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Multi-Fault Rupture Plausibility Inferred from a Deterministic Earthquake Simulator

Session: Exploring Rupture Dynamics and Seismic Wave Propagation Along Complex Fault Systems [Poster]

Type: Poster

Date: 4/19/2021

Presentation Time: 03:45 PM Pacific

Description: 

When building an earthquake rupture forecast (ERF) for probabilistic seismic hazard analysis (PSHA), a key step involves the enumeration of all plausible significant earthquakes in a region (i.e., those likely to damage the built environment or result in casualties). The 3^rd Uniform California Earthquake Rupture Forecast (UCERF3) was the first comprehensive ERF to include multi-fault ruptures, consistent with many examples in nature. The set of ruptures included in UCERF3 was determined through binary filters which aimed to reduce the near-infinite fault section combinations to a tractable set of physically plausible ruptures. These plausibility criteria used hard cutoff values that were ad hoc or based on limited modeling, e.g., maximum jump distance (5 km) and maximum fault-to-fault azimuth change (60 degrees). A physical constraint was included that assessed the Coulomb compatibility of jumps between faults, though it was only applied to the portion of faults immediately before and after each jump.

We test the UCERF3 multi-fault rupture plausibility criteria against physically-consistent synthetic seismicity catalogs generated with the Rate-State Earthquake Simulator (RSQSim) on the UCERF3 fault system. Prior studies have shown agreement between PSHA results obtained from RSQSim and UCERF3; here we examine individual ruptures in detail. We find that RSQSim catalogs produce multi-fault ruptures at a similar rate to UCERF3, and most (>80% of M≥6.5 ruptures) pass all UCERF3 plausibility criteria. We identify a number of plausible fault jumps that occur in RSQSim catalogs but are not allowed under the UCERF3 rules, and propose modifications to the plausibility criteria for the next UCERF model to incorporate inferences from RSQSim. Specifically, we propose removal of the azimuth change criteria, which were most appropriate for jumps between faults with similar rakes, and improvements to the Coulomb criterion that assess the physical consistency of the entire rupture.

Presenting Author: Kevin Milner

Student Presenter: No

Authors