1811-12 New Madrid earthquake strengths questioned in new research

Thursday, April 14, 2011 | 5:25 p.m. CDT

MEMPHIS, Tenn. — Previous estimates of the strength of the 1811-12 New Madrid earthquakes in northeast Arkansas and southeast Missouri were too high, some earthquake experts say.

A paper to be presented at the annual meeting of the Seismological Society of America under way in Memphis argues that the quakes during the winter of 1811-12 weren't nearly as powerful as previous estimates of magnitude 7.7 or greater.

According to The Commercial Appeal newspaper, the paper by Susan E. Hough — a research seismologist with the U.S. Geological Survey — says new reviews by independent experts put the magnitude of the three main earthquakes between Dec. 16, 1811, and Feb. 7, 1812, at a maximum of about 7.0.

Hough said in an interview that historical accounts of the quakes' effects in St. Louis, the only major city of the region at the time, "weren't that bad."

University of Memphis seismologist Chris Cramer said accurate estimates of the power of those quakes could help predict how buildings will hold up in any new major quake in the area.

Seismologists have said in recent years that another major earthquake in the New Madrid Seismic Zone — named for the small southeast Missouri town along the Mississippi River that was near the quakes' epicenters — could occur any time, putting at risk an area where millions of people now live. Millions of dollars have been spent to upgrade the earthquake resistance of several bridges across the Mississippi River between Arkansas and Memphis.

The 1811-12 quakes were felt across a huge part of the nation. According to accounts at the time, some sections of the Mississippi River appeared to run backward for a short time, intense shaking awoke residents of Pittsburgh, Pa., and Norfolk, Va., church bells were rung by the shaking as far away as Boston and sidewalks were cracked and broken in Washington, D.C.

The Seismological Society holds its annual meeting in different locations and chose Memphis this year largely because of the upcoming bicentennial of the New Madrid quakes. In the wake of a series of major earthquakes around the world in recent months — notably Japan, New Zealand, Chile and Haiti — this year's meeting has attracted seismologists from around the world.

Thomas L. Holzer, an engineering geologist with the USGS, said that, although the New Madrid events might seem distant, the Japan quake highlights the importance of learning about previous seismic activity. He said Japanese experts "basically underestimated" the potential magnitude of temblors in the area where a 9.0 magnitude quake struck March 11.

A paper presented at the meeting Wednesday by seismologist Mary Lou Zoback estimated that a magnitude 6.4 to 6.9 quake near Memphis could cause up to $130 billion in damage to private property and businesses, while losses from a 7.7-magnitude event could surpass $250 billion. Zoback, a former USGS research scientist, is vice president of earthquake-risk applications at Risk Management Solutions.

She estimated that at least 65 percent of the damage from such a quake would be covered by insurance.

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Ellis Smith April 14, 2011 | 6:48 p.m.

What the magnitude of the 1811-1812 New Madrid earthquakes may have been is academically interesting, but what will be far more "interesting" will be the magnitude of any future earthquakes, should such occur. We do not live in the past (or at least many of us do not).

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