Shear Wave Splitting Forward Model for the 3-D Hawaiian Plume : the Sensitiveness of Interpretation
Abstract
The Hawaiian volcanism is thought to be generated by a thermal mantle plume. A 3-D convection code using the hybrid spectral/finite difference technique of Christensen & Harder (1991) describes the interaction of the Hawaiian plume with the moving Pacific lithosphere (Ribe & Christensen, 1994). A steady state flow field solution allows to calculate the velocity gradient field and the path of rocks. This can be used to integrate along streamlines either the finite deformation or the Lattice Preferred Orientation (LPO) of upper mantle minerals (olivine, orthopyroxene). The code D-Rex describing the deformation of a mineral aggregate by dislocation creep and dynamic recrystallization provides the necessary tool to obtain the LPO (Kaminski, Ribe & Browaeys, 2004). The equivalent elastic tensor at each position of the model is calculated using both the Orientation Distribution Function related to the LPO and tabulated elastic tensor of minerals. The tensor is then reduced to its transverse isotropic part by decomposition into different symmetry class components (Browaeys & Chevrot, 2004). The convolution of the sensitivity kernels for shear wave splitting in a transverse isotropic medium (Favier & Chevrot, 2004) with the 3-D distribution model of transverse isotropy gives variation of the splitting intensity I(α ) with the backazimuth α of the teleseismic wave. The splitting intensity can be related to the parameters of classical ray theory (time delay δ t and fast axis direction φ 0) by the relationship I(α )=δ t sin2 (α -φ 0). A comparison between the fast axis orientations in the 3-D model and the fast direction deduced from the classical expression of I(α ) is done. It shows that in regions where the wave propagates through inhomogeneous anisotropic properties compare to the typical wavelength of a teleseismic wave (i.e. λ ∼ 50 km), there is no simple relation between the seismic anisotropy observations and the underlying anisotropic structure in the upper mantle.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.T41G..05B
- Keywords:
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- 7260 Theory and modeling;
- 8121 Dynamics;
- convection currents and mantle plumes;
- 7203 Body wave propagation;
- 7218 Lithosphere and upper mantle;
- 3210 Modeling