HR: 0800h
AN: T11B-1256    [Abstracts]
TI: New observations of Q quality factors of a few gravest normal modes from the Global Geodynamics Project (GGP)
AU: * ROULT, G
EM: groult@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, PARIS, 75005 France
AU: ROSAT, S
EM: Severine.Rosat@eost.u-strasbg.fr
AF: Ecole et Observatoire des Sciences de la Terre, 5 rue Descartes, STRASBOURG, 67084 France
AU: HINDERER, J
EM: Jacques.Hinderer@eost.u-strasbg.fr
AF: Ecole et Observatoire des Sciences de la Terre, 5 rue Descartes, STRASBOURG, 67084 France
AU: MILLOT-LANGET, R
EM: rmillot@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, PARIS, 75005 France
AU: CLEVEDE, E
EM: clevede@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, PARIS, 75005 France
AB: he high quality of the GGP superconducting gravimeters contributes to the clear observation of seismic normal modes at frequencies lower than 1mHz and offers a good opportunity for studying the behaviour of these modes. The interest of scientists for the gravest normal modes is due to the fact that these modes do contribute to a better knowledge of the density profile in the Earth, helping to constrain Earth's models. These modes have been clearly identified after some large recent events recorded on superconducting gravimeters. The Peruvian earthquake of June 2001 provided us with individual spectra (in a unique station) with a clear splitting of the fundamental mode 0S2 and identification of each of the five individual singlets, with a resolution never obtained from broad-band seismometers records. The Q quality factors have been determined from the apparent decrease of the amplitude of each singlet with time, according to a well suited technique (Roult & Cl‚v‚d‚, 2000). The results are compared to the theoretical frequencies and Q quality factors computed in the PREM model, taking into account the rotation and the ellipticity of the Earth. The two datasets (frequencies and Q quality factors) exhibits a small shift between the splitting of the observed values and that of the predicted ones. That seems to point out that the rotation and the ellipticity don't explain the observations and that we have to take into account additional effects. A new dataset of Q quality factors of all singlets of the gravest modes is under construction, including the 0S2 and 0S3 modes, the radial 0S0 mode and the 2S1 mode recently identified by Rosat et al. (2003).
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7207 Core and mantle
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 1236 Rheology of the lithosphere and mantle (8160)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting