Winter storms source of Earth's hum: geologists

LONDON - The Earth's silent hum is created by interactions between the atmosphere, ocean and sea floor, researchers say.

Planet Earth produces a deep, low frequency rumble far below the limit of human hearing.

A low-frequency hum emanates from the Earth.

The noise, between two and seven millihertz, is likely caused by the release of energy near the planet's surface.

Scientists were puzzled, though, because the hum has been recorded even when no earthquakes are happening – the most likely source of the energy.

To find the source of the hum, researchers at the University of California at Berkeley collected measurements from seismometers in California, Europe and Japan.

Barbara Romanowicz and colleague Junkee Rhie determined the hum originates mainly in northern winters, and the South Atlantic during southern winters.

"We conclude that the Earth's hum is generated by the interaction between atmosphere, ocean and sea floor," the pair wrote in Thursday's issue of the journal Nature.

They theorize storm energy may be converted to seafloor vibrations, causing the hum.