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Humming Along: Ocean waves may cause global seismic noise

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11:05am, September 29, 2004

The slow and nearly constant vibrations of Earth's crust stem from severe winter weather over some of the world's oceans, a new analysis of seismic data suggests.

Our planet's outer shell is constantly pulsing. Earthquakes trigger many of these ripples, but the ground undulates imperceptibly even on days devoid of significant temblors. Scientists have dubbed these persistent vibrations "Earth's hum." The largest undulations in this seismic background noise occur at frequencies between 2 and 7 millihertz, or once every few minutes, says Barbara A. Romanowicz, a seismologist at the University of California, Berkeley.

Each day, the energy driving these worldwide oscillations is the equivalent of that released during a magnitude 5.7 earthquake. That's more energy than can be explained by all of the planet's small daily earthquakes, says Romanowicz.

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