Earthquakes are violent, distractive and unpredictable. The overall history of earthquakes leads to one general rule: The more time that has passed since the earthquake, the bigger the chance one will strike. Scientists therefore use information about past earthquakes to guess probabilities about future earthquakes. For example, they say that within the next 30 years, there is a sixty percent probability that an earthquake will hit somewhere in southern California. But exactly where or when is a mystery. In at least one case, an earthquake in Northern China has been predicted by paying attention to clues from nature. In China, earthquakes-happen study for nearly 4000 years. And there are records of more than 9000 earthquakes going back to the year 1831 BC. The official earthquake records of the state of California only go back to 1930. In their long, hard look at earthquakes, the Chinese have observed many things. Before an earthquake, animals start to act strangely. The ground changed shape, and the earth magnetic field gets stronger in the earthquake area. The water in wells bubbles up and then returns to its normal level. Also a serious of small earthquakes can mean that a big quake is on its way. The Chinese use these clues in 1974 to make the first successful prediction of an earthquake. The United States’ geological survey, on the other hand, has never predicted a major earthquake.
Question 23: What is the general rule about the occurrence of an earthquake?
Question 24: According to the speaker, which area is likely to be hit by an earthquake within the next 30 years?
Question 25: How long have the Chinese studied earthquakes?
Question 26: Which of the following is not a clue that is used by the Chinese to predict an earthquake?
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