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WHAT CAUSES A QUAKE? Earth's crust is very hard, and it is cracked in many places. In fact, it is broken into large pieces called plates. Even the smallest plate is bigger than the whole United States. These plates move very slowly, but constantly. (Most plates are moving about as fast as your fingernails are growing—not very fast!) Some plates are moving apart, and the space between them is being filled by new rock from deep within the Earth. Other plates are slowly jamming together. California's famous San Andreas Fault is the result of the Pacific Plate (which underlies most of the Pacific Ocean) sliding past the North American Plate (which carries North America, Greenland, a piece of northeastern Asia, and the Arctic and northern Atlantic Oceans). Eventually—perhaps over hundreds of years—the stress on the rocks becomes too great, and they break or move suddenly. This results in an earthquake. For more information about Earth's plates and their movement, see Voyager: Earth Like a Puzzle. |
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