2013 M7.0 Andreanof Islands Earthquake

Mainshock and Aftershocks: 

A magnitude 7.0 earthquake occurred on Friday, August 30 at 8:25 am AKDT (16:25 UTC) in the Andreanof Islands region of Alaska (red star on the map). It was located 108 km (67 miles) SW of Atka and 115 km (72 miles) ESE of Adak. AEC located about 600 aftershocks (open circles) through September 4. Aftershocks as small as magnitude 1.5 are being detected. About 50 aftershocks had magnitudes of 4.0 or greater. The largest aftershock, magnitude 6.5, occurred on September 3 at 6:32 pm AKDT (September 4, 2:32 UTC).

Felt Reports: 

This earthquake was felt strongly in Adak and Atka. Maximum intensity of shaking, IV - light, was reported in Atka. Click here for DYFI map. Multiple aftershocks were also felt. No damage has been reported, however some residents reported items falling off the shelves.

Tectonic Setting: 

This is the first earthquake in this region to reach magnitude 7 since the magnitude 7.9 event in 1996. The earthquakes in the Adak area occur on the convergent boundary between the Pacific and North American crustal plates. This region, where the Pacific Plate is subducting under the North American plate, is one of the world's most active seismic zones. Over one hundred earthquakes of magnitude seven or larger have occurred along this sunduction boundary in the past hundred years. The 1957 Andreanof Islands magnitude 8.6 earthquake ruptured an 800 km-long portion of the plate boundary; in 1986 and 1996 portions of the western half of this 1957 zone failed again in earthquakes of magnitude 7.9. The M7.0 earthquake of August 30 re-ruptured a smaller patch of the 1986 fault.

Source Mechanism: 

The elastic-wave radiation pattern of the M7.0 event and its aftershocks is consistent with the earthquakes occurring as the result of underthrusting motion of the Pacific plate under the North American plate.

Tsunami: 

No significant tsunami was generated by this event.