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Earthquake swarm rattles area near California-Mexico border

San Andreas Fault line
Craig Aurness | Corbis | VCG | Getty Images
San Andreas Fault line

A cluster of earthquakes in Southern California the past two days jolted an area near the San Andreas Fault and was closely being watched by seismologists.

In all, more than 140 earthquakes have shaken Imperial County's Salton Sea area, including at least two 4.3-magnitude temblors that struck Monday south of Bombay Beach, according to a U.S. Geological Survey seismologist.

A spokesperson for the Imperial County Sheriff's Department said Tuesday there were no reports of injuries or damage.

USGS seismologist Robert Graves said the swarms started occurring at 4 a.m. on Monday in the region and are similar to those that jolted the Imperial County area previously in 2001 and 2009.

"They are not strongly damaging earthquakes but obviously the fact there are so many of them and they are occurring so close in time is something that deserves our attention," said Graves.

Imperial County, along the U.S.-Mexico border, is where a number of active fault strands are located, including the "main fault" being the San Andreas, according to Graves. "Obviously, we're looking at that very closely," he said.

The feared San Andreas Fault , which runs the length of California, is capable of 8.0-magnitude earthquakes and starts near Imperial County's Bombay Beach.

"There's always the potential that a larger earthquake could occur," he said of the recent quake swam. "We haven't seen anything in the current set of observations that would suggest that that is going to happen but we obviously cannot rule it out."

The USGS seismologist estimates there's a 5 percent chance that a larger earthquake will occur and explained that the swarm of earthquakes means that the probability doesn't diminish quite as quickly. "That doesn't necessarily mean it will be the Big One," he said.

He put the probability of a large earthquake happening of 7.0-magnitude or above to be "far less than one percent." The last major earthquake along the southern part of the San Andreas Fault was a 1857 quake estimated to be 7.8-magnitude.

Meantime, experts say California is overdue for a major quake and note most Californians live within 30 miles of an active fault.

In a release issued Tuesday, the California Earthquake Authority—the largest residential earthquake insurer in the state—said it has seen a jump in the number of Californians signing up for earthquake insurance coverage so far this year. CEA said it signed up about 29,000 policies in the first eight months of this year, or nearly twice the amount of new policies purchased in all of 2015. As a result, CEA said it now has more than 908,000 policies in force.

Still, only about 10 percent of California homeowners have earthquake insurance. CEA is a not-for-profit, privately funded and publicly managed organization. About three-fourths of the earthquake policies in the state are through the CEA.