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3D elastic full waveform inversion for subsurface characterization.Study of a shallow seismic multicomponent field data

Theodosius Marwan Irnaka 1
1 Cycle sismique et déformations transitoires
ISTerre - Institut des Sciences de la Terre
Abstract : Full Waveform Inversion (FWI) is an iterative data fitting procedure between the observed data and the synthetic data. The synthetic data is calculated by solving the wave equation. FWI aims at reconstructing the detailed information of the subsurface physical properties. FWI has been rapidly developed in the past decades, thanks to the increase of the computational capability and the development of the acquisition technology. FWI also has been applied in a broad scales including the global, lithospheric, crustal, and near surface scale.In this manuscript, we investigate the inversion of a multicomponent source and receiver near-surface field dataset using a viscoelastic full waveform inversion algorithm for a shallow seismic target. The target is a trench line buried at approximately 1 m depth. We present the pre-processing of the data, including a matching filter correction to compensate for different source and receiver coupling conditions during the acquisition, as well as a dedicated multi-step workflow for the reconstruction of both P-wave and S-wave velocities. Our implementation is based on viscoelastic modeling using a spectral element discretization to accurately account for the wave propagation's complexity in this shallow region. We illustrate the inversion stability by starting from different initial models, either based on dispersion curve analysis or homogeneous models consistent with first arrivals. We recover similar results in both cases. We also illustrate the importance of taking into account the attenuation by comparing elastic and viscoelastic results. The 3D results make it possible to recover and locate precisely the trench line in terms of interpretation. They also exhibit another trench line structure, in a direction forming an angle at 45 degrees with the direction of the targeted trench line. This new structure had been previously interpreted as an artifact in former 2D inversion results. The archaeological interpretation of this new structure is still a matter of discussion.We also perform three different experiments to study the effect of multicomponent data on this FWI application. The first experiment is a sensitivity kernel analysis of several wave packets (P-wave, S-wave, and surface wave) on a simple 3D model based on a Cartesian based direction of source and receiver. The second experiment is 3D elastic inversion based on synthetic (using cartesian direction's source) and field data (using Galperin source) with various component combinations. Sixteen component combinations are analyzed for each case. In the third experiment, we perform the acquisition's decimation based on the second experiment. We demonstrate a significant benefit of multicomponent data FWI in terms of model and data misfit through those experiments. In a shallow seismic scale, the inversions with the horizontal components give a better depth reconstruction. Based on the acquisition's decimation, inversion using heavily decimated 9C seismic data still produce similar results compared to the inversion using 1C seismic of a dense acquisition.
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Theodosius Marwan Irnaka. 3D elastic full waveform inversion for subsurface characterization.Study of a shallow seismic multicomponent field data. Earth Sciences. Université Grenoble Alpes [2020-..], 2021. English. ⟨NNT : 2021GRALU004⟩. ⟨tel-03202027⟩

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