REPRESENTATIVE FAULT SLIP RATES FROM METHODS INTEGRATING FIELD-BASED OBSERVATIONS, QUATERNARY GEOCHRONOLOGY AND NUMERICAL MODELING (Invited Presentation)

We present developments toward integrating field-based observations, Quaternary geochronology and numerical modeling to determine representative fault slip rates along the California transform plate boundary. Seismic hazard assessments currently depend on fault slip rates, the cumulative offset over many earthquakes along individual faults, to determine the probability of earthquakes of a certain magnitude over a certain time period and the resulting ground motions. Geologic fault slip rates are determined by a combination of field and laboratory techniques. Here, we use these field-based slip rate data to constrain elastostatic models of slip along complex, three-dimensional networks of intersecting and discontinuous, non-planar faults in response to plate motions. These models produce uplift rates and lateral slip rates that vary with fault shape, connectivity to nearby faults, and interactions with fault neighbors. While geologic slip rates confirm this dependence of slip rate on fault system geometry, the models provide a controlled environment in which to study the influence of these factors on slip rate behavior and help determine representative rates for faults. Elastostatic modeling methods have been applied in southern California and we present development of a new model spanning 200 square kilometers of the plate boundary in northern California, where we are focusing on slip partitioning between the San Andreas, Hayward and Calaveras faults. Here, recent developments along the Calaveras fault reveal uplift rates as well as lateral slip rates, increasing the parameter space by which to constrain the models. In addition to the potential of these integrative methods to inform representative fault slip rates, they also have the potential to determine critical sites for future field investigations and to supplement the sparse geologic slip rate data currently available. The methods also reveal how slip rates change as a fault's shape and its connectivity and interactions with nearby faults evolve, providing new insights into plate boundary deformation over geologic timescales.