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Physically-based Non-ergodic Event Terms in the 2023 U.S. National Seismic Hazard Research and Development Model

Description: 

We create new physics-based spatially varying (non-ergodic) event terms for the research and development model of the U.S. Geological Survey’s 2023 National Seismic Hazard Model (NSHM) for the conterminous U.S. The 2023 NSHM is developed by synthesizing the latest science on potential earthquake ruptures and ground motions and using these to make models that are incorporated in public policy documents such as building design codes, risk assessments, insurance rates, and other official applications. For the next several years we will be proposing updated research and development model components. In this application of the research and development model, we explore alternative physical parameters that can reduce event variability and uncertainties across hundreds of thousands of sites in the hazard maps. We compile spatial data on potential physical parameters: crustal temperature, Bouguer gravity, shear wave velocity, stress drops, relative stress, strain rate, fault density, fault misalignment, smoothed seismicity rates, geologic-physiographic provinces, topography, slope, and quality factor to investigate optimal parameters for reducing the event-term variability. Current ground motion models (GMMs) depend on magnitude and the depth to the top of rupture parameter (Z_TOR) to estimate event terms. We do not have better size estimates, but we can compare the new potential physical parameters (described above) with Z_TOR to assess the potential improvements in the model. Our assessments show that several of these new physical-based spatially varying parameters are better than applying the Z_TOR parameter alone in reducing variability. These other spatially varying parameters may be applied in conjunction with Z_TOR to reduce regional variability and improve ground motion event terms. However, additions of several new parameters may lead to model overfitting making the model too complex. Therefore, it is important to assess the correlations in these new inputs to provide the most efficient and effective GMMs that allow for incorporation of significant new spatially varying physical data and models to be considered.

Session: Recent Advances in Modeling Near-source Ground Motions for Seismic Hazard Applications - II

Type: Oral

Date: 4/16/2025

Presentation Time: 10:45 AM (local time)

Presenting Author: Yuehua

Student Presenter: No

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