Earth's Mysterious Humming Noise is Recorded at the Ocean Floor

Sunday, 10 December 2017 - 12:48PM
Sunday, 10 December 2017 - 12:48PM
Earth's Mysterious Humming Noise is Recorded at the Ocean Floor
NASA/Reid Wiseman
It's been known for awhile now that the Earth gives off "free oscillations," which is a fancy way of saying that the planet makes a low humming noise, which can be detected when everything else is quiet. In short, the Earth is vibrating for some reason that's unrelated to earthquakes (more on that in a bit).

And for the first time, researchers managed to get a better "look" at the hum after recording it from the Indian Ocean floor, publishing their research in Geophysical Research Letters. The process was long, and required about 57 seismometers to be deposited around the ocean floor from 2012 to 2013.

After that came the hard part: detecting the hum underneath the endless background activity an ocean tends to have.

Attempts to measure the hum from the ocean floor have been tried before, since doing so could be extremely helpful in pinpointing a specific source of the hum, or more accurately detecting how powerful these vibrations are. But nobody could eliminate background noise from sea currents and other aquatic noisemakers, until now. The researchers employed a number of techniques to cut down on background frequencies and zero in on the hum.

The study's lead author, Martha Deen, a geophysicist at the Paris Institute of Earth Physics, thinks the hum could be used to better map out the Earth's interior, being a distinct frequency coming from somewhere underneath the surface:

Opening quote
"Earth is constantly in movement, and we wanted to observe these movements because the field could benefit from having more data."
Closing quote

It was back in 1959 that the "free oscillations" were first discovered, with more research being done in the 1990s, but this is the first to document it from so close to its source. The hum is extremely low and ranges from 2.9 and 4.5 millihertz, according to the American Geophysical Union, and since the lowest frequency a human being can hear is around 20 hertz, that's probably you haven't heard it yourself.

It's a curious scientific phenomenon that doesn't have a complete explanation yet, registering on seismic equipment while being distinctly less violent than tectonic plate movements. Its presence also has no known relation to earthquakes, humming off regardless of how many earthquakes have been in the area. 

Other possible sources for the Earth's hum include atmospheric turbulence or ocean waves, although nobody's settled on anything specific yet, which is part of why this new research could be so helpful.

And it's probably not related to the Bristol or Taos Hum, which is more X-Files fodder than Earth science.
Science News