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Should Memphis Build For California Style Earthquakes?
Washington - May 14, 2003 The federal government is urging Memphis and other parts of the Midwest to adopt a new building code that would make buildings as earthquake resistant as those in southern California, where shaking is much more likely to seriously damage a building. A new study by researchers at Northwestern University, the Reaves Firm in Memphis, and Los Alamos National Laboratory finds that the prescribed measures for the Midwests New Madrid seismic zone (NMSZ) would cost far more than the damage prevented. The New Madrid seismic zone includes parts of Tennessee, Kentucky, Missouri, Arkansas, Illinois, Indiana, and Mississippi. The study, by seismologist Seth Stein of Northwestern, Joseph Tomasello, structural engineer at the Reaves Firm in Memphis, Tennessee, and Andrew Newman, a seismologist at the Los Alamos National Laboratory in New Mexico, appears in the May 13 issue of Eos, published by the American Geophysical Union. "We need to learn more about earthquakes in the Midwest, but we already know that New Madrid and California are very different earthquake problems," said Stein, whose measurements in the NMSZ using the Global Positioning System indicate that the ground is moving very slowly, if at all. "The hazard for New Madrid is significantly less than for California." The question is how to protect Memphis and other areas from earthquakes. Earthquakes in the NMSZ are typically small and more a nuisance than a catastrophe. Still, large (low magnitude 7) earthquakes occurred in 1811 and 1812, and geological records suggest that similar or slightly smaller earthquakes occur about every 500 years. Memphis and many other communities currently have building codes for earthquake-resistant construction. Now, states, counties and municipalities in the NMSZ are considering a much stronger code developed under the direction of the Federal Emergency Management Agency (FEMA). This code, IBC2000, would increase the earthquake resistance of new buildings to levels similar to those in southern California. The code would suggest the need to retrofit existing critical buildings, including schools, hospitals, fire and police stations, and infrastructure such as highways and bridges. "Surprisingly," said Stein, a professor of geological sciences, "the new code has been proposed with almost no consideration of the costs and benefits. We've looked at the numbers and they don't make economic sense." "They're not even close," said Tomasello, who has studied the costs of designing buildings with the new guidelines. "FEMA estimates that, averaged over hundreds of years, Memphis faces about $17 million in earthquake damage per year, which the new code might cut in half. "The problem is that since the Memphis metropolitan area has about $2 billion in construction each year, and the new code would raise costs about 10 percent, we'd be spending about $20 for every one dollar we'd save. "On top of that, we would want to upgrade important existing buildings, costing 25 to 33 percent of the cost of a new building. The economic impact, including reduced new construction, job losses, and reduced housing affordability, is likely to be significant." Buildings in California are much more likely to be shaken seriously during their useful life of about 50 years. "FEMA accepts that; their estimate shows that the risk of earthquake damage in Memphis and St. Louis is about one-fifth to one-tenth of the risk in San Francisco and Los Angeles," said Stein. "Therefore we shouldn't use the same building strategy unless it's justified by careful analysis. If we think this through, we can probably do a lot better." "The bottom line," said Tomasello, "is not to rush into this." Instead, the study recommends that communities carefully consider the costs and benefits of alternative strategies and decide on a level of earthquake-resistant construction that makes political and economic sense. "I think that the proposed code illustrates the old line that every problem has an obvious, simple, solution -- and it's often wrong," said Stein. "Given the large sums at stake, time spent getting this right would be well spent." The article by Seth Stein, Joseph Tomasello, and Andrew Newman, "Should Memphis Build for Californias Earthquakes," appears in Eos, Volume 84, number 19 (13 May 2003), page 177. Related Links Northwestern's study of the New Madrid seismic zone SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express
A Fiery Debate About Volcanoes
Berkeley - May 14, 2003In a Perspective in the May 9 issue of Science, geochemist Don DePaolo and geodynamicist Michael Manga defend a fundamental assumption of Earth science, the mantle plume model of hotspots, against an outbreak of seismic skepticism. |
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