Priority Faults for Improving Seismic Hazard Models in the Intermountain West Region

Description

Abstract This data release includes a list of high-priority hazardous faults and associated spatial data (regional polygons and buffered fault traces) for the Intermountain West (IMW) region of the United States. These are the top five faults or regions of concern per IMW state, based on the 2025 (version 1.0) meeting of the Basin and Range Province Earthquake Working Group. In general, the list includes important, understudied faults where additional research would help to improve regional earthquake rupture forecasts and hazard modeling, reduce earthquake risk, and expand our knowledge of earthquake processes in the IMW region. This information will be used to guide IMW-specific priorities for research included in the USGS Earthquake Hazards Program external research priorities. Disclaimer: This database has been approved for release by the U.S. Geological Survey (USGS). Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, the database is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Introduction In February 2025, the Basin and Range Province Earthquake Working Group (BRPEWG; Utah Geological Survey, 2025a) met in Salt Lake City, Utah to discuss priority faults and topics in the Intermountain West (IMW) region. BRPEWG members and state representatives joined the meeting from Arizona, Colorado, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, and Wyoming. Discussions followed previous meetings on fault and topical priorities convened by the U.S. Geological Survey (USGS) (Crone and others, 2009; Briggs and Hammond, 2011; Koehler and Anderson, 2019; Briggs and Gold, 2015). The overall goal was to present and rank the top five faults or regions of concern in each IMW state and update the priority fault list included in Briggs and Gold (2015). This information will be used to guide IMW-specific priorities for research included in the U.S. Geological Survey (USGS) Earthquake Hazards Program external research priorities. Criteria Used to Select Faults of Concern State representatives each presented a list of the top five faults or regions of concern in their states. Criteria for inclusion varied by state but mostly followed three themes: (1) High-risk faults, such as those crossing or proximal to urbanized regions or critical facilities. (2) Faults or regions lacking adequate characterization for seismic or displacement hazard analyses (for example, 3D fault geometry, paleoearthquake history, or slip rate). (3) Faults that can facilitate regional or topical earthquake research, such as characterizing faults in an unstudied region or advancing our understanding of earthquake rupture behavior. Faults of Concern in the IMW Region The following list of high-priority hazardous faults and regions was presented at the 2025 BRPEWG meeting. These are the top five faults or regions of concern considered most important to understanding earthquake hazards and reducing earthquake risk in each IMW state. Notably, this is a subjective and incomplete list; additional faults in the IMW may meet the criteria included above but not be listed below. Spatial data associated with this list include buffered fault traces and regional polygons; for individual fault traces, refer to USGS (2025). Arizona: Big Chino–Little Chino faults, Needles Graben faults, Toroweap fault, Hurricane fault, and Bellemont fault. Colorado: Gore Range frontal fault, Williams Fork Mountains fault, Sawatch fault (southern section), Poncha fault, and Uncompahgre Plateau region faults. Idaho: Lost River–Lemhi–Beaverhead faults, Sawtooth–Boulder Front faults, West Ola Valley–Jakes Creek–Big Flat faults, Long Valley faults, and Grand Valley–Rexburg–Heise fault. Montana: Bitterroot Valley and Missoula area faults, Butte area and Deer Lodge Valley faults, Helena Valley and Canyon Ferry Lake faults, Mission–Swan–South Fork Flathead faults, and Northwest Greater Yellowstone–Centennial Tectonic Belt faults. For more information, refer to Montana Bureau of Mines and Geology (2025). New Mexico: Alamogordo fault, Albuquerque basin region, border faults on the west side of Tularosa basin, Southern Sangre de Cristo fault, and Pajarito fault system. Nevada: Carson Range front faults, distributed faults in the North Valleys area of Reno, Frenchman Mountain fault, intra-basin faults in Las Vegas Valley, and northern Walker Lane faults. For additional information, refer to Nevada Bureau of Mines and Geology (2025). Oregon (IMW portion): Klamath–Sky Lakes fault system, Chemult–LaPine Graben fault system, Bend Area fault system, Grande Ronde Valley fault system, and Goose Lake Graben fault system. Wyoming: Rock Creek fault, Grand Valley fault, Southeast Yellowstone region faults, Jackson Hole region faults, and Stagner Creek fault. Utah: Wasatch fault zone, Cache Valley regional faults, Southern Utah regional faults, Tooele and Rush Valley regional faults, and Great Salt Lake and Utah Lake faults. For additional information, refer to Utah Geological Survey (2025b). Priority faults and regions were provided by BRPEWG State Representatives, including Jeri Ben Horin, Arizona Geological Survey; James McCalpin and Enrique Chon, Colorado Geological Survey; Zach Lifton, Idaho Geological Survey; Yann Gavillot and Mike Stickney, Montana Bureau of Mines and Geology; Dan Koning, New Mexico Bureau of Geology & Mineral Resources, New Mexico Institute of Mining & Technology; Richard Koehler, Nevada Bureau of Mines and Geology, University of Nevada, Reno; Lalo Guerrero, Oregon Department of Geology and Mineral Industries; James Mauch, Wyoming State Geological Survey; and Adam Hiscock and Rachel Adam, Utah Geological Survey. Explanation of Data Spatial data for IMW faults and regions of concern are included with this data release. Faults (for example, the Wasatch fault zone), grouped faults (for example, the Sawtooth–Boulder Front faults), and regions (for example, faults within the Uncompahgre Plateau region) are represented as polygons and organized into a single geographic information systems (GIS) file in both shapefile and Google Earth keyhole markup language (kml) formats. For individual or grouped faults, a polygon forming a 2.5-km-wide buffer (5 km total width) around the Qfaults trace is provided. Polygons for regional areas are also included and intended to represent areas of interest and/or distributed faulting. Justification for priority faults and regions is included in a plain text, comma separated value (csv) file. Fault and region polygons have the following fields: Name – Name of the IMW fault, grouped faults, or region. For example, Sawatch fault (individual fault), San Andres fault system (grouped faults), and Uncompahgre Plateau region faults (region). Fault naming convention follows the USGS Quaternary fault and fold database of the United States (Qfaults; USGS, 2025); regional names provided by BRPEWG state representatives. Type – Type of polygon. Fault – individual fault; grouped fault – one or more faults grouped; region – area of distributed faulting or general area of concern. Faults – Faults included in a regional polygon or set of grouped faults. For example, the Cache Valley region faults include the East Cache and West Cache faults; the San Andres fault system includes the San Andres Mountains and Organ Mountain faults. For individual faults, this field is NULL. State – State within which the majority of the fault, grouped faults, or region is located. Source – Source of spatial data. “Buffered USGS Qfaults traces” indicates USGS (2025) fault traces with a 2.5-km-wide buffer added. Other sources of data, including regional polygons, are provided. NSHM – Whether the fault or faults are included as earthquake sources in the 2023 update of the USGS National Seismic Hazard Model (Hatem and others, 2021). Partial – some but not all faults within a region or fault grouping are included in the model. Notes – Short statement provided by BRPEWG state representatives and only included in the csv file. This field includes justification for the priority fault designation, information on data gaps or remaining questions, and/or how additional research would help characterize hazard and reduce risk in the IMW region. References Crone, A.J., Haller, K.M., and Maharrey, J.Z., 2009, Evaluation of hazardous faults in the Intermountain West region—Summary and recommendations of a workshop: U.S. Geological Survey Open-File Report 2009-1140, 72 p. Briggs, R.W., and Hammond, W.C., 2011, Evaluation of geodetic and geologic datasets in the northern Walker Lane—summary and recommendations of the workshop, U.S. Department of the Interior: U.S. Geological Survey Open-File Report 2011-1282. Briggs, R., and Gold, R., 2015, U.S. Geological Survey workshop summary: Evaluation of hazardous faults in the Intermountain West region—2015 update, in Lund, W.R., editor, Proceedings volume, Basin and Range Province Seismic Hazards Summit III: Utah Geological Survey Miscellaneous Publication 15-5, variously paginated. Hatem, A.E., Collett, C.M., Briggs, R.W., Gold, R.D., Angster, S.J., Powers, P.M., Field, E.H., Anderson, M., Ben-Horin, J.Y., Dawson, T., and others, 2021, Earthquake geology inputs for the U.S. National Seismic Hazard Model (NSHM) 2023 (western U.S.) (ver. 3.0, December 2023): U.S. Geological Survey data release, https://doi.org/10.5066/P9AWINWZ. Koehler, R.D., and Anderson, J.G., 2019, 2018 Working Group on Nevada Seismic Hazards – Summary and recommendations of the workshop, Nevada Bureau of Mines and Geology Open-File Report 19-2, 44 p. Nevada Bureau of Mines and Geology, 2025, Earthquake research priorities for Nevada, EHP FY22, available at http://www.nbmg.unr.edu/_docs/Earthquakes/NBMG_priorities_NEHRP.pdf, accessed February 2025. Montana Bureau of Mines and Geology, 2025, GIS Data Hub: Geohazards, available at https://gis-data-hub-mbmg.hub.arcgis.com/pages/geohazards, accessed February 2025. Utah Geological Survey, 2025a, Basin and Range Province Earthquake Working Group, available at: https://geology.utah.gov/hazards/info/workshops/working-groups/basin-and-range-earthquakes/, accessed February 2025. Utah Geological Survey, 2025b, Utah Quaternary fault parameters, available at: https://geology.utah.gov/hazards/info/workshops/working-groups/q-faults/, accessed February 2025. U.S. Geological Survey, 2025, Quaternary fault and fold database of the United States, available at https://www.usgs.gov/programs/earthquake-hazards/faults, accessed February 2025.

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