TECTONIC SETTING OF YUCCA MOUNTAIN, NEVADA, IN EVALUATIONS OF FAULT, EARTHQUAKE, AND VOLCANIC HAZARDS

Since Yucca Mountain, Nevada, was first proposed as a potential repository for high-level nuclear waste more than 15 years ago, numerous tectonic models have been proposed to explain the present geologic setting of the region. These tectonic models can be grouped into three types: (1) volcano-genic models in which the present geology is largely manifest from late Miocene silicic volcanism or continental rifting; (2) crustal extension models in which the present geology is the product of Miocene and younger normal and low-angle detachment faulting; and (3) pull-apart models in which the present geology results from regional dextral shear. Many of these models were developed from limited data sets (e.g., 2D seismic) or to address a specific technical issue (e.g., groundwater flow in the saturated zone). To varying degrees, elements of many of these models were incorporated into probabilistic seismic and volcanic hazard assessments conducted on behalf of the U.S. Department of Energy (DOE) to provide necessary inputs for DOE assessment of the total system performance of the proposed Yucca Mountain repository. Over the past decade, tectonic studies have been performed at the CNWRA to provide the U.S. Nuclear Regulatory Commission (NRC) with sufficient scientific basis for independent technical evaluations of these DOE hazard assessments. This work at the CNWRA has emphasized the utility of integrating data and results from a wide variety of geologic and geophysical studies to develop an understanding of Yucca Mountain geology. Here, I present a revised summary of the tectonic setting of the Yucca Mountain region, one that is based on a consideration of existing geological and geophysical information combined with new structural, sedimentological, paleomagnetic, radiometric, and geochemical data. This interpretation encompasses early Tertiary deformation and basin formation; Miocene extensional deformation, volcanism, and exhumation of the Bare Mountain footwall; and Pliocene and Quaternary faulting and volcanism.

[This abstract is an independent product of the CNWRA and does not necessarily reflect the views or regulatory positions of the U.S. Nuclear Regulatory Commission]