This post has been updated. See note below for details.
Some residents in Long Beach and the north Orange County coast reported feeling and hearing what some thought was an earthquake Wednesday afternoon.
But Caltech seismologist Kate Hutton said no earthquakes were reported in the area during the time the shaking was reported.
"It's not an earthquake. It's probably an offshore sonic boom," Hutton said.
Federal Aviation Administration spokesman Ian Gregor said any sonic boom would come from a military aircraft.
"Civil aircraft do not exceed the speed of sound, so any sonic boom would come from a military aircraft," he said. "Military aircraft do not fly supersonically in civilian airspace; they would only do so in restricted military airspace out over the ocean."
[Updated at 5:09 p.m. PST, April 9:
The rumbling appears to have actually been caused by a supersonic Navy flight.
The U.S. Navy confirmed an aircraft flew faster than the speed of sound as part of an exercise with the USS Ronald Reagan aircraft carrier about 50 miles off the coast this afternoon.
The sonic boom at around 1 p.m. was felt across a wide area, from Malibu to Orange County. Many assumed it was an earthquake, but Caltech seismologists said they did not record any earth movement.
Navy Cmdr. Kevin Stephens noted that when the Navy conducted a similar flight further south in the summer of 2012, "pretty much all of San Diego felt it."
Scott Conner, who lives in the Big Rock neighborhood of Malibu, said he was convinced the shaking he felt just after 1 p.m. was a quake.
He said the shaking was so intense one of his computer monitors would've tipped over if he wasn't there to steady it.
"I had to put out my hand to keep it from tipping over," Conner said in a telephone interview.
"I thought it was the biggest quake I've ever been in…. This thing was big, big," he said. "The whole house just lifted.
"I've been around air force bases. I know what sonic booms are. There was no boom, either," Conner said.]