M7.5 - Craig, Alaska

Tectonic Summary

The January 5, 2013 M 7.5 earthquake off the west coast of southeastern Alaska occurred as a result of shallow strike-slip faulting on or near the plate boundary between the Pacific and North America plates.  At the location of this earthquake, the Pacific plate is moving north-northwestward with respect to the North America plate at a velocity of appoximately 51 mm/yr.

This earthquake is likely associated with relative motion across the Queen Charlotte fault system offshore of Alaska and British Columbia, Canada, which forms the major expression of the Pacific:North America plate boundary in this region. The surrounding area of the plate boundary has hosted 8 earthquakes of magnitude 6 or greater over the past 40 years. In 1949, a M 8.1 strike-slip earthquake nucleated in the Pacific:North America plate boundary region approximately 200 km to the southeast of the January 5 event, and the causative fault ruptured close to, or into, the January 5 source region. In October of 2012, a M 7.8 earthquake occurred in the plate-boundary region approximately 330 km to the south east of the January 5 earthquake, and was associated with oblique-thrust faulting. The January 5, 2013 earthquake is related to that Haida Gwaii earthquake three months previously, and is an expression of deformation along the same plate boundary system.

The January 5 event broke a fault approximately 50 km in length, and slipped 7-8 m. Aftershocks of the earthquake can be seen here.