Americans are accustomed to thinking of earthquakes something that only Californians have to worry about. That's a potentially lethal mistake. In fact, about 90 percent of the nation's population lives in areas considered seismically active. More than 3,500 earthquakes have been recorded east of the Mississippi River since 1700, and a few of them have been pretty scary. In 1886, for example, Charleston, S.C. was caught off guard by a massive quake, variously estimated at between 7.1 and 7.5, that leveled much of the city and killed 60 people.

An offshore quake in 1775 measuring 6.3 on the Richter scale knocked down walls and chimneys in Beantown, but it took another 200 years for the city to start thinking about precautions. Today, Boston is filled with old buildings that would crumble in the event of a significant quake — that is, if the soft fill beneath two-thirds of downtown doesn't liquefy first. To make matters worse, the rocks beneath the surface of New England are cooler in temperature than those beneath California, and would more readily transmit — and even amplify — the force of a quake. A 6.0 in Boston would be far more deadly than a similar quake in California, claiming 360 lives and causing up to $12 billion in property damage.

There's some scientific disagreement today about how big the New Madrid quakes of 1811 and 1812 really were. Did they hit the monstrous 8-plus level, which would have made them stronger than the 1906 San Francisco quake, or were they closer to 7, as a team of university researchers calculated a few years ago? Either way, it didn't matter much in the early 19th Century, when the area was mostly wilderness. Today, in the worst-case scenario, an 8-pointer would wreak havoc over a much more densely populated 5-state area. Particularly at risk is Memphis, Tenn. 35 miles west of the epicenter of a 6.8 quake in 1843. Researchers have warned that a huge quake might cause widespread flooding in the low-lying city and destroy a major bridge, in addition to damaging scores of buildings and endangering oil and natural gas pipelines. A 1990 federal disaster drill projected as many as 2,200 dead and 18,000 injured. Property damage? Perhaps as high as $40 billion.

Manhattan Island is crisscrossed by earthquake faults, and twice in its history — 1737 and 1884 the nation's biggest city has been jolted by relatively mild quakes in the 5.0 range. Whenever the next one strikes, scientists worry that it could be far bigger. Much of Manhattan sits on a deep layer of soft, post-Ice Age sediment over extremely hard rock, a juxtaposition of geological extremes that bodes ominously. A 6.0 quake could shake the city's buildings with nearly the intensity of the 6.8 quake in Kobe. Inexplicably, the city dragged its feet about adding earthquake-mitigating requirements to its building codes until the mid-1990s. The generally well-designed towers in the Manhattan's skyline most likely would survive a 6.0, but the unreinforced masonry townhouses where most residents live might not fare so well. A 1989 study estimated that a quake would cause more than 130 simultaneous blazes, which could put the fire department under severe strain.

In the event of a major earthquake, a city may have a lot more to worry about besides just collapsing buildings. City dwellers depend upon pipelines for water to drink and energy to heat and light their homes. Those buried conduits are vulnerable to the ground waves of a quake's force. In the central U.S., the petroleum pipelines are relatively recent, and able to better withstand quakes; they face more danger from the soil liquefaction and landslides that quakes sometimes trigger. In the East, energy pipelines and water systems are older and made of more brittle materials that pose a much greater risk of failure.