Study And Application Of The Forward Modeling In Seismic Computerized Tomography

The seismic Computerized Tomography is one of an important geophysics technology utilized to obtain the medium information in the course of wave breaking process of the earthquake and on the ray route by analyzing kinematics and dynamics characteristic of seismic wave while penetrating through the earth. The medium information in different depth of the earth can be obtained either by natural earthquake or by artificial earthquake according to different researching purposes and needs. But the observing precision and realizing efficiency of seismic Computerized Tomography is directly influenced by the forward modeling technology of seismic wave which is a key step in the processing course of CT observation and it is essential to focus the study on the forward modeling simulation technology of seismic wave. Based on existing methods, a new kind of forward modeling simulation method, the dynamic scanning method, is proposed and realized by the developing of the forward modeling system. By comparative study, the global error of dynamic scanning method is about 10-6s, the mean deviation of relative error for dynamic scanning method is under 1.5 which is less than that of the shortest path method more than 25. Based on the high accuracy, separately imitating the spread of seismic wave in different geological model inland from time field and space field, its result is in conformity with fact basically. Under observation system of cross-well CT, the first break rule of seismic wave is simulated and the relational expression between the first break and the depth is established. In addition, the unusual body in the model is identified by seismic wave-fronts. Except for the above-mentioned works, the researches on several velocity functions of near-surface layer with variable velocity and seismic wave propagation law have been completed. Equations of wave-front and ray-paths in a continue velocity medium with vertical as well as horizontal velocity gradients are deduced which prepare the theoretical basis for the subsequent forward problems of first arrival times. The basic principles of all forward modeling methods and their processing courses are discussed and based on these methods the dynamic scanning method is proposed. The forward modeling of the reflection wave is completed on the basis of the computerized processing system developed for the classical ray method.The mian initiative of this paper: under observation system of cross-well CT, the simulating process of the first break rule of seismic wave is achieved by accurate dynamic scanning method, and the methods, which identifying the unusual body in the model by seismic wave-fronts and establishing the relational expression between the first break and the depth by the forward modeling, is proposed and realized.