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 approximately northwestward with respect to the North America plate at a velocity of 51 mm/yr.
This earthquake is likely associated with relative motion across the Queen Charlotte fault system offshore of 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 earthquake occurred close to the Pacific:North America plate boundary approximately 230 km to the south east of the January 5th earthquake, as a result of strike-slip faulting.
In October of 2012, a M 7.8 earthquake occurred approximately 330 km to the south east of the January 5th event, slightly inboard of the plate boundary, and was associated with oblique-thrust faulting. The latter earthquake was likely an expression of the oblique component of deformation along this plate boundary system.
The January 5th, 2013 earthquake is related to that Haida Gwai earthquake three months previously, and is an expression of deformation along the same plate boundary system.Meanwhile, CBC Radio is telling me they're picking up about a dozen aftershocks an hour--"more than a hundred so far." All are relatively small so far.