ESTIMATION OF CURRENT PLATE MOTIONS IN PAPUA-NEW-GUINEA FROM GLOBAL POSITIONING SYSTEM OBSERVATIONS

Plate tectonic motions have been estimated in Papua New Guinea from a 20 station network of Global Positioning System sites that has been ob served over five campaigns from 1990 to 1996. The present velocities o f the sites are consistent with geological models in which the South B ismarck, Woodlark, and Solomon Sea Plates form the principal tectonic elements between the Pacific and Australian Plates in this region. Act ive spreading is observed on the Woodlark Basin Spreading Centre but a t a rate that is about half the rate determined from magnetic reversal s. The other major motions observed are subduction on the New Britain Trench, seafloor spreading across the Bismarck Sea Seismic Lineation, convergence across the Ramu-Markham Fault and left-lateral strike slip across the Papuan Peninsula. These motions are consistent with a 8.2 degrees Myr(-1) clockwise rotation of the South Bismarck Plate about a pole in the Huon Gulf and a rotation of the Woodlark Plate away from the Australian Plate. Second order deformation may also be occurring; in particular, Manus Island and northern New Ireland may be moving nor thward relative to the Pacific Plate at similar to 5-8 mm yr(-1) (sign ificant at the 95% but not at the 99% confidence level) which may sugg est the existence of a North Bismarck Plate.