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Earth Sense: Quakes a rare threat in our part of the world

POSTED: February 16, 2014 12:05 a.m.

The earthquake occurring 17 miles outside of Chamberlain, S.D.. on Feb. 7 didn’t receive major news coverage. At 2.9 on the magnitude scale, it wasn’t anywhere near the level of quakes that have destroyed entire cities in the past.

In 2010, Chile lost hundreds of lives in an 8.8 earthquake near the town of Concepcion. This was dwarfed by the January 2010 quake in Haiti, which killed 200,000 people, shaking the city of Port-Au-Prince with 7.0 magnitude.

The Chamberlain quake scared a few residents, but tremors of magnitude 3 or below don’t destroy buildings, and most people don’t even feel them. Earthquakes east of the Rocky Mountains are quite rare because our part of the continent is located on a very solid portion of its tectonic plate.

The globe experiences several quakes each day. A government map (earthquake.usgs.gov/earthquakes/map/) showing the most recent ones confirms that there is a pattern. Where the building blocks of the solid earth, the tectonic plates, touch each other, trouble is likely. This puts the high-risk spots nearest to us into the Caribbean, particularly the island of Hispaniola which is home to Haiti and the Dominican Republic.

Elsewhere in the U.S., quakes are likely on a line from Baja, Mexico through California and northward all the way to Alaska. Longtime residents of Anchorage remember the catastrophic quake of 1964 which had buildings collapse into trenches and ships keeling over in the harbor. The Southeastern U.S. is located near the center of the American Plate, making Georgia a very safe place as far as earthquakes are concerned.

The Richter scale, which indicates magnitude, is sometimes misunderstood. An event registering “6” isn’t twice as powerful as a “3.” It’s 1,000 times that. Every unit increase on the Richter scale means a tenfold rise in destructive power. The world’s so-called “great earthquakes” start at 7. Theoretically, the scale is unlimited at the top, but the strongest ever measured occurred in Chile (1960) with 9.5 magnitude.

By themselves, earthquakes don’t kill. It’s the buildings that do. Catastrophic events happen where a strong quake finds poorly constructed apartment buildings, often between 6 and 9 stories tall. Subdivisions built on soft ground, like San Francisco’s Marina District, are also at risk.

For people living near the centers of tectonic plates, though, like South Dakota or Georgia, an occasional tremor in the 2 to 3 range isn’t anything to lose sleep over.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.


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