Concealed Quaternary strike-slip fault resolved with airborne lidar and seismic reflection: The Grizzly Valley fault system, northern Walker Lane, California

The Grizzly Valley fault system (GVFS) strikes northwestward across Sierra Valley, a low-relief basin situated within a network of active dextral slip faults in the northern Walker Lane, California. Quaternary motion along the Grizzly Valley fault system has not been previously documented. We used high-resolution (0.25m) airborne lidar data in combination with high-resolution, P wave, seismic reflection imaging to evaluate Quaternary deformation associated with the GVFS. We identified suspected tectonic lineaments using the lidar data and collected seismic reflection data along six profiles across the lineaments. The seismic reflection images reveal a deformed basal marker that we interpret to be the top of Tertiary volcanic rocks overlain by a 120-450m thick suite of subhorizontal reflectors that we interpret to be Plio-Pleistocene lacustrine deposits. Three profiles image features that we interpret to be the principal active trace of the GVFS, which is a steeply dipping fault zone that vertically offsets the volcanic rocks and the lacustrine basin fill. These data suggest that the GVFS may have been active in latest Quaternary time because (1) the lidar data show subtle surficial geomorphic features that are typical of youthful faulting, including a topographic lineament marked by an similar to 1 m high ridge composed of discontinuous, left-stepping lobes, and (2) the seismic profiles demonstrate shallow faulting of the lacustrine strata that coincides with the left-stepping ridge. This investigation illustrates the potential for unidentified, low-rate, strike-slip faults in basins and emphasizes the value of high-resolution topographic data and subsurface imaging as a means of identifying these structures.