Magnitude 6.5 - 77 miles SE of Okmok Caldera

October 12, 2009 21:37:21 AKDT (October 13, 2009 05:37:21 UTC)
52.5917°N 166.9252°W Depth 8.2 miles (13 km)

This event has been reviewed by a seismologist

78 miles (126 km) SE of Mt. Recheshnoi
82 miles (132 km) SE of Mt. Vsevidof
85 miles (137 km) E of Nikolski
89 miles (144 km) S of Makushin Volcano
90 miles (145 km) S of Unalaska
91 miles (147 km) S of Dutch
104 miles (168 km) SE of Bogoslof Island
106 miles (171 km) S of Akutan Pass
117 miles (189 km) SW of Akutan
120 miles (194 km) E of Kagamil Island
123 miles (199 km) E of Uliaga Island

Magnitude type: M_w²
Event type: N/A

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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.