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| Ardhuin, Fabrice; Gualtieri, Lucia; Stutzmann, Eleonore. |
| Microseismic activity, recorded everywhere on Earth, is largely due to ocean waves. Recent progress has clearly identified sources of microseisms in the most energetic band, with periods from 3 to 10 s. In contrast, the generation of longer-period microseisms has been strongly debated. Two mechanisms have been proposed to explain seismic wave generation: a primary mechanism, by which ocean waves propagating over bottom slopes generate seismic waves, and a secondary mechanism which relies on the nonlinear interaction of ocean waves. Here we show that the primary mechanism explains the average power, frequency distribution, and most of the variability in signals recorded by vertical seismometers, for seismic periods ranging from 13 to 300 s. The secondary... |
| Tipo: Text |
Palavras-chave: Hum; Infragravity waves; Numerical model; Microseisms. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00251/36219/34769.pdf |
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| Gualtieri, Lucia; Stutzmann, Eleonore; Farra, V.; Capdeville, Y.; Schimmel, M.; Ardhuin, Fabrice; Morelli, A.. |
| Secondary microseismic noise is generated by non-linear interactions between ocean waves at the ocean surface. We present here the theory for computing the site effect of the ocean layer upon body waves generated by noise sources distributed along the ocean surface. By defining the wavefield as the superposition of plane waves, we show that the ocean site effect can be described as the constructive interference of multiply reflected P waves in the ocean that are then converted to either P or SV waves at the ocean-crust interface. We observe that the site effect varies strongly with period and ocean depth, although in a different way for body waves than for Rayleigh waves. We also show that the ocean site effect is stronger for P waves than for S waves. We... |
| Tipo: Text |
Palavras-chave: Body waves; Site effects; Theoretical seismology. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00190/30087/28634.pdf |
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| Farra, V.; Stutzmann, Eleonore; Gualtieri, Lucia; Schimmel, M.; Ardhuin, Fabrice. |
| 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... |
| Tipo: Text |
Palavras-chave: Seismic interferometry; Body waves; Seismic noise; Wave propagation. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00344/45509/45063.pdf |
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