Origin of the in situ stress field in south-eastern Australia

The in situ stress field of south-eastern Australia inferred from earthquake focal mechanisms and bore-hole breakouts is unusual in that it is characterised by large obliquity between the maximum horizontal compressive stress orientation (S-Hmax) and the absolute plate motion azimuth. The evolution of the neotectonic strain field deduced from historical seismicity and both onshore and offshore faulting records is used to address the origin of this unusual stress field. Strain rates derived from estimates of the seismic moment release rate (up to similar to10(-16) s(-1)) are compatible with Quaternary fault-slip rates. The record of more or less continuous tectonic activity extends back to the terminal Miocene or early Pliocene (10-5 Ma). Terminal Miocene tectonic activity was characterised by regional-scale tilting and local uplift and erosion, now best preserved by unconformities in offshore basins. Plate-scale stress modelling suggests the in situ stress field reflects increased coupling of the Australian and Pacific Plate boundary in the late Miocene, associated with the formation of the Southern Alps in New Zealand.