AN AUTOMATED RAY METHOD FOR DIFFRACTION MODELING IN COMPLEX MEDIA

We present the computational concept and first results of an automated 2-D ray-tracing algorithm which combines the standard ray method with the method of edge waves and paraxial ray tracing. Reliable ray synthetic seismograms are obtained for subsurface structures of high complexity. Both diffracted and multiple diffracted arrivals are automatically computed, complementing all types of primary arrivals (reflected, multiple reflected, converted waves, etc.) where geometric shadow zones are caused by edges (inhomogeneities) in the subsurface model. The method of computation can be summarized as follows: (1) during standard ray tracing, properties of central and paraxial rays are computed for a set of neighbouring rays. (2) Diffraction points (edges) are identified by comparing the amplitude and traveltime differences of neighbouring rays with the corresponding values of their paraxial approximation. (3) Detected edges art: used as source points for diffracted rays. (4) Repetition of (1)-(3) for diffracted rays allows computation of multiple diffractions ('diffracted diffractions'). (5) The amplitude decay of diffracted arrivals is computed according to the theory of edge waves. Its critical variables are expressed in terms of second-order paraxial traveltimes. The method is demonstrated for a simple and complex synthetic model and a real data complex model.