Australia

Australia is one of the world's most tectonically stable continents, situated in the interior of the Indo-Australian Plate far from any plate boundary. Most of the continent is underlain by Precambrian cratons — ancient rigid blocks of crust up to 3.5 billion years old — that transmit seismic energy efficiently but generate earthquakes only rarely. Despite this stability, Australia is not seismically inactive: it experiences a significant number of intraplate earthquakes each year, including occasional events of magnitude 5 and above that can cause damage because the old, cold crust transmits [[seismic-wave]]s with little attenuation over large distances, meaning even moderate events are felt over vast areas. The highest seismic hazard is concentrated in the southwest of Western Australia, in the Flinders Ranges of South Australia, and in parts of southeastern Australia, where stress concentration along ancient craton margins and fault reactivation produces the most activity. The most serious long-term seismic hazard for Australia comes not from intraplate events but from its proximity to the plate boundaries to the north and east, where the Indo-Australian Plate is colliding with Eurasia and the Pacific arc systems.

Australia's largest recorded earthquakes reflect the intraplate character of its seismicity — moderate-to-large events in geologically ancient terrain with long recurrence intervals. The 14 October 1968 Meckering earthquake in Western Australia (magnitude 6.6) ruptured approximately 37 kilometres of surface faulting, the longest onshore fault rupture in Australia's instrumental record, and caused severe damage in the small wheatbelt town of Meckering, razing virtually every building. The 2 March 1979 Cadoux earthquake (magnitude 6.1) again struck the Western Australian wheatbelt. The 28 December 1989 Newcastle earthquake (magnitude 5.4) killed 13 people and caused 4 billion Australian dollars in damage, prompting the first major revision of Australia's earthquake code to include the east coast; the [[epicenter]] lay beneath the densely built Newcastle city centre on a previously unrecognised intraplate [[fault]], demonstrating that seismic hazard is not limited to tectonically obvious zones. The 28 June 2016 Petermann Ranges earthquake in the Northern Territory (magnitude 6.1) produced one of the best-documented examples of surface rupture on an intraplate [[fault]] in any continent, with GPS and satellite imagery recording up to 90 centimetres of vertical slip on a new scarp.

The tectonic setting of Australia reflects its long history as a stable continent with a complex assembly of Archaean and Proterozoic cratons. The oldest rocks are the Pilbara and Yilgarn cratons of Western Australia, with ages up to 4.4 billion years in detrital zircons. The Indo-Australian Plate is currently colliding with Eurasia along the Himalayas and with the Pacific Arc along the New Guinea and New Zealand boundaries, generating compressional stress that is transmitted thousands of kilometres into the Australian interior. This diffuse intraplate stress field is expressed as occasional fault reactivation on ancient structures that were formed during much earlier tectonic regimes. Neotectonic fault scarps — visible topographic features recording Quaternary surface rupture on previously unrecognised faults — have been discovered across Australia in recent decades, suggesting the continent has more active fault structures than previously appreciated. The recurrence intervals on individual Australian intraplate faults are typically measured in tens of thousands to hundreds of thousands of years, making probabilistic hazard assessment challenging. Geoscience Australia operates the national seismograph network and maintains the Atlas of Neotectonic Features in Australia.