Angle gathers for depth migrated PP and PS data from flat and dipping reflectors

Saul E. Guevara and Gary F. Margrave

ABSTRACT

Angle gathers have been identified as an appropriate domain for amplitude and velocity analysis of prestack migrated data, especially in complex geological settings, where other gathers appear prone to errors. This report analysis angle gathers from depth migration of multicomponent data, PP and PS, using synthetic data and a shot-profile PSPI (wave-equation) migration method. Two methods were applied. A ray based method was implemented to obtain the angle gathers, assuming a known velocity model. The characteristics of the method and its application to P-wave and converted wave data and to horizontal and dipping reflectors are illustrated through data generated using two simple models, namely one with a flat interface and the other one with a dipping interface. Ray tracing, as well as Finite Difference (FD) modeling, were used to obtain the synthetic data for migrationfor comparison. An analysis of amplitudes was considered by means of a comparison between the theoretical results according to the Zoeppritz equations, and the actual results obtained. Another method, due to Ricker and Sava (2002), and based in the extended imaging condition, was also applied to the same data. It showed meaningful results with PP waves. However the results with PS-waves appear less evident.

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