Three-dimensional elastic dislocation modeling of the postseismic response to the 1964 Alaska earthquake

[1] GPS velocity observations from the Kenai Peninsula and Kodiak Island, Alaska, display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying Pacific-North American plate interface. Velocities of sites on the eastern Kenai Peninsula and Kodiak Island are consistent with elastic strain accumulation at the plate interface, whereas velocities of sites on the western Kenai Peninsula and Cook Inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 Alaska earthquake. We can reproduce the observed velocities using a three-dimensional elastic dislocation model to estimate the variation in coupling between the Pacific and North American plates. Two different inversion schemes are examined to check the robustness of the results. We find that the GPS data can be satisfied by the presence of a locked area near southwest Prince William Sound, a locked area near southwest Kodiak Island, and an area of postseismic reverse slip beneath and north of the western Kenai Peninsula. The shallow plate interface trenchward of the western Kenai Peninsula does not appear to be locked. The locked areas correspond to the Prince William Sound and Kodiak Island asperities that ruptured in 1964, and the area of postseismic slip lies downdip of the 1964 rupture area. The correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another.