Fault slip and distributed deformation in the eastern California shear zone

Abstract:

Understanding fault slip rates in the eastern California shear zone (ECSZ) is complicated by possible near-fault or broadly distributed deformation. Furthermore, geodetically-constrained models that include elastic deformation due to locked faults require fault geometries to be prescribed, and incorrect fault parameterization may introduce off-fault deformation artifacts. We address the potential role of block model fault system geometry in describing ECSZ deformation with total variation regularization (TVR), an L₁ regularization method that allows for an algorithmic assessment of the best-fitting geometry based on geodetic observations from a combined Western United States velocity field. Beginning with 62 ECSZ blocks, we reduce the number of active faults to identify a simpler block model geometry containing only 9 ECSZ blocks. We find that this model fits GPS observations with a regional mean residual velocity (MRV) of 1.5 mm/yr with deformation due to block rotations and elastic strain accumulation alone. This approach does not resolve discrepancies between geologically and geodetically estimated slip rates in the eastern California shear zone, reproducing only 5 of 11 geologic slip rates within their reported uncertainties. The largest remaining slip rate discrepancies occur on the Calico and Garlock faults. Furthermore, the presence of additional deformation processes, as quantified by the internal deformation likelihood, cannot be rejected in the southeastern Mojave, adjacent to the 1992 Landers and 1999 Hector Mine earthquake rupture zones, where postseismic deformation is ongoing.