The February 6th, 2013 M 8.0 earthquake in the Santa Cruz Islands occurred as the
result of shallow thrust faulting on or near the plate boundary interface
between the Australia and Pacific plates.
In the region of this earthquake, the Australia plate converges with and
subducts beneath the Pacific plate, moving towards the east-northeast at the
rate of approximately 94 mm/yr. The February 6th earthquake is located approximately
700-750 km ESE of the Mw 8.1 Solomon Islands earthquake of April 1, 2007, and the Mw
7.1 Solomon Island earthquake of January 3, 2010. It is over 900 km to NNW of the
February 2, 2012 Mw 7.1 Vanuatu earthquake, and approximately 200-300 km north of
a series of earthquakes in October, 2009 along the Vanuatu Trench that included two
earthquakes larger than magnitude 7 (Mw 7.8, Mw 7.4).
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. Over the month leading up
to the February 6th earthquake, there have been dozens of earthquakes in the epicentral
region - over 40 M 4.5 or larger in the preceding 7 days alone, 7 of which were larger than
M 6. Faulting mechanisms for these earthquakes suggested a mixture of strike-slip, normal and
thrust faulting events. Within an hour of the February 6th M 8.0 mainshock, there were also
two large aftershocks with magnitudes greater than M 6.