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Dr. Keith D. Koper
Department of Geology and Geophysics, University of Utah
Title: Forensic Seismology in the Intermountain West of the U.S.
The Intermountain Seismic Belt (ISB) in the western U.S. is a north-south trending band of mostly normal and strike-slip faulting earthquakes that stretches from northern Arizona through Utah, Wyoming, Idaho, and Montana. It has moderate-to-low strain rates and reflects an extensional stress regime associated with the broad zone of deformation between the Pacific and North America tectonic plates. Major ISB earthquakes in the instrumental era include an M6.6 in Hansel Valley, UT, in 1934, an M7.5 in Hebgen Lake, MO, in 1959, and an M7.3 near Borah Peak, Idaho, in 1983. Owing to the high seismic hazard, the ISB has been seismically monitored for decades. Currently, there are ~600 permanent seismograph stations in the ISB, operated and maintained by ~25 distinct networks representing universities, state agencies, and federal agencies. The large, dense monitoring system leads to a wide range of seismic sources being recorded, including tectonic earthquakes, volcanic earthquakes, mine blasts, mine collapses, and military explosions, as well as earthquakes induced by the injection of high-pressure fluid into the subsurface and underground coal mining. Here I discuss the methods we use to distinguish tectonic earthquakes from other seismic sources, with implications for the monitoring of nuclear test ban treaties.
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