Rumblings felt in South Jersey earlier this month are no longer a mystery.

They were the result of military jets breaking the sound barrier over an offshore area called the “Racetrack.”

Initial reports of loud noises and windows rattling in the region March 19 could not be linked to an earthquake or military training from nearby bases. The U.S. Geological Survey’s National Earthquake Information Center said there was no recorded seismic activity in the area, and calls to nearby military bases revealed no testing had taken place.

But several calls later revealed the source — fighter jets flying from the Naval Air Station Patuxent River in Maryland.

Douglas Abbotts a spokesman for the Naval Air Warfare Center’s Aircraft Division, said residents were experiencing the sonic boom from either an F-35 or F16 jet flying 30 miles offshore that may have carried due to “just the right” elements present in the atmosphere.

These jets typically are not allowed to fly at such high speeds, according to geophysicist Don Blakeman, with the National Earthquake Information Center.

But there is one place they can — a defined air space, nicknamed “The Racetrack,” which is controlled by the U.S. Department of Defense, Abbotts said. The test track runs from Ocean City, Md., to Atlantic City, and the jets fly at altitudes starting at 10,000 feet.

Blakeman said that when jets go supersonic, they create shockwaves and a resulting sonic boom.

“There are several factors that can influence sonic booms — weight, size, and shape of the aircraft or vehicle, plus its altitude, attitude and flight path, and weather or atmospheric conditions,” according to NASA’s website.

The distance it travels depends on the altitude of the jets, which results in a “boom carpet” — equivalent to one mile for each 1,000 feet of altitude, NASA’s website says.

Colder weather allows the sound waves to “travel farther in shorter amounts of time,” said Joseph Trout, an assistant professor of Physics at Richard Stockton College. He explained the likelihood of feeling the supersonic effects are higher from November to April.

NEIC geophysicist John Bellini said reports of loud noises and tremors on March 19 were received along the coast in Delaware and Virginia as well.

Blakeman said from what he understands, the distance of the waves traveling acts a bit the way thunder does. It travels as sound waves and the wind speed and direction can carry it farther out.

The reason why it doesn’t register on equipment set to pick up seismic activity is because those instruments are farther underground, he said.

“They don’t put much energy into the ground,” so the energy isn’t transferred into detectable waves for the instruments, Blakeman said.

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