2012 M5.8 Northern Cook Inlet Earthquake

Mainshock and Aftershocks: 

A magnitude 5.8 earthquake occurred on Monday, December 3, 2012 at 4:42 pm AKST (December 4, 1:42 UTC) in the Cook Inlet region of Alaska (red star on the map). It was located 29 km (18 miles) NE of Tyonek and 44 km (27 miles) W of Anchorage. AEIC located about 110 aftershocks (open circles) within the following week, with the magnitudes ranging between 1.0 and 3.2.

Felt Reports: 

This earthquake was felt strongly in southcentral Alaska, felt reports ranged from Kodiak in the south to Fairbanks in the north and Valdez in the east. Largest intensity of shaking, V - moderate, was reported in Anchorage, Willow and Cooper Landing. See Did You Feel It archive for distribution of felt reports.

Tectonic Setting: 

This is the largest event to occur in the region since the July 28, 2011 magnitude 5.3 earthquake located about 100 km to the northwest. According to its depth (60 km or 37 miles) this event occurred inside the subducting Pacific plate.

Source Mechanism: 

Waveform modeling shows reverse faulting, indicating down-dip extension of the Pacific slab as it being pulled into the mantle.