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 Montana.
ShakeOut Points of Contact
Please note: Because Montana schools will not be in session on October 17th, Montana participants are encouraged to hold their drills at
people are currently registered to participate in this year's Great Rocky Mountain ShakeOut ShakeOut.
are from Montana
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Montana is one of the most seismically-active states in the United States. Montana’s earthquake activity is concentrated mostly in the mountainous western third of the state, which lies within the Intermountain Seismic Belt. A great earthquake (magnitude 8.0 or greater) is not likely in Montana, but major earthquakes with magnitudes as large as 7.5 may occur in the state.
Starting with a small tremor on October 3, 1935, the city of Helena, Montana suffered through a series of several hundred earthquake shocks, including three damaging earthquakes with magnitudes 5.8, 6.3, and 6.0. During the Helena earthquakes, two people were killed by falling bricks, several were injured, and property damage was estimated at about $3 million (over $50 million in adjusted dollars). The Helena Montana earthquakes disproved a then-popular misconception that all seismic activity within the U.S. occurred solely in California and Alaska.
The largest earthquake on October 18 was felt across an area of about 596,000 square kilometers (approximately 230,000 square miles) that included the western three quarters of Montana, most of Idaho, northwestern Wyoming, and parts of southern Canada. The strongest tremor caused damage in varying degrees to about 300 buildings. In total, the Helena shocks caused structural damage to 65 percent of Helena’s buildings. The newly completed Helena High School suffered the greatest damage of any single structure with total collapse of one wing of the building. A total of 1,347 aftershocks from this series were listed up to the end of 1935.
The Hebgen Lake magnitude 7.3 earthquake, which occurred on August 18, 1959, was the largest historic earthquake in Montana and the 14th largest earthquake in the contiguous U.S. in historic times. This earthquake caused 29 fatalities and about $11 million ($78.6 million in adjusted dollars) in damage.
The Hebgen Lake earthquake caused 29 km (18 miles) of surface faulting on two major faults along the northeast side of Hebgen Lake, down dropping the lake and adjacent parts of the Hebgen basin as much as 6.7 m (22 feet). The sudden tilting of the valley beneath Hebgen Lake generated a large wave that overtopped the badly damaged Hebgen Dam. One of the most disastrous effects of the earthquake was the huge landslide that cascaded from the steep south wall of the Madison River Canyon. The Madison Canyon landslide, the largest seismically triggered landslide in North America, dammed the Madison River creating Earthquake Lake with a depth of 53 meters (over 173 feet).
The earthquake was felt as far as Seattle, Washington, to the west; Banff, Canada, to the north; Dickinson, North Dakota, to the east; and Provo, Utah, to the south. This area includes nine Western States and three Canadian Provinces. Aftershocks continued for several months the four largest of which ranged from magnitude 6.0 to 6.5.
Please visit the following links for more information on earthquake hazards and preparedness:
American Red Cross of Montana: http://www.redcross.org/montana
Governor’s Office of Community Service - Ready Montana: http://ready.mt.gov
Lewis & Clark County Earthquake Hazards - 1935 Helena Earthquakes: http://www.lccountymt.gov/disaster-and-emergency-services/hazards/earthquakes.html
Montana Bureau of Mines and Geology: Earthquake Studies: http://mbmgquake.mtech.edu/index.html
Personalizing the Earthquake Threat: UUSS - Personalizing the Earthquake Threat
State of Montana Disaster and Emergency Services:
USGS Montana Earthquake Information: http://earthquake.usgs.gov/earthquakes/states/?region=Montana