Extending the Spatiotemporal Scales of Physics-Based Seismic Hazard Analysis

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Earthquake simulations at the spatiotemporal scales required for probabilistic seismic hazard analysis (PSHA) present some of the toughest computational challenges in geoscience. PSHA is the scientific basis for many engineering and social applications: performance-based design, seismic retrofitting, resilience engineering, insurance-rate setting, disaster preparation and warning, emergency response, and public education. This project will extend deterministic earthquake simulations to seismic frequencies of 2 Hz and greater with the goal of reducing the epistemic uncertainties in physics-based PSHA. The research will address fundamental scientific problems that limit the scale range in current representations of source physics, anelasticity, and geologic heterogeneity. The research will improve the physical representations of earthquake processes and the deterministic codes for simulating earthquakes, which will benefit earthquake system science worldwide. The consequent decrease in mean exceedance probabilities, which could be up to an order of magnitude at high hazard levels, would have a broad impact on the prioritization and economic costs of risk-reduction strategies.Previous research on Blue Waters has verified the scalability and computational readiness of the simulation codes. These codes will be used to advance physics-based PSHA through a coordinated program of numerical experimentation and large-scale simulation targeted at three primary objectives: (1) validation of high-frequency simulations against seismic recordings of historical earthquakes; (2) computation of high-frequency CyberShake hazard models for the Los Angeles region to support the development of high-resolution urban seismic hazard maps by the U. S. Geological Survey and the Southern California Earthquake Center (SCEC), and (3) high-frequency simulation of a M7.8 earthquake on the San Andreas fault to revise the 2008 Great California ShakeOut scenario and improve the risk analysis developed in detail for that scenario. The plan to accomplish this research has five computational milestones: (a) dynamic rupture simulations up to 8 Hz that include fault roughness and near-fault plasticity; (b) simulations of historic earthquakes up to 4 Hz for model validation; (c) simulations of the 1994 Northridge Earthquake up to 8 Hz for verification and validation; (d) extension of the 2008 ShakeOut scenario to 4 Hz; and (e) calculation of a complete CyberShake hazard model for the Los Angeles region up to 2 Hz.