Saturday, April 30, 2011

[Geology2] (Tiny) Earthquake (Barely) Rattles Minn.

(Tiny) Earthquake (Barely) Rattles Minn.

April 29, 2011 2:00 PM

Reporting James Schugel

MINNEAPOLIS (WCCO/AP) – A rare earthquake struck western Minnesota early Friday, rattling ceiling tiles and prompting a few curious callers to phone 911 but going largely unnoticed by most of the sleeping public, authorities said.

The quake, which the U.S. Geological Survey said was magnitude-2.5, struck at 2:20 a.m. and was felt mostly in the Alexandria area.

"It was like a big boom, and right when that was happening, the house shook," said Sandy Pederson of Alexandria, Minn.

Sgt. Tom Egan of the Douglas County sheriff's office said staff at the county's 911 center felt it and took 25 to 30 calls from the public, mostly from people who were just curious. By contrast, he said, county dispatchers typically get hundreds of calls during severe thunderstorms.

Callers reported some noise and minor movement, including "ceiling tiles bouncing just a touch," Egan said. But he said nobody reported any damage or anyone hurt. Relatively few people in the largely rural area would have been awake at the time, he said. He said the department was referring callers to the USGS web site for further information.

Minnesota gets a "feelable" earthquake every five to 10 years on average, though that can vary a lot, and more often than not they're in west-central Minnesota, said Val Chandler, a geophysicist with the Minnesota Geological Survey. The last one confirmed felt was in 1994 in Granite Falls, he said. Chandler said one official in Alexandria who felt this quake told him it felt like a bulldozer going by his house for about 15 seconds.

The USGS says the largest earthquake recorded in Minnesota was a magnitude 4.6 quake that caused minor damage to walls and foundations in Stevens County around Morris. But Chandler said the most destructive was in Staples in 1917. Its magnitude was estimated at 4.3, and it knocked over chimneys, shook items off shelves and shattered windows, he said.

"You can have an earthquake just about anywhere but you only have big earthquakes on faults that are active," said Gary Patterson, a geologist at the Center for Earthquake Research and Information at the University of Memphis.

The Alexandria area is not on an active fault, Chandler said. The prevailing theory on such midcontinent earthquakes is that they're linked to stresses in the large North American plate that might occasionally jostle ancient faults into weak activity.

The USGS put the epicenter about three miles west of Alexandria but qualified that with a large, seven-mile degree of uncertainty.

(TM and © Copyright 2011 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2011 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

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