Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

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

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1976_A6_7 P37.pdf [ 3.25MB ]
Metadata
JSON: 831-1.0052995.json
JSON-LD: 831-1.0052995-ld.json
RDF/XML (Pretty): 831-1.0052995-rdf.xml
RDF/JSON: 831-1.0052995-rdf.json
Turtle: 831-1.0052995-turtle.txt
N-Triples: 831-1.0052995-rdf-ntriples.txt
Original Record: 831-1.0052995-source.json
Full Text
831-1.0052995-fulltext.txt
Citation
831-1.0052995.ris

Full Text

A IONG F E B I C E RAYLEIGE WAVE EXPERIMENT IN THE VANCOUVER ISLAND REGICN by GERMAN J, PABEOA B . S c , C a l i f o r n i a S t a t s P o l y t e c h n i c U n i v e r s i t y , 1971 A THESIS SUE PIT TEE IN FART3AI F U I F I I E O T CF THE REQUIREMENTS FCR THE DEGREE OF MASTER CF SCIENCE i r t h e D e p a r t m e n t c f G e o p h y s i c s and A s t r c n o t r y We a c c e p t t h i s t h e s i s as c c n f c r i r i n c t c t h e r e q u i r e d s t a n d a r d The U n i v e r s i t y c f E r i t i s h C o l u m b i a May, 1975 In p resent ing t h i s t he 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 t permiss ion fo r ex ten s i ve copying of t h i s t he 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 ep re sen t a t i v e s . It i s understood that copying or p u b l i c a t i o n of t h i s t he 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 permi s s ion . Department of The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date 2-3 TfrA-y /?7jT i AESTB ACT A study cf the d i s p e r s i o n of l o n g - p e r i o d E a y l e i g h waves was proposed i n c r d e r to a c q u i r e a d d i t i o n a l knowledge a t c u t the l i t h c s p h e r i c s t r u c t u r e c f the Vancouver I s l a n d r e g i o n . Three p o r t a b l e , l o n g - p e r i o d seismographs were designed and b u i l t t c operate i n f i e l d c o n d i t i o n s . An a r r a y was e s t a b l i s h e d with s t a t i o n s at V i c t o r i a , Vancouver and Quadra I s l a n d ; during s i x weeks of o p e r a t i o n , s e v e r a l earthquakes were rec o r d e d , of which two were a l i g n e d c o n v e n i e n t l y viith the a r r a y . Another network with s t a t i o n s at U c l u e l e t , Quadra I s l a n d and v i c t o r i a was set up l a t e r ; no usable data were recorded. Cne earthquake r e c o r d was chosen f c r a n a l y s i s , and g r o u p - v e l o c i t y d i s p e r s i o n c a l c u l a t i o n s were begun. Eccr r e s o l u t i o n on t h e s e data and a l a c k cf ether usable r e c c r d s prevented the c o n t i n u a t i o n c f the data p r o c e s s i n g . No c o n c l u s i o n s are drawn abcut the l i t h c s p h e r i c s t r u c t u r e ; however, recommendations are made r e g a r d i n g p o s s i b l e f u t u r e e x p e r i m e n t a t i o n with the e x i s t i n g apparatus. i i T A BLE OF CONTENTS I . I n t r o d u c t i o n 1 1.1 G e o p h y s i c a l B a c k g r o u n d 1 1.2 The P r o j e c t ^ I I . I n s t r u m e n t a t i o n 6 2.1 I n t r o d u c t i o n 6 2.2 The S e i s m o m e t e r s 6 2.3 A m p l i f i c a t i o n a r d F i l t e r i n g 9 2.4 R e c o r d i n g S y s t e m 12 2.5 C a l i b r a t i o n 14 2.6 A c c u r a c y 16 I I I . F i e l d Ex p e r i roe n t s 13 3.1 I n t r o d u c t i o n 18 3.2 T y p i c a l F i e l d I n s t a l l a t i o n . 18 3.3 C h r o n o l o g i c a l A c c o u n t 20 3.4 R e s u l t s 21 3.5 The S e c o n d F i e l d E x p e r i m e n t 24 I V . A n a l y s i s 27 4.1 I n t r o d u c t i o n 27 4.2 D i g i t i z a t i o n and o t h e r P r e l i m i n a r i e s 27 4.3 D i s p e r s i o n A n a l y s i s 3 0 4.4 C a l c u l a t i o n o f P h a s e V e l o c i t i e s 32 4.5 M u l t i p l e F i l t e r A n a l y s i s 34 4.6 A p p l i c a t i o n t c R e a l D a t a 36 4.7 D i g i t a l C o m p u t a t i o n o f P h a s e V e l o c i t i e s 38 i i i V. C o n c l u s i o n 41 5.1 I n t r o d u c t i o n 41 5.2 P r o b l e m s w i t h t h e Mass P o s i t i o n 41 5.3 V e r i f i c a t i o n c f t h e P h a s e C a l i b r a t i o n .......... 42 5.4 O t h e r I n s t r u m e n t a l C o n s i d e r a t i o n s 43 B i b l i o g r a p h y 44 A p p e n d i x — O p e r a t i o n Of The A p p a r a t u s 47 A. 1 D e s c r i p t i o n 47 A.2 I n s t a l l a t i o n P r o c e d u r e 49 A. 3 T e m p e r a t u r e C o n t r o l l e r 50 A.4 C a l i b r a t i o n and O p e r a t i o n 51 i v LIS T OF FIGURES 1.1 M a j o r p l a t e t e c t o n i c f e a t u r e s i n t h e v i c i n i t y o f V a n c o u v e r I s l a n d 2. 2.1 C i r c u i t d i a g r a m c f t h e t e m p e r a t u r e c o n t r o l l e r .... 8 2.2 S e i s m o m e t e r d a m p i n g c o m p o n e n t s 10 2.3 C i r c u i t d i a g r a m o f t h e a c t i v e l e w - p a s s f i l t e r .... 11 2.4 The W i l l m o r e b r i d g e as a p p l i e d t o t h e c a l i b r a t i o n o f t h e p o r t a b l e s y s t e m s 15 2.5 C a l i b r a t i o n c o n f i g u r a t i o n o f t h e p o r t a b l e s e i s m o g r a p h s 16 3.1 Map s h o w i n g l o c a t i o n s o f s e i s m i c s t a t i o n s o p e r a t e d i n t h e autumn o f 1973 , 22 3.2 Phase v e l o c i t y d e t e r m i n a t i o n w i t h a t r i p a r t i t e a r r a y 23 3.3 L o c a t i o n s o f f i e l d s t a t i o n s o p e r a t e d f r o m F e b r u a r y t o A p r i l , 1974 25 4.1 D i g i t i z a t i o n p r o c e d u r e 2.8 4.2 VCT and QUA r e c o r d s c f t h e 5 O c t o b e r 1973 e a r t h q u a k e 29 4.3 R e s u l t o f m u l t i p l e f i l t e r i n g a n a l y s i s a p p l i e d t o t h e QUA r e c o r d o f C h i l e e a r t h q u a k e 37" A. 1 W i r i n g d i a g r a m c f t h e i n s t r u m e n t p a n e l s 48 A.2 D e v i c e u s e d t o c h e c k t h e n a t u r a l p e r i o d c f t h e s e i s m o m e t e r s 49 V L I S T OF TABLES I. P o r t a b l e s t a t i o n s — T e s t s and f i e l d s i t e s . . . . . . . . . 19 I I . Earthquakes r e c o r d e d— A uturon, 1 973 23 v i ACKNOWLEDGMENT F o r t h e i r a s s i s t a n c e and a d v i c e d u r i n g t h e e x p e r i m e n t a l s t a g e o f t h e p r o j e c t , t h e a u t h c r i s i n d e b t e d t o Mr. Eo f c e r t M e l d r u m and Mr. H a j i m e Ueda. The p a t i e n c e and h e l p f u l n e s s o f Dr. Ron C l o w e s d u r i n g t h e p r e p a r a t i o n o f t h e m a n u s c r i p t a r e a l s o g r a t e f u l l y a c k n o w l e d g e d . Dr. G a r y R o g e r s , o f t h e V i c t o r i a G e o p h y s i c a l O b s e r v a t o r y , and Mr. O s c a r E d w a r d s , o f U c l u e l e t , g r a c i o u s l y l e n t t h e i r s e r v i c e s t o w a r d s t h e o p e r a t i o n o f t h e f i e l d s i t e s . Mr. Ray G r i g g m o n i t o r e d t h e Q u a d r a I s l a n d s i t e and e x t e n d e d h i s h o s p i t a l i t y t c t h e a u t h c r a n d h i s c o m p a n i o n s on s e v e r a l o c c a s i o n s . The D e f e n c e R e s e a r c h B e a r d c f Canada s u p p o r t e d t h i s p r o j e c t u n d e r g r a n t number 95 1 1-76 (UG) . 1 I . INTRODUCTION 1.1 G e o p h y s i c a l B a c k g r o u n d The p l a t e t e c t o n i c s o f t h e n o r t h e a s t e r n P a c i f i c r e g i c n h a s been d e s c r i b e d by A t w a t e r (1970) , S r i v a s t a v a (1973) and o t h e r s . A t r i p l e j u n c t i o n o f t h e f a u l t - r i d g e - t r e n c h t y p e b e t w e e n t h e l a r g e A m e r i c a n a n d P a c i f i c p l a t e s and t h e much s m a l l e r J u a n de F u c a p l a t e i s b e l i e v e d t o be l o c a t e d n e a r 51°N and 130ow, o f f N o r t h e r n V a n c o u v e r I s l a n d ( F i g . 1 . 1 ) . S t a c e y (1974) s u g g e s t s t h a t t h e o c e a n i c p l a t e m a t e r i a l p r o d u c e d a t t h e J u a n de F u c a - 2 x p l o r e r r i d g e s y s t e m h a s been s u b d u c t e d o b l i q u e l y u n d e r t h e A m e r i c a n p l a t e , and t h a t t h e r e m n a n t o f i t s o l d l i t h o s p h e r i c m a t e r i a l i s i n f l u e n c i n g t h e c u r r e n t t e c t o n i c p r o c e s s e s o f t h e C a n a d i a n C o r d i l l e r a . S u p p o r t i n g e v i d e n c e f c r t h i s h y p o t h e s i s , b a s e d on s e i s m i c i t y a n d f o c a l mechanism s t u d i e s , i s p r o v i d e d t y C h a n d r a ( 1 9 7 4 ) . However, no a c t i v e B e n i o f f z o n e e x i s t s t o t h e e a s t o f t h e p r o p o s e d l o c a t i o n o f t h e t r e n c h . A n o m a l o u s r e s u l t s a r e t h u s o b t a i n e d f o r t h e c r u s t a l s t r u c t u r e o f V a n c o u v e r I s l a n d . G r a v i t y d a t a a n a l y z e d by S t a c e y ( 1973) • l e a d t o e i t h e r a t h i n c r u s t (20 km d e p t h t o c r u s t / m a n t l e b o u n d a r y ) w i t h low m a n t l e d e n s i t i e s (3.2 g / c m 3 ) , o r t o a t h i c k , d e n s e c r u s t (60 t o 70 km and 3.09 g / c m 3 ) . S e i s m i c r e f r a c t i o n s u r v e y s f r o m t h e 1 9 6 0 ' s n o t e d t h e a b s e n c e o f t h e Pn p h a s e a s a f i r s t a r r i v a l t o d i s t a n c e s o f 360 km ( W h i t e and S a v a g e , 1 9 6 5 ) . A l a y e r e d c r u s t a l 2 F i g u r e 1.1 M a j o r p l a t e t e c t o n i c f e a t u r e s i n t h e v i c i n i t y o f V a n c o u v e r I s l a n d The l o c a t i o n s o f t h e r i d g e c r e s t s and t h e , • s p e c u l a t i v e b o u n d a r y b e t w e e n t h e J u a n de F u c a and A i r e r i c a n p l a t e s a r e shown. A d a p t e d f r o m S t a c a y ( 1 9 7 4 ) . m o d e l , w i t h 6 km o f u p p e r c r u s t a l r o c k s u n d e r l a i n by 45 km o f m a t e r i a l w i t h a v e l o c i t y o f 6.8 km/s, was t h e p r e f e r r e d i n t e r p r e t a t i o n c f t h e s e s e i s m i c d a t a . Tseng (1968) a n a l y z e d t h e same e x p l o s i o n d a t a and p o s t u l a t e d a f o u r - l a y e r c r u s t a l m o d e l and t h e n o n - e x i s t e n c e c f t h e M c h o r o v i c i c d i s c o n t i n u i t y u n d e r V a n c o u v e r I s l a n d . W i c k e n s (1971) i n t e r p r e t e d s u r f a c e wave p h a s e - v e l o c i t y d a t a f r c m C a n a d i a n n e t w o r k s t a t i o n s and f o u n d h e t e r o g e n e i t y i n t h e u p p e r m a n t l e as w e l l a s a l e w v e l o c i t y z o n e (4.2 km/s) j u s t b e l o w a 30-km deep c r u s t a l s e c t i o n ; i t s h o u l d be n o t e d , h o w e v e r , t h a t t h e d a t a i n c l u d e d 3 r e c o r d i n g s f r o m FNT, I DM and F S J s t a t i o n s , w h i c h l i e o u t s i d e V a n c o u v e r I s l a n d . Compared t o e a s t e r n N o r t h A m e r i c a , t h e w e s t e r n C o r d i l l e r a i s a r e g i o n o f h i g h u p p e r - m a n t l e e l e c t r i c a l c o n d u c t i v i t i e s ( C a n e r , 1 9 7 0 ) , w h i c h s u g g e s t s an a n o m a l o u s l y t h i n l i t h o s p h a r e o r e v e n a l a y e r o f p a r t i a l m e l t i n g ( S t a c e y , 1974) . Heat f l e w d a t a g e n e r a l l y s u p p o r t t h i s i n t e r p r e t a t i o n . Hyndman (1975) has s u m m a r i z e d e x i s t i n g h e a t f l o w m e a s u r e m e n t s a c r o s s B r i t i s h C o l u m b i a and i n t e r p r e t e d them i n t h e l i g h t o f c u r r e n t p l a t e t e c t c n i c t h e o r i e s . A c c o r d i n g t o t h e s e r e s u l t s , t h e h i g h h e a t f l o w (and t h i n l i t h o s p h e r e ) o f t h e w e s t e r n C o r d i l l e r a c h a n g e s t c much l e w e r h e a t f l o w (and t h i c k e r l i t h e s p h e r e ) b e n e a t h t h e S t r a i t o f G e o r g i a and V a n c o u v e r I s l a n d ; t h e h e a d s o f t h e c c a s t a l i n l e t s f o r m t h e a x i s c f t h e t r a n s i t i o n . A t h i c k e r c r u s t and l i t h o s p h e r a u n d e r n e a t h V a n c o u v e r I s l a n d a r e t h e r e f o r e c o n s i s t e n t w i t h t h e s e i s m i c r e s u l t s d e s c r i b e d a b o v e . T h u s , t h e t o t a l i t y o f t h e g e o p h y s i c a l e v i d e n c e s u g g e s t s t h a t t h e J u a n de F u c a p l a t e i s b e i n g s u b d u c t e d u n d e r t h e A m e r i c a n p l a t a , w i t h t h e d o w n w a r p i n g b e g i n n i n g a t a b c u t t h e c o n t i n e n t a l m a r g i n . The c r u s t / l i t h e s p h e r e s e g u e n c e o f t h e V a n c o u v e r I s l a n d r e g i o n i s l i k e l y t o be c o m p l e x . T h e r e f o r e , a d d i t i o n a l g e o p h y s i c a l s t u d i e s a r e r e q u i r e d t o p r o v i d e new i n f o r m a t i o n f o c u s s i n g on t h e p r o b l e m . 4 1 • 2 The P r o j e c t I n r e s p o n s e t o t h e n e e d f o r more g e o p h y s i c a l e v i d e n c e c o n c e r n i n g t h e l i t h o s p h e r i c s t r u c t u r e o f t h e V a n c o u v e r I s l a n d r e g i o n , a s u r f a c e wave s t u d y was p l a n n e d a l o n g t h e l i n e s m e n t i o n e d by W i c k e n s ( 1 9 7 1 ) . He had s u g g e s t e d t h a t f u r t h e r e x p e r i m e n t a t i o n w i t h p o r t a b l e e q u i p m e n t would be d e s i r a b l e , s p e c i f i c a l l y t o o b t a i n f u n d a m e n t a l and h i g h e r - m o d e s u r f a c e wave d a t a a l o n g l i n e s where s e i s m i c r e f r a c t i o n d a t a e x i s t s . T h r e e p o r t a b l e l o n g - p e r i c d v e r t i c a l - c o m p o n e n t s e i s m o m e t e r s and r e c o r d i n g e q u i p m e n t were a v a i l a b l e . I n s t r u m e n t a t i o n s t u d i e s b e g u n by B o l d u c (1971) were c o n t i n u e d i n 1 9 7 2 , w i t h t h e aim o f r e c o r d i n g t e l e s e i s m i c R a y l e i g h s u r f a c e waves i n a r r a y s on V a n c o u v e r I s l a n d . The f r e g u e n c y band e x t e n d e d f r o m 0.0 1 Hz t o 0.2 Hz, t o a l l o w s h e a r - w a v e v e l o c i t y i n t e r p r e t a t i o n t o a b o u t 100 km d e p t h . Mass p o s i t i o n s t a b i l i t y t o ±2 mm had t o be a c h i e v e d by c o n t r o l l i n g t h e t e m p e r a t u r e c f t h e s e i s m o m e t e r s . The f i e l d s t a t i o n s r e q u i r e d AC power and h i g h w a y a c c e s s , w h i c h r e s t r i c t e d t h e c h c i c e o f l o c a t i o n s a v a i l a b l e t o t h e e x p e r i m e n t e r . The a n a l y s i s c f s u r f a c e wave d i s p e r s i o n i s q u i t e w e l l d e v e l o p e d . G roup and p h a s e v e l o c i t y d i s p e r s i o n c u r v e s . m a y be o b t a i n e d f r o m t h e a p p l i c a t i o n c f m u l t i p l e f i l t e r a n a l y s i s ( D z i e w o n s k i and H a l e s , 1972) and c r o s s - m u l t i p l i c a t i c n m e t h o d s ( B i o c h and H a l e s , 1968) t c d i g i t i z e d s e i s m o g r a m s . 5 Assuming a l a y e r e d c r u s t a l s t r u c t u r e , t h e o r e t i c a l R a y l e i g h wave d i s p e r s i o n curves can be produced with computer programs, such as those developed by H a r k r i d e r and Anderson (1962) . From t h e s e , s a t i s f a c t o r y c r u s t a l models can be determined by l e a s t squares i n v e r s i o n techniques (Dorian and Ewing, 1962) , where other knowledge of the g e o p h y s i c a l s i t u a t i o n may be brought t o bear. 6 I I . INSTRUMENTATION 2.1 Introduction L o n g - p e r i o d s e i s m o g r a p h s r e c c r d g r o u n d m c t i c n e v e r - a f r e g u e n c y r a n g e c h o s e n t c e m p h a s i z e s u r f a c e wave a r r i v a l s a n d f r e e o s c i l l a t i o n s o f t h e e a r t h . I n t h i s s t u d y , t h r e e l o n g - p e r i o d , v e r t i c a l - c o m p o n e n t p o r t a b l e s e i s m i c s y s t e m s were d e s i g n e d and b u i l t t o o p e r a t e u n d e r f i e l d c o n d i t i o n s . T h ey f o r m e d a t h r e e s t a t i o n n e t w o r k e s t a b l i s h e d p r i m a r i l y t o r e c o r d R a y l e i g h wave t r a i n s g e n e r a t e d by t e l e s e i s m i c s o u r c e s . The f r e q u e n c y band o f o p e r a t i o n e x t e n d s f r o m 0,01 Hz t o 0.2 Hz, and t h e r e s p o n s e i s s h a p e d t y t h e f r e q u e n c y c h a r a c t e r i s t i c s c f t h e s e n s o r s a s w e l l a s a n e t w o r k o f f i l t e r s . S y s t e m a t i c c a l i b r a t i o n s a r e n e c e s s a r y t o d e t e r m i n e t h e e x a c t r e s p o n s e and t o c o m p e n s a t e f o r c h a n g i n g e n v i r o n m e n t a l f a c t o r s . 2.2 The S e i s m c m s t e r s T h r e e l o n g - p e r i o d v e r t i c a l s e i s m o m e t e r s , two o f w h i c h w e r e G e o t e c h model S L - 2 1 0 ' s and one a Co 1 u m b i a - d e s i g n e d S p r e n g n e t h e r m o d e l S-5007-V, were a v a i l a b l e f o r t h i s r e s e a r c h . T h e i r e l e c t r i c a l and m e c h a n i c a l c h a r a c t e r i s t i c s w e r e d e s c r i b e d i n d e t a i l by B c l d u c (1971) , who a l s o made r e c o m m e n d a t i o n s c o n c e r n i n g t h e s e i s m o g r a p h c o n f i g u r a t i o n . E a c h i n s t r u m e n t c o n s i s t s c f two p i c k - u p c o i l s w h i c h move 7 r e l a t i v e t o p e r m a n e n t s r a g n e t s , a n d w h i c h a r e a n c h o r e d t o t h e boom i n a manner t h a t f a i t h f u l l y r e p r o d u c e s t h e l a t t e r ' s m o t i o n . Hence, t h e e l e c t r i c a l c u t p u t i s r e l a t e d t c t h e v e l o c i t y o f boom t r a v e l r a t h e r t h a n t o i t s d i s p l a c e m e n t . One of t h e c o i l s i n t h e p a i r i s t r e a t e d as a main c e i l , t h e o t h e r as a c a l i b r a t i o n c e i l . I n t h e S p r e n g n e t h e r i n s t r u m e n t t h e two c o i l s a r e i d e n t i c a l . However, i n t h e G e o t e c h i n s t r u m e n t s t h e c a l i b r a t i o n c e i l c o n s i s t s o f f e w e r t u r n s t h a n t h e main c o i l , a l t h o u g h b o t h c o i l s a r e wound cn t h e same f o r m , s h a r i n g t h e same magnet. T h e s e c h a r a c t e r i s t i c s n e c e s s i t a t e d d i f f e r e n t c a l i b r a t o n c i r c u i t s i n t h e r e s p e c t i v e f i e l d a p p a r a t u s . The s e i s m o m e t e r s may be a d j u s t e d s o t h a t t h e y o s c i l l a t e f r e e l y a t a s e l e c t e d p e r i c d b e t w e e n 10 and 30 s e c o n d s . F or a l l t h r e e s e i s m o m e t e r s a p e r i o d o f 20 s e c o n d s was c h o s e n a s t h e c e n t r e o f a s t a b l e b a n d . M e l t o n (1971) e x p l a i n s i n d e t a i l t h e m a t h e m a t i c a l t h e o r y o f t h e L a C o s t e s u s p e n s i o n , w h i c h p r o v i d e s t h e s e l e n g n a t u r a l p e r i o d s . I t was known f r o m E o l d u c ' s (1971) s t u d y t h a t t h e v e r t i c a l p o s i t i o n o f t h e boom d r i f t e d w i t h c h a n g e s i n a m b i e n t t e m p e r a t u r e , t h e r e b y i n t r o d u c i n g c h a n g e s i n t h e p h y s i c a l p a r a m e t e r s c f t h e e l e c t r o m a g n e t i c s e i s m o m e t e r , a. g . , t h a d a m p i n g moment c o n s t a n t , t h e s p r i n g moment c o n s t a n t , t h e c e i l m e t e r c o n s t a n t , a s w e l l a s t h e n a t u r a l p e r i o d ( d s f i n a d a s i n K o l l a r and R u s s e l l , 1 9 6 6 ) . The phase r e s p o n s e o f t h e i n s t r u m e n t f o r a g i v e n i n p u t was a f f e c t e d by t h e s e c h a n g e s . W h i l e t h e S p r e n g n e t h e r s e i s mc ire t e r had 8 b u i l t - i n m e c h a n i c a l c o m p e n s a t i o n f o r t e m p e r a t u r e d r i f t , t h e more c o m p a c t G e o t e c h s d i d n e t have s u c h a f e a t u r e . I n o r d e r f o r a f i e l d c a l i b r a t i o n t o r e m a i n v a l i d , i t was n e c e s s a r y t o r e s t r i c t m a s s - p o s i t i o n d r i f t t o l e s s t h a n ± 2 mm, w h i c h c a l l e d f o r a r e l i a b l e method c f h o l d i n g t e m p e r a t u r e c h a n g e s t o l e s s t h a n ± 0.5°C. F o r t h i s p u r p o s e , a h e a t e r w h i c h c o u l d k e e p t h e e n t i r e s e i s m o m e t e r and a s u r r o u n d i n g e n c l o s u r e a t a f i x e d t e m p e r a t u r e was d e s i g n e d . R.D. Meldrum d e v e l o p e d a d e v i c e c o n s i s t i n g o f a c o m p a r i s o n b r i d g e , w i t h a t h e r m i s t o r a s t h e p r o b e and a z e r o - v c l t a g e s w i t c h t e s t i n g t h e c u r r e n t f l o w and t h e n c e c o n t r o l l i n g t h e g a t e o f a t r i a c ( F i g . 2 . 1 ) . T h i s i n t u r n s w i t c h e s a l i g h t b u l b w h i c h a c t s a s a h e a t s o u r c e , g i v i n g a l s o a v i s u a l c h e c k on p e r f o r m a n c e . A l t h o u g h t h i s new d e v i c e c o u l d h o l d a s t e a d y 120 y 6oHz Heavy t>uty 5Wt Bui b F i g u r e 2.1 C i r c u i t d i a g r a m o f t h e t e m p e r a t u r e c o n t r o l l e r -9 t e m p e r a t u r e i n s i d e t h e t h e r m a l l y i n s u l a t e d s e i s m o m e t e r e n c l o s u r e s w i t h v a r i a n c e s c f l e s s t h a n + 0.2°C, power i n t e r r u p t i o n s i n t h e f i e l d s i t e s were common enough t o r e s t r i c t i t s u s e f u l n e s s . The s o l u t i o n s a v a i l a b l e were ( i ) t h e u s e o f b a t t e r i e s t c p r o v i d e power t o t h e h e a t e r and ( i i ) t h e p r e s e n c e o f an o p e r a t o r m o n i t o r i n g m a s s - p c s i t i c n c h a n g e s . The f i r s t a p p r o a c h was s e t a s i d e due t o t h e r e l a t i v e l y h e a v y power d r a i n and t h e c o n t i n u o u s n a t u r e c f t h e p r o j e c t . D a i l y c h e c k s o f m a s s - p o s i t i o n were o b v i a t e d i n t h e c a s e o f t h e S p r e n g n e t h e r s e i s m o m e t e r , w h i c h i s w e l l c o m p e n s a t e d ; t h e s t a t i o n s u t i l i z i n g G e o t e c h s e i s m o m e t e r s were m o n i t o r e d . Upon e x a m i n a t i o n o f t h e r e c o r d s , t h e s y s t e m s had t o be r e c a l i b r a t e d by r e c r e a t i n g t h e c o n d i t i o n s w h i c h e x i s t e d a t t h e t i m e o f any i n t e r e s t i n g e a r t h q u a k e s . I t i s d i f f i c u l t t o e s t i m a t e j u s t how much u n c e r t a i n t y i s i n t r o d u c e d by t h i s method, b u t i t i s c e r t a i n l y n e t a n i d e a l s o l u t i o n . 2.3 A S E l i f i c a t i o n and F i l t e r i n cj The s i g n a l f r c m t h e main c e i l c f t h e s e i s m o m e t e r must p a s s t h r o u g h an e l e c t r o n i c n e t w o r k w h i c h s h a p e s t h e r e s p o n s e t o t h e d e s i r e d c h a r a c t e r i s t i c s . Damping i s p r o v i d e d by t h e t o t a l r e s i s t a n c e p r e s e n t i n t h e l o o p c o n t a i n i n g t h e main c o i l , t h e a m p l i f i e r i n p u t i m p e d a n c e , and a damping r e s i s t o r ( F i g . 2.2) . The l a t t e r i s c h o s e n t c make t h e s e i s m o m e t e r b e h a v e a s a s l i g h t l y u nderdamped o s c i l l a t o r , w i t h a damping 10 F i g u r e 2.2 S e i s m o m e t e r d a m p i n g c o m p o n e n t s F o r t h e G e o t e c h s e i s m o m e t e r s , R1 = 1.8 kchm, R2 = °° . F o r t h e S p r e n g n e t h e r s e i s m o m e t e r , R1 = 0, R2 = 82 0 ohm. c o e f f i c i e n t o f 0.7 t c 0.9. To a c h i e v e t h i s , t h e G e o t e c h s e i s m o m e t e r s r e q u i r e a s e r i e s r e s i s t o r R1, w h e r e a s t h e S p r e n g n e t h e r i s damped by a p a r a l l e l c o m b i n a t i o n c f R2 and t h e a m p l i f i e r i n p u t i m p e d a n c e . The s i g n a l f r o m t h e G e o t e c h i s n e c e s s a r i l y a t t e n u a t e d i n c o m p a r i s o n w i t h t h a t c f t h e S p r e n g n e t h e r . The a m p l i f i e r s u s e d a r e G e o t e c h m o d e l AS-330, w h i c h h a v e a b a l a n c e d i n p u t , w i t h a 4 kchm i m p e d a n c e . They e m p l o y o p e r a t i o n a l a m p l i f i e r s t o p r o v i d e two o u t p u t s t a g e s . The l o w - g a i n o u t p u t has a maximum a m p l i f i c a t i o n o f 70 d b , w h i c h c a n be a t t e n u a t e d i n 6 db s t e p s t o a minimum o f 28 db. The h i g h - g a i n o u t p u t g i v e s t h e c p t i c n c f a d d i t i o n a l g a i n s t e p s o f 3 0 , 3 6 , o r 42 db. E o t h o u t p u t s a r e n o r m a l l y r e c o r d e d ; a t y p i c a l f i e l d s e t t i n g i s 64 db g a i n f r c m t h e l o w o u t p u t w i t h 30 db s e p a r a t i o n , f o r a t o t a l a m p l i f i c a t i o n c f 94 db, e q u i v a l e n t t o a v o l t a g e g a i n o f 50000 t i m e s . B o t h o u t p u t s a r e f i l t e r e d by a s i n g l e s e t o f p a s s i v e RC f i l t e r s , w i t h f r e q u e n c y c o r n e r s a t 0.01 and 5.0 Hz, and 12 d b / o c t a v e r o l l - o f f . T h i s i s t h e l o w e s t b a n d p a s s r a n g e 11 a v a i l a b l e f r o m t h e m a n u f a c t u r e r f o r t h e AS-330 a m p l i f i e r . I t i s n o t p r a c t i c a l f c r l o n g p e r i o d s u r f a c e wave e x p e r i m e n t a t i o n b e c a u s e o f i n c r e a s e d t e m p e r a t u r e d r i f t i f an e x t e n s i o n i s d e s i r e d b e l o w 0.01 Hz; t h i s a p p e a r s t c be due t o t h e c h a r a c t e r i s t i c s c f t h e c a p a c i t o r s e m p l o y e d i n t h e f i l t e r s . An a c t i v e l o w - p a s s f i l t e r was d e s i g n e d t o a t t e n u a t e f r e q u e n c y c o m p o n e n t s a b o v e 0.04 Hz ( 2 5 - s e c p e r i o d ) and i n s e r t e d a f t e r t h e AS-330 a m p l i f i e r h i g h - g a i n s t a g e . As shown i n F i g . 2.3, i t c o n s i s t s o f an o p e r a t i o n a l a m p l i f i e r f o l l o w i n g an RC n e t w o r k w i t h c o r n e r f r e q u e n c y o f F i g u r e 2.3 C i r c u i t d i a g r a m o f t h e a c t i v e l e w - p a s s f i l t e r 0. 036 Hz ( 2 8 - s e c p e r i o d ) , and i t f e a t u r e s max i mal l y - f l a t 12 r e s p o n s e b e l o w t h e c o r n e r , w i t h a 12 d b / o c t a v e r c l l - c f f . The g a i n i n t h e f l a t - r e s p o n s e r e g i o n c a n be a d j u s t e d a l t h o u g h a p r a c t i c a l l i m i t a t i o n i s t h e p h y s i c a l s i z e o f t h e c a p a c i t o r s (Tobey e t a l . , 1971, pp. 295- 2 9 8 ) . I n o p e r a t i o n , t h e o u t p u t c f the a c t i v e f i l t e r , i s d i v i d e d b y an a t t e n u a t i n g n e t w o r k and f e d t c t h e t a p e r e c o r d e r i n p u t a t r e l a t i v e l e v e l s o f 0 d b , -12 db and -24 d b . T h i s p r o v i s i o n was made t o accommodate l a r g e e a r t h q u a k e s w i t h i n t h e 30 t c 35 db d y n a m i c r a n g e o f t h e t a p e r e c o r d e r . D u r i n g c a l i b r a t o n , t h e l o w - g a i n o u t p u t o f t h e a m p l i f i e r i s t h e f i l t e r i n p u t and t h e f i l t e r e d s i g n a l i s r e c o r d e d a t r e l a t i v e l e v e l s o f 0 and -12 db. I n t h i s m anner, t h e c a l i b r a t i o n c a n be p e r f o r m e d w i t h o u t c h a n g e s i n t h e i n p u ; t d r i v i n g v o l t a g e , and w i t h o u t f e a r c f o v e r l o a d i n g t h e t a p e r e c o r d e r i n p u t . 2*4 Rs£2£ding_ S y s t e m S e v e n - c h a n n e l f r e q u e n c y - m o d u l a t e d a n a l o g t a p e r e c o r d e r s m a n u f a c t u r e d by G e c t e c h (model 17373) and P r e c i s i o n I n s t r u m e n t s (models 5104 and 5100) were u t i l i z e d . l a p e s p e e d s o f 15/160 i . p . s . a l l o w e d f i v e d a y s of c o n t i n u o u s r e c o r d i n g . The i n p u t s e n s i t i v i t i e s were a d j u s t e d t c ± 2.8 v o l t s f o r ± HQ% d e v i a t i o n i n c a r r i e r f r e q u e n c y , with, a s t a n d a r d 84.4 Hz c e n t r e f r e q u e n c y . . I n p u t i m p e d a n c e s r a n g e d b e t w e e n 10 kohm and 50 kchm, s i n g l e - e n d e d t o g r o u n d , w h i c h were h i g h c o m p a r e d t o t h e 1 kohm a s s o c i a t e d w i t h t h e c u t p u t 13 a t t e n m . t o r b r i d g e t h a t f o l l o w s t h e a c t i v e l e w - p a s s f i l t e r . Maximum s i g n a l - t o - n c i s e r a t i o s , w h i c h d e t e r m i n e t h e d y n a m i c r a n g e , ware n o r m a l l y b e t w e e n 30 and 35 db , w i t h an o c c a s i o n a l i m p r o v e m e n t t o 38 db d e p e n d i n g upon t h e q u a l i t y o f t h e t a p e o r t h e s t a t e o f t h e r e c o r d i n g h e a d s . Tape s p a e d v a r i a t i o n s , w h i c h a r e r e s p o n s i b l e f o r f l u t t e r , were c o u n t e r e d d u r i n g t h e p l a y b a c k a nd d i g i t i z a t i o n p r o c e d u r e s (see C h a p t e r I V ) . T i m e i n f o r m a t i o n was r e c o r d e d cn a l l t a p e s t o e n a b l e p r o p e r a l i g n m e n t o f r e c o r d s f r o m d i f f e r e n t s t a t i o n s . WWVB r e c e i v e r s , D e v e l c o m o del 3202A and D r u i d Mk. I , d e m o d u l a t e d t h e r a d i o s i g n a l and p r o v i d e d a c o d e d o u t p u t w h i c h i s a t t e n u a t e d and r e c o r d e d on t a p e . As a b a c k - u p , c h r o n o m e t e r s ( S p r e n g n e t h e r model TS-100-R) and U B C - d e s i g n e d t i m i n g u n i t s w e r e a v a i l a b l e ; t h e s e , h o w e v e r were n e t d e p e n d a b l e o v e r l o n g * p e r i o d s o f t i m a , due t o d r i f t p r o b l e m s , and were e l i m i n a t e d . AC power f o r t h e s y s t e m i s d e r i v e d f r o m t h e m a i n s s u p p l y a t t h e r e c o r d i n g s t a t i o n s . F o r e q u i p m e n t r e q u i r i n g d .c. power, s t a n d a r d power s u p p l i e s were u s e d . Wooden e n c l o s u r e s were b u i l t t o house t h e a m p l i f i e r , a c t i v e f i l t e r s and t h e i r power s u p p l y , a s w e l l a s t h e d i s t r i b u t i o n n e t w o r k e n d i n g l o g i c a l l y a t t h e t a p e r e c o r d e r i n p u t . The o p e r a t i o n and c i r c u i t d i a g r a m a r e d e s c r i b e d i n t h e A p p e n d i x . 14 2«5 C a l i b r a t i o n The t o t a l r e s p o n s e o f a s e i s m o g r a p h i n a g i v e n f r e g u e n c y r a n g e i s known i f b o t h t h e a m p l i t u d e , i . e . , t h e o u t p u t f o r a g i v e n g r o u n d m o t i o n , and the phase d e l a y a r e a l s o known. D u r i n g t h e c a l c u l a t i o n o f p h a s e v e l o c i t i e s , t h e p h a s e r e s p o n s e must be w e l l c a l i b r a t e d a s i t i s n e c e s s a r y t o remove t h e p h a s e f u n c t i o n i n t r o d u c e d by t h e i n s t r u m e n t . I f t h e c o m p u t a t i o n i s made f o r a p a i r o f n e a r l y i d e n t i c a l s e i s m o g r a p h s , t h e a s s u m p t i o n o f e q u a l i t y o f p h a s e l a g s i s j u s t i f i e d . H o w e v e r , when one d e a l s w i t h d i f f e r e n t s e n s o r s a s w e l l a s s e n s o r s w i t h f l u c t u a t i n g mass p o s i t i o n s , t h e n e c e s s i t y o f r o u t i n e p h a s e c a l i b r a t i o n s becomes c l e a r . The s t a n d a r d method o f c a l i b r a t i n g s e i s m o g r a p h s , f c r e x a m p l e t h a t u s e d f o r c a l i b r a t i n g C a n a d i a n n e t w o r k s t a t i o n s , * i s d e s c r i b e d by W i l l u i o r e ( 1 9 5 9 ) . I t u s e s an i m p e d a n c e b r i d g e w i t h t h e s e i s i t c m e t e r main c e i l a s t h e unknown b r a n c h , a n d i t i s b a l a n c e d by a r e s i s t o r and c a p a c i t o r n e t w o r k w h i l e a l t e r n a t i v e l y c l a m p i n g and unc l a m p i n g the boom o f t h e s e i s m o m e t e r , as i t i s d r i v e n t h r o u g h t h e d e s i r e d f r e q u e n c y r a n g e . The a b s o l u t e a m p l i t u d e r e s p o n s e r e s u l t s f r o m t h e b a l a n c e c o n d i t i o n s . The p h a s e c a l i b r a t i c n c a n be o b t a i n e d w i t h a W i l l m o r e b r i d g e i f t h e o u t p u t s i g n a l i s c o m p a r e d w i t h t h e i n p u t d r i v i n g v o l t a g e f c r e a c h f r e q u e n c y , c o m p o n e n t . U s i n g t h e t a p e r e c o r d e r t o m o n i t o r b o t h s i g n a l s , a r e c o r d i s p r o d u c e d w h i c h can be d i g i t i z e d and a n a l y z e d w i t h s t a n d a r d c o m p u t e r 1 5 p r o g r a m s . However, w i t h t h e t a p e r e c o r d e r s a v a i l a b l e f o r t h i s r e s e a r c h , t h i s method i s u n w o r k a b l e . As shown i n F i g . 2.4, t h e i n p u t i m p e d a n c e o f t h e t a p e r e c o r d e r s h u n t s b o t h t h e s e i s m o m e t e r c e i l and e e t o g r o u n d , m a k i n g t h e W i l l m o r e b r i d g e u n s u i t a b l e f o r t h e c a l i b r a t i o n c f t h e • F i g u r e 2.4 The w i l l t n c r a b r i d g e a s a p p l i e d t o t h e c a l i b r a t i o n o f t h e p o r t a b l e s y s t e m s p o r t a b l e s y s t e m s . I t was d e c i d e d t o f o r e g o t h e k n o w l e d g e o f t h e a b s o l u t e a m p l i t u d e r e s p o n s e and t c d e v i s e a method by w h i c h t h e p h a s e r e s p o n s e a l o n e c o u l d be e s t a b l i s h e d . The c a l i b r a t i o n c o i l i n b o t h s e i s m o m e t e r m o d e l s c a n be d r i v e n -by an e x t e r n a l s i g n a l , w h i ch f o r c e s t h e boom t o o s c i l l a t e a t t h e known f r e q u e n c y , t h u s a f f o r d i n g an o p p o r t u n i t y t o r e c o r d t h e 16 o u t p u t o f t h e s e i s m o g r a p h ( s e i s m o m e t e r p l u s a m p l i f i e r and f i l t e r ) f o r a known i n p u t ( F i g . 2 . 5 ) . A s i g n a l g e n e r a t o r p r o v i d e s t h e d r i v i n g v o l t a g e , and i t s o u t p u t i s r e c o r d e d N (%>~ MA»AV F i g u r e 2.5 C a l i b r a t i o n c o n f i g u r a t i o n c f t h e p o r t a b l e s e i s m o g r a p h s s i m u l t a n e o u s l y w i t h t h e f i l t e r e d a m p l i f i e r o u t p u t . A f i e l d c a l i b r a t i o n t a k e s a b c u t s i x t y m i n u t e s t o p e r f o r m and a paper-c h a r t c a n be o b t a i n e d as a b a c k - u p r e c o r d . The c a l i b r a t i o n d a t a can be a n a l y z e d by f o r m i n g t h e c r o s s - c o r r e l o g r a m s o f t h e i n p u t and o u t p u t t i m e s e r i e s , a f t e r d i g i t i z a t i o n c f t h e t a p e r e c o r d s . 2.6 A c c u r a c y B o l d u c (1971) assumed t h a t t h e i n s t r u m e n t a l p h a s e r e s p o n s e a t one s t a t i o n c o u l d be d e t e r m i n e d t o ± 2 ° , w i t h an a d d i t i o n a l ± 1° due t o t e m p e r a t u r e f l u c t u a t i o n s . Hence, t h e most p r o b a b l e e r r o r f c r t w c - s t a t i o n m e a s u r e m e n t s was c a l c u l a t e d t o be a b o u t + 3.2°. A d i r e c t c a l c u l a t i o n o f t h i s 1 7 error had been one of the objectives of the present thesis; however, due tc the premature cessation of the data an a l y s i s , no such c a l c u l a t i o n was made. An experiment aimed at solving this problem i s suggested in Chapter V. 18 I I I . FIELD EXPERIMENTS 3. 1 I n t r c d u c t i c n S i n g l e - s t a t i o n t e s t s under f i e l d c o n d i t i o n s were beg.un i n September, 1972. From the r e s u l t s of these experiments and f u r t h e r work i n the l a b o r a t o r y , the f i e l d system was redesigned and t e s t e d f u r t h e r the f o l l o w i n g summer at a s i t e i n V i c t o r i a . Having e s t a b l i s h e d that s i t e , three systems were completed and a t r i p a r t i t e array was i n s t a l l e d i n October, 1973, with s t a t i o n s a t V i c t o r i a , Quadra I s l a n d , and the. UBC campus. The instruments were run c o n t i n u o u s l y f c r two months, but a f t e r p r e l i m i n a r y a n a l y s i s , i t became obvious t h a t i n s u f f i c i e n t data had been recorded f c r the d e t e r m i n a t i o n of group and phase v e l o c i t i e s . A second t r i p a r t i t e network was deployed i n February, 1974 with s i t e s i n U c l u e l e t , Quadra I s l a n d and V i c t o r i a , thus p r o v i d i n g a wider aperture a r r a y . Mechanical problems prevented continuous o p e r a t i o n and the experiment was d i s c o n t i n u e d i n A p r i l , 1974, with no u s e f u l data having been o b t a i n e d . 3.2 T y p i c a l F i e l d I n s t a l l a t i o n Within a p r e s e l e c t e d geographic a r e a , the search for. a s i t e was based on a number of c r i t e r i a , such as: (i) bedrock f o u n d a t i o n , ( i i ) a v a i l a b i l i t y cf AC power, ( i i i ) d i s t a n c e from ambient n o i s e . s o u r c e s , e.g. r a i l r o a d s , water courses, 19 h i g h w a y s , ( i v ) i n h a b i t a t i o n t o p r o v i d e manning c f t h e a p p a r a t u s , (v) cement f l e e r t o s e r v e a s a s e i s m o m e t e r p i e r , a n d ( v i ) w o r k i n g s p a c e f o r c a l i b r a t i o n and o t h e r r o u t i n e p r o c e d u r e s. B e d r o c k s i t e s were f o u n d f c r a l l t h e s e i s m o m e t e r s ( T a b l e I ) , e x c e p t a t t h e UBC campus, where t h e e x i s t i n g cement p i e r s ( a t t h e G e o l o g i c a l S c i e n c e s C e n t r e ) r e a c h a d e p t h of 2 m e t r e s , t h e f o u n d a t i o n b e i n g g l a c i a l t i l l . S t a t i o n C o o r d i n a t e s P e r i o d s o f o p e r a t i o n UBC i 4 9 0 1 6 ' H , 123015'W Via y - J u l , 1972 Aug- Sep, 1973 Cc t - K o v , 1973 VCT 48°31'N, 1230 25'W Sep-N ov, 1972 J u n - N o v , 1973 F e b - A p r , 1974 QUA 5C0C5«N, 125013'Vi Se p-No v , 1973 F e b - A p r , 1974 UCL 48055'N, 125°32«W F e b - A p r , 1974 TABLE I . PORTABLE S T A T I O N S — TE STS AND F I E I D S IT ES Founda t i o n s i n e a c h c a s e a r e c e m e n t on b e d r o c k , e x c e p t f o r t h e [f EC s t a t i o n ( s e e t e x t ) . 1 T h i s s t a t i o n ha a l s o been o p e r a t e d w i t h a H e l i c o r d e r as a d i s p l a y (1 972- 1975) . The t y p i c a l s t a t i o n , t h e n , was l o c a t e d i n a p e r m a n e n t b u i l d i n g , s e r v i c e d by AC power, w i t h t h e s e i s m o m e t e r p l a c e d on a f l a t s l a b o f cement p o u r e d d i r e c t l y c n b e d r o c k , and c o v e r e d by a f i v e - s i d e d s t y r e f c a m e n c l o s u r e . A l o n g c a b l e c o n n e c t e d b o t h c a l i b r a t i o n and main c o i l s t c the. c o n t r o l p a n e l , w h i c h was h o u s e d i n a wooden e n c l o s u r e and s i t u a t e d on a n o t h e r f l o o r , a d j a c e n t t o t h e power s u p p l i e s , t a p e 20 r e c o r d e r and ViWVB r e c e i v e r . The ViWVB a n t e n n a was mounted i n d o o r s and a l i g n e d t o the p o s i t i o n w h i c h gave t h e b e s t o u t p u t s i g n a l . On a n a p p r o x i m a t e l y d a i l y b a s i s , t h e o p e r a t o r r e c o r d e d t h e mass p o s i t i o n , t e m p e r a t u r e i n s i d e t h e e n c l o s u r e and t h e d a t e and t i m e o f o b s e r v a t i o n . E v e r y f i v e d a y s t a p e s were c h a n g e d and s e n t t c t h e u n i v e r s i t y . E v e n t s s u c h a s power i n t e r r u p t i o n s , i f d e t e c t e d , e q u i p m e n t f a i l u r e s , and o t h e r s o u r c e s o f d i s t u r b a n c e were n o t e d on e a c h t a p e ' s l o g s h e e t . A s u p p l y of t a p e s e n s u r e d c o n t i n u o u s o p e r a t i o n a t e a c h s i t e . 3.3 C h r o n c l e x i c a l A c c o u n t When B o l d u c ' s (1971) p r o j e c t was r e s u m e d i n t h e s p r i n g o f 1 9 7 2 , R.D. Meldrum a d j u s t e d t h e S p r e n g n e t h e r s e i s m o m e t e r 0 f o r l o n g - p e r i o d o p e r a t i o n , and d e s i g n e d a t e m p e r a t u r e c o n t r o l s y s t e m . L a t e r , t h e a c t i v e f i l t e r s were b u i l t and t e s t e d , and a s i m p l e c c n t r c l p a n e l was c o n s t r u c t e d . The S e o t e c h s e i s m o m e t e r s were r e t u r n e d f r o m T e x a s , .where f a c t o r y a l i g n m e n t was p e r f o r m e d and new, i m p r o v e d c o i l s were f i t t e d . T e s t s i n t h e s e i s m i c v a u l t l o c a t e d i n t h e G e o l o g i c a l S c i e n c e s C e n t r e , UBC, shewed t h a t s u r f a c e waves w i t h p e r i o d s t o a b o u t s i x t y s e c o n d s c o u l d be r e c o r d e d w i t h a d e q u a t e s i g n a l - t o - n o i s e r a t i c s . F i e l d e x p e r i m e n t s were c o n d u c t e d a t t h e V i c t c r i a G e o p h y s i c a l O b s e r v a t o r y s t a r t i n g i n S e p t e m b e r , 1972. The o r i g i n a l l o c a t i o n was n o t i s o l a t e d s e i s m i c a l l y f r c m t h e r o a d 21 s u r f a c e , so a naw s i t s was e s t a b l i s h e d i n t h e ba s e m e n t c f a n e a r b y , a b a n d o n e d h o u s e . The t e m p e r a t u r e c o n t r o l d e v i c e s p r o v e d c a p a b l e o f m a i n t a i n i n g t h e n e c e s s a r y c c n d i t i c n s t o h o l d m a s s - p o s i t i o n f l u c t u a t i o n s t c l e s s t h a n ± 2 mm. H o w e v e r , i t was f e l t t h a t t h e e l e c t r o n i c s c o u l d be made more r e l i a b l e t h a n t h e s i m p l e c c n f i g u r a t i o n w h ich was u s e d . F i e l d t e s t s were r e s u m e d i n J u n e , 1973, a f t e r new i n s t r u m e n t p a n e l s had been c o n s t r u c t e d and a c a l i b r a t i o n p r o c e d u r e had been d e v i s e d . C o n f l i c t i n g r e q u i r e m e n t s c f o t h e r p r o j e c t s made most c f t h e t i m i n g and t a p e r e c o r d i n g e q u i p m e n t u n a v a i l a b l e u n t i l t h e autumn o f 1973. B e c a u s e c f t h e e x i s t e n c e o f s e i s m i c r e f r a c t i o n d a t a f r o m t h e e a s t c o a s t o f V a n c o u v e r I s l a n d ( W h i t e and S a v a g e , 1 9 6 5 ) , i t was d e c i d e d t o i n s t a l l a t l e a s t c n e s t a t i o n i n t h e C a m p b e l l F i v e r a r e a . O p e r a t i o n began i n a p r i v a t e home a t Q u a d r a I s l a n d i n l a t e S e p t e m b e r , and by e a r l y O c t o b e r , a t h i r d s t a t i o n .was i n s t a l l e d i n t h e s e i s m i c v a u l t a t UBC. T h i s a r r a y ( F i g . 3.1) was e s s e n t i a l l y a t w o - s t a t i o n n e t w o r k , n a m e l y V i c t o r i a - Q u a d r a , a s o n l y d a t a r e c o r d e d on V a n c o u v e r I s l a n d c o u l d be a p p l i e d t c t h e p r o b l e m c f i t s c r u s t a l s t r u c t u r e . 3.4 R e s u l t s Among t h e d a t a r e c o r d e d i n t h i s p a r t o f t h e p r o j e c t .two a a r t h g u a k e s , w i t h e p i c e n t r e s i n C h i l e and i n M e x i c o , w a r r a n t e d f u r t h e r e x a m i n a t i o n as t h e i r s o u r c e - t c - r e c e i v e r a z i m u t h s w e re w i t h i n 5° c f the i n t e r s t a t i o n a z i m u t h r e l a t i n g 22 nf F i g u r e 3.1 Map s h o w i n g l o c a t i o n s o f s e i s m i c s t a t i o n s o p e r a t e d i n the autumn o f 1973 VCT and QUA ( T a b l e I I ) . A s i m p l e " p e a k and t r o u g h " c a l c u l a t i o n was p e r f o r m e d a s d e s c r i b e d by G a r l a n d ( 1 9 7 1 , pp. 6 3 - 6 4 ) . The p h a s e v e l o c i t y c and t h e a n g l e c f a p p r o a c h A are r e l a t e d as f e l l o w s ( s e e F i g . 3.2) : c = a, s i n A/AT, , [ 3. 1 ] or c = d g s i n (A + a ) / A T 4 , [ 3 . 2 ] w h e r e AT, and AT^ a r e t h e i n t e r s t a t i c n t i m e d e l a y s f o r a 23 D a t e T i m s h E p i c e n t r e Mag D e p t h A z 1 (UT) km 29 Sep 1973 00: (43: 58 .7 41 , 9 N , 130. 92 N. K o r e a 7 . 1 549 160 5 O c t 19 73 0 5: 45: 27 .2 33 . OS, 71.9W C h i l e 6 .6 20 40 6 O c t 1973 1 5: 0 7: 37 .0 6 0 . 8 S , 21.6W S. S a n d w i c h I s . 7 .0 80 9 O c t 1973 07: 57: 32 1 4 . 2 S , 167.2E New H e b r i d e s 5 .8 19 7 8 0. 11 O c t 1973 02: 07: 52 0 . 6 N , 2 9 . 5 W M i d - A t l . R i d g e 5 .9 33 560 18 O c t 1973 10: 49: 36 1 9 . 3 N , 105.0W M e x i c o 6 .0 73 4 o TABIE I I . EARTHQUAKES RECORDED — AUTUMH , 1973 l D i f f e r e n c e b e t w e e n t h e s o u r c e - t o - r e c e i v e r a z i m u t h and t h e QUA-VCT a z i m u t h . D a t a o b t a i n e d f r o m N E I S , B c u l d e r . F i g u r e 3.2 P h a s e v e l o c i t y d e t e r m i n a t i o n w i t h a t r i p a r t i t e a r r a y Method i n t r o d u c e d by P r e s s ( 1 9 5 6 ) ; d i a g r a m a d a p t e d f r o m G a r l a n d (1971) . p a r t i c u l a r peak. A, a, d, and d 2 c o u l d be c a l c u l a t e d f r c m 24 t h e e p i c e n t r e and s t a t i o n c o o r d i n a t e s , w h i l e AT, and AT2 c o u l d be m e a s u r e d f r o m t h e r e c o r d s . T c c o n f i r m t h a t t h e s u r f a c e wave t r a i n s t r a v e r s e d t h e a r r a y a t t h e c a l c u l a t e d a z i m u t h , A , t h e e q u i v a l e n c e o f [ 3 . 1 ] and [ 3 . 2 ] was s o u g h t . F o r t h e C h i l e q u a k e , t h e a g r e e m e n t was g o o d , w i t h i n 2.5?. F o r t h e M e x i c o e v e n t , h o w e v e r , no r e c o g n i z a b l e peak c r t r o u g h c o u l d be f o u n d t o a g r e e by t h a t s i m p l e c a l c u l a t i o n . I t was s u r m i s e d t h a t e i t h e r r e f r a c t i o n a t a g e o l o g i c a l b o u n d a r y i n t h e wave p a t h , c r d i f f r a c t i o n a r o u n d some d i s c o n t i n u i t y was r e s p o n s i b l e f o r t h i s l a c k c f a g r e e m e n t ; t h e e n t i r e l y c o n t i n e n t a l wave p a t h h i n t e d a t t h e p o s s i b i l i t y o f t h e s e phenomena. T h u s , o n l y c u e e a r t h q u a k e was a v a i l a b l e f o r s t u d y , and t h e two s e i s m o g r a m s o b t a i n e d a t t h e i s l a n d s t a t i o n s (VCT and QUA) w e r e d i g i t i z e d a s d e s c r i b e d i n C h a p t e r I V . The t a p e c o n t a i n i n g t h e r e c o r d f r o m t h e UBC s i t e was p a r t i a l l y m u t i l a t e d by a m a l f u n c t i o n c f a t a p e p l a y b a c k d e c k , l e a v i n g o n l y a s l o w - s p e e d c h a r t r e c o r d made p r e v i o u s l y . 3*5 The S e c o n d F i e l d S x _ p e r i m e n t As i s d i s c u s s e d i n C h a p t e r I V , a n a l y s i s o f t h e d i g i t i z e d s e i s m o g r a m s p r o g r e s s e d u n t i l g r o u p v e l o c i t y d i s p e r s i o n c u r v e s were p r o d u c e d . These a p p e a r e d t o show t h a t t h e b e h a v i o u r o f t h e d i s p e r s i o n f u n c t i o n a t p e r i o d s l o n g e r t h a t 40 c r 50 s e c o n d s c o u l d n o t be d e l i n e a t e d ( s e e F i g . 4 . 3 ) . Even t h e r e c o v e r y o f t h e UBC r e c o r d f r c m p a p e r 25 c h a r t would h a v e been o f l i m i t e d a s s i s t a n c e . Kore d a t a were n e e d e d , and t h i s r e q u i r e d mere f i e l d work. I n o r d e r t o i n c r e a s e t h e c h a n c e o f o b t a i n i n g u s a b l e e a r t h q u a k e d a t a , p r e f e r a b l y w i t h r e l a t i v e l y s i m p l e s o u r c e - t o - r e c e i v e r p a t h s , i t was d e c i d e d t c s e a r c h f c r a t h i r d s t a t i o n on V a n c o u v e r I s l a n d . The r e s u l t i n g a r r a y F i g u r e 3.3 L o c a t i o n s c f f i e l d s t a t i o n s o p e r a t e d f r o m F e b r u a r y t o A p r i l , 1974 26 s h o u l d h ava a w i d e r a p e r t u r e t h a n t h e f i r s t o n e , a s w e l l . Hence, i n F e b r u a r y , 1974, a new s i t e was e s t a b l i s h e d on t h e P a c i f i c c o a s t , n e a r U c l u e l e t . T h i s s t a t i o n , c o m b i n e d w i t h t h e V i c t o r i a and Q u a d r a I s l a n d s i t e s , w h i c h were r e - i n s t a l l e d , t e r m e d a t r i p a r t i t e a r r a y w i t h i n t e r s t a t i . o n s e p a r a t i o n s r a n g i n g f r o m 218 km t o 132 km ( F i g . 3 . 3 ) . As B o l d u c (1971) had p o i n t e d o u t , s e p a r a t i o n s o f t h i s o r d e r w o u l d ba r e q u i r e d t o a c h i e v e t w o - f i g u r e a c c u r a c y i n p h a s e v e l o c i t y d e t e r m i n a t i e n s up t c 80 s e c o n d s p e r i o d , w h i c h was a p p r o x i m a t e l y a t t h e l i m i t o f d e t e c t i o n o f t h e i n s t r u m e n t s i n t h e i r c u r r e n t s t a t e . D i s a p p o i n t i n g l y , e q u i p m e n t p r o b l e m s p l a g u e d t h e e n t i r e p e r i o d o f r e c o r d i n g , a n d e v e n t u a l l y r e n d e r e d i t f r u i t l e s s . Tape r e c o r d e r s m a l f u n c t i o n e d a t a l l t h r e e s i t e s , a n d WWVB s i g n a l s became i l l e g i b l e i n t h e QUA t a p e s . Among t h e d a t a t h a t wera o b t a i n e d , n o t a s i n g l e e v e n t was r e c o r d e d s i m u l t a n e o u s l y a t a l l s i t e s w i t h c l e a r t i m i n g i n f o r m a t i o n o r s u f f i c i e n t l y h i g h s i g n a l - t o - n o i s e r a t i o s . The e x p e r i m e n t was c o n c l u d e d i n A p r i l , 1 974, w i t h nc d a t a a p p l i c a b l e t o t h e s o l u t i o n o f t h e o r i g i n a l p r o b l e m . 27 I V . ANALYSIS 4.1 I n t r o d u c t i o n S u r f a c e wave d a t a were o b t a i n e d w i t h an a n a l o g t a p e s y s t e m as d e s c r i b e d i r ; C h a p t e r I I I . T h e i r a n a l y s i s was a i m e d a t p r o d u c i n g g r o u p - and p h a s e - v e l o c i t y d i s p e r s i o n c u r v e s , w h i c h w ere t c ba f i t t e d t c s t r u c t u r a l m o d e l s o f t h e V a n c o u v e r I s l a n d r e g i o n . T h i s c h a p t e r c o v e r s t h e p r o c e d u r e and t h e o r y of t h e v a r i o u s a n a l y s i s t e c h n i q u e s . The d a t a c h o s e n f o r a n a l y s i s a r e r e c o r d s c f an e a r t h q u a k e i n C h i l e , cn 5 O c t o b e r 1973 ( s e e T a b l e I I , pg. 2 3 ) . T h e s e were t a p e r e c o r d e d a t Q u a d r a I s l a n d , V i c t o r i a and UBC. The QUA and VCT r e c o r d s were d i g i t i z e d , b u t t h e UBC t a p e was c u t and r e n d e r e d u s e l e s s when a t a p e p l a y b a c k d e c k m a l f u n c t i o n e d . ^•2 D i q i t i z a t i o n and o t h e r P r e l i m i n a r i e s The f i r s t s t e p i i : t h e a n a l y s i s i s t c d i g i t i z e t h e i n t e r e s t i n g p o r t i o n c f t h e e a r t h q u a k e r e c o r d . The i n s t r u m e n t a t i o n u s e d f o r t h i s p r o c e s s i s shown s c h e m a t i c a l l y i n F i g . 4.1. The o r i g i n a l t a p e i s p l a y e d back a t 10 t i m e s t h e r e c o r d i n g s p e e d on a d e c k w h i c h c o m p e n s a t e s f c r s m a l l s p e e d v a r i a t i o n s , i n t r o d u c e d by the' r e c o r d e r , by c o m p a r i n g t h e o u t p u t o f c h a n n e l t h r e e , w h i c h has had i t s i n p u t s h o r t e d d u r i n g r e c o r d i n g , t o t h e o t h e r o u t p u t s , and r e m o v i n g any 28 OO A n o . l o c\ Tape. DscJc A/D Conv\ 5.D. S. < t — < C o ff.j)u"l£<-j Inter A iitix Fee a.-] c Jf ' 1 OO Recorder F i g u r e 4.1 D i g i t i z a t i o n p r o c e d u r e c o r r e l a t e d f l u c t u a t i c n s . T h r e e c h a n n e l s o f d a t a , c o n s i s t i n g o f t h e a c t i v e f i l t e r o u t p u t a t 0 and -12 db l e v e l s a s w e l l a s WWVB, a r e h a n d l e d by t h e d i g i t i z e r . T h i s u n i t i s d r i v e n by a p u l s e g e n e r a t o r whose p u l s e r e p e t i t i o n r a t e e s t a b l i s h e s t h e s a m p l i n g f r e g u e n c y . To a v o i d f r e q u e n c y a l i a s i n g , t h e d i g i t i z a t i o n r a t e i s c h o s e n t c be a t l e a s t t h e N y q u i s t f r e q u e n c y , w h i c h i s t w i c e t h e h i g h e s t f r e q u e n c y t c be r e c o v e r e d f r o m t h e d i g i t a l t i m e s e g u e n c e . I n t h e p r e s e n t a p p l i c a t i o n , t h e r a t e h a d t o be s e t h i g h enough t o f a i t h f u l l y r e p r o d u c e t h e WWVB t i m e c o d e . A v a l u e o f 20 Hz was c h o s e n . The ' d i g i t i z e r s a m p l e s f r o m t h e t h r e e c h a n n e l s a n d h o l d s t h e i n f o r m a t i o n , w h i c h i s s t o r e d i n t h e I n t e r d a t a ' s memory a n d f i n a l l y t r a n s f e r r e d t c t h e d i g i t a l t a p e r e c o r d e r i n d i s c r e t e b l o c k s c f 480 p o i n t s i n m u l t i p l e x e d f o r m a t . At t h i s s t a g e t h e d a t a a r e i n a m a c h i n e - r e a d a b l e f o r m a t b u t must u n d e r g o f u r t h e r t r a n s f o r m a t i o n s . P r i m a r i l y , t h e 7 - t r a c k d i g i t a l t a p e i s c o n v e r t e d t o an I E ^ - c o r a p a t i b l s 9 - t r a c k f o r m a t . The d a t a a r e d e m u l t i p l e x e d s o t h a t t h e y may 29 be e x a m i n e d i n t h e t r a c e mode and t h e s e i s m i c r e c o r d s a r e d e c i m a t e d , i . e . , t h e l e n g t h o f the s e r i e s i s r e d u c e d . D e c i m a t i o n can i n d u c e f r e g u e n c y a l i a s i n g ( C z i e w o n s k i and H a l e s , 1972) and i t i s n e c e s s a r y t o l o w - p a s s f i l t e r t h e t i m e S October F i g u r e 4.2 VCT a n d QUA r e c o r d s o f t h e 5 O c t o b e r 1973 e a r t h q u a k e F o r c l a r i t y , c n l y p a r t i a l s e c t i c n s o f 750 p o i n t s (10 min r e a l t i m e ) a r e shown. s e r i e s ; t h e p r o c e s s was a c h i e v e d by p r o d u c i n g t h e d i s c r e t e F o u r i e r t r a n s f o r m w i t h 2 1 6 p o i n t s , t h e n c a l c u l a t i n g t h e i n v e r s e d i s c r e t e F o u r i e r t r a n s f o r m w i t h 2 1 2 p o i n t s . T h u s , 54 m i n u t e s , 36.8 s e c o n d s o f d a t a were r e p r e s e n t e d by 4096 p o i n t s w i t h a N y q u i s t f r e q u e n c y c f 0.625 Hz ( F i g . 4 . 2 ) . The number o f p o i n t s was c h o s e n t o be a power c f twc t c t a k e a d v a n t a g e o f a f a s t e r d i s c r e t e F c u r i e r t r a n s f o r m a l g o r i t h m . S i n c e i t i s assumed t h a t t h e p c i n t s a r e a t e q u a l t i m e i n t e r v a l s , the' r e c o r d i n g s p e e d was c h e c k e d t y r e p r o d u c i n g s e l e c t e d r e c o r d s c f WWVB d a t a . The r e s u l t s showed t h a t b o t h 30 QUA and VCT t a p e r e c o r d e r s r a n s l i g h t l y f a s t , t h e i r m u t u a l d i f f e r e n c e b e i n g 0.03 1?. T h i s was n o t c o n s i d e r e d t o be s i g n i f i c a n t , a s t h e e r r o r i n t r o d u c e d i n p h a s e v e l o c i t y c a l c u l a t i o n s w o u l d be + 0.001 km/s a t t y p i c a l v e l o c i t i e s . 4.3 D i s p e r s i o n A n a l y s i s C o n s i d e r a s e i s m c g r a m f ( t ) c f an e a r t h q u a k e r e c o r d e d a t a d i s t a n c e r and a z i m u t h & f r o m t he e p i c e n t r e . I t s F o u r i e r t r a n s f o r m i s F ( c o ) = I f ( t ) e x p ( - i c o t ) d t , [ 4 . 1 ] where f (t) = 0 f o r a l l t < 0. T h r o u g h o u t t h i s r e s e a r c h , t h e a m p l i t u d e and p h a s e f u n c t i o n s a r e t r e a t e d s e p a r a t e l y , e . g . F(co) = A ( r , e , c o ) e x P ( i 0 (r , e , co) }. [ 4 . 2 ] F o r t h e e y e n t u a l d e t e r m i n a t i o n c f phase v e l o c i t i e s , t h e p h a s e s p e c t r u m i s o f more i m m e d i a t e c o n c e r n , and i t c a n be e x p r e s s e d a s t h e sum o f t h r e e t e r m s : (f> (t, e, co) = <f> ( 0 , oo) + cf>. (to) + k(o))»r, [ 4 . 3 ] where k (CO) i s t h e wavenumber, k = 2 7T/A., (p ( 6 , co) i s t h e ph a s e s h i f t i n t r o d u c e d a t t h e s o u r c e , a n d cb (CO) i s t h e p h a s e s h i f t i n t r o d u c e d t y t h e i n s t r u m e n t . L o o k a t k(co)»r mere c l o s e l y , t h e s e i s m o g r a m f ( t ) c a n a l s o be w r i t t e n a s t h e i n v e r s e F o u r i e r t r a n s f o r m c f [ 4 . 2 ] , f ( t ) - = _ l _ I A ( r , 6 , co) e x p { i ( c o t - k r ) ] dco . [ 4 . 4 ] A m o n o c h r o m a t i c wave o f f r e q u e n c y cO c t r a v e l s a t a v e l o c i t y w h i c h s a t i s f i e s t h e p r i n c i p l e c f s t a t i o n a r y p h a s e : 31 c 0 0 t - k(t0 0)«r = a c o n s t a n t , [ 4 . 5 ] f o r a l l r , p r o v i d e d t h a t k i s i n d e p e n d e n t o f r . I t f e l l o w s t h a t : L00 d t / d r - k (co„ ) = 0, f r o m w h i c h t h e p_hase v e l o c i t y c(co) e m e r g e s a s c(co) = d r / d t = co 0/k (co0 ). [ 4 . 6 ] I f c (to) i s n e t c o n s t a n t , t h e s i g n a l i s s a i d t o be ^i^£§I5ll' s i n c e d i f f e r e n t f r e q u e n c i e s co^ w i l l t r a v e l a t d i f f e r e n t v e l o c i t i e s , cic°j ) • I n t l i e c a s e c f f u n d a m e n t a l mode R a y l e i g h w a v e s , t h e l o w e s t f r e g u e n c i e s t r a v e l f a s t e s t , a n d a r r i v a l s b e g i n w i t h t h e l o n g e s t p e r i o d s (Ewing e t a l . , 1 957 , pg. 1 7 8 ) . The maximum e n e r g y t r a v e l s a t t h e 9[rou£ v e l o c i t y . E v a l u a t i n g [ 4 ^ 4 ] i n t h e n e i g h b o u r h o o d o f a p a r t i c u l a r f r equ ency LOa , a>0+s f ( t ) =J- ( A { r , © , u > ) e x p [ i ( w t - k r ) } dto , [ 4 . 7 ] co0-e. we n o t e t h a t f ( t ) , , w i l l be a maximum when a l l t h e waves x ' CO o w i t h i n t h e band (to0-S, ooat £ ) a r e i n p h a s e , c r d/Aco (cot- k r ) = 0 . [ 4 . 8 ] The g r o u p t r a v e l t i m e i s V = t w = { d k ( C J ) / d ^ > } . r , [ 4 . 9 ] and t h e g r o u p v e l o c i t y i s g i v e n by u(o>) = r / t - d W / d k . [ 4 . 1 0 ] I n g e n e r a l , t h e g r o u p v e l o c i t y c a n t e e x p r e s s e d i n 32 t e r m s of t h e ph a s e v e l o c i t y : u(u>) = c ( c o ) + k (to ) »dc (co) / d k ( c o ) , [4.11] w h i c h r e q u i r e s a k n o w l e d g e o f t h e wavenumber k ( t o ) . 4 • 4 S l i S l l i ^ i i c n o f P h a s e V e l o c i t i e s The d i r e c t c a l c u l a t i o n c f p h a s e v e l o c i t i e s was d e m o n s t r a t e d by P r e s s (1956), whc i n t r o d u c e d t h e t r i p a r t i t e method by w h i c h a n e t w o r k o f t h r e e s e i s m o g r a p h s i s u s e d t o r e c o r d t e l e s e i s m s s i m u l t a n e o u s l y . T h i s method a l l o w s t h e a n a l y s i s o f r e c o r d s w i t h a r b i t r a r y a z i m u t h s . S t a t i o n s e p a r a t i o n s must be g r e a t e r t h a n t h e w a v e l e n g t h s t o be a n a l y z e d , w h i c h , i n t u r n , d e t e r m i n e t h e d e p t h s t o w h i c h t h e s u r f a c e waves a r e t h o u g h t t o be i n f l u e n c e d by t h e l o c a l s t r u c t u r e . , C o n s i d e r a d i g i t i z e d s e i s m c g r a m c o n t a i n i n g f u n d a m e n t a l mode R a y l e i g h waves. I t s F o u r i e r t r a n s f o r m c a n be w r i t t e n as i n . F q n . [ 4 . 2 ] o f t h e p r e c e d i n g s e c t i o n : F (to ) = A ( r , e, co) exp{-i0 <r, e, co) }. [ 4 . 2 ] The p h a s e d e l a y f u n c t i o n ( r , O , to) i s f o r m e d by t h e c o n t r i b u t i o n s o f t h e s o u r c e f u n c t i o n , t h e i n s t r u m e n t a l r e s p o n s e , t h e n a t u r e c f t h e d i s p e r s i o n a s d e s c r i b e d by t h e wavenumber, and an a r b i t r a r y number o f f u l l c i r c l e s , 2n7T, t o a s s u r e t h e c o n t i n u i t y o f t h e f u n c t i o n . T h u s , [ 4 . 3 ] can be r e w r i t t e n a s k ( < o ) o r = ( r , e, to) - 4> ( e , co) - (co ) + 2 n TT. [ 4 . 1 2 ] 33 The i n s t r u m e n t a l p h a s e r e s p o n s e c a n be o b t a i n e d f r o m t h e c a l i b r a t i o n p r o c e d u r e d e s c r i b e d i n C h a p t e r I I , o r i t may be c a l c u l a t e d f r o m t h e a m p l i t u d e r e s p o n s e , a s shown by E o l d u c e t a l . ( 1 9 7 2 ) . The s o u r c e p h a s e s h i f t i s more d i f f i c u l t t o f i n d , b e c a u s e i t r e q u i r e s a s o l u t i o n f o r t h e e a r t h q u a k e m e c h a n i s m , w h i c h i s n o t a l w a y s a v a i l a b l e . I f t h e r e a r e two s t a t i o n s r e c o r d i n g t h e same e a r t h q u a k a , t h e c a l c u l a t i o n o f p h a s e d i f f e r e n c e s o b v i a t e s t h e n e c e s s i t y o f k n o w i n g t h e s o u r c e p h a s e s h i f t . I n a s i m p l e c a s e , where t h e two s t a t i o n s a r e a t t h e same a z i m u t h f r o m t h e e p i c e n t r e , one c a n w r i t e t h e f o l l o w i n g r e l a t i o n s h i p s : k<co)°r,= 4> ( r . , e , c u ) - cj> ( 6 , co) - <£ (to) - 2n1T, [ 4 . 1 3 ] k ( l o ) * r = ch (r- ,e,o>) - ch ( e , c o ) - d> {co ) - 2mTT . [ 4 . 1 4 ] S u b t r a c t i n g t h e two e q u a t i o n s and f o r m i n g t h e phase v e l o c i t y , we have c (u>) = co/k(u>) = CO ( r - r , ) / (6 - 6-cp + c7j> + 2 j f T ) . [ 4 . 1 5 ] *• 1 I CZ ll A f u r t h e r s i m p l i f i c a t i o n i s p o s s i b l e i f b o t h i n s t r u m e n t s a r e i d e n t i c a l , b e c a u s e t h e i r p h a s e f u n c t i o n s c a n c e l c u t . A n o t h e r way t c c a l c u l a t e t h e phase v e l o c i t y as a f u n c t i o n of f r e q u e n c y e m p l o y s t h e c r o s s - c o r r e l a t i c n c f t h e s e i s m o g r a m s . L e t f ( ( t ) a n d f £ ( t ) r e p r e s e n t t h e s e i s m o g r a m s a s r e c o r d e d a t two s t a t i o n s , and l e t F, (co ) and F^ (co) be t h e i r F o u r i e r t r a n s f o r m s . Then c o n s i d e r F 2 l ( C O ) = ( F A / T , ) = {Ft • F * ) / | F I | Z w h i c h i s t h e d e c o n v o l u t i o n o f t h e s e c o n d s i g n a l w i t h r e s p e c t 34 t o t h e f i r s t . The p h a s e d e l a y i n f o r m a t i o n i s c o n t a i n e d i n F«(t*>) * F * ( c o ) , a s c a n be s e e n i f t h i s i s e x p a n d e d : ( F Z ° F * ) / | F , | 2 = (A 2 / A , ) • e x p { i ( t o t - < ^ + ^ () } = (A £ / A , ) o e xp ( i c o t ) e a xp ( - i ci> ) w h e r e <p = <f>f - <f> . L a n d i s m a n e t a l . ( 1969) were t h e f i r s t t o p r o p o s e t h e u s e c f t h i s method t o c a l c u l a t e p h a s e v e l o c i t i a s . However, a s D z i e w c n s k i and H a l e s (1972) p o i n t o u t , b o t h o f t h e ab o v e methods a r e v e r y u n s t a b l e when t h e r e c o r d s a r e n o i s y . The c r o s s - c o r r e l a t i o n t e c h n i q u e c a n be made more s t a b l e by s u m m a t i o n o f s e v e r a l c r o s s - c o r r e l o g r a m s ; t h i s i s p o s s i b l e as l o n g a s t h e e v e n t s a r e s i t u a t e d c l o s e t o t h e g r e a t c i r c l e j o i n i n g t h e r e c o r d i n g s t a t i o n s . A n o t h e r t e c h n i q u e u s e d t o r e d u c e t h e d i s p e r s i v e p r o p e r t i e s o f t h e s i g n a l i s " r e s i d u a l d i s p e r s i o n " ( D z i e w o n s k i e t a l . , 197-2). I n t h i s m e t h o d , T{ (u)) i s r e p l a c e d by a s y n t h e t i c s i g n a l , whose d i s p a r s i o n a p p r o x i m a t e s t h a t o f t h e s e i s m c g r a m F 2 (t-o). T h i s r e d u c e s t h e ' r a n g e o f c/) (to) , and i n c r e a s e s t h e s i g n a 1 - t o - n o i s a r a t i o n e a r t h e z e r o - t i m e l a g . 4.5 Wulti£le F i l t e r A n a l y s i s Tha d e f i n i t i o n o f g r o u p t r a v e l t i m e i n Eqn. [ 4 . 9 1 s u g g e s t s a way t o compute g r o u p v e l o c i t y d i s p e r s i o n . I f t h e f r e q u e n c y band (c0o - £ , too+£. ) i s a p p r o x i m a t e d by a d i s c r e t e number o f f r e q u e n c y p o i n t s i n t h e F o u r i a r t r a n s f o r m c f 35 F (CO) , than the maximum of the envelope of f ( t ) ^ w i l l occur at the grcup t r a v e l time f c r the frequency 6 0 0 . Tha F o u r i e r transform has to be windowed i n c r d e r to s e l e c t the narrow band ( coa - £. , 60 0+€L) , but the windowing f u n c t i o n has to allow good r e s o l u t i o n i n the frequency and v e l o c i t y domains. Dziewonski et a l . (1969) chose the S a u s s i a n f u n c t i o n \(co) = ex pf - <x ) 2 } [4.16] t o meet these requirements. The parameter oc c o n t r o l s the r e s o l u t i o n and i t s value depends upon the nature of the d i s p e r s i o n i n the saismogram. In order to reduce computational c o s t s , the Gaussian f u n c t i o n i s t r u n c a t e d , which makes i t a b a n d - l i m i t e d f u n c t i o n . However, by t r u n c a t i n g a t a l e v e l of a t l e a s t 30 db down from the peak, Dziewonski et a l . (1969) c l a i m that t h e f u n c t i o n remains a nearly optimum f i l t e r f u n c t i o n . When working with d i s c r e t e F o u r i e r transforms, the t r u n c a t i o n p o i n t s are chosen to approximate the exact f r e q u e n c i e s U)n . U s u a l l y no mora than 2% d e v i a t i o n from the exact f r e q u e n c i e s i s n ecessary. Tha i n v e r s e transform of the windowed spectrum i s analyzed to f i n d the amplitude at each frequency f o r a s e l e c t e d sat of g r o u p - v e l o c i t y values ( u s u a l l y i n a l i n e a r p r o g r e s s i o n , whereas the p e r i o d s are i n a l o g a r i t h m i c p r o g r e s s i o n ) . However, tha t r a n s f o r m c o n t a i n s only the in-phase s i g n a l f o r each 6 J n . One must form tha quadrature spectrum Q (to) to e v a l u a t e the instantaneous s p e c t r a l 36 a m p l i t u d e s and p h a s e s . From t h e i n - p h a s e s p e c t r u m G n ( c o ) , t h e q u a d r a t u r e s p e c t r u m i s o b t a i n e d : 2 h (w) = G n (co) »exp ( i 7T/2) . [4.17] T h e n , t h e i n s t a n t a n e o u s a m p l i t u d e s and p h a s e s a r e e x p r e s s e d by \ (tm) = f 9 n 2 ( t « ) + q„ 2(tn,) j 1 / * [4.18] (j> ( t m ) = t a n - x { ( t m ) / g n ( t m ) }. [4.19] The f u n c t i o n A n ( t m ) r e p r e s e n t s t h e e n v e l o p e o f t h e windowed s e i s m o g r a m f ( t ) w , and t ^ i s t h e g r o u p t r a v e l t i m e w h i c h c o r r e s p o n d s t o a d i s c r e t e s t e p i n g r o u p v e l o c i t y f o r t h e p a r t i c u l a r e a r t h q u a k e and r e c o r d i n g s t a t i o n u n d e r s t u d y . The e n t i r e c o m p u t a t i o n a l p r o c e s s j u s t o u t l i n e d i s known as " m u l t i p l e f i l t e r a n a l y s i s " , w h i c h was d e s c r i b e d by D z i e w o n s k i e t # a l . 1969). F u r t h e r r e f i n e m e n t s , as e x p l a i n e d by D z i e w o n s k i and H a l e s (1972) , a r e needed b e c a u s e t h e a b o v e r e s u l t s a r e o n l y good t o t h e f i r s t o r d e r i n £O n; t h e s e c o n d o r d e r , t h e o r y shows, t h a t i n g e n e r a l t h e maximum o f t h e e n v e l o p e A n ( t ) d o e s n o t c o r r e s p o n d t o t h e e x a c t g r o u p t r a v e l t i m e . S y s t e m a t i c e r r o r s a r e r e d u c e d by a p p l i c a t i o n o f t h e " r e s i d u a l d i s p e r s i o n " method, m e n t i o n e d a b o v e . 4.6 A p p l i c a t i o n t c R e a l D a t a The C h i l e e a r t h q u a k e o f 5 C c t o b e r 1973 was c h o s e n f o r s t u d y and t h e s e i s m o g r a m s were n o r m a l i z e d by t h e i r r o o t - m e a n - s g u a r e e n e r g y . A c o m p u t e r p r o g r a m was w r i t t e n t o 37 >* {-< M O s o 40! 3.8 3.4 3.2. 3.01 2.6 * 55 b l t i 65 65 67 bO 64 5'* 6 3 M 58 56 57 4 9 47 62 6 i 6C 64 Id 54 5 1 b9 59 6? 54 6 1 4 ) 60 53 b? ft t 6 4 b9 43 5? 64 63 6* 64 67 6 l 6? 54 55 6 1-61 59 61 bC 60 bf 6 i 60 o 5 5b bd 5 J 49 1 60 6? 6 1 6 1 6g 65 60 6 J 59 54 % 1 59 57 be 5C 61 4 7 66 63 7 1 66 7 1 5 4 6 5 6b 60 5 1 60 65 69 72 tt> 6". SI 51 55 6 » 6S tb 61 59 46 bt 63 tt Li 50 b l 61 6? 68 10 6t 62 61 61 67 71 7 i b B 5b 52 56 6 7 7L 72 bfl 61 58 40 6b 70 7 1 b 7 6 7 ftH b« bs 7 1 7 1 61 62 62 5? 6b 7J 6b tb 66 t 9 7*. 7o 66 66 6*. 7? 7 7 rfU ftf /C 71 74 74 7} b l 6/ 6b o l bt 6 a tb 68 66 t b 59 7C 6b 70 70 t b 6*. 75 11 76 U 6 9 69 71 70 64 6 6 7? 7? 69 74 71 72 6b 67 7C 6a be t b 72 71 66 6C 7C 6 1 5 T 64 69 66 69 ; 1 7 1 6 6 t*i 6 9 69 6 7 < 6 t e 69 7 I 7? 74 7 1 66 7C 70 70 60 6 7 6 1 67 7 J 74 7b 71 67 7? 68 6 ^ 6b ft! 6b 6 " 74 7". 7b 74 70 7C 64 59 6 b 72 71 76 76 71 71 76 12 ft 7 50 66 1? 76 79 UC »8 67 74 78 75 6 8 6 7 72 7b 79 H i rt4 H2 7M 7P BC 77 bb 72 7b 7b 79 r14 82 fl I 78 7b 7P 71 J? Hi 31 89 I 16 fl4 fl? 7H H 1 H 1 IA- -r*>" 'Hr T V 1 'J 9 o\ 8 8 K4 P l 79 tl 1 1 j /' Ml 9C fl 1 /*) " 0 76 66 'J C V tt I> ~njSi / I ) >• 4 •n -k -i* ' ft 68 b9 69 oO 62 b2 t l 64 b9 tB 6 7 bT 71 b7 6b 71 bO t 6 'ft tb (4 *Q bb 6 1 70 )7 B/ bf ll 7 1 74 7 7 bf 7 1 H t t 7 i,l I I 7 H bO 6 f 7K o4 6 1 6 7 t'> tit bb 6 4 6 9 7 5 1 7 fc J-/? || / ft? 'I1. « H ^ ? 7 1 f?>')/j 9 'J 9 ,* 9 1 X C 1% 6J>T4 I l_j*'> ^ r"^. 7 9 7 7 rirt J u _ £ ' ^ 9 ) » t / l b ;74 7 / 54 h 1 79 11 It 7 *1 64 d l ris a s il i 7 9 M b Pb f ? •^0 tt H4 80 74 74 It f ; 81 h i 1- i 79 b i Ky. e 1 6 9 b'V rt 79 -IC b t 7 j fi «C 7ri 8 1 7t 6ft M O H4 f» 4 74 7^ ti 1 111 79 fl J Pb 7 9 7S d 4 7fl 76 e4 ti ) 74 6 4 76 6 7 5 7 7 1 71 61 6fc 71 71 65 69 7? ti 7 3 74 J? 7C 71 t J 67 76 7b 73 67 be 7 9 7 7 tl 7 7 7 1 6 1 6 5 70 69 69 d l V) 71 65 1? 71 &2 flC 74 7 1 7 1 7 1 7 j 74 7 7s 6 7 74 / , U I 7 4 6 P 7 6 H| u J i l 7b 7) 79 •14 H 4 HI 7 7 6t M 1 t -# 7 5 7 5 7 4 7 1 I 7 4 6 7 7 6 7b 6 7 79 If 74 66 Hi 7 9 7 1 6 5 H? 7 P. 7C. 5 6 IP. II II 7 1 bC 74 K 7b 12 65 HG 7M 74 7C 60 7 7 75 7 3 6 7 5 1 7C 6 1 57 7Q 61 59 rtC 11 6 5 bb 7 1 00 tJ4 Rb 7 7 63 12 b 1 69 5 i 6 1 45 56 bb 64 5 9 66 bf 6 7 Z 5 I b9 b2 63 54 49 bfl 62 64 6b 59 bO 5 9 6 7 b4 bb jyrrdTT'nr'Krt.) r C va 1111 1 •! n__'J v.4 7b HQ N l A - t i ' * T " 7 ' 7 * * 7 ^ * ' / 9 fl? 73 7a M tf 1 (i J 79 75 7fl s .' 56 61 T4 hP b.1 f £ ~ r r - - n s 7t- «i0 6 7 bH f C /6 79 H / > V - ^ i / Ii n !l / 71 71 7 5 7 7 7 7 / 4 t, d 6 7 7 1 7 1 71 7 i 75 )5 74 He H4^J*n"*5 « / 69 7 1 76 79 7 7 » l - ^ ^ J j J J j i J W Hil 66 6b 6b « 0 t>4 K-T~fiJ t'l 12 6 9 6 7 '.f 75 7/ 1; *i ^4 f* I 7 4 64 tl 6^ 7 1 7 7 li i* yT5>, .(4 . i / »9 7b i-O fQ~f7 ' "7 !7 *-y ~1H 74 7*. 7 t 7ft HG d-vji 1 ft?. HI i l l flf; 75 T d r i I i 7 " > , / N « i i 69 ll t l 69 ?<• )7 8C n J ^ 5 V tl I H) « V « l 76 72 ;*> 7b 7 7 7 8 7 1 lij) '/<J~9y H' l j/-) 64 tn 75 e? a; us iu_4wA—'x<y n i 7 1 7ft 14 7b aC 79 77 12 6 « 64 74 7 7 7b 76 7« 7 7 71 69 o 9 6b 6 I t I ti 7 4 7 4 L* 65 6H bb 79 7 1 12 74 7 s 1? 6 7 64 ft ) «2 76 5 f 71 7» 70 59 5fc 6C A i Hi. 7s 12 12 6*' 1 b I 5 7 Bs 76 74 7 4 6H 5 7 5 8 5 7 fl 7 M4 f 1 7 7 7 2 69 6 b 6 3 $ 9 'I C 74 1.2 69 b i 55 64 6 1 5 7 IH ll t s 6K 65 59 •, 7 61 60 (.5 61 5 9 59 b SI 6 9 11 b6 M 5ri 5 3 4H 5 1 64 t 9 bb bb 56 64 67 7C 71 JJ 74 79 ft j * T j i.f 62 45 t.H 6 1 6 1 ii 7 5 1 55 I I 54 bf S2 51 46 47 46 b4 51 54 b4 54 53 b? 4? 5 7 6C 5d 50  74 tO o2 b6 59 6C SS 61 6 7 C9 6S 57 55 60 57 tb ftt 7C 6fl bb 6 3 6 3 62 65 64 64 62 54 4 3 49 51 51 52 50 45 4 7 61 62 61 62 54 45 4 8 49 52 52 50 4 7 48 53 5<; 62 62 56 48 45 4 7 52 5 I 50 48 49 4 7 53 b l b l 5il 50 43 46 51 50 50 49 50 53 4 1 b2 b l 59 5 1 4 1 46 50 49 4 9 50 51 60 be 6 1 64 60 5 3 46 47 50 48 48 50 5 I 66 64 65 64 60 54 49 48 49 45 47 51 52 70 67 bb 64 60 55 bl 50 48 41 46 51 52 72 6H tb 64 59 55 5 1 51 46 14 4b 50 52 72 6 7 67 6 3 58 55 54 52 4 P 26 44 >0 51 70 66 6 7 6? 55 54 54 52 49 38 44 4 9 51 67 bt t f 61 46 53 54 51 50 43 44 46 50 70 fte bfl 60 12 50 5 1 53 51 45 45 47 49 75 7 1 68 60 45 4 7 52 54 5? 46 44 45 48 7H 1 3 b9 60 46 44 51 54 52 4 7 4 ) 4 1 4 7 78 7 ) 69 6 I 47 4 4 51 54 5 1 48 40 42 45 7B 73 69 6 t 49 46 51 54 5 J 48 18 42 44 75 70 68 61 53 4H 51 54 54 49 40 42 42 72 65 6 7 61 55 49 50 54 54 5C 44 43 4 1 70 54 67 64 56 4 7 4 A 54 54. 5 1 4 7 44 41 71 bt. 67 64 56 42 4b 53 5 5 5 1 49 45 41 72 7C 68 64 5b 4 t 44 5 ( 55 54 51 46 41 72 71 bfl 6 3 5b 45 46 53 55 54 5? 4 7 45 7? 7 1 6 7 6 1 55 4b 4 fl 54 55 54 5? 48 46 71 7C 65 60 54 42 50 54 55 54 52 49 46 70 6M 60 5H 55 4 I 51 54 54 53 52 49 4 7 70 6 7 55 57 56 51 53 54 5? 5 1 51 4 9 4 7 71 b 7 6 0 5P 5 « 56 55 b 1 4*J 49 4 9 46 47 70 6 7 6 1 59 59 58 57 51 45 4 7 46 4b 4 7 67 t t 61 59 59 59 57 50 34 4b 42 44 4 7 59 6? 60 5 7 56 5-) 58 M 19 4b 18 4 3 47 53 6C 5 7 46 57 59 53 51 46 4b 40 4 3 48 61 60 5 I 49 55 58 5H 55 49 46 4 3 45 48 6 2 b? bfl 53 53 b t bfl bb b l 46 45 4 7 49 61 62 5F 50 4 H 56 53 56 51 45 46 49 50 61 59 5 7 48 44 55 5 7 b5 49 42 46 50 51 5fi 56 53 50 50 55 5 7 55 4a 32 4 4 51 5? SO 5* 46 4 7 52 56 57 54 4 7 36 4b 51 52 55 55 44 45 51 56 5 7 51 46 4 3 4 1 51 52 t o 5 b 4 6 3ft 50 5fc 57 5? )9 46 49 51 52 60 52 49 4b 51 57 5B 5 2 19 47 50 51 51 57 4 3 5 » 54 5 6 5 9 bfl 54 48 48 50 50 50 59 5 2 55 56 5 ft 59 59 55 b l 48 4 9 49 48 61 56 54 55 57 5 8 5 8 5 5 50 4 1 47 46 4b 58 5 : 49 4 fi 52 S6 57 5 3 45 45 44 40 4 1 5 3 44 4C 2H 44 54 56 51 34 43 43 23 41 51 39 44 40 4fl 54 55 5 I 44 4 3 44 18 4 1 52 51 49 52 5 1 55 54 5 2 4 8 46 45 42 42 29 5C 54 5 5 55 5 4 52 49 48 4 7 4ft 44 42 5t 54 b4 5 5 5b 5? 4b 45 45 46 4fa 44 4 1 5B L»3 16 53 54 50 40 40 38 42 45 45 4 1 56 5 t 5 1 52 5 1 5C 4 1 41 11 37 44 46 44 5 7 5 7 54 45 4 7 50 49 43 17 3 9 44 4U 4 7 56 5 1 56 50 4fl 50 49 4b 27 40 45 48 48 4? b 3 5 7 6 4 48 46 4 9 4<« 44 45 4 7 4 b 4 7 52 5 1 5P 56 49 46 51 52 50 48 4 7 4 7 45 52 b 7 59 56 52 51 51 51 5 I 45 4 1 4b 44 57 59 59 5 4 17 50 54 54 bC 17 36 46 4b 54 5 7 59 56 5? 52 5 1 53 5C 44 42 45 4b 59 5 7 56 52 4 1 43 50 49 48 4 4 41 43 45 J 1 l_L 10 20 30 40 50 (f> 7o & «o 100 PERIOD (Sec) F i g u r e 4.3 fiesult o f m u l t i p l e f i l t e r i n g a n a l y s i s a p p l i e d t c t h e QUA r e c o r d o f C h i l e e a r t h q u a k e I n s t a n t a n e o u s s p e c t r a l a m p l i t u d e s i n d b , a s f u n c t i o n s o f g r o u p v e l o c i t y and p e r i o d , have t e e n n o r m a l i z e d t c a maximum o f 99 db. F i l t e r p a r a m e t e r oc = 50. C o n t o u r i n g a s s i s t s i n t h e i n f e r e n c e o f g r o u p v e l o c i t y v a l u e s . p e r f o r m m u l t i p l e f i l t e r a n a l y s i s , and a p p l i e d t o t h e VCT and QUA s e i s m o g r a m s . The m a t r i x o f a m p l i t u d e s shown i n F i g . 4.3 r e p r e s e n t s t h e r e s u l t c f t h e g r c u p v e l o c i t y a n a l y s i s o f t h e QUA d a t a . I t i s a p p a r e n t t h a t f c r p e r i o d s l o n g e r t h a n 40 s e c o n d s , 38 t h e r e s o l u t i o n i s n o t s u f f i c i e n t and hence f u r t h e r a n a l y s i s i s r e g u i r e d . B e c a u s e o f t h e l a c k o f a t h i r d - s t a t i o n r e c o r d i n g t h e e v e n t , i t was d e c i d e d t o r e - i n s t a l l t h e f i e l d a p p a r a t u s i n o r d e r t o o b t a i n more d a t a . H o w e v e r , as h a s b e e n r e p o r t e d i n t h e p r e v i o u s c h a p t e r , t h e p r o j e c t was d i s c o n t i n u e d w i t h no new d a t a and s u p p o r t i n g f u n d s were e x h a u s t e d . 4.7 D i c j j . t a l Ccre_putati.cn o f P h a s e V e l o c i t i e s B i o c h and H a l e s (1968) d e s c r i b e two methods c f c o m p u t i n g p h a s e v e l o c i t i e s f r c m t w o - s t a t i o n s u r f a c e wave r e c o r d s . One o f them i n v o l v e s t h e sum o r d i f f e r e n c e c f t h e d i g i t i z e d s e i s m o g r a m s , and t h e e t h e r , w h i c h t h e y f i n d more e f f i c i e n t , c o m p u t e s t h e c r o s s - p r o d u c t o f t h e s e i s m o g r a m s a f t e r b a n d p a s s f i l t e r i n g and t i m e - s h i f t i n g i s a p p l i e d . The method o f sums and d i f f e r e n c e s i s d e r i v e d f r o m t h e p r i n c i p l e t h a t t h e sum o f two f u n c t i o n s i s a maximum when t h e y a r e i n p h a s e f o r a g i v e n f r e q u e n c y (and v i c e v e r s a f c r t h e d i f f e r e n c e ) . The c o m p u t a t i o n i s c a r r i e d o u t by f i r s t f o r m i n g t h a F o u r i e r t r a n s f o r m o f t h e sum and d i f f e r e n c e f u n c t i o n s : oa H ( T , t O ) = [ [ f , (t+t) + fz (t) ) eexp ( - i c o t ) d t [ 4 . 2 0 ] R (T , co ) _ = ] * { f, (^  + r ) " f 2 ( t ) } * e x p ( - i w t ) d t [ 4 . 2 1 ] a n d i n t h a s e c o n d s t a g e f o r m i n g t h e i r r a t i o : G ( T , w ) = H ( T ,to )_ /H ( r ,CO)+ . [ 4 . 2 2 ] 39 G { T , to ) , as p l o t t e d v e r s u s p e r i o d , i s t h e a m p l i t u d e m a t r i x , and t h e d e l a y s - T a r e c h o s e n t o r e p r e s e n t s t e p s i n p h a s e v e l o c i t y . Capcn (1969) a p p l i e d a maximum-1 i k e l i h c c d f i l t e r t o a c h i e v e b e t t e r s i g n a l - t c - n c i s e r a t i o s . A l s o , an a r b i t r a r y number o f r e c e i v e r s may be u s e d ; t h e n t h e d i r e c t i o n o f a p p r o a c h c f t h e K a y l e i g h wave t r a i n may be s t u d i e d . The c r o s s - p r o d u c t method i n v o l v e s t i m e - d o m a i n f i l t e r i n g o f t h e two s e i s m o g r a m s s o t h a t t h e y a r e e s s e n t i a l l y s i n g l e - f r e g u e n c y t i m e s e r i e s , s a y Aocos (wt ) and B«cos ( t o t + <f> ) , w i t h <j> b e i n g t h e i r r e l a t i v e ph a s e . T h e i r c r o s s - p r o d u c t i s g(t,<j&) = (AB/2) »{cos (2 to t + <f> ) + c o s <f> }, [ 4 . 2 3 ] w h i c h i s a f u n c t i o n w i t h t w i c e the f r e g u e n c y and a d . c . s h i f t p r o p o r t i o n a l t o c o s $ . B i o c h and H a l e s (1 968) c a l c u l a t e d t h i s d.c. s h i f t by m e a s u r i n g a maximum, g , and max t h e f o l l o w i n g minimum, g , f r o m w h i c h d.c . l e v e l - ( g ^ + g m V ) )/2. [ 4 . 2 4 ] The phase v e l o c i t y m a t r i x c o n s i s t s o f t h e d.c. l e v e l s f c r c h o s e n s t e p s i n ph a s e v e l o c i t y and f o r the p e r i o d r a n g e o f i n t e r e s t . In; p r a c t i c e , t h e s e i s m o g r a m s a r e windowed f o r e a c h p e r i o d a t t h e c o r r e s p o n d i n g g r o u p - d e l a y t i m e . T h i s r e q u i r e s a k n o w l e d g e c f t h e g r o u p v e l o c i t y d i s p e r s i o n o f t h e s e i s m o g r a m . The a d v a n t a g e s t h e a u t h o r s n o t e a r e t h a t F o u r i e r a n a l y s i s , t i m e - v a r i a n t f i l t e r i n g and i n t e g r a t i o n o f uo t h e t i : n e s e r i e s a r e m i r i m i z e d c r e l i m i n a t e d a s c o m p a r e d t o p r e v i o u s m e t h o d s . The c u r r e n t i n v e s t i g a t i o n d i d n e t p r o g r e s s beyond t h e a n a l y s i s o f g r o u p v e l o c i t y d i s p e r s i o n . I t i s c l e a r , h o w e v e r , t h a t t h i s s t e p was a p r e l i m i n a r y t c t h e phase v e l o c i t y c a l c u l a t i o n s , b e c a u s e a k n o w l e d g e o f t h e g r o u p t r a v e l t i m e s s e r v e s i n r e d u c i n g c o m p u t a t i c n t i m e i n t h e e a r l y s t a g e s o f t h e c a l c u l a t i c n ( D l c c h and H a l e s , 1 9 6 8 ) . 41 V. CONCLUSION 5. 1 I n t r c d u c t i c n Tha g o a l s o f t h i s p r o j e c t w i t h r e s p e c t t o t h e l i t h o s p h e r i c s t r u c t u r e o f V a n c o u v e r I s l a n d were n e t a c h i e v e d . H owever, t h r e e f u n c t i o n i n g l o n g - p e r i o d s e i s m o g r a p h s h a v e been d e v e l o p e d and t e s t e d u n d e r f i e l d c o n d i t i o n s . I t i s t h e p u r p o s e o f t h i s c h a p t e r t o s u g g e s t p o s s i b l e i m p r o v e m e n t s t o t h e s e s y s t e m s i n o r d e r t h a t t h e i r p o t e n t i a l may be u t i l i z e d f u l l y . 5.2 Pl2kIS2i§ w i t h t h e Mass P o s i t i o n As was r e p o r t e d i n C h a p t e r I I , t h e c o n s t a n c y c f t h e mass p o s i t i o n , p a r t i c u l a r l y i n t h e c a s e o f t h e G e o t e c h s e i s m o m e t e r s , r e m a i n e d p r o b l e m a t i c e v e n a f t e r t h e i n t r o d u c t i o n o f t h e t e m p e r a t u r e c o n t r o l l e r s . AC power f a i l u r e s were r e s p o n s i b l e f o r u n c o n t r o l l a b l e c h a n g e s i n t h e t h e r m o s t a t e d env i r cn iren t s . I t i s s u g g e s t e d t h a t an a u t o m a t i c s w i t c h i n g d e v i c e be b u i l t t o p r o v i d e b a t t e r y power d u r i n g e m e r g e n c i e s , t h u s c o n s e r v i n g t h e b a t t e r i e s and a s s u r i n g c o n t i n u o u s o p e r a t i o n . I n a d d i t i o n , t h e mass p o s i t i o n s h o u l d he m o n i t o r e d c o n t i n u o u s l y u s i n g a s p a r e t a p e . r e c o r d e r c h a n n e l . One s u g g e s t i o n i s t c p l a c e l i g h t w e i g h t s t r i p s o f M y l a r on t h e boom and f r a m e o f t h e s e i s m o m e t e r . T h e s e w o u l d a c t a s a 42 v a r i a b l e c a p a c i t o r , w h i c h c o u l d be u s e d t c d r i v e an o s c i l l a t o r c i r c u i t whcse c h a n g e s would be r e c o r d e d on t a p e . I n t h i s manner, a c o n t i n u o u s r e c c r d c f mass p o s i t i o n w o u l d be a v a i l a b l e and p h a s e c a l i b r a t i o n s c o u l d be p e r f o r m e d a f t e r e x a m i n a t i o n o f t h e r e c o r d s . 5.3 V e r i f i c a t i o n o f t h e P h a s e C a l i b r a t i o n The f o l l o w i n g e x p e r i m e n t i s p r o p o s e d as a means c f v e r i f y i n g t h a t t h e r e l a t i v e c a l i b r a t i o n , p e r f o r m e d as d e s c r i b e d i n C h a p t e r I I , can be r e m o v e d f u l l y f r c m t h e s e i s m i c , r e c o r d s . The t h r e e p o r t a b l e s y s t e m s a r e i n s t a l l e d i n t h e same room, and a l l t h r e e o u t p u t s i g n a l s a r e m o n i t o r e d w i t h a t a p e r e c o r d e r . I n due t i m e , an e a r t h q u a k e w i l l be r e c o r d e d w i t h s u f f i c i e n t l y h i g h s i g n a 1- t c — n o i s e r a t i o s a t l o n g p e r i o . d s . The r e c o r d s a r e e x p e c t e d t o be d i f f e r e n t f r o m e a c h e t h e r a s t h e s e i s m o m e t e r s a r e n o t i d e n t i c a l a n d t h e i r m a s s - p o s i t i o n s may f l u c t u a t e w i t h " t i m e . The t h r e e s y s t e m s a r e c a r e f u l l y c a l i b r a t e d , w i t h c o n s i d e r a t i o n o f t h e m a s s - p o s i t i o n a t t h e t i m e c f t h e e a r t h q u a k e . F c r e a c h f r e q u e n c y c o m p o n e n t , t h e c r o s s - c o r r e l a t i o n o f t h e i n p u t and o u t p u t t i m e s e r i e s r e c o r d e d d u r i n g t h e c a l i b r a t i o n i s f o r m e d . The p h a s e r e s p o n s e o f t h e s e i s m o g r a p h s i s d e d u c e d f r o m t h i s c o m p u t a t i o n . Then t h e phase t e r m s a r e removed f r o m t h e F o u r i e r t r a n s f o r m s o f t h e d i g i t i z e d s e i s m o g r a m s . when t h i s 43 p r o c e s s i s f i n i s h e d , t h e t h r e e s e i s m o g r a m s s h o u l d be i d e n t i c a l . T h i s e x p e r i m e n t i s e s s e n t i a l t o p r o v e t h a t t h e f i e l d c a l i b r a t i o n s a r e s u f f i c i e n t f o r l a t e r r e m o v a l o f t h e a f f e c t o f t h e i n s t r u m e n t s on t h e s e i s m i c r e c o r d s . 5.4 O t h e r I n s t r u m e n t a l C o n s i d e r a t i o n s A w i d e r d y n a m i c r a n g e t h a n i s c u r r e n t l y a t t a i n a b l e w i t h t h e a n a l o g FM t a p e r e c o r d e r s w o u l d be d e s i r a b l e . E v e n t h o u g h an a d v a n t a g e c f t h e p o r t a b l e s y s t e m s i s t h e i r l o w o p e r a t i n g c o s t , t h e y a r e i n a d e q u a t e t o r e c o r d t h e w i d e r a n g e o f a m p l i t u d e s t c be e x p e c t e d i n t e l e s e i s m i c s u r f a c e wave t r a i n s , and a g a i n - r a n g i n g d i g i t a l s y s t e m s h o u l d be c o n s i d e r e d as an a l t e r n a t i v e . The G e o t e c h AS-330 a m p l i f i e r s s h o u l d t e o p e r a t e d i n 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 e n c l o s u r e s . T h i s would a l l o w t h e e x t e n s i o n o f t h e r a n g e o f t h e i r p a s s i v e RC f i l t e r s t o d . c . w i t h o u t i n c r e a s i n g t h e d r i f t a t the o u t p u t s t a g e s . Long o p e r a t i n g p e r i o d s must be a n t i c i p a t e d i n c r d e r t o g a t h e r enough u s a b l e d a t a . I n a b o u t f o u r months o f r e c o r d i n g a t t h e f i e l d s i t e s , o n l y t h r e e e a r t h q u a k e s c f p o s s i b l e u t i l i t y i n f u r t h e r a n a l y s i s were r e c o r d e d . A l l o w i n g f o r down t i m e due t o e q u i p m e n t f a i l u r e s , a p e r i o d o f one y e a r w o u l d a p p e a r t c be t h e minimum t o be a l l o w e d , i n p l a n n i n g f u r t h e r e x p e r i m e n t s . 44 BIBLIOGRAPHY A t w a t e r , T. (1970) I m p l i c a t i o n s o f p l a t e t e c t o n i c s f c r t h e C e n o z o i c t e c t o n i c e v o l u t i o n of w e s t e r n N o r t h A m e r i c a . B u l l . G e o l . S o c . Am., 8J, 3 5 1 3 - 3 5 3 5 . B i o c h , S. and A.L. H a l e s (1968) New t e c h n i q u e s f o r . t h e d e t e r m i n a t i o n o f s u r f a c e wave p h a s e v e l o c i t i e s . B u l l . S e i s m . S o c . Am., 58, 1021- 1034. B o l d u c , P.M. (1971) A f e a s i b i l i t y s t u d y f o r a p o r t a b l e l o n g p e r i o d s e i s m o g r a p h . 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 c f B r i t i s h C o l u m b i a , 66 pp. B o l d u c , P.M., R.M. E l l i s a n d R.D. R u s s e l l (1972) D e t e r m i n a t i o n o f t h e s e i s m o g r a p h p h a s e r e s p o n s e f r c m t h e a m p l i t u d e r e s p o n s e . B u l l . S e i s m . Soc. Am., 6 2 , 1 6 6 5 - 1 6 7 2 . C a n e r , B. ( 1970) 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 . jG§oma.gn. G e c e l e c . , 22 , 1 1 3 - 1 2 9 . C a p o n , J . ( 1969) H i g h - r e s o l u t i o n f r e q u e n c y - w a v e number s p e c t r u m a n a l y s i s . P r o c . I E E E , 57, 1408- 14 18 . C h a n d r a , U. (1 974 ) S e i s r o i c i t y , e a r t h q u a k e m e c h a n i s m s , and t e c t o n i c s a l o n g t h e w e s t e r n c o a s t o f N o r t h A m e r i c a , f r c m 4 2 0N t o 61 ON. B u l l . S e i s m . S o c . Am., 64, 1529- 1 54 9. Dorman, J . and M. .Swing (1962) N u m e r i c a l i n v e r s i o n o f s e i s m i c s u r f a c e wave d i s p e r s i o n d a t a and c r u s t - m a m ; l e s t r u c t u r e i n t h e New Y o r k - P e n n s y l v a n i a a r e a . J . G e o p h y s . R e s . , 67 , 5227-5241 . D z i e w o n s k i , A.M., S. B i o c h and M. l a n d i s m a n (1969) A t e c h n i q u e f c r t h e a n a l y s i s c f t r a n s i e n t s e i s m i c s i g n a l s . B u l l . S e i s m . S o c . Am., 5 9 , 4 2 7 - 4 4 4 . 45 D z i e w o n s k i , A.K. and A.L. H a l e s (1972) N u m e r i c a l a n a l y s i s of d i s p e r s e d s e i s m i c w a v e s . I n Methods i n C c m j r u t a t i c n a J L P h y s i c s , v o l . 11, B. ft. B o l t , ed. New Y o r k : A c a d e m i c P r e s s . Pp. 39-85. D z i e w o n s k i , A., J . M i l l s and S, B i o c h (1 972 ) R e s i d u a l d i s p e r s i o n m e a s u r e m e n t — A new method of s u r f a c e - w a v e a n a l y s i s . B u l l . J ^ s i s r n . S c c . Am., 62 , 129-139. Ewing, M. , W.S. Jardetzky and F. Press (1957 ) E l a s t i c waves i n layered media. New York: McGraw-Hill Beck Co. 380 pp. Sarland, G.D. (1971) I n t r o d u c t i o n to Geophysics—man t i e , core and c r u s t . Philadelphia:~W.BT Saunders ~Co.7 420 FP. H a r k r i d e r , D.G. and D.L. Andersen ( 1962) Computation cf surface wave d i s p e r s i o n f o r m u l t i l a y e r e d a n i s o t r o p i c media. B u l l . Seism. Soc. Am., 52, 32 1- 332 . Hyndman, R.D. (1975) H e a t f l o w m e a s u r e m e n t s i n t h e i n l e t s o f s o u t h w e s t e r n B r i t i s h C o l u m b i a . ( S u b m i t t e d t c J. G s o p h y s . Res. ) K o l l a r , F. and R.D. R u s s e l l ( 1966) using an e l e c t r i c current analog, Am. , 56 , 11 93-1205. Seismometer a n a l y s i s B u l l . Seism. Soc. Landisman, M. , A. improvements observations. 369-4 03 . D z i e w o n s k i a n d Y. i n t h e a n a l y s i s G§oi'h_vs. j . R o j . Sato (1969) Recent of surface wave Astron. Sec., ]_J, Melton, B.S. (1971) The La coste s u s p e n s i o n — p r i n c i p l e s and p r a c t i c e . Gecphvs. J. R c j . Astron. Sec., 22, 52 1-54 3 . Press , F. (1956) Determination of c r u s t a l s t r u c t u r e from phase v e l o c i t y of Rayleigh waves. Part I: Southern C a l i f o r n i a . B u l l . Geol. Sec. Am., 67, 1647-1658. 46 S r i v a s t a v a , S.P. (1973) I n t e r p r e t a t i o n , o f g r a v i t y and m a g n e t i c m e a s u r e m e n t s a c r o s s t h e c o n t i n e n t a l m a r g i n c f B r i t i s h C o l u m b i a , Canada. Can, J . E a r t h S c i . , ]_0, 1 6 6 4 - 1 6 7 7 . S t a c e y , R.A. (1 973 ) G r a v i t y a n o m a l i e s , c r u s t a l s t r u c t u r e and p l a t e t e c t o n i c s i n the C a n a d i a n C o r d i l l e r a . Can. J . Earth S c i . , 10 , 6 1 5 - 6 2 8 . S t a c e y , R.A. (1974) P l a t e t e c t o n i c s , v c l c a n i c s a n d t h e l i t h o s p h e r e i n B r i t i s h C o l u m b i a . N a t u r e , 250 , 133-134, T o b e y , G.E. , J.G. Graeme and L . P . Hue I s man (1971) 2£§£§ii22^i A m n l i f i e r s - - D e s j . 2 n and A p p l i c a t i o n s . New Y o r k : M c G r a w - H i l l . 473 pp. T s e n g , K. (1968) A new m o d e l f o r t h e c r u s t i n t h e v i c i n i t y o f V a n c o u v e r I s l a n d . 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 o f B r i t i s h C o l u m b i a , 83 pp. W h i t e , W. R. H. and J . C. S a v a g e (1965) A s e i s m i c r e f r a c t i o n and g r a v i t y s t u d y o f t h e e a r t h ' s c r u s t i n E r i t i s h C o l u m b i a . B u l l . S e i s m . S o c . Am., 55, 435- 486. tt B i c k e n s , A . J . (1971) V a r i a t i o n s i n l i t h o s p h e r i c t h i c k n e s s , i n C a n a d a . C a n . J . E a r t h S c i . , 8, 11 5 4 - 1 1 6 2 . W i l l m o r e , P.L. (1959) The a p p l i c a t i o n o f t h e M a x w e l l i m p e d a n c e b r i d g e t c t h e c a l i b r a t i o n c f e l e c t r o m a g n e t i c s e i s m o g r a p h s . B u l l . S e i s m . S oc. Am., 4 9 , 99- 1 1 4 . 47 APPENDIX--OPERATION OF THE APPARATUS A. 1 D e s c r i n t . i o n Tha i n s t r u m e n t p a n e l s were d e s i g n e d t o d i s t r i b u t e power t o t h e a m p l i f i e r and a c t i v e f i l t e r ; t o r e c e i v e t h e s e i s m i c i n p u t ; t o d e l i v e r t h e f i l t e r e d o u t p u t t o t h e t a p e r e c o r d e r ; and t o s e r v e as an a i d i n c a l i b r a t i n g t h e s y s t e m s . A l l c f t h e p a n e l s may be u s e d f c r n o r m a l o p e r a t i o n a s w e l l as c a l i b r a t i o n , and w i l l a c c e p t e i t h e r t h e S p r e n g n e t h e r c r G e o t e c h i n s t r u m e n t s . Each o f t h e wooden e n c l o s u r e s c o n t a i n s an a m p l i f i e r , an a c t i v e f i l t e r , and t h e i n p u t t e r m i n a l s f o r t h e s e i s m o m e t e r , s i n e wave g e n e r a t o r , WWVB, t a p e r e c o r d e r and a s p a r e c h a n n e l . Two o f t h e t h r e e b o x e s a l s o h o u s e A n a t e k 512 power s u p p l i e s ; t h e t h i r d s u b s t i t u t e s a j a c k f o r an e x t e r n a l power s u p p l y . The w i r i n g d i a g r a m i s shown on F i g . A . 1. S h i e l d e d c a b l i n g i s u s e d f o r t h e c c n n e c t i c n b e t w e e n t h e f r o n t p a n e l s e i s m o m e t e r j a c k and t h e a m p l i f i e r i n p u t t e r m i n a l s , i n c r d e r t o m i n i m i z e s t r a y s i g n a l s . R e s i s t o r s R1, R2 a t t h e i n p u t p r o v i d e c r i t i c a l d a m p i n g f o r t h e s e i s m o m e t e r c e i l , and R3, R4 a t t e n u a t e t h e d r i v i n g c u r r e n t f r o m t h e s i n e - w a v e g e n e r a t o r i n " c a l i b r a t i o n " mode. R e s i s t o r v a l u e s f c r R5 t h r o u g h R9 were c h o s e n t o d i v i d e t h e f i l t e r e d o u t p u t i n t o r e l a t i v e l e v e l s o f 0 db, -12 db and -24 d t i n " o p e r a t i o n " mode; i n " c a l i b r a t i o n " mode, t h e l e v e l s a r e 0 and -12 db. Aid I ' ofERATE 8 2 0 . O . I " 0 , R>D C>' Test* I A A I [ F Y SABRE WWVB * I0 Figure A.1 Wiring diagram of the instrument pa neIs. 49 RIO a t t e n u a t e s t h e WWVi: s i g n a l , t o a v o i d o v e r d r i v i n g t h e t a p e r e c o r d e r ' s v o l t a g e c o n t r o l l e d o s c i l l a t o r ; i t s v a l u e d e p e n d s upon t h e p a r t i c u l a r r e c o r d e r and WWVE r e c e i v e r u s e d . S w i t c h S1 a l l o w s a t e s t s i g n a l t o e n t e r t h e f i l t e r d i r e c t l y ; S2 s h o r t s t h e a m p l i f i e r i n p u t s f c r t h e p u r p o s e o f b a l a n c i n g i t s o u t p u t s ; S3 i s u s e d t o m o n i t o r e i t h e r o f t h e two i n p u t c h a n n e l s ( n o r m a l l y t i m i n g s i g n a l s ) a t t e r m i n a l T3. A ' 2 I n s t a l l a t i o n P r o c e d u r e A t t h e f i e l d s t a t i o n , t h e t i l t o f t h e s e i s m o m e t e r f r a m e must be, s e t so t h a t t h e n a t u r a l p e r i o d o f t h e teem i s 20 s e c o n d s . To f a c i l i t a t e t h i s p r o c e d u r e , a s m a l l d e v i c e w h i c h c o n t a i n s an o p e r a t i o n a l a m p l i f i e r was h u i l t ( F i g . A . 2 ) . The lok -n. r— VWWA- . F i g u r e - A. 2 D e v i c e used t c check, t h e n a t u r a l p e r i o d o f t h e s e i s m o m e t e r s s e i s m o m e t e r i s c o n n e c t e d t c t h i s d e v i c e v i a a c o m p a t i b l e 5 0 t e r m i n a l , and p c w e r i s d e r i v e d f r c m t h e same power s u p p l y t h a t t h e a m p l i f i e r u s e s . E i t h e r s e i s m o m e t e r may be u s e d , b u t s w i t c h S1 must be t u r n e d t c t h e c o r r e c t p o s i t i o n . A s t e p i n p u t t o t h e s e i s m o m e t e r ' s c a l i b r a t i o n c e i l i s c o n t r o l l e d by t h e p u s h b u t t o n s w i t c h S 3 , and t h e n a t u r a l p e r i o d c a n be r e a d i l y d e t e r m i n e d w i t h a s t o p w a t c h f r c m z e r o c r o s s i n g s o f a c e n t r e - z e r o g a l v a n o m e t e r . When a d j u s t i n g t h e t i l t , b e a r i n mind t h a t r a i s i n g t h e f r o n t end c f t h e f r a m e i n c r e a s e s t h e n a t u r a l p e r i o d o f t h e bocm, and v i c e v e r s a . A. 3 T e m p e r a t u r e C o n t r o l l e r E a c h o f t h e l a r g e s t y r e f c a m e n c l o s u r e s c a n be f i t t e d w i t h a t e m p e r a t u r e c c n t r c l u n i t , w h i c h c o n s i s t s o f t h e e l e c t r o n i c s and a t h e r m i s t o r p r o b e , i n one box, and an i n c a n d e s c e n t lamp ( s e e F i g . 2 . 1 ) . The f o r m e r i s a t t a c h e d t o t h e w a l l o f t h e e n c l o s u r e so t h a t t h e t h e r m i s t o r p r o t r u d e s as f a r away as p o s s i b l e f r o m t h e w a l l ; t h e lamp ca n be f a s t e n e d on t o p o f t h e G e o t e c h s e i s m o m e t e r s o r i n f r o n t c f t h e S p r e n g n e t h e r s e i s m o m e t e r . A t h e r m o m e t e r c a n be u s e d t o m o n i t o r the t e m p e r a t u r e i n s i d e t h e e n c l o s u r e . O p e r a t i n g t e m p e r a t u r e s s h o u l d be s e t s e v e r a l d e g r e e s a b o v e t h e a m b i e n t t e m p e r a t u r e , b e c a u s e t h e c o n t r o l l e r s work mere e f f i c i e n t l y when t h e l a m p s a r e b l i n k i n g f r e q u e n t l y . 51 A « 4 C a l i b r a t i o n a n d O p e r a t i o n In " c a l i b r a t i o n " node, a s i n e - w a v e g e n e r a t o r , s u c h a s t h e w i d e - b a n d Wavetek m c d e l 111, i s used t o d r i v e t h e c a l i b r a t i o n c o i l o f t h e s e i s m o m e t e r . B o t h i n p u t and c u t p u t s i g n a l s may be m o n i t o r e d f r c m t h e f r o n t p a n e l j a c k s and d i s p l a y e d on a c h a r t r e c o r d e r . When c a l i b r a t i n g a t l o n g p e r i o d s , t h e s y s t e m i s a l l o w e d t c s t a b i l i z e f o r a b o u t two f u l l p e r i o d s b e f o r e a l t e r i n g t h e i n p u t f r e q u e n c y . A t i m i n g c h a n n e l s h o u l d be r e c o r d e d t c p r o v i d e a r e f e r e n c e p o i n t on t h e t a p e . F i n a l l y , f c r n o r m a l o p e r a t i o n , t h e f r o n t p a n e l s w i t c h e s a r e b o t h "up" and t h e mods c o n t r o l i s s e t a t " o p e r a t e " . The h i g h g a i n f i l t e r e d o u t p u t ( C h a n n e l 7) c a n be m o n i t o r e d a t t h e f r o n t p a n e l , t h r o u g h t h e j a c k s l a b e l l e d " f i l t e r o u t p u t " . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0052995/manifest

Comment

Related Items