The 1812 Ventura earthquake (also known as the Santa Barbara earthquake) occurred on the morning of December 21 at 11:00
Pacific Standard Time (PST). The 7.1–7.5 magnitude
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
, with a
Modified Mercalli intensity scale
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...
rating of X (''Extreme''), along with its resulting
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...
, caused considerable damage to present-day
Santa Barbara and
Ventura County
Ventura County () is a County (United States), county in Southern California, the southern part of the U.S. state of California. As of the 2020 United States Census, 2020 census, the population was 843,843. The largest city is Oxnard, California ...
, California, which was at the time a territory of the
Spanish Empire
The Spanish Empire ( es, link=no, Imperio español), also known as the Hispanic Monarchy ( es, link=no, Monarquía Hispánica) or the Catholic Monarchy ( es, link=no, Monarquía Católica) was a colonial empire governed by Spain and its prede ...
. One person was killed as a result of the earthquake while another from the aftershock. The earthquake occurred just as the region was recovering from another event on the
8th of December the same year. Both events are thought to have been related.
Geological setting
''see also:
Thrust tectonics
Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, ...
and
Transverse Range''
The
San Andreas is the "master fault" of California, it is the main
plate boundary
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...
in the San Andreas Fault System, consisting of other major active faults. This zone of interaction between the
Pacific
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
and
North American Plates have resulted in hundreds of
faults crisscrossing California. There are several
strike-slip, reverse and
thrust faults
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
hidden under the
Santa Barbara Channel
The Santa Barbara Channel is a portion of the Southern California Bight and separates the mainland of California from the northern Channel Islands. It is generally south of the city of Santa Barbara, and west of the Oxnard Plain in Ventura Cou ...
that could produce devastating earthquakes and tsunamis, including a thrust fault that runs along the base of the
Santa Monica Mountains
The Santa Monica Mountains is a coastal mountain range in Southern California, next to the Pacific Ocean. It is part of the Transverse Ranges. Because of its proximity to densely populated regions, it is one of the most visited natural areas in ...
.
These faults are a result of the "Big Bend" in the San Andreas Fault when it meets with 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 ...
, exerting compression in the crust, forcing thrust and reverse faults to push crustal blocks upwards.
Earthquake origins
Studies have placed the source of this earthquake on two faults. The location and source have not been agreed on, with some researchers providing the epicenter north of Wrightwood or in the Santa Barbara Channel.
San Andreas Fault
Based on
tree-ring sampling, forests were found to have suffered some type of trauma, and were experiencing slow growth in 1812. They were found to have been missing rings and crowns at around the same time.
The trees took several years or decades to fully recover and return to their normal stage. These affected trees were found only in close proximity to the San Andreas Fault; in an event of a strong quake, trees at a considerable distance should also display evidence of trauma. A plausible cause might be that during slippage, the roots of these trees were severed, thus reducing the intake of nutrients and water required for growth. The violent shaking might also knock branches and parts off the trees off.
It is believed that the San Juan Capistrano earthquake on December 8 triggered a second
rupture
Rupture may refer to:
General
* Rupture (engineering), a failure of tough ductile materials loaded in tension
Anatomy and medicine
* Abdominal hernia, formerly referred to as "a rupture"
* Achilles tendon rupture
* Rupture of membranes, a "wate ...
on the San Andreas Fault on December 21.
The rupture on December 21 initiated in the south, and progressed northwards to
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 ...
. Both events ruptured a total length of 170 km on the fault.
The northern end of the rupture is still uncertain because of the overlapping southern rupture end of the
1857 Fort Tejon earthquake
The 1857 Fort Tejon earthquake occurred at about 8:20 a.m. (Pacific time) on January 9 in central and Southern California. One of the largest recorded earthquakes in the United States, with an estimated moment magnitude of 7.9, it ruptured ...
, 44 years later.
However, if the earthquake was sourced from the San Andreas Fault, the aftershocks should not be felt around the coastal regions of California. The documented aftershocks were felt locally, and there were reports of "odd disturbances" in the sea. Another challenge to the San Andreas hypothesis source is the lack of damage at Santa Barbara during the much more powerful 1857 earthquake. The section involved in the 1857 quake was closer to Santa Barbara and Ventura but were not felt severely like in the 1812 earthquake.
Claims of a tsunami and odd disturbances in the sea, can be attributed to a quake triggered
landslide.
San Cayetano Fault
The
San Cayetano Fault
The San Cayetano Fault is an east-west trending thrust fault in Ventura County, Southern California. It stretches for , north of the city of Ventura, near the Topatopa Mountains, Piru, Fillmore, Santa Paula, Sulphur Springs, and Ojai.
Geology
...
is a 40 km long, north dipping reverse fault that extends from Ventura to the Sespe Mountains.
An epicenter proposed in the Santa Barbara Channel was based on reports of the large tsunami that flooded coastal communities.
A study along the San Cayetano Fault in Ventura County revealed evidence of a fresh slip dating between 1660 and 1813 and has been interpreted as a powerful earthquake that was generated by the fault.
Two large slip events were found at the trench dating back to the past 350 years along the fault. The magnitude of these events was estimated to be greater than 7.0 and likely ruptured the entire length of the fault.
Santa Barbara would later be damaged by another
earthquake in 1925, that earthquake triggered a moderate, non-destructive tsunami. That earthquake may have occurred along the Mesa Fault or the
Santa Ynez Fault System.
Impact and aftermath
The first earthquake which may have been a
foreshock
A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full se ...
, occurred at around 10:00–10:15 a.m.. At
Mission La Purisima
Mission (from Latin ''missio'' "the act of sending out") may refer to:
Organised activities Religion
*Christian mission, an organized effort to spread Christianity
*Mission (LDS Church), an administrative area of The Church of Jesus Christ of ...
, padres, soldiers, and
Native Indians ran out of the mission's buildings. They were still outside when the mainshock struck fifteen minutes later. This time, the shaking intensity was much more violent. Bells of the mission church started ringing and the adobe walls began to fracture and collapse. At the mission, a large fissure carved through the slopes of a hill erupted mud and water.
Damage was reported at
Mission Santa Ines,
Mission Santa Barbara
Mission Santa Barbara ( es, link=no, Misión de Santa Bárbara) is a Spanish mission in Santa Barbara, California. Often referred to as the ‘Queen of the Missions,’ it was founded by Padre Fermín Lasuén for the Franciscan order on December ...
,
Santa Barbara Presidio
Santa Claus, also known as Father Christmas, Saint Nicholas, Saint Nick, Kris Kringle, or simply Santa, is a legendary figure originating in Western Christian culture who is said to bring children gifts during the late evening and overnight ...
,
Mission San Buenaventura
Mission San Buenaventura ( es, Misión San Buenaventura), formally known as the Mission Basilica of San Buenaventura, is a Catholic parish and basilica in the Archdiocese of Los Angeles. The parish church in the city of Ventura, California, Uni ...
(Ventura), and
Mission San Fernando as well. One person was killed by a falling boulder at
Agua Caliente. At the various missions, many houses, churches, chapels, and other structures totally collapsed.
Three adobe buildings were destroyed by the advancing tsunami. At Mission San Buenaventura and Mission Santa Barbara, the destruction was great, and a native man died when a building collapsed on him during an aftershock.
The low death toll for this large earthquake was attributed to a foreshock which occurred 15 minutes before the mainshock. The foreshock had driven many people out of buildings that would collapse later.
Devastation from this earthquake was comparable to the
1906 San Francisco and 1857 Fort Tejon earthquakes, but over a much smaller area. Frightened
Chumash Chumash may refer to:
*Chumash (Judaism), a Hebrew word for the Pentateuch, used in Judaism
*Chumash people, a Native American people of southern California
*Chumashan languages, indigenous languages of California
See also
*Chumash traditional n ...
people on
Santa Cruz and
Santa Rosa
Santa Rosa is the Italian, Portuguese and Spanish name for Saint Rose.
Santa Rosa may also refer to:
Places Argentina
*Santa Rosa, Mendoza, a city
* Santa Rosa, Tinogasta, Catamarca
* Santa Rosa, Valle Viejo, Catamarca
* Santa Rosa, La Pampa
* S ...
islands fled to the mainland in their canoes and relocated there. For fears of another tsunami and aftershocks persisting, the missions were abandoned until April 1813.
Tsunami
The captain of the ''Thomas Newland,'' a ship that was in
Refugio Bay, watched as the sea receded, and later returned in a wave that lifted the ship and dumped it at Refugio Canyon, before taking it back out to sea.
Run-up heights of 3–4 meters were recorded at
Gaviota, although eyewitness said the tsunami may have been up to 15.2 meters (50 feet) high.
The tsunami was also recorded at
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 ...
.
See also
*
List of earthquakes in California
*
List of earthquakes in the United States
*
1927 Lompoc earthquake
References
{{Santa Barbara County, California
Earthquakes in California
1812 earthquakes
1812 in Alta California
1810s in Alta California
History of San Bernardino County, California
History of Southern California
Earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
December 1812 events
1812 in New Spain
Spanish missions in California
Tsunamis in the United States
Geology of San Bernardino County, California