Extraction of amplitude-preserving angle gathers based on vector wavefield reverse-time migration

摘要

Angle-domain common-image gathers (ADCIGs) transformed from the shotdomain common-offset gathers are input to migration velocity analysis (MVA) and prestack inversion.ADCIGs are non-illusion prestack inversion gathers,and thus,accurate.We studied the extraction of elastic-wave ADCIGs based on amplitude-preserving elastic-wave reversetime migration for calculating the incidence angle of P-and S-waves at each image point and for different source locations.The P-and S-waves share the same incident angle,namely the incident angle of the source P-waves.The angle of incidence of the source P-wavefield was the difference between the source P-wave propagation angle and the reflector dips.The propagation angle of the source P-waves was obtained from the polarization vector of the decomposed P-waves.The reflectors' normal direction angle was obtained using the complex wavenumber of the stacked reverse-time migration (RTM) images.The ADCIGs of P-and S-waves were obtained by rearranging the common-shot migration gathers based on the incident angle.We used a horizontally layered model,the graben medium model,and part of the Marmousi-II elastic model and field data to test the proposed algorithm.The results suggested that the proposed method can efficiently extract the P-and S-wave ADCIGs of the elastic-wave reverse-time migration,the P-and S-wave incident angle,and the angle-gather amplitude fidelity,and improve the MVA and prestack inversion.