The United States Geological Survey recorded a Magnitude 6.5 Earthquake at a depth of 10.0 km about 72 km to the west of Challis in Custer County, Idaho, slightly after 4.50 pm local time (slightly after 11.50 pm GMT) on Tuesday 31 March 2020. There are no reports of any serious damage or injuries associated with this event, but it was felt across much of western North America, from Vancouver and Calgary in the north to Las Vegas and Los Angeles in the south.
A rockfall on Highway 21 near Lowman, Idaho, following a Magnitude 6.5 Earthquake on 31 March 2020. Tyler Boyer/The Spokesman Review.
The quake took part in an area known as the Central Idaho Seismic Zone, which is bisected by six active faults, the Madison, Centennial, Beaverhead, Lemhi, Lost River, and Sawtooth. These faults are associated with the Yellowstone Magma Chamber in the northeast of Wyoming, an area that suffers more-or-less constant small tremors due to the movement of magma beneath the surface, but which seldom experiences larger quakes. The constant small movements around Yellowstone can lead to stress building up in rocks further away, leading to Earthquakes as the rocks release the strain by readjusting their positions, which can affect Wyoming as well as neighbouring Idaho and Montana. The same faults also suffer stress due to more distant rock movements, notably on the subduction zone on the American west coast.
The approximate location of the 31 March 2020 Custer County Earthquake. USGS.
Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.
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