Fracture, faulting, and gouge development in Tuff: A case study at Hoover Dam, Clark County, Nevada and Mojave County, Arizon

The faulted cavity criterion, a slip direction indicator in the Miocene Tuff of Hoover Dam, is disproven. The orientations of the faulted cavities in the tuff do not indicate slip direction, but indicate a foliation intersection with fault and joint surfaces. Field observations from the Tuff of Hoover Dam, a welded ash flow tuff with porosity ranging from five to twenty-five percent, indicate that faults nucleate on preexisting fractures. A linear fault gouge thickness versus fault displacement relationship can be inferred in the Tuff of Hoover Dam. This result is in accordance with other work in brittle fault zones.