Even without earthquakes, seismometers constantly record seismic energy. They record periods of oscillations about every 6 seconds as background noise.
Earth hum was once thought to be very mysterious in nature. It went unexplained for decades. But now scientists discovered that these oscillations are due to ocean waves constantly crashing into continents.
Ocean waves pound continents vibrating like a bell. Then land masses shake back and forth like a metronome. And during storms, it worsens as the reverberations are amplified.
So let’s get started with Earth hum. Because even when it’s silent, there’s a bit of background noise reverberating.
Low frequency background noise
Humans are unable to hear Earth’s hum because it ranges between 2.9 and 4.5 mHz. In general, humans can hear anything from 20 Hz to 20 kHz.
So this means that Earth’s hum is about 10,000 times lower than what we are capable of hearing. That’s why we need special seismometers to detect this ultra-low frequency.
There’s been claims that submarine activity and hidden military operations caused this low frequency noise. But in 1998, this phenomenon has been attributed to ocean waves pounding the edge of continents.
Like the reverberations of a bell, scientists have clearly listened to Earth hum. By installing seismometers in the Indian Ocean, they gathered signals from the ultra-low frequency sound to conclude where it was coming from.