【英语时差8,16】断层线（在线收听）

 Scientists say the surface of the Earth is cracked like a giant eggshell. They call the pieces tectonic plates. As many as twenty of them cover the Earth. The plates float about slowly, sometimes crashing into each other, and sometimes moving away from each other. When the plates move, the continents move with them. Tectonic plates can cause earthquakes as they move. Modern instruments show that about ninety percent of all earthquakes take place along a few lines in several places around the Earth. Other earthquakes take place at the edges of continents. Pressure increases as two plates move against each other. When this happens, one plate moves past the other, suddenly causing the Earth's surface to split.One example of this is found in California, on the West Coast of the United States. Scientists say the Pacific plate is moving toward the northwest, while the North American plate is moving more to the southeast. Where these two huge plates come together is called a fault line. A major earthquake in nineteen-ninety-four was centered along one of these smaller fault lines.