Shaken and stirred

Earthquake rattles Dillon early Thurs.
Map courtesy of the US Geological Survey.

No injuries or significant damages to property occurred. But many people in Dillon and throughout the region got a rude awakening early Thursday morning from a powerful earthquake that stirred many people from their slumbers.

“I was asleep at home in bed when it struck. It woke me up,” said Dillon resident Lynn Giles of the temblor that rumbled through the area on July 6.

Epi-centered about five miles southeast of Lincoln--which sits around 160 miles north of Dillon--the earthquake struck at 12:30 p.m. and lasted approximately 30 seconds, registering a 5.8 on the Richter Scale, according to the United States Geological Survey (USGS).

“We weren’t sure what was going on. We thought someone had hit the corner of the building,” said Michael Wiggins, a University of Montana Western student who works at Little Town Pump in Dillon, where he was enjoying some food friends had brought him when the shaking began.

“We walked around and looked for damage after we realized it was an earthquake, but nothing had happened.”

People from Billings to Spokane, to southern Idaho, to north of the border in Canada reported feeling the effects of the temblor to the USGS, which placed the origin of the earthquake at a depth of about eight and a half miles below the earth's surface.

In the hour following the seismic event Thursday, the USGS also recorded numerous aftershocks, at least one of which could be felt in Dillon about five minutes after the initial quake.

Those aftershocks will probably keep up for months, maybe longer, according to a local expert.

“Absolutely. The aftershocks will continue for a long time,” said Rob Thomas, a professor of geology in the University of Montana Western’s environmental sciences department.

“For instance, we have had aftershocks that people didn’t feel recently in Dillon related to the 2005 earthquake,” noted Thomas, referring to the 5.6 magnitude earthquake that struck 12 years ago, about nine miles northeast of Dillon.

The largest earthquake recorded that year in the U.S., the 2005 earthquake hit in July and continued to send shivers down locals spines for about a year with aftershocks, many of which could definitely be felt.

Due to its relative proximity to Dillon, the earthquake 12 years ago proved much more dramatic to locals than last week’s temblor.

“That one was a lot more violent and it lasted like two or three times longer,” recalled Dillon resident Daniel Thornton of the 2005 quake he experienced while downstairs at his parents house in Dillon.

“It actually knocked pictures off the shelves and other stuff,” added Thornton.

“You think really weird thoughts during earthquakes,” laughed Giles, recalling her reaction to the 2005 seismic event.

“One of our home’s original light covers hangs down about three feet from the ceiling in the bedroom. It was swinging. I thought, I’ve got to stand up on the bed and catch this thing before it breaks,” said Giles, who noted that western Montana has endured a number of strong earthquakes over the past century, the first in the mid-1920s.

“We had a big one in 1925,” said Giles of a 6+ magnitude quake centered near Three Forks that did extensive damage to numerous buildings, including some in Dillon.

“I was doing some research on churches in Dillon and found out the original Baptist Church had a big, brick steeple that kept falling down after the earthquake. They had to finally take it down in the 1930s,” said Giles, the director of the Beaverhead County Museum in Dillon.

Ten years later, a series of quakes struck over the course of about a month near Helena, leading to four deaths and serious damage to a number of buildings in the state’s capital.

The biggest recorded earthquake in the state struck in August 1959, when a 7+ magnitude earthquake over 100 times more powerful than last week’s hit the Hebgen Lake area by Yellowstone National Park, triggering landslides that buried several campgrounds and killed 28 people.

“We here in the Dillon area live in an active, seismic zone,” said Thomas, noting that western Montana lies within the Intermountain Seismic Belt, a seismically active area stretching from southern Nevada up through western Montana.

“People should know that earthquake activity is not rare here. We should remember it is part of living in southwest Montana and take precautions in our homes,” advised Thomas.

“The good news is that all the old buildings in Dillon survived the Hebgen Lake Earthquake in 1959,” said Thomas, who lives in an old Victorian home in Dillon.

“It provides us with some measure of comfort to know that the older homes and buildings in Dillon withstood that earthquake in 1959.”

Dillon tends to feel earthquakes and aftershocks more dramatically, due to its geology, according to Thomas.

“Much of Dillon is built on top of water-saturated gravel, sand and clay from old lake sediments,” said Thomas, who in 2009 was named Outstanding Baccalaureate Colleges Professor of the Year by The Carnegie Foundation for the Advancement of Teaching and the Council for Advancement and Support of Education.

“As a result the shaking is really magnified here in the valley by that substrate, that ground surface we live on. It’s a bit like living on top of a bowl of jello versus living on top of a bowl of solidified concrete. If you live on top of hard rock, the shaking is not as dramatic as it is if you’re living on top of sediment that is water-saturated—that’s the bowl of jello.”