Seismic travel-time tomography for detailed global mantle structure

The object of this thesis is to use travel-time tomography to focus and enhance the existing global image of the Earth's mantle and crust. This image is still rather blurred with respect to the considerably sharper pictures commonly obtained in regional studies. The improvement is basically obtained in two steps: In the first step a more or less conventional tomography method is applied to a reprocessed and sensibly averaged data set for a more sophisticated, irregular discretization of the study volume, and in the second step the (global) method itself is refined by introducing 3-D ray tracing to calculate accurate seismic ray paths through heterogeneous velocity models (nonlinear tomography).