Abstract：Based on the 3-D prestack depth migration results in Tianshan southern margin, the paper built up 2-D seismic-geologic model of Yakenbei area. In the design of model, we considered the gravel layer with high velocity that rapidly changes in lateral direction in Quaternary Xiyu Formation of shallow layer in Yakenbei area and the low-velocity gypsum mudstone layer that significantly changes in structural feature in Tertiary Jidike Formation of deep layer. The shot gather records were computed by simulation of field geometry in the area, then the common stack velocity and stack-migration sections were further yielded, with which the practical mean-square-root (msr) velocity values of the model and seismic-geologic models ware correlated. It is shown by analyzed results that the velocities gradually changing laterally above the target makes the stack velocities be lower than msr velocities; existence of shallow gravel layer makes the stack velocities be higher than msr velocities above the target. Abovementioned both integrative influences make the stack velocities increasing by 8% in comparison with msr velocity. The influence of shallow high-velocity gravel layer on time imaging of underburden is lower, but makes the stack velocities higher in deeper parts on both sides of high-velocity gravel layer, leading depth section to produce false sag image, and also to increase the structural variation amplitude near sag. Therefore, there is important meaning for guiding the error correction of common velocity analysis that quantitatively analyzing the errors of ordinary velocity analysis produced by velocity anomaly of two anomalous velocity zones: shallow high-velocity gravel layer and low-velocity gypsum mudstone layer in Yakenbei area and variation law.
