Seismic Analysis of the 2020 Magna, Utah, Earthquake Sequence: Evidence for a Listric Wasatch Fault

The 18 March 2020 M(w)5.7 Magna earthquake near Salt Lake City, Utah, offers a rare glimpse into the subsurface geometry of the Wasatch fault system-one of the world's longest active normal faults and a major source of seismic hazard in northern Utah. We analyze the Magna earthquake sequence and resolve oblique-normal slip on a shallow (30-35 degrees) west-dipping fault at similar to 9- to 12-km depth. Combined with near-surface geological observations of steep dip (similar to 70 degrees), our results support a curved, or listric, fault shape. High-precision aftershock locations show the activation of multiple, low-angle (<30-35 degrees) structures, indicating the existence of a complicated fault system. Our observations constrain the deep structure of the Wasatch fault system and suggest that ground shaking in the Salt Lake City region in future Wasatch fault earthquakes may be higher than previously estimated.