No matter how closely you listen, you will not hear the Earth hum—but humming it is.
Far, far below the range of human hearing, waves of energy are coursing through the crust, causing the ground beneath your feet to rise and fall about three-millionths of an inch every few minutes. First detected by networks monitoring seismic activity in 1998, the tiny ripples were initially chalked up to the many small earthquakes that occur each day around the world. But studies over the past decade have proved that the hum is far too constant for that explanation.
In February, oceanographer-turned-seismologist Spahr Webb, of Columbia University’s Lamont-Doherty Earth Observatory, reported finding the hum’s likely origin: ocean waves colliding over continental shelves. When two trains of waves, traveling in different directions, smash into one another, they send a continuous cacophony down to the seafloor. That energy triggers vibrations that ripple through the planet, ...
