Insights into Wasatch fault vertical slip rates using the age of sediments in Timpanogos Cave, Utah

Abstract

Timpanogos Cave, located near the Wasatch fault, is about 357 m above the American Fork River. Fluvial cave sediments and an interbedded carbonate flowstone yield a paleomagnetic and U–Th depositional age of 350 to 780 ka. Fault vertical slip rates, inferred from calculated river downcutting rates, range between 1.02 and 0.46 mm yr − 1 . These slip rates are in the range of the 0–12 Ma Wasatch Range exhumation rate (∼ 0.5–0.7 mm yr − 1 ), suggesting that the long-term vertical slip rate remained stable through mid-Pleistocene time. However, the late Pleistocene (0–250 ka) decelerated slip rate (∼ 0.2–0.3 mm yr − 1 ) and the accelerated Holocene slip rate (∼ 1.2 mm yr − 1 ) are consistent with episodic fault activity. Assuming that the late Pleistocene vertical slip rate represents an episodic slowing of fault movement and the long-term (0–12 Ma) average vertical slip rate, including the late Pleistocene and Holocene, should be ∼ 0.6 mm yr − 1 , there is a net late Pleistocene vertical slip deficit of ∼ 50–75 m. The Holocene and late Pleistocene slip rates may be typical for episodes of accelerated and slowed fault movement, respectively. The calculated late Pleistocene slip deficit may mean that the current accelerated Wasatch fault slip rate will extend well into the future.