SYNTHETIC SEISMOGRAMS IN HETEROGENEOUS MEDIA BY ONE-RETURN APPROXIMATION

When reverberations between heterogeneities or resonance scattering ca n be neglected but accumulated effects of forward scattering are stron g, the Born approximation is not valid but the De Wolf approximation c an be applied in such cases. In this paper, renormalized MFSB (multipl e-forescattering single-backscattering) equations and the dual-domain expressions for scalar, acoustic and elastic waves are derived by a un ified approach. Two versions of the one-return method (using MFSB appr oximation) are given: One is the wide-angle dual-domain formulation (t hin-slab approximation); the other is the screen approximation. In the screen approximation, which involves a small-angle approximation for the wave-medium interaction, it can be seen clearly that the forward s cattered, or transmitted waves are mainly controlled by velocity pertu rbations; while the backscattered or reflected waves, by impedance per turbations. The validity of the method and the wide-angle capability o f the dual-domain implementation are demonstrated by numerical example s. Reflection coefficients of a plane interface derived from numerical simulations by the wide-angle method match the theoretical curves wel l up to critical angles. For the reflections of a low-velocity slab, t he agreement between theory and synthetics only starts to deteriorate for angles greater than 70 degrees. The accuracy of the wide-angle ver sion of the method could be further improved by optimizing the wave-nu mber filtering for the forward propagation and shrinking the step leng th along the propagation direction.