SCEC Award Number 19227 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Continued Development of OpenSHA/UCERF3 in Support of Operational Earthquake Forecasting, Hazard Assessment, and Loss Modeling
Investigator(s)
Name Organization
Christine Goulet University of Southern California Thomas Jordan University of Southern California Edward Field United States Geological Survey Kevin Milner University of Southern California
Other Participants
SCEC Priorities 4c, 4d, 5a SCEC Groups CS, EFP, EEII
Report Due Date 03/15/2020 Date Report Submitted 04/06/2020
Project Abstract
 The 2019 Ridgecrest earthquake sequence provided a great opportunity to test and improve upon the UCERF3-ETAS model. The first UCERF3-ETAS simulations were running 33 minutes after the M6.4, and then were updated 66 times over the coming days and months as new features were added and in response to subsequent events (e.g., the M7.1 and its aftershocks). UCERF3-ETAS results were disseminated to researchers through response.scec.org, and used in public messaging by the USGS (on the Ridgecrest event page and in statements summarized in a Los Angeles Times article on July 25, 2019). We learned a lot about model sensitivities to finite rupture surfaces, and necessary steps before full operationalization of the model, which are discussed in detail in Milner at al. (2020). We also developed tools to fetch earthquake data directly from the U.S. Geological Survey Comprehensive Catalog including earthquake locations and finite fault estimates. Our response to the Ridgecrest sequence was possible largely due to the rewrite of the UCERF3-ETAS codebase supported by the 2018 award.

Significant progress was also made with a nonergodic physics-based PSHA model combining the RSQSim full-cycle physics-based earthquake simulator with CyberShake. This is the first comprehensive PSHA study that employs deterministic source and ground motion simulation models. We first prototyped this calculation in 2018, and focused our efforts in 2019 on validating the variance structure of the simulated ground motions.
Intellectual Merit One of the three bullets in SCEC’s mission statement is to “Integrate information into a comprehensive, physics-based understanding of earthquake phenomena.” To that end, we continued our work on the first probabilistic seismic hazard study using exclusively three-dimensional, physics-base models (RSQSim and CyberShake) in this reporting period.
Broader Impacts The first UCERF3-ETAS Ridgecrest simulations were disseminated to the SCEC community(at response.scec.org) within an hour of the M6.4 and updated throughout the sequence. OpenSHA, and it’s implementation of the UCERF3 models, continues to be a valuable tool for the SCEC community. OpenSHA is used by engineers, researchers, and students. OpenSHA is also used in conjunction with CyberShake to generate seismic hazard maps and to generate data products for the UGMS project, including a public facing design response spectra tool for engineers (https://data2.scec.org/ugms-mcerGM-tool_v18.4/).
Exemplary Figure Figure 1
Percentile scenarios: Map view of Uniform California Earthquake Rupture Forecast, Version 3–epidemic‐type aftershock sequence (UCERF3‐ETAS) synthetic catalogs of aftershocks to the Ridgecrest sequence (preferred model). Shown are 30 days of simulated seismicity immediately following the M 7.1 event. UCERF3 faults in the map region are plotted with gray outlines, except for faults that participate in events in the synthetic catalogs, which are plotted in the same color as the event hypocenter. (a) A typical catalog, defined as the catalog that lies at the 50th percentile with respect to the total number of simulated aftershocks across all 100,000 simulations. That catalog has 2584 M≥2.5 events and multiple M≥5 events, but no supraseismogenic events on UCERF3 faults. (b) A less probable catalog (97.5th percentile, 7574 M≥2.5 events) in which the Garlock fault was triggered in an M≥7 supraseismogenic aftershock. (c) The most extreme catalog from the suite of 100,000 simulations with 39,550 M≥2.5 events in which an M≥7 Garlock aftershock triggered an M≥8 earthquake on the San Andreas fault. (d) The observed earthquakes with M≥2.5 within 30 days of the M 7.1, accessed from Comprehensive Catalog (ComCat) on 6 December 2019. The color version of this figure is available only in the electronic edition.
Credits: Kevin Milner (USC), from Milner et al. (2020)