Tremors in New York and New Jersey on Thursday -- likely the result of flight tests in Maryland -- left locals speculating about what had happened.
Up to five waves of tremors were reported throughout southern New Jersey before 2 p.m., according to Patch. An employee there likened the shaking to "a large truck passing by on the street, strong enough to rattle the house.”
Local police agencies investigated, asking residents to stop calling 911, according to reports.
The U.S. Geological Survey ruled out an earthquake, pointing to a sonic boom as the probable cause of the shaking. A sonic boom is defined as "the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound," according to NASA. The reverberations can be felt hundreds of miles away, according to the USGS.
The National Weather Service confirmed a sonic boom on Twitter on Thursday afternoon:
The Navy later said that F-35C jets were conducting flight tests out of the Naval Air Station in Patuxent River, Maryland, according to NBC New York. The tests "included activities which may have resulted in sonic booms," the Navy said in a statement.
Supersonic flights are an almost daily occurrence in the area, a Naval official told WBAL, but most sonic booms are never felt on land.
Federal aviation regulations state that no civilian jets are allowed to fly at supersonic speeds over residential areas in the United States, and military jets are under similar restrictions when flying below 10,000 feet, according to a Department of Defense flight manual obtained by The Huffington Post.
Meteors have also been known to cause sonic booms, even if you're not able to see them breaking up in the atmosphere.
This story has been updated to reflect the Navy's statement that flight tests likely caused the sonic booms residents felt in New York and New Jersey on Thursday.