By David Jacobson, Temblor
At 3:36 a.m. local time, a M=6.4 earthquake struck Papua New Guinea just off the island of New Ireland. The eastern part of the country is sparsely populated meaning people were only exposed to light and lesser degrees of shaking. Because of this damage and fatalities are unlikely, and so far no reports of them have come in. Another reason why strong shaking was not felt is because the earthquake occurred offshore and at a depth of 47 km, according to the USGS (The European-Mediterranean Seismological Centre assigned it a depth of 40 km). Based on the USGS focal mechanism, this earthquake was thrust in nature. While compressional earthquakes are common in this region, given the proximity to the New Britain Trench, the strike of today’s earthquake makes it hard to reconcile.
In the region around today’s earthquake, much of the seismicity is dominated by the subduction of the Australian Plate. North of the New Britain Trench, the Pacific Plate has been broken up into numerous microplates, all of which are being pushed in various directions. In the USGS map below, relative plate motions are shown, illustrating the complex dynamics of the region. Because of these plate motions, strike-slip and extensional earthquakes are also common. Nonetheless, large subduction zone earthquakes, including a M=7.9 in December 2016 are the events which cause the most damage and fatalities.
Based on the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, today’s earthquake should not be considered surprising. This model uses global strain rates and seismicity since 1977 to forecast the likely earthquake magnitude in your lifetime anywhere on earth. From this model, which is in the figure below, one can see that a M=7.75+ earthquake is likely in your lifetime in this area. Such a large magnitude is likely because the area is undergoing rapid deformation due to plate motions of upwards of 100 mm/yr. Should there be any large aftershocks (so far there is only one M=4.8 in our catalog) we will update this post.
European-Mediterranean Seismological Centre