Active steady-state creep on a nontectonic normal fault in southeast Utah: Implications for strain release in a rapidly deforming salt system

Abstract

Characterizing short-term temporal variations of fault creep provides insight into the evolution, mechanics, and strength of fault systems. Using spirit leveling and an extensome- ter, we measured surface displacement of a fault southwest of the Needles District, Canyon- lands National Park, Utah, where extension is driven by differential unloading of a subsur- face salt layer due to incision of the Colorado River. Results show continuous creep at max- imum 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 infil- tration; however, we found no significant relationship between precipitation and transient events. Detailed mapping of regionally widespread, fault-parallel sinkholes provide evidence for dilation of faults at shallow depth, a process that lowers fault strength. We propose con- tinuous slip is related to low fault strength and differential unloading, as opposed to other salt systems where dissolution has been linked to episodic slip.