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Pergamon PII: S0148-9062(97)00313-6I n t . J . R o c k M e c h . M i n . S c i . Vol. 34, No. 8, pp. 1213-1228, 1997 1997 Elsevier Science Ltd. All rights reservedPrinted in Great Britain0148-9062/97 $17.00 + 020

S eism ic: P a r a m e t er s a n d R o c k b u r s t H a z a r da t M t C h a r lo t te M i n eR . F. P O P L A W S K I

Results of the fir st modern seismic monitoring program in Australia underta-ken in an underground mine are presented. A new dimension to mining atMt Charlotte underground gold mine commenced with the commissioning ofa portable seismic system (PS S) in 1994. Since that time useful data havebeen collected, assisting mine planning in practical terms, providing data forscientific research and providing insight into the dynamic behaviour of rockin relation to local geology and mine production. Conventional data assess-ment involving one or two seismic parameters was found to have shortcom-ings for seismic hazard identification. A new method, "'departure indexing",is being developed to provide a robust tool for rockburst hazard evaluation,and possibly for rockburst prediction in the longer term. 1997 ElsevierScience Ltd.

I N T R O D U C T I O NI n t h e e a r l y y e a r s o f o p e r a t i o n , s e i s mic e v e n t s a t MtC h a r lo t t e w e r e r e c o r d e d a s w r i t t e n r e p o r t s b y s h i f tb o s s e s . T h e s e r e p o r t s d id n o t i n c lu d e s e i s mic p a r -a m e t e r s a n d e v e n t l o c a t i o n w a s d o u b t f u l . L a t e r , as i n g l e g e o p h o n e w a s i n s t a l l e d e n a b l i n g m o n i t o r i n g o f" r o c k - n o i s e " . B a s i c s e i s mic p a r a me te r s s u c h a s e v e n tl o c a t i o n o r m a g n i t u d e w e r e s t il l n o t k n o w n , a n d i t w a ss o o n r e c o g n i z e d t h a t s u c h m o n i t o r i n g w a s o f li m i t e dv a lu e . W e s t e r n A u s t r a l i a n s e i s mic e v e n t s o f R i c h t e rm a g n i t u d e M > 2 a r e r e c o r d e d b y a g l o b a l n e t w o r k o fs e i s m o g r a p h s o p e r a t e d b y M u n d a r i n g O b s e r v a t o r y a n dd e s i g n e d t o r e c o r d t e c t o n i c e a r t h q u a k e s . D u r i n g t h el a s t d e c a d e , s i x ma jo r s e i s mic e v e n t s o f R i c h t e rM a g n i t u d e b e t w e e n 2 . 5 a n d 4 . 3 t o o k p l a c e a t M tC h a r l o t t e . D a m a g e f r o m s u c h e v e n t s w a s o f t e n e x t e n -s iv e . S e v e r a l r e s e a r c h e r s ma d e v a lu a b l e p r o g r e s st o w a r d s b e t t e r r e c o g n i ti o n o f t h e s e is m i c n a t u r e o f M tC h a r lo t t e min e [ 1 - 1 3 ] . T h i s p a p e r d e s c r i b e s p r o g r e s s i nth e a n a ly s i s o f v a r i o u s s e i s mic p a r a m e te r s a n d t h e i r r e-l a t i o n t o t h e min e g e o lo g y , s t r e s s f i e l d a n d p r o -d u c t i v i t y . A n a t t e m p t h a s b e e n m a d e t o w a r d sr o c k b u r s t p r e d i c ti o n .

MT CHARLOTTE MINEDescription of the mine

M t C h a r l o t t e u n d e r g r o u n d g o l d m i n e i s l o c a t e da d j a c e n t t o t h e c i t y o f K a l g o o r l i e - B o u l d e r i n W e s t e r nA u s t r a l i a ( F ig . 1 ) . T h e min e e x t e n t i s ca 1 4 00 m n o r th -- s o u th , 5 0 0 m e a s t - w e s t a n d 1 20 0 m b e lo w th e s u r fa c e .* T h e U n i v e r s i ty o f M e l b o u r n e , D e p a r t m e n t o f C i v il a n d

E n v i r o n m e n t a l E n g i n e e r i n g , P a r k v i l le , V ic , A u s t r a l i a .

A l o n g h o l e o p e n s t o p i n g m e t h o d i s g e n e r a l l y u s e d .O p e n s t o p e s a r e min e d i n a b lo c k a lo n g s t r i k e , a n dth e n r i b / c r o w n p i l l a r s a r e ma s s b l a s t e d w i th w a s t er o c k f i l l f r o m a b o v e c a s c a d in g o n to t h e b r o k e n o r e .E x t r a c t i o n i s f r o m d r a w p o i n t s b e l o w , u n t i l w a s t e r o c kd i l u t i o n b e c o me s e x c e s s iv e . B lo c k y w a s t e r o c k f i l l i sc o n t i n u a l l y a d d e d a t t h e s u r f a c e G lo r y P i t ( F ig . 2 ).

R o c k r e i n f o r c e m e n t i n s t a l l e d i n t h e m i n e c o m p r i s e sr e s in - a n c h o r e d 2 . 4 m lo n g r e b a r s , 8 - 1 5 m lo n g g r o u t e dc a b l es , 4 m lo n g r e b a r s . I n 1 99 4 3 m lo n g c o n e b o l t sw e r e i n t r o d u c e d t o r e in f o r c e d r a w p o in t p i l l a r s s u s c e p -t i b le t o r o c k b u r s t . R e in f o r c e m e n t o f b a c k s i s su p -p l e me n te d b y e x t e n s iv e u s e o f s t e e l s t r a p s . A r e a ss u s p e c t e d t o b e v u ln e r a b l e , o r w h e r e o ld r e in f o r c e me n ti s c o r r o d e d , r e c e iv e a d d i t i o n a l s u p p o r t . S o me w a l l s a r er e in f o r c e d w i th r o c k b o l t s , a n d p i l l a r s a r e r e in f o r c e dw i th r o c k b o l t s a n d s t r a p s . S h o t c r e t e a n d s t e e l me s h i sg e n e r a l l y n o t u s e d e x c e p t a t p l a t s a n d c r i b r o o ms .T y p ic a l d r i v e o p e n in g s a r e a p p r o x ima te ly r e c t a n g u l a r ,6 m w i d e b y 5 m h i g h . A r c h e d b a c k s w e r e i n t r o d u c e din D e c e mb e r 1 9 9 5 .

T h e h o s t r o c k ma s s i s d o l e r i t e , w i th t y p i c a l l a b o r a -t o r y p r o p e r t i e s o f U C S = 1 80 M P a , e l a s ti cm o d u l u s = 6 5 M P a a n d P o i s s o n ' s r a t io = 0 . 26 . T h e s ep r o p e r t i e s v a r y f r o m s i te t o s i te , e s p e c ia l l y i n f r a c tu r e do r f a u l t z o n e s w h e r e t h e in situ v a l u e s m i g h t b e c o n -s i d e ra b l y l o w e r t h a n t h e l a b o r a t o r y v a l u e s.

T h e m a j o r s t r es s a l i s o r i e n t e d a p p r o x i m a t e l y n o r t h -- s o u th , a 2 i s e a s t - w e s t a n d 0 " i s s u b v e r t i c a l . T h e ma g -n i t u d e o f t h e n o r t h - s o u t h s tr es s i s a p p r o x i m a t e l y t w i c et h a t o f t h e e a s t - w e s t s t r e s s a n d a p p r o x i m a t e l y t h r e et imes a s la rge a s the ve r t ica l s t r e ss a t any g iven leve lb e lo w th e s u r f a c e . R e p r e s e n t a t i v e s t r e s s v a lu e s a r e a sfo l lows:

1 2 1 3

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1 2 1 4 P O P L A W S K I :SEISMIC PARAMETERS AND ROCKBURST HAZARD AT MOUNT CHARLOTTE MINE

21tm!

rl~N

Fig. 1. Location of Mt Charlotte mines.

A t 6 0 0 m d e p t h : 0 " 1 : 60, 0 " 2 : 30, 0"3 = 20 M Pa .A t 1200 m d ep th: 0-1 : 80, 02 = 40, 0"3 ~--- 3 0 M P a .

A n i n t e r e st i n g p h e n o m e n o n i s t h a t t h e d i r e c t i o n o f t h em a j o r s tr e ss i s c o i n c id e n t a l w i t h t h e d i r e c t i o n o f t h eo r e b o d y s t r i k e .

G e o l o g yA t M t C h a r l o t t e t h e o r e o c c u r r e n c e is as s o c i a t e d

w i t h s t o c k w o r k s o f q u a r t z v e i n s a d j a c e n t t o m a j o ro b l i q u e f a u l t s , a n d g e n e r a l l y r e s t r i c t e d t o a g r a n o p h y -r i c u n i t w i t h i n . t h e G o l d e n M i l e D o l e r i t e . Q u a r t z v e i n si n t h e s t o c k w o r k a v e r a g e 8 0 m m t h i c k [ 1 4 -1 6 ] .

T h e r e a r e t w o d i s t i n c t o r e b o d i e s b o u n d e d b y as e ri e s o f t h r e e s u b v e r t i c a l fa u l t s ( M a r i t a n a , R e w a r da n d C h a r l o tt e ) . T h e C h a r l o t t e o r e b o d y ( C O B ) w h i c h iss e p a r at e d f r o m t h e R e w a r d o r e b o d y ( R O B ) b y t h eR e w a r d f a u l t i s t h e l a r g e r o f t h e t w o . B o t h o r e b o d i e sd i p n e a r l y v e r t i c a l l y a n d a r e o n s i m i l a r s t ri k e . T h eG o l d e n P i k e f a u l t d i p p i n g a t ca 7 0 f o r m s t h e s o u t h e r nb o u n d a r y o f t h e m i n e. D i s p l a c e m e n t o n t h e s e f au l tsv a r i es f r o m 6 0 t o 2 0 0 m .

A s e c o n d s er ie s o f fa u l t s ( N e p t u n e , F l a n a g a n a n dS h e a ) d i p a t ca 4 5 t o t h e w e s t a n d f a u l t d i s p l a c e m e n t sv a r y b e t w e e n 1 0 a n d 1 5 0 m . T h e r e is a s i g n i f i c a n t n u m -b e r o f s m a l l e r f a u l t s w i t h i n t h e m i n e . T h e s e f a u l t s t r u c -t u r e s t o g e t h e r w i t h m i n e o p e n i n g s p l a y a s i g n i f i c a n tr o l e i n m i n e s e is m i c b e h a v i o u r .

T h e r e i s e v i d e n c e o f g r o u n d w a t e r s e e p a g e in t o M tC h a r l o t t e m i n e o n t h e l o w e s t l e v e l s o n l y a n d g e n e r a l l y ,g r o u n d w a t e r is n o t a p r o b l e m .

M a j o r m i n e a r ea sS e is m i c b e h a v i o u r o f s e v e ra l m a j o r m i n e a r e a s w e r e

m o n i t o r e d f o r t h i s s tu d y . T h e l o c a t i o n s o f t h e s e a re a sa r e s h o w n i n F i g . 2 . A c t i v e s t o p e s d u r i n g t h e p e r i o d o fs t u d y w e r e R O B - 5 , C D O B - I 1 , C D O B - I 2 a n d R O B - 3 .

S E I SM I C M O N I T O R I N G S Y S T E MJ u s t i f i c a t io n f o r t h e se i s m i c s y s t e m i n s t a ll a t io n

A m a j o r m o t i v a t i o n f o r th e i n s ta l l a ti o n o f a m o d e r ns e i s m i c m o n i t o r i n g s y s t e m a t M t C h a r l o t t e w a s t h ef a c t t h a t m o r e e c o n o m i c a l a n d s a f e r m i n i n g w a si n c r e a s i n g l y d e s i r a b l e . O n e o f t h e p r a c t i c a l b e n e f i t s o fh a v i n g s u c h a s y s t e m i n s t a l l e d o n s i te is t h a t i f a s ei s-m i c e v e n t t a k e s p l a c e , i t s l o c a t i o n c a n b e f o u n dq u i c k l y a n d i t is r e la t i v e l y e a s y t o m a k e a v i s u a li n s p e c t i o n f o r i n d u c e d d a m a g e . T h i s b o t h h e l p s toq u a n t i f y t h e s e is m i c h a z a r d a n d a s si st s m i n e p e r s o n n e lr e s p o n d t o a n e v e n t . T i m e p r e v i o u s l y l o s t a f t e r am a j o r e v e n t d u e t o t h e n e e d f o r t o t a l m i n e e v a c u a t i o na n d l a b o r i o u s v i s u a l i n s p e c t i o n ( w i t h o u t t h e k n o w l e d g eo f e v e n t l o c a t i o n ) c a n n o w b e s a v e d . T h e p r e c is e lo -c a t i o n o f a s e is m i c e v e n t w o u l d a l s o h e l p i n t h e c a se o fa m o r e s e r i o u s e m e r g e n c y .

M o d e r n s e i s m i c s y s t e m s c a n p r o v i d e u s e f u l i n f o r -m a t i o n r e g a r d i n g s e i s m i c p a r a m e t e r s , t h e i r v a l u e s a n dt r e n d s . T h i s i n c l u d e s n o t o n l y l o c a t i o n a n d l o c a l P S SR i c h t e r m a g n i t u d e , b u t a l s o o t h e r i m p o r t a n t p a r -a m e t e r s s u c h a s s e i s m i c m o m e n t , s e i s m i c e n e r g y , s t r e s sd r o p a n d a p p a r e n t v o l u m e . K n o w l e d g e o f s u ch p a r -a m e t e r s a n d t h e i r v a r i a b i l i t y c a n g i v e a n i m p o r t a n ti n s i g h t i n t o r o c k m a s s b e h a v i o u r .

T h e d e c i s i o n t o i n s t a l l a s e i s m i c s y s t e m w a s p r o b -a b l y a l s o i n f l u e n c e d b y a n i n c r e a s e d e n v i r o n m e n t a lc o n s c i o u sn e s s . T h e p r o x i m i t y o f th e m i n e t oK a l g o o r l i e ( d w e l l i n g s w i t h i n 2 0 0 m ) c r e a t e d a s i t u a t i o ni n w h i c h th e i n s t a ll a t io n o f a m o n i t o r i n g t o o l b e c o m ei m p o r t a n t f o r l i a b il it y r e a so n s .

T h i s r a t h e r s t r a i g h t f o r w a r d j u s t i f i c a t i o n d i d n o ta p p e a r t o b e s o s i m p l e p r i o r t o t h e s y s t e m i n s t a l l a t i o n ,a n d s o m e s e r i o u s d o u b t s w e r e c a s t b y n u m e r o u s p e r -s o n s r e g a r d i n g t h e n e c e s s it y a n d t h e c o s t s i n v o lv e d .D i s c u s s i o n " f o r a n d a g a i n s t " a s w e l l a s a c o m p a r i s o nw i t h c o m p e t i t i v e i n s t r u m e n t a t i o n i s g i v e n b yM i k u l a [ 5 ] .

T h e d e c i s io n w a s e v e n t u a l ly m a d e t o p u r c h a s e a p o r -t a b l e s e i s m i c s y s t e m ( P S S ) f r o m C S I R ( S o u t h A f r i c a ) .T h e s y s t e m w a s c o m m i s s i o n e d a t a n e x p e n s e o f ca$ 2 2 0 0 0 0 a n d t h e b r e a k - e v e n p o i n t w a s r e a c h e d a f t e r1 0 m o n t h s o f o p e r a t i o n [5 ].P o r t a b l e s e i s m i c s y s t e m h a r d w a r e

T h e 3 2 - c h a n n e l P S S c o m m i s s i o n e d o n 2 4 M a r c h1 9 9 4 a t M t C h a r l o t t e m i n e w a s t h e f ir s t m o d e m s y s t e mo f t h is k i n d i n A u s t r a l i a. R e g u l a r d a t a c o l l e c ti o ns t a r t e d i n M a y 1 9 9 4 a n d s i n c e t h a t t i m e m u c h i n t e r e s t -i n g i n f o r m a t i o n h a s b e e n a c c u m u l a t e d . T h e P S S c o m -p r i s e s n i n e t r i a x i a l g e o p h o n e s e t s i n s t a l l e d a t v a r i o u sl o c a t i o n s u n d e r g r o u n d , a n d f o r a s h o r t p e r i o d t h e r e

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POPLAWSKI: SEISMIC PARAMETERS AND ROCKBURST HAZAR D AT MOUNT CHARLOTTE MINE 1215

|NOI~H SO U! - (~ ~ ~ ' " ~ ' 1

SL N O B

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Q Seismic on i t o r i ng S t a t i on !~ ; ~ ] S t o ~ . d B lo c k s( ~ ResourceOufllne

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Fig. 2. Mt Charlotte mine showing studied areas and monitoring sites.

39L

w a s a l s o o n e t r i a x i a l g e o p h o n e s e t m o u n t e d a t t h e s u r -f a c e ( F i g s 2 a n d 3 ) .

G e o p h o n e l o c a t i o n s w e r e c h o s e n s o t h a t o r e b o d i e sa n d m a j o r g e o l o g i c a l f e a t u r e s a s w e l l a s m i n e d e v e l o p -m e n t s i te s w e r e g e n e r a ll y e n c lo s e d w i t h i n t h e g e o p h o n en e t w o r k . T h e t e n o p e r a t i o n a l s e i s m i c s t a t i o n s p r o v i d ea t o t a l o f 3 0 c h a n n e l s o f f u ll w a v e f o r m d a t a . S i g n al sf r o m t h e g e o p h o n e s a r e a m p l i f i e d a n d f r e q u e n c ym o d u l a t e d i n t h e u n d e r g r o u n d o u t s t a t i o n s , a n d t h e n

s e n t v i a t w i s t e d p a i r t e l e p h o n e c a b l e t o t h e t w o d a t aa c q u i s i t i o n u n i t ( D A U ) c o m p u t e r s i n s t a l l e d i n t h e s u r -f a c e o f f ic e a r e a . T h e s i g n a ls a r e d i g i t iz e d i n t h e D A Uc o m p u t e r s a n d t h e n s e n t t o a n I B M - P C t o b e l o a d e do n t o h a r d d i sk . A f t e r t h i s p r o c e d u r e , t h e c o l l e c t e d d a t aa r e v i e w e d a n d a s s e s s e d a s r e q u i r e d . T h e s y s t e me n a b l e s r e la t i v e ly s im p l e d a t a m a n i p u l a t i o n a n d i n -t e r p r e t a t i o n . T h e w h o l e o p e r a t i o n i s c o n t r o l l e d f r o mt h e o f f ic e a r e a .

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1216 POPLAWSKI: SEISMIC PARAMETERS AND ROCKBU RST HAZARD AT M OUNT CHAR LOTTE MINE l o c a t i o n o f s ei sm i c e v e n t ( X , Y , Z c o o r d i n a t e s ) ; d a t e a n d t i m e ; l o c a l P S S r i c h t e r m a g n i t u d e ; s e i sm i c m o m e n t f o r P , S o r P + S w a v e s ; s e i sm i c e n e r g y , f o r P , S o r P + S w a v e s ; a p p a r e n t v o l u m e , f o r P , S o r P + S w a v e s ; s e i sm i c so u r c e r a d i u s f o r P , S o r P + S w a v e s ; t h e P , S c o r n e r f re q u e n c i e s ; t h e b v a l u e s ( t o b e d e f i n e d a n d d i s c u s se d l a t e r ); m o m e n t t e n so r ; s t a t i c s t r e s s d r o p .

Fig. 3. Schematic diagram o f the PSS seismic mon itoring hardware(after R ef. [24]).

PSS softwareT h e P S S s o f t w a r e i s a c o m b i n a t i o n o f s e v e ra l s u b -

p r o g r a m s a n d r o u t i n e s w r i t t e n i n F o r t r a n o r P a s c a l f o rd i f f er e n t t a s k s. T h e s t r u c t u r e o f th e s u b - p r o g r a m s f a -c i l i t a t e s c o m m u n i c a t i o n b e t w e e n t h e m , e n a b l i n g t h er e q u e s t e d p a r a m e t e r s o r g r a p h s t o b e d i s p l a y e d b y t h eP C .

T h e c h a r a c t e r is t i c s o f t h e s e is m i c w a v e f o r m s c a n b eq u i c k l y a n a l y s e d u s i n g s c r e e n g r a p h i c s . S u c h g r a p h i c sm a k e t h e a n a l y s i s a n d i n t e r p r e t a t i o n o f v a r i o u s s e is m i cp a r a m e t e r s s u c h a s s e i s m i c e n e r g y , s e i s m i c m o m e n t ,s tr e ss d r o p o r a p p a r e n t v o l u m e , r e l a ti v e l y s t r a i g h t f o r -w a r d . T h e P S S s o f t w a r e i s g e n e ra l l y u s e r f r i e n d l y a n dr e l a t i v e l y e a sy t o o p e r a t e .

Seismic parametersT h e f i r s t q u e s t i o n s o f t e n a s k e d r e g a r d i n g a s e i s m i c

e v e n t i n a n u n d e r g r o u n d m i n e c o n c e r n l o c a t io n a n dm a g n i t u d e o f t h e e v e n t. T h e P S S s e i s m ic e v e n t lo c a t i o na l g o r i t h m i s b a s e d o n t h e P - a n d S - a r r i v a l t i m e s , p l u sp o l a r i z a t i o n i f w a v e f o r m c l a r it y p e r m i ts . T y p i c a l c o m -p u t e d p r e c i s i o n o f l o c a t io n i s 3 1 5 m . T h e a v e r a g e r e -l ia b i li ty o f e v e n t l o c a t i o n , b y c o m p a r i s o n w i t hc a l i b r a t i o n b l a s t s a t k n o w n l o c a t i o n s i s 1 2 m , w i t h ar a n g e o f 2 - 2 5 m . T h e m o s t i m p o r t a n t p a r a m e t e r s c o l -l e c te d a u t o m a t i c a l l y b y t h e P S S a r e:

S E IS M I C B E H A V I O U R O F M T C H A R L O T T E M I N ED u r i n g t h e o n e a n d a h a l f y e a r m o n i t o r i n g p e r i o d

f r o m 2 6 M a y 1 9 94 t o 2 6 N o v e m b e r 1 99 5 s o m e in t e r -e s t i n g d a t a w e r e c o l l e c t e d . T h e m o s t i n t e r e s t i n g s e i sm i cp h e n o m e n a c o l l e c te d w i t h in t h i s s e l ec t ed p e r i o d a r eb r i ef l y p r e s e n t e d h e r e . S e i s m i c m o n i t o r i n g i s a c o n t i n u -o u s p r o c e s s , a n d d a t a c o l l e c t io n a s w e l l a s r e s e a r c h i so n g o i n g . S o m e e a r l i e r o b s e r v a t i o n s c a n b e f o u n d i nM i k u l a a n d P o p l a w s k i [ 1 0 ] .Seismic parameters for the whole mine

Event magnitude and occurrence. T h e f r e q u e n c y a n dm a g n i t u d e o f s ei sm i c e v e n ts m o n i t o r e d a t M t C h a r -l o t t e i n d i c a t e t h a t s e i sm i c a l l y a c t i v e a n d p a s s i v ep e r i o d s c a n b e d i s t i n g u i s h e d . F o r e x a m p l e , t h e p e r i o df r o m 1 4 S e p t e m b e r 1 9 9 4 t o 7 A p r i l 1 9 9 5 c a n b e r e c o g -n i z e d a s s e i sm i c a l l y a c t i v e , a n d t h e p e r i o d a f t e r 7 A p r i l1995 as re l a t ive ly qu ie t (F ig . 4 ) .

A c o n t r o v e r s i a l p h e n o m e n o n d i s c u ss e d b yG r e g s o n [ 1 7 ] c o n c e r n s t h e r e l a t io n s h i p b e t w e e n m i n ei n d u c e d s e i sm i c i t y a n d r e g i o n a l t e c t o n i c s e i sm i c i t y i nt h e E a s t e r n G o l d f i e l d s a r e a . F o r t h i s r e a s o n m a g n i t u d ed a t a f r o m t h e P S S i n s t a l l e d a t M t C h a r l o t t e a n d d a t ac o l l e c t e d a t t h e M u n d a r i n g o b s e r v a t o r y w e r e c o m -p a r e d . E v e n t s w i t h l o c a l P S S R i c h t e r m a g n i t u d e o fz e r o o r g r e a t e r w e r e s e l e c t e d ( F i g . 4 ) . F o r s e v e r a lr e a so n s , t h e l o c a l e v e n t m a g n i t u d e r e c o r d e d b y t h e M tC h a r l o t t e s y s t e m d if f er s f r o m t h e R i c h t e r m a g n i t u d e o ft h e g l o b a l m o n i t o r i n g s y s t e m [ 1 0 ] . D a t a f r o m o t h e rm i n e s i n t h e E a s t e r n G o l d f i e l d s a r e a a r e n o t a v a i l a b l e .I t i s d i f f i c u l t t o f i n d a r e l i a b l e r e l a t i o n sh i p b e t w e e nt h e se t w o s e t s o f e v e n t s a t t h e p r e se n t t i m e , h o w e v e r ,s o m e s u g g e s t io n s c a n b e m a d e . S e i sm i c e v e n t s p r i o r t o1 4 J u n e 1 9 9 4 f o r m e d a d i s t i n c t i v e c l u s t e r r e c o r d e d b yb o t h s y s te m s . A n o t h e r c l u s t e r o f g l o b a l te c t o n i c s ei s-m i c e v e n ts w a s r e c o r d e d o n 1 5 A p r i l 1 99 5. A b o u t aw e e k l a t e r t h i s w a s f o l l o w e d b y a r o c k b u r s t ( l o c a l P S SR i c h t e r m a g n i t u d e + 0 . 1) a t M t C h a r l o t t e .

Parameter b. T h e p a r a m e t e r b r e l a t i n g l o c a l P S SR i c h t e r m a g n i t u d e a n d f r e q u e n c y o f o c c u r re n c e o f as e i sm i c e v e n t f o r a g i v e n c l u s t e r o f e v e n t s w a s e s t a b -l i s h e d f o r t h e w h o l e M t C h a r l o t t e m i n e ( F i g . 5 ) a s w e l la s f o r e a c h m a j o r m i n e a r e a . T h e p a r a m e t e r b m a y b ec o n s i d e r e d a n i n d i c a t o r o f se i sm i c r is k . A s m a l l bv a l u e su g g e s t s t h a t s e i sm i c e n e r g y i s b e i n g r e l e a se d i n

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5 . 04 . 5

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f / ~ N . - ' . " I J , _ , ' ~ , J & , r . ' l ' ~ ~ u / i i J I , . t : ~ ; . . g I . ' , ; I~L 3 . . ~ ~ . t , I .. i I . ,, I ., t ~ i t l . i , . ~ _ , ~ , i . i

! . . . . ! . . . ! . . . . . . . . . . . ! . . . . . . ! , , , , ! . . . . ! , . . , ! , ,

T imeFig. 4. Mt Charlotte events (PSS Richter magnitude) and W estern A ustralia earthquakes (Richter magnitude).

b i g g e r e v e n t s . F o r e x a m p l e i n t h e S o u t h A f r i c a n B l y -v o o r u i t z i c h t m i n e , i f t h e b v a l u e d r o p s b e l o w 0 . 6 5 c o n -t i n u o u s l y f o r 3 d a y s i n a n y p r o d u c t i o n a r e a , a na s se s sm e n t o f s ei sm i c r i sk i n t h a t s e c t i o n o f t h e m i n e i sc o n d u c t e d .D u r i n g t h e o n e a n d a h a l f y e a r p e r io d o f m o n i t o r i n ga t M t C h a r l o t t e , a b v a l u e o f c a 1 . 0 5 w a s r e c o r d e d f o rt h e w h o l e m i n e , s u g g e s t i n g t h a t t h e s e is m i c h a z a r d a tM t C h a r l o t t e m i g h t b e l o w . T h e m o s t a c t i v e a r e a s o ft h e m i n e in t e r m s o f d e v e l o p m e n t a n d p r o d u c t i o n ,s u c h a s R O B - 5 s t o p e a n d C D O B - I 2 s t o p e e x p e r i e n c e d

a b v a lu e in t h e r a n g e 0 . 8 - 1 .5 . T h e s m a l l n u m b e r o fe v e n t s in t o t a l , m e a n s t h a t b v a l u e c a lc u l a t i o n s f o ro t h e r m i n e a r e a s a t t r a c t s i g n i f i c a n t s t a t i s t i c a l e r r o r .

R o c k q u a l i ty f a c t o r . S e i s m i c m o n i t o r i n g c a n b e u s e da s a f a s t m e t h o d t o a s s es s r o c k q u a l i t y . A " r o c k q u a l -i t y f a c t o r " c a n b e c a l c u l a t e d f o r e a c h e v e n t . T h e m a -j o r i t y o f s e is m i c e v e n t s a t M t C h a r l o t t e a r ec h a r a c t e r i z e d b y r o c k q u a l i t y f a c t o r s o f < 2 0 ,s u g g e s t i n g t h a t m o s t s e i s m i c e v e n t s t o o k p l a c e i n t h eh i g h l y f r a c t u r e d r o c k i n t h e v i c in i t y o f th e s t o p e s( F i g . 6 ) . T h i s c a n b e v e r i f i e d b y a n a l y s i s o f c o o r d i n a t e s

J

=~ r& .

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1,0 " xMin.Ma ~ - ~b-value: 1.06 ~4--0,09 ~o~. confidence) ~ ~ ,0 . 0 n I i i ! I I n n , I g I I n ! t i i i ! n i i i ! i g i i ! i I N . I i ! i i i i

-2.50 -2.00 -1 ,50 -I ,00 -0 ,50 -0 ,00 0 ,50 1 ,00

Fig. 5. Parameter b fo r the whole mine (PSS graph).

I I I t I I1.50 2.00M a g n i t u d e

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1218 P O P L A W S K I : S E IS M I C P A R A M E T E R S A N D R O C K B U R S T H A Z A R D A T M O U N T C H A R L O T T E M I N E6 0

. . 5 o i . . I I4 0 i ' "

- n m im nn

: , : ." ) ! ; : : i ._ : . ' . . . , . m , m[m m [ k = m m m

~ 3 1 0 : | | * '~ " I ] . . l i ~ : ' "a " . . ~ "_ u m , m 11 p _ _ _ _ m ~ . ~ I ~ i . a _ _ ,0

T i m eF i g . 6 . R o c k q u a l i t y f a c t o r Q .

o f s e is m i c e v e n t s , a n d a l s o b y t h e f a c t t h a t t h e m a -j o r i t y o f s e i s m i c e v e n t s w e r e a s s o c i a t e d w i t h b l a s t i n ga c t iv i t y a n d o c c u r r e d w i t h in b l a s t t i m e w i n d o w s .

Proportion of seismic energy in P- and S-waves. S o m es e i s m i c e v e n t s a r e c h a r a c t e r i z e d b y a r e l a t i v e l y l a r g ec o n t e n t o f s e i s m i c e n e r g y i n t h e P - w a v e . I t i s s u g g e s t e dt h a t t h e s e a r e e v e n t s o f i m p l o s i o n a l c h a r a c t e r c l o s e t ot h e s t o p e s . O t h e r c l u s t e r s o f e v e n t s w i t h a l a r g e c o n -t e n t o f s e i s m i c e n e r g y i n t h e S - w a v e a r e b e l i e v e d t o b ea s s o c i a t e d w i t h s l i p o n e x i s t i n g g e o l o g i c a l f a u l t s . T h e s ep r o p o r t i o n s o f P - a n d S - w a v e e n er g y c o n t e n ts f o r m ad i s t in c t i v e f a m i l y o f e v e n t s ( F i g . 7 ) .

Source radius. T h e r a d i u s o f a se i s m i c s o u r c e c a n b eu n d e r s t o o d a s th e r a d i u s o f a n i m a g i n a r y s p h e r e e nv e l -o p i n g a r e g i o n o f i n e la s t i ca l l y d e f o r m e d o r s h e a r e dr o c k d u e t o t h e s e i s m i c e v e n t . A t M t C h a r l o t t e t h e s er a d ii v a r i e d b e t w e e n 2 a n d 4 8 m , w i t h m a j o r i t y o fe v e n t s < 2 5 m .Seismic energy, moment and apparent volume com-pared with local Richter magnitude. R i c h t e r m a g n i t u d eh a s b e e n c r i t i c i z e d f o r n o t b e i n g a b l e t o r e p r e s e n t s e i s -m i c e v e n t s p r o p e r l y [ 1 8, 1 9 ] . I t w a s f o u n d a t M t C h a r -l o t t e t h a t s e i s m i c e n e r g y f o r e v e n t s w i t h t h e s a m e l o c a lP S S R i c h t e r m a g n i t u d e v a r i e d s i g n i f i c a n t l y ( F i g . 8 ) .F o r e x a m p l e , s e i s m i c e n e r g y f o r t y p i c a l e v e n t s a t M tC h a r l o t t e w i t h lo c a l P S S R i c h t e r m a g n i t u d e o f - 1 . 5v a r i e d f r o m 2 0 t o 3 0 0 0 0 J . A s i m i l a r o b s e r v a t i o n c a nb e m a d e f o r t h e s e is m i c m o m e n t ( w h i c h is r el a t ed t ot h e a m o u n t o f s li p o n t h e g e o l o g i c a l fa u l t) i n c o m p a r i -s o n t o t h e l o c a l P S S R i c h t e r m a g n i t u d e ( F i g . 9 ). F o re x a m p l e , t h e s ei s m i c m o m e n t f o r e v e n t s w i t h a l o c a lP S S R i c h t e r m a g n i t u d e o f - 1 . 5 v a r i e d f r o m1 .1 E + 05 k N m t o 3 . 0 E + 09 k N m . A p p a r e n t v o l u m e

( v o l u m e o f t h e r o c k m a s s u n d e r g o i n g i n el a st ic d e f o r -m a t i o n d u e t o t h e s e i s m i c e v e n t ) v a r i e d f r o m1 . 0 E - 1 1 m 3 to 1 . 7E + 01 m 3 f o r - 1 . 5 l o c al P SS R i c h -t e r m a g n i t u d e e v e n t s ( F i g . 1 0 ). C u r r e n t l y , e f f o r t s a r eb e i n g m a d e t o w a r d s f i n d i n g a m o r e c o n s i s te n t a n dm e a n i n g f u l d e s c r i p t i o n o f a s e i sm i c e v en t .

Seismic parameters for major mine areas. S e i s m i cp a r a m e t e r s w e r e e s t a b li s h e d f o r e a c h m a j o r m i n e a r e a .C o m p a r i s o n o f v a r i o u s t r e n d s d i sp l a y e d b y th e s e p a r -a m e t e r s e n a b l e d b e t t e r u n d e r s t a n d i n g o f r o c k m a s s

1 . 0 0 E + 0 7

1 . 0 0 E + 0 6 tO 1 1 . 0 0 E + 0 5

- t. 0 0 E + 0 4> , !~ 1 . 0 0 E + 0 3

. ~ 1 . 0 0 E + 0 2"~ ) 1 .0 0 E + 0 1 -n ' 1 . 0 0 E + 0 0

1 . 0 0 E - 0 t : . . . . . . . . ' . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . : . . . . . . . . ; . . . . . . . ~ . . . . . . .

-, ,t, ,,, ., ,,, ., ,t, ,,, ,,,o ~ o o o o o o c~=. . q = . o . o . o . ~ o ." F c e " "- S s m E n r g y { l o g l o }F i g . 7 . P r o p o r t i o n o f s e is m i c e n e r g y i n S - a n d P - w a v e .

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1 . 0 0 E + 0 7O ) 1 , 0 0 E + 0 6_o, - ~ 1 . 0 0 E + 0 5- )> ~ 1 . 0 0 E + 0 4

1 . 0 0 E + 0 3U Jl : : 1 . 0 0 E + 0 2.~ _( / ) 1 . 0 0 E + 0 1( / )4 -n 1 . 0 0 E + 0 0

t . 0 0 E - 0 1- 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 - 0 . 5 0 . 0 0 . 5

M L - l o c a l R i c h t e r M a g n i t u d e ( P S S )1.0 1.5

Fig . 8 . Seismic energy and PSS Richter magnitude.behaviour and response to mining . The most interes t -ing f indings are presented as fo l lows:

Distribution of seismic events. S i x h u n d red a n dtwenty three se i smic events were recorded a t Mt Char-lo tte mine during the one and a ha l f year s tudy period(F ig . 11) . The greatest numb ers o f se i smic events ( i.e.179 and 152 events ) were associa ted wi th mining o fCD OB -I1 an d ROB -5 s topes , respect ive ly . Dur ing thist ime , C D O B -I 1 w a s th e l a rg es t mi n e p ro d u c t i o n s to p e ,w h i l e fo r R O B -5 s to p e , p ro d u c t i o n w a s co mp l e ted , b u tthe s tope w as not yet backf il led . Se i smic events in

large numbers were expected to be associa ted wi thmi n i n g R O B -5 s to p e d u e to th e g eo metry o f th e s to p e(large, on ly partial ly fi l led void ) and d ue to the m ined ev e l o p men t .

Cumulative seismic energy per cumulative apparentvolume. The most se i smica l ly act ive mine areas , sucha s a ro u n d th e R O B -5 a n d C D O B -I 1 s to p es w h ere th etota l number o f se i smic events was the greates t , d i s -played a relatively sma ll average ratio of seism icenergy per apparent vo lum e (F ig . l 1 ). This phenom -enon i s probably due to the fact that the se i smic events

, . , , 1 . 0 0 E + 1 2O~ ) 1 . 0 0 E + 1 1O 1 . 0 0 E + 1 0

I m m lE 1 . 0 0 E + 0 9Z , 1 . 0 0 E + 0 81 . 0 0 E + 0 7~ 1.00E+06: ~ 1 . 0 0 E + 0 5lm; : 1 . 0 0 E + 0 4" 3 1 . 0 0 E + 0 3U ) 1 . 0 0 E + 0 2( n+ 1 . 0 0 E + 0 1n" ~ 1 . 0 0 E + 0 0

= . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . = . . . . .

"~ x tt} : ~ 2 2 ~ : " = = ' i ~ ' p k ~ : - : : ~ 2 :

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- 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 ~ . 5 0 . 0 0 . 5 1 . 0 1 . 5M L - l o c a l R i c h t e r M a g n i t u d e ( P S S )

Fi g . 9 . Se i smi c mo me nt a nd PSS Ri c hte r ma g ni tude .

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, . ~ 1 . 0 0 E + 0 3O~ .. 1 . 0 0 E + 0 2O IO 1 . 0 0 E + 0 1" " 1 . 0 0 E + 0 0~ " 1 . 0 0 E - 0 1 1 . 0 0 E - 0 6 1 . 0 0 E - 0 7

1 . 0 0 E - 0 8Q . 1 . 0 0 E - 0 9Q .< I { 1 . 0 0 E - I 0( / ) 1 . 0 0 E - 1 1+ 1 . 0 0 E - 1 2n" - " 1 . 0 0 E - 1 3

m l I a - i l

I , , _ i i l l s ~ ~ _ : F l ~ i - - 0 i ~ l i l l i ' l - : I tI t ~ i , m , , - i ~ r ~ . ! I , *i l l i - - ,' ,7I ; i

i t . l , . . , . 1 : I 1i 1 ' . . . . . . . i i

I ' i i i l li ,

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- 2 . 5 - 2 - ! . 5 - 1 - 0 . 5 0 S ~ . 5 1M L l o c a l R i c h t e r M a g n i t u d e ( P S1 . 5

F i g . 1 0. A p p a r e n t v o l u m e a n d P S S R i c h t e r m a g n i t u d e .

are situated closer to the openings where they aremore likely to be implosional in character. In theseareas the seismic energy is more efficient, producinglarge volumes o f inelastically deformed rockmass.

Cumula t i ve num ber o f even ts . The cumulative numberof seismic events was plotted for each major mine area(Fig. 12). Several distinctive behavioural patterns wereobserved. Events associated with ROB-5 stope dis-played several sharp step increases in the number ofseismic events. The trend of events associated withCDOB-I1 stope follow a logarithmic shape, and eventsassociated with CDOB-I2 stope follow an exponential

g l C u m u l n t l v e S e is m i c P + S E n e r g y p e r C u m u l a t i v e A p p a re n t V o lu me [ k J I m ^ 3 ][ I I O b s e r v e d t o ta l n u m b e r o f s e is m i c e v e n t s [

t . 0 0 E + 0 3i 1.00E+01Iu 1 . 0 0 E - O 1

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1 . 0 0 E - 0 90t u t . 0 0 E - 1 1

623 152 23 179 81

1 . 0 0 E - 1 31 2 3 4 5A r e a

F i g . 1 1. D i s t r i b u t i o n o f s e i s m i c e v e n t s , a n d c u m u l a t i v e s e i s m i c e n e r g yp e r c u m u l a t i v e a p p a r e n t v o l u m e f o r m a j o r m i n e a r e as .

shape. These trends are due to stope geometry, mininghistory and geological influences.Rock burs t hazard evalua tion

Considerable computational effort was made toassess potential rockburst indicators for Mt Charlottemine. One of the key questions often asked in mineseismology is, "what is a good indicator of an impend-ing rockburst". Extensive work has been already donein this direction by a number of researchers [18, 20]. Inthis study, an assessment of rockburst predictabilitywas made by investigating a relatively large rockburstwith local PSS Richter magnitude +0.8, whichoccurred on 27 February 1996 adjacent to CDOB-I2stope, well outside any blast window.

Var ia tion o f se ismic param eters be fore +0 .8 loca lR ich ter magn i tude rockburs t . Various seismic par-ameters and ratios (such as: seismic energy to seismicmoment ratio, energy to apparent volume ratio, seis-mic moment to static stress drop ratio and variousdeparture indices as defined later in this work) weretested to see whether their changes might indicate anoncoming seismic event (Figs 13 and 14). Until 6 minbefore the + 0.8 rockburst , the majori ty of seismic par-ameters and ratios demonstrated increases (timebetween 19:15:00 and 0:10:30). A small seismic eventoccurring abou t three minutes before the +0.8 rock-burst (Fig. 14) showed a drop in a majority of par-ameters. Only the ratio of seismic moment to staticstress drop experienced a gentle increase.A second series of parameters (such as: PSS energyindex, P-energy to S-energy ratio, P-moment to S-moment ratio, P + S kappa, RVMAx, F kappa, p R A ,

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1 . 1 0 E + 0 21 . 0 0 E + 0 2>w 9 . 0 0 E + 0 1

~ 8 . 0 0 E + 0 1' E 7 . 0 0 E + 0 1

6 . 0 0 E + 0 1 I I I . J ' -. M = + . , i I IE = , o o . o 1

Z o n n , . + 0 1 | ~ n ~ ~ Jr I , . , , v , . + - - 1

EO

4

T i m eFig . 12. Cum ula t ive number o f even ts.

- - e - R O B - 5- o - R O B - 3

CDOB-I1"-m- CDOB-12

! I "U - CDOB-12-pi llari ~ Ric ht e rI M a g n i t u d e O B .9] S_(M>=0)/ x ~ . c h~r- I Ma gni t ude/ CDOB-12M>=O),, , A RichterI M a g n i t u d eCDOB-I1 (M>=0)

where : p i s the dens i ty , R i s the se ismic source rad ius ,A i s t h e p e a k g r o u n d a c c e l e r a t i o n [ 2 1 ]) w a s a n a ly se d( F ig . 1 5 ) a n d f o u n d to h a v e a s imi l a r t r e n d , w i th mo s ts e i smic p a r a me te r s e x p e r i e n c in g a r i s e u n t i l 6 minb e f o r e t h e r o c k b u r s t , a n d t h e n ca 3 min b e f o r e t h er o c k b u r s t a lmo s t a l l t h e s e i smic p a r a me te r s e x p e r i -

e n c e d a d r o p a s f o r t h e f i r st s er ie s o f p a r a me te r s ,e x c e p t t h e r a t i o o f P t o S s ei smic e n e r g y a n d p a r -a m e t e r pRA. T h i s s t y l e o f e x c i t a t i o n ( t u r b u l e n c e ) i nse i smic p a r a me te r s mu s t b e v e r i f i e d w i th mo r e d a t a .A t t h e p r e se n t t ime , e f f o r t s a r e f o c u se d o n a r e l i a b l er o c k b u r s t p r e d i c t i o n a l g o r i t h m .

~ 1 . 0 0 E + 0 6

1 . 0 0 E + 0 4

~ 1.00E+02~ 1.00E+00= "

1 . 0 0 E - 0 2O .~ 1 . 1 ~ E 4 ~

~ t . 0 0 E 4 ~ 6 , , , , , , , , , , , , , ;0 0 0 0 ,e -

N N ~ 1 N NT i m e ( h o u r , m i n u t e )

- m - E n e r g y t o M o m e n t ra t io[J INm]- E ) - E n e r g y t o M o m e n t D e p.I n d e x- - x - - E ne r gy D ep . I ndex

t l - - o - E n e r g y t o A p p a r e n tJ l V lum e r a tJ [ J im^ 3 ]~11 - o - E n e r g y t o A p pa r e n tz~ / I V o lume D ep . I ndex

/!| l - e - M o m e n t t o S ta U c S t r e ss11 Drop ra t io [NmlPa]/ I - o - M o m e n t t o S ta t ic S t r e s s? / I D r op D ep . I ndex

' q B las t w indo w ( 15 m in .)-': PSS R i c h t e r M a g n i t u d e

Fig. 13. CD OB -I2 stope, seismic param eters leading to the + 0.8 PSS Richter ma gnitu de rock burst ( logari thm ic scale presen-tat ion) .

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2 22 P O P L AW S K I : S E IS M I C P A R A M E T E R S A N D R O C K B U R S T H A Z A R D A T M O U N T C H A R L O T T E M I N E

1 . 0 0 E + 0 6_ o(0o 1 . 0 0 E + 0 4

~ 1 . 0 0 E + 0 218 1 . 0 0 E + O 0E. ~ 1 . 0 0 E . 0 2mQ.

, 2E 1 . 0 0 E - 0 4._ ~u ) 1 . 0 0 E - 0 6

I ~ L -.a-- Energy to Mom ent rat io, = " j ' I II [J /Nm]I I I: Index. ;- ~, h- 8 --x-- Energy Dep. IndexE Li r, ~ ~ - ~ - E ne rg y t o A pp ar en tL ~ ~ ~ - - - - ~ V o lum e ra tio [J /m ^3]

~ h - ~ - - ~ ~ , , ' ~ ~ v -- " - ~ ~ __ - -O - E n er gy t o A p pa re nt- ~ I o Vo lume Dep. Indexi - e - Mom ent to S ta t ic S tressi I Drop rat io [Nm/Pa]

' I I I ~ I I I I I I I , I i ' ;o I t ) O I n - ~-- %1 r4D D D D

D a t e & T i m e ( M o n t h , D a y , Y e a r , h o u r , m i n u t e )

- -o - Mom ent to S ta ti c S tressDrop Dep. Index B las t win dow (15 ra in . ): : PSS Richter Mag ni tude

Fig . 14 . CDOB-I2 s tope , s e i sm ic pa ra m e te r s shor t ly be fore the +0 .8 PSS Ric hte r m a gni tude roc kburs t ( loga r i thm ic sc a lepre se nta t ion) .

me lC' ~ ) 3 .50E+01I nOv 3 .00E+01

' ~ ~ 2 . 5 0 E 0 1. m =t - 1 - 2 . 0 0 E 0 1m e~e ."~ O 1 . 5 0 E 0 1

~ " > 5.00E00E.w_ 0.00E00 O

gDN

b l a s t_ = _ _ _ ~ _ _ ~ _ . . . _ _w m o o wi

N NT i m e ( h o u r , m i n u t e )

- -a - [PS$ Energy Index]*5- a - P IS E ne rgy ra ti o--x-- [PIS Mom ent rat io]*3-~ - [P +S kappa] *4000- -o - [R V max ]*30

z [Fo kappa]*20- D - [ r h o R A ]* 10-a l - B l as t w i ndow (15 m i n. )

: : Rich ter Magn i tude

Fig . 15 . CD OB -I2 s tope , se ism ic pa ra m e te r s l ea ding to the +0 .8 PSS R ic hte r m a g ni tude roc k burs t ( e nha n c e d da ta va lue spre se nta t ion) .

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POPLAWSKI: SEISMICPARAMETERSAND ROCKBURST HAZARD AT M OUNT CHARLOTTEMINE 12233 . 5 03 . 0 0 - -

A 2 . 5 0m0 2 . 0 0~ = 1 . 5 0.=" ~ : 1 , 0 0o ')m 0 . 5 0

I i o . o oJ .ca . 0 . 5 0

- 1 . 0 0o . - 1 . 5 0

- 2 . 0 0- 2 . 5 0

i I I I I I i+ B l a s t s ( P r o d u c t i o n ) - !P S S R i c h t e r M a g n i t u d e !

x B l a s t s ( D e v e l o p m e n t ) - !P S S R i c h t e r M a g n i t u d e IIc ; S e i s m i c E v e n t s -P S S R i c h t e r M a g n i t u d e

I

"

. , - , i ~ x ~I ~ o i , ~ . , ,

: : . . . . . . . ! . . . ! . . . . , . . . . . . . . i . . . . .

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i ,.,i . ] j +, '4 " 4 , , i - I -" 9 + + i +~ ' ~ i + +. 4 , J , J l - , ' I "

+ ' + + ' ' + D J+ + i E l i

I x '

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1 2 2 4 P O P L A W S K I :SEISMIC PARAMETERS AND ROCKBURST HAZARD AT MOUNT C HARLOTTE MINEc h a r a c t e r o f a p o p u l a t i o n . T h i s is i m p o r t a n t i f s e v-e r a l p o p u l a t i o n s o f e v e n t s h a v e t o b e c o m p a r e d , a n da t r e n d i n s e i sm i c b e h a v i o u r d e t e c t e d .

R e g u l a r p a t t e r n s o f s o m e s e is m i c p a r a m e t e r s o f t e na r e o f l im i t e d v a l u e i n t e rm s o f r o c k b u r s t p r e d i c t i o na n a l y s i s o r s e i sm i c e v e n t m e c h a n i sm i d e n t i f i c a t i o n .

W h e n t w o o r m o r e l i n e s r e p r e s e n t i n g c h a n g e s o fp a r a m e t e r s ( o r t h e i r c u m u l a t i v e v a l u e s ) i n t i m e a r ep l o t t e d o n t h e s a m e g r a p h ( e . g . X - c o o r d i n a t e r e p r e -s e n t in g t i m e p a s s a g e , a n d Y - c o o r d i n a t e r e p r e s e n ti n gt r e n d s d i sp l a y e d b y s e l e c t e d p a r a m e t e r s ) , i t i s p o s s -i b l e t o a c h i e v e a c r o s s i n g o f t h e se l i n es a t a n yd e s i r e d p o i n t b y a p p r o p r i a t e s c a l e a d j u s t m e n t . T h i sc a n b e a s e r i o u s p r o b l e m i f t h e c r o s s i n g o f t w o l i n eso r c u r v e s i s b e l i e v e d t o i n d i c a t e a r o c k b u r s tc o n d i t i o n [ 1 8, 2 0] .

I f t h e c o l le c t e d d a t a a r e a n a l y s e d i n s u c h a w a y t h a tc u m u l a t i v e s ei s m ic p a r a m e t e r s a r e a v o i d e d a s m u c ha s p o s s i b l e , a n d i n s t e a d , o t h e r p a r a m e t e r s a n dm e t h o d s a r e u s e d , t h e a n a l y s i s c a n b e m o r e r o b u s t .T h i s i s e sp e c ia l l y t r u e i f so m e e v e n t s a r e n o t p i c k e du p b y t h e s y s t e m , f o r e x a m p l e d u e t o w e a k s i gn a l,o v e r f l o w o f d a t a , s m a l l s a m p l i n g r a t e o r p o w e r i n t e r -r u p t i o n .

I f a l i n e a r s c a le is u se d f o r p l o t t i n g o f c u m u l a t i v ev a l u e s o f se i sm i c p a r a m e t e r s , t h e n p a r a m e t e r s w i t hsm a l l a b so l u t e v a l u e s a r e sh o w n a s a f l a t l i n e p o s i -t i o n e d c l o s e t o z e r o . H o w e v e r , i f a l o g a r i t h m i c s c a l ei s a d o p t e d , a f t e r a sh o r t w h i l e a l l n e w v a l u e s , e v e n i fl a r g e , m e r g e w i t h a c c u m u l a t e d d a t a p r o d u c i n g n ovi sua l e f fec t .

I f t h e d a t a c a n n o t b e p r e s e n t e d s u c c e s s f u ll y w i t h t h el i n e a r o r l o g a r i t h m i c s c a l e , a n a l t e r n a t i v e i s t o p l o t" e n h a n c e d d a t a v a l u e s " , d e f i n e d a s p a r a m e t e r v a l u e sm u l t i p l i e d b y a p p r o p r i a t e f a c t o r s a d o p t e d t o b r i n ga l l p a r a m e t e r s u p t o t h e s a m e t h r e s h o l d . T h i s p r o -v i d e s t h e o p p o r t u n i t y t o e a s i l y d e t e c t i n c r e a s i n g o rd e c r e a s i n g t r e n d s o f s e v e r a l p a r a m e t e r s s i m u l -t a n e o u s l y .

T h e m a g n i t u d e o f a n y g i v e n s e is m i c e v e n t e x p r e s s e db y a n y s i n g l e p a r a m e t e r ( e . g . R i c h t e r m a g n i t u d e ,s e i s m i c e n e r g y o r s e i s m i c m o m e n t ) w a s f o u n d t o b ei n a d e q u a t e , a n d a n a r r a y o f m o r e t h a n t h r ee p a r -a m e t e r s o r r a t i o s o f p a r a m e t e r s i s c o n s i d e r e d b e t t e r .

A r o c k b u r s t h a z a r d i d e n t i f i c a ti o n f u n c t i o n b a s e d o no n l y o n e o r t w o s e is m i c p a r a m e t e r s w o u l d a p p e a r t ob e v e r y u n r e l i a b l e . I t i s su g g e s t e d t h a t a t l e a s t fi v es e i s m i c p a r a m e t e r s , r a t i o s o r d e p a r t u r e i n d i c e s ( a se x p l a i n e d a s f o l l o w s ) s h o u l d b e c o n s i d e r e d i n t h ef o r m u l a t i o n o f a n y s u c h f u n c t io n .

T h e a n a l y s is o f g r a p h s p r e s e n t e d s o f a r i n t hi s p a p e rh a v e t h e v a r io u s s h o r t c o m i n g s a n d p r o b l e m s ju s tl i st e d . I t w a s i n o r d e r t o o v e r c o m e t h e se d i f f ic u l ti e s ,t h a t a n e w " d e p a r t u r e i n d e x in g m e t h o d " w a s d ev e l-o p e d .

N E W D E P A R T U R E IN D E X I N G M E T H O D P R O P O S E DF O R M I N E S E I S M I C S T U D I E S

D e p a r t u r e i n d e x i n g m e t h o dA n e w " d e p a r t u r e i n d e xi n g m e t h o d " f o r r o b u s t

a n a l y s i s o f s e i sm i c c h a r a c t e r i s t i c s i s p r e se n t e d h e r e .T h e f u l l d e sc r i p t i o n o f th e m e t h o d i s g i v e n i n R e f , [ 13 ].T h i s m e t h o d i s b e i n g f u r t h e r d e v e l o p e d a n d t e s t e d ,a n d i f su c c e s s f u l , i t w i ll p r o v i d e a t o o l f o r r o c k b u r s th a z a r d e v a l u a t i o n a n d p o s s i b l y r o c k b u r s t p r e d i c t i o n a swel l .D e p a r t u r e i n d e x

T h e d e p a r t u r e i n d e x is d e f in e d a s t h e r a t i o o f t h ea c t u a l v a l u e ( o f a p a r a m e t e r o r r a t i o o f p a r a m e t e r s )m e a su r e d f o r a g i v e n s i n g l e s e i sm i c e v e n t t o t h e a v e r -a g e v a l u e c a lc u l a t e d w i th i n a n a d o p t e d p e r i o d o f ti m e .T h i s r a t i o c a n b e e x p r e s se d a s f o l l o w s :

I D ( P i / P j ) = [ ( P i / P j ) m s d ] [ ( P i / P j ) a v e r ( T = t ) ] (1)w h e r e : ID(Pi /Pj ) i s t h e d e p a r t u r e i n d e x o f a g i v e n r a t i oo f p a r a m e t e r s P i a n d P f i P i , P j a r e s e i s m i c p a r a m e t e r sa d o p t e d i n t h e a n a l y s i s ( e . g . s e i s m i c e n e r g y , a p p a r e n tv o l u m e ) ; P i / P j i s th e r a t i o o f s e is m i c p a r a m e t e r s ( i fo n l y a s in g le s e i sm i c p a r a m e t e r i s u s e d t h e n P j = 1 );( P i / P j ) m s d i s th e r a t i o o f s e i sm i c p a r a m e t e r s c a l c u l a te df o r a g i v e n s e i sm i c e v e n t ; ( P i / P j ) a v e r ( T = t ) i s ther a t i o o f s ei s m ic p a r a m e t e r s a v e r a g e d f o r t h e g i v e n s u b -se t o f e v e n t s c o l l e c t e d w i t h i n a s e l e c t e d p e r i o d o f t i m eT = t , wh ere

( P i / P j ) a v e r ( r = t) = {Z(PdPj)m/M} (1 .1)m i s a g i v e n s e i sm i c e v e n t , m = 1 ,2 . . . . . M a n d M i st h e n u m b e r o f s ei s m ic ev e n t s in t h e a d o p t e d p e r i o d o ft i m e T .

A n e x a m p l e o f a d e p a r t u r e i n d e x i s g iv e n inF i g . 1 7 w h e r e e n e r g y d e p a r t u r e i n d e x , a n d f o r c o m -p a r i s o n , o r d i n a r y s e is m i c e n e r g y v al u e s , a r e p l o t t e d i nr e s p e c t t o t h e l o c a l P S S R i c h t e r m a g n i t u d e . V a r i o u sb e n e f i t s o f s u c h d a t a p r e s e n t a t i o n a r e d e s c r i b e d l a t e ri n t h i s p a p e r ( s e e S e c t i o n 5 . 4 ) .R o c k b u r s t h a z a r d i n d i c a t i o n

R o c k b u r s t h a z a r d i n d i c a t i o n c a n b e d e s c r i b e d u s i n gt h e f o l l o w i n g f o r m u l a :

R ~ I = Y ~ { A D I [ ( P i / P j ) I ] + A ~ 2 [ ( P i/ P s )2 ] + . . .q- ADn[(Pi /Pj )n] } < Ralcrit (2)

w h e r e : R m i s t h e R o c k b u r s t h a z a r d i n d i c a t i o n ; a n dA D(P i / P j ) f u n c t i o n w i t h v a l u e 1 o r 0 d e p e n d i n g o n t h ev a l u e o f th e d e p a r t u r e i n d e x .

I f t h e d e p a r t u r e i n d e x r is e s a b o v e o r i s e q u a l t o t h ee x p e r i m e n t a l l y s e l e c t e d c r i t i c a l l o c a l v a l u e , t h e n

A D ( P i / P j ) = 1 , i f b e l o w t h e n A D ( P i / P j ) = 0

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> , 1 .0 0 E+0 7~ ) 1 .00E+06, , : , . l . O O , : . o s

~'_ 1.00E +04N I .o * E o 3:~ ~ 1 .00E+02

"~ 1.00E+00tU.~ ~ 1 .00E-01_m l.oo,:.oa, g a , . o o E - ,/ ~ 1 . 0 0 E - 0 44 .a _ 1 .0 0 E-0 5

1.00E-06- 2 . 5 - 2 . 0 -1 .5 -1 .0 4 ) . 5 0 .0 0 .5

M L - l o c a l R i c h t e r M a g n i t u d e ( P S S )Fig. 17. Energy departur e index and plain seismic energy vs PSS Richter magnitude.

1 .0 1 .5

A D ( P i / P j ) = { 1 i f l D ( P i / P j ) k > iD c ( P i / P y )k (seismic r isk)a n d

{0 i f I D ( P i / P O k < iD c ( e i / P j ) k (no seismic r isk)w h e r e : i D c ( P f f P j ) k i s t he c r i t i ca l l oca l va lue adop ted ex -per ime n ta l ly : fo r a g iven depar tu re index ;k = 1 ,2 . . . . n ; n i s t he num ber o f de par tu re ind icest aken in to the ana lys i s and se l ec t ed by loca l exper i -ence ; R H lc r i t i s t he c r i t i ca l rockburs t hazard va luees t ab l i shed em pi r i ca lly .

Equat ion (2 ) can a l so be wr i t t en in the fo l lowingform wi th d i s t inc t componen t s (a ) , (b ) and (c ) :

R a i = Z { a k * A o k [ ( P d P j ) k ] }(a )+ z { [b~*AD~[(L , /L j )~ ] ] - ' }

(b )- t -Z{ck*ADk[(e iDi - - e jDj)k]} R H Ic r it t h i s i nd ica tes tha t a rockburs t i si mmi n e n t .Em pi r i ca l para me ter RHIeri t i nd ica t ing a c r i t ica l s t a t eo f t h e r o c k ma s s c a n b e f o u n d b y t h e a p p l i c a t io n o f t h e

a lgor i thm def ined in Pop laws k i [13] . Br ie f ly , fo r e achmine a rea recogn ized as se i smica l ly ac t ive [13] , par -a m e t e r R H Ic r i t i s in i t ial ly es tabl ished as RHierit=RHi,w h e r e v a l u e o f Rn i i s c o m p u t e d a c c o r d i n g t oE q u a t i o n ( 3) b y a p p l i c a ti o n o f p a r a m e t e r s a s s o c i a t e dwi th a g iven c r i t i ca l t remor (e .g . p roducing excess ived a m a g e t o t h e mi n e o p e ni n g s) . I f th e p a r a m e t e r R H le r i thas to be es t ab l i shed p roper ly , i t mus t be ind iv idua l ly" t u n e d " [ 1 3 ] f o r v a r i o u s mi n e a r e as , a s a d o p t e d u n d e -s i red se i smic even t migh t be as soc ia t ed wi th d i f fe ren tva lues o f the g iven se t o f para me ters (e .g . a d i f fe ren tv a l u e o f l o c a l PSS R i c h t e r m a g n i t u d e ).

A s i mp l e a r b i t r a r y e x a mp l e s h o w i n g b a s i c p r i n c i p l e so f t h e d e p a r t u r e i n d e x i n g me t h o d a s w e l l a s t h em e t h o d o f o b t a in i n g R H Ic r i t value i s g iven in Append ixA .

A d v a n t a g e s o f t h e d e p a r t u r e i n d e x i n g a p p r o a c hI n t h e mi n i n g e n v i r o n me n t a t Mt Ch a r l o t t e a n d p e r -haps e l sewhere , an ind ica t ion o f a se i smic even t o r arockburs t i s o f t en man i fes t ed by a tu rbu lence in se i s -mi c a n d s t a t i c p a r a me t e r s p r i o r t o t h e e v e n t . T h ed e p a r t u r e i n d e x i n g c o n c e p t i s b a s e d o n a s s e s s i n g t u r -

bu lence and emph as izes tha t c arefu l se l ec t ion o f c r i -t e r i a invo lv ing severa l se i smic parameters can l ead to ab e t t e r r o c k s e i s mi c b e h a v i o u r p r e d i c t i o n . A n u mb e r o fa d v a n t a g e s o f t h e p r o p o s e d d e p a r t u r e i n d e x i n ga p p r o a c h c a n b e f o r e c a s t :

RMM S 34/8---G

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1 2 2 6 P O P L A W S K I :S E I S M I CP ARAMETERS AND ROCKBURS T HAZARD AT M OUNT CHARLOTTE MINE1 . I t a l l o w s s i m u l t a n e o u s a n a l y s i s o f s e v e r a l s e is m i c

p a r a m e t e r s a n d r a t i o s , gi v in g a n a d v a n t a g e o v e ra p p r o a c h e s w h e r e o n l y o n e o r t w o o f t e n q u e s t i o n -a b l e p a r a m e t e r s a r e u se d .

2 . I t h a s g r e a t e r r o b u s t n e s s , b e c a u s e i n s t e a d o f t r u ev a l u e s w h ic h m i g h t b e o f q u e s t i o n a b l e a c c u r a c y( i . e . l a r g e s y s t e m a t i c e r r o r ) , u n i t l e s s r a t i o s a r eu s e d .

3 . I t h a s t h e a b i l i t y t o i n c o r p o r a t e i n t o t h e a n a l y s i sa s m a n y s e i s m ic p a r a m e t e r s a n d r a t i o s a s d e s ir e d .

4 . S h o u l d t h e i m p o r t a n c e o f a n y g iv e n p a r a m e t e r i nt e r m s o f s e is m i c h a z a r d i n d i c a t io n b e q u e s t i o n a b l e ,i t c a n b e c o m p e n s a t e d f o r b y o t h e r p a r a m e t e r sp r e s e n t i n t h e e q u a t i o n , b e c a u s e t h e v a l u e o f t h eu n r e l i a b l e p a r a m e t e r c a n b e s t a t i s t i c a l l y " m e l t e d "w i t h n u m e r o u s m o r e r e l i a b l e p a r a m e t e r s . L i k e w i s ea n y r a n d o m e r r o r m a d e d u r i n g t h e d a t a c o ll e c ti o na n d p r o c e s s in g c a n b e s i m i la r l y c o m p e n s a t e d .

5 . F o r v a r i o u s p a r a m e t e r s i t i s p o s s i b l e t o s e t d i f f e r -e n t c r i t e r ia , f o r e x a m p l e , f o r t h e s e i s m i c e n e r g y , ad e p a r t u r e i n d e x o f 3 0 m i g h t b e a d o p t e d a s c ri ti c al ,w h i l e f o r t h e s e i s m i c e n e r g y t o a p p a r e n t v o l u m ed e p a r t u r e i n d e x t h e c r i t i c a l v a l u e m i g h t b e t e n .

6 . V a r i o u s D e p a r t u r e I n d i c es c a n b e s h o w n s i m u l -t a n e o u s l y o n a w r i t t e n g r a p h , a n d c o m p a r e d f o rt r e n d s b e c a u s e t h e y u s u a l l y o c c u p y a s i m i l a rr a n g e .

7 . A t r e n d o r a s h a p e o f a g i v e n c l u s t e r o f e v e n t s d is -p l a y e d g r a p h i c a l l y i s v e r y s i m i l a r f o r b o t h t h e a b -s o l u t e v a l u e s a n d t h e d e p a r t u r e i n d i c e s , t h e r e f o r et h e d a t a i s p r e s e n t e d i n t h e f a m i l i a r f a s h i o n , w h e r ea c l u s t e r o f s e is m i c e v e n t s is p l o t t e d i n X - a n d Y -s y s t e m o f c o o r d i n a t e s .

8 . T h e i n d e x i n g m e t h o d c a n i n c l u d e " f i n d i n g a ni n t e rs e c t io n o f t w o p a r a m e t e r s " a n d t h is m i g h t i n -d i c a t e a n i n c o m i n g s e i s m i c e v e n t .

9 . S t a t i c p a r a m e t e r s ( e . g . s t a t i c s t r e s s c h a n g e s ) c a n b ee a s i ly i n c o r p o r a t e d i n t o t h e a n a l y s i s.

1 0. T h e i n d e x i n g s y s t e m p r o v i d e s a f l e x ib l e t o o l w h e r ei n d ic e s o f g r e a te r i m p o r t a n c e c a n b e k e p t , n e w i n -d i c e s a d d e d , a n d t h o s e r e c o g n i z e d a s i n s i g n i f i c a n ta b a n d o n e d . T h i s c a n b e a c h i e v e d a s m o r e d a t aa n d k n o w l e d g e a r e a c c u m u l a t e d , o r a s m i n e d e v e l -o p m e n t p r o g r e s s e s , a n d t h e n a t u r e o f s e is m i c it yc h a n g e s .

1 1. T h e i n d e x i n g c o n c e p t i s r e l a t iv e l y c le a r a n d e a s y t ou n d e r s t a n d .

N e w s t r a t e g y a d o p t e d a t M t C h a r l o t t e a i m e d a t m i t i g a -t i o n o f r o c k b u r s t h a z a r d

R e s u l ts o f s e is m i c m o n i t o r i n g p e r f o r m e d a t M tC h a r l o t t e m i n e c o m b i n e d w i t h s t r e s s m e a s u r e m e n t sa n d v i s u al o b s e r v a t i o n s l e d t o a d o p t i o n o f a n ew s t r a t -e g y a im e d a t r o c k b u r s t h a z a r d a c t iv e a n d p a s s i v e m i t i -g a t i o n . T h i s s t r a t e g y i n v o l v e d p r o p e r p i l l a rp r e c o n d i t i o n i n g [ 1 0 ] , a n d i n a n o t h e r c a s e k e e p i n g a no r e p a s s f u l l a s t h i s w a s r e c o g n i z e d a s t h e b e s t w a y o fc o n t r o l l i n g a b r e a k o u t [ 1 0] . I t w a s a l so o b s e r v e d t h a t

t h e s iz e o f a g i v e n s e is m i c e v e n t w a s d e p e n d e n t o n t h es i ze o f w e d g e r e l e a s e d b y a g i v e n b l a s t [ 10 ]. S e i s m i cm o n i t o r i n g a l s o a s s i s t e d m i n e p l a n n i n g i n s u c h a w a yt h a t i d e n t i f i e d s e i s m i c a l l y a c t i v e a r e a s w e r e s u p p o r t e db y " c o n e b o l t s " [ 22 , 2 3 ] p r i o r t o m i n i n g [1 0] .

C O N C L U S I O N S1 . T h e s e i sm i c s y s t e m i n st a l l ed a t M t C h a r l o t t e h a s

p r o v e d v e r y u s e f u l , i n t e r m s o f s e i s m i c e v e n t l o -c a t i o n a n d m a g n i t u d e , a n d m a n y o t h e r i m p o r t a n ts e i s m i c p a r a m e t e r s .

2 . D u r i n g t h e f i r st o n e a n d a h a l f y e a r p e r i o d o f t h em o n i t o r i n g p r o g r a m , s i g n i f i c a n t p r o g r e s s h a s b e e nm a d e t o w a r d s b e t t e r u n d e r s t a n d i n g o f t h e r o c km a s s r e s p o n s e t o m i n i n g .

3 . I t w a s f o u n d t h a t t h e v a r i a t i o n o f o n e o r t w o s e is -m i c p a r a m e t e r s a l o n e w a s u n l i k e l y t o b e h e l p f u l f o rs e is m i c h a z a r d p r e d i c t io n . T h e p r o b l e m s a n d s h o r t -c o m i n g s o f c o n v e n t i o n a l a n a l y si s o f s e i sm i c p a r -a m e t e r s b e c a m e o b v i o u s d u r i n g t h e r e s e a r c h .

4 . A n e w " d e p a r t u r e i n d e x i n g " c o n c e p t h a s b e e n p r o -p o s e d . I t o f f er s p r o m i s e a s a r o b u s t r e l i a b l e m e t h o df o r e v a l u a t i o n o f r o c k b u r s t h a z a r d .

Acknowledgements--Special thanks are d ue to the follow ing personsand organizations for the ir substantial support and encouragement:Dr Peter Mikula, (KCGM ) for various forms of support, assistancewith data collection and valuable comments; Dr Bill Bamford (TheMelbourne Un iversity, Department o f C ivil and EnvironmentalEngineering) for vario us forms of sup port. S pecial thanks are due toth e management of KCG M for permission to pub lish this paper.

Accepted fo r publication 31 July 1997

R E F E R E N C E S1. Fotakis, D. M . M ount Charlotte Seismic Event--3 .13 p.m., 28thMarch 1990. Kalgoorlie Consolidated Gold Mines, memoran-dum to I. G rljusich, 3 M ay 1990.2. Fotakis, D. M. Mining and rock mechanics history 1893-1991.Internal Report o f Kalgoorlie Consolidated Gold Mines Pty L td,Mount Charlotte Mine, August 1993.3. Hugh, R. L. Mount Ch arlo t te Earth t re m or , GM KMe moran dum , KL V files, 21 February 1972.4. Le e, M. F. , Beer, G. and W indsor, C. R. Interaction of stopes,stresses and geologic structure at the M ount Ch arlotte Mine,Western Au stralia. In Rockburst and Seismicity in Mines, pp .337-343. Balkema , Rotterdam , 1990.5. Mikula, P. A. Seismic mon itoring system ---capital expenditurerequest (CER)--year 1993/94, Ka lgoo rlie Consolidated GoldMines Pty Ltd, (KCGH) Mt Charlotte Operations, Kalgoorlie,W. A ustralia, 1994.6. M ikula, P. A. The introd uction of continuo us seismic mon itoringat Mt Charlo t te go ld mine. In proceedings 3rd CanadianConference on C om puter Applications in the Mineral Industry,(CAM I) Montreal, 3 October 1995, pp. 483-491.7. Mikula, P. A., Seismic monitoring at M t C harlotte G old M ine,Kalgoorlie, Western Australia. ACG Newsletter , 1995, 4, 1-2.8. Mikula, P. A. Seismic monitoring of a hard rock pillar at M tCharlotte Gold Mine. Lecture presented at the Seminar: AppliedGeomechanics in Underground Mining, Western Austra l ianSchool of Mines, (WASH) Curtin University of Technology,Kalgoorlie, W. Australia, Seminar notes issued by W AS H, 11 -12 Novem ber, 1995.

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P O P L A W S K I: S E IS M I C P A R A M E T E R S A N D R O C K B U R S T H A Z A R D A T M O U N T C H A R L O T T E M I N E 12 279 . M i k u l a , P . A . , L e e , M . a n d M c N a b b , K . T h e p r e c o n d i t i o n i n ga n d y i e l d i n g o f a h a r d r o c k p i l l a r a t M t C h a r l o t t e . I n p r o c e e d -ings 8th International Congress on Rock Mechanics, T o k y o , p p .1289-1293, Ba lka m a , Rot te rda m , 1995.10 . Miku la , P . A . a nd Popla wsk i , R . F . Th e se i sm ic m o ni to r ing de -c i s i o n a t M t C h a r l o t t e g o l d m i n e . I n Proceedings 6thUnderground Operators" Conference, p p . 7 9 - 8 6 . A u s t r a l a s i a nI n s t i t u t e o f M i n i n g a n d M e t a l l u r g y , C u r l * on , V i c t o r ia , 1 9 95 .11 . Popla wski , R . F . Se i sm ic i ty unde rground wi th pa r t i c u la r r e fe r -

e n c e t o r o c k b u r s t p r o b l e m s . I n Proceedings First Australia-NewZealand Young Geotechnical Professionals Conference, p p . 1 6 7 -1 7 5 . U n i v e r s i t y o f N e w S o u t h W a l e s, S y d n e y , 9 - 1 2 F e b r u a r y ,1994.12 . Popla wski , R . F . Se i sm ic Re se a rc h Re p or t a t M t Ch a r lo t t eM i n e , S e p t e m b e r - D e c e m b e r 1 9 9 4 . K C G M I n t e r n a l R e p o r t ,A p r i l . K C G M , K a l g o o r l ie , W . A u s t r a l i a , U n i v e rs i t y o fM e l b o u r n e , 1 9 9 5.13 . Popla wski , R . F . Se i sm ic i ty unde rground wi th pa r t i c u la r r e fe r -e n c e t o r o c k b u r s t p r o b l e m s a t M t C h a r l o t t e m i n e . P h D t h e s i s ,T h e U n i v e r s i t y o f M e l b o u r n e , M e l b o u r n e .

14 . B isc hoff , K . a n d M or le y , C . Ge ology, r e sourc e s de f in i t ion a ndr e s e r v e e s t i m a t i o n a t M o u n t C h a r l o t t e , K a l g o o r l i e , W e s t e r nAus t r a l i a . In Proceedings of the International Mining GeologyConference, Vol . 5 /93 , pp . 1-17 . Au s t r a la s ia n Ins t i tu te of M ininga nd Me ta l lurgy , Pa rkvi l l e , V ic tor ia , Aus t r a l i a , 1993.1 5. C l a r k , M . L o c a l i s a ti o n o f g o l d , M o u n t C h a r l o t t e , K a l g o o r l i e,W e s t e r n A u s t r a l i a . B s c ( H o n s ) t h e s i s , U n i v e r s i t y o f W e s t e r nAus t r a l i a , Pe r th , 1980.16 . E le va tor sk i , E . A . Wor ld gold . In Mines-Deposits-Discoveries,Vol . I I , Europe , Af r ic a , As ia , Oc e a nia , Aus t r a l i a , pp . 1-9 a nd88-141. Min obr a s Minin g Se rv ice s , Fa l lbrook , 1988.

17 . Gre gso n, P . J . M oni tor in g se i sm ic e ve nt s , Ea s te rn Goldf ie lds ,We s te rn Aus t r a l i a . In Proceedings Australian Conference onGeotechnical Instrumentation and Monitoring in Open Pit andUnderground Mining, pp. 175-181. Ba lke m a , Rot te rda m , 1993.1 8 . M e n d e c k i , A . J . M o n i t o r i n g r o c k m a s s r e s p o n s e t o m i n i n g . I nProceedings Australian Conference on Geotechnical Instru-mentation and Monitoring in Open Pit and Underground Mining,p p 3 5 7 - 3 6 4 . B a l k e m a , R o t t e r d a m , 1 9 9 3 .19 . Me nde c ki , A . J . Pe r sona l c om m unic a t ion , June , 1993.20 . Me nde c ki A . J . , Va n Aswe ge n G . , N ie wia dom ski J . , S ta nkie wic zT . , Dz ha fa rov A . H . , K i jko A . , Sc ioc a t t i M. , Funk C . ,M o u n t f o r t P . , H e w l e t t P ., G r e e n R . W . E ., B r i n k A . V a n Z . a n dF i n n i e G . S e i s m o l o g y f o r r o c k b u r s t p r e v e n t i o n , c o n t r o l a n d p r e -d ic t ion . In Proceedings of Safety in Mines Research AdvisoryCommittee Symposia SIMRAC Symposium, pp. 1-13 , 1995.21 . Sp ot t i swoode , S . lV l. Se i sm ic a t t e nu a t io n in de e p- le ve l m ine s . InRockburst and Seismicity in Mines, p p 4 0 9 - 4 1 4 . B a l k e m a ,R o t t e r d a m , 1 9 9 3 .22 . The Cone Bolt. T e c h n i c a l b o o k l e t i s s u e d b y t h e R o c kE n g i n e e r i n g , D i v i s i o n o f M i n i n g T e c h n o l o g y , C S I R , A u c k l a n dP a r k , S o u t h A f r i c a.2 3 , T e c h n i c a l in f o r m a t i o n o n t h e y i e l d in g c o n e b o l t s i n c l u d e d i n t h el e t t e r w r i t t e n b y S . G . D a w e f r o m S t r a t a C o n t r o l S y s t e m s P r y

L t d ( S o u t h A f r i c a ) a n d a d d r e s s e d t o J a m e s A s k e w a n dAssoc ia te s P ty L td , (Pe r th , We s te rn Aus t r a l i a ) (20 Augus t 1991) .2 4 . P S S U s e r s M a n u a l - P o r t a b l e S e i s m i c S y s t e m S o f t w a r e S o l u t i o n sP t y L t d , C O M R O / C S I R , S o u t h A f r i ca , 1 9 93 .

T a b l e 2 . D e p a r t u r e i n d e x i n g m e t h o d ( e x am p l e ): c a l c u l a ti o n o f d e p a r -ture ind ic e s ID(Pi/Pj) o r v a r i o u s p a r a m e t e r sP a r a m e t e r 1 2 3 4N o . M o m e n t t o E n e r g y t os ta t i c s t r e s s Ene rgy to a pp a re n td r o p m o m e n t E n e r g y v o l u m eP a r a m e t e r d e p a r t u r e d e p a r t u r e d e p a r t u r e d e p a r t u r en a m e i n d e x i n d e x i n d e x i n d e xEve nt A 0 .50 0 .23 0 .050 0 .033Eve n t B 0 .23 0 .36 0 .067 0 .096Eve nt C 0 .06 0 .62 0 .026 0 .140Ev ent D 0.05 0.33 0.011 0.075Eve n t E 0 .65 0 .24 0 .034 0 .017Eve nt F 0 .17 1.19 0.268 0.513Eve nt G 0 .24 0 .47 0 .024 0 .034E v e n t H * 1 0 . 8 3 0 . 9 6 4 6 . 9 6 0 1 . 4 2 5(No. 27993)Se i sm ic Eve n t 27933, r e f . to F igs 13-15 .*Eve nt H (No. 27993) wa s + 0 .8 loc a l PSS Ric h te r m a gni tu de roc k-b u r s t , p r o d u c i n g a n u n a c c e p t a b l e l e ve l o f s e i sm i c d a m a g e .N o t e , t h a t i n t h i s e x a m p l e t h e e v e n t F i s q u e s t i o n e d i f t h e d e p a r t u r eindic e s a s soc ia te d w i th i t d i sp la ye d the i r c r i t i c a l va lue s or not ,

b e c a u s e t h e m a j o r i t y o f p a r a m e t e r s a s s o c i a te d w i t h t h i s e v e n t d i s-

A P P E N D I X ADeparture Indexing Method, An Example

A s im ple e xa m ple ha s be e n se le c te d to i l lus t r a te the a ppl ic a t ion ofthe de pa r ture inde xing m e thod ( se e F igs 13-15) . F i r s t o f a l l , l e t ag ive n m ine a re a "CDOB-I2" be c la s s i f i e d a s s e i sm ic a l ly a c t ive . Thefo l lowing se i sm ic pa ra m e te r s ha ve be e n se le c te d to i l lus t r a te thee xa m ple : r a t io o f P + S se i sm ic m o m e nt to s t a t i c s t r e s s drop , r a t ioof P + S se i sm ic e ne rgy to P + S se i sm ic m om e nt , P + S se i sm ice n e rg y , a n d r a t i o o f P + S s e i sm i c e n er g y t o a p p a r e n t v o l u m e(Ta ble 1) . As m e nt ione d e a r l i e r , s e ve ra l pa ra m e te r s a nd r a t ios ha veb e e n s e l e c t e d , a s a s t u d y b a s e d o n o n l y o n e o r t w o p a r a m e t e r sw o u l d b e i n a d e q u a t e .

As the ne x t s t e p , c um u la t ive a ve ra ge va lue s of the se pa ra m e te r s c o l -l e c te d w i th in ca 21 m o nth p e r iod ( i .e . f rom M a y 1994 t i l l J a n ua r y1996) ha ve be e n c a lc u la te d (Ta ble 1) .The a ve ra ge va lue s (Pi/Pj)aver(T= t ) shown in Ta ble 1 a re c a lc u-la te d by a ppl ic a t ion of Equa t ion (1 .1) . Now i t i s pos s ib le to c a lc u la ted e p a r t u r e i n d i c e s ID(Pi/Pj) f o r e a c h p a r a m e t e r a c c o r d i n g t oE q u a t i o n ( 1) . S u m m a r y o f t h e s e c a l cu l a t i o n s i s p r e se n t e d i n T a b l e 2 .F r o m T a b l e 2 i t c a n b e s e e n t h a t p r i o r t o t h e + 0 . 8 l o c a l P S SR i c h t e r m a g n i t u d e r o c k b u r s t ( e v e n t H ) , t w o s e is m i c e v e n t s o c c u r re d( e v e n t F a n d G ) a n d t h e p a r a m e t e r s as s o c i at e d w i t h e v e n t F d e m o n -s t r a t e d u n u s u a l d e p a r t u r e s f r o m t h e i r a v e r a g e v a l u e s . I t h a s b e e no b s e r v e d a t M t C h a r l o t t e t h a t t h e s e d e p a r t u r e s ( u p w a r d s o r d o w n -w a r d s ) a r e n o t i c e a b l e f o r s o m e p r e - r o c k b u r s t e v e n t s . I t m u s t b e

e s ta b l i she d , whe the r the pa ra m e te r s a s soc ia te d w i th the e ve nt F or Ga re in the i r c r i t i c a l va lue s or not , de spi t e the f a c t tha t the l a rge s t

T a b l e 3 . D e p a r t u r e i n d e x i n g m e t h o d ( e x a m p l e ) : a d o p t i o n o f l o c a lc r i t i c a l va lue s iDc(Pi/Pj)k o r v a r i o u s p a r a m e t e r sP a r a m e t e rTa ble 1 . De p a r ture ind e xing m e tho d ( e xa m ple ) : c um ula t ive * a ve ra gev a l u e s f o r v a r i o u s p a r a m e t e r s N o .

P a r a m e t e r 1 2 3 4 P a r a m e t e rN o . n a m eM o m e n t t o E n e r g y t oP a r a m e t e r s t a ti c s t re s s E n e r g y t o a p p a r e n tn a m e d ro p , m o m e n t E n e r g y v o l u m eAve ra ge * 1 .27E + 04 4 . 7 6 E -0 6 19 .4E + 03 4 .63Se i sm ic e ve nt 27933, r e fe re nc e to F igs 13-15 .*Cum ula t ive a ve ra ge va lue s c a lc u la te d for a g ive n se i sm ic pa ra m e te ro v e r t h e p e r i o d o f ca 21 m o nth s ( i .e . s inc e M a y 1994 ti l l J a n ua ry1996).

1 2 3 4M o m e n t t o E n e rg y t os ta t i c s t r e s s Ene rgy to a pp a re n td r o p m o m e n t E n e r gy v o l um e

Loc a l c r i t i c al - - 1.2 0.25 0.5values*De l ta 0 1 1 1p a r a m e t e rADxi(P,/Pj)k]Se ism ic e ve nt 27933, r e fe re nc e to F ig s 13-15 .*Adopte d " loc a l c r i t i c a l va lue s" iDc(Pi/Pj) ( i . e . p re - roc kburs t va lue sa s soc ia te d w i th s e i sm ic F) .

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1 2 2 8 P O P L AW S K I : S E IS M I C P A R A M E T E R S A N D R O C K B U R S T H A Z A R D A T M O U N T C H A R L O T T E M I N Ede pa r ture s f rom the a ve ra ge va lue s a re a s soc ia te d w i th the a c tua lr o c k b u r s t ( e v e n t H ) .T h e j u s t i fi c a t io n f o r s u c h a p p r o a c h l ie s i n t h e f a c t t h a t t h e m a i n a i mo f t h e s t u d y i s t o s e a r c h f o r a r o c k b u r s t h a z a r d w a r n i n g a l g o r i t h m ,t h e r e f o r e t h e f l u c t u a t i o n s ( t u r b u l e n c e s ) o f p a r a m e t e r s p r i o r t o ag ive n roc kb urs t pos se s s h igh s igni fi ca nce . In o the r wo rds , the " lo c a lc r i t i c a l va lue s " i D c ( P i / P j ) k s h o u l d b e u n d e r s t o o d a s c r i t ic a l p r e- r o c k -bur s t va lue s ( suc h a s those a s soc ia te d w i th e ve nt F) , a nd the re forethe se va lue s a re a dopte d a s c r i t i c a l in th i s s tudy . Howe ve r , in c a se ssuppor te d by e xpe r ie nc e , the " loc a l c r i t i c a l va lue s" i D c ( P i / P j ) t , m i g h tbe s l igh t ly inc l ine d towa rds " loc a l roc kburs t c r i t i c a l va lue s" ( suc h a sthose a s soc ia te d w i th e ve nt H) .In the e xa m ple pre se nte d , on ly s e ve n se i sm ic e ve nt s pr ior to roc k-b u r s t a r e s h o w n i n T a b l e 2 ( e v e n t s A t o G ) , h o w e v e r , t h e n u m b e r o fe v e n t s t a k e n i n t o c o n s i d e r a t i o n i s u s u a l l y d e p e n d e n t u p o n t h ea m ount of s e i sm ic e ve nt s oc c ur r ing w i th in the s e le c te d t im e f r a m e ,o r l e n g t h o f t h e a d o p t e d t i m e f r a m e . F o r e x a m p l e , d u r i n g t h e i n i t i a lc a l i b r a t i o n p r o c e s s , w h e n t h e b a c k a n a l y s i s o f a g i v e n r o c k b u r s t i sinvolve d , a wa rn ing t im e window m u s t be s e le cte d (e .g . 12 h- t im ew i n d o w ) i n c o r p o r a t i n g e v e n t s p r i o r t o t h e a c t u a l r o c k b u r s t , a n d t h e nthe e x t r e m e va lue s d i sp la ye d by the c a lc u la te d de pa r ture indic e s c a nbe t a ke n a s loc a l c r i t i c a l va lue s . In th i s wa y, loc a l c r i t i c a l va lue si D c ( P i / P j ) k a r e a s s i g n e d f o r e a c h p a r a m e t e r a n d t h e y a r e s h o w n i nT a b l e 3 .Fol low ing th i s proc e dure , de l t a pa ra m e te r s ADk[ (PdPj)1] a re a do pte d:

A D I [ ( P i / P j ) I ] = O, A D 2 [ ( P i / P j ) 2 ] = 1 ,AD3[(Pi /P j )3] = 1, A D 4 [ ( P i / P j ) 4 ] = 1 .

A S c a n b e s e e n f r o m T a b l e 3 , t h e v a l u e o f t h e p a r a m e t e r A D I w a sa s s igne d a s z e ro for the f i r s t pa ra m e te r ( i . e . r a t io of P + S se i sm icm o m e n t t o s t a t ic s t r es s d r o p ) , a s t h e r e a r e n o v i s ib l e t r e n d s i n d e p a r -

ture s f rom i t s a ve ra ge va lue for s e ve n se i sm ic e ve nt s pr ior to ther o c k b u r s t ( e v e n t s A t o G ) .A l l im por ta n c e c oe f f ic ie n ts ( a s 64 ek) a re t a ke n he re for s im pl ic i ty tob e e q u a l t o 1 . R o c k b u r s t h a z a r d l e v e l R m c a n n o w b e c o m p u t e da c c o r d i n g t o E q u a t i o n ( 3 );R H I = Z I A D I [ ( P i / P j ) I ] 4 - A D 2 [ ( p i /P j ) 2 ] - ~ - .. .

+ a D . [ ( e , / e j ) . ] } = 0 + i + 1 + l = 3 .T h i s r o c k b u r s t h a z a r d l e v e l R H I = 3 a nd a t th i s s t a ge th i s i s e qua l toth e r o c k b u r s t h a z a r d c r i ti c a l v a l u e R H i e r i t , the re fore

RHlerit = RH I 1 = 3 .

In th i s e xa m ple , th i s in i t i a l c r i t i c a l va lue R H l e r i t = 3 i s c a lc u la te d fore v e n t F , a n d i t is a ss o c i a te d w i t h t h e + 0 . 8 l o c a l P S S R i c h t e r m a g n i -t u d e r o c k b u r s t ( e v e n t H ) p r o d u c i n g u n d e s i r e d d a m a g e t o m i n e w o r k -ings . I f for a ne w se t of s e i sm ic e ve nt s , the c a lc u la te dR H I -- > R H l e r i t = 3 , t h a n t h e r o c k b u r s t h a z a r d m u s t b e d e c l a re d .The c r i t i c a l va lue R H I e r i t c a n be opt iona l ly e xpre s se d fur the r a s ar a t i o o f n u m b e r o f p a r a m e t e r s w h i c h a l r e a d y d i s p l a y e d l o c al c r i ti c a lv a l u e s t o t h e t o t a l n u m b e r o f p a r a m e t e r s u s e d i n t h e a n a ly s i s. I n t h i sc a s e :

Rrllcrit = 3/ 4 = 0.75.A s m e n t i o n e d e a r l i e r t h e a l g o r i t h m r e q u i r e s " t u n i n g " w h a t w o u l da l so invo lve prop e r s e le c t ion o f im p or ta n c e c oe ff ic ie n ts ( a k b~ e k),a n d a l s o t h e m o s t s u i t a b l e m e t h o d f o r o b t a i n i n g a v e r a g e v a l u e s (e .g .m oving a ve ra ge s ) .