Earthquake Swarm Rattles California: Over 400 Quakes in 2 Weeks


San Ramon, California, appears to have broken a new earthquake record over the last two weeks: A total of 408 small quakes have shaken the East Bay city, almost four times the record set in 2003 in half the amount of time.

“I’ve not felt so many tremors in decades,” Mark Stone said outside a San Ramon Starbucks on Tuesday morning. “My dog, Gimmel, she’s the first one to know a couple of seconds before.”

And his dog has been extra alert lately.

The U.S. Geological Survey reports that as of Oct. 13, the Northern California Seismic Network had detected 408 earthquakes – at least a dozen since 10 p.m. on Monday, with other quakes spilling into the early hours of Tuesday. Most quakes have clocked in with magnitudes ranging from 2.0 to 3.0. San Ramon is about 45 miles east of San Francisco.

In an Oct. 14 interview, Senior U.S. Geological Survey research geologist David Schwartz said the swarm is not all that unusual, noting that San Ramon Valley is at the “center of earthquake swarm activity” in the Bay Area. He recalled a 2003 swarm of 120 earthquakes over 31 days in San Ramon, with the largest clocking in at a magnitude of 4.2.

The biggest swarm on record in the same general area, Schwartz noted, was in 1990 in neighboring Alamo, about 30 miles east of San Francisco. That’s when 351 earthquakes struck over 42 days, with the largest recorded at a magnitude of 4.4.

The current swarm of 408 – and counting – tops both those numbers.

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SOURCE:  Lisa Fernandez, Stephanie Chuang and Shawn Murphy
NBC Bay Area