The Pocatello segment of the Wasatch fault zone extended into southeast Idaho: A reactivation structure of the Paris-Willard thrust fault

In the western United States, the Wasatch fault zone marks a fundamental structural boundary between the Basin and Range province to the west and the Sevier fold and thrust belt to the east. This normal fault zone lies along the western edge of the Wasatch Mountain Range and is associated with Basin and Range extension that has occurred over the past 17 million years. The Neogene-Quaternary Wasatch fault zone lies west of the older, westerly-dipping Paris thrust fault, which was active during Cretaceous shortening associated with the Sevier orogeny. Based upon detailed mapping, we propose that: the Wasatch normal fault zone continues 80 km northward beyond its previously documented northern terminus in Malad City to Pocatello, Idaho; the Pocatello segment has served as an imbricate reactivation ramp within the Paris thrust fault system during the Neogene and Quaternary; and the stratigraphic throw across this fault is up to 6 km. To this end, we hereby define the reactivated Pocatello segment as the Wasatch fault extension (WFE) which has been active during the Neogene and Quaternary. As an active component of the Wasatch fault zone, the Pocatello segment has the potential to generate M7 earthquakes.