First-arrival Wave Seismic Tomography Research

The research of the internal structure of the Earth has always been a very important basic science in the development of the long river of Geophysics. Seismic tomography is an effective means that can reflect the internal structure of the Earth. Through the development and effective use of seismic tomography technology, the internal structure of the Earth has been a deeper understanding by people, and the future scientific research and the use of ecological resources has been enhanced profitably.This paper reviews the history of the tomography and geophysical inversion, and described the current development of tomography and geophysical inversion at all over the world, especially for first-arrival wave seismic tomography.First-arrival wave is the first acceptable waveform by station, First-arrival wave tomography can reduced the precision errors because of the judge for waveform and reading for arrive times, has been accepted and licensed by more and more people. In this paper, the Asakawa method-based linear travel-time interpolation method of the ray tracing has been improved and expanded. For the first-arrival wave two-dimensional ray-tracing method, Newton travel-time interpolation method replaces the original linear travel-time interpolation. From the numerical simulation calculated results, it's obviously found that the accuracy can be significantly improved and the advantages of the original algorithm that can trace multi-wave also be retained, and the effectiveness and accuracy of tomography has been enhanced better. For the first-arrival wave three-dimensional ray-tracing method, through linear travel-time interpolation to grid border and partial derivative calculation, the location and travel-time of the intersection point can be confirmed. Through go on using forward-backward ray-tracing process, all the grid nodes travel-time and any place ray path can be calculated. From the numerical simulation calculated results, it's obviously found that the accuracy of the algorithm increases with the surface mesh subdivision, and the method meets the Fermat theorem. At the same time from the inversion results can find that the algorithm fit the horizontal block model and the condition of speed abnormity.Make use of three-dimensional ray-tracing method to seismic tomography and seismic tomography; first-arrival wave; velocity structure; the earthquakes concentrated region...