Applications And Researches Of First Break Seismic Tomography

For the surface seismic survey, elevation, lithology, velocity, structure, etc. of near-surface will lead to seismic profiles phase distortion, greatly influences the image of stacked section and the structure,is an important factor constraining seismic exploration. Thesis used travel time and path of seismic first break aimed at complex near-surface problem in seismic prospecting, providing velocity information through reasonable travel time inversion.Firstly, this paper briefly reviews the development process of ray tracing and tomography inversion around seismic tomography of first break. Furthermore, the paper analyzed the regularity of propagation and style character of first break in surface model based on the regularity of seismic wave propagation. Programming in this thesis realized the method of shortest path ray tracing based on Fermat's principle. This method is to use beelines of the minimum travel time between the network nodes to approximate seismic ray paths, at the same time, it can calculate traveltime and corresponding ray paths of all points from source to space. The important is that ray-theory can not constraint it and traveltime are minimum.Finally,we describe two inversion methods:algebraic reconstruction technique (ART), simultaneous iterative reconstruction technique (SIRT), realized programming.At the end of paper, we introduce the process of first break tomography inversion, by using the theoretical model to test and by applying the method of tomography inversion of first break travel-time in surface model, we acquired reliable surface speed model and proved correctness and feasibility of shortest path ray tracing and SIRT algorithm.With a clear understanding of relationship between first break and near-surface, we could use more reasonable and more accurately the information of first break to solve near-surface problem, laying a good foundation to deal with complex surface seismic data processing.