Seismic First Break Travel-time Tomography And Its Application In Near-surface Velocity Model Building

The accurate velocity model building is the key for seismic exploration, especially building near-surface velocity model.There are many methods of building near-surface velocity model, such as refraction method, surface wave method, tomography method, and so on. First break tomography is shot in one place and receive the first break travel-time in another to inverse the velocity of seismic wave or the structure between shot and receiver. Through this method, the paper researches near-surface velocity model building, providing velocity information for further static correction or shallow-project seismic exploration.The paper briefly reviews the development course of the seismic tomography technology, and discusses the principle of the first break travel-time tomography. We introduce the ray tracing method of the first break travel-time and inversion algorithm of tomography, deducing primary algorithm, programming the ray tracing method of LTI and the SIRT inversion algorithm.On this base, we study and summarize forward-inversion effect and its partial influential factors, such as initial velocity model, velocity restraint condition, density of ray cover. Tests with seven theory models, one theory model with random noise, and two real data show that: 1) The LTI ray tracing method is easier, faster and more precise than the other methods. 2) SIRT algorithm can provide stable and converged solution. 3) Through the tests of theory model with random noise, it can be known that the forward-inversion algorithm in the paper has anti-noise ability. 4) The program's reliability and usability have been proved by testing with theory models and real data.