Magnitude 5.1 quake strikes in San Francisco Bay Area

A magnitude 5.1 earthquake has rattled the San Francisco Bay Area

A magnitude 5.1 earthquake rattled the San Francisco Bay Area on Tuesday, causing delays of some commuter trains. There were no immediate reports of damage or injuries.

The U.S. 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 hill country about 40 miles (64 kilometers) southeast of downtown San Francisco.

Lucy Jones, a veteran California seismologist, told KNTV-TV that the quake happened on the Calaveras fault, one of eight major faults in the Bay Area.

“The Calaveras fault is one that tends to have smaller earthquakes,” Jones said.

It was the largest earthquake in the Bay Area since a magnitude 6.0 jolt in the Napa wine country in 2014, Jones said in a social media post.

The 138-mile (220-kilometer) long Calaveras fault is a major branch of the San Andreas fault and runs from San Juan Bautista in the south to San Ramon in the north, Jones said.

Numerous moderate earthquakes have occurred along the Calaveras fault, including the 6.2 Morgan Hill earthquake in 1984, Annemarie Baltay, a seismologist with the U.S. Geological Survey, said in a video statement posted on Twitter.

Rich Constantine, the mayor of Morgan Hill, a city next to San Jose, said he was in the kitchen of his home when Tuesday's “long and steady” quake struck.

“We had a frame in the house fall, everything was shaking but once it stopped, there was no damage,” he said.

Constantine said Morgan Hill's City Hall and other city offices were evacuated but that everyone returned to work soon after.

People reported feeling the quake as far south as the scenic Big Sur coast, 75 miles (120 kilometers) south of the epicenter in the region of Joseph Grant Ranch County Park, a huge natural area.

Nearly 100,000 people reported receiving a warning before the shaking started through California’s earthquake early warning system, according to the California Governor’s Office of Emergency Services, or Cal OES.

“Advance notice varied from two seconds for those very near the epicenter to 18 seconds for those in San Francisco,” the agency said.

MyShake, a statewide cellphone app that went live to the general public in late 2019, relies on an earthquake detection and notification system developed by the U.S. Geological Survey and partners.

A 3.1 aftershock followed about 5 minutes later, according to the U.S. Geological Survey.

Several commuter train 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 by early afternoon.