulting  associated  Queen C h a r l o t t e  on a n o r t h w e s t  The l o c a t i o n  trending  system set  up f o r  Six with  normal  The r e m a i n i n g  Zone and s h o u l d be c h a r a c t e r i z e d by  checked  events.  T r e n c h and s h o u l d be c h a r a c t e r i z e d by  on a n o r t h e a s t  17 and 19)  slip  surveys  Thus an a b s o l u t e  The s u p p o s i t i o n has b e e n made t h a t  the  A model  to the  some u n c e r t a i n t y  the model.  simple  and c o n t i n e n t a l  travel  of  fact  discontinuity  refraction  Reference  This  a  Columbia.  m o d e l showed g o o d agreement  of  Several these  o f western  Because  terms  upper mantle relative  a l o n g the  r e g i o n , combining oceanic  in  3.2-7).  c o u l d be u n d e r s t o o d as  constructed using available  upper c r u s t terms  i n km ( F i g u r e  (numbers  Islands  right-lateral  strike-  plane. this  study w i l l  provide  74 accurate  determination  of epicenters  activity  on a r e g i o n a l  scale-.  A r e c o r d i n g network  PHC,  and a s i m i l a r  station  on t h e Queen C h a r l o t t e  FSJ  would p r o v i d e  adequate  Columbia,  A l a s k a n Panhandle  taining This  the  the  area  bacause  Queen C h a r l o t t e  is  seismicity  interesting  has  the  w i t h the  been thus  oceanic  Aleutian In  ridge  Trench  general,  environment  of  the  any  as  a segment Basin.  the  all  shallow  and a d j a c e n t Fault  Islands  British areas  and r e l a t e d  far  poorly established,  seismic  including  oceanic  two r e a s o n s ;  s y s t e m moves  focus  of western  for  first,  con-  systems.  because and  the  second,  onshore b e f o r e  joining  System. study  related  a Mesozoic trench of  of  Islands  of  continental  s h o u l d be u l t i m a t e l y region  coverage  for  ocean r i d g e  the  geological-geophysical  margin of western  to e i t h e r system or system i n  the the the  North  history recent  of  America the  development  adjacent  Pacific  of  75  BIBLIOGRAPHY  Bolt,  B . A . , L o m n i t z , C . , and M c E v i l l y , T . V . , S e i s m o l o g i c a l E v i d e n c e on t h e T e c t o n i c s o f C e n t r a l and N o r t h e r n C a l i f o r n i a on t h e M e n d o c i n o E s c a r p m e n t , B u l l . S e i s m . S o c . A m . , 58_, N o . 6 , 1725-1768 , 1968 .  Bostrom,  R . C . , P a t h o f the America, P a c i f i c  Dehlinger,  Francis,  East P a c i f i c Rise i n Western G e o l o g y , 1_, 1, 1968 .  North  P., Chibus, E.F., and C o l l i v e r , M . M . , L o c a l T r a v e l Time C u r v e s and t h e i r G e o l o g i c I m p l i c a t i o n s f o r t h e P a c i f i c N o r t h w e s t S t a t e s , B u l l . S e i s m . S o c . Am. 5 5 , No. 3, 5 8 7 - 6 0 7 , 1 9 6 5 .  T . J . G . , D e t a i l e d S e i s m i c i t y of the Mid-Oceanic Ridges ( A b s t r a c t ) , T r a n s . Am. G e o p h y s . U n i o n , 5 0 , N o . 4 , 235, 1967.  Freedman,  H.W., Bull.  S e i s m o l o g i c a l Measurement and Measurement E r r o r , S e i s m . S o c . A m . , 5_8, N o . 4 , 1261-1272 , 1968 .  Graybill,  F r a n k l i n A . , An I n t r o d u c t i o n t o L i n e a r Statistical M o d e l s , Volume I. M c G r a w - H i l l Book Company, I n c . , New Y o r k , 1 9 6 1 .  Hamilton,  R.M., O r i g i n of the G u l f of S o c . Am. , 7_2, 1307 , 1 9 6 1 .  California,  Bull.  Geol.  Herrin,  E . , T u c k e r , W., T a g g a r t , J . H . , G o r d o n , D.W., and L o b d e l l , J . L . , E s t i m a t i o n o f S u r f a c e Focus P T r a v e l T i m e s , B u l l . S e i s m . S o c . A m . , 5_8, N o . 4 , 1273-1292 , 1 9 6 8 .  Isacks,  B.,  McManus, Menard, Milne,  O l i v e r , J . , and S y k e s , L . R . , S e i s m o l o g y and the G l o b a l T e c t o n i c s , J . G e o p h y s . R e s . , 73_, N o . 1 8 , 5855-5900, 1968.  R.A., east  New  P h y s i o g r a p h y o f t h e Cobb and G o r d a R i s e s , N o r t h P a c i f i c O c e a n , B u l l . G e o l . S o c . A m . , 7_8_, 527 , 1 9 6 7 .  H.W., M a r i n e G e o l o g y o f New Y o r k , 1 9 6 4 .  the  Pacific,  McGraw-Hill,  A . A . , The W o r l d o f P o o h ; the Complete Winnie-the-Pooh t h e House a t Pooh C o r n e r , D u t t o n , New Y o r k , 1 9 5 7 .  Minakami,  and  T . , Fundamental Research f o r P r e d i c t i n g V o l c a n i c Eruptions. P a r t 1. E a r t h q u a k e s and C r u s t a l D e f o r m a t i o n s O r i g i n a t i n g from V o l c a n i c A c t i v i t y , B u l l . Earthquake Research I n s t . Tokyo U n i v . , 3 8 , 497-544, 1960.  76 Morgan, Raff,  W.J., R i s e s , T r e n c h e s , G r e a t F a u l t s and C r u s t a l J . G e o p h y s . R e s . , 73 , 1959 , 1 9 6 8 .  Blocks,  A . D . , and M a s o n , H . G . , M a g n e t i c S u r v e y o f f t h e West C o a s t of North A m e r i c a , 40°N L a t i t u d e to 50°N L a t i t u d e , B u l l . G e o l . S o c . Am., 72, 1259, 1961.  Richter, Seismic  Smith,  C . F . , E l e m e n t a r y S e i s m o l o g y , W.H. San F r a n c i s c o , 1 9 5 8 .  Freeman and Company,  D a t a L a b o r a t o r y R e p o r t N o . 133 Long Range S e i s m i c M e a s u r e m e n t s - Long S h o t , UED E a r t h S c i e n c e s D i v i s i o n , Teledyne I n c . , A i r Force T e c h n i c a l A p p l i c a t i o n s Center. W . E . T . , W h i t h a m , K . , and P i c h e , W . T . , A M i c r o e a r t h q u a k e Swarm i n 1965 n e a r M o u l d B a y , N . W . T . , C a n a d a , B u l l . S e i s m . S o c . Am. 5_8, No. 6 , 1991-2012 , 1 9 6 8 .  S u t h e r l a n d - B r o w n , A . , T e c t o n i c H i s t o r y o f the I n s u l a r B e l t o f B r i t i s h C o l u m b i a , i n T e c t o n i c H i s t o r y and M i n e r a l D e p o s i t s of the Western C o r d i l l e r a , Can. I n s t . M i n i n g and M e t . S p e c . V o l . 8_, 8 3 , 1968 . Suzuki,  Z . , A S t a t i s t i c a l S t u d y on t h e O c c u r r e n c e o f S m a l l E a r t h q u a k e s ( f o u r t h p a p e r ) , S c i e n c e R e p t . Tohoku U n i v . S e r . 5, G e o p h y s . 1 1 , 1 0 - 5 4 , 1 9 5 9 .  Tobin,  D . G . , and S y k e s , L . R . , S e i s m i c i t y and T e c t o n i c s o f t h e N o r t h e a s t P a c i f i c O c e a n , J . G e o p h y s . R e s . , 73^, N o . 1 2 , 3821-3846, 1968.  Tseng,  K.,  Tucker,  Vine,  W. , H e r r i n , E . , and F r e e d m a n , H.W., Some S t a t i s t i c a l A s p e c t s o f the E s t i m a t i o n o f S e i s m i c T r a v e l T i m e s , B u l l . S e i s m . S o c . Am. 5_8, N o . 4 , 1 2 4 3 - 1 2 6 0 , 1 9 6 8 .  F.J.,  White,  A New M o d e l f o r t h e C r u s t i n t h e V i c i n i t y o f V a n c o u v e r I s l a n d , M.Sc. T h e s i s , Department o f G e o p h y s i c s , U n i v e r s i t y of B r i t i s h C o l u m b i a , 1967.  and W i l s o n ,  Ocean Ridge  J.T.,  Magnetic Anomalies Over  o f f Vancouver  Island,  Science,  a Young  150, 485, 1965.  W . R . H . , and S a v a g e , J . C . , A S e i s m i c R e f r a c t i o n and Study o f the E a r t h ' s C r u s t i n B r i t i s h C o l u m b i a , S e i s m . S o c . A m . , 5_5_, 4 6 3 , 1965 .  Gravity Bull.  W h i t e , W . H . R . , Summary o f T e c t o n i c H i s t o r y , i n T e c t o n i c H i s t o r y and M i n e r a l D e p o s i t s o f t h e W e s t e r n C o r d i l l e r a , C a n . I n s t . M i n i n g and M e t . S p e c . V o l . 8, 9 6 , 1 9 6 8 . Wilson,  J . T . , T r a n s f o r m F a u l t s , O c e a n i c R i d g e s and M a g n e t i c Anomalies Southwest o f Vancouver I s l a n d , S c i e n c e , 150, 482, 1965.  77  APPENDIX A  O r i g i n Time From P and S An e s t i m a t i o n made  if  the  arrival  The method e m p l o y s (1)  Both  of  times the  Ratio  refraction  the  that  not  the  (2)  follow  the  paths  of  the  earth,  is  assumed t h a t  of  the  travel  at  with k layers  is  T  T  can be  c a n be  obtained.  from s o u r c e  p  n  S n  ray  to  path.  may be made t o paths  these  encountered  velocity  discontinuities,  However,  to  the  extent  applicable,  encounter  the  in  this  do n o t  that it  same  conditions:  the  is  study,  follow concept  only  layers  in  transit,  identical.  of Poisson's  Ratio  may be e x p e c t e d  when a l a y e r e d  such v a r i a t i o n s  are  model i s  confined to  in  the  crust  considered. a small  It  portion  path. the  having  a surface  given  be  especially  Consider  For  a s e i s m i c event  same p a t h  a l o n g the  typical  Pn and Sn p a t h s  Variations  Hj .  of  P and S waves  a h o r i z o n t a l l y - l a y e r e d model i s  that  time  assumptions:  constant  for  same. p a t h .  required  Sn  the  objections  P and S a r r i v a l s  including  of  for  following  is  The f o l l o w i n g  exactly  origin  station.  Poisson's  (1)  the  P and S a r r i v a l s  recording (2)  Arrivals  simple  case  seismic  focus  of  a horizontally-layered  velocities  earthquake  a and & and a  the. a r r i v a l  time  crust  thickness o f Pn  and  by - 0 =' 2 Z H.  /l-(  a ; j  / a ) 2 /a. n  - 0 = 2 I H. / l - ( g / e ) j  n  2  /6  j  + A/a  n  + A/B  n  (A-l)  (A-2)  78 where  A is  epicentral  Poisson's velocities  distance  Ratio  (a)  and 0 i s  origin  time.  may be e x p r e s s e d i n  terms  of  seismic  as  o = i(l-e )/(l-2 2) 2  where  e =  B/a.  The a s s u m p t i o n t h a t seismic  (A-3)  £  velocities  a is  constant  corresponds to  being constant.  Thus  = e  n  e,  the  for  ratio  all  k,  of  and  f r o m A - l and A-2 T  To d e t e r m i n e  Sn  "  T  Pn  origin T  n  n  directly  in  A-4 was  Pn * ^ S n - W  and T g - T  at  p n  terms  A least  +  the  used i n  the  form  < " >  0  A  squares  5 stations of  (A-4)  n  time,  Adhere k = e / ( l - e ) . Tp  = (Tp -0)(l-e)/e  gave  intercept  fit  of  a value of  the  a straight  line  for  time  origin  straight  line  5  to  (Figure  A-l). Estimates The v a l u e s  for  o f 0 and k f o r  the  USCGS e s t i m a t e s . Ratio  of 0.26.  be r e a d TQ  at  The v a l u e O r i g i n times  accurately PHC o n l y ,  o r i g i n times  at  all  8 events are  4 to  are  given  6 sec e a r l i e r  for k suggests a value f o r events  5 stations  assuming t h i s  value  f o r which T  were e s t i m a t e d for  in Table A - l .  Poisson's  for S  n  than  the  Poisson's c o u l d not  from T Ratio.  p  n  and  79  TABLE A - l ORIGIN TIME FROM S-P EVENT NUMBER  ORIGIN TIME (SEC)  INTERVAL VARIANCE P(SEC)  K  2  -29.55  +  4.62  1.32  +  0 .10  +  3.46  4  -30.24  +  3.57  1.36  +  0 .09  +  2.69  7  -32.22  +  3.48  1.45  +  0 .09  +  2.57  13  -32.14  +  2.05  1.37  +  0 .09  +  1.50  17  -31.35  +  5 .81  1.41  +  0 .10  +  4.35  19  -29.12  +  3.39  1.28  +  0 .09  +  2 .60  20  -31.21  +  3.03  1.36  +  0 .09  +  2 .26  21  -28.22  +  1.98  1.29  +  0 .09  +  1.54  89  -30.88  +  1.28  1.29  +  0 .09  +  0.96  81  APPENDIX B  Test  of  the  Location  To t e s t earthquake as  the  Procedure reliability  of  the  o f December 2 7 , 1963 n e a r  r e p o r t e d by D e h l i n g e r ,  Chibus  Station  Portland,  and C o l l i v e r  (km)  T  27.8  BLL  348  50.6  TON  454  63.9  BKR  493  67.4  HLY  767  101.5  as g i v e n by D e h l i n g e r time  (7.87  1968)  was  km/sec).  were t o  crustal  used except D e p t h was  An e s t i m a t e  of  origin  the  (1965).  (1965)  is:  123.38°N the  east  of  g e o l o g i c a l b o u n d a r i e s were c r o s s e d by t h e  al,  Idaho  45.63°N  longitude  The s t a n d a r d  O r e g o n and  02.36.18.5  latitude  stations  the  (sec)  180  origin  et  p n  LON  The e p i c e n t e r  All  l o c a t i o n program  model f o r for  time  source  ray  a lower  area:  major  paths.  regional  constrained to three  the  distances  basement  (Herrin  velocity  10 km.  epicentral  parameters  (02.36.16.6+2.3)  latitude  (45.53±0.18)°N  longitude  ( 1 2 3 . 5 H O . 2 4 ) °W  sec  gave  82 If  origin  remaining  t i m e was  constrained  two p a r a m e t e r s  t o 0 2 . 3 6 . 1 8 . 5 an e s t i m a t e  gave  latitude  (45.61±0 . 0 3 ) ° N  longitude  (123 . 3 1 ± 0 . 0 3 ) ° W  of  the  THE P ARRIVAL H/M/S AUGUST 2 7 , 1967 06/22/50 06/23/20 06/24/00 06/34/30.0 07/04/19.0 07/07/30 08/34/12.0 08/35/08.8 09/29/20 11/52/40 12/01/05.4 12/32/50 12/57/02.0 13/01/30.0 13/11/20 13/12/42.0 13/33/36.0 13/35/19.8 14/00/50 14/08/04.6 15/17/50 15/19/06.8 16/59/30 17/40/41.0 17/44/30 17/52/23.0 18/29/32.4 18/34/40 20/44/50  APPENDIX C SWARM AT PHC  S-P (SEC)  P AMPLITUDE V N E  0.0 21.6 0.0 22.8 22.2 0.0 22.4 23.0 0.0 0.0 22.4 0.0 22.6 23.0 0.0 22.2 22.2 22.0 0.0 21.4 0.0 22.0 0.0 22.4 0.0 22.2 21.4 0.0 0.0  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1 1 1 1 1 4 1 1 1 1 2 1 1 1 1 11 1 1 1 2 1 1 1 2 6 1 1  1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 5 1 1 1 2 1 1 1 1 3 1 1  (MM)  S AMPLITUDE V N E 1 3 1 2 2 2 3 26 2 1 3 1 6 2 1 3 5 24 2 2 1 6 2 20 2 30 33 2 2  2 3 1 2 2 2 4 8 2 1 4 2 7 2 1 3 6 80 2 2 1 7 2 22 2 34 60 3 2  2 3 2 2 2 2 4 6 3 1 4 2 6 2 1 4 4 55 2 2 2 7 2 15 1 20 44 3 2  MAGNITUDE RICHTER BODY 2.5 2.6 2.3 2.5 2.5 2.5 2.8 3.0 2.6 2.2 2.8 2.5 3.0 2.5 2.2 2.7 2.9 4.0 2.5 2.5 2.3 3.0 2.5 3.4 2.3 3.6 3.9 2.6 2.5  .  2.9 3.1 2.8 2.9 2.9 2.9 3.3 3.5 3.1 2.6 3.3 2.9 3.5 2.9 2.6 3.2 3.4 4.6 2.9 2.9 2.8 3.5 2.9 4.0 2.8 4.2 4.5 3.1 2.9  APPENDIX C (CONT.) P  ARRIVAL H/M/S  AUGUST 2 8 04/03/30 05/56/11.6 08/52/30 09/05/20 09/21/23.0 10/57/10 10/58/40 11/31/30 11/32/32.8 11/35/30 11/36/30 11/39/50 11/41/39.8 11/45/58.0 11/54/10 -  11/58/00 11/59/27.4 12/05/28.2 12/06/5.0.0 12/10/50 12/11/50 12/13/10 12/16/00 12/19/00 12/20/00 12/23/32.8 12/25/50 12/27/19.0 12/30/30 12/31/30 12/34/40 12/36/10 12/39/41.8 12/44/18.6  S-P (SEC)  P AMPLITUDE V N E (MM)  0.0 22.0 0.0 0.0 21.0 0.0 0.0 0.0 22.6 0.0 0.0 0.0 22.2 22.4 0.0 0.0 21.8 22.8 22.4 0.0 0.0 0.0 0.0 0.0 0.0 21.8 0.0 21.0 0.0 0.0 0.0 0.0 22.4 22.0  1 1 1 1 1 1 1 1 1 1 1 1 2 2 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 2 1  1 1 1 1 1 1 1 1 1 1 1 1 2 2 1 1 2 1 2 1 1 1 1 1 1 2 1 2 1 1 1 1 3 1  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1  S AMPLITUDE V N E 2 13 1 1 6 1 1 1 10 1 1 1 5 5 1 2 5 3 2 1 1 2 2 1 1 4 2 8 1 2 2 2 16 9  2 10 1 1 7 1 1 1 14 1 1 1 10 9 1 2 • 9 3 2 1 1 2 2 1 1 4 2 10 1 2 2 2 15 12  2 12 1 1 1 1 1 15 1 1 1 6 6 1 2 13 3 3 1 1 2 2 1 1 4 2 10 1 2 2 2 22 10  MAGNITUDE RICHTER BODY WAVE 2.5 '3.2 2.2 2.2 3.0 2.2 2.2 2.2 3.3 2.2 2.2 2.2 3.1 3.0 2.2 2.5 3.2 2.6 2.6 2.2 2.2 2.5 2.5 2.2 2.2 2.8 2.5 3.2 2.2 2.5 2.5 2.5 3.4 3.2  2.9 3.8 2.6 2.6 3.6 2.6 2.6 2.6 3.9 2.6 2.6 2.6 3.6 3.6 2.6 2.9 3.8 3.1 3.1 2.6 2.6 2.9 2.9 2.6 2.6 3.3 2.9 3.7 2.6 2.9 2.9 2.9 4.0 3.8  APPENDIX C (CONT.) P  ARRIVAL H/M/S  S-P (SEC)  P AMPLITUDE V N E  12/47/50 12/50/29.8 12/53/00 12/53/40 12/55/00 12/56/30 12/57/20 12/58/10 12/59/20 13/05/10 13/07/10 13/11/00 13/12/50 13/17/05.0 13/19/50 13/29/30 13/34/50 13/41/20 13/47/10 13/50/10.0 13/59/50 14/03/50 14/06/30 14/17/24.0 14/19/40 14/21/20 14/23/30 14/34/20 14/43/20 14/44/03.0 14/59/50 15/02/10 15/06/16.0 15/07/36.0  0.0 22.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 21.8 0.0 0.0 0.0 0.0 0.0 21.6 0.0 0.0 0.0 22.2 0.0 0.0 0.0 0.0 0.0 22.2 0.0 0.0 21.4 22.2  1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 3  I 1 1 1 1 1• 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4  (MM)  1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 2 1 1 1 , 1 1 1 1 1 1 1 1 1 1 3  S AMPLITUDE V N E 2 9 2 2 1 1 1 2 3 3 2 3 3 10 3 2 1 1 3 13 1 1 1 2 1 2 1 2 1 11 1 1 3 15  2 7 2 2 1 1 1 2 3 3 2 3 3 15 3 2 1 1 2 28 1 1 1 3 1 2 1 2 1 11 1 1 4 24  2 9 2 2 1 1 1 2 3 3 2 2 3 10 2 2 1 1 2 22 1 1 1 3 1 2 1 2 1 11 1 1 4 15  MAGNITUDE RICHTER BODY WAVE 2.5 3.1 2.5 2.5 2.2 2.2 2.2 2.5 2.6 2.6 2.5 2.6 2.6 3.3 2.6 2.5 2.2 2.2 2.5 3.6 2.2 2.2 2.2 2.6 2.2 2.5 2.2 2.5 2.2 3.2 2.2 2.2 2.8 3.4  2.9 3.6 2.9 2.9 2.6 2.6 2.6 2.9 3.1 3.1 2.9 3.1 3.1 3.8 3.1 2.9 2.6 2.6 2.9 4.2 2.6 2.6 2.6 3.1 2.6 2.9 2.6 2.9 2.6 3.8 2.6 2.6 3.3 4.0  '  APPENDIX ARRIVAL H/M/S  S-P (SEC)  15/14/10 15/26/17.0 15/37/10 15/41/30 15/45/22.0 15/47/51.0 15/50/30 15/52/50 15/58/10 16/00/04.7 16/02/00 16/04/30 16/08/50 16/20/31.4 16/28/30 16/31/50 16/32/20 16/34/33.0 16/44/50 16/45/38.0 16/50/30 17/07/20 17/09/10 17/12/21.8 17/18/20 17/19/50 17/20/30 17/22/28.8 17/30/00 17/42/00 17/47/10 17/51/00 17/53/30 18/02/00 18/14/51.0 18/16/50  0.0 0.0 0.0 0.0 20.4 21.2 0.0 0.0 0.0 20.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 21.0 0.0 21.8 0.0 0.0 0.0 22.0 0.0 0.0 0.0 20.2 0.0 0.0 0.0 0.0 0.0 0.0 . 21.8 0.0  P  P AMPLITUDE V N E  1 15 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 22 1 1 1 1 1 1 1 1 1 1 1 18 1 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1  1 7 1 1 1 1 1 1 1 1 1 1 1 4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  C  (CONT.)  (MM)  S V  2 75 1 1 2 3 1 3 1 3 1 1 2 55 3 1 2 2 1 3 1 1 2 11 1 1 2 3 2 2 3 1 3 1 3 1  AMPLITUDE N E  2 75 1 2 2 3 2 2 2 2 1 1 2 55 3 2 2 2 1 2 1 1 2 7 1 1 2 2 2 2 2 1 3 1 2 1  2 75 1 2 2 3 2 3 3 2 2 1 2 55 3 2 2 2 1 2 1 1 2 12 1 1 2 2 3 2 3 1 3 1 3 1*  MAGNITUDE R I C H T E R BODY I  2.5 4.0 2.2 2.5 2.5 2.6 2.5 2.6 2.6 2.5 2.3 2.2 2.5 3.9 2.6 2.5 2.5 2.5 2.2 2.5 2.2 2.2 2.5 3.1 2.2 2.2 2.5 2.5 2.6 2.5 2.6 2.2 2.6 2.2 2.6 2.2  2.9 4.7 2.6 2.9 2.9 3.1 2.9 3.1 3.1 2.9 2.8 2.6 2.9 4.5 3.1 2.9 2.9 2.9 2.6 2.9 2.6 2.6 2.9 3.7 2.6 2.6 2.9 2.9 3.1 2.9 3.1 2.6 3.1 2.6 3.1 2.6  APPENDIX P  ARRIVAL H/M/S  18/18/50 18/27/05.0 18/37/50 18/46/40 18/51/50 19/12/10 19/15/10 19/36/00 19/48/50.4 19/50/50 20/25/34.4 20/28/50 20/30/50 20/33/56.0 20/44/30 20/46/00 20/48/13.8 20/56/50 21/07/40 21/14/40 21/54/40 22/11/16.2 22/15/24.8 22/18/41.0 22/41/30 23/09/00 23/17/09.4 23/38/30 23/47/50 23/53/10 GUST  29  00/08/40 00/23/20 00/23/40 00/27/10  S-P (SEC)  P V  0.0 22.0 0.0 0.0 0.0 0.0 0.0 0.0 21.8 0.0 20.8 0.0 0.0 21.6 0.0 0.0 22.0 0.0 0.0 0.0 0.0 21.0 21.4 20.6 0.0 0.0 21.0 0.0 0.0 0.0  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 l l l l l l  0.0 0.0 0.0 0.0  l l l l  AMPLITUDE ' N E  1  C  (CONT.)  (MM)  S AMPLITUDE N E V  MAGNITUDE R i C H T E R BODY  1 1 1 1 1 1 1 1 i l l l l l  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1  2 3 2 1 1 1 1 2 2 1 2 1 2 2 1 2 14 2 2 1 1 2 2 3 1 2 2 1 1 2  2 2 2 1 1 1 1 2 2 1 2 1 2 3 2 3 12 3 2 1 1 2 3 3 1 2 2 2 1 2  2 2 3 1 1 1 1 3 3 1 2 1 2 3 1 2 12 2 2 1 1 2 2 3 1 1 3 1 1 2  2.5 2.5 2.6 2.2 2.2 2.2 2.2 2.6 2.6 2.2 2.5 2.2 2.5 2.6 2.3 2.6 3.2 2.6 2.5 2.2 2.2 2.5 2.6 2.6 2.2 2.3 2.6 2.3 2.2 2.5  2.9 2.9 3.1 2.6 2.6 2.6 2.6 3.1 3.1 2.6 2.9 2.6 2.9 3.1 2.8 3.1 3.8 3.1 2.9 2.6 2.6 2.9 3.1 3.1 2.6 2.8 3.1 2.8 2.6 2.9  l i l l  1 1 1 1  1 1 1 1  1 2 2 1  1 1  2.2 2.3 2.3 2.2  2.6 2.8 2.8 2.6  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  3.  1  WAVE  APPENDIX C (CONT.) P  ARRIVAL H/M/S  S-P (SEC)  P AMPLITUDE V N E  00/55/04.6 01/15/40 01/33/20 02/02/00 03/21/12.6 04/06/40 05/05/12.0 05/10/30 05/37/50 05/59/50 06/18/04.6 06/22/30 07/04/30 07/21/50.0 09/07/30 10/22/49.6 10/25/39.2 10/26/15.4 17/54/30 18/59/30 19/04/52.0 19/14/50 21/03/00 22/56/14.8 23/53/10.4  22.2 0.0 0.0 0.0 20.0 0.0 21.8 0.0 0.0 0.0 20.8 0.0 0.0 22.2 0.0 21.6 21.0 21.8 0.0 0.0 22.2 0.0 0.0 21.0 23.0  1  AUGUST 30 13/42/30 20/22/41.0 23/34/50  0.0 21.0 0.0  AUGUST 31 00/43/20 04/00/40.0 06/56/20  0.0 20.6 0.0  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2  1 1 1 1 1 1 1 • 1  i.  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1  1 1 1  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2  (MM)  S AMPLITUDE V N E  MAGNITUDE RICHTER BODY WAVE  3 1 1 1 2 1 4 1 1 1 2 1 1 1 3 3 2 2 1 1 6 2 1 5 5  2 1 1 1 2 1 4 1 1 1 3 2 1 1 3 2 2 2 1 1 10 2 2 5 5  3 1 1 1 2 1 4 1 1. 1 2 2 1 2 3 2 2 1 1 1 13 2 1 4 6  2.6 2.2 2.2 2.2 2.5 2.2 2.8 .2.2 2.2 2.2 2.6 2.5 2.2 2.3 2.6 2.5 2.5 2.3 2.2 2.2 3.2 2.5 2.3 2.8 2.9  3.1 2.6 2.6 2.6 2.9 2.6 3.3 2.6 2.6 2.6 3.1 2.9 2.6 2.8 3.1 2.9 2.9 2.8 2.6 2.6 3.8 2.9 2.8 3.3 3.4  1 4 1  1 6 1  1 5 1  2.2 2.9 2.2  2.6 3.4 2.6  1 3 2  1 2 2  2.2 2.6 2.5  2.6 3.1 2.9  APPENDIX C (CONT.) P  ARRIVAL H/M/S  S-P (SEC)  P AMPLITUDE V N E  07/32/40 07/54/40 08/32/40 08/43/31.0 08/50/34.4 08/56/00 09/06/20 10/05/17.2 11/43/17.2 12/00/05.5 14/56/00 16/34/10 19/15/50 19/34/43.0 22/15/30  0.0 0.0 0.0 22.6 22.0 0.0 0.0 21.0 21.6 21.2 0.0 0.0 0.0 21.0 0.0  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  0.0 0.0 0.0 0.0  1 1 1 1  SEPTEMBER 1 03/04/50 12/14/50 12/33/30 13/06/40  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1  1  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  (MM)  S AMPLITUDE V N • E 1 1 1 2 1 1 2 2 5 3 1 1 1 3 1 2 1 2 1  1 1 1 3 1 1 2 2 5 4 1 1 1 3 1  1  2 2 1  1  MAGNITUDE RICHTER BODY WAVE  1 1 1 2 2 1 3 2 5 3 1 2 1 4 1  2.2 2.2 2.2 2.6 2.3 2.2 2.6 2.5 2.9 2.7 2.2 2.3 2.2 2.7 2.2  2.6 2.6 2.6 3.1 2.8 2.6 3.1 2.9 3.4 3.2 2.6 2.8 2.6 3.2 2.6  2  2.5 2.2 2.5 2.2  2.9 2.6 2.9 2.6  2 1  

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