HR: 14:00h
AN: T13F-02    [Abstracts]
TI: Contemporary Deformation and Slip Rates in the Taiwan Fold and Thrust Belt
AU: * Johnson, K M
EM: kaj@seismo.berkeley.edu
AF: UC Berkeley, Department of Earth & Planetary Science 307 McCone Hall, Berkeley, CA 94720-476
AU: Segall, P
EM: segall@pangea.stanford.edu
AF: Stanford University, 397 Panama Mall , Stanford, CA 94305-2215
AB: The GPS velocity field during a seven year time period leading up to the 1999 Chi-Chi earthquake shows horizontal contraction across the Western Foothills fold and thrust belt. In central Taiwan, across the Chelungpu fault, which ruptured during the Chi-Chi earthquake, the velocities are roughly parallel to the plate convergence direction and perpendicular to the trend of the major frontal thrust faults. The shortening rate is nearly uniform across the Western Foothills. In southern Taiwan the horizontal velocities have a large fault-parallel component and the fault perpendicular shortening is not so nearly uniform across the Western Foothills. The shortening is concentrated near the frontal thrusts. To explain these observations, we develop and use kinematic and mechanical earthquake cycle models consisting of faulting in an elastic lithosphere overlying a viscoelastic asthenosphere. In the kinematic model, uniform slip is prescribed on the faults at a constant rate. In the mechanical model, the faults slip in response to shear stresses in the lithosphere. We show that the GPS velocity field in Central Taiwan can be explained with creep between earthquakes on a $\sim~10\deg$ dipping d \`{e}collement surface underlying the Western Foothills and the western Central Ranges and periodic earthquakes on the frontal thrusts which are locked interseismically to about 8-10 km depth. The combined slip rate on the frontal thrusts is 30-45 mm/yr. The localized shortening and fault-parallel motion in southern Taiwan cannot be explained with creep on a d \`{e}collement buried 8-10 km deep. Instead, the data are consistent with shallower oblique slip on the thrust faults. Thus the locking depths of the frontal thrust faults may be shallower in southern Taiwan than in northern Taiwan, a result that might have important implications for seismic hazard assessment.
DE: 8107 Continental neotectonics
DE: 8159 Rheology--crust and lithosphere
DE: 1242 Seismic deformations (7205)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting