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Développement d'un outil de traitement et d'interprétation des données gravimétriques et gradiométriques : application aux observations GOCE

Abstract : Nowadays, the scientific community has at its disposal gravity and gravity gradient datasets with unprecedented accuracy and spatial resolution that enhances our knowledge of Earth gravitational field at various scales and wavelengths, obtained from ground to satellite measurements. In parallel with gravimetry, the advancement of satellite observations provides the community with more detailed digital elevation models to reflect the Earth’s structure geometry. Together, these novel datasets provide a great opportunity to better understand the Earth’s structures and dynamics at local, regional, and global scales. The use and interpretation of these high-quality data require refinement of standard approaches in gravity-related data processing and analysis. This thesis consists of a series of studies aiming to improve the precision in the chain of gravity and gravity gradient data processing for geodynamic studies. To that aim, we develop a tool, named GEEC (Gal Eötvös Earth Calculator) to compute precisely the gravity and gravity gradients effects of due to any mass body regardless of its geometry and its distance from measurements. The gravity and gravity gradients effects are computed analytically using the line integral solution of an irregular polyhedron. The validations at local, regional, and global scales confirm the robustness of GEEC’s performance, where the resolution of the model, that depends on both size of the body mass and its distance from the measurement point, control strongly the accuracy of the results. We present an application for assessing the optimum parameters in computing gravity and gravity gradients due to topography variations. Topography has a major contribution in Earth gravitational attraction, therefore the estimation of topography effects must be carefully considered in the processing of gravity data, especially in areas of rugged topography or in large-scale studies. For high-accuracy gravity studies at a global scale, the topography correction process must consider the topography effect of the entire Earth. But for local to regional applications based on relative variations within the zone, we show that truncated topography at a specific distance can be adequate, although, ignoring the topography pas this distance could produce errors. To support these arguments, we show the relationships between gravity relative errors, topography truncation distance, and the extent of study zone. Lastly, we approach the issue: Are GOCE measurements relevant to obtain a detailed image of the structure of a subducting plate, including its geometry and lateral variation? The results of gravity gradient forward modelling using synthetic subduction models computed at GOCE’s mean altitude (255 km) demonstrate that both subduction edges and lateral variations of subduction angle produce gravity gradient variations that are detectable with GOCE dataset (∼100 km wavelength and 10 mE amplitude). However, in the application to the real case of Izu-Bonin-Mariana subduction zone, the second-order geometric features of the subducting plate are difficult to be detected due to the presence of the remaining crustal effects. This is caused by the inaccuracy of the existing global crustal model, that leads to inaccurate crustal effect removal.
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https://tel.archives-ouvertes.fr/tel-02063449
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Submitted on : Monday, March 11, 2019 - 11:17:18 AM
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Anita Thea Saraswati. Développement d'un outil de traitement et d'interprétation des données gravimétriques et gradiométriques : application aux observations GOCE. Earth Sciences. Université Montpellier, 2018. English. ⟨NNT : 2018MONTG077⟩. ⟨tel-02063449⟩

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