A Catastrophic New Madrid Earthquake Scenario
In the winter of 1811 and 1812, three earthquakes with moment magnitudes between 7.5 and 8.0 struck the lower Mississippi Valley over a two-month period. Although few people lived in the region at the time, the effects on the landscape remain clear 200 years later. Studies of the geologic record show that similar sequences of major earthquakes have happened previously, at least twice before about 1450 and 900 AD.
An earthquake with moment magnitude of 7.5 or greater would cause significant structural damage to buildings would occur in at least eight states. Lifelines crossing the region, including highways, bridges, and oil and gas pipelines leading to the northeastern U.S. would be severely damaged, particularly in the Mississippi Valley. If the earthquakes were to occur when the Ohio and Mississippi Rivers were high, loss of levees is likely along with flooding of low-lying communities. The City of Memphis, with over 1 million people in its metropolitan area, would be the most affected urban center. Memphis has an aging infrastructure and many of its large buildings, including unreinforced schools and fire and police stations, are particularly fragile when subjected to severe ground shaking. Very few buildings were built using modern building codes that have some provision for seismic-resistant design.
Landslides occurred along the bluffs from Mississippi to Kentucky in connection with the 1811 and 1812 Mississippi Valley earthquake events. Today a repeat event could be expected to result in a similar scenario for downtown Memphis. At least one highway and one railroad bridge crossing the Mississippi River are unlikely to survive a major New Madrid earthquake and many old overpasses would likely collapse. A significant hazard in the New Madrid region is a type of soil failure called liquefaction, which in1811 and 1812 affected a region from south of Memphis to St. Louis. Liquefaction causes soil to flow and form deep cracks that may make roadways in the Mississippi Valley of Arkansas and Missouri (such as I-55) impassible. The liquefaction can cause flooding of fields and roads with water, sand, and mud, disrupting agriculture for an extended period of time. Liquefaction and failure of levees and riverbanks could make the Mississippi River unnavigable - possibly for many weeks. Although Memphis is likely to be the focus of major damage in the region, St. Louis, Little Rock and many small and medium-sized cities would also sustain damage.
One characteristic of New Madrid earthquakes is particularly important to highlight. In 1811 and 1812 there was a sequence of large earthquakes within a three-month period as opposed to a single large earthquake event. Geologic evidence suggests that such sequences of major earthquakes are characteristic of the region. This means that during recovery efforts, earthquakes as strong as the first shock can be expected to occur following the initial shock and must be considered when deciding where to shelter people and when to start rebuilding.
The USGS estimates that there is about a 10% chance of a major New Madrid earthquake occurring in the next 50 years. Additionally, the occurrence of a moderate-sized earthquake located in close proximity to urban centers like Memphis or St. Louis could be equally devastating locally. The USGS estimates the chances of a magnitude 6.0 or larger earthquake occurring in the New Madrid region in the next 50 years is 25-40%. Results from a recent regional-scale loss estimation study by FEMA suggest immediate losses from just one M7.7 New Madrid earthquake would total between $68 and $77 billion. However, additional studies will be required to assess potential losses from multiple earthquakes and to provide such assessments at scales appropriate for mitigation and response planning within the most vulnerable urban areas.
Society´s actions before natural hazard events will determine the magnitude of the losses. Science can tell us the likely consequences of a repeat New Madrid earthquake sequence. That information can be used to reduce the vulnerability of lifelines, retrofit critical structures, improve monitoring systems, develop scenarios, and educate our citizens.
...Education is the only viable approach to encourage the securing of contents of buildings. Damage to contents caused $12 billion of the $40 billion losses in the 1994 Northridge earthquake that struck southern California.
from http://resourcescommittee.house.gov/transportation/pbed/02-24-06/schweig.pdf - portions cut.
Aired August 8, 2005
DOBBS: There are fears tonight of what could be a major earthquake developing along the Mississippi River. A recent study detected new signs of activity at the so-called New Madrid Zone.
This is one of the most seismically active regions in the country, and certainly east of the Rocky Mountains. Between 1811 and 1812, three catastrophic earthquakes hit that area in a three-month period. The U.S. Geological Survey says a repeat of those earthquakes would cause widespread loss of life and hundreds of billions of dollars in property damage.
Joining me tonight is Eugene Schweig. He's central and eastern U.S. coordinator for the U.S. Geological Survey. It is good to have you with us.
This report in "Nature" magazine has sparked considerable concern. Give us your best assessment as to how concerned we should be about this region. It's about a 150-mile fault line -- a zone, as geologists call it. How concerned should be we be about the imminence of an earthquake there, a major earthquake?
EUGENE SCHWEIG, CENTRAL AND EASTERN U.S. COORDINATOR: Well, I don't think we should be concerned about the imminence of the earthquake. I think that these results really confirm what many of us have been saying for a long time and that is that there are earthquakes that occur in the New Madrid region. And they occur every few hundred years, and they're going to happen again, and we need to keep the region prepared for repeats of those earthquakes.
DOBBS: To keep the region prepared -- and we've got a map up showing basically that zone that runs between basically Memphis up to just south of St. Louis. I mean, that's a huge region, densely populated now as compared to 200 years ago when that -- those severe earthquakes hit. Much needs to be done here, if we're to allow those people to survive anything of the magnitude of those 1811, 1812 earthquakes, aren't we?
SCHWEIG: That's absolutely true. Now, people -- many people are aware of the earthquakes. Certainly since a prediction that happened in 1990 that of course never came true, many people sort of became aware of the possibility of an earthquake. They got their earthquake kits together, emergency supplies. But it's been 15 years now, and many people have forgotten that the earthquake threat exists, but it does.
DOBBS: It does indeed. And for many of us, if you will, who do not live in the nation's heartland, we think of California, certainly the West Coast, as being the most seismically active part of the country, and never once think about the Midwest. It seems solid, rock solid. And yet this is a major seismic area, isn't it?
SCHWEIG: That's right. And certainly, we do have fewer large earthquakes than they do in California, and we don't expect them because we're not on the edge of one of Earth's big tectonic plates. But the fact that this part of the continent is so solid is one of the problems. Earthquake waves travel much more efficiently in this part of the country, so for the same magnitude earthquake here and in California, we would have damage over a much larger area, and people would feel it over a much, much larger area.
DOBBS: What are the estimates -- the article in "Nature," of course, expressed the frequency of a major earthquake that is in excess of 7.5. Give us your best sense of what the likelihood is that a major earthquake will hit that region over the course of the next 50 years, that zone and the surrounding area?
SCHWEIG: Sure. Well, using a combination of the pre-historic record of earthquakes, our understanding of how often earthquakes are happening now, plus these GPS results, everything we can learn about the area, we estimate that there's a 7 to 10 percent chance of a repeat of what happened in 1811 and 1812 happening in the next 50 years and a 25 to 40 percent chance a magnitude six or bigger happening in the next 50 years.
DOBBS: And the extent of damage that would result should six or better occur along that -- the New Madrid Zone?
SCHWEIG: Well, it really depends upon exactly where that earthquake occurs. Now, if it were like 1811 and '12, the entire fault zone would rupture, there would be damage over a very large area. If it were a magnitude six, it depends whether it happened in the southern or the northern part of the fault zone. If it were in the southern part, it would affect St. Louis, Memphis more. If it were in the northern part, it might affect St. Louis and the other -- and many of the rural, small town communities up in southeastern Missouri, southern Illinois.
DOBBS: Right. The fault -- the New Madrid Fault is named after the town that was nearest the epicenter of the 1811, 1812 earthquakes.
SCHWEIG: That's right.
DOBBS: But millions and millions of people in those cities, tremendous cities, have been built along the entire region. Give us your best estimate as -- if we saw a repeat of what happened 200 years ago, give us your sense as to how well prepared we are in terms of earthquake standards, and preparation to respond to the disaster that would follow?
SCHWEIG: Well, in terms of what would happen and how well prepared we are, that's not so much my expertise, but it certainly varies from state to state, from region to region, from city to city.
Right now, there's a patchwork of building codes throughout the area, and so some communities are preparing for the earthquake more than others. But the main point is, even with building codes, improved building codes, we have so many old buildings. I would estimate -- guess that 90 percent of the buildings were built before there were any sort of seismic building codes, at least that many. And so, those old buildings are still standing. And they're still what we're living in and what we're working in.
DOBBS: And Eugene, as we were talking, video there of the Mississippi River, the Mississippi River, which reversed course over a significant stretch of that mighty river as a result of those earthquakes in 1811.
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