At least 26 aftershocks rattle San Francisco after 4.5-magnitude quake, experts say

Two earthquakes rattled the San Francisco Bay area shortly after 10 p.m. Monday, and residents of the Pleasant Hill area report the violent shaking was preceded by what some described as an equally terrifying “sonic boom.”

The first was a 2.5 magnitude quake around 10:23 p.m. Pacific Time, followed by a 4.5 magnitude earthquake at 10:33 p.m., according to the U.S. Geological Survey. Both were centered around Pleasant Hill, a city northeast of San Francisco., officials said.

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People in the area took to social media shortly after, reporting they first heard “a boom” then felt “a big jolt” and ”a variety of rolling and hard shakes” that prompted pets to run in terror and objects to fly off shelves.

The Contra Costa County sheriff’s office said on Twitter shortly after the quake that it had no reports of injuries or serious damage.

By 11 p.m., about 30,000 people had reported feeling the quake to the U.S. Geological Survey, KPIX reported. Some were as far away as Reno and Fresno.

“Still a little surprising, but not entirely,” said Amy Vaughn with USGS, according to the station. She said it’s not unusual for San Francisco-area quakes to be widely felt.

Bay Area residents said they felt a jolt followed by a hard rolling motion for several seconds, KPIX reported.

“Thought a truck was coming in my window,” said Janet McIntosh in Walnut Creek, according to the station.

“Like a strong sonic boom, (from below),” posted Hugh P. Drake III on Facebook, “and two seconds later a slow back and forth rolling, for a few seconds.”

“It was a Bang then hard shaking 3 or 4 seconds ,all strong shaking, and it died off quick like a light switch. There was nothing gentle about it,” posted Tim Chung in Pleasant Hill on the KPIX Facebook page.

“I live in Martinez. Big jolt and everything shook not a roll,” reported Terry Conners on Facebook. “Glass candle fell and broke. Canned goods fell out of pantry. Boxes fell from rafters in garage. Very scary. I’m hugging my dog right now.”

“Thought the roof was going to come down,” Leonard Young said on Facebook.

“HUGE here in our home in Martinez,” posted Stephanie McKim Gracy. “Our three dogs scared to death!! We are checking for cracks in the stucco and foundation.”

The quake also caused flaring at two Martinez refineries, which shut down as a result of the temblor, The Mercury News reported. But county environmental officials said the incidents were not unusual and did not require any warnings to residents.

“A good little shaker,” said Casey Ashimine, a bartender at a Pleasant Hill bar, the Los Angeles Times reported. “A couple people looked around, but nobody freaked out.”

U.S. Geological Survey officials said the quake struck deep below the surface at “a point of tension” between the Calaveras and Concord faults, The San Francisco Chronicle reported.

Three foreshocks, including the 2.5 magnitude quake, preceded the larger quake, and 26 aftershocks have followed so far, according to the publication.

“Some of those aftershocks go down to nearly magnitude zero,” said Keith Knudsen, deputy director of the USGS Earthquake Science Center, The San Francisco Chronicle reported. “Most of those were not felt. They were only sensed by our instruments.”

Photos from a Safeway store in Pleasant Hill showed cans and other products toppled from shelves by the quake, KNTV reported.

San Francisco’s Bay Area Rapid Transit reported on Twitter Monday night that trains “are running at reduced speeds completing track inspections.” Residual delays of 10 to 15 minutes throughout the BART system were to be expected, the agency said.

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Mark Price has been a reporter for The Charlotte Observer since 1991, covering beats including schools, crime, immigration, the LGBTQ issues, homelessness and nonprofits. He graduated from the University of Memphis with majors in journalism and art history, and a minor in geology.