Overview
- More than 300 small earthquakes have rattled San Ramon over the past month after a magnitude 3.8 event on November 9, with recent quakes around magnitude 2–3.
- USGS geophysicists Sarah Minson and Annemarie Baltay say the sizes and locations of the tremors indicate no significant risk of triggering the region’s primary faults right now.
- Researchers point to local fault complexity and possible fluid movement through the crust as likely drivers of the cluster of minor quakes.
- UC Berkeley’s Roland Burgmann and USGS’s Minson say the pattern may reflect an extended aftershock sequence from the initial 3.8 rather than a classic swarm.
- USGS records show similar bursts struck the area in 1970, 1976, 2002, 2003, 2015, and 2018 without leading to a large earthquake, even as the Calaveras–San Andreas system remains a long-term hazard.