Excitation of Earth's continuous free oscillations by atmospher-ocean-seafloor coupling
Junkee Rhie and Barbara Romanowicz
Abstract
The Earth undergoes continuous oscillations, and free oscillation peaks have been consistently identified in seismic records in the frequency range 2-7 mHz, on days without significant earthquakes. The level of daily excitation of this 'hum' is equivalent to that of magnitude 5.75 to 6.0 earthquakes, which cannot be explained by summing the contributions of small earthquakes. As slow or silent earthquakes have been ruled out as a source for the hum (except in a few isolated cases), turbulent motions in the atmosphere 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 the excitation of the hum. Our results demonstrate that the Earth's hum originates mainly in the northern Pacific Ocean during Northern Hemispheric winter, and in the Southern oceans during Southern Hemispheric winter. We conclude 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.
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%%Listen to the 'hum' created by Terrence Averkamp based on our measurment
Press Coverage
BBC News : Science pinpoints Earth's 'Hum'
Guardian : Scientists rumble Earth's hum CBC News : Winter stroms source of Earth's hum: geologists The Herald : Reveald: secret of the deep on why the world is humming
Science News : Humming Along: Ocean waves may cause global seismic noise
NewScientist : Earth's 'hum' springs from stormy seas
Der Spiegel : Warum der Meeresboden singt
Frankfurter Allgemeine Zeitung, 29.11.2004, Nr. 279, S. 34
For all enquiries contact:
Barbara Romanowicz at barbara@seismo.berkeley.edu
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