An earthquake happens when two plates rub (碰撞) together. The earth plates travel in different directions and at different speeds. If one plate is slowly forced underneath the other, pressure builds up until the plates break apart. This process causes the ground to move. It is an earthquake. In other words, earth-quakes are the shaking of the earth’s surface caused by the earth’s rocky outer layer as a result of the energy stored within the earth. The strain within the rocks is suddenly released (释放). The damage an earthquake causes depends on where it is and the time it is happening. If an unpopulated region is struck, there will be low loss of life or property. If it hits a large city, there may be many in-juries and much destruction. Many of the areas at risk are largely populated now. Major earthquakes hitting those areas today could produce terrible damage. Actually, there are several million small earth-quakes every year. Large earthquakes such as the 1964 Alaskan quake that measured 9.2 on the Richter scale, cause millions of dollars in damage. In the last 500 years, millions of people have been killed by earth-quakes around the world — including 240,000 in the 1976 Tangshan earthquake in China. A 60-second or less earthquake can cause devastation that continues for years after the first tremor (小震). In 1972, a series of severe earthquakes struck Managua, Nicaragua. Fifteen years later, the city still looked the way it had a week after the earthquake hit, because the country did not have the necessary money to rebuild it. The shaking of the earth is sometimes not the greatest disaster. It is in the ensuing fires and floods that often the greatest damage occurs. In the 1906 earthquake, it was the fires caused after it that did the majority of the damage. An earthquake can also destroy dams high above a city or valleys, causing floods to sweep down and sweep away everything in their path. 小题1:Which of the following is the main idea of the first paragraph?
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