Velocity estimation

The state-of-the-art in velocity estimation is represented by traveltime tomography (104; 14; 3; 33; 55). Such methods are fast and accurate for relatively simple models with small velocity contrasts. However, traveltime tomography often fails due to the instability of ray tracing for complex velocity models with sharp boundaries.

A second goal of this thesis is to overcome those limitations by designing a velocity analysis method based on wavefield extrapolation. A method of this type naturally inherits the characteristics of wavefield extrapolation, mainly robustness in presence of large and sharp velocity contrasts, band-limited model sensitivity and multipathing.

Conventional migration velocity analysis employs traveltime perturbations derived from moveout measurements on migrated common image gathers. In this dissertation, I modify this methodology to employ image perturbations , which can be defined either from moveout differences and/or from spatial focusing. Such analysis requires development of image perturbation methods (residual migration) and techniques for analysis of image quality (angle transformation).