Nearly 200 earthquakes shake San Ramon

A swarm of earthquakes continued to rock San Ramon in the East Bay. Image from October 19th, 2015 shows the latest quakes in red and earlier quakes in orange and yellow. (USGS) A swarm of earthquakes continued to rock San Ramon in the East Bay. Image from October 19th, 2015 shows the latest quakes in red and earlier quakes in orange and yellow. (USGS) Image 1 of / 17 Caption Close Nearly 200 earthquakes shake San Ramon 1 / 17 Back to Gallery

An earthquake swarm continues to shake the San Ramon Valley with almost 200 temblors rippling through the region through Monday afternoon, when a 2.8 quake struck at 4:02 p.m followed by a 3.5 quake,the largest in the series, and a second 2.8 quake, both at 4:21.

The 4:21 quakes were widely felt in the East Bay.

Most of the 25 quakes, which started at 11:58 p.m. Saturday, were felt within the Tri-Valley region of Contra Costa and eastern Alameda counties. The swarm could last for days or weeks, then end without notice, say earthquake experts.

“The good news is that most of these earthquakes stay under magnitude 4,” Susan Garcia, a spokeswoman with the The U.S. Geological Survey’s Earthquake Science Center, said Sunday. “An earthquake swarm is not unusual in that area.”

A quake storm hit the same region last week, the most prominent being a 3.4 shaker that struck near San Ramon at 6:10 a.m. Thursday. It was felt as far north as Vallejo and as far south as Pleasanton. There have been no reports of major damage. There have been 191 quakes in the area, and counting, in the last week.

Joe Garofoli is a San Francisco Chronicle staff writer. E-mail: jgarofoli@sfchronicle.com Twitter @joegarofoli