M8.0 Earthquake and Tsunami in Solomon Islands, West Pacific: 6 February 2013

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Location and tectonic setting of the earthquake and aftershocks 6 February. Image credit: USGS

Location and tectonic setting of the earthquake and aftershocks 6 February. Image credit: USGS

The Solomon Islands, in the western Pacific, were struck by a tsunami triggered by a magnitude 8 (M8.0) earthquake on February 6th. 2013 (The evening of the 5th, U.S. time).

The epicentre of the tremor, which occurred at a depth of 29 km, was just to the west of the Santa Cruz Islands, a group of islands within the Solomon Islands province.

Although a tsunami warning was issued for many countries in the southern and western Pacific, this was subsequently cancelled when it became clear that any wave generated was likely to have only local impact. News reports suggest that five people were killed in the Solomon Islands by a tsunami of around a metre in height.

The M8 tremor appears to have been the mainshock of a series of earthquakes to have struck the region over the preceding week. USGS data indicate that it was preceded by 22 foreshocks of at least M5.0 and at the time of writing 38 aftershocks of a similar magnitude had been recorded.

Solomon Islands Quake: Tectonic Setting

The boundary between the Australian and Pacific tectonic plates is notably complex, with several changes in the nature of the contact and in the direction and speed of movement. The February 6th earthquake and its associated tremors occurred at the junction between the roughly east-west trending South Solomon Trench, and the roughly north-south trending New Hebrides Trench. Both of these are subduction zones, linked by a short section of laterally-moving crust.

Data from the USGS suggest that the epicentre was at the northern end of the New Hebrides trench and that the dominant fault movement was thrusting, as the two tectonic plates converge at a rate of around 94 mm per year.

Thrusting involves vertical movement, a key component in the generation of tsunamis. The USGS also suggests, however, that the swarm of earthquakes preceding and following the mainshock resulted from a range of different motions.

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