A magnitude 4.4 earthquake struck northeast of Lima just around 12:15 p.m. on Tuesday, and a 3.5 aftershock registered about three minutes later.
That's according to John Bellini, a geophysicist with U.S. Geological Survey's National Earthquake Information Center in Golden, Colorado.
He said these are considered "light" earthquakes, though they were likely felt near the epicenter and perhaps as far away as Butte.
"With a 3.5 (earthquake), people feel the jolt," Bellini said. "A 4.5 can knock things off a shelf near the epicenter. You might see some cracks in some old plaster. ... Ten miles away, you’re probably not going to see anything other than a jolt.”
Brian Rayburn, superintendent of the Lima School District, said students and teachers at the town school could feel the quake but that it "came and went pretty fast" and no damage was done.
Rayburn said the earthquakes occurred while students were on lunch and recess break and that it provided "a good opportunity for us to go over earthquake drills, after the fact."
Mike Stickney, director of the earthquake studies office at the Montana Bureau of Mines and Geology, said such preparation and precaution is warranted.
“I’d just say that it (Tuesday's seismic activity) is a reminder that we live in an earthquake zone and that a significant earthquake can come along anytime without prior warning," Stickney said. "So it’s best to be prepared.”
Stickney noted that "there have been other earthquakes in the Lima area that were this large in recent decades" and that southwest Montana is a seismically active zone.
“Today’s earthquake occurred in what's called the Centennial Tectonic Belt," Stickney said. "It’s a zone that starts over near West Yellowstone and runs westward through the very southern edge of southwest Montana ... and continues westward into central Idaho. It’s a seismically active zone and also includes some active faults."
According to Stickney, earthquakes like those on Tuesday occur because the Earth's tectonic plates are "being pulled apart or stretched," often leading to one side being uplifted to form a mountain and the adjacent side dropping down to form a valley.
While noting seismologists "can’t predict or forecast" earthquakes, Bellini said he "wouldn’t be surprised to see a couple of other smaller ones. That would not be unusual or unexpected. Some of them may be large enough for people in the area to feel the vibrations from.”
Stickney said he expected small aftershocks to "continue for the next several days at least.”