2014 M6.3 Skwentna Earthquake

Mainshock and Aftershocks: 

A magnitude 6.3 earthquake occurred on Thursday, September 25 at 9:51 am AKDT (17:51 UTC) in southcentral Alaska (red star on the map). It occurred at a depth of 109 km (65 miles) and was located 32 km (20 miles) W of Skwentna, 95 km (59 miles) WNW of Willow and 129 km (81 miles) NW of Anchorage. The Alaska Earthquake Center reported about 10 aftershocks (open circles on the map). The largest aftershock was magnitude 2.3. It is common for deeper events to produce very few aftershocks.

Felt Reports: 

This earthquake was felt widely in Southcentral and Interior Alaska. Maximum shaking of intensity VI (strong) was reported in Indian and Skwentna. No major structural damage has been reported; however, many residents and businesses reported damaged ceiling tiles, cracks in walls, and items falling off shelves.

Tectonic Setting: 

This earthquake occurred in the downgoing portion of the subducting Pacific Plate. The Aleutian trench marks the boundary between the subducting Pacific and overriding North American plates in southern Alaska and the Aleutian Islands. While the largest earthquakes occur on the interface between these two plates (like the 1964 magnitude 9.2 earthquake), the downgoing portion of the Pacific Plate produces earthquakes down to 200 km (150 miles) in southern and central Alaska. The faulting type of this earthquake is consistent with down dip extension of the Pacific Plate as it is pulled into the mantle under its own weight. This is the largest intermediate-depth earthquake in this region since the May 1, 1991 M6.3 earthquake (orange star).

Source Mechanism: 

The elastic-wave radiation pattern of the M6.3 event indicates strike-slip faulting consistent with down dip extension of the Pacific Plate as it being pulled into the mantle under its own weight.