San Andreas fault

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San Andreas fault,

great fracture (see faultfault,
in geology, fracture in the earth's crust in which the rock on one side of the fracture has measurable movement in relation to the rock on the other side. Faults on other planets and satellites of the solar system also have been recognized.
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) of the earth's crust in California. It is the principal fault of an intricate network of faults extending more than 600 mi (965 km) from NW California to the Gulf of California. The San Andreas fault, a strike-slip fault, also extends vertically at least 20 mi (30 km) into the earth. It is located on the boundary between two sections of the earth's lithosphere—the North American plate and the Pacific plate (see plate tectonicsplate tectonics,
theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history.
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)—and separates SW California from the North American continent. The Pacific plate is moving northwest in relation to the North American plate, and it is believed that the total displacement along the fault since its formation more than 30 million years ago has been about 350 mi (560 km). Movement along the fault causes earthquakes; several thousand occur annually, although only a few are of moderate or higher magnitude. The destructive San Francisco earthquake of 1906 was caused by a movement in which land surfaces on either side of the fault were displaced horizontally up to 21 ft (6.4 m).
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

San Andreas Fault


an extensive fracture of the earth’s crust in the state of California in the USA. Approximately 1,300 km long, it extends from Cape Mendocino in the north to the Gulf of California in the south and apparently continues in a southeasterly direction along the bottom of the gulf.

The San Andreas Fault is a dextral strike-slip fault. The horizontal displacements that have occurred are estimated at 1.5–3 km since the Holocene, 16–24 km since the Pleistocene, and 50–105 km since the Miocene; estimates of up to 500 km have been made for the period since the end of the Jurassic, but they are less reliable. Movements along the fault have often been observed during earthquakes; over the past 100 years such movements have been recorded by special instruments. The displacement was greater than 6 m along a section more than 300 km in length during the San Francisco earthquake of 1906 and was 4.5 m along a section of approximately 70 km during the Imperial Valley earthquake of 1940. Precise geodetic measurements have established that horizontal movements occur along the fault in the periods between earthquakes; these displacements range from 1 to 6 cm per year in different sections of the fault.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.