Climatically driven displacement on the Eglington fault, Las Vegas, Nevada

The Eglington fault is one of several intrabasinal faults in the Las Vegas Valley, Nevada and is the only one recognized as a source for significant earthquakes. Its broad warp displaces late Pleistocene paleo-spring deposits of the Las Vegas Formation, which record hydrologic fluctuations that occurred in response to millennial and submillennial-scale climate oscillations throughout the late Quaternary. The sediments allow us to constrain the timing of displacement on the Eglington fault and identify hydrologic changes that are temporally coincident with that event. The fault warps deposits that represent widespread marshes that filled the valley between 31.7 and 27.6 ka. These marshes desiccated abruptly in response to warming and groundwater lowering during Dansgaard-Oeschger (D-O) events 4 and 3, resulting in the formation of a pervasive, hard carbonate cap by 27.0 ka. Vertical offset by as much as 4.2 meters occurred after the cap hardened, and most likely after younger marshes desiccated irreversibly due to a sudden depression of the water table during D-O 2, beginning at 23.3 ka. The timing of displacement is further constrained to before 19.5 ka as evidenced by undeformed spring deposits that are inset into the incised topography of the warp. Coulomb stress calculations validate the hypothesis that the significant groundwater decline during D-O 2 triggered fault displacement through unloading of vertical stress of the water column. The synchroneity of this abrupt hydrologic change and warping on the Eglington fault suggests that climatically modulated tectonics operated in the Las Vegas Valley during the late Quaternary.