Earthquake Swarm in San Ramon Is Felt Around Bay Area, With Over 20 Small Quakes

A flurry of earthquakes shook San Ramon early Monday, the latest swarm of small quakes that have rattled residents in recent months.

The U.S. Geological Survey has recorded 21 quakes near the Contra Costa County city through the morning, with the largest registering at a magnitude 4.2 just after 7 a.m.

The quake originated southeast of San Ramon, with the most intense shaking felt in the city and nearby Dublin. People in large parts of the East Bay, from Oakland and Hayward to Pleasanton, as well as eastern parts of San Francisco, also reported rattling.

In San Ramon, Rachael Heys was woken up by the 4.2 magnitude quake, which she said was one of the biggest she’s felt in a long time. It knocked over some things throughout her home and sent her cats into hiding.

“This is getting really scary,” Heys said after another quake, which registered at magnitude 3.8, occurred just before 7:30 a.m.

The other quakes ranging from magnitude 2.5 to 3.8 occurred around Alcosta Boulevard, south of Bollinger Canyon Road. They likely originated along the Calaveras Fault, which produced another swarm of earthquakes in San Ramon in December.

It’s common for the fault to produce such flurries, according to seismologists. Experts say smaller quakes don’t generally signal a “Big One” is imminent, and the USGS reports that after Monday’s seismic activity, there’s less than a 6% chance of a larger quake in the next week.

But the slip-strike fault is believed to have about an 11% chance of producing a larger quake by 2033. Calaveras is capable of producing a 6.7 magnitude earthquake. It shook Morgan Hill with a magnitude 6.2 in 1984.

“This has been an absolutely crazy hour,” Mona Epstein, another San Ramon resident, said after the initial flurry of quakes. “It just won’t stop. My nerves are frazzled.”

No major damage or injuries resulting from Monday’s shaking has been reported, but Epstein said the quakes kept her awake much of the early morning, and Nextdoor was “blowing up” with fears and reactions from neighbors. Epstein said her doors popped open during one of the quakes.

BART reduced train speeds to conduct track safety inspections following the shaking. The agency said to expect delays up to 20 minutes systemwide as it recovers.

The last quake in the area occurred just after 9 a.m.

KQED’s Ezra David Romero contributed to this report.