M 7.8 - 135 km SE of Kokopo, Papua New Guinea

Tectonic Summary

The November 16, 2000, M 7.8 earthquake in the New Ireland region of Papua New Guinea occurred as the result of shallow thrust faulting on or near the plate boundary interface between the subducting Australia and overriding Pacific plates and can also be considered an aftershock of the M 8.0 earthquake that occurred only 3 hours previously and about 100 km to the northwest. In this region, the Australia plate moves to the east-northeast with respect to the Pacific plate at a velocity of about 105 mm/yr. 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 Australia and the Pacific, including the Solomon Sea and South Bismark microplates local to this event. In this context, the November 16th event occurred along the boundary between the Solomon Sea and South Bismark microplates. The Solomon Sea microplate moves slightly faster and more northeasterly with respect to the Pacific plate (and South Bismark microplate) than does the Australia plate due to sea-floor spreading in the Woodlark Basin several hundred kilometers to the southeast of the November 16th earthquake, facilitating the classic subduction evident beneath New Britain and New Ireland. Focal mechanism solutions and finite-fault modeling of globally recorded seismic data for the November 16th M 7.8 event are consistent with its occurrence on the shallow subduction interface in this region.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Thrust-faulting events of the size of the November 16, 2000, M 7.8 earthquake are typically about 120x50 km (length x width); modeling of this earthquake implies dimensions of about 80x60 km, predominantly surrounding the hypocenter.

Shallow earthquakes represent deformation along plate boundaries and associated structures, rather than within subducted slabs where intermediate-depth earthquakes (70–300 km) nucleate. However, this area of Papua New Guinea commonly experienes both shallow and intermediate-depth events, and the Australia plate in this region is known to be seismically active to depths of more than 500 km. Within 400 km of the November 16th M 7.8 earthquake, 30 other events of at least M 7 have occurred over the preceding 40 years. Three of these events were M 8 or larger, with one being the damaging M 8.0 earthquake that occurred only 3 hours prior to this 07:42 UTC event.

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)