HR: 1340h
AN: S43B-1002    [Abstracts]
TI: Waveform modeling of Rayleigh waves and shear-velocity structure of the Southeast Indian Ocean upper mantle
AU: * Kuo, B
EM: byk@earth.sinica.edu.tw
AF: Inst Earth Sciences, Academia Sinica, POB 1-55 Nankang, Taipei, 115 Taiwan
AU: Debayle, E
EM: eric@tomo-u.strasbg.fr
AF: CNRS and Universite Louis Pasteur, 5 rue Rene Descartes, Strasbourg, 67084 France
AB: Recent work of dynamic modeling demonstrated that an anomalously cold blob under the mid-ocean ridge tends to collapse by its own weight despite in the buoyant environment. However, there are two conditions under which this relatively dense blob can achieve dynamic balance with the upward flow field and be even lifted to the surface. One is when the low viscosity asthenosphere is absent, and another with a fast spreading rate or a flow field that is enhanced by additional tectonic forces, such as continental rifting. A test ground for this dynamics vs. kinematics tug-of-war is in the Australian-Antarctic Discordance (AAD). Earlier dynamic models have suggested that the associated topography and geochemistry result from a Cretaceous detached slab redrawn to the surface during the southeast Indian Ocean opening. Recent tomographic studies have delineated this structure with increasing details. We employ the waveform modeling technique of Cara and Leveque (1987) to invert for the path-averaged shear velocity structure from Rayleigh wave waveforms recorded by GSN, Geoscope, and Skippy stations for the ridge events, and then construct a 3-D image of the region. The method takes advantage of the secondary observable that is the cross-correlation function of the observed and synthetic seismograms, which stabilizes the inversion process for a multimode Rayleigh wave seismogram. Short path ensures relatively small Fresnel zone and better resolution. Preliminary results show that in addition to the off-axis anomaly to the west of the AAD zone as previously identified, positive anomalies underly the Australian continent-ocean boundary at 100-150 km depths. Seismological depictions of the upper mantle beneath AAD can aid formulation and distinction of dynamic models.
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7207 Core and mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting