1. A method for optimizing a lithologic model of subsurface earth layers, said lithologic model being derived from a real previously fully migrated seismic section consisting of a plurality of real wavelet-processed, zero-offset seismic traces from a corresponding plurality of seismic stations distributed in a survey area at or near the surface of the earth, comprising: preparing an initial lithologic model of subsurface earth layers by combining non-seismic data with the lithologic model derived from seismic recordings; assigning an initial set of layer parameters to said subsurface earth layers; selecting a plurality of model points among the plurality of seismic stations in the survey area; establishing a plurality of calculation points between said model points within a zone of interest within said subsurface earth layers; assigning layer parameters to the subsurface earth layers at each said calculation point by interpolation between adjacent model points; calculating a reflectivity series at each said seismic station within said zone of interest by interpolation of layer parameters between calculation points; generating a synthetic seismic trace from said reflectivity series at each said seismic station to create a synthetic seismic section; measuring the goodness of fit between said synthetic seismic section and a corresponding real seismic section; systematically perturbing the layer parameters, at each said calculation point; generating new synthetic seismic traces after each perturbation to create a new synthetic seismic section and measuring the average goodness of fit between said new synthetic seismic section and said real seismic section; continuing the perturbative process until the average goodness of fit between said synthetic and real seismic sections is optimized to create an optimal lithologic model; and displaying said optimal model.