Wake-up shake up: Small earthquake rattles valley

“It rattled the whole house,” reported Charlo resident Martha Hyvonen of the 3.7 magnitude temblor that shook many Mission Valley residents awake last Wednesday.

Theodora Lambson, who lives southeast of St. Ignatius just 2.5 miles from the epicenter, said it felt like a corner of her house collapsed.

“A waker-upper,” said Joanne Bigcrane on Facebook.

“I stood up and my house started shaking, my window rattling, and the rez girl in me gave out a 'YE! Good Morning to you too Creator, let's get started with a shake!,’” wrote Vina LittleOwl.

“Biggest earthquake I ever felt in Montana,” wrote Michelle Miner.

Even the Polson Chamber chimed in, suggesting that “even our bedrock” was getting excited about the next evening’s SPLASH event.

Seismograph stations that are part of the Montana Regional Seismic Network pinpointed the earthquake’s center at 2.5 miles southwest of St. Ignatius and 7.4 miles below sea level. It was preceded by a magnitude 3.2 earthquake on Oct. 15 about 2 miles southwest of last week’s epicenter and was followed by a dozen or so tiny aftershocks.

More than 350 people in western Montana reported in to the U.S. Geological Survey’s site, Did You Feel It (earthquake.usgs.gov/data/dyfi/) and provided a response to their experience.

“They don’t come out of the blue, they out of the dark from beneath our feet,” said Mike Stickney, director of the Earthquake Studies office at the Montana Bureau of Mines and Geology in Butte. “It’s not a natural feeling to feel the ground shake.”

Stickney said several secondhand reports from people at the south end of the Mission Valley “described booms or explosions” rather than the tremors usually associated with earthquakes.

“That’s pretty typical for observers that are near the epicenter where there’s still a lot of high frequency energy coming up out of ground,” he said. “You hear the seismic waves basically vibrate the atmosphere at frequencies your ears can hear.”

Observers reported hearing a rumble, a blast, or a sound like a freight train. “Somebody even thought their pickup truck blew up in the driveway,” says Stickney. All of this “is pretty typical of a small to moderate earthquake near the epicenter.”

Despite one Facebook user accusing Californians moving to Montana of bringing that state’s earthquakes with them, Stickney says western Montana is an active seismic zone where small temblors are common and moderate earthquakes can occur. The Mission Valley and parts of northwest Montana are located on a belt of seismic activity that’s about 100-miles wide and roughly runs from Yellowstone National Park to Kalispell.

He called last Wednesday’s wake-up shake “small as earthquakes go, but certainly still large enough for many, many people throughout the Flathead Valley and beyond” to experience its reverberations. People from Helena to Trout Creek and Hamilton to Columbia Falls reported feeling it, with reports trickling in from as far afield as Great Falls and Spokane.

Stickney says the Montana Regional Seismic Network (MRSN) operates 45 seismic-sensing stations around western Montana including six on the Flathead Reservation. They also share the data they collect with other institutions across the region, including those in Washington, Canada and Yellowstone Park.

MRSN has collaborated with the Confederated Salish and Kootenai Tribes for a few decades to track temblors on the reservation, especially in light of the many earthen dams located here.

“That’s primarily why the Tribes started getting interested in monitoring seismicity,” he says. “They recognized that some dams might be susceptible to damage from a very large earthquake.”

Over the past two decades, the Safety of Dams program has rebuilt impoundments at McDonald Lake and Pablo Reservoir in the Mission Valley and Lower Dry Fork Reservoir near Lone Pine to modern standards.

“There are other old dams that haven’t been rebuilt, but we maintain active monitoring systems to keep track of what kind of activity is in the area and what that can tell us about the seismic hazards,” Stickney says.

In places like California, where larger seismic events are more common, people tend to be better educated about precautions. In Montana, however, where the last major earthquake occurred at Hebgen Lake in 1959, people aren’t particularly tuned in to earthquake safety.

Stickney says most injuries occur when heavy objects get shaken down from shelves, or bricks fall from chimneys. He says the FEMA website offers a list of recommendations on how to live more safely in a quake-prone zone.

“This last earthquake is yet another reminder we live in earthquake country and a big one could come along at any time,” he says. “We can’t predict them and fortunately they’re not very frequent, but it’s better to expect they could occur and be prepared.”