Cardwell, R.K.

Chen, A.

Isacks, B.L.

Latham, G.V.

Louat, Rémy

Horizon / Pleins textes

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. FIRST RESULTS FROM A NEW SEISMOGRAPH NETWORK 
I N  THE CENTRAL NEW*HEBRIDES I S W D  ARC 
, . . .  
' .  R.. K. Cardwcll 
* B. L. I sacks  (both at: Dept. Geological Sciences., ' I 
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-.' . Cornel l  Un ive r s i ty ,  I t haca ,  N.Y. 14853) ' i  
.. -..'R. Louat ( Off i ce  d e  l a  Recherche Sc ien t i f ique  
. G. V. Latham 
e t  Technique Outre-Mer, Noumea, New Caledonia). 
A. Chen (both at: Univ. of Texas Marine Science . 
. Ins t . ,  Geophys. Lab., Galveston, Texas 77550) 
A 10 s t a t i o n  te lemetered seismograph network . 
was es t ab l i shed  dur ing  1978 i n  an  area tentative-. 
l y  i d e n t i f i e d  as a se i smic 'gap  for l a r g e  ear th-  
quakes i n  the  centra1 New Hebrides.During 15 
days i n  September the network was augmented by 7 
OBS s t a t i o n s  loca t ed  i n -  t he  arc-trench gap. Mure 
- than  200 events  were located,.-Wth t h e  ex tens ive  .. i 
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network coverage l o c a t i o n s  of events  within the . i 
main t h r u s t  zone of t h e  p la te  boundary'can be re- 
solved i n  r e l a t i o n  t o  events  w i th in  . the descend-. 
ing and upper p l a t e s .  A magnitude 5 event: was . . 
caught a long w i t h  numerous small af tershocks.  The 
main shock has a thrust  type mechanism but  after-  
shocks inc lude  bo th  i n t e r -  and in t r a -p l a t e  
events. Combination of  t h e s e  d a t a  wi th  data f rom 
previous temporary networks operated i n  t h e  New 
Hebrides and wi th  focal mechanism so lu t ions  f o r  
l a r g e r  events  f o r  t h e  p a s t  1 7  yea r s  i n d i c a t e  
tha t  t h e  reg ion  covered by t h e  new neiwork is un- 
usual.  I n t r a p l a t e  a c t i v i t y  ad jacent  t o  the  main 
zone of t h r u s t i n g  is predominant relative t o  t h a t  
wi th in  t h e  t h r u s t  zone.Also, t he  region has no t  , 
had a l a r g e  t h r u s t  type  earthquake f o r  a t  least:  . ' 
the  past: 20-30 years .  The p o s s i b i l i t y  thus  arises I j 
t h a t  t he  predominance of i n t r a p l a t e  a c t i v i t y - i s  a i i 
t r a n s i e n t  f e a t u r e  of t'ne cycle of major p l a t e  
boundary s l ippage.  For example, the events  may be . 
r e l a t ed  t o  stress accumulation i n  a locked sect- 
ion  o f  t h e  plate  boundary. 
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First results from a new seismograph network in the central New Hebrides island arc

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