Abstract：To overcome difiiculties of structure mapping in low-amplitude and deep or ultra deep structural area, this paper proposes a tomographic variable-velocity structure mapping method. Combining geologic, seismic, and log data, this method is different from the existing variable-velocity structure mapping methods. considering sedimentary basins as divided into threefold structure, viz. before forming period, forming period, and after forming period, 3D seismic interpretation is performed on a few geological fields. Using sonic logging data with interval velocity, interval time difference, and its thickness, an interval velocity Held is bul. Isopach maps can be obtained by multiplying interval velocity field and its time difference. So strati-graphic structures can be mapped by combining different isopach maps. This method coincides with geologic theory, and also coincides with theory of seismic waves. Results obtained from the tomographic variable-velocity structure mapping method are closer the true geology.
