HR: 1340h
AN: G13A-0909    [Abstracts]
TI: Three years of post seismic deformation in Central Andaman Islands
AU: * Paul, J
AF: Center for Earthquake Information, 3876 Central Ave, Memphis, TN 38152, United States
AU: Lowry, A
AF: Dept of Geology, Utah State University, Utah, UT 84322, United States
AU: Bilham, R
AF: Dept of Geological Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Sen, S
AF: Society of Andaman Nicobar Ecology, Middle Point, Port Blair, AN 763001, India
AB: As of early 2007, GPS sites in the Andaman Islands had risen 15 to 26 cm following the 2004 Great Sumatra- Andaman earthquake. Near Port Blair, the uplift reversed co-seismic subsidence by 30%. The uplift, observed at eight GPS sites, has shifted the co-seismic neutral axis separating subsidence from uplift gradually eastward. Horizontal motions were 30 to 45 cm in a similar WSW to SW direction observed coseismically. The decay timescale for these motions is relatively short (~0.8 year), and the GPS time series at the westernmost sites now evidence a reversal in the north component of motion. Simulations of the GPS postseismic displacements as viscoelastic relaxation of coseismic stress change and as slip on the plate interface indicate that slip down- dip of the seismic rupture dominates near-field deformation during the first two years. The displacement gradients and decay timescale of GPS measurements cannot be duplicated with any reasonable parameterization of a viscoelastic model, and the relationship of horizontal- to vertical- displacements at the sites is opposite that predicted for poroelastic response. Postseismic slip beneath the Andaman Islands released moment equivalent to a magnitude M_w≥7.5 earthquake, and the distribution suggests deep slip in the stable frictional regime accelerated to catch up to the coseismic rupture. In this presentation we will update the GPS time series at nine sites in central Andaman to the present, assess possible implications of the fault slip patterns for properties of the Andaman subduction thrust, and discuss our plans to capture future deformation in which the viscoelastic signal should dominate.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
SC: Geodesy [G]
MN: 2007 Fall Meeting