Abstract: This paper presents the analyses and discussions of several base-levels definitions, static correction methods and static computations as well as corresponding relations to individual surface structures and velocity fields that are commonly applied in production nowadays. The study shows that the common midpoint (CMP) reference surface is the smooth surface corresponding to the surface elevation without changing relations to the surface structure and velocity. The relations among the time, depth and velocity of vertical seismic profile (VSP) can be corresponded to the stratigraphic relations under CMP reference surface one by one. The methods for correction and computation of VSP's time, depth and velocity based on different base-levels' seismic data and the method for related time- depth conversion and structural mapping are proposed, which provide bases for VSP calibration, time-depth conversion and structural mapping in stage of seismic data processing.

Key words: base-level, datum, static correction, VSP, calibration, structural mapping