USING STREAM CHANNEL PROFILES TO ASSESS FAULT SLIP RATE VARIABILITY AND TO EVAULATE FAULT SEGMENTATION: A CASE STUDY FROM THE WASSUK RANGE NORMAL FAULT, WESTERN NEVADA

The Wassuk Range, on the western margin of the Basin and Range Province, represents the uplifted footwall of an active, east-dipping normal fault. Acting as a counterbalance to fault-related growth of topographic relief, erosional processes have removed rock, leading to incision of the footwall and the evolution of stream channels. These channels serve as records that we use to reveal unmapped faults in the footwall, to document differences in uplift rates along the range-bounding fault (RBF), and to explore segmentation of the RBF system.

We used ArcMap and Matlab software to generate stream channel profiles from digital elevation models of the Wassuk Range. We then identified abrupt changes in gradient for each profile and determined which of these changes marked lithologic boundaries or faults. We also compared profiles from different positions along the RBF, revealing important variations in profile character. For example, stream heads are at relatively lower elevations in the north, with lower average gradients, while further south, average stream-head elevations and gradients are significantly higher, consistent with previous research that revealed higher rates of fault slip in the south. Abrupt fault-parallel changes in profile character allowed us to divide the range into distinct structural blocks, with profiles from each block affected by differences in uplift rate and, in some cases, differences in fault slip direction (i.e., a change in normal versus strike-slip components of slip). We hypothesize that these differences in slip rate and/or direction for adjacent structural blocks are accommodated by previously-mapped fault systems at high map-view angles to the dominant RBF and suggest RBF segmentation. Gravity data from the hanging wall of the RBF support this segmentation, with values that indicate thicker sedimentary basin fill adjacent to structural blocks with higher range-crest elevations and steeper channel gradients. We believe that this method could be especially valuable if applied to less well-studied fault systems elsewhere, revealing structural information that might impact neotectonic studies and seismic hazard evaluation.