2010 M6.5 and M6.3 Bering Sea Earthquakes

Mainshock and Aftershocks: 

The Alaska Earthquake Information Center recorded an unusual sequence of earthquakes located about 260 km (160 miles) west of St.Matthew Island that began on April 30, 2010. The mainshock, magnitude 6.5, occurred on April 30 at 23:11:44 UTC. It was preceded by a magnitude 4.3 foreshock, 1 minute earlier, and followed by a magnitude 6.3 aftershock, 5 minutes later. Due to the offshore location of these earthquakes, only larger events (magnitude 3.5 and greater) can be located. The nearest seismic stations are located about 350 miles away, at Gambell and St. Paul. As of May 5, 2010, only 10 aftershocks have been located by AEIC. All have large location uncertainties.

Tectonic Setting: 

Central region of the Bering Sea is virtually aseismic. In the north, a wide diffuse zone of seismicity extends from western Alaska across Bering Strait into eastern Russia. This zone is believed to mark northern boundary of the Bering microplate. Southern edge of the Bering Sea is marked by the Aleutian Arc, where seismicity is associated with the ongoing subduction processes. In 1991, a magnitude 6.6 earthquake occurred about 210 km (150 miles) to the southeast of the April 30, 2010 earthquakes. The 1991 and 2010 earthquakes indicate N-S extension and E-W compression of the crust.

The source area of the April 30, 2010 event might be structurally linked to the graben-like structure that underlies the headwall area of Zhemchug Canyon, which is the largest submarine canyon in the world (by volume). The structural grain of the headwall structures is NW-SE, parallel to the left-lateral nodal plane of the April 30 events. The right-lateral nodal plane is parallel to the crustal fabric of the hypothetical offshore continuation of the great family of NE-SW trending strike-slip faults of western Alaska (Kaltag, Kobuk, Denali, etc.). If these crustal structures continue offshore, they may be source of the April 30 earthquakes.

Source Mechanism: 

Both the mainshock and largest aftershock are strike-slip earthquakes. The faulting can be associated either with the right-lateral motion on SW-NE trending fault or the left-lateral motion on SE-NW trending fault.