## A SCEC CyberShake Physics-Based Probabilistic Seismic Hazard Model for Northern California

Scott Callaghan, Philip J. Maechling, Christine A. Goulet, Kevin R. Milner, Mei-Hui Su, Robert W. Graves, Kim B. Olsen, Brad T. Aagaard, Kathryn E. Wooddell, Albert R. Kottke, Thomas H. Jordan, & John E. VidalePublished August 15, 2018, SCEC Contribution #8752, 2018 SCEC Annual Meeting Poster #295

The Southern California Earthquake Center (SCEC) has developed CyberShake, a simulation platform that performs physics-based probabilistic seismic hazard analysis (PSHA) using 3D deterministic wave propagation simulations. The CyberShake PSHA calculations begin by simulating time- and space-varying Strain Green Tensors. An earthquake rupture forecast (ERF) is then extended by varying hypocenters and slips on finite faults, generating hundreds of thousands of events per site of interest. Seismic reciprocity is used to calculate synthetic seismograms for each event at each site, which are processed to obtain intensity measures (IMs) such as RotD50 spectral acceleration. These IMs are combined with ERF probabilities to produce hazard curves. PSHA results from hundreds of locations across a region are interpolated to produce hazard maps.

In 2018 SCEC initiated CyberShake Study 18.8, whose goals is to produce a physics-based PSHA hazard model for a large Northern California region that includes the San Francisco Bay Area. PSHA calculations up to 1 Hz for 869 locations in Central and Northern California were performed on the NCSA Blue Waters and ORNL Titan supercomputers. To support simulation volumes that included most of California, we tiled three separate 3D community velocity models (SCEC-CCA-06, USGS Bay Area 08.3.0, and SCEC-CVM-S4.26.M01) into a composite statewide model and applied smoothing around interfaces to minimize unrealistic reflections and refractions. To improve representation of near-surface velocity structure in the tomographically-derived models, we inserted a geotechnical layer (GTL) in the top 500 meters by applying the Ely (2010) method, assuming Vs30 values from the Wills (2015) map.

This computational effort enabled the calculation of a continuous physics-based PSHA map for a large portion of California, obtained by combining results from multiple CyberShake studies. We will present our new hazard results for a variety of sites and discuss the impacts of including a GTL and background seismicity on the overall hazard estimates.

**Key Words**

probabilistic seismic hazard analysis, high performance computing, computational seismology

**Citation**

Callaghan, S., Maechling, P. J., Goulet, C. A., Milner, K. R., Su, M., Graves, R. W., Olsen, K. B., Aagaard, B. T., Wooddell, K. E., Kottke, A. R., Jordan, T. H., & Vidale, J. E. (2018, 08). A SCEC CyberShake Physics-Based Probabilistic Seismic Hazard Model for Northern California. Poster Presentation at 2018 SCEC Annual Meeting.

**Related Projects & Working Groups**

Community Modeling Environment (CME)