A 3.9 magnitude earthquake struck on the border of Danville and San Ramon Wednesday morning, according to the United States Geological Survey.
The quake hit at 11:43 a.m. and was centered 1 mile northeast of San Ramon, 2.7 miles southeast of Danville, 5.3 miles southeast of Alamo and 6.4 miles north-northwest of Dublin, the USGS reported.
"Things started shaking really good," Mitch Rascano of San Ramon said. "The closet doors were rattling like a mad dog. My dogs were going crazy. They freaked out. They were running for the hills. It got my attention. Usually the little ones, I just kind of shake off. This one got my attention a little bit."
The Contra Costa County Fire Protection District said it didn't receive any reports of damage or injuries.
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Several smaller quakes rattled the same area in the minutes and hours after the 3.9 quake, according to the USGS. Check out the list below for a breakdown of the stronger quakes.
- 2.6 magnitude at 11:46 a.m.
- 3.0 magnitude at 11:58 a.m.
- 2.8 magnitude at 4:01 p.m.
- 3.3 magnitude at 8:35 p.m.
Geologist David Schwartz felt the big jolt and the aftershocks that followed from his home in Danville.
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"A few little things toppled off shelves in my office," he said.
Schwartz said the San Ramon Valley is known as the home of earthquake swarms – a series of minor but sometimes significant earthquakes that can last for days, weeks or even months.
"Usually the largest earthquakes are only in the mid-4's, but there can be hundreds of them," Schwartz said.
Schwartz said the last major earthquake swarm to hit the San Ramon Valley was back in 2015. He added there’s no sure way to know if Wednesday marked the start of another swarm.
"It may sound trite, but we are in earthquake country and you can never forget that, and you should always be prepared," Schwartz said.
