1886: Quake wrecks Charleston

WASHINGTON At 9:51 p.m. on Aug. 31, 1886, a powerful earthquakejolted Charleston, S.C., from the somnolence of a sultry evening andsent residents fleeing into the streets. Eight minutes later, asecond large quake struck the seaport city.

"People immediately began to gather in Charleston's large publicsquare to escape injury from toppling buildings," said Carl A. vonHake of the federal government's National Geophysical Data Center inBoulder, Colo. "Throughout the night, there was great anxiety."

The two quakes have been estimated at magnitude 7.7 on theRichter scale (devised in 1935 by Charles Richter to measure theenergy released by an earthquake). Shock waves from the two quakesreached as far as Boston, Minneapolis, Cuba and Bermuda.

In the light of morning, residents saw the awesome damage naturehad wrought.

At least 60 people lay dead in Charleston; some 50 more died inthe surrounding countryside. Ninety percent of the city's structureswere damaged and 102 were destroyed.

As Charleston discovered a century ago, eastern North America isnot immune to killer quakes.

And though they cannot say when, Earth scientists expect anothersuperquake with far more damaging results somewhere between the RockyMountains and the Atlantic coast.

Large earthquakes east of the Rockies are a different breed thanthose of the West - much less common but potentially far moredestructive. Eastern quakes shake a far wider area than Westerntremors of the same size because their shock waves attenuate, orweaken more slowly in the soil and rock of the East.

Since quakes are less common in the East, far fewer buildingsare designed to take the rolling, shaking and shifting of the grounda large quake produces. This adds to the potential for severe damageand death.

The question is not whether another large quake will strike eastof the Rockies, but when and where. Charleston, experts say, will behit hard again by a quake as strong as that in 1886.

Physical evidence of several prehistoric earthquakes discoveredin recent years and probability studies based on seismic activity ofthe last 90 years suggest large tremors strike the Charleston regionabout every 1,500 to 2,000 years.

"That's a maximum estimate," said geologist Pradeep Talwani ofthe University of South Carolina in Columbia.

Geophysicist David Amick of Ebasco Services Inc., anarchitectural engineering company, has worked on probability ofdamaging quakes at Charleston. "In the period 1986 to 2086, we comeup with an estimate of 6 percent or less" for a major quake, he said.

But the chance of a quake large enough to topple bricks, breakwindows and crack foundations in the next century is 70 percent.

The largest earthquakes in the nation's history struck not SanFrancisco in 1906 (estimated Richter magnitude 8.3), but in theMississippi Valley south of St. Louis almost a century before.

On Dec. 16, 1811, the area around New Madrid, Mo., was hit by atremor estimated at magnitude 8.6. This was followed by quakes of8.4 and 8.7 on Jan. 23, and Feb. 7, 1812. The jolts rang churchbells as far away as Boston, changed the course of the MississippiRiver in places and created new lakes.

Scientists suggest that the next killer quake will come 400 to1,200 years from now.