Thursday 5 April 2012

Earthquake shakes New Britain.

Slightly before 6.30 am on Thursday 5 April, local time (slightly before 8.30 pm on Wednesday 4 April GMT) an Earthquake shook the Papuan province of East New Britain. The quake was centered 21 km north of Rabaul, at a depth of 16.7 km, and measured 5.5 on the Richter Scale according to the United States Geological Survey. There are no reports of any casualties or serious damage, and no tsunami warning has been issued.

Map showing the location of the quake, and the areas that suffered the strongest shaking. USGS.

Rabaul was the capital of East New Britain Province, until 1994, when it was largely destroyed by a volcanic ashfall that caused 80% of the buildings to collapse (this is common in heavy ashfalls, the ash piles up on the roofs of buildings, which then collapse under the weight), after which the capitol was shifted to Kokopo, 20 km to the east. The city is located on the rim of the (largely submerged) Rabaul Caldera, which periodically erupts causing severe local problems. In 1937 an eruption from Rabaul killed 500 people.

Rabaul Caldera. USGS.

New Britain lies on the boundary between the South Bismarck and Solomon Sea tectonic plates. The Solomon Sea Plate is being subducted beneath the South Bismarck Plate, which causes friction as the plates rub together, occasionally leading to Earthquakes. As the Solomon Sea Plate sinks into the Earth it is melted by the heat of the planets interior. Some of the melted material then rises through the overlying South Bismarck Plate, fueling the volcanoes of New Britain.

The subduction of the Solomon Sea Plate beneath New Britain. Oregon State University.

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