A magnitude 4.2 earthquake jolted San Ramon residents awake on Feb. 2, the strongest of 72 tremors that struck the city that day.
According to the Southern California Earthquake Data Center, the earthquake swarm began at 6:27 a.m. with a magnitude 3.8 tremor. While shaking continued all day, most tremors with magnitudes of 2.5 or higher occurred within the first two and a half hours, including the highest magnitude, 4.2, at 7:01 a.m. The epicenters of the quakes were concentrated along the northern segment of the Calaveras Fault.
“It’s not the first time I’ve experienced earthquakes. It’s been going on in San Ramon for many months now,” said Josephine San, a San Ramon resident. “But the one that was on Monday was really big, so it was very scary.”
This swarm is the latest in a series of more than 300 earthquakes to rattle San Ramon since Nov. 9, 2025, continuing to impact local schools and businesses.
Quakes disrupt morning routines
The epicenter of the magnitude 4.2 quake was at the southern end of Canyon Lakes Golf Course and Brewery.
“I heard a lot of cracking in the wall and saw a lot of shaking,” said Ty Roller, Canyon Lakes manager. “We have bottles of liquor on our walls, and some of those fell down as well.”
The intensity of the shakes was concentrated between 6:27 a.m. and 9:03 a.m. as residents prepared for work and school, resulting in 20-minute delays on Bay Area Rapid Transit for track inspections and brief evacuations across the San Ramon Valley Unified School District (SRVUSD).
“One or two schools evacuated, but there was no imminent danger,” said Cathy McSweeney, SRVUSD coordinator of communications. “Staff used the opportunity to practice as they would in the event of a real emergency.”
Stress triggers earthquake swarms
While a typical earthquake sequence involves one large event followed by smaller aftershocks, San Ramon’s geology follows a different pattern.
“A swarm has many earthquakes of similar magnitudes. Most mainshock-aftershock sequences have much more small events than large events,” said Emily Brodsky, a professor of earth and planetary sciences at the University of California, Santa Cruz. “Swarms are also generally more prolonged.”
The U.S. Geological Survey attributes San Ramon’s swarm activity to stresses built up from the broad motion of tectonic plates, but the reason for the city’s susceptibility to swarms remains a mystery.
“It is the subject of much current research,” Brodsky said. “No one knows why that region is more prone to swarms than elsewhere.”
Some residents hope the frequent swarm occurrences mean the earth is “letting off steam” to avoid a larger catastrophe. However, seismologists have warned that small quakes do not significantly reduce the stress required to prevent a major event.
“The general feeling is that having multiple magnitudes three and four earthquakes is actually better,” San said. “Because at least hopefully it’s not going to be one big one coming soon.”
Preparedness ensures community safety
The intensity of the San Ramon swarms has some Carlmont students rethinking their own readiness.
“I’m a bit frightened now,” said sophomore Ella Needleman. “We know to take cover, and our house is reinforced under the code for earthquakes, but I want to talk to my parents and see what we can do to prepare.”
When the tremors struck Feb. 2, SRVUSD schools activated the Standard Response Protocol, a safety system used by school districts nationwide.
“All schools used the standard earthquake safety protocol of drop, cover, and hold on. We’ve managed the recent swarms by ensuring our staff is prepared,” McSweeney said.
At Canyon Lakes, modern technology notifies golfers of potential hazards in real time. Roller plans to use digital screens on golf carts to reach players in the event of an earthquake.
“In case a big one were to occur, I would send a message to all the golf carts and warn them to stay away from large trees and to take cover,” Roller said. “For me, I would get under a table and get a good 30 seconds of no shaking before proceeding to check if anything is in disarray or if anyone needs help.”
Earthquake swarms have struck San Ramon in eight different years from 1970 to 2025, but each has tapered off without triggering a larger, more damaging event.
Despite swarms historically causing minimal damage, the lived experience remains unsettling for residents at the epicenter.
“I did experience it. It was really scary because it was really, really big,” San said.
