ANISOTROPIC SEISMOLOGY IN ANTARCTICA

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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

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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)

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(From Christensen and Lundquist, 1982)
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Cracks, Fluid inclusions
Crust
Inner Core
(Babuska and Cara, 1991)
(Singh et al., 2001)
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Hot
Cold
Montagner Guillot, 2001
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Da Anisotropy Effect DT Temperature Effect
Olivine (60) Opx (40)
Da DT
Montagner Guillot, 2001
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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)
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SKS- Splitting
gt
SH If anis.
core
Transverse
Mantle
Radial
Radial
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S-wave Splitting Measurements
(Savage, Rev. Geophys., 1999)
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S- Velocity Radial Anisotropy Azimuthal Anisotr
opy
Interpretation
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Paths of paths in block 5 x5º
paths
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Sieminski Lévêque, 2003
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Sieminski Lévêque, 2003
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Radial
Azimuthal
reference
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Ridge
Ridge
Continent-ocean boundary
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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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Anisotropy- Geodynamics Relationship
Gaboret et al., 2003
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• Boundary layer gt observable seismic anisotropy

lt
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(Montagner and Guillot, 2001)