How to Live Dangerously

  • A textbook on the essential lessons of the Kobe earthquake and the one that struck the Northridge section of Los Angeles on the same date a year earlier would read something like this:

    Earthquakes are unpredictable. They almost invariably strike not only at times but at places nobody expects, and no one quake is exactly like any other.

    Designing or, worse, retrofitting buildings to withstand the tremors is extremely expensive. Nonetheless, recent efforts have been in some ways a heartening success--and in other ways a shocking failure.

    Some of the most potentially effective precautions are relatively cheap and easy, and people could take many on their own. But they don't, or won't.

    If those maxims sound obvious, contradictory, or both, well, the facts about earthquakes are too. Upheavals of the earth have stunned humans and ravaged their works since prehistoric times: some scholars believe the ancient Minoan civilization and the biblical cities of Sodom and Gomorrah were wiped out by quakes. Nonetheless, the tremors have never ceased to spring surprises on those who study them and try to cope with them.

    Twenty years ago, that seemed to be changing. Breakthroughs in scientific understanding of plate tectonics--the incessant shifting of continent-size hunks of the earth's crust--spurred hope that major upheavals could be predicted. In Japan polls showed that 50% or more of the public thought they could be. Tokyo even established an Earthquake Assessment Committee of six eminent seismologists to advise the Prime Minister when he ought to issue a public earthquake warning. But in 17 years no such warning has ever been issued, and many experts think the $100 million a year Japan devotes to trying to predict earthquakes could be better spent on something else, like improving coordination among disaster-relief agencies to handle a crisis when it occurs.

    Earthquakes, it turns out, have a lot in common with tornadoes: they are capricious beasts ruled by what physicists refer to as nonlinear dynamics, which means precise forecasting of when and where they will occur is impossible. In theory, major earthquakes should be preceded by smaller shocks. They are, but the earliest foreshocks may be so weak as to be hard to distinguish from background seismic ``noise." And for every small tremor that is followed by a big quake, others may not be followed by anything much.

    In Japan, at least, scientists may also have been looking and listening in the wrong places. Japanese seismologists understandably have positioned underground sensors to pick up rumblings along the notorious faults that run under the Pacific off Japan; they are believed to be the source of the devastating 1923 temblor that killed 143,000 people in Tokyo and Yokohama. American scientists have kept a close watch on the San Andreas fault that runs for 650 miles through California from north of San Francisco nearly to the Mexican border. But the Kobe and Northridge quakes occurred not along these major inter-plate faults--cracks where continent-size plates grind against one another--but on intra-plate faults that spiderweb a single giant plate.

    The intervals between eruptions along the big faults are measured in centuries, whereas the secondary cracks ``may only slip in a big earthquake every 1,000 to 5,000 years," notes seismologist Wayne Thatcher of the U.S. Geological Survey. ``Yet there are so damn many of them that they pose a seismic hazard equivalent to the Big One we've all been so focused on." Seismologists also point out that quakes could endanger places where citizens have rarely thought about them: Seattle, for instance, which sits close to a fault under the Pacific that seismologists now conclude has triggered major quakes in the past.

    The destructive behavior of each quake is subject to countless variables: the direction of fracturing, the composition of underlying soils, whether the motion occurs close to the surface (as in Kobe) or deeper underground (Northridge), even the time of day or night. The severity of a quake as gauged by energy released is also no measure of its destructiveness. A small quake in the center of a city can kill 1,000 people for every life lost to a monster tremor in a thinly populated place--like the death toll if any (there doesn't seem to be an exact count) in New Madrid, Missouri, in 1811-12, when it was rocked by one of the most severe series of earthquakes ever to strike the U.S. The Kobe quake was only slightly bigger than the Northridge tremor but more disastrous in part because its full force appeared to hit densely populated parts of the city. The 6.7 Northridge quake slammed 80% of its kinetic energy into the sparsely populated Santa Susana mountains rather than the buildings of downtown Los Angeles.

    Given all these vagaries, how can cities plan to withstand earthquakes? One cardinal rule probably ought to be, Do not build on filled land. Such areas are subject to a phenomenon called liquefaction. Quake vibrations rupture the surface, allowing water-saturated soil to rise up and turn what seemed to be solid ground into something like a quaking bowl of Jell-O. In both Kobe and the Marina district of San Francisco, site of the worst damage from the 1989 Loma Prieta quake, liquefaction proved disastrous; the same could happen in the Oakland area across San Francisco Bay. Warns Ross Stein, Geological Survey physicist in Menlo Park, California: ``Kobe is almost a dress rehearsal for an earthquake on the Hayward fault in the East Bay."

    Progress has been made in designing earthquake-resistant--but not earthquake-proof--buildings. U.S. building codes are written to save lives, not prevent all damage. Modern structures are designed to sway and maybe even crack in a quake, but not to break apart and crush their inhabitants under falling debris. Says Bill Iwan, director of the earthquake engineering research laboratory at Caltech: ``With buildings, if you walk out after a quake, the designers did their job."

    Skyscrapers built to sway with a buckling earth and low-rise buildings that sit on rubber pads that act like shock absorbers, a common feature of hospital design, have proved their worth. In Kobe it appears that few, if any, buildings constructed after 1980, when a stricter code was enacted, were destroyed. And the widespread wreckage of wooden houses in Kobe is no clue to what might happen elsewhere; wooden houses in Northridge, built to a very different pattern, stood up well.

    Scientists believe the tectonic system beneath Los Angeles is fully capable of producing tremors up to a magnitude of 7.5, or about 15 times the energy of the 20-second Northridge quake. What would happen if that pulse roared for 40 or 50 seconds--higher-magnitude quakes typically shudder for 60 seconds or more--through the Elysian Park fault under downtown Los Angeles? ``The only way to get a full picture of how buildings react in an earthquake is to have one," says Thomas Heaton, a Geological Survey seismologist. But computer simulations undertaken by Heaton and collaborators show that steel- frame high-rises could have their feet kicked out from under them, and low buildings sitting on spongy pads could be smashed against their concrete foundation walls.

    A year later, hidden damage is turning up in many steel-frame buildings that appeared to withstand the Northridge quake. Of 300 buildings inspected, reports Karl Deppe, an assistant chief with the Los Angeles department of building and planning, 100 sustained dangerous cracks, mostly in the welds at building joints, and the other 200 are ``suspicious." Many are office buildings in which people are still working, blissfully unaware of any damage. ``Repair has to be done," says Deppe. But the potential cost is enormous: anywhere from $750,000 to $2.4 million just to inspect the 500 to 600 joints in a single 20-story building, plus $15,000 to $22,000 to repair even one damaged joint.

    Engineers and local politicians are arguing whether the joints should merely be restored to their prequake state or upgraded, whether such upgrading is even possible and, if it is, what is the best method. Similar debate swirls around how to revise building codes to do better in new construction and, even more important, how to retrofit older buildings--and who will pay the bill. Says Iwan of Caltech: ``The really difficult issue is what to do with the existing stock of less-safe, potentially hazardous structures. They're already built and paid for, there is probably a different owner, and now you've discovered there's a flaw. Who is responsible, the owner or the original builders?"

    In Los Angeles there is only one rather minor incentive to retrofit: low-cost city loans to repair unreinforced masonry. San Francisco, says Iwan, more than five years after the Loma Prieta quake, is ``having a great deal of difficulty implementing anywhere near the kinds of retrofit regulations and laws that Southern California has," even though ``there are some very hazardous buildings there," many concentrated around Chinatown. In an era of government cutbacks, neither the state nor Washington seems likely to foot the bill. Insurance companies are not much help either. After picking up about half of the $20 billion losses from Northridge, most have stopped selling quake insurance.

    Much of the property damage from earthquakes, however, and not a small number of injuries, result not from cracking buildings but from heavy objects flying around and slamming into human flesh. Homeowners can be far more earthquake savvy, securing furniture, TV sets, bookcases and especially water heaters to the walls. Fires in the wake of an earthquake often do more damage than the quake itself, and many a fire has been caused by a top-heavy water heater keeling over, ripping a gas line out of a cellar wall and breaking it in the process. There is little evidence that people are taking these simple precautions, however. Few of those living around major faults really believe an earthquake is likely to strike until it actually does--and then, of course, it is too late.