HR: 14:25h
AN: DI43A-04    [Abstracts]
TI: Evidence for Two Layered Convection Constrained by Seismological Heterogeneity Spectra
AU: * Takeuchi, N
EM: takeuchi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: One of the most important contributions of seismic tomography is to constrain scale lengths of mantle flow. However difficulty arises in comparing the scale of heterogeneity in various regions inside the Earth because the resolution of the model is different for each region. To overcome this problem we developed a data weighting method to homogenize the resolution of the resultant model (Takeuchi & Kobayashi 2004, GJI). In this study, we apply our data weighting method to invert for whole mantle S wave structure model. To maximize the resolution of the oceanic regions where the resolution was the poor in the previous models, we carry out waveform inversion and fully utilize information included in the observed data. To minimize the degradation of the resolution caused by incorporation of the optical ray approximation, we rigorously compute the effect of the finite wavelength. The required CPU time is large, however it is now feasible if we use our efficient computational method (Direct Solution Method; e.g. Takeuchi et al. 2000, PEPI) and the Earth simulator. We inverted broadband waveform data from about 200 events for degree-18 whole mantle S wave structure. Both in the upper mantle and lower mantle, the top and the bottom layers show relatively red spectra, whereas the middle layers show relatively white spectra. These results indicate that we have two layered mantle convection and lateral scale lengths become longer in the boundary layers in each convection cell. Existence of stagnant slabs is one of the important evidences for two layered convection (e.g. Fukao et al. 1992, JGR; Fukao et al. 2001, Rev. of Geophys.), but power spectra of seismological heterogeneity obtained by this study should give another important evidence.
DE: 7200 SEISMOLOGY
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7270 Tomography (6982, 8180)
SC: Study of Earth's Deep Interior [DI]
MN: Fall Meeting 2005