Review of previous geologic, paleoseismic, seismic, and geodetic studies at Yucca Mountain, Nevada--implications for understanding seismic hazards at the proposed high-level nuclear waste repository

Abstract

Curious about Yucca Mountain? This report provides a summary of the geologic setting and previous studies of the area, including discussion of existing data gaps that limit understanding of seismic hazards in the region. Yucca Mountain is a potential geological repository for high-level radioactive waste. The site is situated on federal land adjacent to the Nevada National Security Site (formerly Nevada Test Site) in Nye County, Nevada, about 130 km (80 miles) northwest of Las Vegas Valley. The site lies in an active tectonic setting within a segment of the Pacific–North American plate boundary. As such, active faults and recent volcanic activity characterize the area. Seismic activity could affect the suitability and safety of storage of nuclear waste. Thus, a thorough and accurate assessment of previous and potential future seismic activity in the region surrounding the proposed repository is critical. From the late 1970s to mid-1990s, deformation related to active faulting in the Yucca Mountain region was extensively studied by the U.S. Department of Energy, U.S. Geological Survey, both the Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory at the University of Nevada, Reno, and other institutions to assist in the evaluation and site characterization of the area for the proposed high-level radioactive waste repository. These studies documented multiple faults with recent activity, significant current seismicity, and ongoing crustal motion related to the Pacific–North American plate boundary and San Andreas fault system. Although these studies applied the most advanced techniques existing at the time, the ages of faulted deposits, essential for precise earthquake hazard estimates, were limited by the available experimental techniques. Significant advances in analysis and dating of faulted materials (i.e., paleoseismology), fault identification by remotely sensed methods, GPS geodetic data, and the scientific community’s general understanding of the regional tectonic setting over the last two decades suggest that the previous studies may not completely describe the seismic hazards in the region. In this report, the preexisting studies are evaluated in an effort to better understand the state of knowledge of the seismic hazards, as well as the adequacy of the approaches applied to characterize the hazard. Potential information and data gaps that may not have been included in the original evaluation are also addressed. The regional tectonic setting and paleoseismic, seismic, and geodetic studies are all reviewed. The paleoseismic studies record deformation over the past tens to hundreds of thousands of years; the seismic investigations reflect deformation over the past ~150 years; and the geodetic studies account for ongoing crustal deformation in the region (i.e., past couple decades). These datasets permit an overview of recent and geologically relevant deformation important for estimating future seismic hazards in the vicinity of Yucca Mountain.