Collaborative Research: Tests of Postseismic Deformation Models with Continued Absolute Gravity and GPS Measursements in Alaska, Phase I

University Of Alaska Fairbanks Campus, Fairbanks AK

Investigators

Abstract

EAR-0207957 Jeffrey Freymueller This project is measuring the absolute value of gravity, co-located with GPS measurements, in Alaska. Proposed explanations for the transient deformation after great earthquakes include viscoelastic response, aseismic creep and combinations of the two. Different models of postseismic viscoelastic relaxation predict observable gravity changes over 1000 km length scales, with a complex spatial pattern. To date, the viscosity profile is best determined by postglacial rebound studies. Gravity and GPS measurements offer the opportunity to obtain viscosity profile estimates for the Alaskan plate boundary. The area is especially interesting, as the viscosity of subduction zone materials may be very different from that beneath the centers of continental and oceanic plates. Aseismic creep is predicted to produce deformation of a more limited and markedly different spatial character than that of viscoelastic relaxation. Determining the contribution of aseismic creep in postseismic deformation is important in estimating recurrence intervals for great earthquakes. This project is establishing a baseline gravity network of fifteen stations in Alaska. The bulk of the network forms a transect perpendicular to the predicted contours of maximum gravity change in the far field. Additional points are located within the deformation near field. Gravity measurements are collocated with existing GPS stations. These initial measurements form the basis for testing different postseismic deformation models. Additional activities include collecting auxiliary data to correct the gravity data for signals such as water table variations. A portion of a 1964-1965 relative gravity survey is being repeated as well, in order to determine the total gravity change over the Kenai Peninsula since the earthquake. Data are distributed through traditional means and an Internet website.