San Andreas Fault


Staff member
Jun 3, 2020
The San Andreas Fault is a sliding boundary between the Pacific Plate and the North American Plate, which slices California in two from Cape Mendocino to the Mexican border. It extends roughly 1,200 kilometers (750 mi) through California.

What type of fault is the San Andreas?
San Andreas Fault is a continental transform fault with a right-lateral strike-slip (horizontal) motion. The slip rate along the fault ranges from 20 to 35 mm (0.79 to 1.38 in)/yr. This is the average motion but the plates don't constantly move. They lock up against each other and the strain keeps building until it breaks into a few feet motion at once, which usually results in earthquakes.

History of San Andreas Fault
Professor Andrew Lawson of UC Berkeley discovered the northern zone in 1895. The fault was named after the San Andreas Lake, a small body of water that was formed in a valley between the two plates. However, according to Lawson's reports from 1895 and 1908, the lake was named after the surrounding San Andreas Valley. The 1906 earthquake made Lawson come to the conclusion that the the fault extended all the way into southern California. A geologist named Thomas Dibblee interpreted in 1953 that hundreds of miles of lateral movement could occur along the fault.

The next San Andreas Earthquake
San Andreas is the world's most famous fault and a threat of earthquake is a reality. However, the geologists and the Government organizations are taking every preventive measure. A study published in 2006 in the journal Nature found that the San Andreas fault has reached a sufficient stress level for an earthquake of magnitude greater than 7.0 on the moment magnitude scale to occur. This study also found that the risk of a large earthquake may be increasing more rapidly than scientists had previously believed. Moreover, the risk is currently concentrated on the southern section of the fault, i.e. the region around Los Angeles, because massive earthquakes have occurred relatively recently on the central (1857) and northern (1906) segments of the fault, while the southern section has not seen any similar rupture for at least 300 years.


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