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New Notes in Earth's Hum

Scientists discover more complex oscillations in planetary symphony

By Harry Kimball,  Newser Staff

Posted Apr 17, 2008 7:45 PM CDT

(Newser) – Scientists have discovered a new dimension to the sub-aural sound emanating from our planet’s crust, dubbed “Earth’s hum.” Researchers have known about the hum, detectable only by seismometers, for a decade, though its ultimate cause is unclear. They expected to find hidden oscillations, but the amplitude of the new “ring-like waves” dwarfed expectations, LiveScience reports.

The hum is caused by rock in the Earth’s crust moving almost imperceptibly against itself, but what makes it move continues to puzzle scientists. While the older waves, described as “spheroidal,” might be caused by oceanic or atmospheric forces pressing down on the planet, the new circular waves could be the result of shearing forces caused by the ocean, the atmosphere, or even the sun.

Earth as seen by the Apollo 17 crew.
Earth as seen by the Apollo 17 crew.   (AP Photo/Courtesy of Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center)
A 1968 image from NASA.
A 1968 image from NASA.   (AP Photo/Courtesy of Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center)
University of Utah seismograph center.
University of Utah seismograph center.   (AP Photo/The Salt LakeTribune, Francisco Kjolseth)
This image provided by NASA shows a gibbous moon visible in this view of Earth's horizon and airglow.
This image provided by NASA shows a gibbous moon visible in this view of Earth's horizon and airglow.   (AP Photo/NASA)
Earth's horizon and the blackness of space.
Earth's horizon and the blackness of space.   (AP Photo)
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