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  3. What Causes Earthquakes? People have tried to explain the cause of earthquakes since earliest times. Some people thought tha

What Causes Earthquakes? People have tried to explain the cause of earthquakes since earliest times. Some people thought tha

admin2011-03-05  94
问题                    What Causes Earthquakes?
    People have tried to explain the cause of earthquakes since earliest times. Some people thought that quakes were sent from heaven to punish the wicked. Others believed that the earth rested on the backs of animals. We now have more scientific explanations of the cause of these destructive earth tremors. Earthquakes are evidence that some process is at work below the surface of the earth. Large bodies of magma may be in motion. These and other internal movements can result in a sudden release of energy by breaking the overlying, brittle rocks. During earthquakes, rocks beneath the surface are clearly bent and broken. In other cases deformation takes place slowly and without recognizable earthquake shocks. For example, in a drill hole in the Great Valley of California, earth movements have been measured for years. The rocks here are moving at a rote of about one meter per century. In some places pressure slowly builds up until the rocks break and quickly snap back into position. The faulting releases energy that may have built up in the rocks for hundreds or thousands of years. This sudden burst of energy causes vibrations that travel through the rocks. These vibrations are an earthquake. Most earthquakes are so small that they can be detected only by sensitive instruments along the fault surface.  However, energy may continue to trickle off in aftershocks. These shocks are much less severe than the main shock and may continue for months after the initial earthquake.
    Summary:
    Scientifically speaking, earthquakes are caused when【71】movements of the earth suddenly release energy by breaking the overlying rocks on the surface. During earthquake, rocks are clearly bent and broken. Elsewhere, rocks may slowly【72】over many years. Then the pressure may increase until the rocks break and snap back. This break【73】the energy in the rocks and causes vibrations. Most earthquakes are so small that they can be barely【74】, but large violent earthquakes can destroy inhabited areas. Sometimes【75】many follow after the first movement.
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本试题收录于： A类竞赛（研究生）题库大学生英语竞赛（NECCS）分类
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