TESTING A PREDICTIVE MODEL OF FAULT SEGMENTATION USING STREAM PROFILE ANALYSIS: A CASE STUDY FROM THE WASSUK NORMAL FAULT SYSTEM, NEVADA

Segmentation behavior along major fault zones can provide important information regarding the potential for seismic activity. However, researchers need large data sets to document and understand how segmentation occurs along major fault systems, and obtaining these data sets can require years of field work. We propose a model that serves as a reconnaissance level tool to begin to document these basic characteristics before entering the field.

We examine the potential for a combination of stream, gravity anomaly, and range-crest profiling to reveal structural characteristics related to fault segmentation along major range-bounding fault (RBF) systems. To test such an integrated method, we chose the Wassuk Range of western Nevada, which is bound by an active normal fault system with well-documented structural geometries and fault-slip history. We used ArcMap and Matlab software to generate stream channel profiles along the RBF side of the Wassuk Range. We then compared profiles from different positions along the RBF, revealing important variations in profile character. 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., changes between normal and strike-slip components). Comparison of this data with gravity anomaly and range-crest elevations leads us to 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 strong RBF segmentation.

We demonstrate that the integration of stream profile analysis with gravity anomaly and crest profile data permits researchers to (1) identify strike-parallel differences in stream profile morphology that relate to changes in fault segment behavior; and (2) reveal possible unmapped lithologic changes or faults within the footwall of active normal fault systems. We believe that this transferrable model could be especially valuable if applied to less well-studied fault systems elsewhere, revealing structural character of major normal fault systems that might impact neotectonic studies and seismic hazard evaluation.