| Seismic tomography technology has become one of the most effective methods onstudying the earth’s internal structure and the anisotropy, and seismic traveltime tomographyis a method of studying underground velocity structure. Generally speaking, seismic raytracing is an important part of seismic traveltime tomography methods. There are many raytracing methods, such as the shooting method, the bending method (or pseudo bendingmethod) and the Gaussian beam method; the grid-cell based method, such as thefinite-difference Eikonal equation solver (FD) and the shortest-path method (SPM); and thecombined method, such as the wave front construction method.Meanwhile there are somecurrent algorithms, such as multiple arrival tracking and multi-valued wave front tracing (e g,the level set method and the phase space method).Generally speaking, the forward problem is perfect, and its causality is clearly, but theinversion problem is very difficult essentially, its multi-solutions are still with us, this makessome phenomena hard to explain. There are many inverse methods, such as the least squaremethod, the Monte Carlo method, the steepest descent method, the Newton method, theconjugate gradient method and the subspace method.This research paper mainly includes three parts:(1)In the seismic forward modelingmethods, we focus on the fast marching method(FMM);(2)In the seismic inversion methods,we concentrate ourselves on subspace method;(3) We conduct seismic tomographytechnology by combined the subspace inversion solver with the multistage fast marchingmethod. At last, we successfully realize the traveltime tomography with both the fist arrivalsand reflected arrivals, the numerical result of tomographic image is good in general. Thismethod has important research significance and practical value to application of multiplewaves and improving tomography resolution. At the same time, it has wide usage to delineateand explain the complex velocity structure. |
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