POTENTIAL EFFECTS OF OROGRAPHIC PRECIPITATION ON RATES OF EROSION AND ISOSTATIC UPLIFT OF THE WASATCH FAULT ZONE FOOTWALL

A range of factors affect drainage network evolution in uplifted normal fault footwalls, including climate, variations in lithology, uplift rate, and interactions of independent fault segments. Past studies have shown that geomorphic analysis can help constrain the strength of linkages between fault segments in normal faults and therefore can inform seismic hazard analysis of active fault systems. In this study, we focus on the Salt Lake City (SLC) segment of the Wasatch fault zone (WFZ), which lies adjacent to the largest metropolitan area in Utah. Ideally, paleoseismic data could be used to better understand segment interactions and inform seismic hazard, but earthquakes only occur in the region every 100 to 500 years. Instead, we use geomorphic analysis of the uplifted WFZ footwall to improve our understanding of long-term (10⁴-10⁶ yr) interactions between the SLC segment and the segments to the north and south.

We performed ArcGIS analysis of channel long-profile data and lithologic, fault, outlet elevation, range crest elevation, relief, channel length, slope, catchment area, and sinuosity data from 26 different channels along the SLC segment. We plotted these variables relative to along-strike position and relative to segment boundaries. We also analyzed long-channel profiles and documented locations with significant changes in slope and marked each profile with locations of mapped faults and lithologic contacts.

Our results show that changes in stream channel variables do not correlate with along-strike position along the SLC; instead, variations in lithology appear to control footwall catchment morphology. We hypothesize that the orographic precipitation effect along the Wasatch front accelerates rates of erosion, especially compared to more arid regions, so the relative resistance of geologic units to erosion affects drainage evolution more strongly than effects caused by fault segmentation. We also posit that isostatic uplift of the footwall, driven by accelerated erosion, might also impact long-term (10⁶-yr) fault slip rates along the WFZ system.