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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, B03407, doi:10.1029/2005JB003946, 2006

Tectonic stressing in California modeled from GPS observations

Tom Parsons

U.S. Geological Survey, Menlo Park, California, USA


Abstract

What happens in the crust as a result of geodetically observed secular motions? In this paper we find out by distorting a finite element model of California using GPS-derived displacements. A complex model was constructed using spatially varying crustal thickness, geothermal gradient, topography, and creeping faults. GPS velocity observations were interpolated and extrapolated across the model and boundary condition areas, and the model was loaded according to 5-year displacements. Results map highest differential stressing rates in a 200-km-wide band along the Pacific-North American plate boundary, coinciding with regions of greatest seismic energy release. Away from the plate boundary, GPS-derived crustal strain reduces modeled differential stress in some places, suggesting that some crustal motions are related to topographic collapse. Calculated stressing rates can be resolved onto fault planes: useful for addressing fault interactions and necessary for calculating earthquake advances or delays. As an example, I examine seismic quiescence on the Garlock fault despite a calculated minimum 0.1–0.4 MPa static stress increase from the 1857 M∼7.8 Fort Tejon earthquake. Results from finite element modeling show very low to negative secular Coulomb stress growth on the Garlock fault, suggesting that the stress state may have been too low for large earthquake triggering. Thus the Garlock fault may only be stressed by San Andreas fault slip, a loading pattern that could explain its erratic rupture history.

Received 18 July 2005; accepted 11 December 2005; published 21 March 2006.

Keywords: stressing rate; finite element model; GPS.

Index Terms: 1209 Geodesy and Gravity: Tectonic deformation (6924); 7230 Seismology: Seismicity and tectonics (1207, 1217, 1240, 1242); 8106 Tectonophysics: Continental margins: transform; 8164 Tectonophysics: Stresses: crust and lithosphere.

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Citation: Parsons, T. (2006), Tectonic stressing in California modeled from GPS observations, J. Geophys. Res., 111, B03407, doi:10.1029/2005JB003946.