The United States Geological Survey recorded a Magnitude 3.1 Earthquake at a depth of 3.2 km in western Sweetwater County in southwest Wyoming, slightly before 2.55 am local time (slightly before 8.55 am GMT) on Saturday 28 September 2013. There are no reports of any damage or injuries arising from this event, though it is likely to have been felt locally.
The approximate location of the 28 September 2013 Sweetwater County Earthquake. Google Maps.
Wyoming typically suffers two or three moderate sized Earthquakes per year, though quakes large enough to cause significant damage are rare. The mountainous areas of the east of the state have a number of deeply buried faults where occasional movement occurs. This can be caused by movement around the Yellowstone Magma Chamber in the northeast of the state, 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.
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.
See also Magnitude 2.8 Earthquake in Oklahoma County, Oklahoma, Magnitude 3.2 Earthquake in Love County, south Oklahoma, Magnitude 2.7 Earthquake in Yellowstone National Park, northwest Wyoming, Magnitude 2.6 Earthquake near the Grand Canyon in Arizona and Magnitude 2.7 Earthquake in Okfuskee County, Oklahoma.
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