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 in Teton County, Wyoming
October 26th Jackson, Wyoming

Three earthquakes have occurred in the last two days in northeastern Teton County, Wyoming-- the first and largest triggered a landslide witnessed by a hunter.

The largest of the three, a magnitude 4.4 temblor, took place Sunday at 11:44 am October 24th East of the Red Hills area along the Gros Ventre River. The earthquake was located 20 miles east-northeast of Jackson, and 40 miles west of Dubois at a depth of 3.1 miles.

Geologists from the Wyoming State Geological Survey responded to a request from Rich Ochs, The Teton County Emergency Manager who received notice of an On-Star report of a small landslide in the Ditch Creek drainage, northeast of Kelly, Wyoming.

“We interviewed eight hunters in the area, spoke with Don Cooper of Gillette, who sent the On-Star report and listened to his son, Derek Cooper’s eyewitness account of the earth rolling beneath him and then the roar of trees snapping and ground moving as the land 20 feet in front of him separated from the crest of the mountain and ran down-slope a few hundred yards” offered State Geologist Wallace Ulrich.

Ulrich and Geologist Jason Rolfe located the slide area in the South Fork of Ditch Creek with the aid of the Coopers and Jackson Hole hunters John and Mac Bickner. The area is of hummocky topography, ponds at the base of ridges, shale and mudstone geologic formations with bentonite --all of which indicate unstable land. More slides in the area might be expected.

As weather permits the site will be flown and photographed and will appear on future survey maps. “I am sure we’ll be calling it the ‘Cooper Slide’. Witnessing a natural event of that much power and force a few feet away is a once-in-lifetime opportunity, to say the very least.” Ulrich added.

The trigger event was felt as intensity IV in Kelly and intensity III in Jackson and Moose; other areas in the Teton Valley and surrounding counties experiences intensity II shaking.

Two smaller earthquakes occurred very near the quake in the evening hours of October 25th. The first earthquake, magnitude 3.9, occurred at 7:24 pm and at 10:12 pm a magnitude 3.3 event occurred slightly east of the 3.9 event. The events are most likely tied to recent earthquakes in the Gros Ventre area. Beginning August 4th, 6 earthquakes occurred in a 4 day period, causing significant shaking in Kelly and the surrounding communities.

The October 25th magnitude 3.3 event marks the 19th earthquake to happen in the area since the beginning of this latest earthquake sequence on August 4th, 2010.

Wyoming State Geological Survey scientists with the help of the USGS scientists at Golden Colorado, continue monitoring seismicity in the region. Recently two seismic stations (strong motion accelerometers) have been placed in the area to provide additional strong motion data on seismic events, broadcasting live real-time data. Coupled with the high quality data from the Teton Seismic Network scientists are gathering information for public safety and study.

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 www.wsgs.wyo.gov.

Click on the RED BUTTON and fill 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.

Visit the Wyoming State Geological Survey

For further information on this media advisory:
Wallace Ulrich
Acting Director and State Geologist

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