The Garlock Fault is a left-lateral

strike-slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

running northeast–southwest along the north margins of the

Mojave Desert The Mojave Desert (; ; ) is a desert in the rain shadow of the southern Sierra Nevada mountains and Transverse Ranges in the Southwestern United States. Named for the Indigenous peoples of the Americas, indigenous Mohave people, it is located pr ...

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...

, for much of its length along the southern base of the Tehachapi Mountains.

Geography

Stretching for , it is the second-longest fault in California, and one of the most prominent geological features in the southern part of the state. It marks the northern boundary of the area known as the Mojave Block, as well as the southern ends of the

Sierra Nevada The Sierra Nevada ( ) is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primari ...

and the valleys of the westernmost

Basin and Range province The Basin and Range Province is a vast United States physiographic region, physiographic region covering much of the inland Western United States and Northern Mexico, northwestern Mexico. It is defined by unique basin and range topography, charac ...

. The Garlock Fault runs from a junction with the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

in the

Antelope Valley The Antelope Valley is a valley primarily located in northern Los Angeles County, California, United States and the southeast portion of Kern County, California, Kern County, and constitutes the western tip of the Mojave Desert. It is situated ...

, eastward to a junction with the Death Valley Fault Zone in the eastern Mojave Desert. It is named after the historic mining town of Garlock, founded in 1894 by Eugene Garlock and now a

ghost town A ghost town, deserted city, extinct town, or abandoned city is an abandoned settlement, usually one that contains substantial visible remaining buildings and infrastructure such as roads. A town often becomes a ghost town because the economi ...

. Relatively few communities lie directly along the Garlock, as it is primarily situated in the desert, with Frazier Park, Tehachapi, Mojave, and

Johannesburg Johannesburg ( , , ; Zulu language, Zulu and Xhosa language, Xhosa: eGoli ) (colloquially known as Jozi, Joburg, Jo'burg or "The City of Gold") is the most populous city in South Africa. With 5,538,596 people in the City of Johannesburg alon ...

being the closest to it.

Geology

The Garlock Fault is believed to have developed to accommodate the strain between the

extensional tectonics Extensional tectonics is concerned with the structures formed by, and the Tectonics, tectonic processes associated with, the stretching of a planetary body's Crust (geology), crust or lithosphere. Deformation styles The types of structure and the ...

of the

Great Basin The Great Basin () is the largest area of contiguous endorheic watersheds, those with no outlets to the ocean, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja Californi ...

crust and the right lateral strike-slip faulting of the

crust. Unlike most of the other faults in California, slip on the Garlock Fault is left-lateral; that is, the land on the other side of the fault moves to the left from the perspective of someone facing the fault. Thus, the terrain north of the fault is moving westward and that on the south is moving eastward.

Activity

The Garlock Fault moves at a rate of between 2 and 11 mm a year, with an average slip of around 7 millimeters. While most of the fault is locked, certain segments have been shown to move by

aseismic creep In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip i ...

, which is motion without resulting earthquakes. The Garlock is not considered to be a particularly

active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...

, seldom producing any shaking detectable by humans, although it has been known to generate sympathetic seismic events when triggered by other

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

s and in one instance by the removal of

ground water Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit of rock or an unconsolidat ...

. These events, as well as continuing microearthquake activity and the state of the scarps from previous ruptures, do indicate that the Garlock will produce another major quake at some point in the future. A study published in October 2019 in the journal ''

Science Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...

'' indicated that a part of the Garlock fault slipped after being triggered by the series of earthquakes in the Ridgecrest area which occurred in July 2019. Reports in the

Los Angeles Times The ''Los Angeles Times'' is an American Newspaper#Daily, daily newspaper that began publishing in Los Angeles, California, in 1881. Based in the Greater Los Angeles city of El Segundo, California, El Segundo since 2018, it is the List of new ...

indicated that a magnitude 8 earthquake along the Garlock fault would have the potential for grave disaster. The last significant ruptures on the Garlock were thought to be in the years 1050 AD and 1500 AD. Research has pinned the interval between significant ruptures on the Garlock as being anywhere between 200 and 3,000 years, depending on the segment of the fault. The most recent notable event in the Garlock Fault Zone was a magnitude 5.7 near the town of Mojave on July 11, 1992. It is thought to have been triggered by the Landers earthquake, just two weeks earlier. However, no surface slippage of the fault itself had been recorded in modern times until 2019. Following a series of earthquakes on nearby minor faults in late July 2019, the Garlock Fault was observed moving about 2 cm (0.8 in) between July and October accompanied by numerous minor earthquakes, a state known as fault creep, and producing a bulge in land observed by satellite radar images.

References

External links

Southern California Earthquake Data Center: Faults in Southern California
{{Faults Seismic faults of California Natural history of the Mojave Desert Natural history of Kern County, California Natural history of Los Angeles County, California Natural history of San Bernardino County, California Tehachapi Mountains Strike-slip faults