Earthquake Swarm Around San Francisco Persists

October 28, 2015

The U.S. Geological Survey reports that in the last two weeks more than 400 small earthquakes have hit a city east of San Francisco.

KNTV reported that the city of San Ramon appears to have broken an earthquake record with a total of 408 small quakes since Oct. 13.

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.

earthquakeSan 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 quakes are unlikely to be a foreshock to a larger quake.

The biggest swarm on record in the same general area was in 1990 in Alamo. That’s when 351 earthquakes struck over 42 days.

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