Unexplained booms (also called "skyquakes") are unexplained sounds that resemble the sound of the sonic boom of a supersonic aircraft. However, they are unexplained because they do not take place in the same area and time as a supersonic flight.
- An explosive burst of sound, rather than a constant rumble.
- Usually results in brief earthquake-like tremors.
- Sometimes associated with a bright flash of light in the sky.
- January 12th, 1999 - Denver, Colorado - Residents from Colorado Springs to Denver reported an incredibly bright flash of light in the sky, described as a "big blue fireball." Some reported seeing secondary explosions. The military denied any involvement and no meteorite activity was tracked in the area.
- February 2011 - Wilmington, North Carolina - Loud, window-rattling booms were heard in the Wilmington North Carolina region in February of 2011. There were no visible phenomena associated with the booms, and no earthquakes were detected in the area at the time.
In the 1800s, before the advent of aircraft, strange booms were reported in coastal areas. They were given the name "Seneca Guns", as they were most notably heard near Seneca Lake in New York. Similar sounds were heard up and down the US eastern coastline. The US Geological Survey ruled out a variety of causes for the Seneca Guns phenomenon. To this date, they remain unexplained.