Kirchhoff prestack time migration of PS-wave data for the layered anisotropic medium
层状各向异性介质转换波克希霍夫叠前时间偏移

The method of calculating travel times of seismic wave in Kirchhoff pre-stack time migration (PSTM) plays an important role of determining the quality of imaging for large offsets. The travel times are computed by the non-hyperbolic equation based on single layer anisotropic medium in the conventional 3D PS-wave anisotropic PSTM equations so that the events are over-migrated in common imaging point gathers (CIP) when the offset/depth ratio is greater than a threshold value. The uneven events have negative effects on migrated stack response, decrease frequency and lead to contaminating the quality of imaging. We proposed a new method to calculate travel times based on the layered anisotropic medium in PS-wave PSTM technology utilizing the migrated velocity model which was generated in the conventional 3D PS-wave anisotropic PSTM. The new method can improve the precision of travel times for the large offsets and overcome the over-migration events for a large offset/depth ratio in CIP gathers. The realistic 3D PS-wave data from two areas of West China demonstrated that the continuity and resolution of imaging section had obviously been improved by using the new PSTM comparing to conventional PS-wave PSTM and enhanced the interpretation of structures on imaging section.