FREQUENCY DOMAIN REVERSE TIME MIGRATION FOR ACOUSTIC-ELASTIC COUPLED MEDIA USING THE WAVEFIELD SEPARATION METHOD

摘要

Recent research results concerning frequency domain reverse time migration based on the adjoint-state of the acoustic wave equation have highlighted several limitations imposed by the use of an acoustic-based algorithm. In marine seismic exploration, targeted areas are located within elastic media. Elastic wave components, such as S-waves, surface waves and mode converted waves can remain obscured by reverse time migration based on the acoustic wave equation in the targeted media. Several research papers addressing the topic of acoustic-elastic coupled media with full waveform inversion have shown that this method can generate more accurate inversion results for P-wave velocity models than acoustic-based algorithms. This paper formulates the frequency domain reverse time migration for acoustic-elastic coupled media based on the adjoint-state of the wave equation. It goes on to adopt the wavefield separation method to reduce the effects of crosstalk artifacts on migrated images. The validity of the proposed algorithm is demonstrated using a synthetic dataset generated by elastic staggered grid time modeling. The image of the frequency domain reverse time migration for acoustic-elastic coupled media calculated using the wavefield separation method is then compared to the results of the acoustic reverse time migration and reverse time migration for acoustic-elastic coupled media using a conventional zero-lag cross-correlation approach. Comparison of the migration images revealed that the images of acoustic-elastic coupled media from the wavefield separation method resolved geological structures with greater accuracy and exhibited fewer noise-contaminated components than those obtained from the acoustic and conventional acoustic-elastic coupled media imaging methods. We also analyze the reverse time migration method's sensitivity to correct P- and S-wave inputs and density model assumptions.