| Humans are forever forgetting that they
can't control nature. Exactly 20 years ago, a magazine cover story announced
that "scientists are on the verge of being able to predict the time, place and
even the size of earthquakes". The people of quake-ruined Kobe learned last week
how wrong that assertion was. None of the methods praised two decades ago have succeeded. Even now, scientists have yet to discover a uniform warning signal that precedes all quakes, let alone any sign that would tell whether the coming quake is mild or killer. Earthquake formation can be triggered by many factors, says Hiroo Kanamori, a seismologist (地震学家) at the California Institute of Technology. So, finding one all-purpose warning sign is impossible. One reason: Quakes start deep in the earth, so scientist can't study them directly. If a quake precursor (预兆) were found, it would still be impossible to warn humans in advance of all dangerous quakes. Places like Japan and California are filled with hundreds, if not thousands, of minor faults. It is impossible to place monitoring instruments on all of them. And these inconspicuous sites can be just as deadly as their better-known cousins like the San Andreas. Both the Kobe and the 1994 Northridge quakes occurred on small faults. Prediction would be less important if scientists could easily build structures to withstand every new quake reveals unexpected weaknesses in "quake-resistant" structure, says Terry Tullis, a geophysical at Brown University. In Kobe, for example, a highway that opened only last year was damaged. In the Northridge earthquake, on the other hand, well-built structures generally did not collapse. But engineers have since found hidden problems in 120 steel-frame buildings that survived. Such structures are supposed to sway with the earth rather than crumple (崩溃). They may have swayed, but the quake also unexpectedly weakened the joints in their steel skeletons. If the shaking had been longer or stronger, the buildings might have collapsed. A recent report in Science adds yet more anxiety about life on the fault lines. Researchers can computer simulations to see how quake-resistant buildings would fare in a moderate-size tremor, taking into account that much of a quake's energy travels in a large "pulse of focused shaking". The results: Both steel-frame buildings and buildings that sit on insulating rubber pads suffered severe damage. More research will help experts design stronger structures and possibly find quake pressures. But it is still a certainty that the next earthquake will prove once again that every fault cannot be monitored and every highway cannot be completely quake-proofed. |