The reflection of elastic waves at a solid-solid boundary in elastic media has been treated by many authors. But there have been only a few papers on the reflection of the waves at a solid-viscous fluid boundary. In this paper, the author treated this probrem in detail, comparing the solid-fluid reflection with the solid-solid one, especially with respect to amplitudes.
The results obtained are as follows; if the incident waves are of infinite coherence of sine-waves, the amplitude of the reflected waves is not effected so much by the density ratio (ρ′/ρ) as by the ratio (ρ′νp/ρμ) and is twice as much as that at a solid-solid boundary, if the incident angle is small and the ratio (ρ′νp/ρμ) is not close to unit. If the incident waves are of finite coherence of sine-waves with “zero-angle” incidence, the reflected waves are deformed slightly at their heads and tails, but the amplitudes are the same as in the above mentioned case.

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In determining the instrumental magnitude of an earthquake we often experience that magnitudes determined for the same earthquake at different stations differs considerably from one another.
In the present paper, the discrepancies which are caused by the mechanism of an earthquake occurrence are investigated in the case when the magnitudes are determined by amplitudes of surface waves at each station.
We investigated in particular, the seismograms of the earthquake which occurred off the coast of Boso Peninsula, Japan, Nov. 25, 1958, recorded at 29 stations in various azimuths, and computed the energies of Rayleigh waves corresponding to the respective stations. The discrepancy which happened in magnitudes deduced from the energies are discussed.
The results obtained are as follows:
1) The relation between the energy of Rayleigh waves and the azimuth is expressed by formula (3) or figure (1).
2) The maximum discrepancy of magnitudes owing to the difference in azimuth is about 0.7 in magnitude scale.

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First, the free vibration of the coupled system is discussed. It is mathematically proved that the vibration is always damped.
As an extreme case we have undamped harmonic vibrations. The necessary and sufficient conditions for this case are given. Namely, the coupling factor σ²=1 and the proper period of the pendulum is equal to that of the galvanometer.
Second, the case, that the galvanometer and pendulum are respectively critically damped, is solved.
Movements of a galvanometer in the early stage of a forced vibration are given.
Third, a realistic example is given, that is, ε₁=n₁, ε₂=n₂, n₁=2π/4.5sec^-1, n₂=2π/7.5sec^-1, σ=0.15, and the circular frequency of a sine motion, Asinωt, of the earth, commencing at t=0, is ω=2π/4sec^-1.
In fig. 1.
φ₀: An incident wave 0.179sin2π/4t.
φ₁: Free vibration excited by the sudden commencement of the incident wave.
φ₃: Forced vibration caused by the infinite train of the incident waves.
φ: Movements of the galvanometer finally obtained.

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The state of stress and seismic wave attenuation characteristics near an explosive seismic origin in a viscoelastic medium are investigated. For this purpose, the seismic records obtained by the Seismic Exploration Group of Japan are analysed. In the experiments the SIE magnetic tape recording system and ETL three-element-type detector are used. The seismic records are obtained at four points, 15, 45, 75, and 105 meters apart from the source. These points are all 12 meters in depth under the ground.
The wave attenuation characteristics are obtained by the comparison of Fourier components of bodily waves at various distances from the seismic origin. The attenuation law can be approximately explained by the viscoelasticity of Voigt type of the medium. An approximate law of the decrease in amplitude with distance is determined. The decrease in amplitude with distance r is intermediate between 1/re^-αr and r^-n(n=2.22).
The state of stress near seismic origin is deduced from the wave velocity and the coefficient of viscosity. The model of wave generation mechanism is assumed. The theoretical wave motion resulting from the application of a pressure pulse of a form p₀(1-e^-αt) to the interior surface of a spherical source agrees with the observed motion if the radius of spherical cavity equal to 5-10 meters is assumed.

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