Two earthquakes in the Marion area west of Kalispell on Sunday night and Monday morning, Nov. 30 and Dec. 1, bring the number of quakes in Northwest Montana in less than three weeks to four.

This seismic activity is not considered unusual, according to Mike Stickney, director of the Earthquake Studies Office with the Montana Bureau of Mines and Geology in Butte.

“The area south of McGregor Lake is experiencing what we call an earthquake swarm,” he said. “Swarms have had an historical presence in the area.”

Earthquake swarms consist of small- to mid-sized earthquakes that occur over a period of time — a few hours or days up to several months, Stickney said.

“There’s no way to predict when the bursts of activity will happen,” he said.

A 3.0-magnitude quake shook the Marion area on Sunday night at 10:40 p.m. with an epicenter 33 miles southwest of Kalispell. It was followed by a 3.5-magnitude quake on Monday at 1:13 a.m. centered 31 miles southwest of Kalispell.

These two quakes come after a 4.0-magnitude quake near Marion on Nov. 11 and a 3.9-magnitude quake near Columbia Falls on Nov. 14. The Columbia Falls quake, centered close to the Half Moon area, was felt by thousands of people across the Flathead Valley.

According to the U.S. Geological Survey, Montana is one of the most seismically active states in the U.S. due to its mountainous area. Much of this activity, however, is small and not felt by residents.

Stickney said it’s unknown exactly what caused the recent swarm of earthquakes. He attributed them to pressure under the Earth’s crust that cannot be released in a single quake.

“Swarms are not well understood,” he said. “Usually they’re common near a volcanic area, but they can also be present in areas well away from volcanic areas.”

While there’s no cause for alarm, Stickney said he wouldn’t be surprised if the activity continues over the next several weeks or months.

In 1995, a swarm took place near Kila over several weeks, with quakes between 4.0 and 4.5 magnitude. In 1969, a 4.7 magnitude quake was followed by 325 smaller quakes near Big Arm over several years.

“This is a reminder that we do live in earthquake country and regular precautions need to be taken,” Stickney said.