Mysterious Sounds: Solving The Riddle

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Video: Mysterious Sounds: Solving The Riddle

Video: Mysterious Sounds: Solving The Riddle
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Mysterious Sounds: Solving The Riddle
Mysterious Sounds: Solving The Riddle
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One Saturday morning in 2010, Jodie Smith, a resident of Carolina Beach, North Carolina, was disturbed by a rather unusual, rapidly increasing sound. She was not alone, for when she ran out into the street, she bumped into a crowd of neighbors, similarly disturbed by the noise.

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The clear blue sky ruled out the possibility of thunder. Then Smith returned to the house and posted a message on Facebook in which she asked everyone who heard these sounds to respond. Within minutes, she received many confirmatory responses, some of which were within 25 kilometers of her.

This was not the first time Smith had heard these sounds. She says she hears these rapidly increasing sounds several times a year. Local journalist Colin Hackman decided to investigate these sounds, but was simply unable to explain them by any human activity. These sounds could not give rise to either the military or, for example, explosions in the quarry. “I have heard these sounds several times and there is really a mystery in them,” says Hackman.

North Carolians aren't the only ones who have heard inexplicable, rapidly rising sounds. Strange rumbles, whistles and explosions have been reported all over the world for centuries. In the area of Lake Seneca, New York, USA, they are called "Seneca weapons", in the Italian Apennines they are described as "brontidi", which means similar to thunder, in Japan they are "yan", and on the coast of Belgium they are called "mistpouffers". or belching of fog.

So what is their reason? Some of these sounds have very obvious explanations, such as storms or the collapse of ocean waves. But in many cases, such as in North Carolina, no one knows the cause of these sounds. But this does not stop people offering their explanations. And if some of their theories turn out to be correct, they can change our ideas so much that we admit that the earth itself can make these sounds.

Mysterious Sounds has a long history. For example, the village of Mudus in Oregon was originally called Machimoodus, or "the place of bad noise" by the Native Americans. In 1938, amateur seismologist Charles Davison documented sounds heard throughout the UK, with explanations ranging from the noise of the engines and the firing of a distant weapon to the noise of a huge cluster of partridges (Bulletin of the Seismological Society of America, vol 28, p 147)

Thunder is the most likely explanation for many of the sounds. These sounds are generated by a sharp expansion of air due to a sharp increase in pressure and temperature around the lightning channel. In coastal areas, the ocean can act as another source of sound. According to Milton Garcese, an expert acoustician at the University of Hawaii, there are many ways the ocean can generate rapidly rising sounds. This is the crest of a wave falling on the surface of the ocean, air squeezed out of the wave, a giant cloud of bubbles present in the waves, or just a wave crashing into the coastline. These sounds are quite loud and well known to surfers. Such sounds can easily travel several miles inland over land, says Garsese (Geophysical Research Letters, vol 30, p 2264). But what people in North Carolina have heard cannot be explained by these reasons. The calm weather throughout the region ruled out thunder, as well as the sounds of the stormy ocean.

This came to the attention of David Hill, a renowned scientist from the United States Geological Society (USGS), Manlo Park, California. In an article published last year, Holm pointed out that the above reasons cannot explain the causes of sounds in North Carolina (Seismological Research Letters, vol 82, p 619).

However, in the case of North Carolina, Holm does not rule out that the sounds were caused by secret military activities at a nearby military base, such as the sounds of a jet plane or the shots of naval guns. However, he points out that people were reporting these sounds even before this base was built and the supersonic aircraft was invented. The same goes for other messages around the world.

Meteorite noise

In principle, meteorites could explain these sounds, since they can cause a lot of noise when entering the atmosphere, and especially if something happens to them. By the time the sound waves could be heard, the visible trail that meteorites leave as they enter the atmosphere would have gone out long ago.

However, meteorites cannot be the cause of the sounds that are heard every few months or years in regions such as North Carolina, because, as Michael Hedlin, a geophysicist at the University of California, San Diego, argues, “If you really heard a meteorite explosion, then it would probably be a one-off event."

Then the explanation of this phenomenon may lie in the field of geology. In some areas of the world, dunes can emit whispers, whistles and even rapidly increasing sounds. Large dunes with a steep leeward slope are the most likely sources of these sounds (Contemporary Physics, vol 38, p 329). How sound is generated in these dunes is still very poorly understood, but it is known that this requires a combination of loosely packed, almost spherical sand grains with very low moisture content. Singing Sands are found in about 30 locations including California, Egypt, China, and Wales. However, the Carolina coast is not included in this list.

The most exotic theory Holm considers is the case when the sounds are caused by a giant release of methane. The fact is that some deep sea layers are composed of methane hydrate and they are capable of releasing methane when disturbed. This gas can ignite and explode with a rapidly increasing sound, this theory claims. “The problem with this idea is that methane is unlikely to come up suddenly enough and in enough quantities to explode,” Hill says.

This remark leaves him with only one reason for the sounds in North Carolina and elsewhere - an undetected earthquake. “The seismograph network in this area is very rare and there may have been a small earthquake that went unnoticed,” Hill says.

Hill believes that a strong earthquake is not required for the sound to originate. Small earthquakes without perceptible soil vibrations occur constantly and even far from the boundaries of tectonic plates. They are often recorded only by seismographs. But this does not mean that the earthquake happened near you. “The sound of an earthquake can travel much more widely than most people imagine,” he says.

Anyone who has experienced an earthquake knows that they are by no means quiet. However, the noise that most people remember is actually caused by vibrations of buildings, soil, but not directly the sound of an earthquake.

Yet earthquakes are indeed accompanied by sound waves that precede the earthquake itself. Malcolm Johnson, Holm's USGS colleague, turned out to be exactly the person who was close enough to the epicenter to hear these sounds. In 2008, he was struck by an earthquake when he was at the very bottom of a gold mine in South Africa near a rift fault he was about to study. Johnson recalls: “I was at a depth of 3.6 kilometers in a small tunnel within the error of determining the rift, tuning the instruments. Suddenly there was a magnitude 2 earthquake, and its epicenter was 20 meters away from me. I heard a sound that sounded like a thunderclap, overlaid with a complex high frequency noise. As soon as I heard him, I realized that I would remember him forever. And this is despite the fact that I tried to avoid falling stones and realized that if this gap went through the tunnel in which I was, I would be the filling for the pie."

On the surface, we are often unable to hear such a sound, since only very low frequency sound waves that lie outside our range of perception reach us. The waves we hear with a frequency between 20 hertz and 20 kilohertz are most likely to be absorbed and scattered by the rocks through which they propagate. Much the same when you hear only bass sounds while your neighbor is playing an instrument.

However, under certain conditions, Hill says, earthquake sounds can sing from the Earth. Here is an example where a weak earthquake can excite sound waves that reach the surface. If hard, fine-grained rocks such as granite are in the path of the sound, we will probably be able to hear these sounds, since these rocks are less likely to scatter sound frequencies. Or if the waves meet on the way the interface of two media, then along it they can be transferred directly to the surface and directly into the air. “The earth around man acts like a giant subwoofer,” says Hill.

In addition, certain weather conditions can contribute to the propagation of sound waves over long distances. For example, on a cool, foggy morning, when a cold layer of air is trapped under a warmer atmospheric blanket. Then, reflecting from the warm layer, sounds can "jump" over long distances.

But can weak earthquakes go undetected? Jonathan Lees, a geophysicist at the University of North Carolina, is very skeptical about such claims. “The instruments used to record earthquakes are very sensitive. If loud sounds cannot be caused by earthquakes, then they are probably of a different nature,”he says. However, he acknowledges that at least some of the sounds reported must have natural causes. Numerous field observations support the idea that small earthquakes can generate strong noise. Back in 1975, Holm and his colleagues were setting up seismic stations in Impairl Valley, California. One night, their microphone recorded three rapidly increasing noises, which coincided exactly with three earthquakes, magnitudes 2 and 3 (Bulletin of the Seismological Society of America, vol 66, p 1159). Later, Matthew Silvander of the University of Toulouse, France, recorded the rapidly increasing noise associated with small earthquakes in the French Pyrenees. “When an earthquake is right under your feet, you hear a rapidly developing sound, but if it is far away, the sound will be in lower tones. Probably many of the funny noises can be blamed on tectonics rather than poltergeist,”says Silvaner.

North Carolina, with its constant noise, could be the place to solve this mystery once and for all. The EarthScope project is a network of seismic stations located 70 kilometers apart, covering the entire United States from west to east. It should reach North Carolina in a few years and will be sensitive enough to test the Hill earthquake theory.

They also began to collect reports on the sounds heard during earthquakes. For example, Patricia Tosi of the National Institute of Geophysics and Volcanology in Rome, Italy, and her colleagues are asking people to report the earthquake sounds they hear through an online survey. Using this data, they reproduced a map of the noise heard during the magnitude 6, 3 earthquake that struck the city of L'Aquila in 2009. Many of these sounds were most likely caused by vibrating buildings, but some of the messages from the 100 km zone near the epicenter are directly related to the noise expected from the earthquake itself.

Regardless of what caused the sounds Jodie Smith heard that day in North Carolina, our planet seems to be making a lot more sounds than we thought. The dissonance of our world means that most of us are accustomed to attributing loud noises to human activity. But the sound you mistake for the rumble of a distant truck may actually be the voice of the Earth itself.

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