The reflection and refraction of plane SH waves incident upon a high-speed layer with a constant thickness d were studied. Numerical calculations were executed in a case when B₁/B₂=0.5507, μ₂/μ₁=3.25, and medium 1 and 3 are equal, and the results are given graphically. According to the results, the so-called total reflection is considered to be taken place when d/L≥5, and no plane SH waves can be propagated parallel to the discontinuous layer.

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The earth's crust is divided into the granitic layer and intermediate layer on account of the distribution of seismic wave velocity, etc., and there is a mantle called the peridotite layer under them. These layers may have different physical properties one another, but very little is known thereof. The writer was able to see their properties, by taking the earth's crust as a visco-elastic body.
1. The damping in each layer was computed from the distributions of the amplitudes of initial motions of the seismic wave (P-wave) of near earthquakes.
The attenuation coefficients at different layers are as follows:
Granitic layer Kg=7.9×10^-7cm^-1
Intermediate layer K*=1.3×10^-7cm^-1
Peridotite layer Kn=2.9×10^-8cm^-1
2. The relaxation time was obtained, understanding this damping as due to the viscosity of the earth's crust. The relaxation times in the three layers are as follows:
Granitic layer τ_g=0.45sec.
Intermediate layer τ*=3.5sec.
Peridotite layer τn=16.5sec.
3. The fact that the distribution of velocity of P-wave in the earth's crust by the artificial explosion caried out recently at various places of the world is different from that of the seismic P-ware may be explained as a dispersion phenomena of the visco-elastic wave. It was revealed that the velocity Pgseis. caused by earthquake is about 5.4-5.75km/sec. as against Pgexpl. =6.0km/sec, of the velocity of P-wave caused by explosion of granitic layer. On the other hands the fact was revealed that there is almost no difference between P-wave velocities caused by such explosion or earthquake in the case of the intermediate layer or peridotite layer.

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A magnetic microseismic spectrometer was constructed, which is essentially an ordinary no-damping torsion seismometer placed in the magnetic field of a Helmholtz coil. The inertial mass which is made of soft iron oscillates in the magnetic field. The natural frequency of oscillation is continuously varied according to the intensity of the magnetic field which is controlled by the current flowing through the coil. Working characteristics of the apparatus is described. The conception of spectrum for tremors of the ground is clarified and brief considerations on the results obtained are given.

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Due to the inconsistencies between the energy and the initil motion of both the principal (1946, 12, 21) and after (1948, 4, 18) shocks of Nankaido Earthquake, the author decided that these shocks were A type (unsymmetrical pull cone type) and unable to be explained except by the magma explosion theory.

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A huge dam is now under construction at a point 3km downstream from the village of Ikari on the Ojika-gawa, a tributary of the Kinu-gawa in Tachigi Prefecture. The geology of the district specially studied by the writer is briefly described and illustrated by a geological map. Special reference is then given to the past earthquake phenomena observed in the district, the most important of which is as follows.
Among the several strong earthquakes which visited the district in historical times, the Tenna earthquake of October 20, 1683 was the severest in this district. It is considered to be originated in the very district. It caused a tremendous landslide damming up the Ojikagawa and formed a lake which lasted about 50 years. The site of this lake is now called Umi-ato (which literally means old site of a lake). According to the tradition in the village, the disappearance of this lake was due to the breaking down of the natural dam by another earthquake that took place in 1731, although we have no record of this event at present. In the catalogue of large earthquakes in this country we find in this year a strong earthquake which caused some damage at the town of Koori in Fukushima Prefecture. Notwithstanding somewhat large distance of the sites of these two events, the tradition seems to suggest that these events were kindred phenomena. No matter what this was truely the case or not, it may be a matter of no small importance from the seismological and engineering point of view.
Some descriptions of the design of the dam are also given.

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The ground-tilts caused by pumping-up the underground water were observed with tiltmeter at several points closed by a well.
The ground within several meters from the well tilt towards the well in the time of pumping, but at points more than several meters distant from the well, the ground tilt, contrary to our expectation, to the direction against the well.

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γ-intensity was measured by a G. M. counter at various points in the adits of Myoho Copper Mine. It is remarkable that counting numbers measured at points close by the ore-vein are exceedingly small.

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