Stress Accumulation and Interseismic Deformation of the Death Valley Fault Zone

The Death Valley Fault Zone (DVFZ), located in southeastern California, is an active fault system with an evolved pull-apart basin that has been deforming over the last 15 Myr. Our objectives are to study the interseismic motion and long-term stress accumulation of the DVFZ in order to better understand the nature of present-day loading conditions of the fault zone. Using a 3-D semi-analytic viscoelastic deformation model, constrained by geodetic velocities, we aim to establish best-fitting model parameters for interseismic slip rate, apparent locking depth, elastic plate thickness and mantle viscosity. We allow the model to accommodate variable locking depths (8-14 km) and slip rates (2-5 mm/yr) and tune the model to fit a set of local EarthScope continuous and campaign geodetic velocities. Our best fitting preliminary model, consisting of 200 fault elements, provides a good fit to the data (0.63 mm/yr fault-perpendicular RMS misfit and 1.00 mm/yr fault-parallel RMS misfit) and reveals an appropriate sensitivity to fault geometry. In particular, we obtain rates of 0.3-0.4 mm/yr of subsidence and 1.0-1.2 mm/yr of extension in the Death Valley pull-apart basin. We compare these modeled rates to geologic estimates of 15 Myr of basin evolution, a 3 km basin depth (including sediment fill), and a 15 km basin width, which yield geologic deformation rates of 0.2-0.3 mm/yr of subsidence and 0.3-1 mm/yr of extension. We also compute shear and normal stresses along the major fault strands and use these to compute present-day Coulomb stress accumulation rates for the primary DVFZ segments. Using a coefficient of friction of 0.6, we obtain stress accumulation rates of 0.4-0.6 MPa per century, in agreement with long-term estimates of earthquake recurrence intervals on the order of 1000 years, assuming typical stress drops of 4 MPa or higher for major DVFZ earthquakes. We are developing a stress and deformation time series model that reconstructs opening of the pull-apart basin based on present-day observations and the geologic history of the DVFZ region.