"The waves we are studying are ordinary ocean waves, not seismically generated ones," Aster said.
(Related: "Mysterious Tremors' Strength Ebbs With Tides" [November 22, 2007].)
"We are basically using the long-term seismic record to see if Earth is getting systematically ['noisier'] due to changing ocean waves."
Though the signals are small, "we do see these trends of a few percent a decade that appear to be robust," Aster added.
The study appeared in the March/April edition of the journal Seismological Research Letters.
Seismic Noise
Paul Earle, a research geophysicist for the U.S. Geological Survey, was not associated with the study.
He said the research shows how microseisms can be used to study patterns in ocean-storm intensity.
"It is interesting that microseisms are more commonly called 'seismic noise' and early instruments were specifically designed to suppress and remove this signal," Earle said.
"This study highlights the importance of archiving and preserving continuous geophysical measurements—even if their use is currently unknown."
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