HR: 1340h
AN: G13A-0797    [Abstracts]
TI: Postseismic and Interseismic Deformation of Large Normal-Faulting Earthquakes in the Basin-Range
AU: * Chang, W
EM: wchang@mines.utah.edu
AF: Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AU: Smith, R B
EM: rbsmith@mines.utah.edu
AF: Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AB: We 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 observation of large normal-faulting earthquake in the Basin-Range. Time-dependent changes of baseline length across the fault were used to constrain the rheological structure of the crust and upper mantle beneath the Hebgen Lake fault zone. A Monte Carlo approach revealed less viscous, or weaker, lower crust and upper mantle southeast of the fault zone compared with those implied by baseline changes northwest of the fault. The local tectonism can explain this lateral variation, of which high heat flow and a thin brittle layer has been observed at the nearby Yellowstone caldera, locating 30 km southeast of the Hebgen Lake fault. We also applied the postseismic deformations measured by leveling in the Yellowstone-Hebgen Lake region and five GPS sites near epicentral area of the Ms=7.3, Borah Peak, Idaho, earthquake to examine the Hebgen-Lake rheological model. This model, moreover, is similar to the lithospheric structures of the eastern-Basin-Range implied by the long-term deformation of the lacustrine shoreline caused by the Lake Bonneville rebound, and thus was used to estimate combined postseismic responses caused by the most recent paleoearthquakes (M$>$7.0) on the Wasatch and the East Great Salt Lake faults and large historic earthquakes (M$>$5.5) in the Wasatch Front area, Utah. Contemporary surface deformation of the Wasatch Front area measured by campaign and continuous GPS was used to model the interseismic fault-loading rate of the Wasatch fault, where paleoseismic data from trenching revealed long-term fault-slip rate of the fault. Combining these results provide important new insights on temporal variations of the seismic cycle and constraints on related earthquake hazards.
DE: 7205 Continental crust (1242)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1242 Seismic deformations (7205)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting