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View of the San Andreas Fault in central
CaliforniaThe San Andreas Fault is a right-lateral strike-slip fault that spans a length of roughly 800 miles (1287 kilometers) through California. The San Andreas Fault marks a transform boundary between the Pacific Plate and the North American Plate. This fault is famous for producing large and devastating earthquakes.
Current News
On September 28, 2004 at 10:15 am, a magnitude 6.0 earthquake struck along the San Andreas Fault about halfway between San Francisco and Los Angeles, just 7 miles southeast of Parkfield, California. There were no immediate reports of damage or injuries, but the temblor was felt across much of the state. This was 11 years later then the 22 year cycle that was predicted.
Segments
The San Andreas Fault can be divided into 3 segments.
The southern segment begins in near the Salton Sea and runs northward before it begins a slow bend to the west when it meets the San Bernardino Mountains. Here, it runs along the southern base of the San Bernardino Mountains, crosses through the Cajon Pass and continues to run northwest along the northern base of the San Gabriel Mountains. These mountains are a result of movement along the San Andreas Fault and are commonly called the Transverse Range.
After crossing through Frazier Park, the fault begins to bend northeast. This area is referred to as the "Big Bend" and is thought to be where the fault locks up in Southern California as the plates try to move past each other. This section of the fault has a recurrance interval of roughly 140 - 160 years.
The central segment of the fault runs in a northwestern direction from Parkfield to Hollister. While the southern section of the fault and the parts through Parkfield experience earthquakes, the rest of the central section of the fault exhibits a phenomenon called aseismic creep. This results in the fault being able to move without the need of earthquakes.
The northern segment of the fault runs from Hollister, through the San Francisco Penninsula where it briefly goes offshore, then follows the coast of California fairly closely before it makes a sharp turn west and goes offshore near Eureka, California.
Scientific Research
The small town of Parkfield, California lies along the San Andreas Fault. Seismologists discovered that this section of the fault consistantly produces magnitude 6.0 earthquakes about every 20 years. Following earthquakes in 1857, 1881, 1901, 1922, 1934 and 1966, scientists predicted an earthquake to hit Parkfield in 1993. The expected earthquake never materialized. Despite this, Parkfield has become one of the most popular spots in the world to try to capture and record a large earthquake.
In 2004, work began just north of Parkfield on the San Andreas Fault Observatory at Depth (SAFOD). The goal of SAFOD is to drill a hole nearly 2.5 miles (4 kilometers) into the Earth's crust and into the San Andreas Fault. An array of sensors will be installed to capture and record earthquakes that happen near this area.
Other research that monitors slip rates along the fault has shown that Los Angeles and San Francisco (which rest on opposite sides of the San Andreas Fault) move towards one another at a rate of a 1/4 inch (0.6 cm) a year.
Notable Earthquakes
The San Andreas Fault has had three notable earthquakes in historic times:
See also
External links
de:San-Andreas-Verwerfung
sv:San Andreassprickan
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