M 7.6 - 68 km ESE of Aitape, Papua New Guinea

Tectonic Summary

The September 8, 2002, M 7.6 earthquake near the north coast of New Guinea, Papua New Guinea, occurred as the result of shallow reverse faulting in the subduction zone near the eastern end of the New Guinea Trench. Focal mechanism solutions indicate that rupture occurred on either a steep, northwest-striking reverse fault or on a moderately dipping, southeast-striking reverse fault. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the southeast-striking fault. At the location of the earthquake, the Pacific plate is moving west-southwest relative to the Australia plate at a velocity of about 100 mm/yr. The earthquake reflects the complex interaction between these two major plates and the smaller Bismarck, Caroline, and Woodlark microplates. The Bismarck plate itself is divided into two smaller pieces (the North and South Bismarck plates), interrupting the New Guinea Trench that follows the northern coast of Papua New Guinea. The depth, location, and focal mechanism solutions for this earthquake demonstrate how the complex motions of these numerous small microplates accommodate the large-scale convergence between the Pacific and Australia plates.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Reverse-faulting events of the size of the September 8, 2002, earthquake are typically about 90x45 km (length x width); modeling of this earthquake implies dimensions of about 70x35 km, predominantly up-dip and east of the hypocenter.

This region has recently suffered several damaging earthquakes. The most significant was on July 17, 1998, when a M 7.0 earthquake generated a tsunami that resulted in at least 2,183 fatalities and injured thousands.

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)