The 2023 US 50-State National Seismic Hazard Model: Overview and implications
Authors: Petersen Mark D , Shumway Allison M , Powers Peter M , Field Edward H , Moschetti Morgan P , Jaiswal Kishor S , Milner Kevin R , Rezaeian Sanaz , Frankel Arthur D , Llenos Andrea L , Michael Andrew J , Altekruse Jason M , Ahdi Sean K , Withers Kyle B , Mueller Charles S , Zeng Yuehua , Chase Robert E , Salditch Leah M , Luco Nicolas , Rukstales Kenneth S , Herrick Julie A , Girot Demi L , Aagaard Brad T , Bender Adrian M , Blanpied Michael L , Briggs Richard W , Boyd Oliver S , Clayton Brandon S , DuRoss Christopher B , Evans Eileen L , Haeussler Peter J , Hatem Alexandra E , Haynie Kirstie L , Hearn Elizabeth H , Johnson Kaj M , Kortum Zachary A , Kwong N Simon , Makdisi Andrew J , Mason H Benjamin , McNamara Daniel E , McPhillips Devin F , Okubo Paul G , Page Morgan T , Pollitz Fred F , Rubinstein Justin L , Shaw Bruce E , Shen Zheng-Kang , Shiro Brian R , Smith James A , Stephenson William J , Thompson Eric M , Thompson Jobe Jessica A , Wirth Erin A , Witter Robert C 
Published: December 2023

The US National Seismic Hazard Model (NSHM) was updated in 2023 for all 50 states using new science on seismicity, fault ruptures, ground motions, and probabilistic techniques to produce a standard of practice for public policy and other engineering applications (defined for return periods greater than ∼475 or less than ∼10,000 years). Changes in 2023 time-independent seismic hazard (both increases and decreases compared to previous NSHMs) are substantial because the new model considers more data and updated earthquake rupture forecasts and ground-motion components. In developing the 2023 model, we tried to apply best available or applicable science based on advice of co-authors, more than 50 reviewers, and hundreds of hazard scientists and end-users, who attended public workshops and provided technical inputs. The hazard assessment incorporates new catalogs, declustering algorithms, gridded seismicity models, magnitude-scaling equations, fault-based structural and deformation models, multi-fault earthquake rupture forecast models, semi-empirical and simulation-based ground-motion models, and site amplification models conditioned on shear-wave velocities of the upper 30 m of soil and deeper sedimentary basin structures. Seismic hazard calculations yield hazard curves at hundreds of thousands of sites, ground-motion maps, uniform-hazard response spectra, and disaggregations developed for pseudo-spectral accelerations at 21 oscillator periods and two peak parameters, Modified Mercalli Intensity, and 8 site classes required by building codes and other public policy applications. Tests show the new model is consistent with past ShakeMap intensity observations. Sensitivity and uncertainty assessments ensure resulting ground motions are compatible with known hazard information and highlight the range and causes of variability in ground motions. We produce several impact products including building seismic design criteria, intensity maps, planning scenarios, and engineering risk assessments showing the potential physical and social impacts. These applications provide a basis for assessing, planning, and mitigating the effects of future earthquakes.