Past seismicity as a natural constraint on initial stress heterogeneity in dynamic rupture models for ground motion prediction

Abstract:

An avenue to improve seismic hazard assessment in engineering applications, particularly at magnitudes and distances that lack empirical data, is numerical modeling of dynamic earthquake rupture and ground motion. The initial fault stress is one of the influential input parameters for such a physics-based approach, and many studies highlight its heterogeneous nature. Here, we develop and validate a new method to generate stochastic heterogeneous initial stresses as the superposition of residual stresses produced by past seismicity governed by the regional statistics: Gutenberg-Richter frequency-magnitude distribution and depth distribution. The model is further constrained by earthquake scaling laws and tuned to agree with ground motion prediction equations. We studied Mw 5-7 strike-slip earthquake models for California and scoped to assess the role of background seismicity on rupture dynamics and near-field ground motion. The resultant source-time functions follow an omega-squared decay at high frequencies, in agreement with observations. The high-frequency radiation emerges from the whole rupture, in contrast to models dominated by radiation from stopping phases. Our analyses demonstrate that past seismicity has a significant effect on the complexity of rupture propagation and on peak ground motion amplitude (preliminarily resolved up to 1 Hz). The next steps are to extend the studied frequency band to 5 Hz, and to better anticipate the final magnitude of simulated events based on fracture mechanics theory and scale-dependent fracture energy.