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ABSTRACT
Announced in 1998, and arguably the hottest topic in geoscience in the year
which followed its publication, was some work by Japanese researchers. By
analyzing quiet earth superconducting gravimeter records, that had been collected by others over a period of 20 years;
they showed that the Earth exhibits free oscillations on a near continuous basis, and not just after large earthquakes, as had been
previously thought. They also postulated that atmospheric disturbances are the source of this 'hum' of the Earth. Near continuous records,
collected with Mercer instruments during the last few months, reveal a small number of the same modes as reported by the Japanese. We believe that both the modes observed by the Japanese, and the longer period similar free oscillations, observed
intermittently with our instrument for years before the Japanese studies; result from the same mechanism--the tidal force of our moon and
sun. The data strongly suggest that it is the discontinuous relaxation of the weathered layer of the crust, under tidal forcing, that couples
to the 'elastic' underbody to produce these free oscillations. |