Abstract
Wave noises or coda part of seismic waves may be interpreted as composed of single or multiple reflection waves as well as of dispersive or induced surface waves. Sometimes reflection waves observed on seismograms are due to various composite reflections caused by a set of closely spaced reflecting surfaces. Here we assume that the wave medium consists alternatively of two kinds of elastic layers whose thickness is such that the wave travelling time through each layer is just the same. Since this is a kind of regular system, it may represent the case of largest effect of multiple reflections.
The results obtained theoretically in this paper are as follows;
1) Reflections of higher orders cannot be neglected.
2) In our rough estimation, the general appearance of resulting waves is determined by the value “Na”, where N is the number of layers between the source and the receiving point, “a” is a constant relating to the reflecting factor “k” (a=k2/1-k2).
3) The attenuation and reverberation of waves and elongation of wave length are noticed in some cases, but their characters are too much complicated to be expressed in a simple formula.
4) The wave reverberation is remarkably reduced for long waves and a very long wave (the wave length more than eight times of the thickness of a layer) travels as if it were propagated through a homogeneous medium, though there can be seen some slight change in its wave form.
