1. A method for the generation of three dimensional fractal subsurface structure by Voronoi tessellation and computation of gravity response of such fractal structure, by generation of fractal subsurface structures which are very close to the natural setting of the subsurface geology and provides computation of forward gravity response of such structures for delineation of the underlying anomalous object, said method comprising: (a) selecting Voronoi centers at a plurality of locations over a region of interest, the Voronoi centers being represented by X, Y, Z co-ordinates; (b) generating an initial model of the subsurface fractal geological object, having variation in physical property such as density in lateral and vertical directions; the initial model being generated by tessellating, the Voronoi centers, and assigning values of physical property variations during generation of the model on the basis of pre-determined assumptions in the model; (c) assigning different colours to regions in the model which have different physical properties such as density to enable demarcation.