The Predictive Skills of Elastic Coulomb Rate-and-State Aftershock Forecasts during the 2019 Ridgecrest, California, Earthquake Sequence

Simone Mancini, Margarita Segou, Maximilian J. Werner, & Tom Parsons

Published June 23, 2020, SCEC Contribution #10017

Operational earthquake forecasting protocols commonly use statistical models for their recognized ease of implementation and robustness in describing the short‐term spatiotemporal patterns of triggered seismicity. However, recent advances on physics‐based aftershock forecasting reveal comparable performance to the standard statistical counterparts with significantly improved predictive skills when fault and stress‐field heterogeneities are considered. Here, we perform a pseudoprospective forecasting experiment during the first month of the 2019 Ridgecrest (California) earthquake sequence. We develop seven Coulomb rate‐and‐state models that couple static stress‐change estimates with continuum mechanics expressed by the rate‐and‐state friction laws. Our model parameterization supports a gradually increasing complexity; we start from a preliminary model implementation with simplified slip distributions and spatially homogeneous receiver faults to reach an enhanced one featuring optimized fault constitutive parameters, finite‐fault slip models, secondary triggering effects, and spatially heterogenous planes informed by pre‐existing ruptures. The data‐rich environment of southern California allows us to test whether incorporating data collected in near‐real time during an unfolding earthquake sequence boosts our predictive power. We assess the absolute and relative performance of the forecasts by means of statistical tests used within the Collaboratory for the Study of Earthquake Predictability and compare their skills against a standard benchmark epidemic‐type aftershock sequence (ETAS) model for the short (24 hr after the two Ridgecrest mainshocks) and intermediate terms (one month). Stress‐based forecasts expect heightened rates along the whole near‐fault region and increased expected seismicity rates in central Garlock fault. Our comparative model evaluation not only supports that faulting heterogeneities coupled with secondary triggering effects are the most critical success components behind physics‐based forecasts, but also underlines the importance of model updates incorporating near‐real‐time available aftershock data reaching better performance than standard ETAS. We explore the physical basis behind our results by investigating the localized shut down of pre‐existing normal faults in the Ridgecrest near‐source area.

Mancini, S., Segou, M., Werner, M. J., & Parsons, T. (2020). The Predictive Skills of Elastic Coulomb Rate-and-State Aftershock Forecasts during the 2019 Ridgecrest, California, Earthquake Sequence. Bulletin of the Seismological Society of America, 110(4), 1736-1751. doi: 10.1785/0120200028.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP), CSEP, WGCEP