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6.4 Magnitude Earthquake Strikes Southern California

A 6.4 earthquake strikes near Ridgecrest in the Mojave desert on July 4, 2019.

Credit: U.S. Geological Survey

Above: A 6.4 earthquake strikes near Ridgecrest in the Mojave desert on July 4, 2019.

UPDATED: 1:50 p.m., July 4, 2019:

A magnitude 6.4 earthquake was felt throughout the Southland Thursday, shaking up local residents celebrating the Fourth of July.

The quake, which began at 10:33 a.m., was centered about 7 miles southwest of Searles Valley, a sparsely populated part of the Mojave Desert near Kern County and northwestern San Bernardino County, according to the U.S. Geological Survey.

Southland police and fire agencies quickly took to social media, reporting no injuries from the shaking, but some possible damage and one structure fire.

The Los Angeles Department of Water and Power reported a water main break on Wilshire Boulevard and La Jolla Avenue, power outages affecting the Garment District downtown, a portion of San Pedro, and 20 customers in Granada Hills — though officials later said the water main break might have been unrelated to the earthquake.

The Los Angeles Fire Department reported that "all 106 fire stations are out conducting a strategic survey of their districts to determine if any damage exists. Once this process is complete, an overall assessment of the impact in the City of Los Angeles will be compiled."

The Los Angeles County Fire Department's Division 8, which encompasses Diamond Bar, Hacienda Heights, Industry, Rowland Heights, La Puente, Walnut, Pomona and Valinda, reported that a structure fire possibly ignited from a gas line break due to the earthquake.

The Department was sending a battalion chief and a task force to Ridgecrest, near Bakersfield, to assist the Kern County Fire Department in earthquake recovery efforts.

The Los Angeles Police Department reported that they have not received any reports of damage or calls for service within the city in relation to the earthquake.

Los Angeles Mayor Eric Garcetti said at 1:30 p.m. that the city was "in great shape," with no significant damage to report.

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Officials at LAX said all runways were inspected and no damage was found.

Ride operations were briefly suspended at Six Flags Magic Mountain and Hurricane Harbor in Santa Clarita, but the theme parks tweeted shortly after the quake that operations had resumed as normal.

It was the strongest quake to be felt in Southern California since 1999, according to seismologist Lucy Jones of Caltech, founder of the Dr. Lucy Jones Center for Science & Society.

Jones said the quake was not on the San Andreas fault.

"It is an area with a lot of little faults but no long fault," she tweeted.

Jones said the "shake alert" computer system at Caltech's seismic facility registered a 48-second warning that shaking had begun, but the warning signal did not go out to the public.

Los Angeles officials later explained that, tweeting: "The #ShakeAlertLA app only sends alerts if shaking is 5.0+ in LA County. Epicenter was 6.4 in Kern County, @USGS confirms LA's shaking was below 4.5. We hear you and will lower the alert threshold with @USGS_ShakeAlert"

A magnitude 4.0 quake that preceded the main quake by about 30 minutes was a "foreshock," Jones said.

Officials with the San Bernardino County Fire Department tweeted that they were conducting an assessment of the region and "no injuries reported, however buildings and roads have sustained varying degrees of damage."

A later tweet said multiple buildings had been found with minor cracks, along with broken water mains, downed power lines and rockslides on certain roads.

The Kern County Fire Department announced that it was responding to "nearly 2 dozen incidents ranging from medical assistance to structure fires in and around the city of Ridgecrest."

Officials with SoCalGas said an initial inspection revealed "no significant impacts to the natural gas system." The epicenter is within the utility's service area.

Several aftershocks in the magnitude-3 range were reported by the USGS, as expected following a substantial quake. Jones said there was a better than 50-percent chance of a larger aftershock in the magnitude-5 area "sometime this afternoon."

Southland police agencies were reminding the public not to use 911 for earthquake questions unless they have injuries or dangerous conditions to report.

The last Southern California earthquake to exceed 6.4 was on Oct. 16, 1999, when a magnitude 7.1 quake struck in the Mojave Desert near Twentynine Palms Marine Corps Base. That quake knocked an Amtrak passenger train off its tracks and damaged two highway bridges.

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