SEISMOLOGISTS believe they have pinpointed
the source of a mysterious low-frequency "hum" that emanates from
the Earth, the British science journal Nature
reports.
The persistent noise - at between two and seven
milliHertz, way below the threshold of human hearing - is clearly
caused by large emissions of energy near or at the Earth's surface.
But the puzzle is that the hum can be recorded even on days when
there are no major earthquakes, the likeliest source for such
massive energy release.
In the Nature report, University of California at Berkeley
experts Junkee Rhie and Barbara Romanowicz note that the hum
originates mainly in the northern Pacific Ocean during the northern
hemisphere winter, and separately in the Southern Ocean.
They suggest the hum is generated by interaction between
atmosphere, ocean and sea floor.
Their theory is that storm energy in the winter is converted to
deep ocean waves which then interact with the seabed, creating
vibrations that cause the hum.
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