SCEC Award Number 16224 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Fault Displacement Hazard Methodology For Southern California Water Infrastructure Using the Time-Independent UCERF3
Name Organization
Glenn Biasi University of Nevada, Reno
Other Participants none
SCEC Priorities 1a, 6b SCEC Groups WGCEP, Geology, EEII
Report Due Date 03/15/2017 Date Report Submitted 02/28/2017
Project Abstract
The December 2014 report, Resilience by Design, by the Los Angeles Mayoral Seismic Safety Task Force identified vulnerabilities to the water supply and delivery infrastructure as most susceptible to direct damage from earthquakes, and potentially most consequential if it fails badly. This project supports efforts by SCEC to improve distributed systems resilience by providing methodologies for using UCERF3 to estimate fault displacement probabilities for the major active faults in California. The method builds on a capability developed through previous SCEC projects to analyze UCERF3 at the fault model subsection level. Because of how ruptures are modeled in UCERF3, and especially segmentation of the fault model was dropped, traditional methods for displacement hazard cannot directly be applied. In our approach, given a fault crossing location, we extract all ruptures in UCERF3 that use the subsection crossed by infrastructure. The location of the site within the rupture is tracked, and used to adjust expected rupture displacements up or down relative to an average for the rupture length. Magnitude-dependent displacement variability is then applied. Probabilities of displacement are taken from UCERF3 rupture probabilities. In a cumulative probability format the conditional probability of displacement and the expected absolute annual rate of displacement are developed. The case of multiple crossings follows directly. We include an outline for implementation of the method in OpenSHA.
Intellectual Merit Estimating fault displacement hazard using UCERF3 requires new methods relative to previous rupture forecasts including UCERF2. This project develops a new pathway, showing how to UCERF3 in probabilistic fault displacement hazard analysis. We demonstrate that rupture variability around a nominal elliptical rupture shape is necessary, and further that the variability must be drawn from similar length empirical measurements in order to achieve greater realism. Results are suitable for performance-based engineering applications at infrastructure crossings of UCERF3 faults. Large displacements are produced by UCERF3, large enough that water utility engineers could be averse to adopting them; UCERF4 would do well to manage maximum displacements relative to fault length in scaling relations.
Broader Impacts Benefits to society will follow if greater earthquake resilience is achieved by adoption of the results of this study.
Exemplary Figure igure 8. Annual rate and return time of displacements at the west California Aqueduct crossing of the San Andreas fault for the set of UCERF3 ruptures passing the site. Red line includes length-matched variability, blue line uses analytic shape only, with no displacement variability. Figure by the author.