In the previous paper, the author deduced dispersive wave forms expected at various distances from the origin due to various initial pulses and dispersions. He investigated the validity of the conventional method of analysis of observed results for determining the crustal structure. In the present paper, he assumes a simplified dispersion curve which is similar to a rigorous one for some seismic surface waves and investigates the method of analysing observed results, that will give the best agreement to the true dispersion curve of surface waves in the crust under consideration. The results are as follows;
(1) At a certain epicentral distance, the duration of oscillations of seismic waves is independent of the thickness of the layer but the larger is the thickness of the layer, the longer become the periods of waves. If the thickness is the same, the duration becomes the longer, the larger is the epicentral distance. In the case of the same distance and thickness, the larger is the velocity- or rigidity-ratio of lower and upper media, the shorter are the periods of waves.
(2) The relation between group-velocity (U_n) and period (T_n) should be taken as U_n=Δ/2[1/t_n+1/t_n+1], T_n=2(t_n+1-t_n)(cf. Fig. 8).
(3) The relation between phase-velocity (c_n) and period should be taken as c_n=δ/2[1/t_{2, n}-t_{1, n}+1/t_{2, n+1}-t_{1, n+1}], T_n=(t_{1, n+1}-t_{1, n})+(t_{2, n+1}-t_{2, n}) (cf. Fig. 9).
In the case of tripartite array, we can obtain the corresponding relation by the equation (41) and (42) in this paper. In this case, we must take δ smaller than c_n×T_n, in order to avoid misidentification of troughs and crests for different stations.

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In this paper, the present author investigates the character of refracted waves which are generated by a periodic SH-type line source situated in one of two homogemeous, isotropic, semi-infinite elastic media in horizontal contact. He takes πH₀(κr) as the source, and has obtained the following expression for the displacement due to refracted waves.
V=1/πυ³√υ/γ(υ²-1)(L_s/x)^3/2e^-i{√κ²-κ′²(z+H)+κ′x}+ipt+π/4i+π/2i
Here, υ is the velocity ratio of the waves in the two media, γ the density ratio and L_s means the wave-length of S-waves in the softer medium. And x is the epicentral distance, while the exponent gives the travel-time and phase lag of the waves.
Moreover, he has found the waves are not aff eced very much by the existence of the free surface.

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Two rotation seismometers are built in order to observe rotational movements of thee ground around the vertical (z-) axis. If the construction and characteristics of these two seismometers are exactly equal, and if they respond to no other movements than rotation around z-axis, the output signals from them must be perfectly equal (correlation coefficient between the signals is just +1) when they are set up closely to each other buf in different azimuths. By observing the correlation coefficient between them during the adjustment, the writer successfully constructs a pair of reliable rotation seismometers. The sensitibity of the seismometer is such that a rotation of 0.1″ produces a deflection of 1cm on recording paper.

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In this study, an analysis was made of earthquake waves recorded with a magnetic tape recorder. A velocity seismometer with a magnetic tape recorder was operated intermittently at Mt. Tsukuba from November 30, 1957 to December 9, 1957, and about 400 near-by earthquakes were recorded in 25 hours in total. Since the records are taken with a tape recorder and are therefore reproducible, various characteristics of the seismic waves other than velocity can be obtained by means of electric circuit device and investigated. First the relation between predominant periods and maximum trace amplitudes of the seismograms reproduced from the magnetic tape was studied. Acceleration seismograms were also obtained from the records of the velocity seismometer through a differentiating circuit, and the frequency distributions of maximum acceleration (α) and maximum velocity (υ) amplitudes are compared. They are found to be expressed by the following equations respectively,
N(υ)dυ=κυ^-mdυ, (1)
N(α)dα=κ′α^-m′dα, (2)
where, m=1.82, m′=2.05.
From these values of m and m′, we can deduce the relation between predominant periods (T) and υ; T=const.·υ^0.22. This equation is transformed into the relation between T and A (maximum displacement);
T=const.·A^0.18.. (3)

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