Apr 18, 2008 11:14 pm US/Central
Good Question: How Rare Are Minnesota Earthquakes?
(WCCO)
In the "Windy City," it's not normally an earthquake that causes the skyscrapers to sway. But a 5.2 quake centered in Southern Illinois was felt as far away as Milwaukee. And it made us wonder: How often are there earthquakes in Minnesota?
"Not as often as Illinois," said Val Chandler, geophysicist at the Minnesota Geological Survey housed at the University of Minnesota.
Chandler counts 19 earthquakes in the state, dating back to the 1860 quake in Long Prairie. That's estimated at about a 5.0 on the Richter Scale.
"The closest one to the Twin Cities was in Cottage Grove I think, it was a very weak event," he said.
That was on April 24, 1981 and measured a 3.6 on the Richter Scale.
Most of Minnesota's earthquake activity has centered on West-Central Minnesota, including two near Morris, one In 1975, another in 1993. The 1975 quake measured a 4.8, the 1993 quake was a 4.1.
The last quake was February 9, 1994 in Granite Falls. It was a tiny one, measuring a 3.1 on the Richter scale.
"I got a call from the administrator in Willmar, who said the compressors at the ice arena stopped working. He knew that vibrations could cause that, so he asked, 'Could it be an earthquake?'" according to Chandler.
Indeed, it was an earthquake.
Chandler said there are hundreds, maybe thousands of faults in Minnesota. The Douglas Fault runs from the Southwest to the Northeast, just north of the Twin Cities.
"For some reason it appears to be a seismic dud," said Chandler.
Earthquake activity in the Midwest generally happens 3 to 5 feet below ground, according to Chandler.
"I think the prevailing theory is there's a lot of ancient faults, that the very process of building a continent which takes place over millions of years, is very messy," he said.
The exact reason for earthquakes in the Midwest isn't clear, said Chandler, but it may be related from the westward drift of the North American plate away from the center of the United States.
He said there's little chance of a catastrophic earthquake happening in the Midwest.
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