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Surge Desk

Indiana Earthquake: The New Madrid Seismic Zone Explained

Dec 30, 2010 – 1:11 PM
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David Knowles

David Knowles Writer

As residents of Indiana discovered this morning, the ground beneath their feet is not always so steady.

Registering a somewhat modest 3.8 on the Richter scale, today's quake was centered in the north-central part of Indiana, an area not all that accustomed to seismic activity. While the specific fault has yet to be determined, the area borders the New Madrid Seismic Zone, a large area of interconnecting fault lines that has produced the country's most powerful recorded quakes.

Surge Desk takes a look at the possible seismological culprit.

1. How big is the New Madrid Seismic Zone?
Stretching over 150 miles, the fault zone covers portions of Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi.

2. What is a fault zone doing in the center of the United States?
Geologists believe that approximately 750 million years ago, the New Madrid Seismic Zone was formed when the supercontinent Rodinia began to split apart. While what eventually became known as North America did not eventually split apart in the plate tectonic dance, the faults created by that movement remained, only to be obscured by millions of years' worth of sediment, according to the U.S. Geological Survey.

3. Have there been any major earthquakes in the New Madrid Seismic Zone?
Several. In 1811 and 1812, four separate earthquakes believed to have registered with a magnitude higher than 7.0 rocked places like northeast Arkansas and New Madrid, Mo., destroying homes and uprooting trees. A 6.6 quake in Charleston, Mo., in 1895 caused extensive damage to the town, and a 5.4 temblor in 1968 hit Dale, Ill., according to the U.S. Geological Survey.

4. How active are the faults in the New Madrid Seismic Zone?
Not very. In an average year, the faults have been found to be traveling at an annual speed of 0.2 millimeters. While quakes too small to be felt are continually happening in the fault zone, about one each year rises to a newsworthy magnitude.

5. So should Midwesterners be worried about a major earthquake?
It depends on whom you ask. While seismologists at the USGS tend to agree that there is a strong likelihood of another earthquake along the New Madrid Seismic Zone, predicting when that might occur is a tricky proposition.

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