The Alaska Earthquake Information Center located a strong earthquake that occurred on Sunday, November 20, 2005 at 3:53 AM local time (12:53 UTC) in the Unimak Island region of Alaska  (red star on the above map). The AEIC located nearly 100 aftershocks (open circles) through the end of the month (M>=1.9). The largest aftershock of magnitude M5.6 occurred on November 22 at 6:09 AM local time (15:09 UTC, white star).

The mainshock was felt strongly in Unalaska and False Pass (Internet Community Intensity Map). Several aftershocks were also felt.

The M 6.2 earthquake occurred on the convergent boundary between the subducting Pacific and overriding North American crustal plates. This region, where the two plates are being forced directly into one another, is one of the world's most active seismic zones. Over one hundred earthquakes of magnitude seven or larger have occurred along this boundary in the past hundred years. A separate map illustrates the recent earthquakes as circles, superimposed on stippled areas illustrating the rupture zones of major earthquakes. Generally speaking, the magnitude of an earthquake is roughly proportional to the area involved in its faulting. Each major rupture is labeled with the earthquake's year and a black dot indicating the epicenter for the associated earthquake. With the exception of the Unalaska and Shumagin seismic gaps, all portions of this plate boundary have ruptured within the past hundred years.

The 1957 Mw 8.6 Andreanof Islands earthquake ruptured a ~600 km-long portion of the plate boundary to the west of Unimak Island. The current sequence of earthquakes is located at the eastern end of the 1957 rupture zone.