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The 1857 Fort Tejon earthquake occurred at about 8:20 a.m. (
Pacific time The Pacific Time Zone (PT) is a time zone encompassing parts of western Canada, the western United States, and western Mexico. Places in this zone observe standard time by subtracting eight hours from Coordinated Universal Time ( UTC−08:00). ...
) on January 9 in central and
Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban a ...
. One of the largest recorded earthquakes in the United States, with an estimated
moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...
of 7.9, it ruptured the southern part of the San Andreas Fault for a length of about 225 miles (350 km), between Parkfield and Wrightwood. Though the shock was centered near Parkfield, the event is referred to as the
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 (''La Cañada de las Uvas'') between the San Emigdio Mountains and ...
earthquake, because that was the location of the greatest damage. Fort Tejon is just north of the junction of the San Andreas and
Garlock Fault The Garlock Fault is a left-lateral strike-slip fault running northeast–southwest along the north margins of the Mojave Desert of Southern California, for much of its length along the southern base of the Tehachapi Mountains. Geography Stretc ...
s, where the Tehachapi, San Emigdio, and Sierra Pelona Transverse Ranges come together. The earthquake is the most recent large event to occur along that portion of the San Andreas Fault, and is estimated to have had a maximum perceived intensity of IX (''Violent'') on the Modified Mercalli scale (MMI) near Fort Tejon in the
Tehachapi Mountains The Tehachapi Mountains (; Kawaiisu: ''Tihachipia'', meaning "hard climb") are a mountain range in the Transverse Ranges system of California in the Western United States. The range extends for approximately in southern Kern County and northwe ...
, and along the San Andreas Fault from Mil Potrero (near Pine Mountain Club) in the
San Emigdio Mountains The San Emigdio Mountains are a part of the Transverse Ranges in Southern California, extending from Interstate 5 at Lebec and Gorman on the east to Highway 33–166 on the west. They link the Tehachapis and Temblor Range and form the souther ...
to Lake Hughes in the Sierra Pelona Mountains. Accounts of the events' effects varied widely, including the time of the main shock as well as foreshocks that occurred at several locations earlier in the morning.


Tectonic setting

The 1857 earthquake ruptured about of the southern part of the San Andreas Fault, the structure that accommodates most of the displacement along the
transform boundary A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
between the North American Plate and the Pacific Plate. The Pacific Plate is moving north relative to the
Sierra Nevada-Great Valley Block Sierra (Spanish for "mountain range" and "saw", from Latin '' serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a mountain range in Baja California, Mexico * Sierra de las Nieves, a mountain range i ...
of the North American Plate at about per year. The displacement rate along the various sections that ruptured is per year along the Parkfield, Cholame, Carrizo and Big Bend sections and and per year along the Mojave north and Mojave south sections. Paleoseismic studies have found evidence for many prehistoric earthquakes in the last 3,000 years on this part of the San Andreas Fault.


Earthquake

The earthquake ruptured a substantial portion of the southern San Andreas fault, but not the entire length. Thomas H. Jordan, director of the
Southern California Earthquake Center The Southern California Earthquake Center (SCEC) is a collaboration of more than 1,000 scientists across 100 research institutions with a mission to: conduct research on earthquakes in Southern California and elsewhere by gathering data, conductin ...
, stated that the slip likely stopped in the area near Cajon Pass, perhaps because the tectonic stresses on that part of the fault had been released several decades earlier during the
1812 Wrightwood earthquake The 1812 San Juan Capistrano earthquake, also known simply as the Capistrano earthquake or the Wrightwood earthquake, occurred on December 8 at in Alta California. At the time, this was a colonial territory of the Spanish Empire. Damage occurred ...
. The average slip along the fault was , and a maximum offset of was recorded in the Carrizo Plain area in southeastern San Luis Obispo County. With an estimated magnitude of 7.9, this was the last "Big One" in
Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban a ...
. The extreme southernmost portion of the San Andreas fault, which terminates near Bombay Beach at the Salton Sea, last ruptured in 1680. Surface faulting may have extended beyond the boundaries of the regularly acknowledged slip length. Researchers recorded first and second-hand accounts of the ground crack, which was understood to be recent surface faulting and not just the topography of the existing rift. On the extreme northern end of the rupture zone, the surface cracking extended north of Cholame into
San Benito County San Benito County (; ''San Benito'', Spanish for " St. Benedict"), officially the County of San Benito, is a county located in the Coast Range Mountains of the U.S. state of California. As of the 2020 census, the population was 64,209. The co ...
. On the southern end, the population centers were not as close to the fault, and early observers were probably limited to the stretch of the fault between Fort Tejon and Elizabeth Lake, as that was close to the Stockton – Los Angeles Road, the primary inland north−south route then. Evidence of uprooted and displaced trees south of Elizabeth Lake indicates surface faulting along a mole track (an "array of en echelon primary Riedel shears with linking compressional rolls and minor thrusts") that ran directly under three Jeffrey Pines. Two of the three trees examined were tilted in their lower extremity, while the upper portions remained relatively untilted. Tree ring dating confirmed that the trees had originated 10 and 25 years before 1857 and also that the rings began to grow twice as thick on the side in the direction of the tilt. This is a frequently noted compensation of tree tilt. Seismologist Kerry Sieh determined that fault slip and the associated ground disturbance was the source of the mole track and subsequent tree tilt.


Foreshocks

Various accounts of the event indicate the presence of foreshocks between one and nine hours before the main event, and based on the (uncertain) distribution of those shocks, it is assumed that the beginning of the fault rupture (the
epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...
) was in the area between Parkfield and Cholame, about northwest. The lack of standardized timekeeping during this period of California's history contributed to some of the inaccurate reports of when the pre-shocks occurred. Local
solar time Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Two types of solar time are apparent solar time (sundial ti ...
was being used in 1857 and San Francisco would have been the locality with the most accurate time kept as it was a center of commerce and other activity. Standard time was not followed until the 1880s, with the Pacific Time Zone being aligned with the 120th meridian. The differences in local times were substantial, with
San Francisco San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17th ...
at 122.43 W and San Diego at 117.10 W, the difference between the two would be around 22 minutes (4 minutes per degree). At least one individual reported foreshock times that varied by as much as half an hour when speaking to two different newspapers. The firsthand reports were most abundant for the shocks felt at 1, 2, and 4 hours before the main shock which were later labeled the predawn, dawn, and sunrise shocks. The predawn event shook residents of San Francisco (MMI II – III), San Jose (MMI IV), and Santa Cruz (MMI IV). The dawn shock was felt in those locales plus Fort Tejon and possibly the Carrizo Plain. The sunrise shock was felt in San Francisco (MMI III),
Monterey Monterey (; es, Monterrey; Ohlone: ) is a city located in Monterey County on the southern edge of Monterey Bay on the U.S. state of California's Central Coast. Founded on June 3, 1770, it functioned as the capital of Alta California under bot ...
(MMI IV), and
Visalia Visalia ( ) is a city in the agricultural San Joaquin Valley of California. The population was 141,384 as per the 2020 census. Visalia is the fifth-largest city in the San Joaquin Valley, the 42nd most populous in California, and 192nd in ...
(MMI II – III). Sacramento and
Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
did not report any of these events. Several mid-twentieth-century earthquakes had similar felt reports to the dawn and sunrise shocks and with close inspection, Sieh theorizes that both events were local to coastal
central California Central California is generally thought of as the middle third of the state, north of Southern California, which includes Los Angeles, and south of Northern California, which includes San Francisco. It includes the northern portion of the S ...
, probably between
Point Conception Point Conception (Chumash: ''Humqaq'') is a headland along the Gaviota Coast in southwestern Santa Barbara County, California. It is the point where the Santa Barbara Channel meets the Pacific Ocean, and as the corner between the mostly north ...
and Monterey. Also, during that period, no central California earthquake with a magnitude of less than five had a felt area as large as the two foreshocks, while events larger than magnitude six have had "somewhat larger" felt areas, so it could be said that the foreshocks most likely were between magnitude five and six.
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. The San Andreas fault runs through this town, and six successive magnitude 6 earthquakes occurre ...
s occurred with exceptionally regular intervals (between 20 and 30 years) between 1857 and 1966. Sieh studied four of these events (1901, 1922, 1934, and 1966) and found that they helped to determine the southeast boundary for the origination of the dawn foreshock. The coverage and intensities of felt reports for that earthquake show a solid resemblance to the Parkfield events. Only one of the four Parkfield events was not felt further southeast than the dawn shock, so Sieh concluded that if the San Andreas was the source of the event, then it was reasonable to assume that the Parkfield to Cholame stretch of the fault was responsible for producing the dawn felt intensities, though the San Andreas is not the only possible source for the dawn event. For example, the November 22, 1952, magnitude six Bryson earthquake "nearly duplicates" the felt reports. That event may have occurred west of the San Andreas on the Nacimiento fault, though the highest felt reports were along the Rinconada fault around southwest of the San Andreas.


Damage

Most of the adobe buildings at
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 (''La Cañada de las Uvas'') between the San Emigdio Mountains and ...
were badly damaged and several people were injured there. More buildings were destroyed along a twenty-mile stretch between Fort Tejon and southeast to Elizabeth Lake, a sag pond that was formed directly on the San Andreas fault. Streams and springs experienced disturbances in San Diego and Santa Barbara Counties, while the Kern River, Kern Lake, and
Los Angeles River , name_etymology = , image = File:Los Angeles River from Fletcher Drive Bridge 2019.jpg , image_caption = L.A. River from Fletcher Drive Bridge , image_size = 300 , map = LARmap.jpg , map_size ...
all spilled over their banks. Farther north in Santa Clara County the flow of well water was affected. Ground cracks from liquefaction of swampy ground were observed near the
Pueblo de Los Angeles In the Southwestern United States, Pueblo (capitalized) refers to the Native tribes of Puebloans having fixed-location communities with permanent buildings which also are called pueblos (lowercased). The Spanish explorers of northern New Spain ...
and in the Oxnard Plain, and ground fissures were reported near the
Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
, Santa Ana, and Santa Clara Rivers. Central and southern California were thinly populated at the time and this likely helped limit the damage from the earthquake, but the lack of people present also reduced the number of perspectives to use in determining intensity estimates. Areas with the highest population density like San Francisco, Stockton, and Los Angeles provided enough information about the effects of the earthquake to provide the best estimates of intensity. At downtown Los Angeles, with a maximum perceived intensity of VI, some homes and buildings were cracked, but no major damage was reported. In Ventura (MM VII) the roof of Mission San Buenaventura collapsed and the bell tower was damaged, and farther north, the front wall of the old adobe
Mission Santa Cruz Mission Santa Cruz (''La Misión de la Exaltación de la Santa Cruz'', which translates as the Mission of the Exaltation of the Holy Cross), was the twelfth of twenty-one Spanish missions in California (today's U.S. state), established by the Fr ...
chapel collapsed. One of the two deaths reported included a woman who was killed by a collapsing adobe house in nearby Gorman, and an elderly man may have collapsed and died in the Los Angeles area as a result of the earthquake.


Aftershocks

The main shock was followed by a series of aftershocks that continued for at least 3.75 years, although the total number of large aftershocks was less than would be expected for an earthquake of this size. The four largest aftershocks all had magnitudes greater than 6, although there are large uncertainties in both location and magnitude due to the limited number of data points available. On the night of January 9 there was a large aftershock with an estimated magnitude of about 6.25, with a possible epicenter near the
Garlock Fault The Garlock Fault is a left-lateral strike-slip fault running northeast–southwest along the north margins of the Mojave Desert of Southern California, for much of its length along the southern base of the Tehachapi Mountains. Geography Stretc ...
. The largest aftershock occurred on the afternoon of January 16 with an estimated magnitude of about 6.7, with a possible offshore location, and high felt intensities in Southern California communities. Santa Barbara and
San Bernardino San Bernardino (; Spanish for "Saint Bernardino") is a city and county seat of San Bernardino County, California, United States. Located in the Inland Empire region of Southern California, the city had a population of 222,101 in the 2020 cen ...
reported an MM intensity of V and Los Angeles reported V and VI. Two significant events occurred in the San Bernardino area on December 15–16, 1858, with the latter having an estimated magnitude of about 6. The last recorded major aftershock occurred on April 16, 1860, with an estimated magnitude of about 6.3, with an epicenter close to the Parkfield section of the San Andreas Fault.


Future threat

Scientists and public service officials have speculated on the threat of another very large earthquake occurring in southern California and what type and scale of damage might result. The portion of the fault that ruptured in 1857 has settled into a period of dormancy and this has given rise to suggestions that future slip along that zone may be characterized by a very large 1857-type event followed by another period of inactivity. The communities of Frazier Park,
Palmdale Palmdale is a city in northern Los Angeles County in the U.S. state of California. The city lies in the Antelope Valley region of Southern California. The San Gabriel Mountains separate Palmdale from the Los Angeles Basin to the south. On Aug ...
, and Wrightwood are all located very close to the San Andreas fault, though much of the Los Angeles area could be affected even at a greater distance from the rupture area if a similar event were to reoccur there. Swaminathan Krishnan, assistant professor of civil engineering and geophysics at the
California Institute of Technology The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
, said that if a similar rupture from Parkfield to Wrightwood were to happen again, it would severely affect the Los Angeles area, with the San Fernando Valley being particularly hard hit. The Los Angeles Aqueduct and California Aqueduct, two of the principal water transfer infrastructure systems supplying Greater Los Angeles, both cross the San Andreas fault within the main damage zone of the Fort Tejon earthquake, in the Tehachapi and Sierra Pelona Mountains.


See also

* List of earthquakes in California * List of earthquakes in the United States *
List of historical earthquakes Historical earthquakes is a list of significant earthquakes known to have occurred prior to the beginning of the 20th century. As the events listed here occurred before routine instrumental recordings, they rely mainly on the analysis of written ...


References


Bibliography

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Further reading

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External links


Reports of the Great California Earthquake of 1857
Scripps Institution of Oceanography
The San Andreas Fault System, California – USGS Professional Paper #1515
United States Geological Survey {{DEFAULTSORT:Fort Tejon Earthquake, 1857 1857 1857 earthquakes 1857 in California History of Southern California San Emigdio Mountains Sierra Pelona Ridge Tehachapi Mountains History of Kern County, California History of Ventura County, California History of Los Angeles County, California History of Santa Barbara County, California Mountain Communities of the Tejon Pass January 1857 events