Unraveling Diffuse Deformation in the Drum Mountains, Utah, with Paleoseismology, Modern Geodesy, and Historical Aerial Photography

The Drum Mountains fault zone in central Utah is a diffuse zone of surface faulting that covers ~250 km², and comprises over 200 linear km of north-south trending fault scarps. Scarps range in height from ~1 to 7 m and display both down-to-the-east and down-to-the-west senses of displacement, with complex cross-cutting relationships. The origin of this fault system is unresolved. Here, we present an approach to studying a diffuse fault zone through paleoseismology and analysis of a high resolution DSM produced from historical aerial imagery. Paleoseismic studies were undertaken along two major and oppositely-dipping fault traces, separated by ~3 km across the fault zone. High resolution topographic data were collected at both paleoseismic sites via terrestrial LiDAR. Single-grain OSL and ¹⁴C ages were obtained from the sites and constrain the most recent events (MREs) on the two fault traces to be c. 800 years BP and between >580-c. 1200 years BP, allowing the possibility of co-rupture or temporally-clustered surface rupturing events. A penultimate event identified at The Crossing trench site returned an age of between c. 3.5-5.3 ka on that trace. Local LiDAR surveys were supplemented by cross-fault zone RTK GPS topographic transects. Together, these modern geodetic observations were used to refine the generation of a SfM digital elevation model from ~200 scanned single frame aerial photographs (1960-1980) that span the entirety of the Drum Mountains fault zone. In addition to evaluating the potential of an air photo DEM to augment local, high-resolution topographic surveys in understanding diffuse fault systems, we provide new insights into this enigmatic fault zone. The short recurrence interval, along with time-integrated, cumulative extension rates of c. 0.4 mm yr^-1 since ~35 ka across the entire fault zone, would suggest that the Drum Mountains fault zone is one of the faster slipping faults in the eastern Basin and Range. Refining the rate and spatial distribution of slip across the Drum Mountains fault zone will help resolve competing hypotheses of regional extension, salt tectonics, and magma-assisted faulting for it origin.