Active Steady-State Creep on A Nontectonic Normal Fault in Southeast Utah: Implications for Strain Release in a Rapidly Deforming Salt System

Characterizing short-term temporal variations of fault creep provide insight into the evolution, mechanics, and strength of fault systems. Using spirit leveling and an extensometer, we measured active slip of a surface fault southwest of the Needles District, Canyonlands National Park, Utah, where exteis driven by differential unloading of a subsurface salt layer due to incision of the Colorado River. Results show continuous creep at maximum rates of 0.7 +/- 0.2 mm/yr without large temporal variations typical of episodic creep events. Occasional, minor transient events in fault slip velocity coincided with water infiltration; however, we found no significant relation between precipitation and transient events. Detailed mapping of widespread, fault-parallel sinkholes provide evidence for dilation of faults at shallow depth, a process that lowers fault strength. We propose continuous slip is related to low fault strength and differential unloading, as opposed to other salt systems where dissolution has been linked to episodic slip.