Expanding CyberShake Physics-Based Seismic Hazard Calculations to Central California

As part of its program of earthquake system science, the Southern California Earthquake Center (SCEC) has developed a simulation platform, CyberShake, to perform physics-based probabilistic seismic hazard analysis (PSHA) using 3D deterministic wave propagation simulations. CyberShake performs PSHA by first simulating a tensor-valued wavefield of Strain Green Tensors. CyberShake then takes an earthquake rupture forecast and extends it by varying the hypocenter location and slip distribution, resulting in about 500,000 rupture variations. Seismic reciprocity is used to calculate synthetic seismograms for each rupture variation at each computation site. These seismograms are processed to obtain intensity measures, such as spectral acceleration, which are then combined with probabilities from the earthquake rupture forecast to produce a hazard curve. Hazard curves are calculated at seismic frequencies up to 1 Hz for hundreds of sites in a region and the results interpolated to obtain a hazard map. In developing and verifying CyberShake, we have focused our modeling in the greater Los Angeles region. We are now expanding the hazard calculations into Central California. Using workflow tools running jobs across two large-scale open-science supercomputers, NCSA Blue Waters and OLCF Titan, we calculated 1-Hz PSHA results for over 400 locations in Central California. For each location, we produced hazard curves using both a 3D central California velocity model created via tomographic inversion, and a regionally averaged 1D model. These new results provide low-frequency exceedance probabilities for the rapidly expanding metropolitan areas of Santa Barbara, Bakersfield, and San Luis Obispo, and lend new insights into the effects of directivity-basin coupling associated with basins juxtaposed to major faults such as the San Andreas. Particularly interesting are the basin effects associated with the deep sediments of the southern San Joaquin Valley. We will compare hazard estimates from the 1D and 3D models, summarize the challenges of expanding CyberShake to a new geographic region, and describe our future CyberShake plans.