Anisotropy detection by tomography and polarization analysis in a 3D three-component VSP

Vertical Seismic Profiles (VSP) allow borehole information (e.g. well logs and geological ties) to be extended to the surrounding space. Well logs span only one dimension i.e. depth along the well itself, but with a very high resolution. Conversely, conventional surface seismic data provides information with a lower resolution, but with a much wider 2D or 3D extent. Matching of events in the VSP and the surface seismic increases the physical and geological consistency of the Earth model we can build in depth. Depth is the natural dimension for VSP data, while surface seismic provides a reflectivity image of the Earth in the time domain. The velocity of seismic waves connects the two worlds. Seismic tomography estimates a 2D or 3D velocity field by jointly inverting different wave types, i.e. diret, reflected and refracted arrivals. It provides a macro-model for the velocity field that is consistent with the resolution of the available signal, without assuming simple shapes for the interfaces or smooth velocities. Thus, it can bridge both the gap between the time and depth domains, and also between data with different resolution scales: almost 100 m for seismic waves, and about 1 m for sonic logs.