Overview
- The sequence intensified between 6:27 a.m. and about 7 a.m., capped by a magnitude 4.2 centered roughly 2.5 miles southeast of San Ramon at about 5–6 miles deep.
- USGS feeds logged at least 17–19 earthquakes in roughly one to two hours, and one compilation counted 48 events in 24 hours as data reviews continued.
- Shaking was felt widely across the Bay Area and into the Central Valley, with reports extending toward Sacramento, Stockton, and Modesto.
- BART operated trains at reduced speeds during safety inspections, resulting in systemwide delays of about 20 minutes.
- The swarm follows months of elevated Tri‑Valley seismicity, and seismologists note prior swarms in the area were not followed by larger earthquakes.