December 17th, 2017

EARTHQUAKE FELT IN CITY


By Mabell, Dave on July 7, 2017.

City residents experienced tremor in Montana

Dave Mabell and Nick Kuhl

Lethbridge Herald

dmabell@lethbridgeherald.com

The Earth’s crust, nearly 400 kilometres south of Lethbridge in Montana, crunched a little on Thursday. But the 5.8-magnitude earthquake that followed was felt by many residents of southern Alberta and as far distant as Saskatoon.

No injuries or significant damage have been reported from the quake, centred in the Rocky Mountains between Helena and Lincoln. Seven smaller quakes were recorded shortly after the 12:34 a.m. tremor, one reaching a magnitude of 4.4.

In Lethbridge, residents said the rolling sensation lasted several seconds. Closer to the epicentre, holidaying Lethbridge families were recounting more dramatic scenes.

Roisin Gibb and her family were in Whitefish.

“I was woken up by a noise,” she says.

“The glasses in the cupboard started to rattle. Initially I thought it was the Whitefish train which goes by frequently and there is sometimes a bit of a shakiness with it.

“However, I quickly realized that it was much stronger and the whole house started shaking,” Gibb recalls. “It lasted about a minute or so. Then there were a few episodes of aftershocks which lasted about 10 seconds or so over the next hour.”

Fortunately, no one was hurt.

Jason Daffy, taking in July 4 festivities with his family, was also in Whitefish.

“I woke up at about 12:34 a.m. and the bed was rocking like it was in windy waters,” he says.

“The curtains were slapping together like they were applauding me on my overly dramatic level of fright. I ran into the next room to grab the wife and kids but it ended when I got there.”

Lethbridge geography professor Rene Barendregt had a more audible wakeup. Coyotes near his home began howling, he says, and birds roosting nearby circled with cries of alarm.

A veteran researcher and teacher at the University of Lethbridge, he describes the quake as a “lateral strike slip fault movement” similar to events along the San Andreas Fault.

“Earthquakes are a reminder that we live on a dynamic crust, composed of seven main plates that move around,” he says. “Unlike some of the other rocky planets in our solar system, we have a liquid core,” allowing rocks, minerals and water to be continuously “recycled and refreshed.”

Fluid movements in that core, adds Barendregt, generate a strong magnetic field that shields us from harmful radiation.

“Earthquakes are not at all a bad thing, in the broadest sense,” he suggests. “They are part of the plate tectonic history of our planet’s crust. But we do need to learn how to live near them, in regions where they do occur.”

Lethbridge trucker Brad Duda had one of those learning experiences after he pulled over for the night at Shelby.

“I was sleeping in my bunk when I felt my trailer rock pretty hard, which is unusual while fully loaded,” he says. At first he thought some kind of a theft was underway.

“I sat up and started checking my mirrors. Nobody was there and my load was still secure so I went back to bed.”

But soon, “it happened again.”

It wasn’t until morning, after speaking with another trucker, that Duda heard him repeat the same story and they learned what had happened.

Lethbridge’s Mike Wilson and his family were in Montana also, camping near Glen Lake south of the Roosville, B.C. border crossing.

“We were sitting around the fire and basically the chairs started shaking, felt like someone was grabbing them and shaking them,” Wilson said.

“I couldn’t really tell what else was shaking at the time because it was so dark and it is very quiet out here. When I got back to the trailer we were staying in, some stuff that was on the countertop was on the floor. I wasn’t sure what had happened until I looked at Twitter when I went to bed.”

While small earthquakes are common a little further east, in Yellowstone National Park, Barendregt says the Lincoln quake may not be related to volcanic activity there.

“But that cannot be ruled out at this point,” he adds.

The Yellowstone hotspot, he explains, “is characterized by magma close to the surface, many earthquakes, and active faults systems.”

But Barendregt says there’s no indication that a major event is brewing in Yellowstone.

“Yellowstone erupts infrequently but when it does, the results are typically catastrophic. There is an enormous ash fall, some of which can still be found in the stratigraphic record in southern Canada and the northern U.S.,” he says.

“One can safely assume that this ash fall severely disrupts plant and animal life for several hundred kilometres around Yellowstone, and does so for several years after the eruption.”

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