HR: 1340h
AN: G53A-0875    [Abstracts]
TI: Elastic and viscoelastic strain loading models of the Wasatch fault, Utah, from GPS measurements and comparisons with geological observations
AU: * Chang, W
EM: wchang@earth.utah.edu
AF: Department of Geology and Geophysics, University of Utah, 135 South 1460 East, Salt Lake City, UT 84112-0111 United States
AU: Smith, R B
EM: rbsmith@earth.utah.edu
AF: Department of Geology and Geophysics, University of Utah, 135 South 1460 East, Salt Lake City, UT 84112-0111 United States
AU: Harris, R
EM: ron_harris@byu.edu
AF: Department of Geology, Brigham Young University, S-349 Eyring Science Center, Provo, UT 84602-4606 United States
AB: The development of geodetic methods to measure ground movements using high precision GPS offers a new tool to deduce contemporary crustal deformation and fault-loading rates. Geologic evidence such as paleoearthquakes, on the other hand, provide in-plane, near-vertical displacements of a normal fault that may be used to imply long-term horizontal surface displacement and compare with the geodetic observations. We measured contemporary crustal deformation of the 370 km-long Wasatch fault zone, Utah, using continuous and campaign GPS. The overall observations indicate a horizontal displacement rate of 1.6±0.4 mm/yr across a 65-km wide area spanning the Wasatch fault. Employing a simple-shear rupture model for a dip-slip normal fault, where the hanging-wall is deformed by simple shear with the inclination of the shear plane equal to the dip of the antithetic fault, we converted the horizontal displacement rate to in-plane near-vertical fault slip rate. Results based on our preferred dips for the Wasatch and its antithetic faults implied that the contemporary geodetic strain-loading rate (1.6±0.4 mm/yr in the horizontal direction) is consistent within the 95% confident-interval with the Holocene-average geological strain-release rate (1.7±0.5 mm/yr in vertical). Other possible fault-geometry models, however, suggest different results: lower dips for fault and antithetic shear planes result in lower strain-loading rate, thus lower earthquake occurrence rate, at present than in the Holocene period, but steeper dips imply the opposite. Based on these constraints, we suggest that the comparison between geologically and geodetically implied horizontal extension rates across a normal fault like the Wasatch should be done with the knowledge of fault rupturing models. This requires a working model of fault dip and how the hanging-wall beds were deformed (or sheared) during earthquakes to estimate surface horizontal extension from vertical fault displacement.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Geodesy [G]
MN: Fall Meeting 2005