Cross-hole Seismic Tomography Study

Cross-hole seismic tomography is a high exculpation rate seismical investigation technique which can explore circumstance of underground medium by seismic wave. Based on the basic principle of cross-hole seismic tomography, this paper detailedly discussed the data acquisition, the choice of instrument, the design of system, and the edition and handle of originality data, numerical imitation of the positive deduce, research of inverse algorithm. At last, the software of seismic tomography was programmed.This paper mainly introduced two methods of picking first break which are the largest Signal-to-Noise and the Ratio of energy. Vidale method (finite-different method of the eikonl equation ) and the LTI method were discussed detailedly in ray tracing algorithm, deduction and realization of algorithm were discussed too. It proved that Vidale method was a especial example of LTI method by deducing formula. But the result of data using LTI method in rays tracing was more accuracy than that using Vidale method in rays tracing. A new rays tracing method called parabola traveltime interpolation method (PTI) was proposed in this paper .By giving theories model and processing ray tracing, it showed that PTI arithmetic was more higher accurate than LTI algorithm. The problem of cross-hole seismic tomography reverse can be deduced to solve a large sparse matrix. This paper discussed the LSQR algorithm , and given the main calculating procedures of LSQR algorithm .The software of LSQR algorithm was programmed in Matlab language. The inverse image gotten from LSQR algorithm using BPT algorithm's inverse initial velocity indicated that the inverse algorithm worked efficiently.