1989 年 42 巻 3 号 p. 391-403
We review recent theoretical studies on wave propagation in the near field of seismic sources. These include theories for horizontally layered media as well as those for irregularly layered media. Ray theory and its extensions are easily applied to arbitrarily inhomogeneous media, but they include serious approximations. The finite difference method is also flexible, but requires extensive computation. Except for these methods, we should note that all the methods currently available for irregularly layered media belong to the category of the method of weighted residuals.