We've now seen the destruction after the earthquake in Chile, and the utter devastation after the earthquake in Haiti. It is true, says a NASA geophysicist, that a major earthquake can shift the earth's axis by a couple of inches.
Could such earthquakes happen here in the U.S.? They have before and will again. Can we protect against them? Yes.
Some years ago I found myself on a catwalk beneath the San Francisco-Oakland Bay Bridge, wearing jeans, work boots and a body harness.
The 1989 Loma Prieta earthquake had happened years before. Now California was trying to get ahead of the game.
Cuts would be made in the beams supporting the bridge, just beneath the roadway. Sections of steel would be pulled out, and replaced with "isolation bearings" -- flexible joints that sometimes look like gargantuan shock absorbers.
I followed an an engineer, Ray Zelinski, down a narrow ladder. The wind howled. We were tethered to a catwalk. If I missed a step I would be dangling a hundred feet above the water.
I'm not terrible about heights, but this was dicey. Zelinski was fine. He crouched on the catwalk.
"This whole truss will be able to move up to four feet, transversely and longitudinally, on top of these bearings," he said.
It was an ambitious, expensive plan, which quickly got caught in bureaucracy. Before much of the work was done, California decided it needed to replace much of the aging bridge anyhow.
Swaying Instead of Giving Way
But San Francisco's city hall is now on 590 isolators, installed in the hope that if the ground vibrates, the building will more gently sway back and forth above it. The building won't escape damage if The Big One hits, but engineers say it is far less likely to collapse.
These are examples of how structures in earthquake-prone areas can be designed to survive a disaster -- the kind that happened Saturday in Chile.
"This is the ultimate earthquake," said Peter Yanev, a California-based structural engineer. "This is the earthquake that we can learn the most from, both the positive and the negative."
How to Protect Against an Earthquake
The Chilean government got serious about earthquake protection after a disaster in 1985. It imposed some of the kinds of building codes California has.
Engineers say there are some basic ideas that can help protect buildings and the people in them:
It is better for a house to bend than to break. Wooden houses, for instance, tend to fare better than brick.
Tall buildings can be buttressed with diagonal beams, so that they hold together. Poured concrete can be reinforced with steel rods.
Taller buildings do best if they are firmly anchored to their foundations. Shorter buildings may do better on isolation bearings.
Chile's major cities appear to have fared far better than Port-au-Prince did after the earthquake in Haiti on Jan. 12. As seismologists told us afterward, Haiti's cinderblock buildings -- common in an impoverished country -- were the worst kind of construction for an earthquake zone. In many cases they turned to dust.
"Buildings -- designed to withstand gravity -- have to be built to withstand lateral motion," said Art Lerner-Lam of Columbia University's Lamont-Doherty Earth Observatory.
Which is where those isolators come in. They're expensive -- unless a major earthquake hits.
Yanev, the California structural engineer, was packing to go to Chile when we reached him.
"This is the biggest earthquake you can have," he said. "If you can survive this, you can survive anything."