Late Pleistocene Record of Off-Fault Deformation and Vertical Slip Rates from the Wasatch Fault Zone, Utah: Implications for Fault Segmentation from Lake Bonneville Shorelines

In an effort to better understand the Pleistocene history of the Wasatch fault zone, we evaluate the deformation and displacement of the Bonneville and Provo high-stand shorelines of Lake Bonneville along the Wasatch Front. We apply an automated shoreline elevation measurement application developed as part of this study to measure Lake Bonneville shoreline elevations along the Weber and Brigham City segments of the fault, adding to a previously published dataset of shoreline elevations on the Salt Lake City segment. Tectonically deformed shorelines on the footwall of the fault demonstrate elevation patterns that are inconsistent with the idea that the Pleasant View salient, a bedrock salient marking the segment boundary between the Weber and Brigham City segments of the fault, is a persistent barrier to fault rupture since the late Pleistocene. Shoreline features are elevated similar to 20 m across the segment boundary as compared to shoreline features on the northern part of the Brigham City segment. We suggest the possibility that fault rupture through the Pleasant View salient has been common since the late Pleistocene and speculate that a similar relationship could exist between the Provo and Salt Lake City segments, based on similarities between the shoreline elevation patterns on the Brigham City and Salt Lake City segments of the fault. Vertical slip rates measured from displaced shorelines at the Pleasant View salient (Brigham City-Weber segment boundary) are generally higher compared to those at the Honeyville spur (Collinston-Brigham City segment boundary). Statistically significant vertical slip rates calculated from the Provo shoreline at the Pleasant View salient (0.8 +/- 0.5 to 0.9 +/- 0.6 mm/yr and 0.7 +/- 0.5 to 0.9 +/- 0.6 mm/yr) suggest that late Pleistocene vertical slip rates are slightly lower than Holocene rates; however, large uncertainties in the shoreline elevation measurements exist.