Joint Migration Velocity Analysis Of PP And PS-waves In The Angle Domain

Joint migration velocity analysis of PP and PS waves in the angle domain consists of the following steps:(1) Extracting the artifact-free ADCIGs of PP and PS waves based on elastic Kirchhoff migration and the extended imaging condition;(2) Assessing the accuracy of the migration velocity according to the ADCIGs flatness criterion and the PP and PS waves image-depth consistency principle;(3) if the conditions above are satisfied, then establishing the precise migration velocity fields; otherwise, updating the migration velocities in accordance with the velocity updating functions in angle domain and repeating the process above again until the conditions are satisfied. To improve the accuracy of joint migration velocity analysis of PP and PS waves in the angle domain, this paper focuses on the calculation of the original migration velocities of PP and PS waves and the migration velocity updating functions in angle domain.As one of the fundamental input data, the initial velocity will influence the accuracy of migration velocity analysis. To obtain the initial velocity, this paper proposes a velocity analysis method for PP and PS waves running on common normal emergence point gathers based on the theory of elliptic development of reflections, which abandons the constrains of horizontally layered media and is able to obtain the accurate RMS velocity, and thus improves the accuracy of data processing. Furthermore, initial migration velocity fields of PP and PS waves can be determined by a conversion from time domain to depth domain.The existing migration velocities updating functions in the angle domain are usually based on various assumptions whose range of application is limited. To solve the problems, this paper combines the geometrical relationships, the equal travel-time principle, the distribution equations for all possible reflection points and the Snell’s law, which are valid in the propagation of seismic waves, and further derives new residual depth equations of PP and PS waves that can be applied to dip interfaces. The derived equations are more accurate and have a wider range of application, which makes it possible to update the migration velocities of PP and PS waves more efficiently.The method presented in this paper is tested on synthetic data and real data. The results show that better initial migration velocity fields of PP and PS waves can be determined by the velocity analysis of PP and PS waves based on the elliptic development method, and the joint migration velocity analysis of PP and PS waves in the angle domain has a higher accuracy with the proposed residual depth equations.