What Is the San Andreas Fault?
The San Andreas fault is a large transform fault that runs through California. The fault is a result of the moving tectonic plates beneath the earth's surface, and it stretches 800 miles across the most populous state in the country. The fault is known as a strike-slip fault and separates the large Pacific Plate with the large North American Plate, and has caused some of the largest earthquakes in the western United States.
Southern and Central Segments
The plates of the San Andreas fault spread horizontally next to each other at three main locations. Two of these locations are the Southern and Central Segments. The Southern Segment stretches from the San Bernardino Mountains to the Salton Sea and is characterized by a 140-160 year earthquake range. The Central Segment is a much more dormant fault ridge, which is capable of moving without producing quakes.
Northern Segment
The Northern Segment of the San Andreas fault runs through the Santa Cruz Mountains and was largely responsible for the formation of those mountains. It produced the 1906 and the 1989 earthquakes, and a portion of its ridge runs underwater, making it capable of producing large waves and even tidal waves.
Plate Movement
The movement of the plates at the San Andreas fault takes place at a uniform pace and pattern, and has done so for centuries. The large plates of the Pacific Ocean are slowly moving to the northwest, while the plates to the east of the fault are slowly moving to the southwest, causing the plates to grind against each other in this direction.
San Andreas Research
Parkfield, the spot of one of the biggest quakes ever produced by the San Andreas, has been established as one of the epicenters of earthquake research in the world. The area has produced large earthquakes of at least a 6.0 magnitude about every 22 years, and is the current site of the San Andreas Fault Observatory at Depth, which plans to drill a hole 3 km into the earth's crust.
Notable Earthquakes
As mentioned, the San Andreas fault has produced some of the largest earthquakes that have ever rocked the United States. Among these notable earthquakes are the 1857 Fort Tejon Earthquake, which was an 8.0 magnitude that ruptured nearly 200 miles in Northern California; the 1906 San Francisco earthquake that killed an estimated 3,000 people; and the 1989 Loma Prieta earthquake that interrupted the 1989 World Series and caused millions of dollars of damage in the San Francisco Bay Area.
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