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6.5 Magnitude Earthquake Hits Idaho

A 6.5 magnitude earthquake hit southcentral Idaho early Tuesday evening local time, the strongest earthquake to hit the state since 1983. No casualties have been reported so far; the worst of the shaking occurred away from major population centers.

The reported epicenter of the earthquake was in the mountains northwest of Stanley and 45 miles west of Challis, about 78 miles northeast of Boise and roughly 200 miles from Yellowstone National Park. Several smaller aftershock earthquakes were reported in Yellowstone, according to the U.S. Geological Survey (USGS), and visitors said that eruptions of Old Faithful were noticeable longer.

The earthquake hit at 5:52 p.m. Tuesday local time, according to USGS. As of Wednesday morning, inspection efforts revealed no major damage, but local officials said they were still surveying for impact. The tremors were widely felt, with more than 15,000 residents reporting to USGS that they felt the shaking.   

By about 8:00 a.m. local time Wednesday there were at least 36 aftershocks reported. An avalanche that occurred after the earthquake forced the closure of a stretch of Idaho State Highway 21, about 25 miles south of the Stanley area, according to local officials.

No damage was reported to the two major health systems in the state, each of which operate several hospitals. So far Idaho has reported more than 500 confirmed coronavirus cases.

The U.S. Geological Service released a forecast predicting that over the next week, there is a 4 percent chance that one of the future aftershocks in Idaho could be greater than magnitude 6.5.

In 1983, the 6.9-magnitude Borah Peak earthquake, the strongest in the state’s recorded history, killed two people.

For more information on earthquake resilience preparation, see the Security Management story “Extreme Resilience.”