Roland MARTIN
2018-09-05 21:45:01
Institution: CNRS - Geosciences Environnement Toulouse
Open Until: 2018-10-15
Postdoc position at GET / CNRS Laboratory in Toulouse (FRANCE)
Subject : Lithospheric imaging by joint inversion of teleseismic waveforms, local tomography and gravimetric anomalies - Application to the Pyrenees
Keywords: seismic tomography, 3-D wave propagation modeling, waveform inversion, spectral-element method, gravimetry
Project description:
The main goal of this postdoc project is to develop new methods for the joint inversion of seismic and gravity data, in order to obtain finely resolved 3D models of density at the regional scale. It is now well understood that owing to the non-uniqueness of gravity data inversions, it is hopeless to obtain such models from gravity data alone. It is also well-known that to first order the phase of elastic waves is only sensitive to seismic velocities. On the other hand, the complete seismic wavefield does provide a sensitivity to density through the contributions of back-scattered waves, whose amplitude are sensitive to impedance and thus to density. In addition, full waveform inversion approaches provide much finely resolved models of both Vp and Vs compared to classical imaging approaches. Therefore, by imposing correlations between seismic velocities and density or on their structural gradients through a penalty on cross-gradients, the joint inversion of gravity data and complete seismic waveforms should allow us to reach the challenging goal of obtaining 3D models of density at the regional scale.
The full waveform inversion methods that will be used is the method that we have developed over the years in our group in Toulouse (Monteiller et al., 2013; Monteiller et al., 2015; Wang et al., 2016). We have also recently developed a spectral element gravity modelling code (Martin et al. 2017). We thus have all the basic ingredients to build such a joint inversion approach.
Once validated on synthetic experiments, the method will be applied on the Pyrenees. The gravity dataset (~300000 measurements) will come from the global database of the Bureau Gravimétrique International. The seismological dataset comprises the data from the permanent networks operating in the Pyrenees (~ 50 broadband stations), the 2D backbone of the IBERARRAY and PYROPE experiments (~120 temporary broadband stations), 6 dense transects (Chevrot et al. 2018) and the large-N Maupasacq experiment (~ 450 stations deployed in the western Pyrenees). Overall, these different datasets provide a unique opportunity to decipher the deep architecture of a collisional orogen at the lithospheric scale with unprecedented resolution.
The postdoc student will have access to different computing facilities in the laboratory and to the supercomputers of the PRACE European network and of the new regional Olympe platform in Toulouse.
References
S. Chevrot, M. Sylvander, J. Diaz, R. Martin, F. Mouthereau, G. Manatschal, E. Masini, S. Calassou, F. Grimaud, H. Pauchet, M. Ruiz. The non-cylindrical crustal architecture of the Pyrenees. Scientific Reports, 8 (2018), p. 9591,
Martin R., S. Chevrot, D. Komatitsch, L. Seoane, H. Sprangenberg, Y. Wang, G. Dufréchou, S. Bonvalot and S. Bruinsma, A high-order 3D spectral-element method for the forward modelling and inversion of gravimetric data - Application to the western Pyrenees, Geophys. J. Int., 209, 406-424, 2017.
Monteiller, V., Chevrot, S., Komatitsch, D., and N. Fuji, A hybrid method to compute short-period synthetic seismograms of teleseismic body waves in a 3-D regional model, Geophys. J. Int., 192, 230-247, 2013.
Monteiller, V., Chevrot, S., Komatitsch, D., and Y. Wang, Three-dimensional full waveform inversion of short-period teleseismic wavefields based upon the SEM-DSM hybrid method, Geophy. J. Int., 202, 811-827, 2015.
Wang, Y., Chevrot, S., Monteiller, V., Komatitsch, D., Mouthereau, Manatschal, G., Sylvander, M., Diaz, J., Ruiz, M., Grimaud, F., Benahmed, S., Pauchet, H., and R. Martin, The deep roots of the western Pyrenees revealed by full waveform inversion of teleseismic P waves, Geology, 44, 475-478, 2016.
Salary: 3000€/month (gross pay).
PhD advisory team: Roland Martin & Sébastien Chevrot (CNRS GET, Toulouse), Vadim Monteiller & Dimitri Komatitsch (CNRS LMA, Marseille). The PhD/Postdoc work will also involve close collaboration with the TOTAL research team in Pau, and the seismology group at CSIC in Barcelona (Antonio Villaseñor and Jordi Diaz).
The host institution and the laboratory: Observatoire Midi-Pyrénées is the biggest observatory in France covering a wide range of disciplines in Earth and Universe Sciences. It is a component of the university Toulouse III - Paul Sabatier. The GET is the laboratory of Earth and environmental sciences within the Observatoire Midi Pyrenees. It has 165 permanent employees. The Geophysics team develops a multidisciplinary research related to forward modeling and inversion of gravimetric, magnetic and seismological data.
Eligibility: The candidate must have received his/her PhD in seismology at the closing date of the call. Knowledge in French language is not required. A solid background in HPC or numerical modeling of wave propagation is a plus.
Funding context: The research and the scholarship will be funded by the OROGEN Program which involves the CNRS, TOTAL, and the BRGM.
Application: Applicants must send CV, with name and contact information with one or two referees, and a brief statement of purpose to Dr. Roland Martin (roland.martin<at>get.omp.eu) or Dr. Sébastien Chevrot (sebastien.chevrot<at>get.omp.eu). Deadline for submission is 1st October, 2018 but applications will be considered until the position is fulfilled. The starting date could be anytime from November 2018 to January 2019.
Open Until: 2018-10-15
Postdoc position at GET / CNRS Laboratory in Toulouse (FRANCE)
Subject : Lithospheric imaging by joint inversion of teleseismic waveforms, local tomography and gravimetric anomalies - Application to the Pyrenees
Keywords: seismic tomography, 3-D wave propagation modeling, waveform inversion, spectral-element method, gravimetry
Project description:
The main goal of this postdoc project is to develop new methods for the joint inversion of seismic and gravity data, in order to obtain finely resolved 3D models of density at the regional scale. It is now well understood that owing to the non-uniqueness of gravity data inversions, it is hopeless to obtain such models from gravity data alone. It is also well-known that to first order the phase of elastic waves is only sensitive to seismic velocities. On the other hand, the complete seismic wavefield does provide a sensitivity to density through the contributions of back-scattered waves, whose amplitude are sensitive to impedance and thus to density. In addition, full waveform inversion approaches provide much finely resolved models of both Vp and Vs compared to classical imaging approaches. Therefore, by imposing correlations between seismic velocities and density or on their structural gradients through a penalty on cross-gradients, the joint inversion of gravity data and complete seismic waveforms should allow us to reach the challenging goal of obtaining 3D models of density at the regional scale.
The full waveform inversion methods that will be used is the method that we have developed over the years in our group in Toulouse (Monteiller et al., 2013; Monteiller et al., 2015; Wang et al., 2016). We have also recently developed a spectral element gravity modelling code (Martin et al. 2017). We thus have all the basic ingredients to build such a joint inversion approach.
Once validated on synthetic experiments, the method will be applied on the Pyrenees. The gravity dataset (~300000 measurements) will come from the global database of the Bureau Gravimétrique International. The seismological dataset comprises the data from the permanent networks operating in the Pyrenees (~ 50 broadband stations), the 2D backbone of the IBERARRAY and PYROPE experiments (~120 temporary broadband stations), 6 dense transects (Chevrot et al. 2018) and the large-N Maupasacq experiment (~ 450 stations deployed in the western Pyrenees). Overall, these different datasets provide a unique opportunity to decipher the deep architecture of a collisional orogen at the lithospheric scale with unprecedented resolution.
The postdoc student will have access to different computing facilities in the laboratory and to the supercomputers of the PRACE European network and of the new regional Olympe platform in Toulouse.
References
S. Chevrot, M. Sylvander, J. Diaz, R. Martin, F. Mouthereau, G. Manatschal, E. Masini, S. Calassou, F. Grimaud, H. Pauchet, M. Ruiz. The non-cylindrical crustal architecture of the Pyrenees. Scientific Reports, 8 (2018), p. 9591,
Martin R., S. Chevrot, D. Komatitsch, L. Seoane, H. Sprangenberg, Y. Wang, G. Dufréchou, S. Bonvalot and S. Bruinsma, A high-order 3D spectral-element method for the forward modelling and inversion of gravimetric data - Application to the western Pyrenees, Geophys. J. Int., 209, 406-424, 2017.
Monteiller, V., Chevrot, S., Komatitsch, D., and N. Fuji, A hybrid method to compute short-period synthetic seismograms of teleseismic body waves in a 3-D regional model, Geophys. J. Int., 192, 230-247, 2013.
Monteiller, V., Chevrot, S., Komatitsch, D., and Y. Wang, Three-dimensional full waveform inversion of short-period teleseismic wavefields based upon the SEM-DSM hybrid method, Geophy. J. Int., 202, 811-827, 2015.
Wang, Y., Chevrot, S., Monteiller, V., Komatitsch, D., Mouthereau, Manatschal, G., Sylvander, M., Diaz, J., Ruiz, M., Grimaud, F., Benahmed, S., Pauchet, H., and R. Martin, The deep roots of the western Pyrenees revealed by full waveform inversion of teleseismic P waves, Geology, 44, 475-478, 2016.
Salary: 3000€/month (gross pay).
PhD advisory team: Roland Martin & Sébastien Chevrot (CNRS GET, Toulouse), Vadim Monteiller & Dimitri Komatitsch (CNRS LMA, Marseille). The PhD/Postdoc work will also involve close collaboration with the TOTAL research team in Pau, and the seismology group at CSIC in Barcelona (Antonio Villaseñor and Jordi Diaz).
The host institution and the laboratory: Observatoire Midi-Pyrénées is the biggest observatory in France covering a wide range of disciplines in Earth and Universe Sciences. It is a component of the university Toulouse III - Paul Sabatier. The GET is the laboratory of Earth and environmental sciences within the Observatoire Midi Pyrenees. It has 165 permanent employees. The Geophysics team develops a multidisciplinary research related to forward modeling and inversion of gravimetric, magnetic and seismological data.
Eligibility: The candidate must have received his/her PhD in seismology at the closing date of the call. Knowledge in French language is not required. A solid background in HPC or numerical modeling of wave propagation is a plus.
Funding context: The research and the scholarship will be funded by the OROGEN Program which involves the CNRS, TOTAL, and the BRGM.
Application: Applicants must send CV, with name and contact information with one or two referees, and a brief statement of purpose to Dr. Roland Martin (roland.martin<at>get.omp.eu) or Dr. Sébastien Chevrot (sebastien.chevrot<at>get.omp.eu). Deadline for submission is 1st October, 2018 but applications will be considered until the position is fulfilled. The starting date could be anytime from November 2018 to January 2019.
