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Electrical conductivity inhomogeneities in the earth's upper mantle Hyndman, Roy David 1963

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ELECTRICAL CONDUCTIVITY INHOMOGENEITIES IN THE EARTH fS UPPER MANTLE by ROY DAVID HYNDMAN B*A,Sc., U n i v e r s i t y of B r i t i s h Columbia, 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department o f PHYSICS We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA November, 1963 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of 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 that per mission f o r extensive copying of 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 representativeSo I t i s understood that copying or p u b l i  c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p e r mission. Department of The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. Date MftRCM 4 J9&4 i ABSTRACT T h i s study was undertaken i n order t o i n v e s t i g a t e the p o s s i b l e occurrence of h o r i z o n t a l v a r i a t i o n s 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 of the E a r t h 1 s upper mantle i n southwestern Canada, u s i n g a s e r i e s of simultaneous magnetic v a r i o g r a p h r e c o r d i n g s . U n t i l r e c e n t l y no v a r i a t i o n i n the c o n d u c t i v i t y i n a h o r i z o n t a l d i r e c t i o n had been a n t i c i p a t e d nor^ observed. During the pa s t f i v e years P a r k i n s o n i n A u s t r a l i a , R i k i t a k e i n Japan, Schmucker i n Germany and others have observed marked d i f f e r e n c e s i n the magnetograms a t c l o s e l y spaced s t a t i o n s . Secondary magnetic f i e l d s produced by i n d u c t i o n i n h i g h c o n d u c t i v i t y r e g i o n s i n the E a r t h 1 s upper mantle have been suggested as the causa o f these d i f f e r e n c e s . The p r o f i l e d e s c r i b e d i n t h i s t h e s i s i n d i c a t e s c o n d u c t i v i t y inhomogeneities i n southwestern B r i t i s h Columbia and southwestern A l b e r t a . The v e r t i c a l magnetic f i e l d s produced by i n d u c t i o n i n these inhomogeneities f o r magnetic v a r i a t i o n s w i t h p e r i o d s from 10 to 120 minutes have magnitudes o f about 30 to 60 percent o f the normal h o r i z o n t a l oomponent. The normal v e r t i c a l component i s about 20 percent o f the h o r i z o n t a l . These r e g i o n s appear to be e s s e n t i a l l y two d i m e n s i o n a l w i t h anomalous i n d u c t i o n r e s u l t i n g o n l y from t h a t component of the i n c i d e n t magnetic v a r i a t i o n s which i s p e r p e n d i  c u l a r to t h e i r s t r i k e . T h i s s t r i k e and the i n t e n s i t y o f the i i induced f i e l d have been estimated a t each s t a t i o n . A pronounced d i f f e r e n c e has a l s o been found between the v e r t i c a l component o f the d i u r n a l geomagnetic v a r i a t i o n s a t a s t a t i o n In the Rocky Mountains and those a t the r e s t o f the s t a t i o n s along the p r o f i l e . v i i i ACKNOWLEDGEMENTS Much of the work and r e s u l t s o f t h i s t h e s i s must be a c c r e d i t e d t o the many people who have p r o v i d e d the author w i t h a s s i s t a n c e and c o u n s e l , i n p a r t i c u l a r , P r o f e s s o r J, A. Jacobs who s u p e r v i s e d the r e s e a r c h and Mr. J". M a r t i n who a s s i s t e d throughout the f i e l d program. Others who have g i v e n major a i d are Dr. T. Watanabe who p r o v i d e d many h e l p f u l t h e o r e t i c a l d i s c u s s i o n s , Mr. B. Caner of the V i c t o r i a Magnetic Observatory who pr o v i d e d v a l u a b l e a s s i s t a n c e i n d e a l i n g w i t h the problems encountered i n making magnetic observations,;-" the f a c u l t y and graduate students o f the I n s t i t u t e of E a r t h S c i e n c e s a t the U n i v e r s i t y o f B r i t i s h Columbia and Dr. K . Vozo.ff of the U n i v e r s i t y o f A l b e r t a . i l l TABLE OF CONTENTS Page I INTRODUCTION 1 II LOCATION AND INSTALLATION OF INSTRUMENTS 7 I I I DESCRIPTION AND OPERATION OF THE INSTRUMENTS 10 1 Askania variographs, 10 1.1 Accuracy and d e t a i l s of variograph records 12 1*2 Poor or l o s t records; 13 2 Fluxgate recording magnetometers, 15 2.1 Accuracy and d e t a i l s of fluxgate records, 15 2.2 Poor or l o s t records.. 17 3 P ro ton precession magnetometer 18 4 Earth currents -{ 18 IY INDUCTION ANALYSIS 20 1 Induced currents i n a uniform Earth 20 2 Induction i n conductivity inhomogeneities, 23 3 Condition f o r i n phase induction, 26 4 Conditions under which the e l e c t r i c f i e l d of a source may "be negleoted. 28 5 Model c a l c u l a t i o n s . 28 (i) Cylinder, 32 ( i i ) Sphere. , 33 ( i i i ) H o r i zontally discontinuous structure 34 l v TABLE OF CONTENTS (continued) Y RESULTS AND ANALYSIS 40 1 General r e s u l t s 40 ( i ) P u l s a t i o n s (0.5 to 5 min. period) . 40 ( i i ) Bays and storm f e a t u r e s (5 to 120 min.) 41 ( i i i ) D i u r n a l v a r i a t i o n s . 42 2 Determination o f the s t r i k e o f c o n d u c t i v i t y inhomogeneities by extreme val u e s 46 3 De t e r m i n a t i o n o f I n d u c t i o n c o e f f i c i e n t s as a f u n c t i o n o f frequency from a s p e c t r a l a n a l y s i s . 51 4 Determination o f the l o c a t i o n and s i z e o f an assumed i n f i n i t e c y l i n d e r 51 5 Frequency dependence of the anomalous. induced f i e l d s , 57 71 SUGGESTIONS FOR FURTHER STUDY 59 ¥11 CONCLUSIONS 61 V FIGURES Page 1. L o c a t i o n Map Showing S i t e s of Recording S t a t i o n s . 8 2. Photographs o f the A s k a n l a V a r i o g r a p h and Switch Box U n i t s ! 14 3. Photographs of the F l u x g a t e E l e c t r o n i c Assembly, Recorder and D e t e c t o r Head. 16 4. Image Source R e p r e s e n t a t i o n of I n d u c t i o n i n a U n i f o r m E a r t h of i n f i n i t e C o n d u c t i v i t y i 20 5. A p p l i c a t i o n o f Snell»s Law to the E a r t h - A i r Boundary. 21 6. I n d u c t i o n i n Terms o f Simple C i r c u i t Elements^.: 27 7. R e p r e s e n t a t i o n o f a C y l i n d e r i n a Slowly V a r y i n g Magnetic, F i e l d : • 29 8. • Form o f the Anomalous Induced f i e l d s over a C y l i n d e r f o r a H o r i z o n t a l I n c i d e n t Magnetic F i e l d V a r i a t i o n , 32 9. R e p r e s e n t a t i o n of a Sphere i n a S l o w l y V a r y i n g Magnetic F i e l d . 33 10. I n Phase and Out of Phase I n d u c t i o n C o e f f i c i e n t s f o r a Conducting C y l i n d e r and Sphere. 35 11. R e p r e s e n t a t i o n of a H o r i z o n t a l l y D i s c o n t i n u o u s S t r u c t u r e . 36 12. D i u r n a l Geomagnetic V a r i a t i o n s , Magnetic East-West (D) Component/ 43 13. D i u r n a l Geomagnetic V a r i a t i o n s , V e r t i c a l ( z ) Component.. 44 14. D i u r n a l Geomagnetic V a r i a t i o n s , Magnetic North-South (H) Component. 45 v i 15. Measurement o f the Extreme Value o f a Feature on a Magnetogram/ 48 16. S t r i k e of C o n d u c t i v i t y Inhomogeneitles from Leas t Squares Extreme Value A n a l y s i s ; 50 17. S p e c t r a l D e n s i t i e s f o r a Bay Type Feature a t Grand Forks on August 4, 1963 i' 52 18. S p e c t r a l D e n s i t i e s f o r a Bay Type Feature a t Kootenay Lake on August 4, 1963; 53 v i i TABLES 1. S t r i k e o f C o n d u c t i v i t y Inhomogeneities and Approximate I n Phase I n d u c t i o n C o e f f i c i e n t s from Extreme Yalue A n a l y s e s / 50 2. C y l i n d e r Parameters f o r C o n d u c t i v i t y Inhomogeneities Observed a t the Crescent Y a l l e y , Kootenay Lake and Kimberley S t a t i o n s / 55 3. Depth o f P e n e t r a t i o n o f D i u r n a l Magnetic V a r i a t i o n s if 58 • ' APPENDICES I . ' L o c a t i o n and D e t a i l s o f the S t a t i o n s ! 62 I I . Table of Extreme Values sf 63 I I I . Magne tograms li 75 1 I . INTRODUCTION As a p a r t o f the Canadian Upper Mantle P r o j e c t a s e r i e s of geomagnetic v a r i o g r a p h s t a t i o n s was set up a l o n g a p r o f i l e e xtending a c r o s s southern B r i t i s h Columbia and A l b e r t a i n order to i n v e s t i g a t e the occurrence of any h o r i z o n t a l v a r i a t i o n s 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 of the E a r t h ' s upper mantle. (12) (2) D e t a i l e d a n a l y s e s by N i b l e t t et a l , C a n t w e l l , (7) Garland and Webster and ot h e r s u s i n g the m a g n e t o t e l l u r i c method and by C h a p m a n ^ and R i k i t a k e u s i n g a s p h e r i c a l harmonic a n a l y s i s . o f world wide magnetic v a r i a t i o n s have o u t l i n e d the v e r t i c a l d i s t r i b u t i o n o f c o n d u c t i v i t y assuming a h o r i z o n t a l l y l a y e r e d E a r t h . I n p a r t i c u l a r they have found a sharp d i s c o n t i n u i t y a t a depth o f the or d e r o f 100 k i l o m e t e r s . Recent s t u d i e s u s i n g c l o s e l y spaced v a r i o g r a p h s t a t i o n s have shown, t h a t i n a d d i t i o n to t h i s v e r t i c a l v a r i a t i o n , there are marked c o n d u c t i v i t y v a r i a t i o n s i n the h o r i z o n t a l d i r e c t i o n a t some l o c a t i o n s . The cause o f these v a r i a t i o n s i s an open q u e s t i o n , but s i n c e e l e c t r i c a l c o n d u c t i v i t y may be r e l a t e d to temperature ( T o z e r ^ 2 ^ ^ , i r r e g u l a r i t i e s i n the temperature and heat f l o w d i s t r i b u t i o n i n the upper mantle have been (18) f r e q u e n t l y suggested. I n p a r t i c u l a r R i k i t a k e has p o s t u l a t e d (21) the e x i s t e n c e o f h i g h temperature magma po c k e t s . Sohmuoker v ' has a l s o suggested t h a t there may be i r r e g u l a r i t i e s o r l o c a l deformations of the 100 k i l o m e t e r d i s c o n t i n u i t y noted above. T h i s e x p l a n a t i o n i n t u r n has been g i v e n as evidence f o r the e x i s t e n c e o f c o n v e c t i o n c e l l s i n the mantle. 2 Numerous strong l o c a l i z e d zones of high e l e o t r l o a l conductivity have been found throughout the world. The main evidence for the existence of these regions i s a large s p a t i a l change i n the v e r t i c a l magnetic component, which f o r a h o r i z o n t a l l y s t r a t i f i e d Earth should be small at a l l locations. (16)(17)119) Rikitake ' has described the very large changes i n the geomagnetic f i e l d v ariations that occur across Japan and has suggested as an explanation, a rather complicated conductivity configuration. This involves a highly conducting loop r i s i n g from depth on eit h e r side and extending across the i s l a n d , and, i n order to obtain s u f f i c i e n t induoed current i n t e n s i t y , underlain by a low conductivity wedge. (21) In north Germany, Sohmucker has found a narrow region of apparent high conductivity. He has shown that the observed anomaly i n magnetic variations cannot be explained In terms of inhomogeneities i n the sedimentary layer or deeper inhomo- genelties r e f l e c t e d by gravity surveys, and suggests that they are caused by an i r r e g u l a r temperature d i s t r i b u t i o n i n the E a r t h s upper mantle. More recently he has investigated a s i m i l a r but more oomplex anomaly i n the southwestern United (22) States . Part of the anomaly l i e s at the Paolfio coast, and may be caused by the influence of the land-sea oontact. The large v e r t i c a l components of magnetic disturbances which appear i n A u s t r a l i a have been attributed to such a contact by Parkin so n * 1 3 *. Another i n t e r e s t i n g example presented by Whitham and (32) Anderson , involves a high conductivity zone l y i n g between Ellesmere Island i n northern Canada and Greenland. They have evaluated the parameters for a cylinder model and, although the data are l i m i t e d , have obtained s a t i s f a c t o r y r e s u l t s . (33) Wiese has used a l e a s t squares determination of the c o r r e l a t i o n between the horizontal and v e r t i c a l magnetic f i e l d v a r i a t i o n s at a number of stations to determine the s t r i k e of conductivity anisotropics that e x i s t i n a large area i n East Germany. The magnetotelluric method ( C a g n l a r d ^ , Price and Wait^ 8 8^ ) i n which the r a t i o of orthogonal horizontal components of the e l e c t r i c and magnetic f i e l d s are calculated and phase r e l a t i o n s determined, has been successfully used f o r o u t l i n i n g a conductivity structure consisting of h o r i z o n t a l layering. Although t h e o r e t i c a l work has been done on suoh d i s c o n t i n u i t i e s as a v e r t i c a l f a u l t ( d ^ r c e v i l l e and Kunetz^ 6 \ Weaver ^ 3 0^) and a v e r t i c a l dike (Rankin^ 5^, i t has not been successfully applied. With a single variograph s t a t i o n , the subsurface conductivity i s p a r t i a l l y indeterminate, but when a series of simultaneous observations i s made at a number of stations so that the h o r i z o n t a l d i s t r i b u t i o n of a magnetio v a r i a t i o n i s known, both a layered structure and horizontal v a r i a t i o n s may be determined. The layered structure may be found from a f i q l d r e l a t i o n (14) (Price ) which gives the r a t i o of orthogonal h o r i z o n t a l 4 e l e c t r i c and magnetic f i e l d components from the three o r t h o g o n a l magnetic components. Standard m a g n e t o t e l l u r i c curves are then used. T h i s procedure has not been found as s a t i s f a c t o r y as the normal m a g n e t o t e l l u r i c technique i n which the e l e c t r i c f i e l d component i s measured by e a r t h e l e c t r o d e s . In o r d e r to i n v e s t i g a t e the h o r i z o n t a l changes i n c o n d u c t i v i t y i t i s necessary to determine the induced secondary magnetic f i e l d produced by induced c u r r e n t s i n the s t r u c t u r e . I f the h o r i z o n t a l change i n c o n d u c t i v i t y i s I n d i c a t e d by anomalous observed f i e l d v a r i a t i o n s of l i m i t e d s p a t i a l e x t e n t , the s i m p l e s t method o f s e p a r a t i n g t h a t p a r t o f the f i e l d r e s u l t i n g from the c o n d u c t i v i t y v a r i a t i o n from the normal f i e l d , (given by the e x t e r n a l f i e l d p l u s that due to i n d u c t i o n i n a u n i f o r m l a y e r e d s t r u c t u r e ) , i s to s u b t r a c t the normal f i e l d found at a nearby s t a t i o n from the t o t a l measured f i e l d . I n t e r p o l a t i o n between s t a t i o n s on e i t h e r s i d e o f the anomalous r e g i o n may a l s o be used. T h i s method, o f course, assumes r e l a t i v e l y u n i f o r m e x t e r n a l f i e l d s over the r e g i o n c o n s i d e r e d . A technique f o r s e p a r a t i n g any observed magnetic v a r i a t i o n i n t o e x t e r n a l and i n t e r n a l p a r t s , u s i n g the p o t e n t i a l method of Gauss, has been a p p l i e d by S c h m u c k e r ^ ^ , and o t h e r s . A n ecessary c o n d i t i o n i n t h i s method i s t h a t , a t the s u r f a c e o f the E a r t h , the magnetic v a r i a t i o n s may be d e r i v e d from a p o t e n t i a l f u n c t i o n . T h i s i m p l i e s t h a t there must be no a p p r e c i a b l e c u r r e n t f l o w between the ionosphere and the E a r t h . 5 I f one c o n s i d e r s the p o t e n t i a l s to he expressed as a F o u r i e r s e r i e s o f harmonic components, each decaying e x p o n e n t i a l l y w i t h depth, the p o t e n t i a l due to e x t e r n a l c u r r e n t s may be expressed i n the form oo -n z e LLQ n Sim nx - I n n Cosnx or Z where x i s measured i n the h o r i z o n t a l d i r e c t i o n o f the f i e l d v a r i a t i o n and z v e r t i c a l l y downward. The p o t e n t i a l due to i n t e r n a l induced c u r r e n t s may be s i m i l a r l y expressed In the form Vi fr,2) The t o t a l f i e l d components a t the s u r f a c e are then h o r i z o n t a l F(x) = jL (b« f B n ) Sin + + ftn ) Co s n * oo v e r t i c a l £ fo) = L (-&n-RA)s Cos nx From a F o u r i e r a n a l y s i s o f the s p a t i a l d i s t r i b u t i o n of the l o c a l magnetic v a r i a t i o n s , the c o e f f i c i e n t s may be found f o r oo = £ nz 5 ' n nx +• Cos n* or 6 each F o u r i e r component from the r e l a t i o n s FU) - - an Another procedure f o r s e p a r a t i o n , which permits t o t a l I n t e r n a l and e x t e r n a l components of a f i e l d v a r i a t i o n to be determined r e q u i r e s an e s t i m a t i o n of the world wide d i s t r i b u t i o n of m a g n e t i c . p o t e n t i a l d u r i n g a magnetic d i s t u r b a n c e . (3 ) Chapman and B a r t e I s h a v e determined a w o r l d wide average of the r a t i o o f i n t e r n a l to e x t e r n a l p a r t s , making a s p h e r i c a l harmonic a n a l y s i s o f the p o t e n t i a l d i s t r i b u t i o n and d i s c u s s i n g the r e l a t i o n between the v a r i o u s c o e f f i c i e n t s of the e x t e r n a l and i n t e r n a l p a r t s . R l k i t a k e * ; has determined the r a t i o a t each magnetic s t a t i o n by approximating the p o t e n t i a l by that obtained from two p a i r s of r a d i a l l y opposed d l p o l e s , one o u t s i d e the E a r t h f o r the p o t e n t i a l a s s o c i a t e d w i t h e x t e r n a l c u r r e n t s and one i n s i d e the E a r t h f o r the p o t e n t i a l a s s o c i a t e d w i t h the i n t e r n a l induced c u r r e n t s . Once t h a t p a r t o f the observed f i e l d v a r i a t i o n s which i s produced by the c o n d u c t i v i t y inhomogeneity has been determined, i t may be compared w i t h the f i e l d to be expected from v a r i o u s i d e a l i z e d g e o m e t r i c a l s t r u c t u r e s . The Induced f i e l d has been g i v e n for. a sphere ( W a i t ^ 2 7 ^ , a c y l i n d e r (Whitham and (32) 133) Anderson and Wlese v ' and a v e r t i c a l f a u l t and a v e r t i c a l d i k e ( d ' E r c e v l l l e and K u n e t z ^ 6 ) , R a n k i n ^ 1 5 *, W e a v e r ^ 3 0 ) , and Goode I I . 7 LOCATION AND INSTALLATION OF INSTRUMENTS Geomagnetic} Variographs were set up a t 12 s t a t i o n s approximately 80 k i l o m e t e r s a p a r t along an east-west p r o f i l e from V a n c o u v e r , B r i t i s h Columbia to L e t h b r i d g e , A l b e r t a (Figure 1 ) . The d i r e c t i o n and l o c a t i o n o f the p r o f i l e were chosen to be approximately magnetic east-west and to be p e r p e n d i c u l a r to the Canadian C o r d i l l e r a . The east-west d i r e c t i o n m a i n t a i n s a constant d i s t a n c e from the a u r o r a l zone and thus should minimize any d i f f e r e n c e s i n e x t e r n a l f i e l d v a r i a t i o n s a t d i f f e r e n t s t a t i o n s . The p r o f i l e was e s t a b l i s h e d a c r o s s the s t r i k e o f the g e o l o g i c a l s t r u c t u r e i n an attempt to be perpen d i c u l a r t o , and to i n t e r s e c t any anomalous c o n d u c t i v i t y zones. The southern Trans-Canada Highway p a r a l l e l s , the p r o f i l e and provided easy access to the s t a t i o n s . V a r i o g r a p h l o c a t i o n s were chosen w i t h the f o l l o w i n g requirements: 1. Freedom from l o c a l magnetic d i s t u r b a n c e s . An attempt was made to keep the d e t e c t o r u n i t s a t l e a s t 100 meters from any l a r g e q u a n t i t y of s t a t i o n a r y magnetic m a t e r i a l and s e v e r a l hundred meters from any moving magnetic m a t e r i a l such as automobiles or t r a i n s . 2. R e l i a b l e 110 v o l t , 60 c y c l e l i n e power su p p l y . 3. Easy access by road f o r the t r a n s p o r t o f heavy instruments. 4. S a t i s f a c t o r y s h e l t e r . T h i s was p a r t i c u l a r l y important f o r the f l u x g a t e e l e c t r o n i c u n i t s . 5. A v a i l a b l e personnel to make p e r i o d i c checks and to 122* I20 e 118* Rbvelstoke incetc jKelowna •Penticton x/Pen»icton ^ GrandFcf-ksT 1 1 116* Kootenay Lake *resfdn X FLUXGATE STATION O ASKANIA STATION Il4e N (geographic) 50 e [Kimberly ^rowsnest Pincher Zreek CANADA " U S A 3thbridge> 4 9 ° . 48* F i g u r e 1. L o c a t i o n Map Showing S i t e s o f Recording S t a t i o n s 9 pr o v i d e maintenance. At 7 of the 12 s i t e s , c o o p e r a t i o n was r e c e i v e d from the Department of T r a n s p o r t weather s t a t i o n , a e r a d i o s t a t i o n and a i r p o r t p e r s o n n e l . Other l o c a t i o n s were attended by l o c a l r e s i d e n t s and employees o f business e n t e r p r i s e s . The instruments were s e t up by a two man p a r t y which a l s o v i s i t e d each l o c a t i o n a t l e a s t once a week, I n i t i a l l y the instruments were s e t up from Westham I s l a n d (Vancouver) to Kootenay Lake. These were operated from June 15 to J u l y 11, 1963. By J u l y 16 the western f o u r s t a t i o n s were moved on to complete the p r o f i l e to L e t h b r i d g e . The i n t e r v e n i n g s t a t i o n s were operated throughout both phases of the.program. Removal o f a l l the instruments was commenced on August 5, 1963. The l o c a t i o n of each s t a t i o n and i t s p e r i o d o f o p e r a t i o n are g i v e n i n Appendix I . 10 I I I . DESCRIPTION AND OPERATION OF THE INSTRUMENTS 1. Askania variographs I n 1962 f o u r Askania variographs were purchased by the N a t i o n a l Research C o u n c i l of Canada from the Askania Werke D i v i s i o n of C o n t i n e n t a l E l e k t r o i n d u s t r i e of B e r l i n , Germany f o r use i n upper mantle s t u d i e s . They were loaned along w i t h : f o u r Serson type f l u x g a t e u n i t s to the U n i v e r s i t y of B r i t i s h Columbia. The Askania instruments r e q u i r e d a minimum of s h e l t e r and maintenance and gave e x c e l l e n t records throughout the program. Figure 2 shows the variograph and switchbox u n i t s . Although b a t t e r y o p e r a t i o n i s p o s s i b l e w i t h these i n s t r u  ments, l i n e power i s needed f o r any extended operation of the thermostat and heater which are used to m a i n t a i n a constant instrument temperature. Line power of 60 c y c l e s , 110 to 120 v o l t s was used at a l l s t a t i o n s . The D (magnetic east-west) and H (magnetic north-south) magnet systems are f a c t o r y temper ature ,compensated but the H ( v e r t i c a l ) system r e q u i r e s adjustment f o r d i f f e r e n t values of the v e r t i c a l f i e l d . The H magnet system i s suspended by two h o r i z o n t a l f i b e r s w i t h d i f f e r e n t thermal p r o p e r t i e s . By a d j u s t i n g t h e i r r e l a t i v e s t r e s s e s , temperature induced d e f l e c t i o n s may be e f f e c t i v e l y e l i m i n a t e d . Seven days were spent at the V i c t o r i a Magnetic Observatory making t h i s adjustment. The compensation was then found to be s u f f i c i e n t to e l i m i n a t e any d e f l e c t i o n on the 11 magnetic t r a c e that might he caused by the s m a l l temperature v a r i a t i o n s p e r m i t t e d by the thermostat. S e v e r a l subsequent power f a i l u r e s i n d i c a t e d t hat more p r e o i s e adjustment would be r e q u i r e d i f the instruments were to be operated e f f e c t i v e l y without the h e a t e r and thermostat. Since the d r i v e motor s u p p l i e d w i t h the instruments r e q u i r e d 50 c y c l e power, a g r a v i t y d r i v e mechanism was used to t r a n s p o r t the r e o o r d i n g photographic paper. T h i s p r o v i d e d the a d d i t i o n a l advantage that d u r i n g a power f a i l u r e , although no t r a c e s would be produced, the f i l m motion would c o n t i n u e , thus p r e s e r v i n g the time s c a l e . The d r i v e c o u l d operate unattended f o r one week a t a c h a r t speed o f 2 cm/hr. The three magnetic components H, D and Z , the i n s t r u  ment temperature and a b a s e l i n e were recorded on 120 m i l l i  meter wide photographic paper, " O s c i l l o x " from Teohnophot Dr. Rudolf F i s c h e r Kg., B e r l i n - N e u k o l l n . A 10 meter r o l l f i l l e d each magazine, and t h i s was s u f f i c i e n t f o r 20 days of o p e r a t i o n . Two magazines were used w i t h each instrument, so t h a t one c o u l d be operated w h i l e the other was being processed. Developing was done w i t h Kodak " D e k t o l " developer, an a c e t i c a c i d stop bath and Kodak g e n e r a l purpose f i x e r . The paper was washed w i t h a Kodak hypo c l e a r i n g agent. C a l i b r a t i o n of the v a r i o g r a p h components was p r o v i d e d by b u i l t - i n Helmholtz c o i l s around each magnet system, a s m a l l 1.5 v o l t b a t t e r y and an ammeter r h e o s t a t system i n the s w i t c h box. 12 H o u r l y time marks were produced on the photographic paper by an a u x i l i a r y lamp ac t u a t e d by German Unghans J chronometers. 1.1 Accuracy and d e t a i l s o f v a r i o g r a p h £ecords The l i g h t beam f o r each magnetic component i s s p l i t i n t o three by r e f l e c t i o n and t r a n s m i s s i o n w i t h h a l f s i l v e r e d m i r r o r s so t h a t the width o f the photographic paper may be covered three times. The e f f e c t i v e range i s t h e r e f o r e approximately 1000 gammas (If ) a t a s c a l e v alue of 3V/W>v Some d i f f i c u l t y i s encountered i n measuring f e a t u r e s extending beyond the range of one l i g h t spot s i n c e the p o s i t i o n of one spot when the next appears i s not p r e c i s e l y known. The Helmholtz c o i l f a c t o r s are given by the manufacturer to be w i t h i n t 0.7 T /mm., the ammeter c o u l d be read to w i t h i n t 0.005 ma. a t 1 or 2. ma., and the d e f l e c t i o n d i s t a n c e on the t r a c e c o u l d be measured to w i t h i n about ± 0.3 mm. at 25 or 50 mm. The o v e r a l l c a l i b r a t i o n a ccuracy i s then about ±- 0.04 If /mm. f o r a l l components. D i f f e r e n c e s as l a r g e as 0.04 "t /mm. were observed between c a l i b r a t i o n s a t the top and bottom o f the range o f a s i n g l e l i g h t t r a c e w h i l e f o r d i f f e r e n t l i g h t t r a c e s o f the same component the d i f f e r e n c e i n c a l i b r a t i o n values was as l a r g e as 0.15 tf/mm. The time marks were found to have l e s s than 0.5 minutes p a r a l l a x w i t h the component t r a c e s . The chronometers were maintained by W.W.V. or C.H.TJ. s h o r t wave time s i g n a l s to l e s s than 1.5 min. e r r o r . Records were a l s o kept of the g a i n or 13 l o s s by each chronometer so that times may be determined on the t r a c e s t o w i t h i n ± 0 . 8 min. 1.2 Poor or l o s t r e c o r d s On s e v e r a l o c casions wind noi s e was superimposed oh the t r a c e s o f instruments which were covered o n l y by plywood s h e l t e r s (Figure 2 ) . This was p a r t i c u l a r l y e v i d e n t a t Lethbridge where an exposed l o c a t i o n was s u b j e c t to winds up to 75 km/hr. Time marks were l o s t f o r a week a t one s t a t i o n because of a break i n the chronometer connecting c a b l e and f o r a week a t another because the chronometer stopped. Record was l o s t f o r a number of p e r i o d s a t the Kootenay Lake S t a t i o n because of an u n r e l i a b l e l i n e power supply. A p e r i o d o f s e v e r a l hours was r e q u i r e d a f t e r power r e s t o r a t i o n before a constant temperature c o u l d be maintained by the h e a t e r . At s e v e r a l s t a t i o n s the a i r temperature o c c a s i o n a l l y rose above the thermostat s e t t i n g and f l u c t u a t i o n s i n instrument temperature r e s u l t e d . The t h e r m o s t a t i c a l l y c o n t r o l l e d temperature was a l s o found to change o c c a s i o n a l l y because of unexplained e f f e c t s w i t h i n the thermostat system. Each v a r i o g r a p h was set up e i t h e r on an e x i s t i n g concrete f l o o r o r on concrete pads l a i d before the i n s t a l l a t i o n so that d r i f t s i n l e v e l and i n o r i e n t a t i o n were present o n l y d u r i n g the f i r s t few days of o p e r a t i o n . Figure 2. Askania Variograph and Switchbox. 15 2. F l u x g a t e r e c o r d i n g magnetometers The f o u r f l u x g a t e type r e c o r d i n g magnetometers were of the type designed by S e r s o n v ' f o r the Dominion Observatory and b u i l t by Canadian A p p l i e d Research L i m i t e d d u r i n g the I n t e r n a t i o n a l G e o p h y s i c a l Year (Figure 3 ) . The instruments c o n s i s t Of a three component d e t e c t o r head which may be set up o u t s i d e away from l o c a l magnetic d i s t u r b a n c e s and an e l e c t r o n i c assembly and r e c o r d e r which are connected to i t by a 6 conductor c a b l e . The output o f the magnetometer i s 3 d.c. v o l t a g e s which are p r o p o r t i o n a l to the three magnetic f i e l d components a t 10 v./lOOO)^ . The constant p o r t i o n of the f i e l d i s balanced by a d j u s t a b l e and c a l i b r a t e d b i a s v o l t a g e s . A Sorensen a.c. v o l t a g e r e g u l a t o r was used to prevent any d r i f t of the t r a c e s caused by poor s t a b i l i t y i n the l i n e power supply. Leeds and Northrup 6 channel Speedomax type G, model S, 6000 s e r i e s r e c o r d e r s w i t h a f u l l s c a l e d e f l e c t i o n of 10 mv. were used. Channels 1 and 4, 2 and 5 and 3 and 6 were connected i n p a r a l l e l except a t one s t a t i o n ( P e n t i c t o n ) where e a r t h c u r r e n t s were a l s o measured, so t h a t a p o i n t was p r i n t e d every 9 seconds on the t r a c e f o r each component. The c h a r t speed was set a t 1 i n . / h r . 2.1 Accuracy and d e t a i l s of f l u x g a t e r e c o r d s An a t t e n u a t i o n p otentiometer c i r c u i t was used to reduce the i n p u t to the r e c o r d e r by a f a c t o r of 500 g i v i n g a s e n s i t i v i t y of 50 Y/ln. o r 500 (f f u l l s c a l e . With the ac c u r a c y o f the 18 F i g u r e 3< F l u x g a t e Recorder, E l e c t r o n i c s and Deteotor Head. 17 ..output of the magnetometer g i v e n by Serson as w i t h i n - 1% and 1% r e s i s t o r s i n the potentiometer, t h i s c a l i b r a t i o n should be a c c u r a t e to w i t h i n ± 4%. Approximate t i m i n g was p r o v i d e d by the one i n c h g r i d on the c h a r t and more p r e c i s e l y by Unghans J chronometers a c t u a t i n g a marking pen on the s i d e of the c h a r t paper. Times on the t r a c e s c o u l d be determined to w i t h i n - 3 minutes. 2.2 Poor or l o s t records The major problem encountered w i t h the f l u x g a t e u n i t s was long p e r i o d d r i f t . T h i s was p a r t i c u l a r l y e v i d e n t a t the P e n t i c t o n . s t a t i o n where the D component e x h i b i t e d d a i l y v a r i a t i o n s exceeding 500 <T . S e v e r a l o t h e r u n i t s showed d a i l y d r i f t s of up to 100 V , p a r t i c u l a r l y i n the % component. The d i u r n a l magnetic v a r i a t i o n f o r the p e r i o d of the study should be about 30 Y . These d r i f t s appear to be the r e s u l t of a temperature induced e f f e c t i n the d e t e c t o r elements. A t h e r m o s t a t i c a l l y c o n t r o l l e d case or s h e l t e r i s suggested f o r any f u t u r e use of these i n s t r u m e n t s . The d e t e c t o r heads were mounted on 1-3/8 i n . aluminum tu b i n g set i n c o n c r e t e . T h i s p e r m i t t e d n e g l i g i b l e d r i f t s i n l e v e l or o r i e n t a t i o n but d i s a l l g n m e n t s d i d r e s u l t from j a r r i n g by people and a n i m a l s . Record was a l s o l o s t because of t r o u b l e w i t h the r e c o r d e r . On two u n i t s a s m a l l stop behind the potentiometer s p l i t d r i v e gear loosened and jammed the pen c a r r i a g e . On another there was s l i p p i n g o f the a c t u a t i n g wheels f o r the p r i n t i n g pen. 18 I t should be noted that i n a comparison between the Askania and f l u x g a t e u n i t s , the Askanias gave good r e s u l t s f o r magnetic v a r i a t i o n s w i t h p e r i o d s from 5 min, to 24 h r . w i t h narrow un i f o r m t r a c e s , and almost no r e c o r d l o s t , w h i l e the f l u x g a t e s w i t h Leeds and Northrup r e c o r d e r s gave f a i r r e s u l t s f o r p e r i o d s from 15 min. to 2 h r . , w i t h wide i r r e g u l a r t r a c e s and an average o f 5 days of r e c o r d l o s t on each instrument o p e r a t i n g over a p e r i o d of 6 weeks. 3. P r o t o n p r e c e s s i o n magnetometer A s m a l l b a t t e r y operated proton p r e c e s s i o n magnetometer was r e c e i v e d on l o a n from the Dominion Observatory magnetic s t a t i o n , V i c t o r i a , B.C. T h i s was a model CM.-102 made by B a r r i n g e r Research of Toronto O n t a r i o , w i t h a d i r e c t r e a d i n g of t o t a l f i e l d to 10 <f . Readings were g e n e r a l l y r e p r o d u c i b l e to w i t h i n i 20 or 30 y . At each Askania or f l u x g a t e s t a t i o n , nine r e a d i n g s were taken on a square 100 f t . g r i d w i t h the set up a t the c e n t e r , to ensure that there were no l a r g e magnetic bodies near the s i t e and to determine the t o t a l f i e l d i n t e n s i t y a t the s t a t i o n . 4. E a r t h c u r r e n t s An attempt was made to re c o r d the time v a r i a t i o n i n the p o t e n t i a l d i f f e r e n c e between two 500 f t spaced b u r i e d copper e l e c t r o d e s a t the P e n t i c t o n and Crescent V a l l e y s t a t i o n s . Together w i t h the magnetic r e c o r d s these could be used i n 19 m a g n e t o t e l l u r i c s t u d i e s . The Crescent V a l l e y measurements were u n s u c c e s s f u l because o f l o c a l p o t e n t i a l s induced i n the ground by a nearby b u r i e d t e l e t y p e c a b l e . The p o t e n t i a l induced by t h i s cable was much g r e a t e r than t h a t induced by e x t e r n a l magnetic v a r i a t i o n s f o r a d i s t a n c e o f a t l e a s t 500 f t . from the c a b l e . At P e n t i c t o n the p o t e n t i a l d i f f e r e n c e was record e d f o r magnetic east-west and magnetic n o r t h - s o u t h e l e c t r o d e p a i r s f o r a three week p e r i o d . Two channels on the Leeds and Northrup r e c o r d e r s were used. Very s c a t t e r e d t r a c e s were obta i n e d , and no a n a l y s i s has been undertaken of these r e s u l t s . 20 IV. INDUCTION ANALYSIS 1. Induced c u r r e n t s i n a u n i f o r m E a r t h The magnetic v a r i a t i o n s which are observed a t the s u r f a c e of the E a r t h have been found to a r i s e p a r t l y from c u r r e n t s i n the ionosphere and p a r t l y from c u r r e n t s induced i n the E a r t h by these e x t e r n a l sources. For an E a r t h of i n f i n i t e c o n d u c t i v i t y , the induced o r i n n e r f i e l d opposes and completely c a n c e l s the v e r t i c a l component of the e x t e r n a l f i e l d a t the E a r t h ' s s u r f a c e but a i d s and doubles the h o r i z o n t a l component. A simple a p p l i c a t i o n o f images g i v e s the r e q u i r e d r e s u l t . C o n s i d e r i n g an e x t e r n a l l i n e c u r r e n t source, the boundary c o n d i t i o n s a r e s a t i s f i e d by an image source w i t h i n the E a r t h w i t h o p p o s i t e d i r e c t i o n o f c u r r e n t flow. Magnetic field lines line current current into paper of: paper image source current out //////// Field vector from image F i g u r e 4. Image Source R e p r e s e n t a t i o n of I n d u c t i o n i n a U n i f o r m E a r t h of I n f i n i t e C o n d u c t i v i t y . 21 I f the c o n d u c t i v i t y i s f i n i t e , the same image r e p r e s e n  t a t i o n h o l d s except t h a t the image c u r r e n t i s not as s t r o n g as the e x t e r n a l source. The h o r i z o n t a l component i s s t i l l increased and the v e r t i c a l decreased, although the v e r t i c a l component i s not completely c a n c e l l e d . S n e l l ' s Law may be a p p l i e d to the E a r t h - a i r boundary to determine q u a n t i t a t i v e l y the extent to which the i n c i d e n t e x t e r n a l f i e l d i s i n c r e a s e d i n the h o r i z o n t a l and decreased i n the v e r t i c a l d i r e c t i o n . Incident wave of form H = Hfle i (cut - k- nD • r) k 2 c a 2+ i)82=c6mplexe wave number in medjum (z) k, = a, + i yS, = complex wave number in medium (T) F i g u r e 5. A p p l i c a t i o n of S n e l l ' s Law to the E a r t h - A i r Boundary. 22 By S n a i l ' s Law k, sm c5, " kz s i n e \ . For a nonconductor such as a i r (rl.K.S. Unih) and f o r a conductor such as the E a r t h The angle of the r e f r a c t e d wave i s then given by Sin <9, = Sin &o As the c o n d u c t i v i t y of the E a r t h , 6X , and the f i e l d measured a t the s u r f a c e l e n t to a v e r t i c a l l y i n c i d e n t f i e l d . i n c r e a s e s , s i n 0, —*- O of the E a r t h i s equiva-23 The amplitudes o f the r e f l e c t e d and t r a n s m i t t e d f i e l d s at the s u r f a c e may then be determined by a p p l y i n g F r e s n e l ' s e q u a t i o n s . I n terms o f the i n c i d e n t wave they are found to be R e f l e c t e d R = _ L _ kz C o s e° " k' kz- C o S e< yU u> kz COS 60 4-K, COS e, Transmitted y = _ J _ h k g - cos Op  yuu) cos B.0 +• Cos8{ The magnetic d i s t u r b a n c e v e c t o r i s assumed to be i n the plane of the above diagram. 2. I n d u c t i o n i n c o n d u c t i v i t y inhomogeneities The a n a l y s i s o f the c o n d u c t i v i t y and geometry of zones causing anomalous magnetic f i e l d v a r i a t i o n s i n v o l v e s c o r r e l a t i n g the induced secondary f i e l d produced by the c o n d u c t i v i t y inhomogeneity w i t h the I n c i d e n t f i e l d . The i n t e n s i t y and nature of the . i n c i d e n t f i e l d w i l l depend on the e x t e r n a l ionospheric' 24 c u r r e n t sources and on the c u r r e n t s produced by these e x t e r n a l f i e l d s i n the E a r t h e x t e r n a l to the zone. P r o v i d e d some estimate can be made of the depth to the inhomogeneous zone and of the changes i n c o n d u c t i v i t y with depth i n the surrounding r e g i o n , good estimates may be made of the f i e l d i n c i d e n t on the inhomogeneity. A more common assumption i s t h a t the i n c i d e n t f i e l d i s the same as t h a t measured a t the s u r f a c e away from the i n f l u e n c e of the inhomogeneity. T h i s r e q u i r e s that the depth t o the anomalous zone i s much l e s s than the s k i n depth of the surrounding E a r t h f o r the p e r i o d s o f the magnetic v a r i a t i o n s used. Under t h i s assumption, and pr o v i d e d t h a t the induced f i e l d components are independent of each other, 18 c o r r e l a t i o n c o e f f i c i e n t s are r e q u i r e d to completely s p e c i f y the c o r r e l a t i o n between the i n d u c i n g and induced f i e l d s . T h i s i n c l u d e s the p o s s i b i l i t y o f i n phase and out of phase components i n the induced f i e l d . A knowledge of these c o e f f i c i e n t s f o r a l l p e r i o d s o f f i e l d v a r i a t i o n completely s p e c i f i e s the i n f o r m a t i o n a v a i l a b l e from a s i n g l e v a r i o g r a p h s t a t i o n . To o u t l i n e such three d i m e n s i o n a l bodies as a sphere i s thus q u i t e d i f f i c u l t u n l e s s s i m p l i f y i n g assumptions are made. I f the r e g i o n of inhomogeneous c o n d u c t i v i t y i s two dim e n s i o n a l , o n l y those components of f i e l d v a r i a t i o n s perpen d i c u l a r to the s t r i k e o f the r e g i o n should be e f f e c t i v e i n produci n g induced c u r r e n t s . Once t h i s s t r i k e i s known, 8 c o r r e l a t i o n c o e f f i c i e n t s are l e f t to be determined. Assuming 25 a l i n e a r r e l a t i o n between the induced c u r r e n t s and the normal f i e l d components (ohmic r e s i s t a n c e ) and a h o r i z o n t a l two dimensional zone, the d e f i n i n g r e l a t i o n s f o r a harmonically v a r y i n g f i e l d are Fh = Fn, S i n <Jt + fox cos, oJ t normal h o r i z o n t a l (perpendloular to the s t r i k e of the zone) J=CL - F a , Sincjt + FAx cosu>± anomalous h o r i z o n t a l (perpendicular to the s t r i k e of the zone) 2n - 2n, sinu)t <• £ n,^sa>t normal v e r t i c a l Z a « ZQ.\ sin u)t * £0,2. C o s o t anomalous v e r t i c a l FA., = £, Fn, +' .D, . * Cz Fnz + Fa z • v ? z Fn, f 2n, + £, Fn 4 +• £, B n i where C 1, D^^ r e f e r to the components of the induoed f i e l d i n phase w i t h the inducing f i e l d and A 2, B 2, C 2, D 2 r e f e r t o the out of phase components. 86 To u t i l i z e geomagnetic v a r i a t i o n data, the time v a r y i n g f i e l d s must be transformed i n t o harmonic terms, e i t h e r by e s t i m a t i n g the dominant harmonic component of each of a number of magnetic v a r i a t i o n f e a t u r e s or by expressing the magnetic changes as frequency f u n c t i o n s by F o u r i e r transforms. The frequency f u n c t i o n s A((J) and B(to) represent s p e o t r a l d e n s i t i e s o f harmonio f u n o t i o n s and may be used i n the same manner as t r u e harmonio time f u n c t i o n s . Once the c o r r e l a t i o n c o e f f i c i e n t s have been determined as a f u n c t i o n of p e r i o d , a comparison mayvbe made w i t h those to be expected f o r any i d e a l i z e d geometry and c o n d u c t i v i t y c o n f i g u r a t i o n . 3. C o n d i t i o n f o r i n phase i n d u c t i o n The above computations are g r e a t l y s i m p l i f i e d i f the lnduoed f i e l d i s i n phase w i t h the i n c i d e n t i n d u c i n g f i e l d , i . e . A 2, B 2, C 2 and D 2 are a l l s m a l l . The c o n d i t i o n f o r i n phase induced f i e l d s may be expressed i n termjs of simple c i r c u i t elements. i . e . Z(t) = I f oo A(u>) coswt dol + 7 B(u>) Sin ijt diO 27 o L / Y Y Y V i n d u o l n g p o t e n t i a l R - v w - F i g u r e 6. I n d u c t i o n i n Terms o f Simple C i r c u i t Elements. For a h a r m o n i c a l l y v a r y i n g source V - V 0 Cos Q t , the cu r r e n t induced i n the c i r c u i t i s g i v e n by I — V0 \_Rcosu)t + (UJ L - ZJC ) S i n CJ t ] R 2 -h (u)L The i n d u c i n g p o t e n t i a l i s p r o p o r t i o n a l to the time r a t e change of the e x t e r n a l magnetic f i e l d B, so that i f B e - 3e0 s'mot j , V = (consist) Bea Cos cj t the induced f i e l d i s then Bi - (constat) Be0 Rcosu)t+ (u>L ~ UJC) S i n t o t 28 s i n c e the induced f i e l d i s i n phase w i t h the induced c u r r e n t . The c o n d i t i o n s f o r i n phase induced seoondary f i e l d s a r e then (1> lcoL-dc\ > > R ( i i ) u j i > ZJQ Q R LO3- LC >\ 4. C o n d i t i o n s under which the e l e c t r i c f i e l d o f a souroe may  be n e g l e c t e d . Any souroe o f a magnetic f i e l d v a r i a t i o n must produoe an a s s o c i a t e d time v a r y i n g e l e c t r i c f i e l d . Since most souroes of magnetic v a r i a t i o n s may be represented, as magnetic d i p o l e s or are c l o s e d c u r r e n t systems which may be r e p r e s e n t e d by the s u p e r p o s i t i o n of a number of magnetic d i p o l e s , the e l e o t r i o f i e l d near the source f a l l s o f f w i t h the d i s t a n o e squared w h i l e the magnetic f i e l d f a l l s o f f w i t h the .distance cubed. Thus w i t h i n one wavelength of the source (near f i e l d r e g i o n ) the magnetic f i e l d i s found to be dominant. F o r f i e l d v a r i a t i o n s w i t h p e r i o d s of a few minutes the wavelength i s o f the o r d e r of 1 0 1 1 meters so t h a t a l l o b s e r v a t i o n p o i n t s should s a t i s f y t h i s c o n d i t i o n . 5 . Model c a l c u l a t i o n s . S ince i t i s d i f f i c u l t to c a l c u l a t e the s t r u c t u r e and c o n d u c t i v i t y c o n t r a s t r e s u l t i n g i n anomalous magnetic v a r i  a t i o n s d i r e c t l y from the i n d u c t i o n c o e f f i c i e n t s ; , i t i s expedient to determine these parameters f o r v a r i o u s t h e o r e t i c a l models and then make comparisons w i t h the observed r e s u l t s . T h i s method p r o v i d e s no guarantee o f the uniqueness of the s o l u t i o n but c e r t a i n c o n f i g u r a t i o n s are more p h y s i c a l l y - p l a u s i b l e than o t h e r s . (1) C y l i n d e r F i g u r e 7. R e p r e s e n t a t i o n of a C y l i n d e r i n a Slowly V a r y i n g Magnetic F i e l d . A magnetic v e c t o r p o t e n t i a l 0 may be chosen such that the magnetic f i e l d i n s i d e and o u t s i d e the c y l i n d e r i s g i v e n by T = C u r l 0 I t i s found t h a t 0 must s a t i s f y 30 (a) V*~ 0 " io 47r^0 i n s i d e the c y l i n d e r (b) V2" (J) = o o u t s i d e the c y l i n d e r A s a t i s f a c t o r y s o l u t i o n i n c y l i n d r i c a l c o o r d i n a t e s o u t s i d e the c y l i n d e r i s given by $ = (V ~ X . ) (Psin oi + B.cos*) where A and B are the h o r i z o n t a l and v e r t i c a l components of the p o t e n t i a l r e s u l t i n g from the e x t e r n a l f i e l d , and I i s the c o e f f i c i e n t of i n d u o t i o n i n the c y l i n d e r . I i s dependent on the diameter and c o n d u c t i v i t y of the c y l i n d e r and on the p e r i o d of the magnetic v a r i a t i o n s . The r a d i a l and a z i m u t h a l f i e l d s are g i v e n by H r = J _ 1 ^ = (\- X. ) (ft COS x - 8 s i n * ) The components i n the h o r i z o n t a l and v e r t i c a l d i r e c t i o n s are thus F = ft - ZJB. COS ZoL t I B sin ZoC Z = B + 1R S-/n Zot f IB. Cos Lot 31 These expressions may be solved f o r c< the dip angle to the center of the cylinder using the observed values of F = Fn -h Fa. j 2 ° 2nt24.; R = Fn > B = En The induction c o e f f i c i e n t I may be found by applying the boundary conditions at the surface of the cylinder to the above solu t i o n and to the solut i o n of (a). Only the f i r s t mode of o s c i l l a t i o n (dipole) need be considered since the wavelength associated with the f i e l d v a r i a t i o n may be taken to be much greater than the dimensions of the region of measurement. The (9) solution i s found to be where k 4w6iu) and J0 and a r e Bessel functions of order zero and two res p e c t i v e l y . This solution may be separated into i n phase and out of phase parts. The dependence of these terms on the conductivity and radius of the cylinder and on the frequency of the magnetlo variations i s given i n Figure 10. I f the cylinder i s approximated by a perfeot oonduotor k -*•<*> and I-*- ^ 2 . The conditions under which t h i s i s a sa t i s f a c t o r y assumption are given by examination of Figure 10. The induced f i e l d components then become Jo (VT/cp) I ~ p2- (M + IN) 32 H \ - fl [' COS ZoC + B s in 2.ocJ H a * [/9 Sin ZoC + B C o s fcecj E i t h e r of these e q u a t i o n s may be used to f i n d the r a t i o -jlr The form o f the s p a t i a l v a r i a t i o n of the anomalous induced f i e l d s over a h i g h l y c o n d ucting b u r i e d c y l i n d e r , assuming a h o r i z o n t a l l y i n o i d e n t magnetic f i e l d v a r i a t i o n i s g i v e n i n F i g u r e 8. Horizontal Fa Anomalous Induced Fields Vertical Za //////////////// incident field variation F i g u r e 8. Form o f the Anomalous Induced F i e l d s Over a C y l i n d e r f o r a H o r i z o n t a l I n c i d e n t Magnetio F i e l d V a r i a t i o n . ( i i ) Sphere 33 External Fields A B conductivity cr permeability I Figure 9. Representation of a Sphere i n a Slowly Varying Magnetic F i e l d . The solution of Laplaoe's equation f o r the veotor p o t e n t i a l , (fr^O outside the sphere gives seoondary magnetic f i e l d components resolved along the axes r Wo. fl (/~ 3ca$2c9 cos2e<) R •/• ( 3coS 6 Cos ot S i n * < )B J Hx« * v=3 ( 3 5 > m &COS& cos**) R + (3 S\*&CoS<X S i n o d ) B ] Zo, (down) = ^ ( 3cos B.cos oc s i n J f l + (1-3 S i * 2 * ) fij These equations may be solved f o r <?C and 6 34 A p p l y i n g the boundary c o n d i t i o n s at the surface of the sphere to the above equations and those a p p l i c a b l e to the I n s i d e of the sphere gives j — +• j - - c o s h y where Y = ^16-> This may be separated i n t o i n phase and out of phase components I- - j . o* [M + iN • I f the sphere i s assumed to have i n f i n i t e c o n d u c t i v i t y t h i s becomes 1 = i3 and may be i n s e r t e d i n t o the expressions f o r the induced f i e l d components to g i v e a value o f -^r . ( i l l ) H o r i z o n t a l l y discontinuous s t r u c t u r e Mo exact s o l u t i o n f o r the secondary f i e l d s produced by a magnetic f i e l d v a r i a t i o n i n c i d e n t on a h o r i z o n t a l l y d i s c o n t i n  uous s t r u c t u r e has been obtained but the f o l l o w i n g d i s c u s s i o n o u t l i n e s the nature of the anomalous f i e l d v a r i a t i o n s and log) t h e i r orders o f magnitude 1 '. Figure 10 Iii Phase and Out of Phase Induction Coefficients for a Conducting Cylinder and Sphere 36 Hx incident field ® cr, cr =0 CTZ (2) O) <r2 F i g u r e 11, R e p r e s e n t a t i o n of a H o r i z o n t a l l y D i s c o n t i n u o u s S t r u c t u r e . At p l a c e s s u f f i c i e n t l y f a r from the I n t e r f a c e x - o , i . e . x < X, , or x >Xj, , the e l e c t r i c and magnetic f i e l d s should be approximately equal to that f o r a u n i f o r m conduotor (provided and dz are both s u f f i c i e n t l y l a r g e t h a t most of the i n c i d e n t f i e l d s are r e f l e c t e d i n both c a s e s ) . The a t t e n u a t i o n of the magnetic f i e l d w i t h i n c r e a s i n g depth i n a conductor such as the E a r t h may be determined from the d i f f u s i o n e q u a t i o n a) %ltLx = Hx ( l n gaussian u n i t s ) 37 thus b) .\u = ZHo e - P z where p = 47faiu> and Z H0 i s the f i e l d a t the surfaoe z. = O . Si n c e ^l>oyx the f i e l d i s s t r o n g e r i n Q than © because there i s l e s s r e f l e c t i o n of the i n c i d e n t f i e l d i n © than i n The e l e c t r i c f i e l d i n the E a r t h w i l l be governed by the d i f f u s i o n e quation o) V a £ y = 4rr/ a' E._y where _cf_=. D , i . e . the d i f f u s i o n 4r6 c o n s t a n t . The By f i e l d thus d i f f u s e s from (D to © . From Maxwell's second equation d) } By = _L i i f a i t f o l l o w s that a v e r t i c a l magnetic f i e l d should be a s s o c i a t e d w i t h t h i s d i f f u s i o n . An order of magnitude estimate of H2 a t the su r f a c e z * O may be o b t a i n e d by r e p l a c i n g by ^ Ey i n (d). Take but from v 7 X H — 4lf "Q £ ^ Maxwell's f i r s t e q uation, and from (b) ^ _. % H0 p e £ 2. - p a 38 A t the s u r f a c e then A Ey = Ho v^ T I _ _ The width of the t r a n s i t i o n zone L- m a y b e approximated by V D T (where T i s the p e r i o d of the f i e l d v a r i a t i o n ) , which i s the c h a r a c t e r i s t i c d i s t a n c e over which the d i f f e r e n c e In f i e l d i n t e n s i t y should be e l i m i n a t e d i n one p e r i o d . The d i f f u s i o n c onstant may be taken as D = s i n c e the r a t e of d i f f u s i o n i s f a s t e r i n ® than Thus z-rr JTcJJj The anomalous a t the s u r f a c e may then be found from (d) to be | H 2 | - 4Ifr~ -/ - A 2 H< where 2. H0 i s the approximate h o r i z o n t a l f i e l d i n t e n s i t y - d i s t a n t from the d i s c o n t i n u i t y . The h o r i z o n t a l f i e l d measured a t the s u r f a c e away from the d i s c o n t i n u i t y i s H* = 2 H0 ( I - k v T ) Y. k = c 39 thus I f k« Y, whioh r e q u i r e s that GO be s m a l l and 6 l a r g e , Hx i s independent of 6 and there i s no h o r i z o n t a l v a r i a t i o n aoross the d i s c o n t i n u i t y . I f t h i s o o n d i t l o n i s not s a t i s f i e d , the magnitude of the anomalous H x bas not been s a t i s f a c t o r i l y determined. 40 V. RESULTS AND ANALYSIS ,1. General r e s u l t s U) P u l s a t i o n s (0»5 to 5 min. period) Geomagnetio v a r i a t i o n s w i t h periods from 0.5 to 5 min. could be observed onl y on the Askania r e c o r d s . No c o n d u c t i v i t y inhomogeneity i n d i c a t e d by anomalously l a r g e v e r t i o a l components was observed a t the f o u r western Askania s t a t i o n s , Abbotsford to Kootenay Lake. The r a t i o of the amplitude of f e a t u r e s i n the h o r i z o n t a l d i r e o t i o n tq,those i n the v e r t i c a l d i r e o t i o n i s 5 to 1 or g r e a t e r . The V i o t o r i a Magnetio Obser vatory and the two eastern s t a t i o n s , Crowsnest and Lethbridge, show muoh l a r g e r v e r t i c a l amplitudes. The h o r i z o n t a l to v e r t i o a l amplitude r a t i o i s around 2 to 1. There i s a l s o some c o r r e l a t i o n between the h o r i z o n t a l and v e r t i o a l magnetic t r a c e s . This suggests a c o n d u c t i v i t y a n i s o t r o p y i n the near surfaoe l a y e r s . Such an a n i s o t r o p y has been demonstrated by S r l v a s t a v a et a l ^ 2 4 ^ i n southwestern A l b e r t a through magneto- t e l l u r i o and t e l l u r i c measurements. The r e s u l t s a t V i o t o r i a oould be caused by the nearby land-sea contact. C h r i s t o f f e l e t (4) a l have found s i m i l a r r e s u l t s i n m i c r o p u l s a t i o n s t u d i e s extending from V i o t o r i a , i n l a n d . Beoause of the very s m a l l amplitudes of the fe a t u r e s of these periods on the magnetograms, no d e t a i l e d a n a l y s i s has been attempted. 41 (11) Bays and Storm Features (5 to 120 min.) For geomagnetic disturbances with periods between 5 and 120 min., the records from the western 7 stations V i c t o r i a to Grand Forks, were normal. The r a t i o of h o r i z o n t a l to v e r t i c a l amplitudes i s : generally around 5 to 1. For the eastern 6 stations, Oresoent V a l l e y to Lethbrldge, the v e r t i c a l amplitudes are much large r , with the r a t i o being about 2 to 1. In general the horizontal oomponents are similar aoross the p r o f i l e , with the v e r t i o a l oomponents at these l a s t 6 stations d i f f e r i n g widely. At these eastern 6 stations a c o r r e l a t i o n i s also apparent between the horizontal and v e r t i c a l magnetio traoes. This suggests that the large v e r t i o a l amplitudes are caused by currents induced,largely by the h o r i z o n t a l disturbance, i n conductivity inhomogeneities . With Increasing period the induced v e r t i o a l component shows decreasing amplitude. At 60 min. i t i s about h a l f that at 10 min. In addition to these e f f e c t s that part of the v e r t i o a l component whioh i s present at a l l stations appears to Increase with Increasing period. This suggests that e i t h e r the ionospheric current systems responsible f o r the longer period features produce a greater v e r t i c a l magnetio oomponent than those responsible f o r the shorter period.ones or that the conductivity i s lower at the greater depths penetrated by the long period v a r i a t i o n s . The l a t t e r p o s s i b i l i t y does not agree with the r e s u l t s of S r i v a s t a v a ^ 2 4 ^ , N l b l e t t ^ 1 2 ) and Cantwell^ 2) 42 who found by m a g n e t o t e l l u r i c methods an i n c r e a s i n g c o n d u c t i v i t y below a depth o f about 80 km. ( i i i ) D i u r n a l Geomagnetic V a r i a t i o n s The d i u r n a l v a r i a t i o n s i n the geomagnetic f i e l d ( periods from 6 to 24 hrs.) were examined onl y a t A s k a n i a s t a t i o n s s i n c e the d a i l y temperature d r i f t of the Fluxgate magnetometers was very pronounced. Two c o n s e c u t i v e a p p l i c a t i o n s of running means of adjacent v a l u e s were used to determine tihe d i u r n a l v a r i a t i o n s d u r i n g a q u i e t day i n each p e r i o d o f o p e r a t i o n ( F i g u r e s 12, 13 and 14). The p l o t s are a l l s i m i l a r i n the H and D components, but the Z components a t d i f f e r e n t s t a t i o n s show some pronounced d i f f e r e n c e s . At Crowsnest i n the c e n t r a l Rooky Mountains, there i s a s t r o n g morning r i s e (peak a t 0800 L.M.T.) of 25 If which i s not present a t the o t h e r s t a t i o n s . Since the a d j a c e n t Askania s t a t i o n s 150 km. to the e a s t and west show no such behaviour, and s i n c e the D and H p l o t s show no d i f f e r e n c e s , i t may be r e a s o n a b l y assumed t h a t the e x t e r n a l c u r r e n t source i s u n i f o r m a c r o s s the p r o f i l e and that the anomaly i s caused by i n d u c t i o n e f f e c t s i n the E a r t h . A mean of f o u r q u i e t days has a l s o shown t h a t t h i s r e s u l t i s not p a r t i c u l a r to one day. The anomalous v a r i a t i o n i s o f g r e a t i n t e r e s t s i n c e a s i m i l a r e f f e o t has been (22) noted by SohmuckerV i n southwestern New Mexico, U.S.A. T h i s i s about 2000km.south of Crowsnest and s i m i l a r l y s i t u a t e d about 600 km. from the c o a s t . An anomaly not present a t a d j a c e n t s t a t i o n s and a ppearing F i g u r e 12. D i u r n a l Geomagnetic V a r i a t i o n s , Magnetic*East-West (D) Component J U L Y 2 2 VICTORIA 0 4 8 12 16 20 24 JULY 28 JULY 29 6 ^ — ^ 1 2 f / " — ^ V 4 6 — - ^ r e i N C E T O N O 1 •*•' i . . . i6 i 12 & ^ ^ V \ _ ^ y ^ GRAND FORKS \ In ten sify  ) ^ ^ ^ ^ x ^ ^ y ^ K D O T E N A Y LAKE ^ / ~~ • LETHBRIDGE F i g u r e 13. D i u r n a l Geomagnetic V a r i a t i o n s , V e r t i c a l (Z) Component JULY 22 VICTORIA 0 ^^r^ < T X 12 16 20 24 JULY 28 JULY 29 6 J p — - \ 12 16 ^ - ^ 2 0 0 4 6 " ' 1 1 v 1 1 1 \ ^ ^ ^ " A B B 0 T S F 0 R D « N V \ ^ / ^ ^ ~ ^ P R I N C E T O N :l281 i - 4 Int en sity  ^ \ ^ ^ / ^ ^ LAKE ^CROWSNEST LETHBRIDGE F i g u r e 14. D i u r n a l Geomagnetic V a r i a t i o n s , North-South- (H) Component 46 only i n the v e r t i c a l component suggests a sharp v e r t i c a l d i s c o n t i n u i t y (see model f o r a h o r i z o n t a l l y discontinuous i s t r u c t u r e ) 0 The skin depth f o r d i u r n a l v a r i a t i o n s should be of the order of 400 km. Some much smaller differences i n the Z component are also indicated at the Abbotsford and V i c t o r i a s t a t i o n s . 2» Determination of the s t r i k e of conductivity  inhomogeneities by extreme values An attempt has been made to determine the d i r e c t i o n , l o c a t i o n and i n t e n s i t y of the nonhomogeneous induetion that hap produced the anomalous bay and magnetic storm features observed on the magnetograms f o r the 6 eastern stations. A comparison has been made between the extreme values of the normal f i e l d variations found at the Grand Forks s t a t i o n and those found at the anomalous stati o n s . In section I V on induction analysis i t was noted that f o r a two dimensional structure, only the Incident f i e l d components perpendicular to the s t r i k e of the structure are e f f e c t i v e i n producing induced currents. The anomalous induced v e r t i c a l f i e l d i s then given by A Ec * C AF« cos (oi-o(0) where A Fn i s the normal t o t a l horizontal f i e l d component oC Is the angle the perpendicular to the s t r i k e of the conductivity inhomogeneity makes with magnetio north oC0 ^ t&.n~* ^/H » the angle the normal ho r i z o n t a l f i e l d v a r i a t i o n makes with magnetio north. 4 7 The f o l l o w i n g assumptions are neoessary f o r the v a l i d i t y of t h i s equation. 1. The anomalous zone i s two dimensional* I t should be noted t h a t i f the anomalous zone i s roughly s p h e r i c a l oC d e f i n e s the d i r e o t i o n from the s t a t i o n t o the center of the zone. 2. The induced f i e l d i s approximately i n phase w i t h the lnduoing f i e l d . T h i s appears to be t r u e f o r the p e r i o d s used i n t h i s study. 3 . The normal v e r t i c a l f i e l d makes a n e g l i g i b l e c o n t r i b u t i o n to the induoed currentsv The amplitude of the normal v e r t i o a l f i e l d i s l e s s than 20% of the normal h o r i z o n t a l so t h a t the e r r o r i n t r o d u c e d i n the value o f G by t h i s assumption should be about 20%. I n any case t h i s assumption should introduce no e r r o r i n the s t r i k e of the anomaly th a t i s found. 4 . The anomalous p a r t of a disturbance may be approximately determined by s u b t r a c t i n g the normal p a r t as found a t a "normal" s t a t i o n i n the v i c i n i t y . Whitham^ 3 1^ has made estimates of the d i f f e r e n c e s to be expeoted between normal s t a t i o n s . From h i s r e s u l t s i t appears that f o r (a 200 km. east-west p r o f i l e p a r a l l e l t o the a u r o r a l zone and d u r i n g a p e r i o d of only moderate magnetic a o t i v i t y the d i f f e r e n c e s should be l e s s than about 10% p a r t i c u l a r l y when averaged over a number of f e a t u r e s . To o b t a i n another estimate of the p o s s i b l e e r r o r introduced here, an approximate s t r i k e of the inhomogeneous zone was found at the s t a t i o n (Lethbridge) 4 8 farthest away from the reference s t a t i o n (Grand Forks), an$ the difference i n the horizontal components for the two stations, p a r a l l e l to th i s s t r i k e determined. The component p a r a l l e l to the s t r i k e should exhibit no anomalous Induction e f f e o t s . The difference averaged over 10 features was found to be 7.5$ which i s given as Ml the l i m i t of error f o r a l l stations. This technique might be used to scale the normal oomponent values with respect to the reference station, but was not used here* Extreme values o f amplitude f o r a number of magnetogram features of d i f f e r e n t dominant harmonic periods and d i f f e r e n t azimuths of the magnetic vector were used to evaluate oC and C using a le a s t squares method. The amplitudes and periods were measured as shown i n Figure 15. The ohoice of the points of measurement i s somewhat a r b i t r a r y but Is of less importance than the requirement that the same points be taken on eaoh record. A s t a t i s t i c a l averaging should reduce any random erro r s . This method of measurement, i n an approximate manner, eliminates both the longer period harmonios and instrumental d r i f t . •<— PERIOD Figure 15. Measurement of the Extreme Value of a Feature on a Magnetogram. 49 I n o r d e r to f a c i l i t a t e a l e a s t squares computation o f o< and C, i t i s convenient to u t i l i z e the data i n the three component form g i v e n on the r e o O r d s ^ 3 3 ) . The above equation i s e q u i v a l e n t to AZor #£Dn-r B A H n _ where Oco = f a n " 1 fl/s and C \IR 27 D i v i d i n g by ^ j j M or /\ H n g i v e s •&Za. = R+- &AJin or AZ*. = B + ffADn A Dn ADn • A Hr AHn These forms have been used i n a l e a s t squares computation of A and B. They are p r e f e r a b l e to the equation o b t a i n e d by d i v i d i n g by which tends to be sm a l l e r than ^D n or AHn and thus c o n t a i n s a l a r g e r percentage e r r o r . As i t i s d i f f i c u l t to a s s i g n a s p e o i f l c p e r i o d to any magnetogram f e a t u r e C and cC were determined f o r three ranges of p e r i o d s , 7 to 20 min., 25 to 45 min., and 60 to 110 min. The computed valu e s are g i v e n i n Table 1. The s t r i k e s o f the c o n d u c t i v i t y inhomogeneities are east-west f o r the Cresoent V a l l e y and Kootenay Lake s t a t i o n s and n o r t h - s o u t h f o r the e a s t e r n 4 s t a t i o n s . The c o n s i s t e n t d i r e c t i o n s g i v e some weight to the h y p o t h e s i s t h a t the zones are two d i m e n s i o n a l . The rec u r r e n c e o f the same type o f zone i n the r e g i o n o f the e a s t e r n 4 s t a t i o n s i n d i c a t e s the anomalous f i e l d s are r e s u l t i n g from 50 O Approximate- Strfke of inhomogeneity .Direction from Station to anomaly F i g u r e 16. S t r i k e of C o n d u c t i v i t y Inhomogeneities From Least Squares Extreme Value A n a l y s i s . P e r i o d o f Featur e s S t a t i o n 7 - 20 min. i 25 - 45 min. 60 - 110 min. - i Crescent V a l l e y 0 109° t 3 ° (6«»9-) 106°30* i 3 ° 121°30' i 15° C 0.36 i 0.04 0.31 ± 0.03 0.28 ±„0.06 Kootenay Lake $ 100°30' ± 3 ° 95° ± 3 ° 108°50' ± 12° c 0.67± 0.03 0.53 ± 0.03 0.50 *.0.10 Kimberley 2 ° 3 0 ' t 4 ° 4? ± 4 ° 59°30» - 30° c 0.30 ±0.04 0.23 ± 0.03 0.27 ± 0.07 Crowsnest 26° ± 3 ° 2 2 ° * 5 ° ,.~ 69° ± 3 0 ° c 0.50 ±0.03 0.40 ± 0 . 0 4 0.26 i 0.07 Pin e h e r Creek (3 23°30' - 5 ° 42°30r± 6° 5° ± 4 0 ° c 0 . 2 4 ± 0 . 0 4 0.30 ± 0.04 0.08 ± 0.10 Le t h b r i d g e § 22° i 8° A A 0 4- r -0 44 ± 5 58°30'*-15° c 0.25 ± 0 . 0 5 0.24 ± 0.04 0.28 ± 0.06 Table 1. S t r i k e o f C o n d u c t i v i t y Inhomogeneities ('$') and I n Phase I n d u c t i o n C o e f f i c i e n t s (C) From Extreme Value A n a l y s e s . 51 some r e c u r r e n t s t r u o t u r e ^ s u o h as a system o f l a r g e n o r t h - s o u t h t r e n d i n g d i k e s o f h i g h c o n d u c t i v i t y . 3. :'Determination o f l n d u o t l o n c o e f f i c i e n t s as a f u n c t i o n o f frequency from a s p e o t r a l a n a l y s i s A s p e c t r a l a n a l y s i s was performed on a bay type magnetic d i s t u r b a n c e on August 4, 1963 a t the Grand Forks and Kootenay Lake s t a t i o n s . F o u r i e r components f o r f r e q u e n c i e s from 0.008 to 0.200 oyoles/min. were determined from r e a d i n g s a t 2.5 min. i n t e r v a l s f o r a t o t a l l e n g t h o f 60 min. Simpson's i n t e r p o l a t i o n rulai:; wars J used on a d i g i t a l oomputer. The s p e o t r a l d e n s i t i e s are g i v e n i n F i g u r e s 17 and 18. A c o r r e l a t i o n between Z and H and an i n v e r s e c o r r e l a t i o n between D and H i s q u i t e d e a r a t the Kootenay Lake s t a t i o n . No c o r r e l a t i o n i s apparent a t Grand F o r k s , 120 km. to the west. An attempt has been made to determine the i n phase and out of phase i n d u c t i o n c o e f f i c i e n t s a t Kootenay Lake as a f u n c t i o n of frequency from t h i s d a t a , u s i n g the s p e o t r a l d e n s i t i e s a t Grand Forks as the normal f i e l d . T h i s was u n s u c c e s s f u l , w i d e l y s o a t t e r e d v a l u e s b e i n g o b t a i n e d . I t i s apparent t h a t e i t h e r there i s an a p p r e c i a b l e d i f f e r e n c e between the e x t e r n a l v a r i a t i o n s a t the two s t a t i o n s o r the s p e c t r a l a n a l y s i s was not s u f f i c i e n t l y p r e o l s e . I t i s suspeoted t h a t the e x t e r n a l f i e l d i s not s u f f i c i e n t l y u n i f o r m over the 120 km. d i s t a n c e , t o g i v e acourate r e s u l t s . 4. D e t e r m i n a t i o n of the l o c a t i o n and s i z e of an assumed  i n f i n i t e c y l i n d e r I n t h i s s e c t i o n the c o n d u c t i v i t y Inhomogeneities have been 52 SINE TERMS , Figure 17. Speotral Densities f o r Bay Type Feature at Grand Forks on August 4, 1963. 8 0 5 3 F i g . 18. Spectral Densities f o r Bay Type Feature at Kootenay Lake on August 4, 1963. 55 S t a t i o n C r e s c e n t V a l l e y Kootenay Lake Kimberley Dip Angle 46 51°± 3 o 71° ± 4 o 50° 6° ( S p e c t r a l A n a l y s i s ) R a t i o o f Radius to D i s t a n c e 0.60± 0,06 0,82 ± 0.04 0.76 ± 0.07 0.93 ± 0.20 ( S p e c t r a l A n a l y s i s ) Table 2. C y l i n d e r Parameters f o r the C o n d u c t i v i t y Inhomogeneities Observed from the Crescent V a l l e y , Kootenay Lake and Kimberley S t a t i o n s . Ah examination of Table 2 shows that an assumed c y l i n d r i  c a l zone south o f C r e s c e n t V a l l e y must extend almost to the s u r f a c e w h i l e the computed c y l i n d e r to the south o f the Kootenay Lake s t a t i o n extends to o r s l i g h t l y above the s u r f a o e . An i n f i n i t e c y l i n d e r thus can be o n l y a very rough approximation to the shape o f the h i g h c o n d u c t i v i t y zone. I f the assumed e f f e c t i v e l y i n f i n i t e c o n d u c t i v i t y i s reduced, a l a r g e r c y l i n d e r i s r e q u i r e d which would extend even f u r t h e r above the s u r f a o e . A s p h e r i c a l body i s even more d i f f i c u l t to r e c o n c i l e w i t h the observed data s i n c e a l a r g e r value o f ^ would be r e q u i r e d f o r the same magnitudes of seoondary induced f i e l d s . T h i s adds weight to the c o n c l u s i o n t h a t the anomalous zones may be c l o s e l y approximated by two d i m e n s i o n a l s t r u c t u r e s . Other i d e a l i z e d models such as a v e r t i c a l d i s c o n t i n u i t y and a v e r t i c a l d i k e have not been examined i n t h i s t h e s i s beoause o f the l a c k 56 of t h e o r e t i c a l e x p r e s s i o n s f o r the secondary induced f i e l d s . F i n a l l y , an estimate has been made of the c o n d u c t i v i t y of an assumed c y l i n d e r as seen from the Kootenay Lake s t a t i o n , u s i n g the s p e c t r a l d e n s i t i e s f o r the bay d i s t u r b a n c e on August 4 t h . For a two dimensional s t r u c t u r e , s e c t i o n IV gave the r e l a t i o n s Zc,{ - A, Fn, T-B,Zn( + Pi;. Fn^ + Bz 2 n i Z*.z - Fn, + Bz En, + f), Fnz + B, Znz Since the normal v e r t i c a l f i e l d i s s m a l l f o r t h i s d i s t u r b a n c e i t has been n e g l e c t e d . L e t t i n g M and N r e p r e s e n t the i n phase and out of phase c o e f f i c i e n t s r e s p e c t i v e l y , these equations become ZLa, = M Fn, - N Fnz Z A J , = N Fn{ + M Fnz S o l v i n g f o r M and N g i v e s M = jgq , , F n , -f Ea.z Fnz Fn,1 +• Fnz2 N — ~ Za, Fh2 -f Z.a.z Fn, Fn,2 Fn^ 2 i 57 The a x i s of the h y p o t h e t i c a l c y l i n d e r has been taken from the extreme value a n a l y s i s , and the mean values of' M and N eval u a t e d f o r the p e r i o d range from 25 to 125 min. These means are M = 0.65 ± 0 . 1 0 N = 0.22 + 0.05 M/N =• 0,34 ± 0.14 A very rough estimate o f the c o n d u c t i v i t y of the anomalous zone may be found by a p p l y i n g these v a l u e s to the computed curves f o r the i n phase and out of phase components of i n d u c t i o n i n a c y l i n d e r . A value o f approximately 1000/o2 e.m.u. i s obtained where >^ i s the r a d i u s o f the c y l i n d e r i n cm. A c y l i n d e r w i t h a r a d i u s o f 10 km. thus r e q u i r e s a c o n d u c t i v i t y o f 10" 9 e.m.u. (102 (ohm-m)" 1). A l a r g e r r a d i u s w i l l g i v e a c o r r e s p o n d i n g l y lower c o n d u c t i v i t y . At ^ = 30 km, 6 =» 10~ 1 0 e.m.u. T h i s i s of the same o r d e r o f magnitude as found by Whltham between E l l e s m e r e I s l a n d and Greenland and by Sohmuoker f o r a r e g i o n i n Germany. I f the normal c o n d u c t i v i t y -14 / (24)-v i s taken to be 10 e.m.u. ( S r i v a s t a v a et a l ) the 4 c o n d u c t i v i t y c o n t r a s t i s about a f a c t o r o f 10 . 5. Frequency dependence o f the anomalous induced f i e l d s The extreme value a n a l y s i s shows a decrease i n the r a t i o of induced to normal f i e l d components w i t h i n c r e a s i n g p e r i o d of magnetio v a r i a t i o n at a l l the anomalous s t a t i o n s . The s p e o t r a l a n a l y s i s was i n c o n c l u s i v e . The s h o r t e s t p e r i o d range 58 s t u d i e d by extreme values ( 7 - 2 0 min.), showed the l a r g e s t i n t e n s i t y of i n d u c t i o n . For a r e s i s t i v i t y value g i v e n by S r i v a s t a v a et a i ^ 2 4 ) f o r the southwestern A l b e r t a r e g i o n of about 1000 ohm - m. f o r depths from 2 - 8 km., a low r e s i s t i v i t y surfaoe l a y e r and decreasing r e s i s t i v i t y below 80 km., the s k i n depth f o r t h i s p e r i o d range i s of the order of 100 to 150 km. The c o n d u c t i v i t y inhomogenelties may be expeoted to l i e above t h i s depth. The anomalous d i u r n a l v a r i a t i o n s should r e s u l t from very much deeper inhomogenelties. For d i u r n a l magnetic v a r i a t i o n s w i t h a p e r i o d o f 12 hours, the s k i n depths f o r d i f f e r e n t E a r t h r e s i s t i v i t i e s are given i n Table 3. (ohm - m) d ( s k i n depth i n km.) 0.2 47 5 230 50 740 1000 3300 Table 3. Depth of P e n e t r a t i o n of D i u r n a l Magnetic V a r i a t i o n s . 59 71. SUGGESTIONS FOR FUTURE STUDY The f i r s t requirement fo r a more detailed study of the regions of inhomogeneous conductivity i s a more olosely spaced network of variograph stations. With the p r o f i l e described i n t h i s thesis, only one or at most two stations are appreciably affected by the seoondary f i e l d s from a single anomalous conductivity zone. The p r o f i l e also appears to p a r a l l e l the zone e x i s t i n g to the south of the Cresoent Valley and Kootenay Lake stat i o n s . With more detailed information i t should be possible to make comparisons with the r e s u l t s f o r other i d e a l i z e d models such as a v e r t i c a l d i s c o n t i n u i t y and a v e r t i c a l dike. More the o r e t i o a l work or laboratory model studies would also be necessary to determine the seoondary induoed f i e l d s to be expeoted f o r these and more oomplex structures. With more de t a i l e d data i t should also be possible to determine the i n t e r n a l and external parts to the observed f i e l d v a r i a t i o n s using the method outlined i n the introduction. This would eliminate the problem encountered i n determining the normal incident f i e l d from a non-anomalous s t a t i o n . No c o r r e l a t i o n has been attempted with other techniques f o r investigating the deeper regions of the Earth's crust and upper mantle. Results from seismology, gravity, aeromagnetio, and geologioal studies should be considered. The difference between the v e r t i c a l component of the d i u r n a l variations at Crowsnest and that at the remainder of the 60 s t a t i o n s i s o f major i n t e r e s t because o f the depth of the s t r u c t u r e i t must r e f l e c t . A d e t a i l e d p r o f i l e a c r o s s t h i s a r e a should be attempted. One o t h e r concern t h a t should be i n v e s t i g a t e d i s the d i f f e r e n c e i n the i n t e n s i t y of the induced c u r r e n t s produced by d i f f e r e n t magnetic f e a t u r e s a t the same s t a t i o n , w i t h the same p e r i o d and approximately the same d i r e o t i o n o f the magnetic d i s t u r b a n c e v e c t o r . The r a t i o of Induced to i n d u c i n g f i e l d s a t Kootenay Lake v a r i e s from 20 to 80 percent;, onu the same magnetogram. Such i r r e g u l a r i t i e s may i n v a l i d a t e any r e s u l t s from a s p e c t r a l a n a l y s i s o f a s i n g l e magnetogram f e a t u r e . 61 VII. CONCLUSIONS The study presented In this thesis suggests conductivity inhomogeneities of a varied nature extending from Crescent Valley, B r i t i s h Columbia to Lethbrldge, A l b e r t a . These have been detected by the anomalous seoondary induced f i e l d compon ents observed i n the period range from 5 to 12G min. Using a l e a s t squares method the s t r i k e of the anomalous conductivity zones has been found at each anomalous station. This evaluation requires the assumption that a l l the zones are two dimensional. By making the add i t i o n a l assumption (which must be considered of doubtful v a l i d i t y ) that the inhomogeneities approximate to highly conducting cylinders, estimates have been made of the po s i t i o n and size of the zones r e l a t i v e to the Cresoent Valley, Kootenay Lake and Kimberley stations. An estimate of the conductivity contrast has also been made from the Kootenay Lake data. A difference has been detected between the v e r t i o a l oomponents of the diu r n a l geomagnetio variations at a s i t e i n the Rocky Mountains and those along the remainder of the p r o f i l e . This should be of major i n t e r e s t . 62 APPENDIX I. LOCATION AND DETAILS OF THE STATIONS Total Duration Type of Oeographio Elev» Field of Station Instrument Long* Lat<» (ft) (gauss) Observation Westham Island Fluxgate 124°49 W 49°5'N 10 0*5699 Jun 6 - Jul 11 Abbots-/ ford Askania 122°2l' 49°l' 180 0*5735 Jun 15 - Tul 11 Hope Fluxgate 121°29* 49022, 130 0.5706 Tun 15 mm Tul 11 Prinoe- ton Askania 120°29* 49°28t 2300 0.5811 Tun 15 mm Tul 12 Pentio- ton DoriuObs. Fluxgate 119°38' 49°191 1800 0.5777 Jun 15 Aug 8 Grand Forks Askania 49°l' 1500 0»5777 Tun 14 mm Aug 7 Cresoert y^iiey Fluxgate l l ? ^ ' 49°87' 2000 0*5811 Jun 20 mm' Aug 7 Kootenay Lake Askania 116°45f 49°28' 1800 0«5830 Tun 15 mm Aug 7 Kimberley Fluxgate 49°43f 3000 0.5849 Tul 14 - Aug 6 Crows nest Askania 114°45* 49°39' 4300 a) 0«5866 b) 0©5877 Jul 15 — Aug 6 Pinoher Creek Fluxgate 113°57' 49°29* 3790 0*5917 Tul 16 mm Aug 6 Leth- bridge Askania 1L8°47'' 49°391 3000 0*5903 Tul 16 Aug 5 63 APPENDIX I I . TABLE OF : EXTREME VALUES (Gammas) PHASE I Time June 17 2150 Period (Min.) 25 D Westham Z H Abbotsford D Z 25.7 9.2 H -15.7 18 0640 65 34.3 -11.7 17.1 20 0030 55 -62.2 -19.5 -38.3 20 0440 55 -13.4 ^8.9 -12.0 26 0100 60 -128.0 -59.0 -32.0 -130.0 -58.1 -33.9 26 1910 40 5.0 12.0 39.5 5.4 10.0 40.4 27 0130 50 52.5 15.0 -15.0 53.6 11.7 -15.4 28 0150 90 -41.5 -25.5 -14.0 -41.5 -25.0 0 30 1930 75 23.0 9.0 19.0 25.5 9.7 20.5 30 1715 8 -5.0 0 16.5 -5.4 2.2 16.8 July 2 1715 10 -5.1 2.2 19.5 2 1740 7 -2.1 1.4 16.8 4 1800 35 15.5 -3.0 -54.0 15.3 -5.6 -58.1 4 2300 85 110.0 60.0 -28.0 113.9 53.4 -35.9 5 1750 20 -17.0 0 16.0 -11.5 2.5 20.2 6 0040 35 47.0 17.5 44.0 45.6 13.9 44.5 8 0010 40 -75.0 -19.0 -34.5 -76.9 -17.0 -34.2 8 0900 6 -8.0 0 9.0 -16.1 0.8 14.0 8 1355 7 3.5 10.5 -6.7 1.7 8.9 8 1535 50 12.0 -6.0 -35.0 10.7 -3.9 -36.3 8 2100 40 68.5 14.5 -41.5 69.7 13.3 -43.8 8 2350 55 -58.0 -35.0 -26.5 -56.3 -26.4 -24.3 64 Time Period (Min.) D Hope Z June 17 2150 25 29.0 11.5 18 0640 65 34.0 -14.0 20 0030 55 -66.0 -17.5 20 0440 55 -14.0 -7.0 26 0100 60 -134*0 -63.0 26 1910 40 5.0 6.5 27 0130 50 57.0 13.0 28 0150 90 -43.5 -26.5 30 1930 75 25.0 9.0 30 1715 8 -4.5 1.5 July 2 1715 10 0 1.5 • 2 1740 7 -4.0 1.0 4 1800 35 15.0 1.0 2300 85 120.0 60.0 5 1750 20 -12.5 0 6 0040 35 46.0 14.0 8 0010 40 -79.0 —23.5 8 0900 8 -15.5 0 6 1355 7 -8.5 -1.5 8 1535 50 16.0 -11.0 8 2100 40 75.0 8.0 8 2350 55 -58.5 -31.0 Prinoeton H D Z H -14.5 32.5 17.0 -16.7 15.0 34.4 -18.5 20.8 -42.5 -69.9 -22.9 -45.7 -13.5 -25.0 -9.8 -14.3 -40.5 -146.3 -70.6 -51.1 41.5 5.4 10.4 45.7 -19.0 61.9 14.6 -17.7 -16.0 -46.0 -35.2 -6.8 21.0 26.9 22.2 17.5 -6.2 0.3 17.1 15.0 -5.1 0.6 22.2 20.5 -2.4 0.3 17.1 -58.0 15.6 -3.9 -64.1 -26.5 129.7 66.5 -31.4 20.0 -12.9 1.2 22.8 45.0 43.0 17.9 49.4 -41.5 -83.7 -17.9 -45.4 12.5 -16.4 -1.2 15.3 9.0 -7.5 0.6 10.2 -38.0 12.1 -5.1 -41.6 44.0 80.2 16.4 -46.4 -28.5 -61.9 -35.6 -28.0 65 Time P e r i o d (Min.) D P e n t l o t o n Z H Grand Forks D Z H June 17 2150 25 28.0 14.5 -15.0 38,2 15.6 -18.7 18 0640 65 30.4 -18.7 31.7 20 0030 55 -63.0 -21.0 -44.0 -66.6 -21.5 -48.2 20 0440 55 -24.0 -9.0 -13.5 -16,3 -10.0 -15.9 26 0100 60 -139.5 -70.5 -57.0 -150.0 -71.8 -75.1 26 1910 40 5.0 13.5 45.0 5.4 11.9 50.7 27 0130 50 65.0 15.5 -20.0 68.1 15.0 -19.7 28 0150 90 -41.5 -27.0 -18.5 -46.4 -31.5 -15.9 30 1930 75 21.5 10.0 20.5 30.4 6.9 24.7 30 1715 8 -5.0 3.0 17.5 -5.7 -0.9 19.0 J u l y 2 1715 10 -1.5 1.0 17.5 -4.6 -2.2 25.4 2 1740 7 -4.0 -2.0 22.0 -2.1 -1.6 19.3 4 1800 35 4 2300 85 120.0 63.5 -30.0 ) 5 1750 20 -11.0 -1.5 23*0 -14.7 1.9 22.8 6 0040 35 35.0 16.0 42,0 33.5 15.6 57.1 8 0010 40 -80.5 -21.0 -47.5 -80.2 -13.4 -57.1 8 0900 8 8 1355 7 -6.0 2,0 10.0 -7.7 0 9.8 8 1535 50 23.5 -9.0 -41.5 13.9 -5.9 -47.5 8 2100 40 78.0 17.5 -43.5 86.4 17.2 -41.2 8 2350 55 -59.3 -35.9 -30.1 66 Time Period (Min.) Tune 17 2150 25 18 0640 65 20 0030 55 20 0440 55 26 0100 60 26 1910 40 27 0130 50 28 0150 90 30 1930 75 30 1715 8 July 2 1715 10 '2 1740 7 '4 1800 35 4 2300 85 5 1750 20 6 0040 35 8 0010 40 8 0900 8 8 1355 7 8 1535 50 8 2100 40 8 2350 55 Crescent Valley D Z H 153.5 -92.5 -102.5 5.5 22.5 59.5 66.5 12.0 -34.0 -46.0 -39.5 -27.0 31.0 11.0 25.0 -6.5 4.5 24.0 0 6.5 28.0 -1.5 7.0 31.5 14.0 -15.0 -79.0 145.0 76.5 -25.0 -14.0 7.5 27.5 35.0 51.5 67.5 -80.5 -38.0 -61.0 -18.0 4.5 17,5 -9.0 -4.5 8.5 11.0 -15.0 -60.0 88.0 14.0 -64.0 -61.5 -55.0 -23.0 Kootenay Lake D Z H 30.1 -34.9 33.4 -78.7 -29.1 -55.4 -12.7 -27.5 -17.4 -96.1 -131.6 -168.2 8.9 30.9 55.7 85.0 -18.7 -26.1 -43.0 -54.2 -24.1 32.6 12.2 26.4 -8.9 7.0 20.3 -10.1 11.9 29.0 -7.3 11.6 23.2 24.5 -24.2 -74.0 170.0 80.2 -31.3 -19.7 76.5 69.0 18.2 14.4 26.1 -70.8 -43.1 -69.9 -24.8 11.3 17.7 -10. i 6.1 10.4 22.3 -24.5 -53.4 97.4 0 -45.0 -60.7 -73.4 -31.0 Time P e r i o d (Min.) J u l y 17 G500 70 17 2330 100 18 0015 35: 18 0415 45 18 2030 30 19 0000 45 21 0300 10 22 0145 15 22 1045 7 22 2125 20 22 2300 45 23 1400 15 23 1850 35 24 0220 60 24 1000 35 24 1025 45 24 1415 35 24 1435 35 24 2155 25 25 0020 30 26 0115 80 PHASE I I Pe n t i o t o n D Z H -20.0, -3.0 15.0 0 3.0 11.5 -10.0 -6.0 -24.0 25.0 1.5 13.0 7.5 3.0 -8.5 9.5 1.0 17.0 35.0 7.0 -24.0 20.5 0 12.0 89.0 14.0 46.0 -22.5 -2.5 30.5 21.5 2.0 -27.0 —2 . 5 4.5 32.5 2.0 -2.5 -26.0 105.0 6.0 45.0 45.0 0 50.0 Grand Porks D Z H -93,9 -39.9 -74.5 36.1 4.7 -20.6 -33.3 -3.1 13.3 -11.9 -6.2 -13.3 -3,1 -0.6 15.2 19.4 0 1.3 -10.3 -3.7 -28.5 26.8 1.2 15.6 12.4 0 -12.4 11.4 -1.9 18.4 41.8 5.9 -25.4 30.6 -1.6 18.4 87.2 13.1 65.4 -63.0 -18.1 -29.2 -28.4 -1.9 33.3 28.4 0.9 -28.5 -4.6 3.1 35.5 1.0 0.6 -33.0 107.8 5.9 55.8 59.3 0.6 60.2 -59.3 -35.6 -17.7 68 Time P e r i o d P o n t i c t o n Grand Forks (Min.) D Z H D Z H J u l y 27 0955 8 -10.3 0 6.6 27 1545 45 9.0 0 -30.4 30 1930 60 -7.7 0 22.2 30 2145 35 25.0 -5.0 -15.0 37.4 1.6 -15.9 31 0600 110 -87.7 -22.4 -29.2 31 1015 7 -20.1 0 13.9 31 1930 90 35.6 8.7 36.1 Aug. 1 1615 30 -12.9 3.1 34.2 1 2310 15 10.0 -1.0 -11.0 20.6 0 -15.2 .2 1950 30 45.0 -2.5 -29.0 48.5 -1.6 -33.3 2 2150 40 49.0 6.2 -33.3 3 0825 8 -13.2 -0.3 9.2 3 1610 10 -2.3 -0.3 12.4 4 0920 7 8.8 -0.3 -8.9 4 1110 7 9.8 0.6 -9.5 4 1600 30 -8.3 3.1 28.5 5 0500 80 -42.3 -15.0 -33.6 5 1400 35 -9.8 12.5 21.6 69 Time P e r i o d (Min-.) J u l y 17 0500 70 17 2330 100 18 0015 35 18 0415 45 18 2030 30 19 0000 45 21 0300 10 22 0145 15 22 1045 7 22- 2125 20 22 2300 45 23 1400 15 23 1850 35 24 0220 60 24 1000 35 24 1025 45 24 1415 35 24 1435 35 24 2155 25 25 0020 30 26 0115 80 Crescent V a l l e y D Z H -93.0 -60.0 -91.0 32.5 -2.5 -17.5 -21.0 3.0 21.0 -11.0 -13.0 -16.0 -4.0 5.0 17.5 19.5 -5.0 2.0 -15.0 -12.5 -29.0 25.0 5.0 11.5 10.0 -3.5 -6.5 10.5 5.0 21.0 42.0 2.5 -25.5 21.5 7.5 21.0 98.5 28.5 65.5 -63.0 -39.0 -46.0 -25.0 10.0 40.5 25.0 -13.0 -41.0 1.5 12.5 45.0 -1.5 -11.5 -41.0 106.0 9.0 54.5 60.0 27.0 65.5 -60.0 -53.0 -20.5 Kootenay Lake D Z H -97.9 -69.8 -86.4 40.5 9.2 -23.2 -27.8 7.7 16.8 -8.1' -16.5 -16.8 -5.6 6.7 16.8 22.8 -6.7 1.2 -10 ; i -21.4 -28.4 25.8 7.3 12.2 17.5 -8.6 -12.2 10.1 6.1 19.7 48.1 v -9.2 -26.1 18.2 11.0 20.3 87.3 30.6 65.3 -58.2 -45.3 -39.4 -38.0 22.6 43.5 38.0 -21.1 -32.8 -10.6 17.7 .f;;40 .0 8.6 -17.7 -37.1 114.1 5.8 51.6 48.1 20.8 60.9 -57.2 -58.8 -20.9 70 Time P e r i o d C rescent V a l l e y (Min.) D Z H J u l y 27 0955 8 -11.0 3.5 9.0 27 1545 45 0 -11.0 -40.0 30 1930 60 -9.0 6.0 25.0 30 2145 35 35.5 -10.0 -23.5 31 0600 110 -88.5 -31.5 -30.0 31 1015 7 -19.0 3.5 15.0 31 1930 90 36.5 12.5 42.5 Aug. 1 • 1615 30 -9.0 14.0 40.0 1 2310 15 20.5 -6.5 -20.5 2 1950 30 45.5 -11.0 -43.0 2 2150 40 50.0 -5.0 -40.0 3 0825 8 -13.5 3.5 9.5 3 1610 10 1.5 3.5 13.5 4 0920 7 8.0 -2.5 -8.5 4 1110 7 6.0 -4.5 -8.5 4 1600 30 -6.0 13.5 38.5 5 0500 80 -44.5 -22.5 -44.0 5 1400 35 -8.0 8.0 25.5 Kootenay Lake D Z H 12.9 6.1 8.7 11.4 -15.6 -32.5 10.1 10.7 24.6 47.6 -19.6 -22.6 •86 .& -33.7 -37.1 25.0 11.9 14.5 38.0 14.7 37.7 •20.2 22.0 38.3 25.3 -14.7 -17.4 53.1 -22.0 -37.7 57.2 -18.4 -33.4 •17.2 6.4 8.7 -4.6 5.5 11.6 11.1 -8.0 -11.9 9.9 -6.7 -9.3 •15.2 20.2 34.8 •39.5 -23.9 -38.3 •13.2 12.9 24.9 71 Time P e r i o d Kimberley Crowsnest (Min.) D Z H D Z H J u l y 17 0500 70 -124.0 -35.0 -85.0 -98,3 -39.1 -87.0 17 2330 100 45.0 -12.5 -22.5 38.3 15.6 -22.8 18 0015 35 -43.0 -13.5 24.0 -24.7 -15.3 13.3 18 0415 45 -7.5 -8.0 -16,0 -9.4 -6.2 -14.0 18 2030 30 -10.0 0 15,5 -6.4 -2.5 14.0 19 0000 45 33.5 4.5 4.0 21.7 7.4 4,2 21 0300 10 -24.0 -10.0 -26.0 -7.9 -10.2 -23.9 22 0145 15 30.0 9,0 12.0 21.7 10.8 12.6 22 1045 7 24.0 3.5 -13.5 14.8 9.9 -12.6 22 2125 20 18.0 3.0 21,0 7.9 1.4 16.8 22 2300 45 •68.5 16.0 -26.0 48.9 19.2 -31.9 23 1400 15 26.5 5.5 22.0 17.3 2.8 21.4 23 1850 35 127.5 52.5 71.5 24 0220 60 -66.0 -30.0 -42.0 -52.4 -24.9 -38.6 24 1000 35 -60.0 -11.5 37.0 24 1025 45 57.0 8.5 -31.0 24 1415 35 -25.0 0 42.0 -9.9 -5.6 35.1 24 1435 35 23.5 4.0 -35.0 8.4 6.2 -30,2 24 2155 25 154.5 42.0 52.0 103.7 45.0 53.7 25 0020 30 46.0 33.5 -> 69.0 33.1 11.3 58.3 26 0115 80 51.0 61.0 -25.0 -61.3 -53.2 -26.0 72 Time P e r i o d (Min.) J u l y 27 0955 8 27 1545 45 30 1930 60 30 2145 35 31 0600 110 31 1015 7 31 1930 90 Aug. 1 1650 30 2310 15 2 1950 30 2150 40 3 0825 8 1610 10 4 0920 7 1110 7 1600 30 5 0500 80 1400 35 Kimberley D Z H 22.5 -1.0 6,5 23.5 0 -30.0 15.0 -5.0 25.0 78.5 13.0 -20.5 95.0 -40,5 -37.0 36.5 -4.5 13,5 45,0 10.0 38.0 35.5 -2.5 41.5 40.5 6.5 -19,5 75.5 20.0 -39.5 90.0 25.0 -36.0 24.0 —3 o 5 10.5 -9.0 1.0 13.5 17.0 1.5 -6.0 19,5 1.5 -10,0 31.5 -1.5 36.0 38.0 -15.5 —41 o 5 20,0 -3.0 24.5 Crowsnest D Z H -11.4 -5.1 7.0 10.9 3.1 -28.0 -8.6 -5.7 21.1 44.0 13.0 -21.0 -86.4 -23,2 -37.2 -24.5 -8.5 12.6 37.1 11.3 37.2 -18.3 0 31.6 22.7 13.0 -17.6 48.4 21.5 -33.7 52.9 30.0 -31.6 -16.8 -7.4 9.1 -4.7 -2.6 10.9 10.9 4.5 -6.7 8.6 5.7 -9.8 -12.4 -5.7 30.2 —32.6 -15.8 -44.9 -13.3 -5.7 20.4 73 Time P e r i o d (Min.) P i n c h e r Creek D Z H Le D th b r i d g e Z • H , J u l y 17 05G0 70 • -82.5 -34.0 -80.0 -95.4 -43.8 -89.2 17 2330 100 35.0 7.5 -20.0 39.4 14.1 -22.3 18 0015 35 -23.0 -13.0 11.5 -24.6 -12.5 9.6 18 0415 45 -9.0 -6.0 -15.0 -9.8 8.8 -15.8 18 2030 30 -6.0 -3.0 10.5 -3.9 -2.8 13.0 19 0000 45 20.0 4.5 6.5 20.2 2.5 6.2 21 0300 10 -13.0 -8.0 -19.0 r8.-9 -9.4 -24.0 22 0145 15 24.0 6.5 11.5 19.2 8.1 11.0 22 1045 7 11.0 3.5 -9.5 12.1 6.9 -11.7 22 2125 20 8.5 -1.5 18.0 7.6 -2.5 14.4 22' 2300 45 48.7 14.4 -20.2 23 1400 15 19.0 0 20.5 17.2 -2.5 23.7 23 1850 35 94.0 40.0 74.0 86.1 33.5 74.1 24 0220 60 -51.5 -25.0 -34.0 -55.6 -28.2 -39.1 24 1000 35 -29.0 -10.0 28.0 -29.5 -9.4 27.4 24 1025 45 26.0 11.0 -20.5 29.5 8.8 -20.6 24 1415 35 -5.9 -5.0 33.6 24 1435 35 3.4 5.0 -27.4 24 2155 25 93.0 30.4 52.8 25 0020 30 27.1 5.0 54.9 26 0115 80 -67.9 -61.3 -28.1 74 Time P e r i o d P i n c h e r (Mlii.) D Z J u l y 87 0955 8 27 1545 45 30 1930 60 30 2145 35 43.5 15,0 31 0600 110 -72.0 -30.0 31 1015 7 -18.5 -4.0 31 1930 90 34.5 18.5 tog. 1 1650 30 -11.0 -5.5 2310 15 27,5 8.0 2 1950 30 46.0 16.0 2150 40 50.0 26 .0 3 0825 8 -14.0 -4.5 1610 10 4.5 -1.0 4 0920 7 9.5 3.0 1110 7 9.0 1.5 1600 30 -10.0 -4.5 5 0500 80 "•33 a 5 -14.5 1400 35 ;•«"• 9 . 5 -5.5 Le t h b r i d g e H D Z H -9.6 2.8 5 ^  5 6.9 2.5 -30.2 -7.4 -6.3 20.6 -11.0 41,3 9.4 -13.0 -35.0 -83.6 -25.0 -43.9 10.5 -17.5 -3,4 15.1 35.5 40.3 6.3. 35.7 25.0 -12.8 0 33.6 -14.0 22.1 7.5 -17.8 -28.0 48.2 14.5 -30.9 -25.0 50.2 23.5 -27.4 6.0 -14.3 -3.4 7.2 11.0 -2.5 -2.5 10.6 -4,0 7.9 1.9 -4.8 -7.5 5.4 2.8 -7.5 30.0 -8.4 -1.9 30.9 -38,* 5 -35.9 -15.0 -41.2 18.5 -9.8 -5.6 19.9 7 5 77 7S 81 i 4 1 S _ H \ ft 1 0 3 \ ] $2 S3 REFERENCES 1. Cagniard, L., P r i n c i p a l s of the M a g n e t o t e l l u r i c Method, a New Method o f G e o p h y s i c a l P r o s p e c t i n g . Geophysics, 18, p 605, 1953. 2. 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