Applications And Researches Of The Seismic Tomography With First Break Phase And Shortest Path Method In Near-surface

Seismic tomography is a new method that has been developed on the basisof Computerized Tomography (simply CT). It uses seismic data to invertmaterial properties of the underground medium, which is an effective means ininvestigating and researching underground geologic structure. It was widelyapplied in the field of energy and mineral development, engineering survey,geological disaster assessment and so on.The thesis realized a set of methods for tomographic inversion of seismicfirst break aimed at complex near-surface problem in seismic prospecting. Thismethod was to use first break travel-time and ray path in inverting the velocitystructure of medium. It had the advantage of the vertical and horizontal variablevelocity and using direct wave, diving wave, refraction wave, combination ofthe three to realize inversion in complex surface model that the velocity can varyarbitrarily. Through processing the theoretical model and real data, thesis provedthat the method was correct and effective. Firstly, this thesis briefly reviewed the development process of seismictomography and the current research status of existing methods around firstbreak seismic tomography. Furthermore, we introduced theoretical basis of firstbreak travel-time tomography, mainly describing the shortest path ray tracingand inversion algorithm of tomography, deducing primary algorithm,programming the ray tracing method of the shortest path ray and the LSQRinversion algorithm.On this base, we finished the forward modeling, analyzing the effect andinfluence factors. The results proved that the shortest path ray tracing algorithmwas an effective and precise method, and the error would reduce as increasingmesh and expanding the search radius. And then, through combining with LSQRinversion algorithm the paper completed trial of theoretical model and gat agood inversion effect, verifying the validity and feasibility of the shortest pathray tracing method and the LSQR inversion algorithm.In the end, for actual seismic data the thesis used first break travel-timetomography to invert velocity, we acquired reliable near-surface speed mode. The results of the treatment was consistent with actual geological condition,validated again the method was reliable in practical application.