Deformation in the northern San Francisco Bay Area is dominated by a series of sub-parallel strike-slip faults. Existing GPS observations provide some constraint on the slip rates of these faults, however these have only limited resolution for resolving shallow fault behavior, such as brittle creep. We use Permanent Scatterer InSAR (PS-InSAR) data to dramatically increase the density of surface deformation observations. We find a discontinuity in observed surface velocities across the Rodgers Creek fault, around Santa Rosa and further north, consistent with shallow creep at rates of up to 6 mm/yr (Funning et al., ,2007). The creeping segments are located in areas of local transtension, suggesting that lowered normal stresses may play a role in the distribution of creep. The existence of creep could significantly reduce expected moment release in future earthquakes on the Rodgers Creek fault, and thus has implications for seismic hazard assessment.
Berkeley Seismological Laboratory
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