SAN RAMON (CBS SF) — San Ramon appears to have broken a 1990 earthquake swarm record for the Tri-Valley region just east of San Francisco.
Senior U.S. Geological Survey research geologist David Schwartz told CBS SF the biggest swarm on record in the same general area was in 1990 in Alamo, a community north of San Ramon. About 350 earthquakes struck over 42 days, with the largest measuring in with a magnitude of 4.0.
In less than half that time since Oct. 13, over 400 small quakes have rattled San Ramon and surrounding area.
Most of the quakes have clocked in with magnitudes ranging from 2.0 to 3.0. The largest was a 3.6-magnitude on Oct. 19. On Tuesday, a 3.1-magnitude struck the area.
QUAKE SWARM: What’s With All The San Ramon Tremors?
San Ramon and other nearby cities have a history of quake swarms as they sit on the Calaveras Fault. Based on other swarms, the USGS predicts that the swarm may continue for several more weeks.
The 2003 Working Group of California Earthquake Probability, which builds forecasts of earthquakes, said there is an 11 percent chance the Calaveras Fault will produce a 6.7- magnitude earthquake or larger in the next 30 years.