Ray-theoretical modeling of secondary microseism P-waves

Type Article
Date 2016-09
Language English
Author(s) Farra V.1, Stutzmann Eleonore1, Gualtieri Lucia2, Schimmel M.3, Ardhuin FabriceORCID4
Affiliation(s) 1 : PRES Sorbonne Paris Cite, Inst Phys Globe Paris, CNRS UMR 7154, 1 Rue Jussieu, F-75005 Paris, France.
2 : Columbia Univ, Lamont Doherty Earth Observ, 61 Route 9W, Palisades, NY 10964 USA.
3 : CSIC, Inst Earth Sci Jaume Almera, Lluis Sole & Sabaris S-N, E-08028 Barcelona, Spain.
4 : Univ Brest, IFREMER, CNRS, IRD,LOPS,IUEM, F-29200 Brest, France.
Source Geophysical Journal International (0956-540X) (Oxford Univ Press), 2016-09 , Vol. 206 , N. 3 , P. 1730-1739
DOI 10.1093/gji/ggw242
WOS© Times Cited 38
Keyword(s) Seismic interferometry, Body waves, Seismic noise, Wave propagation
Abstract Secondary microseism sources are pressure fluctuations close to the ocean surface. They generate acoustic P-waves that propagate in water down to the ocean bottom where they are partly reflected, and partly transmitted into the crust to continue their propagation through the Earth. We present the theory for computing the displacement power spectral density of secondary microseism P-waves recorded by receivers in the far field. In the frequency domain, the P-wave displacement can be modeled as the product of (1) the pressure source, (2) the source site effect that accounts for the constructive interference of multiply reflected P-waves in the ocean, (3) the propagation from the ocean bottom to the stations, (4) the receiver site effect. Secondary microseism P-waves have weak amplitudes, but they can be investigated by beamforming analysis. We validate our approach by analyzing the seismic signals generated by Typhoon Ioke (2006) and recorded by the Southern California Seismic Network. Back projecting the beam onto the ocean surface enables to follow the source motion. The observed beam centroid is in the vicinity of the pressure source derived from the ocean wave model WAVEWATCH IIIR. The pressure source is then used for modeling the beam and a good agreement is obtained between measured and modeled beam amplitude variation over time. This modeling approach can be used to invert P-wave noise data and retrieve the source intensity and lateral extent.
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