The boom that rattled Orange County may have been an earthquake after all, USGS says
The “large boom sound” that startled people across central Orange County just before noon Thursday may have been a small earthquake after all, according to the N.C. Geological Survey.
The initial report from a state geologist on Thursday was that the sound likely was caused by a sonic boom from military aircraft. That theory took a hit when the military told the county it had no planes in the area on Thursday.
Josh Kastrinsky with the N.C. Department of Environmental Quality said the U.S. Geological Survey confirmed a magnitude 2.2 earthquake approximately three miles deep in a phone call Friday with The News & Observer.
A USGS map provided to The N&O shows the earthquake just south of Grady Brown Elementary School and Cedar Ridge High School, between Orange Grove and Dimmocks Mill roads.
Orange County Schools staff started doing visual inspections of its campuses on Friday as a precaution, district spokesman Kevin Smith said. Only River Park Elementary School near downtown briefly put its students on lockdown during the quake, he said.
“I think we were all sort of taken by the fact that there were no reports of damage, no property, personal injury,” Smith said.
The N.C Geological Survey is working to get details about whether that size of earthquake could cause the rumbles and noise reported in Hillsborough, Katrinsky said.
The U.S. Geological Survey, after reviewing additional seismograph information, said in a statement issued Friday that the sound and vibration from the earthquake did not register on seismographs.
“We can confirm that it indeed was an earthquake,” the USGS said. “These small earthquakes often do not get picked up by our computer algorithms because they are so small. When we got felt reports, an analyst looked at it but initially thought it was a quarry blast because it is right near a quarry (visible on Google Earth). Re-examining it this morning, though, we confirmed that it was an earthquake.”
The sound prompted dozens of people to call 911 after it rattled windows and buildings around Hillsborough around 11:50 a.m. Earthquakes are “extremely rare” in the Triangle, according to state geologist Kenneth Taylor, with the N.C. Geological Survey.
Taylor, a seismologist by training, checked the logs from several stations across the Piedmont and western part of North Carolina on Thursday afternoon and found there were two distinct events at 9 a.m. and at 10:28 a.m.
The seismology report, sent to The News & Observer Thursday evening, also showed multiple events between 10:30 and noon.
On Friday, county officials provided The N&O with an email from the Department of Defense stating there were no F-15E Strike Eagles from Seymour Johnson Air Force Base flying near Hillsborough on Thursday.
The Department of Defense spokesperson told Orange County emergency officials in the email that their aerospace managers checked with the U.S. Navy, as well, but they also “did not have any scheduled flights in the area.”
Some residents reported on social media that the noise was more like a boom followed by a rumble or a sound similar to thunder.
“It will go out in a pattern, so the further out it goes, it would take longer to get there. But for these, it was all at the exact same time, which means it was very, very close to the surface,” Taylor said.
“You don’t have sonic booms very often, because the aircraft folks, the military, are usually restricted very very strongly to not be making sonic booms like that,” he said. “You do not want to scare people, because they have a bang” that startles people.
According to the U.S. Air Force website, a sonic boom can sound like thunder and is typically caused by a jet moving faster than sound, “about 750 miles per hour at sea level.” A jet dropping sonic booms is similar to something dropped from a moving vehicle as it flies at supersonic speeds, the website said.
“The sound heard on the ground as a ‘sonic boom’ is the sudden onset and release of pressure after the buildup by the shock wave or ‘peak overpressure,’” it says. “The change in pressure caused by a sonic boom is only a few pounds per square foot — about the same pressure change we experience on an elevator as it descends two or three floors — in a much shorter time period.”
Courthouse evacuated, search for source
The boom Thursday morning came as the Orange County Courthouse was winding down for lunch and prompted deputies to evacuate the building in downtown Hillsborough, said Clerk of Superior Court Mark Kleinschmidt, who was in the Colonial Inn at the time and felt the boom.
“The whole building shook. It felt like a big truck had run into the side of the Colonial Inn,” Kleinschmidt said. “Everybody kind of looked around. There was no truck in the restaurant, so we continued.”
He got a call saying the courthouse was being evacuated; fortunately, there were fewer people in the building than usual because of the judges are in conference, he said. The evacuation ended once they realized it did not involve that building, he said.
“It was just bizarre,” Kleinschmidt said.
Orange County Sheriff’s Office spokeswoman Alicia Stemper said their office also got a number of calls.
“People heard it. People felt it. But we are not getting corresponding calls of property injury or personal injury, so deputies are out there going to likely places,” she said.
The boom did not come from the quarry near downtown Hillsborough or the construction at the Collins Ridge development or the work on Interstate 40, she said. Sheriff’s deputies also sent their drone up to take a look around, but did not spot anything, she said.
Orange County emergency officials posted on Facebook around 2 p.m. that they had ruled out bombs, explosions, crashes, falling planes and building failures as the source of the loud boom.
Event marking earthquake awareness
Ironically, Thursday marked International ShakeOut Day — an earthquake preparedness event — and over 547,000 North Carolinians, including students and staff at local schools, were expected to participate in the Great SouthEast ShakeOut Drill at 10:19 a.m.
Orange County Emergency Services Director Kirby Saunders offered these tips for responding when an earthquake strikes:
▪ Drop to your hands and knees to prevent being knocked down and bend over to protect your internal organs.
▪ Crawl to shelter, if possible, such as under a sturdy table or desk.
▪ Cover your head with your hand and arm to protect it from falling objects.
▪ Stay away from windows and seek shelter near an interior wall.
▪ Hold onto your shelter and move with a table or desk if they shift until the shaking stops.
▪ If you don’t have shelter, cover your head and neck with both arms and hands.
This story was originally published October 19, 2023 at 12:55 PM.
