Magnitude 5.8 - 3 miles SE of Kasatochi Island

August 7, 2008 10:30:00 AKDT (August 7, 2008 18:30:00 UTC)
52.1373°N 175.4824°W Depth 4.1 miles (6 km)

10 miles (16 km) NW of Atka Pass
16 miles (25 km) W of Koniuji Island
23 miles (37 km) W of Mt. Sergief
28 miles (45 km) E of Great Sitkin Island
48 miles (77 km) E of Mt. Adagdak
53 miles (85 km) E of Adak
54 miles (87 km) W of Atka
55 miles (89 km) E of Mt. Moffett
73 miles (118 km) E of Kanaga Volcano
85 miles (137 km) E of Bobrof Island
114 miles (184 km) E of Tanaga Volcano

Magnitude type: M_w²
Event type: N/A

Tectonic Setting of the Aleutian Islands

The world's largest earthquakes originate along convergent plate boundaries such as the Aleutian megathrust. Starting in 1938, a series of three great earthquakes ruptured the subduction zone along its entire length from the Alaska Peninsula to the western Aleutians with the exception of a small gap near the Shumagin Islands. The sequence began with a M8.2 earthquake southwest of Kodiak Island. A M8.6 in the Andreanof Islands followed in 1957, and the sequence concluded with the Rat Islands M8.7 in 1965. The Shumagin Gap still has not ruptured, but GPS observations suggest that little strain has built up in this region.

Another notable source of seismicity in the arc are the intermediate depth earthquakes within the subducting Pacific Plate, known as the Wadati-Benioff zone. The largest recorded earthquake of this kind was the 2014 M7.9 Little Sitkin event. Shallow earthquakes associated with volcano processes and crustal faults within the overriding North American plate occur regularly and may produce vigorous aftershock or swarm-like sequences.