RELATIONSHIP BETWEEN RAY DISTRIBUTION AND RECONSTRUCTED VELOCITY IMAGE IN REFLECTION TOMOGRAPHY

The present paper studies the relationship between seismic ray distrib ution and reconstructed velocity image in reflection seismic tomograph y method. In travel time seismic velocity tomography, the result of ve locity inversion is restricted by seismic rays. There are two meanings of seismic rays. The first one is the geometric paths of seismic rays , and the second one is the uniformity of seismic ray distribution und erground. There is great interest in calculating accurate paths of the seismic rays, however, in this study, we discuss primarily the second problem. In the result of seismic velocity image, some of the events are formed by a geological body, some of the events are not formed by a geological body. We call the events as pseudoimages that are not for med by the geological body. Although we have already tried our best to remove the pseudoimages in the inversion algorism, they certainly app ear in the result of the velocity image. There may be many reasons for pseudoimages. In this paper, an effect by nonuniformity of seismic ra y distribution is principally discussed. Pseudoimages will appear in t he case of nonuniformity of seismic ray distribution in the inversion calculation. In our study, we used one geological model for simulation studies. The conclusion from the results of the simulation study is: Nonuniform rays can lead to false velocity disturbance in the result o f the velocity image. The result of this study has a directive functio n to the field data acquisition method and geological interpretation i n seismic reflection tomography.