HR: 1340h
AN: MR23A-0184    [Abstracts]
TI: Crystallographic preferred orientation and seismic anisotropy of the Post-Perovskite phase in the D" layer
AU: * Mainprice, D
EM: david@dstu.univ-montp2.fr
AF: Laboratoire de Tectonophysique, CNRS/Universit‚ de Montpellier II, Montpellier, 34095 France
AU: Tommasi, A
EM: deia@dstu.univ-montp2.fr
AF: Laboratoire de Tectonophysique, CNRS/Universit‚ de Montpellier II, Montpellier, 34095 France
AB: The recent discovery of the post-perovskite phase and prediction of its elastic constants using atomistic modeling has major implications for the interpretation of seismic anisotropy of the D" layer. In an effort to determine the mechanisms for crystallographic preferred orientation development for the post-perovskite phase and interpretation of the seismic anisotropy of D" layer a series of VPSC plasticity models has been conducted. For VPSC models the glide systems have been classified into easy [100](010), [001](001), moderate [100](001), [001](100) and difficult [100](001), [001](-110), [101](-101),[-101](101),[010](001) based on the type of bonds that have to be broken (Mg-Mg,Mg-O or Si-O) for dislocation glide. The VPSC models predict [100] parallel to the flow direction and [010] normal to the flow plane, resulting in an orthorhombic anisotropy pattern with the fastest Vp parallel to the flow direction and slowest normal to the flow plane. The anisotropy of the S-waves depends in a more complex way on the details of the CPO and hence on the imposed slip systems' strengths. However, in general, splitting is highly variable within the flow plane with a minimum value parallel to the lineation and the fastest S-wave is polarized in the flow direction. We also evaluate the anisotropy induced by a shape-preferred orientation of tabular post-perovskite crystals flattened parallel to [010], which is the most likely shape given the crystal structure. Orientation of [010] normal to the foliation results in a transverse isotropy pattern with the slowest Vp normal to the foliation. The S wave pattern is again complex with low splitting both parallel and normal to the foliation plane. For waves propagating within the foliation plane, the fastest S wave is polarized parallel to the flow plane. Waves propagating oblique (30-50 degrees) to the foliation show strong splitting with fast polarization directions oblique to both foliation and lineation. If the foliation is horizontal both models may explain the common observation that horizontally polarized shear waves travel faster than vertically polarized one. However, CPO-induced anisotropy will depend on the propagation azimuth whereas shape-induced anisotropy not.
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 3902 Creep and deformation
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting