Extraction of P- and S-wave angle-domain common-image gathers based on first-order velocity-dilatation-rotation equations

Abstract

Accuracy of angle-domain common-image gathers (ADCIGs) is the key to multi-wave AVA inversion and migration velocity analysis, and of which Poynting vectors of pure P- and S-wave are the decisive factors in obtaining multi-component seismic data ADCIGs. A Poynting vector can be obtained from conventional velocity-stress elastic wave equations, but it focused on the propagation direction of mixed P- and S-wave fields, and neither on the propagation direction of the P-wave nor the direction of the S-wave. The Poynting vectors of pure P- or pure S-wave can be calculated from first-order velocity-dilatation-rotation equations. This study presents a method of extracting ADCIGs based on first order velocity-dilatation-rotation elastic wave equations reverse-time migration algorithm. The method is as follows: calculating the pure P-wave Poynting vector of source and receiver wavefields by multiplication of P-wave particle-velocity vector and dilatation scalar, calculating the pure S-wave Poynting vector by vector multiplying S-wave particle-velocity vector and rotation vector, selecting the Poynting vector at the time of maximum P-wave energy of source wavefield as the propagation direction of incident P-wave, and obtaining the reflected P-wave (or converted S-wave) propagation direction of the receiver wavefield by the Poynting vector at the time of maximum P-(S-) wave energy in each grid point. Then, the P-wave incident angle is computed by the two propagation directions. Thus, the P- and S-wave ADGICs can obtained Numerical tests show that the proposed method can accurately compute the propagation direction and incident angle of the source and receiver wavefields, thereby achieving high-precision extraction of P- and S-wave ADGICs.