Geologic Slip Rates and Interseismic Deformation in the Ventura Region, Southern California

The Ventura region lies in the Transverse Ranges of southern California and contains a complex network of non-planar reverse, oblique slip, and reactivated normal faults. Existing two-dimensional models of the region match much of the recent geodetic velocity field, but utilize highly simplified fault geometries. To determine if a model incorporating geologically-reasonable three-dimensional fault surfaces can match geodetic velocities in the region, we create a set of numerical models based on the Southern California Earthquake Center Community Fault Model and compare results to an updated GPS velocity field. Because significant non- tectonic ground motions occur in southern California, we use Principal Component Analysis to remove non- tectonic transient signals from a network of 15 permanent GPS stations in the Ventura region. Instead of prescribing slip rates to the modeled faults a priori, we use GPS velocities to determine a regional shortening rate. We apply this shortening rate to the model to drive slip along frictionally-weak fault surfaces. To simulate interseismic deformation, we subtract the portion of fault slip within the seismogenic crust and compare the model-predicted surface velocities to geodetic velocities. We find that the three-dimensional model agrees well with geologic slip rate estimates and matches much of the regional GPS velocities. Model- GPS residuals suggest that zones of localized contraction at the edges of the Ventura sedimentary basin are more pronounced in the GPS velocities than the model results, suggesting that a homogeneous crustal structure may be insufficient to match high rates of contraction observed at the margins of the Ventura sedimentary basin.