Slip rates on San Francisco Bay area faults from anelastic deformation of the continental lithosphere

Long-term slip rates on major faults in the San Francisco Bay area are pred icted by modeling the anelastic deformation of the continental lithosphere in response to regional relative plate motion. The model developed by Bird and Kong [1994] is used to simulate lithospheric deformation according to a Coulomb frictional rheology of the upper crust and a dislocation creep rhe ology at depth. The focus of this study is the long-term motion of faults i n a region extending from the creeping section of the San Andreas fault to the south up to the latitude of Cape Mendocino to the north. Boundary condi tions are specified by the relative motion between the Pacific plate and th e Sierra Nevada - Great Valley microplate [Argus and Gordon, 2000], Rheolog ic-frictional parameters are specified as independent variables, and predic tion errors are calculated with respect to geologic estimates of slip rates and maximum compressive stress directions. The model that best explains th e region-wide observations is one in which the coefficient of friction on a ll of the major faults is less than 0.15, with the coefficient of friction for the San Andreas fault being approximately 0.09, consistent with previou s inferences of San Andreas fault friction. Prediction error increases with lower fault friction on the San Andreas, indicating a lower bound of mu (S AF) > 0.08. Discrepancies with respect to previous slip rate estimates incl ude a higher than expected slip rate along the peninsula segment of the San Andreas fault and a slightly lower than expected slip rate along the San G regorio fault.