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| Obrebski, Mathias; Ardhuin, Fabrice; Stutzmann, E.; Schimmel, M.. |
| The location of oceanic sources of the micrometric ground displacement recorded at land stations in the 0.1-0.3 Hz frequency band ("double frequency microseisms") is still poorly known. Here we use one particularly strong noise event in the Pacific to show that small swells from two distant storms can be a strong deep-water source of seismic noise, dominating temporarily the signals recorded at coastal seismic stations. Our interpretation is based on the analysis of noise polarization recorded all around the source, and the good fit achieved for this event and year-round between observed and modeled seismic data. The model further suggests that this is a typical source of these infrequent loud noise bursts, which supports previous inconclusive evidences of... |
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| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00085/19625/17262.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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| 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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| Schimmel, M.; Stutzmann, E.; Ardhuin, Fabrice; Gallart, J.. |
| We quantify, analyze, and characterize the frequency-dependent microseismic noise recorded by worldwide distributed seismic stations. Microseismic noise is generated through the interaction of ocean waves. It is the strongest ambient noise, and it is observed everywhere on Earth. We introduce a new approach which permits us to detect polarized signals in the time-frequency domain and which we use to characterize the microseismic noise. We analyze 7 years of continuous seismograms from the global GEOSCOPE network. Microseisms are dominated by Rayleigh waves, and we therefore focus on elliptically polarized signals. The polarized signals are detected in the time-frequency domain through a degree of polarization measure. We design polarization spectra and... |
| Tipo: Text |
Palavras-chave: Microseismic noise; Polarization; Primary and secondary microseisms; Seismology. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00041/15219/12713.pdf |
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| Stutzmann, E.; Ardhuin, Fabrice; Schimmel, M.; Mangeney, A.; Patau, G.. |
| The strongest seismic noise, called secondary microseisms, is generated by ocean wave interactions and we model this noise using the theory of Longuet-Higgins generalized to random ocean gravity waves. Noise sources are computed with an ocean wave model that takes into account coastal reflections. Variations of the source locations are consistent with seasonal variations of seismic noise spectra. Noise spectra are modelled over many years for stations representative of various environments such as continent, island and polar area to constrain, for each environment, the parameters involved in the modelling. For each station, we quantify the trade-off between ocean wave coastal reflection and seismic wave attenuation that both affect the amplitude of the... |
| Tipo: Text |
Palavras-chave: Surface waves and free oscillations; Theoretical seismology; Wave propagation. |
| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00107/21839/19436.pdf |
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| Davy, C.; Stutzmann, E.; Barruol, G.; Fontaine, F. R.; Schimmel, M.. |
| Ocean waves activity is a major source of microvibrations that travel through the solid Earth, known as microseismic noise and recorded worldwide by broadband seismometers. Analysis of microseismic noise in continuous seismic records can be used to investigate noise sources in the oceans such as storms, and their variations in space and time, making possible the regional and global-scale monitoring of the wave climate. In order to complete the knowledge of the Atlantic and Pacific oceans microseismic noise sources, we analyse 1 yr of continuous data recorded by permanent seismic stations located in the Indian Ocean basin. We primarily focus on secondary microseisms (SM) that are dominated by Rayleigh waves between 6 and 11 s of period. Continuous... |
| Tipo: Text |
Palavras-chave: Surface waves and free oscillations; Indian Ocean. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00287/39825/38335.pdf |
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