SAN FRANCISCO: A magnitude 5.1 earthquake rocked the San Francisco Bay Area on Tuesday, causing delays to some commuter trains. No damage or injuries were immediately reported.
The US Geological Survey said the 11:42 a.m. quake was centered 12 miles (19 kilometers) east of San Jose at a depth of about 4 miles (6 kilometers). The area is a mountainous region about 64 kilometers southeast of downtown San Francisco.
Lucy Jones, a veteran California seismologist, told KNTV-TV the quake happened on the Calaveras Fault, one of eight major faults in the Bay Area.
“The Calaveras Fault is the one that tends to have smaller earthquakes,” Jones said.
It was the largest earthquake in bay area since a magnitude 6.0 tremor in the Napa wine country in 2014, Jones said in a social media post.
The 138-mile (220-kilometer) Calaveras Fault is a major branch of the San Andreas Fault and stretches from San Juan Bautista in the south to San Ramon in the north, Jones said.
Many moderate earthquakes have occurred along the Calaveras Fault, including the 6.2 Morgan Hill earthquake in 1984, US Geological Survey seismologist Annemarie Baltay said in a video statement posted to Twitter.
Rich Constantine, the mayor of Morgan Hill, a town neighboring San Jose, said he was in the kitchen of his home when Tuesday’s “long and steady” earthquake struck.
“We had a frame in the house that fell, everything was shaking but once it stopped, there was no damage,” he said.
Constantine said Morgan Hill City Hall and other city offices were evacuated, but everyone returned to work soon after.
People reported feeling the quake as far south as the scenic Big Sur coast, 120 miles south of the epicenter in the area of ​​Joseph Grant Ranch County Park, a huge natural area.
According to the California Governor’s Office of Emergency Services, or Cal OES, nearly 100,000 people said they received a warning before the tremors began thanks to the California Earthquake Early Warning System.
“Advance notice ranged from two seconds for those very close to the epicenter to 18 seconds for those in San Francisco,” the agency said.
MyShake, a statewide cell phone app that went live for the general public in late 2019, is based on an earthquake detection and notification system developed by the U.S. Geological Survey and his partners.
A 3.1 aftershock followed about 5 minutes later, according to the US Geological Survey.
Several commuter rail companies, including Cal Train and the Bay Area Rapid Transit system, known as BART, held trains to check for damage. BART returned to normal service in the early afternoon.

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