ASSESSING ALLUVIAL FAN SURFACE AGES ALONG INACCESSIBLE PORTIONS OF THE EASTERN GARLOCK FAULT, SOUTHEASTERN CALIFORNIA, WITH AERIAL LIDAR, SAR BACKSCATTER, AND MULTISPECTRAL DATA: IMPLICATIONS FOR SLIP RATE STUDIES

The Garlock fault is a major left-lateral strike-slip fault that cuts across much of southern California and bounds distinct tectonic provinces, separating the western Basin and Range province from the Mojave block, which together contain faults that make up the Eastern California shear zone (ECSZ) and Walker Lane. A key area that has not been adequately studied is the eastern segment of the fault, particularly near its intersection with the Brown Mountain fault, which links the southern Panamint Valley fault with the Garlock fault and the Owl Lake fault. Much of the eastern Garlock fault lies within the boundaries of Fort Irwin and China Lake NAWS (Naval Air Weapons Station) and has been used as a bombardment range, making it generally inaccessible due to unexploded ordnance (UXO) in the area. Constraining the slip rate of the eastern Garlock fault is key to understanding its interactions with faults of the ECSZ/Walker Lane and ultimately, its role within the region of diffuse plate boundary strain. Excellent aerial LiDAR coverage over the entire fault allows precise measurement of offset features, but without accurate age constraints, slip rates are difficult to determine. To help overcome this, we are examining the correlation between various radiometric and surface roughness indices with relative and absolute surface ages. These indices include: relative band brightness in the VNIR-SWIR bands (such as from ASTER, Landsat 8, or Sentinel-2), SAR (e.g. ALOS-PALSAR, Sentinel-1) backscatter brightness, and surface roughness (e.g. point cloud standard deviation) from aerial LiDAR. In the case of multispectral data, these show the accumulation of iron and manganese oxides and certain clays, while the SAR and LiDAR roughness show the winnowing of certain fine portions and development of desert pavement. We are examining several inaccessible alluvial fans within the boundaries of Fort Irwin / China Lake NAWS to observe the correlation between these indices and relative age assessed through traditional means. While there are clear trends in these data that correlate with relative age, future work will entail obtaining absolute ages for fans with similar characteristics in accessible sites, and then using those results to estimate the age of fans in inaccessible UXO sites.