Fully physics-based PSHA: coupling RSQSim with deterministic ground motion simulations

Kevin R. Milner, Bruce E. Shaw, Thomas H. Jordan, Scott Callaghan, & Christine A. Goulet

Published August 15, 2018, SCEC Contribution #8683, 2018 SCEC Annual Meeting Poster #032

Probabilistic seismic hazard analysis (PSHA) is typically performed by combining an earthquake rupture forecast (ERF) with a set of empirical ground motion prediction equations (GMPEs). ERFs have typically relied on observed fault slip rates, scaling relationships, and regional magnitude-frequency distributions to estimate the rate of large earthquakes on pre-defined fault segments. GMPEs, which regress against recorded ground motions, often lack data at short site-rupture distances and for large, complex ruptures. The CyberShake platform (Graves et al., 2011) replaces GMPEs with deterministic three-dimensional ground motion simulations, characterizing the effects of basin response and other path effects which are parameterized or treated as aleatory variability in GMPEs. We replace traditional ERFs with a multi-cycle physics-based earthquake simulator, the Rate-State Earthquake Simulator (RSQSim), developed by Dieterich & Richards-Dinger (2010). RSQSim simulations on the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3) fault system produce seismicity catalogs that match long term rates on major faults and yield remarkable agreement with UCERF3 when carried through to GMPE-based PSHA calculations. Unlike traditional ERFs, RSQSim produces full slip-time histories for all simulated ruptures which can be used directly as input to deterministic wave propagation simulations. We couple the RSQSim model with CyberShake to create the first fully physics-based PSHA model. Resultant ground motions match GMPE estimates of mean and variability of shaking well over magnitudes and distances for which GMPEs are well constrained. Aggregated over many sources and sites, variability is similar to ergodic GMPE predictions. Variability is reduced for individual pairs of sources and sites, which sample a single path. This is expected in a non-ergodic model, and reduces exceedance probabilities for extreme ground motions at many sites. We will present these comparisons and preliminary fully physics-based RSQSim/CyberShake hazard curves.

Key Words
PSHA, RSQSim, Simulators, CyberShake, GMPEs, GMMs, Variability, BBP

Citation
Milner, K. R., Shaw, B. E., Jordan, T. H., Callaghan, S., & Goulet, C. A. (2018, 08). Fully physics-based PSHA: coupling RSQSim with deterministic ground motion simulations. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Collaboratory for Interseismic Simulation and Modeling (CISM)