INVESTIGATING RECENTLY ACTIVE FAULTS BASED ON THE GEOMORPHOLOGY OF EPHEMERAL CHANNELS IN THE GUADALUPE AND BROKEOFF MOUNTAINS, WEST TEXAS AND SOUTHEASTERN NEW MEXICO

Landscape topography driven by faulting and ephemeral stream erosion sheds light on relatively recent tectonic activity without the use of geophysical methods. The Brokeoff and Guadalupe Mountains, located in western Texas and southeastern New Mexico, were formed together as an ancient reef system during the Permian. Nearby Rio Grande Rift activity caused normal faults to form throughout the area after sporadic Laramide thrust faulting. Our study investigates relatively active faults using ephemeral channel morphology in the Brokeoff Mountains. Using Google Earth and ArcGIS, we analyzed stream channels that intersect fault lines within five zones positioned from east to west within the mountain range. By classifying stream segments using the Shreve stream order classification model and comparing stream lengths, we identified a progression of tectonic activity across the Brokeoff Mountains. Zones with long, first order streams perpendicular to faults were younger than short, complex, high order streams. Next we created watersheds for each of our study zones to see the larger scale elevation and stream drainage patterns. All of the streams in our study zones that lie on top of the Brokeoff Mountain Range meet at trunk streams to drain north. However, streams along the westernmost escarpment in the Brokeoff Mountains drain directly west. Lastly, we created a fault escarpment model to simulate earthquakes and the effects of seismic activity on nearby inactive faults. We found that shaking fractures nearby rock units and causes rock movement on inactive faults, as well as on top of the escarpment. The nearby seismicity also speeds erosion by displacing sediments during active earthquakes, making nearby inactive faults either appear more active than they are or more eroded. Obtaining USGS earthquake data ranging from 1990-2016 within the Rio Grande rift area shows recent activity occurring just outside the Brokeoff and Guadalupe Mountains. Moreover, a 3.1 earthquake within one of our study zones occurred on May, 17th, 2016. We conclude that faults in our study area are influenced by both erosional and seismic activity. Extensional processes may be ongoing; and the study of erosion and seismic activity increase awareness of potential geo-hazard risks within the Brokeoff and Guadalupe Mountain Ranges.