M7.3 - NEW BRITAIN REGION, PAPUA NEW GUINEA

Tectonic Summary

The M7.3 New Britain, Papua New Guinea earthquake of July 18, 2010 (13:35 GMT) occurred as a result of thrust faulting on or near the plate boundary between the Solomon Sea and South Bismarck plates, microplates involved in the accommodation of large-scale convergence between the Australia and Pacific plates in the Woodlark Basin region of the southwest Pacific. At the location of this earthquake, the Solomon Sea plate moves approximately northwards with respect to the South Bismarck plate at a velocity of roughly 120 mm/year, thrusting under the South Bismark plate at the New Britain trench and dipping to the north-northwest. The July 18 (13:35) earthquake's location, depth, and focal mechanism are consistent with the earthquake having occurred as thrust faulting associated with subduction along this plate boundary.

This earthquake occurred approximately 10 km to the north and 30 minutes after a M6.9 earthquake. That smaller foreshock was deeper, and occurred as a result of reverse faulting in a direction highly oblique to the plate convergence direction. It is thus likely that the earlier M6.9 event occurred within the subducting Solomon Sea plate, rather than on its thrust interface. The subducting Solomon Sea plate is seismically active to depths of about 600 km beneath the island.

The New Britain region experiences a high level of earthquake activity, with 15 events of magnitude 7 and larger having been recorded within 3 degrees (336 km) of today's event since 1973. The region also has a history of large earthquakes occurring close together in time; of those 15 events, 11 occurred within several days-to-months of another nearby large earthquake. In November 2000, three earthquakes of M7.8 or larger occurred over a two day period approximately 300 km to the northeast of today's earthquake.

Earthquake Information for Papua New Guinea