M 7.0 - 33 km NW of Lata, Solomon Islands

Tectonic Summary

The February 6, 2013 (01:54:15 UTC), M 7.0 earthquake in the Santa Cruz Islands occurred as a result of shallow strike-slip faulting within the oceanic lithosphere of the Pacific plate, above the northern edge of the subduction zone interface between the Australia and Pacific plates. Focal mechanism solutions indicate that rupture occurred on either a right-lateral northeast-striking fault or a left-lateral northwest-striking 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 about 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, 75 km to the southwest.

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 earthquake is 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.

Though close to the subduction zone plate boundary in the region, the depth and focal mechanism solutions of this M 7.0 earthquake indicate intraplate faulting within the overlying Pacific plate, rather than deeper thrust faulting directly related to the subduction process. The event was likely driven by the stresses generated by the earlier M 8.0 mainshock. Over the month leading up to the February 6th earthquakes, dozens of earthquakes were recorded in the epicentral region; over 40 M 4.5+ events 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 7.0 being the second 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)