MAPPING AND CHARACTERIZING ACTIVE FAULTS IN UTAH

In the last decade, airborne high-resolution topographic data (lidar) has been collected along many fault zones and metropolitan areas of the state of Utah, providing a robust dataset for detailed mapping and characterization of active faults. Since 2014, the Utah Geological Survey (UGS) has partnered with the U.S. Geological Survey (USGS), the Idaho Geological Survey, and the Arizona Geological Survey to map Quaternary faults in Utah and across state lines. These high-resolution data, along with previous geologic and fault mapping, historical aerial photos, and field reconnaissance, have allowed the UGS to map active fault zones in high detail (1:24,000 scale or better) and identify previously unmapped faults. The UGS recently completed detailed mapping of all 10 segments of the 220-mile-long Wasatch fault zone, stretching from southern Idaho to central Utah. Areas currently being mapped by the UGS and neighboring states include the East and West Cache fault zones in Cache Valley, Utah; the East and West Bear Lake fault zones in southern Idaho and northern Utah; the Topliff and Oquirrh fault zones along the eastern margin of Tooele and Rush Valleys, Utah; and the Hurricane, Washington, and Sevier fault zones in southern Utah and northern Arizona. Surface-fault-rupture special study areas are delineated around each mapped fault trace to assist local governments and planning agencies, to facilitate understanding of the hazard and associated risk for future development, and to encourage the creation and implementation of geologic-hazard ordinances dealing with active faults. Additionally, we identified undisturbed fault scarps that are favorable for future paleoseismic trenching, which is especially crucial for faults where paleoseismic earthquake data are lacking. As the work is completed, new mapping is made publicly available through the UGS’s Utah Quaternary Fault and Fold Database, is added to the USGS Quaternary Fault and Fold Database of the United States, and will be used for future updates to the USGS National Seismic Hazard Map in 2023 and beyond. This work is critical to raise awareness of earthquake hazards in areas of Utah experiencing rapid growth.