Imaging artefacts of artificial diving waves in reverse time migration: cause analysis in the angle domain and an effective removal strategy

Abstract

ABSTRACTIn areas with strong velocity gradients, traditional reverse time migration based on cross‐correlation imaging condition not only produces low‐frequency noise but also generates diving wave artefacts. The artefacts caused by diving waves have no typical low‐frequency characteristics and cannot be eliminated by simple high‐pass filtering approaches. We apply the wave‐field decomposition imaging condition to analyse the causes of false images in reverse time migration by decomposing the full wave‐field into up‐going and down‐going components in the angle domain. We find that artificial diving wave imaging artefacts, which are generated by the cross‐correlation between the up‐going source and down‐going receiver wave‐fields in areas with strong velocity gradients, arise at large angles. We propose an efficient strategy by means of the wavelength‐dependent smoothing operator to eliminate artefacts from artificial diving waves in reverse time migration. Specifically, the proposed method provides more reasonable down‐going wave‐fields in areas with sharp velocity constructs by considering the factor of varying seismic wavelengths during wave propagation, and the artificial components of diving waves are eliminated in a straightforward manner. Meanwhile, the other wave‐field components that contribute to true subsurface images are minimally affected. Benefiting from a smoothed velocity, the proposed method can be adapted to the traditional reverse time migration imaging frame, which reveals significant implementation potential for the seismic exploration industry. A salt model is designed and included to demonstrate the effectiveness of our approach.