Geophysicai Prospecting zyxwvutsr 39,1015-1029,199 1 zyxwvu MULTICOMPONENT COMMON-RECEIVER GATHER MIGRATION OF SINGLE-LEVEL WALK-AWAY SEISMIC PROFILESl G. M. JACKSON, 1. M. MASON and DELMAN LEE2 ABSTRACT JACKSON, G.M., MASON, I.M. and zyxwv LEE, D. 1991. Multicomponent common-receiver gather migration of single-level walk-away seismic profiles. Geophysical Prospecting 39, 1015-1029. Seismic data are usually separated into P-waves and S-waves before being put through a scalar (acoustic) migration. The relationship between polarization and moveout is exploited to design filters that extract the desired wavetype. While these filters can always be applied to shot records, they can only be applied to a triaxial common-receiver gather in special cases since the moveout of scattered energy on the receiver gather relates to path differences between the surface shots and the scatterer while the polarization is determined by the path from scatterer to downhole geophone. Without the ability to separate wavefields before migration, a zyxwvut ‘ vector scalar ’ or an elastic migration becomes a necessity. Here the propagation of the elastic wavefield for a given mode (e.g. P-S) is approximated by two scalar (acoustic) propagation steps in a ‘vector scaiar’ migration. ‘Vector’ in that multicomponent data is migrated and ‘scalar’ in that each propagation step is based on a scalar wave equation for the appropriate mode. It is assumed that interaction between the wavefields occurs only once in the far-field of both the source and receiver. Extraction of the P, SV and SH wavefields zyxwvut can be achieved within the depth migration (if one assumes isotropy in the neighbourhood of the downhole receiver) by a projection onto the polarization for the desired mode. Since the polarization of scattered energy is only a function of scatterer posi- tion and receiver position (and not source position), the projection may be taken outside the migration integral in the special case of the depth migration of a common-receiver gather. The extraction of the desired mode is then performed for each depth migration bin after the separate scalar migration of each receiver gather component. This multicomponent migration of triaxiai receiver gathers is conveniently implemented with a hybrid Split-step Fourier-excitation-time imaging condition depth migration. The ray- tracing to get the excitation-time imaging condition also provides the expected polarization for the post-migration projection. The same downward extrapolated wavefield can be used for both the P-P and P-S migrations, providing a flexible and effcient route to the migration of multicomponent data. ’ Based on paper read at the 52nd EAEG meeting, Copenhagen, May-June 1990; received August 1990, revision accepted June 1991. Department of Engineering Science, Oxford University, Parks Road, Oxford 0x1 3PJ, U.K. zyxwvuts 1015