M 7.2 - 252 km ENE of Kuril’sk, Russia

Tectonic Summary

The April 19, 2013, M 7.2 earthquake east-northeast of Kuril’sk, Russia, occurred as a result of oblique normal faulting at an intermediate depth, approximately 110 km beneath the Kuril Islands within the subducting lithosphere of the Pacific plate. Focal mechanism solutions indicate that rupture occurred on either a near-vertical, southwest-striking normal fault, or on a shallow, southeast-striking normal fault. At the location of this earthquake, the Pacific plate converges with the North America plate (and the smaller Okhotsk microplate) towards the west-northwest at a velocity of about 82 mm/yr, and subducts beneath the Kuril Islands at the Kuril-Kamchatka Trench about 160 km to the southeast of the April 19th event. The depth of this earthquake, and its oblique-faulting mechanism, indicate that it involved intraplate faulting within the subducting slab, rather than being an interplate thrust event on the shallower seismogenic zone between the two tectonic plates. Slip on a fault aligned with either nodal plane of the focal mechanism solution is consistent with this intraplate setting.

The Kuril-Kamchatka Arc has frequent moderate to large earthquakes and has hosted more than three-dozen M 6.5+ events within 250 km of the April 19th earthquake over the past 40 years. None are known to have caused shaking-related fatalities. The largest of these was the November 2006 M 8.3 interplate thrust event, approximately 200 km to the east of the April 19th earthquake. However, while the Pacific slab is seismically active in this region to depths of almost 700 km, just one of these nearby M 6.5+ events has occurred at depths greater than 70 km—a M 6.7 event in October 1994, 130 km to the southwest. 

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 Pacific plate beneath the Sea of Okhotsk to the northwest. Earthquakes have been reliably located to depths of about 600 km in this region.

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)