In most situations in which diffracted multiples are a serious problem, the wave propagation is rather complex, for example for multiples diffracted off the edge of salt bodies. Thus, the moveout of primaries and multiples tend to be very complex, making the application of data-space moveout-based methods for the removal of multiples difficult. In ADCIGs, however, since the complexity of the wavefield has already been taken into account by prestack migration (to the extent that the presence of the multiples allows an accurate enough estimation of the migration velocity field), the residual moveout of multiples is generally smoother and better behaved Sava and Guitton (2003).
In this paper we focus on attenuating diffracted multiples in ADCIGs by redefining the tangent-squared Radon transform of Biondi and Symes 2003 to add an extra dimension to account for the shift in the apexes of the moveout curves of the diffracted multiples. We show with a 2D seismic line from the Gulf of Mexico that our approach is effective in attenuating both, the specularly-reflected and the diffracted multiples. In contrast, ignoring the apex shift results in poor attenuation of the diffracted multiples.
The real impact of our method for attenuating diffracted multiples is likely to be in 3D rather than in 2D, though the results that we show in this paper are limited to 2D. Biondi and Tisserant 2003 have presented a method for computing 3D ADCIGs from full 3D prestack migration. These 3D ADCIGs are functions of both the aperture angle and the reflection azimuth. Simple ray tracing modeling shows that out-of-plane multiples map into events with shifted apexes (like the 2D diffracted multiples) and different reflection azimuth than the primaries. Attenuation of these multiples from 3D ADCIGs can be accomplished with a methodology similar to one we present in this paper.