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An earthquake that struck Tuesday in a rural area near the Idaho-Montana border was felt as far away as Helena and was followed by multiple aftershocks, but no damage was immediately reported.
The main quake struck just after noon Tuesday 4 miles northeast of Lima, Montana, a town of about 230 people along Interstate 15 in the southwestern corner of the state. It had a preliminary magnitude of 4.4 and was about 6 miles deep, U.S. Geological Survey research geophysicist William Yeck said.
“That potentially could cause some damage, but generally 4.4 is in the ‘felt’ range, but not damaging,” he said.
Earthquakes of magnitude 2.5 or 3 are usually the smallest that are felt by people. It generally takes a magnitude 5 earthquake or larger to cause structural damage, USGS geophysicist Don Blakeman said.
People 134 miles north in Helena and 87 miles south in Idaho Falls, Idaho, reported feeling the quake, according to USGS data.
The main quake was followed by a series of aftershocks, the largest a preliminary magnitude 3.5 quake that struck about three minutes later, according to the agency.
Mike Stickney, the director of the Montana Bureau of Mines and Geology’s Earthquake Studies Office, said he recorded about a dozen aftershocks within 90 minutes of the main earthquake, and there are likely to be more shocks over the next several days.
Stickney said the activity is happening along a seismic zone called the Centennial Tectonic Belt that stretches from just outside Yellowstone National Park through southwestern Montana and into central eastern Idaho.
Small earthquakes are common along the belt and are only occasionally large enough to feel, he said.
The last major quake to strike along that belt was the magnitude 6.9 earthquake in central Idaho in 1983, Stickney said.
“This is a reminder that we live in earthquake country,” Stickney said. “Being prepared is never a bad idea.”