Tectonic Summary

The February 6, 2013 (01:23:19 UTC), M 7.1 earthquake in the Santa Cruz Islands occurred as a result of shallow normal faulting within the oceanic lithosphere of the Australia plate, just west of the New Hebrides Trench where the Australia plate begins its eastward subduction beneath the western edge of the Pacific plate. Focal mechanism solutions indicate that rupture occurred on either a northwest- or south-southeast-striking, moderately dipping normal fault. Slip on a fault aligned with either nodal plane is consistent with this intraplate setting. At the location of this earthquake, the Australia plate moves towards the east-northeast with respect to the Pacific plate at a velocity of approximately 94 mm/yr. This event can be considered an aftershock of the damaging M 8.0 Santa Cruz Islands earthquake that occurred earlier on the same day, 50 km to the northeast.

This earthquake is located adjacent to a complex section of the Australia-Pacific plate boundary, where the Solomon Trench to the west is linked to the New Hebrides (Vanuatu) Trench to the south by a short segment of dominantly strike-slip plate motion. The February 6th earthquakes are located at the northern end of the New Hebrides (Vanuatu) segment. To the north and west of this event, the plate boundary changes in character, is oriented more west-to-east, and connects the segment ruptured by this event with the continuation of the subduction zone along the Solomon Islands.

The February 6th M 7.1 earthquake occurred only 20 minutes after and approximately 50 km southwest of the M 8.0 Santa Cruz Islands earthquake. Over the month leading up to the February 6th events, dozens of earthquakes were recorded in the epicentral region; more than 40 M 4.5+ occurred in the preceding 7 days alone, 7 of which were larger than M 6. Faulting mechanisms for these earthquakes suggest a mixture of strike-slip, normal, and thrust-faulting events. Within an hour of the February 6th M 8.0 mainshock, there were two large aftershocks with magnitudes greater than M 7, this M 7.1 being the first of the two. None of these events have been associated with recorded damage or casualties.

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)

Event Details

Event Map

Tectonic Summary

Historical Magnitude 4.5+ (100km)

Tectonic Summary

Historical Magnitude 4.5+ (100km)