Earthquakes occur in California often. This is because California is located on an earthquake fault. Without warning we wake up in the middle of the night because of the sometimes violent, sometimes slow rolling motion of the earth; other times we are driving on the freeway, walking in the mall, or even just watching television when an earthquake occurs. So what are earthquakes? What causes them? Why do earthquakes feel so different from one another?
Earthquakes are the Earth's natural means of releasing tension. When the Earth's plates move against each other, stress is put on the lithosphere. When this stress is great enough, the lithosphere breaks or shifts. As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy that moves through the Earth in the form of waves, which we feel and call an earthquake.
Faults
Faults are surfaces along which rocks have fractured and been displaced. There are three major types of faults: strike-slip, normal, and reverse. The tectonic stresses caused by plate motions build up over time and eventually cause breaks in the crust of the Earth along which the rocks sporadically grind past one another. When this happens, earthquakes occur.
Seismograph: an instrument used to record seismic waves.
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