A method for extracting P-SV-converted wave angle-domain common-image gathers based on elastic-wave reverse-time migration

Multicomponent seismic technology utilizes the kinematic and dynamic characteristics of reflected P-waves and converted S-waves to reduce ambiguity in seismic exploration. The imaging and inversion accuracy of P-SV-converted waves are important in determining whether multicomponent seismic exploration can achieve higher exploration accuracy than conventional P-wave exploration. Pre-stack inversion of P-SV-converted waves requires precise input of P-SV-converted wave angle-domain common-image gathers. Consequently, the P-SV-converted wave angle-domain common-image gather extraction accuracy will significantly affect the P-SV-converted wave inversion accuracy. However, existing methods for extracting P-SV-converted wave angle-domain common-image gathers are constrained by issues such as the P- and S-wave crosstalk artefacts, low-frequency noises and inaccurate calculation of P-wave incident angles, leading to poor imaging accuracy. We study an angle-domain cross-correlation imaging condition and address three key issues based on this condition: the decoupling of P- and S-waves, the separation of up-going and down-going waves and the precise calculation of P-wave incident angles. Our strategies facilitate high-precision extraction of P-SV-converted wave angle-domain common-image gathers using elastic wave reverse-time migration. In this paper, first, we employ the first-order velocity-dilatation-rotation elastic wave equations to decouple P- and S-waves automatically during source and receiver wavefield extrapolations. Second, we calculate the optical flow vectors of P- and S-waves to ensure stable calculations of wave propagation directions. Based on this, we obtain up-going and down-going waves of P- and S-waves. Meanwhile, we calculate the incident angle of the source P-wave using geometric relations. Lastly, we apply the angle-domain imaging condition to achieve high-precision extraction of P-SV-converted wave angle-domain common-image gathers. Model examples demonstrate the effectiveness and advantages of the proposed method.