Updates to the Fault-System Inversion Approach for use in the 2023 U.S. National Seismic Hazard Model

Kevin R. Milner, & Edward H. Field

Published September 11, 2022, SCEC Contribution #12261, 2022 SCEC Annual Meeting Poster #202

A 50-state update to the U.S. National Seismic Hazard Model will be released in 2023 (NSHM23). NSHM23 will utilize an inversion-based methodology for active fault systems in the Western U.S., building upon the approach used in the 3rd Uniform California Earthquake Rupture Forecast (UCERF3). The fault-system inversion approach enables relaxation of fault segmentation assumptions, inclusion of multi-fault ruptures, and mediation between and better fitting of competing data constraints (e.g., slip rates, paleoseismic recurrence intervals, and regional seismicity).

We will describe a number of model improvements, including: a variable segmentation constraint to dial the propensity of multi-fault ruptures up and down; a decoupling from the gridded seismicity model; a simpler methodology for determining the regional target magnitude frequency distribution (MFD); a wider range of fault section MFD nucleation constraint options; better constraint weighting to more evenly fit all available data relative to their uncertainties; and several improvements to the simulated annealing algorithm that solves the inversion. In aggregate, these changes lead to a suite of models that better fit the available data constraints, encompass a broader range of uncertainties, and are more computationally efficient than UCERF3. We will then present preliminary NSHM23 fault system inversion solutions and compare them with prior models.

Key Words
NSHM23, ERF, OpenSHA, UCERF3

Citation
Milner, K. R., & Field, E. H. (2022, 09). Updates to the Fault-System Inversion Approach for use in the 2023 U.S. National Seismic Hazard Model. Poster Presentation at 2022 SCEC Annual Meeting.

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