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We suggest that faults in high slip tendency orientations tend to develop larger displacements than other faults. Consequently, faults that accumulate larger displacements are more likely to be reliable indicators of the longer term stress field and should be weighted accordingly in paleostress estimation. Application of a stress inversion technique that uses slip tendency analyses and fault displacements to interpret populations of coherent normal faults within the Balcones Fault System of south-central Texas provides stress estimates that are consistent with established regional stress analyses. Although the method does not require measurement of slip directions, these data, where available, and sensitivity analyses of the angular mismatch between measured slip directions and those predicted by inverted stress states provide high confidence in the stress estimates generated using slip tendency analyses. Close inspection of the fault orientation and displacement data further indicates that subpopulations of faults with orientations different from the regional pattern have formed in response to stress perturbations generated by displacement gradients on an adjacent seismic scale fault. [ABSTRACT FROM AUTHOR]

Yucca Mountain, Nevada, is the sole candidate site for underground disposal of high-level radioactive waste in the United States. The mountain is composed of Tertiary (12.8–11.6 Ma) volcanic tuff, cut by west-dipping normal faults that divide the mountain into north-trending, east-dipping cuestas. Geologic characterization of Yucca Mountain by the U.S. Department of Energy (DOE) has focused on mapping lithostratigraphic units, faults (including single plane, small-displacement surfaces of discontinuity, and large-displacement fault zones), and fractures (quasi-planar zones that have experienced loss of cohesion, including joints, partially mineralized joints, veins, and small-displacement faults). Faults and fractures are important to repository design because they affect seismic hazard, rockfall, and fluid transmissivity in the surrounding rock mass. Geologic maps and detailed studies of rock pavements and tunnel walls reveal that faults and fractures within Yucca Mountain are not uniform in orientation or intensity. We investigate two aspects of distributed deformation arising from fault displacement patterns at Yucca Mountain. First, fault-parallel strains (elongation parallel to cutoff lines where stratigraphic horizons intersect fault planes) develop as a result of lateral fault displacement gradients. Using existing data, we analyze the likely state of strain in fault blocks at Yucca Mountain. Second, fault-strike-perpendicular strains can develop where two normal faults propagate past each other. A component of the total strain is distributed into the surrounding rock to produce synthetic layer dip or a network of smaller faults and fractures. We find that small-scale faulting and fracturing at Yucca Mountain is variable and is strongly controlled by larger scale fault system architecture. [Copyright &y& Elsevier]