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  3. Most earthquakes occur within the upper 15 miles of the earth’s surface. But earthquakes can and do occur at all depths to about

Most earthquakes occur within the upper 15 miles of the earth’s surface. But earthquakes can and do occur at all depths to about

admin2009-02-10  67
问题      Most earthquakes occur within the upper 15 miles of the earth’s surface. But earthquakes can and do occur at all depths to about 460 miles. Their number decreases as the depth increases. At about 460 miles one earthquake occurs only every few years. Near the surface earthquakes may mn as high as 100 in a month, but the yearly average does not vary much. In comparison with the total number of earthquakes each year, the number of disastrous earthquakes is very small.
     The extent of the disaster in an earthquake depends on many factors. If you carefully build a toy house with an erect set, it will still stand no matter how much you shake the table. But if you build a toy house with a pack of cards, a slight shake of the table will make it fall. An earthquake in Agadir, Morocco, was not strong enough to be recorded on distant instruments, but it completely destroyed the city. Many stronger earthquakes have done comparatively little damage. If a building is well constructed and built on solid ground, it will resist an earthquake. Most deaths in earthquakes have been due to faulty building construction or poor building sites. A third and very serious factor is panic. When people rush out in- to narrow streets, more deaths will result.
     The United Nations has played an important part in reducing the damage done by earthquakes. It has sent a team of experts to all countries known to be affected by earthquakes. Working with local geologists and engineers, the experts have studied the nature of the ground and the type of most practical building code for the local area. If followed, these suggestions will make disastrous earthquakes almost a thing of the past.
     There is one type of earthquake disaster that little can be done about. This is the disaster caused by seismic sea waves, or tsunamis. (These are often called tidal waves, but the name is incorrect. They have nothing to do with tides. )
     In certain areas, earthquakes take place beneath the sea. These submarine earthquakes sometimes give rise to seismic sea waves. The waves are not noticeable out at sea because of their long wave length. But when they roll into harbors, they pile up into walls of water 6 to 60 feet high. The Japanese call them" tsunamis", meaning "harbor waves", because they reach a sizable height only in harbors.
    Tsunamis travel fairly slowly, at speeds up to 500 miles an hour. An adequate warning system is in use to warn all shores likely to be reached by the waves.
    But this only enables people to leave the threatened shores for higher ground.
    There is no way to stop the oncoming wave.
The destruction of Agadir is an example of ______.
选项 A、faulty building construction
B、an earthquake’s strength
C、widespread panic in earthquakes
D、ineffective instruments
答案A
解析 文章第二段首先举例说明运用不同的建筑方法和材料所修建的房屋的抗震能力是不同的，进而就提到了发生在摩洛哥Agadir的地震虽然震级不大，却摧毁了整个城市，而许多更强烈的地震所造成的损失却很小，由此作者得出结论：如果建筑物修建得好并且建在坚固的地面上，那么它就能抵御地震；地震中大多数的死亡是由于不良的建筑结构或不当的建筑地点造成的。由此可知作者引用摩洛哥的Agadir的毁灭主要是要说明不良的建筑结构(faulty building construction)，故选项A为正确答案。
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