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Pré-Publication, Document De Travail Année : 2012

Double-frequency noise generation by surface gravity waves in finite depth: gravity, acoustic and seismic modes

Résumé

Oceanic observations, even in very deep water, and atmospheric pressure or seismic records, from anywhere on Earth, contain noise with dominant periods between 3 and 10 seconds, that can be related to ocean waves. This noise has been explained by a nonlinear wave-wave interaction mechanism, and takes the form of surface gravity waves, acoustic or seismic waves. Previous theoretical works on seismic noise focused on surface (Rayleigh) waves, while acoustic studies have generally considered an unbounded ocean, and atmospheric noise theory has been limited to vertical sound propagation. Here we show how directional wave spectra, through the same theory, produce seismic waves (including Rayleigh and body waves) and associated acoustic-gravity waves in the ocean. In the limit of slow phase speeds, the theory gives the known and well-verified gravity wave result, previously derived for an incompressible ocean. This consistent approach makes it possible to account for noise generation by finite depth surface gravity waves, which is particularly relevant for the noise periods larger than 10~s, and requires the consideration of the direct wave-induced pressure at the ocean bottom, a contribution previously overlooked in the context of seismic noise. For acoustic and seismic modes, that are much faster than the ocean waves, the noise level of each mode is given by a mode-specific amplification of the same wave-induced pressure field near the zero wavenumber.
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Dates et versions

hal-00711326 , version 1 (23-06-2012)
hal-00711326 , version 2 (22-09-2012)
hal-00711326 , version 3 (29-10-2012)

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  • HAL Id : hal-00711326 , version 1

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Fabrice Ardhuin, Thomas H. C. Herbers. Double-frequency noise generation by surface gravity waves in finite depth: gravity, acoustic and seismic modes. 2012. ⟨hal-00711326v1⟩
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