地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
ジオ・トモグラフィの基礎
笠原 順三
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ジャーナル フリー

1995 年 104 巻 7 号 p. 913-921

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The “Geo-Tomography” is now an essential tool to study geo-sciences.
There are severalapplications of tomography in geophysics. e. g., seismology, geodesy, geomagnetism, gravity, etc. The tomography using cosmic ray, “Muons”, is a new application. In this paper, theauthor intends to give a general view of the geo-tomography and present the relation amongdifferent methods. Detailed description of each application is described by different authors inthis special volume.
There are several different methods in tomography: Matrix method, ART or SIRT, CG, backprojection, backpropagation, p-tau trans form and Fourier method. These are overlappedeach other by some extents. The tomography initiated in the medical use and it is called “C omputed Tomography”. In the medical use, sets of (X-ray) parallel projections along lineswith a constant angle to the reference axis are used. In the filtered backprojection method, the convolution of the result of parallel projection to filter-function is integrated over wholeprojection angles. In the contrast with the medical projection method, geophysical applicationsof tomography tend to be limited in narrow projection angles. This narrow aperture will blurthe real image.
Several methods have been used in the geo-tomography. DLSQ, SIRT and CG are themost powerful tools for traveltime tomography such as crosshole-VSP tomography and seismictravel time tomography. Recently, waveform inversion using high-frequency seismic wavessuggested its powerfulness to obtain the fine structure of the earth. However, since the waveforminversion has a nature of strong nonlinearity, it is necessary to use traveltime tomography withor in advance of the waveform inversion.

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