Abstract

Recent interpretation of northeastern Irian Jaya using air photographs and LANDSAT imagery in conjuction with the results of oil exploration has revealed the broad structural framework which correlates in remarkable detail with the seismicity of the region.

The major structures along the northern fringe of the island result from convergence between the Pacific and Australian plates and probably date from the middle Pleistocene. The direction of maximum convergence as shown by these structures is directed along a southwesterly trend and supports the direction of relative plate motion derived from world-wide computer modelling as shown on the Plate Tectonic Map of the Circum-Pacific region (AAPG 1982).

The main mechanism of convergence over most of the region has been by southwards underthrusting of the Pacific Plate along thrust zones at right angles to the regional stress accompanied by very major lateral offsets parallel to the regional stress.

The underthrusting has been accompanied by deep sedimentation in restricted sedimentary troughs and also by extraordinarily extensive diapiric intrusion (Williams and Amiruddin in press, and Williams et al, in press).