The island of Papua New Guinea, on the western edge of the Pacific Ocean, was struck by a major earthquake on 14 December 2011. Originally recorded as having a magnitude of 7.3, the tremor was later downgraded by the United States Geological Survey to M7.1, though it still rates as one of the year’s largest earthquakes.
The Papua New Guinea Earthquake of December 2011
Initial data released by the USGS show that the earthquake occurred almost 140 miles NNW of the island’s capital, Port Moresby, at a depth of around 75 miles. Despite the scale of the ‘quake, the onshore (rather than offshore) location of its epicentre meant that no tsunami was generated and at the time of writing no injuries or significant damage had been reported.
Tectonic Setting of Papua New Guinea
Papua New Guinea is located on the Pacific margin and is part of the highly-active seismic and volcanic zone surrounding the ocean which is known as the Pacific Ring of Fire. At its simplest, the situation is usually explained in terms of the relationship between two of the earth’s major tectonic plates, with the Pacific plate moving towards the Australian plate, on which the main island of Papua New Guinea is situated.
In fact, the situation is more complex and subject to various interpretations. Sandwiched between the two main plates are several smaller plates which are, in effect, jostling for position between their two larger neighbours. Spreading centres off the south east of New Guinea are generating new ocean crust, which is moving northwards and being subducted (forced downwards) beneath the South Bismarck microplate.
This plate in turn is moving laterally against its northern neighbour, the North Bismarck plate – and also southwards against the Australian plate, squeezing yet another plate between them. Although there is no detailed seismological information available at the time of writing – and the exact configuration of the microplates unclear – the location and depth of the earthquake suggest that it is the latter relationship which caused the December 2011 earthquake.
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