4th of July Was a ‘Foreshock,' Main Event Was 7.1 Earthquake

There were more than 200 earthquakes in the area measuring 2.5 or higher in between Thursday's 6.4 quake and Friday's 7.1 main event, according to the USGS.

A magnitude 7.1 earthquake centered in Ridgecrest in Kern County rattled Southern California Friday night, which appeared to be the main event after a "foreshock" centered in the same city measuring 6.4 shook the region on the Fourth of July holiday.

Friday's earthquake struck at 8:16 p.m., but it was followed by at least 15 aftershocks measuring 3.0 or higher centered in Kern County in the two hours that followed, according to the Unites States Geological Survey.

Thursday's earthquake, which was also centered in Ridgecrest, was a magnitude 6.4 earthquake. There were more than 200 earthquakes measuring 2.5 or higher nearby between Thursday's 6.4 quake and Friday's 7.1 main event in the same area, including a 5.4 shaker, according to the USGS.

Friday's earthquake was 10 miles deep according to the USGS, while Thursday's precursor was only 6.6 miles deep.

"This is an earthquake sequence," Dr. Lucy Jones said at an impromptu news conference Friday night. "These earthquakes are related."

"The early warning system worked well," Jones said, while saying that the system did not inform the public due to a USGS policy decision.

Jones pointed out that the pair of earthquakes were from a different fault line than the San Andreas fault, which would likely cause catastrophic damage to the LA basin. Jones said this earthquake was about four fault lengths away from from the San Andreas fault.

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