Seismicity of the Indo-Australian/Solomon Sea Plate boundary in the Southeast Papua region

Abstract

Seismicity and earthquake focal mechanism plots of the Southeast Papua and Woodlark Basin region for the period January 1960 to May 1979 show that: 1. (a) the West Woodlark Basin spreading centre extends from the deep West Woodlark Basin, through Dawson Strait into Goodenough Bay, Southeast Papua; 2. (b) a southeast seismic trend in the West Woodlark Basin is associated with a left-lateral transform fault, but a gap exists between this zone and the seismic East Woodlark Basin spreading centre; 3. (c) Southeast Papua Seismicity divides into a shallow earthquake zone in which the earthquakes occur mainly in the northeast side of the Owen Stanley Range, and an intermediate depth southwest dipping Benioff zone which extends almost from Mt. Lamington to Goroka. The Benioff zone indicates the presence of a southwest dipping slab of Solomon Sea Plate beneath the Indo-Australian Plate in the Southeast Papua and Ramu-Markham Valley region. This subduction zone has collided with the New Britain subduction zone of the Solomon Sea Plate along the Ramu-Markham Valley. The Solomon Sea Plate is now hanging suspended in the form of an arch beneath Ramu-Markham Valley, inhibiting further subduction beneath Southeast Papua.