SEISGAMA: A Free C# Based Seismic Data Processing Software Platform

Seismic reflection is one of the most popular methods in geophysical prospecting. Nevertheless, obtaining high resolution and accurate results requires a sophisticated processing stage. There are many open-source seismic reflection data processing software programs available; however, they often use a high-level programming language that decreases its overall performance, lacks intuitive user-interfaces, and is limited to a small set of tasks. These shortcomings reveal the need to develop new software using a programming language that is natively supported by Windows® operating systems, which uses a relatively medium-level programming language (such as C#) and can be enhanced by an intuitive user interface. SEISGAMA was designed to address this need and employs a modular concept, where each processing group is combined into one module to ensure continuous and easy development and documentation. SEISGAMA can perform basic seismic reflection processes. This ability is very useful, especially for educational purposes or during a quality control process (in the acquisition stage). Those processes can be easily carried out by users via specific menus on SEISGAMA’s main user interface. SEISGAMA has been tested, and its results have been verified using available theoretical frameworks and by comparison to similar commercial software

Caractérisation de la subsurface par inversion de forme d'onde complète 3D élastique. Etude d'un jeu de données sismiques de proche surface multi-composantes

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.L'inversion de forme d'onde complète (FWI) est une procédure d'ajustement itératif des données entre les données observées et les données synthétiques. Les données synthétiques sont calculées en résolvant une équation d'onde. La FWI vise à reconstruire les informations détaillées des propriétés physiques du sous-sol. La méthode FWI a été développée au cours des dernières décennies, grâce à l'augmentation de la capacité de calcul et au développement de la technologie d'acquisition. La FWI a également été appliquée à à des échelles variées, allant de l'échelle globale, lithosphérique, crustale, jusqu'à la proche surface, c'est à dire quelques mètres de profondeur.Dans ce manuscrit, nous étudions l'inversion d'un jeu de données de source et de récepteur multicomposantes en utilisant un algorithme d'inversion de forme d'onde complète viscoélastique pour une cible sismique peu profonde. La cible est une ligne de tranchée enterrée à environ 1 m de profondeur. Nous présentons le pré-traitement des données, y compris une correction par déconvolution pour compenser les différentes conditions de couplage de la source et du récepteur pendant l'acquisition, ainsi qu'un procédé d'inversion en plusieurs étape pour la reconstruction des vitesses des ondes P et S. Notre mise en œuvre est basée sur une modélisation viscoélastique utilisant une discrétisation par éléments spectraux pour rendre compte avec précision de la complexité de la propagation des ondes dans cette région peu profonde. Nous illustrons la stabilité de l'inversion en partant de différents modèles initiaux, soit basés sur l'analyse des courbes de dispersion, soit des modèles homogènes cohérents avec les premières arrivées. Nous obtenons des résultats similaires dans les deux cas. Nous illustrons également l'importance de la prise en compte de l'atténuation en comparant les résultats élastiques et viscoélastiques. Les résultats 3D permettent de localiser précisément la ligne de tranchée en termes d'interprétation. Ils montrent également une autre structure de ligne de tranchée, dans une direction formant un angle de 45 degrés avec la direction de la ligne de tranchée ciblée. Cette nouvelle structure avait été précédemment interprétée comme un artefact dans les anciens résultats d'inversion 2D. L'interprétation archéologique de cette nouvelle structure est actuellement en discussion.Nous réalisons également trois expériences différentes pour comprendre l'effet des données à composantes multiples sur la FWI. La première expérience est une analyse de sensibilité de plusieurs paquets d'ondes (onde P, onde S et onde de surface) sur un modèle 3D simple basé sur une direction cartésienne de la source et du récepteur. La seconde expérience est une inversion élastique 3D basée sur des données synthétiques (utilisant la source de direction cartésienne) et de champ (utilisant la source Galperin) avec diverses combinaisons de composants. Seize combinaisons de composantes sont analysées pour chaque cas. Dans la troisième expérience, nous effectuons la décimation de l'acquisition sur la base de la deuxième expérience. Nous démontrons un avantage significatif des données multicomposantes FWI grâce à ces expériences. Dans une échelle sismique peu profonde, les inversions avec les composantes horizontales donnent une meilleure reconstruction en profondeur. En se basant sur la décimation de l'acquisition, l'inversion utilisant des données sismiques 9C fortement décimées produit des résultats similaires à l'inversion utilisant des données sismiques 1C sur l'acquisition complète

3x3C Seismic’s Sensitivity Analysis on Near-Surface towards Full Waveform Inversion

International audienceFull Waveform Inversion (FWI) is a high-resolution seismic imaging tool which has been intensively developed during the past decade. At the near surface scale, FWI faces several challenges including 3D acquisition deployment, a strong presence of elastic effects, relatively high attenuation effects, and difficulties to propagate high-frequency waves. In order to better characterize such shallow targets, one of the solutions is to take into account data from multi-component sources and receivers. In this study, we analyze the benefit of 3x3C seismic data: 3x3C seismic is an acquisition technique which contains three orthogonal directions of the source and three component receivers. Although 3x3C seismic is feasible in practice, the benefit of such data for FWI is still not clear. This research uses two different synthetic models to assess the interest of 3x3C seismic data through the construction and analysis of the sensitivity kernel of both P-wave and S-wave velocities for each wave type (P-wave, S-wave, and surface wave), and each component. The results show that 3x3C data provide complementary information on the kinematic, dynamic and polarization of the wave propagation, yielding a potentially better reconstruction of the subsurface properties

Assessment of optimal transport based FWI: 3D OBC Valhall case study

International audienceOptimal transport (OT) distances have been recently proposed to mitigate the non-convexity of the $L_2$ misfit function in FWI. However, OT is only applicable to positive and normalized data. To overcome this difficulty, we have proposed two strategies, one based on the Kantorovich-Rubinstein (KR) norm, which extends a specific OT distance to the comparison of signed data, the other based on the interpretation of the discrete graph space of the data through OT. In this study, we compare these two approaches for the inversion of 3D OBC data from the Valhall field, using a visco-acoustic time-domain FWI algorithm. Starting from a crude initial velocity model, both KR and graph space approaches provide more reliable results than $L_2$, the best results being obtained with the graph space approach. Thanks to a recently developed numerical approach, the computational cost increase is limited in this case to approximately 15 % compared to standard $L_2$ FWI

Towards 3D 9C Elastic Full Waveform Inversion of Shallow Seismic Wavefields - Case Study Ettlingen Line

International audienceFull Waveform Inversion (FWI) is a high-resolution seismic imaging tool, based on an iterative data fitting procedure. In this research, we focus on a near-surface application using three-component sources and three-component receivers (9C). The target is the Ettlingen Line, a defensive trench line located at Rheinstetten, Germany. In this work, we describe the first application of 3D elastic FWI method to a dense 3D dataset equipped with 9C. In practice, due to the limited number of equipment, the acquisition has been split into six parts (each part has the all source locations but only part of receiver locations). This separation leads to an inconsistent dataset concerning both amplitudes and phases. Therefore, a first step has led to the application of matching filter to homogenize the dataset. Several FWI strategies such as Vp - Vs parameter binding, gradient Bessel smoothing, and multi-scale approach have been considered during the inversion process to ensure a good convergence. Starting from a homogeneous model, we can achieve significant improvement in data-fit as well as a realistic reconstructed model. The location and dimension of the trench match with the previous experiments based on the inversion of surface wave dispersion curves with an additional increase in resolution