Events of 2021

• January 4th 2021: Gaoshan Guo joins the WIND group as PhD student. The main focus of his PhD is the application and assessment of extended time-domain FWI to various real data sets. * Xiaole Zhou also joins the WIND group in the framework of a co-supervizion agreement with the Chinese Academic of Science, Institute of Geology and Geophysics (main supervisors: Prof. Ling Chen and Prof. Haiqiang Lan). In collaboration with Serge Sambolian, she will extend slope tomography based upon eikonal solver and adjoint method to 3D with a special emphasis on the application to 3D areal acquisitions. * Serge Sambolian will defend his PhD on February 8th 2021 (online). The PhD thesis is entitled "Kinematically consistent slope tomography: theory and applications to velocity model building and event location". The committee will be composed of Romain Brossier (ISTerre - Université Grenoble Alpes), Stefan Buske (TU Bergakademie Freiberg), Hervé Chauris (Mines ParisTech - PSL), Jean-Xavier Dessa (Geoazur - Sorbonne UNiversité), Gilles Lambaré (CGG), Stéphane Operto (Geoazur), Alessandra Ribodetti (Geooazur), Steven Roecker (Rensselaer Polytechnic Institute) and Jean Virieux (Université Grenoble Alpes).

• January 15th 2021: Two extended abstracts are submitted to the annual EAGE meeting. One deals with the time-domain formulation of IR-WRI and the second one with Anderson acceleration of IR-WRI.

• January 20th 2021: The paper entitled "Efficient extended-search space full-waveform inversion with unknown source signatures" by H. Aghamiry, F. Mamfoumbi, A. Gholami and S. Operto" was submitted to the Geophysical Journal International. H. Aghamiry proposes a computationnaly-efficient method to estimate source signature in IR-WRI when the latter is implemented in the frequency domain. The draft is available on the sponsor page.

• January 2021: The 3D FFWI frequency-domain FWI code has been revalidated with the Valhall case study on the Occigen super computer of CINES. Mono-parameter FWI for vertical wavespeed and Multi-parameter FWI for vertical wavespeed, density and attenuation have be rerun in the 3.5Hz-10Hz frequency band. Next step involves pushing the inversion up to 15Hz using the BLR version of MUMPS. The code will be released on the sponsor page soon.

• February 10th 2021: The paper entitled "Mitigating the ill-posedness of first-arrival traveltime tomography with slopes: application to the eastern Nankai Trough OBS dataset (Japan)" by S. Sambolian, A. Gorszczyk, S. Operto, A. Ribodetti and B. Tavakoli F. has been submitted for publication in the Geophysical Journal International. The draft is available on the sponsor page.

• February 10th 2021: The PhD thesis and the oral defense of Serge Sambolian can be downloaded from the sponsor page.

• The paper entitled On efficient frequency-domain Full-Waveform Inversion with extended search space by H. Aghamiry, A. Gholami and S. Operto is published in the March-April issue of Geophysics. The final version have been uploaded in the sponsor page. This paper has been selected as the Geophysics bright spot.

• March 2021: The 3D FFWI frequency-domain FWI code is performing the Valhall case study on the Jean-Zay super computer of IDRIS. Mono-parameter FWI for vertical wavespeed and Multi-parameter FWI for vertical wavespeed, density and attenuation have be rerun in the 3.5Hz-10Hz frequency band. Next step involves pushing the inversion up to 15Hz using the BLR version of MUMPS.

• March 12th 2021: The paper entitled Extended-space Full Waveform Inversion in the time domain with the augmented Lagrangian method by H. Aghamiry, A. Gholami and S. Operto has been submitted for publication in Geophysics. This paper describes an efficient algorithm to implement extended-space FWI with the Augmented Lagrangian method in the time domain. The search space extension is generated by a relaxation of the wave equation allowing for an accurate data fit with inaccurate subsurface models. This search space extension generates extended sources in time and space. The subsurface parameters are updated by minimizing both the residual data mismatch and the artificial source extension. The method is formulated with a variable projection method to enforce the reconstructed wavefields in the parameter estimation problem. The draft of the paper is available on the sponsor page.

• March 25th: Two abstracts are submitted to the Fifth EAGE Workshop on High Performance Computing for Upstream. The first is entitled "Up to date assessment of 3D frequency-domain full waveform inversion based on the sparse multifrontal solver MUMPS" by P. R. Amestoy, A. Buttari, L. Combe, M. Gerest, J.-Y. L'Excellent, T. Mary, S. Operto, and C. Puglisi is proposed in the frame of a colaboration with the MUMPS developer team. It provides an up to date discussion about the kinds of 3D frequency-domain FWI applications (in terms of size) that can be performed today with the sparse direct solver MUMPS. Simulations are performed on the Jean-Zay supercomputer of IDRIS and the occigen supercomputer of CINES.

The solver is re-assessed with the MUMPS solver for problems involving 50 millions of unknowns. 3D frequency-domain VTI visco-acoustic FWI of OBC data in the north sea using the Jean-Zay supercomputer of IDRIS (http://www.idris.fr/jean-zay) and the MUMPS multifrontal solver. (a-d) Horizontal and vertical sections in the final FWI model. Maximum frequency is 10 Hz (see also Operto & Miniussi (2018)). (e-f) Reflectivity images (sum of the horizontal and vertical derivatives). (g-h) Attenuation (Q) reconstruction across and away from the gas cloud. (i) Wavefield simulation at 13Hz involving 45M of unknowns. 70 nodes and 140 MPI processes were used for this simulation. FWI is currently performed at this frequency. The second is entitled "Large-scale finite-difference and finite-element frequency-domain seismic wave modeling with multi-level domain-decomposition preconditioner" by P.-H. Tournier, V. Dolean, P. Jolivet, L. Combe, S. Operto, S. Riffo. This abstract discusses an alternative to performing large-scale seismic modeling in the frequency domain based upon a direct/iterative solver and the multi-level ORAS (Optimized Restricted Additive Scharwz) domain decomposition preconditioner. An optimal setup and a scalability analysis of the solver are discussed as well as a comparison of the accuracy and complexity of a Lagrange-polynomial finite-element discretization on unstructured tetrahedral meshes and the 27-point finite difference stencil with adaptive coefficients using an analytical solution in a velocity gradient model. The draft of the two abstracts is available on the sponsor page.

• 5 April 2021: The paper entitled "GO_3D_OBS: the multi-parameter benchmark geomodel for seismic imaging method assessment and next -generation 3D survey design (version 1.0)" by A. Gorszczyk and S. Operto is published in Geoscientific Model Development. This paper describes a realistic 3D isotropic visco-elastic geomodel discretized on a Cartesian grid representative of a subduction zone. This geomodel has been designed by A. Gorszczyk to assess imaging techniques and design large-scale 3D surveys for regional crustal scale exploration. The geomodel is freely available on https://dataportal.igf.edu.pl/dataset/go_3d_obs. The publication can befreely dowloaded on https://doi.org/10.5194/gmd-14-1773-2021

Inline vertical section N° 1001 of the GO_3D_OBS geomodel.

• April 2021: Submission to EAGE 2021 and SEG 2021

1. H. S. Aghamiry, F. W. Mamfoumbi-Ozoumet, A. Gholami, and S. Operto, ADMM-based full-waveform inversion with unknown source signatures, Submitted to the 91st Annual SEG meeting (Denver).
2. K. Aghazadeh, A. Gholami, H. S. Aghamiry, and S. Operto, Stochastic extended full-waveform inversion with augmented Lagrangian method, submitted to the 91st Annual SEG meeting (Denver).
3. A. Gholami, H. Aghamiry and S. Operto. Clarifying some issues on Extended FWI: scattered-field equation, time reversal and source reconstruction, submitted to the 91st Annual SEG meeting (Denver).
4. A. Gholami, H. Aghamiry and S. Operto. A data reconstruction inversion approach to extended FWI, submitted to the 91st Annual SEG meeting (Denver).
5. A. Rezaei, H. S. Aghamiry, A. Gholami, and S. Operto, Iterative reconstruction of data assimilated wavefields in the extended-source full-waveform inversion, Submitted to 82th Annual EAGE Meeting (Amsterdam).
6. A. Gholami, H. Aghamiry, and S. Operto. Data Reconstruction Inversion: an augmented Lagrangian based full-waveform inversion in the time domain. Submitted to 82th Annual EAGE Meeting (Amsterdam).
7. K. Aghazadeh, A. Gholami, H. S. Aghamiry, and S. Operto, Augmented Lagrangian based full-waveform inversion with Anderson acceleration, Submitted to 82th Annual EAGE Meeting (Amsterdam)

Abstract 1 proposes an approach to perform source signature estimation during frequency-domain WRI. Abstract 2 proposes to mitigate the computational burden of multi-source modeling in IR-WRI with random source encoding. Abstract 3 clarifies the mechanisms through which wavefield reconstruction inversion with extended sources works. Abstract 4 reformulates the wavefield reconstruction inversion method where the concept of intermediate data is introduced following the heuristic approach of Yao et al. (2019). Abstract 5 assesses different preconditioners to compute data-assimilated wavefields with the iterative linear conjugate gradient method. Abstract 6 describes an efficient algorithm to implement WRI in the time domain with an augmented Lagrangian method. Abstract 7 assesses the Anderson acceleration optimization scheme in the framework of WRI.

The PDF of these abstract are available on the sponsor page.

• May 2021: The paper entitled "Efficient extended-search space full-waveform inversion with unknown source signatures" by H. Aghamiry, F. Mamfoumbi, A. Gholami and S. Operto" is accepted for publication in the Geophysical Journal International.

• June 2021: The paper entitled "Anderson accelerated augmented Lagrangian for extended waveform inversion" by Kamal Aghazade, Ali Gholami, Hossein S. Aghamiry, and Stéphane Operto has been submited to Geophysics. This paper recasts WRI as fixed-point problem to improve its convergence rate with Anderson method. The preprint is available on the sponsor page.

• June 30 2021: The paper entitled "Mitigating the ill-posedness of first-arrival traveltime tomography using slopes: application to the eastern Nankai Trough (Japan) OBS dataset" by S. Sambolian, A. Gorszczyk, S. Operto, A. Ribodetti and B. Tavakoli, is accepted for publication in the Geophysical Journal International.

• August 09 2021: The paper entitled "Randomized Source Sketching for Full Waveform Inversion" by Kamal Aghazade, Hossein S. Aghamiry, Ali Gholami, and Stéphane Operto has been submitted to IEEE TGRS. In this paper, different source-encoding strategies used in seismic imaging are formulated into a unified framework based on the randomized sketching. Then, the randomized sketching strategies are used to increase the computational efficiency of the IR-WRI algorithm. The preprint is available on arXiv.

• August 19 2021: The paper entitled "Accurate 3D frequency-domain seismic wave modeling with the wavelength-adaptive 27-point finite-difference stencil: a tool for full waveform inversion" by H. Aghamiry, A. Gholami, L. Combe and S. Operto has been submitted to Geophysics. This paper presents a wavelength-adaptive 27-point finite-difference stencil whose accuracy is dramatically increased compared to the non adaptive one. The finite-difference frequency-domain (FDFD) method is benchmarked against the Convergent Born series method with several 3D large-scale complex benchmarks. We use the multifrontal MUMPS solver to compute the FDFD solutions. The preprint is available on the sponsor page.

Accuracy of the new wavelength-adaptive 27-point FDFD stencil. 9-Hz wavefield computed in the 3D SEG/EAGE Salt model. Column 1: wavefield computed with the highly-accurate convergent Born series method (used as a reference). Column 2: wavefield computed with the non-adaptive 27-point FDFD stencil. Column 3: Difference between column 1 and 2. Column 4: wavefield computed with the wavelength-adaptive 27-point FDFD stencil. Column 5: Difference between column 1 and 4.

Large-scale finite-difference frequency-domain simulation in a 102 km x 20 km x 28.3 km of the GO_3D_OBS subduction-zone velocity model. Velocities range between 1.5km/s and 8.6km/s. Frequency is 3.75 Hz. Number of degrees of freedom if 67.5 millions. Eighty nodes of the occigen supercomputer of CINES (https://www.cines.fr/calcul/materiels/occigen) are used. The linear system is solved with the massively parallel MUMPS multifrontal solver (https://mumps-consortium.org) using the block low rank function with a compression threshold parameter of epsilon=1e-5. Elapsed time for LU factorization is 869 s. Elapses time to compute 130 wavefields is 34 s.

• September 1st 2021: The paper entitled "Extended-space full waveform inversion in the time domain with the augmented Lagrangian method" by A. Gholami, H. Aghamiry and S. Operto is accepted for publication in Geophysics. This paper presents an algorithm based upon the augmented Lagrangian method for efficient implementation of wavefefield reconstruction inversion (WRI) in the time domain. The preprint is available on the sponsor page.

• September 17th 2021: The prerecorded SEG presentations (mp4) of the WIND team are available on the sponsor page.

1. H. S. Aghamiry, A. Gholami, and S. Operto, Dual variable compression: remedy the memory issue of full-space approaches for full-waveform inversion.
2. A. Gholami, H. Aghamiry, and S. Operto. A data reconstruction inversion approach to extended FWI.
3. A. Gholami, H. Aghamiry, and S. Operto. Clarifying some issues on Extended FWI: scattered-field equation, time reversal and source reconstruction.
4. H. S. Aghamiry, F. W. Mamfoumbi-Ozoumet, A. Gholami, and S. Operto, ADMM-based full-waveform inversion with unknown source signatures.

• September 20th 2021: The papers Anderson accelerated augmented Lagrangian for extended waveform inversion and Randomized Source Sketching for Full Waveform Inversion by Kamal Aghazade, Ali Gholami, Hossein S. Aghamiry, and Stéphane Operto are accepted for publication in Geophysics and IEEE TGRS. Congratulation to Kamal!

• September 23rd 2021: The pre-registered audio presentation of P. Amestoy entitled Up to date assessment of 3D frequency-domain full waveform inversion based on the sparse multifrontal solver MUMPS given at the Fifth EAGE Workshop on High Performance Computing for Upstream is available on the sponsor page.

• August 19 2021: The paper entitled "Accurate 3D frequency-domain seismic wave modeling with the wavelength-adaptive 27-point finite-difference stencil: a tool for full waveform inversion" by H. Aghamiry, A. Gholami, L. Combe and S. Operto has been submitted to Geophysics. This paper presents a wavelength-adaptive 27-point finite-difference stencil whose accuracy is dramatically increased compared to the non adaptive one. The finite-difference frequency-domain (FDFD) method is benchmarked against the Convergent Born series method with several 3D large-scale complex benchmarks. We use the multifrontal MUMPS solver to compute the FDFD solutions. The preprint is available on the sponsor page.

• October 25 & 26: A short course on FWI entitled "A guided tour on Full Waveform Inversion (FWI)" is given at the 17th International Congress of the Brazilian Geophysical Society & Expogef. The slides are available on the Landing Page (page Short Course).

• October 28th 2021: The paper entitled "Three-dimensional finite-difference & finite-element frequency-domain wave simulation with multi-level optimized additive Schwarz domain-decomposition preconditioner: A tool for FWI of sparse node datasets" by P.-H. Tournier, P. Jolivet, V. Dolean, H. S. Aghamiry, S. Operto, and S. Riffo has been submitted to Geophysics. This paper introduces a leading-edge massively-parallel hybrid direct-iterative solver to simulate 3D wave propagation in the frequency-space domain (Helmholtz problem). We introduce this method as a possible forward engine for 3D large scale applications of frequency domain Full Waveform Inversion (FWI) from sparse long-offset node datasets. The Helmholtz problem is indefinite and hence challenging to solve with iterative methods without a good preconditioner. We present a multi-level domain decomposition preconditioner based on a multi-level optimized additive Schwarz method with absorbing conditions between subdomains. The global system is solved with a Krylov subspace method while the local subproblems are tackled with a sparse direct solver. Moreover, we assess two discretization methods based on P3 continuous finite elements on unstructured tetrahedral meshes and the recently proposed wavelength-adaptive 27-point finite-difference method on regular Cartesian grids. With a 3D large-scale benchmark, we first discuss how to tune several features of the solver (arithmetic precision, stopping criterion of iteration, choice of the direct solver, Krylov-basis orthogonalization) in order to achieve the best compromise between computational efficiency and accuracy. Then, we compare the accuracy and the computational efficiency of the solver when the two discretization schemes are used to tackle four different benchmarks. We conclude our numerical analysis with a strong and weak scalability analysis of the method. We conclude the paper with a discussion section that reviews the potential pros and cons of our method compared to the widely-used explicit time marching method for FWI applications, the discussion being illustrated with a numerical example. The preprint is available on the sponsor page.

• November 5th 2021: The 2021 WIND activity report is available on the intranet page for sponsors.

• November 12th 2021: Two abstracts from our team in colabration with the OPIRA team are accepted for the next SPIE Photonics West conference in San Francisco:
  1. Ranjbaran, M., Aghamiry, H. S., Gholami, A., Operto, S. & Avanaki, K. (2022). High-resolution speed of sound estimation from ultrasound waves using extended full-wave inversion. In SPIE Photonics West, San Francisco.
  2. Ranjbaran, M., Aghamiry, H. S., Gholami, A., Operto, S. & Avanaki, K. (2022). 2D-FC-ADMM reconstruction algorithm for quantitative optoacoustic tomography in a highly scattering medium: a simulation study. In SPIE Photonics West, San Francisco.

• November 17 & 18 2021: The second WIND sponsor meeting took place at Geoazur Institute. The PDF and MP4 of the presentations are available on the intranet page for sponsors (menu AnnualMeeting).