1. A method for building a velocity model for a geographical area of interest (GAI), comprising: determining a ray based tomography velocity image of said GAI using acquired data; determining a high resolution velocity guide (HRVG) image of said GAI; scaling said determined HRVG of said GAI; adding the scaled HRVG to the ray based tomography velocity image to determine an updated ray based tomography velocity image; and determining whether said updated ray based tomography velocity image has experienced convergence by determining whether a cost function of said ray based tomography velocity image does not improve compared to a previously determined cost function value of said ray based tomography velocity image.