2015 San Ramon swarm (Calaveras–Concord–Mt. Diablo step-over)
A major swarm near San Ramon produced thousands of small events in a complex fault step-over area. USGS-linked research tied swarm behavior to fault-zone complexity and possible involvement of crustal fluids, while cautioning that swarms can—sometimes—precede larger ruptures.
The sequence tapered without a headline-grabbing mainshock.
It became a case study for why San Ramon repeatedly hosts swarms.
It’s the closest modern template for today’s swarm—and a reminder that swarm mechanics aren’t just random noise.
