来源：网络 2010-07-22 08:00
When The Earth Quakes（地震时刻）
6. To answer that question we must first understand some things about the earth itself. Forty miles deep in the earth is the edge of the outer crust of the earth, and there it is so hot that instead of hard rock there is material much like the hot lava that a volcano erupts. It is the earth's 40 mile deep crust with which we are concerned when we seek the cause of earthquake. The earth's crust is formed of many different layers of rocks. The layers of rocks are not laid evenly, as a bricklayer would build a wall. Instead, the earth's crust is made of rock layers that are often uneven and not perfectly balanced. Because of the great weight pressing down on them, these layers tend to fold downward at weak spots, and this finally causes an actual break in the crust. When this break occurs, or when the sides of an old break slip, the earth quakes, or shakes, while the crust is settling into a new position.
7. Sometime these faults are very small, and we then feel only little tremor. The tremor may even be so light that only the most delicate machine will record it. Most earthquakes are of this weak kind. Sometimes a break in the earth's crust comes about, which starts such a landslide as the which occurred in Madison Canyon. It then takes not one, but many shakes for the earth to heal the fault and settle. That is why many after-shocks follow a major earthquake. Sometimes these go on for several years.
8. Some Parts of the earth are more likely to have quakes then others. This is usually true of mountainous country, because there the layers of rocks which make up the earth's crust are not at all even. But quakes may often be felt in level country, too, because the waves which come from the center of a quake run often for thousands of miles.
9. It is easy to understand why man is so frightened by an earthquake. People used to think that when there was an earthquake, the ground opened, swallowed great numbers of people, and then closed, leaving no trace of those who perished. We know now this does not happen.
10. What we need to fear most are the after-effects of a bad earthquake: fires, flood, and landslides. Since the Yellowstone earthquake some people have said that they would never go to that area for fear of being caught in a landslide such as occurred after the earthquake. That is foolish. Such a fear would keep us from mountains the rest of our lives. Even though earthquakes happen every day, an occurrence like the Madison River landslide does not happen very often. We can realize gratefully that few of us will suffer because of such disaster. At the same time we can understand the need of being ready to help those who do suffer such trouble.