Monday, Nov. 02, 2009

Its Earthquake Awareness Week

Today: Earthquake drills for schools, 6:30 p.m., College of Charleston, Room 344, Science Building, 58 Coming St.

Wednesday: Earthquake safety drill, public schools throughout South Carolina.

Wednesday: The 1886 earthquake near Summerville, historical impacts and how an earthquake might affect the area today. 6:30-8:30 p.m. Summerville library, 76 Trolley Road, Summerville.

Saturday: Earthquake and geology interactive displays and talks, 10:30 a.m.-4:30 p.m. State Museum, 301 Gervais St., Columbia.

Sponsored by South Carolina Earthquake Education and Preparedness and the S.C. Emergency Management Division.

Big risks from 'moderate' quakes?

What if the big one hits again - that's how talk goes about the possibility of an earthquake in the Lowcountry. The earthquake of 1886 keeps rumbling through people's fears.

But the more immediate danger in South Carolina might be a smaller quake, a "moderate" 5 magnitude on the Richter scale. That's the kind often seen in California, where people feel the ground rolling beneath their feet but there's not usually much damage.

In the Charleston area, it would be a different story - potentially billions of dollars' damage, injuries and a few deaths. That's the conclusion of recent computer model studies at the College of Charleston. Even more alarming, the damage estimates are for Charleston County alone, where the study was confined. But one of the studies looked at the damage from a moderate earthquake near Summerville, where the 1886 quake struck.

"It might be worse than what you would expect," said Norm Levine, a College of Charleston associate geology professor who works with the college's S.C. Earthquake Education and Preparedness Program, who led the studies with students. "Something normally considered moderate could do damage. We really do have an issue here. Let's see what we can do to protect against it."

The difference would be the ground itself. The soil and subsurface beneath the buildings, roads, bridges and other structures in the Charleston area is, essentially, softer. There are fewer fault lines than in California, where the faults act like shock absorbers. So, temblors here travel farther.

The 7.3 magnitude earthquake that occurred in 1886 killed 100 people and destroyed or damaged most of the buildings in Charleston and Summerville.

The seismic history of the 1886 quake indicates that it erupts on the average every 500 years. But moderate quakes can and do occur here, and not so rarely.

Two 3.6 temblors and one 3.2 temblor have rattled Summerville since December 2008. As recently as 2002, a 4.4 magnitude quake erupted in the ocean off Kiawah Island. Summerville had two 4.1 quakes in the 1990s. They didn't do much more than rattle nerves. But a 5 magnitude quake would be 10 times stronger, and some 800 of them occur across the globe every year.

Moderate quakes are a great concern to emergency managers, said Cathy Haynes, Charleston County Emergency Preparedness director. "The biggest thing in my mind would be the uncertainty. With the big one, we're going to know the building is falling down. In a moderate quake we may not know. The damage might not be visible to the naked eye - buildings, bridges, any infrastructure."

One study looked at the impact of a 5.3 quake in the same spot as the 1886 quake, under the Ashley River near Middleton Place. The other study looked at the impact of a 5.5 magnitude quake in the same spot 17 miles offshore as the 4.4 quake in 2002.

The 5.3 magnitude quake could be expected to cause nearly $9 billion in damage and economic losses in Charleston County alone, the models estimated.

One in every six buildings would have moderate damage and 5,000 people would be homeless. The 5.5 magnitude quake could be expected to cause $4 billion in damage and losses.

Most of the damage and losses in both scenarios would be to transportation, utilities and the ports. But structures on marshy ground also are very vulnerable; that could include the city's hospitals, built on fill areas.

The quakes "would not be breaking down overpasses and stopping the bridges," Levine said. But they could crack the supports for the approaches to either.

"There would be isolated areas or isolated islands where people might not be able to be reached so easily."

Most of the damage from an offshore quake would be confined to areas east of or near U.S. 17. Kiawah Island and Folly Beach would see much more damage than Mount Pleasant. But oddly enough, with either quake "there would be a few casualties, but nothing major in terms of fatalities," Levine said.

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