Mechanisms of Australian earthquakes and contemporary stress in the Indian ocean plate

Abstract

Orientation of contemporary stress within plates of lithosphere, inferred mainly from earthquake mechanism solutions, is an important constraint to be satisfied by proposed driving mechanisms for global tectonics. Axes of maximum compressive stress in western Australia, India and the intervening oceanic region are nearly horizontal. In the NW part of this region, adjacent to the Burmese, Andaman and western Sunda arcs, axes of minimum compressive stress are also horizontal. Here stress axes are oriented in such a way as to suggest interaction of two stress fields; one generated by continental collision along the Himalayas and the other generated by body forces acting on parts of this plate that are descending into the upper mantle. We speculate that release of tectonic stress within large plates is to some extent localized by epirogenic processes some of which may operate independently of mechanisms that drive the plates.