SAN RAMON, Calif. – A sequence of small to moderate earthquakes struck the East Bay region on Sunday afternoon, shaking communities from Dublin to Walnut Creek and briefly startling residents across the San Francisco Bay Area.
According to the U.S. Geological Survey (USGS) and the California Integrated Seismic Network (CISN), at least six measurable earthquakes occurred between 10:18 a.m. and 11:50 a.m. PST (18:18–19:50 UTC), all centered 3 to 4 kilometers southeast of San Ramon in Contra Costa County.
The sequence included magnitudes of 2.5, 2.9, 3.0, 3.2, 3.7, and 3.8, with depths ranging from 6.9 km to 9.2 km. The strongest of the swarm—a magnitude 3.8 quake at 9:38 a.m. local time—generated “light shaking” (Intensity IV) felt reports from San Ramon, Dublin, Danville, and Pleasanton, according to over 1,600 responses submitted to USGS’s Did You Feel It? program.
While the shaking was widely felt, there were no immediate reports of damage or injuries. The quakes originated along the Calaveras Fault Zone, one of several active systems running through the East Bay, capable of producing both small swarms and larger, isolated events.
Earthquake swarms like this are not uncommon in the San Ramon Valley. A similar sequence occurred in 2015, when more than 400 small tremors were recorded over a two-week span.
Seismologists at UC Berkeley and the USGS Menlo Park office continue to monitor the cluster closely. As of Sunday evening, aftershocks and additional small quakes were still possible in the region.
Residents are reminded to review earthquake preparedness plans and check emergency kits. For the latest updates, visit earthquake.usgs.gov.
