Postseismic crustal uplift near Anchorage, Alaska

Abstract

Results of four leveling surveys carried out by the National Geodetic Survey between Anchorage and Whittier, Alaska, combined with an analysis of sea level measurements at Anchorage, indicate as much as 0.55 m of land uplift in the decade following the 1964 Prince William Sound earthquake. The pattern of uplift is parabolic in shape, convex upward, and reaches a maximum approximately halfway between Anchorage and Whittier, or about 300 km northwest of the Aleutian trench axis. The data suggest that the position of maximum uplift is migrating away from Anchorage, i.e., toward the Aleutian trench. The observed uplift occurs in a region which subsided as much as 1.9 m during the earthquake. The rate of uplift has decreased exponentially since the time of the 1964 earthquake. These movements appear to represent postseismic deformation associated with the 1964 Alaska earthquake. The observations are most easily explained by creep along the downdip extension of the fault which ruptured during the 1964 earthquake, although viscoelastic rebound and long‐term elastic strain accumulation mechanisms may play a part. There is no evidence supporting magma intrusion or dilatancy mechanisms. These results provide new constraints for models of tectonic processes at convergent plate margins.

Seismic and non-seismic influences on coastal change in Alaska--Fieldtrip guide and conference abstracts, 5th International Conference of IGCP 588

“…2.1.7, right panel). Evidence for this feature was noted as early as Brown et al (1977), but a definitive explanation has not been proposed. As Larsen et al (2003) noted, it is possible to explain this feature in terms of propagating slip pulses on the megathrust, although any such model would be very poorly constrained.…”

“…Observations post 1964 indicate ~0.3 m land uplift by 1975 (Brown et al, 1977) and 0.7 m by 1995-2000 (Freymueller et al, 2008) …”

“…Due to postseismic afterslip, some parts of the region experienced rapid postseismic uplift after the earthquake, totaling several decimeters or more. Along Turnagain Arm, uplift relative to the Anchorage tide gauge in the first year after 1964 exceeded 10 cm (Brown et al, 1977), and they estimated that ~50 cm of postseismic uplift occurred within the first decade after the earthquake. This section begins with these decadal scale data.…”

“…The horizontal displacements computed by Parkin (1969) settled any remaining doubts about the megathrust model for the earthquake. Postseismic uplift over the first decade after the earthquake was estimated by Brown et al (1977) based on repeated leveling surveys by the NGS along Turnagain Arm. Unfortunately, there was a nearly two decade hiatus in observations after the mid1970s, aside from the permanent tide gauge sites.…”

Geodetic Monitoring of Tectonic Deformation: Toward a Strategy

“…For the 1964 Alaskan earthquake, Brown et al ( 1977) found postseismic relaxation effects with a time scale on the order of 5 years. As shown in Figure 3.2, a large fraction of the vertical displacements occurred in the first year after the earthquake; it is not clear from the data how much of this early displacement is related to aftershocks, or whether there might be crustal relaxation processes on a time scale shorter than 5 years.…”