Researchers have for the first time recorded mysterious ‘hum’ generated by Earth’s movement – using seismic instruments on the bottom of the ocean. The first attempt to detect this low-frequency vibrational signal was made in 1959, but it wasn’t until 1998 that researchers were able to prove it exists.
According to the paper published in the journal Geophysical Research Letters, the hum is caused by “low-frequency seismic signals called – free oscillations – that can only be measured with sensitive instruments” or “the subtle expansion and contraction of the Earth.” It’s not clearly understood where these oscillations are originated from, but it has previously been suggested to come from pounding of waves on the ocean floor and the atmospheric turbulences.
Source: American Geophysical Union
Woaaah. So cool. I wish there was a sound clip
Unfortunately, I couldn’t find it. Also, as researchers noted, which I didn’t mention here, the vibrations are 10,000 times smaller than the lower hearing threshold of the human ear, which is 20 hertz.