HR: 08:50h
AN: T51B-04 INVITED     [PDF]
TI: Modeling seismic anisotropy in 3D mantle flow beneath Hawaii
AU: * Browaeys, J T
EM: browaeys@ipgp.jussieu.fr
AF: IPG Paris, 4, place jussieu, Paris, 75252 France
AU: Ribe, N M
EM: ribe@ipgp.jussieu.fr
AF: IPG Paris, 4, place jussieu, Paris, 75252 France
AU: Kaminski, E
EM: kaminski@ipgp.jussieu.fr
AF: IPG Paris, 4, place jussieu, Paris, 75252 France
AB: Large-scale measurements of azimuthal anisotropy in the Pacific ocean show a global alignment of fast directions with the motion of the plate. However, significant disturbances occur around the Hawaii hotspot. Direct geodynamical modeling of seismic anisotropy can be used to extract information about mantle flow from these observations. The steady flow field around a thermal plume interacting with a moving lithosphere is determined using a 3-D variable-viscosity convection code. Next, the lattice preferred orientation of olivine and enstatite at each grid point is determined by along-streamline integration of the evolution equations of Kaminski and Ribe (Earth Planet. Sci. Lett., 2001) which account for plastic deformation of the crystals and for dynamic recrystallization by nucleation and grain boundary migration. Finally, the full elastic tensor at each grid point is calculated using a Voigt average. The anisotropy is strongest around the plume conduit and in the depth range 80-150 km where the hot plume material spreads laterally, and its orientation varies substantially as a function of both lateral position and depth. To apply our results to the Hawaiian region, we calculate synthetic anisotropic phase velocity maps at different depths and compare them with maps inferred from seismic observations. We will also present preliminary calculations of synthetic seismic observables, using the spectral element code of Komatitsch and Tromp (Geophys. J. Int., 2002) and a simplified version of our model in which the full elastic tensor at each point is replaced by the best-fitting hexagonal approximation.
UR: http://www.ipgp.jussieu.fr/~kaminski
DE: 3210 Modeling
DE: 3902 Creep and deformation
DE: 7218 Lithosphere and upper mantle
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Tectonophysics [T]
MN: 2003 Fall Meeting