Tectonic Summary

The January 22nd, 2017, M 7.9 earthquake west of Panguna, Papua New Guinea, occurred as the result of reverse faulting at an intermediate depth (~150 km) beneath the island of Bougainville (North Solomons). At the location of the earthquake, the Australia plate is converging with and subducting beneath the Pacific plate in an east-northeast direction at a rate of approximately 103 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, South Bismarck and Manus microplates local to this event. In this context, the January 22nd event occurred along the boundary between the Solomon Sea microplate and the Pacific plate. The Solomon Sea microplate moves slightly faster and more northeasterly with respect to the Pacific plate (and South Bismarck and Manus microplates) than does the Australia plate due to sea-floor spreading in the Woodlark Basin to the southeast of the January 22nd earthquake, facilitating the classic subduction evident beneath New Britain and New Ireland. Focal mechanism solutions for the January 22nd event indicate the earthquake occurred on a moderately dipping fault striking either northwest or southeast. The location, depth and focal mechanism solution all indicate the earthquake occurred as a result of intraplate faulting within the subducting lithosphere of the Australia plate (Solomon Sea microplate), rather than on the overlying plate interface.

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 January 22, 2017, M 7.9 earthquake are typically about 135x60 km (length x width).

Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed "intermediate-depth" earthquakes. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters. "Deep-focus" earthquakes, those with focal depths greater than 300 km, also occur in the subducted Australia plate. Earthquakes have been reliably located to depths of about 500 km in this region.

The Papua New Guinea region frequently hosts large earthquakes. Over the preceding century, 29 other earthquakes with M 7+ occurred within 250 km of the January 22nd event. One of these occurred at intermediate (70-300 km) - the March 1983 M 7.6 earthquake, over 200 km northwest of the January 22nd event - while two others occurred at deep (>300 km) depths. The December 17, 2016, M 7.9 intermediate earthquake occurred just under 300 km to the northwest of the January 22nd earthquake.

Event Details

Event Map

Tectonic Summary

Tectonic Summary

Historical Magnitude 4.5+ (100km)