San Andreas Fault

From Free net encyclopedia

(Redirected from San Andreas fault)

Image:San Andreas Fault - Carrizo Plains.jpg San Andreas Fault is a geological fault that spans a length of roughly 800 miles (1287 kilometres) through California, United States. The fault, a right-lateral strike-slip fault, marks a transform boundary between the Pacific Plate and the North American Plate.


Contents

[edit]

Segments

The San Andreas Fault can be divided into three segments.

The southern segment (known as the Mojave segment) begins 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. This segment of the fault is the most commonly analyzed of any earthquake fault in the world by geologists. This is due to a cutout of the fault in Palmdale, the second largest city directly sitting on the fault, where the Antelope Valley Freeway passes through it, and the deep layers of "shifted" crust can clearly be seen.

After crossing through Frazier Park, the fault begins to bend north. 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 recurrence interval of roughly 140 - 160 years. Northwest of Frazier Park, the fault runs through the Carrizo Plain, a long treeless plain within which much of the fault is plainly visible. The Elkhorn Scarp defines the fault trace along much of its length within the plain. Image:San Andreas Fault Map.gif

The central segment of the San Andreas 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 Peninsula where it briefly goes offshore, then follows the coast of California fairly closely to Cape Mendocino, where there is an unstable triple junction where three tectonic plates come together to form a geologically complex and highly unstable zone. To the north lies the Cascadia subduction zone, where the Juan de Fuca plate and the last bit of its lower section sometimes called the Gorda plate, are being subducted under the margin of the North American plate. And west, along the continental shelf, lies the Mendocino fault zone, the strike-slip boundary between the main Juan de Fuca plate and the Pacific plate.

[edit]

Scientific research

The small town of Parkfield, California lies along the San Andreas Fault. Seismologists discovered that this section of the fault consistently produces magnitude 6.0 earthquakes about every 22 years. Following earthquakes in 1857, 1881, 1901, 1922, 1934 and 1966, scientists predicted an earthquake to hit Parkfield in 1993. This quake eventually struck in 2004 (see Parkfield earthquake). Because of this frequent activity and prediction, Parkfield has become one of the most popular spots in the world to try to capture and record large earthquakes.

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 3 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. [1]

Other research monitoring slip rates along the fault has shown that Los Angeles and San Francisco (which rest on opposite sides of the San Andreas Fault) are moving towards one another at a rate of 1/5 inch (0.6 cm) a year.

[edit]

Notable earthquakes

The San Andreas Fault has had three notable earthquakes in historic times:

On September 28, 2004 at 10:15 am, a magnitude 6.0 earthquake struck at Parkfield, California on the San Andreas Fault. This earthquake was originally expected to occur in 1993 based on the latest earthquake prediction theories known at the time. Eleven more years elapsed before this prediction was finally fulfilled. Despite the extra time between events (38 years compared to an average recurrence interval of 22 years), the magnitude of the earthquake was no larger than originally expected.

[edit]

Trivia

  • The plot of the original Superman movie had Lex Luthor purchasing massive amounts of land east of the fault and then detonating a nuclear missile at the fault line, causing all land west of the fault to plunge into the sea.
  • The video game Grand Theft Auto: San Andreas, is set in a fictional state named after this fault.
  • There is a myth that, eventually, a portion of California will break away from the continental U.S. at the fault, or drop below sea level. This is not true; it would be more correct to say the land will move northwest, because the fault is a transform fault (the two land masses are sliding by each other, not moving apart).
[edit]

See also

[edit]

External links

cs:San Andreas de:San-Andreas-Verwerfung es:Falla de San Andrés fi:San Andreasin siirros fr:Faille de San Andreas it:Faglia di Sant'Andrea pl:San Andreas (uskok) pt:Falha de Santo André simple:San Andreas Fault sv:San Andreasförkastningen

Retrieved from "http://www.netipedia.com/index.php/San_Andreas_Fault"