F/A-18 Super Hornet caused sonic boom some believed was quake

It was a lone F/A-18 Super Hornet fighter jet that produced the sonic boom Wednesday that produced the rumbling so intense some Los Angeles and Orange County residents insisted it was an earthquake.

The confirmation Thursday from the U.S. Navy came as some questioned that the rumbling came from an aircraft, while others suggested it was a test of the fabled Aurora spy plane.

“It’s maddening these things draw up these conspiracy theories,” said Peter Merlin, an aerospace historian and an author on military and experimental aircraft.

The F/A-18 jet was flying in the Pacific Ocean about 35 miles southwest of San Diego when it flew faster than the speed of sound, said Navy Cmdr. Kevin Stephens.

Because the jet was headed in a northern and northwest direction, the sonic boom produced by the fighter jet headed toward the coast of Los Angeles and Orange counties — more than 100 miles away.

“The sound will propagate in the direction it’s flying,” Stephens said. The speed of sound is about 761 miles per hour.

The jet was flying as part of a demonstration of the U.S.S. Ronald Reagan aircraft carrier, which was on a daylong “open house” cruise out of its home port in Coronado.

“It allows family members, spouses and kids to come out and experience for one day what life is like out at sea,” Stephens said. The F/A-18 had flown from Naval Air Station Lemoore’s VFA-137 squadron in central California.

While some may equate sonic booms to sounding like sharp cracks, the farther away you are from the jet, the more likely you might hear a rumbling sound that can shake buildings.

NASA aerospace engineer Edward Haering compared it to lightning strikes. The closer you are to the lightning, the more likely you’ll hear a sharp crack. The farther away you are, the more likely you’ll hear a rumble.

“It actually can shake the house. If you have a large building, the pressure hits the wall and vibrates it, and so the room will kind of vibrate a little bit,” said Haering, who works at the NASA Armstrong Flight Research Center in Edwards, Calif.

Sonic booms are produced when aircraft go faster than the speed of sound. They are like a 3-D version of the V-shaped waves that can be seen in the wake of a moving motor boat.

Instead of choppier water, the sonic boom vibrates the air, making a loud sound.

Haering said it can be hard for pilots to know where and how far sonic booms will travel. A lot depends on the weather and the direction of the wind, which helps determine where the sound will go.

“We’re working on efforts to make quiet supersonic aircraft that won’t disturb people,” Haering said.

It’s understandable that people might be spooked by hearing a sonic boom along the L.A. and Orange County coast, experts said. Sonic booms would be more expected over Edwards Air Force base, for instance.

“Sometimes, you see something out of context, and sometimes, it’s a little mysterious,” said Merlin, the aerospace historian.

Wednesday’s sonic boom as well as earlier similar incidents have caused some to speculate it could be the testing of the mythical top-secret Aurora spy plane project.

Merlin said Aurora is a fantasy, based on a misreading of a federal budget document in the 1990s as the government phased out the SR-71 Blackbird spy plane. Some thought Aurora was to be its replacement, but in fact, it was the codename of the well-known B-2 stealth bomber, which does not fly faster than the speed of sound, Merlin said.

The F/A-18 is a twin-engine fighter jet made by Boeing Co. that has been a fixture on U.S. Navy aircraft carriers since 1983. The plane is flown by the Blue Angels, the Navy’s flying aerobatic team.

The Super Hornet version of the aircraft became operational in 2001.

The aircraft’s fuselage sections are manufactured by Northrop Grumman Corp. in Los Angeles, in a 1-million-square-foot facility on Aviation Boulevard, about a mile south of Los Angeles International Airport.

It’s not uncommon for sonic booms to be mistaken for earthquakes. In February, residents along the Maryland coast were startled and reported floors shaking and doors rattling.

The boom coincided with a flight of supersonic jets, an F-35C and an F/A-18, flying from Patuxent Naval Air Station, the Baltimore Sun reported.

Scott Conner, who lives in the Big Rock neighborhood of Malibu, said Wednesday he was convinced the shaking 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.”

Kit Fox, who works at Rancho Palos Verdes City Hall, said people walked out of their offices after being rattled.

“It was really just a short, sharp jolt, I think the shaking went on for about 3 to 5 seconds at most, but it definitely rattled people,” he said.

Fox said it felt more like the building shaking rather than the ground shaking.

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Twitter: @ronlin | Facebook | Google+

ron.lin@latimes.com

Times staff writer W.J. Hennigan contributed to this report.