3.2 quake rattles San Ramon amid swarm of tiny quakes

SAN RAMON, Calif. (KTVU) -  A 3.2 magnitude earthquake rattled San Ramon at 6:10 a.m. Thursday. 

There are reports the quake was also felt in Walnut Creek, Martinez, Danville, Dublin, Oakland and Fremont. 

This comes after a swarm of more than 30 earthquakes rocked San Ramon Tuesday and Wednesday, with the majority of them centered around the area of the Crow Canyon Country Club just east of I-680.       

Employees at Bay Books thought for sure they'd be walking in to a big mess Wednesday morning.

"When I heard there was that many it did cross my mind," says employee Kyle Hval.

Instead there wasn't a book out of place. While the quakes have been steady, they've been small.

The largest of the quakes so far was a 3.0 at 8:14 a.m.

"I was sitting at my desk and it shook the house. I felt it very vividly," said resident Dani McInnes.

"The bed shook a little bit. What I didn't know at the time was it was right beneath my feet," said Don McInnes.

At the U.S. Geological Survey, they call this phenomenon an earthquake "swarm," meaning the events are small, but clustered together. This one is centered along the Calaveras Fault zone.

Experts can't say exactly why swarms happen, only that they are more likely in places with a maze of fault lines.

"It's really the complex areas that have these swarms," said Brad Aagaard, a research geophysicist with the USGS.

And he says there's no telling how long it will last.

"We've had in the past, swarms that lasted several months so a swarm that lasts a few days, it doesn't really raise our eyebrows much at all," said Aagaard.

Residents say it does make them a bit uneasy.

"You're a bit scared because, is it leading up to something bigger?" asked resident Cathie Young.

Experts say not necessarily, but it's a good reminder to be prepared. Since 1970, there have been four significant swarms in this area.

The biggest was in nearby Alamo in 1990, when they had 350 earthquakes over 42 days.