HR: 17:15h
AN: G44A-06    [Abstracts]
TI: Mechanics of Afterslip Following the 2002 Denali and 2004 Parkfield Earthquakes
AU: * Johnson, K M
EM: kaj@geology.indiana.edu
AF: Indiana University, Department of Geological Sciences, 1001 E. 10th St. , Bloomington, IN 47405
AU: Burgmann, R
EM: burgmann@seismo.berkeley.edu
AF: UC Berkeley, Department of Earth and Planetary Science, 307 McCone Hall, Berkeley, CA 94720-4767
AB: We investigate the mechanics of afterslip following the 2002 Denali Fault, Alaska earthquake and the 2004 Parkfield earthquake using continuous GPS data. Afterslip is modeled on a fault in an elastic half-space or in an elastic lithosphere overlying a viscoelastic asthenosphere. Modeled afterslip is governed by rate- and state-dependent friction or power-law viscous flow in a shear zone. Postseismic deformation following the Parkfield earthquake is best explained with shallow afterslip adjacent to coseismic slip patches and localized within the upper 5 km of the crust. The rate-state frictional parameter A-B, which is an indicator of frictional stability, is estimated to be in the range 10^-4-10^-3 at 50 MPa normal stress, about an order of magnitude lower than experimental values for granite at conditions well above or below the transition from potentially unstable (negative A-B) to nominally stable (positive A-B) friction. The estimate of A-B values fall within a wide range of experimental values reported for Serpentinite, which outcrops along the San Andreas fault zone. The critical slip distance, d_c, which characterizes the distance over which strength breaks down during slip episodes, is in the range 0.01-0.1 m, consistent with seismic estimates and a fault gouge thickness of 1-10 m. Postseismic deformation following the Denali earthquake is best explained by a combination of two mechanisms: viscous flow in the lower crust and upper mantle and afterslip above 30 km depth governed by a nonlinear relationship between stress and slip rate. We show that the observations are consistent with either rate-state friction or power-law creep on the fault. Unlike the deformation following the Parkfield earthquake, deformation following the Denali earthquake occurs largely at depths below coseismic rupture.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
SC: Geodesy [G]
MN: Fall Meeting 2005