New study: Charleston overreacting to earthquake threat 

A Watched Pot Never Rattles

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  • Charleston 1886

Seismic concerns have led a debate over Rivers School renovations — with similar issues likely to lead to multi-million dollar repairs at other downtown schools. Building Director Bill Lewis told board members last week that he wanted no part of the Rivers rehab project if it didn't include the seismic upgrades. Fortunately for him, several school board members were reading from the same page of dire predictions.

"We have a responsibility," said Charleston County School Board member Gregg Meyers. "I just hope that the earthquake that is inevitable will hold off long enough for us to do it, or come in the summer."

A recent study from Northwestern University seismologists suggests the worries of the school district and others regarding an imminent earthquake in Charleston may be a good 250 years too soon. It's not that the threat is nonexistent — the region was home to one of the largest historical quakes on the East Coast in 1886, killing 60 people and causing about $6 million in damage.

While standard hazard predictions suggest that the next quake could happen at any time, the new study by seismologist Seth Stein and Northwestern senior James Bebden notes existing data does not account for the relatively short time that's passed since the last quake. They argue that the threat for the next few decades is less than half what federal hazard maps currently predict. Under Stein's model, it will take until about 2300 or later before we're at the threat levels that Charleston is currently designing buildings to withstand.

The traditional way to predict earthquake hazards has been to determine where a quake had happened before and the previous magnitude, and then plot out just how bad the next one will be. Under that model Charleston is just as likely to have an earthquake tomorrow as Reno or St. Louis, where quakes have shaken residents in the last few weeks. But Stein argues that earthquakes are not only dependent on where earthquakes have happened in the past, but also how long it's been since that last one.

"In general, (seismologists) tell you that some places are overdue for an earthquake," Stein says. "Like parts of the San Andreas fault — we're amazed it hasn't happened yet. That implicitly means that we believe the world is building up for an earthquake."

If the stress has to build before the next quake, Charleston (which has an estimated cycle of about 550 years) is far less likely to see an earthquake today than it is hundreds of years from now.

"When we make a seismic hazard map, we take the opposite view," Stein says. "It's treating earthquakes like hurricanes. Three weeks after the first one, you could have another."

State building code standards use these time-independent federal hazard maps to determine how stringent guidelines should be, but Stein argues the existing threat level in Charleston is about 56 percent less than those estimates currently used.

Even if the state requirements were modified, construction on many peninsula buildings would not be affected because of more stringent hurricane protection standards, says Tom Scholtens, chief building codes official for the city.

"Typically, the wind load is greater than the expected seismic loads for our buildings," he says. "The only buildings that would typically see the lateral seismic considerations govern are larger buildings that are taller or oddly shaped, or those more closely located to the north of I-526."

The school district's debate over seismic upgrades at the Rivers School raises the question of whether a building should be upgraded for seismic protection if, according to Stein's model, the structure will likely never face those threats.

Organizers of the Charleston Charter School for Math and Science, which is expected to move in after repairs are complete, had hoped to keep costs at just over $10 million — which the district had already budgeted for. But district officials have come back with at least $17 million in additional electrical, utility, and structural improvements.

Topping that list is more than $4 million in seismic improvements that include reinforcing walls and restraining utility lines and suspended ceilings, as well as installing earthquake joints for the L-shaped building to survive a quake. The district currently has no funding source for the additional work, which could potentially push the completion date for the project out another three years.

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District staff want to make it a priority to upgrade all the district schools at risk for seismic impacts, including Memminger, Buist, and James K. Simmons, with Rivers first because the property will be going through renovations anyway. But Math and Science organizers, who say they've fought opposition from the district for two years now, say the seismic work and the other improvements are the latest — and possibly last — attempt to keep the parent-controlled school out of the district-owned property.

"They've effectively condemned the building," says Park Dougherty, a Math and Science organizer. "It's all a blocking maneuver."

Local building codes would not require the seismic improvements, Dougherty says.

District staff never asked architecture firm Davis and Floyd whether the improvements were required, Lewis says. Instead, they wanted to know what would happen in a major earthquake and the firm found the building would collapse. Even allowing for a lighter earthquake, it still predicted substantial injuries.

Even if local officials wouldn't require the seismic work, Lewis says more stringent state standards for schools negates the argument. He also points to a 1998 paper done by Citadel professor Charles Lindbergh that paints a bleak picture for Charleston schools if an earthquake strikes. The study predicted more than 1,000 fatalities in schools in the Charleston-Berkeley-Dorchester region, with 659 from Charleston schools. And it's hard to argue with those numbers when the same logic that birthed them — those doom- and-gloom hazard maps — continue to apply today.

Considering school buildings are designed with a 50-year shelf life, the existing Rivers building will have long been replaced by the time an earthquake hits, according to Stein's model.

The time-dependent theory has received some traction. The U.S. Geological Survey, which has recently begun developing additional time-dependent models in California, noted last month that these new models "are a reasonable basis for the earthquake-resistant provisions in building codes and long-term mitigation strategies."

But any attempt to replace the existing hazard maps is likely to face heated debate, if not out-and-out opposition.

"If all the newly constructed buildings withstand the (next) event, does that mean we were excessive in our requirements?" Sholtens asks. "Is the test for a success in our codes seeing the building collapse or seeing a building resist the actual forces? If the buildings are expected to endure, a margin of safety must be built into our code requirements to be built into our buildings. It is not prudent to build them just good enough."

Stein agrees that you've got to do better than "good enough," but thinks his time-dependent model should be used to find a new, lower median for Charleston.

"It says that standards people have been calling for are too high," he says. "One should neither overreact to the problem nor ignore it. To me, there's no question that some are overreacting right now."


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