DECIPHERING ISOSTATIC AND TECTONIC UPLIFT ALONG THE WASATCH USING A GEOGRAPHICAL INFORMATION SYSTEMS (GIS) APPROACH

The two most striking geomorphic features accenting the Wasatch Front are the Pleistocene pluvial terraces of Lake Bonneville and the Wasatch Fault scarp. The Lake Bonneville and Provo high stands are prominent geomorphic surfaces that provide markers of both time and elevation. Indeed, in places where the fault crosscuts these surfaces, their ages have been used to estimate the fault’s slip rate. However, in other locations, the Wasatch Fault crosscuts the landscape at elevations above or below the pluvial terraces. Thus, normal slip at different locations has down dropped, uplifted, or offset the terraces. Additionally, previous geomorphic studies and geophysical modeling efforts have shown that the entire region has been subjected to isostatic uplift following the recessions of Lake Bonneville.

By building a geographic information system (GIS) that includes the magnitudes and gradients of differential isostatic uplift (from other studies’ modeling efforts), the locations and elevations of pluvial terraces relative to fault scarps (from existing maps combined with high resolution DEMs), and data from previous earthquake geology investigations we are poised to decipher the differential displacements experienced by the terraces of Lake Bonneville. This investigation will lead to insights about the distribution of slip along the Salt Lake City and Provo segments of the Wasatch Fault over the late Pleistocene to Holocene. Specific questions that are being addressed include: Has recent slip along this portion of the Wasatch fault been distributed in a segmented pattern, with higher slip at the interior of segments and lower slip at segment boundaries? How asymmetric is the distribution of slip between the hanging wall and foot wall of the fault? And, is there a spatial relationship between the magnitude of isostatic uplift and the distribution of slip in recent earthquakes along the Wasatch Fault?