Audiomagnetotelluric characterization of range-front faults, Snake Range, Nevada

Abstract

Two controlled-source audio-magnetotelluric (CSAMT) profiles were collected on the eastern flank of the Snake Range in eastern Nevada across geologically complex terrain to investigate the suspected presence of faults along the range front. The location of the range-bounding faults is not easily determined on geologic grounds because of the presence of extensive young sedimentary cover and overall geologic complexity. Characterization of the presence, location, and structural style of the range-front faults is critical to assessment of connectivity of groundwater aquifers near the mountain front and in adjacent alluvial basins. A total of 48 CSAMT soundings were recorded along two lines that were chosen to maximize subsurface geologic information. Two generations of faults were interpreted based on the CSAMT data: an older, low-angle fault that is cut by a younger, more steeply dipping fault. Lack of deep boreholes in the region required that the subsurface interpretation rely on analogy from surface outcrops within and adjacent to the study area. The success of the CSAMT method as applied in this study hinged on near-ideal collection conditions, the relatively high contrast in electrical resistivity provided by the rock types involved, and well-developed geologic conceptual models of the region.