M7.1 - MACQUARIE ISLAND REGION

Tectonic Summary

The April 12th, 2008 earthquake south of the Macquarie Islands indicates thrust faulting on the plate boundary between the Australian and Pacific Plates in the southwest Pacific Ocean. The earthquake is located in a region of rapid transitions in plate motion from convergence at the Hjort Trench (just south of the earthquake) to strike-slip motion along the Macquarie Ridge (north of the earthquake), brought about by the close proximity of this section of the plate boundary to the Australia:Pacific pole of rotation. This plate boundary transition is delineated by earthquakes of both thrust and strike-slip orientation in the vicinity of the 04/12/2008 earthquake. In the epicentral region of this event, the Australian Plate moves north-northeast with respect to the Pacific Plate at a rate of approximately 27 mm/yr.

The Australia-Pacific plate boundary south of New Zealand experiences numerous strong earthquakes, and has hosted great (M8+) earthquakes in recent history. In 1989, a magnitude 8.1 earthquake occurred on the plate boundary approximately 380km north of the 04/12/2008 event, and most recently a magnitude 8.1 event occurred within the Australian Plate west of the plate boundary another 250 km further north. The 04/12/2008 event is the largest known historic earthquake on the section of the plate boundary south of the 1989 event since a nearby magnitude 8.3 earthquake in 1924.