MODELING ROUGH INTERFACES ON SEISMIC-REFLECTION PROFILES - THE APPLICATION OF FRACTAL CONCEPTS

The distortion of reflection continuity and amplitude by overburden st ructure in seismic reflection images of the subsurface is easily recog nised and modelled when the wavelength of the shallower structure is r elatively large. The effects of shorter wavelength structure although giving rise to little reflective response itself, cause significant di stortion of the propagating wavefield, particularly when a moderate or strong acoustic impedance contrast is present in the shallow sub-surf ace. Here we show how short as well as long spatial wavelengths of hor izon roughness affect deeper reflection continuity, and develop a new method using fractal interpolation techniques to predict the total rou ghness of sub-surface horizons from information contained in seismic r eflection sections. Fractally complete depth-velocity models are used in forward models, using the finite difference technique, to produce s ynthetic seismic profiles. The technique is illustrated with data from the Edoras Bank area of the Rockall Plateau, NE Atlantic, where appar ently discontinuous reflectors underlying basalt flows are shown to be from continuous sedimentary horizons distorted by overlying rough hor izons.