抄録
Explosion seismic data in two regions are studied by utilizing the time-term method. The results of two profiles in the Matsushiro earthquake swarm area agree very well with the previous models by ASANO et al. In one profile, the travel-time residuals plotted in the ordinate to distances in the abscissa show a convex tendency which strongly suggests vertical velocity gradient in the basement layer. The distance-dependent velocity is determined accurately with the modified time-term method.
Some defects in the model by HASHIZUME et al. for the Kesennuma-Oga profile are removed by the model obtained with the time-term method in the present study. It is particularly remarkable that the possibility of the lateral change in the Pn velocity near the Honshu-Japan Sea boundary is pointed out.
