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Various efforts have been made over the centuries to predict earthquakes, including noting lights in the sky and abnormal animal behavior. More scientific methods, such as studying periods between earthquakes, have met with mixed success.

Another approach is to track physical and chemical changes above and below ground, including small movements, that might herald impending quakes. In one long-term study, geologists and seismologists in the early 1980s began using seismographs, creep meters, strain meters, and other devices to measure ground motion at a segment of the San Andreas Fault near Parkfield, California, about halfway between San Francisco and Los Angeles. A major earthquake predicted to occur before 1993, based on these observations, did not materialize. But data from Parkfield and other studies are used to study probabilities.

Since earthquakes will happen whether they’re predicted or not, communities in many earthquake-prone areas such as southern California have upgraded building codes to make their structures less susceptible to damage. Japan has invested heavily in earthquake-proofing buildings in such areas as downtown Tokyo, hoping to save lives and property when the next big one comes calling.

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Seismology—the scientific study of all aspects of earthquakes—has provided answers to many age-old questions about earthquakes, such as why and how they occur.

Although California is commonly thought of as the most active quake area in the United States, Alaska is the state with the most major earthquakes.

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