People along New Jersey's eastern coast reported feeling at least six tremors on Thursday afternoon in what many thought was a series of small earthquakes.
Not so.
It was a "sonic boom," according to seismologists with the USGS Earthquake Hazards Program, which noted that the first shake, felt at 1:24 p.m. local time, was the "first of multiple over the following hour after this event."
Not an earthquake but a sonic boom in New Jersey: https://t.co/eUr4sB28Wm pic.twitter.com/TQFlkGr633— USGS (@USGS) January 28, 2016
The tremors were felt across a wide area, the USGS said, from southern New Jersey along the Eastern Seaboard and up through Long Island, New York.
The reports led to New York's official emergency notification system to send an alert warning of "unconfirmed reports of an earthquake in NYC/NJ area" and that there were "no reports of damage." Columbia University's Earth Institute tweeted that the “earthquakes” appeared to be caused by nearby "military aircraft."
Unconfirmed reports of an earthquake in NYC/NJ area. No earthquake activity identified by US Geological Survey. No reports of damage.— NYCEM - Notify NYC (@NotifyNYC) January 28, 2016
Unconfirmed, but #NJ “earthquakes” appear to be sonic booms from military aircraft. No reports from @USGS.— Earth Institute (@earthinstitute) January 28, 2016
Sonic booms create a "thunder-like noise" that is heard by people ground "when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound," a NASA fact sheet explains. "As objects travel through the air, the air molecules are pushed aside with great force and this forms a shock wave much like a boat creates a bow wave. The bigger and heavier the aircraft, the more air it displaces."
Those who felt the tremors said they were intense. "They seem to be getting stronger each time" wrote Rob Kelly, a professional surfer. "Much more intense than when there are training exercises at the joint base," Andrea Dick wrote on the Jersey Shore Hurricane News Facebook page.
This was the 6th shake I felt in southern NJ #Earthquake #NewJersey pic.twitter.com/XmcklvAYeE— BeautyObsessed (@anitanj21) January 28, 2016
"I'm used to the sonic booms. First one felt like a large one of those," added Julia Mason Lockhart from Northfield, New Jersey. "Second one a few mins later felt a lot more like the earthquakes I felt when I lived in Japan...walls and doors rattling, with the ground shifting rather than vibrating. And then a smaller one like the "normal" booms about 25 mins later."
That's 6 times and they seem to be getting stronger each time. #new jersey #earthquake? #sonicboom— Rob Kelly (@robkellysurf) January 28, 2016
Others reported that their doors and windows began shaking as their dogs "freaked out." One man posted video of his "door dancing" for those who didn't believe the claims.
Overhead door dancing for the non believers #earthquake #nj #newjersey pic.twitter.com/rDKwmgdwrV— kshoulders609 (@kshoulders609) January 28, 2016
The United States Air Force maintains a base in Burlington County, New Jersey, about 15 miles south of Trenton. McGuire Air Force Base is home to a variety of what are mostly refueling and transport aircraft, ferrying troops, fuel and cargo from the U.S. and abroad.
In other words, as far as we can tell, there are no planes that typically break the sound barrier normally stationed at McGuire, though that's not to say they weren't in the area or hidden under an enclosure. Fighters from bases in Virginia and Massachusetts are also often doing maneuvers off the New York and New Jersey coasts.
So the military may be to blame for today's shakes -- or, of course, aliens.