Geometric Models of Faulting at Yucca Mountainby Stephen R. Young, Southwest Research Inst, San Antonio, United States,
Gerry L. Stirewalt, Southwest Research Inst, San Antonio, United States,
Alan P. Morris, Southwest Research Inst, San Antonio, United States,
Abstract: Yucca Mountain, Nevada, is currently being studied as a potential site for a geologic repository of high-level radioactive waste. Alternative conceptual tectonic models are expected to be used by the U.S. Department of Energy (DOE) to fulfill part of the requirement of 10 CFR Part 60 to describe and assess subsurface conditions, and to evaluate conditions that may be potentially favorable or adverse to effective waste isolation. Effective assessment of risk due to geologic hazards such as fault rupture, earthquake seismicity, and volcanic eruptions will involve the use of tectonic and structural geologic models of Yucca Mountain. Estimation of the effects of fault movement and associated distributed deformation on fracture patterns, and potential concomitant changes in bulk hydrogeologic properties, requires knowledge of fault geometry and displacement. Yucca Mountain is located in a tectonically active region, and has a recent geological history of extensional tectonic deformation. Geometric models of faults at Yucca Mountain, as described in this paper, suggest that individual fault segments may be curved at depth and flatten into a regional low-angle detachment fault surface at a depth of approximately 7 to 8 kms. Magnitude and recurrence of earthquake seismicity in the Great Basin region is strongly dependent on fault geometry. Discrimination between planar and listric fault styles is critical to assessment of earthquake seismic risk. The modeled fault system suggests that distributive displacement is probably characteristic of the Yucca Mountain fault system. The Yucca Mountain fault system may not have significant influence on deep-seated magma ascent. However, the listric fault system may exert significant shallow influence on location of eruptive events. Considerations of the likely seismic character of the modeled fault system indicate the need for acquisition of additional seismic reflection data from areas on and adjacent to Yucca Mountain.
Subject Headings: Geological faults | Radioactive wastes | Geometrics | Seismic tests | Structural models | Seismic effects | Earthquakes | Nevada | North America | United States
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