San Andreas Fault

San Andreas Fault

Overview


The San Andreas Fault is a continental strike-slip fault that runs a length of roughly 810 miles (1,303.6 km) through California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The fault's motion is right-lateral strike-slip (horizontal motion). It forms the tectonic
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...

 boundary between the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

 and the North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

.

The fault was first identified in Northern California
Northern California
Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...

 by UC Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

 geology professor Andrew Lawson
Andrew Lawson
Andrew Cowper Lawson July 25,1861- June 16,1952 was a professor of geology at the University of California, Berkeley. He was the editor and co-author of the 1908 report on the 1906 San Francisco Earthquake which became known as the "Lawson Report"...

 in 1895 and named by him after a small lake which lies in a linear valley formed by the fault just south of San Francisco, the Laguna de San Andreas.
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Encyclopedia


The San Andreas Fault is a continental strike-slip fault that runs a length of roughly 810 miles (1,303.6 km) through California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The fault's motion is right-lateral strike-slip (horizontal motion). It forms the tectonic
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...

 boundary between the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

 and the North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

.

The fault was first identified in Northern California
Northern California
Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...

 by UC Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

 geology professor Andrew Lawson
Andrew Lawson
Andrew Cowper Lawson July 25,1861- June 16,1952 was a professor of geology at the University of California, Berkeley. He was the editor and co-author of the 1908 report on the 1906 San Francisco Earthquake which became known as the "Lawson Report"...

 in 1895 and named by him after a small lake which lies in a linear valley formed by the fault just south of San Francisco, the Laguna de San Andreas. After the 1906 San Francisco Earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...

, Lawson also discovered that the San Andreas Fault stretched southward into Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

. Large-scale (hundreds of miles) lateral movement along the fault was first proposed in a 1953 paper by geologists Mason Hill and Thomas Dibblee
Thomas Dibblee
Thomas Wilson Dibblee, Jr. was an American geologist best known for his extensive geological mapping...

.

Segments of the fault


The San Andreas Fault can be divided into three segments.

Southern segment


The southern segment (known as the Mojave
Mojave Desert
The Mojave Desert occupies a significant portion of southeastern California and smaller parts of central California, southern Nevada, southwestern Utah and northwestern Arizona, in the United States...

 segment) begins near Bombay Beach on the Eastern edge of the Salton Sea
Salton Sea
The Salton Sea is a shallow, saline, endorheic rift lake located directly on the San Andreas Fault, predominantly in California's Imperial Valley. The lake occupies the lowest elevations of the Salton Sink in the Colorado Desert of Imperial and Riverside counties in Southern California. Like Death...

 at the northern terminus of the East Pacific Rise
East Pacific Rise
The East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate...

 and runs northward before it begins a slow bend to the west where it meets the San Bernardino Mountains
San Bernardino Mountains
The San Bernardino Mountains are a short transverse mountain range north and east of San Bernardino in Southern California in the United States. The mountains run for approximately 60 miles east-west on the southern edge of the Mojave Desert in southwestern San Bernardino County, north of the...

. It runs along the southern base of the San Bernardino Mountains, crosses through the Cajon Pass
Cajon Pass
Cajon Pass is a moderate-elevation mountain pass between the San Bernardino Mountains and the San Gabriel Mountains in Southern California in the United States. It was created by the movements of the San Andreas Fault...

 and continues to run northwest along the northern base of the San Gabriel Mountains
San Gabriel Mountains
The San Gabriel Mountains Range is located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east...

. These mountains are a result of movement along the San Andreas Fault and are commonly called the Transverse Range. In Palmdale
Palmdale, California
Palmdale is a city located in the center of northern Los Angeles County, California, United States.Palmdale was the first community within the Antelope Valley to incorporate as a city on August 24, 1962; 47 years later, voters approved creating a charter city in November, 2009. Palmdale is...

, a portion of the fault is easily examined as a roadcut for the Antelope Valley Freeway runs directly through it. Box Canyon, just southeast of Palm Springs, is a dramatic section.

After crossing through Frazier Park
Frazier Park, California
Frazier Park is an unincorporated community and census-designated place in Kern County, California. Frazier Park is west of Lebec, at an elevation of 4,639 feet . It is one of the Mountain Communities of the Tejon Pass...

, the fault begins to bend northward. This area is referred to as the "Big Bend" and is thought to be where the fault locks up in Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

 as the plates try to move past each other. This section of the fault has an earthquake-recurrence interval of roughly 140–160 years. Northwest of Frazier Park, the fault runs through the Carrizo Plain
Carrizo Plain
The Carrizo Plain is a large enclosed plain, approximately 50 miles long and up to 15 miles across, in southeastern San Luis Obispo County, California, about 100 miles northwest of Los Angeles, California...

, 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.

Research has shown that the Southern segment, which stretches from Parkfield in Monterey County, California
Monterey County, California
Monterey County is a county located on the Pacific coast of the U.S. state of California, its northwestern section forming the southern half of Monterey Bay. The northern half of the bay is in Santa Cruz County. As of 2010, the population was 415,057. The county seat and largest city is Salinas...

 all the way down to the Salton Sea, is now capable of a Richter scale 8.1 earthquake. An earthquake of that size on the Southern segment (which, at its closest, is 40 miles away from Los Angeles) would kill thousands of people in Los Angeles, San Bernandino, Riverside, and other areas, and cause hundreds of billions of dollars in property and economic damage.

Central segment


The central segment of the San Andreas fault runs in a northwestern direction from Parkfield
Parkfield, California
Parkfield is an unincorporated community in Monterey County, California. It is located on Little Cholame Creek east of Bradley, at an elevation of 1529 feet...

 to Hollister
Hollister, California
Hollister is a city in and the county seat of San Benito County, California, United States. The population was 34,928 at the 2010 census. Hollister is primarily an agricultural town.-History:...

. 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
Aseismic creep
In geology, aseismic creep is measurable surface displacement along a fault in the absence of notable earthquakes.An example is along the Calaveras fault in Hollister, California. Streets crossing the fault in Hollister show significant offset and several houses sitting atop the fault are notably...

, where the fault slips slowly without causing earthquakes.

Northern segment


The northern segment of the fault runs from Hollister, through the Santa Cruz Mountains
Santa Cruz Mountains
The Santa Cruz Mountains, part of the Pacific Coast Ranges, are a mountain range in central California, United States. They form a ridge along the San Francisco Peninsula, south of San Francisco, separating the Pacific Ocean from San Francisco Bay and the Santa Clara Valley, and continuing south,...

, epicenter of the 1989 Loma Prieta earthquake, then on up the San Francisco Peninsula
San Francisco Peninsula
The San Francisco Peninsula is a peninsula in the San Francisco Bay Area that separates the San Francisco Bay from the Pacific Ocean. On its northern tip is the City and County of San Francisco. Its southern base is in Santa Clara County, including the cities of Palo Alto, Los Altos, and Mountain...

, where it was first identified by Professor Lawson in 1895, then offshore at Pacifica
Pacifica, California
Pacifica is a city in San Mateo County, California, on the coast of the Pacific Ocean between San Francisco and Half Moon Bay.-Overview:The City of Pacifica is spread along a six mile stretch of the north central California coastal beach and hills, nestled in several small valleys spanning between...

 at Mussel Rock
Mussel Rock
right|thumb|Mussel Rock is a rock formation on the coast of San Mateo County, California, offshore from Daly City. It consists of one large and numerous smaller rocks of a type known as a stack, where a headland is eroded unevenly, leaving small islands....

. This is the approximate location of the epicenter of the 1906 San Francisco earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...

. The fault returns onshore at Bolinas Lagoon
Bolinas Lagoon
Bolinas Lagoon is a tidal estuary, approximately in area, located at in the West Marin region of Marin County, California, United States. It is a part of the Gulf of the Farallones National Marine Sanctuary. The lagoon is a back bay of Bolinas Bay on the Pacific coast approximately 15 mi ...

 just north of Stinson Beach
Stinson Beach, California
Stinson Beach is a census-designated place in Marin County, California, on the west coast of the United States. Stinson Beach is located east-southeast of Bolinas, at an elevation of 26 feet . The population of the Stinson Beach CDP was 632 at the 2010 census.Stinson Beach is about a 35-minute...

 in Marin County. It returns underwater through the linear trough of Tomales Bay
Tomales Bay
Tomales Bay is a long narrow inlet of the Pacific Ocean in Marin County in northern California in the United States. It is approximately 15 miles long and averages nearly 1.0 miles wide, effectively separating the Point Reyes Peninsula from the mainland of Marin County. It is located...

 which separates the Point Reyes Peninsula from the mainland, runs just east of the Bodega Heads through Bodega Bay and back underwater, returning onshore at Fort Ross. (In this region around the San Francisco Bay Area
San Francisco Bay Area
The San Francisco Bay Area, commonly known as the Bay Area, is a populated region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses metropolitan areas of San Francisco, Oakland, and San Jose, along with smaller urban and rural areas...

 several significant "sister faults" run more-or-less parallel, and each of these can create significantly destructive earthquakes.)
From Fort Ross the northern segment continues overland, forming in part a linear valley through which the Gualala River
Gualala River
The Gualala River is a river on the northern coast of California. Most of the river is in Sonoma County, but a portion is in Mendocino County. The headwaters of the river are high in the Coast Range, and it empties into the Pacific Ocean...

 flows. It goes back offshore at Point Arena. After that, it runs underwater along the coast until it nears Cape Mendocino
Cape Mendocino
Cape Mendocino located on the Lost Coast entirely within Humboldt County, California, USA, is the westernmost point on the coast of California. It has been a landmark since the 16th century when the Manila Galleons would reach the coast here following the prevailing westerlies all the way across...

, where it begins to bend to the west, terminating at the Mendocino Triple Junction
Mendocino Triple Junction
The Mendocino Triple Junction is a geologic triple junction where the San Andreas Fault meets the Mendocino Fault and the Cascadia subduction zone, separating three tectonic plates: the Pacific Plate, the North American Plate and the Gorda Plate...

.

Evolution


The evolution of the San Andreas dates back to the mid Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...

, to about 30 Mya (million years ago). At this time, a spreading center between the Pacific Plate and the Farallon Plate
Farallon Plate
The Farallon Plate was an ancient oceanic plate, which began subducting under the west coast of the North American Plate— then located in modern Utah— as Pangaea broke apart during the Jurassic Period...

 (which is now mostly subducted, with remnants including the Juan de Fuca Plate
Juan de Fuca Plate
The Juan de Fuca Plate, named after the explorer of the same name, is a tectonic plate, generated from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone...

, Rivera Plate
Rivera Plate
The Rivera Plate is a small tectonic plate located off the west coast of Mexico, just south of the Baja California Peninsula. It is bounded on the northwest by the East Pacific Rise, on the southwest by the Rivera Transform Fault, on the southeast by a deformation zone, and on the northeast by...

, Cocos Plate
Cocos Plate
The Cocos Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it.-Geology:...

, and the Nazca Plate
Nazca Plate
]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the...

) was beginning to interact with the subduction zone off the western coast of North America. The relative motion between the Pacific and North American Plates was different from the relative motion between the Farallon and North American Plates, so when the spreading ridge was 'subducted', a new relative motion caused a new style of deformation. This style is chiefly the San Andreas Fault, but also includes a possible driver for the deformation of the Basin and Range, separation of Baja California, and rotation of the Transverse Range.

The San Andreas Fault proper, at least the Southern Segment, has only existed for about 5 million years. The first known incarnation of the southern part of the fault was Clemens Well-Fenner-San Francisquito fault zone around 22–13 Ma. This system added the San Gabriel Fault
San Gabriel Fault
The San Gabriel Fault is a geological fault in Los Angeles County, California, running about southeastward from the Ridge Basin in the Sierra Pelona-San Emigdio Mountains juncture area to the western San Gabriel Mountains that forms their southwestern face near Sunland and the northeastern San...

 as a primary focus of movement between 10–5 Ma. Currently, it is believed that the modern San Andreas will eventually transfer its motion toward a fault within the Eastern California Shear Zone. This complicated evolution, especially along the southern segment, is mostly caused by either the "Big Bend" and/or a difference in the motion vector between the plates and the trend of the fault(s).

Plate movement


All land west of the fault on the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

 is moving slowly to the northwest while all land east of the fault is moving southwest (relatively southeast as measured at the fault) under the influence of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

. The rate of slippage averages approximately 33 to 37 mm (1.3 to 1.5 in) annually across California.

The westward component of the motion of the North American Plate creates compressional forces which are expressed as uplift in the Coast Ranges. Likewise, the northwest motion of the Pacific Plate creates significant compressional forces where the North American Plate stands in its way, creating the Transverse Ranges in Southern California, and to a lesser, but still significant, extent the Santa Cruz Mountains, site of the Loma Prieta Earthquake
Loma Prieta earthquake
The Loma Prieta earthquake, also known as the Quake of '89 and the World Series Earthquake, was a major earthquake that struck the San Francisco Bay Area of California on October 17, 1989, at 5:04 p.m. local time...

 of 1989.

Studies of the relative motions of the Pacific and North American plates have shown that only about 75 percent of the motion can be accounted for in the movements of the San Andreas and its various branch faults. The rest of the motion has been found in an area east of the Sierra Nevada
Sierra Nevada (US)
The Sierra Nevada is a mountain range in the U.S. states of California and Nevada, between the California Central Valley and the Basin and Range Province. The Sierra runs north-to-south, and is approximately across east-to-west...

 mountains called the Walker Lane
Walker Lane
The Walker Lane is a geologic trough roughly aligned with the California/Nevada border southward to where Death Valley intersects the Garlock Fault, a major left-lateral strike-slip fault...

 or Eastern California Shear Zone. The reason for this is not as yet clear, although several hypotheses have been offered and research is ongoing. One hypothesis which gained some currency following the Landers Earthquake in 1992 is that the plate boundary may be shifting eastward, away from the San Andreas to the Walker Lane.

Assuming the plate boundary does not change as hypothesized, projected motion indicates that the landmass west of the San Andreas Fault, including Los Angeles, will eventually slide past San Francisco, then continue northwestward toward the Aleutian Trench
Aleutian Trench
The Aleutian Trench is a subduction zone and oceanic trench which runs along the southern coastline of Alaska and the adjacent waters of northeastern Siberia off the coast of Kamchatka Peninsula. It is classified as a "marginal trench" in the east as it runs along the margin of the continent, and...

, over a period of perhaps twenty million years.

Scientific research



Research at Parkfield


In central California is the small town of Parkfield, California
Parkfield, California
Parkfield is an unincorporated community in Monterey County, California. It is located on Little Cholame Creek east of Bradley, at an elevation of 1529 feet...

, which 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
Parkfield, California
Parkfield is an unincorporated community in Monterey County, California. It is located on Little Cholame Creek east of Bradley, at an elevation of 1529 feet...

 in 1993. This quake eventually struck in 2004 (see Parkfield earthquake
Parkfield earthquake
Parkfield earthquake is a name given to various large earthquakes that occurred in the vicinity of the town of Parkfield, California, United States...

). 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
San Andreas Fault Observatory at Depth
The San Andreas Fault Observatory at Depth is one of three components of the Earthscope Project, funded by the National Science Foundation in conjunction with the USGS and NASA. The SAFOD site is located just north of the town of Parkfield, California...

 (SAFOD). The goal of SAFOD is to drill a hole nearly 2 miles (3.2 km) 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.

The University of California study on "the next big one"


A study completed by Yuri Fialko in 2006 has demonstrated that the San Andreas fault has been stressed to a level sufficient for the next "big one," as it is commonly called; that is, an earthquake of magnitude
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....

 7.0 or greater. The study also concluded that the risk of a large earthquake may be increasing more rapidly than researchers had previously believed. Fialko also emphasized in his study that, while the San Andreas Fault had experienced massive earthquakes in 1857 at its central section and in 1906 at its northern segment (the 1906 San Francisco earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...

), the southern section of the fault has not seen a similar rupture in at least 300 years.

If such an earthquake were to occur, Fialko's study stated, it would result in substantial damage to Palm Springs
Palm Springs, California
Palm Springs is a desert city in Riverside County, California, within the Coachella Valley. It is located approximately 37 miles east of San Bernardino, 111 miles east of Los Angeles and 136 miles northeast of San Diego...

 and a number of other cities in San Bernardino
San Bernardino County, California
San Bernardino County is a county in the U.S. state of California. As of the 2010 census, the population was 2,035,210, up from 1,709,434 as of the 2000 census...

, Riverside
Riverside County, California
Riverside County is a county in the U.S. state of California. One of 58 California counties, it covers in the southern part of the state, and stretches from Orange County to the Colorado River, which forms the state border with Arizona. The county derives its name from the city of Riverside,...

 and Imperial
Imperial County, California
Imperial County is a county located in the Imperial Valley, in the far southeast of the U.S. state of California, bordering both Arizona and Mexico. It is part of the El Centro Metropolitan Area, which encompasses all of Imperial County. The population as of 2000 was 142,361. The county seat is the...

 counties in California, and Mexicali municipality in Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...

. Such an event would be felt throughout much of Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

, including densely populated areas of metropolitan Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

, Orange County
Orange County, California
Orange County is a county in the U.S. state of California. Its county seat is Santa Ana. As of the 2010 census, its population was 3,010,232, up from 2,846,293 at the 2000 census, making it the third most populous county in California, behind Los Angeles County and San Diego County...

, San Diego, Ensenada
Ensenada, Baja California
Ensenada is a coastal city in Mexico and the third-largest city in Baja California. It is located south of San Diego on the Baja California Peninsula. The city is locally referred to as La Cenicienta del Pacífico, or, The Cinderella of the Pacific...

 and Tijuana
Tijuana
Tijuana is the largest city on the Baja California Peninsula and center of the Tijuana metropolitan area, part of the international San Diego–Tijuana metropolitan area. An industrial and financial center of Mexico, Tijuana exerts a strong influence on economics, education, culture, art, and politics...

, Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...

, San Luis Rio Colorado
San Luis Río Colorado
San Luis Río Colorado is a city and its surrounding municipality lying in the northwestern corner of the state of Sonora, Mexico.- Location :...

 in Sonora
Sonora
Sonora officially Estado Libre y Soberano de Sonora is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo....

 and Yuma
Yuma
-Places:* Yuma Desert, desert in southwest U.S. and northwest MexicoUnited States* Yuma County, Arizona** Yuma, Arizona** Marine Corps Air Station Yuma** United States Army Yuma Proving Ground** Yuma Territorial Prison* Yuma County, Colorado** Yuma, Colorado...

, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

.

"The information available suggests that the fault is ready for the next big earthquake but exactly when the triggering will happen and when the earthquake will occur we cannot tell," Fialko said. "It could be tomorrow or it could be 10 years or more from now," he concluded in September 2005.

Cascadia connection


Recent studies of past earthquake traces on both the northern San Andreas Fault and the southern Cascadia subduction zone
Cascadia subduction zone
The Cascadia subduction zone is a subduction zone, a type of convergent plate boundary that stretches from northern Vancouver Island to northern California. It is a very long sloping fault that separates the Juan de Fuca and North America plates.New ocean floor is being created offshore of...

 indicate a correlation in time which may be evidence that quakes on the Cascadia subduction zone may have triggered most of the major quakes on the northern San Andreas during at least the past 3,000 years or so. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. The 1906 San Francisco earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...

 seems to have been a major exception to this correlation, however, as it was not preceded by a major Cascadia quake, and the rupture moved mostly from south to north.

Notable earthquakes



The San Andreas Fault has had some notable earthquakes in historic times:
  • 1857 Fort Tejon earthquake
    Fort Tejon earthquake
    The Fort Tejon earthquake occurred at about 8:20 AM on January 9, 1857. It ruptured the San Andreas Fault for a length of about 225 miles , between Parkfield and Wrightwood. The average slip along the fault was 4.5 meters , and a maximum offset of 9 meters was recorded in the Carrizo Plain area...

    : About 217 miles (349.2 km) were ruptured in central and southern California. Though it is known as the Fort Tejon
    Fort Tejon
    Fort Tejon in California is a former United States Army outpost which was intermittently active from June 24, 1854, until September 11, 1864. It is located in the Grapevine Canyon area of Tejon Pass along Interstate 5, the main route through the mountains separating the Central Valley from Los...

     earthquake, the epicenter is thought to have been located far to the north, just south of Parkfield. Only two deaths were reported. The magnitude
    Richter magnitude scale
    The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....

     was about 7.9.
  • 1906 San Francisco earthquake
    1906 San Francisco earthquake
    The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...

    : About 267 miles (429.7 km) were ruptured in Northern California. The epicenter was near San Francisco. At least 3000 people died in the earthquake and subsequent fires. This time the magnitude was estimated to be 7.8.
  • 1989 Loma Prieta earthquake
    Loma Prieta earthquake
    The Loma Prieta earthquake, also known as the Quake of '89 and the World Series Earthquake, was a major earthquake that struck the San Francisco Bay Area of California on October 17, 1989, at 5:04 p.m. local time...

    : About 25 miles (40.2 km) were ruptured (although the rupture did not reach the surface) near Santa Cruz, California
    Santa Cruz, California
    Santa Cruz is the county seat and largest city of Santa Cruz County, California in the US. As of the 2010 U.S. Census, Santa Cruz had a total population of 59,946...

    , causing 63 deaths and moderate damage in certain vulnerable locations in the San Francisco Bay Area. Moment magnitude
    Moment magnitude scale
    The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...

     this time was about 6.9. The earthquake also postponed game 3 of the 1989 World Series
    1989 World Series
    †: Game 3 was originally slated for October 17 at 5:35 pm; however, it was postponed when an earthquake occurred at 5:04 pm.-Game 1:Saturday, October 14, 1989 at Oakland-Alameda County Coliseum in Oakland, California...

     at Candlestick Park. This quake occurred on October 17, 1989, at approximately 5:04 P.M. PDT.
  • 2004 Parkfield earthquake
    Parkfield earthquake
    Parkfield earthquake is a name given to various large earthquakes that occurred in the vicinity of the town of Parkfield, California, United States...

    : On September 28, 2004, at 10:15 A.M. PDT, a magnitude 6.0 earthquake struck California on the San Andreas Fault.


See also


  • Calaveras Fault
    Calaveras Fault
    The Calaveras Fault is a major branch of the San Andreas Fault located in northern California in the San Francisco Bay Area. To the east of the Hayward-Rodgers Creek fault, the Calaveras fault extends 123 km, splaying from the San Andreas fault near Hollister and terminating at Danville at its...

  • Garlock Fault
    Garlock Fault
    The Garlock Fault is a left-lateral strike-slip fault running approximately northeast-southwest in the Mojave Desert of southern California. It runs for much of its length along the southern base of the Tehachapi Mountains...

  • Geologic timeline of Western North America
    Geologic timeline of Western North America
    A timeline of significant geological events in the evolution of western North America. Dates are approximate. -External links:* http://www.geog.ucsb.edu/~joel/g148_f06/readings/geol_history/geol_history.html*...

  • Hayward Fault Zone
    Hayward Fault Zone
    The Hayward Fault Zone is a geologic fault zone capable of generating significantly destructive earthquakes. This strike-slip fault is about long, situated mainly along the western base of the hills on the east side of San Francisco Bay...

  • Laguna Salada Fault
    Laguna Salada Fault
    The Laguna Salada Fault is a geological fault between the United States and Mexico. About to long, it straddles the Imperial County-California–Baja California border.-Earthquakes:...

  • North Anatolian Fault
    North Anatolian Fault
    The North Anatolian Fault is a major active right lateral-moving strike-slip fault in northern Anatolia which runs along the transform boundary between the Eurasian Plate and the Anatolian Plate. The fault extends westward from a junction with the East Anatolian Fault at the Karliova Triple...

  • Central Valley (California)

Further reading

  • The California Earthquake of April 18, 1906: Report of the State Earthquake Investigation Commission, Andrew C. Lawson, chairman, Carnegie Institution of Washington Publication 87, 2 vols. (1908) - Available online at this USGS webpage.

External links