SORTING OF CONVERTED WAVE DATA IN THETAU-P DOMAIN

摘要

Converted-wave (P-SV) data are characterized by asymmetric ray paths caused by therndifferent velocities of the down- and upgoing wavefield. In contrast to pure-mode (P-P) data,rnthe conversion points of P-SV data are not located beneath common midpoints (CMP), evenrnin a 1D medium, but describe a trajectory that moves from the asymptotic conversion pointrnfor small offset/depth ratios towards the receiver for larger offset/depth ratios. Commonrnconversion point (CCP) sorting is required to correct for the conversion-point dispersal beforernstacking, and before pre-stack amplitude analysis. Sorting is typically achieved by solvingrnanalytic approximations describing the conversion-point trajectory or by pre-stack timernmigration.rnAn alternative data-driven CCP sorting technique was applied to data from a recent marinernmulti-component survey where sorting and stacking was done in the tau-p domain. Thernquality of the P-SV stacked section after applying this new CCP sorting technique was similarrnto that achieved by depth-variant converted-wave mapping. However, pre-stack amplitudesrnwere found to differ significantly after CCP sorting as predicted, and it is recommended thatrnP-SV AVO analysis is performed only after CCP sorting. Pre-stack amplitude analysis is notrnpossible using the conventional sorting techniques since they directly create a stacked trace.