Poster of the Vanuatu Earthquakes of 07 October 2009 - Magnitudes 7.6, 7.8 and 7.3

Tectonic Summary

The Vanuatu Region earthquakes of October 7, 2009: M7.6, Torres Islands, 22:03:15; M7.8 Santa Cruz Islands, 22:18:26 UTC; and M7.3, Torres Islands, 23:13:49 occurred on or near the plate boundary between the Australia and Pacific plates. In the region of the earthquake, the Australia plate moves to the east-northeast with respect to the Pacific plate at a velocity of about 91 mm/year. The Australia plate thrusts under the Pacific plate at the New Hebrides trench and dips to the east-northeast. The October 7 earthquake's location, depth, and focal mechanism are consistent with the earthquake having occurred as thrust-faulting associated with subduction along the Australia-Pacific plate boundary.

The earthquake of October 7, 2009, 23:13 UTC occurred about 15 km southeast of, and 1 hour after, a larger earthquake of the same date, 22:03 UTC. A second event of a similar size to the first occurred at 22:18 UTC, 60 km to the north of the first event. All three events are likely related; while the first two similarly sized events may be considered a earthquake doublet, preliminary analysis suggests the October 7, 2009, 23:13 UTC is likely a large aftershock of the previous events.

The Vanuatu region experiences a very high level of earthquake activity, with over a dozen events of magnitude 7 and larger having been recorded since the early decades of the twentieth century. Recent large earthquakes near the October 7 events include a M 7.2 earthquake in 2007 and a M 7.3 earthquake in 1999. The subducting Australia plate is seismically active to depths of about 350 km beneath the islands.