"Excitation of Earth's continuous free oscillations by atmosphere-ocean-se=
afloor coupling", Nature, 431, p552-556, 2004
ABSTRACT
The Earth undergoes continuous oscillations, and free oscillation peaks=
have been consistently identified in seismic records in the frequency rang=
e 2-7 mHz, on days without significant earthquakes. The level of daily exci=
tation of this 'hum' is equivalent to that of magnitude 5.75 to 6.0 earthqu=
akes, which cannot be explained by summing the contributions of small earth=
quakes. As slow or silent earthquakes have been ruled out as a source for t=
he hum (except in a few isolated cases), turbulent motions in the atmospher=
e or processes in the oceans have been invoked as the excitation mechanism.=
We have developed an array-based method to detect and locate sources of th=
e excitation of the hum. Our results demonstrate that the Earth's hum origi=
nates mainly in the northern Pacific Ocean during Northern Hemispheric wint=
er, and in the Southern oceans during Southern Hemispheric winter. We concl=
ude that the Earth's hum is generated by the interaction between atmosphere=
, ocean and sea floor, problably through the conversion of storm energy to =
oceanic infragravity waves that interact with seafloor topography.
|