These faults are frequently the sites of major earthquakes as the tectonic plates that cover the surface of the Earth shift. Pictured above is San Andreas Fault in California , one of the longest and most active faults . Visible as the linear feature to the right of the mountains, San Andreas Fault reaches 15 kilometers deep and is about 20 million years old. Along San Andreas Fault , the titanic Pacific Plate is shifting relative to the huge North American Plate by an average of a few centimeters per year. At that rate, in a few million years, the Earth's surface will look quite different than it does today.
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