Fig, 1. PSI -criterion in action:from left to right(from top to bottom) :1. tau-p gather (P-primaries are given, generated with reflectivity codes under the true well-log, and source wavelet is of 50 Hz, 2 ms sampling ); 2. PSI-gather(depth images which correspond to each and every trace of the tau-p gather when the kinematic model is chosen ) with the initial kinematic model (pink line on the Fig.2): 3. PSI-gather with the true kinematic model (red line on the Fig.2); 4. PSI-gather with reconstructed kinematic model (blue curve on the Fig.2 ).

Fig, 2. PSI -criterion in action: P-velocity reconstruction with no apriori information.represens the 'true' well log,Red linestands for the initial model,pink lineshows the results of iterations. The first jump corresponds to the steepest descent of the PSI-criterionblue curve