Applications And Researches Of Refraction Seismic Tomography Method In Xi'an Ground Fissures

The seismic tomography is a new method founded on the computerized tomography (CT) and is effective for investing and understanding the geologic framework.It is extensively applied to the field of geology disaster and geo-exploration and so on.It is a technique which uses seismic date to invert the material attribute of underground structure and determine the fine structure of the earth interior and regional in-homogeneity.It includes model parameterization,forward modeling calculation,and invert calculation,its key is invertion technology.On the basis of extesively referring to domestic and foreign documents, this article introduce the forward and invertion calculation theory of seismic tomography and contrast the three invertion algorithm.The article introduced LSQR which simulate to invertion Xi'an ground fissure theoretic geology model and make sure this method's preciseness and feasibility.In the end of the paper,it is successful to apply the technology of the refraction seisimic tomography to the exploration of Xi'an ground fissure.In this paper,the main contents of chapters as follows:The part of prolegomenon discussed the development of CT technology,and introduced the basic conception of the CT,its sort and the present research.Chapter 2 introduced the basic principle of the seismic wave and discussed the equation to the trend curve of refracted wave.Chapter 3 introduced the basic invertion model theory of CT,by the forward and invertion theory modle of CT,and compared the three invertion calculation.Chapter 4 introduced the method of making tracks for radial and its basic theory,designed the theory model,according to the practical geological situation of Xi'an ground fissure then made a forward and invertion calculation.At last it deal the practical exploring seismic date of the Xi'an ground fissure with CT,which generalize velocity field around rapidity section plane. The velocity within ground fissure is apparently different.The result coincided with real situation.CT firstly apply to the physical prespection of Xi'an ground fissure.By the above research,the achievement as follow:1 After comparation of the ART,SIRT,LSQR,it is proved that LSQR method is good at inversion speed,stability and precision.2 It is successful to prob the Xi'an ground fissure,accuratly determine the position, tendency,azimuth of the ground fissure in refraction seismic tomography profile.3 On the baise of not increasing the conventional reflected wave workload from sismic exploring to use refractive wave information,which can determine velocity field of stratum secion.It just offset vacancy of Xi'an ground fissure refractive wave seismic survey.