M7.3 - FIJI

Tectonic Summary

The Fiji earthquake of 9 November 2009 occurred at the northern end of the inclined seismic zone that dips to the west beneath Tonga and Fiji. The broad-scale tectonics of the earthquake region are dominated by the relative convergence of the Pacific and Australia plates. The inclined seismic zone lies within the Pacific plate, which subducts westward beneath the Australia plate at the Tonga trench. At the latitude of the earthquake, the Pacific plate moves westward with respect to the interior of the Australia plate at a velocity of about 86 mm/y.

The earthquake occurred in response to stresses generated by slow distortion of the Pacific plate, rather than on the thrust fault that constitutes the interface between the Australia and Pacific plates and which is seismically active near the earth's surface. The Pacific plate is active to depths of about 700 km in the region of the earthquake.

Earthquakes that have focal depths greater than 300 km are commonly termed "deep-focus" earthquakes. Deep-focus earthquakes cause less damage on the ground surface above their foci than is the case with similar magnitude shallow-focus earthquakes, but large deep-focus earthquakes may be felt at great distance from their epicenters. The largest recorded deep-focus earthquake had a magnitude of 8.2