HR: 0800h
AN: DI41A-1245    [Abstracts]
TI: Global tomography of the upper mantle and transition zone
AU: * Debayle, E
EM: Eric.Debayle@eost.u-strasbg.fr
AF: EOST, CNRS and Universite Louis Pasteur, 5 rue Rene Descartes, Strasbourg, 67084 France
AU: Maggi, A
EM: alessia@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, 1200 E California Blvd, MS 252-21, Pasadena, CA 91125 United States
AU: Priestley, K
EM: keith@madingley.org
AF: Bullard Laboratories, Madingley Rise Madingley Road, Cambridge, CB30EZ United Kingdom
AU: Kennett, B
EM: brian@rses.anu.edu.au
AF: Research School of Earth Sciences, ANU, Mills Road, Canberra, ACT 0200 Australia
AB: We have built a global upper mantle tomographic model of Sv-wave heterogeneities and azimuthal anisotropy as a function of depth, from the analysis of over 100,000 fundamental and higher mode Rayleigh waveforms. The selected waveforms are mostly associated with epicenter-station paths shorter than 6000 km and typical of regional surface wave tomography at the scale of a tectonic plate. They provide a global coverage of the Earth with an original dataset, less likely to be affected by spurious effects such as multipathing or focusing/defocusing, compared to the longer R1 and R2 paths classically used in global tomography. Fast-moving plates show a good overall agreement between fast anisotropic directions at asthenospheric depths and present day plate motion. In oceanic regions this agreement is observed in a layer approximately 100 km thick extending from the bottom of the oceanic lithosphere to 150-200 km depth. In continental regions such an agreement is observed only for the fast moving australian plate, in the depth range 175-300 km. We infer that the fast-moving Australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy. Despite the use of higher modes which provide sensitivity in the transition zone, we have as yet found no evidence for the exitence of significant large scale shear wave anomalies in the depth range 300-700 km. High seismic velocities associated with downgoing slabs and evidence for deeply rooted low velocity anomalies whose lateral extension are compatible with mantle plumes have been found in the transition zone. However, large scale seismic anomalies correlated with shallow tectonics vanish near 200-250 km depth, with the extinction of the high velocity signature of cratonic roots.
UR: http://eost.u-strasbg.fr/recherche/ERIC/eric.html
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8180 Tomography (6982, 7270)
SC: Study of Earth's Deep Interior [DI]
MN: Fall Meeting 2005