A PRELIMINARY LOOK AT WHETHER ACTIVITY ON THE POLARIS FAULT COULD INCREASE THE POTENTIAL FOR ACTIVITY ON THE DOG VALLEY FAULT NEAR TRUCKEE, CALIFORNIA

A fundamental goal of Engineering Geoscience is to recognize geologic hazards and work with society to avoid or mitigate risk from those hazards. In 1966, the Dog Valley Fault (DVF) near Truckee, California, generated a M6 earthquake, prior to the completion of Stampede Dam by the US Bureau of Reclamation in 1970. Although some geomorphic evidence exists in the area of the DVF, its coherent ground-surface trace remains uncertain to this day. Similar magnitude future earthquakes along the DVF could endanger Prosser Creek Dam, Boca Dam, and Stampede Dam, which lies perhaps on or nearly adjacent to the DVF trace (USBR, 2012, p. B14-B15). More recently, the nearby, NW-trending Polaris fault (PF), which can be considered a SE extension of the Mohawk Valley fault zone along the SW boundary of the northern Walker Lane shear zone, was recognized and judged to be an active right-lateral fault. The PF is capable of generating earthquakes in the M6-7 range that could endanger the earth-fill dams along Martis Creek and Prosser Creek (Hunter et al., 2011, BSSA v. 101, 1162). Water and debris from failed dams in this area would flow down the Truckee River and into Reno, Nevada, potentially causing damage and human casualties.

Based on our preliminary analysis using hillshade images made from a lidar-based DEM at 1 m resolution, the DVF is interpreted to intersect or perhaps cross the PF. Slip on one structure could result in significant stress changes and slip on the other, in a manner similar to the 2019 Ridgecrest and the 1987 Elmore Ranch-Superstition Hills earthquake sequences. Attempts to interpret the potential seismicity of the DVF as a singular, isolated structure without considering its structural context along with the active PF likely underestimates the hazard potential. Our objective is to conduct [1] seismo-lineament analysis and statistical best-fit-plane evaluation of relocated earthquakes and [2] structural-geomorphic analysis of hillshade maps created from lidar data. This analysis includes lineament mapping with GIS-based techniques such as convolution filtering, drainage network analysis, and stream deflection mapping, augmented by additional soil survey and near infra-red vegetation data to identify possible faults. We will also use GPS-site velocity data to measure present-day crustal strain in the area of the DVF.