Geometric Analyses of Alternative Models of Faulting at Yucca Mountain, Nevada

by Stephen R. Young, Cent for Nuclear Waste, San Antonio, United States,
Alan P. Morris, Cent for Nuclear Waste, San Antonio, United States,
Gerry L. Stirewalt, Cent for Nuclear Waste, San Antonio, United States,

Abstract: Realistic cross section tectonic models must be retrodeformable to geologically reasonable pre-deformation states. Furthermore, it must be shown that geologic structures depicted on cross section tectonic models can have formed by kinematically viable deformation mechanisms. Simple shear (i.e., listric fault models) is consistent with extensional geologic structures and fault patterns described at Yucca Mountain, Nevada. Flexural slip models yield results similar to oblique simple shear mechanisms, although there is no strong geological evidence for flexural slip deformation. Slip-line deformation is shown to generate fault block geometries that are a close approximation to observed fault block structures. However, slip-line deformation implies a degree of general ductility for which there is no direct geological evidence. Simple and hybrid 'domino' (i.e., planar fault) models do not adequately explain observed variations of fault block dip or the development of 'rollover' folds adjacent to major bounding faults. Overall tectonic extension may be underestimated because of syn-tectonic deposition (growth faulting) of the Tertiary pyroclastic rocks that comprise Yucca Mountain. A strong diagnostic test of the applicability of the domino model may be provided by improved knowledge of Tertiary volcanic stratigraphy.

Subject Headings: Geological faults | Radioactive wastes | Geometrics | Deformation (mechanics) | Model analysis | Model tests | Structural models | Flexural strength | Nevada | North America | United States

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