2007 M7.1 Andreanof Islands Earthquake

Mainshock and Aftershocks: 

A major earthquake, magnitude 7.1, occurred in the Andreanof Islands region of the Aleutian Islands on December 19, 2007 at 12:30 am AKST (9:30 UTC) (red star on the above map). The event was situated 116 kilometers (73 miles) ESE of Amchitka and 209 km (130 miles) WSW of Adak. The AEIC located over 250 aftershocks through the end of December (magnitudes 2.0 and greater, white circles). Of these, eleven had magnitudes 5.0 or greater. The largest aftershock (M6.2) occurred on December 20 at 10:24 pm AKST (December 21, 7:24 am UTC).

Felt Reports: 

The earthquake was felt strongly on Adak but did not cause damage. 

Tectonic Setting: 

The M7.1 earthquake occurred in the area separating the rupture zones of the 1965 M8.7 Rat Islands earthquake to the west and the 1957 M8.6 Andreanof Islands earthquake to the east (approximate extent of the rupture zones is shown in red). The most significant recent earthquakes in the area, M6.6 July 8, 2006 and M6.7 August 2, 2007, occurred to the east and west of the M7.1 event, respectively (yellow stars on the above map). The westernmost area of the 1957 fault zone reruptured repeatedly in the 1986 M8.0 and 1996 M7.9 earthquakes. The eastern portion of the 1965 fault zone was reruptured recently in the M7.7 earthquake on November 17, 2003.

All these events occurred along the megathrust boundary between the subducting Pacific and overriding North American plates. Within the past ten years, the region shown on the map had on average two magnitude 6 or greater events per year. The Aleutian megathrust, where the two plates are being forced directly into one another, is one of the world's most active seismic zones.