CHARACTERIZATION OF MULTISCALE FAULT/FRACTURE PATTERNS IN THE VALLEY OF FIRE STATE PARK, NEVADA

Most faults and associated secondary fractures in the subsurface cannot be resolved by remote methods such as seismic techniques and their patterns are too complex to predict by other means. It is then required to develop a statistical methodology for characterizing faults and related fractures in order to represent these structures at the subsurface. We present such an attempt in an analog reservoir/aquifer in the Jurassic Aztec Sandstone of the Valley of Fire State Park, SE Nevada. The strike-slip fault network that is exposed in the park developed hierarchically by a repeated sheared joint mechanism (Myers and Aydin, 2004; Flodin and Aydin, 2004) during the Miocene Basin and Range deformation. This deformation mechanism produced faults and fractures on a centimeter to kilometer scale, the different scales of the structures being related to different stages of fault evolution. In this presentation, we describe a new methodology for the statistical characterization of these multiscale fault/fracture patterns, based on field measurements and the analysis of aerial photographs. First, we consider the relationships between parent faults and their splays. The maximum splay length appears to be correlated to parent fault length and parent fault slip by linear and power laws, respectively. Furthermore, kink angles between faults and splays are influenced by the fault configuration; average kink angles are small (~20°) in the case of isolated fault configurations and large (~50°) where faults interact. Combining the results from these two data sets provides insights into the linkage of neighboring faults by way of splaying. Second, we consider the characteristics of secondary fractures along several scanlines across well-exposed portions of two faults. The data collected are combined with those from previous studies (Myers, 1999; Flodin and Aydin, 2004) to constrain the statistical characteristics of the fault/fracture patterns at different scales. The results suggest that fault/fracture characteristics vary with the scale of the structures; at small scale, fracture lengths and fracture spacings exhibit lognormal distributions whereas at a larger scale, fault lengths and fault spacings exhibit lognormal and/or power distributions.