Rotation of stress and blocks in the Lake Mead, Nevada, Fault System

Abstract

The Coulomb criterion, has been widely used to infer paleostresses from fault slip data, assuming that faults are optimally oriented relative to the tectonic stress direction. Consequently if the stress direction is fixed during deformation so must be the faults. Freund [1974] has shown however that faults, when arranged in sets, must generally rotate as they slip. Nur et al. [1986] showed that large rotations require the development of new faults more favorably oriented to the principal direction of stress. This leads to older faults sets offset by younger ones, both having the same sense of slip. Because stress rotates as well, paleostress analysis must include the possible effect of stress field rotation.The combined effects of stress field rotation and material rotation were found in the Lake Mead, Nevada Fault System (LMFS). Fault inversion results imply an apparent 60° clockwise (CW) rotation of the stress field since mid‐Miocene time. In contrast, structural data from the Great Basin suggest only a 30° CW stress field rotation. By incorporating paleomagnetic declination anomalies it is inferred that slip on faults caused a local 30° counterclockwise (CCW) rotation of blocks and faults in the Lake Mead area, so that the inferred 60° CW rotation of the stress field in the LMFS is actually only 30°.