FAULT DETECTION USING MULTISCALE REMOTE SENSING TECHNIQUES, NEAR CHALLIS, IDAHO

Between 2014-2016, a linear cluster of seismicity was observed near Challis, Idaho. The orientation of this seismicity is nearly identical to the trend of the northern half of the Lost River Fault System and so we hypothesize that this seismicity may relate to Basin and Range faulting, beyond its current mapped extent. The objective of this study is to develop and implement a multiscale remote sensing approach to identify the geologic structures that correspond to faulting in this area. Multispectral analysis included visible, near infrared, short wave infrared, and thermal sensors from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Sentinel-2, Worldview2, National Agriculture Imagery Program (NAIP) data resources. Multispectral analyses included vegetation and mineralogical indices, image classification, principal component analysis, and decorrelation stretching to delineate compositional differences in the study area. Topographic observations were based on the USGS National Elevation Dataset (NED). Possible fault locations were identified following the same rules that one would follow to interpret geology in the field, such as scarps/cliffs, topographic discontinuities, linear topographic depressions, changes in vegetation patterns, lithologic offsets, and anomalous lineaments. Preliminary mapping was unable to confidently identify a surface expression of any active faults in the area that could be responsible for recent seismicity. Although investigations of potential alternate localities are still ongoing, this may suggest that: 1) a blind fault is present in the area and does not yet offset surface features; or 2) a step-over or transfer fault may occur near the modern Salmon River, which results in a spatial offset relative to the mapped Lost River fault system to the southeast.