HR: 0800h
AN: G21C-0680    [Abstracts]
TI: Distributed Plate Boundary Deformation Across the San Andreas Fault System, Central California
AU: * Dyson, M
EM: mark.e.h.dyson@gmail.com
AF: Carleton College, One North College St., Northfield, MN 55057, United States
AU: Titus, S J
EM: stitus@carleton.edu
AF: Carleton College, One North College St., Northfield, MN 55057, United States
AU: DeMets, C
EM: chuck@geology.wisc.edu
AF: University of Wisconsin - Madison, 1215 W. Dayton St., Madison, WI 53706, United States
AU: Tikoff, B
EM: basil@geology.wisc.edu
AF: University of Wisconsin - Madison, 1215 W. Dayton St., Madison, WI 53706, United States
AB: Plate boundaries are now recognized as broad zones of complex deformation as opposed to narrow zones with discrete offsets. When assessing how plate boundary deformation is accommodated, both spatially and temporally, it is therefore crucial to understand the relative contribution of the discrete and distributed components of deformation. The creeping segment of the San Andreas fault is an ideal location to study the distribution of plate boundary deformation for several reasons. First, the geometry of the fault system in central California is relatively simple. Plate motion is dominated by slip along the relatively linear strike-slip San Andreas fault, but also includes lesser slip along the adjacent and parallel Hosgri-San Gregorio and Rinconada faults, as well as within the borderlands between the three fault strands. Second, the aseismic character of the San Andreas fault in this region allows for the application of modern geodetic techniques to assess creep rates along the fault and across the region. Third, geologic structures within the borderlands are relatively well-preserved allowing comparison between modern and ancient rates and styles of deformation. Continuous GPS stations, alignment arrays surveys, and other geodetic methods demonstrate that approximately 5 mm/yr of distributed slip is accumulated (on top of the fault slip rate) across a 70-100 km wide region centered on the San Andreas fault. New campaign GPS data also suggest 2-5 mm/yr of deformation in the borderlands. These rates depend on the magnitude of the coseismic and postseismic corrections that must be made to our GPS time series to compensate for the 2003 San Simeon and 2004 Parkfield earthquakes, which rupture faults outside, but near the edges of our GPS network. The off-fault deformation pattern can be compared to the style of permanent deformation recorded in the geologic record. Fold and thrust belts in the borderlands are better developed in the Tertiary sedimentary rocks west of the fault than in their Mesozoic counterparts on the east side of the fault. This combination of geodetic and geologic methods is a powerful way to better understand distributed plate boundary deformation that neither method could provide independently.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8106 Continental margins: transform
DE: 8158 Plate motions: present and recent (3040)
SC: Geodesy [G]
MN: 2007 Fall Meeting