Aftershocks hit Western Montana
HELENA – Eight aftershocks rumbled through southwestern Montana early Tuesday in the wake of an earthquake late Monday measuring a magnitude 5.6 that rattled windows and buildings and damaged highway bridges.
The U.S. Geological Survey said the earthquake and its aftershocks were centered about 13 miles northeast of Dillon, although residents across a wide swath of Montana, Idaho, Washington and other areas reported feeling the main temblor about 10:10 p.m.
Reports came in from as far away as Seattle, 490 miles to the west; and Hardin, 246 miles to the east; Calgary, Alberta, more than 500 miles to the north; and Denver, 841 miles to the south.
Some residents reported two distinct tremors, several seconds apart, lasting about eight to 10 seconds in all.
The aftershocks measured between 2.8 and 3.8 and occurred between 10:30 p.m. Monday and 6:45 a.m. Tuesday, the USGS said.
In Dillon, Beaverhead County Commissioner Mike McGinley said there were scattered reports of broken glass and other minor damage around town. Bricks had fallen off several buildings and chimneys, but the quake’s epicenter was on an old geologic fault line with “no population in the area,” police Chief John Gutcheck said Tuesday.
One man suffered a heart attack at a Dillon motel after the quake and survived. No other injuries were reported.
Charity Watt-Levis, state Transportation Department spokeswoman, said Tuesday the epicenter was just 6 miles east of Interstate 15. Further inspections found cracks in a railroad bridge south of Butte and broken bolts in another I-15 bridge north of Dillon, department director Jim Lynch said. Both lanes of I-15, however, remained open in the area Tuesday afternoon.
“It’s not serious enough to stop traffic, but it is serious enough to have our engineers take a look at it,” Lynch said.
The USGS categorized the earthquake as “moderate.” Initial reports said it occurred about 25 miles underground, but the USGS later said the quake was at a much more shallow depth – only about 3 miles below the surface.
Bud Revious, the deputy response coordinator for the state Disaster and Emergency Services office in Helena, said officials there were busy monitoring the state’s scattered wildfires when the office shook.
“We thought maybe we were having one of those microbursts like we had a couple weeks ago, but we looked around and there was no wind,” he said.
Revious called the quake “heavy” but confirmed state officials had not received any immediate reports of significant damage.
The largest earthquake in Montana’s history struck Hebgen Lake near Yellowstone National Park on Aug. 18, 1959. It registered 7.3, killed 28 people and caused $11 million in damage. The quake caused a massive landslide on the wall of the Madison River Canyon, blocking the river’s flow and forming a new lake.