During the first half of 2020, the U.S. Intermountain West region of the United States experienced four significant earthquake sequences, spanning multiple states. In the new issue of SRL, 15 papers characterize these major earthquakes and discuss how they are helping seismologists gain new insights into the tectonics of the region.
The Intermountain West is bounded by the eastern margin of the Sierra Nevada and Cascade Mountains to the west and the Rocky Mountains to the east. While its earthquake risk is often overlooked in comparison to those in California and the Pacific Northwest, the region contains several major fault systems and a growing urban population, particularly near Salt Lake City in Utah.
Last year's four major earthquakes in the region include the 18 March magnitude 5.7 Magna, Utah earthquake; the 31 March magnitude 6.5 Stanley, Idaho earthquake; the 15 May magnitude 6.5 Monte Cristo earthquake in Nevada and the 24 June magnitude 5.8 earthquake near Lone Pine, California. In all cases, these earthquake sequences were the largest to occur in the area for several decades.
The focus section papers cover the overall seismotectonics of the region and examine the specific fault geometry, aftershocks, ground failure and other aspects of the major earthquake sequences. The research reflects the expanded "toolkit" of seismologists, including GPS stations, satellite and geophone data and machine learning, that helped the researchers quickly characterize the seismic activity--while contending with work and travel restrictions during the COVID-19 pandemic.
Six focus section papers (Mesmeri et al.; Kleber et al.; Holt et al.; Pollitz et al.; Wong et al.; and Baker et al.) in the focus section cover the Magna, Utah earthquake, which likely occurred on the Wasatch fault and was the largest earthquake to occur in Utah since 1992. The event caused more than $150 million in damage.
Five papers explore the Stanley (Liberty et al.; Pollitz et al.) and Monte Cristo (Bormann et al.; Hammond et al., Koehler et al.) earthquakes, and one paper (Hauksson et al.) investigates the Lone Pine sequences. Other papers in the section look at the Intermountain West region broadly (Wesnousky; Crowell) and include a study of a 2017 Montana earthquake (Smith et al.) that bears on faulting in the region.