The 1964 great Alaska earthquake: present day and cumulative postseismic deformation in the western Kenai Peninsula

Global Positioning System (GPS), triangulation and leveling data are used to derive models for the present day (last ∼5 years) and the 30-year average postseismic deformation on the Kenai Peninsula, Alaska following the 1964 Alaska earthquake. The two datasets are inverted using a three-dimensional elastic dislocation model to estimate the magnitude and spatial distribution of slip on the North America–Pacific plate interface, allowing us to examine the time dependence of the processes controlling postseismic deformation. We determine that the 30-year average postseismic slip rate beneath the western Kenai Peninsula was about twice as large as the present day slip rate. The observations suggest a time-decaying process, but are not consistent with a single exponentially decaying relaxation process initiated immediately after the 1964 earthquake. We conclude that the postseismic deformation observed on the western Kenai Peninsula cannot be explained in terms of any single time-decaying process. Either multiple processes acting on different timescales or significant spatial propagation of the postseismic deformation, or both, must occur. In the latter case, postseismic deformation would not begin everywhere at the same time and the rate of spatial propagation would affect the timescale inferred for the postseismic processes.