Series of earthquakes strikes east of San Diego County

SAN DIEGO (FOX 5/KUSI) — A series of earthquakes struck east of San Diego County near El Centro overnight Monday after a preliminary magnitude 4.8 rattled the area.

The initial — and largest — earthquake was recorded just after 12:30 a.m. at a depth of about three kilometers, according to the U.S. Geological Survey.

It set off nearly two dozen additional quakes, most ranging in magnitude from about 2.5 to 3.9 with one hitting a 4.5. The latest to strike, a magnitude 2.5, was reported by USGS near the Interstate 8 just after 9:30 a.m.

According to the USGS “Did You Feel It?” survey, the strongest shaking with the earthquakes was reported in Calexico, El Centro and Brawley. Some in San Diego County also reported experiencing some light tremors.

No damage or injuries have been reported at this time.

However, the first earthquake, USGS says, did trigger the Shake Alert system as it was initially detected as a magnitude 5.0, sending out notifications to the cell phones of those living in around the epicenter.

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These types of back-to-back shocks, called a “swarm,” are not necessarily rare for the area, but they are not considered a frequent occurrence.

The last swarm reported near El Centro was last May, when three different swarm events were triggered in San Diego and Imperial counties the span of a few days.

As Professor of geology emeritus at San Diego State University Dr. Pat Abbott explained to FOX 5 at the time, the eastern San Diego area is particularly susceptible to these series of earthquakes due to the geothermal energy in the stretch of land just south of the Salton Sea.

The 35-mile stretch of land between the tip of the San Andreas fault at the bottom of the sea and the top of the Imperial Fault, which runs up into Imperial County from Mexico, houses a lot of magma and warm volcanic rocks under the surface at a low depth. This creates energy that contributes to a lot of movement and subsequently, earthquake activity.

And these swarms, Abbott said, rarely serve as a foreshock to a bigger earthquake on the horizon.

“Every time we get a swarm of earthquakes, we take them seriously, but we also know from history that usually it’s not going to lead to anything bigger,” he continued. “It’s just sort of like one of the little features about living in California – we get lots of little earthquakes … I prefer to label them as reminders (that) we live in earthquake country.”

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