A series of loud, unexplained booms, seemingly focused on the Unites States but reported worldwide, continue to mystify experts. So far, the strange noises have occurred in the states of Alabama, California, Colorado, Idaho, Michigan, New Jersey, and Tennessee; as well as in the countries of Russia, Denmark, England, and Australia.

Residents in these areas have reported loud booms sometimes accompanied by brief, violent shaking of their surroundings.

"I was sitting on my sofa and it sounded like a one boom, followed by a slightly louder boom,” said Jim Coker, Director of the Jefferson County Emergency Management Agency in Alabama, who heard one such boom on November 26th.

"We have not received any information from any sources about what this may be."

The National Weather Service in Alabama tweeted that they were unable to name the source of the strange sounds.

Re: loud boom heard: we do not see anything indicating large fire/smoke on radar or satellite; nothing on USGS indicating an earthquake. We don't have an answer, and can only hypothesize with you. 1) sonic boom from aircraft; 2) meteorite w/ current Leonid shower?
— NWS Birmingham (@NWSBirmingham) November 14, 2017

A similar sound in Colorado is being blamed on an empty oil storage tank that over-pressurized, causing its lid to be blown from the tank; something local officials believe could have caused a sufficiently loud noise to trigger alarm.

Other possible explanations for this and other incidents of loud booms include meteors exploding in the atmosphere as part of the Leonid meteor shower, sonic booms from aircraft, and seismic events. However, astronomy experts argue that the Leonid meteors are too small to create such an effect; no military aircraft have been known to be flying in the area of the booms; and no seismic activity has been recorded near the mysterious sounds.

NASA representatives say they are unsure of the source of the booms.

Worldwide Mystery 'Booms' Baffle Experts