Poster Presentation

Faults that creep at a constant rate impose a steady influx of stress to their tips. The Needles Fault District and the Moab Fault Zone form arrays of normal faults cutting the Navajo Sandstone (Utah) that experience steady-state creep related to salt tectonics. We used a combination of aerial orthophotography and lidar data to map faults and secondary fractures at both locations. From these maps, we analyze the distribution of fracture density and orientation within fault damage zones. Fractures are organized into a single set at Moab and two perpendicular sets at Needles and may be indicative of regional tectonics instead of fault activity. Fracture densities are unevenly distributed along strike of the faults, focusing at fault tips and areas of geometrical complexity (bends and step-overs). At both locations, there is a gradient in fracture density throughout the fault array, where fracture density steadily decreases over two orders of magnitude with distance away from the locus of deformation. This indicates that, even if the fracture networks are inherited, their reactivation and growth respond to the ongoing fault creep.