M 7.6 - 70 km E of Kainantu, Papua New Guinea

Tectonic Summary

The September 10, 2022, M 7.6 Papua New Guinea earthquake occurred as a result of normal faulting at a depth of approximately 90 km beneath eastern Papua New Guinea, near the northern edge of the Australia plate. Focal mechanism solutions indicate that rupture occurred on an east-striking, steeply-dipping fault or a northwest-striking shallowly-dipping fault. At the location of the earthquake, the Australia plate moves towards the east-northeast relative to the Pacific plate at a velocity of about 100 mm/yr. Earthquakes in this geographical region are generally associated with the large-scale convergence of these two major plates and with the complex interactions of several associated microplates, most notably the South Bismarck plate, the Solomon Sea microplate, and the Woodlark plate.

Papua New Guinea experiences a high rate of seismic activity, with 78 events of M 6+ occurring within 250 km of the September 10, 2022, event in the previous 50 years. Of these, 31 occurred within 100 km. In 1989, a M 7.1 earthquake occurred approximately 25 km away from the September 10, 2022, event.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal faulting events of the size of the September 10, 2022, earthquake are typically about 75 km x 30 km in size (length x width).

Earthquakes like the September 10th 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 distances from their epicenters. “Deep-focus” earthquakes, those with focal depths greater than 300 km, also occur in beneath Papua New Guinea and the Bismarck Sea to the northeast.