complex system of left-lateral faulting in the Bismarck Sea connect- 

 ing poorly defined NE-striking active spreading axes (Malahoff and 

 Bracey, 1974; Connelly, 1976; Taylor, 1979). 



The northern New Guinea focal mechanisms shown by Hayes and 

 Taylor (1978) indicate an extremely complex tectonic regime. The 

 principal stress seems to be NE-SW directed horizontal compression 

 across a broad zone which extends along the entire northern part of 

 the island, connecting on the east with the Bismarck Sea seismic 

 zone and on the west (at Japen Island) with the left-lateral Sorong 

 Fault. 



A focal mechanism determination for an earthquake (at 0.2°S/ 

 132, 4°E) near the small trench north of the "birds head" of New 

 Guinea by Fitch (1972) , indicated SSW-oriented thrusting with some 

 components of strike-slip motion. 



There are several shallow epicenters in the Ayu Trough. Weissel 

 and Anderson (1978) made a focal mechanism determination for one 

 event (at 2. 9°N/132. 8°E) for which they found a strike-slip mechanism. 

 Of the two possible solutions, they preferred a N60°W plane with 

 right-lateral motion. 



Earthquake activity is very sparse at both the Palau and Yap 

 Trenches relative to the activity at other trench-island arc systems. 

 At the Yap Trench, Fitch (1972) determined one event (at 8. 7°N/137 . 7°E) 

 to be an east-west thrusting mechanism. 



There are only two shallow events in the Sorol Trough. No focal 

 mechanism determinations have been done on these earthquakes. 



23 



