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ANISOTROPIC SEISMOLOGY IN ANTARCTICA

ANISOTROPIC SEISMOLOGY IN ANTARCTICA. Jean-Paul Montagner, Geneviève Roult and Eric Beucler Institut de Physique du Globe Université Paris VII-Denis Diderot. JEAN-PA. Importance of seismic anisotropy ANISOTROPY is the RULE not the Exception. Anisotropy is present at all scales.

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ANISOTROPIC SEISMOLOGY IN ANTARCTICA

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  1. ANISOTROPIC SEISMOLOGY IN ANTARCTICA Jean-Paul Montagner, Geneviève Roult and Eric Beucler Institut de Physique du Globe Université Paris VII-Denis Diderot JEAN-PA

  2. Importance of seismic anisotropyANISOTROPY is the RULE not the Exception Anisotropy is present at all scales • From microscopic scale to macroscopic scale. • Efficient alignment mechanisms: • (L.P.O.: lattice preferred orientation • S.P.O.: shape preferred orientation; Fine layering)

  3. (From Christensen and Lundquist, 1982)

  4. Cracks, Fluid inclusions Crust Inner Core (Babuska and Cara, 1991) (Singh et al., 2001)

  5. Hot Cold Montagner &Guillot, 2001

  6. Da: Anisotropy Effect DT: Temperature Effect Olivine (60%) +Opx (40%) Da ≈ DT Montagner &Guillot, 2001

  7. Importance of seismic anisotropyANISOTROPY is the RULE not the Exception Anisotropy is present at all scales • From microscopic scale to macroscopic scale. • Efficient alignment mechanisms: • (L.P.O.: lattice preferred orientation • S.P.O.: shape preferred orientation; Fine layering) ANISOTROPY IS NOT A SECOND ORDER EFFECT ANISOTROPY IS REFLECTING AN INNER ORGANIZATION Anisotropy is observed on different kinds of seismic waves - Body waves (Pn, Shear wave splitting) - Surface waves (Rayleigh-Love discrepancy; Azimuthal anisotropy)

  8. SKS- Splitting > +SH If anis. core Transverse Mantle Radial Radial

  9. S-wave Splitting Measurements (Savage, Rev. Geophys., 1999)

  10. S- Velocity Radial Anisotropy Azimuthal Anisotropy Interpretation

  11. Paths of paths in block 5 x5º paths

  12. Sieminski & Lévêque, 2003

  13. Sieminski & Lévêque, 2003

  14. Radial Azimuthal reference

  15. Ridge Ridge Continent-ocean boundary

  16. CONCLUSIONS • Seismic anisotropy is not a second order effect. • Anisotropy is a good MARKER of deformation processes. • Antarctic Plate: • Continental shield root around 220km. • Azimuthal anisotropy large and orthogonal to ridges • Intense deformation from PAI triple junction up to Africa: shear zone, fossil or present anisotropy (reality or artefact?)

  17. Anisotropy- Geodynamics Relationship Gaboret et al., 2003

  18. Boundary layer => observable seismic anisotropy <===

  19. (Montagner and Guillot, 2001)

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