Processing and interpretation of satellite and ground based gravity data at different lithospheric scales (2013)

Global availability of gravity data allows the regional investigation (<100 km anomaly wavelengths) of the lithosphere. This thesis describes the processing and use of satellite gravity data for modelling at different lithospheric scales. The first part shows comparisons of satellite gravity from different missions (GRACE and GOCE) and ground based data in den Andean mountain range and Costa Rica. First, the terrain corrected Bouguer anomaly were compiled from two geodteic definitions: the geodetic "classical" gravity anomaly and the geodetic gravity disturbance. Large deviations from ground data are observed in areas of high topography. Second, comparisons with an existing density model at the Andes (between 36°S and 42°S) prove, that satellite gravity can be used to model regional gravity effects (e.g. subducting slab, crust and mantle). The volcanic back arc do not show up in the satellite gravity data. \nThe second part of the thesis presents the development of a new accurate algorithm for topographic correction based on a polyhedral representation by triangulation of topographic surfaces. The new algorithm also considers sphericity of the earth, calculates gravity gradients, deals with large datasets and uses an adaptive approach for resampling topography to save computation time. The resampling algorithm bases on a quad tree representation of the topography grid with different resolutions. High resolutions of the topography grid are only considered if it has a significant influence on the gravity at the station. Thus, this approach links the resampling of topography during the calculation with distance and geometry of topography. This leads to an accurate representation of distant terrain and a massive speed up of computation time. The new algorithm will be tested in an area of central Asia in the Himalayan mountain range and compared to existing algorithms. Furthermore, the impact of grid resolutions on the correction will be discussed. Results show significant differences between corrections for different resolutions (e.g. 10 *10^-5 m/s^2 root mean square error between 1 km and 90 m grid resolution). Recalculations of existing Bouguer anomaly compilations show slight differences. Topographic correction of gradients are calculated in the Andes which leads to an improved representation of lithospheric structures in the measured gradients. Another test is conducted at a passive continental margin to investigate the effect of topographic corrections in another environment. Bouguer anomalies of the North Perth basin are recalculated which improves the fit of anomalies and geological structural elements. A 3D model is set up based on ground data to investigate the sedimentary basins at the isostatic state of the area. The results will be compared to satellite data to estimate the usability of satellite data in such an environment. The comparison shows that satellite data can be used to calculate the Moho interface in this area. However, small structures like sedimentary basins do not show up in the gravity field. The results are in agreement with the investigations in the area of an active continental margin (Central Andes).