2009 Vanuatu earthquakes
The 2009 Vanuatu earthquakes were three earthquakes with magnitudes ranging from 7.4 to 7.8, constituting some of the largest earthquakes in Vanuatu's history.
Tectonic Setting
The Vanuatu earthquakes of October 7, 2009: M 7.7, Vanuatu, 22:03:14; M 7.8 Santa Cruz Islands, 22:18:51 UTC; and M 7.4, Vanuatu, 23:13:48; all occurred as a result of shallow reverse faulting on or near the plate boundary interface between the Indo-Australian Plate and Pacific Plates. In the region of these earthquakes, the Indo-Australian Plate moves to the east-northeast with respect to the Pacific Plate at a velocity of about 91 mm/yr. The Indo-Australian Plate thrusts under the Pacific Plate at the New Hebrides Trench and dips to the east-northeast. The locations, depths, and focal mechanism solutions for the October 7th events are all consistent with them resulting from reverse faulting associated with subduction along the Australia-Pacific Plate boundary.The 7.8 earthquake of October 7, 2009, occurred about 60 km north, and 15 minutes after, a slightly smaller earthquake with a 7.7 of the same date Occurred. A third, smaller event at 7.4 occurred at 23:13 UTC, 15 km to the southeast of the first event. All three events are likely related; while the first two similarly sized events may be considered a doublet earthquake, preliminary analysis suggests that the 7.4 earthquake is likely a large aftershock of one of the events.