Study On The Cross-hole Seismic Tomography With First Break Travel Time Based On The Ray Theory

Cross-hole seismic tomography has been become an important technique in the field of production seismic, for its unique observation system and resolution which is higher at least an order of magnitudes than that of surface seismic.The paper briefly reviewed the development course of the seismic tomography technology and its domestic and abroad development present situation. Under the elementary theory of seismic exploration instruction, the method and principle of the cross-hole seismic tomography with first break travel time has been elaborated, the ray tracing method of first break travel time and the inversion algorithm of tomography have been deduced detailedly as well as, and then the programs have been compiled for the ray tracing method of linear travel time interpolation and the LSQR inversion algorithm. Finally, the algorithms in the paper have been tested with four typical models and one example. Several conclusions and cognition have been got in this paper: 1) It is easier, faster and more precise for the method of linear travel time interpolation ray tracing than that of shooting method. 2) SIRT algorithm is superior than that of ART, but LSQR algorithm is more superior than SIRT algorithm, and the LSQR algorithm convergence rate is quicker than the SIRT algorithm. 3) Through the theoretical model computation, the algorithm of the forward and inversion in the article is correct, reliable, and it has the certain compatibility to the weak anisotropic medium. 4) It is proved that the program has certain usability with the satisfied result for the actual data. 5) The inversion precision is close to the receive distance and the element size. The receive distance and the element is more slight, the inversion precision will be more high, that is the resolution will be more high.