f Comparison of gradient and Quasi-Newtonian inversion

The power of Seismic inversion Algorithms has groven particularly rapidly during the last ten years. However as the problem is highly nonlinear for the relation between the velocity field and the seismic record the most works dealt with the recovery of the linear part of the model (the short wave lengths of the velocity). Also this study revealed to be difficult. The first reason is the cost of the forward modelleng essential in all inversion processen. The second one came from the huge dimensions of the problem. In fact for complex applications it is no more possible to compute the explicit solution (involving the inversion of a big square matrix: the hessian) and iterative algorithms have to be implemented.