2 strong earthquakes per day happened in California: what residents should prepare for

Two noticeably strong earthquakes in Northern California in less than 15 hours excited the residents of the San Francisco Bay Area. They began just a few days before the 30 anniversary of the devastating earthquake in Loma Prieta, which killed dozens of people.

Фото: Depositphotos

The earthquakes began on Monday at 22: 33 evenings when shocks of magnitude 20 occurred in the suburb of Contra Costa, in the East Bay, about 12 miles (4,5 km) northeast of San Francisco. Then, on 12: 42, an earthquake of 4,7 score occurred on Tuesday in the remote mountains of San Benito County. No serious structural damage was reported. Los Angeles Times.

Seismic forces put the East Bay at high risk of a major earthquake, including from the dangerous Hayward Fault, which runs along densely populated areas. On Thursday, Californians will undergo annual ShakeOut earthquake training, which falls on the 30th anniversary of the magnitude 6,9 quake that killed 63 people in Northern California.

The epicenter of the Monday earthquake was the area surrounded by Walnut Creek, Pleasant Hill and Concord. The quake had a preliminary depth of about 9 miles (5,5 km), quite deep for this part of the planet, said Keith Knudsen, a geologist at the US Geological Survey and deputy director of the Earthquake Science Center, in an interview.

According to scientists, the depth of the earthquake led to the fact that the shocks were felt over a wide area, but the sensations of trembling on the surface were less intense than if the earthquake were not so deep.

The epicenter is located northwest of Mount Diablo, one of the highest peaks of the Gulf. The area is a seismically active area, "an area of ​​uplift, folding and pushing," said David Schwartz, an honorary scientist at the US Geological Survey. A series of earthquakes of 5 magnitude occurred in 1980 on the southeast side of the mountain in the Greenville Fault zone.

An earthquake of magnitude 4,7 scores was felt in Morgan Hill, Santa Cruz, Monterey Carmel, Salinas, King City and Gilroy, writes CBS San Francisco. It all started with tremors with the power of 2,6 score in 12: 55. Seismologists first rated the estimated maximum magnitude as 4,8, but later revised the data.

This earthquake occurred two days before the 30 anniversary of the deadly and destructive Loma Priet earthquake in the 1989 year, which occurred along the same fault line. As a result of the earthquake, 63 people died, about 4000 were injured, and significant damage was done.

On the subject: A strong earthquake hits California: what can residents expect

Experts say it is unlikely that the current earthquake with the 4,7 score was a harbinger of a larger seismic event.

“The San Andreas Fault was central to the 1989 earthquake... as well as the 1906 event (Great San Francisco Earthquake),” said Anne Marie Baltay of the USGS. “San Andreas is capable of a much bigger event.” We don't think that this particular region is going to experience a really big earthquake. And we don’t think that this was his harbinger.”

“But there is always a chance that a larger event could occur,” the seismologist added.

KPIX 5 reporter Len Ramirez was in Santa Cruz when the earthquake struck.

“I sat in the shaking SUV and looked around, thinking it might be an earthquake,” he said. “No one reacted on the street.” People were just minding their own business. Everything lasted about 30-50 seconds.”

But Stacy Pinkham of Santa Cruz said the quake shook her area.

“Santa Cruz was pretty shaken up!” she wrote on her Facebook page.

Edward Kiliberti of Monterey recalled the 1989 earthquake of the year.

“I remember the big earthquake in Monterey, and today was felt much stronger,” he wrote. “Perhaps because the epicenter of today's earthquake was in the Pinnacles, much closer to us.”

Jessica Torres Vazquez from Greenfield commented on the rumbling sound that could precede an earthquake.

“There was a loud noise, like a plane taking off close by, it was strange,” she wrote.

The earthquake occurred along the moving San Andreas Fault stretch of about 90 miles (56 km) and was an 10 earthquake of more than 4 magnitude over the last 20 years in the area, according to seismologists.

On the subject: 10 strongest earthquake in California history

San Andreas in California. Photo: Depositphotos

San Francisco Bay Area most dangerous faults

The San Andreas Fault was created by a massive earthquake in 1906, creating a 300-mile (186 km) rift in the Earth's crust between San Juan Bautista in San Benito County and Cape Mendocino. A long strip of the southern San Andreas last faulted in 1857, from Parkfield in Monterey County to Wrightwood in San Bernardino County. Both earthquakes were estimated to have a magnitude of 7,8. Whether large earthquakes can continue to shake the surface of the earth above the San Andreas Fault is still being studied.

Concord Green Valley and Calaveras faults are some of the most significant in the San Francisco Bay area. A hypothetical earthquake of 6,8 magnitude along the Concord Green Valley fault can cause a strong shake in the counties of Contra Costa, Solano and Napa and can damage the Kinder Morgan Concord pumping station, which is responsible for pumping fuel through the northern half of California. All five Gulf region refineries export refined fuel through this pumping station.

Such a likely earthquake will be strong enough to disperse across all the Gulf counties. A strong concussion will be felt in the Karkines Strait, connecting the bays of San Francisco and San Pablo with the two longest rivers in California, Sacramento and San Joaquin. An earthquake can cause the edges of the dredging canals to enter the waterways. The last major Concord Green Valley fault earthquake occurred in 1610. The 5,4 magnitude earthquake occurred at the fault site in the 1955 year.

The Calaveras Fault could produce a magnitude 7 earthquake, and it's possible it could also trigger the Hayward Fault, one of the nation's most dangerous faults that runs directly beneath densely populated East Bay cities like Oakland, Berkeley, Hayward and Fremont.

According to Ross Stein, executive director of Temblor.net and a former geophysicist at the US Geological Survey, the largest historical earthquake in the Calaveras Fault in 1911 was 6,6 points. According to Berkeley's seismological laboratory, just one spike in activity in the 2015 year, which occurred near the Calaveras Fault, caused 4000 earthquakes in 5 months. The epicenter of the earthquake is in the San Ramon Valley, where over the past few decades there have been many bursts that did not lead to a major earthquake.

According to a report published in 2018 by the USGS, at least 800 people could be killed and another 18 injured in a hypothetical magnitude 000 earthquake on the Hayward Fault centered beneath Oakland. Hundreds more could die from fire after the quake along the 7-mile (52m) long fault - 32-plus fires (the equivalent of 400 homes) are possible - and water shortages for firefighters caused by collapsing old pipes underground could make matters worse.

Hayward Fault is so dangerous because it runs through some of the most densely populated areas of the Bay Area, extending over the entire length of the East Bay from San Pablo Bay to Berkeley, Auckland, Hayward, Fremont and Milpitas. Of the total 7 millionth population of the region, 2 million people live at the top of the fault, and this proximity brings potential danger.

According to USGS, the most memorable earthquake in the Hayward Fault occurred in the 1868 year and was rated as an 6,8 magnitude earthquake. As a result, about 30 people were killed and huge material damage was caused, including the collapse of the second floor of the Alameda County Courthouse and severe damage to the Mission's historic church in San Jose in southern Fremont.

In addition to the Hayward, Calaveras, Concord Green Valley and Greenville faults, there are three more: the Rogers Creek fault passing through Santa Rosa and the San Gregorio fault, which extends west of San Andreas, roughly off the coast of the Gulf region and along the coastal areas of Marin and San Mateo counties, further south to Monterey Bay.

On October 1 of 1969 of the year near Santa Rosa, two devastating earthquakes of magnitude 5,6 and 5,7 occurred, which at that time were the largest in the area of ​​the bay since 1906 of the year. Earthquakes up to 7 points are possible here. According to a study published in the Bulletin of the Seismological Society of America in 1997, the last major event in the San Gregorio Fault (between 7 and 7,25 points) probably occurred between 620 and 1400 years.

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