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.
Dieter Kurrle and Rudolf Widmer-Schnidrig of the University of Stuttgart in Germany studied 11 years of data from seismometers at four isolated locations in Germany, Japan and China. The seismometers were…
