Operational earthquake forecasting during the 2019 Ridgecrest, California, earthquake sequence with the UCERF3-ETAS model

Kevin R. Milner, Edward H. Field, William H. Savran, Morgan T. Page, & Thomas H. Jordan

Submitted October 1, 2019, SCEC Contribution #9937

The first UCERF3-ETAS aftershock simulations were running on a high-performance computing cluster within 33 minutes of the July 4, 2019, M6.4 Searles Valley earthquake. UCERF3-ETAS (Field et al., 2017), an extension of the third Uniform California Earthquake Rupture Forecast, is the first comprehensive, fault-based, epidemic-type aftershock sequence model. It produces ensembles of synthetic aftershock sequences both on and off explicitly modeled UCERF3 faults to answer a key question repeatedly asked during the Ridgecrest sequence: What are the chances that the earthquake that just occurred will turn out to be the foreshock of an even bigger event?

As the sequence unfolded--including one such larger event, the July 5, 2019, M7.1 Ridgecrest earthquake almost 34 hours later--we updated the model with observed aftershocks, finite rupture estimates, sequence-specific parameters, and alternative UCERF3-ETAS variants. While configuring and running UCERF3-ETAS was not fully automated, considerable effort was focused in 2018 to improve model documentation and ease of use with a public GitHub repository, command line tools, and JSON configuration files. These efforts allowed us to respond quickly and efficiently configure new simulations as the sequence evolved. Here, we discuss lessons learned during the Ridgecrest sequence, including sensitivities of fault triggering probabilities to poorly constrained finite-rupture estimates and model assumptions, as well as implications for UCERF3-ETAS operationalization.

Citation
Milner, K. R., Field, E. H., Savran, W. H., Page, M. T., & Jordan, T. H. (2019). Operational earthquake forecasting during the 2019 Ridgecrest, California, earthquake sequence with the UCERF3-ETAS model. Seismological Research Letters, (submitted).