The D" layer is one of Earth's most heterogeneous location, hosting poorly understood features, which are most likely linked to the global dynamics of the mantle. Present days tomographic approaches cannot resolve correctly this area. The resolution of images from Earth's inner structure is strongly linked to precisely localizing earthquakes, and to have a good knowlegde of the frequency content of seismic waves. This thesis aims at building a global database of seismic travel times, data used for the development of tomographic images. Our method uses a more precise determination of the depths of earthquakes, allowing an improvement in measuring travel times. To a better evaluation of the frequency content, these measurements are performed in several frequency bands. A new approach for the computation of corrections to the complexity of the crust is presented as well. Finally, a preliminary imaging is presented, at regional and global scale, under the approximation of the ray theory, before a more complete description under Born approximation.
