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Reference : UMR7329-STEOPE-007
Workplace : VALBONNE
Date of publication : Tuesday, May 04, 2021
Type of Contract : FTC Scientist
Contract Period : 24 months
Expected date of employment : 1 September 2021
Proportion of work : Full time
Remuneration : 2675,27€ gros monthly minimum
Desired level of education : PhD
Experience required : 1 to 4 years
Formulate a seismic full-waveform imaging method by wavefield reconstruction inversion (WRI) for teleseismic configurations and assess this approach with the data from the European AlpArray initiative (http://www.alparray.ethz.ch/home).
The candidate will have first to modify an existing 3D FWI code to implement the new formulation based on wavefield reconstruction and implement suitable hybrid regularization combining total variation and Tikhonov regularizations. In a second step, the code will be assessed against a synthetic case study representative of the Alps before its application on the real data of the AlpArray.
Numerical resolution of partial differential equations (finite-element method for the elastodynamic equations), inverse problem theory, numerical optimization (local optimization methods, constrained optimization, penalty and augmented Lagrangian methods, adjoint-state method), seismic imaging by Full Waveform Inversion, signal processing (spectral analysis, deconvolution), high-performance computing (parallel programming, Fortran90, MPI, OpenMP), basic geology, processing of seismological data.
The WRI method is a variant of full-waveform inversion (FWI) where a relaxation of the wave equation is introduced to better fit the observables with inaccurate Earth's parameters. This relaxation is obtained by solving the wave equation with extended sources containing a feedback term to the data. From the algorithmic viewpoint, it can be implemented with an augmented Lagrangian method where the wave equation is processed as a weak constraint with a penalty term while the equation errors generated by the relaxation are progressively corrected in iterations with a Lagrangian term such that the physics of the problem is honored at the convergence point. This relaxation allows us to extend the linear regime of the inversion by augmenting the search space compared to the classical FWI where the constraint is strictly satisfied at each iteration. This method has been recently tested for exploration geophysics applications. The aim of this project is to adapt WRI for teleseismic configurations (the sources are quasi plane waves impinging the base of the target located below the station array), which are suitable for the imaging of the Earth's crust and upper mantle and to assess its potential and limits with the data collected during the AlpArray experiment (http://www.alparray.ethz.ch/home).
This research will take place at Geoazur Laboratory of University Côte d'Azur (https://geoazur.oca.eu/fr/acc-geoazur) with few short-term missions at LMA (http://www.lma.cnrs-mrs.fr). The researchs will be supervized by Stéphane Operto (https://geoazur.oca.eu/fr/stephane-operto) and Vadim Monteiller (Laboratory of Mechanics and Acoustics of Marseille. email: email@example.com). This research will be performed in the framework of the LISAlps project funded by the French National Research Agency (ANR) (call of order AAPG 2020). This project involves Geoazur, LMA and ISTerre Laboratories.
Geoazur (https://geoazur.oca.eu/fr/acc-geoazur) is a research institute in Earth and Universe sciences with pluri-disciplinary activities in the domains of seismology, geodesy, natural hazards, rock mechanics, earth imaging, active margins and astrophysics. It belongs to University of Côte d'Azur, CNRS, IRD and Observatory of Côte d'Azur. It is located on the Sophia Antipolis technopole 20km from the Nice city. The candidate will be a member of the Imaging & Wave team, focused on the development of imaging techniques for Earth exploration, with interactions with the Seism team. The candidate will profil from high-performance computing facilities made available by Geoazur, Observatory of Cote d'Azur (mesocentre SIGAMM) and GENCI (National centers such as Genci and IDRIS).
This post-doctoral research will be performed at the same time as a PhD thesis devoted to the application of classical FWI on the AlpArray data. The results obtained during the PhD will be used as a reference to assess the added value provided by the new FWI formulation.
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