[quest-info] PhD position in laboratory scale/computational seismology
yann.capdeville at univ-nantes.fr
Fri Mar 1 09:14:30 CET 2019
We are looking for a PhD student in a seismic reduced scale experiments
/ full wave form inversion / homogenisation context.
We would be grateful if you could forward this announcement to
potentially interested students.
The deadline for application is short (April 7th)
Contacts: Donatienne Leparoux (donatienne.leparoux at ifsttar.fr), Yann
Capdeville (yann.capdeville at univ-nantes.fr)
*Detailed form :*
Title : Near-surface seismic imaging by waveform inversion and
downscaling: feasibility using a combined numerical and experimental
approach at laboratory and field scales
Main host Laboratory - Referent Advisor GERS-GeoEND - LEPAROUX
Donatienne donatienne.leparoux at ifsttar.fr tél. : 02 40 84 56 69
Director of the main host Laboratory ABRAHAM Odile -
odile.abraham at ifsttar.fr
PhD Speciality Géophysique
Axis of the performance contract 2 - COP2017 - More efficient and
Main location Nantes
Doctoral affiliation UNIVERSITE DE NANTES
PhD school EGAAL - Ecologie, Géosciences, Agronomie et Alimentation
Planned PhD supervisor LEPAROUX Donatienne - Ifsttar - GERS-GeoEND
Planned PhD co-supervisor CAPDEVILLE Yann - CNRS - LPG Nantes
Planned funding Contrat doctoral - Ifsttar
In climatic change context and energy transition, the need for imaging
and characterizing the underground media and infrastructures is
increasing, for land planning dedicated to new technologies (wind
turbine in off-shore or on-shore contexts) or for monitoring sites and
structures or anthropogenic zones (sea dikes, natural hazard assessment
in urban areas ..etc).
Among the non destructive methods developed in applied geophysics,
seismic imaging techniques provide a mechanical information of the
described targets. Usually based on arrival times of Body Waves, their
adaptation to the near surface needs to take into account Surface Waves.
The latter have long been identified as noise for deep investigations
such as oil exploration.
At the same time, the last decades have seen the development of the
so-called "Full Wave Form Inversion". These methods are based on the
entire seismic signal to finely reconstruct the underground parameters
(Virieux and Operto, 2009). This approach has been successful in deep
exploration for hydrocarbons and some recent studies propose to
integrate Surface Waves for near-surface auscultation. The interest is
based on taking into account complex propagation phenomena and in
particular mode conversions. However, this type of method is currently
based on a local optimization approach by linearization of the inverse
problem for computation time reasons. To be successful, such approach
requires the knowledge of an initial model close to the solution, which
is difficult to define in complex subsurface and civil engineering
environments. Moreover, the non-unique nature of the solution makes it
difficult to interpret the results.
*Objective and Approach*
To overcome these difficulties, an innovative alternative approach
proposes a 2-step process "by inversion of the homogenized model and
downscaling" (Capdeville and Methivier, 2018): the first stage is based
on the result of the inversion of the waveform in terms of a homogenized
model at the scales of the propagated wavelengths (Capdeville et al.,
2010) and the second stage is based on a “interpretation inversion”.
This second inversion is a global optimization of the reconstructed
parameters designed to obtain a model distribution that can be
interpreted in terms of the parameters needed for the targeted
applications. The theoretical developments of this new approach as well
as the first experimental 2D laboratory tests for non-attenuating media
are being developed within the ANR HIWAI project (directed by Y.
Capdeville, LPG). The prospects of this entirely new approach allow us
to consider unsurpassed imaging capabilities for complex subsurface
media if the information carried by surface waves can be integrated.
In this context, the proposed PhD topic aims to develop the feasibility
of the approach of inversion by "homogenization and downscaling" for the
problems of subsurface environments, generally very attenuating,
including many heterogeneities with strong contrasts at surface wave
propagation depths. This dual approach makes it possible to go beyond
the traditional inversion of S wave velocities and assess the complete
elastic tensor for then using anisotropy to provide more accurate
information on the targeted targets. Here, the latter correspond to
areas of alteration of the subsoil or the anthropogenic structures it
contains and underground cavities. The objective is to define the
potential for detection, localization and geometrical characterization
of damage areas and cavities.
The proposed approach focuses on the theoretical analysis of the
methodology by introducing superficial heterogeneities affecting surface
waves and on the analysis of reduced-scale experimental laboratory data
by taking into account not only the vertical but also the horizontal
component (Bretaudeau et al., 2010 ; Pageot et al., 2017). To this end,
reference models typical of the subsurface, of gradual complexity, will
be defined and developed numerically and experimentally by reduced-scale
*Scientific issues :*
The main scientific issues of the thesis include the above-mentioned
integration elements necessary for subsurface imaging that have not been
explored or resolved to date, namely:
• integration of the horizontal component: contribution in numerical and
• the integration of surface heterogeneities into non-periodic
• the integration of attenuating media (involving a short propagation
• experimental validation for subsurface applications in anthropogenic media
*Modeling tools :*
The numerical and experimental modeling tools are those developed at the
LPG at the University of Nantes and at the ifsttar respectively:
• The 2D and 3D numerical codes based on the Spectral Element Method
(SEM) developed in the LPG lab provide a fine simulation of the complex
structures of underground media with a non-structured meshing.
• The MUSC bench developed in ifsttar provide a quantitative simulation
of seismic recordings in a controlled environment. It provides both the
vertical and the horizontal components.
The complementarity of both the numerical and experimental modeling has
been already successfully tested in regional projects VIBRIS, PROSE and
the ANR project, through the partnership of this thesis supervision teams.
Multi-component field data provided by the industrial project R2S
managed by IFSTTAR will contribute to test the method in this PhD thesis.
*Required profile :*
Wave propagation (acoustic, seismic, ultrasonic)
Physics of continuous media
Signal and data processing
Python, Matlab or Scilab, C, fortran - or other tools for scientific
An experience in numerical modeling (finite differences, finite
elements, spec- elements, etc.)
traux, ...) is recommended.
Thesis supervision: Donatienne Leparoux and Yann Capdeville (thesis
Capdeville Y. & Métivier L. (2018) Elastic FWI based on the
homogenization method... illustrations. Geophys.J.Int. 213 (2), 1093-1112.
Pageot D. et al. (2017) Improving the seismic small-scale modelling ...
numerical methods. Geophys.J.Int. 211(1), 637-649.
Virieux J, OpertoS, 2009, An overview of full waveform inversion in
exploration geophysics, GEOPHYSICS,VOL.74,NO.6,NOVEMBER
Bretaudeau F. et al. (2011) Small-scale modeling of onshore seismic
experiment... methods. Geophysics, 76(5), T101-T112.
Capdeville Y. et al. (2010) 2D nonperiodic homogenization to upscale
elastic media for P-SV waves. Geophys. J. Int. 182, 903-922.
Keywords : Seismic Imaging, Invers Problem, Subsurface, non périodic
homogeneization, Waveform, Numerical Modeling, experimental Modeling
LPGNantes - UMR CNRS 6112
Laboratoire de Planétologie et Géodynamique de Nantes
Département des Sciences de la Terre et de l'Univers
Université de Nantes - 2 rue de la Houssinière BP 92205
44322 Nantes Cedex 3 (FRANCE)
Tél: +33 (0)2 51 12 54 66 / Fax: +33 (0)2 51 12 52 68
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