M 7.3 - 141 km W of Isangel, Vanuatu

Tectonic Summary

The December 25, 2010, M 7.3 Vanuatu region earthquake occurred as the result of shallow normal faulting within the Australia plate, in the region of the boundary between the Australia plate and the Pacific plate. Focal mechanism solutions indicate that rupture occurred on either a north- or south-southeast-striking, moderately dipping normal fault. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the south-southeast-striking fault. In the epicentral region of the earthquake, the Australia plate moves east-northeast relative to the Pacific plate at a velocity of about 80 mm/yr. The Australia plate subducts beneath the Pacific plate at the New Hebrides Trench, just east of the December 25th earthquake, and is seismically active to a depth of 300 km. The stresses that generated the earthquake result from the bending of the Australia plate as it subducts beneath the Pacific plate.

The western margin of the Pacific plate that lies to the east of the New Hebrides Trench is commonly viewed as being subdivided into several microplates that move with respect to each other at rates of a few centimeters per year, whose differential motions help to accommodate the overall convergence between the Australia and Pacific plates. These include the New Hebrides microplate local to this earthquake.

The New Hebrides Arc region of the Australia/New Hebrides plate boundary experiences numerous strong earthquakes. In the past quarter century, the 1,000-km section of the arc centered on the epicenter of the December 25th earthquake has produced 19 earthquakes of M 7+, the largest having M 7.7.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)