What we don’t know about liquefaction could hurt us

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On August 19, 2008

In one corner of a huge civil engineering
laboratory on campus, Dr. Ronaldo Luna watches a machine shake silt from the
Mississippi River until it
liquefies.         

“This is what would happen during a major
earthquake along the Mississippi River,” says Luna, an associate professor of
civil, architectural and environmental engineering at Missouri University of
Science and
Technology.         

Researchers don’t fully understand the
liquefaction process for silts (they have a better understanding of how it
works with sands), but Luna is confident, based on his tests, that a 6.5
magnitude earthquake or bigger would cause solid surfaces along the banks of
the Mississippi River to turn, momentarily, into
liquid.         

This would be very bad. For instance,
liquefaction of river silts would cause bridges to fail in St. Louis during a
big
earthquake.         

Last spring, Luna presented a paper,
“Liquefaction Behavior of Mississippi River Silts,” at the Geotechnical
Earthquake Engineering and Soil Dynamics Conference in Sacramento, Calif. The
conference is only held once every 10
years.        

“We are providing data points to what is
already known about liquefaction in other areas,” Luna
says.         

Researchers and scientists have had plenty of
chances to study what happens during and immediately after a major earthquake
in well-shook places like California. But the last really big quakes in the
Midwest occurred in
1812.        

We do know that, due to differences in
geography, major quakes in the Midwest are felt over a greater area than
similar-sized quakes in
California.         

According to Luna, river silts in the New
Madrid region are similar to those in earthquake-prone areas of China and
India.
                       

Last May, a devastating 7.9 earthquake caused
extensive damage throughout the Sichuan province in the interior of
China.

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On August 19, 2008. Posted in Research