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Updated Mar. 23: The United States Geological Survey has reported that the mysterious booms that shook the town of Clintonville, Wis., were the result of a 1.5-magnitude earthquake. Although not a huge event, the earthquake caused a swarm of several small quakes in a short time. Paul Caruso, a geophysicist from the U.S. Geological Survey told the local Fox News affiliate that most people wouldn't normally feel a 1.5-magnitude earthquake, but that the rock in Wisconsin is very old and well consolidated, allowing residents to feel otherwise sensitive rumblings. via Fox11
From Mar. 22: The small town of Clintonville, Wis., can hardly be called a boom town -- until recently.
On the evening of Sunday, March 18, five loud, mysterious booms thundered through the town at approximately two-hour intervals starting at around 8 p.m. They occurred again the following night, and, much to the sleepless residents' relief, finally stopped Tuesday night. The town thought it was over, but then it started again Wednesday night.
Police, after receiving nearly 100 concerned calls about the sounds, investigated and found nothing. There were no known gas or sewer explosions, no landslides. It was not a military exercise, nor mining explosions. Some think it might be related to sonic booms, groundwater, or earth settling -- though no earthquakes have been recorded.
Some thought it might be a clandestine meth house exploding -- at least the first time, probably not over and over again. Others suspect pranksters with powerful fireworks or dynamite.
Authorities have assured the town that they will continue to search for the source of the booms, though residents are frustrated at the lack of progress. In theory, it should not be difficult for well-equipped technicians to locate the source of a loud boom. After all, you just listen for the sound and go in the direction you hear it, right?
Not so fast. We know from physics that sound travels in waves, and identifying the source of a sound can be very difficult in urban areas where concrete, glass, and buildings can reflect, change, and amplify sound waves.
Those nearest the sound will, in theory, hear it the loudest. However there are confounding factors; for example people farther away may hear it more loudly than people living closer but who have large buildings in between them and the source of the sound that dampen the volume.
Furthermore, without some objective measure of how loud the sound is, witnesses may have difficultly describing variation in volume: was it "loud" or "really loud?" (To most people awakened in their beds very early in the morning by the boom, the most likely response would be an annoyed "too damn loud.")
The first step to locating the source of the sounds would be to place a dozen or more carefully calibrated audio recorders on a grid system throughout (and surrounding) the town. The next time a mysterious boom is recorded, scientists can collect data from all the recorders, determine which microphones recorded the highest volume, and triangulate the location from that information.
It won't conclusively identify the sounds, but will (literally) point them in the right direction.
Even as far as mysterious sounds go, the Clintonville booms are unusual. The vast majority of unexplained sounds are faint, ambiguous, and transitory. For example there's the Taos Hum, a low-frequency rumble heard by some residents in Taos, N.M. since the early 1990s. Not everyone hears it, but those who do variously describe it as sounding like a running refrigerator or a buzzing bee.
In some cases, videos of supposed "mystery noises" have been revealed as hoaxes.
The mystery continues, but for Clintonville residents the answer can't come soon enough.