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Geomagnetic variation anomaly at Kootenay Lake, B.C. Lajoie, Jules Joseph 1970

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THE GEOMAGNETIC VARIATION ANOMALY AT KOOTENAY LAKE, B.C. by JULES JOSEPH LAJOIE B . S c , U n i v e r s i t y of Ottawa, 1968 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF M.Sc. i n the Department of . GEOPHYSICS We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1970 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 f o r 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 reference and study . I f u r t h e r agree tha permiss ion fo r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying 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 ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada ABSTRACT The purpose of t h i s t h e s i s was t o stu d y the geomagnetic v a r i a t i o n anomaly a t Kootenay Lake, B.C., f i r s t r e p o r t e d by Hyndman i n 1 9 6 3 . The anomaly i s c h a r a c t e r i z e d by a v e r y h i g h c o r r e l a t i o n between the v e r t i c a l and h o r i z o n t a l n o r t h - s o u t h geomagnetic components; t h i s i n d i c a t e s anomalous c u r r e n t s s t r i k i n g magnetic e a s t - w e s t , t o the s o u t h of Kootenay Lake. D u r i n g the summer of 1968, t w e n t y r e c o r d i n g s t a t i o n s were s e t up i n the Kootenay Lake a r e a , u s i n g f o u r A s k a n i a v a r i o g r a p h s and t h r e e f l u x g a t e magnetometers. S p e c t r a l a n a l y s i s shows t h a t the main 'low I - h i g h I ' d i s c o n t i n u i t y was t r a v e r s e d over a r e l a t i v e l y s h o r t d i s t a n c e on a n o r t h - s o u t h p r o f i l e , t o the so u t h of Kootenay Lake. P o l a r i z a t i o n s t u d i e s i n d i c a t e anomalous c u r r e n t s s t r i k i n g magnetic e a s t - w e s t i n the same g e n e r a l a r e a of the above d i s c o n t i n u i t y . The model proposed i s a l o c a l i z e d d i s t o r t i o n of the main 'low I - h i g h 1 1 d i s c o n t i n u i t y , r e s u l t i n g i n a w e l l d e f i n e d c o n d u c t i v i t y s t e p , s t r i k i n g magnetic e a s t - w e s t , t o the s o u t h of Kootenay Lake. i i TABLE OF CONTENTS Page I INTRODUCTION 1 A The Anomaly 1 o B Hyndman's I n t e r p r e t a t i o n 2 C Lower C r u s t and Upper M a n t l e S t r u c t u r e i n We s t e r n Canada 4 I I THEORY 7 A I n d u c t i o n I n a Step D i s c o n t i n u i t y 7 B P a r k i n s o n Diagrams, I n d u c t i o n Arrows, and the M e r c a t o r P r o j e c t i o n . 8 C Power S p e c t r a l A n a l y s i s 10 I I I EXPERIMENTAL PROCEDURE 13 A I n s t r u m e n t a t i o n 13 B F i e l d E x p e r i m e n t 14 IV ANALYSIS AND INTERPRETATION 17 A S e c t i o n s of G.D.S. Magnetograms ' 17 • B Power S p e c t r a l A n a l y s i s 20 C Ma g n e t i c Survey 25 D P o l a r Diagrams 29 E I n t e r p r e t a t i o n 34 V CONCLUSION 40 I i i L I S T OP FIGURES M a g n e t i c Record a t B o s w e l l , J u l y k, 1968 L o c a t i o n Map of Geomagnetic Depth Sounding and M a g n e t o - T e l l u r i c S t a t i o n s i n Western Canada P e t r o l o g i c a l Model f o r Western Canada P a r k i n s o n Diagram L o c a t i o n Map Showing A s k a n i a and F l u x g a t e S t a t i o n s Two S i m u l t a n e o u s P r o f i l e s of.G.D.S. Records Power S p e c t r a l E s t i m a t e s : a M i r r o r Lake t o R y k e r t s and Newport b Brouse t o Salmo and Newport Power S p e c t r a l R a t i o s : a M i r r o r Lake t o R y k e r t s and Newport b Brouse t o Salmo and Newport L o c a t i o n Map Showing M a g n e t i c Survey P r o f i l e F i l t e r e d M a g n e t i c Survey w i t h Wavelength C u t o f f s Shown P a r k i n s o n Diagrams and C o r r e s p o n d i n g M e r c a t o r P r o j e c t i o n s : a M i r r o r Lake t o R y k e r t s b Brouse t o Salmo P o l a r Diagrams and C o r r e s p o n d i n g M e r c a t o r P r o j e c t i o n s : a M i r r o r Lake t o R y k e r t s b Brouse t o Salmo i v Page 13 L o c a t i o n Map Showing Anomalous S t a t i o n s 35 14 Proposed Model E x p r e s s e d i n Depth C o n t o u r s t o H i g h l y • C o n d u c t i n g L a y e r 37 V ACKNOWLEDGEMENTS I w i s h t o acknowledge the. a d v i c e , encouragement, and p a t i e n t s u p e r v i s i o n of Dr. G.K.C. C l a r k e d u r i n g the co u r s e of t h i s r e s e a r c h . S p e c i a l t h a n k s are g i v e n t o Dr. B. Caner .of the Dominion A s t r o p h y s i c a l O b s e r v a t o r y i n V i c t o r i a , f o r d i r e c t i n g and s u p e r v i s i n g the f i e l d o p e r a t i o n s , and f o r many h o u r s of d i s c u s s i o n s which l e d t o the i n t e r p r e t a t i o n of the anomaly. I would a l s o l i k e t o thank the Dominion O b s e r v a t o r y i n Ottawa, f o r the use of the t h r e e f l u x g a t e u n i t s d u r i n g the s u r v e y ; and the U.S. Coast and G e o d e t i c Survey f o r the Newport M a g n e t i c O b s e r v a t o r y magnetograms. 1 I INTRODUCTION I n the summer of 1968, t h e Department of G e o p h y s i c s a t the U n i v e r s i t y of B r i t i s h C olumbia, i n c o o p e r a t i o n w i t h t h e . D i v i s i o n of Geomagnetism of the O b s e r v a t o r i e s B r a n c h , a t V i c t o r i a , s ponsored a geomagnetic depth s o u n d i n g (G.D.S.) s u r v e y t o i n v e s t i g a t e t h e geomagnetic v a r i a t i o n anomaly at Kootenay Lake, B.C. Because of the h i g h s o l a r f l a r e a c t i v i t y i n 1968, t h i s p r o v e d t o be a most f a v o u r a b l e time t o conduct t h e e x p e r i m e n t . Four A s k a n i a GV-3 v a r i o g r a p h s and t h r e e f l u x g a t e - t y p e c o n t i n u o u s r e c o r d i n g magnetometers were used. A t o t a l o f twenty s t a t i o n s was s e t up t o map the anomalous zone. A The Anomaly The anomaly a t B o s w e l l , on the e a s t e r n shore of Kootenay Lake, was f i r s t r e p o r t e d by Hyndman, on the b a s i s o f an e a s t - w e s t G.D.S. p r o f i l e a t l a t i t u d e 4 9 . 5°N (Hyndman, 1 9 6 3 ) . I t i s c h a r a c t e r i z e d by a s t r o n g c o r r e l a t i o n between t h e v e r t i c a l (z) and magnetic n o r t h - s o u t h (H) i n t e n s i t i e s . T h i s i s q u i t e e v i d e n t i n a sample magnetogram f o r t h i s s t a t i o n ( F i g . 1 ) . A s i m i l a r but weaker c o r r e l a t i o n was a l s o r e p o r t e d a t C r e s c e n t V a l l e y , B.C. The anomaly i s of p a r t i c u l a r i n t e r e s t because i t may be r e l a t e d t o a change i n upper mantle and/or l o w e r c r u s t a l s t r u c t u r e a s s o c i a t e d w i t h the e a s t e r n edge o f the w e s t e r n 2 c o r d i l l e r a ( C a n e r a n d C a n n o n , 1 9 6 5 ) . G e o l o g i c a l l y , t h e a n o m a l y i s a t t h e c e n t e r o f a m a j o r t e c t o n i c f e a t u r e k n o w n a s t h e K o o t e n a y A r c , w h i c h s w e e p s i n a b r o a d c u r v e a r o u n d t h e N e l s o n b a t h o l i t h ( C r o s b y , 1 9 6 8 ) . T h e d i r e c t i o n a l d e p e n d e n c e o f t h e i n d u c e d Z f i e l d s u g g e s t s a t o n c e a l a t e r 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 y s t r i k i n g m a g n e t i c e a s t - w e s t , t o t h e s o u t h o f B o s w e l l , B . C . 12:00 U.T. 15:00 U.T. D F i g . 1 M a g n e t i c R e c o r d a t B o s w e l l , J u l y 4, 1 9 6 8 . B H y n d m a n ' s I n t e r p r e t a t i o n H y n d m a n (1963) a t t e m p t e d t o f i t a n I n f i n i t e c y l i n d e r m o d e l t o t h e d a t a . H i s c a l c u l a t i o n s d i s c l o s e d , h o w e v e r , t h a t a c y l i n d e r , s t r i k i n g m a g n e t i c e a s t - w e s t , t o t h e s o u t h o f B o s w e l l a n d C r e s c e n t V a l l e y , r e q u i r e d u n u s u a l l y l a r g e v a l u e s o f c o n d u c t i v i t y a n d r a d i u s , t o s a t i s f y t h e d a t a . F o r e x a m p l e , t h e r a d i u s o f a n i n f i n i t e l y c o n d u c t i n g c y l i n d e r r e q u i r e d i t P i g . 2 L o c a t i o n Map of Geomagnetic Depth Sounding and Magneto-T e l l u r i c S t a t i o n s i n Western Canada ( a f t e r Caner, 1970). 4 t o e x t e n d b e y o n d t h e s u r f a c e . H e n c e , a f i n i t e c o n d u c t i v i t y c o n t r a s t f o r t h e c y l i n d e r d e m a n d e d a n u n r e a s o n a b l y l a r g e r a d i u s . T h e r e f o r e , H y n d m a n c o n c l u d e d t h a t t h e I n f i n i t e . c y l i n d e r c o u l d o n l y b e a v e r y r o u g h , a p p r o x i m a t i o n t o t h e s h a p e o f t h e c o n d u c t i v i t y z o n e . T h i s p r o m p t e d t h e m o r e d e t a i l e d G . D . S . s u r v e y r e p o r t e d i n t h i s t h e s i s , t o map t h e a n o m a l y a n d r e s o l v e t h e p r o b l e m . C L o w e r C r u s t a n d U p p e r M a n t l e S t r u c t u r e i n W e s t e r n C a n a d a R i k i t a k e . (1966) s h o w s t h a t t h e i n d u c e d Z f i e l d a t t h e s u r f a c e o f a n i d e a l h i g h l y c o n d u c t i n g ' f l a t ' e a r t h , c o m p l e t e l y c a n c e l s t h e i n d u c i n g Z f i e l d . F o r t h e e a r t h , h o w e v e r , t h e e x t e n t o f t h e a t t e n u a t i o n i n t h e Z c o m p o n e n t d e p e n d s o n t h e c o n d u c t i v i t i e s o f t h e s u b s u r f a c e l a y e r s , t h e i r d e p t h s , a n d t h e f r e q u e n c y o f t h e i n c i d e n t E . M . w a v e . T h e p a r a m e t e r g e n e r a l l y u s e d t o m e a s u r e t h i s ' a t t e n u a t i o n i s t h e I r a t i o d e f i n e d a s T _ lAZl 1 ~ [(AD) + ( A H ) ] " * T h e f i r s t e x t e n s i v e G . D . S . p r o f i l e a c r o s s t h e w e s t e r n c o r d i l l e r a w a s c a r r i e d o u t i n t h e U . S . A . b y S c h m u c k e r f r o m 1959 t o 1962, a t l a t i t u d e 32°N ( S c h m u c k e r , 1 9 6 4 ) . T h e I r a t i o s o f s t a t i o n s t o t h e e a s t o f L a s C r u c e s a n d C o r n u d a s , New M e x i c o , w e r e t h r e e t i m e s h i g h e r t h a n t h o s e o f s t a t i o n s t o t h e w e s t . T h i s p r o m p t e d f u r t h e r p r o f i l e s t o be c a r r i e d o u t a c r o s s t h e c o r d i l l e r a , t o d e t e r m i n e i f t h i s d i s c o n t i n u i t y w a s e i t h e r a l o c a l o r c o n t i n e n t a l f e a t u r e . SELKIRK KOOTENAY MOUNTAINS LAKE PURCELL MOUNTAINS ROCKY MTN. TRENCH (KOOTENAY VALLEY) t ROCKY MOUNTAINS PLAINS 20 * 40 \ \ t I0 - I5KM\ C O N D U C T I V E , H Y D R A T E D L O W E R C R U S T ( P R O B A B L Y P A R T I A L M E L T I N G ) 60 a 80 -\ \ \ \ R E S I S T I V E , N O R E S O L U T I O N A \ \ \ \ \ \ \ t \ \ \ X 3 0 - 3 5 K >750°C M O D E R A T E L Y C O N D U C T I V E U P P E R M A N T L E , T> 8 0 0 ° C , C O M P O S I T I O N U N D E F I N E D F i g . 3 P e t r o l o g i c a l Model f o r Western Canada, L a t i t u d e 4 9 . 3 N. ( h o r i z o n t a l s c a l e = v e r t i c a l s c a l e ) . ( a f t e r Caner, 1970) The n e x t two p r o f i l e s i n the U n i t e d S t a t e s , a t l a t i t u d e s 34°N (Caner, Cannon, and L i v i n g s t o n , 1967) and 3<3.5°N by Gough and R e i t z e l i n 1966, i n d i c a t e d t h a t the d i s c o n t i n u i t y was r o u g h l y c o r r e l a t e d t o the e a s t e r n edge of the c o r d i l l e r a . I n s o u t h w e s t e r n Canada, s u r v e y s by Hyndman ( 1 9 6 3 ) , Cannon ( 1 9 6 7 ) , D r a g e r t i n 19&9, and the Dominion O b s e r v a t o r y are i n t e g r a t e d i n t o F i g u r e 2, which i n c l u d e s the anomalous s t a t i o n a t Kootenay Lake (K00). T h i s f i g u r e d e f i n e s the app r o x i m a t e l o c a t i o n of the low I - h i g h I d i s c o n t i n u i t y i n s o u t h w e s t e r n Canada. Caner (1970) i n t e g r a t e d t h e s e r e s u l t s w i t h s e i s m o l o g i c a l , a e r o m a g n e t i c , and heat f l o w d a t a t o c o n s t r u c t a p e t r o l o g i c a l and e l e c t r i c a l c o n d u c t i v i t y model of the l o w e r c r u s t and upper mantle f o r w e s t e r n Canada ( F i g . 3 ) . I n the w e s t e r n r e g i o n , the l o w e r c r u s t i s assumed t o be h i g h l y c o n d u c t i v e due t o h y d r a t i o n . Water s a t u r a t i o n was f i r s t p roposed by Hyndman and Hyndman (1968) i n o r d e r t o e x p l a i n the h i g h e l e c t r i c a l c o n d u c t i v i t y found i n the l o w e r c r u s t of young, t e c t o n i c a l l y a c t i v e , c o n t i n e n t a l a r e a s of the e a r t h . 7 I I THEORY A I n d u c t i o n i n a Step D i s c o n t i n u i t y Madden and S w i f t (1969) s t u d i e d the m a g n e t o - t e l l u r i c e f f e c t i n a t w o - d i m e n s i o n a l model of an anomalous upper mantle f e a t u r e - r e s e m b l i n g a p o o r l y d e f i n e d s t e p d i s c o n t i n u i t y i n c o n d u c t i v i t y . I t i n c l u d e d a 10/i-m. s e d i m e n t a r y l a y e r on the s u r f a c e . They r e p o r t e d t h a t f o r t h e case when the e l e c t r i c f i e l d was p e r p e n d i c u l a r t o the s t r i k e o f the f e a t u r e , the e l e c t r i c f i e l d tended t o i n c r e a s e when a p p r o a c h i n g the t r a n s i t i o n zone from the more r e s i s t i v e s i d e , and t o d e c r e a s e when a p p r o a c h i n g i t from the c o n d u c t i v e s i d e . However, t h e r e was no n o t i c e a b l e change a c r o s s the zone when the e l e c t r i c f i e l d was p a r a l l e l t o the s t r i k e . T h i s i n d i c a t e d t h a t the e l e c t r i c c u r r e n t s i n d u c e d by the e x t e r n a l f i e l d were f l o w i n g p a r a l l e l t o the s t r i k e of the anomalous f e a t u r e . The s h a l l o w s e d i m e n t a r y l a y e r tended t o mask the deeper anomalous f e a t u r e s a t the h i g h e r f r e q u e n c i e s . Schmucker (1964) i n v e s t i g a t e d the s t e p d i s c o n t i n u i t y i n c o n d u c t i v i t y f o r the s t e a d y s t a t e c a s e , and showed t h a t t h e l i n e s of magnetic f i e l d c o nverged onto the upper c o r n e r o f the s t e p . Hence, c u r r e n t s i n d u c e d i n such a c o n d u c t o r by an e x t e r n a l t i m e - v a r y i n g magnetic f i e l d , are t h e n I n t e n s i f i e d a t t h e c o r n e r and f l o w p a r a l l e l t o i t . The more s h a r p l y d e f i n e d the s t e p , the more c u r r e n t w i l l f l o w . Weaver (1963) s t u d i e d a t w o - d i m e n s i o n a l model c o n s i s t i n g of'two r e g i o n s , one b e i n g more r e s i s t i v e t h a n t h e 8 o t h e r , r e p r e s e n t i n g a l a n d - s e a i n t e r f a c e . He f o u n d t h a t t h e r a t i o |Z| / IYI w h e r e Y i s t h e h o r i z o n t a l m a g n e t i c f i e l d p e r p e n d i c u l a r t o t h e s t r i k e o f t h e d i s c o n t i n u i t y , i n c r e a s e d a s t h e b o u n d a r y was a p p r o a c h e d f r o m e i t h e r s i d e . H o w e v e r , a w a y f r o m t h e b o u n d a r y , t h e r a t i o d i m i n i s h e d m u c h m o r e r a p i d l y o v e r t h e s e a t h a n o n t h e l a n d w a r d s i d e . T h e r e s u l t o v e r t h e s e a i s i n a g r e e m e n t w i t h R i k i t a k e ' s t h e o r e t i c a l m o d e l f o r t h e c a n c e l l a t i o n o f t h e s o u r c e v e r t i c a l c o m p o n e n t o f m a g n e t i c f i e l d b y i n d u c e d c u r r e n t s i n a s e m i - i n f i n i t e c o n d u c t i n g b o d y ( R i k i t a k e , 1 9 6 6 ) . I f a w e l l d e f i n e d s t e p d i s c o n t i n u i t y i n c o n d u c t i v i t y o c c u r r e d a t l o w e r c r u s t a n d u p p e r m a n t l e d e p t h s , l o w e r f r e q u e n c y E . M . w a v e s w o u l d p e n e t r a t e t h r o u g h t h e u p p e r c r u s t a n d i n d u c e c u r r e n t s i n t h e u p p e r c o r n e r o f t h e s t e p . L o c a l l y , t h e r e s u l t i n g i n d u c e d f i e l d w o u l d be a d d e d t o t h e p r i m a r y f i e l d a t t h e s u r f a c e o f t h e e a r t h . The s e c o n d a r y o r i n d u c e d f i e l d w o u l d be c o r r e l a t e d t o t h e p r i m a r y f i e l d v a r i a t i o n s p e r p e n d i c u l a r t o t h e s t r i k e o f t h e d i s c o n t i n u i t y . B P a r k i n s o n D i a g r a m s , I n d u c t i o n A r r o w s , a n d t h e M e r c a t o r P r o j e c t i o n . L e t T d e f i n e t h e t o t a l v e c t o r c h a n g e o f t h e g e o m a g n e t i c f i e l d i n a s p e c i f i e d i n t e r v a l o f t i m e . T h e n , T = \ / ( A D ) 2 + ( A H ) 2 + ( A Z ) 2 a n d i t s d i r e c t i o n i s s p e c i f i e d b y t w o a n g l e s : 6, t h e a n g l e b e t w e e n T\ a n d t h e v e r t i c a l , a n d (J), t h e a z i m u t h m e a s u r e d c l o c k w i s e f r o m H . © a n d (J) a r e c o n v e n i e n t l y p l o t t e d a s p o i n t s 9 N N F i g . 4 P a r k i n s o n D i a g r a m . o n a d i a g r a m a s s h o w n i n F i g . 4 ( P a r k i n s o n , 1959), w h e r e t h e t w o c i r c l e s r e p r e s e n t s u p w a r d a n d d o w n w a r d c h a n g e s i n t h e v e r t i c a l c o m p o n e n t . The h o r i z o n t a l v e c t o r i s c o r r e c t e d f o r d e c l i n a t i o n , so t h a t N i n F i g . 4 , r e p r e s e n t s g e o g r a p h i c N o r t h . T h e r a d i a l d i s t a n c e f r o m t h e c e n t e r o f t h e c i r c l e i s 6, w h e r e 6=90° i s a t t h e c i r c u m f e r e n c e , a n d 6=0° i s a t t h e c e n t e r . H e n c e , t h e c l o s e r a p o i n t . i s p l o t t e d t o t h e c e n t e r o f t h e c i r c l e , t h e l a r g e r i s t h e Z v a r i a t i o n o f t h e e v e n t . I f , f o r many e v e n t s T , p o i n t s a r e p l o t t e d o n t h e s u r f a c e o f a u n i t s p h e r e , c o r r e s p o n d i n g t o t h e d i r e c t i o n o f 10 T f r o m t h e s p h e r e ' s c e n t e r , t h e n i t i s g e n e r a l l y f o u n d , a t n o n - p o l a r s t a t i o n s , t h a t t h e p o i n t s c l u s t e r a b o u t a ' p r e f e r r e d p l a n e ' , c u t t i n g t h e s p h e r e i n h a l f . T h e P a r k i n s o n d i a g r a m i s t h e n a r e p r e s e n t a t i o n o f t h e p r e f e r r e d p l a n e o n t h e h o r i z o n t a l p l a n e . U s u a l l y , t h e p r e f e r r e d p l a n e i s h o r i z o n t a l , d e f i n i n g a n o r m a l s t a t i o n . H o w e v e r , i n many c a s e s ( P a r k i n s o n , 1959, 1962; W i e s e , 1962; R i k i t a k e , 1964; S i m e o a n d S p o s i t o , 1964; W h i t h a m a n d A n d e r s o n , 1962), t h e p r e f e r r e d p l a n e i s t i l t e d . F o r e x a m p l e , t h e g r e a t c i r c l e r e p r e s e n t e d by. t h e d a s h e d l i n e i n t h e ' U P 1 c i r c l e o f F i g . 4, r e p r e s e n t s a p r e f e r r e d p l a n e d i p p i n g a t a n a n g l e o f 90° - 6 ' i n t h e (f)1 - l8o° d i r e c t i o n . T h i s i m p l i e s a c o r r e l a t i o n b e t w e e n Z a n d t h e h o r i z o n t a l (})1 - l80° v e c t o r , a n d h e n c e a c o n d u c t i v i t y I n h o m o g e n e i t y s t r i k i n g p e r p e n d i c u l a r t o t h e (J)' d i r e c t i o n . T h e i n d u c t i o n a r r o w i s d e f i n e d a s a v e c t o r w h o s e g e o g r a p h i c a z i m u t h i s . 90°- e' (p1 a n d m a g n i t u d e ^QS— A n o t h e r u s e f u l m e t h o d o f r e p r e s e n t a t i o n i s t h e M e r c a t o r p r o j e c t i o n , w h e r e t h e d i p o f t h e g e o m a g n e t i c f i e l d c h a n g e i s p l o t t e d a s a f u n c t i o n o f g e o g r a p h i c a z i m u t h . C P o w e r S p e c t r a l A n a l y s i s i ) C o n t i n u o u s C a s e ( L a t h i , 1968) T h e p o w e r s p e c t r a l d e n s i t y o f a f i n i t e f u n c t i o n f T ( t ) i s d e f i n e d a s : 11 Frp(w) S f(w) = 11m r T ^ ; (1) T-»a> T where, F,p(w) i s the F o u r i e r t r a n s f o r m of f ( t ) , and, (f(t) lt| < T/2 f T ( t ) = (2) I 0 o t h e r w i s e An a l t e r n a t e method of o b t a i n i n g the s p e c t r a l d e n s i t y i s g i v e n by the F o u r i e r t r a n s f o r m of the time a u t o c o r r e l a t i o n f u n c t i o n of f ( t ) : CO S f(w) = / R f ( T ) e - j W T d T (3) -oo where t h e time a u t o c o r r e l a t i o n f u n c t i o n i s x R f ( T ) = l i m - ^ - J f ( t ) f ( t+T ) d t G O i i ) D i s c r e t e Case (Bendat and P i e r s o l , 1967) The f u n c t i o n f T ( t ) i s now sampled N t i m e s a t e q u a l i n t e r v a l s h (Nh=T). To a v o i d a l i a s i n g e f f e c t s , the s a m p l i n g i n t e r v a l must be s m a l l enough so t h a t the c u t o f f f r e q u e n c y f c = 2 n ~ i s a t l e a s t g r e a t e r t h a n the l a r g e s t f r e q u e n c y component i n f ( t ) . F o r s i m p l i c i t y , t he N sampled v a l u e s of f T ( t ) a re denoted { x - ^ X ^ X . ^ . The s e t { x ^ i s f i r s t t r a n s f o r m e d such t h a t X-0. The e s t i m a t e d a u t o c o r r e l a t i o n f u n c t i o n a t the d i s p l a c e m e n t r h i s 1 R r = R ( r h ) = _ ^ V W r = 0 , 1 , 2 , ....m (5) where r i s the l a g number and m i s the maximum l a g number. An e s t i m a t e of the t r u e s p e c t r a l d e n s i t y i n the range 0 ^.f < f i s r - 1 c c J m+1 e s t i m a t e s a re made of S ( f ) a t the d i s c r e t e f r e q u e n c i e s f = k f /m, k = l , 2, ,m.- (6) becomes The F o u r i e r t r a n s f o r m of a f i n i t e l e n g t h of r e c o r d , f ( t ) , i s e q u i v a l e n t t o the c o n v o l u t i o n of F ( w ) , the s p e c t r a l e s t i m a t e of the i n f i n i t e random p r o c e s s f ( t ) w i t h a s i n e f u n c t i o n . A s i n e f u n c t i o n has the u n d e s i r a b l e e f f e c t of h a v i n g c o n s i d e r a b l y l a r g e s i d e l o b e s , so t h a t the power s p e c t r a l d e n s i t y u s i n g t h i s method can o n l y be a 'raw' e s t i m a t e of the t r u e s p e c t r a l d e n s i t y . A b e t t e r e s t i m a t e may be o b t a i n e d by u s i n g a Hanning window, s i n c e i t s s i d e l o b e s i n t h e f r e q u e n c y domain are much s m a l l e r . A l t h o u g h b e t t e r windows now e x i s t , the Hanning window was r e t a i n e d t o o b t a i n r e s u l t s c o n s i s t e n t w i t h p r e v i o u s w o r k e r s . The Hanning window i s d e f i n e d by -^-(l+cos(Trr/m)) r = 0 , 1 , 2 > • • • • > m (8) D ( r h ) - • 0 r>m T h i s may be m u l t i p l i e d by the a u t o c o r r e l a t i o n f u n c t i o n i n (7) t o g i v e r m-1 S ( k f /m) = 2h'R + 2 ] > Z D ^ c o s ( 7 r r k / m ) r = l (9) s i n c e D = 1 , D =0 o ' m 13 I I I EXPERIMENTAL PROCEDURE A I n s t r u m e n t a t i o n i ) 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 . v a r i o g r a p h r e c o r d s time v a r i a t i o n s of the e a r t h ' s magnetic f i e l d on f i l m , a t the r a t e of one i n c h per hour, and s e n s i t i v i t y of about t h r e e gammas per mm. H o u r l y time marks ( u s i n g an e x t e r n a l c h r o n o m e t e r ) , b a s e - l i n e , and i n s t r u m e n t t e m p e r a t u r e a re a l s o r e c o r d e d . I t houses t h r e e independent o p t i c a l systems (D,Z,H) w i t h m i r r o r s mounted on s m a l l A l n i c o - a l l o y magnets, each system b e i n g e q u i p p e d w i t h c a l i b r a t i o n Helmhotz c o i l s . These i n s t r u m e n t s proved most r e l i a b l e i n the su r v e y , though c o n s i d e r a b l e c a r e was n e c e s s a r y i n s i t e s e l e c t i o n . The A s k a n i a v a r i o g r a p h must be housed i n a w e a t h e r p r o o f b u i l d i n g w i t h s o l i d f l o o r , power, and f a r from magnetic d i s t u r b a n c e s such as t r a n s f o r m e r s , moving v e h i c l e s , e t c . Once a s u i t a b l e s i t e i s foun d , however, the i n s t r u m e n t i s o p e r a t i o n a l w i t h i n the hour. I I ) The P l u x g a t e Magnetometer The Dominion O b s e r v a t o r y f l u x g a t e u n i t c o n s i s t s of a f i e l d s e n s i t i v e head c o n t a i n i n g t h r e e o r t h o g o n a l magnetic d e t e c t o r s ( S e r s o n , 1957), a t r a n s i s t o r i z e d e l e c t r o n i c assembly, and a c h a r t r e c o r d e r . The magnetic head may be o p e r a t e d out of d o o r s a t the end of a l o n g c a b l e , away from a r t i f i c i a l d i s t u r b a n c e s . A l t h o u g h the q u a l i t y of the d a t a i s g e n e r a l l y p o o r e r t h a n t h a t of the p h o t o g r a p h i c v a r i o m e t e r , i t has the advantage of p r o v i d i n g the o b s e r v e r w i t h an 1^ immediate v i s u a l r e c o r d , and s i t e s e l e c t i o n i s l e s s s t r i n g e n t . T h i s i n s t r u m e n t was i n t e n d e d t o supplement the d a t a f r o m the A s k a n i a v a r i o g r a p h s . U n f o r t u n a t e l y , the chopper b a r t y p e r e c o r d e r , which was used e a r l y i n the s u r v e y , p r o v e d u n r e l i a b l e and r e s u l t e d i n h i g h r e c o r d l o s s . L a t e r , b e t t e r r e s u l t s were o b t a i n e d w i t h two-channel H e w l e t t - P a c k a r d (Mosley) r e c o r d e r s . B F i e l d E x p e r i m e n t R. Hyndman had p o s t u l a t e d a c y l i n d r i c a l body s t r i k i n g e a s t - w e s t t o the s o u t h of two of h i s s t a t i o n s a t B o s w e l l and C r e s c e n t V a l l e y . I n an attempt t o c r o s s the anomalous zone, a p r o f i l e was s e t up between S l o e a n P a r k and B l u e b e r r y Creek w i t h i n t e r m e d i a t e s t a t i o n s a t Thrums and S h o r e a c r e s ( F i g . 5 ) . A f l u x g a t e s t a t i o n was a l s o s e t up midway between Thrums and S h o r e a c r e s . A f t e r t h r e e weeks of o b s e r v a t i o n (June 2 - 2 1 ) , the a n t i c i p a t e d c r o s s o v e r was not f o u n d , and one of the A s k a n i a s ( B l u e b e r r y Creek) was moved t o C r e s c e n t V a l l e y t o r e c o v e r Hyndman's o r i g i n a l anomaly at t h a t s i t e . On J u l y 2nd, the i n s t r u m e n t s were moved t o a second p r o f i l e a t Kootenay Lake, i n an attempt t o i n t e r c e p t Hyndman's anomaly at B o s w e l l (K00 i n F i g . 2 ) . S u i t a b l e s i t e s were f o u n d a t L a F r a n c e Creek, B o s w e l l , Sanca, Kuskanook ( f l u x g a t e ) , and Wynndel ( F i g . 5 ) . The anomaly was r e c o v e r e d a t a l l of t h e s e s t a t i o n s . On J u l y 13 , Sanca and L a F r a n c e 15 117.5 w 1 1 6 . 5 ° V m i l e s S c h r o e d e r P o i n t M i r r o r Lake t.OLaFrance Ck. A s k a n i a o _ F l u x g a t e X Roads B.C. X|*'CRESTON IQ R y k e r t s Idaho F i g 5 L o c a t i o n Map Showing A s k a n i a and F l u x g a t e S t a i o n s . 16 Creek s t a t i o n s were moved t o M i r r o r Lake and R y k e r t s t o o u t l i n e the boundary of the anomaly. On J u l y 27, the t h i r d and l a s t p r o f i l e was s e t up between Brouse and Salmo, w i t h i n t e r m e d i a t e s t a t i o n s a t S l l v e r t o n , S l o c a n ( f l u x g a t e ) and Taghum. Two' a d d i t i o n a l f l u x g a t e i n s t r u m e n t s were a c q u i r e d f r o m the Dominion O b s e r v a t o r y (Ottawa) and i n s t a l l e d a t S c h r o e d e r P o i n t and Howser t o e x t e n d the second p r o f i l e . The i n s t r u m e n t s were o p e r a t e d u n t i l . A u g u s t 27. Shown i n F i g . 2, i s the l o c a t i o n of the Newport Magnetic O b s e r v a t o r y , on the Washington-Idaho b o r d e r . Records f r o m t h i s o b s e r v a t o r y were o b t a i n e d t h r o u g h the c o u r t e s y of the U.S. Coast and G e o d e t i c S u r v e y . The l o c a t i o n i s of normal 'low I ' t y p e , and c o u l d be used as a c o m p a r i s o n r e f e r e n c e f o r the f i e l d r e c o r d i n g s . I n an attempt t o o b t a i n f u r t h e r i n f o r m a t i o n on the b o u d a r i e s of the anomaly, a s t a t i c magnetometer s u r v e y was co n d u c t e d between R e v e l s t o k e and Bonner's F e r r y , Idaho, on May 1 s t , 1969, u s i n g a McPhar v e r t i c a l magnetometer. 17 I V A N A L Y S I S AND I N T E R P R E T A T I O N A S e c t i o n s o f G . D . S . M a g n e t o g r a m s I n F i g . 6, s i m u l t a n e o u s r e c o r d s f r o m t w o n o r t h - s o u t h p r o f i l e s a r e s h o w n d i g i t i z e d a n d r e p l o t t e d a t e q u a l s e n s i t i v i t y , w i t h N e w p o r t a s a common r e f e r e n c e , i M i r r o r L a k e - R y k e r t s a n d N e w p o r t ( F i g . 6, r i g h t s i d e ) T h r o u g h o u t t h i s p r o f i l e , t h e h o r i z o n t a l c o m p o n e n t s a r e a l m o s t i d e n t i c a l , e x c e p t f o r t h e l a t i t u d e e f f e c t , i m p l y i n g a u n i f o r m s o u r c e f i e l d f o r t h e s e s t a t i o n s . T h e v e r t i c a l c o m p o n e n t , h o w e v e r , c h a n g e s c h a r a c t e r b e t w e e n S a n c a ( S A N ) a n d R y k e r t s ( R Y K ) . R y k e r t s s h o w s n o r m a l l o w - Z ( w e s t e r n t y p e ) c h a r a c t e r , i d e n t i c a l t o t h a t o b s e r v e d a t N e w p o r t ( N E W ) . T h e s t a t i o n s f r o m S a n c a t o M i r r o r L a k e ( M I R ) e x h i b i t v e r y h i g h Z a m p l i t u d e s , s t r o n g l y c o r r e l a t e d t o H , a s h a s a l r e a d y b e e n s h o w n f o r B o s w e l l i n F i g . 1. K u s k a n o o k i s s t i l l h i g h l y c o r r e l a t e d t o H , b u t w i t h s l i g h t l y r e d u c e d a m p l i t u d e ; a t W y n n d e l ( W Y N ) , t h e a n o m a l o u s ( H - c o r r e l a t e d ) c o m p o n e n t i s b a r e l y p e r c e p t i b l e . A l t h o u g h n o s i m u l t a n e o u s r e c o r d i n g s a r e a v a i l a b l e n o r t h o f M i r r o r L a k e , s t a t i o n s w e r e o c c u p i e d a t a s u b s e q u e n t d a t e ; t h e r e c o r d i n g s f r o m H o w s e r (HOW) a r e s h o w n . o n t h e l e f t s i d e o f F i g . 6 ; t h e y a r e s t i l l s t r o n g l y a n o m a l o u s , w i t h H - c o r r e l a t e d Z f l u c t u a t i o n s a t l e a s t t w i c e a s l a r g e a s t h o s e o b t a i n e d a t B r o u s e ( B R O ) , o n l y a b o u t 50 k m . t o t h e w e s t . T h e v e r y s h o r t d i s t a n c e o f a p p r o x i m a t e l y 25 m i l e s o v e r w h i c h t h e d i s c o n t i n u i t y o c c u r s i n a n o r t h - s o u t h F i g . 6 Two S i m u l t a n e o u s P r o f i l e s of G.D.S. Rec o r d s . 19 d i r e c t i o n i s now emphasized. On o t h e r geomagnetic d e p t h s o u n d i n g p r o f i l e s a c r o s s the e a s t e r n edge of the c o r d i l l e r a , the same d i s c o n t i n u i t y i s o b s e r v e d over a l a r g e r d i s t a n c e o f r o u g h l y 150 km. i n an e a s t - w e s t d i r e c t i o n , i i B r o u s e - Salmo and Newport ( F i g . 6 , l e f t s i d e ) Anomalous ( H - c o r r e l a t e d ) f l u c t u a t i o n s i n Z are o b s e r v e d on t h i s p r o f i l e a l s o , but w i t h c o n s i d e r a b l y reduced a m p l i t u d e s . The s i m u l t a n e o u s r e c o r d i n g f rom Howser, f r o m the e a s t e r n p r o f i l e , i s shown f o r c o m p a r i s o n t o i n d i c a t e the r e d u c t i o n i n a m p l i t u d e . The s t a t i o n s f r o m Taghum (TAG) t o Brouse show al m o s t i d e n t i c a l r e c o r d s ; a t Salmo (SAL), the anomalous Z a m p l i t u d e s are s l i g h t l y reduced, but s t i l l c l e a r l y l a r g e compared t o t h e normal low Z s t a t i o n a t Newport. The t r a n s i t i o n f r om 'anomalous' t o 'normal w e s t e r n low I ' s t a r t s at Salmo on t h i s p r o f i l e . However, s i n c e no s t a t i o n s were a v a i l a b l e s o u t h of Salmo, i t i s n o t c l e a r i f the t r a n s i t i o n w i l l be as sharp as t h a t o b s e r v e d between Kuskanook and R y k e r t s ; a c l o s e l y spaced network of s t a t i o n s between Salmo and Newport would be r e q u i r e d t o d e t e r m i n e t h i s d e t a i l . At t h i s s t a g e , i t can o n l y be c o n c l u d e d t h a t a) the anomaly on the Brouse - Salmo p r o f i l e i s c o n s i d e r a b l y l e s s pronounced t h a n f o r the M i r r o r Lake - R y k e r t s p r o f i l e ; b) s t a r t of the t r a n s i t i o n o c c u r s a t r o u g h l y the same l a t i t u d e , c o n f i r m i n g t h e e a s t - w e s t s t r i k e of the s t r u c t u r e . One o f the most s t r i k i n g f e a t u r e s d e m o n s t r a t e d by F i g . 6 i s t h e d i f f e r e n c e between t h e two p r o f i l e s ; t h e a m p l i t u d e of the anomaly changes v e r y s t r o n g l y o v er an e a s t - w e s t d i s t a n c e o f t h e o r d e r o f o n l y about 40 km. ( f o r 20 e x a m p l e , M i r r o r L a k e t o S l l v e r t o n ) . T h i s i n d i c a t e s a s t r o n g s t r u c t u r a l c h a n g e i n . t h i s d i r e c t i o n a s w e l l , i . e . t h e a n o m a l i e s c a n n o t be e x p l a i n e d i n t e r m s o f s i m p l e t w o - d i m e n s i o n a l s t r u c t u r e s . B P o w e r S p e c t r a l A n a l y s i s S i m u l t a n e o u s r e c o r d s f r o m t h e t w o p r o f i l e s o f t h e p r e v i o u s s e c t i o n w e r e d i g i t i z e d a t a s a m p l i n g r a t e o f 64 p o i n t s p e r h o u r w i t h t h e d i g i t i z i n g m a c h i n e b u i l t b y W. C a n n o n o f t h e D e p a r t m e n t o f G e o p h y s i c s a t U . B . C . T h e p o w e r s p e c t r a l e s t i m a t e s w e r e c o m p u t e d o n t h e I B M 360 w i t h e q u a t i o n (9) o f s e c t i o n I I C . T h e r e c o r d l e n g t h s u s e d w e r e 12 a n d 1-3 h o u r s , f o r t h e B r o u s e - S a l m o a n d M i r r o r L a k e -R y k e r t s p r o f i l e s , r e s p e c t i v e l y . A 20°/c l a g w a s u s e d i n t h e a n a l y s i s , w h i c h g i v e s a n o r m a l i z e d s t a n d a r d e r r o r a s h i g h a s 45^. H o w e v e r , t h e r e s u l t i n g i n c r e a s e i n r e s o l u t i o n i s p r e f e r a b l e s i n c e t h e e s t i m a t e s a r e u s e d f o r c o m p a r i s o n p u r p o s e s o n l y . I n b o t h p r o f i l e s s h o w n i n P i g . 7a a n d Jb, t h e h o r i z o n t a l s p e c t r a l e s t i m a t e s (D a n d H) a r e c l o s e l y r e l a t e d , e x c e p t f o r a s l i g h t l a t i t u d e e f f e c t w h i c h b e c o m e s p r o g r e s s i v e l y m o r e n o t i c e a b l e a t t h e h i g h e r f r e q u e n c i e s . T h e Z e s t i m a t e s o f t h e M i r r o r L a k e - R y k e r t s a n d N e w p o r t p r o f i l e ( F i g . 7a) a r e o f s p e c i a l i n t e r e s t h e r e . M i r r o r L a k e a n d S a n c a a r e v e r y s i m i l a r a n d e x h i b i t h i g h Z p o w e r l e v e l s . R y k e r t s h a s t h e same h i g h f r e q u e n c y c u t o f f a s N e w p o r t , w h i c h i s a k n o w n l o w I s t a t i o n . W y n n d e l i s i n t e r m e d i a t e b e t w e e n t h e 2 1 . LOG 1 0 (3 ' 7 C . R M . ) M I R R O R L A K E S A N C A W Y N N D E L R Y K E R T S - N E W P O R T 0.02 • 0.06 0.10 F R E Q U E N C Y , C R M . P i g . 7a Power S p e c t r a l E s t i m a t e s , M i r r o r Lake t o R y k e r t s and Newport. 22 0.02 0.06 0.10 F R E Q U E N C Y , C R M , F i g . 7b Power S p e c t r a l E s t i m a t e s , Brouse t o Salmo and Newport. 23 STATION LOCATION ' F i g . 8a Power S p e c t r a l R a t i o s , M i r r o r Lake t o R y k e r t and Newport. 24 .Fig 8b Power S p e c t r a l and Newport. R a t i o s , Brouse t o Salmo 25 t w o g r o u p s . T h i s r e s u l t i s a q u a n t i t a t i v e e x p r e s s i o n o f t h e v i s u a l c o m p a r i s o n s c a r r i e d o u t i n t h e p r e v i o u s s e c t i o n . T h e Z s p e c t r a l e s t i m a t e s o f t h e B r o u s e - S a l m o a n d N e w p o r t p r o f i l e , do n o t show a s h a r p d i s c o n t i n u i t y ( F i g . 7 b ) . A s m e n t i o n e d i n s e c t i o n I I I A , a m o r e c l o s e l y s p a c e d G . D . S . p r o f i l e w o u l d h a v e b e e n d e s i r a b l e b e t w e e n S a l m o a n d N e w p o r t . H o w e v e r , s t a t i o n s B r o u s e t o S a l m o show e v i d e n c e o f b e i n g l e s s a n o m a l o u s , i . e . Z p o w e r l e v e l s , a n d m o r e c l o s e l y r e l a t e d t o w e s t e r n t y p e N e w p o r t t h a n t o t h e s t r o n g l y a n o m a l o u s s t a t i o n s M i r r o r L a k e t o W y n n d e l . F r o m t h e a b o v e r e s u l t s , P /P s p e c t r a l r a t i o s w e r e Z xl f o u n d a t p e r i o d s o f 20, 35> a n d 50 m i n . w h i c h s h o w e d h i g h c o h e r e n c y . T h e s e w e r e n o r m a l i z e d w i t h r e s p e c t t o a l o w I s t a t i o n i n e a c h p r o f i l e a n d p l o t t e d a s a f u n c t i o n o f g e o g r a p h i c l a t i t u d e ( F i g . 8a a n d 8 b ) . T h i s F i g u r e a g a i n i l l u s t r a t e s t h e d i s t i n c t d i s c o n t i n u i t y o n t h e e a s t e r n p r o f i l e ( M i r r o r L a k e - N e w p o r t ) , a t a l l t h r e e f r e q u e n c i e s ; i t a l s o s h o w s a f r e q u e n c y d e p e n d e n c e f o r t h e d i s c o n t i n u i t y o n t h e B r o u s e - N e w p o r t p r o f i l e . C M a g n e t i c S u r v e y U p o n s t u d y i n g a n e a s t - w e s t a e r o m a g n e t i c p r o f i l e a c r o s s t h e U n i t e d S t a t e s , p a s s i n g n e a r D e n v e r , C o l o r a d o , a s t r i k i n g d i f f e r e n c e w a s f o u n d b e t w e e n p r o f i l e s t o t h e e a s t a n d t o t h e w e s t o f t h e R o c k y M o u n t a i n s ( P a k i s e r a n d Z i e t z , 1 9 6 6 ) . T h e e a s t e r n p r o f i l e i n c l u d e d b o t h s h a r p l o c a l a n o m a l i e s a n d b r o a d e r r e g i o n a l a n o m a l i e s w h e r e a s t h e l a t t e r 26 P i g . 9 L o c a t i o n Map Showing Magnetic Survey P r o f i l e . UJ o CO _ l LU i> UJ CC UJ CO o a : UJ 1C cr c c o c c c c CO o 1X1 cc UJ }C c c c c UJ c c UJ o CQ W I U E R E D 1 0 . 0 3 M J 2 5 . 0 0 MI n.oom • 7 5 . 0 0 MI ro 2 0 HUES P i g . 10 F i l t e r e d Magnetic Survey w i t h Wave! ength C u t o f f s Shown. 28 was absent i n the west. T h i s change i n c h a r a c t e r o c c u r r e d about 100 m i l e s west of Denver, which i s a p p r o x i m a t e l y the l o c a t i o n of the G.D.S. d i s c o n t i n u i t y (Caner, Cannon, and L i v i n g s t o n , 1 9 6 7 ). T h i s agreement between the p a t t e r n of aeromagnetic p r o f i l e s and G.D.S. d i s c o n t i n u i t i e s was a l s o o b s e r v e d i n w e s t e r n Canada (Caner, 1 9 7 0 ) . The smoothing e f f e c t i n the west may be e x p l a i n e d by a r i s e i n the C u r i e p o i n t i s o t h e r m ( P a k i s e r and Z i e t z , 1965) or perhaps by a more s i l i c i c l o w e r c r u s t w i t h low m a g n e t i t e c o n t e n t (Caner, 1 9 6 9 ) . U s i n g l o n g aeromagnetic p r o f i l e s , Caner's work r e q u i r e d the f i l t e r i n g of w a v e l e n g t h s up t o 100 km. b e f o r e the magnetic d i s c o n t i n u i t y became a p p a r e n t . I t would t h e r e f o r e seem r a t h e r u n l i k e l y t h a t t h i s c o u l d be d e t e c t e d i n a s h o r t ground s u r v e y . However, i t was thou g h t p o s s i b l e t o d e t e c t t h e d i s c o n t i n u i t y on the M i r r o r Lake - R y k e r t s p r o f i l e because of the r e l a t i v e l y s h o r t d i s t a n c e o ver which i t o c c u r s . I n t h e s p r i n g of 1969, a ground s u r v e y was conducted between R e v e l s t o k e , B.C., and S a n d p o i n t , Idaho, u s i n g a McPhar v e r t i c a l magnetometer ( P i g . 9 ) . The d a t a was c o r r e c t e d f o r time v a r i a t i o n s , u s i n g the V i c t o r i a magnetograms, and a l s o f o r l a t i t u d e dependence. Low pass f i l t e r i n g i n the f r e q u e n c y domain was a p p l i e d w i t h s u c c e s s i v e w a v e l e n g t h c u t o f f s o f 10 , 25 , 5 0 , and 75 m i l e s . The r e s u l t s shown i n F i g . 10 are i n c o n c l u s i v e . A smoothing of t h e l o n g e r w a v e l e n g t h a n o m a l i e s i s not app a r e n t 29 s o u t h o f R y k e r t s . H o w e v e r , t h i s n e g a t i v e r e s u l t , i . e . t h e a b s e n c e o f m a g n e t i c s o u r c e s i n t h e h i g h I r e g i o n , d o e s n o t d i s p r o v e t h e r e s u l t s o f t h e l a s t s e c t i o n . D P o l a r D i a g r a m s Two t y p e s o f p o l a r d i a g r a m s , w h i c h d i f f e r i n p l o t t i n g o f t h e d i p , w e r e u s e d t o i n v e s t i g a t e t h e a z i m u t h a l d e p e n d e n c e o f t h e v e r t i c a l f i e l d c o m p o n e n t a t t h e f o l l o w i n g s t a t i o n s , b e l o n g i n g t o t h e t w o p r o f i l e s o f t h e p r e v i o u s s e c t i o n : B r o u s e , S i l v e r t o n , T a g h u m , a n d S a l m o ; M i r r o r L a k e , S a n c a , W y n n d e l , a n d R y k e r t s . T h e s e s t a t i o n s w e r e e q u i p p e d w i t h A s k a n i a v a r i o g r a p h s . T h e f l u x g a t e r e c o r d s w e r e n o t u s e d i n t h i s a n a l y s i s b e c a u s e t h e t h r e e o r t h o g o n a l c o m p o n e n t s o f m a g n e t i c f i e l d c o u l d n o t a l l be r e c o r d e d a t t h e s e s i t e s , d u e t o r e c o r d e r l i m i t a t i o n s . A b o u t o n e h u n d r e d a n d f i f t y p e a k t o p e a k m a g n e t i c s t o r m v a r i a t i o n s w e r e m e a s u r e d b y h a n d f r o m t h e m a g n e t o g r a m s o f t h e a b o v e s t a t i o n s . F r o m t h e s e e v e n t s , P a r k i n s o n d i a g r a m s a n d M e r c a t o r p r o j e c t i o n s , a s d e f i n e d i n s e c t i o n I I B , w e r e d e r i v e d , u s i n g t h e p l o t t e r o u t p u t o f t h e I B M 3^0 c o m p u t e r , a n d a r e s h o w n i n F i g . 1 1 a a n d l i b . A n a t t e m p t was made t o o b t a i n p o l a r d i a g r a m s d i r e c t l y f r o m t h e d i g i t i z e d d a t a , t o e l i m i n a t e t h e t e d i o u s a n d t i m e c o n s u m i n g t a s k o f m e a s u r i n g m a g n e t i c v a r i a t i o n s b y h a n d . A p r o g r a m w a s c o m p o s e d t o c o m p u t e t h e v e c t o r c h a n g e s i n 10 m i n u t e i n t e r v a l s o n t h e d i g i t i z e d s e c t i o n , a n d c h o o s e t h e l a r g e s t 450 o f t h e s e , t o p l o t o n a p o l a r d i a g r a m . T o o b t a i n O F i g . 11a P a r k i n s o n Diagrams and C o r r e s p o n d i n g M e r c a t o r P r o j e c t i o n s -D i p ( - 9 0 ° t o 90°) vs Geographic Azimuth Measured f r o m N o r t h ( - 1 8 0 ° t o l 8 0 ° ) M i r r o r L a k e . t o R y k e r t s . i F i g . l i b Parkinson Diagrams and Corresponding Mercator Projections -Dip ( -90° to 90°) vs Geographic Azimuth Measured from North ( - l 8 0 to 180 ) Brouse to Salmo. LO ro F i g . 12a P o l a r Diagrams and C o r r e s p o n d i n g M e r c a t o r P r o j e c t i o n s -Dip ( -90° t o 9 0 ° ) vs Geographic Azimuth Measured f r o m N o r t h ( - 1 8 0 ° t o l 8 0 ° ) M i r r o r Lake t o R y k e r t s . F i g . 12b P o l a r Diagrams and C o r r e s p o n d i n g M e r c a t o r P r o j e c t i o n s -D i p ( -90° t o 90°) vs Geographic Azimuth Measured f r o m N o r t h ( -180 t o 180 ) Brouse t o Salmo. 34 a t r u e h o r i z o n t a l p r o j e c t i o n o f t h e p r e f e r r e d p l a n e , t h e r a d i a l d i s t a n c e f r o m t h e c e n t e r o f t h e c i r c l e w a s t a k e n t o be c o s w h e r e § i s t h e d i p o f t h e e v e n t , a s c o m p a r e d t o t h e P a r k i n s o n d i a g r a m w h e r e t h e r a d i a l d i s t a n c e i s -TJ- - T h i s c o m p u t a t i o n a l p r o c e d u r e , h o w e v e r , h a s t h e d i s a d v a n t a g e o f n e g l e c t i n g t h e p h a s e d i f f e r e n c e b e t w e e n c o m p o n e n t s d u r i n g m a g n e t i c e v e n t s . T h e s e r e s u l t s a l o n g w i t h t h e c o r r e s p o n d i n g M e r c a t o r p r o j e c t i o n s a r e s h o w n i n F i g . 12a a n d 12b, a n d , h e r e , a r e c a l l e d p o l a r d i a g r a m s . I n b o t h t y p e s o f d i a g r a m s , a c o r r e l a t i o n b e t w e e n d i p a n d a z i m u t h i s e v i d e n t a t t h e f o l l o w i n g s i t e s : M i r r o r L a k e , S a n c a , B r o u s e , S i l v e r t o n , T a g h u m , a n d S a l m o . I t i s d e b a t a b l e w h e t h e r W y n n d e l s h o w s a n y c o r r e l a t i o n , a n d n o n e i s e v i d e n t a t R y k e r t s . I n d u c t i o n a r r o w s , a s d e f i n e d i n s e c t i o n I I B , w e r e d e r i v e d f r o m t h e s e r e s u l t s , a n d a r e s h o w n i n F i g . 14, w h i c h i s d e s c r i b e d i n t h e n e x t s e c t i o n . . L a F r a n c e C r e e k a n d B o s w e l l a r e g i v e n i n d u c t i o n a r r o w s e q u a l t o t h a t o f S a n c a , s i n c e t h e i r m a g n e t o g r a m s a r e i d e n t i c a l . T h e e r r o r s , o f c o u r s e , i n s u c h r e s u l t s a r e v e r y l a r g e a n d a r e a p p r o x i m a t e l y - 1 5 ° f o r d i r e c t i o n a n d 20% f o r a m p l i t u d e . H o w e v e r , t h e g e n e r a l t r e n d o f t h e a r r o w s i s v e r y h e l p f u l i n d e t e r m i n i n g t h e d i r e c t i o n t o t h e i n h o m o g e n e i t y c a u s i n g t h e a n o m a l y . E I n t e r p r e t a t i o n T h e a n o m a l o u s s t a t i o n s a r e s h o w n i n F i g . 13- A f e w o t h e r s t a t i o n s f r o m p r e v i o u s p r o f i l e s a r e i n c l u d e d t o show UI F i g . 13 L o c a t i o n Map Showing Anomalous S t a t i o n s . 36 the a p p r o x i m a t e boundary of the low I - h i g h I d i s c o n t i n u i t S e v e r a l m a g n e t o - t e l l u r i c s t a t i o n s which were used t o c o n s t r u c t the model of F i g . 3 are a l s o i n c l u d e d . The i n d u c t i o n , arrows i n F i g . 14 show t h a t the anomalous zone i s much l a r g e r than was p r e v i o u s l y a n t i c i p a t s u g g e s t i n g a deeper i n h o m o g e n e i t y . A l s o , t h e y i n d i c a t e anomalous c u r r e n t s s t r i k i n g a p p r o x i m a t e l y magnetic east-wes to the south of the s t a t i o n s . I f the anomaly was caused by an i s o l a t e d c o n d u c t o r , such as a c y l i n d e r i n the l o w e r c r u s t , s t r i k i n g e a s t - w e s t , one would e x p e c t the i n d u c t i o n arrows t o r e v e r s e upon c r o s s i n g i t w i t h a n o r t h - s o u t h p r o f i l e . T h i s i s not so. I n s t e a d , the low I - h i g h I d i s c o n t i n u i t y i s e n c o u n t e r e d as a r a t h e r sharp s t e p . T h i s t h e n s u g g e s t s a c o n v o l u t i o n i n the major c o n t i n e n t a l low I - h i g h I d i s c o n t i n u i t y . The model proposed i s shown i n F i g . 14, and i s p r e s e n t e d i n terms of d e p t h c o n t o u r s t o the s u r f a c e of the h i g h l y c o n d u c t i n g ( h y d r a t e d ? ) l o w e r c r u s t ( r e f e r t o F i g . 3) The d e p t h s shown are based on the m a g n e t o - t e l l u r i c d a t a f r om t h e two r e g i o n s (Caner, 1 9 6 9 ) . The i n t e r m e d i a t e c o n t o u r s are o f c o u r s e a r b i t r a r y i n so f a r as a b s o l u t e d e p t h i s c o n c e r n e d , but t h e i r c o n c e n t r a t i o n s o u t h of Wynndel i s a g r a p h i c r e p r e s e n t a t i o n of the ' c l i f f - l i k e ' d i s c o n t i n u i t y s t r i k i n g magnetic e a s t - w e s t . Induced c u r r e n t s f l o w i n g i n the upper c o r n e r and/or v e r t i c a l f a c e o f the s t e are t h e n r e s p o n s i b l e f o r the o b s e r v e d anomaly. The model p r e s e n t e d here i s q u a l i t a t i v e o n l y . The LO F i g . 14 Proposed Model E x p r e s s e d i n Depth Contou r s t o H i g h l y C o n d u c t i n g L a y e r . 38 power s p e c t r a l a n a l y s i s served as a mapping t e c h n i q u e t o l o c a t e the low I - h i g h I d i s c o n t i n u i t y , w h i l e the i n d u c t i o n a r rows i n d i c a t e d the d i r e c t i o n t o the anomalous c u r r e n t s . The c o n t o u r s shown i n Pig-. 14 c o u l d be v e r y much i n e r r o r . Prom Caner's r e s u l t s (Caner, 1970), the c o n d u c t i v i t y c o n t r a s t f o r the model i s a t l e a s t 50:1. The lower c r u s t I n the anomalous r e g i o n may be v i s u a l i z e d as t h a t of P i g . 3, but w i t h a s i n i s t r a l f a u l t s t r i k i n g magnetic e a s t - w e s t . The l a t e r a l d i s p l a c e m e n t i s unknown but i t s h o u l d be of the o r d e r of 50 t o 100 m i l e s , s i n c e the low I - h i g h I d i s c o n t i n u i t y i s r e c o v e r e d a g a i n 100 m i l e s west of Denver, C o l o r a d o . At the time of w r i t i n g , P. F o m i n o f f , of the Department of G e o p h y s i c s a t U.B.C., i s c o n s t r u c t i n g an e x p e r i m e n t a l model based on F i g . 14, t o i n v e s t i g a t e the i n d u c t i o n e f f e c t s of t h i s model. An attempt was made t o c o r r e l a t e t h e o f f s e t i n the low I - h i g h I d i s c o n t i n u i t y w i t h s u r f a c e g e o l o g y and the t e c t o n i c s of the a r e a , but w i t h o u t s u c c e s s . However, i t may be i n t e r e s t i n g t o note t h a t the d i r e c t i o n of the o f f s e t , extended e a s t w a r d , i n t e r s e c t s the s o u t h e r n l i m i t of the Rocky Mo u n t a i n T r e n c h . Perhaps the f e a t u r e o r i g i n a t e d w i t h the N e v adian d i s t u r b a n c e i n l a t e J u r a s s i c , o r the Laramide r e v o l u t i o n i n l a t e C r e t a c e o u s , two of the major d i s t u r b a n c e s r e s p o n s i b l e f o r the. f o r m a t i o n of the w e s t e r n c o r d i l l e r a . The model l e n d s support t o the t h e s i s t h a t the h i g h c o n d u c t i v i t y o b s e r v e d i n the lo w e r c r u s t i n the west, i s caused by h y d r a t i o n r a t h e r t h a n a r i s e i n t e m p e r a t u r e . I n 39 t h e l a t t e r c a s e , d i f f u s i o n would not p e r m i t the e x i s t e n c e of a w e l l d e f i n e d s t e p , u n l e s s of c o u r s e the f e a t u r e o r i g i n a t e d i n g e o l o g i c a l l y r e c e n t t i m e s . 40 V CONCLUSION Prom t h i s r e s e a r c h , i t i s c o n c l u d e d t h a t the geomagnetic v a r i a t i o n anomaly a t Kootenay Lake, B.C., o r i g i n a t e s i n a l o c a l i z e d d i s t o r t i o n of the main low I -h i g h I d i s c o n t i n u i t y . , r e s u l t i n g i n a w e l l d e f i n e d s t e p i n c o n d u c t i v i t y s t r i k i n g magnetic e a s t - w e s t , t o the s o u t h o f Kootenay Lake, B.C. The f i n a l model i n F i g . 14, i s q u a l i t a t i v e o n l y . I t s u p p o r t s the t h e s i s t h a t the h i g h c o n d u c t i v i t y of the lo w e r c r u s t , i n the west, i s due t o some c o m p o s i t i o n a l r a t h e r t h a n t h e r m a l e f f e c t , perhaps h y d r a t i o n as su g g e s t e d by Caner (Caner, 1 9 6 9 ) . 41 REFERENCES 1. Bendat, J.S., A.G. P i e r s o l , Measurement and a n a l y s i s of random d a t a , 2 9 0 - 2 9 3 , W i l e y , New York, 1 9 6 7 . 2. Caner, B., W.H. 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 America, N a t u r e , 207, 9 2 7 - 9 2 8 , 1 9 6 5 . 3 . Caner, B., W.H. Cannon, C.E. L i v i n g s t o n , Geomagnetic depth s o u n d i n g and upper mantle s t r u c t u r e i n the C o r d i l l e r a r e g i o n of w e s t e r n N o r t h A m e r i c a , J . Geophys. Res., 72 , 6 3 3 5 - 6 3 5 1 / 1 9 6 7 . 4 . Caner, B., Long aeromagnetic p r o f i l e s and c r u s t a l s t r u c t u r e i n w e s t e r n Canada, E a r t h and P l a n e t . Sc. L e t t e r s , 7, 3 -11 , 1 9 6 9 . 5 . Caner, B., 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 i n w e s t e r n Canada and p e t r o l o g i c a l i n t e r p r e t a t i o n , J . Geomag. G e o e l e c , Japan, A p r i l , 1 9 7 0 . 6 . Cannon, W.H., Geomagnetic depth s o u n d i n g i n s o u t h e r n B r i t i s h Columbia and A l b e r t a , U n p u b l i s h e d 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 C olumbia, Vancouver, 1967 . 7. C r o s b y , P., T e c t o n i c , p l u t o n i c , and metamorphic h i s t o r y of the c e n t r a l Kootenay A r c , B r i t i s h Columbia,. Canada, G e o l . Soc. Amer., s p e c i a l paper 9 9 , B o u l d e r , 1 9 6 8 . 8 . Hyndman, R.D., 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 the e a r t h ' s upper m a n t l e , U n p u b l i s h e d 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 C o lumbia, Vancouver, 1 9 6 3 . 9 . Hyndman, R.D., D.W. Hyndman, Water s a t u r a t i o n and h i g h 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 l o w e r c o n t i n e n t a l c r u s t , E a r t h and P l a n e t . Sc. L e t t e r s , 4 , 4 2 7 - 4 3 2 , 1 9 6 8 . 1 0 . L a t h i , B . P . , A n i n t r o d u c t i o n t o r a n d o m s i g n a l s a n d c o m m u n i c a t i o n t h e o r y , 5 7 - 6 3 , I n t e r n a t i o n a l T e x t b o o k , S c r a n t o n , 1 9 6 8 . 1 1 . M a d d e n , T . R . , C M . S w i f t , J r . , M a g n e t o - t e l l u r i c s t u d i e s o f 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 s t r u c t u r e o f t h e c r u s t a n d u p p e r m a n t l e , A m . G e o p h y s . 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W h i t h a m , I n t e r p r e t a t i o n o f t h e A l e r t a n o m a l y i n g e o m a g n e t i c v a r i a t i o n s , C a n . J . E a r t h S c . , 1, 3 5 - 6 2 , 1964. 1 8 . S c h m u c k e r , U . , A n o m a l i e s o f g e o m a g n e t i c v a r i a t i o n s i n 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 . G e o m a g . G e o e l e c . , j a p a n , .15, 1 9 3 - 2 2 1 , 1964. 1 9 . S e r s o n , P . H . , A n e l e c t r i c a l r e c o r d i n g m a g n e t o m e t e r , C a n . J . P h y s . , 3 5 , 1387-139^, 1 9 5 7 . 20. S i m e o , G . , A . S p o s i t o , A n o m a l i e s i n g e o m a g n e t i c v a r i a t i o n s i n I t a l y , J . G e o m a g . G e o e l e c . , 15 , 249 - 2 6 7 , 1 9 6 4 . 43 Weaver, J.T., The e l e c t r o m a g n e t i c f i e l d w i t h i n a d i s c o n t i n u o u s c o n d u c t o r w i t h r e f e r e n c e t o geomagnetic m i c r o p u l s a t i o n s n e a r a c o a s t l i n e , Can. J. Phys., 41, 484-495, 1 9 6 3 . Whitham, K., F. Anderson, The anomaly i n geomagnetic v a r i a t i o n s a t A l e r t i n the A r c t i c A r c h i p a l e g o of Canada, Geophys. J., 7, 220-243, 1 9 6 2 . Wiese, I i . , Geomagnetische t i e f e n t e l l u r i k t e i l I I : wie s t r e i c h r i c h t u n g der u n t e r g r u n d s t - r u k t u r e n wes e l e k t r i s c h e n w i d e r s t a n d e s , e r s c h l o s s e n aus geomagnetischen v a r i a t i o n e n , G e o f i s . Pura E. A p p l i c . , 5 2 , 8 3 , 1 9 6 2 . 

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