USGS Updates Seismic Hazard Model
Dr. Gehrig Schultz
Director Business Development, Sustainable Services at EPI Group
2023 50-State Long-term National Seismic Hazard Model ACTIVE
The 2023 50-State Update of the U.S. National Seismic Hazard Model (NSHM) defines the potential for earthquake ground shaking for various probability levels across the conterminous United States, Alaska, and Hawaii and is applied in seismic provisions of building codes, insurance rate structures, risk assessments, and other public policy. The updated model represents an assessment of the best available science in earthquake hazards and is an update to the previous NSHMs for the conterminous U.S. (2018), Alaska (2007), and Hawaii (2001).
This 50-state update is a time-independent probabilistic seismic hazard model. New data and methods include earthquake catalogs (excluding induced earthquakes), alternative declustering methods, spatially smoothed seismicity, new geodetic- and geologic-based fault and deformation models, and earthquake rupture forecast models accounting for a more complete representation of potential earthquakes in Alaska, Hawaii, and the conterminous U.S.
Improved ground motion models (GMMs) consider new NGA-Subduction, modified NGA-East and NGA-West2 GMMs. Amplification models also consider available 3D simulations to supplement the empirical GMMs, and basin specific data in California’s San Francisco Bay, Central Valley, and Los Angeles regions Seattle Washington, Salt Lake City Utah, and near Portland Oregon. Amplification in the central and eastern U.S. Gulf and Atlantic Coastal Plains is also considered.
New stress drop, tomographic, and other geophysical models help refine the complex boundary between the tectonically stable and active regions used in assigning GMMs.
Resulting seismic hazard calculations yield hazard curves, maps, uniform hazard response spectra, and disaggregations which are developed for spectral accelerations at 21 oscillator periods, two peak parameters (PGV and PGA), and eight site classes that are now required by the 2020 NEHRP Recommended Seismic Provisions and applied in multiple other public policy products
Happy to be in the blue bit