Begining with a foreshock of mag 6.5, a bigger shock of 7.2 and then a series of aftershocks of 5+; all within several hours of immense rumbling and shaking in the Solomon islands at the junction of the Australian plate and the Pacific plate. In the map below the plate boundary trends NW-SE just south of the islands.
Here is the tectonic summary from USGS:
The Solomon Islands earthquake of January 3, 2010, likely occurred
at the boundary between the Pacific and Australian plates, where the
Australian plate subducts beneath the Pacific towards the northeast at
a rate of approximately 95 mm/yr. The mechanism of the January 3rd
earthquake is consistent with its occurrence in relation to
underthrusting of the Australia plate beneath the Pacific plate, as
part of this subduction process.
The Solomon Islands arc as a whole experiences a very high level of
earthquake activity, and many shocks of magnitude 7 and larger have
been recorded since the early decades of the twentieth century. The
January 3rd, 2010 earthquake nucleated approximately 50 km to the
southeast of a M8.1 earthquake in April 2007, which with an associated
tsunami caused at least 50 fatalities and destroyed several coastal
villages on nearby islands. An M6.5 foreshock occurred less than one
hour before this main shock, in approximately the same location.
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