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Geomagnetic depth-sounding in the southwest U.S.A. and in southern British Columbia Livingstone, Charles Edward 1967

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GEOMAGNETIC DEPTH-SOUNDING IN THE SOUTHWEST U.S.A. AND IN SOUTHERN BRITISH COLUMBIA by Charles Edward L i v i n g s t o n e B.Sc,  The U n i v e r s i t y of B r i t i s h Columbia, 1965  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Geophysics  We accept t h i s required  t h e s i s as conforming to the  standard  THE UNIVERSITY OF BRITISH COLUMBIA March, 1967  In  presenting  for  this  an a d v a n c e d  that  thz  study. thesis  degree  Library  Department  at  the  of  this  t  e  thesis  for  permission.  Geophysics .  May  H  Columbia  f  for  the  1Q67.  It  requirements  Columbia,  I  reference  and  permission for extensive  representatives.  by h i s  British  available  or  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a a  freely  of  p u r p o s e s may be g r a n t e d  w i t h o u t my w r i t t e n  D  University  it  agree that  f u l f i l m e n t of  scholarly  or p u b l i c a t i o n of  Department  in p a r t i a l  s h a l l make  I further for  thesis  copying of  this  by t h e Head o f my  is understood that  financial  agree  gain  shall  not  be  copying allowed  ABSTRACT Three f o u r - s t a t i o n c h a i n s of A s k a n i a V a r i o g r a p h s were operated f o r p e r i o d s of two months d u r i n g 1965 and 1966 i n B r i t i s h  Columbia,  New Mexico, Texas, and Oklahoma t o form two magnetic d e p t h sounding p r o f i l e s , one i n w e s t e r n Canada, and t h e o t h e r i n the s o u t h w e s t e r n U.S.A.  Records were a l s o o b t a i n e d from some I.G.Y.  s t a t i o n s and permanent magnetic o b s e r v a t o r i e s i n t h e v i c i n i t y of t h e U.S.A. p r o f i l e . A n a l y s e s of t h e r e c o r d s show t h a t t h e i n l a n d  geomagnetic  v a r i a t i o n anomaly observed by Hyndman (1963) a t Kootenay  Lake, B.C.  reappears t o t h e n o r t h between G o l d e n and J o h n s t o n Canyon and t h a t the anomaly which Schmucker (p.964) observed between l a s Cruces and Cornudas, N.M. reappears t o t h e n o r t h between Sayre ©nd Norman, Okla. Power s p e c t r a l r a t i o s o f t h e form " h i g h - I s t a t i o n / l o w - I s t a t i o n " suggest t h a t t h e main f e a t u r e s of t h e s u b s u r f a c e e l e c t r i c a l c o n d u c t i v i t y s t r u c t u r e s under b o t h t h e Canadian end the U.S.A. p r o f i l e s are very s i m i l a r .  2  TABLE OF CONTENTS  INTRODUCTION  II  III  IV V  VI  THEORY (1) I-ratios (2) The i n d u c i n g f i e l d and i t s e f f e c t o n A z (3) C o n d i t i o n s f o r d i r e c t d e t e r m i n a t i o n o f conductivity-depth p r o f i l e s EXPERIMENTAL PROCEDURES (1) The A s k a n i a V a r i o g r a p h (2) F i e l d work DATA PROCESSING RESULTS (1) I - r a t i o n s and p o l a r p l o t s (2) Power s p e c t r a l a n a l y s i s APPENDIX Two-layer model c u r v e s REFERENCES  FIGURES Map of t h e s o u t h - w e s t e r n U.S.A. showing station locations Map of w e s t e r n Canada showing locations  station  C o n d u c t i v i t y s t r u c t u r e f o r western North A m e r i c a , a f t e r Caner and Cannon (1965) S i m p l i f i e d model f o r c o n d u c t i v i t y step showing f i e l d component r e l a t i o n s Mean d e v i a t i o n of power s p e c t r a from S.A.D* check (Coherence)  2  from S.A.D. check  Parkinson p l o t , Price  (Utah)  Parkinson p l o t , Burlington  (Colorado)  P a r k i n s o n p l o t , Norman (Oklahoma) P a r k i n s o n p l o t , J o h n s t o n Canyon (B.C.) I - r a t i o : .and d i p a n g l e v s . a z i m u t h p l o t , (Utah)  Price  I - r a t i o and d i p a n g l e v s . a z i m u t h p l o t , B u r l i n g t o n (Colorado) I - r a t l o and d i p a n g l e v s . a z i m u t h p l o t , Norman (Oklahoma) I - r a t i o and d i p a n g l e v s . a z i m u t h p l o t , J o h n s t o n Canyon (B.C.) South w e s t e r n U.S.A. I - r a t i o  distribution  Western Canada I - r a t i o d i s t r i b u t i o n Power s p e c t r a l d e n s i t y r a t i o ( R e v e l s t o k e / C a l g a r y , Z/H ) Power s p e c t r a l d e n s i t y r a t i o ( R e v e l s t o k e / C a l g a r y , Z/Z) Power s p e c t r a l d e n s i t y r a t i o ( R e v e l s t o k e / C a l g a r y , H/H) Power s p e c t r a l d e n s i t y r a t i o s ( J o h n s t o n Canyon/Calgary, H/H, D/D)  FIGURES  (Continued)  (21)  Power s p e c t r a l d e n s i t y r a t i o ( J o h n s t o n Canyon/Calgary, Z/Z)  (22)  Power s p e c t r a l d e n s i t y r a t i o s ( J o h n s t o n Canyon/Calgary, Z/H,  (23)  Power s p e c t r a l d e n s i t y r a t i o s ( N e w k i r k / D a l l a s , Z/D, Z/H)  40  (24)  Power s p e c t r a l d e n s i t y r a t i o ( N e w k i r k / D a l l a s , Z/Z)  42  (25)  Power s p e c t r a l d e n s i t y r a t i o s ( N e w k i r k / D a l l a s , D/D, H/H)  42  (26)  Power s p e c t r a l d e n s i t y r a t i o ( B u s h l a n d / D a l l a s , Z/H)  43  (27)  Power s p e c t r a l d e n s i t y r a t i o s ( B u s h l a n d / D a l l a s , Z/Z, H/H)  43  (28)  Power s p e c t r a l d e n s i t y r a t i o (Norman/Dallas, Z/Z)  46  (29)  Power s p e c t r a l d e n s i t y r a t i o s (Norman/Dallas, D/D, H/H)  46  (30)  Comparison of n o r m a l i z e d Z/H power s p e c t r a l density ratios  47  APPENDIX  39  Z/D)  39  TWO-LAYER MODEL CURVES  (31a)  VL slO^cni," , h  *100  (31t>)  V  (32a)  V = 5 X l O ^ c m . - , h - 100 km.  51  (32b)  V ^5  52  (33a)  V =10~  (33"b)  V «10-7  (34a)  V = 2 X 10 " 7 c m . - , h - 1 0 0  (34b)  VL=2X10 - 7 c m . - l ,  (35)  E f f e c t s of v a r y i n g h  1  slO^cm." , 1  L  2  49  km.  h =150km.  50  2  1  L  L  L  L  2  X lO-Scm.- , h ^ 1 5 0 1  2  7  km.  cm." , h * 100 km.  53  1  2  cm. , -1  h - 1 5 0 km.  54  2  1  L  2  km.  55  112-I50 km.  55  and V L  56  2  4  ACKNOWLEDGEMENTS I am p l e a s e d t o acknowledge t h e v a l u a b l e a s s i s t a n c e and welcome c r i t i c i s m g i v e n by Mr. B. Caner, o f t h e V i c t o r i a Observatory.  Magnetic  I am a l s o i n d e b t e d t o D r . U. Schmucker f o r h i s  generous p e r m i s s i o n t o use u n p u b l i s h e d r e c o r d s , and to' D r . Y. Nakamura f o r s u p p l y i n g r e c o r d c o p i e s from t h e Norman G e o p h y s i c a l ' JL  O b s e r v a t o r y . Thanks a r e a l s o due t o the many*people i n b o t h w e s t e r n Canada and t h e s o u t h w e s t e r n U.S.A. w i t h o u t whose a s s i s t a n c e i n o b t a i n i n g instrument' s i t e s t h i s t h e s i s would not have been p o s s i b l e . The work has been s u p p o r t e d i n p a r t by a g r a n t from t h e Defense H e s e a r c h Board o f Canada,  5  I  Introduction "Geomagnetic depth-sounding"  surface e l e c t r i c a l  i s a t e c h n i q u e used to measure sub-  c o n d u c t i v i t i e s employing s i m u l t a n e o u s , t h r e e  component, geomagnetic d a t a from a l i n e a r a r r a y of temporary  magnetic  o b s e r v a t o r i e s . To measure the e l e c t r i c a l o c o n d u c t i v i t y as a f u n c t i o n of  depth f o r a minimum depth of 10 km.,  to  150 km. and magnetometers w i t h an upper c u t o f f f r e q u e n c y of  cpm  a s t a t i o n s e p a r a t i o n of 50 0.1  ( c y c l e s p e r minute) a r e n e c e s s a r y . S e v e r a l such s u r v e y s have been c a r r i e d out i n w e s t e r n N o r t h  America  s i n c e 1959 when Schmucker  began h i s work i n the  southwestern  U.S.A. Schmucker (1964) operated an east-west l i n e a r p r o f i l e from La J o l l a , C a l i f o r n i a t o Sweetwater, Texas ( F i g u r e 1 ) , and from the d a t a made the f o l l o w i n g o b s e r v a t i o n s : (a)  From c e n t r a l s o u t h e r n C a l i f o r n i a t o Las C r u c e s , New  Mexico,  t h e v e r t i c a l f i e l d v a r i a t i o n s (A"Z) were u n i f o r m l y s m a l l f o r bay  type  disturbances. (b)  From Hope, New  f o r m l y l a r g e f o r bay (c)  Mexico, t o Sweetwater, Texas, &"Z were u n i -  type d i s t u r b a n c e s .  Between Las Cruces and Cornudas,  r a p i d l y f o r a p a r t i c u l a r type of source (d)  A t Cornudas and Orogrande, New  New  Mexico,A"Z i n c r e a s e d  field. Mexico, t h e r e was a d e f i n i t e  c o r r e l a t i o n between A 2 and the a z i m u t h of the h o r i z o n t a l  field.  Schmucker t e n t a t i v e l y i n t e r p r e t e d these r e s u l t s as a downward s t e p i n a h i g h l y c o n d u c t i v e s u b s t r a t u m (assumed t o have i n f i n i t e a p p r o x i m a t e l y under Orogrande.  conductivity)  He d e r i v e d a n o r t h - s o u t h s t r i k e f o r t h e  edge of t h i s s t e p . Hyndman (1963) r e p o r t e d the r e s u l t s of a s i m i l a r survey c a r r i e d j u s t n o r t h of the Canada - U.S.A. b o r d e r , a l o n g an east-west  profile  out  •0*  I  N«~  «7  OK.LA HOM/*  .4*  UfO F&KL. P£Rir\AMENT [  V  J  [  — i  o  0  o  OAS  SCHML/CK&R ® LWIN0-STONE  O  Map o f the s o u t h - w e s t e r n ' U . S . A . showing s t a t i o n  (13SS-I&O2)  locations  19661  11*  1X6  l i s  XZO  X22  • \  GrOLDEN\»  -rnHNSON CANYON "  CA|U GARY  RE f£L5TO/<£. 1  N..  CACHE CREEfy KAMLOOPS  SALMON ARM  B R I T I S H  ©.-....  \  B S O L U M B I A KiMBERLY  C  o  BAR  O  K0OT"£/v/»y LAKE  CRESCENT O  ©  PEN TIC TON  HOPE ABBOTS rotf/T"  O _ GRANb  O HYNDMAN CANNON  |  O  B O S T O N  €  \ A L B E R T A  o  CHER VALLEY  C A N A D A U . S . A .  (1963)  CS965J  © LIVINGSTONE (1966)  F i g . 2 . Map o f w e s t e r n Canada showing s t a t i o n  locations.  CREEK  f r o m L e t h b r i d g e A l b e r t a t o V i c t o r i a B.C. ( F i g u r e 2 ) . Hyndman s r e s u l t s 1  were v e r y s i m i l a r i n f o r m t o t h o s e o f Schmucker, showing- a f a i r l y a b r u p t t r a n s i t i o n from s m a l l  i n the west t o l a r g e  i n the east.  I n 1965 Lambert and Caner suggested a model based on Schmucker's and Hyndman's r e s u l t s as w e l l as on s e i s m i c d a t a . The model assumed a r e l a t i v e l y s h a l l o w h i g h c o n d u c t i v i t y zone under the w e s t e r n p a r t of N o r t h A m e r i c a w h i c h , i t was s u g g e s t e d , was due t o a h i g h temperature zone. Whitham (19&5) suggested t h a t a r i s e o f m a t e r i a l w i t h a c o n d u c t i v i t y o f 10"" - 1  1  emu t o w i t h i n 200 km. of t h e e a r t h ' s s u r f a c e c o u l d o f f e r a p l a u s -  i b l e e x p l a n a t i o n o f Hyndman's l o w s t a t i o n s »  Caner and Cannon (1965)  proposed a g e n e r a l i z e d e l e c t r i c a l c o n d u c t i v i t y model ( F i g u r e 3) f o r w e s t e r n N o r t h A m e r i c a , w h i c h was c o m p a t i b l e w i t h o t h e r g e o p h y s i c a l d a t a f o r the r e g i o n . Cannon ( 1 9 6 6 ) , w o r k i n g i n c e n t r a l B r i t i s h Columbia, attempted t o i n t e r c e p t t h e boundary o f t h i s proposed h i g h c o n d u c t i v i t y zone n o r t h o f Hyndman's p r o f i l e , u s i n g a n e a s t - w e s t chain, o f magnetometers e x t e n d i n g f r o m R e v e l s t o k e t o Cache Creek ( F i g u r e 2 ) . T h i s east-west p r o f i l e was l i n k e d t o Hyndman's by a n o r t h - s o u t h p r o f i l e from Cache Creek t o Hope. Cannon's attempt t o i n t e r c e p t t h e boundary was u n s u c c e s s f u l . The r e s u l t s r e p o r t e d here c o n s t i t u t e a c o n t i n u a t i o n of t h i s  invest-  i g a t i o n . The e x p e r i m e n t a l work was c a r r i e d out i n t h r e e p h a s e s . I n August and September of 1965 f o u r A s k a n i a GV-3 v a r i o g r a p h s were o p e r a t e d f o r s i x weeks a t Horse S p r i n g s , Copper Canyon (near Magdelena),  Scholle,  and Negra i n New Mexico ( F i g u r e 1) i n a n a t t e m p t t o i n t e r c e p t a n o r t h ward e x t e n s i o n o f t h e Schmucker anomaly.  I n May and June of 1966 t h e  p r o f i l e was extended eastward w i t h s t a t i o n s a t E n c i n o and Newkirk, New Mexico* B u s h l a n d , Texas; and S a y r e , Oklahoma ( F i g u r e 1 ) . F i n a l l y , f o r 9  100 KM I  GEOMAGNETIC ANOMALIES  "CREST" (Q>2.0) 200-300 KM  1  500 -1000 KM (Q>l.2/i',CAL/CM  Pn>8 KM/S  2  L O W - x | HIGH ~x < >  SEC)  >v  CRUST  "NORMAL MANTLE  1  Pp< 7.9 KM/S \ "LOW  Pn" MANTLE  \  /// , > 1000°-1200°?  / /  M  > 8 KM/S CONTRAST IN 100 KM: \ 8T>I00°C \ Scr > x|0  115 KM ( ± 25)  /7// >4///  /  /  /  >600°-IOOO°C/  ( S-VEL LAYER / / / / / / / .(a) VERTICAL EXAGGERATION 5M  / // / / / ^ISOTHERMS  100 KM I 1 "LOW  Pn" Z O N E  H  O  F i g , 3o  CD)  C o n a  u"ctivi€y  /TO  SCALE  M "NORMAL" MANTLE LOW S-VEL. L A Y E R / / / / /../.. / /  /  s t r u c t u r e ~ f o r w e s t e r n N o r t h A m e r i c a , a f t e r Caner and Cannon  (1965).  n i n e weeks d u r i n g J u l y , August and September, o p e r a t e d a t R e v e l s t o k e and G o l d e n , B.C.,  1966, f o u r s t a t i o n s were  and a t J o h n s t o n Canyon and  C a l g a r y , A l b e r t a ( F i g u r e 2 ) . I n a d d i t i o n , d a t a were used from the U.S.G.S. permanent o b s e r v a t o r i e s a t D a l l a s (Texas) and B o u l d e r ( C o l o r a d o ) as w e l l as from the temporary I.G.Y. o b s e r v a t o r i e s a t P r i c e  (Utah),  Casper (Wyoming), L e a d v i l l e ( C o l o r a d o ) , B u r l i n g t o n ( C o l o r a d o ) , and B e l o i t ( K a n s a s ) . A d d i t i o n a l d a t a were o b t a i n e d f r o m t h e U n i v e r s i t y of Oklahoma's Leonard G e o p h y s i c a l Observatory a t Norman, Oklahoma, and from two of S c h m u c k e r s s t a t i o n s - Las Cruces and Cornudas, New Mexico ( F i g u r e 1 ) . 1  The I965 New  Mexico p r o f i l e was chosen i n an attempt t o c o r r e l a t e  t h e e x p e c t e d n o r t h w a r d e x t e n s i o n of Schmucker"s anomaly w i t h an ore l e a d i s o t o p e c o m p o s i t i o n anomaly r e p o r t e d by Slawson ( 1 9 6 2 ) . T h i s anomaly c o n s i s t s of a narrow band, a p p r o x i m a t e l y 40 km. i n w i d t h , r u n n i n g d i a g o n a l l y n o r t h w e s t through S o c o r r o , New  Mexico, i n w h i c h the i s o t o p i c  c o m p o s i t i o n of o r e l e a d s I s d i f f e r e n t from t h a t found on e i t h e r  side.  Slawson suggested t h a t the l a c k of excess r a d i o g e n i c l e a d i n t h i s  zone  might i n d i c a t e an a n c i e n t f a u l t i n the basement r o c k s .  11  II (1)  THEORY I - ratios  Magnetic i n d u c t i o n theory shows t h a t the e f f e c t of a t h i c k , h i g h l y conductive, near surface suppress the v e r t i c a l meter f o r e s t i m a t i n g  tt  stratum on a time v a r y i n g magnetic f i e l d i s t o component of t h a t f i e l d . Thus, a crude p a r a -  the s u b s u r f a c e c o n d u c t i v i t y i s l - t  AZ  ~ •  , where  i s the measured peak t o peak a m p l i t u d e of the v e r t i c a l component of a disturbance,  andAfcandAHare the changes i n the  n o r t h - s o u t h components r e s p e c t i v e l y . h i g h s u b s u r f a c e c o n d u c t i v i t y and  magnetic east-west  and  A s m a l l v a l u e of I corresponds t o a  a l a r g e v a l u e to a low  subsurface  conductivity. A "normal" s t a t i o n i s d e f i n e d  as any  s t a t i o n where the a m p l i t u d e  of the v e r t i c a l component i s independant of the a z i m u t h of the t a l f i e l d . Any lous . n  s t a t i o n where t h i s i s not  horizon-  the case i s d e f i n e d as "anomar  An anomalous s t a t i o n i n d i c a t e s the presence of a nearby l a t e r a l  boundary i n the e l e c t r i c a l c o n d u c t i v i t y F i g u r e 4 shows a two  structure.  l a y e r model of the e a r t h ' s c r u s t and  mantle,  w i t h the lower l a y e r h a v i n g a h i g h e r e l e c t r i c a l c o n d u c t i v i t y than the upper.  Progressing  a c r o s s the l a t e r a l c o n d u c t i v i t y boundary from the  s h a l l o w t o the deep s u b s t r a t u m , the s t a t i o n s f a l l i n t o f o u r groups: normal low I, anomalous low I, anomalous h i g h I, and n o r m a l h i g h I . Over uniform, h o r i z o n t a l l y s t r a t i f i e d regions, d i r e c t i o n of  "A"  and  "C",  the magnitude  and  are not c o r r e l a t e d w i t h the d i r e c t i o n of the h o r i z o n t a l  magnetic f i e l d . However, near a h i g h c o n d u c t i v i t y  zone boundary,  "B",  magnetic i n d u c t i o n c a l c u l a t i o n s show a c o r r e l a t i o n of £ 2 w i t h c e r t a i n h o r i z o n t a l magnetic f i e l d d i r e c t i o n s . More s p e c i f i c a l l y , magnetic changes normal to the s t e p boundary at "B"  produce h i g h e r  current  field  SURFACE  F i g . 4.  MAGNETIC  FIELD  S i m p l i f i e d model f o r c o n d u c t i v i t y  VARIATIONS  s t e p showing f i e l d component  relations.  d e n s i t i e s i n the upper substratum on the "A"  s i d e of the boundary t h a n  they do a t the same d e p t h i n the lower c o n d u c t i v i t y m a t e r i a l on the  "C"  s i d e of the boundary. T h i s l a t e r a l c u r r e n t d e n s i t y v a r i a t i o n produces i n t u r n a l a r g e r t h a n normal v e r t i c a l f i e l d v a r i a t i o n a t the s u r f a c e i n the v i c i n i t y of "B".  F o r i n d u c i n g f i e l d changes p a r a l l e l t o the boundary,  the f l u c t u a t i o n s of the v e r t i c a l f i e l d are of normal a m p l i t u d e p a r t i c u l a r r e g i o n . A t the low f r e q u e n c i e s  ( l e s s than 0.1  cpm)  f o r the used i n  these i n v e s t i g a t i o n s , the i n d u c i n g f i e l d sources a r e p o s t u l a t e d t o be i o n o s p h e r i c e l e d t r l c c u r r e n t systems of l i m i t e d s i z e (Akasofu,1965), c r u d e l y c e n t e r e d about the e a r t h ' s geomagnetic p o l e .  (2)  The  i n d u c i n g f i e l d and  i t s e f f e c t on  Ag.  I n the m i d - l a t i t u d e r e g i o n s t h e r e i s a d e c r e a s e i n i n d u c i n g  field  s t r e n g t h ( i n a l l components D,H,Z) w i t h d e c r e a s i n g l a t i t u d e , and predictable s t a t i s t i c a l f r o m n e a r l y equal "D"  s h i f t i n energy d i s t r i b u t i o n among components  and  "H"  e n e r g i e s i n the v i c i n i t y of the  c u r r e n t systems (upper m i d - l a t i t u d e s ) , t o a p r e d o m i n a n t l y  "H"  source field far  f r o m the source c u r r e n t s (lower m i d - l a t i t u d e s ) . A l s o , a l t h o u g h H components have s t a t i s t i c a l l y  equal energies  l a t i t u d e s , f o r any p a r t i c u l a r bay D and H may line  i n the upper  the D  and  mid-  event the energy d i s t r i b u t i o n between  change from p o i n t t o p o i n t a l o n g the same geomagnetic  (Hostoker,1966). I n summary, as the i n d u c i n g f i e l d i s not c o n s t a n t  s u f f i c i e n t l y large area, experimental may  a  not be compared i n terms of  i n s t r e n g t h over a  r e c o r d s from d i f f e r e n t s t a t i o n s  a l o n e , and n o r m a l i z a t i o n of A 2 .  r e s p e c t t o the t o t a l h o r i z o n t a l f i e l d change ( v e c t o r sum i s necessary.  The  I-ration ( ^ ^ A H  £  with  of A D and AH )  ) p r o v i d e s a s u i t a b l e parameter f o r 14  comparison between s t a t i o n s a t t h e same l a t i t u d e o n l y , s i n c e t h e mean I - r a t i o i s a f u n c t i o n of l a t i t u d e as w e l l as of s u b s u r f a c e  conductivity  structures.  (3)  C o n d i t i o n s f o r d i r e c t d e t e r m i n a t i o n of c o n d u c t i v i t y - d e p t h p r o f i l e s .  The mathematical  s t u d i e s of magnetic i n d u c t i o n i n a h o r i z o n t a l l y  s t r a t i f i e d c o n d u c t o r , i n c l u d i n g P r i c e ' s (1962) work w i t h  nonuniform  s o u r c e s and Watanabe's (1964) " s e l f c o n s i s t e n t s o l u t i o n " method f o r e l e c t r i c a l c o n d u c t i v i t y , r e q u i r e a knowledge of t h e magnetic  field  v a r i a t i o n over a s u r f a c e . An e x a m i n a t i o n of t h e problem by Cannon (1966) shows t h a t a two d i m e n s i o n a l s p a t i a l F o u r i e r a n a l y s i s i s a s u i t a b l e method f o r r e d u c i n g d a t a o b t a i n e d from s i m u l t a n e o u s measurements by a two d i m e n s i o n a l a r r a y of v a r i o m e t e r s . I n o r d e r t o use t h e method of Cannon o r t h a t o f Watanabe, s i m u l t a n e o u s r e c o r d i n g s must be made a t a s u f f i c i e n t l y l a r g e number of p o i n t s i n o r d e r t o d e f i n e t h e magnetic v a r i a t i o n as a c o n t i n u o u s f u n c t i o n over t h e measuring In  field  surface.  s p i t e of t h e obvious d e s i r a b i l i t y of two d i m e n s i o n a l v a r i o m e t e r  a r r a y s , a l l t h e f i e l d work d i s c u s s e d i n t h i s t h e s i s was c a r r i e d out w i t h l i n e a r p r o f i l e s . T h i s was p u r e l y f o r economic r e a s o n s ; a two d i m e n s i o n a l a r r a y , s u f f i c i e n t l y l a r g e t o p e r m i t a unique d e t e r m i n a t i o n of the c o n d u c t i v i t y - d e p t h p r o f i l e , i s p r o h i b i t i v e l y expensive. F o r i n i t i a l r e a s o n a b l y spaced  surveys,  l i n e a r v a r i o m e t e r p r o f i l e s p e r p e n d i c u l a r t o the expected  anomaly s t r i k e s a r e t h e most p r a c t i c a l . U s i n g the data from such  linear  a r r a y s , b o t h depths and c o n d u c t i v i t i e s cannot be d i r e c t l y d e t e r m i n e d . I n o r d e r t o o b t a i n a r e a s o n a b l e e s t i m a t e of t h e v a r i a t i o n of e l e c t r i e a l c o n d u c t i v i t y w i t h d e p t h , observed power s p e c t r a l r a t i o s c a n be compared w i t h a s e r i e s of - t h e o r e t i c a l " l a y e r model" response c u r v e s u s i n g t h e method d e s c r i b e d by Whitham ( 1 9 6 3 ) .  A number of L a y e r model curves a r e p r e s e n t e d 15  i n t h e a p p e n d i x . These a r e the r a t i o s between c a l c u l a t e d densities  f o r two " s t a t i o n s " , l o c a t e d  " e a r t h s " h a v i n g t h e same c o n d u c t i v i t y  over h o r i z o n t a l l y  power  spectral  stratified  parameters h u t d i f f e r e n t d e p t h  p a r a m e t e r s . The t h e o r e t i c a l power s p e c t r a were computed a c c o r d i n g t o Price's  t h e o r y u s i n g a m a t h e m a t i c a l t e c h n i q u e s i m i l a r t o t h a t g i v e n by  Cannon (1966)  16  Ill (1)  EXPERIMENTAL PROCEDURES The A s k a n i a V a r i o g r a p h  The A s k a n i a GV-3  variograph i s a m e c h a n i c a l - o p t i c a l instrument  c a p a b l e of o p e r a t i n g on 220/110 v o l t s AC, i n an i n s u l a t e d e n c l o s u r e c o n t a i n i n g the n e c e s s a r y h e a t e r s and thermostat t o p e r m i t maintenance of a c o n s t a n t i n t e r n a l temperature when b a t t e r y power i s not b e i n g used.  The  d e t e c t o r system c o n s i s t s of permanent magnets w i t h a t t a c h e d m i r r o r s suspended on q u a r t z f i b r e s . Two  of t h e s e (H and D d e t e c t o r s ) a r e v e r t i c a l l y  mounted, suspended by s i n g l e f i b r e s and a r e temperature third  compensated; the  (Z d e t e c t o r ) i s h o r i z o n t a l l y mounted, suspended between two  torsion  f i b r e s of d i f f e r e n t t h e r m a l c h a r a c t e r i s t i c s t o p e r m i t a degree of temperature compensation.  The  l i g h t source i s a s i x v o l t lamp set i n a  movable mount w i t h f o u r degrees  of freedom ( t h r e e t r a n s l a t i o n a l and  one  r o t a t i o n a l ) . L i g h t i s passes t h r o u g h a s l i t and c o l l i m a t o r and t h e beam is  t h e n s p l i t t o p r o v i d e a b a s e - l i n e marker, an i n t e r n a l temperature r e c o r d  ( a b i m e t a l s t r i p thermometer w i t h a t t a c h e d m i r r o r i s u s e d ) , and beams, one f o r each.of  three  the d e t e c t o r s , The d e t e c t o r o u t p u t s a r e f o c u s s e d  by a c y l i n d r i c a l l e n s on p h o t o g r a p h i c paper;  "two-level" mirrors set  i n t o t h e d e t e c t o r h o u s i n g s p r o v i d e secondary  t r a c e s t o p r e v e n t l o s s of  r e c o r d due t o the main t r a c e s moving o f f s c a l e . A s e p a r a t e lamp and  slit  a r e used t o produce time marks. D u r i n g o p e r a t i o n the r e c o r d i n g paper i s h e l d i n a c l i p - o n magazine and i s advanced by e i t h e r a 220 v o l t , 50 cps e l e c t r i c d r i v e ( 24mm/hr when o p e r a t e d a t 60 cps) o r a g r a v i t y d r i v e  (20mm/hr). The g r a v i t y  r e q u i r e s r e w i n d i n g every seven d a y s . The magazine h o l d s 10 m of 12  drive cm  ( w i d t h ) r e c o r d i n g p a p e r , i . e . s u f f i c i e n t paper f o r twenty days r e c o r d ing  a t 20 mm/hr.  The v a r i o m e t e r c a l i b r a t i o n system c o n s i s t s of t h r e e H e l m h o l t z c o i l s (one i n each d e t e c t o r h o u s i n g ) powered by a d r y c e l l i n s e r i e s w i t h a m i l l i a m e t e r and a r h e o s t a t .  I n the manufacturer's s p e c i f i c a t i o n s the  c o i l c o n s t a n t s a r e g i v e n t o O.'y^/ma. The c a l i b r a t i o n meter can be r e a d to  0.005 ma a t 1 and 2 ma s e t t i n g s . I n p r a c t i c e , w i t h a t r a c e t h i c k n e s s  of  0.5 mm and 21 mm d e f l e c t i o n a t 1 ma c a l i b r a t i o n c u r r e n t , t h i s  r e p r e s e n t s a p o t e n t i a l c a l i b r a t i o n a c c u r a c y of ± 3 . 5  %,  The l a r g e s t  o b s e r v e d p r o b a b l e e r r o r i n s e t s of c a l i b r a t i o n checks was ±-3.0 %. The c l o c k time marks were o n l y used a s i n d i c a t o r s , t h e r e c o r d s b e i n g compared w i t h nearby a c c u r a t e l y timed permanent o b s e r v a t o r i e s . 120 v o l t , 60 c y c l e AC, power was used a t a l l s i t e s , a s was t h e i n t e r n a l temperature c o n t r o l system. The v e r t i c a l component s u s p e n s i o n f i b r e s were compensated f o r temperature v a r i a t i o n by B. Caner a t t h e V i c t o r i a Magnetic Observatory.  A l t h o u g h r e a s o n a b l e temperature  independence  c o u l b e be o b t a i n e d f o r v a r i a t i o n s of 10°C o r l e s s , t h e f i b r e c h a r a c t e r i s t i c s d i d n o t p e r m i t b e t t e r adjustment and d a i l y temperature  fluctua-  t i o n s of the o r d e r of 20*C were n o t uncommon a t t h e s t a t i o n s i t e s . Thus the  i n t e r n a l temperature c o n t r o l system was n e c e s s a r y t o p e r m i t v a l i d  work f o r l o n g e r p e r i o d s . S e c t i o n s of r e c o r d showing v a r i a t i o n were n o t used f o r a n a l y s i s because  temperature  of t h e p o s s i b i l i t y o f  temperature-caused changes i n A B . . (2)  F i e l d work.  D u r i n g t h e f i r s t p a r t of t h e 1965 f i e l d  season a c h a r t speed o f  2k mm/hr was used; t h e r e s t of t h e work was c a r r i e d out w i t h a c h a r t speed of 20mm/hr. The change i n c h a r t speed was n e c e s s i t a t e d by c o n t i n u o u s break-downs of t h e e l e c t r i c d r i v e system and subsequent replacement by g r a v i t y  drive. 18  The r e c o r d s were c a l i b r a t e d a t t h e b e g i n n i n g and t h e end of each 5m c h a r t s e c t i o n w i t h c a l i b r a t i o n c u r r e n t s e t t i n g s of +1 ma., +-2 ma., =2ma., - 1  ma. on each component s e p a r a t e l y , u s i n g 30 s e c . d u r a t i o n a t  each s e t t i n g and a 30 s e c . s p a c i n g .  The s c a l i n g f a c t o r s used i n p r o c -  e s s i n g were t h e averages of a l l u s a b l e r e c o r d e d  calibrations.  A c a r e f u l check o f i n s t r u m e n t l e v e l and component p o s i t i o n i n g was made each time the r e c o r d s were changed (every seven days on t h e average) i n o r d e r t o c o r r e c t f o r any component  drift.  The s t a t i o n s i t e s were i n e x i s t i n g b u i l d i n g s s e l e c t e d from those a v a i l a b l e i n t h e a r e a s of i n t e r e s t a c c o r d i n g t o t h e f o l l o w i n g c r i t e r i a : (1)  a v a i l a b i l i t y of 120 v o l t , 60 c y c l e AC power  (2)  solid  (3)  a t l e a s t 50 m. d i s t a n t from the n e a r e s t t r a v e l l e d road  (4)  a t l e a s t 100 m. d i s t a n t from t h e n e a r e s t h i g h v o l t a g e lines  (5)  sound r o o f  (6)  absence of conspicuous  IV  floor  supply  q u a n t i t i e s of exposed i r o n  DATA PROCESSING  The r e c o r d i n g s were f i r s t checked f o r u n i f o r m i t y of l a y e r i n g u s i n g Parkinson's  (1959,1962)  p o l a r p l o t method. The I - r a t i o s ( or©= a r c t a n / I ) x  f o r s e v e r a l events were p l o t t e d as a f u n c t i o n of t h e a z i m u t h  (measured  f r o m magnetic n o r t h ) o f t h e h o r i z o n t a l v a r i a t i o n f i e l d v e c t o r , as d e f i n e d by t h e a n g l e $ = a r e t a n D/H. The r e c o r d i n g s were manually s c a l e d and t h e peak-to-peak a m p l i t u d e s  o f o n l y those events i n w h i c h A D and A H were  g r e a t e r than 3 mm. a n d A Z was measurable were used. Thus, f o r a c a l i b r a t i o n accuracy  of 1 3 %, AD and A H r e c o r d a m p l i t u d e s  of 3 mm., and 19  Az  r e c o r d a m p l i t u d e of 1.5 mm. and s c a l i n g e r r o r of ± 0 . 5 mm, t h e e x p e c t ed maximum e r r o r s i n I and $ a r e about 20 %,  The d a t a from those  s t a t i o n s a t w h i c h nonuniform l a y e r i n g was suggested by t h e P a r k i n s o n p l o t s were f u r t h e r examined by computing and p l o t t i n g I r a t i o s and d i p a n g l e s ( a r c t a n l ) as a f u n c t i o n of i n d u c i n g measured from geographic n o r t h .  f i e l d a n g l e <j> ( &<(f>d80)  The maxima of these s c a t t e r p l o t s  g i v e t h e d i r e c t i o n normal t o t h e s t r i k e as p o i n t e d This s t r i k e d i r e c t i o n i s the only i n f o r m a t i o n the  out i n s e c t i o n I I .  w h i c h was e x t r a c t e d  from  "anomalous" s t a t i o n s ; a l l o t h e r q u a n t i t a t i v e work was c a r r i e d out  w i t h r e c o r d s from "normal" s t a t i o n s . Records from n o r m a l s t a t i o n s on o p p o s i t e s i d e s of t h e observed c o n d u c t i v i t y i n e d i g i t i z e d on a semiautomatic d i g i t i z e r  zone b o u n d a r i e s were mach(S.A.D.) developed f o r t h e  U.B.C. Geophysics Department by W. Cannon. The S.A.D. output was checked f o r s e l f - c o n s i s t e n c y by d i g i t i z i n g a s i n g l e t r a c e  (Revelstoke  H component 2100 J u l y 27 - 2100 J u l y 28, 1966) f o u r t i m e s and comparing the r e s u l t a n t time s e r i e s power s p e c t r a and coherence squares 5, 6 ) .  (figures  The f r e q u e n c y a t w h i c h t h e mean d e v i a t i o n i n t h i s t e s t r e a c h e d  15 fo and coherence square dropped below 0.80 was t a k e n as t h e h i g h frequency cut-off point f o r the processing  of experimental data. F o r  frequencies higher than t h i s c u t - o f f point  (0.032 cpm), the p r o c e s s i n g  n o i s e - l e v e l becomes.prohihitivly  l a r g e f o r t h i s type of r e c o r d i n g .  W i t h i n t h e u s e f u l band (0.002 t o 0.032 cpm), a n o v e r a l l s i g n i f ance l e v e l of 5 % i n a m p l i t u d e (which i n c l u d e s A s k a n i a c a l i b r a t i o n u n c e r t a i n t i e s as w e l l as measurement e r r o r s )  corresponds t o a dt. 10$  l e v e l i n power s p e c t r a l d e n s i t i e s f o r a s i n g l e component, or about i 2 0 % f o r t h e r a t i o of two components. Any d i f f e r e n c e s below t h i s l e v e l 20  cannot be a c c e p t e d as s i g n i f i c a n t . The S.A.D. output from magnetograms f o r p e r i o d s over 1 2 hours was s c a l e d and power s p e c t r a computed u s i n g t h e B.M.D.P. Spec, program as m o d i f i e d f o r d i s c on the U.B.C., I.B.M. 7040 computor. The power spectral r a t i o s ( P i / P Z  D]^/(PZ2/  P  D 2 ) n d ( P z i / PHl)4>Z2/pH2) (where t h e &  s u b s c r i p t s 1 and 2 d e s i g n a t e low and h i g h I s t a t i o n s r e s p e c t i v e l y ) were c a l c u l a t e d and p l o t t e d as f u n c t i o n s of f r e q u e n c y .  21  Pig.5.  a-  DIGITIZER MEAN  CHECK  DEVIATION  GENERATED  In.  W  OF HCWE? POWER SPECTRA  MACHINE  OF FOUR TIME SERIES o  o ;3.7"HR, OF STORM  DIGITIZING  MAGNETOGRAM AT 2.21 MIN INTERVALS  o.  o  h < >  UJ  LU  plfioy  Pig.  §1..  a'-to  «E  (7 .'iff  O.Vff  6  ° DIGITIZER 8  CHECK  %•$  olzi  u^io  FRE(JU£A/CV  IN  (COHERENCE)  2  O'.-ttl  o)»e  «V«  C.P.M.  VS. F R E Q U E N C Y IN C R M ,  8.  CHOSEN HI&H FREQUENCY C(^T OFF  C-1'00  O.OtW  O.O LOD:r>i«r  0.0 zo  «o z.5  cw 3 0  oo asr  O.OHS O.O'SU  P. t)5"tT  22  V  RESULTS  (1)  I - r a t l o s and p o l a r p l o t s  Peak-to-peak a m p l i t u d e s  of d i s t u r b a n c e s o f d u r a t i o n g r e a t e r than  20 min. were hand s c a l e d t o p r o v i d e data f o r I - r a t i o s and e s t i m a t e s of the u n i f o r m i t y of c o n d u c t i v i t y l a y e r i n g . Some r e s u l t s of t h e l a y e r u n i f o r m i t y check o u t l i n e d i n s e c t i o n IV a r e p r e s e n t e d i n f i g u r e s 7 to 10 i n the form of " P a r k i n s o n " p l o t s . A l l o t h e r s t a t i o n s showed no c o r r e l a t i o n between A z and t h e azimuth o f t h e h o r i z o n t a l variation vector.  field  Schmucker's r e s u l t s f o r Las Cruces and Cornudas  a r e quoted from Schmucker (1964) and c o u l d n o t be o b t a i n e d  successfully  by t h e p r e v i o u s method because of i n s u f f i c i e n t d a t a . Those s t a t i o n s whose " P a r k i n s o n " p l o t s suggested  t h e p o s s i b i l i t y o f non-uniform  l a y e r i n g ( P r i c e , U t a h ; B u r l i n g t o n , C o l o r a d o ; Norman, Oklahoma; J o h n s t o n Canyon, B.C.) were f u r t h e r examined by I - r a t i o v s . " h o r i z o n t a l v a r i a t i o n f i e l d " azimuth p l o t s , ( f i g u r e s 11 t o 14) I n s u f f i c i e n t were a v a i l a b l e t o p e r m i t q u a n t a t i v e s t r i k e e s t i m a t e s from these I t s h o u l d be c l e a r l y understood  data  results.  t h a t mean I - r a t i o s have no  s i g n i f i c a n c e a t anomalous s t a t i o n s , s i n c e t h e mean depends on t h e a z i m u t h d i s t r i b u t i o n of the p o i n t s chosen f o r a n a l y s i s . Thus i n T a b l e 1, those s t a t i o n s vohose " P a r k i n s o n " r e s u l t s l e a v e some doubt about l o c a l s u b s u r f a c e l a y e r u n i f o r m i t y a r e c l e a r l y marked and the mean I - r a t i o means a r e n o t of e q u a l r e l i a b i l i t y  ;  as some a r e based on much s m a l l e r  samples than o t h e r s . The number of events measured t o produce each mean has been I n s e r t e d i n t h e t a b l e t o f a c i l i t a t e e s t i m a t e s o f reliability.  23  STATION  MEAN I-RATIO  NUMBER OF EVENTS  Casper Price Boulder  0.441 0.316 # 0.285  73 n o 197  Beloit Norman  0.394 0.428 #  6l 148  Dallas Golden J o h n s t o n Canyon  0.171 0.481 0.628 #  37 102 184  Burlington Leadvllle  O.372 # 0.246  Sayre  0.226 #  Calgary  O.508  # indicates  63 47  63  131  a s t a t i o n t h a t may be anomalous. Table 1.  The s p a t i a l d i s t r i b u t i o n of "low I " and " h i g h I " s t a t i o n s f o r t h e work i n t h e s o u t h - w e s t e r n U.S.A.is p r e s e n t e d i n f i g u r e 15 and f o r t h a t i n w e s t e r n Canada, i n f i g u r e 1 6 . As can be seen i n f i g u r e 15, t h e "low I " - " h i g h I " boundary  l i e s between Las Cruces and Cornudas on  Schmucker's p r o f i l e , between Sayre and Norman on L i v i n g s t o n e ' s p r o f i l e and between B u r l i n g t o n  and B o u l d e r on t h e I.G.Y. p r o f i l e . The s t a t i o n  a t P r i c e , a l t h o u g h i t s P a r k i n s o n p l o t s u g g e s t s t h e p o s s i b i l i t y of a conductivity  l a y e r boundary  t o t h e west of P r i c e , has no s t a t i o n  close  enough t o v e r i f y t h i s r e s u l t and no w e s t e r n s t a t i o n t o check I - r a t i o change. The s t a t i o n a t Casper has been t e n t a t i v e l y i d e n t i f i e d as a " h i g h I " s t a t i o n i n F i g u r e 1 5 . However, no o t h e r s t a t i o n was a v a i l a b l e a t t h e same l a t i t u d e t o p e r m i t comparison of mean I - r a t i o l e v e l s . The w e s t e r n Canada "low I " - " h i g h I " boundary,  ( f i g u r e 1 6 ) , has  been found a t two p o i n t s , between Golden and J o h n s t o n Canyon on L i v i n g s t o n e ' s p r o f i l e and between C r e s c e n t V a l l e y and Kimberley on Hyndman's p r o f i l e (Hyndman,1963• Cannon, 1 9 6 6 ) . I n summary, a l t h o u g h t h e "low I " - " h i g h I " b o u n d a r i e s were i d e n t i f i e d as l y i n g between two p o i n t s ,  i n neither  t h e 1965 n o r t h e 1966 f i e l d 24  P i g . 7»  Parkinson p l o t , Price  (Utah).  26  27  . 10,  P a r k i n s o n p l o t , J o h n s t o n Canyon (B.C.).  PRICE "I RATIO ' VS. HORIZONTAL VARIATION FIELD A Z I M UTH ( 0° IS K E O & R A P H I C NORTH ) ° 1  o o ° o  o : O  o  ooo o o ° o  5 c  O  <  o  O o oo  o o o  o O  Oo o  o  o  (fe  CO  - O  o  o  o O 9ko  ° o° ° °oo°  o  ° o  oo  o  o  o  o o  01  "IP  33  to  2y  (VeOff-RflPM IC  DIP VS. HORIZONTAL  7?  A Z I M U T H  VARIATION  IN  ISi  lis-  j iff  <T5  TJ?  i?3  O E & R H E S  F E I L D  A Z I M U T H  o  o  o o  o Lu  o  u («• 0  o  o  o O  OO - o o °  O  0  O  3  o o o  a  o  o CP o o  o  o  vb Ui  o  o  0  OO  o o  (  o o o  o  o  o  o  O o  Poo °  o  o CO o o  —I— 30  IS  t-0  7y  o °  °s « o o o  4.9"  o 0  o °oo  0  9w~  »?0  AZIML/TH >/V  DBCrREZS  F i g . 11. I - r a t i o and d i p angle v s . azimuth p l o t , P r i c e  (Utah).  29  BURLINGTON  CB  -5 •  o  T RATI0 'VS.  HORIZONTAL  V  CO"  Si  VARIATION'  o o  o  o  O o  «<?T  o  «o  -75-  90  AZIMWTH  GEOGRAPHIC  DIP  O  o  o  3 0  o  o o  o  %  o  o  Iff  AZ/MiJTH  IS G - E O C r R ' A P H I C ' i N O R T I - l )  o  o  FIELD  IPS'  IN  13?  IZO  15X>  180  DEC-REES  VS. H O R I Z O N T A L V A R I A T I O N FIELD A Z f MVTH  If.  o o  o o  UJ wi  a o  HI .  Q o Z Cs  oo  o  T  O  o  o  o  ^I  O  o o o  o  1  xb"  T  :«0  o  -r;  -rz  ZT^  -TO  toU  •/o  G-EOG-RAPHlC  DO  AZIMUTH  7T~Z  7!~.  TT^  iipi  i&w  iao  1  i5"C)  TZ ifcSf  Tt 190  I N DECREES  F i g . 12o I - r a t i o and d i p angle v s . azimuth p l o t , B u r l i n g t o n  (Colorado) 30  NORMAN I RATIO VS. HORIZONTAL VARIATION FIELD AZIMUTH ( 0 ° IS, G E O G R A P H I C  NORTH)  o o o o O O  o  oo  O  O  I— o o «  o  0  0  %  0  o @  0  °o o  o  o <-  oO  0  oo  O  3  o  o ° o  a  o  o  o  o  o  o  o o  0  o@  °0  7-S"  •3t>  log  AZIMUTH  &E0&-RAPHIC  T?T  -  i3»  IN D E C R E E S  DIP VS. HORIZONTAL VARIATION FIELD AZIMUTH. o  o o Cl  o  o o oo  ,o o  '01 UJ  W or  In.  o  CM  o  o o  o  o, o  <b °  o  o  o  O Oo  o  o o o  o  °o o  OO  oo  oo  c?  °  o o  °4  TF  —r~  30  o  O 0  "7F  o  o  CD  °  o o  "To"  GEOGRAPHIC  TS"  9'0  AZIMUTH  lbs"  i'EO  O  135"  IN DE&RE.ES  0  °  o  e  o  1?0  F i g . 13= I - r a t i o and d i p v s . azimuth p l o t , Norman (Oklahoma).  7]'o  31  . J O H N S T O N - X A N Y O N I RATIO"  .VS.  C O " 15 o  HORIZONTAL  6EO&-KAPH/C  VARIATION  FE/LD  AZIMUTH  iVORTH)  00 o o •' o  <  c?°  o o  °  o  cP  c 0 In  O  * o  e  o  04  »o  15  0  30  0  C  PIP  yo  AZIMUTH  8  o• , .  UJ o  c  cB  (  o  o  Q  P i g , 14.  —r~ 30  *2o  IN  H- a  DE&REES  F/£LD  AZIMUTH  (2D  o  0  o  o o  ® <  Q  o  165"  OOo°  o  O  o  O  Qss  p  o 00 O  °  0  o  0  0  n  —I— 135"  CD  <9  3>o 0 0  6 o  7F  o  ^ o ° o  o  O Oj o o  o  00  .0  QD  o 00  ics"  HORIZONTAL VARIATION  o  o  0 0  o_°  7a  60  ui a:  COO  o  o  >+5  VS.  0  O  &EOG-RAPH/C OJ  o  Oo  -» » O  o  6  0  O  0  c  o  Q J O  o e  o  o  0  0  o  o  8*c  o  o  —nr 7b  GEOGRAPHIC  T 90 10*5" 1.20 13 "5" ISO AZIMUTH IN DE&REES  .iT/r  "73o  I - r a t i o and d i p v s . azimuth p l o t , J o h n s t o n Canyon (B.C.) 32  work was a s t a t i o n s i t u a t e c l o s e enough t o a boundary t o measure i t s strike.  (2)  Power s p e c t r a l  analysis  Because o f i n s t r u m e n t d r i v e f a i l u r e s only one e v e n t , a magnetic storm a t 0300 UT J u l y 27 - 1600 UT J u l y 28, was a v a i l a b l e f o r s i m u l t aneous power s p e c t r a l a n a l y s i s a t b o t h "low I " and " h i g h I " s t a t i o n s i n t h e Canadian c h a i n . T h i s 37 hour i n t e r v a l was machine d i g i t i z e d a t 2.21 min. i n t e r v a l s from r e c o r d s t a k e n a t R e v e l s t o k e , J o h n s t o n Canyon and  C a l g a r y . The r e s u l t a n t power s p e c t r a l d e n s i t y  s t o k e and C a l g a r y , ( P Z ( R ) /  H (R)V ( Z (C ) ^ H (C)) P  p  P  P  L  r a t i o s f o r RevelO  T  '  T  E  ^  a  s  function  8  of f r e q u e n c y ( f i g u r e 17) a r e v e r y s i m i l a r t o the r e s u l t s o b t a i n e d by Cannon (1966) from a p a i r o f s i m i l a r l y p i e c e d s t a t i o n s and  (Grand F o r k s  L e t h b r i d g e ) on Hyndman's p r o f i l e , thus i n d i c a t i n g s i m i l a r s u b s u r -  face conductivity  s t r u c t u r e s beneath t h e two c h a i n s o f s t a t i o n s . The  power s p e c t r a l d e n s i t y plotted  ratios P z ( R ) / ^z(C)  a n <  ^ ^ H ( R ) / ^H(C)  w  e  r  e  a  l  s  o  ( f i g u r e s 18 and 19) t o check t h e p a t t e r n of t h e Z and H  components i n d i v i d u a l l y . The c u r v e ^ ( R j / ^ Z i C )  (  f i  S  u r e l o >  )  i  s  o  f  t  h  e  e x p e c t e d f o r m as R e v e l s t o k e i s a normal "low I " s t a t i o n and C a l g a r y i s a normal "high I  N  s t a t i o n . The curve P H ( R ) /  p l o t t e d t o check h o r i z o n t a l f i e l d u n i f o r m i t y r e c o r d e d and thus Prj(B,)/ • D ( C ) P  IV,  c o u l ( 3  '  n  o  t  1  °  eu s e d  p  z(C)^  f l s u r e  w  a  s  (D a t R e v e l s t o k e was n o t ) •  A  s  outlined i n section  t h e s i g n i f i c a n c e l e v e l of power s p e c t r a l d e n s i t i e s d e r i v e d  i n these  measurements i s 2$% i n the range 0.002 t o 0.032 cpm. P ( g ) / H ( C ) p  H  ( f i g u r e 19) i s u n i t y w i t h i n t h e s e l i m i t s f o r t h e frequency range 0.009 t o 0.016 cpm b u t i s l a r g e r f o r t h e ranges 0.002 t o 0.007 cpm and 0 . 0 1 8  t o 0.032 cpm. To f u r t h e r check t h e h o r i z o n t a l f i e l d u n i f o r m i t y  33  t h e power  Pig. UJ VJ1  16.  Western Canada I - r a t i o  distribution.  s p e c t r a l d e n s i t y r a t i o s f o r two " h i g h I " s t a t i o n s ( J o h n s t o n Canyon/ C a l g a r y ) were computed and p l o t t e d i n f i g u r e s 20 t o 2 2 . The g e n e r a l downward t r e n d o f P H ( J ) / M ( C ) P  a  n  d  P  D ( J ) / D ( C ) ( f i g u r e 20) suggests  eith  p  - e r a s o u r c e e f f e c t o r t h e i n f l u e n c e of a s u b s u r f a c e c o n d u c t i v i t y l a y e r boundary.  p  z(J)/ Z(C)( ig p  f  u r e  21) i s r e l a t i v e l y u n i f o r m between  J o h n s t o n Canyon and C a l g a r y ( t o w i t h i n a 20 % t o l e r a n c e l i m i t ) f o r t h e frequency  ranges 0.002 t o 0.007 cpm and 0.014 t o 0.018 cpm.  In the f r  -equency ranges 0.009 t o 0.014 cpm and 0.020 t o 0.027 cpm t h e power i n t h e Z component a t J o h n s t o n Canyon i s l e s s than t h a t a t C a l g a r y . A g a i n t h e e f f e c t c o u l d be e i t h e r due t o source c u r r e n t p r o x i m i t y o r t o the p r o x i m i t y o f one of t h e s t a t i o n s ( J o h n s t o n Canyon) t o a c o n d u c t i v i t y zone boundary;  t o d e c i d e between t h e s e two p o s s i b i l i t i e s  would r e q u i r e s e v e r a l more u s a b l e d i s t u r b a n c e s a t a l l t h r e e s t a t i o n s . The c h a i n o f s t a t i o n s i n t h e s o u t h w e s t e r n U.S.A. was a l s o p l a g u e d by d r i v e f a i l u r e s ; however, two d i s t u r b a n c e s were a v a i l a b l e f o r s i m u l t a n e o u s power s p e c t r a l a n a l y s i s a t b o t h low and h i g h I s t a t i o n s . These were a magnetic istorm w h i c h l a s t e d f r o m 2300 TJT May 25 t o 0400 UT, May 27 and was r e c o r d e d a t Newkirk,' Norman and D a l l a s and a sequence o f bays from 0900 UT June 24 t o 1100 June 25 r e c o r d e d a t B u s h l a n d , Norman and D a l l a s .  B o t h d i s t u r b a n c e s were  machine d i g i t i z e d a t 2.21 min. i n t e r v a l s f o r Newkirk, Bushland and D a l l a s and a t 1.82 min i n t e r v a l s f o r Norman.  The Norman Z component  f o r 0900 June 24 t o 1100 June 25 was l o s t i n t h e d a t a p r o c e s s i n g due t o a computer paper tape r e a d i n g e r r o r ; a l s o t h e D component a t B u s h l a n d was due t o a poor lamp adjustment on the magnetometer t h e r e . The  " n o r m a l i z e d " power s p e c t r a l d e n s i t y r a t i o s ( P z ( N ) / P ] 3 ( N ])/  ( Z ( ) / H(Dj) ( Z(N)/ D(N)4 Z(D) ( ^ ^ ^ ^ f i g u r e 2 3 . The g e n e r a l form of b o t h c u r v e s i s a s expected b u t t h e P  p  alld  P  P  >  /Pr)  D  k  l  r  k  a  l  l  a  a  r  e  s  h  D  36  o  w  n  l  n  P O W E R  S P E C T R A L  R E V C L S T O K E /  STORM:  030UUT  TULY  Pz,/P„,/ P^/PH,  27  DENSITY  (?AT|0  CALO-firRY TO  Uf  VS.  JULY  2S?  FREQUENCY  5°  IN  *>Q.DOO  OOOS-  (I.oil?  O.OIS  O.OZO  0.OZ6  0.020  FREQUENCY IN F i g , 17.  Q.UJ.S  O.OI-o  O.OfS'  CRM.  Power s p e c t r a l d e n s i t y r a t i o ( R e v e l s t o k e / C a l g a r y , Z/H). 37  SPECTRAL DENSITY RATIOS  POWER  L S T O KE / C ALG-ARY  R F V E  STORM  P£R/  P?C  0  V5.  3  0  0  U  T J U L Y  27  TO  1 6 0 0  U  T  J U L Y ' 2 8  F R E Q U E N C Y  4.0 -ZO »/  P  ©  0  a  a  a  \  I  i _ L  CUT  s  60'. W W  O.'uOj  O'OW  o'.aib  o'.0?.0  o\(lZS  FREQUENCY  Pig.  IN  OFF  0-03)7  0-030  FREQUENCY c-'ots  u'oyo  &6so  '  C R M .  18. Power s p e c t r a l d e n s i t y r a t i o  ( R e v e l s t o k e / C a l g a r y , Z/Z)  F R E Q U E N C Y  V S . o Ui  9  o  a  •  a a  • "  • CL  o  a  a  •  I  a a e  a  a a e  a e  -i Fig.  a 0--JV-/.  @ i  |  i  i  T  r |3 £ Q  -  IJ  1  E- |v ('. Y  CUT OFF  " 1 — —  ! !\!  1  F K F . U U t M C V 1  \  '  —  '  (  CJ . M . 3  19. Power s p e c t r a l d e n s i t y r a t i o ( R e v e l s t o k e / C a l g a r y , H/H). 38  S P E C T R A L DENS I T V  POWER  CANYON/ 0300 UT. JULY  JOHNSOM'S STORM:  RATIOS  CALG-ARY 2 - 7 T O 1600UT-  •  PZT/PHS / f W P i *  VS. FREQUENCY  o  Pzr/Po.r/  V.S, F R E Q U E N C Y  PtJPo,  JULYZti  ° O  o  Q I  a.  r  o  v  a. N  6  8  3  a.  e  d i e  CUT otW  o.ooy  O.CtO  O.OLT 0.020 0.0«i: FREQUENCY IN  O-O.'JO C . P , M.  PREQUE.NCY  OFF  0.035  O.OW  O.Otff  O.0«"0  F i g . 22. Power s p e c t r a l d e n s i t y r a t i o , ( J o h n s t o n Canyon/Calgary, Z/H, PH.. / P * C  I +2  VS;. FREQUENCY  Z/  M  D  )  -vi  a-  CKTOFF  41  O.000  0.005  0.O1O  0 , 0 1 5 O.O20  0.025"  0-O3O  IN  C P-N-  FREQUENCY  0.035  F(?EG>UENCY  -r  0.0*fO  0.04-5" COSY)  0.055  F i g . 21. Power spec^trajL^dens^Jy r^fcJLj^ ^^hnston Canyon/Calgary, Z/Z) E  o  JN Q  0  ~\ 0  ©—  C"  t.C —  VS.  K O •/« —  8 o  '«  sv.. C K  Pnr / Poc  o  0  •  w  —  0  0  O  If  2 i f  FREQUENCY  0  o  I o  eo  * e"  o  CUTOFF O • OI~<  (.I'.UIK-  O'• t) 10  ( . / ,'01T  0-'O 2.0  oToZ5  o!o30  p'ojS?  •  o • o  FREQUENCY' o'OfO  (l'"»5  TTpSO  A'C6"5  F i g . 20. Power s p e c t r a l d e n s i t y r a t i o s ( J o h n s t o n Canyon/Calgary,H/H, D/D ). 39  POWER  SPECTRAL  N E WK/R K / STORM:  RATIOS  DENSITY  DALLAS  2 3 0 0 L/T M A Y 2.5" T O O < f 0 0 U T M A Y 2 7  •  P* /PH* /  O  P  N  a v  / POH /  P?0/  Ptp/Pnt>  V/S. F R E Q U E N C Y  PooV S .  FREQUENCY  *0 d 3  4  ~ OS  HI •?  a. z  o  O  3 i  it  o •  Q_ ^  (  C U T OFF  Sn'.onoo!rt)fr  O^OtO  O.'olS  o'.OZO 0.'0?5  F R E Q U E N CY  IN  O.'o30  oToJ?  PREQUENCV 0:0*0  o'-0H5  0-05O  o'.055  C.RM.  p i g . 23. Power s p e c t r a l d e n s i t y r a t i o s (Newkirk/Dallas,Z/D,Z/H ). 40  z/%  p  The  curve shows c o n s i s t e n t l y h i g h e r r a t i o s than the P / P c u r v e . z  graphs of P ( ) / P ( ) , P H ( N ) / ? H ( D ) a n d z  N  z  PD (N)/^D ( D )  D  w e r e  D  t  n  e  n  plotted  s e p a r a t e l y , w i t h o u t n o r m a l i z a t i o n , ( f i g u r e s 24 and 25) t o determine the cause o f t h i s d i s c r e p a n c y . H(N)/ H(D)  P  f  P  PD(N)  o  r  a  1  p  c o n s i s t a n l y l a r g e r than  l s  f r e q u e n c i e s i n the range 0.002 t o 0.032 cpm;  1  approximately  i s  D(N)/- D(D)  p  equal t o P ( j ) ) f o r a l l f r e q u e n c i e s i n the range D  0.002 t o 0.009 cpm and t h e n i s l a r g e r between 0.011 and 0.032 cpm;  P/H(N)  i s  always s m a l l e r than P p j ^ a n d f o r t h e requency range 0.002  t o 0.007 cpm P £ ^ i s l a r g e r t h a n P (£>)While from 0.011 t o 0.032 cpm Z  Z(N)^  P  S  S  M  A  H  E  :  N  Z  P  than 2 ( D ) *  P  p  *Z(N)/"^Z(D) ( f i §  n c e of t h e expected  r e s e  w i t h i n c r e a s i n g frequency  u r e  a t t e n u a t i o n of  i n d i c a t e s that  D a l l a s i s indeed a " h i g h I" s t a t i o n and Newkirk a "low I " s t a t i o n . The  PH(JT)/^H(D)  a n ( 3  ' ^D(N)/ D(D) P  C U R V E S  S  U  SS  e  s  t that the consistent  d i f f e r e n c e between t h e P / P a n d P / P c u r v e s i s s i m p l y a l a t i t u d e z  H  z  D  level  effect,  D a l l a s b e i n g a t a s l i g h t l y lower geomagnetic l a t i t u d e t h a n Newkirk, o r perhaps i s due t o i n a c c u r a t e c a l i b r a t i o n a t Newkirk. The  power s p e c t r a l d e n s i t y r a t i o s f P . / P . J/fP , /P \(BushV ' Z ( B ) H ( B ) A z ( D ) H(D)' v  F  /  t t  l a n d / D a l l a s ) a r e p l o t t e d i n f i g u r e 26 f o r t h e June 24/25 d i s t u r b a n c e ; a g a i n t h e form o f t h e curve i s c o r r e c t f o r a power s p e c t r a l r a t i o of "low  I s t a t i o n / h i g h I s t a t i o n " , and a g a i n t h e c u r v e  P  z(g)/ ( )(figure P  Z  D  27) I n d i c a t e s t h e p r e s e n c e o f a l a t i t u d e e f f e c t . U n f o r t u n a t e l y , t h e D traoie a t B u s h l a n d was n o t a b a i l a b l e t o c o n f i r m  this.  To check h o r i z o n t a l f i l e d u n i f o r m i t y and t h e s u i t a b i l i t y o f Norman as a "normal" " h i g h I" r e f e r e n c e s t a t i o n , z ( N o / Z ( D ) ' p  P  D(No/ D(D) P  A N D  P  H(No ( H(D) J  P  W E R E  P  l o t t e d  l  n  figures  2  P  8  a  n  d  2  9 . The r a t i o  P H ( N O / H ( D ) ( f i g u r e 29) shows a r o u g h l y u n i f o r m r i s e from P  0.06 a t 0.002 cpm t o a p p r o x i m a t e l y  approximately  1.30 a t 0.052 cpm, a s compared  POWER  SPECTRAL  RATIOS  DENSITY  N E W K I R K / DALLAS STORM:  UT M A Y Z5  2300  Pa /Pro  T O OHOO  MAY27  VS F f f F Q U E M C Y  w  l.o - eo>i  CUT §t!eJU3  o.nosr  n.'mo  o-'uis  w'oiiO  o'.oio  O-oe.5  FRITfflOEIVCY  IM  OFF  FRE-CJUgWCY  oToIF  C.P.M.  O'vto  O  O'.OHB  o.'e?'™  o'nrfr  P i g . 24. Power s p e c t r a l d e n s i t y r a t i o s ( N e w k i r k / D a l l a s , Z/Z). •  P H N / P H "  VS  F R E Q U E N C Y  Q  PON/POO  V S  FREOUo  I  o o  o  o  ,  o  *o o  o  o  o~ ~ b ~ ~ Co 4-zo-/. v.-  ENC/  o  O  o  l.o -10 */. S  6  a. =  CfT O F F F«F«(I£NUY <$O-<JOO  oloos  o'.oio  o.'olS"  olovn  fl?EQUENICY  o'ozff I'M  o.'oao  y.'rt35"  o'.oto  o'.cn*^  o!o<r?>  oTcTaT"  C.P.M.  P i g . 2 5 . Power s p e c t r a l d e n s i t y r a t i o s ( N e w k i r k / D a l l a s , D/D,H/H).  POWER  S P E C T R A L  BUSHLAND/ BAYS•  osoo  DENSITY  RATIOS  DALLAS  U T T U N E Z ^ -  T O  pM/flteAftp/RfD  IIOO U T  \/S.  JUHEZS  FREQUENCY  \  N Q l X TO 6' t> d'  •  l  <3 In  6 I O>T J 0,000  •  C'-fOf  •  O.OIO  1  l  i  P.Pi.<T  O02.0  CUT  1  O-WCS  F R E Q U E N C Y  OA30 IN  OFF  r-R.feQUE.MCY  1  1  O-O^S  6. K  1  O.OW  1  O.Vt-S  0-050  1 0.055  M.  P i g . 26. Power s p e c t r a l d e n s i t y r a t i o ( B u s h l a n d / D a l l a s , Z/H). O  P r t 8 / P  o  P a a / P z D  H  r  >  VS.  F R E Q U E N C Y  VS  FREQUENCY  Q —s  IN  Cu  i.Oc  e o  Z0%  o  0  °  I I Cl/T O F F O O O  0 ^ 0 0 5  o'.OiO  OlOi;>  O.'OZO  FREQUENCY  tlluii.?  iV&T?  O'.OH-O  0'O^o  ( B u s h l a n d / D a l l a s , Z / Z , H / H ) . 43  IN C . P . M .  P i g . 27* Power s p e c t r a l d e n s i t y r a t i o  o'.ujb  FREQUENCY D.'o  t o t h e n e a r l y c o n s t a n t r a t i o o f 0.5 observed i n t h e N e w k i r k / D a l i a s results  (figure 25).  The r a t i o E ( N / D ( D ) p  P  s h o w s  a  s l l  0  S  h t l  y  m  o  r  e  complex b e h a v i o r , r e a c h i n g a peak v a l u e o f 1.55 a t 0.020 cpm. The r e l a t i v e positions  of the P ( N $ D . ( D )  a n f l  P  D  do n o t suggest a marked l a t i t u d e e f f e c t . ratios P ( H  N 0  /  P  (D)» D ( N ) P  H  0  / P  D(D)  s h o w  n  0  H(No/ H(D) P  c u r v e s  (  f l  S  9)  u r e 2  S i n c e t h e Norman/Dallas marked l a t i t u d e e f f e c t ,  p z ( N o  Z(D)  s h o u l d be v e r y n e a r l y u n i t y f o r the frequency range 0.002 t o  0.032  cpm i f Norman i s a "normal"  P  would be w i t h i n P  ( i d e a l l y the r a t i o  20 % o f 1.0 a t a l l f r e q u e n c i e s i n t h i s range.) The  ratios 2(No/ Z(D^ P  "high I " s t a t i o n  ^  f l g u r e  exceed u n i t y by a very wide margin over  t h e e n t i r e f r e q u e n c y r a n g e . The curve does n o t f o l l o w  relatively  c o n s t a n t r a t i o s g r e a t e r than 1.0 which c o u l d be expected f o r two "normal"  "high I",stations  with a small latitude difference,  n o r does  i t demonstrate t h e expected a t t e n u a t i o n w i t h f r e q u e n c y o f a "low I station/high  I s t a t i o n " c u r v e . As no s i g n i f i c a n t h o r i z o n t a l  field  d i s c r e p a n c i e s i n d i c a t i v e of a source e f f e c t a r e observed f o r e i t h e r N e w k i r k / D a l l a s o r Norman/Dallas, the o n l y obvious r e a s o n f o r t h i s high P £ Z  N o  / " P ^ r a t i o l s ~ a. s u b s u r f a c e c o n d u c t i v i t y z  inhomogeneity  near  enough t o Norman t o cause a s i g n i f i c a n t a l t e r a t i o n o f t h e Z component of t h e magnetic v a r i a t i o n f i e l d a t Norman. T h i s , however, has o n l y been found f o r one event and thus t h e I d e n t i f i c a t i o n o f Norman as a n anomalous s t a t i o n by means o f power s p e c t r a l d e n s i t y r a t i o s i s strictly  tentative.  Comparison of t h e power s p e c t r a l r a t i o s f o r R e v e l s t o k e / C a l g a r y w i t h N e w k i r k / D a l l a s and B u s h l a n d / D a l l a s by t r a n s p o s i n g a l l p l o t s t o the same p o i n t a t 0.002 cpm ( f i g u r e 30) shows t h a t the r a t i o s f o r R e v e l s t o k e / C a l g a r y and B u s h l a n d / D a l l a s a r e very s i m i l a r  throughout  t h e f r e q u e n c y range 0.002 t o 0.032 cpm. The r a t i o s R e v e l s t o k e / C a l g a r y kk  and N e w k l r k / D a l l a s do n o t compare q u i t e as w e l l . A l t h o u g h t h e s c a t t e r of t h e N e w k i r k / D a l l a s data i s much h i g h e r , t h e curves i n d i c a t e a more r a p i d power a t t e n u a t i o n w i t h f r e q u e n c y than t h e R e v e l s t o k e / C a l g a r y curves. C o n s i d e r i n g t h e d i f f e r e n c e i n l a t i t u d e between t h e two p r o f i l e s , the agreement between t h e R e v e l s t o k e / C a l g a r y and B u s h l a n d / D a l l a s power s p e c t r a l density r a t i o s i s s u f f i c i e n t l y close to confirm the suggestion of Caner and Cannon (1965) t h a t t h e two anomalies a r e i n d e e d p a r t of the same s t r u c t u r e r a t h e r t h a n i s o l a t e d f e a t u r e s . A l t h o u g h  insufficient  d a t a were o b t a i n e d t o p e r m i t f u r t h e r q u a n t i t a t i v e work, t h i s c o n f i r m a t i o n of s t r u c t u r a l c o n t i n u i t y i s i n i t s e l f a s i g n i f i c a n t result.  45  Pig.  28. Power s p e c t r a l d e n s i t y r a t i o  ;"  POWER  SPECTRAL  (Norman/Dallas,Z/Z) DENSITY"  RATIOS  N 0 R MAM/OALLAS STORM;  PHN.  2.300 UT  / P ^ a  VS.  Z 5 TO  MAY  0<+00 U T M A Y £ 7  FREQUENCY  1 z i  v  I  |  'u.oan  Pig.  1  o.omr  ,  I  1  I ! CI;T OFP ' 1  1  I  o.o?.o o.a?.s 0.030 0.03S F-RBUHSNCV IN C. P.M.  o.oio  i»ft«« • I o.oto  0.015  i/ewcy 1 o.ote  I  1  o-oso  29. Power s ^ c t i ? ^ d e n ^ t ^ ^ a J ^ ( ^ o r m a n / D a l l a s ,D/D,H/H) c  n  o  VS.  PPN./Poo  FREQUENCY  9,  e  o S'TC  "c  o  _*  «  •  c~  o • 0  0  0  o  e  o  .1.0 -zr> /c 5  o 1  too  o-aos  1  o,Oi.O  1  1  o.o?o  1  1  <i:o'«i  o-OKS  F R E Q U E N C Y  C. U T OFF FREQUENCY  1  I N  C.  o.O'jf  C \-\-  1  Outto  1  f>.0<*-?>  : O.iTU  ;  P i g . 30. Comparison o f n o r m a l i z e d Z/H power s p e c t r a l d e n s i t y C O M P A R I S O N D E N S I T Y  1.0  A T  O P  P O W E R  O.OO?-  S P E C T R A L  {NORMALISED  R A T I O S  C  R  M  ratios.  TO  .  X  Pz»/P»»/P20 / Pn°  (NEWKIRK/DALLAS)  t  PZN/PDN/too/  CNEW'KlRK/  e  P»B./PMfl  / PJTD/PWO  o PZ*/PH*/  P?C/PHC  POD  DALLAS)  eBUSH'L/NA/D/ D A L L A S . ) (ReVEi:STai<',E/CvALcVARY>-••!  fo o  t  61  0r  ^  0  <5. •  x  o  o .0  X  £<1 o  t  I  e  o  t I  i  >' *  is EL 5  i  X  I  5"  ^  o  I X  I I  o  I W  t  1  1  F R E Q U E N C Y  ,• ( . t i l O F - f P«E^)UC.)NCy  x  iM C R M  47  J  VI  APPENDIX  T h i s appendix  c o n t a i n s a number of t h e o r e t i c a l power s p e c t r a l r a t i o  c u r v e s f o r t w o - l a y e r models, as o u t l i n e d i n s e c t i o n 1 1 ( 3 ) .  and S  g  are  t h e e l e c t r i c a l c o n d u c t i v i t i e s of t h e o v e r l y i n g l a y e r and o f t h e s u b s t r a t u m r e s p e c t i v e l y , i n emu., and hi and hg a r e t h e depths t o t h e c o n d u c t i n g s u b s t r a t u m i n km. a t t h e two " s t a t i o n s " . F o u r groups of c u r v e s a r e shown ( f i g u r e s 31 t o 3 4 ) , c o r r e s p o n d i n g t o s p a t i a l wave-numbers V 2 x 10 "''em  F o r each  10"  8  cm ""•*-, 5 x 10"^ cm"" , lO^^cm" , and 1  1  group, two s e t s of curves a r e shown:  (a) h]_ v a r i e d f o r h = 100 km, and (b) h-^ v a r i e d f o r h « 150 km. The s o l i d 2  2  c u r v e s a r e f o r c o n d u c t i v i t y v a l u e s S]_/S = 10" 2  /10~"  .  In addition,  d o t t e d l i n e s on each f i g u r e g i v e t h e c u r v e s f o r two o t h e r contrasts  (lO"^/10"  1 1  and l O ^ V l O "  Some o f t h e c u r v e s have  1 0  conductivity  ) a t two v a l u e s of h .  been regrouped  x  i n f i g u r e 35 t o show:  ( i ) the e f f e c t of v a r y i n g V L f o r the same s t r u c t u r e and ( i i ) t h e e f f e c t of v a r y i n g h  ?  a t f i x e d h-,.  48  -3  F i g . 31bV L = 10'  P i g . 32a.  ff.ooo  oloos' o'oio  obi?  oioao o'.02S oToio o.oaS oioto o'.ofs- 6'.oso o\oss oio60 FREQUENCY IW C.P.M.  dobs  51  olo  P i g . 32b. V L = 5X  10  CO  FREQUENCY  IN  CPM  52  Pig.33a. VL = IO"  7  54  55  P i g . 35. EFfteCTSOOTF VARTiMrN© '- ~Q€- £f> t-iA.YE'P- ' E 7 E P T H VARYING  SPATIAL  WAW  LENGTH  -16  L  =  .  OF  - «  Si=10  ^  ANO  (V>.)  Sa=iO  io~  Ki/'h.-  iS/l50  VAX I t O  PARAMETER  hi/hi  VARIED  PARAMETER  Vi  • FREQUENCY  IN C.P.M.  56  REFERENCES A k a s o f u , S - I . The P o l a r E l e c t r o j e t •/ J . Atmos. T e r r . Phys. ( p r e p r i n t ) Canner, B. and Cannon, ¥. Geomagnetic d e p t h - s o u n d i n g and c o r r e l a t i o n w i t h o t h e r g e o p h y s i c a l d a t a i n w e s t e r n N o r t h A m e r i c a . Nature 207, 927  (1965).  Cannon, W. M.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia  (1966)  Hyndman, R. E l e c t r i c a l c o n d u c t i v i t y i n h o m o g e n e i t i e s i n t h e E a r t h ' s upper m a n t l e . M.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia  (I963).  Lambert, A. and Caner, B. Geomagnetic "depth-sounding",and.the c o a s t e f f e c t i n w e s t e r n Canada. Can. J . E a r t h S c i . 2, 4 8 5 , ( 1 9 6 5 )  t>  P a r k i n s o n , W. D i r e c t i o n s o f r a p i d geomagnetic f l u c t u a t i o n s . J.  2, 1  Geophys'.  (1959)  P a r k i n s o n , W. The i n f l u e n c e of c o n t i n e n t s and oceans on geomagnetic v a r i a t i o n s . Geophys. J . 6, 4 4 l (1962)  P r i c e , A. The t h e o r y o f m a g n e t o - t e l l u r i c methods when t h e source f i e l d s a r e c o n s i d e r e d . J . Geophys. R e s . j6£, IO97 (1962)  R o s t o k e r , G. M i d - l a t i t u d e t r a n s i t i o n bays and t h e i r r e l a t i o n t o t h e s p a t i a l movement o f overhead c u r r e n t systems. J . Geophys. R e s . 21,  79  (1966)  Schmucker, U. Anomalies of geomagnetic v a r i a t i o n s i n the s o u t h - w e s t e r n U n i t e d S t a t e s . J . Geomag. G e o e l e c t . JLj>, 193 (1964) Slawson, W. F. and A u s t i n , C.F.  Econ. G e o l .  2  1  (19^2)  Watanabe, T. A " s e l f c o n s l s t a n t s o l u t i o n " method f o r d e t e r m i n i n g t h e e l e c t r i c a l c o n d u c t i v i t y i n t h e s u b s u r f a c e r e g i o n s of t h e e a r t h . Can. J . E a r t h S c i . 2, 206 (1964) Whitham, K. An anomaly i n t h e geomagnetic v a r i a t i o n s a t Mould' Bay i n the A r c t i c A r c h i p e l a g o o f Canada. Geophys. J . 8, 26 (19^3) Whitham, K. Geomagnetic v a r i a t i o n anomalies i n Canada. J . Geomag. G e o e l e c t . 1£, 481 (1965)  57  

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