Earthquake study says New Madrid might have fizzled

University of Memphis researchers skeptical of Northwestern's findings

By Tom Charlier, Memphis Commercial Appeal
January 24, 2010

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

Your Jan. 27 editorial on earthquake preparedness was a tribute to The Commercial Appeal and to the governments of Memphis and Shelby County.

There is no higher function of government than to prepare for extreme events that threaten the health and well-being of the public. All one has to look at to realize this truth is the appalling human disaster in Haiti.

But the editorial was wrong on one issue. There is scientific consensus on the hazards of large earthquakes in the New Madrid Seismic Zone.

I know what the Northwestern University researchers say. But that's just the way science works. You get 10 scientists in the same room to talk about the same thing and you'll likely hear 10 different stories.

Why? Because we are trying to figure out something that is outside of our experience and our knowledge. Taking opposite viewpoints is very effective in examining a problem from as many angles as possible.

The best science occurs in that dark place of ignorance. We are trying to figure out something that is not known, building on the cumulative knowledge of our predecessors and the experience of our peers.

Scientists are an eclectic and contentious lot, but we have our ways of coming to a consensus. Such a consensus has been in place regarding earthquake hazards in the New Madrid Seismic Zone for many years.

The U.S. Geological Survey is the national authority for disseminating accurate information about earthquakes worldwide and for determining earthquake hazards within the United States. The USGS facilitates the process of evaluating the hazards of large earthquakes in any one region, such as the central United States.

This process involves hundreds of scientists from academia, other government agencies and industry. We meet, discuss results, formulate hypotheses, argue and ultimately, within focused workshops, come up with a set of facts that become the basis for deciding on the potential of damaging earthquakes occurring in a region.

This process is ongoing as more data are collected. Earthquake hazards in the New Madrid Seismic Zone have most recently been evaluated in 2006 when a group of geologists, geodesists and seismologists reviewed exciting new results that had been obtained over the previous 10 years.

Here are the facts. Geologists have found evidence of repeated large and destructive earthquakes in the New Madrid Seismic Zone over the past 4,500 years, with an average time interval between clusters of large events of about 500 years.

The New Madrid Seismic Zone and surrounding regions within a 200-mile radius experience some 200 small earthquakes each year that are registered and located by seismologists at the Center for Earthquake Research and Information at the University of Memphis. Historical accounts tell us that there were at least three large earthquakes in the winter of 1811-1812 that destroyed early European and Native American settlements, caused massive disruption of the Mississippi River channel, and produced shaking felt as far away as the East Coast.

The one piece of data that seems to be at odds with this view of an active and dangerous seismic zone comes from precise GPS measurements that show little, if any, active deformation of the crust. But what is the meaning of this data?

In California and in Haiti, earthquakes are a byproduct of motion between two major plates of the Earth that are moving in opposite directions. This deformation can be measured accurately using GPS, allowing geoscientists to come up with a number of good guesses on how earthquakes occur on faults between the plates.

We have even made some progress in making long-term forecasts for earthquakes at plate boundaries.

But the central United States and New Madrid Seismic Zone are nowhere near a plate boundary. We do not expect to see widespread crustal deformation in the GPS signal, and very little deformation is exactly what is seen. It is not likely that our understanding of earthquakes at plate boundaries will be very effective in understanding why earthquakes occur here.

The conclusion? Saying that earthquakes will suddenly stop in an area that has had numerous large earthquakes in the past is an extraordinary claim. Extraordinary claims need extraordinary evidence. We simply do not have the deep understanding necessary to make a prediction like this.

This is not just my opinion; it is the scientific consensus on earthquake hazards in the New Madrid Seismic Zone. As scientists, we will play with all sorts of ideas trying to understand why earthquakes occur. However, as responsible citizens, we need to rely on the consensus process to give the public our best estimate of hazard. The consensus exists.

It is there for government officials, emergency planners and the public to use. Please don't mistake ongoing scientific debate as lack of consensus.

Charles A. Langston is director of the Center for Earthquake Research and Information at the University of Memphis. 2/5/10  Memphis Commercial Appeal