Geologists have detected a new continuous seismic signal in the Earth, but its cause is anybody's guess
Listen closely, and you'll hear the Earth humming - in not just one note, but two. The source of this second signal is a mystery.
For around a decade we've known about Earth's quiet "vertical" hum, probably caused by the steady thumping of deep waves on the ocean floor. Now a team in Germany has discovered a second "horizontal" note, too, and nobody knows what's causing this new signal.They found evidence of a "horizontal" signal at all four stations. The signal migrates by around 1 micrometre one way or the other every three minutes or so, and its horizontal orientation distinguishes it from Earth's "vertical" oscillation. (Geophysical Research Letters)
Though certain events seem to amplify this constant signal - such as earthquakes, volcanoes and large storms - the source is a mystery. "Something entirely new to us is causing this hum," says Spahr Webb of the Lamont-Doherty Earth Observatory in New York, who studied the original hum.
"Something entirely new to us is causing this hum. Its frequency suggests something is 'twisting' the surface of the crust."
