May 13, 2003
Should Midwest Build for California Earthquakes?
EVANSTON, Ill. --- 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
than in the New Madrid seismic zone.
A new study by Northwestern University seismologist Seth Stein
and colleagues, however, finds that the prescribed measures for
the New Madrid seismic zone (NMSZ) would cost far more than the
damage prevented.
The
study, by Stein, Joseph Tomasello, structural engineer at the
Reaves Firm in Memphis, Tenn., and Andrew Newman, a seismologist
at the Los Alamos National Laboratory in New Mexico, is published
in the May 13 issue of Eos, the weekly newspaper of 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
in the New Madrid seismic zone, which includes parts of Tennessee,
Kentucky, Missouri, Arkansas, Illinois, Indiana and Mississippi.
Typical earthquakes in the NMSZ are small and more of a nuisance
than a catastrophe. Large (low magnitude 7) earthquakes occurred
in 1811 and 1812, however, and geological records suggest that
similar or somewhat 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, 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 issue, the study argues, is deciding between alternative
uses of resources. Funds spent strengthening school buildings may
not be available to hire teachers; upgrading hospitals may result
in covering fewer uninsured patients; and building stronger bridges
may result in hiring fewer police officers and fire fighters. A
similar argument applies to saving lives. The proposed code might
over time save a few lives per year, whereas the same sums invested
in public health or safety measures, such as flu shots, defibrillators
and highway upgrades, could save many more.
Conceptually, the issues are essentially those faced in daily
life. For example, a home security system costing $200 per year
makes sense if one anticipates losing $1,000 in property to a burglary
about every five years (a loss of $200 a year), but not if this
loss is likely only once every 50 years (a loss of $20 a year).
“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.” |