Fault Trace Mapping and Surface-Fault-Rupture Special Study Zone Delineation of the East and West Cache Fault Zones and Other Regional Faults, Utah

Document Type

Report

Publisher

Utah Geological Survey

Publication Date

2024

Journal Article Version

Version of Record

First Page

1

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Last Page

39

Abstract

The Cache Valley region in northern Utah and southern Idaho contains and is surrounded by several large, hazardous faults which pose significant earthquake risk. The 40-mile-long (65 km) East Cache fault zone (ECFZ) and the 35-mile-long (56 km) West Cache fault zone (WCFZ) bound the Cache Valley graben and both show evidence of large surface-faulting earthquakes in the late Quaternary. Other hazardous faults in the Cache Valley region include the intrabasin Dayton-Oxford fault, the Mantua area faults within the Wellsville Mountains, and the James Peak fault at the very southern end of the ECFZ. this region is a rapidly growing area of northern Utah, with development spreading along the margins of the valley and encroaching on these hazardous fault zones. Airborne light detection and ranging (lidar) elevation data was collected in the Cache Valley area in 2016, 2018, and 2020. High-resolution topographic data derived from these lidar datasets has allowed for a complete update of the mapping of surface traces of the ECFZ, WCFZ, and other regional faults. Previously, the surface location and extent of fault traces associated with these fault zones were not well understood in many areas, owing to limited areal photography coverage, heavy vegetation near range fronts, and the difficulty in recognizing moderate ( < 1 m) scarp heights in the field or on aerial photographs. In addition to lidar-derived elevation data, other datasets including previous geologic mapping, paleoseismic investigations, historical aerial photography, and field investigations were used to identify and map surface fault traces and infer fault locations. Special-study zones were delineated around fault traces to facilitate understanding of the surface-rupturing hazard and associated risk. The fault geometries, attributes, and special-study zones were published in the Utah Geologic Hazards Portal simultaneously with this Report of Investigation. Defining surface-fault-rupture special-study zones encourages the creation and implementation of municipal and county geologic-hazard ordinances dealing with hazardous faults. We identified potential paleoseismic investigation sites where fault scarps appear relatively pristine, are in geologically favorable settings, and where additional earthquake timing data would be beneficial to earthquake research of the ECFZ, WCFZ, and other regional faults. This report contains supplementary material describing the data and methods used to perform the mapping and in locating potential paleoseismic investigation sites in the study area. This work is critical to raise awareness of earthquake hazards in areas of Utah experiencing rapid growth.

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