The Great Rocky Mountain ShakeOut is a multi-state earthquake drill spanning much of the mountainous western United States. This page has information for participants living in Wyoming.
ShakeOut Point of Contact
Earthquakes are common in Wyoming. Historically, earthquakes have been felt in each Wyoming county, with most earthquakes occurring in the western third of the state. The first reported earthquake occurred in Yellowstone National Park in 1871 and the most recent likely occurred there. Yellowstone National Park is one of the more seismically active areas in the United States. In fact, during the third week of January 2010 there was a swarm of more than 1,200 earthquakes with magnitudes between 0.5 and 3.8 in Yellowstone National Park.
A dynamic magma chamber beneath Yellowstone, combined with regional tectonic forces, results in significant seismic activity. Many of Wyoming’s earthquakes are associated with movement within or around the magma chamber. Others are associated with active faults.
Yellowstone is a super-volcano, and explosively erupted 0.64 million, 1.3 million, and 2.1 million years ago. The explosive eruptions led to the formation of giant calderas, the collapse of which led to the formation of faults in the vicinity. In addition, after the major eruptions, resurgent domes formed within the calderas. The doming process led to the formation of other faults.
Faults in Wyoming are capable of generating damaging earthquakes anywhere in the state. Historically, Wyoming earthquakes are tied to faults that are buried. Buried faults are faults that have never broken the surface and are generally considered to be capable of generating up to magnitude 6.5 earthquakes. Since the distribution of buried faults is not well known and many faults remain unmapped in Wyoming, it is assumed that earthquakes up to magnitude 6.5 can occur anywhere in the state.
In 1959 a magnitude 7.5, intensity X earthquake occurred just west of Yellowstone National Park, near Hebgen Lake, Montana. The Hebgen Lake earthquake is a model for the types of earthquakes that can occur in western Wyoming.
Wyoming’s earthquake history spans only 130 years and there are gaps in the record for the late 19th Century and first half of the 20th Century. Even though Wyoming has not experienced an earthquake epicenter with a magnitude 7.5 within its borders in the last 130 years, the potential does exist. After the Hebgen Lake earthquake in 1959, monitoring in Wyoming started to improve. Prior to the 1950s most earthquakes were detected and located by personal reports. After the 1950s, earthquakes were more commonly located by seismometers.
Recent earthquake activity in Wyoming prompted the Wyoming State Geological Survey Office to develop 16 earthquake scenarios. The scenarios include four earthquakes based on data from historic earthquakes occurring near Casper, Gillette, Laramie Peak, and Estes Park, Colorado. The scenarios can be found on line at http://www.wsgs.uwyo.edu/data/gis/ims-projects.aspx.
A detailed description by county of recorded earthquakes in Wyoming can be found on line at www.wrds.uwyo.edu/wrds/wsgs/hazards/quakes/seischar/seischar.html. Following is a table of Wyoming’s ‘Top Ten Recent Earthquakes’ which either caused damage or concern for Wyoming residents, listed in chronological order with the most recent first:
|February 3, 1995||Near Little America||5.3 / V|
|February 3, 1984||Draney Peak Idaho near Star Valley||5.9 / VII|
|November 3, 1984||Atlantic City||5.1 / VI|
|October 18, 1984||Albany County||5.5 / VI|
|June 30, 1975||Yellowstone National Park||6.4 / VII|
|August 17, 1959||Hebgen Lake, just outside Yellowstone National Park||7.5 / X|
|March 26, 1932||Jackson||Unknown / VI|
|June 12, 1930||Near Grover in Star Valley||Estimated 5.8 / VI|
|November 14, 1897||Casper||Unknown / VI-VII|
|November 7, 1882||Bewtween Laramie and Estes Park, Colorado||6.2-6.5 / VII|
Please visit the following links for more information on earthquakes hazards and preparation: