San Ramon, CA – A significant earthquake swarm rattled parts of central California Monday morning, with more than 30 earthquakes recorded near San Ramon over a span of several hours, according to federal seismic data.
According to the U.S. Geological Survey (USGS), the strongest earthquake struck at approximately 9:01 a.m. Monday, measuring magnitude 4.2 and centered about 4 kilometers east-southeast of San Ramon. The quake occurred at a depth of roughly 9.4 kilometers, increasing the likelihood of noticeable shaking across the East Bay.
Following the main shock, USGS recorded a rapid series of aftershocks ranging from magnitude 2.5 to 3.8, many occurring just minutes apart. The earthquakes were clustered primarily between 4 and 5 kilometers southeast of San Ramon, impacting parts of Contra Costa County, including Danville, Dublin, Pleasanton, and surrounding communities.
Residents across the region reported brief but repeated shaking, with some describing rattling windows and light objects shifting. As of Monday afternoon, no injuries or major structural damage had been reported. Local fire departments and emergency agencies said they were aware of the activity and continued to monitor conditions.
Seismologists note that earthquake swarms — clusters of multiple quakes without a single dominant event — are relatively common in California, particularly along the Calaveras Fault system, which runs through the East Bay. While most swarms remain minor, officials remind residents that California remains seismically active.
Emergency officials continue to urge residents to review earthquake preparedness plans, secure heavy furniture, and keep emergency supplies accessible.
Anyone who felt shaking is encouraged to submit a “Did You Feel It?” report through the USGS website to assist researchers.
