Abstract：Crosshole seismic velocity tomography based on seismic ray theory has seen its preliminary application in oil development and shallow engineering exploration,and exhibits its good ability to cope with complicated geologic problems Some easy neglected problems in the velocity tomography using travel times of direct transmitted wave are discussed,which involve the travel time determination of direct transmitted wave ,the indefiniteness of steep-formation tomography,and the influence due to the nonuniformity of seismic rays The article also describes how we distinguish the phenomena of these problems,design crosshole model for forward computation, analyse their generation mechanisms quantitatively and qualitatively,and take some satisfactory measures for coping with them so as to improve the effect of tomography.
