材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
既知の情報を用いた制約付き速度再構成による弾性波トモグラフィ解析の精度の向上
渡辺 俊樹藤本 顕治佐々 宏一
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1995 年 44 巻 502 号 p. 874-879

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A constrained velocity reconstruction method was developed by use of a priori information to improve the accuracy of seismic traveltime tomography. Constraints are required to reduce the reconstruction error caused by the non-uniqueness of nonlinear inverse problems. In this method, the lower and the upper limits of the velocity (slowness) values are given to each cell to constrain the velocity (slowness) of the cells. These values are estimated by use of a priori information such as the results of other geophysical testings and the geological knowledge of the site. The allowable range of the velocity limitation is to be varied according to the reliability of the estimation. At first, slowness of each cell is assigned by using a usual inversion technique. If the slowness of some cells violates the given constraints, the slowness of such cells is fixed to the boundary value of the limitation. The contribution of these cells to ray-paths is removed. Then the traveltime or the traveltime residual is redistributed to the rest of cells. This process is to be repeated until the slowness of all cells satisfies the constraints. It is quite easy to implement this method of constraints for any types of inversion technique. The result of numerical simulations shows that both the time residual and the reconstruction error are considerably reduced by applying constraints on velocity reconstruction. This method is quite practical for the application to field data, because one can easily take geophysical and geological knowledge into tomography analysis.

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