CALCULATING VERTICAL OFFSET OF THE BORAH PEAK FAULT SCARP USING CONTEMPORARY DIGITAL METHODS

In October of 1983, a magnitude 7.3 earthquake ruptured along the Lost River normal fault, which bounds the western flank of the Lost River Range, central Idaho. Within a few years of the Borah Peak rupture, several studies were completed along the new 34 km long fault scarp to document the geology, seismology, and geodesy of this earthquake. To build on that initial research, this project employs Light Imaging, Detecting and Ranging (LiDAR) collected in 2005 along the Borah Peak rupture, a high resolution data set (0.5 m per pixel DEM resolution) never before used at this location.Using the LiDAR data, nine topographic profiles, distributed along a 5 km long section of the fault scarp, were generated across and orthogonal to the fault scarp. These profiles were used to measure the vertical offset across the 1983 fault scarp. Maximum and minimum vertical offset measurements are 2.0 m and 1.0 m; the average vertical offset is 1.5 ± 0.3 m (±1σ). Using a levelling staff, Crone et al. (1984) measured maximum vertical offset of 2.7 m and an average of 1.8 ± 0.7 m. Discrepancies between Crone et al. and my measurements can be attributed to errors in levelling staff measurements in the field, resolution of LiDAR data, and/or differences in location of topographic profiles. To address the viability of this LiDAR data for measuring vertical offset, comparison of levelling staff vs. LiDAR measurements need to be made in the same locations.