HR: 0800h
AN: S41A-0230    [Abstracts]
TI: A new catalog of eigenfrequencies from the 26th December 2004 Sumatra-Andaman mega- event and first perspectives
AU: * ROULT, G
EM: groult@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, PARIS, 75252, France
AU: ROCH, J
EM: roch@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, PARIS, 75252, France
AU: CLEVEDE, E
EM: clevede@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, PARIS, 75252, France
AB: The high quality of the records obtained after the Sumatra-Andaman earthquake of December 2004 from the FDSN broad-band seismological stations offers a good opportunity for studying the free oscillations of the Earth and the behaviour of some particular modes. The observation and clear identification of singlets of the gravest seismic normal modes (frequency lower than 1 mHz) and of some particular anomalously split modes should offer strong constraints on Earth structure, and their analysis is particularly promising. The curiosity of scientists for these modes is due to the fact that they are rarely observed. Their interest is the key role they play for constraining Earth's models. Since the 1960 Chile event these modes have been identified and studied after large events recorded from broad-band seismometers or supraconducting gravimeters, but their excitation never reached the signal to noise ratio of the 2004 event and the amount of data never reached the number of present available recordings. The 2004 Sumatra-Andaman event provides us individual spectra exhibiting a clear splitting of the gravest spheroidal modes and a clear identification of each of the individual singlets, with an unprecedented resolution. We carefully analyzed 21 different modes and report the detailed results of some of them, showing an enhancement on the eigenfrequencies determination associated with the high quality of the measurements. Our results correspond mainly to analysis of vertical component recordings but also to additional horizontal components. We present modal frequencies measurements of some spheroidal fundamental gravest modes and modal frequencies measurements of some particular higher modes, inner-core modes and inner-core anomalously split modes. The results are compared to the theoretical frequencies computed for the PREM model, taking into account both rotation and ellipticity effects of the Earth. Clear observations of the individual singlets of rarely observed modes such as Slichter mode's overtones or anomalously split inner core modes allow to construct a new useful eigenfrequencies dataset. At low frequency, the misfit between our measurements and the theoretical corresponding values (computed for the PREM model in a rotating Earth with ellipticity) point out that some parameters (density or attenuation values) used for constructing the PREM theoretical model are not constrained enough to explain our observations. A small change in the density profile model (or the attenuation profile model) may provide new eigenfrequencies values and a better fit with our observations. At larger frequency the lateral heterogeneities of the Earth can also affect the results and we have to discriminate among the different effects. That new catalog of modal eigenfrequencies offers a plethora of perspectives, it is an important step towards the resolution of a density (or attenuation) profile model.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 7207 Core (1212, 1213, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7255 Surface waves and free oscillations
SC: Seismology [S]
MN: 2007 Fall Meeting