Tectonic Summary

The May 7, 2015, M 7.1 earthquake southwest of Panguna, Papua New Guinea, occurred as the result of normal faulting within the Australia plate, a few tens of kilometers to the southwest of the plate boundary where Australia begins its subduction beneath the Pacific plate at the New Britain Trench. At the location of the earthquake, the Australia plate moves towards the east-northeast at a velocity of 103 mm/yr with respect to the Pacific plate. The moment tensor and location of the event are consistent with its occurrence near what has been termed the outer rise region outboard of the subduction zone, rather than farther to the north on the plate boundary (thrust) interface, on a normal fault dipping shallowly to the northeast or steeply to the southwest. Finite-fault modeling of globally recorded seismic data for this earthquake is not able to distinguish between these two possibilities. Note that at the location of the earthquake, some researchers consider the edges of the Australia and Pacific plates to be divided into several microplates that take up the overall convergence between the Australia and Pacific plates, including the Solomon Sea microplate local to this event. The Solomon Sea microplate moves slightly faster and more northeasterly with respect to the Pacific plate than does the Australia plate due to sea-floor spreading in the Woodlark Basin a few hundred kilometers to the southeast of the May 7th earthquake, facilitating the classic subduction evident beneath New Britain and the Solomon Islands.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal-faulting events of the size of the May 7, 2015, earthquake are typically about 45x20 km (length x width).

The plate boundary between the Australia and Pacific plates in the Papua New Guinea region is very active seismically; 26 M 7+ events have occurred within 250 km of the May 7, 2015, earthquake over the past century. Most occurred on the subduction zone thrust interface to the north of this event, and few are known to have caused shaking-related fatalities because of the remoteness of the region. Just one of these large nearby events was the result of normal faulting to the south of the plate boundary—a M 7.0 earthquake in October 1987, 15 km to the southwest of the May 7, 2015, event.

The May 7 earthquake was also preceded by a series of moderate to large earthquakes on the portion of the plate boundary several hundred kilometers to the northwest over the previous 6 weeks, beginning with a M 7.5 event on March 29, 2015, and continuing with another M 7.5 earthquake on May 5, 2015. The May 7th earthquake is also 75 km to the southwest of a M 7.5 earthquake in April 2014, just offshore of the North Solomon Islands.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)

Event Details

Event Map

Tectonic Summary

Tectonic Summary

Historical Magnitude 4.5+ (100km)