Why Does San Ramon Get So Many Earthquakes?

SAN RAMON, CA — San Ramon has been shaking for many years, according to scientists from the U.S. Geological Survey. Over the past two months, the city has been the epicenter of 21 earthquakes over 2.0, ranging from 2.9 to 4.0 in magnitude, according to USGS research geophysicist Annemarie Baltay. But that’s just the start: SFGate reported that 90 total quakes have struck San Ramon just this month.

San Ramon trembled most recently on Monday, when a series of earthquakes ranging from 2.8 to 3.7 shook the area from around 2:33 a.m. to 9:07 a.m.

Scientists and long-time residents are quick to point out this is nothing new for the city. The city sits along the Calaveras Fault, and several micro-faults along the main fault result in swarms of quakes. When fluids like water or gas move through a complex web of cracks in tiny faults, this can trigger many dozens of small quakes in quick succession.

“It is also possible that these smaller earthquakes pop off as the result of fluid moving up through the earth's crust, which is a normal process, but the many faults in the area may facilitate these micro-movements of fluid and smaller faults,” Baltay said.

According to the USGS, there have been similar clusters very close by in 1970, 1976, 2002, 2003, 2015, and 2018:

The strongest was in Alamo in 1990, when 177 earthquakes as strong as a 4.4 rattled the area over a period of 42 days.

Despite the swarms every few years, Baltay says she is not unusually concerned that anything bigger will hit San Ramon. But that doesn’t mean you should put away your earthquake kits.

“These small events, as all small events are, are not indicative of an impending large earthquake,” she said. “However! We live in earthquake country, so we should always be prepared for a large event. In here, you can see that there is a 72% chance of a M6.7 or larger anywhere in the Bay Area, between now and 2043. So we should all be aware and be prepared.”

See here for the USGS’s full earthquake preparation guide.

SEE ALSO:

• Series of Earthquakes Rattle The Bay Area Monday Morning: Did You Feel Them?
• Swarm Of Earthquakes Hits San Ramon: Did You Feel It?
• Swarm Of Quakes Rattles East Bay
• CA's 'Big One' May Look Like No Other Quake In History Or Forecast Models, Researchers Warn
• Are You Living on a Fault Line?