San Ramon, California — A small earthquake swarm struck east-southeast of San Ramon on Friday, prompting light shaking reports but no immediate damage.
According to the U.S. Geological Survey, three earthquakes occurred within minutes of each other about 4 kilometers (2.5 miles) east-southeast of San Ramon in Contra Costa County. The largest registered a magnitude 3.0, followed by magnitude 2.8 and 2.6 events.
The strongest quake occurred shortly after 8 a.m. local time and was centered at a depth of about 8.2 kilometers. The subsequent earthquakes struck nearby at depths between roughly 7.7 and 8.8 kilometers, indicating closely related seismic activity rather than isolated events, according to preliminary USGS data.
USGS “Did You Feel It?” reports show residents across the Tri-Valley area — including San Ramon, Danville, Dublin, and parts of San Jose — reported brief shaking. Community Internet Intensity Maps indicated shaking levels ranging from weak to light, consistent with minor earthquakes.
All three events were reviewed or automatically processed by the California Integrated Seismic Network, a partnership between UC Berkeley and the USGS. No injuries or structural damage have been reported as of Friday afternoon.
Seismologists refer to this pattern as an earthquake swarm, a series of small earthquakes occurring in the same area over a short period without a single dominant mainshock. Such swarms are not uncommon in Northern California and do not necessarily signal a larger earthquake.
The quakes occurred in a seismically active region near multiple fault systems, though the USGS has not identified a specific fault associated with Friday’s activity.
For commuters, the timing meant many residents felt the shaking during the morning rush, though no transportation disruptions were reported.
Residents are encouraged to report shaking experiences through the USGS website to help scientists refine intensity maps and improve earthquake monitoring.
