Revised Earthquake Geology Inputs for the Central and Eastern United States and Southeast Canada for the 2023 National Seismic Hazard Model

Abstract

It has been about a decade since updates to seismic and fault sources in the central and eastern United States (CEUS) were last assessed for the 2012 Central and Eastern United States Seismic Source Characterization for nuclear facilities (CEUS-SSCn) and 2014 U.S. Geological Survey National Seismic Hazard Model (NSHM) for the conterminous United States. In advance of the 2023 NSHM update, we created three related geospatial databases to summarize and characterize new fault source information for the CEUS. These include fault section, fault-zone polygon, and earthquake geology (fault slip rate, earthquake recurrence intervals) databases that document updates to fault parameters used in the prior seismic hazard models in this region. The 2012 CEUS-SSCn and 2014 NSHM fault models served as a foundation, as we revised and added fault sources where new published studies documented significant changes to our understanding of fault location, geometry, or activity. We added nine new fault sections that meet the criteria of (1) a length ≥7 km, (2) evidence of recurrent Quaternary tectonic activity, and (3) documentation that is publicly available in a peer-reviewed source. The prior CEUS models only included six fault sections (sources) and 10 fault-zone polygons (previously called repeating large-magnitude earthquake [RLME] polygons). The revised databases include 15 fault sections and 12 fault-zone polygons. Updates to the faults constitute a 150% increase in fault sections, and two additional fault-zone polygons, although some fault-zone polygons differ from RLME polygons used in the prior models. No faults were removed from the past models. Several seismic zones and suspected faults were evaluated but not included in this update due to a lack of information about fault location, geometry, or recurrent Quaternary activity. These updates to the fault sections, fault-zone polygons, and earthquake geology databases will inform fault geometry and activity rates of CEUS sources during the 2023 NSHM implementation.

The 2023 US 50-State National Seismic Hazard Model: Overview and implications

“…The fault model and geologic constraints for the CEUS were updated by Thompson Jobe et al (2022a, 2022b), including the addition of five new faults (Central Virginia, Saline River, Joiner Ridge, Crowley’s Ridge (South), and Crowley’s Ridge (West)). They also made fault-geometry adjustments to four previously utilized faults (Axial, Bootheel, New Madrid West, and Reelfoot), and added explicit surfaces to five faults previously represented with zones (Commerce, Eastern Margin (North), Eastern Margin (South), Crittenden County, and Meeman-Shelby, the latter of which was previously called River Picks).…”

“…CEUS fault-based sources, described by Shumway et al (2023), are based on the updated fault models and geologic constraints discussed above (Thompson Jobe et al, 2022a, 2022b). All are either represented with a fault zone (area source) or with an explicit fault surface.…”