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• W2912765534 abstract "This thesis combines observations, simulations and development of high-performance numerical tools in the field of underwater acoustics, and in particular for the study of T-waves.The term T-waves is generally associated with acoustic waves generated by seismic events that subsequently travel horizontally in the ocean at the speed of sound. After a thematic review of the literature on T-waves we analyzed real data recorded in Sicily and Calabria following earthquakes occurring near the West coast of Greece. In order to model the phenomenon, we developed an axisymmetric spectral-element solver (2.5-D) in the time domain, which we present and validate. This tool allowed us to realistically reproduce numerically one of the Greek earthquakes studied as well as the propagation of the resulting T-waves up to Sicily.We also present a two-stage parametric study of the influence of seafloor slope in a typical T-wave generation/conversion scenario. The energy and duration of these waves is particularly sensitive to the environment. In particular, the slopes and characteristics of the seabed play a crucial role for both solid-fluid and fluid-solid conversion. These characteristics can mislead localization algorithms. Likewise, the depth and position of the earthquake relative to the slope is of great importance, with the presence of privileged areas for the generation of T-waves, which we have mapped. In addition, in the case of the conversion of an acoustic wave on a coast, our simulations predict that in some cases a strong Rayleigh wave can be generated, whose signal, recorded inland, is very sensitive to the slope and to the characteristics of the environment, but not very sensitive to the modal structure of the incident wave. This phenomenon may have interesting implications that we discuss.However, our studies confirm that at regional distances (< 1000 km) the sound speed profile in the ocean is only a second-order parameter. To evaluate its impact we have developed a procedure for the calculation of transmission-loss and time-dispersion maps from full-wave numerical simulations in the time domain. In the configurations studied, the presence of the SOFAR channel slightly limits the time dispersion but only introduces a gain in terms of energy transmission of a few thousandths of dB per kilometer.In a second step, we show that a medium-sized commercial vessel, as there are tens of thousands nowadays in the oceans of the globe, can generate by diffraction some T-waves of significant amplitude (of the order of those created by downslope conversion on a slope of 12^{circ}) and of low dispersion. This mechanism of T-wave generation, to our knowledge undocumented, must be particularly frequent in areas in which maritime traffic is substantial and could explain some abyssal T-waves that are still not well understood. Taking the atmosphere into account in these simulations, we realized that the presence of these vessels could also produce guided infrasound in the lower layers of the atmosphere. This mechanism of infrasound production could be an alternative explanation to the evanescent coupling proposed by Evers et al. (2014) to explain the waves observed in Tasmania following an earthquake on the Macquarie Ridge.Finally, we presented and validated some numerical tools to calculate the acoustic field created by a moving source. The method was applied to a light aircraft flying over the ocean. This configuration, presented by Buckingham (2010), can be used to estimate the pressure wave speed in marine sediments." @default.
• W2912765534 created "2019-02-21" @default.
• W2912765534 creator A5089442900 @default.
• W2912765534 date "2018-09-13" @default.
• W2912765534 modified "2023-09-23" @default.
• W2912765534 title "Full-wave numerical simulation of T-waves and of moving acoustic sources" @default.
• W2912765534 hasPublicationYear "2018" @default.
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