INSIGHTS INTO SEGMENTATION AND SURFACE RUPTURE HISTORY OF THE OQUIRRH – GREAT SALT LAKE FAULT SYSTEM, UTAH, USA, FROM FAULT SCARP HEIGHTS AND LAKE BONNEVILLE SHORELINE ELEVATIONS

The Great Salt Lake Fault (GSLF), North Oquirrh Fault (NOF), South Oquirrh Fault (SOF), and Topliff Hills Fault form a >200 km long, range-bounding, west dipping fault system in the eastern Basin and Range, near the populous Wasatch Front. The GSLF connects at its south end to the ~27 km long NOF, but it is submerged beneath the Great Salt Lake so its paleoseismology is not well known. The NOF and SOF are separated by a structural complexity that obscures their linkage, although tentatively identified fault scarps in the complexity may provide insights. We investigate segmentation behavior between the GSLF and NOF using the along – strike distribution of surface offset in the most recent event (MRE) and earlier surface – rupturing earthquakes, combined with the elevation of Lake Bonneville shorelines that parallel the NOF and were displaced by surface faulting. 220 measurements of net vertical displacement (offset) were made along the scarp of the NOF using LiDAR digital topography. Our preliminary results show that total offset across fault scarps fall into three groups: one-event offsets that range from 2 to 3 m, two-event offsets that range from 5 to 7 m, and three or more event offsets that range from 7 to 10.5 m, which is consistent with the results of trenching studies (Olig et al., 2001). Near the middle of the NOF, MRE offset is ~2.4 m, whereas 10 km to the north, where NOF connects with the GSLF, MRE offset is 3.4 m. A pooled T-test at 95% confidence indicates that this upward trend to the north is statistically significant. This suggests that the MRE on the NOF may have included rupture on at least the southern part of the GSLF, consistent with an estimated >40 km rupture length of the MRE based on offset (Wells and Coppersmith, 1994, Olig et al., 2001). Lake Bonneville shorelines in the NOF footwall, which pre-date the MRE and post-date the penultimate event (PE), increase in elevation to the north supporting this hypothesis, although it is difficult to separate isostatic rebound and tectonic effects on shoreline elevation. In contrast, preliminary results indicate that offset in the PE may decrease towards the north end of the NOF, suggestive of a different rupture distribution in that event. Ongoing work includes analysis of offset along the southern NOF and SOF to address segmentation between those faults.