For years, scientists have been puzzled by the "humming" sound coming from the Earth, first detected during the 1990s. According to new research, they may have finally found the answer.

A study conducted by the National Center for Scientific Research (CNSR) in France revealed that the mysterious hum is most likely caused by ocean waves colliding with each other and creating small seismic waves. This microseismic activity, however, is believed to be too faint for humans to detect it.

This new theory offers a more plausible explanation compared to initial suggestions, which include electromagnetic radiation and even secret military operations, namely submarine activity.

Fabrice Ardhuin, an oceanographer from the CNSR, said that waves coming from the seafloor make the Earth "vibrate like a bell," creating the hum that is heard by some people.

"I think our result is an important step in the transformation of mysterious noise into an understood signal," Ardhuin said.

Using computer-generated models of the wind, ocean and seafloor, Ardhuin and his fellow oceanographers, Lucia Gualtieri and Eléonore Stutzmann from the Paris Institute of Earth Physics, were able to determine the exact type of waves that create the humming sound. These waves, in turn, produce the faint seismic activity within 13 to 300 seconds. This is enough time for the ripple to reach the ocean floor, possibly even traveling beyond the Earth's mantle and into its core.

"We have made a big step in explaining this. Now we know where this ringing comes from, and the next question is: what can we do with it," Ardhuin added.

The researchers believe that the result of their study is only one possible explanation for the hum and that there could be other reasons behind it. These may include the ocean waves colliding with shorelines or mountains beneath the ocean. Mid-oceans could also contribute to the phenomenon.

Ardhuin and his colleagues hope that their study can be used to advance research regarding the Earth's interior by creating a more precise picture of the planet's structure.

The incessant humming sound has caused discomfort in people who can hear it, causing stress and loss of sleep. There have also been cases involving individuals who were driven to the brink of madness and even suicide.

In the United Kingdom, a reported 800 people who suffer from the "Bristol hum" have complained to their local newspaper, claiming that the sound caused them to have nosebleeds and headaches.

The CNSR study is published in the journal Geophysical Research Letters.

Photo: Tim Sackton | Flickr