Geotimes - July 2003 - Quake Protection in the Heartland

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Earthquakes
Quake protection in the heartland

In 1996, the U.S. Geological Survey (USGS) released a map detailing earthquake risk throughout the country. It showed that the New Madrid Seismic Zone, which stretches from just west of Memphis, Tenn., to southern Illinois, is just as prone to devastating ground shaking as southern California, even though the zone lies hundreds of miles from any plate boundary.

Four years later, the International Code Council released a new building code, based on the USGS map, suggesting that buildings within the New Madrid zone should meet the same seismic standards as those in California. Tennessee is currently considering adopting the International Building Code (IBC), which provides guidelines for jurisdictions throughout the world that are tailored to local hazards. The Codes Enforcement Section of the Department of Commerce in Tennessee has recommended that the state commissioner adopt the code, and the new standards could be on the books by the beginning of 2004. If they are, Memphis and all other jurisdictions within the state will have a maximum of six years to develop local building codes that meet, or surpass, the requirements laid out in the IBC.

Concord EFS, an electronic service provider, chose to meet strict seismic standards in the International Building Code when they put up a new headquarters in Memphis, Tenn. The box frame at right gives the building extra strength, but came at considerable cost. Photo by Mike Kitchens, Montgomery Martin Construction Co.

Tennessee would be joining three other states within the seismic zone that have already adopted the code: Kentucky, Arkansas and Illinois.

But not everyone thinks the code is a good idea. According to a team of seismologists and engineers reporting in the May 13 Eos, the USGS maps greatly exaggerate the seismic risk in New Madrid and the costs of meeting the strict seismic requirements would far exceed the benefits,

The USGS maps assume that a magnitude-7.5 to 8.0 quake hits the region, on average, once every 500 years. This rate seems unlikely, says lead author Seth Stein, a seismologist at Northwestern University. In contrast to California, where magnitude-6.0 quakes routinely rumble through the countryside, similar quakes rarely rock New Madrid. The last major earthquakes to hit the region occurred during the winter of 1811 to 1812. And GPS measurements indicate that today different parts of the ground across the seismic zone are moving very slowly, if at all, relative to one another, Stein says. He argues it would take thousands of years to build up enough srain to trigger another large quake.

But the paleorecord provides the best evidence for recurrence time, says Art Frankel, a geophysicist at the USGS in Denver and lead developer of the National Seismic Hazard Map. Deposits of liquefied sand from past earthquakes indicate that the USGS maps get the risk right, he says.

Even if the USGS assessment is correct, the costs of IBC’s seismic mitigation still outweigh benefits, says Joseph Tomasello, a co-author on the Eos paper and an engineer with the Reaves Firm, a large consulting and engineering firm in Memphis. He estimates that the new standards would raise the cost of construction by 10 percent or more. They would impact every level of construction, he says, from requiring more cross beams to support floors to sophisticated braces to secure water heaters. In Memphis alone, he says, construction companies would pay roughly an additional $200 million each year to meet the standards. In contrast, the Federal Emergency Management Agency (FEMA) anticipates that the average cost of earthquake damage in the region over the long term will be about $17 million annually.

If IBC standards become mandatory in Tennessee, brick veneers on buildings in high hazard areas will be one of many design features that will not be permitted for new buildings, says Joseph Tomasello, an engineer in Memphis. Photo by Joseph Tomasello, The Reaves Firm.

“Roughly speaking, you would be spending 10 to 20 dollars to save one dollar in damage,” Stein says. Much of that additional cost would go toward structural features aimed at preventing the loss of property, Tomasello says. He argues that building codes should outline the minimum requirements for saving lives during a quake. When it comes to property, he argues, building owners should be allowed to make their own calculations about how much they want to spend to protect against possible losses.

But the International Code Council did design IBC principally to protect lives, says an official from the FEMA, which partially funded the code’s development. IBC ensures that people will survive through the largest earthquake expected to hit the region with a 2 percent probability in 50 years, he says. Designing to that standard necessarily protects against some property loss as well, but that is not the goal.

“There is not a clear line in the sand where on one side is life safety and the other is property protection,” the FEMA official says.

Because the IBC’s goal is to ensure safety, a cost-benefit analysis is not appropriate, he adds: the buildings should meet those standards, irrespective of cost. Al Hancock, assistant director of Codes Enforcement in Tennessee, agrees. His section recommended the code to the state commissioner without having done a formal cost-benefit analysis.

Even if costs are relevant, the Eos article may exaggerate them, Frankel says. He argues that the 10 percent price tag for mitigation is much too high. He estimates those measures would cost only an additional 2 or 3 percent, which significantly tips the scale when weighing the code’s merits and expenses.

Tennessee’s commissioner will soon decide which argument prevails.

Greg Peterson

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