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A long period Rayleigh wave experiment in the Vancouver Island region Pareja, German J. 1975

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A IONG F E B I C E R A Y L E I G E THE  VANCOUVER  WAVE E X P E R I M E N T IN  ISLAND  REGICN  by J,  GERMAN B.Sc,  California  PABEOA  Stats  1971  University,  A THESIS THE  Polytechnic  SUE P I T T E E I N F A R T 3 A I  FUIFII EOT  REQUIREMENTS  DEGREE  MASTER  ir  FCR THE  CF  OF  SCIENCE  the Department cf  Geophysics  We  accept tc  The  this  and  Astrcnotry  thesis  the required  as  standard  University cf Eritish May,  1975  ccnfcririnc  Columbia  CF  In p r e s e n t i n g t h i s t h e s i s  in p a r t i a l f u l f i l m e n t o f the requirements  for  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and I f u r t h e r agree t h a t p e r m i s s i o n  for e x t e n s i v e copying of t h i s  study. thesis  f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department or by h i s  representatives.  It  i s understood that c o p y i n g or p u b l i c a t i o n  o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my written  permission.  Department of The U n i v e r s i t y o f B r i t i s h Columbia 2075 W e s b r o o k P l a c e V a n c o u v e r , Canada V6T 1W5  Date  2-3 TfrA-y /?7jT  i  AESTB ACT  A study  c f the  was  proposed  the  lithcspheric Three  and  built  in crder  were the  were  with  during  array.  acquire  structure cf  tc operate  in  which  Another  Island  and  Vancouver  Island  seismographs  conditions. Victoria,  operation,  two  Eayleigh  with  victoria  was  record  was  set  An  designed  array  several  and  earthquakes  at  later;  was  Quadra  conveniently  stations up  atcut  region.  were  Vancouver  were a l i g n e d  network  waves  a d d i t i o n a l knowledge  the  field  s t a t i o n s at  of  long-period  long-period  s i x weeks o f  recorded,  Quadra  to  portable,  established Island;  d i s p e r s i o n of  no  viith  Ucluelet, usable  data  recorded. Cne  earthquake  group-velocity resolution  on  prevented  the  conclusions however,  dispersion these  are  data  and  abcut  recommendations are  experimentation  with  the  fcr  calculations  continuation drawn  chosen  a lack cf the  were  cf ether  the  data  apparatus.  begun.  usable  and Eccr  reccrds  processing.  lithcspheric  made r e g a r d i n g  existing  analysis,  No  structure;  possible  future  i i  T A B L E OF  I.  CONTENTS  Introduction  1  1.1  Geophysical  1.2  The  II.  Background  1  Project  ^  Instrumentation  6  2.1  Introduction  6  2.2  The  6  2.3  A m p l i f i c a t i o n ard  2.4  Recording  2.5  Calibration  14  2.6  Accuracy  16  III.  Field  Seismometers  9  System  12  Ex p e r i roe n t s  3.1  Introduction  3.2  Typical  3.3  Chronological  3.4  Results  3.5  The  IV.  Filtering  13 18  Field  Installation  .  Account  18 20 21  Second  Field  Experiment  Analysis  24 27  4.1  Introduction  4.2  Digitization  4.3  Dispersion  4.4  Calculation  4.5  Multiple  4.6  Application  4.7  Digital  27 and  other  Preliminaries  Analysis of  Filter tc  Phase  30 Velocities  Analysis Real  Computation  27  32 34  Data  36  of  38  Phase V e l o c i t i e s  i i i  V.  Conclusion  41  5.1  Introduction  41  5.2  Problems  5.3  V e r i f i c a t i o n cf  5.4  Other  with  the  Mass  the  Instrumental  Phase C a l i b r a t i o n Considerations  ..........  42 43 44  Bibliography Appendix—Operation  41  Position  Of  The  Apparatus  47  A. 1  Description  47  A.2  Installation  Procedure  49  A. 3  Temperature C o n t r o l l e r  50  A.4  Calibration  51  and  Operation  iv  LIS T  1.1  Major  plate  Vancouver Circuit  2.2  Seismometer  2.3  Circuit  2.4  The  2.5  tectonic  features  i n the  vicinity  of 2.  diagram  cf the  damping  diagram  Willmore  the  FIGURES  Island  2.1  of  OF  of  temperature  ....  components the a c t i v e  b r i d g e as  portable  controller  10 lew-pass  applied  to the  filter  ....  15  configuration  of  the  portable  seismographs 3.1  Map in  3.2  16  showing  the  autumn  Phase  locations of  of seismic  1973  velocity  stations  operated  ,  22  determination  with  a  tripartite  array 3.3  23  L o c a t i o n s of to  April,  field  stations  operated  from  February  1974  4.1  Digitization  4.2  VCT  and  25 2.8  procedure QUA  records  cf  the  5 October  1973  earthquake 4.3  Result the  QUA  11  calibration  systems  Calibration  8  29  of  multiple  record  of  A. 1  W i r i n g diagram  A.2  Device  used  seismometers  filtering analysis  Chile cf the  to  applied  to  earthquake  37"  instrument panels  48  check  the  natural  period  cf  the 49  V  L I S T OF  I.  Portable  II.  Earthquakes  stations—Tests  TABLES  and f i e l d  r e c o r d e d — A uturon, 1 973  sites  .........  19 23  vi  ACKNOWLEDGMENT  For stage  a s s i s t a n c e and a d v i c e  of the project, the authcr  Meldrum of  their  and  Mr. H a j i m e  Dr. Ron C l o w e s  are  during  also gratefully Dr.  Gary  Ueda.  Rogers,  lent  services  extended several The project  The p a t i e n c e of  to  Mr. E o f c e r t  and h e l p f u l n e s s the  manuscript  acknowledged.  a n d Mr. O s c a r  sites.  the experimental  i s indebted  the preparation  Observatory, their  during  Mr. R a y G r i g g  of  Edwards,  towards monitored  hishospitality  the  the  Victoria  Geophysical  of Ucluelet, operation  t h e Quadra  t c the authcr  graciously of the f i e l d  Island  site  and  a n d h i s c o m p a n i o n s on  occasions. Defence under grant  Research  Beard  c f Canada  n u m b e r 9 5 1 1-76 (UG) .  supported  this  1  I.  1.1  The has  Geophysical  plate  been  others.  A triple  between  the  smaller 51°N  Juan  and  Stacey  of the northeastern  by A t w a t e r  junction  large  130ow,  plate  the  i s believed  produced  at the Juan  subducted  obliquely  that  to  t h e American  current  tectonic  Supporting and  evidence  f o c a l mechanism  However,  no a c t i v e  proposed  location  Anomalous structure Stacey  ( 1973)  • lead  g/cm ).  Seismic  of  absence 3 6 0 km  to  a  zone e x i s t s  are  thus  to either  material  system and  based  h a s been that  the  Cordillera. on  seismicity  ty Chandra  to the  with  obtained  Gravity  (1974).  east  of  the  low  r e f r a c t i o n surveys  Savage,  f o r the c r u s t a l  data  a thin crust mantle  t h i c k , dense c r u s t  and  ( F i g . 1.1).  trench.  1965).  analyzed  densities  the arrival A  by  (20 km d e p t h  ( 6 0 t o 70 km  from  o f t h e Pn p h a s e a s a f i r s t  (White  near  i s influencing the  i s provided  Island.  boundary)  or  3  of the  results  g/cm ), 3  Benioff  a n d t h e much  plate  Canadian  hypothesis,  studies,  of Vancouver  crust/mantle  the  fcrthis  the  type  located  plate,  of i t s o l d lithospheric material of  (1973) and  Island  ridge  remnant  processes  be  oceanic  de F u c a - 2 x p l o r e r  under  plates  Vancouver the  regicn  fault-ridge-trench  and P a c i f i c  o f f Northern  suggests  Pacific  (1970) , S r i v a s t a v a  of  American  de F u c a  (1974)  Background  tectonics  described  INTRODUCTION  to  (3.2  a n d 3.09  1960's  noted  to  distances  layered  crustal  2  Figure The  model, of  1.1  with  6 km with  interpretation same  of upper c r u s t a l  a velocity  c f these  explosion  data  under  Vancouver  wave  phase-velocity  found  heterogeneity  section;  Island. data  i t should  km/s,  data.  the ,  underlain was  Tseng  the  by 45  km  preferred  (1968)  a four-layer  analyzed crustal  c f the Mchorovicic d i s c o n t i n u i t y  Wickens frcm  km/s)  be n o t e d ,  (1971)  interpreted  Canadian network  i n t h e upper  (4.2  rocks  and p o s t u l a t e d  and t h e n o n - e x i s t e n c e  zone  o f 6.8  seismic  model  velocity  i n the  locations of the ridge crests and • s p e c u l a t i v e b o u n d a r y b e t w e e n t h e J u a n de Fuca and A i r e r i c a n p l a t e s are shown. Adapted from Stacay (1974).  material  the  Major p l a t e t e c t o n i c f e a t u r e s v i c i n i t y o f Vancouver I s l a n d  just  mantle below  however,  as  well  a 30-km  that  surface  s t a t i o n s and as deep  t h e data  a  lew  crustal included  3  recordings  from  Vancouver  FNT, I DM  Cordillera  to  i s  Heat  i n  According  the  flow  Georgia inlets  l i e outside  data (1975)  of  the axis  consistent Thus,  t h e Juan  plata,  continental  with  margin.  Island  plate  tectcnic  focussing  interpreted theories.  flow  (and  thin  beneath  the S t r a i t  the  heads  Vancouver results  of  the  A thicker  Island described  i s  being  i s likely studies  are  of  ccastal and  therefore  above.  subducted  suggests  under  the  beginning at abcut the seguence  t o be c o m p l e x . are required  on t h e p r o b l e m .  lewer  crust  of the geophysical evidence  The c r u s t / l i t h e s p h e r e  information  heat  lithesphere)  the downwarping  geophysical  existing  and  heat  this  t c much  plate  additional  (Stacey,  support  Columbia  c f the t r a n s i t i o n .  region  anomalously  changes  the seismic  de F u c a  electrical  melting  has summarized  the high  Island;  the t o t a l i t y  western  Cordillera  underneath with  s u g g e s t s an  generally  current  thicker  the  upper-mantle  of partial  across British  light  (and  form  Vancouver  a layer  Hyndman  and Vancouver  American  which  of t h e western  lithosphera  that  1970),  t o these r e s u l t s ,  lithosphere) heat  high  flew  measurements  America,  of  o r even  interpretation.  them  North  region  (Caner,  lithosphare  1974) .  eastern  a  conductivities  flow  which  Island.  Compared  thin  and F S J s t a t i o n s ,  of  the  Therefore,  t o p r o v i d e new  4  1•  The  2  In  Project  response  concerning  the  the  need  region,  lines  mentioned  a surface by  wave  refraction  surface data  Three  wave  and  in  Rayleigh  surface  freguency  band  1972,  with  He  had  Vancouver along  the  suggested  that  equipment  obtain  would  fundamental  lines  long-pericd  where  be and  seismic  extended  the  begun  the  aim  from  by of  0.0  ±2  temperature  required the  on  1 Hz  AC  cf  power  chcice  mm  and  of  available.  Bolduc  (1971)  Vancouver to  0.2  to  be  Island.  100  locations  allow  km  depth.  The  by field  access,  available  The  to  achieved  seismometers. highway  were  teleseismic  Hz,  to about  had the  were  recording  interpretation to  vertical-component  equipment  waves i n a r r a y s  velocity  restricted  the  planned  along  recording  Mass p o s i t i o n s t a b i l i t y  stations  was  portable  data  studies  continued  controlling  of  evidence  exists.  Instrumentation  shear-wave  geophysical  (1971).  to  portable  seismometers  study  with  specifically  higher-mode  more  structure  Wickens  experimentation  desirable,  for  lithospheric  Island  further  to  which to  the  experimenter. The  analysis  developed. be  Group  obtained  from  (Dziewonski  and  methods  cf  (Bioch  surface and  the  phase  velocity  a p p l i c a t i o n cf  Hales, and  wave d i s p e r s i o n  1972)  Hales,  1968)  quite  dispersion  multiple  and  i s  filter  well  curves.may analysis  cross-multiplicaticn  tc d i g i t i z e d  seismograms.  5  Assuming wave  a layered  dispersion  programs, Anderson can  be  (Dorian  such (1962) .  determined and  geophysical  crustal  structure,  curves  can  as  those From by  Ewing, situation  be  produced  developed  these, least  1962) , may  theoretical  be  with  by  where brought  crustal  inversion other to  computer  Harkrider  satisfactory  squares  Rayleigh  and models  techniques  knowledge o f  bear.  the  6  II.  2.1  Introduction  Long-period freguency and  free  INSTRUMENTATION  seismographs  range  chosen  oscillations  reccrd  t c emphasize  of the earth.  long-period,  vertical-component  were d e s i g n e d  and b u i l t  They  formed  record  to  The f r e q u e n c y 0.2  filters.  were  were  Seism  model model  Their  described  recommendations Each  field  i s shaped  primarily  by  a  compensate  to  teleseismic from  ty the  as  systems  conditions.  0,01  frequency  network  are necessary  to  of  to  determine  f o r  changing  cmsters  long-period vertical  Geotech  research.  and  three  seismic  of o p e r a t i o n extends  well  arrivals  study,  established  as  ever- a  factors.  The  Sprengnether  under  wave  this  generated  calibrations  response  environmental  Three  band  c f the sensors  Systematic  exact  2.2  trains  Hz, and t h e r e s p o n s e  characteristics  the  wave  In  network  mcticn  surface  portable  to operate  station  Rayleigh  sources. Hz  a three  ground  instrument  SL-210's  seismometers,  two  and  1umbia-designed  S-5007-V, electrical  in detail  by  concerning consists  were  o n e a Co  available  and m e c h a n i c a l Bclduc the  c f two  (1971) ,  for  which  this  characteristics who  seismograph pick-up  of  coils  also  made  configuration. which  move  7  relative boom  t o permanent  i n  a  motion.  Hence,  velocity One  manner  of  the  boom  two  coils  than  the  same  form,  i n the pair  field  are  main  s h a r i n g t h e same different  freely  seismometers  both  magnet.  calibraton  the  ceil,  in of  the  instrument the Geotech  fewer  turns  coils  a r e wound c n t h e  These  characteristics  circuits  i n the respective  detail  of  a  It  was  stable  these known  position  ambient  temperature,  physical g.,  constant, period  (dsfinad  response  boom  thereby the  moment  as i n K o l l a r  While  was c h o s e n  as  explains i n  Coste  suspension,  periods. (1971)  drifted  study with  introducing  constant,  changes  the  and R u s s e l l ,  as  the in  i n the  seismometer, spring  moment  the  natural  1966).  input  Sprengnether  that changes  electromagnetic  f o r a given  the  For  (1971)  meter c o n s t a n t , a s w e l l  of the instrument  changes.  Melton  Eolduc's  the  oscillate  10 a n d 3 0 s e c o n d s .  of the La  natural  cf  damping  the ceil  theory  leng  of  parameters tha  band.  from  vertical  between  a p e r i o d o f 20 s e c o n d s  the mathematical provides  be a d j u s t e d s o t h a t t h e y  pericd  seismometers  centre  which  may  at a selected  three  these  as a main  consists  although  tc  to i t s displacement.  However,  ceil  latter's  related  I n the Sprengnether  identical.  coil,  i s  the  to the  apparatus. The  a.  cutput  i s treated  ceil.  a r e anchored  reproduces  r a t h e r than  the calibration  necessitated  the  travel  as a c a l i b r a t i o n  instruments  all  that faithfully  the electrical  of the c o i l s  other  sragnets, and which  The  phase  was a f f e c t e d s e i s mc ire t e r  by had  8  built-in more for  mechanical  compact a  field  restrict  compensation  Geotechs  d i d net  calibration  for a reliable  to  than  less For  to remain  method  this  purpose, and  a  a  designed.  consisting  of  a comparison  turn  a zero-vcltage  controlling switches  giving  also  In  order  necessary  less  2 mm,  a  a  Although  this  R.D.  than  ±  to  which  temperature  switch  light check new  of  keep  enclosure  with  testing a triac  bulb on  could  changes  the at  which  entire a  Meldrum d e v e l o p e d  bridge,  the gate  visual  which  surrounding  was  thence  a feature.  the  v a l i d , i t was  cf holding  heater  temperature  and  to  such  drift,  ± 0.5°C.  seismometer  probe  have  mass-position drift  called  for temperature  fixed  a  device  a thermistor the c u r r e n t ( F i g . 2.1).  acts  as  a heat  as  the  flow  and  This  in  source,  performance.  device  could  120 y 6oHz  hold  a  steady  Heavy t>uty 5  Figure  2.1  Circuit  diagram of the controller-  Wt  temperature  Bui b  9  temperature  inside  enclosures  with  interruptions restrict (i)  the  t h e p r e s e n c e o f an  relatively  heavy  project.  the  case  first  the the  which  Upon  i s difficult  introduced  at  was  set  aside  method,  nature  Geotech  i s well  seismometers  the  records,  the  much  cf  obviated i n  which  t h e t i m e o f any i n t e r e s t i n g how  due t o t h e  were  by r e c r e a t i n g  just  were  mass-pcsiticn  continuous  of  enough t o  t o t h e h e a t e r and  seismometer,  utilizing  power  available  of mass-position  examination  to estimate  by t h i s  common  power  and t h e  h a d t o be r e c a l i b r a t e d existed  were  monitoring  Sprengnether  stations  monitored.  systems  operator  seismometer  + 0.2°C,  solutions  t c provide  checks  than  sites The  drain  insulated  less  approach  power  Daily  of  compensated; were  cf  field  use of b a t t e r i e s  The  It  variances  in  changes.  the  thermally  i t s usefulness.  the  (ii)  the  conditions  earthquakes.  uncertainty  but i t i s c e r t a i n l y  the  i s  net an  ideal  seismometer  must  solution.  2.3  The pass to  ASElif ication  signal  a n d F i l t e r i n cj  f r c m t h e main c e i l  t h r o u g h an e l e c t r o n i c the desired  total coil, (Fig. behave  resistance  characteristics. present i n the  the a m p l i f i e r 2.2) .  network  input  The l a t t e r  as a s l i g h t l y  c f the which Damping  loop  impedance,  i s chosen  underdamped  shapes  tc  the response  i s provided  containing  the  and a damping make  the  oscillator,  by t h e main  resistor  seismometer  with  a damping  10  Figure For  2.2  Seismometer damping  the Geotech seismometers, R1 = 1.8 kchm, R2 = °° . For the Sprengnether s e i s m o m e t e r , R1 = 0, R2 = 82 0 ohm.  coefficient  of  0.7  t c 0.9.  To  achieve  seismometers  require  a  series  Sprengnether  i s damped  by  a parallel  the is  components  a m p l i f i e r input  resistor  impedance.  necessarily attenuated  in  this,  The  the  whereas  the  combination  cf  and  signal  the  comparison  R1,  Geotech  from  with  R2  that  Geotech cf  the  S prengnet her. The have  a  amplifiers balanced  operational low-gain can  be  input,  output  has  attenuated  of  or  36,  42  db.  field  30  separation,  equivalent Both filters, db/octave  to  a  outputs with  frequency  roll-off.  impedance.  two  output  They  which employ  stages.  The  db,  which  db  28  db.  The  c p t i c n cf a d d i t i o n a l gain  steps  for  are  kchm  model AS-330,  70  steps the  to  a minimum  outputs  i s 64  voltage  4  provide  Eoth  setting  a  Geotech  maximum a m p l i f i c a t i o n o f  gives  typical db  a  in 6  output  are  with  a m p l i f i e r s to  high-gain 30,  used  a gain  db  gain  of  corners i s  the  low  output  0.01  the  cf  a with  94  db,  times.  a single set  at  recorded;  amplification  50000 by  normally  frcm  total  filtered  This  are  of  and lowest  5.0  of  passive  Hz,  and  bandpass  RC 12  range  11  available  from  It  not  i s  the manufacturer practical  experimentation extension to  the  for  f c r  the  long  because o f increased  i s desired  below  characteristics  0.01 cf  AS-330  period  amplifier.  surface  temperature  Hz; t h i s  wave  drift  appears  tc  i f an  be  the c a p a c i t o r s employed  due  i n the  f i l t e rs. An  active  frequency inserted shown  i n  following  low-pass  components after  filter above  t h e AS-330  was  designed  0.04  Hz  amplifier  to  attenuate  (25-sec  period)  and  high-gain  stage.  As  F i g . 2 . 3 , i t c o n s i s t s o f an o p e r a t i o n a l a m p l i f i e r an  Figure  RC  2.3  network  Circuit  with  diagram  corner  frequency  of the active  of  lew-pass  filter 0. 036  Hz  (28-sec  period),  and  i t  features  max i m a l l y - f l a t  12  response The  below  gain  although  in a  the  (Tobey  by  an  recorder  et  at  1971,  pp.  the  output  earthquakes  w i t h i n the  30  recorder.  During  recorded  at  manner, the the  the  recorder  2*4  by  Instruments of  volts  for ±  standard between were  84.4 10  high  kohm  and  db  tape  and  of  fear  the  tape  of  the  signal  is  db.  without  -24 large  output  -12  centre  in  analog  17373) 5100)  In  this  changes  cf  in  overloading  days were  carrier  frequency..  50  kchm, s i n g l e - e n d e d  compared  to  the  1 kohm  recorders Precision  utilized. of  adjusted  tc ±  impedances to  associated  ground, with  lape  continuous  frequency,  Input  and  tape and  were  five  sensitivities  deviation Hz  -12  range  and  without  allowed  input  HQ%  db,  the  filtered  0  (model  5104  i.p.s.  The  tc  low-gain  frequency-modulated  (models  recording.  filter,is  accommodate  performed  and  the  System  Gectech  15/160  be  of  input.  Rs£2£ding_  manufactured  can  fed 0  the  of  adjusted  active  dynamic  and  levels  voltage,  Seven-channel  speeds  input  relative  driving  ;  tape  filter  of  the  be  298).  the  to  db  rcll-cff.  physical size  and  made  calibraton,  calibration  inpu t  cf  levels  t c 35  can  295-  network  relative  db/octave  region  al. ,  was  i s the  12  i s the  provision  amplifier  a  limitation  attenuating  input  This  with  flat-response  operation,  divided  db.  corner,  practical  capacitors In  the  the  with,  2.8 a  ranged which cutput  13  attenm.tor Maximum  bridge  that  follows  signal-to-ncise  range,  ware  normally  the active  ratios, between  which 30  lew-pass  determine  and  35  occasional  improvement  t o 38 d b d e p e n d i n g  of  or the state  of the recording  the tape  variations, countered (see  the  responsible  the  db , upon  with the  heads.  for  dynamic an  quality  Tape  spaed  flutter,  playback and d i g i t i z a t i o n  were  procedures  Chapter I V ) .  proper  information  alignment  receivers, radio  signal  was r e c o r d e d c n a l l  o f r e c o r d s from  Develco  attenuated  model and  3202A  provided  model TS-100-R)  available;  t h e s e , however  tapes  different  and D r u i d a  a n d r e c o r d e d on t a p e .  (Sprengnether were  are  during  Time  the  which  filter.  WWVB  I , demodulated  output  As a b a c k - u p ,  which  i s  chronometers  and U B C - d e s i g n e d were  enable  stations.  Mk.  coded  to  timing  net dependable  units  over  long  *  periods  of tima,  AC p o w e r the  f o r the system  recording  standard  distribution input. the  supplies  and  The o p e r a t i o n  Appendix.  were  their  network  from  For equipment  enclosures  filters  problems,  i s derived  stations.  power  Wooden active  due t o d r i f t  were  the mains requiring  eliminated. supply  at  d.c. power,  used. built  power  ending  and were  t o house  supply,  logically  and c i r c u i t  as  the amplifier, well  at the tape  diagram  are  as  the  recorder  described  in  14  2«5  Calibration  The  total  freguency output also  range  for  phase  the  During  the  justified. well  the  example that  used  and of  a  of  when one  with  standard  motion,  for  as  the  delay  are  velocities,  the  phase  instrument.  of  nearly  equality  of  phase  mass  If  lags  the  clear.  seismographs,  Canadian  is  sensors  positions,  becomes  to  identical  with d i f f e r e n t  calibrating  for calibrating  given  i.e.,  pair  deals  a  i t i s necessary  the  phase c a l i b r a t i o n s of  the  phase  fluctuating  method  in  amplitude,  i n t r o d u c e d by  made  routine  the  calibrated  assumption  sensors of  The  is  seismograph  calculation well  However,  as  necessity  be  a  i f both  function  computation  of  ground  the  must  phase  seismographs,  as  given  response  remove  i s known  a  known.  response  network  fcr  stations,  *  is  described  bridge and  by  w i t h the  Willuiore seisitcmeter  i t i s balanced  alternatively seismometer, range.  The  balance  by  and  i t i s driven  absolute  It  main c e i l  a resistor  clamping as  (1959).  and  as  uses the  amplitude  boom  desired  response  branch,  network  the  the  impedance  unknown  capacitor  unc l a m p i n g through  an  while  of  the  frequency  results  from  the  conditions.  The  phase the  calibraticn  bridge  i f  output  driving  v o l t a g e f c r each  signal  tape  r e c o r d e r to monitor  which  can  be  digitized  can  and  be  obtained is  frequency, both  compared  a  with  Willmore  with  component.  signals,  analyzed  with  the Using  input the  a record i s  produced  standard  computer  15  programs.  However,  this  research,  Fig.  2.4,  both  the  this  the  input  bridge  • Figure  portable  unworkable.  impedance of ceil  and  recorders  e  e  for  As  the  tape  to  ground,  the  available shown  recorder making  calibration  for in  shunts the  cf  The w i l l t n c r a b r i d g e a s a p p l i e d t o c a l i b r a t i o n of the portable systems  was  decided  amplitude  response  response  alone  both  is  unsuitable  2.4  tape  the  the  systems.  It  in  the  method  seismometer  Willmore  with  frequency,  which thus  and  could  seismometer  signal,  to  forego  the  tc devise be  a  method  established.  models can  forces  knowledge  the  affording  be  boom an  by  The  driven to  of  which  absolute the  calibration -by  oscillate  opportunity  the  to  an at  phase coil  external the  record  known the  16  output  of  filter)  f o r a known i n p u t  provides  the  the  seismograph  driving  (seismometer  ( F i g . 2.5).  voltage,  N  and  plus  A  amplifier  signal  i t s output  and  generator is  recorded  (%>~  MA»AV  Figure simultaneously calibration chart  can  data  can  the  input  tape  with  takes be  be  C a l i b r a t i o n c o n f i g u r a t i o n cf portable seismographs the  abcut  obtained  analyzed and  sixty as  by  output  filtered  a  amplifier  minutes  back-up  forming  time  output.  perform  record.  the  series,  to  the  The  A  and  field a  paper-  calibration  cross-correlograms  after  digitization  of  cf  the  records.  2.6  Accuracy  Bolduc response  (1971)  a t one  additional most  2.5  ±  1°  probable  calculated  t o be  assumed  station due  to error  about  could  that be  the  determined  temperature fcr + 3.2°.  instrumental ±2°,  fluctuations.  twc-station A  to  direct  phase with  Hence,  measurements calculation  of  an the was this  17  error  had been one of the o b j e c t i v e s  however, analysis, at s o l v i n g  due  tc  the  premature  no such c a l c u l a t i o n t h i s problem  was  of the present cessation  made.  i s suggested  the  data  An experiment  aimed  i n Chapter  of  thesis;  V.  18  III.  3. 1  EXPERIMENTS  Intrcducticn  Single-station in  September,  and  f u r t h e r work  redesigned in  FIELD  tests  1972.  and  under  From t h e  i n the  laboratory,  Having and  a  October,  with  stations at  UBC  two  months,  obvious  campus.  that  tripartite in  continuous  Typical  Within site  was  with  no  site  u s e f u l data  Field  on  i t  velocities.  Victoria,  the e x p e r i m e n t having  in  Island,  and  became  been r e c o r d e d  Mechanical  and  installed  analysis,  had  systems  continuously f c r  i n February,  I s l a n d and  three  Quadra  were r u n  phase  deployed  was  Victoria,  data  and  site,  array  fcr  A  1974  the  second  with  sites  thus  providing a  problems  prevented  was been  discontinued in obtained.  Installation  a p r e s e l e c t e d geographic  based  a number  foundation,  (ii)  from  noise.sources,  ambient  f o l l o w i n g summer a t a  preliminary  array.  operation  1974,  3.2  was  Quadra  aperture  April,  group  network  Ucluelet,  wider  after  of  field  experiments was  instruments  insufficient  determination  the  beg.un  system  tripartite  The  but  of these  e s t a b l i s h e d that  were c o m p l e t e d 1973,  c o n d i t i o n s were  results  t e s t e d f u r t h e r the  Victoria.  the.  field  of  area,  criteria,  availability e.g.  c f AC  the  such power,  railroads,  search  as:  for.  a  (i) bedrock  ( i i i ) distance water  courses,  19  highways,  (iv)  apparatus,  (v) c e m e n t  and  working  (vi)  inhabitation fleer  space  to  provide  manning  cf  to s e r v e as a seismometer for calibration  and  the pier,  other  routine  p r o c e d u r e s. Bedrock  sites  (Table  I ) , except  cement  piers  depth  were at  the  f c r  UBC  Sciences  the foundation  Station  existing reach  a  t i l l .  Periods of operation  123015'W  VCT  48°31'N,  1230 25'W  QUA  5C0C5«N,  125013'Vi  UCL  48055'N,  125°32«W  PORTABLE  the  Centre)  being g l a c i a l  49016'H,  I.  seismometers  where  Coordinates  i  TABLE  a l l the  campus,  (at the Geological  of 2 m e t r e s ,  UBC  found  Via y - J u l , Aug- Sep, Cc t - K o v , Sep-N o v , Jun-Nov, Feb-Apr, Se p-No v , Feb-Apr, Feb-Apr,  S T A T I O N S — TE STS S IT ES  AND  1972 1973 1973 1972 1973 1974 1973 1974 1974  FIEID  in each c a s e a r e c e m e n t on b e d r o c k , Founda t i o n s (see except for the [f EC st a t i o n station ha also been text) . This with a H e l i c o r der as a operate d d i s p l a y (1 9 7 2 - 1 9 7 5 ) . 1  The building, on  a  covered  typical  station,  serviced  b y AC  flat by  connected panel, on  slab  which  another  was  power,  o f cement  a five-sided both  t h e n , was  floor,  poured  in a  adjacent  and wooden to  in a  permanent  the seismometer directly  styrefcam enclosure.  calibration housed  with  located  main  coils  enclosure the  power  placed  cn bedrock, A  long  and  cable  t c the. c o n t r o l and  situated  supplies,  tape  20  recorder  and  indoors  and  output  ViWVB r e c e i v e r . aligned  to  The the  antenna  position  was  which  mounted  gave t h e  best  signal.  On a n a p p r o x i m a t e l y d a i l y the  mass p o s i t i o n ,  date  and  changed  of observation.  and  sent  inside Every  A  of  tapes  ensured  Chronclexical  When B o l d u c ' s 1 9 7 2 , R.D.  five  days  Events  such  failures,  on e a c h  continuous  tapes  were  as  power  and  tape's  other  l o g sheet.  o p e r a t i o n a t each  site.  Account  (1971)  Meldrum  noted  recorded  the e n c l o s u r e and t h e  i f detected, equipment  o f d i s t u r b a n c e were  3.3  the operator  t c the u n i v e r s i t y .  sources supply  basis,  temperature  time  interruptions,  of  ViWVB  project  was  resumed  i n the  adjusted the Sprengnether  spring  seismometer  0  for  long-period  control  operation,  system.  Later,  tested,  and  Seotech  seismometers  alignment Tests  a simple  was  in  Sciences  Centre,  to  sixty  about  Field  experiments  location  new,  vault  could  filters was  from  were  Texas,  located surface  be  temperature built  constructed.  improved  that  a  factory  were  fitted.  the  waves  recorded  The  .where  coils in  and  Geological with  periods  with  adequate  the  Victcria  ratics.  Geophysical Observatory original  and  shewed  seconds  signal-to-noise  panel  were r e t u r n e d  seismic UBC,  designed  the active  ccntrcl  performed  the  and  was  were starting  conducted in  not i s o l a t e d  at  September,  seismically  1972. frcm  the  The road  21  surface,  s o a naw s i t s  nearby,  abandoned  proved  capable  hold  house. of  Field  the simple  tests  instrument  panels  procedure  had  other  the of  Vancouver  to  install  Island  at least  September,  installed (Fig.  began  i n  3.1)  was  constructed  and  be made  a  Conflicting  c f the timing  more  calibration  requirements cf  t h e autumn o f 1973.  Because c f  cne s t a t i o n  and  data  and Savage,  from  the east  1965),  i t was  i n the Campbell  by e a r l y O c t o b e r , a t h i r d vault  at  recorded  could  t c the problem  UBC.  two-station on  area.  Island  i n  s t a t i o n .was This  array  network,  Vancouver  cf i t s crustal  coast decided  Fiver  i n a p r i v a t e home a t Q u a d r a  data  new  recording  refraction  seismic  mm.  tape  as only  namely Island  structure.  Results  Among t h e d a t a aarthguakes,  azimuths  ± 2  1973, a f t e r  Victoria-Quadra,  warranted  than  June,  a  3.4  less  i n  essentially  be a p p l i e d  ccnditicns to  resumed  (White  and  the  tc  devices  was u s e d .  until  of seismic  Operation  t h e necessary  cf a  c c n f i g u r a t i o n which  devised.  made m o s t  control  the e l e c t r o n i c s could  had been  unavailable  existence  late  were  been  projects  equipment  that  i n t h e basement  temperature  fluctuations  H o w e v e r , i t was f e l t than  The  maintaining  mass-position  reliable  was e s t a b l i s h e d  with  recorded  epicentres  f u r t h e r examination were w i t h i n  i n this i n as  part  o f t h e p r o j e c t .two  Chile  their  and  i n  Mexico,  source-tc-receiver  5° c f t h e i n t e r s t a t i o n  azimuth  relating  22  nf  F i g u r e 3.1 Map s h o w i n g l o c a t i o n s o f s t a t i o n s o p e r a t e d i n the autumn VCT  and  QUA  calculation 63-64). are  was  The  related  (Table  performed phase  as  II). as  A  "peak  d e s c r i b e d by  velocity  fellows  simple  c and  (see F i g .  c  = a, s i n A/AT,  c  =  the  seismic of 1973 and  Garland angle  cf  trough"  (1971,  pp.  approach  A  3.2) : ,  [ 3. 1 ]  or  w h e r e AT, a n d  AT^ a r e  d s i n (A + a ) / A T g  the  4  ,  interstaticn  [3.2] time  delays  for  a  23  Date  Tims h (UT)  29  Sep  1973  0 0 : (43: 58 .7  5  Oct  19 73  0 5: 45: 27 .2  6  Oct  1973  1 5: 0 7: 37 .0  9  Oct  1973  0 7 : 57: 32  11  Oct  1973  0 2 : 07: 52  18  Oct  1973  10: 49: 36  TABIE l  II.  Epicentre  Mag  Depth A z km  ,9N , 130. 92 N. K o r e a 3 3 . OS, 71.9W Chile 60.8S, 21.6W S. S a n d w i c h I s . 14.2S, 167.2E New H e b r i d e s 0 . 6 N , 2 9 . 5W Mid-Atl. Ridge 1 9 . 3 N , 105.0W Mexico  7.1  549  160  20  40  41  EARTHQUAKES  6 .6 7 .0  1  80  5 .8  19  7 8 0.  5 .9  33  560  6 .0  73  4o  RECORDED — AUTUMH , 1 9 7 3  D i f f e r e n c e between the s o u r c e - t o - r e c e i v e r azimuth a n d t h e QUA-VCT azimuth. Data obtained from NEIS, B c u l d e r .  Figure  3.2  Phase v e l o c i t y d e t e r m i n a t i o n tripartite array  Method i n t r o d u c e d from Garland particular  peak.  by P r e s s (1971) .  A, a , d,  (1956);  and d  2  diagram  could  with  a  adapted  be c a l c u l a t e d  frcm  24  the  epicentre  be  measured  wave A,  from  trains  For  traversed  trough  could  boundary  in  discontinuity the  entirely these  the QUA)  to agree  the  either  wave  were  was r e s p o n s i b l e  azimuth,  no  sought.  was g o o d ,  by  that  cr  path  w i t h i n 2.5?.  recognizable simple at  a  lack  hinted  peak  cr  calculation.  diffraction  for this  c o n t i n e n t a l wave  cue earthquake  digitized the  geological around  some  cf  agreement;  at the  possibility  As  chart  The S e c o n d  i s  digitized  discussed  curves  the behaviour that  4.3).  record  40 Even  i n  the  cf a  Field  seismograms  dispersion  at t h e i s l a n d  from  by a m a l f u n c t i o n  3*5  was a v a i l a b l e f o r s t u d y ,  as described  record  a slow-speed  longer  at the calculated  refraction  path,  two s e i s m o g r a m s o b t a i n e d  mutilated  that  that  only  containing  only  surface  phenomena.  Thus,  Fig.  be f o u n d  could  2  the  the agreement  however,  AT, a n d AT  that  o f [ 3 . 1 ] and [ 3 . 2 ] was  event,  was s u r m i s e d  while  Tc confirm  the array  t h e C h i l e quake,  the Mexico  It  coordinates,  the records.  the equivalence For  of  and s t a t i o n  UBC  tape  IV.  site  playback  The  was  tape  partially  deck,  leaving  made p r e v i o u s l y .  Chapter  progressed  of the  Chapter  (VCT a n d  Sx_periment  in  were  stations  and  until  produced. dispersion  c r 50 s e c o n d s c o u l d the recovery  IV,  analysis group  These  at  t o show periods  n o t be d e l i n e a t e d  o f t h e UBC  record  the  velocity  appeared  function  of  frcm  (see paper  25  chart  would  needed, In  and  have  been  this  required  order  earthquake  to  data,  source-to-receiver third  station  Figure  on  3.3  of l i m i t e d  assistance.  mere f i e l d  increase  paths, Vancouver  i t  with was  Island.  were  data  work.  t h e chance  preferably  Kore  of obtaining  usable  relatively  simple  decided The  t c search resulting  f c r a array  Locations cf f i e l d stations operated from F e b r u a r y t o A p r i l , 1974  26  should  hava  a wider  Hence, the  Pacific  with  the  i n February, coast,  Victoria  re-installed, separations Bolduc would  ranging had  ba r e q u i r e d  their  Tape  recorders became wera  2 1 8 km t o  pointed  out,  to achieve  sufficiently concluded  solution  array 132 km  combined  which  with  were  interstati.on  ( F i g . 3.3).  separations  of this  accuracy  up t c 80 s e c o n d s  in  period,  of detection of  equipment  malfunctioned illegible  problems  the  As  order phase  which  was  instruments  not  a  of the o r i g i n a l  rendered  tapes.  sites, Among  event  clear  timing  with  1974, with problem.  ratios. nc d a t a  the entire  i t  single  signal-to-noise  i n April,  plagued  at a l l three  i n t h e QUA  at a l l sites  high  station,  sites,  two-figure  well.  state.  obtained,  simultaneously  was  tripartite  one, as  was e s t a b l i s h e d o n  This  Island  of r e c o r d i n g , and e v e n t u a l l y  signals that  a  from  Disappointingly, period  Ucluelet.  at the limit  current  the first  Quadra  determinatiens  approximately in  and  than  1 9 7 4 , a new s i t e  near  termed  (1971)  velocity  aperture  was  fruitless. a n d WWVB the  data  recorded  information or The  experiment  applicable to the  27  IV.  4.1  Introduction  Surface system  as  aimed  at  curves,  wave  data  described  were  grouptc  ba  region.  and  of  various  The  data  earthquake  in  23).  the  and UBC  playback  Chile,  cn  were  UBC.  deck  ^•2  was  in  Fig.  4.1.  The  the  recording  speed  during  and  cut  and  rendered  of  VCT  other  i i : the  are  the  the  procedure  records  1973  cf  (see  at  Table  Quadra  records  were  useless  an II,  Island, digitized,  when  a  tape  original on  a  tape  to  the  by  which  other  digitize  record.  i s shown  i s played  which  introduced  i s tc  earthquake process  deck  three,  Preliminaries  analysis  the  for this  channel  recording,  and  cf  variations,  output  was  dispersion  models of  covers  recorded  QUA  portion used  the  analysis  tape  techniques.  The  step  instrumentation  speed  analog  malfunctioned.  first  interesting  chapter  October  tape  Diqitization  The  Their  analysis 5  an  structural  analysis  for  tape  with  phase-velocity  tc  This  chosen  These  Victoria but  the  and  fitted  Island  theory  obtained  ir; Chapter I I I .  producing  which  were  Vancouver  pg.  ANALYSIS  at  compensates  has  had  outputs,  10  times  fcr by  small  comparing  i t s input and  The  schematically  back  the' r e c o r d e r ,  the  shorted  removing  any  28  OO  A/D Conv\  j Inter A iitix  5.D. S.  <  A n o . l o c\ T a p e . DscJc  OO  C o ff.j)u"l£<-  ]  c  t  '  Jf  —<  1  Recorder  Fee a.-  Figure correlated of  4.1  fluctuaticns.  the active  filter  Digitization Three  output  channels  WWVB, a r e h a n d l e d  by t h e d i g i t i z e r .  by  a pulse  whose  the  sampling  digitization  rate  frequency, recovered  from  application,  was  chosen.  and  holds  at  be  which  from i s  cf  i s driven  aliasing, the  least  the  Nyquist  frequency In  the  A value  present to  of  Hz  stored  20  channels i n the  t cthe  480  t c be  enough  the three  transferred  blocks  as well  establishes  s e t high  code.  samples  finally  i n discrete  consisting  digital  points  i n  format.  this  must  time  the information, and  frequency  seguence.  had t o  t h e WWVB  memory  rate  t h e highest  time  The ' d i g i t i z e r  multiplexed  but  the rate  recorder  At  the d i g i t a l  reproduce  Interdata's tape  t c be  i s twice  This unit  repetition  To a v o i d  i s chosen  which  faithfully  pulse  freguency.  o f data,  a t 0 a n d -12 d b l e v e l s  as  generator  procedure  stage  the data  undergo  further  7-track  digital  tape  9-track  format.  The data  are i n a machine-readable transformations.  i s converted  to  an  format  Primarily, the IE^-corapatibls  a r e d e m u l t i p l e x e d s o t h a t t h e y may  29  be  examined  i n  t h e t r a c e mode a n d t h e s e i s m i c  decimated,  i.e.,  the  Decimation  can  induce  Hales,  1972)  length  of  the  freguency  and i t i s n e c e s s a r y  series  aliasing  records i s  reduced.  (Cziewonski  t o low-pass  filter  are  the  and time  S October  Figure For  c l a r i t y , cnly (10 m i n r e a l  series;  the  process  Fourier  transform  inverse  discrete  54  minutes,  points  with  number  of  advantage  36.8  intervals,  p a r t i a l s e c t i c n s of time) a r e shown. was a c h i e v e d  with  2  points  frequency  was  discrete  i t i s assumed  records  chosen  that  recording  then  c f WWVB d a t a .  with 2  were  t o be Fcurier  The  the  1  points.  2  Hz  the Thus,  by  ( F i g . 4.2). c f twc t c  transform are at  checked  results  discrete  calculating  a power  the p c i n t s was  points  represented  c f 0.625  speed  750  producing  points,  6  seconds of data  a Nyquist  the'  1  by  Fourier transform  of a faster  Since  selected  4.2 VCT a n d QUA r e c o r d s o f t h e 5 October 1973 earthquake  ty  4096 The take  algorithm. equal  time  reproducing  showed  that  both  30  QUA  a n d VCT  tape  difference  recorders  being  0.03 ?.  as  calculations  would  a  r  phase  I  phase  at typical  f (t)  t o be  velocity  velocities.  c f an e a r t h q u a k e r e c o r d e d  &  from  f ( t )e x p ( - i c o t )  =A(r,e,co)  the e p i c e n t r e .  a s t h e sum e, co)  =  dt,  Throughout  at Its  [4.1]  this  research,  [4.2]  P  c f phase  immediate concern,  of three  the  s e p a r a t e l y , e.g.  e x ( i 0 ( r , e , co) }.  determination  s p e c t r u m i s o f more  (f> (t,  considered  in  functions are treated  the eyentual  expressed  mutual  Analysis  azimuth  =  and phase  For  km/s  f o r a l l t < 0.  F(co)  not  their  i s  F(co) w h e r e f (t) = 0  was  introduced  be + 0.001  and  transform  amplitude  error  a seismcgram  distance  Fourier  the  Dispersion  Consider  This  1  significant,  4.3  ran s l i g h t l y fast,  velocities, and i t  the  can  be  terms:  <f> ( 0 , oo) +  cf>. (to)  [4.3]  where  k (CO) i s t h e w a v e n u m b e r ,  (p  i s t h e phase  shift  introduced  a t the  source,  cb (CO) i s t h e p h a s e  shift  introduced  ty the  instrument.  ( 6 , co)  and  Look also  be  a t k(co)»r  A  monochromatic  which  mere c l o s e l y ,  w r i t t e n as t h e i n v e r s e  f(t)-=_l_  satisfies  I  k =  + k(o))»r,  A ( r , 6 , co)  the seismogram  Fourier transform  f ( t ) can cf [4.2],  e x p { i ( c o t - k r ) ] dco .  wave o f f r e q u e n c y the principle  2 7T/A.,  cO  c  travels  at  [4.4]  a  c f s t a t i o n a r y phase:  velocity  31  c0 t  - k(t0 )«r = a c o n s t a n t ,  0  for  [4.5]  0  a l l r , provided  that  k i sindependent  of r .  I t  fellows  t hat: L0 from  which  t h e p_hase  c (to)  i s  = dr/dt  net  since  different  velocities,  and  1 957 , pg. The  0  i °j  the  )•  [4.6]  0  signal  I  n  i s said  co^  frequencies  c c  with  emerges a s  c o / k (co ).  t h e lowest  begin  will  case  t l i e  freguencies  t h e longest  to  travel  be at  c f fundamental travel  periods  fastest,  (Ewing e t a l . ,  178).  maximum  Evaluating f r equ e n c y  different  waves,  arrivals  =  constant,  ^i^£§I5ll'  mode R a y l e i g h  c(co)  velocity  c(co) If  - k (co„ ) = 0,  dt/dr  0  energy  [4^4]i n  travels  at  t h e 9[rou£  t h e neighbourhood  of  a  velocity. particular  LO , a  a> +s 0  f (t)  =J-(  A { r , © , u > ) e x p [ i ( w t - k r ) } dto ,  [4.7]  co -e. 0  we  note  that  f (t), ,  within  (to -S,  t h e band  group  travel V  and  the group  = t  a  (cot- k r )  =0.  = {dk(CJ)/d^>}  w  velocity  general,  when a l l t h e w a v e s  [4.8]  time i s  u(o>) In  b e a maximum  oo t £ ) a r e i n p h a s e , c r  0  d/Aco  The  will  ' CO o  x  .r ,  [4.9]  i s g i v e n by  = r / t - dW/dk. t h e group  velocity  [4.10] can t e expressed  i n  32  of  terms  t h e phase  = c(co)  u(u>)  which  requires  4  •  The  by  of  analyzed,  a network  be  which,  greater  thought  in.Fqn.  a digitized waves.  [4.2]  phase  velocities  tripartite  seismographs  i sused t o  This  method  allows  azimuths.  than  wavelengths  be  was  the  arbitrary the the  depths  influenced  the  Station to  be  t o which t h e  by  the  of  the  and  to  assure  be  rewritten as =  containing  local  transform  can  fundamental be  t h e source  section:  ( r , O , to)  [4.2 ]  i s formed  function,  the  an a r b i t r a r y  number  of full  c o n t i n u i t y of thef u n c t i o n .  - 4> ( e , co)  -  by t h e  circles,  Thus,  (co )  by t h e  instrumental  c f t h ed i s p e r s i o n a s d e s c r i b e d  ( r , e , to)  written  e x p { - i 0 <r, e, co) }.  function  t h enature  wavenumber,  seismcgram  of t h epreceding  delay  contributions  r  phase  whc i n t r o d u c e d  Its Fourier  F (to ) = A ( r , e, co)  k(<o)o  k (to).  ,  mode R a y l e i g h  response,  cf  determine to  [4.11]  Velocities  o f three  with  i nturn,  waves are  Consider  The  wavenumber  simultaneously.  records  must  structure.  as  (1956),  by P r e s s  teleseisms  separations  o f Phase  calculation  which  analysis  surface  a knowledge o f the  direct  demonstrated  record  + k (to ) »dc (co) / d k ( c o ) ,  SliSlli^iicn  4  method  velocity:  2n7T,  [4.3]  + 2 n TT.  can  [4.12]  33  The  instrumental  phase  calibration  procedure  calculated  from  et  a l . (1972).  find,  stations phase  write  i t requires  which  phase  t h e same e a r t h q u a k a ,  the c a l c u l a t i o n of  the  In  a  simple  the epicentre,  = ch (r- , e , o > ) - ch ( e , c o )  - d>  {co )  we  two  equations  the  t h e two one c a n  and  [4.13]  - 2mTT .  forming  [4.14]  the  phase  have = CO ( r - r , ) / (6 - 6-cp 1  simplification  identical,  because  Another  way  their tc  I  i spossible phase  + c7j> + 2 j f T ) .  CZ  i f both  the  [4.15]  ll  functions  calculate  of f r e q u e n c y employs  seismograms.  instrumentsare  cancel  phase  cut.  velocity  thecross-correlaticn  as a  c f the  L e t f (t) a n d f ( t ) r e p r e s e n t t h e seismograms (  £  r e c o r d e d a t two s t a t i o n s , Fourier  transforms. F  which  from  where  (to) - 2 n 1 T ,  further  their  case,  knowing  relationships:  *•  as  of  - <£  = co/k(u>)  function  necessity  - cj> ( 6 , co)  the  to  I f t h e r e a r e two  a r e a t t h e same a z i m u t h  velocity,  A  i s more d i f f i c u l t  available.  shift.  Subtracting  c (u>)  by E o l d u c  f o r the earthquake  k<co)°r,= 4> ( r . , e , c u ) k(lo)*r  be  solution  obviates  the following  I I , o r i t may  r e s p o n s e , a s shown  a  i sn o t always  recording  stations  i n Chapter  the amplitude  differences  source  described  c a n be o b t a i n e d f r o m t h e  The s o u r c e phase s h i f t  because  mechanism,  response  2 l  (CO)  =  and  F^ (co)  be  Then c o n s i d e r  (F /T,) A  a n d l e t F, (co )  =  {F  t  •F*)/|F |Z  i s t h e d e c o n v o l u t i o n of the second  I  signal  with  respect  34  to  the first.  The  phase  delay  F«(t*>) * F * ( c o ) , a s c a n b e s e e n (F  °F*)/|F,|  Z  2  <p = <f> - <f> .  where  propose  the  i fthis  i s  contained  (A /A, ) • e x p { i ( t o t - < ^ + ^ ) }  =  ( A / A , ) o e x p ( i c o t ) e a xp ( - i ci> )  use  in  i s expanded:  =  2  (  £  Landisman  f  information  cf  et a l .  this  ( 1969)  method  were  to  the f i r s t  calculate  to  phase  velocitias. However, of  the above  noisy. stable  as  of several  long  as  used  to  the  reduce  method,  whose  disparsion  This  reduces  signa1-to-noisa  4.5  Tha suggests frequency  T  {  (u))  t h e ' range ratio  Filter  definition  of  band  a l . , 197-2).  of t h e seismcgram and  signal, F  2  increases  (t-o). the  Analysis  group  travel  group  (c0 - £ , to +£. )  number o f f r e q u e n c y  of the  the zero-time l a g .  t o compute o  Another  by a s y n t h e t i c  o f c/) (to) ,  near  Wulti£le  a way  i s replaced  et  i s  to the  properties  (Dziewonski  that  this  stations.  the d i s p e r s i v e  are  c a n b e made m o r e  are situated close  recording  approximates  o u t , both  cross-correlograms;  i s "residual dispersion"  this  point  when t h e r e c o r d s  technique  the events  joining  (1972)  unstable  cross-correlation  circle  signal  and H a l e s  are very  by summation  technique  In  methods  The  possible great  as Dziewcnski  o  points  time  i n Eqn. [ 4 . 9 1  velocity dispersion. i s approximated  i n  the  Fouriar  I f the  by a d i s c r e t e transform  cf  35  F (CO) , occur  than  the  at t h e Tha  select  maximum  grcup  travel  of time  F o u r i e r transform the  function  narrow  has  velocity  domains.  envelope  f c r the  has  to  be  of  a  f (t)^  frequency  windowed  ( co - £. , 60 +€L) , b u t  band  to a l l o w  the  0  60 . 0  in  crder  the  windowing  good r e s o l u t i o n  i n the  Dziewonski  a l . (1969)  et  will  to  frequency  and  chose  the  Saussian function \(co) to  meet  these  requirements.  resolution  and  dispersion  i n the  In  is  function. db the  reduce  However, by peak,  f u n c t i o n remains  points  with are  Usually  no  mora  [4.16]  parameter upon  oc  the  computational which  makes  controls  nature  the  of  Dziewonski  a  nearly  Fourier  2%  a  level  al.  optimum  to approximate  than  et  c o s t s , the it  truncating at a  discrete  chosen  }  2  the  saismogram.  to  the  The  depends  truncated,  down from  working  is  i t s value  order  function  )  = ex pf - <x  transforms, the e x a c t  d e v i a t i o n from  band-limited of a t l e a s t  (1969)  filter  the  Gaussian  30  claim  that  function.  When  the t r u n c a t i o n  f r e q u e n c i e s U) . n  exact  frequencies  necessary. Tha  analyzed selected  inverse to  find  sat  progression,  transform the  of  amplitude  the  However,  in-phase  f o r each 6 J  Q  (to)  at  periods  progression).  spectrum  the  windowed each  group-velocity values  whereas  signal  of  to  tha n  .  evaluate  are  transform One the  spectrum  frequency  (usually in  a  in a  a  linear  logarithmic  contains  must form  for  is  tha  instantaneous  only  the  quadrature spectral  36  amplitudes the  and phases.  quadrature  From  spectrum 2  (w)  h  t h ein-phase  spectrum  G (co), n  i s obtained:  = G  n  (co) »exp ( i 7T/2) .  Then, t h e i n s t a n t a n e o u s amplitudes  [4.17]  and phases  are  expressed  by  \  (j> ( t The  function  seismogram  particular The as  order,  time.  n  The  shows,  (t) does  the  root-mean-sguare  step  m  o f t h e windowed  travel  i n group  process  just  which  velocity  t o t h ef i r s t that  order  i n general  which f o r the  study.  outlined  i s known  described  t cReal  earthquake seismograms  because  by  t h e above  i n £O ; t h e n  the  maximum  t o t h e exact  a r e reduced  method,  energy.  under  was  (1972) , a r e n e e d e d  errors  time  Further refinements, as explained  n o tcorrespond  Application  and  [4.19]  ( t ) }.  n  analysis",  and Hales  Chile  1  and r e c o r d i n g s t a t i o n  1969).  dispersion"  4.6  m  discrete  #  A  (t )/g  computational  Systematic  "residual  study  a  a r e o n l y good  envelope  2  , and t ^ i st h e group  filter  theory  [4.18]  q„ (tn,) j / *  m  et al.  Dziewonski  +  (t«)  ) = tan-x{  w  entire  2 n  ( t ) r e p r e s e n t s t h e envelope  to  "multiple  results  n  m  f9  earthquake  Dziewonski by  A  f(t)  corresponds  =  (tm)  group  by a p p l i c a t i o n  mentioned  second of the travel of the  above.  Data  o f 5 Cctober were  A computer  1973  was c h o s e n f o r  normalized program  by  was w r i t t e n  their to  37  40!  * 55 b l t i 65 65 67 bO 64 5'* 6 3 M 58 56 57 4 9 47 62 6 i 6C 64 Id 54 5 1 b9 59 6 ? 54 6 1 4 ) 60 53 b ? ft t 6 4 b9 4 3 5 ? 64 63 6 * 64 67 6l 6? 54 5 5 6 1-61 59 61 bC 6 0 bf 6 i 60 o 5 5b bd 5 J 49 60 6 ? 6 1 6 1 6g 65 60 6 J 59 54 % 1 59  3.8  3.4  >*  3.2.  {-< M O  3.01  61 6b 66 ftf bl tb 6b 68 b2 tB b7 bO tb bb bf bf i,l bO  1  s o  6b tt> tb Li 6t bB bfl b 7  2.6  Z  6 1  bb  57 5C 4 7 63 66 54 bb 63 b 1 5i 45 bb 59 bf  be 61 66 7 1 7 1 65 7 1 12 69 6 1 56 64 66 6 7  5 I b2 54 bfl 64 59 59 b4  b9 63 49 62 6b bO 6 7 72 bb  1  00  6 5 64 64 6 2 61 62 61 62 53 5<; 62 62 4 7 53 b l b l 53 4 1 b2 b l 60 be 6 1 6 4 66 64 65 64 70 67 bb 64 72 6H tb 64 72 6 7 67 6 3 70 6 6 6 7 6 ? Hi 'Hr 67 bt t f 61 -r*>" 62 6 2 5? 6b 7J Ml 70 fte bfl 6 0 9C tb 6 6 t 9 7*. 7o 75 7 1 68 6 0 66 'J C V tt 6 6 6*. 7? 7 7 rfU I> 7H 1 3 b9 6 0 >• 4 •n -k -i*' ft I ) /C 71 74 74 7} 78 7 ) 69 6 I « H ^ 6 / 6b o l bt 6 a /? 7B 73 69 6 t 68 6 6 t b 59 7C 75 70 68 6 1 70 70 t b 6*. 75 72 6 5 6 7 6 1 ? 7 1 f?>')/j 9'J 9 , * 9 1 X C 1% b 9 6 9 oO 6 62 70 54 67 64 t l 64 b 9 76 6 7 5 7 7 1 71 bt. 67 64 6 7 b T 71 6 J > T 4 I l_j*'> ^ r"^. 7 9 7 7 71 61 6fc 71 72 7C 68 64 6 b 71 71 6 5 6 9 7? 72 71 bfl 6 3 rirt J u _ £ ' ^ 9 ) » t / l b ;74 7 / 54 t 6 'ft ti 7 3 74 J? 7C 71 7? 7 1 6 7 6 1 (4 *Q t J 6 7 76 7b 73 6 7 be 71 7C 65 6 0 6 1 70 )7 B/ ll 7 1 74 7 7 7 9 7 7 tl 7 7 7 1 6 1 6 5 70 6M 60 5H 70 6 9 6 9 70 6 7 55 57 7 1 H tt 7 dl 71 65 1? 71 71 b 7 6 0 5P I I 7H h 1 &2 flC 74 7 1 7 1 70 6 7 6 1 59 6 f 7K o4 1 t -# 7 5 7 5 7 4 7 167 t t 6 1 59 79 11 It 7 *1 64 7 1 7 j 74 7 d l ris a s il i 7 9 7s 6 7 74 / , U II 7 4 6 7 7 6 7b 6 7 59 6 ? 60 5 7 79 If 74 6 6 53 6C 5 7 46 6 7 t'> tit M b Pb f ? ^•0 tt 7 4 6 P 7 6 H| u J H4 80 74 74 It Hi 7 9 7 1 6 5 61 6 0 5 I 49 H? 7 P. 7C. 5 6 6 2 b ? bfl 5 3 h i 1i f; 81 b i K. e 1 IP. II II 7 1 bC 61 62 5F 50 6 4 6 9 7 5 79 6 9 b'V rt 79 -IC 74 K 7b 12 6 5 61 59 5 7 48 HG 7M 74 7C 6 0 5fi 56 53 5 0 bt 7 j fi « C 7ri 8 1 7t 6ft M O H4 il 7b 7 ) 79 7 7 75 7 3 6 7 5 1 SO 5* 46 4 7 •14 H 4 HI rtC 11 6 5 7C 6 1 57 55 55 44 45 7fcJ- f» 4 74 7^ ti 1 7 9 7 7 6t M 7Q 61 59 t o 5 b 4 6 3ft 79 fl J Pb 7S 7fl 7 1 7ft 14 7b aC 79 77 12 6 « 64 60 52 49 4b d4 76 e4 ti ) 74 6 4 74 7 7 7b 76 7 « 7 7 71 6 9 o 9 6 b 57 4 3 5 » 54 6 I t I ti 7 4 7 4 L* 6 5 6H b b 59 5 2 55 56 tJ4 Rb 7 7 C va 79 n__'J 7 1v.412 74 7 s 1? 6 7 64 ft ) 61 56 54 55 HQ N l A - t i ' * T " 7 ' 7 * * 7 ^ * ' / 9 fl? «2 76 5 f 71 7» 70 59 5fc 6C 58 5 : 49 4 fi 7a M tf 1 (i J 79 75 7fl s .' 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HI i l lflf;75 b4 51 54 b4 54 5 3 52 5 1 5P 56 ll J J 74 79 ft j * TTdjr i I i 7 " > / N « i i 6 9 b ? 4? 5 7 6C 5 d 5 0 52 b 7 59 56 6 9 ?<• )7 8C n J ^ 5 V tl I H ) « V « l 76 74 tO o 2 b6 5 9 6C 57 59 59 5 4 ;*> 7b 7 7 7 8 7 1 lij) '/<J~9y H ' l j / - ) 61 6 7 C9 6S 57 5 5 6 0 5 7 54 5 7 59 56 t b ftt 7C 6fl bb 6 3 6 3 6 2 59 5 7 56 52  60 6". 61 50 62 5b 61 6 7  5 1 SI 59 bl 61 52 58 ftH  60 51 46 61 61 56 40 b«  56 67 71 71 69 66 64 bb 56 67 71 tl  69 6» 63 68 71 7L 70 7 1  72 6S tt 10 7i 72 7 1 7 1  11 76 U 74 71 72 6C 7C 6 1 t*i 6 9 69 7C 70 70 7? 68 6^ 7C 64 59 ft 7 50 66 6 8 6 7 72 bb 72 7b 7b 7P 71 H 1 H 1 IAtl 1 1 j 76 ~njSi / || / ft? 'I .  69 6b 5 T 6 7 60 6b 6b 1? 7b 7b J?  /'  69 67 64 < 6 6 7 ft! 72 76 79 79  71 7C  7? 7 ? 6 9 66 t b 72 71 66 69 ; 1 7 1 6 6 7? 74 7 1 66 74 7b 71 67 7". 7b 74 70 71 71 76 12 67 74 78 75 7M 7P BC 77 r14 82 fl I 78 31 89 I 16 fl4 fl? 7H K4 P l 79 T V 1 'J 9 o\ 8 fl 1/*) " 0  70 6a 69 t e 69 6 1 67 6b 6 " 71 76 79 UC H i rt4  64 be 66 7 I 7 J 74 76 »8 H2  8  1  V)  y  111  r  7b 73  65 55 bt 6? 67 6 7 6b bs  jyrrd1111 TT'nr'K1 r1t.•)! 1  L  I  ,  SS  64 tn 75 e? a; us iu_4wA—'x<y n i  30  20  10  40  54 4 3 49 51 54 45 4 8 49 56 48 45 4 7 5il 50 43 4 6 59 5 1 4 1 46 6 0 5 3 46 47 60 54 49 48 6 0 55 bl 50 59 55 5 1 51 58 55 54 52 55 54 54 52 46 53 54 51 12 50 5 1 53 45 4 7 52 54 46 44 51 54 47 4 4 51 54 49 46 51 54 53 4H 51 54 55 49 50 54 56 4 7 4 A 54 56 42 4b 53 5b 4 t 44 5 ( 5b 45 46 53 55 4b 4 fl 54 54 42 50 54 55 4 I 51 54 56 51 53 54 5 « 56 55 b 1 59 58 57 51 59 59 57 50 56 5-) 58 M 57 59 53 51 55 58 5H 55 53 b t bfl bb 4 H 56 53 56 44 55 5 7 b5 50 55 5 7 55 52 56 57 54 51 56 5 7 51 50 5fc 57 5? 5 1 57 5B 5 2 5 6 5 9 bfl 54 5 ft 59 59 55 57 5 8 5 8 5 5 52 S6 57 5 3 44 54 56 51 4fl 54 55 5 I 5 1 55 54 5 2 55 5 4 52 49 5b 5 ? 4b 45 54 50 40 40 5 1 5C 4 1 41 4 7 50 49 43 4fl 50 49 4b 48 46 4 9 4<« 49 46 51 52 52 51 51 51 17 50 54 54 5 ? 52 5 1 53 4 1 43 50 49  51 52 52 51 50 50 49 48 46 4P 49 50 51 5? 52 5 1 5 J 54 54 54. 55 55 55 55 55 54 5? 4*J 45 34 19 46 49 bl 51 49  4a  4 7 46 )9 19 48 bl 50 45 34 44 4 8 48 45 38 11 17 27 44 50 5 I bC 5C 48  50 50 50 50 49 48 47 46 4b 44 44 44 45 44 4 ) 40 18 40 44 4 7 49 51 5? 5? 52 52 51 49 46 42 18 40 4 3 45 46 42 46 32 4 4 36 4b 4 3 4 1 46 49 47 50 48 50 48 4 9 4 1 47 45 44 43 43 4 3 44 46 45 4 7 4ft 46 4fa 42 45 37 44 3 9 44 40 45 45 4 7 48 4 7 45 4 1 17 36 44 42 44 41  52 52 5 I 50 49 48 45 41 14 26 38 43 45 46 4 7 48 48 49 5C 5 1 5 1 54 54 54 54 53 5 1 49 4 7 4b 4b 4b 46 46 45  45 4 7 48 49 50 50 51 51 50 >0 49 46 47 45 4 1 42 42 42 43 44 45 46 4 7 48 49 49 49 46 4b 44 4 3 4 3 45 4 7 49 50 51 51 51 51 51 50 49 46 40 23 18 42 44 44 45 46 4U 48 4b 4 7 4b 46 45 43  4 7 48 49 50 51 5 I 52 52 52 51 51 50 49 48 4 7 45 44 42 4 1 41 41 41 45 46 46 4 7 4 7 47 4 7 4 7 47 48 48 49 50 51 5? 52 52 52 51 50 48 4b 4 1 41 4 1 42 42 4 1 4 1 44 4 7 48 4 7 45 44 4b 4b 45  J 1 l_L (f> 7o & «o 100  50  PERIOD (Sec) Figure  4.3  fiesult applied  of multiple filtering analysis t c t h e QUA r e c o r d o f C h i l e earthquake  Instantaneous spectral amplitudes i n db, f u n c t i o n s o f group v e l o c i t y and period, have t e e n n o r m a l i z e d t c a maximum o f 99 d b . F i l t e r p a r a m e t e r oc = 50. C o n t o u r i n g assists in the inference of group velocity values. perform QUA  multiple  seismograms.  represents QUA  filter  a n a l y s i s , and a p p l i e d  The matrix  theresult  o f amplitudes  c f the grcup  as  t o t h e VCT a n d  shown i n F i g .  velocity analysis  4.3  of the  data. It i s apparent  that  f c r periods  longer  t h a n 40  seconds,  38  the  r e s o l u t i o n i s not s u f f i c i e n t  is  reguired.  recording  the event,  apparatus been  Because  in  reported  discontinued  to  the  with  the  lack  i t was d e c i d e d  order i n  of  and hence  obtain  new  of  a  chapter,  data  analysis  third-station  to r e - i n s t a l l  more d a t a .  previous  no  further  the  However, the  field as has  project  and s u p p o r t i n g  was  funds  were  methods  cf  surface  wave  exhausted.  4.7  D i c j j . t a l  Bioch computing  and  Hales  phase  records.  of Phase  (1968)  describe  velocities  One o f t h e m  Velocities  frcm  involves  two  two-station  t h e sum o r d i f f e r e n c e c f  digitized  seismograms,  and t h e e t h e r ,  which  efficient,  computes  cross-product  of  after  bandpass The  they the  filtering  method  principle  that  are  t h e sum o f t w o f u n c t i o n s  i n phase  tha  f o r a given  more  seismograms  transform  i s derived i s  frequency  The c o m p u t a t i o n  Fourier  the  find  and t i m e - s h i f t i n g i s a p p l i e d .  o f sums a n d d i f f e r e n c e s  difference) .  forming  the  they  the  a  from t h e  maximum  when  (and v i c e v e r s a f c r  i s carried  out  of  and d i f f e r e n c e  t h e sum  by  first  functions: oa  H(T,tO)  =  [  [ f , (t+t)  R (T , co ) _ = ] * { , (^ ) f  and  i n t h a second  +r  stage  G(T,w)  + f  " f  z  2  (t) )eexp ( - i c o t )  (t) } * e x p ( - i w t )  forming  their  dt  dt  [4.20]  [4.21]  ratio:  = H ( T , t o )_ /H ( r ,CO)+ .  [4.22]  39  G { T , to ) , matrix,  as  plotted T  and t h e delays-  phase  velocity.  filter  to achieve  arbitrary direction  (1969)  better of  period,  are chosen  Capcn  number  versus  i s the amplitude  to represent  applied  steps  a maximum-1 i k e l i h c c d  signal-tc-ncise ratios. receivers  may  of approach  cf the  Kayleigh  cross-product  method  involves  in  be  Also,  used;  wave  an  then  train  the  may  be  studied. The of  the  two  seismograms  single-freguency  time  B « c o s ( t o t + <f> ) , cross-product  d.c.  i s shift  <j>  being  they  are  essentially  Aocos(wt)  say their  filtering  relative  and  ph a s e .  Their  i s ( A B / 2 ) »{cos (2 to t + <f> )  a  function  with  proportional  calculated  that  series,  with  g(t,<j&) = which  so  time-domain  this  twice  to cos $.  d.c. s h i f t  + c o s <f> }, the  freguency  Bioch  by m e a s u r i n g  [4.23]  and  and  Hales  a maximum,  a  (1 968)  g  , and  max  the  following  minimum, g d.c.  The  phase  chosen  , from  l e v e l -  v e l o c i t y matrix  steps  i n phase  ( g ^ g +  m V )  consists  which )/2.  of  [4.24] the  d.c. l e v e l s f c r  v e l o c i t y and f o r the p e r i o d  range of  interest. In; p r a c t i c e , period a  seismograms  a t the corresponding  knowledge  seismogram. Fourier  the  cf The  analysis,  the  are  group-delay  group  advantages time-variant  windowed time.  velocity the  dispersion  authors  filtering  This  note  for  each  requires of are  the that  and i n t e g r a t i o n o f  uo  the  ti: e n  series  are mirimized  previous  methods.  The  current  analysis  of  however,  that  velocity travel early  investigation  group  velocity  this  calculations, times  stages  cr eliminated  serves  step  in  dispersion. a a  reducing  of the c a l c u l a t i c n  compared  d i d net progress  was  because  as  It  preliminary knowledge  to  beyond i s  t c the  the  clear, phase  of  the  group  computaticn  time  i n the  (Dlcch  and  Hales,  1968).  41  V.  5. 1  Intrcduct icn  Tha  goals  lithospheric  of  this  seismographs  have  conditions.  been  I t i s the  improvements  potential  may  be  was  of  automatic  In  be  thus  the  is  frame  tc of  a  mass spare  place the  net  under  chapter  to  i n order  in  the the  field  suggest  that  constancy case  of  even  their  cf  the  Geotech the  AC  power  u n c o n t r o l l a b l e changes  built  is to  suggested provide the  position tape  lightweight  seismometer.  strips  These  in  the  that  an  battery  power  batteries  and  should  .recorder  the  after  controllers.  conserving  addition, using  II,  It  operation.  suggestion boom a n d  for  continuous  continuously  were  long-period  tested  systems  temperature  device  emergencies,  this  the  Mass P o s i t i o n  env i r c n iren t s .  switching  and  problematic  were r e s p o n s i b l e  thermostated  assuring  the  i n Chapter  the  Island  to  fully.  remained  introduction  of  these  particularly  seismometers,  during  with  reported  position,  failures  purpose to  respect  functioning  developed  utilized  Pl2kIS2i§  with  Vancouver  three  possible  mass  of  However,  5.2  project  structure  achieved.  As  CONCLUSION  he  monitored  channel. of  would  Mylar act  One on as  the a  42  variable  capacitor,  oscillator  circuit  In be  this  manner,  a continuous  seismic, The room,  that  the  i n Chapter  three  records  II,  can  portable  drive  be r e c o r d e d  on  could  an  tape.  c f mass p o s i t i o n  would  be p e r f o r m e d  proposed  as  a  calibration, be  removed  after  means  cf  performed  as  fully  may  f l u c t u a t e with three  frcm  the  t o be d i f f e r e n t  with  a  tape  be r e c o r d e d a t long  from  each  and t h e i r  with  perio.ds. ether  as  mass-positions  "time.  systems of  earthquake.  Fcr  the  cross-correlation  computation.  will ratios  are not i d e n t i c a l  during  i n t h e same  s i g n a l s are monitored  s i g n a 1- t c — n o i s e  consideration  of  are installed  an e a r t h q u a k e  are expected  seismometers  systems  output  high  the  Fourier  i s  relative  I n due t i m e ,  sufficiently  response  tc  records.  recorder.  recorded  reccrd  used  o f t h e Phase C a l i b r a t i o n  following experiment  and a l l t h r e e  The  would  calibrations  Verification  verifying described  be  of the records.  5.3  The  could  whcse c h a n g e s  a v a i l a b l e and phase  examination  The  which  the the  transforms  carefully  mass-position each  of  Then  are  the  at  frequency input  and  calibration seismographs  t h e phase  calibrated,  terms  of the d i g i t i z e d  i s  the  time  with c f the  component, output  time  formed.  i s are  deduced  the series  The from  phase this  removed  from  the  seismograms.  when  this  43  process  i s  finished,  identical. field  This  of  the  5.4  A the  wider  analog  though  an  dynamic FM  cost,  amplitudes  trains,  The  without Long  gather  possible Allowing of  one  planning  of  the  the  of  the  removal  be  desirable.  systems to  in  record  i s  their  the  wide  Even low range  teleseismic surface  digital  system  amplifiers  periods  field  would  time  their  drift must  wave  should  be  appear  to  experiments.  passive the  operated  in  the  would RC  output  three  analysis  equipment  t c be  This  about  only  further  te  allow  filters  four  to  months  of  earthquakes  cf  were  failures,  minimum  to  stages.  anticipated in crder  In  sites,  due  at  be  data.  in  should  enclosures.  range of  usable  f o r down  further  the  records.  would  expected  i n c r e a s i n g the  utility  year  that  i s c u r r e n t l y a t t a i n a b l e with  inadequate  AS-330  operating  at  seismic  portable  controlled  enough  recording  later  prove  be  alternative.  thermostatically  d.c.  are be  Geotech  extension  than  the  to  should  Considerations  gain-ranging  an  the  the  for  recorders  cf  they  a  as  range  tape  tc  and  considered  sufficient on  seismograms  i s essential  Instrumental  advantage  operating of  are  instruments  Other  three  experiment  calibrations  affect  the  t o be  recorded. a  period  allowed, i n  44  BIBLIOGRAPHY  A t w a t e r , T. (1970) I m p l i c a t i o n s o f p l a t e t e c t o n i c s Cenozoic tectonic e v o l u t i o n of w e s t e r n N o r t h Bull. Geol. Soc. Am., 8J, 3513-3535.  fcr the America.  B i o c h , S. and A.L. H a l e s (1968) New techniques f o r . the determination o f s u r f a c e wave p h a s e v e l o c i t i e s . Bull. Seism. Soc. Am., 5 8 , 1 0 2 1 - 1034. B o l d u c , P.M. (1971) A f e a s i b i l i t y s t u d y f o r a p o r t a b l e long period seismograph. Unpublished M.Sc. thesis, U n i v e r s i t y c f B r i t i s h C o l u m b i a , 66 pp.  Bolduc, P.M., R.M. Ellis and R.D. Russell (1972) D e t e r m i n a t i o n of the seismograph phase response frcm the amplitude response. Bull. Seism. Soc. Am., 62, 1665-1672. Caner, B. ( 1970) Electrical conductivity structure western Canada and petrological interpretation. jG§ G e c e l e c . , 22 , 1 1 3 - 1 2 9 . Capon, J . ( 1969) High-resolution spectrum analysis. Proc. IEEE,  frequency-wave 57, 1 4 0 8 - 14 18 .  in J.  number  Chandra, U. (1 974 ) Seisroicity, earthquake m e c h a n i s m s , and t e c t o n i c s along the western coast of North America, frcm 4 2 N t o 61 ON. Bull. Seism. Soc. Am., 64, 1529- 1 54 9. 0  Dorman, J . and M. .Swing (1962) Numerical inversion of seismic surface wave d i s p e r s i o n d a t a and c r u s t - m a m ; l e structure in the New York-Pennsylvania area. J. Geophys. R e s . , 67 , 5 2 2 7 - 5 2 4 1 .  Dziewonski, A.M., S. Bioch and M. landisman technique f c r the a n a l y s i s cf t r a n s i e n t seismic Bull. Seism. Soc. Am., 59, 427-444.  (1969) A signals.  45  Dziewonski, A.K. and A.L. H a l e s (1972) N u m e r i c a l analysis of d i s p e r s e d s e i s m i c w a v e s . I n Methods i n CcmjrutaticnaJL Physics, vol. 11, B. ft. B o l t , e d . New Y o r k : A c a d e m i c  Press.  Pp.  39-85.  Dziewonski, A., J . Mills and S, dispersion measurement—A new analysis. Bull. J^sisrn. Scc.  Ewing, M. , W.S. Jardetzky waves i n l a y e r e d media. 380 pp.  Bioch (1 972 ) Residual method of s u r f a c e - w a v e Am., 62 , 129-139.  and F. Press (1957 ) E l a s t i c New Y o r k : M c G r a w - H i l l Beck Co.  Sarland, G.D. (1971) I n t r o d u c t i o n t o core and c r u s t . P h i l a d e l p h i a : ~ W . B T FP. H a r k r i d e r , D.G. s u r f a c e wave media. Bull.  Geophysics—man t i e , Saunders ~Co.7 420  and D.L. Andersen ( 1962) Computation c f dispersion f o r multilayered anisotropic Seism. Soc. Am., 52, 32 1- 332 .  H y n d m a n , R.D. (1975) H e a t f l o w m e a s u r e m e n t s i n t h e i n l e t s o f southwestern British Columbia. (Submitted t c J. Gsophys. Res. )  K o l l a r , F. and R.D. R u s s e l l ( 1966) Seismometer a n a l y s i s Bull. Seism. Soc. using an e l e c t r i c c u r r e n t analog, Am. , 56 , 11 93-1205. Landisman, M. , A. improvements observations. 369-4 03 .  Dziewonski and Y. in the analysis G§oi'h_vs. j . Roj.  Sato (1969) Recent of surface wave Astron. Sec., ]_J,  Melton, B.S. (1971) The La c o s t e s u s p e n s i o n — p r i n c i p l e s and practice. Gecphvs. J. R c j . Astron. Sec., 22, 52 1-54 3 . P r e s s , F. (1956) Determination o f c r u s t a l s t r u c t u r e from phase v e l o c i t y of R a y l e i g h waves. Part I : Southern California. Bull. Geol. Sec. Am., 67, 1647-1658.  46  Srivastava, S.P. (1973) Interpretation, of gravity and magnetic measurements a c r o s s t h e c o n t i n e n t a l margin cf British Columbia, Canada. Can, J . E a r t h S c i . , ]_0, 1664-1677. S t a c e y , R.A. (1 973 ) G r a v i t y a n o m a l i e s , c r u s t a l s t r u c t u r e a n d p l a t e t e c t o n i c s i n the C a n a d i a n C o r d i l l e r a . Can. J. Earth S c i . , 10 , 6 1 5 - 6 2 8 . Stacey, R.A. ( 1 9 7 4 ) Plate tectonics, vclcanics lithosphere i n B r i t i s h Columbia. N a t u r e , 250 , Tobey, G.E. , J . G . 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Am., 4 9 , 9 9 - 1 1 4 .  47  APPENDIX--OPERATION  A. 1  Tha to  OF THE  Descr int.ion  instrument  panels  were d e s i g n e d  t h e a m p l i f i e r and a c t i v e f i l t e r ;  input;  to deliver  and  t o serve  the  panels  output  may  be  used  and w i l l  f c r  accept  the  power seismic  to the tape  recorder;  the systems.  A l l cf  normal  either  operation the  as w e l l  as  Sprengnether  cr  an a m p l i f i e r ,  an  instruments.  Each active sine  the filtered  to distribute  to receive  as an a i d i n c a l i b r a t i n g  calibration, Geotech  APPARATUS  o f t h e wooden  filter, wave  enclosures  and t h e i n p u t  generator,  channel.  Two  supplies;  the t h i r d  WWVB,  of the three  contains  terminals tape  f o r the seismometer,  recorder  boxes a l s o  a  spare  512  power  f o r an e x t e r n a l  power  house  s u b s t i t u t e s a jack  and  Anatek  supply. The  wiring  cabling  i s used  seismometer to  R4  stray  relative  levels  in  on F i g . A.1.  between  the  were  driving  chosen  panel  i n crder  R e s i s t o r s R 1 , R2 a t t h e i n p u t  current  mode. to divide  mode,  Shielded  front  terminals,  from  Resistor  ceil,  the l e v e l s  dt  and  the  in  R3,  sine-wave  values  the f i l t e r e d  o f 0 d b , -12 db and -24  "calibration"  the  f o r t h e seismometer  i n "calibration" R9  mode;  signals.  damping  attenuate  through  shown  and t h e a m p l i f i e r i n p u t  critical  generator  i s  f o r the ccnnecticn  jack  minimize  provide  diagram  f c r  output  R5  into  "operation"  a r e 0 a n d -12 d b .  '  ofERATE  C>'  " 820.O.  0,R  >D  Test*  I  I AA  Aid I  I  [  SABRE  WWVB Figure  A.1  *I0  Wiring diagram of the instrument pa neIs.  FY  49  RIO  attenuates  tape  recorder's  depends Switch S2  upon  A  At must  S3 i s u s e d timing  Installation  the f i e l d  avoid  recorder  a n d WWVE r e c e i v e r  To f a c i l i t a t e  contains  an o p e r a t i o n a l  seismometer  i s  used.  directly; balancing  e i t h e r o f t h e two  this  of the seismometer  period  of  the  teem  procedure, a small  a m p l i f i e r was h u i l t  r—  F i g u r e - A. 2  of  value  input  a t t e r m i n a l T3.  the t i l t  the natural  seconds.  the filter  the purpose  to monitor signals)  i t s  the  Procedure  station,  be, s e t s o t h a t  fcr  overdriving  oscillator;  a t e s t s i g n a l t o enter  (normally  '2  to  controlled  the amplifier inputs  outputs;  channels  voltage  the particular  S1 a l l o w s  shorts  its  t h e WWVi: s i g n a l ,  lok-n. VWWA-  device  frame i s  20  which  ( F i g . A . 2 ) . The  .  D e v i c e used t c check, t h e n a t u r a l period of the seismometers  connected  tc  this  device  v i aa  compatible  50  terminal, that but  and  the switch  step  period  increases  S1  turned  tc  must  be  to the  be  of  the  readily  that  natural  period  Temperature  of  the  of  ccntrcl  incandescent  lamp  (see F i g . 2.1).  wall  of  the  as  far  away top  of  Sprengnether  monitor  the  thermistor  e n c l o s u r e so as  possible the  temperatures  s h o u l d be  temperature,  because  when t h e  lamps  are  i s  natural frcm  zero  When a d j u s t i n g end  The  cf  the  the frame  viceversa.  inside  blinking  in  one  wall;  seismometers  the  fitted of  box,  and  the an  or  in can  enclosure.  degrees  controllers frequently.  work  protrudes  the lamp  thermometer  set several the  consists  thermistor  the  A  be  former i s a t t a c h e d to  the  from  Geotech  which  probe,  that  seismometer.  temperature  the  a stopwatch  front  unit,  a  the  and  A  ceil  s t y r e f c a m e n c l o s u r e s can  and  on  S3,  used,  position.  t h e bocm, and  electronics  the  be  calibration  with  the  may  supply  Controller  large  a temperature  fastened  correct  switch  raising  power  seismometer  the  determined  same  a centre-zero galvanometer.  the  Each  the  seismometer's  pushbutton  i n mind  A. 3  with  Either  by  bear  frcm  uses.  can  crossings  i s derived  amplifier  input  controlled  t i l t ,  pcwer  above mere  can  front be  used  be cf to  Operating the  ambient  efficiently  51  A«  In the  Calibration  4  "calibration"  wide-band  calibration signals  be  periods,  the  the  periods before  high the  frcm  be r e c o r d e d  i s  used  Both  When  such  as  to drive the  input  the front  i s allowed  altering  generator,  and  panel  cutput  j a c k s and  calibrating  at  long  t c s t a b i l i z e f o r about two  the input  frequency.  t c provide a reference  A  timing p o i n t on  tape. Finally,  are  111,  recorder.  system  should  mcdel  monitored  on a c h a r t  channel  a sine-wave  of the seismometer.  displayed  full  node,  Wavetek  coil  may  and Operation  both gain front  f c rnormal  operation, the front  " u p " a n d t h e mods c o n t r o l filtered panel,  output  through  (Channel the jacks  panel  switches  i s s e t at "operate". 7) c a n labelled  be  monitored  "filter  The at  output".  


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