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Variations temporelles de la gravité en relation avec la dynamique interne de la Terre - Apport des gravimètres supraconducteurs

Séverine Rosat 1
1 IPGS-DGDA - Dynamique globale et déformation active (IPGS)
IPGS - Institut de physique du globe de Strasbourg
Abstract : The Earth's dynamics and interior structure are badly constrained, particularly in the deep interior, because the surface induced signals are of weak amplitude and low frequency and reach the detection level of seismometers. Gravimetry is then a privileged tool to investigate the Earth's interior at these long periods. Time varying gravity is permanently recorded at the surface by a worldwide network of cryogenic relative gravimeters. We study the noise levels of all these gravimetric stations over a wide frequency range, from the long period seismic normal modes to the tides. We show that superconducting gravimeters can uniquely contribute to the study of the low frequency Earth's vibrations, which sample the Earth from the surface to the core. We highlight (1) the splitting due to rotation and ellipticity of the 0S2 normal mode into five singlets, (2) the first observation of the 2S1 seismic mode, after the 2001, June 23rd Peru earthquake with a magnitude 8.4.
We search for the normal mode of translation of the inner core, which has never been clearly observed. Its detection is essential as it would constrain the density jump at the inner core boundary, probably also the viscosity and the outer core stratification. For that purpose, we develop some stacking, automatic detection of signals methods and a wavelet representation.
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Séverine Rosat. Variations temporelles de la gravité en relation avec la dynamique interne de la Terre - Apport des gravimètres supraconducteurs. Géophysique [physics.geo-ph]. Université Louis Pasteur - Strasbourg I, 2004. Français. ⟨tel-00144439⟩

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