HR: 1330h
AN: S22A-0412    [PDF]
TI: Rheology of an Extending Lithosphere From Postseismic Deformation of Large Basin-Range Normal-Faulting Earthquakes
AU: * Chang, W
EM: wchang@mines.utah.edu
AF: University of Utah, Dept. of Geology and Geophysics 135 S 1460 E, Salt Lake City, UT 84112 United States
AU: Smith, R B
EM: rbsmith@mines.utah.edu
AF: University of Utah, Dept. of Geology and Geophysics 135 S 1460 E, Salt Lake City, UT 84112 United States
AB: The effects of long-term viscoelastic loading and relaxation of the Earth's lithosphere and asthenosphere should be included to better model the complete earthquake cycle. An earthquake is assumed to generate coseismic stresses that cannot be sustained by the ductile lower crust and upper mantle, leading to postseismic relaxation of these materials. Stress and strain are in turn transferred to the upper crust, producing an observable transient geodetic signal. To investigate lithospheric rheology beneath the Wasatch fault zone where no large historic earthquake has been recorded, we first studied the change of surface deformation after the 1959 Ms = 7.5 Hebgen Lake, Montana, earthquake, measured by trilateration and GPS from 1973 to 2000 and the only postseismic observations of large normal-faulting earthquake in the Basin-Range. Time-dependent changes of baseline length across the fault were used to optimize rheological models beneath the Hebgen Lake fault zone. Our results are similar to the rheological structures of the eastern-Basin-Range lithosphere implied by the long-term deformation of the lacustrine shoreline caused by the Lake Bonneville rebound. Based on our optimized Hebgen-Lake rheological models, we then estimated combined postseismic responses caused by the most recent paleoearthquakes on the Wasatch and East Great Salt Lake faults and some Wasatch Front large (M $>$ 5.5) historic earthquakes. Half-space and layered rheological models were used. Comparing these results with the contemporary GPS-observed velocities reveal how postseismic signals contribute to the current surface deformation in the Wasatch Front area.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 7218 Lithosphere and upper mantle
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting