Earthquake study says New Madrid might have fizzled
University of Memphis researchers skeptical of Northwestern's findings
By Tom Charlier, Memphis Commercial Appeal
For all its lethal, concrete-crumbling power, the Haiti earthquake this month was no bigger — and probably a good bit smaller — than the seismic shocks that convulsed the New Madrid fault zone not once or twice, but three times during a ghastly winter nearly 200 years ago.
The magnitude 7.0 Haiti quake, however, occurred at a time of some upheaval over the science and public-policymaking associated with the New Madrid faults — zigzagging fractures in the Earth's crust along the Mississippi River extending to within 35 miles of Memphis.
Researchers led by a Northwestern University scientist have produced a series of studies — the most recent appearing in the journal Nature two months ago — concluding that the New Madrid zone is shutting down as a generator of major quakes. The hundreds of small temblors that still rumble through the region annually, they say, appear to be nothing more than aftershocks from the massive quakes of 1811-12.
The widely published findings are roundly disputed by University of Memphis researchers and many federal scientists. But they have provided ammunition to those opposed to stronger seismic building codes for the area.
The conclusions by Seth Stein, professor of Earth science at Northwestern, are based on Global Positioning System satellite measurements showing that the ground is barely moving — if at all — along the New Madrid faults. Quakes generally occur when the strain, or energy, that has built up as a result of such movement is suddenly released.
By contrast, movement along the fault triggering the Jan. 12 Haiti quake was about 7 millimeters per year — or at least 35 times faster than the maximum 0.2-millimeter rate in New Madrid.
"You could say that the earthquake in Haiti adds credibility to the argument that nothing is happening in New Madrid," said Stein, lead author of the study published in Nature.
Over a two-decade period, measurements of the rate of ground movement in the New Madrid zone show a distinct trend, he said.
"Every year we look, it's smaller. ... It looks like we have a fault that has pretty much shut down."
Along faults that are situated at the edges of continental plates, aftershocks generally occur in the days and weeks following quakes. But in a midcontinent zone such as New Madrid, Stein said, "aftershocks can go on for a couple hundred years."
The conclusions by Stein and co-investigator Mian Lu, professor of geological sciences at the University of Missouri, are controversial.
While acknowledging that Stein's GPS measurements are accurate and important, researchers at the Center for Earthquake Research and Information at the U of M say it's overly simplistic to interpret them as meaning the fault system has shut down.
"It's one piece of data," said Chuck Langston, director of the U of M center.
Despite the lack of movement, the historical record for New Madrid is clear, he said. Every 400-500 years, the fault zone produces huge earthquakes. In addition to the 1811-12 shocks, which were estimated to have magnitudes of up to 7.8, researchers have found geologic evidence of similarly large quakes in the New Madrid zone around the years 1450 and 900 A.D. and as far back as 2350 B.C.
Given the slow pace of geologic changes, Langston questions how a fault zone that produced such powerful quakes only two centuries ago could undergo such a dramatic transformation so quickly.
"It just doesn't work that way," he said. "It takes hundreds of thousands of years for the Earth to do something — either start up or shut off."
In 2006, a panel of experts convened by the U.S. Geological Survey to assess earthquake hazards in the eastern half of the nation evaluated the GPS data on which Stein bases his conclusions. The panel did not find the data to be a "convincing reason" to downgrade the seismic hazard in the New Madrid zone, a USGS report says.
Earthquake-preparedness officials also remain unswayed by Stein's findings.
"Clearly, history has shown we've had large earthquakes, and we continue to have earthquakes, and there's no reason we shouldn't be planning for them," said Jim Wilkinson, executive director of the Central United States Earthquake Consortium.
A 2008 study by the Illinois-based Mid-America Earthquake Center projected the effects that a magnitude 7.7 quake would have on the New Madrid region today. It found that Tennessee would experience the greatest losses, with more than 63,000 people killed or injured, 260,000 others displaced, and economic damages exceeding $56 billion.
Unlike Haiti, where a lack of building codes was a major factor in the catastrophic damage and the estimated 200,000 deaths, Memphis and Shelby County have had seismic construction standards in place for nearly two decades.
However, state auditors last year said the local seismic provisions were outdated. Except for "critical" facilities such as hospitals and police stations, new buildings must meet seismic standards contained in a building code dating back to 1999. As a result, the county soon is expected to adopt newer standards, which could increase construction costs.
Stein, however, questions whether it's worth it, given the new evidence that the New Madrid zone isn't dangerous.
"You ought to look at whether that money could better be spent on schools, the police, hospitals, whatever," he said.
— Tom Charlier: 529-2572
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