The United States Geological Survey recorded a Magnitude 2.7 Earthquake at a depth of 5.1 km, approximately 12 km to the southwest of Lewis Lake in the Yellowstone National Park in northwest Wyoming, slightly after 2.30 am local time (slightly after 8.30 am GMT) on Monday 23 September 2013. A quake this size is unlikely to have caused any damage or injuries, but was probably felt locally.
The approximate location of the 23 September 2013 Yellowstone Earthquake. Google Maps.
The quake occurred on the southern fringe of the Yellowstone Caldera, a vast hotspot volcano that covers an area of roughly 55 by 75 km. Eruptions on the volcano are rare (the last happened around 70 000 years ago) and explosive eruptions even more so (the last happened around 150 000 years ago), but movement is common in the magma chamber beneath the caldera, leading to frequent, if generally rather small, Earthquakes. Magma entering a chamber beneath a volcano does not necessarily erupt as lava at the surface; it can be emplaced in structures such as sills and dykes, igneous rock formations formed entirely beneath the surface.
Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here.
See also Magnitude 2.6 Earthquake near the Grand Canyon in Arizona, Magnitude 2.7 Earthquake in Okfuskee County, Oklahoma, Magnitude 2.9 Earthquake in Payne County Oklahoma, Magnitude 3.1 Earthquake in Madison County, Montana and Magnitude 4.9 Earthquake in the Wind River Mountains of Wyoming.
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