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Unprecedented movement detected by an earthquake failure in California, suitable for 8.0 temblor

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A major Californian error that could cause a magnitude 8 earthquake has begun to move for the first time in the past, a result of this year's Ridgecrest earthquake sequence destabilizing nearby errors, Caltech scientists say in a new study on Thursday in the journal Science was published.

In the modern historical record, the 160-mile-long Garlock error on the northern edge of the Mojave Desert has never been observed to cause a strong earthquake or even creep.

But new satellite radar images now show that the error has begun to move, creating a bulging soil that can be viewed from space.

"This is surprising because we have never seen the Garlock error do anything. Here it suddenly changed behavior, & # 39; said the lead author of the study, Zachary Ross, assistant professor of geophysics at Caltech. "We don't know what it means."

The crawl illustrates how the Ridgecrest – the largest in Southern California in two decades – has destabilized this remote desert area of ​​California between the state's largest mountain range, the Sierra Nevada, and the lowest point, Death Valley.

It also pierces a persistent myth that is circulating in California and beyond – that quakes like the Ridgecrest temblors are somehow a good thing that makes future earthquakes less likely. Earthquakes make future earthquakes more likely. The follow-on quakes are usually smaller. But occasionally they are bigger.

Not only has the Garlock error started to creep into one section, but there has also been a significant swarm of small earthquakes in another section of the fault, and two additional clusters of earthquakes elsewhere – one south of Owens Lake and the other in the Panamint Valley just west of Death Valley.

Whether the destabilization will soon lead to a major earthquake cannot be predicted. In September the US said Geological Survey the most likely scenario is that the Ridgecrest earthquakes are unlikely to cause a larger earthquake. Nevertheless, the USGS said that the July earthquakes increased the probability of an earthquake of 7.5 or more on the nearby Garlock, Owens Valley, Blackwater and Panamint Valley errors in the coming year.

A major earthquake on the Garlock error can cause vigorous shaking in the San Fernando Valley, Santa Clarita, Lancaster, Palmdale, Ventura, Oxnard, Bakersfield and Kern County, one of the nation's most productive regions for agriculture and oil.

Important military installations can also shake considerably, such as Edwards Air Force Base, China Lake Naval Air Weapons Station and Fort Irwin National Training Center. The fault is traversed by two of the most important stocks of imported water from Southern California – the aqueducts from California and Los Angeles – and critical roads such as the Interstate 5, state routes 14 and 58 and the US 395.

A major earthquake on the Garlock error can in turn destabilize the San Andreas. A powerful earthquake on a piece of the approximately 300-mile-long southern San Andreas fault can cause the worst shaking Southern California region has felt since 1857and send destructive vibrations through Los Angeles and beyond.

A plausible scenario concerns the Ridgecrest earthquakes that cause a major shock on the Garlock error, which then causes a seismic event on the San Andreas. The chance that such an event takes place is small. Another plausible scenario, not mapped out, includes a breach of error southeast of the Ridgecrest earthquakes.

(Jon Schleuss / Los Angeles Times)

A creeping error caused by a nearby earthquake does not necessarily mean that a major earthquake is imminent. The southernmost tip of the San Andreas fault has traditionally crept in response to distant quakes, including the magnitude 8.2 quake off the coast of southern Mexico in 2017, nearly 2,000 miles away. "But that doesn't mean San Andreas went off," said USGS research geologist Kate Scharer, who was not part of the study.

What is unusual now, Ross said, is that the Garlock error has so far been seismically silent in historical history. And while it is unclear what the creeping and after-shocks could mean for the near future, the newly included movement emphasizes how much a potential risk the Garlock error is for California should it rupture on a large scale.

The research was written by some of Caltech's most prominent earthquake experts in Pasadena and NASA's Jet Propulsion Laboratory in Flintridge, La Cañada, managed by Caltech.

The findings confirm what some scientists expected from the Ridgecrest earthquakes. The largest earthquake of the series, the magnitude 7.1 event on July 5, broke for 35 miles over a series of previously unidentified errors for 22 seconds. The southeastern ends were only a few kilometers away from the Garlock error.

The Garlock error accumulates seismic stress at one of the higher speeds in California. According to USGS research geophysicist Morgan Page, who was not involved in the research, the average time between earthquakes of at least magnitude 7 on the central part of the error is approximately every 1200 years. But there is a huge variation; sometimes only 200 years can pass between major earthquakes due to the error; however, it can take 2000 years for an encore. The last time a major quake would have hit the Garlock error was about 465 years ago, give or take a century.

For some scientists, the physics of the earthquake with force 7.1 on July 5 immediately suggested that the Garlock error would more likely rupture. Here is a possible explanation: the southwestern side of the error that tore on July 5 swung to the northwest. This had the effect of moving a piece of land away from the Garlock fault, disconnecting it, and making it easier for blocks of land that accumulate on both sides of the Garlock fault, as if a cyclist had decided to release the brakes to make sure that got hold of the strap.

Satellite radar images show that the part of the Garlock error that has begun to crawl is about 20 miles long, with the land on the north side of the error going west, while the other side is moving east. The radar images show that one side of the error has the majority moved about four fifths of an inch relative to the other.

Helping scientists are state-of-the-art observations with incredible high-resolution details that have not been possible in a previous major earthquake in California.

The Ridgecrest earthquakes occurred in an area with a particularly extensive network of earthquake sensors near the seismically active Coso volcanic field from Inyo County, which uses heat from magma to fuel a power plant. Since the last major earthquake in Southern California in 1999, more seismic stations have been installed and frequent satellite radar images are being taken of the earth's surface.

In addition to the Garlock error, there is also reason to focus on the risks of other nearby errors.

There is a line of potentially maturing fault zones along the so-called Eastern California Shear Zone, one of the most important seismic zones of the state, which carries much of the earthquake load needed to absorb tectonic plate movements while the Pacific plate the North American sign slides to the northwest.

They generally include an uninterrupted segment of approximately 30 miles between errors that broke in the 1872 earthquake in Owens Valley and the earthquakes in Ridgecrest, and a 75-mile gap along the Blackwater fault system between the errors that the earthquakes in Ridgecrest and size caused 7.3 Lander's quake of 1992. One day those fracture segments will eventually have to tear to catch up with the movement of the tectonic plates, but it is not known whether that will happen in our lives.

Earthquake scientists who are not affiliated with the study called the discovery of the triggered creep on the Garlock error scientifically interesting, but that should be better understood, but emphasize that its implications are unclear. Although the Garlock has not previously been observed to creep in response to major earthquakes, other errors that have crept have not been seen in major earthquakes.

"It's actually quite common, and if that's the case … it doesn't necessarily mean it predicts something terrible," said USGS Page.

Also, the observed creep was probably only in a relatively shallow area. "What we are really interested in is what happens at the depths of where earthquakes occur," said USGS seismologist Elizabeth Cochran, who was not involved in the study. Earthquakes usually occur between a mile and 10 miles deep; the calculated creep probably took place at the shallowest hundreds of feet below the surface.

More research needs to be done as to whether the release of seismic energy in the form of a creeping error near the surface promotes or delays a subsequent earthquake, Scharer of the USGS said. In this specific case, the amount of creep and its superficiality would have little effect on the timing of when the next earthquake hits the Garlock error, Scharer said.

Sometimes major earthquakes can lead to others; a classic example was in 1992, when the size 6.1 Joshua Tree temblor was followed up two months later by the magnitude 7.3 Landers earthquake, which in turn only a few hours later the magnitude 6.3 Earthquake with big bear; seven years later, a magnitude 7.1 earthquake hit Hector Mine. But other times a single major earthquake and the associated aftershocks can lead to decades of seismic silence, such as the magnitude 6.9 Loma Prieta earthquake of 1989.

Despite the uncertainty, what is happening in this region is being closely watched, given that the Garlock error is a major major error for Southern California. There are some major earthquakes that have been observed in California in modern times, and just because something has not been observed in the past does not mean that it cannot happen.

In addition to Ross, the other co-authors in this study are Benjamín Idini, Zhe Jia, Oliver Stephenson, Minyan Zhong, Xin Wang, Zhongwen Zhan, Mark Simons, Eric Fielding, Sang-Ho Yun, Egill Hauksson, Angelyn Moore, Zhen Liu and Jungkyo Jung.

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