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.
Stretching for 250 kilometers (160 mi), 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 and the valleys of the westernmost Basin and Range province.
The Garlock Fault runs from a junction with the San Andreas Fault in the Antelope Valley, 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. Relatively few communities lie directly along the Garlock, as it is primarily situated in the desert, with Frazier Park, Tehachapi, Mojave, and Johannesburg being the closest to it.
The Garlock Fault is believed to have developed to accommodate the strain between the extensional tectonics of the Great Basin crust and the right lateral strike-slip faulting of the Mojave Desert crust. [1]
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.
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, which is motion without resulting earthquakes.
The Garlock is not considered to be a particularly active fault, seldom producing any shaking detectable by humans, although it has been known to generate sympathetic seismic events when triggered by other earthquakes and in one instance by the removal of ground water. 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. [2]
A study published in October 2019 in the journal Science 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. [3] Reports in the Los Angeles Times indicated that a magnitude 8 earthquake along the Garlock fault would have the potential for grave disaster. [3]
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. [4] The most recent notable event in the Garlock Fault Zone was a magnitude 5.7 near the town of Mojave on July 11, 1992. [5] It is thought to have been triggered by the Landers earthquake, just two weeks earlier. [5] 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) [6] 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. [6] [7] [8]
An earthquake 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, from those that are so weak that they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume. The word tremor is also used for non-earthquake seismic rumbling.
The San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the Californias. It forms the tectonic boundary between the Pacific Plate and the North American Plate. Traditionally, for scientific purposes, the fault has been classified into three main segments, each with different characteristics and a different degree of earthquake risk. The average slip rate along the entire fault ranges from 20 to 35 mm per year.
In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousands of instrumentally detectable aftershocks, which steadily decrease in magnitude and frequency according to a consistent pattern. In some earthquakes the main rupture happens in two or more steps, resulting in multiple main shocks. These are known as doublet earthquakes, and in general can be distinguished from aftershocks in having similar magnitudes and nearly identical seismic waveforms.
The 1857 Fort Tejon earthquake occurred at about 8:20 a.m. 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 the southern part of the San Andreas Fault for a length of about 225 miles, between Parkfield and Wrightwood.
The 1999 Hector Mine earthquake occurred in Southern California, United States, on October 16 at 02:46:50 PDT. Its moment magnitude was 7.1 and the earthquake was preceded by 12 foreshocks, the largest of which had a magnitude of 3.8. The event is thought to have been triggered by the 1992 Landers earthquake which occurred seven years earlier. It also deformed nearby faults vertically and horizontally. The earthquake's hypocenter was at a depth of 20 kilometers and its epicenter at 34.603° N 116.265° W.
The White Wolf Fault is a fault in southern California, located along the northwestern transition of the Tejon Hills and Tehachapi Mountains with the San Joaquin Valley. It is north of the intersection of the San Andreas Fault and the Garlock Fault, and roughly parallel with the latter. It is classed as a reverse fault with a left lateral (sinistral) component.
The 1952 Kern County earthquake occurred on July 21 in the southern San Joaquin Valley and measured 7.3 on the moment magnitude scale. The main shock occurred at 4:52 am Pacific Daylight Time, killed 12 people, injured hundreds more and caused an estimated $60 million in property damage. A small sector of damage near Bealville corresponded to a maximum Mercalli intensity of XI (Extreme), though this intensity rating was not representative of the majority of damage. The earthquake occurred on the White Wolf Fault near the community of Wheeler Ridge and was the strongest to occur in California since the 1906 San Francisco earthquake.
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, or sinistral, strike-slip fault. The north-northwest end of the Walker Lane is between Pyramid Lake in Nevada and California's Lassen Peak where the Honey Lake Fault Zone, the Warm Springs Valley Fault, and the Pyramid Lake Fault Zone meet the transverse tectonic zone forming the southern boundary of the Modoc Plateau and Columbia Plateau provinces. The Walker Lane takes up 15 to 25 percent of the boundary motion between the Pacific Plate and the North American Plate, the other 75 percent being taken up by the San Andreas Fault system to the west. The Walker Lane may represent an incipient major transform fault zone which could replace the San Andreas as the plate boundary in the future.
Episodic tremor and slip (ETS) is a seismological phenomenon observed in some subduction zones that is characterized by non-earthquake seismic rumbling, or tremor, and slow slip along the plate interface. Slow slip events are distinguished from earthquakes by their propagation speed and focus. In slow slip events, there is an apparent reversal of crustal motion, although the fault motion remains consistent with the direction of subduction. ETS events themselves are imperceptible to human beings and do not cause damage.
An earthquake occurred in China on 14 November 2001 at 09:26 UTC, with an epicenter near Kokoxili, close to the border between Qinghai and Xinjiang in a remote mountainous region. With a magnitude of 7.8 Mw, it was the most powerful earthquake in China for 5 decades. No casualties were reported, presumably due to the very low population density and the lack of high-rise buildings. This earthquake was associated with the longest surface rupture ever recorded on land, ~450 km.
The San Jacinto Fault Zone (SJFZ) is a major strike-slip fault zone that runs through San Bernardino, Riverside, San Diego, and Imperial Counties in Southern California. The SJFZ is a component of the larger San Andreas transform system and is considered to be the most seismically active fault zone in the area. Together they relieve the majority of the stress between the Pacific and North American tectonic plates.
The 2019 Ridgecrest earthquakes of July 4 and 5 occurred north and northeast of the town of Ridgecrest, California located in Kern County and west of Searles Valley. They included three initial main shocks of Mw magnitudes 6.4, 5.4, and 7.1, and many perceptible aftershocks, mainly within the area of the Naval Air Weapons Station China Lake. Eleven months later, a Mw 5.5 aftershock took place to the east of Ridgecrest. The first main shock occurred on Thursday, July 4 at 10:33 a.m. PDT, approximately 18 km (11.2 mi) ENE of Ridgecrest, and 13 km (8.1 mi) WSW of Trona, on a previously unnoticed NE-SW trending fault where it intersects the NW-SE trending Little Lake Fault Zone. This quake was preceded by several smaller earthquakes, and was followed by more than 1,400 detected aftershocks. The M 5.4 and M 7.1 quakes struck on Friday, July 5 at 4:08 a.m. and 8:19 p.m. PDT approximately 10 km (6 miles) to the northwest. The latter, now considered the mainshock, was the most powerful earthquake to occur in the state in 20 years. Subsequent aftershocks extended approximately 50 km (~30 miles) along the Little Lake Fault Zone.
The 1981 Westmorland earthquake occurred at 05:09 Pacific Daylight Time on April 26. The moderate strike-slip shock took place in the Imperial Valley of Southern California, just north of the Mexico–United States border. No injuries or deaths occurred, but damage was estimated at $1–3 million. With a Mercalli intensity of VII, this was one of fifteen intensity VII or greater shocks in the Imperial Valley that were observed in the 20th century up until April 1981. The region experiences large stand-alone events and earthquake swarms due to its position in an area of complex conditions where faulting transitions from strike-slip movement to the north and divergence to the south.
The Haiyuan Fault is a major active intracontinental strike-slip (sinistral) fault in Central Asia.
The 1987 Superstition Hills and Elmore Ranch earthquakes were a pair of earthquakes measuring Mw 6.0 and 6.5 that rattled the Imperial Valley of California. The earthquakes caused damage in Southern California and Mexico, but was limited due to their location in a sparsely populated area. It was felt as far as Las Vegas and Phoenix. More than 90 were injured, and two people were killed in Mexico.
The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST, near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). Damage was relatively moderate, and the mainshock was assigned a maximum Modified Mercalli intensity (MMI) of VII. Shaking was felt in Nevada, and Arizona. It was the largest earthquake to strike California since 1952, and its display of afterslip became the subject of scientific interest.
The 1906 Manasi earthquake (玛纳斯地震), also known as the Manas earthquake occurred in the morning of December 23, 1906, at 02:21 UTC+8:00 local time or December 22, 18:21 UTC. It measured 8.0–8.3 on the moment magnitude scale and 8.3 on the surface-wave magnitude scale. The epicenter of this earthquake is located in Manas County, Xinjiang, China. An estimated 280–300 people died and another 1,000 more were injured by the earthquake.
The 1995 Menglian earthquake or 1995 Myanmar–China earthquake occurred on 12 July at 05:46:43 local time in the Myanmar–China border region. The earthquake had an epicenter on the Myanmar side of the border, located in the mountainous region of Shan State. It registered 7.3 on the Chinese surface wave magnitude scale (Ms ) and 6.8 on the moment magnitude scale (Mw ). With a maximum Mercalli intensity assigned at VIII, the quake killed eleven people and left another 136 injured. Over 100,000 homes in both countries were destroyed and 42,000 seriously damaged. Some damage to structures were also reported in Chiang Mai and Chiang Rai, Thailand. The low death toll from this earthquake was attributed to an early warning issued prior to it happening. Precursor events including foreshocks and some seismic anomalies led to an evacuation of the area before the mainshock struck. It is thought to be one of the few successfully predicted earthquakes in history.
The 1850 Xichang earthquake rocked Sichuan Province of Qing China on September 12. The earthquake which caused major damage in Xichang county had an estimated moment magnitude of 7.6–7.9 Mw and a surface wave magnitude of 7.5–7.7 Ms . An estimated 20,650 people died.
The 1955 Zheduotang earthquake, also known as the Kangding earthquake occurred on April 14 at 09:29:02 local time near the city of Kangding in the Garzê Tibetan Autonomous Prefecture, Sichuan. The earthquake had a moment magnitude of 7.0 and a surface wave magnitude of 7.1 and struck at a depth of 10 km. Severe damage occurred in Kangding with the loss of 70 lives.