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California is Shaking


Last updated 10/22/2015 at 10:50am

Last week, three moderate earthquakes hit towns close to Borrego Springs. Two occurred in Big Bear Lake, both reaching a 3.5 on the Richter scale, and a 3.3 hit close to Lake Henshaw. But these towns were not the only ones that shook in California last week. San Ramon, which is about 25 miles east of San Francisco, has been hit by more than 200 quakes in the past week. Even though these are considered small, reaching 4.0 or below in magnitude, the constant rattling can signify that a bigger earthquake is coming, according to seismologists.

“Every small swarm could be a foreshock. We think it’s a very small chance (of a big earthquake) given the history of the fault,” said Ole Kaven, a geophysicist at the United States Geological Survey. “But there’s no telling when and where exactly that type of event could happen.”

San Ramon lies above the Calaveras fault, where swarms have been happening since the 1970s. This fault is especially prone to swarms given its geology. The fault has secondary faults branching perpendicularly from the main fault. When one of these shakes, it initiates a swarm.

Although none of the previous swarms have lead to a bigger earthquake and should go away in two weeks, a swarm could set off another fault, though it is very unlikely. The Hayward fault, which is connected to the Calaveras, is predicted to have a big earthquake soon. Seismologists just recently discovered the extent of the connection between the two because underground faults are poorly mapped. Seismologists depend heavily on looking where the earthquakes happen to then map the faults. After the swarm is over, they might have a better picture of what is happening under San Ramon.

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