LATE QUATERNARY ACTIVITY AND SEGMENTATION ON THE NORTHERN OQUIRRH FAULT AND ISOSTATIC REBOUND GRADIENTS IN THE TOOELE VALLEY FROM PLEISTOCENE LAKE BONNEVILLE SHORELINE ELEVATIONS, UTAH, USA

The Northern Oquirrh fault (NOF) is a normal fault that bounds the west side of the Oquirrh Mountains, Utah, from the Great Salt Lake south for ~30km to a major structural salient. It likely is linked to the Great Salt Lake fault (GSLF) to the north, and the Southern Oquirrh Mountains and Topliff Hills faults to the south, forming a >250km – long system. We measured Lake Bonneville shorelines that are sub-parallel to the fault for its entire length using high resolution topography from airborne LiDAR (Utah AGRC, 2019) and structure-from-motion processing of sUAS photographs. The high and Provo shorelines cross from the footwall to the hanging wall near the NOF’s midpoint and drop ~3.1m in elevation, recording fault slip since abandonment of the Provo shoreline (<14 ka, Godsey et al., 2011). The ~3.1m offset is inferred to be the most recent event (MRE), as identified by Olig et al. (1996). Southward from the crossing, the high shoreline, in the hangingwall, remains downdropped ~3 m until near where the NOF enters the structural salient, at which point it rises back to approximately the level observed in the footwall to the north. Vertical ground displacement from normal fault surface rupture decreases with distance from the fault trace; we corrected for this effect using observations from the 1983 Borah Peak earthquake (Stein and Barrientos, 1985), Coulomb modeling (Toda et al., 2011), the NOF’s mapped trace, and a newly identified NOF scarp in the structural salient. Even after this correction, hangingwall shoreline elevation increases at the structural salient, suggesting the MRE surface rupture terminated near there. If this is correct, then the >70km long surface rupture implied by ~3.1m slip in the MRE may have included rupture of the NOF and the GSLF. High shoreline elevations systematically decrease at ~0.03 to 0.18 m/km towards the south after correction for tectonic offset, which probably reflects the local gradient in post-Bonneville isostatic rebound.