Earthquakes are a result of that process. Plate tectonics is the area of science that explains why the surface of the Earth changes and how those changes cause earthquakes.
VOICE ONE:
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. Sometimes the continents are above two plates. The continents split as the plates move.
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VOICE TWO:
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.
These lines follow underwater mountains, where hot liquid rock flows up from deep inside the planet. Sometimes, the melted rock comes out with a great burst of pressure. This forces apart pieces of the Earth's surface in a violent earthquake.
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.
An aerial image of the San Andreas fault from Carrizo Plain in central CaliforniaVOICE ONE:
One example of this is found in California, on the West Coast of the United States. One part of California is on what is known as the Pacific plate. The other part of the state is on what is known as the North American plate.
最新
2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25