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The Earthquake Forecasts the New Progress of Aspect An accidental discovery has brought earthquake scientists one step close

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问题                 The Earthquake Forecasts the New Progress of Aspect
    An accidental discovery has brought earthquake scientists one step closer to being able to predict earthquakes. As part of an effort to measure underground changes caused by shifts in barometric pressure, a team of researchers found that increases in subterranean pressure preceded earthquakes along California’s San Andreas Fault by as much as 10 hours. If follow-up tests advance the findings, earthquake scientists may eventually be able to provide a few hours’ notice for people to find safe haven prior to quakes. "Predicting earthquakes is the final goal for earthquake scientists," says Feng-lin Niu, the research team’s lead author and a Rice University earthquake scientist. "This is a start."
    Reporting in the July 10 edition of the journal Nature, researchers used a high-tech equivalent of a stereo speaker lowered into a bore hole near Parkfield, Calif. , a half-mile deep and five yards from a measuring device. For two months beginning in late 2005, researchers transmitted pulse signals three times per second, from the speaker to the measuring device, calculating travel time between the two stations. Surprised scientists learned the seismic waves slowed dramatically on only two occasions: two hours prior to a magnitude-1 quake, and a startling 10 hours before a magnitude-3 quake.
    The research team theorizes that the immense amount of pressure building along the fault causes small cracks within the rock during the final hours before an earthquake, increasing rock density and slowing the transmission signals. "The more cracks you have, the slower the seismic velocity," says study coauthor Paul Silver, a geophysicist with the Carnegie Institution of Washington. Still unknown is whether there is any significance to the fact that the magnitude-3 quake had a much longer pre-seismic signal than the lower-magnitude quake, or whether it was simply because its magnitude was larger and its center closer to the sensors.
    If scientists can flesh out the new findings during future earthquakes—a two-year study at the same seismically active location begins this September—it could form the basis of a vastly improved early-warning system for quakes. Current earthquake-warning systems give just a few seconds’ notice because they detectonly P-waves, the fast-moving seismic waves that precede the more destructive waves released during a quake. Upgrading to a seismic stress meter, however, is still a long way off. "To use this for earthquake prediction, you need to know the precursor waves have a physical basis (that is, increased pressure and a pending quake) and that it’s repeatable (with a larger sample size of quakes)," Niu says. He also hopes to test whether the stress signals would still be detectable on a larger scale, with the two sensors spaced more than a few yards apart.
    Except a major effort to drill multiple, half-mile-deep bore holes along fault lines, researchers would also need to develop a surface-based detection system capable of filtering out temperature swings, precipitation and other "noise" that could confuse their seismic readings. Says Silver, "we obviously have more work to do, but we’re certainly encouraged because this is what people are looking for."
Which of the following is true according to the last sentence of the third paragraph?
选项 A、The researchers don’t know whether higher-magnitude quakes have longer preseismic signals than lower-magnitude ones.
B、The researchers believes it important that higher-magnitude quakes have longer preseismic signals than lower-magnitude ones.
C、The researchers don’t think it important that higher-magnitude quakes have longer preseismic signals than lower-magnitude ones.
D、The researchers are not sure about the importance of the fact.
答案D
解析 事实细节题。本题考查对第三段最后一句话的理解。文中之意为：研究人员发现了三级地震的震前信号比低震级的地震长得多的事实，但是他们不知道这一发现是否重要，也许只是因为震级更大，而震中和传感器的距离也更近。由此可以判断答案为[D]。研究人员已经知道“震级大的信号比震级小的长”这一事实，[A]错误．[B]和[C]均错误，因为研究人员目前还无法确定这一事实是否重要。
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