Magnitude 3.8 earthquake shakes Bay Area

SAN LEANDRO — A 3.8 magnitude earthquake jolted the East Bay early Thursday, and was widely felt across the Bay Area, from Santa Rosa to Santa Cruz and out to Tracy.

The quake hit at 8:30 a.m. and originally was measured at magnitude 4.0 by the U.S. Geological Survey. The quake was centered about 2 miles northeast of San Leandro and was about 5½ miles deep below the earth’s surface, according to the agency.

The quake occurred on the Hayward Fault, said Sarah Minson, a research geophysicist with the USGS.

Initial reports indicated there were no injuries or major damage. The quake did cause BART to slow down train service because of track safety inspections.

“This was a fairly small magnitude earthquake,” Minson said. “People who were on top of it experienced light shaking but it’s not enough to cause structural damage.”

So far this year, there have been six other earthquakes in the nine-county Bay Area larger than Thursday’s. The most recent was a 4.2 that occurred July 28 near Cloverdale in Sonoma County. In the East Bay, Thursday’s quake was the largest in six months — since a 4.2 near San Ramon on February 2.

Thursday’s quake was not related to a swarm of dozens of small earthquakes that occurred last fall and winter in the San Ramon area, Minson said.

Those who felt the quake described it both as sharp and wavy. The coordinates show epicenter was near the border of San Leandro and Oakland.

Two aftershocks — measured at 3.0 and 2.8 magnitude — came after 9 a.m. and were centered in the same general area.

Often, when quakes occur, people aren’t sure whether they are feeling a small quake with an epicenter nearby, or a large quake that occurred a long distance away. Minson said one key clue is the amount of time the shaking lasts.

“If you feel weak shaking for just a second you are near a small earthquake,” she said. “If you feel weak shaking that goes on and on, you are far away from a big earthquake.”

Two months ago, a magnitude 5.6 quake shook southern Mendocino County, in the community of Redwood Valley between Ukiah and Willits. That was the largest quake anywhere in California in 3 years. It caused some damage and minor injuries.

That quake, on the Maacama Fault, a northern extension of the Hayward Fault, was the largest earthquake anywhere in California since Dec. 20, 2022, when a 6.4 quake hit near the small town of Ferndale on the Humboldt County coast.

The shaking from it set off earthquake alerts on phones across Northern California, including in the Bay Area. The California Office of Emergency Services reported that 657,000 early warning alerts were sent by the MyShake app during that event.

The last significant damaging earthquake in the nine-county Bay Area was the 6.0 South Napa Quake on Aug. 24, 2014, which killed 1 person, injured 300 and caused $1 billion in damage in Napa and Vallejo. Before that, it was the 6.9 magnitude Loma Prieta Earthquake on Oct. 17, 1989, which disrupted the World Series, and wrecked the Bay Bridge, Oakland’s Cypress Freeway, downtown Santa Cruz and parts of San Francisco, killing 63 people.

There is about a 72% probability of one or more magnitude 6.7 or larger earthquakes within 30 years in the San Francisco Bay Area, according to the USGS.

This is a developing story. Please check back for updates.