The two earthquakes that rattled Northwest Montana last week are a clear reminder that Montana is “earthquake country,” according to a scientist with the Montana Bureau of Mines and Geology.
On Nov. 11, a magnitude 4.0 earthquake shook remote sections of Flathead and Lincoln counties. Just three days later, a 3.9 magnitude earthquake rocked the Whitefish and Columbia Falls area just before midnight on Nov. 14. It was initially reported as a 4.5 magnitude earthquake. The second quake spurred dozens of phone calls to emergency services late Friday and early Saturday morning from rattled residents, but there were no reports of injures or major damage, with the exception of a few cracked walls.
Mike Stickney, director of the Montana Bureau of Mines and Geology’s Earthquake Studies Office, said earthquakes are common in Montana. He said the western portion of the state actually experiences about five earthquakes every day, but most are too small to be noticed. He said there are about a dozen noticeable earthquakes every year in the region.
“Big earthquakes are no stranger to Northwest Montana,” he said. “It’s just been a long time since we’ve had any we actually felt.”
The epicenter of the Nov. 11 earthquake was 3.5 miles beneath the surface of the earth southwest of McGregor Lake, 33 miles west of Kalispell. Considering the size and depth of the quake, and its remote epicenter, it’s unlikely there was any damage, although people in the area may have felt some light shaking. The epicenter of the Nov. 14 quake was 8.4 miles beneath the surface about 3 miles northwest of Columbia Falls. Because it happened in a more populated area, there were many more reports of shaking from local residents.
Stickney said there are 79 active fault lines in Montana, including two major ones in Northwest Montana – the Swan Fault and the Mission Fault. The latter is of particular concern and Stickney said the fault between Pablo and St. Ignatius has the potential for a massive 7.0 magnitude earthquake.
However, Stickney said it does not appear that last week’s two earthquakes were the precursor to a major shake.
“Right now they appear to be two random earthquakes,” he said.
The Flathead Valley has experienced a few notable earthquakes over the years. In 1952, an earthquake impacted the Swan Lake area and caused some minor damage along the east shores of Flathead Lake. A 4.7 magnitude quake in April 1969 caused damage in Big Arm, Dayton, Proctor, Lake Mary Ronan and Polson. There were at least 21 aftershocks felt during the following month and 325 minor aftershocks were reportedly felt from May 1969 until December 1971. In 1975, a 5.0 magnitude earthquake rattled the Creston area. And in 1995 a swarm of earthquakes rattled the Kila area for a few months.
The largest earthquake to ever hit Montana in recorded history was near Hebgen Lake, near Yellowstone National Park, in 1959. The 7.3 magnitude quake resulted in 28 fatalities and $11 million in damage.
“(These recent events) are a subtle reminder that Montana is earthquake country and there is always the potential for a large scale earthquake here,” Stickney said. “Even though it’s been a long time since we’ve had a large earthquake in Montana, we will have a big one… We just can’t predict when.”