Abstract: The study results of low-amplitude structure in Tuohula-Sandaoqiao area of Kuche depression in Tarim basin are summarized, based on which this paper presents the technique for mapping deep low-amplitude structures. The technique can be used to improve the mapping accuracy of low-amplitude structures, verify local structures, reduce risk for exploration. The key of the mapping technique is in un-derstanding of seismic velocity, in which the main procedures are described as following: 1) calculation of interval velocity from Dix formula and obtaining the average velocity by using the stack velocity; 2) calculation of pseudo average velocity from drilling geologic zonation data and seismic interpreted interval as well as its transversal variation gradient; 3) analysis and correlation of the average velocity and variation (i. e. velocity and gradient matching); 4) averaging the difference between steps 2) and 3), and making correction by Kriging interpolation tech-nique; 5) correlation of t₀ interpretation and average velocity change; 6) consideration and remove of 3D boundary effect, and 7) making time- depth conversion.

Key words: seismic velocity, velocity analysis, low-amplitude structure, mapping technique