The United States Geological Survey recorded a Magnitude 7.0 Earthquake at a depth of 33.5 km to the south of the Andreanof Islands in the southern Aleutians at 4.25 am local time (4.25 pm GMT) on Friday 30 August 2013. This is a large quake and could potentially have been very dangerous in a more settled area, though this was in a very remote location, and there are no reports of any damage or casualties, though the quake was felt on Atka Island.
The approximate location of the 30 August 2013 Andreanof Islands Earthquake. Google Maps.
Alaska lies on the North American Plate, with the Pacific Plate underlying the ocean to the south. The Aleutian Trench runs along much of the south coast of Alaska and the Aleutian Islands, with the Pacific Plate being subducted beneath this and passing under Alaska as it sinks into the Earth. This is not a smooth process, and the plates frequently stick together, then break apart as the pressure builds up, causing Earthquakes.
Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here.
See also Eruption on Mount Veniaminof, Further eruptions on Mount Pavlof, Volcanic activity on Mount Veniaminof, Eruption on Mount Pavlof and Eruption on Mount Cleveland.
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