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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

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
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)



Cracks, Fluid inclusions

Crust

Inner Core

(Babuska and Cara, 1991)

(Singh et al., 2001)


Hot

Cold

Montagner &Guillot, 2001


Da: Anisotropy

Effect

DT: Temperature

Effect

Olivine (60%) +Opx (40%)

Da ≈ DT

Montagner &Guillot, 2001


Importance of seismic anisotropy anisotropy is the rule not the exception1
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)


Sks splitting
SKS- Splitting

>

+SH

If anis.

core

Transverse

Mantle

Radial

Radial


S-wave Splitting Measurements

(Savage, Rev. Geophys., 1999)


S- Velocity

Radial

Anisotropy

Azimuthal

Anisotropy

Interpretation



Sieminski &

Lévêque, 2003



Radial

Azimuthal

reference


Ridge

Ridge

Continent-ocean boundary


Conclusions
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?)





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