The October 2009 sequence of earthquakes occurred on the convergent boundary between the subducting Pacific and overriding North American crustal plates. This region, where Pacific plate is being forced under the North American plate, is one of the world's most active seismic zones. In 1957, magnitude 8.6 Andreanof Islands earthquake ruptured a ~600 km-long portion of the plate boundary in the central Aleutian Islands. The current sequence of earthquakes is located near eastern end of the 1957 rupture zone.

Waveform modelling of the mainshocks and largest aftershocks indicated a thrust type of faulting, which is consistent with the slip on plate interface.