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17/02 Séminaires Généraux: Andreas Fichtner (ETH Zurich)

Thème Terre et Planète
Quand ? Le 17/02/2014,
de 14:00 à 15:00
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MULTISCALE FULL WAVEFORM INVERSION

Towards a Comprehensive Seismic Earth Model


Seismic  tomography  is  one  of  our  primary  tools  to  study  the  structure  and  dynamics  of  the  Earth’s  interior.  It  has  drawn  the image of a vigorously convecting planet with hot upwelling plumes, descending lithospheric slabs, and numerous other features.

Despite  the  undeniable  progress,  challenges  remain.  These  include  (1)  the  joint  resolution  of  crustal  and  mantle  structure, required   to  infer  coupling   between   mantle  convection   and  near-surface   processes,   (2)  the  accurate   modelling   of  wave propagation in complex media across a wide range of spatio-­temporal  scales, and (3) the combination of different seismic data types in a fashion that fully honours wave propagation physics.

To address these challenges, we develop a multiscale full waveform inversion that assimilates complete teleseismic and regional seismograms in a broad period range (8-­200 s). Being based on spectral-­element modelling and adjoint techniques, our method simultaneously solves multiple regional-­ and continental-­scale inverse problems in order to jointly resolve crustal and mantle structure. Different scales are coupled via non-­periodic homogenisation,  and tomographic resolution is quantified using second-­order adjoints.

We apply our method to Europe and Western Asia, where resolution is particularly high beneath the North Atlantic, the western Mediterranean  and  Anatolia.  The  multitude  of  geologically  interpretable  features  include  the  Iceland  plume  which  clearly extends into the lower mantle. Furthermore,  we observe two low‐velocity  fingers that extend from the Iceland plume into the North Atlantic asthenosphere, where they correlate with regions of Neogene uplift. Western Anatolia is characterised by the extension-­related  updoming  of lower-­crustal  material.  The deep expressions  of volcanic provinces  in central Anatolia and the North Anatolian Fault Zone are clearly imaged.

The extension  of the multiscale  full waveform  inversion  to the globe is the backbone  of an emerging  Comprehensive  Seismic Earth Model that assimilates the complete range of seismic data into one consistent model of the Earth’s interior by combining various tomographic techniques, including full waveform inversion, ray tomography, and normal-­mode inversion.

 

Host:

Benoit Tauzin

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Département ENS
  • Directeur :
    Stéphane Labrosse
  • Secrétaire :
    Emmanuelle Lousson
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