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Marine deep seismic sounding off the Coast of British Columbia Knize, Stanislav 1976

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MARINE DEEP SEISMIC OFF  SOUNDING  THE COAST OF BRITISH  COLUMBIA  by Stanislav Eng. Czech  of T e c h n i c a l Technical  Knize  and N u c l e a r  University,  Physics  Prague,  1961  THESIS SUBMITTED IN'PARTIAL FULFILMENT OF THE  REQUIREMENTS FOB THE DEGREE OF DOCTOR OF PHILOSOPHY  ~1  :  in  t h e Department of  Geophysics  We a c c e p t  this  and Astronomy  thesis  required  The  University  t o the  standard  Of B r i t i s h  May, @  as c o n f o r m i n g  Columbia  1 9 7 6  Stanislav Knfze, 1 9 7 6  In  presenting  this  an a d v a n c e d d e g r e e the I  Library  further  for  agree  in  at  University  the  make  that  it  partial  freely  permission for  this  written  representatives. thesis  for  financial  is  of.  Geophysics  31,  of  Columbia,  British for  extensive by  the  gain  shall  not |  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, Canada  May  of  1976  and A s t r o n o m y  Columbia  the  requirements  reference copying of  Head o f  understood that  permission.  Department  Date  It  fulfilment  available  s c h o l a r l y p u r p o s e s may be g r a n t e d  by h i s of  shall  thesis  I agree and  be a l l o w e d  that  Study.  this  thesis  my D e p a r t m e n t  c o p y i n g or  for  or  publication  without  my  ABSTRACT  A marine s e i s m i c s y s t e m  f o r recording  i n c i d e n c e to wide-angle r e f l e c t e d with  near-vertical  waves and r e f r a c t e d  p e n e t r a t i o n t o t h e bottom o f t h e c r u s t  sounding  o r DSS) h a s been d e v e l o p e d .  operation, recorded  signals  in digital  origin*  times  from a s i n g l e shooting  from  waves  (deep s e i s m i c  I n a two s h i p -  s i x i n d i v i d u a l hydrophones a r e  f o r m on t h e r e c e i v i n g  and f a c i l i t a t e  subsequent  hydrophone a r e r e c o r d e d  s h i p . To p r o v i d e  processing,  signals  i n FM mode on t h e  ship.  During recorded  1973, DSS p r o f i l e s  a b o u t 20km i n l e n g t h  i n t h r e e r e g i o n s o f f t h e west c o a s t  Hudson .•70,-survey a r e a ,  were  o f Canada: t h e  west o f t h e Queen C h a r l o t t e I s l a n d s  nea-r :.5 :i N, 133°K; o f f Queen C h a r l o t t e Sound; and i n C a s c a d i a v  Basin  0  west o f c e n t r a l  were p r o c e s s e d  with  autopower spectrum deconvolution,  V a n c o u v e r I s l a n d . The r e c o r d e d  various d i g i t a l analysis,  velocity  techniques  such  oceanic  spectrum  analysis,  and s t a c k i n g .  amplitude with  were  i n t e r m s o f v e l o c i t y - v e r s u s - d e p t h models o f t h e  crust.  refraction  as  band-pass f i l t e r i n g ,  A f t e r compilation i n record s e c t i o n s , the data interpreted  data  Two k i n d s o f models were d e r i v e d . . F o r t h e  data,  m o d e l s a r e b a s e d on a t r a v e l t i m e and  i n t e r p r e t a t i o n made by c o m p a r i n g t h e o b s e r v e d  s y n t h e t i c seismograms. F o r t h e r e f l e c t i o n d a t a , t h e  data  m o d e l s a r e b a s e d on a T - X 2  crustal  models d e r i v e d  same b a s i c detailed  analysis  2  from  c r u s t a l l a y e r s , but t h e r e f l e c t i o n  a  '70 a r e a  geology.  obtained  The c r u s t a l  The model compares  well  or a layer  i n t h e same a r e a by Keen and B a r r e t t o f f Queen C h a r l o t t e  i n d i c a t e s s i x sedimentary l a y e r s  of d i f f e r e n t  layer  a t a depth  o f 2.4 km s u b - b o t t o m , and t h e o c e a n i c  :  within;, t h e s e d i m e n t s p o s s i b l y  underneath the c o n t i n e n t a l  thickness  shows f o u r  slope. layers  The model f o r n o r t h e r n within  t h e basement  km s u b - b o t t o m , and t h e o c e a n i c l a y e r sub-bottom. Proposed  interbedding  the sediments of  a t a d e p t h o f 2.7  a t a d e p t h o f 4.2 km  of volcanic  material  with  v e l o c i t y s e d i m e n t s a t t h e t o p o f t h e basement  c o r r e l a t e s with g e o l o g i c a l the  of sediments  1.9 km, a v e l o c i t y t r a n s i t i o n between t h e  s e d i m e n t s and t h e basement,  high  reversals  show t h e i n f l u e n c e o f  g l a c i a t i o n on t h e d e p o s i t i o n  Cascadia Basin  Sound  velocities,  a t a. d e p t h o f 4.5 km s u b - b o t t o m . V e l o c i t y  Pleistocene  with  with the  (1971). The model f o r t h e r e g i o n  basement  of the  shows t h i n s e d i m e n t s o v e r t h e  which c o n s i s t s o f e i t h e r two l a y e r s  velocity gradient.  results  of the structure  and r e l a t e t o r e g i o n a l  model o f t h e Hudson  models show  these l a y e r s .  The models show t h e c o m p l e x i t y oceanic crust  p h a s e s . The  t h e two a p p r o a c h e s i n d i c a t e t h e  v e l o c i t y changes within  basement  of seismic  formative  c r e s t o f t h e n e a r - b y J u a n de F u c a  processes observed a t Ridge.  iii  The  r e s u l t s have shown t h a t  efficient oceanic  technigue  crust  multichannel industry.  and  for detailed  i s an  the  investigation  inexpensive  common d e p t h p o i n t  m a r i n e DSS  alternative  techniques  s y s t e m i s an of to  the the  used i n the o i l  iv  Contents  1 INTRODUCTION  1  1.1 Why Deep Seismic Sounding at Sea ................ 1 1.2 Review of the Seismic Work at Sea ............... 4 1.3 P r o j e c t H i s t o r y and Areas o f Recording 2 DATA ACQUISITION  ,,11  ....................................17  2.1 F i e l d Techniques  ....17  2.2 Instrumentation and Procedure ...................19 2.3 DSS P r o f i l e s  and T h e i r L o c a t i o n s  2.4 Examples of Observed Data  27 31  3 DATA PROCESSING AND ANALYSIS ........................ 44 3.1 F i e l d Data and C o r r e c t i o n s ...................... 44 3.2 Autopower Spectra ............................... 47 3. 3. Band-pass F i l t e r i n g  50  3.3 Deconvolution ................................... 55 3.4 Stacking o f R e f r a c t i o n Data ..................... 71 3.5 V e l o c i t y A n a l y s i s o f R e f l e c t i o n Data 4 INTERPRETATION  76 83  4.1 Methods o f I n t e r p r e t a t i o n ....................... 83 4.2 V e l o c i t y - d e p t h Models ........................... 88 4.3 D i s c u s s i o n  of  the R e s u l t s  ............130  4.4 R e l a t i o n to R e g i o n a l Geology ..,.,,......,,......131 5 CONCLUSIONS  137  V  List  Figure  1.1 L o c a t i o n Map  Figure  2.1 S c h e m a t i c  Two  of Figures  f o r t h e Areas  of Recording  Diagram o f t h e DSS System  Ships  Figure  Using  ............. 18  2.2 S c h e m a t i c  Instrumentation Figure  Diagram o f t h e  on t h e S h o o t i n g  2.3 S c h e m a t i c  Ship  . . . . . . . . . . . . . . . 22  Diagram o f t h e S e i s m i c  Recording  System on t h e R e c e i v i n g S h i p Figure  ,...25  2.4 D e t a i l e d Maps o f t h e L o c a t i o n s o f t h e  Seismic Figure  Profiles  ..29  2.5 A T y p i c a l  Source  wavelet  . . . . . . . . . . . . . . . . . . . 33  F i g u r e .2.6 Example o f a S e i s m i c R e f l e c t i o n T r a c e F i g u r e - 2.7 Example o f F i v e R e f r a c t i o n T r a c e s Simultaneously Figure 2,8 ;  Profile  3.1 A m p l i t u d e  Characteristic Figure  ......36  Recorded  .............,,......................39  Example o f a R e c o r d  Expanding Figure  .,..14  i n AREA  S e c t i o n from t h e  3 ...,.,,.,.,,,,..,..,.,.,41  Normalized  Aotopower S p e c t r a o f  Parts of Seismic Traces  3.2 Examples o f t h e E f f e c t  . . . . . . . . . . . . . 49  of Various  Bandpass  Filters Figure  3.3 E f f e c t s  Deconvolution Figure  52 of the S p e c t r a l D i v i s i o n a l  on a R e f l e c t i o n  Trace  . . . . . . . . . . . . . . . . 60  3.4 C h a r a c t e r i s t i c s o f t h e S h a p i n g  Operator f o r  vi  Spike-Deconvolution Figure  ...............................,64  3.5 Example of t h e a p p l i c a t i o n of Spike  Deconvolution  t o a R e f l e c t i o n Seismogram  66  F i g u r e 3.6 Example of the A p p l i c a t i o n of Deconvolution  with  V a r i a b l e Wavelet t o Seismograms .69  F i g u r e 3.7 Record S e c t i o n s o f the Unstacked and Stacked Data of the R e f r a c t i o n P r o f i l e 73-1 ................ 73 Figure  3.8 V e l o c i t y Spectrum f o r Six Seismic  Traces of the Expanding R e f l e c t i o n P r o f i l e 73-5 ..,,80 F i g u r e 4.1 T r a v e l t i m e - D i s t a n c e  P l o t of t h e R e f r a c t i o n  P r o f i l e 73-1 from AREA 1 Figure 4.2 Reduced  90  Traveltime-Distance  P l o t of the  R e f r a c t i o n P r o f i l e 73-5 from AREA 3 ................ 94 Figure 4.3 Comparison  o f the Observed and S y n t h e t i c  Seismograms of the R e f r a c t i o n P r o f i l e  73-5  .,98  Figure- 4.4 Record Section o f the Expanding R e f l e c t i o n P r o f i l e 73-5 from AREA 3 ,,..,.,.,..,,.......,,.,,..101 F i g u r e 4.5 Record S e c t i o n of the Quasi-Continuous Subcritical  R e f l e c t i o n P r o f i l e 73-6 from AREA 3 .,.,103  F i g u r e 4.6  T -X2  Figure  Velocity-Depth  4.7  2  F i g u r e 4.8 Reduced  Graph f o r the Expanding P r o f i l e Hodel f o r AREA 3  Traveltime-Distance  Reversed R e f r a c t i o n P r o f i l e s Figure 4.9 Comparison  73-5 107 109  P l o t o f the Two  73-2,3 from AREA 2 .,..113  o f the Observed and S y n t h e t i c  Seismograms of the R e f r a c t i o n P r o f i l e  73-2 ....,.,,.116  vii  Figure  4.11 R e c o r d S e c t i o n  Profile Figure  4.11  Pxofxl^ Figure  4.12  7 3-2 f r o m AREA 2 ...........................118 T -X 2  4.13  2  Graph  7 3** 2 ••••• •  Slope  ••••••*••* •••• • « • • • • * • • • • • • • • 12 H  i n AREA  Model f r o m t h e Base o f 2  Quasi-continuous S u b c r i t i c a l  4 from the C o n t i n e n t a l Figure  f o r the Expanding R e f l e c t i o n  Velocity-Depth  Continental Figure  o f t h e Expanding R e f l e c t i o n  123 Profile  73-  S l o p e i n AREA 2 . . . . . . . . . . . . . 126  4.14 S t r u c t u r a l M o d e l o f S e d i m e n t s on t h e  Continental Profile  Slope  and I t s C o r r e l a t i o n w i t h a CSP 128  viii  ACKNOWLEDGMENTS  I would l i k e to thank Dr. R.M. Clowes f o r i n i t i a t i n g t h i s c h a l l e n g i n g p r o j e c t . Because we were both p r e v i o u s l y inexperienced  with work a t sea, on many occasions the  p r o j e c t demanded great endeavour and mutual personal encouragement. Considerable  a s s i s t a n c e was necessary  during the f i e l d  o p e r a t i o n s and f o r t h i s I s i n c e r e l y a p p r e c i a t e d the c o o p e r a t i o n of the o f f i c e r s and crews o f CFAV Laymore. Endeavour and S t . Anthony, who p a r t i c i p a t e d i n the o p e r a t i o n s d u r i n g the p r o j e c t . My p a r t i c u l a r  thanks go t o  Captain- M. Dyers and o f f i c e r s W. Frame and A. Reid f o r t h e i r p e r s o n a l involvment  and f r i e n d s h i p . I a l s o a p p r e c i a t e d the  h e l p f u l a s s i s t a n c e o f my f e l l o w mates, Paul S o m e r v i l l e , L a r r y L i n e s , and others from the Department o f Geophysics and  Astronomy, who shared some of the tough moments a t sea  with me. The suggestions  of Dr. R.A. Wiggins i n the data  a n a l y s i s were c o n s t r u c t i v e and together with the p r a c t i c a l h e l p ' o f my f r i e n d Rob C l a y t o n during computer  programming,  were very much a p p r e c i a t e d . During  part o f t h i s p r o j e c t , t h e author  was supported  ix  by a Graduate Research F e l l o w s h i p from the U n i v e r s i t y o f British  Columbia. F i n a n c i a l support  f o r the p r o j e c t was  provided by N a t i o n a l Research C o u n c i l equipment grant E 3 2 3 5 and  o p e r a t i n g grant A7707, A d d i t i o n a l funds were c o n t r i b u t e d  by Mobil O i l Canada L i m i t e d .  1  1 INTRODUCTION  1.1  Why. Deep Seismic Sounding at S§a  In recent years, i n c r e a s e d research e f f o r t s have been made toward s t u d i e s of the ocean. From a g e o p h y s i c a l viewpoint, two  p r i n c i p a l areas of i n v e s t i g a t i o n have  e v o l v e d , one of a more economic, the other one of a more academic  importance.  An area of f u t u r e economic importance and  i s the l o c a t i o n  recovery of n a t u r a l resources beneath the sea. I t  appears  p o s s i b l e t h a t w i t h i n the next decades the  a c g u i s i t i o n of minerals and petroleum the deep oceans w i l l be f e a s i b l e and  from the r e g i o n s of economically  p r o f i t a b l e . An example of such a promising area i s the Gulf o f Mexico where s a l t  domes with petroleum  been found i n deep water r e g i o n s The  second  i n d i c a t o r s have  (Hatkins et al.,1975).  area of i n t e r e s t concerns  the study of  t e c t o n i c processes and the g e o l o g i c a l h i s t o r y of the e a r t h . For the development of g e o t e c t o n i c t h e o r i e s , a d e t a i l e d knowledge of the s t r u c t u r e of t e c t o n i c a l l y a c t i v e areas a t sea and  of the t r a n s i t i o n zones from the oceans t o the  c o n t i n e n t s i s of prime importance.  However, even t h i s more  2  academic research p u r s u i t cannot be separated from i t s e v i d e n t economic a s p e c t s as d i s c u s s e d r e c e n t l y by Hammond (1975).  Volcanism  a s s o c i a t e d with subduction  zones and  mid-  oceanic r i d g e s cr other a c t i v e c e n t e r s such as hot spots now  thought  are  to give r i s e to c h a r a c t e r i s t i c types of ore  d e p o s i t s . The  c l e a r e s t examples are the copper s u l f i d e  o c c u r r i n g i n the Troodos area of Cyprus and  porphyry  ore  copper  ores i n the Andes of South America. Progress toward the s o l u t i o n of such p r a c t i c a l  and  t h e o r e t i c a l problems r e g u i r e s an e x t e n s i v e knowledge of the s t r u c t u r e and p h y s i c a l c h a r a c t e r i s t i c s of the e a r t h ' s c r u s t and  upper mantle under the oceans. Of the many g e o p h y s i c a l  techniques a v a i l a b l e , the s e i s m o l c g i c a l method p r o v i d e s the most d e t a i l e d i n f o r m a t i o n . In u n i v e r s i t y and r e s e a r c h , two continuous  standard  techniques have been a p p l i e d :  seismic p r o f i l i n g  p r o f i l i n g . The  governmental  (CSF)  and s e i s m i c r e f r a c t i o n  p r i n c i p a l advantage of the CSP  e x c e l l e n t r e s o l u t i o n due  method i s i t s  to the high frequency  content  of  the r e f l e c t e d s i g n a l ; the p r i n c i p a l disadvantage  is its  r e l a t i v e l y shallow  sources  p e n e t r a t i o n due  with a high freguency  to low  content. The CSP  energy  method has been used  f o r more than a decade f o r o b t a i n i n g d e t a i l e d i n f o r m a t i o n about the uppermost p a r t s of the c r u s t , mainly sedimentary  the  l a y e r s , on the other hand, the p e n e t r a t i o n of  the s e i s m i c r e f r a c t i o n method as used at sea i s  3  t h e o r e t i c a l l y u n l i m i t e d hut i t s r e s o l u t i o n i s poorer. The lower frequency content of the s e i s m i c s i g n a l s l i m i t s the p r e c i s i o n of the method f o r d i s t i n g u i s h i n g f i n e s t r u c t u r e s . Since  the s i g n a l u s u a l l y t r a v e l s long d i s t a n c e s ,  averaged parameters along obtained.  the h o r i z o n t a l ray path can be  In a d d i t i o n , v e l o c i t y g r a d i e n t s  cannot be detected  only  and i n v e r s i o n s  without a d d i t i o n a l a n a l y s i s i n c l u d i n g the  use of both t r a v e l t i m e s and amplitudes; even then t h i s can be  difficult. In the petroleum e x p l o r a t i o n  i n d u s t r y , another  technique of i n v e s t i g a t i o n has teen developed. The multichannel  common depth p o i n t  (CDP) procedure has the  c a p a b i l i t y of p r o v i d i n g good r e s o l u t i o n with deep penetration.  The c o s t of the eguipment r e q u i r e d  for this  procedure i s so high t h a t i t s use i n u n i v e r s i t y r e s e a r c h i s unrealistic. However, i t was b e l i e v e d that a technique which would combine the advantages of the s e i s m i c and  the i n d u s t r y ' s  multichannel  r e f r a c t i o n technique  CDP technique might be  e s t a b l i s h e d on a l i m i t e d budget. Using t h e name e s t a b l i s h e d by Russian s e i s m o l o g i s t s technique has been c a l l e d  (Zverev,1967), t h i s compromise marine 'deep s e i s m i c  (DSS), Marine DSS r e f e r s t o a marine seismic recording and  n e a r - v e r t i c a l incidence  sounding'  procedure f o r  to wide-angle r e f l e c t e d  r e f r a c t e d waves with p e n e t r a t i o n  from the ocean bottom  4  to the  upper mantle. Higher frequency s i g n a l s than with  usual r e f r a c t i o n method are recorded at the  near  distances,  thus a l l o w i n g  d e t a i l e d changes i n s t r u c t u r e to  distinguished  even i n the deeper l a y e r s of the c r u s t .  greater  distances,  the  seismic  check the i n f o r m a t i o n Several  Geophysics and  obtained from the  marine DSS  the oceanic c r u s t and  University  on  the s u c c e s s f u l  the  contributed  dominant ones among  use  west c o a s t ,  to the  of the  continuing  throughout  DSS  Marine Geosciences  Survey of Canada i n Vancouver, a l l  initiation  of the  project.  technique , methods of data a n a l y s i s and  examples cf i n t e r p r e t e d representative discussion  location  Geological  T h i s t h e s i s concerns the establishment of the DSS  method  marine  Department of  complementary wcrk by the  Group of the G e o l o g i c a l  Department of  on l a n d . As w e l l , the  of the upper c r u s t by the  S c i e n c e s and  decision  for detailed information  detailed c r u s t a l studies  studies  are used to  r e f l e c t i o n data.  program w i t h i n the  Astronomy at a.B.C. The  these were the n e c e s s i t y  of the  p r o f i l e s and  At  provide  f a c t o r s played important r o l e i n the  to i n i t i a t e the  for  be  refraction signals  average c h a r a c t e r i s t i c s along the  the  velocity-depth  areas o f f the  west coast  marine  interpretation,  structures  in  of Canada, and  of t h e i r g e o l o g i c a l s i g n i f i c a n c e .  a  5  1«2 fieview of the Seismic  During  the l a s t  of the c r u s t and  Work at  Sea  decade our knowledge of the s t r u c t u r e  upper mantle under the oceans i n c r e a s e d  remarkably. Much of the i n f o r m a t i o n i s due to the use s e i s m i c r e c o r d i n g technigues  based on the r e s u l t s obtained  r e c o r d i n g . These technigues information  was  with w e l l e s t a b l i s h e d  ( H i l l , 1 9 5 2 ; O f f i c e r et al.,1959;  Shor, 1.963) using unreversed,  The  data.  o r i g i n a l s e i s m i c model of the oceanic c r u s t  r e f r a c t i o n technigues  new  at sea and the development of  more s o p h i s t i c a t e d methods of a n a l y s i n g recorded The  of  reversed and  split  and  profile  are a r e l i a b l e source  of  i n normal oceanic r e g i o n s such as deep b a s i n s .  model c o n s i s t s of three l a y e r s with a sediment l a y e r at  the top, a basement or secondary l a y e r beneath, and oceanic or t h i r d l a y e r at the bottom. The t h i c k n e s s e s of the l a y e r s can f o r the P a c i f i c Ocean basin  an  velocities  vary widely. The  and  average model  (Shor et a l . , 1970)  shows that  the v e l o c i t y f o r the sediments v a r i e s i n the range from t o 2.5  km/sec and  the t h i c k n e s s from 0 t o 1.6  basement v e l o c i t y v a r i e s from 4.5 t h i c k n e s s from 0.5  to 2.5  km.  to 5.9  The  km/sec and i t s  For the oceanic l a y e r the  v e l o c i t y i s i n the range from 6.7 t h i c k n e s s from 3.3  to 5.8  km.  1.9  t o 7.0  km/sec with  varying  km.  Abnormal oceanic regions such as r i d g e s and  continental  6  margins are c h a r a c t e r i z e d by a more complex c r u s t a l s t r u c t u r e . S e v e r a l d i f f i c u l t i e s are encountered when one t r i e s to o b t a i n r e l i a b l e data technigues  with the use of r e f r a c t i o n  i n such areas. I n t e r f a c e s d i s t o r t e d by f o l d i n g or  broken by f a u l t i n g give complex t r a v e l t i m e curves undulating  or broken i n t o short segments. The most r e l i a b l e  s e i s m i c a r r i v a l s are the f i r s t it  which are  has been d i f f i c u l t  ones. For o p e r a t i o n a l reasons  with r e f r a c t i o n technigues  e x p l o s i v e s t o provide  using  spacing c l o s e enough t o detect  s t r u c t u r a l f e a t u r e s or l a y e r s t h a t appear as f i r s t  arrivals  on the records only over a l i m i t e d d i s t a n c e i n t e r v a l .  Thus  t h i n sedimentary l a y e r s or a t h i n basement l y i n g at g r e a t e r depth can be d i f f i c u l t  to d e t e c t  (Shor and fiaitt, 1969). For  second or l a t e r a r r i v a l s the c o i n c i d e n c e phases makes the a n a l y s i s d i f f i c u l t ,  of two or more  unless there i s an  a p p r e c i a b l e d i f f e r e n c e i n the c h a r a c t e r i s t i c New techniques  frequencies.  of marine r e c o r d i n g and shooting  s o l v e d some of the problems. Recording  have  of v a r i a b l e - a n g l e  r e f l e c t i o n data from c l o s e l y spaced s e r i e s o f shots f i r e d a t s h o r t e r ranges together  (H. .Ewing,1963; J . Ewing and Nafe,1963)  with records of v e r t i c a l r e f l e c t i o n  (Hersey,1963) provide and  valuable a s s i s t a n c e i n the a n a l y s i s  i n t e r p r e t a t i o n of the t r a v e l t i m e curves.  enable determination  profiles  Such data  of the v e l o c i t i e s and t h i c k n e s s e s of  sedimentary l a y e r s , a r e s u l t  which i s not p o s s i b l e with the  7  CSP  method. The v e r t i c a l i n c i d e n c e r e f l e c t i o n s provide  apparent  d i p and topographic c o r r e c t i o n s f o r the  angle r e f l e c t i o n data  variable-  (Le Pichon et al.,1968). R e l i a b l e  measurements of the t h i c k n e s s of basement are obtained by comparing the r e f l e c t e d  wave r e s u l t s with the p o s i t i o n of  the top of the deeper o c e a n i c l a y e r as determined r e f r a c t i o n measurements Another  equipment  (Zverev,1970).  technique with i n c r e a s e d s t r u c t u r a l  uses expendable  sonobuoys and  (Haynard  shot spacing was  from  resolution  precision echo-recording  et al.,1969; Ewing and  Houtz, 1969). The  decreased s i g n i f i c a n t l y through  the use of  a r e p e t i t i v e a i r gun as a s i g n a l source. With t h i s technigue a p r e v i o u s l y undetected oceanic crust  was  l a y e r i n the deep p a r t s of the  i d e n t i f i e d . T h i s high v e l o c i t y  c r u s t a l l a y e r with an average  basalt  s e i s m i c v e l o c i t y of 7.3  under the normal oceanic l a y e r was  km/sec  d i s c u s s e d by Maynard  (1970) and by Sutton et a l . (1971). V a r i a t i o n s i n v e l o c i t i e s and v e l o c i t y g r a d i e n t s w i t h i n the oceanic l a y e r and  upper mantle have been i n v e s t i g a t e d ,  p a r t i c u l a r l y by Russian r e s e a r c h e r s . In t h e i r work, which was  one  of the e a r l i e s t  f o r t h i s purpose, amplitude  a p p l i c a t i o n s of the DSS  they used  technique  both the t r a v e l t i m e and  i n f o r m a t i o n from long expanding  p r o f i l e s with  dense e x p l o s i o n s p a c i n g . In such a study near the  Southern  K u r i l e I s l a n d s near Kamchatka, running p r o f i l e s up to the  8  d i s t a n c e of 160 km with shot spacing of about 6 km, were able to i d e n t i f y v e l o c i t i e s of 8.6 depth of 12 km  below the Mohorovicic  to 9.0  (M-)  they  km/sec a t a  discontinuity  (Zverev,1970). With the r e a l i z a t i o n of the g r e a t e r complexity of the c r u s t and upper mantle under the oceans, new  shooting  procedures and i n s t r u m e n t a t i o n f o r the study of s p e c i f i c problems i n the i n v e s t i g a t i o n of s e i s m i c s t r u c t u r e s have been developed. For example, orthogonal and bave been conducted anisotropy  ring  surveys  t o detect lower c r u s t and upper mantle  ( E a i t t et al.,1971; Keen and  Barrett,1971;  Whitmarsh,1971). In i n s t r u m e n t a t i o n , ocean bottom seismometers with e x p l o s i o n and a i r gun sources t o d e t e c t both compressional and shear wave v e l o c i t i e s d i r e c t l y have been t e s t e d  (Hussong et al.,1969;  Carmichael et al.,1973; L i s t e r and Prothe.ro, 1974;  F r a n c i s and  Porter,1973;  Lewis,1974;  Qrcutt et a l . , 1975, 1976) . The comparison  of  t h e i r exact values with the r e s u l t s of l a b o r a t o r y t e s t s made on rock samples from  deep sea d r i l l i n g  would g r e a t l y help i n  the i n t e r p r e t a t i o n of oceanic s t r u c t u r e i n terms of petrology. Attempts  to i n v e s t i g a t e d e t a i l e d s t r u c t u r e of the deep  c r u s t and upper mantle with the use of the n e a r - v e r t i c a l i n c i d e n c e r e f l e c t i o n technigue have been reported during the l a s t decade. In a two  s h i p o p e r a t i o n i n the Skagerrak  area  9  n o r t h of Denmark, v e r t i c a l i n c i d e n c e r e f l e c t i o n s from the d i s c o n t i n u i t y at a depth of 30 km observed  (Aric,1968). The  M-  below the sea s u r f a c e were  r e s u l t s were compared with  p r e v i o u s r e f r a c t i o n o b s e r v a t i o n s and e x h i b i t e d good agreement. A v e r t i c a l i n c i d e n c e p r o f i l e recorded at the Great  Meteor Bank near the Canary I s l a n d s  (Aric et al.,1970)  i n d i c a t e d a r r i v a l s from a depth corresponding to 10 sec (two-way) t r a v e l t i m e . The r e s u l t s when compared  with  r e f r a c t i o n data recorded with geophones l o c a t e d on the sea bottom at depths between 300 agreement. P e r k i n s  and  800  (1970) observed  m showed good  near-vertical incidence  r e f l e c t i o n s from the deep parts of the c r u s t north of  Puerto  .Rico. Data were recorded  i n a s i n g l e s h i p o p e r a t i o n with the  use of sonobuoys and  kg charges  Stacked  0.8  data show r e f l e c t i o n  as a source of  a r r i v a l s from  basement, o c e a n i c l a y e r and p o s s i b l y from  energy.  w i t h i n the the  M-  discontinuity; Some s p e c i a l a p p l i c a t i o n s of the multichannel procedure  CDP  with the use of r e p e t i t i v e sources to o b t a i n deep  c r u s t a l and  upper mantle r e f l e c t i o n s have r e c e n t l y been  r e a l i z e d . Limond et a l . (1972) reported mantle r e f l e c t i o n s a t n e a r - v e r t i c a l i n c i d e n c e i n the Bay of Biscay north of Spain. T h r e e f o l d stacked data i n d i c a t e v e r t i c a l i n c i d e n c e a r r i v a l s of 9.2 agreed  t o 9,4  sec  well with wide-angle  (two-way) t r a v e l t i m e . The r e f l e c t i o n and r e f r a c t i o n  results data  10  previously recorded using  i n the a r e a ,  a s i m i l a r method, r e c o r d e d  G u l f of Mexico. T h e i r clearly sec  multifold  show a deep r e f l e c t o r  Watkins et a l .  (1975),  deep r e f l e c t i o n s i n data  recorded  the  digitally  ( p o s s i b l y upper mantle) a t  (two-way) t r a v e l t i m e a f t e r t h e f i r s t  water  6.5  bottom  reflection. In the  i n t e r p r e t a t i o n of  u s u a l method u s e d was by J . Ewing  (1963).  the  marine r e f r a c t i o n d a t a ,  s l o p e - i n t e r c e p t method  It is relatively  usually incorporated  structures. in  the As  new  Thus i t can  determination new  i n the i n t e r p r e t e d seismic l e a d t o major e r r o r s , p a r t i c u l a r l y  p r o c e d u r e s and  c f data  Helmberger has  enabled  (1968),  and and  data.  by  i d e n t i f i c a t i o n of  o f a low  underlying a high  by  (1969,1970) and  O r c u t t et a l . (1975,1976),  p r o f i l e s recorded the East  velocity  velocity  Morris  velocity gradients  o c e a n b o t t o m s e i s m o m e t e r on occurrence  F o r e x a m p l e , a method  H e l m b e r g e r and  analyzing seismic refraction  the  obtain  waveform i n f o r m a t i o n d e v e l o p e d  i n v e r s i o n s from r e f r a c t i o n data.  an  methods were a p p l i e d  a n a l y s i s were d e v e l o p e d t o  more i n f o r m a t i o n f r o m r e c o r d e d using the amplitude  i n v e r s i o n s were  of l a y e r t h i c k n e s s e s .  recording  techniques  described  s t r a i g h t f o r w a r d , but  s u c h d e v i a t i o n s as v e l o c i t y g r a d i e n t s and not  the  Pacific  l a y e r o f 4.8  l a y e r o f 6.7  digitally  R i s e , show  km/sec  km/sec. I n  a n a l y s i s o f t h e s e i s m o g r a m s b o t h t r a v e l t i m e and  by  the  amplitude  11  s t u d i e s were used. Recent d e t a i l e d  s t u d i e s i n d i c a t e t h a t the model of the  oceanic c r u s t i s much more complex than was assumed. S u c c e s s f u l l y recorded  s u b c r i t i c a l r e f l e c t i o n s from  the deep parts of the c r u s t suggest r e f l e c t i o n seismology  that the method of  should be developed  to a g r e a t e r extent as one  originally  f u r t h e r and  used  of the p r i n c i p a l means f o r  d e t a i l e d i n v e s t i g a t i o n of the oceanic c r u s t .  1.3  In 1971 program was  P r o j e c t H i s t o r y and  #  Areas of  Recording  the marine deep s e i s m i c sounding  research  i n i t i a t e d at the Department of Geophysics  and  Astronomy, U n i v e r s i t y of B r i t i s h Columbia. The purpose of the p r o j e c t was  to:  1) develop  and  t e s t the i n s t r u m e n t a t i o n i n the  l a b o r a t o r y and at sea; 2)  use the technigue  and economically  for recording in t e c t o n i c a l l y  i n t e r e s t i n g areas o f f Canada's  west c o a s t ; 3) apply data p r o c e s s i n g technigues bandpass f i l t e r i n g , s t a c k i n g and  such  as  deconvolution to  the d i g i t a l l y recorded data t o improve the of the seismograms;  quality  12  4)  analyse  the recorded  data  i n terms of  velocity  structure; 5) i n t e r p r e t t h e understanding; 6)  and  determine the  detailed seismic Two o f two  ships f o r the  feasibilty  of the  s t u d i e s of the  technigue  oceanic  However, the and  data  During  the  marine technique  described  acguisition  system i n  the f i r s t  a s s e m b l e d and  by  Shor  was  t o be  (1963) was  improved with  the  used. A  Scripps  Institute chosen.  multiple  of t h i s t h e s i s  detail.  h a l f of 1971,  the  instrumentation  t e s t e d i n t h e l a b o r a t o r y . The  r e c o r d i n g with the  availability  operation, strongly influenced  d i g i t a l r e c o r d i n g . S e c t i o n 2.1  describes the  for  crust.  b u d g e t , and  s i m i l a r i n c o n c e p t t o t h a t u s e d by  o f O c e a n o g r a p h y and  sensors  thus  basic f a c t o r s , a limited  decisions concerning design  structure to give a geological  designed  technigue  first  a t sea  test  in July  was of  1971  was  u n s u c c e s s f u l . Any  due  t o h i g h n o i s e b a c k g r o u n d c a u s e d by w a t e r wave m o t i o n .  A f t e r a few to  changes i n the  seismic data  acguisition  c o m p e n s a t e f o r t h i s , a n o t h e r c r u i s e was  November 1971. of Los  During  an e x p e r i m e n t c a r r i e d  A n g e l e s an e x p a n d i n g s e i s m i c  recorded. due  p o s s i b l e s e i s m i c i n f o r m a t i o n was  The  sea o p e r a t i o n  t o a s e r i o u s a c c i d e n t on  had one  system  undertaken i n out  p r o f i l e was  t o be s u d d e n l y of the  lost  150  km  west  successfully terminated  s h i p s . In  this  13  experiment  a n a l o g FM  Electrical  firing  shot-instants. was  magnetic  of charges  The  enabled  slowed  d a t a showed a low  o f deep r e f l e c t i o n s  signal  often unreadable  was  For these reasons the considered. reflection and  was  ratio,  noted.  because  of poor  interpretation  no  ship time  radio  of the data  was  o f the  analog  FM  to multichannel d i g i t a l  h y d r o p h o n e s u s p e n s i o n was additional  mechanical  • I n t h e summer o f planned  investigated area  the r e s u l t s  seismic  changed  In  the  from  of waves.  1973,  was  Keen and of our  model d e t e r m i n e d  AREA 2 l i e s  guality  by t h e i n t r o d u c t i o n  the f i n a l  sea experiment  Columbia  west o f t h e s o u t h e r n t i p o f I t was  t h e area of the  where t h e a n i s o t r o p y o f t h e upper  by  not  damping a g a i n s t the p u l l o f s e a  AREA 1 i s l o c a t e d  experiment  was  . C o n c u r r e n t l y , the  improved  t h e Queen C h a r l o t t e I s l a n d s , 70*  reception.  the  f o r t h r e e a r e a s o f f the c o a s t o f B r i t i s h  (Fig.,1.1).  some  subcritical  available.  meantime t h e method o f t a p e r e c o r d i n g was  the  although  made t o a s c e r t a i n i t s o v e r a l l  I n 1972,  procedure  However,the t i m i n g  p r o v i d e d enough e n c o u r a g e m e n t t o c o n t i n u e  development.  exact  t h e o p e r a t i o n . Much o f  However, a r e c o r d s e c t i o n d a t a was  shooting  signal/noise  indication  used.  r e c o r d i n g of the  disadvantage of t h i s  that i t s i g n i f i c a n t l y  recorded  t a p e r e c o r d i n g was  Barrett  (1971).  By  choosing  previous refraction  a t t h e e n t r a n c e t o t h e Queen  HUDSON  mantle  r e c o r d i n g c o u l d be compared from  1  was  this with  work.,  Charlotte  the  Figure  1.1 L o c a t i o n Map Fox the Areas of DSS Recording  Area  510  -  30'  -  Sfjo 58 •  -  510  12'  N  1300 Oii«  _  130O  2 1 '  I  31 •  -  480  34'  N  1330  Area  Area  510 32«  n*  1:  2:  480  3:  1270  The boxes o u t l i n e d e t a i l i n Figs.  2  21«  -  1330 53 • «  1270 25' B  the r e g i o n s which are shown i n more  2.4a and 2.4b. The numbers 74 and 75  designate p r o f i l e l i n e s f o r r e c o r d i n g i n 1974 and 1975. Map a f t e r Chace e t al.,1970. Contours a r e i n fathoms.  16  Sound and  i n c l u d e s a p a r t of the  t e c t o n i c a l l y complex area.  continental slope.  In such a r e g i o n ,  a b o u t t h e d e e p e r s t r u c t u r e s would a s s i s t understanding  of the  in  ocean-continent t r a n s i t i o n  would a l s o c o m p l e m e n t t h e  sheif  and  slope  being  G e o l o g i c a l S u r v e y and  CSP  data  work on t h e  from  this  continental the  Basin  west  southern p a r t of Vancouver I s l a n d . T h i s r e g i o n  is a  show s u f f i c i e n t  penetration  o f t h e t h i c k s e d i m e n t s and a b o u t t h e d e p t h and  northern  had  to reach  Cascadia  CSP the  profiles did  t h e r e f o r e a l a c k of  information  f o r m o f b a s e m e n t , some i n t e r e s t i n  been i n d i c a t e d by  i n t e r e s t to other  f o r t e s t i n g the technigue.  not  basement. Because  t h e o i l i n d u s t r y and  by  groups, the  penetration  and  Also, determination  region  w o u l d be  s e d i m e n t a r y l a y e r s w o u l d e n a b l e an e s t i m a t e  of  data  a good  r e s o l u t i o n of the of the v e l o c i t i e s  this  the  G e o l o g i c a l S u r v e y o f Canada. I n a d d i t i o n t o p r o v i d i n g of  the  O.E.C.  deep s e d i m e n t a r y b a s i n where p r e v i o u s  region  z o n e and  done,by m a r i n e g e o s c i e n t i s t s o f  AREA 3 i s l o c a t e d i n t h e of the  information the  t e c t o n i c h i s t o r y o f t h e r e g i o n . Deep s e i s m i c area  It i s a  area  DSS of  the  their  ^ thicknesses. I n J u l y 1973,  seismic  were s u c c e s s f u l l y r e c o r d e d . a n a l y s i s and  profiles The  data  as i n d i c a t e d i n F i g . a c g u i s i t i o n , and  i n t e r p r e t a t i o n , are presented  of.the t h e s i s .  i n the  1.1  their  remainder  17  2 DATA ACQUISITION  2.1  The  DSS t e c h n i g u e  s h i p s . During receiving  this  Technigues  w h i c h was d e v e l o p e d r e g u i r e s two  p r o j e c t CFAV ENDEAVOUR s e r v e d  v e s s e l a n d CFAV LAYM0SE a s t h e s h o o t i n g 2.1 i l l u s t r a t e s the general  Fig. technigue. freely  Field  During  vessel.  features of the f i e l d  a p r o f i l e run the r e c e i v i n g ship  while t r a i l i n g  as t h e  drifts  t h e n e u t r a l l y b u o y a n t main c a b l e . S i x  i n d i v i d u a l hydrophone systems suspended from t h i s c a b l e used f o r r e c o r d i n g t h e d i r e c t s i g n a l s . ' The s h o o t i n g and  were  w a t e r wave and s e i s m i c  s h i p proceeds along  a chosen  course  d e t o n a t e s c h a r g e s a t p r e d e t e r m i n e d d i s t a n c e s ; The  l o c a t i o n s o f t h e p r o f i l e l i n e s were d e t e r m i n e d w i t h a n accuracy  o f a b o u t 2 km f r o m L o r a n A f i x e s and c h e c k e d  2 km. S h i p - t o - s h i p d i s t a n c e s readings  were d e t e r m i n e d by r a d a r  on b o t h s h i p s . H a t e r d e p t h s were r e c o r d e d  echo-sounding systems operating continuously during  the p r o f i l e run.  every  with  on b o t h  ships  18  F i g u r e 2.1 Schematic Diagram o f the DSS System Osing Two  Top  Ships  - The two ship procedure with d i r e c t water wave,  r e f l e c t e d and r e f r a c t e d wave ray paths i n d i c a t e d .  Bottom - Sketch o f one of the s i x hydrophone systems suspended from the main c a b l e . The b a t t e r y box c o n t a i n s  >i 6-volt G e l - C e l rechargeable  b a t t e r i e s to provide  power f o r the p r e a m p l i f i e r s . F l o t a t i o n i s attached t o make the 15 m c a b l e s with hydrophones n e u t r a l l y buoyant at depth. The S-shapes of these c a b l e s p l u s the shock cord  minimize the e f f e c t s of the s u r f a c e sea waves.  20  2.2 Instrumentation and Procedure  SHOOTING SHIP  As a source o f s e i s m i c energy, Nitrone SM Super commercial e x p l o s i v e was used. T h i s b l a s t i n g agent g i v e s high s e i s m i c energy per unit and was developed  specifically  f o r marine s e i s m i c s h o o t i n g . I t was used i n the form of 0.45 kg cans which were easy to handle on the s h i p . Charges up to 8.1 kg were assembled  f o r shots at the g r e a t e s t  distances.  The shooting procedure was r e l a t i v e l y simple and s i m i l a r t o that o u t l i n e d by Shor  (1963). Charges were prepared f o r  d e t o n a t i o n with a timed-fuse/Seismocap assembly and Primacord  (Malecek, 1976). A f t e r t h e charge was f a s t e n e d to a  l i n e which had one or more b a l l o o n s t i e d to the end of i t , the fuse was l i t f o u r minute  and the charge was dropped overboard. A  fuse allowed time f o r the charge to s i n k to the  r e g u i r e d depth and gave the shooting s h i p time t o s a i l a s a f e d i s t a n c e ahead of the shot. A f t e r the shot was detonated, the d i s t a n c e of the b a l l o o n from the s h i p estimated by v i s u a l  was  sighting.  The optimum depth f o r d e t o n a t i n g charges with r e s p e c t to the minimum l o s s of energy depends on the charge s i z e  21  {.Haiti, 1952) , and f o r TNT  i s given by the e m p i r i c a l formula  (2.2-1)  where H i s the depth C i s the sound 0  weight  (m) of the charge from the sea s u r f a c e ,  velocity  (km/sec) i n sea water, and 8 i s the  (kg) of the charge. T h i s formula i s based on a curve  r e l a t i n g freguency of bubble o s c i l l a t i o n s to charge and the c r i t e r i a  weight  that the d e t o n a t i o n depth should equal a  g u a r t e r of the wavelength f o r the bubble pulse freguency. For the Nitrone SM Super charges 0.45  to 8.1  (60% TNT)  o f s i z e s from  kg the formula gives the optimum depths i n the  range of 30 t o 52 m. A p r e l i m i n a r y t e s t i n g at sea confirmed these v a l u e s , and i t was decided to shoot a l l charges at a uniform depth of 45  m.  In order t o time the d i r e c t  wave a r r i v a l s ,  each  d e t o n a t i o n was r e c e i v e d by a s i n g l e hydrophone l o c a t e d  30m  behind the shooting s h i p . As a back up f o r the hydrophone, geophone was  placed on the deck of the s h i p . These  a  signals,  together with the WBVE time code s i g n a l , were recorded on an FM tape recorder f o r subseguent c h a r t r e c o r d e r was  playback. A two channel  used t o monitor s i g n a l s being r e c o r d e d .  The i n s t r u m e n t a t i o n on the shooting s h i p i s i l l u s t r a t e d s c h e m a t i c a l l y i n F i g . 2.2.  22  F i g u r e 2 . 2 Schematic Diagram Shooting. Ship  of the Ins t r a i S J i t a t i o n on the  S H O O T I N G SHIP  INSTRUMENTATION  BRUSH WWVB  chart recorder  time code receiver DEVELCO  WAVEFORM hydrophone  A M P E X F M 7-channel taperecorder  back-up'geophone on s h i p d e c k  GOULD CH-24  CLEVITE hydrophone  BRUSH  chart  - 220  recorder  24  RECEIVING SHIP  During the running of a p r o f i l e , the r e c e i v i n g drifted  ship  f r e e l y with engines stopped and the main c a b l e  s t r e t c h e d behind. The e f f e c t s of the motion  (due to sea  waves at the surface) o f the main c a b l e on the hydrophone systems  were reduced by means c f rubber shock cords  extending from the main cable to the battery cases. A d d i t i o n a l mechanical damping of the movement of the hydrophones due'to water d i s t u r b a n c e s was e f f e c t e d by a t t a c h i n g s u f f i c i e n t f l o t a t i o n t o the hydrophones and 15 m c a b l e s such t h a t they were approximately n e u t r a l l y at depth  buoyant  (Fig.2;1,lower p a r t ) .  The i n s t r u m e n t a t i o n used on the r e c e i v i n g s h i p i s shewn i n F i g . 2.3. Pressure waves i n c i d e n t on a p i e z o e l e c t r i c c r y s t a l i n the CH-2A hydrophone produce an e l e c t r i c a l  signal  which  system  i s p r e a m p l i f i e d and t r a n s m i t t e d t o an a m p l i f i e r  aboard s h i p . In the l a t t e r , the s i g n a l i s bandpass f i l t e r e d between 0.8 and 100 Hz, and then a m p l i f i e d with the g a i n set manually f o r each shot. The outputs from the s i x a m p l i f i e r s plus the HWVB time code s i g n a l are recorded on magnetic with an IBM-compatible,  tape  14 b i t , multichannel d i g i t a l  a c g u i s i t i o n system. F i v e s e i s m i c data channels and the WHVB time s i g n a l are monitored on a s i x - c h a n n e l c h a r t r e c o r d e r . T h i s enables one t o check data g u a l i t y and make d e c i s i o n s  25  F i g u r e 2.3  Schematic  Diagram of the Seismic  Sistem on the R e c e i v i n g Ship  Recording  SEISMIC  RECORDING  SYSTEM  BRUSH chart recorder 6  6  CLEVITE hydrophone systems  GEO  TECH  AS 330 amplifiers .0.8-100 Hz  A N A L O G I C converter  A/D  receiver  W W V B  KENNEDY formatter & digit, recorder OCEANIC  HYDROPHONE  SYSTEM  CH-2Asensor G O U L D CE-25L preamplifier ( 2 0 d b , 2 Hz - 40 kHz )  A N A L O G I C SERIES AN - 5 8 0 0 14 bit c o n v e r s i o n s y s t e m : AN  2814 digital  16 c h a n n e l  convertor &  multiplexor  KENNEDY  MODEL  8/08  s y n c h r . digital taperecoraer ( 9 t r a c k IBM c o m p a t i b l e ) & BUFFER  FORMATTER  ( sampling interval  8208  AOiisec  )  27  concerning  changes i n gain s e t t i n g s of the a m p l i f i e r s or  changes i n charge s i z e s with i n c r e a s i n g d i s t a n c e  between  ships.  2.3  Two  DSS  P r o f i l e s and  Their  Locations  kinds of s e i s m i c l i n e s were recorded:  p r o f i l e s and  n e a r - v e r t i c a l incidence  former, the shooting  expanding  p r o f i l e s . For  ship detonated charges at i n c r e a s i n g  d i s t a n c e s from the r e c e i v i n g s h i p . Shot spacing f o r small charges  (0.9  kg)  charges  (1.4-2.3 kg)  r e f l e c t i o n s were recorded, (3.2-8. 1 kg)  l a r g e charges  the n e a r - v e r t i c a l i n c i d e n c e detonated 0.9  kg  was  0.2  km  at d i s t a n c e s where n e a r - v e r t i c a l  i n c i d e n c e r e f l e c t i o n s were a n t i c i p a t e d , 0.5 intermediate  the  and  km  for  where wide-angle  approximately  1 km  f o r the  used i n r e f r a c t i o n r e c o r d i n g . p r o f i l e s the  (2 lb) charges at 1 . 1 ,  shooting 0.9,  0.7  For  ship and  0.5  km  behind the s t a t i o n a r y r e c e i v i n g s h i p . A f t e r each set of four detonations l i n e and  the  the r e c e i v i n g s h i p moved along the procedure was  In AREA 1 , recorded. s h i p and the  recording  repeated.  a s i n g l e expanding p r o f i l e 20 km  long  was  Because of the d i r e c t i o n of d r i f t of the r e c e i v i n g the d e s i r e to have the shots detonated i n l i n e  hydrophone c a b l e , the p r o f i l e  was  run o b l i g u e to  the  with  28  r e f r a c t i o n l i n e s of the * HUDSON 70' experiment as shown i n F i g . 2.4a,upper. In ASEA 2, two p a r a l l e l of the l e n g t h s  reversed  profiles  18 and 15 km r e s p e c t i v e l y were recorded. They  were run along the base of the c o n t i n e n t a l s l o p e to determine the v e l o c i t y s t r u c t u r e and p o s s i b l e s l o p i n g of l a y e r s i n the area. v e r t i c a l incidence  As w e l l , a s i n g l e guasi-continuous nearprofile,  36 km long,  was recorded  across  the expanding p r o f i l e s i n order t o f o l l o w s t r a t i g r a p h i c changes of the s t r u c t u r e up the c o n t i n e n t a l (Fig.2.4b),  slope  In ABEA 3 two p r o f i l e s were recorded. An  expanding p r o f i l e over the sedimentary basin near the c o n t i n e n t a l slope  was run to determine l a y e r v e l o c i t i e s , and  a short n e a r - v e r t i c a l i n c i d e n c e ( F i g . 2.4a, l o w e r ) .  p r o f i l e perpendicular  to i t  The l a t t e r one was recorded i n order to  investigate uniformity  of the l o c a l  stratigraphy.  2.4 Examples of Observed Data  During the 1973 c r u i s e , source wavelets and seismograms from 240 shots were recorded. The g u a l i t y of the acquired data v a r i e d depending upon the p h y s i c a l c o n d i t i o n s f o r recording.  29  F i g u r e 2.4 D e t a i l e d Majjs of the L o c a t i o n s of the Seismic Profiles  a) Top - The s e i s m i c p r o f i l e s  of r e c o r d i n g i n AREA 1.  The s o l i d l i n e designated  with 73-1 i s the expanding  p r o f i l e . , T h e dotted l i n e s  are r e f r a c t i o n  profiles  from  HUDSON '70 experiment. D r i f t of the r e c e i v i n g s h i p i s shown by the s o l i d  dots.  Bottom - The s e i s m i c p r o f i l e s AREA 3.,Number 5 designates  of r e c o r d i n g from  the expanding  number 6 the n e a r - v e r t i c a l i n c i d e n c e  b) The s e i s m i c p r o f i l e s 2 and 3 designate  profile,  profile.  of r e c o r d i n g i n AREA 2. Number  the reversed  expanding  profiles,  number 4 the n e a r - v e r t i c a l i n c i d e n c e p r o f i l e . i s CSP p r o f i l e recorded  Line 37  by the G e o l o g i c a l Survey of  Canada i n 1975. (The map s e c t i o n s are parts of the Bathymetric  Map of the C o n t i n e n t a l Margin of Western  Canada, T i f f i n and Seeman,1975. Contours are i n meters.)  31  32  SHOOTING SHIP  An e x a m p l e o f a t y p i c a l  source s i g n a t u r e showing  s e g u e n c e o f b u b b l e p u l s e s i s g i v e n i n F i g . 2.5. signature was  was  r e c o r d e d d u r i n g t h e 1971  done e l e c t r i c a l l y  This  when  firing  and e x a c t s h o t i n s t a n t s were known. As  shown i n t h e d i a g r a m , t h e d i r e c t arrived  cruise  the  wave f r o m t h e e x p l o s i o n  6U msec a f t e r t h e s h o t i n s t a n t . The  peak o f o p p o s i t e p o l a r i t y  and  second  large  d e l a y e d by 7 msec, f o l l o w e d  i m m e d i a t e l y by h i g h f r e g u e n c y r e v e r b e r a t i o n s o f d e c a y i n g a m p l i t u d e s , c o r r e s p o n d s t o t h e wave f r o m t h e e x p l o s i o n was  reflected  i n t o the hydrophone from t h e sea  A f t e r an e x p l o s i o n , a gas b u b b l e r a p i d l y until  (Kramer  f o r m s and  and t h e a m b i e n t  expands  on  the  p r e s s u r e , and b e g i n s c o l l a p s i n g  e t a l . , 1 9 6 8 ) . Hhen i t r e a c h e s i t s minimum d i a m e t e r  and s t a r t s e x p a n d i n g a g a i n i t s e n d s a s i g n a l . (sec)  surface.  i t r e a c h e s i t s maximum d i a m e t e r , d e p e n d i n g  charge s i z e  which  of the f i r s t  b u b b l e c y c l e i s g i v e n by an  The  period  empirical  formula  T  B  = 2.I W  where 8 i s t h e c h a r g e w e i g h t (m)  (H  +  I0)  (2.4-1)  (kg) o f TNT,  and H i s t h e d e p t h  o f t h e c h a r g e d e t o n a t i o n ( W i e l a n d t , 1 9 7 5 ) . The  bubble p u l s e i s observed i n the f i g u r e  first  133 msec a f t e r  the  33  F i g u r e 2,5  A T y p i c a l Source Signature  The top t r a c e : a source waveform f o l l o w e d by a sequence of bubble p u l s e s .  The  bottom t r a c e : shot i n s t a n t s i g n a t u r e recorded i n  e l e c t r i c a l charge f i r i n g  i n 1.971.  recorded simultaneously on a two recorder.)  (Both t r a c e s are channel c h a r t  BUBBLE  PULSE  TRAIN  charge 10 lb  \fh> 64  —  133  ii 7  V 97  it 7  73  >h  II  7 65  msec SHOT TIME  BREAK  d e p t h : 45 m distance : 90 m  »1  35  direct  wave a r r i v a l . The c y c l e of expansion and  r e p e a t s a few times. However i n each of the  collapse  subsequent  p e r i o d s , the d i f f e r e n c e between the maximum and minimum diameter i s s m a l l e r due to the energy l o s s i n the gas bubble. The bubble p u l s a t e s f a s t e r and f a s t e r , and the s i g n a l amplitude decreases r a p i d l y u n t i l the gas bubble, migrating upwards, reaches the water s u r f a c e , and the remaining e n e r g y ' i s r e l e a s e d i n t o the a i r (Kramer et al.,1968). A whole t r a i n of such events can be observed i n 2.5.  Fig.  RECEIVING SHIP  As an example of the g u a l i t y of the n e a r - v e r t i c a l incidence r e f l e c t i o n  seismograms, a s i n g l e t r a c e t o g e t h e r  with the WWVB time code s i g n a l i s shown i n F i g . 2 . 6 . be seen that the s i g n a l / n o i s e r a t i o i s very good. The water  wave a r r i v e s f i r s t ;  I t can direct  the complexity of the waveform i s  due to bubble o s c i l l a t i o n s . The water bottom  reflection  a r r i v e s a l i t t l e more than 1 sec l a t e r . I t i s f o l l o w e d by a high frequency t r a i n of l a r g e amplitudes which correspond to r e f l e c t i o n s from w i t h i n the sediments. Any r e f l e c t i o n s from beneath the sediments would a r r i v e a f t e r second 3 ; they are difficult  to i d e n t i f y from a s i n g l e t r a c e r e c o r d . Toward the  end of the t r a c e , f i r s t order m u l t i p l e r e f l e c t i o n s from the  36  Figure  2.6 Example of a Seismic R e f l e c t i o n Trace  The t r a c e was recorded at the d i s t a n c e o f 2.5 km from the d e t o n a t i o n i n water o f depth 2.1 km. The f i r s t a r r i v a l i s the d i r e c t  water wave, t h e second major wave  t r a i n i s composed of r e f l e c t i o n s from the water and beneath, and the t h i r d t r a i n  bottom  ( a f t e r second 4) i s  due to f i r s t - o r d e r m u l t i p l e r e f l e c t i o n s .  (The t r a c e  below the s e i s m i c l i n e i s the WHVB time code s i g n a l . )  37  38  sea bottom and beneath give the t r a i n of r e v e r b e r a t i o n s which give r i s e to a sudden  i n c r e a s e i n amplitude.  F i g . 2.7 shows a s e c t i o n of f i v e r e f r a c t i o n  traces  recorded s i m u l t a n e o u s l y f o r one s h o t . The s i g n a l / n o i s e v a r i e s very l i t t l e  ratio  with d i f f e r e n t channels, A few s e i s m i c  events can be c l e a r l y c o r r e l a t e d over a l l the t r a c e s . In F i g . 2.8 a complete record s e c t i o n from the expanding p r o f i l e i n ABEA 3 i s shown t o demonstrate the q u a l i t y of s e i s m i c data which has been o b t a i n e d . F i g 2.8a shows mainly the r e f l e c t i o n  part of the p r o f i l e while F i g . 2.8b  i l l u s t r a t e s the r e f r a c t i o n p a r t . Amplitudes o f r e f l e c t e d waves from the upper sedimentary l a y e r s  ( F i g . 2.8a) are  overloaded as a r e s u l t of a m p l i f i e r gain s e t t i n g s chosen to enhance r e f l e c t i o n s from deeper h o r i z o n s . Coherent r e f l e c t i o n a r r i v a l s f o r at l e a s t  2 sec a f t e r the bottom  r e f l e c t i o n a r e c l e a r l y observed on the recorded data. The first  order m u l t i p l e r e f l e c t i o n s from the bottom  and beneath  are obvious at a time o f about 7 s e c and l a t e r . At d i s t a n c e s from 7 to 10 km  ( F i g . 2.8a) the t r a n s i t i o n from  reflection  a r r i v a l s t o r e f r a c t i o n a r r i v a l s i s c l e a r l y shown f o r a strong r e f l e c t o r as i n d i c a t e d i n the f i g u r e . The l a t t e r extend to n e a r l y 22 km  ( F i g . 2*8b), but the q u a l i t y of the  data d e t e r i o r a t e s due t o the use o f small charges and t o poorer p h y s i c a l c o n d i t i o n s at sea.  39  F i g u r e 2.7  Example of F i v e R e f r a c t i o n 2rac.es Recorded  Simultaneously  Charge of 6.8  kg  detonated at the  Darkened wavelets i n d i c a t e s e i s m i c a r r i v a l s . The bottom r e f l e c t i o n s  can  the  direct be  d i s t a n c e of  correlation  water wave and  of  18  possible  first  i d e n t i f i e d c l e a r l y by  high frequency content toward the  end  km.  of each  their trace.  SEISMIC  1  sec  WWVB  REFRACTION  TRACES  41  Figure  2.8  Example of a Becord S e c t i o n from the  Profile_in  Expanding  ABEA 3  a) R e f l e c t i o n p a r t : s e i s m i c a r r i v a l of the f i r s t  bottom  data shown from the r e f l e c t i o n s to beyond the  time f o r most f i r s t - o r d e r m u l t i p l e s  (7 sec and  later).  b) R e f r a c t i o n p a r t : the s t r a i g h t l i n e connects the direct  water wave a r r i v a l s and i t s slope g i v e s the  v e l o c i t y of sound i n water of about  1.5 km/sec. Numbers  near the t r a c e s r e f e r t o shot numbers. Arrows p o i n t out the c o n t i n u i t y of the deep c r u s t a l s e i s m i c a c r c s s the r e c o r d  arrivals  s e c t i o n . They can be followed  n e a r - v e r t i c a l incidence r e f r a c t i o n distances.  through wide-angle t o  Note the change i n the  s c a l e between a) and b) .  from  distance  42  73-5  D  km  43 1.5  6  8  10  12  14  D km  16  18  20  22  44  3 DATA PROCESSING AND ANALYSIS  Procedures digital  f o r handling the f i e l d  data and f o r i t s  processing are d i s c u s s e d i n t h i s chapter. By  a p p l y i n g t r a v e l t i m e and amplitude  c o r r e c t i o n s , normalized  r e c o r d s e c t i o n s - c a n be d i s p l a y e d f o r i n t e r p r e t a t i o n . The a p p l i c a t i o n of d i g i t a l  processing technigues  improves the  q u a l i t y of the data. This i n t u r n enables a c l e a r e r r e s o l u t i o n of the s e i s m i c phases and t h e i r throughout  the record s e c t i o n s .  3.1 f i e l d  The  correlation  Data and C o r r e c t i o n s  data recorded on the f i e l d  tapes were i n an  i m p r a c t i c a l form f o r immediate p r o c e s s i n g and s t o r i n g . The m u l t i c h a n n e l data had been m u l t i p l e x e d , w r i t t e n i n very s h o r t b l o c k s of 512 half-words,  and more than a minute of  data f o r each shot had been recorded  to ensure a complete  HWVB time code. Furthermore, the r e c o r d i n g d e n s i t y was 800 bytes per inch  (BPI) r a t h e r than the more standard  For the above reasons, the f i e l d demultiplexed, b l o c k i n g format  1600 BPI.  data were e d i t e d ,  and w r i t t e n on new tapes i n a convenient with the higher r e c o r d i n g d e n s i t y . The IBM  45  370/68 computer, o p e r a t i n g under the Michigan System  (MTS) a t the U n i v e r s i t y of B r i t i s h Columbia, was used  f o r a l l the d i g i t a l processing  ORIGIN TIME  The  Terminal  data  operations.  CORRECTIONS  r e g u i r e d c o r r e c t i o n s before they could be  d i s p l a y e d f o r a n a l y s i s , o r i g i n times of the s h o t s ,  obtained  from an FM playback of the s i n g l e hydrophone and WWVB s i g n a l s onto a two-channel c h a r t r e c o r d e r , had t o be c o r r e c t e d f o r the s h o t - t o - s h i p d i s t a n c e s . Although the shot i n s t a n t s could be timed t o b e t t e r than 5 msec on the c h a r t r e c o r d e r , an a d d i t i o n a l e r r o r of up t o 15 msec was i n t r o d u c e d by the a p p l i c a t i o n o f the s h o t - t o - s h i p s i n c e these  were • e y e b a l l  e r r o r i n determination f o r l a r g e r detonation Shot-receiver  1  estimated.  distances  (600 to 900 m).  d i s t a n c e s f o r each shot and hydrophone  assuming a constant  recorded  The maximum r e s u l t a n t  of the o r i g i n times was about 20 msec  were c a l c u l a t e d using d i r e c t and  distances  DWW  water wave  (DWW)  traveltimes  v e l o c i t y of 1.48 km/sec as  f o r the depth of about 45 m at the r e g u l a r west  c o a s t Ocean S t a t i o n P by Minkley associated  e t a l . ( 1 9 7 0 ) . The e r r o r  with these c a l c u l a t e d d i s t a n c e s i s l e s s than 3%.  46  TOPOGRAPHY CORRECTIONS  In most cases, topographic  c o r r e c t i o n s were not  r e q u i r e d s i n c e t h e r e were no s u b s t a n t i a l t o p o g r a p h i c a l changes along the p r o f i l e l i n e s as was shown by the continuous  fathometer records. The s i n g l e exception was the  73-4 p r o f i l e running  up the c o n t i n e n t a l s l o p e . However, i n  t h i s case a l s o , the topographic  c o r r e c t i o n s were not a p p l i e d  i n order t o be able t o f o l l o w the r i s i n g topography of the bottom and the shape of the l a y e r s beneath on the r e c o r d section.  AMPLITUDE CORRECTIONS  As i t was intended  to do an i n t e r p r e t a t i o n based on  both t r a v e l t i m e and amplitude i n f o r m a t i o n , c o r r e c t i o n s were necessary  f o r v a r i a t i o n s i n a m p l i f i e r g a i n s e t t i n g s , charge  s i z e s , and g e o m e t r i c a l  spreading.  In order t o keep the magnitude of amplitudes w i t h i n a d e f i n i t e range during r e c o r d i n g along a p r o f i l e , s i q n a l s from d i f f e r e n t d i s t a n c e s were a m p l i f i e d with gains. To get t r u e r e l a t i v e amplitudes,  different  a reference  l e v e l was chosen and a l l amplitudes were normalized The  gain to i t .  c o r r e c t i o n s f o r charge s i z e s were c a l c u l a t e d using  47  an  expression  O'Brien  based on s t u d i e s of underwater e x p l o s i o n s by  (1960). He has shown that f i r s t  seismic  arrival  2/3  amplitudes are p r o p o r t i o n a l t o 8 , where W i s the weight of the charge all  (kg). The c o r r e c t i o n egual t o 1/H  shots i n each  was a p p l i e d t o  profile.  As the energy t r a v e l s away from the e x p l o s i o n , the amplitudes of the s e i s m i c a r r i v a l s decrease. e p i c e n t r a l distance  With i n c r e a s i n g  (r) the wide-angle r e f l e c t i o n  amplitudes  decrease as 1/r- ( B r a i l e and Smith,1975), and the head wave amplitudes f o r < r e f r a c t i o n s as 1 / r  2  (Cerveny and  Havindra,1971); The record s e c t i o n s of wide-angle r e f l e c t i o n data  ( f o r d i s t a n c e s from 4 t o about 8 km) were c o r r e c t e d  using a c o r r e c t i o n f a c t o r egual t o r , and the s e c t i o n s of r e f r a c t i o n data  ( f o r greater d i s t a n c e s than 8 km)  using a  c o r r e c t i o n f a c t o r equal to r . Amplitude c o r r e c t i o n s were 2  not a p p l i e d t o the n e a r - v e r t i c a l i n c i d e n c e r e f l e c t i o n s i n c e amplitude i n f o r m a t i o n  was not used durinq  data  their  interpretation.  3« 2 Autopower Spectra  In order to determine the frequency recorded  content  of the  waveforms and seismic s i q n a l s , necessary f o r  f u r t h e r data p r o c e s s i n q , autopower s p e c t r a were computed  48  with the use-of a f a s t F i g . .3,-1 of  F o u r i e r transform a l g o r i t h m .  shows amplitude  normalized autopower s p e c t r a  some c h a r a c t e r i s t i c parts of s e i s m i c t r a c e s .  The  frequency content of the background n o i s e , the r e f r a c t i o n part of a s e i s m i c trace> r e f l e c t i o n s from beneath the sediments,  and f i r s t - o r d e r m u l t i p l e s from  and beneath are d i s p l a y e d . The background n o i s e Hz  ( F i g . 3.1a)  3.1b)  main freguency content of the  i s i n the i n t e r v a l from  with the maximum amplitude  (Fig.  the water bottom  0 to 20  at 2 Hz. The r e f r a c t i o n t r a c e  has the maximum amplitude  at about 10 Hz,  and  both r e f l e c t i o n t r a c e s ( F i g . 3.1c,d) show maxima between 20 and 30 Hz. Autopower s p e c t r a of primary r e f l e c t i o n s  from  w i t h i n the sediments were not i n v e s t i g a t e d because of amplitude  o v e r l o a d i n g as mentioned  3.3  Eand-pass F i l t e r i n g  Since the freguency r e f r a c t e d energy  earlier.  content of the r e f l e c t e d  and  i s c o n f i n e d to a c e r t a i n band of  f r e g u e n c i e s , d i g i t a l band-pass f i l t e r i n g  was  s i g n a l enhancement technigue. A zero-phase order, r e c u r s i v e . B u t t e r worth band-pass (Kanasewich,1973) was  a p p l i e d as a  s h i f t , fourth  filter  a p p l i e d t o the data.  E f f e c t s of the f i l t e r  f o r d i f f e r e n t frequency  bands on  49  Figure  3.1  amplitude Normalized  £fea£asig£i§^i£  a) Background  flutO£Ower  Spectra, of  Parts of Seismic Traces  noise,  b) r e f r a c t i o n t r a c e , c) r e f l e c t i o n s from beneath the sediments, d) f i r s t - o r d e r m u l t i p l e s of the water bottom and sedimentary l a y e r s .  (Seismic t r a c e s are d i s p l a y e d above, autopower below.)  spectra  50  51  a s i n g l e r e f l e c t i o n t r a c e , on a s e t of s i x r e f l e c t i o n and  traces  on a s e t of s i x r e f r a c t i o n t r a c e s are d i s p l a y e d i n F i g ,  3,2. The diagrams of r e f l e c t i o n data  ( F i g . 3.2a,b) show  c l e a r l y t h a t passbands of 2.5-30 Hz and 5-30 Hz enhance the s e i s m i c s i g n a l s while maintaining  t h e i r character. For  narrower bands of f r e q u e n c i e s , o s c i l l a t o r y e f f e c t s are observed and t h e i d e n t i f i c a t i o n o f the beginnings phases becomes d i f f i c u l t  i f not i m p o s s i b l e .  of s e i s m i c  Similar effects  are seen on the r e f r a c t i o n t r a c e s . The best enhancement of the s i g n a l s without  a d d i t i o n a l r i n g i n g has been  obtained  with 0.5-25 Hz and 2.5-30 Hz f i l t e r s . They g i v e t r a c e s clearly  distinguishable refraction  with  phases.  On the b a s i s of the examples j u s t shown and o t h e r s , passbands of 2.5-30 Hz f o r r e f l e c t i o n data and 0.5-25 Hz f o r r e f r a c t i o n data were chosen and the f i l t e r s the  were a p p l i e d t o  data.  3.3  Deconvolution  Decogvolution  i s used t o improve the g u a l i t y of  seismograms with r e v e r b e r a t i o n p a t t e r n s . The d e s i r a b l e r e s u l t from i t s a p p l i c a t i o n i s sharper a r r i v a l s , achieved s p i k e or p u l s e .  by shaping  r e s o l u t i o n of s e i s m i c  a reverberation into a single  52  Figure  3.2 Examples of the E f f e c t of Various Jjincl-Pass F i l t e r s  a) A s i n g l e r e f l e c t i o n t r a c e reflection  wavelet c h a r a c t e r  b) Six r e f l e c t i o n t r a c e s  (showing the i n f l u e n c e on and s i g n a l / n o i s e  (showing the change i n  g u a l i t y o f c o r r e l a t i o n across  c) S i x r e f r a c t i o n t r a c e s  ratio).  the t r a c e s ) .  (showing the change i n the  amplitude and t h e i r c o r r e l a t i o n with the band-width). Note that as the lower l i m i t of the passband the  increases,  t r a c e s f o r both r e f l e c t i o n and r e f r a c t i o n data  become more o s c i l l a t o r y such that i d e n t i f i c a t i o n of phases becomes more d i f f i c u l t .  53-  a)  i  «  t  i  i  4  5  6  7  8  sec  54  sec  c)  •  7  »  .  8  I  I  I  9  10  11  sec  56  It  was decided  to apply two d i f f e r e n t  techniques t o the r e f l e c t i o n  deconvolution  data; one i n the frequency  domain and one i n the time domain. In the frequency s p e c t r a l d i v i s i o n a l deconvolution simplicity  and because source  domain,  was chosen f o r i t s  wavelets  o f a good q u a l i t y  were a v a i l a b l e . In the time domain, spike d e c o n v o l u t i o n was chosen b e c a u s e ' i t can be used to c o n s i d e r changes of the source  wavelet  with  time.  SPECTBAL DIVISIONAL  DECONVOLUTION  The time domain model f o r the j - t h s e i s m i c t r a c e i s  S j Ct) = W Ct) * Tj (0 t nj (t)  where w (t) i s the source s i g n a t u r e f o r t h e p a r t i c u l a r rj (t) i s the impulse  response  noise sequence, and *  denotes c o n v o l u t i o n .  d e s c r i b e d by  shot,  of the t r a n s m i s s i o n path t o  the j - t h hydrophone, nj (t) i s a white  In the frequency  (3.3-1)  domain a s i n q l e s e i s m i c t r a c e i s  57  (3.3-2)  S(a) * W(u). R t » + N(<o)  where c a p i t a l l e t t e r s denote the F o u r i e r transforms of the v a r i a b l e s i n ( 3 . 3 - 1 ) . To o b t a i n the estimated response B, the spectrum the spectrum  impulse  of the s e i s m i c t r a c e i s d i v i d e d  by  of the source s i g n a t u r e w z  R =  S IWI.R +W*N — iwt W  (3.3-3)  2  where w' i s the complex conjugate of W. As the amplitude of the source s i g n a t u r e becomes s m a l l the f a c t o r  multiplying  the n o i s e component becomes i n c r e a s i n g l y l a r g e . T h e r e f o r e , to o b t a i n an estimated impulse response B which converges to the impulse response B, i t i s e s s e n t i a l t o e s t a b l i s h a minimum amplitude l e v e l f o r the source s i g n a t u r e i n order to l i m i t the g a i n of the d e c o n v o l u t i o n i n p a r t s of the seismogram where the t r a c e c o n t a i n s l i t t l e or no i n f o r m a t i o n . T h i s minimum source s i g n a t u r e amplitude W„ i s termed the w a t e r l e v e l (Helmberger For convenience  and Wiggins, 197 1) .  a r e l a t i v e w a t e r l e v e l TOL i s i n t r o d u c e d  and d e f i n e d as a f r a c t i o n of the maximum source s i g n a t u r e amplitude w : TOL=W /W^, (0-TC1-1). The estimate of mfl)(  0  impulse response B then becomes  58  R  Considering R,  «3.3-„  only the f a c t o r c o n t a i n i n g the impulse response  we can see that as the r e l a t i v e w a t e r l e v e l TOL  zero we  obtain u n r e s t r i c t e d deconvolution  t r a c e S by the source  s i g n a t u r e W.  of the  approaches seismic  As the parameter  TOL  approaches u n i t y , the estimator i s j u s t a s c a l e f a c t o r m u l t i p l i e d by the c r o s s c o r r e l a t i o n of S and W (Clayton, 1975) . U n r e s t r i c t e d deconvolution  attempts t o remove a l l of  the source e f f e c t s from the seismogram, and  the e s t i m a t o r R  g i v e s the best true impulse response. T h i s type of i s best f o r r e s o l v i n g t r a v e l t i m e s . The the l e a s t - s q u a r e s estimate (Helmberger and parameter TOL  estimator  crosscorrelation i s  of the a r r i v a l  amplitude  Wiggins,1971). T h i s means t h a t i f the  equals  u n i t y the best r e l a t i v e  r e s o l u t i o n i s obtained.  The  amplitude  w a t e r l e v e l can t h e r e f o r e be used  i n determining  the  p r e f e r r e d t r a d e - o f f between a r r i v a l  r e s o l u t i o n and  r e l a t i v e amplitude r e s o l u t i o n . These  time  c o n s i d e r a t i o n s suggest t h a t s p e c t r a l d i v i s i o n a l deconvolution should  of a s e i s m i c t r a c e f o r a range of  waterlavels  be attempted.  The  e f f e c t i v e n e s s of s p e c t r a l d i v i s i o n a l  a p p l i e d to the r e f l e c t i o n data  for different  deconvolution waterlevels  TOL  59  i s demonstrated deconvolved  i n F i g . 3 . 3 . A s e i s m i c r e f l e c t i o n t r a c e was  by a source s i g n a t u r e which c o n s i s t s of the  d i r e c t source wave a r r i v a l and the f i r s t  bubble pulse as  recorded f o r the p a r t i c u l a r shot. The source s i g n a t u r e was first  prefiltered  f o r the same passband  of f r e q u e n c i e s as  the s e i s m i c t r a c e i n order to avoid the i n t r o d u c t i o n of higher f r e q u e n c i e s i n t o the deconvolved was performed from  t r a c e . Deconvolution  f o r f i v e d i f f e r e n t w a t e r l e v e l s TOL of values  0.01 t o 1,0. In the f i g u r e , the deconvolved  compared with the f i l t e r e d the deconvolved quality. The  t r a c e s are  t r a c e . In none of the cases do  data show any s i g n i f i c a n t improvement i n  main reason that the data q u a l i t y has not improved  with the a p p l i c a t i o n c f s p e c t r a l d i v i s i o n a l d e c o n v o l u t i o n i s that the frequency content of the source s i q n a t u r e d r a s t i c a l l y changes as i t passes through the sediments and upper l a y e r s . Thus deconvolution using a source s i g n a t u r e recorded i n the water c l o s e to the source i s not p a r t i c u l a r l y e f f e c t i v e . The a p p l i c a t i o n o f a modified source s i g n a t u r e was c o n s i d e r e d , but s i n c e the c o n s t r u c t i o n of i t s t h e o r e t i c a l estimate without a d e t a i l e d knowledge of the upper c r u s t a l s t r u c t u r e i s extremely  difficult,  t h i s idea  was not r e a l i z e d . Another  reason f o r n e g l i g i b l e data improvement i s the  r a t h e r high noise l e v e l i n the freguency domain r e l a t i v e to  Figure 3.3  E f f e c t s of the S p e c t r a l D i v i s i o n a l Deconvolution  Reflection  The  Trace  filtered  d i r e c t source  source  signature  wave a r r i v a l and  Six various waterlevels deconvolving  the f i r s t  c o n s i s t s of a bubble pulse.  were used f o r  the t r a c e s e c t i o n c o n t a i n i n g deep c r u s t a l  r e f l e c t i o n s and layers.  (TOI)  (2.5-30 Hz)  f i r s t - o r d e r m u l t i p l e s from the upper  on  SOURCE WAVELET  (FILTERED)  SEISMIC TRACE  (FILTERED )  T  sec  62  the maximum s p e c t r a l amplitude of the source  signature.  N a t u r a l l y , i f the w a t e r l e v e l i s placed above the noise level,  most of the source  e f f e c t of d e c o n v o l u t i o n  s i g n a t u r e i s c u t o f f and the  i s weak. I f the w a t e r l e v e l i s placed  below the noise l e v e l the e f f e c t of deconvolution  i s largely  lost  SPIKE DECONVOLUTION  In spike deconvolution  we look f o r an i n v e r s e  filter  which when a p p l i e d to a s e i s m i c t r a c e i n c r e a s e s the r e s o l u t i o n o f s e i s m i c a r r i v a l s by shaping i n t o a s i n g l e s p i k e . Such a f i l t e r  the source  wavelet  i s u s u a l l y c a l l e d a spike  o p e r a t o r , and i t s c o e f f i c i e n t s are determined by the i n p u t source  wavelet and the d e s i r e d output  Spike source  deconvolution  wavelets:  first,  of a u n i t s p i k e .  was a p p l i e d with two d i f f e r e n t the recorded  source  s i g n a t u r e , and  then, v a r i b l e wavelets chosen from the s e i s m i c t r a c e .  63  A) Sgike Deconvolution  with a Source Signature  Spike deconvolution using the recorded source  wavelet  was a p p l i e d to the data i n order to o b t a i n a b a s i s f o r comparison of the e f f e c t i v e n e s s of spike deconvolutions constant and v a r i a b l e (time adaptive) operator was designed wavelet  The s p i k e  (2.5-30 Hz)  source  from a given shot using Robinson's modified  subroutine SPIKE of  f o r the f i l t e r e d  wavelets.  with  (Robinson,1967, p.79). The shaping  quality  the operator was t e s t e d by i t s a p p l i c a t i o n to the source  wavelet  and the r e s u l t s are d i s p l a y e d i n F i g . 3.4. The  operator produced a n e a r - i d e a l s p i k e as the output figure  as the  shows.  Fig.  3.5 i l l u s t r a t e s the a p p l i c a t i o n of the operator to  s e i s m i c t r a c e s . The deconvolved together with the unprocessed  t r a c e s are d i s p l a y e d  and f i l t e r e d data i n order to  e v a l u a t e the e f f e c t i v e n e s s of deconvolution. The  deconvolved  data show some r e d u c t i o n i n r e v e r b e r a t i o n compared with the unprocessed  data. However, the improvement i n the a r r i v a l  time r e s o l u t i o n i s not s i g n i f i c a n t  when compared  bandpass f i l t e r e d data. Conseguently, employing a v a r i a b l e source  wavelet  with the  a s e i s m i c model  was c o n s i d e r e d .  64  Figure  3.4  Characteristics  of the Shaping  Operator  gor Sjaike  Deconvolution  a) Input signature  - the p r e f i l t e r e d  (2.5-30 Hz) source  (for the 3 l b c h a r g e ) .  b) Output - a u n i t s p i k e delayed 53.2 msec middle  between the two maxima on the source  (in the wavelet).  (The parameters of the operator a r e : f i l t e r length=90,source Parzen  wavelet  length=50, l e n g t h of the  window=50, l i m i t f o r the spike position=18. The  l e n g t h s are given i n samples; sampling msec.)  i n t e r v a l i s 2.8  INPUT  66  Figure  3 . 5 Example of the A p p l i c a t i o n  £§£2222iu£ipji to a R e f l e c t i o n  of Spike  Seismpgram.  The s i g n a l r e s o l u t i o n of the deconvolved s e c t i o n i s compared with the r e s o l u t i o n of the u n f i l t e r e d and filtered  traces.  (The s i n g l e t r a c e  used to exemplify s p e c t r a l d i v i s i o n a l  d e c o n v o l u t i o n i n F i g . 3.4 was one from seismogram,)  this  SPIKE  BAND  PASS  FILTER  DECONVOLUTION  i  6  WITH  DECONVOLUTION  0.5-30 Hz  SOURCE  •  7  8 sec  68  B  )  Spike Deconvolution .with V a r i a b l e lavele,t  For s p i k e d e c o n v o l u t i o n with a v a r i a b l e wavelet, a segment of the s e i s m i c t r a c e was  used as the source wavelet.  Such a wavelet r e s u l t s from two-way t r a n s m i s s i o n of the source s i g n a t u r e through the l a y e r s of the c r u s t , and changes with each r e f l e c t i n g  h o r i z o n . The v a r i a b l e wavelet  i s the most probable s e i s m i c phase picked along the seismogram w i t h i n a p a r t i c u l a r time i n t e r v a l . Only those events are chosen which can be c o r r e l a t e d over the r e c o r d s e c t i o n or s i g n i f i c a n t  part of i t (at l e a s t 3 s h o t s ) . Thus  f o r a given i n t e r v a l the c o r r e l a t a b l e phases are chosen,  and  f o r each of them a spike operator i s designed. These are then i n d i v i d u a l l y a p p l i e d to the s e i s m i c t r a c e s . Such a procedure i s a s i m p l i f i e d approach t o more expensive time a d a p t i v e d e c o n v o l u t i o n i n which the wavelet changes c o n t i n u o u s l y with time as the o p e r a t o r i s being a p p l i e d along the t r a c e . The e f f e c t s of the d e c o n v o l u t i o n on the data are displayed i n F i g . 3.6.  Six examples of d e c o n v o l u t i o n with  d i f f e r e n t wavelets, chosen from the f i l t e r e d  reflection  r e c o r d , are shown. A n a l y s i s of the deconvolved t r a c e s r e v e a l s an improvement i n the r e s o l u t i o n of the seismograms f o r the i n t e r v a l from  Bhich  the wavelet was chosen. In  a d d i t i o n , there i s a general improvement i n the s i g n a l / n o i s e  69  F i g u r e 3 . 6 Example of the a p p l i c a t i o n of 8eson,yo.3,ution with §. V a r i a b l e Wavelet to Seisicoqrams  S i x d i f f e r e n t wavelets  picked along the uppermost t r a c e  of the bandpass f i l t e r e d data were used. The where a p a r t i c u l a r wavelet indicated.  The  was  location  picked and i t s shape are  numbers on subsequent  deconvolved  r e c o r d s show the time i n t e r v a l s corresponding t o the c h o i c e of  wavelet.  70  6  DECON 6  71  ratio. Since interval  t h e deep c r u s t a l  before  the f i r s t  water bottom  attempt to d e l i n e a t e seismic interval  r e f l e c t i o n s were e x p e c t e d i n t h e multiple a r r i v a l ,  phases p a r t i c u l a r l y  was made. The a p p l i c a t i o n o f s p i k e  with v a r i a b l e wavelet i n d i c a t e d t h a t time deconvolution  would  in this  deconvolution  adaptive  be t h e most a p p r o p r i a t e  method f o r s u c h  enhancement. I t i s p o s s i b l e t h a t any r e f l e c t i o n from deeper mantle  remove t h i s  arrivals  h o r i z o n s , s u c h a s M - d i s c o n t i n u i t y and  l a y e r s , a r e o b s c u r e d fay t h e bottom  should  time reasons t h i s  upper  m u l t i p l e . To  multiple, predictive deconvolution  Treitel,1969)  (Peacock  be a p p l i e d . However, f o r f i s c a l  was n o t a t t e m p t e d  an  as p a r t o f t h i s  and  and research  project.  3.4  Stacking of Refraction  Data  S t a c k i n g i s a s i g n a l enhancement t e c h n i g u e improves  t h e s i g n a l / n o i s e r a t i o and r e d u c e s t h e amount o f  d a t a t o be a n a l y s e d  while maintaining  information. I n order along  which  to stack  the seismic  multichannel  data,  summation  a p r e d e t e r m i n e d l a g t r a j e c t o r y i s p e r f o r m e d . The l a g  trajectory  i s defined  received at d i f f e r e n t  by t h e p a t h s o f s i g n a l s w h i c h a r e distances. For r e f r a c t i o n  arrivals,  72  the t r a j e c t o r y i s a s t r a i g h t l i n e . For s t a c k i n g of r e f r a c t i o n data, optimum v e l o c i t i e s f o r each seismic i m p l i e s a time-varying  phase should  be determined.  v e l o c i t y f o r s t a c k i n g . As  a l t e r n a t i v e to such a d i f f i c u l t using  stacking  various s t a c k i n g  This  an  procedure, stacked  traces  v e l o c i t i e s corresponding t o f i r s t  l a t e r seismic a r r i v a l s along  the  and  t r a c e s were computed. These  showed l i t t l e d i f f e r e n c e between them. T h i s i s a r e s u l t of the  f a c t that the s i x t r a c e s were recorded  d i s t a n c e of only 4 50  m and  over a t o t a l  that the v e l o c i t y c o n t r a s t at  the  ocean bottom r e f r a c t s a l l rays corresponding to head waves i n t o n e a r - v e r t i c a l paths. Thus the s t a c k i n g v e l o c i t y t o used was  not c r i t i c a l  and  so was  chosen to correspond  that v e l o c i t y determined from the f i r s t It  was  first  to  refraction arrivals.  determined from the slope of the l i n e connecting  the  r e f r a c t i o n a r r i v a l s which appeared most f r e q u e n t l y . The  s i x r e f r a c t i o n t r a c e s f o r each shot  qive a s i n q l e t r a c e . F i g . 3.7 r e f r a c t i o n record stacked  Seismic trace.  compares an  seismic  to  unstacked  s i g n a l s on the stacked  traces  t o improvement i n the s i g n a l / n o i s e  phase r e s o l u t i o n i s increased (As an example, note two  8 sec on the  were stacked  s e c t i o n with the corresponding s e c t i o n of  t r a c e s . The  are enhanced due  and  be  t r a c e f o r shot  along  distinct  each  ratio.  stacked  phases between 7  30 compared to a s i n g l e  t r a i n of amplitudes on the corresponding unstacked  traces.)  73  Figure  3.7 U n s t a c k e d  and Stacked E f f r a c t i o n  Record S e c t i o n s  AREA 1  a) Dnstacked s e c t i o n . The f i r s t  r e f r a c t i o n a r r i v a l s are  seen between 6 and 8 sec. The short high freguency wave t r a i n c o n s i s t s of the d i r e c t a r r i v a l s ; the l a r g e amplitude wave t r a i n a r r i v i n g l a t e r are r e f l e c t i o n s from the water bottom and below.  (Because o f the high  n o i s e l e v e l only exemplatory t r a c e s f o r each shot displayed  were  to be able t o f o l l o w each t r a c e on the  section.)  b)  S e c t i o n of the stacked  v e l o c i t y of 4.5 km/sec basement).  data with the s t a c k i n g  (a t y p i c a l v e l o c i t y f o r  S i x t r a c e s f o r each shot  give a s i n g l e trace.  were stacked to  from  73 - 1  a)  D  km  ro -  SUBROUTINE:  "STACK"  73-1  b)  - 2 H LU CO  00  u~>.  H  1^  8  T  9  CNJ  Cvl  —I—  r 11  10  CM  CM  in CM  CD CM  'T— r "T~ IS 15 14 12 DISTANCE (KM) V  00  ~r16  o cn  CO CM  CM  CM  17  -r—  18  19  I 20  76  However, because  o f g r e a t e r i n t e r v a l s between s t a c k e d  traces  some o f t h e r e f r a c t i o n a r r i v a l s a r e more d i f f i c u l t t o c o r r e l a t e across stacked  the seismic s e c t i o n . Therefore,  both  and u n s t a c k e d s e c t i o n s were u s e d f o r f u r t h e r  i n t e r p r e t a t i o n , d e p e n d i n g on p r o c e d u r e s b e i n g  followed.  3,5 V e l o c i t y A n a l y s i s o f R e f l e c t i o n D a t a  A computational  method u s i n g v e l o c i t y  spectra  considered  t o determine the l a y e r v e l o c i t i e s  reflection  record s e c t i o n s of expanding p r o f i l e s .  was  from t h e A  velocity  spectrum i s a g r a p h i c a l d i s p l a y of the r e f l e c t i o n energy  as  a f u n c t i o n o f t h e n o r m a l i n c i d e n c e t r a v e l t i m e and t h e average root-mean-sguare was d e f i n e d  by D i x (1955)  (ms)  n  =  The  rms-velocity  as n  V  velocity.  '  z  n  (3.5-1)  *  Zr.,; where V i s t h e a v e r a g e r m s - v e l o c i t y f r o m t h e s u r f a c e down t o n  the  bottom o f t h e n-th l a y e r , v i s t h e i n t e r v a l v e l o c i t y o f  the  i - t h l a y e r , and T j i s t h e two-way  f  0)  normal  incidence  t r a v e l t i m e i n t h e i - t h l a y e r . The v e l o c i t y s p e c t r a e n a b l e us t o m e a s u r e t h e power c f r e f l e c t i o n s a r r i v i n g v a r i o u s p a t h s d e t e r m i n e d by t h e i r  according  time-distance  to  77  relationships. Approximating p a r t s of expanding  the l a g t r a j e c t o r y f o r the r e f l e c t i n g p r o f i l e s by a hyperbola, the time-  d i s t a n c e r e l a t i o n s h i p can be expressed i n the form  * T n = o,n 2  Xj  where T  X)n  T  +  X  2  —T  (3.5-2)  i s the two-way t r a v e l t i m e f o r a s h o t - t o - r e c e i v e r  d i s t a n c e X, and the l a y e r n, T  on  i s the v e r t i c a l two-way  t r a v e l t i m e , and V f i s the s t a c k i n g v e l o c i t y . s  How  much t h i s  s t a c k i n g v e l o c i t y d i f f e r s from the t r u e r m s - v e l o c i t y depends on the value of the spread-length/depth r a t i o . A l C h a l a b i (1973) has shown t h a t f o r values l e s s than 1 the d i s c r e p a n c y i s l e s s than 0.5$.  and f o r values l e s s than 2.0  i t i s less  than 2%, .In our case, s i n c e the depth of water was more than 2 km,  only the r e f l e c t i o n a r r i v a l s from the  4 km d i s t a n c e were used f o r determination of the In of  always first  velocities.  order to d i s p l a y the r e f l e c t i o n energy i n the form  v e l o c i t y s p e c t r a , measures of the coherency of the s i g n a l  along h y p e r b o l i c paths defined by  (3.5-2) are used.  After  the alignment o f • t h e i n p u t data with r e s p e c t to a given h y p e r b o l i c delay p a t t e r n , a simple d i g i t a l f i l t e r selectively  that would  pass events common to a l l t r a c e s i s computed f o r  each t r a c e . Then, these are stacked together t o g i v e the best estimate of the i n p u t s i g n a l . The power of t h i s  78  estimate i s then computed w i t h i n a s p e c i f i e d around  time gate  the r e f e r e n c e time and t h i s power i s d i s p l a y e d . In  order to generate a v e l o c i t y spectrum, the s e i s m i c t r a c e s are swept with v a r i o u s hyperbolas determined by the v e l o c i t i e s i n a-chosen i n t e r v a l f o r the same r e f e r e n c e time. Then another r e f e r e n c e time point i s chosen at a time i n t e r v a l egual t o h a l f the s p e c i f i e d  time gate and the  procedure i s repeated. The coherency  measures express i n a  g u a n t i t i v e form'the l i k e n e s s of the data content among data channels. A computer program f o r d e r i v i n g and  displaying  v e l o c i t y s p e c t r a with the use of d i f f e r e n t measures of the coherency of s i g n a l s was  w r i t t e n , A f o r t r a n l i s t i n g of the  program i s i n the Appendix, Three d i f f e r e n t technigues f o r measurement of coherency along h y p e r b o l i c paths were a p p l i e d : summation, unnormalized c r o s s c o r r e l a t i o n semblance c o e f f i c i e n t . A l l three are time and the l a t t e r two  and  domain-technigues  are w e l l d e s c r i b e d by N e i d e l and  Taner  (1971). Summation i s a coherency measure g i v i n g an e s t i m a t e of t o t a l s i g n a l amplitude w i t h i n a p a r t i c u l a r time gate. I t i s o b t a i n e d by simple summing of the s i g n a l amplitudes or t h e i r powers w i t h i n the gate. Unnormalized  cross-correlation  measure i s egual t o h a l f the d i f f e r e n c e between the t o t a l energy and s i g n a l energy  within the gate. Semblance  c o e f f i c i e n t i s d e f i n e d as the r a t i o of s i g n a l energy t o t o t a l energy w i t h i n the gate. The r e s u l t s obtained by t h e i r  79  use were compared. An advantage  of semblance i s that i t  r e g u i r e s a s m a l l e r dynamic range f o r the d i s p l a y of the t o t a l s i g n a l amplitude than summation or unnormalized c o r r e l a t i o n , when s i g n a l / n o i s e r a t i o s remain unity  ( N e i d e l l and Taner,1971).  r e s o l u t i o n compared with the two chosen  g r e a t e r than  Since i t a l s o had the best other t e c h n i q u e s , i t was  f o r the g e n e r a t i o n of v e l o c i t y s p e c t r a . To  the use of the coherency  are given here: time  gate 56 msec, time step 14 msec, minimum v e l o c i t y  The semblance was shot  10 km,  v e l o c i t y step 0.1  used at f i r s t  1.4 km/sec.  f o r data from a s i n g l e  (6 s e i s m i c t r a c e s ) , and then f o r the f i r s t  neighbouring shots  illustrate  measures as they were a p p l i e d to  our d a t a , the c h a r a c t e r i s t i c parameters  km/sec, maximum v e l o c i t y  cross-  four  (24 s e i s m i c t r a c e s ) . The former one i s  d i s p l a y e d i n F i g . 3.8. the v e l o c i t y s p e c t r a  The computer program f o r d i s p l a y i n g  was  designed to i n c r e a s e the  spectrum  r e s o l u t i o n by s p i k i n g the coherency measure amplitude. In s p i t e of that the spectrum  r e s o l u t i o n i n the f i g u r e i s poor.  The amplitudes have a tendency to spread along the v e l o c i t y a x i s without showing a s i n g l e peak maximum. T h i s means t h a t the measure of coherency  does not have a sharp s i n g l e  maximum within the corresponding time gate. T h i s i s due to the s m a l l time d i f f e r e n c e s between the ray-paths to the i n d i v i d u a l hydrophones and  (the l a y e r depths  were about 2500 m  more while the hydrophones sere only 90 m a p a r t ) .  The  Figure  3.8  V e l o c i t y Spectrum f o r Six Seismic  Traces of the P r o f i l e  Reflection  73-5  The spectrum i s shown at the top. I t was obtained  using  semblance c o e f f i c i e n t as the measure of coherency of the s i g n a l distances  across  s i x s e i s m i c t r a c e s recorded  near 2.5 km.  One of the t r a c e s i s d i s p l a y e d  at the bottom of the f i g u r e . 7.5  at  The s e c t i o n between  5 and  sec (two-way) t r a v e l t i m e was chosen because deep  crustal reflections seismic  a r r i v e i n t h i s i n t e r v a l . The  a r r i v a l s S1 and S2, and the f i r s t  multiple W  water bottom  from the t r a c e appear c l e a r l y i n the  spectrum. The remaining peaks i n the spectrum are mostly deformed and do not give v e l o c i t i e s which could be a s s o c i a t e d  with the deep c r u s t a l  reflections.  81  82  r e s u l t s obtained by a p p l y i n g the semblance t o a group of shots d i d not show the necessary c o n s i s t e n c y . The i n a c c u r a c y i n determination of the o r i g i n times f o r i n d i v i d u a l  shots  (10-20 msec) l i m i t e d the e f f e c t i v e n e s s of the crosscorrelation  procedure.  Since the computer d e r i v e d s p e c t r a are not s e n s i t i v e to i n d i v i d u a l s e i s m i c t r a c e s ( d i s p l a y i n g the s i g n a l of the stack) and  t h e i r v e l o c i t y r e s o l u t i o n was  kind of data we had, i t was t r a v e l t i m e sguared (Dix,1955) was  poor f o r the  abandoned. A simpler method of  versus d i s t a n c e squared  adopted  coherency  ( T - X ) graphs  for velocity analysis  2  2  and  i n t e r p r e t a t i o n of the r e f l e c t i o n data. The method i s e x p l a i n e d and  presented together with the i n t e r p r e t a t i o n cf  the data i n the f o l l o w i n g c h a p t e r .  83  U INTERPRETATION  • 1 Methods of I n t e r pr et a t i on  In order t o o b t a i n crust  an i n i t i a l  i n each area of r e c o r d i n g ,  were f i r s t  interpreted  model of the o c e a n i c  seismic r e f r a c t i o n a r r i v a l s  . For t h i s , both t r a v e l t i m e  amplitude i n f o r m a t i o n were used by a p p l i c a t i o n of p l o t s and s y n t h e t i c initial  and traveltime  seismograms . A f t e r e s t a b l i s h i n g the  r e f r a c t i o n models, the r e f l e c t i o n data were  interpreted, using T - X 2  2  layer  v e l o c i t i e s and t h i c k n e s s e s were computed  l i n e s with a p p l i c a t i o n of the l e a s t - s g u a r e s  method. F i n a l l y , d e t a i l e d  velocity-depth  models based on the  r e f l e c t i o n and r e f r a c t i o n data are presented and t h e i r geological  implications  TRAVELTIME  The  are g i v e n .  INTERPRETATION  simplest  - REFRACTION  DATA  method used f o r the i n t e r p r e t a t i o n of  marine r e f r a c t i o n data i s the s l o p e - i n t e r c e p t (Ewing,1963) which uses t r a v e l t i m e  method  p l o t s . The method i s  84  b a s e d on a s e i s m i c  model c o n s i s t i n g o f homogeneous  h o r i z o n t a l l a y e r s where w i t h  i n c r e a s i n g depth  subsequent l a y e r has a higher applicability  velocity-depth  method s o m e t i m e s may l e a d  to  artificial  models.  traveltime  velocity-depth arrival  v e l o c i t y . Because o f t h e non-  i n c e r t a i n s i t u a t i o n s of these assumptions the  slope-intercept  The  each  p l o t s used t o d e r i v e  models were c o n s t r u c t e d  the i n i t i a l  from r e f r a c t i o n  p i c k s made on c o m p u t e r p l o t t e d s e i s m o g r a m s . The  maximum e r r o r i n t i m i n g  of the a r r i v a l  p i c k s was a b o u t 15  msec due t o t h e l o w s i g n a l / n o i s e r a t i o on some t r a c e s . Therefore, origin  together  times,  with  the error associated  the estimated  with t h e  maximum t r a v e l t i m e e r r o r was  a b o u t 35 msec. An Fig.  example of a t r a v e l t i m e - d i s t a n c e  4 . 1 . The s t r a i g h t l i n e s  refraction arrival each l i n e  plot i s given i n  are l e a s t sguare f i t s  p o i n t s . The r e c i p r o c a l o f t h e s l o p e f o r  i s the r e f r a c t i o n v e l o c i t y of t h e c o r r e s p o n d i n g  l a y e r ; the time i n t e r c e p t determines the l a y e r The  velocity-depth  models f o r t h e g e n e r a t i o n  seismograms c o n s i s t e n t amplitudes.  thickness.  m o d e l s b a s e d on t h e s e p a r a m e t e r s were  t h e n used as i n i t i a l  and  to the  with  of synthetic  the observed t r a v e l t i m e  curves  85  TRAVELTIME AND  AMPLITUDE INTERPRETATION-REFRACTION DATA  The i n t e r p r e t a t i o n c f s e i s m i c body waves c o n s i s t s of f i n d i n g a range of v e l o c i t y - d e p t h models which would  match  the observed t r a v e l t i u e and amplitude i n f o r m a t i o n . The number of models which are c o n s i s t e n t with the t r a v e l t i m e s of s e i s m i c a r r i v a l s i s g e n e r a l l y q u i t e l a r g e  (McMechan and  Wiggins, 1972; Wiggins and Helmberger, 1973; Bessonova e t a l . , 1 9 7 4 ) . However, the number i s c o n s i d e r a b l y reduced by the requirement of t h e i r c o n s i s t e n c y with the observed amplitudes  (Helmberger and Wiggins,1971; Wiggins and  Helmberger,1973;  Fuchs and Muller,1971).  The computer programs used f o r d e r i v a t i o n o f s y n t h e t i c seismograms i n t h i s work are based on the d i s c ray theory i n t r o d u c e d by Wiggins guantized ray theory d i s c ray theory  (1976). The method was derived from (Wiggins and Madrid,1974), and named  (DRT) because the model of wave propagation  i s given i n terms of planar d i s c s guided by r a y s . In order to generate s y n t h e t i c seismograms both t r a v e l t i m e and amplitude i n f o r m a t i o n the  matching  initial  v e l o c i t y - d e p t h models were expressed i n terms of ray parameter versus e p i c e n t r a l d i s t a n c e  (p-A) c u r v e s . These  were d e r i v e d with the use of a computer r o u t i n e MDLPLT by Wiggins. Using a s p e c i f i e d  called  velocity-depth  and a d i g i t i z e d source wavelet as i n p u t , the program  model  g e n e r a t e s t r a v e l t i m e c u r v e s , p-A c u r v e s and s y n t h e t i c s e i s m o g r a m s a s t h e o u t p u t . To t e s t f o r c o n s i s t e n c y , t h e computed  t r a v e l t i m e c u r v e s were compared  o n e s . The p - A - v a l u e s  were t h e n u s e d  computer program c a l l e d  From  the i n i t i a l  s y n t h e t i c seismograms compared curves  as i n p u t f o r the  HBGLTZ , a l s o by W i g g i n s .  For t h e i n t e r p r e t a t i o n followed.  with the observed  a trial-and-error  was  p-A c u r v e , t r a v e l t i m e c u r v e s and  were g e n e r a t e d  with the observed  procedure  u s i n g HRGLTZ a n d  d a t a . I f n e c e s s a r y , t h e p^A  s e r e m o d i f i e d t o match t h e a m p l i t u d e s a n d t h e  calculation  repeated  u n t i l t h e s y n t h e t i c seismograms  c o n s i s t e n t w i t h t h e recorded data. Since both and a m p l i t u d e s  were  traveltimes  were t c be m a t c h e d , a t r a d e - o f f b e t w e e n t h e  two was s o m e t i m e s n e c e s s a r y . E x a m p l e s o f a s e t o f s t a c k e d s e i s m o g r a m s and o f a s y n t h e t i c r e c o r d s e c t i o n a r e shown i n Fig.  4 . 3 a n d F i g . 4 i 9 . The r e s u l t a n t  derived  from t h e r e f r a c t i o n  models o b t a i n e d from data.  v e l o c i t y - d e p t h models  d a t a were used  a s a check  on t h e  the i n t e r p r e t a t i o n of the r e f l e c t i o n  87  TBAVELTIME INTEBPBETAIION - REFLECTION DATA  I f seismic distances,  t r a c e s are d i s p l a y e d  according t o t h e i r  r e f l e c t i o n a r r i v a l s from common r e f l e c t o r s appear  along p a r t i c u l a r h y p e r b o l i c traveltime  paths. When p l o t t e d as a  sguared versus d i s t a n c e  squared  ( T - X ) graph, 2  they give s t r a i g h t l i n e s of d i f f e r e n t slopes The  r e c i p r o c a l s of the slopes  v e l o c i t i e s from the surface  2  and i n t e r c e p t s .  determine the average rms-  to the bottom of a p a r t i c u l a r  r e f l e c t o r , and the i n t e r c e p t s determine the normal  incidence  a r r i v a l times and hence the depth t o the r e f l e c t o r s (Dix,1955). I t should be mentioned t h a t , a r r i v a l s on the record X  2  s i n c e the time  s e c t i o n are picked  method i s a s u b j e c t i v e  v i s u a l l y , the T 2  one and i t s accuracy l a r g e l y  depends on the i n t e r p r e t e r ' s a b i l i t y to recognize and c o r r e l a t e the r e f l e c t i o n a r r i v a l s on seismograms. From the average  (surface t o r e f l e c t o r ) r m s - v e l o c i t i e s  times determined from the T - X 2  2  and i n t e r c e p t  graphs, the true rms-  v e l o c i t i e s and t h i c k n e s s e s o f i n d i v i d u a l l a y e r s can be calculated. Let the average r m s - v e l o c i t y the  from the s u r f a c e  down t o  top of the k-th l a y e r be V_, . The corresponding normal  incidence  k  two-way t r a v e l t i m e  i s T^, . From the surface  bottom o f t h e k-th l a y e r they are V Then a c c o r d i n g t o the expression  k  and T  k  to the  respectively.  (3.5-1) the i n t e r v a l rms-  88  v e l o c i t y f o r the k-th l a y e r i s given by  The  d e t a i l e d v e l o c i t y - d e p t h models obtained from the  r e f l e c t i o n data are based  4  The  data from  •2  on such  analyses.  V e l o c i t y - d e p t h Models  ARIA 1 were analysed f i r s t i n order t o  compare the r e s u l t s with a p r e v i o u s l y known r e f r a c t i o n model. AREA 3 was approached next because the q u a l i t y of the r e f l e c t i o n data was best and the c r u s t a l s t r u c t u r e i n the area was presumably more normal than that of AREA 2 . T h e r e f o r e , i n t e r p r e t a t i o n was expected t o be more s t r a i g h t f o r w a r d . A f t e r a c g u i r i n g experience from  these  i n t e r p r e t a t i o n s , the data from the more t e c t o n i c a l l y AREA 2 were analysed and i n t e r p r e t e d .  complex  89  AREA 1  S i n c e t h e r e f l e c t i o n d a t a f r o m AREA 1 were o f p o o r g u a l i t y , only the r e f r a c t i o n part was i n t e r p r e t e d ; traveltime  the record  of the expanding p r o f i l e  section  i s shown i n F i g . 3.7. A  p l o t b a s e d on t h e a n a l y s i s  of individual  traces  was u s e d f o r t h e i n t e r p r e t a t i o n and t h e r e s u l t i n g v e l o c i t y depth  model compared w i t h  t h e model o f Keen a n d  (1971) f r o m t h e *HUDSCN 7 0 ' s e i s m i c  Barrett  survey i n the area ( F i g .  2.4a) . The a n a l y s i s that:  plot  ( F i g . 4.1)  1) t h e r e f r a c t i o n s f r o m t h e s e d i m e n t s were  observed as f i r s t the  of the traveltime  two b r a n c h e s o f v e l o c i t i e s  4.0 and 5.5 km/sec, t h e r e f r a c t i o n s as f i r s t  never  a r r i v a l s ; 2) t h e r e f r a c t i o n a r r i v a l s f r o m  basement g i v e a c u r v e w i t h  appeared  shows  o f v e l o c i t y 4.0  a r r i v a l s over a short distance  km/sec  interval  (8-10 km); 3) t h e r e f r a c t i o n s f r o m t h e o c e a n i c l a y e r appeared (from the  as f i r s t  p r o f i l e was t o o s h o r t t o o b s e r v e upper  first  of p r o f i l e  10 t o 20 km) and gave t h e v e l o c i t y o f 6.8 km/sec; 4)  refractions.  In general,  to distinguish  mantle  the phases o f the  a r r i v a l s from t h o s e a r r i v i n g i m m e d i a t e l y a f t e r  difficult. arrivals to  a r r i v a l s f o r most o f t h e l e n g t h  In p a r t i c u l a r to distinguish the oceanic  was layer  f r o m t h e b a s e m e n t r e f r a c t i o n s f o r d i s t a n c e s f r o m 10  17 km was a p r o b l e m . T h e i r  clear separation  could  be  90  F i g u r e 4.1 T r a v e l t i m e - Distance P l o t 12-1  of the I n f r a c t i o n  Profile  from ABEA J '  The  l i n e s correspond  to i n d i v i d u a l  The  a s s o c i a t e d v e l o c i t i e s are given i n km/sec a t t h e i r  ends. L i n e with the v e l o c i t y  refracting  horizons.  2.4 km/sec corresponds  to  the sediments, l i n e s with v e l o c i t i e s of 4.0 and 5.5 km/sec to the upper and lower p a r t of the faesement, and l i n e with the v e l o c i t y layer.  of 6.8 km/sec to the oceanic  (The l i n e s are l e a s t - s g u a r e f i t s t o the observed  a r r i v a l times.)  73-1 2.4  Distance [km]  92  f o l l o w e d only near the end of p r o f i l e  (from  17 t o 20 km).  There i s a p o s s i b i l i t y of a v e l o c i t y g r a d i e n t i n the basement l a y e r which i s i n d i c a t e d by a dashed l i n e connecting  the branches of the basement t r a v e l t i m e curve  between 12 and 15 km. The v e l o c i t y - d e p t h model based on t h i s t r a v e l t i m e p l o t i s compared with the 'HUDSON 70* model i n Table symbols V and H i n the t a b l e , are v e l o c i t y layer thickness  (km)<respectively.  1. The  (km/sec) and  The e r r o r s given i n c l u d e  the t i m i n g e r r o r s (from p i c k i n g the i n d i v i d u a l a r r i v a l s ) and the standard  d e v i a t i o n s (from the l i n e f i t s t o t h e picked  points).  TABLE 1 * ENDEAVOUR 73* Layer Sediment Basement Oceanic  a b  V  H  2.4±,2 4.7* 4.0±.2 5.5±.2 6.8±.2  0.6±.2 2.4 1.1±.3 1.5±.4  *HUDS0N 70* V  H  2.3** 4,5*  0.5 1.6-2.4  6.7-7.0  4.7*  • I n d i c a t e s an average value, ** an assumed  value.  The mean value of 4,5 km/sec f o r the basement v e l o c i t y in  'HUDSON-70* model assumes a v e l o c i t y g r a d i e n t f o r the  l a y e r from 4.0 t o 5.5 km/sec. I n our case, assuming t h a t there i s a v e l o c i t y g r a d i e n t  (between 4,0 and 5 , 5 km/sec) i n  93  the  basement  km/sec. layer  The a v e r a g e  value  a mean v e l o c i t y  f o r the t h i c k n e s s  i n *HUDSON 70* model a s p r e s e n t e d  consider station  an anomalous v a l u e  layer  from  could  profile  our p r o f i l e .  In  enough  of the recorded  was t h e  of the oceanic  o f the small  data,  a t the north  i n o u r model b e c a u s e t h e refractions.  amount and p o o r  t h e v e l o c i t y - d e p t h model o f  1 shows good agreement w i t h  Keen and B a r r e t t  station  to observe mantle  conclusion, i n spite  guality  h e r e does n o t  The t h i c k n e s s  n o t be d e t e r m i n e d  was n o t l o n g  Tnis  o f 4.7  of the oceanic  o f 8.5 km r e c o r d e d  on one o f t h e p r o f i l e s .  furthest  ASIA  l a y e r , we have o b t a i n e d  t h e » HUDSON 70• model o f  (1971).  AREA 3  The i n i t i a l northern the Fig.  v e l o c i t y - d e p t h model f o r AREA 3 i n t h e  Cascadia  refraction 2.8b. From  Basin  part o f the expanding  plot  as f i r s t  indicate  a possibility  with  was c o n s t r u c t e d  73-5 shown i n  seismic traces a  ( F i g . 4.2). I t  1) t h e r e f r a c t i o n s f r o m t h e s e d i m e n t s were n o t  observed  layers  profile  the analysis of i n d i v i d u a l  traveltime-distance shows t h a t  was based on t h e i n t e r p r e t a t i o n o f  arrivals;  velocities  as s e c o n d a r y  arrivals  they  o f two d i s t i n g u i s h a b l e s e d i m e n t a r y o f 1.9 and 2.4 km/sec;  2) t h e  94  F i g u r e 4.2 Reduced T r a v e l t i m e - Distance P l o t of the R e f r a c t i o n P r o f i l e 73-5 from AREA 3  A t y p i c a l v e l o c i t y of 4.5 km/sec f o r basement l a y e r was used to reduce the t r a v e l t i m e s . The s m a l l numbers beside the data p o i n t s are the shot numbers. The associated of each  v e l o c i t i e s i n km/sec are given at the end  line.  K  in I  CO  i  8  ~t  1-  L  9  96  r e f r a c t i o n a r r i v a l s with the v e l o c i t y of 4.0 km/sec d i d not appear as f i r s t shots  a r r i v a l s but are c l e a r l y d i s t i n g u i s h a b l e on  18,20 and 21; 3) the r e f r a c t i o n s g i v i n g the v e l o c i t y  of 4.4 km/sec basement showed as f i r s t a r r i v a l s only over a short d i s t a n c e i n t e r v a l  between 8 and 11 km; 4) the  r e f r a c t i o n s from the oceanic  l a y e r appeared as f i r s t  a r r i v a l s a t a d i s t a n c e s of about 16 km and could be followed to the end of the p r o f i l e at the d i s t a n c e of 22 km; 5) the profile A  was not long enough t o observe the r e f r a c t i o n s from  the H - d i s c o n t i n u i t y , From the slopes and i n t e r c e p t s of the t r a v e l t i m e  lines,  the v e l o c i t i e s and depths of the l a y e r s were determined and the i n i t i a l v e l o c i t y - d e p t h model i s presented  i n Table  2.  TABLE 2 Layer description water Sediment Basement Oceanic  a b a b  v  V  H  1.5 1.9 2.4 4.0 4.4 6.7  2.5 1.3 0.7 0.7 1.7  The symbols V and fl i n the t a b l e are v e l o c i t y (km/sec) and  thickness  (km) r e s p e c t i v e l y . T h i s i n i t i a l  model was used f o r the generation  velocity-depth  of s y n t h e t i c seismograms.  97  The s e c t i o n of the s y n t h e t i c seismograms i s compared with the stacked recorded data i n F i g . 4.3. The r e f r a c t i o n a r r i v a l s with t h e v e l o c i t i e s of 2.4 km/sec (lower sediments), 4.4 km/sec (basement) and 6.7 km/sec (oceanic layer)  are observed on both s e c t i o n s . The upper  sediment  a r r i v a l s with the v e l o c i t y of 1.9 km/sec and the r e f r a c t i o n s from the t r a n s i t i o n between the sediments and the basement do not appear  on the s y n t h e t i c seismograms. The former c o u l d  be e x p l a i n e d by a p o s s i b i l i t y that there i s a s m a l l v e l o c i t y g r a d i e n t i n the sediments caused  ( s l i g h t changes i n the amplitudes  by such g r a d i e n t would be d i f f i c u l t  s m a l l amplitudes.)  t o observe on  The l a t t e r could be e x p l a i n e d s i m i l a r l y  by a s m a l l v e l o c i t y g r a d i e n t i n the upper p a r t o f the basement. Another  p o s s i b l e e x p l a n a t i o n i s that the. v e l o c i t y  corresponds to an i r r e g u l a r t r a n s i t i o n l a y e r with an average t h i c k n e s s l e s s than the l i m i t of the HRG1TZ program r e s o l u t i o n f o r the given v e l o c i t y wavelet  freguency  (4.0 km/sec) and the input  (12 Hz). The r e s u l t s of attempts to  generate these a r r i v a l s would i n d i c a t e t h i s . was  modelled  0.7 km t h i c k  When the l a y e r  (value c a l c u l a t e d from the  t r a v e l t i m e p l o t ) , i t was not p o s s i b l e t o match t h e generated r e f r a c t i o n s from the oceanic l a y e r with those recorded. The match of these was achieved only when the t r a n s i t i o n was modelled as a t h i n l a y e r  (0.3 km). However, such a t h i n  l a y e r d i d not give any observable r e f r a c t i o n s on the  98  Figure  4.3 Comparison o f the Observed and S y n t h e t i c S e c t i o n s Of B e f r a c t i o n P r o f i l e  Seismograms  73-5  L e f t - r e c o r d s e c t i o n of stacked  seismograms.  Bight - r e c o r d s e c t i o n of s y n t h e t i c seismograms.  (5s d i s c u s s e d  i n the t e x t , the a r r i v a l s with  v e l o c i t i e s of 1.9 km/sec and 4.0 km/sec from the s e c t i o n of stacked  seismograms c o u l d not be i n c l u d e d r  i n the s e c t i o n of s y n t h e t i c seismograms.)  •5 -  6 '  1  6 1  1  o  T  [SEC) 8  10  11  12  •  1  1  i  100  s y n t h e t i c seismograms. F i g . 4.4 shows the record s e c t i o n of the f i l t e r e d r e f l e c t i o n data from the expanding p r o f i l e 73-5, and F i g . . 4.5 the record s e c t i o n of the f i l t e r e d data from the nearv e r t i c a l i n c i d e n c e r e f l e c t i o n p r o f i l e 73-6. Coherent a r r i v a l s from i n d i v i d u a l  seismic  r e f l e c t i n g h o r i z o n s can be  d i s t i n g u i s h e d and c o r r e l a t e d  on p a r t s of e i t h e r  o r both  profiles. A series  o f sedimentary r e f l e c t i o n s  arrives  within the  time i n t e r v a l of about 1.7 sec (two-way) t r a v e l t i m e the  first  water bottom r e f l e c t i o n . The f i r s t  reflections  after  identifiable  from w i t h i n the sediments a r e from the  r e f l e c t i n g h o r i z o n A. T h i s r e f l e c t o r  can be f o l l o w e d  clearly  along the s e c t i o n 73-6 and i s c h a r a c t e r i z e d by a sudden change i n both freguency and amplitude. Following the c o n t i n u i t y o f t h i s horizon on the expanding p r o f i l e 73-5 i s d i f f i c u l t because the amplitudes i n t h i s time i n t e r v a l were often distorted amplifiers  due t o the high g a i n s e t t i n g s of the  as mentioned b e f o r e . T h e a r r i v a l s from  reflecting  h o r i z o n B on the expanding p r o f i l e a r e easy t o i d e n t i f y along the s e c t i o n . The r e f l e c t i n g h o r i z o n C can be f o l l o w e d c l e a r l y on s e c t i o n 73-5, but i t s i d e n t i f i c a t i o n on s e c t i o n 73-6  i s more d i f f i c u l t .  near-vertical  Horizons D and E which show on the  i n c i d e n c e r e f l e c t i o n seismograms on both  s e c t i o n s are i m p o s s i b l e to f o l l o w beyond the d i s t a n c e of 3 km.  101  F i g u r e 4.4  Record S e c t i o n of the . E x p a n d i n g R g f i g c t i o n £rof_ile  7 3 - 5 from AREA 3  The water depth was 2 . 5 filtered  (2.5-30  km.  The data were bandpass  Hz). The l e t t e r s d e s i g n a t e r e f l e c t i n g  h o r i z o n s : W- r e f l e c t i o n from the water bottom, A t o Creflections  from sedimentary h o r i z o n s , D to G-  reflections  from the top of the basement and beneath.  The primed l e t t e r s designate f i r s t - o r d e r these r e f l e c t i o n s . waves as f i r s t  m u l t i p l e s of  (Note the emergence of the r e f r a c t e d  a r r i v a l s between 8 and 10  km.)  73-5  D  km  103  Figure  4 . 5 Record Profile  The  Section  7 3 - 6 from  letters  identified  text.)  Subcritical  AREA 3  d e s i g n a t e t h e same p r i m a r y on t h e e x p a n d i n g  (The i n d i v i d u a l the  of the Quasi-continuous  arrivals  profile  reflections  73-5 i n F i g . 4.4.  are discussed  in detail i n  104  T sec  b  105  A r r i v a l s from horizon F,  which appear i n the  of p o s s i b l e basement r e f l e c t i o n s , are and  can  be c o r r e l a t e d  although they are  to the  less clear  end  of the 73-6.  on  r e f l e c t i o n a r r i v a l s which can  be  appear again and  expanding p r o f i l e ,  Horizon G g i v e s  i t is difficult  wide-angle seismograms,  f o r t h e - d i s t a n c e s between 3 and  about 5 km.  After  from t h i s h o r i z o n appear i n the oceanic l a y e r to c o r r e l a t e  they  which f o l l o w c l o s e l y end  of  the  refractions the  first  reflection  arrive  and arrivals  time i n t e r v a l waere  r e f l e c t i o n s could be with the  to  t h a t they  almost s i m u l t a n e o u s l y with other r e f l e c t i o n phases cannot be d i s t i n g u i s h e d from them. The  near-  particularly  i n t e r v a l from 7 to 9 km  i n the  73-6  section  d i s t i n g u i s h e d on the  v e r t i c a l i n c i d e n c e seismograms, but i d e n t i f y them on the  c l e a r on  interval  the  expected. They a l s o from the o c e a n i c  seem  layer  (basement) a r r i v a l s at  the  expanding p r o f i l e .  A l s o , f i r s t - o r d e r m u l t i p l e s of the same h o r i z o n s can  be  e a s i l y d i s t i n g u i s h e d on  s e i s m i c record s e c t i o n  73-5.  m u l t i p l e paths through l a y e r s distinguishable,  however the  The  first  might be  used i n the  the  makes the  interpretation  the  of  phases even more  amplitudes are  r e f l e c t i o n s were not  from  expanding  f i l t e r i n g effect  These m u l t i p l e r e f l e c t i o n a r r i v a l s and with the  reflections  their  attenuated. correlation  analysed, although they to c o n f i r m the  results  106  A T -X 2  2  graph f o r the r e f l e c t i o n a r r i v a l s of p r o f i l e  73-5 was c o n s t r u c t e d  to determine the average r m s - v e l o c i t i e s  of the l a y e r s . From the average v e l o c i t i e s and i n t e r c e p t times,  the i n t e r v a l v e l o c i t i e s and t h i c k n e s s e s o f i n d i v i d u a l  l a y e r s were computed with the use of the l e a s t - s g u a r e method. F i g . 4.6 shows s t r a i g h t l i n e f i t s corresponding the r e f l e c t i o n  to  a r r i v a l s along h y p e r b o l i c t r a j e c t o r i e s on the  expanding p r o f i l e s e c t i o n i n F i g . 4.4. The most r e l i a b l e i n f o r m a t i o n should curves  be obtained  from the f i r s t  p a r t of the  (to about 9 km ), where the h y p e r b o l i c approximation 2  of l a g t r a j e c t o r i e s i s most  accurate.  The values of the i n t e r v a l v e l o c i t i e s and l a y e r t h i c k n e s s e s d e r i v e d from the T - X z  Table  z  graph are presented i n  3 of F i g . 4.7. As w e l l , the i n t e r v a l v e l o c i t i e s of the  upper c r u s t l a y e r s determined from the s e i s m i c r e c o r d i n g i n the southern are entered  Cascadia  Basin near 44°N (Seely e t al.,1974)  i n the t a b l e . They compare w e l l with our v a l u e s .  The f i g u r e a l s o shows a comparison of the r e f l e c t i o n and the r e f r a c t i o n v e l o c i t y - d e p t h models f o r AREA 3 i n the northern Cascadia  Basin. The models agree w e l l f o r the sedimentary  seguence. Since i t was not p o s s i b l e t c c o r r e l a t e the a r r i v a l s from the uppermost r e f l e c t i n g h o r i z o n A on the expanding p r o f i l e *  i t s interval velocity  was assumed to be  that of the r e f r a c t i o n model f o r the upper sediments. The seguence of the r e f l e c t i o n horizons  A,B and C could be  107  \  Figure  4.6  T£-X£ Graph  f o r the  Expandinding  Reflection  Profile  7 3-5  The  individual  letters  corresponding  record  section  picked  visually.  and  lines  and  accompanied  \  to the  The  rms  by  latter their  designated  by  The  arrival  fcrraer the  associated  are  on  points  were computed  along  capital  same r e f l e c t o r s  average v e l o c i t i e s  (sec)  method. The  the  are  i n Fig.4.4.  i n t e r c e p t times  least-sguare  V  reflectors  ordinate. standard  were  (km/sec)  using  given  the  the  along Both  the  are  deviations.  108  109  F i g u r e 4.7 V e l o c i t y - Depth Model f o r AREA 3  Symbols V and H i n Table 3 , i n d i c a t e l a y e r (km/sec) and t h i c k n e s s (km) r e s p e c t i v e l y .  velocity Symbol V*  i n d i c a t e s l a y e r v e l o c i t y recorded i n the southern part of the Cascadia Basin near 44°N  (seely e t  al.,1974). The s o l i d l i n e shows the r e f r a c t i o n model, the dashed l i n e the r e f l e c t i o n model. The l e t t e r s designate the bottoms of i n d i v i d u a l r e f l e c t i n g h o r i z o n s and correspond to the r e f l e c t i o n s observed i n F i g . 4.4 and 4.5.  VELOCITY  -  DEPTH  MODEL  VEL.  1  2  3 •  (km/sec)  4  5 i  i  6  7  i  i  TABLE 3  Reflecting horizon  V  H  V  W  W A B C D E F G  's  6  1' G  1  1. 48 1. 90* 2. 21 2.33 2. 63 U. 5 6 3i 78 4.'4 3  •Indicates  2.5 .30* .50 .48 .60 .41 .40 1.5  an e s t i m a t e d  1. 83 2. 13 2. 68 3. 96  value.  111  modelled on the r e f r a c t i o n  model by a v e l o c i t y g r a d i e n t  from  1.9 to 2.4 km/sec i n the upper sediments, The tops of the r e f l e c t i n g h o r i z o n s D and E are at the same depth as the tops of the corresponding l a y e r s  on the r e f r a c t i o n model.  The t r a n s i t i o n between the sediments and the basement (previously  suggested i n the a n a l y s i s  of the r e f r a c t i o n  t r a v e l t i m e c u r v e s ) h a s t«o d i s t i n c t l a y e r s model; a high v e l o c i t y low v e l o c i t y l a y e r  layer  i n the r e f l e c t i o n  (4.56 km/sec) a t the top and a  (3.78 km/sec) at the bottom. (The  v e l o c i t y of 3.78 km/sec compares with the v e l o c i t y of 3.96 km/sec, the h i g h e s t v e l o c i t y recorded f o r the sediments i n the  Southern Cascadia Basin.) The top of the basement  i s a t the same depth on both models. As w e l l ,  layer  the v e l o c i t y  and t h i c k n e s s of the basement as determined from the r e f l e c t i o n s and r e f r a c t i o n s  are the same. The deepest  r e f l e c t i o n s i n the model are those a r r i v i n g from the top of the  oceanic l a y e r ; In  the  c o n c l u s i o n , the comparison  velocity structure  determined from the r e f l e c t i o n  i n f o r m a t i o n i s quite d e t a i l e d structures  of both models shows that  yet agrees with the v e l o c i t y  obtained from the r e f r a c t i o n  data.  112  AREA2  Three s e i s m i c p a r a l l e l reversed  p r o f i l e s were recorded expanding p r o f i l e s  in AREA 2 :  15 and  18 km  long,  a quasi-continuous n e a r - v e r t i c a l i n c i d e n c e r e f l e c t i o n profile  36 km  long  ( F i g . 2.4b). A reduced  two  cross-  traveltime-  distance  p l o t based on the a n a l y s i s of seismograms from  reversed  p r o f i l e s i s shown i n F i g . 4.8.  d i s t i n g u i s h a b l e l a y e r s with a s s o c i a t e d 2.1,  3.0  and  4.2  and  the  Four c l e a r l y v e l o c i t i e s of  km/sec were observed on  1.8,  seismograms from  both p r o f i l e s . R e f r a c t i o n a r r i v a l s g i v i n g a v e l o c i t y of km/sec were observed at the end  of the SE p r o f i l e . Only  r e f r a c t i o n s from the basement and observed as f i r s t  6.8  the oceanic  a r r i v a l s cn the r e c o r d  a r r i v a l s g i v i n g a v e l o c i t y of 3.4  l a y e r were  section.  Seismic  km/sec appeared on the  SE  profile. The  i n i t i a l r e f r a c t i o n velocity-depth  calculated  using  the t r a v e l t i m e curves of F i g . 4.8  presented i n Table 4 on the next page. The in  the  (km)  t a b l e are v e l o c i t y (km/sec) and  r e s p e c t i v e l y . The  o v e r a l l thickness reversed  model  was and  i t is  symbols V and  layer  H  thicknesses  r e f r a c t i c n model shows that  of sediments i s n e a r l y constant  the along  the  p r o f i l e . R e f r a c t i o n a r r i v a l s having a phase  v e l o c i t y of 3.4  km/sec might correspond to a high v e l o c i t y  sediment l a y e r l y i n g on  the top of the basement.  113  Figure  4.8  Reduced I I a y e l t i m e - D i s t a n c e  fieffaction  Profiles  £lot of the Two  73-2 3 from AREA 2 a  The  t r a v e l t i m e i s reduced with the v e l o c i t y  The  numbers give the v e l o c i t i e s  4.5  p o i n t s f o r p r o f i l e 73-2 73-3.  and  km/sec.  (km/sec) d e r i v e d  the s l o p e s of t r a v e l t i m e l i n e s . Crosses r e f e r  points for p r o f i l e  Reversed  c i r c l e s refer  to  to data  from data  115 TABLE 4 Layer description Water Sediment a b c d Base ment Oceanic Its  V  H'H-station H  SE-station H  1.5  2. 0  2.0  1.8 2. 1 3.0 3.4 4. 2 6. 8  0.7 0.8 0.7  0.5 0.6 0.9 0.4 2.1  2. 2  t h i c k n e s s i s only 0.4  km and i t was observed  only on the  SE p r o f i l e . The basement i s s i t u a t e d at the depth of 2.4 km below the sea bottom and i t s t h i c k n e s s i s about 2.1 km. o c e a n i c l a y e r has a v e l o c i t y of 6.8  The  km, but i t s t h i c k n e s s  could not be determined s i n c e the p r o f i l e s were not long enough to o b t a i n r e f r a c t i o n a r r i v a l s from the Hidisc ontinuity. This i n i t i a l  r e f r a c t i o n model was used f o r the  g e n e r a t i o n of s y n t h e t i c seismograms using HEGLTZ computer program. A l l s e i s m i c a r r i v a l s could be modelled with the s y n t h e t i c seismograms except  the a r r i v a l s with v e l o c i t y of  3.4 km/sec. The l a y e r with t h i s v e l o c i t y was too t h i n to be modelled f o r the given i n p u t wavelet. The s e c t i o n of s y n t h e t i c seismograms i s compared stacked observed  with the s e c t i o n of  seismograms i n F i g . 4.9. The  initial  r e f r a c t i o n model of Table 4 was f u r t h e r used to check the model obtained  from the a n a l y s i s of the r e f l e c t i o n  data.  The expanding r e f l e c t i o n p r o f i l e 73-2 i s d i s p l a y e d i n Fig.  4. 10. The g u a l i t y of the data i s poor and c o r r e l a t i o n  116  F i g u r e 4.9 Comparison of the Observed a.nd S y n t h e t i c Seismograms of the R e f r a c t i o n P r o f i l e 73-2  L e f t - r e c o r d s e c t i o n of the observed  seismograms.-  R i g h t - r e c o r d s e c t i o n of s y n t h e t i c seismograms.  117  T  (StC) to  IS  118  Figure 4,10 Record s e c t i o n o f the Expanding R e f l e c t i o n  Profile  7 3-2 from AREA 2  The l e t t e r s i n d i c a t e horizons, the  a r r i v a l s from the i n d i v i d u a l  (They are not intended t o be c o r r e l a t e d  with  h o r i z o n s of AREA 3.) With the p o s s i b l e e x c e p t i o n of  h o r i z o n F, a l l other r e f l e c t i o n s  a r e from w i t h i n  sediments, W* i s the f i r s t - o r d e r  m u l t i p l e of the water  bottom  reflection.  119  73-2  T  1  1  1  2  1  1  3  1  1  1  1  4  D  km  5  1  1  6  1  1  7  1  120  of i n d i v i d u a l  s e i s m i c phases along the  extremely d i f f i c u l t . s e c t i o n of the the  The  guality  of  whole p r o f i l e i s  the  reflection  reversed expanding p r o f i l e was  s e c t i o n was  not  used i n the  even worse  interpretation.  (Bad  c o n d i t i o n s during r e c o r d i n g i n t h i s area s e v e r e l y the  guality  of  the  reflections.)  a r r i v a l s from horizons C and  In F i g .  D can  be  4.11,  easily  and  the  detailed  a n a l y s i s of  individual  e r r o r i n p i c k i n g the corresponding T - X 2  and  2  for  other h o r i z o n s r e q u i r e d a  about ±25  overall  msec.  graph i s shown i n F i g . 4.11.  i n t e r c e p t s of the  limited  identify  seismograms. The  a r r i v a l s was  weather  identified  i n c i d e n c e r e f l e c t i o n d i s t a n c e s . To phases from the  and  reflection  near-vertical correlate  record  The The  slopes  l i n e f i t s corresponding to the  picked  a r r i v a l s were computed d i r e c t l y  with the  use  of the  least-  sguare method. The  comparison of the  r e f l e c t i o n and  the  refraction  v e l o c i t y - d e p t h models f o r AREA 2 i s shown in F i g . 4.12, agreement between the  models i s e x c e l l e n t . The  v e l o c i t i e s of horizons A and  1.9  and  2.4  km/sec average the  B,  and  C and  D.  The  upper sediments, d e r i v e d from the km/sec. The refractors  v e l o c i t i e s and and  of the  t h i c k n e s s e s of  the  r e f l e c t i n g h o r i z o n s are  i d e n t i c a l . They g i v e an average v e l o c i t y f o r the  lower sediments. There are  refraction  velocities  average v e l o c i t y reflection  two  for  model, i s  of the 1.99  lower sediment almost  of about 3.1  low  The  velocity  km/sec layers  121  F i g u r e 4.11 ££•-!£ Graph f o r the Expanding fief l e c t i o n P r o f i l e 73 2  The l e t t e r s designate l i n e s corresponding to the reflectors  on the record s e c t i o n i n F i g , 10. The  average v e l o c i t i e s  (km/sec) and the i n t e r c e p t  rms  times  ( s e c ) , both accompanied by t h e i r a s s o c i a t e d standard d e v i a t i o n s , are given along the l i n e s and,the o r d i n a t e respectively. observed  (The l i n e s are l e a s t - s g u a r e f i t s t o the  data p o i n t s . )  123  F i g u r e 4.12  V e l o c i t y - D e p t h ijodel from the Bottom of the  C o n t i n e n t a l Slope i n AREA 2  In the diagram, the s o l i d l i n e shows the r e f r a c t i o n model, the dotted l i n e the r e f l e c t i o n letters  designate  model. The  the bottoms of the i n d i v i d u a l l a y e r s .  In Table 5, the symbols V and H i n d i c a t e l a y e r (km/sec) and t h i c k n e s s  (km)  respectively.  \  velocity  VELOCITY  -  DEPTH  MODEL  Velocity 1 i  2 i  3 i  TABLE 5  km/sec 4  i  5 i  6 i  7  Reflecting horizon  V  H  W  1. 48  2.0  A  1. 92  .35  B  1. 74  . 20  C  2. 25  .31  D  2. 04  .34  E  2. 92  .79  F  3.34  .45  i  1  to  125  w i t h i n the upper sediments, 1.72  horizon B with the v e l o c i t y of  km/sec and h o r i z o n D with the v e l o c i t y  2.04  Both are s i t u a t e d below the h o r i z o n s of higher There i s a pronounced change i n the v e l o c i t y  km/sec. velocity.  (0.9 km/sec) a t  the boundary between the upper and lower sediments. deepest  r e f l e c t i o n s observed  The  are from the top of the  basement. The q u a s i - c o n t i n u o u s n e a r - v e r t i c a l i n c i d e n c e r e f l e c t i o n p r o f i l e 73-6,  which c r o s s e s the r e v e r s e d p r o f i l e at r i g h t  angles i s d i s p l a y e d i n F i g . 4.13. observed  on the expanding  The r e f l e c t i o n  p r o f i l e 73-5  seismograms of the p r o f i l e 73-6  from  arrivals  can be i d e n t i f i e d  on  the bottom of the  c o n t i n e n t a l s l o p e . To f o l l o w the a r r i v a l s from  individual  l a y e r s going up the s l o p e i s extremely d i f f i c u l t  because of  the i n c r e a s e d number of m u l t i p l e s i n t e r f e r i n g with the r e f l e c t i o n a r r i v a l s . The l a y e r v e l o c i t i e s d e r i v e d from expanding  reflection  the  p r o f i l e at the bottom of the s l o p e were  used to convert the t r a v e l t i m e s e c t i o n t o a depth-varying s t r u c t u r a l model of the c o n t i n e n t a l s l o p e i n AREA 2. T h i s model i s presented G e o l o g i c a l Survey  together with CSP  of Canada i n F i g . 4.14.  l o c a t i o n of the DSS 1973  p r o f i l e and CSP  The  relative 37 recorded i n  p r o f i l e i n d i c a t e s the  of a number of h o r i z o n t a l l y  h o r i z o n s w i t h i n the sediments.  The  l i n e no.  i s shown i n F i g . ,2.4b. The CSP  presence  l i n e 37 of the  stratified  DSS  reflection  model suggests s i x  126  F i g u r e 4. 13 p.u a s i - c o n t i n u o u s Sub c r i t i c a l  R e f l e c t i o n P r o f i l e , 73-  4 from Along t h e C o n t i n e n t a l Slope i n AREA 2  The  r e f l e c t i o n a r r i v a l s c o r r e l a t e with the a r r i v a l s on  the expanding r e f l e c t i o n p r o f i l e 73-2, f o r which the l o c a t i o n i s shown, and are designated l e t t e r s . W i s the f i r s t »»*  by the same  water bottom r e f l e c t i o n ,  W,  and H' ' are the m u l t i p l e s . (Because of the number 1  of m u l t i p l e s the c o r r e l a t i o n of i n d i v i d u a l along the record s e c t i o n i s d i f f i c u l t , impossible. made.)  reflectors  some places  In s p i t e of t h a t , an attempt has been  127  T (sec)  128  F i g u r e 4.14 Comparison o f the V e l o c i t y S t r u c t u r e Mod,el of Sediments from  the C o n t i n e n t a l Slope with the CSP  Profile  The l e t t e r s i n the model designate the r e f l e c t i n g h o r i z o n s . T h e i r corresponding v e l o c i t i e s are presented i n Table 5 of F i g . 4.11. The CSP p r o f i l e i s part of L i n e 37 recorded by the G e o l o g i c a l Survey o f Canada. (The r e l a t i v e F i g . 2.4b.)  l o c a t i o n of the two p r o f i l e s i s shown i n  1-29  QUEEN CHARLOTTE E C  SOUND  -CONTINENTAL SLOPE -  o-  DISTANCE 10 ->  15 1  (km) 20 1  ZS 1  30 1  35 i_  130  such h o r i z o n s with v a r i o u s v e l o c i t i e s . There i s an i n d i c a t i o n of r i s i n g or t h i c k e n i n g of the basement with the r i s e o f the c o n t i n e n t a l slope i t should be emphasized t h a t the v e l o c i t y s t r u c t u r e presented  i n F i g . 4.14 i s very  t e n t a t i v e . In s p i t e of t h i s , i t does y i e l d some a d d i t i o n a l i n f o r m a t i o n about the approximate t h i c k n e s s e s of the sediment l a y e r s observed  on the CSP p r o f i l e . ,  4.3 D i s c u s s i o n  The  of  the R e s u l t s  i n t e r p r e t a t i o n of the data depends on the methods  of a n a l y s i s and the amount and g u a l i t y o f the data. The standard techniques of i n t e r p r e t a t i o n , such as f i t t i n g t r a v e l t i m e curves f o r the r e f r a c t i o n data , and T - X 2  f o r the r e f l e c t i o n r e c o r d s , determined depth  the f i n a l  2  graphs  velocity-  models. The  s y n t h e t i c seismogram amplitude  a n a l y s i s of the  r e f r a c t i o n data d i d not give any a d d i t i o n a l i n f o r m a t i o n . The r e f r a c t i o n p r o f i l e s were too short f o r s u b s t a n t i a l  amplitude  v a r i a t i o n . The computer programs used to generate the s y n t h e t i c seismograms were near t h e i r l i m i t s of r e s o l u t i o n (for the given i n p u t wavelet) l a y e r s were modelled,  when some o f the t h i n  crustal  and d i d not show the corresponding  a r r i v a l s . The s y n t h e t i c s d i d confirm the r e a l i t y  of the  131  b a s i c r e f r a c t i n g l a y e r s obtained from the observed t r a v e l t i m e curves. The models i n a l l three areas extend to the top o f the o c e a n i c l a y e r . The expanding were too short to observe  only  profiles  M-disccntinuity refractions. A l l  of the f i n a l r e f r a c t i o n v e l o c i t y - d e p t h models a r e c r e d i b l e i n s p i t e of the poor g u a l i t y o f the data i n some a r e a s . The poorest records were obtained from  AREA 1, but s i n c e a  p r e v i o u s l y p u b l i s h e d s e i s m i c model agreed  w e l l with the  presented i n t e r p r e t a t i o n , the r e s u l t s were c o n s i d e r e d adeguate. A modern method of v e l o c i t y a n a l y s i s using computer derived  v e l o c i t y s p e c t r a was a p p l i e d t o the r e f l e c t i o n  but i t proved  t o be u n s u c c e s s f u l f o r reasons  s e c t i o n 3.5. However, the simpler T - X z  2  data,  mentioned i n  method was adeguate  f o r r e f l e c t i o n data of the type and g u a l i t y obtained i n t h i s t h e s i s . The s e i s m i c phases were mostly determined  with  accuracy ±10 msec. An exception was AREA 2 where the e r r o r was about ±25 msec. For the deepest the area  r e f l e c t o r observed i n  ( r e f l e c t o r F o f the v e l o c i t y 3.34 km/sec), t h i s  amounts to 40 m, a value near the l i m i t s of r e s o l u t i o n of the r e c o r d i n g .  132  ^•^  The  R e l a t i o n t o Regional Geology  c o n t i n e n t a l margin of western Canada l i e s w i t h i n a  t e c t o n i c a l l y a c t i v e part of the earth's the t r i p l e  c r u s t which i n c l u d e s  j u n c t i o n of the P a c i f i c , American and Juan de  Fuca p l a t e s . T y p i c a l f o r the area i s : 1) f a u l t i n g  parallel  to the c o n t i n e n t a l margin; 2) changes i n the c h a r a c t e r of the c o n t i n e n t a l s h e l f from north j u n c t i o n ; 3) marginal basins  t o south across  the t r i p l e  to the west of the c o n t i n e n t a l  s l o p e ; 4) quaternary volcanism at the base of the c o n t i n e n t a l s l o p e ; 5) and i n t e r a c t i o n of t e c t o n i c deformation and P l e i s t o c e n e The  margin i s d i v i s i b l e  glaciation. i n t o three  (Chase et a l . , 1 9 7 5 ) : a northern  tectonic  regions  r e g i o n from Dixon Entrance  to Queen C h a r l o t t e Sound • ( c h a r a c t e r i z e d by s t r i k e - s l i p f a u l t i n g ) ; a c e n t r a l region from Queen C h a r l o t t e Brooks Peninsula  on Vancouver I s l a n d  ( c h a r a c t e r i z e d by  f a u l t i n g and f o l d i n g ) ; and a southern region Peninsula  t o Juan de Fuca S t r a i t  Sound t o  from Brooks  ( c h a r a c t e r i z e d by slow  subduction). Each of the areas o f the DSS r e c o r d i n g s i t u a t e d i n one of the t e c t o n i c r e g i o n s ,  ( F i g . 1.1) was  AREA 1 i s west o f  the Queen C h a r l o t t e Trough i n the northern  r e g i o n ; AREA 2 i s  west o f the c e n t r a l part of Queen C h a r l o t t e Sound, i n the c e n t r a l t e c t o n i c r e g i o n ; AREA 3 i s i n the northern  part o f  133  Cascadia  Basin, i n the southern  ABEA 1 served of the DSS  t e c t o n i c region.  only as a convenient  technigue  and  was  new  testing  not of p a r t i c u l a r g e o l o g i c a l  i n t e r e s t to us. Since the recorded not y i e l d any  area f o r the  data  from the area d i d  i n f o r m a t i o n , the geology of the area  not be d i s c u s s e d i n the t h e s i s . The  will  geophysical  c h a r a c t e r i s t i c s of the area are given fay Keen and  Barrett  (1971); the o v e r a l l geology of the t e c t o n i c r e g i o n i s d i s c u s s e d by Chase et a l . (1975). ABEA 2 i s s i t u a t e d at the base of the c o n t i n e n t a l slope between J . Tuzo Wilson southern  Knolls  (to the north) and  canyon of Queen C h a r l o t t e Sound  (to the  the southeast).  Recent f i n d i n g s of young v o l c a n i c m a t e r i a l  (Tiffin,1974,GSC  Beport of A c t i v i t i e s )  K n o l l s prove  at the J . Tuzo Wilson  t h a t there i s v o l c a n i c a c t i v i t y canyon i s the l a r g e s t trough  i n the area.  The  southern  i n Queen C h a r l o t t e Sound. I t  c u t s the c o n t i n e n t a l slope thus p r o v i d i n g a channel f o r t r a n s p o r t a t i o n of the sediments from across the sound to base o f the s l o p e . The  age of the sediments i n Queen  C h a r l o t t e Sound ranges from P l e i s t o c e n e through Upper and Harlequin  and  Osprey c f S h e l l Canada L t d . ;  have been subjected volcanism  and  (luternauer,1972)  Lower P l i o c e n e to Miocene  Geology of the adjacent  the  (wildcats Shouldice,1971).  areas i n d i c a t e s t h a t ABEA 2 c o u l d  to two  Pleistocene  different geological glaciation.  processes,  134  The  v e l o c i t y - d e p t h model f o r the base of the  c o n t i n e n t a l slope i n AREA 2 w i t h i n the sediments. The of 2.0  km/sec, 1.2  km  ( F i g . 4*12)  shows s i x h o r i z o n s  upper sediments  (average  velocity  t h i c k ) comprise a seguence of l a y e r s  with a l t e r n a t e l y high and low  v e l o c i t y . The t h i c k n e s s of  i n d i v i d u a l l a y e r s i s almost uniform  (about 300 m).  The  a l t e r a t i o n of the l a y e r v e l o c i t i e s i n d i c a t e s probably d i f f e r e n t d e p o s i t i o n a l processes. The v e l o c i t y together  suggested  alteration  with the r e g u l a r i t y i n the l a y e r t h i c k n e s s e s  i n d i c a t e t h a t the two occurred  two  processes  with approximately  took place a l t e r n a t e l y  and  the same time p e r i o d . I t i s  that the d e p o s i t i o n of the sediments i n AREA 2  occurred during P l e i s t o c e n e times. During  the advances,  c o a r s e r sediments pushed by a g l a c i e r across the sound were d e p o s i t e d , whereas during r e t r e a t s , d e p o s i t i o n of  finer  sediments took p l a c e . The  lower sediments  t h i c k n e s s 1.2  km)  (average  v e l o c i t y 3.1  are formed by two  high  km/sec,  velocity  layers.  T h e i r v e l o c i t i e s i n d i c a t e t h a t they are h i g h l y compacted dewatered sediments which l i e s 4.4  km  (Nafe and  beneath the sea f l o o r i s 2.3  has a v e l o c i t y of 4.2  km/sec, suggesting  S u b s t a n t i a l deformation The  Drake,1957). The basement t h i c k and  i t i s volcanic.  of the basement was  u n d e r l y i n g oceanic l a y e r has  km  not  observed.  v e l o c i t y of 6.8  (both v e l o c i t i e s , f o r the basement and f o r the  km/sec.  oceanic  135  l a y e r , were determined from the r e f r a c t i o n r e c o r d i n g , ) AREA 3 i s l o c a t e d at the f o o t of the c o n t i n e n t a l slope i n the northern Cascadia Basin. The basin i s a wedge of sediments t h i c k e n i n g toward the c o n t i n e n t a l slope and o v e r l y i n g the b a s a l t i c l a y e r of the southeastern f l a n k of Juan de Fuca Ridge  (Chase et • a l .  f  1975). Sediments of  Cascadia Basin merge with those c f T o f i n o Basin through a zone of f o l d i n g beneath the c o n t i n e n t a l s l o p e . The  volcanic  basement, which i s exposed along the c r e s t of Juan de Fuca Ridge, dips gently eastward and d i s a p p e a r s beneath the slope (Barr,1974). I t s age i n c r e a s e s towards the c o n t i n e n t a l s l o p e . ABEA 3 belongs to a r e g i o n of magnetic anomaly 3 ( H e i r t z l e r scale) which i n d i c a t e s the age of between 4 and 5 myr  (Barr,1974). The v e l o c i t y - d e p t h model of AREA 3 (Fig..4.7) shows a  sequence of sedimentary l a y e r s t o t a l l i n g  1.9  km i n  t h i c k n e s s . V e l o c i t i e s i n c r e a s e almost u n i f o r m l y with depth and range from  1.9 t o 2.63  km/sec. T h i s i n d i c a t e s t h a t the  process of sedimentation i n the area i s a r e g u l a r with subseguent compaction. Sediment  deposition  i s supplied v i a  Vancouver Channel, which extends south from the southern end of Winona B a s i n , and v i a canyons c u t t i n g the slope between Kyuguoit U p l i f t and N i t i n a t  fan (Carson, 1973). An  i n t e r e s t i n g f e a t u r e i n the model i s the occurrence o f a t r a n s i t i o n i n v e l o c i t y between the sediments and the  136  basement: a high v e l o c i t y l a y e r v e l o c i t y layer  (3.78  (4,56  km/sec) o v e r l i e s a  km/sec), which i n turn o v e r l i e s  high v e l o c i t y basement l a y e r  (4.43  km/sec). The  v e l o c i t y f o r the  (4,56  km/sec) i n d i c a t e s  the  upper l a y e r  l a y e r i s made of b a s a l t . The  beneath suggests t h a t sediments, p o s s i b l y a similar velocity  (3.96  km/sec) was  present AREA 3 was  recognized i n  i n the  o r i g i n of the  contemporaneous sedimentation and c r e s t . Contemporaneity has  ridge  sea  layer  deduces t h a t  5  myr  i n t e r b e d d i n g of explained  volcanism at the  at the  by ridge  been observed at the c r e s t of  at the  depth of 2.7  t h i c k and  with v e l o c i t y of-6.7 km/sec  refraction  et  the  Chase (1974) of with  basement i n AREA 3 with v e l o c i t y of  km/sec, i s s i t u a t e d km  the  which were subsequently f i l l e d  volcanic  f l o o r . I t i s 1.5  with  d i f f e r e n t i a l u p l i f t at the c r e s t  formed v a l l e y s  t u r b i d i t e s . The 4.43  (Seely  of Juan de Fuca Ridge, Barr and  show t h a t f a u l t i n g and the  layer  process of formation  with compacted sediments would be  northern end  that  including b a s a l t i c debris. A layer  Juan de Fuca Ridge. The basalt  high  the l a y e r i s composed of compacted  al.,1974). From magnetic anomalies, one the  the  lower v e l o c i t y of the  southern part of Cascadia Basin near 44°N  ago  low  measurements).  km  beneath  l i e s over the  oceanic  (determined from  the  137  5 CONCLUSIONS  In t h i s t h e s i s p r o j e c t a marine DSS  technigue u s e f u l  f o r d e t a i l e d s t r u c t u r a l s t u d i e s of the oceanic c r u s t e s t a b l i s h e d . The technigue  u n i t e s the advantages of the more  standard methods of marine s e i s m i c r e c o r d i n g , such r e f r a c t i o n and  CSP  was  p r o f i l i n g , and  i s an  as  inexpensive  compromise to the multichannel methods used i n the o i l industry. The  technigue  i s simple  i n i t s design  (using an a r r a y  of i n d i v i d u a l hydrophones), e a s i l y adaptable  to changes  (the  number of the hydrophones can be i n c r e a s e d up to e l e v e n ) , and f l e x i b l e  i n i t s a p p l i c a t i o n , with the same eguipment, i t  can be used f o r n e a r - v e r t i c a l i n c i d e n c e r e f l e c t i o n r e c o r d i n g , wide-angle r e f l e c t i o n recording. The the DSS  r e c o r d i n g , and  refraction  . . . . . .  f e a s i b i l i t y of the technigue procedure  was  s t u d i e d by  at sea i n three t e c t o n i c a l l y  testing  different  areas: ABEA 1 -west of the Queen C h a r l o t t e I s l a n d s , ABEA 2 at the c o n t i n e n t a l slope o f f Queen C h a r l o t t e Sound, and  A BE A  3 - i n the northern Cascadia Basin west of Vacouver I s l a n d . The  data were recorded d i g i t a l l y  0.8  to 100  Hz. The  i n the freguency range from  g u a l i t y of the data v a r i e d with the  of r e c o r d i n g , but i n general the s i g n a l / n o i s e r a t i o poor.  was  area  138  The a n a l y s i s of the recorded data has demonstrated  that  the p e n e t r a t i o n of the DSS technique and the s i g n a l / n o i s e r a t i o depends g r e a t l y on the t h i c k n e s s and s t r u c t u r a l q u a l i t y of the sedimentary l a y e r . In r e g i o n s with l i t t l e or no sediments, most of the s i g n a l energy i s r e f l e c t e d the uppermost  l a y e r , the seismograms  are • n o i s y  1  s e i s m i c i n f o r m a t i o n which i s extremely d i f f i c u l t  from  and y i e l d to e x t r a c t .  Such an area of r e c o r d i n g was AREA 1 where i d e n t i f i c a t i o n of any r e f l e c t i o n s from beneath the t h i n l a y e r of sediments was i m p o s s i b l e s i n c e t h e i r amplitudes were s m a l l and obscured by the n o i s e . The deepest p e n e t r a t i o n i s achieved i n r e g i o n s where the d e n s i t y of the sediments i n c r e a s e s g r a d u a l l y with depth and ' s o f t *  (low density) sediments are a t the top  (only a s m a l l part of the energy i s r e f l e c t e d from the f i r s t l a y e r s and more energy i s a v a i l a b l e f o r t r a n s m i s s i o n i n t o the s e c t i o n ) . Such an area of r e c o r d i n g  deeper  was ABEA 3  where the deepest r e f l e c t i o n s observed were from the depth of 4.19 km beneath the sea bottom  (from the top o f the  o c e a n i c l a y e r ) . In the r e g i o n s with v e l o c i t y r e v e r s a l s i n the sediments, the p e n e t r a t i o n of the s i g n a l decreases. Such an area was AREA 2 where the deepest r e f l e c t i o n s observed were from the depth of 2.44 km beneath the sea bottom the top of the basement).  (from  From the frequency content of  i n d i v i d u a l r e f l e c t i o n a r r i v a l s , the r e s o l u t i o n power of the technigue f o r r e f l e c t i o n s within the sedimentary seguence i s  139  c a l c u l a t e d t o be about 25 msec (frequency 20 Hz), and f o r the deeper r e f l e c t i o n s about UO msec  (freguency 12 Hz). (It  should be noted  such as p e n e t r a t i o n and  t h a t the parameters,  r e s o l u t i o n , which s p e c i f y the f e a s i b i l i t y of the e s t a b l i s h e d technigue f o r d e t a i l e d s t u d i e s of the deep c r u s t a l s t r u c t u r e are based  on the a n a l y s i s of the f i r s t  t h i s technigue during t e s t i n g . The  data recorded  with  r e s u l t s depended g r e a t l y  on the poor g u a l i t y and s m a l l amount of the data. In the meantime, data of much b e t t e r g u a l i t y have been a c q u i r e d during f o l l o w i n g c r u i s e s , however they have not been analysed  yet.)  To i n v e s t i g a t e the p o s s i b i l i t y of i d e n t i f y i n g  finer  s t r u c t u r e and/or deeper r e f l e c t i o n s than those a l r e a d y observed,  v a r i o u s methods of data p r o c e s s i n g and  were s t u d i e d . They can be d i v i d e d i n t o two technigues and  analysis  groups, s t a c k i n g  deconvolution technigues. Stacking technigues  (such as v e l o c i t y s p e c t r a a n a l y s i s and s t a c k i n g of r e f l e c t i o n data) origin  r e g u i r e accurate knowledge of the a b s o l u t e  times and s a t i s f a c t i o n of the CDP  n e i t h e r of the reguirements  c o n d i t i o n . However,  can be w e l l s a t i s f i e d  e s t a b l i s h e d technique. Deconvolution  with  the  techniques do not have  these r e s t r i c t i o n s on the data and t h e r e f o r e were more convenient f o r the a p p l i c a t i o n . The r e s u l t s obtained d e c o n v o l u t i o n using v a r i a b l e wavelet  with  i n d i c a t e d that time  a d a p t i v e deconvolution should be a p p l i e d to the data i n the  140  i n t e r v a l before  the f i r s t  water bottom m u l t i p l e a r r i v a l .  the i d e n t i f i c a t i o n of the deep r e f l e c t i o n s obscured by f i r s t - o r d e r water bottom and should  be f i r s t  removed and  used a l s o i n t h i s Within  For  the  upper l a y e r s m u l t i p l e s , these then time adaptive  deconvolution  interval.  the bounds of the determined s i g n a l  and  resolution, detailed velocity-depth  and  middle part of the oceanic  two  regions  i n which no  penetration  models of the  c r u s t have been d e r i v e d  such i n f o r m a t i o n  existed  geology of the areas.  for  previously.  G e o l o g i c a l i n t e r p r e t a t i o n of the models c o n t r i b u t e d understanding of the  upper  to  the  Velocity  r e v e r s a l s w i t h i n the sediments i n ABEA 2 i n d i c a t e the e f f e c t s of P l e i s t o c e n e  g l a c i a t i o n on  the d e p o s i t i o n  of  the  sediments below the c o n t i n e n t a l slope o f f the Queen C h a r l o t t e Sound. A v e l o c i t y r e v e r s a l w i t h i n the of the  upper p a r t  basement in-ABEA 3 i n d i c a t e s the occurrence of  interbedding  of the v o l c a n i c basement with sediments at  top of the basement. The  formation  the  c o r r e l a t e s with the  g e o l o l o g i c a l processes observed r e c e n t l y at the c r e s t of near by Juan de Fuca Ridge. The  main.contribution  e s t a b l i s h e d an inexpensive  of t h i s t h e s i s i s that i t marine r e c o r d i n g  a n a l y s i s procedures which can  be  technigue  used f o r d e t a i l e d  i n v e s t i g a t i o n of the c r u s t i n such a t e c t o n i c a l l y i n t e r e s t i n g area as the west coast of Canada, No  such  and  the  141  similar  technigue convenient f o r d e t a i l e d seismic study o f  the oceanic c r u s t has been used i n t h i s area before. The marine DSS program  p r o v i d e s a d d i t i o n a l i n f o r m a t i o n about  g e o l o g i c a l s t r u c t u r e s and a s s i s t s our understanding of the complex  t e c t o n i c f e a t u r e s o f f the coast of B r i t i s h  T h i s l o c a l a p p l i c a t i o n i s complementary  Columbia.  to the use of other  technigues by marine geoscie.nt.ists. T h i s was demonstrated during  1974 when the DSS system was used s u c c e s s f u l l y f o r  i n v e s t i g a t i o n s over E x p l o r e r Ridge  (Malecek, 1976) , a r e g i o n  where a marine g e o l o g i c a l study i s c u r r e n t l y i n p r o g r e s s . The f o l l o w i n g year 1975, e x t e n s i v e DSS p r o f i l i n g was undertaken i n Winona E a s i n , a deep water sedimentary basin of both t e c t o n i c and economic  i n t e r e s t . Good g u a l i t y  r e f l e c t i o n s from w i t h i n the sediments and deeper have been identified  (Clowes, personal  communication,1976).  Thus the s e i s m i c system which was developed i n t h i s t h e s i s p r o j e c t has already proven i t s worth on subsequent c r u i s e s and f u r t h e r use of i t i s planned f o r the f u t u r e . 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S u b r o u t i n e  (unnormalized coefficient) the  f o l l o w s t h e procedure  described i n  3.5. T h r e e s u b r o u t i n e s a r e c a l l e d f r o m t h e main  program. S u b r o u t i n e into  t o d e r i v e and  s p e c t r a o f t h e s e i s m i c r e f l e c t i o n d a t a . The  o f t h e program  chapter  program i s d e s i g n e d  data. Subroutine  coherency i s presented  from a t a p e  ( s u m m a t i o n ) , UNNOCR  o r SEMBLA  (semblance  t o compute t h e s i g n a l  ELVESP p l o t s  s p e c t r u m . The p r i n c i p l e  expressions  SUMMAX  crosscorrelaticn) i scalled  s e i s m i c data  coherency o f  the derived  velocity  o f each o f t h e measures o f s i g n a l i n section  3.5. The  on w h i c h t h e s u b r o u t i n e s  mathematical  SUMMAX, UNNOCR a n d  SEMBLA a r e b a s e d w e r e d e r i v e d and d i s c u s s e d by T a n e r a n d Koehler  (1969).  154  3  DIMENSION A(20,3S<0),PLTA(20,1 0 0 0 ) ,STCK(1100) DlNFN'S ION V ( 1 0 0 0 ) , VSO( 1000 ) , VHP T ( 3 C) , VP PT 2 ( 30) , CPH V ( 1 0 0 0 ) PI MENS I ON T D I S K 6 D ) ,01 ST (60 ) ,D1STS 0( 60) , R ST ART ( 10) , * J F ( 10) DIMENSION T ( 6 0 ) - K T ( 6 0 ) READ(5, 1 0 0 0 ) T 1 T G T » DT.NCI,VI,V2,DV RFAD(5,11 O O N S H P FAD ( 5., 1100 M N.H ( I ).»I =.1.». NSH) RFAD(5,3000 ) ( R S T A F T (I ),I=1,NSH) M=0 PP 3 T=1.NSH M-M + N H U ) R E A D ( f , 4 0 0 0 ) ( T D I S T U ) ,1=1 ,M) S 1 = 0 .0028 _.. NV=IFIX((V2-V1)/DV+0.5)+1 N G = I FI X ( G T / D T + C 5 ) +1 GT?=GT/?.O : : NG2=(GT2/SI+0.5) IF(NCI-I)11,11,12 T2 = T1+GT . . ....... GO T P 13 Tl=Ti+GT2/2.0 T ? = T I + F L.r.AU.bi.cj J * £ i 2 : : : CPN INUF WPITE<6,777) WPITF (fc ,66 t ) M, N G t M G I _ ..... .. WRITFtt,777) WFITF(6,2000)T1,T2,V1,V2,GT,DT,DV pp i T =i , M : r i S T ( I ) = T D I S T { I 1*1.AE WPITF(6,777 ) V FITE ( 6 , 5 0 0 0 ) (DIST ( I ) ,1=1 , M) . KR I T F ( 6,777) MM = M-1 T T=NPI-1 PP 2 IX=1,KM ri5T5C(IX)=DIST(IX+1J**2-CIST(1X)**2 C A L L RFTAP(A,N5H ) T ( 1 )=T 1 V ( l ) = V3 :  11 12 13  1  T  :  :  2  PP  *•  T V = 1 . N V  :  V S O ( 1V) = V( IV ) * * 2 V( IV + l )=V( I V ) + D V 4-  C P N U N U E  :  :  .  KCT=IF I X ( D T / S I ) r.'STAFT-IFI X ( ( T l - P . S T A R T (1 ) ) / SI+O .5 ) +1 N F N " = T F T X ( (T7-F:«;TAPT( 1) ) / S T + n . » n + v NS = NFNT-N'ST ART WRITFt6,777) W RI T f ( 6, 2 22 JN START , hi END.... 2 2 2 F O R M A T ( ' N S T A R T = » ,I 5 , 5 X , » N E N P = « , ! ) TIK'1=T1 T TN? = TJL+PT NH(1}=NH(1)-l DO 10 IT=1,NGI _4FJ.T__J 6.,JUJJ  _  __.  .  155 WRIT F ( 6 , 6 1 0 0 )T IN 1, T I N 2 V-,FI F ( 6 , 7 7 7 ) CCHMAX=0.0 LQfiQ : DO 2 0 I V=l , NV IC=1 D_0_e.O_.I.N.= l.jNS t K i l l )=IFIX( ( T ( 1 ) - R S T A R T ( I N ) ) / S l + 0 . 5 ) + l N=NH(IN) DXL_3J1_JJ^JL,^1 : '. IC=IC+1 T( IC ) = S 0 R T ( T ( I C - 1 ) * * 2 + DIST SO ( I C - 1 ) / VSP (I V) ) _ K T ( J C) = 1 F IX ( (T (.1 C) - R S T ARj_(J.fc|.U/_SJ+.0.5J+. 1 30 CONTINUE PO CONTIMUF J EJJV_.JC-.JJ-_Grj T P B i C f l l SUKMAX(A,KT,KDT,M,NG,COH) COH'M( IV ) = C'OH I F (COHM( I V) .GT .COHNAX ) I0=IV 1F(C0HM( I V) . G T . C O H N A X ) COHMAX = C C H M ( I V ) GO T O 20 _ e fl_cii.hi!ij.u . a : — 20 CONTINUE DO 4 0 1V=1 , NV COHM( I V ) =CPHM( I V ) / C C H N ' A X _ 40 CCNTJNUF VFI r(6,777) k £ JJ"J_ILJ_9 OQO )_ijD_f_yj JLCJ : IK=IC CF=CPHM(10) V01 = V ( I 0) _ .. SU 5=0.1 41 COHM£X = CCHf'( I O J - S U B : f 0HV, ( T0 ) =r. PHM ( 1 P ) - S U P - 0 . 0 1 r c 45 1V=l,NV IFICCHM(IV).GE-COHNAX) IO=IV I F ( C P Hf- ( I V ) .GE , C O H F £ X ) _ CO.HM AX.ELCJHHNLU V ) 4 ? CONTINUE VP2 = V( I Cl IJLLVX2.r o . v n i ) r-n TP ^-6 GO T p t.i ';6 CONTINUE ... CCH'-:(JK)=.CH WRI F(6,777) W F I T E ( 6 , ° 0 0 0 ) 1 0 , V ( 10) kJUI^A,_£l_nOJ : , 00 50 I V = l ,NV I F ( I V . G E . N V - 4 ) G O TO 36 . FU_B=0.15 _ SN'X = C.O DO 33 1 = 1 , 5 TK=T-1 ___ 5 3 S f* X= SMX + C OH M { I V + I K ) CAV=SKX/S.O I F { C Cm ( I V ) .GT . ( C A V - R U B.J. . A N D . COHN ( I V ) . L T . ( C&V- .RUB ) ) COHM( I V ) = H . ;~> T  T  1  T  156 36  c  0  CONTINUE V>RJ T E ( 6 , 8 0 0 0 ) I V , C C H M I V ) P L T A ( I T , I V ) = C O H M ( I V) rONTTNUF IF(IT.EO.NT) GC T O 1 0 T I N 1=T I N 1 + GT 2  :  ,  •  J J N 2 = T . T M2 + G I 2  _ .•_  T( 1 ) = T ( D+GT2 10  CONTINUE 0PP=C.21 YST=1.5 C A L L PL V F . S P ( P L T A , M G I , N V , Y S T , O R D ) C A L L PL jDTND ... F O R M A T ( • M = » ,I 2 , 2 X , •NG=» , 1 2 , 2 X , • N G I = » , 12 ) FORMAT(• • ) :  666 777 TOOn 1100 2000  F P P M A T ( F 5 . 2 _ . 2 J E 6 ^ 3 _ _ L 3 _ , 2£6_.. 2_, JL5_-.2J FCRMAT(30I2) F O R M A T ( • T l = , F 5 . 2 , 2 X , • T 2= • , F 5 . 2 , 2 X , • V 1= • , F 5 . 2 , 2 X , 'V2=' ,F5.2,2X,'TI *M.F G A T F . = ' , F 6 . 3 , 2 X , T I M E . S T E P = V, F 6 . 3 , 2 X , • V E L OS T C P =.._'» F t . 3 ) . FORM A ( 1 0 F 7 . 3 ) FORMA ((30 X,6 F7.3,8X) ) F OF M A T ( ' D I S T ( K M ) ' , 1 X , 1 7 F 7 . 2 , / . ( 9 X . 1 7 F 7 . 2 , / ) ) FORMAT ( K T ( I ) = , 1 X , 1 9 I 6 ) FORMAT C;OX I N T F R V A L T= ( ' , F 4 . 2 , ' , FA . 2, • ) S E C ' ) F C R M / T ( 9 X , 1 9 I 6 , / , ( 1 I X , 1 9 1 6 , /_).) FORMAT(3X,13,3X,F6-3) F O P MAT ( 1 I X , ' C O H M ' ) F O F M A T ( A R X . ' V ( ' . ? ? . ' ) = ' . F 5 . 7) STOP END 1  1  3000 ^000 5000 6C00 .100 7C00 f 000 FilOC 9000  T  T  ,  ,  157  C SUPRCtlT INE  RET/F.A.NSH)  C DIMENSION PATON(56) ,A(20,3840) INTEGEP*2 L EN 1000 FORMAT(313) . ,2000 FORM* TL_F-I LE NO. ' . 1 3 , ' IS ANALYSE C ) 16 PF.AD(5, 1000, END= 1008)NFSK,NPSK , NPEC NF=NFSK MP SK = ftO-NF FC NPTS=NFEC*96 CALL SKIP(NFSK,NRSK,1) _ . DO 60. J=1,NSH NF=NF+1 DO 61 NCH = 1 ,6 DO 63 I=1.NRFC . 11=1-1 CALL FFAD(DAT0N,LEN,0,LNUN,1, C1008 ) DO 64 K=l, 96 _ 64 A INCH.II*96+K) = CATCN(K ) 63 CONTINUE IX.{NCH. EX . 6 ) GO TO 61 CALL SKIP(C,MRSK,1 ) 61 CONTINUE WFITF U ,2000 INF I F ( J . E O . N S H ) GO TO 60 CALL SKIP. 1 t NF.SK, 1) 6 0 CCNT IJILLF 1008 FETUFN END  SUMKAX.A,KT,KDT M,NG,COH)  SUBROUTINE  T  -C D I_NENSICN  A(20,3840),KT(60),P( 20 )  PMAX=0.0 DO 1 J = 1,NG. .. . P ( J ) = 0.0 DO 2 1=1,M K =KT(I ) P ( J ) = P(J )+A(I,K) 2 CONTINUE: . P ( J ) =/.BS( P( J ) . . * * N ) IF(p(JJ.GT-PMAX) PMAX=P(J) IF(J.FO.NG)  GO  TO 1  D 0_.lJQ_J__E.Lti_ 10 1 20  KT ( I ) = KT ( I )+KDT CONTINUE DO 2 0 I = 1,M . . . K T ( I ) = KT( I ) - ( N G - l ) * K D T COH=PMAX I F_{ C C H . L E . 0 . 0 )._CD H= 0 .jOJ RETURN END  SUEKOUT I K E C  I K EK ' S I C K  SEMBLMA,KT,KCT,M,NG,CGH) A ( 2 0 , 3 E 4 0 ) ,KT ( 6 0 ) , P ( 2 0 ) , Q (  N"A"F=1J. 0 DCL^O.O DO 1 J = 1 , N G ' ~ P T J )"=Omt C(J)=0.0 DO 2 1=1,M  :  Ficmi  P ( J ) = P ( J ) * / U , K )  Q ( J ) = 01 J ) •*-A ( I , K ) * * 2 2  C C M T N I / E "  P(JJ=P(J)**2 N A (- = NAH+ P ( J ) C~CL = D C L + C ( J ) I F ( J . E O . N G ) GO TO 1 DO 10 I = 1 , M 10 K T T l ) = K T ( I H K D T 1 CONTINUE CQ 20 1 = 1 , M 20 K T ( 1 J = K T . ( I ) - ( N G - l J * K C T £C=NAH/M*DCL CGH=(M*SC-1 )/(N-l)  rrcc CTRTC E T C T O T ~ C _H=~GTGT  RETURN ENC  160 SUBROUT1 NP UNNCCR ( /,KT , KTT , M, NG, CPH)  C PI MENS I ON A ( 2 0 , 3 8 A Q ) , K T( 6 0 ) , P ( 20 ) , 0( 20) UNC = C;.C' DO 1 J=1,MG PJ.J) = p.O QiJ)=0.0 DO 2 1=1,M K = KT ( T ) . ' P(J)=P(J)+A(I,K) 0 ( J )=0(J ) + A { I , K ) * * 2 2. CONTINUE P ( J) =P ( J) **2 UNC=UNC+ ( P (J }-0 (J ) ) IF(J.F.Q.NG) GO TO 1 DO 10 I=1,M 10 KT ( I ) = KT ( I ) +KDT I.. CPNT.I.NUF_ DO 20 1 = 1 i M 20 K.T(I) = K T ( I J - ( N G - 1 ) * K D T . CPH =UNC*0. 5 IF(COH.LE.O.O) C0H=0.01 P.FTUPN  SURR0UT1NE  C  nMFNF,TON  P L V E S P . P L T A , ^ G I. K V , Y S T , C F C)  PI TA (70. .nnn )  SC=5.0 PY=0.03 XO = _ P R P DO  1  I =1» NGI  CALL  PLOT.XO+ORD,YST,3)  YJELYST-DY  DO  2  JJ=l NV F  Y=Y+DY X=PLTA{I.JJ)/SC+XCMCRD CALL 2  PLOT(X,Y.2)  CCNTINUE  xo=xo+npn 1  CONTINUE RETURN END  .  .  

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