Updated at 3:30 p.m., PDT.

A strong earthquake rattled a large swath of Southern California and parts of Nevada on July 4, rattling nerves on the Independence Day holiday and causing some damage in a town near the epicenter amid a swarm of ongoing aftershocks.

Officially dubbed the Searles Valley Earthquake, the seismic event began at 10 a.m., PDT, with a magnitude 4.2 quake. This was followed at 10:33 a.m. with a larger, 6.4 magnitude shaker that caused damage and power outages in nearby Ridgecrest and Trona.

Multiple aftershocks of magnitude 3 and 4 plus have hit the area in the hours since the main quake.

According to a 2 p.m., CalTech briefing, “There is an 80 percent chance of a magnitude 5 plus aftershock within 24 hours, decreasing to a 20 percent chance, 24 hours after the initial shock. There is a 9 percent chance of a magnitude 6 plus aftershock in the coming week.”

Peggy Breeden, the mayor of Ridgecrest, a town of 28,000 people, said firefighters were working to put out five fires, at least one of them at a home, but that she didn’t know if any injuries had been reported.

She also said the Ridgecrest Regional Hospital had been evacuated, although the hospital has said the ER and Urgent Care remain open to the community. Some patients are being transferred to other facilities while the buildings integrity is checked.

Utility workers were assessing broken gas lines and turning off gas where necessary, Breeden told CNN.

She said the local senior center was holding a July 4th event when the quake hit and everyone made it out shaken up but without injuries, she said.

“Oh, my goodness, there’s another one (quake) right now,” Breeden said on live television as an aftershock struck.

The quakes appear to involve multiple faults within the Little Lake fault system, a phenomenon known as conjugate behavior or conjugate faulting, according to CalTech spokesperson Dr. Lucy Jones. The main 6.4 quake focused energy toward the city of Ridgecrest. This activated a second adjoining fault, with energy radiating toward the northwest, away from town. Geologists will be surveying the area for obvious evidence of ground and fault shifting, to more accurately pinpoint the epicenter and fault lines involved.

This is the largest quake in the Little Lake fault area in the last century. Little Lake is a potentially volcanic area, and China Lake Naval Weapons Station operates a geothermal facility in the area. China Lake had yet to release any reports of damage as of mid-afternoon, but CalTech’s Jones said she expects that there is some damage at the installation, as it is too close to the epicenter to have gone unscathed.

When asked about the possibility that geothermal energy production activities may have contributed to the quake, Jones stated that if you are changing water pressure and pumping water deep into the earth, it is possible to increase the rate of earthquakes. However, she was quick to make the point that geothermal production has been going on in the area for many decades, and there is no evidence or reason to think that those types of activities contributed to these seismic events. “It would be a negligible contribution, because there hasn’t been a significant change in the pumping. Back in the early 1980s, there were lots of earthquakes in this region, and through the 1980s, and then it went down into a quieter period. When there was a lot of geothermal production going on, it went into a pretty quiet period.” Jones attributed concerns about the relationship of geothermal energy production and earthquakes to our natural human desires to find predictive patterns to earthquakes. She emphasized that earthquakes are inherently random events.

President Donald Trump and local lawmakers including Sen. Kamala Harris, Rep. Kevin McCarthy and Rep. Vince Fong have all been briefed and have offered whatever support is needed.

Little communication has come from Trona, a sparsely populated community of about 1,900, closer to the epicenter and located on a dry lakebed. Social media communications have confirmed road damage in the area.

“It almost gave me a heart attack,” said Cora Burke, a waitress at Midway Cafe in Ridgecrest, of the big jolt. “It’s just a rolling feeling inside the building, inside the cafe and all of a sudden everything started falling off the shelf, glasses, the refrigerator and everything in the small refrigerator fell over.”

People from Las Vegas to the Pacific Coast reported feeling a rolling motion and took to social media to report it.

Local emergency agencies also took to social media to ask people to only call 911 for emergencies.

“We are very much aware of the significant earthquake that just occurred in Southern California. Please DO NOT call 9-1-1 unless there are injuries or other dangerous conditions. Don’t call for questions please,” the LAPD said in a statement published on Twitter.

There were no reports of serious damage or injuries in Los Angeles, the department said.

Much attention has been given to the fact that the recently released Shake Alert LA phone app did not broadcast an alert to users in advance of the quake.

CalTech spokesperson Dr. Rob Graves reports that the Shake Alert system in the Caltech lab did in fact detect that a quake was about to happen. Because the amount of shaking that radiated into the Los Angeles area did not reach the minimum threshold to trigger an alert, the system was not activated to broadcast an alert to those who have the Shake Alert app installed on their phone. The app notifications are set up with a threshold in Los Angeles County of magnitude 5 and above, and magnitude 4 and above for the city of Los Angeles. While the quake was felt as far away as Las Vegas, the degree of shaking felt within the city and county did not the minimum threshold to trigger activation of the Shake Alert LA phone app.

Some news outlets are reporting that Shake Alert LA is going to lower the warning threshold following complaints that Los Angeles County residents did not receive a warning.

Ashleigh Chandler, a helicopter rescue EMT at Fort Irwin, Calif., said the quake happened as she was getting ready for a July 4th party.

“I was just in the living room getting everything ready, we start to feel the shaking, so then I look up and then the wine bottles start rattling and I thought, ‘They’re going to fall.’
“My stepson was in the house and my dog, so we just got everyone outside and then it ended. It was like 15, 20 seconds, maybe. It was pretty good shaking, so I’m out of breath.”

“Everyone’s OK.”

The City of Ridgecrest has activated its Emergency Operations Center and declared a state of emergency. LA County Fire has deployed a battalion to the city of Ridgecrest to assist with first responder efforts.

With temperatures in the 90s, and power out to parts of the city, Ridgecrest has opened a cooling center at Burroughs High School located at 500 French Avenue in Ridgecrest.

Editor’s note: John Antczak and Olga R. Rodriguez of Associated Press, and Lisa Kinison of Aerotech News contributed to this report.