High-resolution integrated dynamic rupture modeling of the 2019 M6.4 Searles Valley and M7.1 Ridgecrest earthquakes

The M6.4 Searles Valley and M7.1 Ridgecrest earthquakes ruptured a complex conjugate fault system. Fault geometry, tectonic stress state, static and dynamic stress transfers play an important role in understanding the sequence and dynamics of both events. For instance, Coulomb stress analysis (Verdecchia and Carena, 2016) accounting for coseismic, interseismic and postseismic stress evolution over 1400 years yields positive stress redistribution loading their source region.

We here present high-resolution, 3D dynamic rupture simulations for both events. Our simulations incorporate the same complex fault system based on aftershock distribution and surface rupture constrained by space geodesy and field observations. All faults are exposed to a transtensional stress state with major rotations (Unruh et al., 2003). A preliminary regional principal stress inversion reveals poorly oriented compressional axes with small spatial variations along major faults. Assuming apparently weak faults due to combined effects of severe velocity-weakening friction, deep creep and elevated fluid pressure we determine optimal stress parameters that maximize the alignment between fault shear tractions and inferred slip by a systematic static approach (Ulrich et al., 2019). Off-fault deformation patterns can be readily compared to observations of fault zone width (Wollherr et al., 2019). Seismic waves propagate respecting high-resolution topography, the CVM-H velocity model, and viscoelastic attenuation. Rupture directivity and velocity of both events can be constrained with calibrated back-projection. Relocated seismicity helps constraining distributed versus localised faulting at depth and along-strike.

Modeling is enabled by the open-source software SeisSol (www.seissol.org) that couples seismic wave propagation of high-order accuracy in space and time (minimal dispersion errors) with frictional fault failure, off-fault inelasticity and visco-elastic attenuation. SeisSol exploits unstructured tetrahedral meshes to account for complex geometries. The achieved degree of realism and accuracy is enabled by recent computational optimisations targeting strong scalability on many-core CPUs and a ten-fold speedup owing to an efficient local time-stepping algorithm (Uphoff et al., SC'17).