SPATIAL VARIATIONS IN FAULT SLIP RATE ALONG THE DEATH VALLEY-FISH LAKE VALLEY FAULT ZONE

The Death Valley-Fish Lake Valley fault zone (DV-FLVFZ) is thought to accommodate much of the relative Pacific-North America plate motion in the eastern California shear zone (ECSZ). Although numerous geodetic campaigns have addressed issues of strain accumulation along this part of the plate boundary, only a few field-based studies have attempted to measure longer-term (1,000 to 100,000 year) geologic slip rates along this fault system, making it difficult to assess the behavior of the plate boundary in the region. We use a multidisciplinary approach that encompasses analysis of offset alluvial fans with LiDAR digital topographic data combined with terrestrial cosmogenic nuclide ¹⁰Be geochronology to determine late Pleistocene slip rates at two locations along the northern part of the DV-FLVFZ in Fish Lake Valley (FLV). Derivation of slope aspect maps, hillshade images, topographic contour maps, and channel thalwegs from LiDAR data allowed us to accurately retro-deform offset fans at Furnace Creek in central FLV and Indian Creek in northern FLV. Based on these data, we determined the late Pleistocene strike-parallel displacement to be ~290 m at Furnace Creek and ~178 m at Indian Creek. Beryllium-10 dates from boulders on the fan surfaces yielded ages of ~94 ka and ~71 ka at Furnace Creek and Indian Creek, respectively. These ages are similar to numerous dates on other alluvial fans in the region, which may indicate a large pulse of sediment deposition during this time. Combining the offset measurements determined from LiDAR data with the ¹⁰Be ages yields a late Pleistocene slip rate of ~2.5 to 3 mm/yr for the northern part of the DV-FLVFZ in FLV. These rates are slower than the ~4.5 mm/yr late Pleistocene rate determined for the fault system in northern Death Valley, indicating slip rates decrease northward along this major fault zone. When summed with the slip rate from the White Mountains fault (WMFZ), the other major fault in this part of the ECSZ, our results suggest that either: (1) deformation at the latitude of FLV is accommodated by structures other than the DV-FLVFZ and WMFZ; or (2) the region is currently experiencing a strain transient similar to that in the Mojave segment of the ECSZ.