Earthquake Magnitude Conversion and Sensitivity Catalogs for the Central and Eastern United States

Earthquake catalogs are essential data inputs for seismic hazard modeling. Because earthquake magnitudes are reported in a variety of types (e.g., local magnitudes, moment magnitudes), magnitude conversion relationships must be used to convert the different magnitude types present in a catalog to a uniform magnitude type to avoid biases in the hazard computation. However, these conversion relationships are often uncertain and have been shown to sometimes perform poorly. In a corresponding journal publication, we investigate the sensitivity of the gridded seismicity component of the U.S. Geological Survey National Seismic Hazard Model (NSHM) to the catalog conversion equations in the eastern United States. In the 2023 NSHM, magnitudes of various types were converted to moment magnitudes using equations developed by the Central and Eastern United States Seismic Source Characterization for Nuclear Facilities (CEUS-SSCn; U.S. Department of Energy and others, 2012), based on least squares regressions made using data from a catalog containing events up through 2008. We recompute these equations using events in the Advanced National Seismic System Comprehensive Earthquake Catalog (U.S. Geological Survey Earthquake Hazards Program, 2017) with multiple magnitudes from 2000 through 2023 using orthogonal regression methods, which account for uncertainties in both dependent and independent regression variables (observed moment magnitude and alternative magnitude type, respectively). In some cases, we find large differences between the CEUS-SSCn conversion and the newly computed ones, especially at smaller magnitudes. We compare the spatial distribution of annual rates using three different models: 1) the 2023 NSHM conversions, 2) our updated conversions, and 3) no conversions. We find that the choice of conversions leads to substantial differences in the rate forecasts, which can greatly impact the seismic hazard model, particularly in regions with low seismicity rates like the eastern U.S. where the hazard is dominated by gridded seismicity rather than a fault model.

This data release includes seismicity catalogs used by Llenos and others (2025) to (1) compute new magnitude conversion equations and (2) perform a gridded seismicity sensitivity analysis.

References

Llenos, A.L., Shelly, D.R., and Shumway, A.M., 2025, Magnitude conversion relations create substantial differences in seismic hazard models: Seismological Research Letters, https://doi.org/10.1785/0220250231.

U.S. Geological Survey, Earthquake Hazards Program, 2017, Advanced National Seismic System Comprehensive Catalog of Earthquake Events and Products: U.S. Geological Survey data release, https://doi.org/10.5066/F7MS3QZH.

U.S. Department of Energy, Electric Power Research Institute, and U.S. Nuclear Regulatory Commission, 2012, Central and Eastern United States Seismic Source Characterization for Nuclear Facilities: NUREG-2115, 6 volumes, 3798 p.