HR: 09:10h
AN: T31D-05    [Abstracts]
TI: Global upper mantle azimuthal anisotropy and the peculiar behavior of the Australian plate
AU: * Debayle, E
EM: Eric.Debayle@eost.u-strasbg.fr
AF: Institut de Physique du Globe de Strasbourg, CNRS and Universite Louis Pasteur, 5 Rue Rene Descartes, Strasbourg, 67084 France
AU: Kennett, B
EM: brian@rses.anu.edu.au
AF: Research School of Earth Sciences, ANU, Mills Road, Canberra, ACT 0200 Australia
AU: Priestley, K
EM: keith@madingley.org
AF: Bullard Laboratories, Madingley rise Madingley road, Cambridge, CB3 OEZ United Kingdom
AB: We have build 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. We observe a peculiar behavior of the fast-moving Australian plate, which appears to be the only continent for which basal drag on the lithosphere is sufficient to cause azimuthal anisotropy aligned with plate motion. Beneath other continents, azimuthal anisotropy vanishes near 150 km depth and supports a frozen-in origin within the lithosphere with no evidence for a deeper layer, which would explain the 1 s delay time typically observed in SKS studies and the good correlation between results from SKS splitting and past tectonics for continents other than Australia. The weak azimuthal anisotropy observed at depth greater than 150 km for continents other than Australia is compatible with simple shear leading to anisotropy with a plunging axis of symmetry.
DE: 8180 Tomography
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting