GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.3 773 models. Progressively improved initial models should be investigated by introducing into the inversion algorithm selected data (frequency sweeping, time windowing and offset weighting are options to be investigated). - Regarding the model-oriented strategy based on parameter selection, the sensitivity of the inversion with respect to the Vs parameter is greater than the sensitivity with respect to the Vp parameter, coming from the physics of SWs propagation and it can be exploited to improve the initial Vs model in the shallow part. - Using the improved Vs model (from mono-parameter FWI) allows a greater and deeper update of both Vp and Vs models. Data-misfit is reduced both in correspondence of the target and for far offsets. Nevertheless, there is still room for improvement. Further analysis might integrate model selection with data hierarchy as follows: - Data-windowing to exploit Body Waves (BWs) for a better reconstruction of the Vp parameter, in parallel with a Vp improvement from the new Vs parameter by using the Poisson’s ratio. These alternatives are expected to be case-dependent. - Offset weighting should be designed to avoid, initially, the effects of far offset data and to increase their influence at later stages of the inversion. - Thanks to the starting Vp and Vs models, SWs could be introduced smoothly during the inversion by a Gaussian weighting around their arrival times. - Frequency sweeping from low to high frequency will also mitigate the cycle-skipping issue. - Additional constraints based on prior information on the model description could also help the reconstruction, which is difficult for near-surface data because all phases are mixed. Acknowledgements. This study was granted access to the HPC resources of CIMENT infrastructure (https:// ciment.ujf-grenoble.fr ). References Born, M. and Wolf, E., 1970. Principles of Optics , 4 th . ed, Pergamon Press. Fichtner, A., 2011. Full Seismic Waveform modelling and Inversion. Springer Science & Business Media, 343 pp. Khosro Anjom, F., Arabi, A., Socco, L.V. and Comina, C., 2017. Application of a method to determine S and P wave velocities from surface waves data analysis in presence of sharp lateral variations . Gruppo Nazionale di Geofisica della Terra Solida (GNGTS), Expanded Abstracts. Métivier, L., Brossier, R., Mérigot, Q., Oudet, E. and Virieux, J., 2016. An optimal transport approach for seismic tomography : Application to 3D FWI . Inverse Problems, 32(11), 115008. Sirgue, L., Barkved, O. I., Dellinger, J., Etgen, J., Albertin, U., and Kommedal, J. H., 2010. Full waveform inversion: the next leap forward in imaging at Valhall . First Break, 28, 65-70. Socco, L.V., C. Comina, and F. Khosro Anjom., 2017 . Time-average velocity estimation through surface-wave analysis: Part 1 - S-wave velocity . Geophysics, 82(3), U49-U59. Socco, L.V., and C. Comina, 2017. Time-average velocity estimation through surface-wave analysis: Part 2 - P-wave velocity . Geophysics, 82(3), U61-U73. Tarantola, A., 2005. Inverse problem theory and methods for model parameter estimation, 2 nd ed. Society for Industrial and Applied Mathematics, Philadelphia, PA. Teodor, D., C. Comina, L.V. Socco, R. Brossier, P. Trinh, and J. Virieux, 2017. Initial model design for Full-Waveform Inversion-Preliminary elastic modeling from surface waves data analysis . Extended Abstract, Gruppo Nazionale di Geofisica della Terra Solida, GNGTS. Teodor, D., Comina, C., KhosroAnjom, F., Socco, L.V., Virieux, J., Trinh, P.-T. and Brossier, R., 2018. Building initial models for Full-Waveform Inversion of shallow targets by surface waves dispersion curves clustering and data transform . SEG International Exposition and 88th Annual Meeting, Anaheim (CA). Trinh, P. T., Brossier, R., Métivier, L., Virieux, J. and Wellington, P., 2017. Bessel smoothing filter for spectral element mesh. Geophysical Journal International, 209 (3): 1489-1512. Trinh, P.-T., Brossier, R., Metivier, L. , Tavard, L. and Virieux, J., 2018 .  Efficient time-domain 3D elastic and visco- elastic FWI using a spectral-element method on flexible Cartesian-based mesh , Geophysics (accepted). van Leeuwen, T., and Herrmann F. J., 2013. Mitigating local minima in full-waveform inversion by expanding the search space , Geophysical Journal International, 195(1), 661–667. Virieux, J. and Operto, S., 2009. An overview of full-waveform inversion in exploration geophysics. Geophysics, 74(6): WCC1-WCC26. Warner, M., Ratcliffe, A., Nangoo, T., Morgan, J., Umpleby, A., Shan, N., Vinje, V., Stekl, I., Guash, L., Win, C., Conroy, G. & Bertrand, A., 2013. Anisotropic 3D full-waveform inversion . Geophysics, 78, R59-R80