M 7.0 - 260 km WSW of Abepura, Indonesia

Tectonic Summary

The April 6, 2013, M 7.0 earthquake beneath Irian Jaya, Indonesia, occurred as a result of oblique normal faulting at an intermediate depth, approximately 70 km beneath New Guinea. Focal mechanism solutions indicate that rupture occurred on either a north-northwest- or southwest-striking, moderately dipping normal fault. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the southwest-striking fault. At the location of this earthquake, the Pacific and Australia plates are converging at a rate of approximately 110 mm/yr in an east-northeast-west-southwest direction, resulting in the southward subduction of the Pacific plate beneath New Guinea at the New Guinea Trench, north of the island. The depth and faulting mechanism of the April 6th earthquake indicate that it likely ruptured a fault within the subducting Pacific lithosphere rather than on the shallower thrust interface between the two plates. 

This region of New Guinea frequently experiences moderate to large earthquakes; several dozen events with magnitudes greater than 6 have occurred within 250 km of the April 6th earthquake over the past 40 years. Many of those events were shallow expressions of microplate interactions at the complicated boundary between the Pacific and Australia plates in this region. The January 19, 1981, M 6.7 earthquake, 140 km to the southeast, struck at a depth of 20 km and caused approximately 1,300 fatalities. In July of 1976, a M 7.1 earthquake 210 km to the east-southeast struck just a few kilometers beneath the surface and resulted in around 6,000 fatalities. In contrast, intermediate-depth earthquakes like the April 6th event are much less hazardous and do not generally cause significant damage or fatalities, though large intermediate-depth (70–300 km) and deep-focus (depth greater than 300 km) earthquakes may be felt at great distances from their epicenters.

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)