Wyoming State Geological Survey
Wallace L. Ulrich

Acting Director & State Geologist
Wyoming State Geological Survey
P.O. Box 1347
Laramie, WY 82073

Wyoming State Geological Survey

Earthquakes Felt in Northern Lincoln County
September 13, 2010

Three earthquakes occurred in northern Lincoln County Sunday, Sept 12th. The first earthquake, a 4.1 magnitude earthquake, occurred at a depth of 3.1 miles. The event was located 25 miles SSE of Jackson and 30 miles NNE of Afton, near Willow Creek. A second earthquake, magnitude 4.0, happened at 4:20 p.m. at an approximate depth of 4.3 miles. The second event was located 25 south of Jackson and 30 miles NNE of Afton along the Little Greys River. At 8:43 p.m. a third earthquake, magnitude 3.6, occurred in the same general area. The 3.6 magnitude event was located 25 miles south of Jackson and 30 miles NNE of Afton, near the McCain Guard Station.

This area is the heart of the seismically active “Wyoming Overthrust Belt” where entire formations of rock are being slowly altered and deformed, resulting in numerous active faults, and earthquakes are a common occurrence. Numerous earthquakes of similar magnitude have been recorded in the area in the last 40 years. It is likely that earthquakes similar to the three events September 12th will happen again.

The 4.1 event was felt as intensity III in Thayne, Bedford, and Alpine, and as intensity II in numerous locations around the area. The second and third events were felt as intensity III near the epicenter and intensity II in areas as well. The State Geologist visited the area, spoke with local residents and first responders who had given aid to and transported to the Jackson hospital, a retired fire-fighter who was thrown from his horse when it spooked during the temblor. WSGS personnel are monitoring the area with the help of the USGS to gather any additional information which may become available.

If you felt ground motions and/or experienced possible damage related to these quakes, WSGS scientists encourage residents to participate in the USGS “Did You Feel It” program by visiting “Did You Feel It” and filling out a short questionnaire, to record data about the earthquake.

Additionally, those with information about an earthquake can contact WSGS geologist Seth Wittke at seth.wittke@wyo.gov or WSGS Acting Director and State Geologist Wallace Ulrich at wallace.ulrich@wyo.gov.

The WSGS has compiled seismological characterizations of all Wyoming counties, which include analyses of historic seismicity. See Earthquake Database for more information. These reports provide historic seismicity and information about long- and short-term seismic hazard analysis.

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