Highlights:
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An earthquake swarm struck San Ramon early Monday, with the strongest earthquake measuring magnitude 4.2
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At least 17 earthquakes were recorded, with shaking felt across the Bay Area
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The earthquake swarm is linked to the creeping Calaveras Fault
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No injuries or property damage were reported, according to authorities
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USGS says nearly 300 earthquakes have occurred in the area since December
An earthquake swarm struck San Ramon, California, early Monday morning, shaking homes and waking residents across large parts of the Bay Area. According to the US Geological Survey, at least 17 earthquakes were recorded in the region, including a magnitude 4.2 earthquake, the strongest tremor in the sequence.
The earthquake activity began shortly after 6:30 a.m. local time with two moderate earthquakes measuring magnitude 3.7 and 3.3. These early tremors marked the start of a broader earthquake swarm that continued through the morning. The largest earthquake, a magnitude 4.2 event, struck shortly after 7 a.m. and was felt across a wide area, including San Francisco and Santa Cruz.
A second notable earthquake, measuring magnitude 3.9, followed soon after. Several smaller earthquakes, many around magnitude 2.0, continued to occur throughout the morning hours.
Earthquake Shaking Reported Across Multiple Cities
Residents across San Ramon, Pleasant Hill, and nearby communities reported noticeable earthquake shaking. At least a dozen people contacted KTVU to describe the tremors, saying the earthquakes were strong enough to rattle furniture and disturb sleeping households.
The earthquake swarm was also felt at KTVU’s studios at Jack London Square in Oakland. San Ramon resident Evan Li shared video footage showing paperclips and loose change vibrating on a table during one of the earthquakes.
Reports of earthquake shaking extended well beyond San Ramon. Miranda Harmon-Smith wrote on social media that her house creaked in Brentwood and her cat reacted to the movement. Tina Hernandez-Romo said her bed shook in Cherryland near San Leandro. Other residents reported feeling the earthquakes in Livermore, Orinda, San Francisco, and several other Bay Area cities.
Despite the widespread impact of the earthquake swarm, local authorities said there were no immediate reports of injuries or damage to buildings or infrastructure.
Earthquake Swarm Linked to Calaveras Fault
Seismologists say the earthquake swarm is not unexpected for the region. San Ramon lies along the Calaveras Fault, a well-known fault system that runs through Alameda and Contra Costa counties.
The Calaveras Fault is classified as a “creeping” fault. Unlike locked faults that accumulate stress over long periods before releasing it in a single major earthquake, creeping faults move gradually and release stress through frequent small-to-moderate earthquakes.
This gradual movement often produces clusters of earthquakes rather than a single dominant event. Seismologists refer to this pattern as an earthquake swarm, where multiple tremors occur over a short period without a clear mainshock.
Earthquake Swarms and Seismic History in the Area
While most earthquakes associated with creeping faults are relatively small, stress can sometimes build up enough to produce earthquakes in the magnitude 4.0 range, as seen in Monday’s San Ramon earthquake.
According to the USGS, approximately 300 earthquakes have been recorded in the same general area since December 1, 2025. Just last week, at least two earthquakes were reported on Friday, along with another nearby earthquake in Dublin.
Scientists continue to monitor the ongoing earthquake activity closely. Experts emphasize that while earthquake swarms can feel alarming, they are a known and recurring feature of seismic behavior along the Calaveras Fault.
What Experts Say About Future Earthquake Risk
Seismologists stress that an earthquake swarm does not necessarily indicate that a larger earthquake is imminent. Instead, the frequent release of energy along creeping faults can reduce the likelihood of stress building up to dangerous levels.
Monitoring efforts remain ongoing, with researchers tracking changes in earthquake frequency, depth, and magnitude. Residents in earthquake-prone areas are advised to stay informed through official channels and review standard earthquake safety guidance.
For now, experts say the San Ramon earthquake swarm reflects typical seismic behavior for the region and does not signal an immediate escalation in earthquake risk.
