Poster of the Eastern New Guinea region, Papua New Guinea Earthquake of 14 December 2011 - Magnitude 7.1
The Eastern New Guinea Region earthquake of December 14, 2011, occurred as a result of oblique-normal faulting deep beneath eastern Papua New Guinea, near the northern edge of the Australian Plate. Earthquakes in this geographical region are associated with the large-scale convergence of the Australia and Pacific plates, and with the complex interactions of several microplates between the two, most notably the South Bismarck plate, the Solomon Sea plate, and the Woodlark plate. At the latitude of this event, the Australian plate moves towards the east-northeast with respect to the Pacific plate at a rate of approximately 10 cm/yr.
The depth of the December 14 earthquake implies that it occurred in subducted or foundered lithosphere. Although there is still not complete geophysical consensus on the location and configuration of subducted plates in the region, the location of the earthquake is consistent with it occurring in a subducted fragment of the Solomon Sea plate that is bent about an approximately east-west axis and subducting both to the north and to the south or southwest. In northern Papua New Guinea, approximately 80 km to the north of the December 14 event, clear north-directed subduction of the Solomon Sea plate beneath the South Bismarck plate occurs, with the associated Wadati-Benioff zone active to depths of over 600 km beneath the Bismarck Sea to the northeast of New Guinea. The location of the December 14 earthquake would place it in the gently south-southwest dipping segment of the Solomon Sea plate.
Papua New Guinea experiences a moderate-to-high rate of seismic activity, with almost 50 events of M6 or larger occurring within 250 km of today's event since 1973. Nearby (within 100 km), only one large earthquake has occurred at depths greater than 100 km - a magnitude 7.3 earthquake 60 km to the west at 180 km depth in 1963.
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