2007 M6.4 Andreanof Islands Earthquake

Mainshock and Aftershocks: 

On August 15, 2007, at 10:22 pm UTC (12:22 pm ADT), a strong earthquake, magnitude 6.4, occurred in the Andreanof Islands region of the Aleutian Islands (red star on the above map). The event was situated 189 kilometers (118 miles) SSW of Adak and 282 km (176 miles) ESE of Amchitka. This earthquake is the second magnitude 6+ event to occur in the region this month. A magnitude 6.7 earthquake (white star on the map) occurred on August 2 and was located 190 km (119 miles) NW of the M6.4 earthquake of August 15.

The AEIC located about 370 aftershocks of the M6.4 event within the first week after the mainshock. Of these, three had magnitudes 4.0 or greater. The largest aftershock (M5.3) occurred about 8 hours after the mainshock.

Felt Reports: 

This earthquake was felt at Adak. No damage was reported.

Tectonic Setting: 

The Aleutian megathrust, where the Pacific tectonic plate is being forced underneath the North American plate, is one of the world's most active seismic zones. Within the past ten years, the region shown on the map had on average two magnitude 6 or greater events per year.

Source Mechanism: 

The August 15 earthquake occurred in the outer rise area of the Aleutian trench. The waveform radiation pattern indicates normal faulting which is typical for the outer rise events. This event originated inside the subducting Pacific plate and is result of the plate bending as it enters the mantle. It was located updip of the rupture zone of the 1957 M8.6 Andreanof Islands earthquake (approximate extent of the rupture zones is shown in red).