In connection with the convection current model proposed by E.G. Bullard, the problem here considered is whether the magneto-hydrodynamical equations have a solution representing the self-exciting process which is appropriate to the model. In Section 3, the problem is reduced to solve the equation (3.9) with conditions (3.3) and (3.4). In Section 4, an approximate solution of the equation is obtained. In Section 5, this approximate solution is shown to he good enough for studying the present problem. The results obtained in this paper show that such a self-exciting dynamo is possible by which the earth's main magnetic field is produced and maintained.

View full abstract

The fundamental assumptions underlying K.E. BULLEN'S study of the density distribution in the mantle of the earth are the existence of a ensity discontinuity at the depth of 400 km. and chemical homogeneities of the materials on both sides of this depth. The assumption of the continuous distribution of one homogeneous material throughout the mantle is known to lead us to an unreasonable result as to the physical state of the core.
Recently, H. BROWN who studied the chemical compositions of the earth's interior referring to those of meteorites, ame to believe that the concentration of metal phase increases linearly with depth in the mantle.
An earth model which has no density iscontinuity in the mantle and which has a continuous concentration increase of metallic material towards the centre is possible. Such a model is investigated in this paper.
The main results obtained are as follows:
(1) The density at the bottom of the mantle may be between 6.289 and 7.970.
(2) The total contents of metal phase in the mantle may be between 11.4 and 22.9 percent.
(3) The atomic ratio of iron to silicate in the whole earth will be 1.559. This value is not affected by the mode of distribution of iron phase between the mantle and the core.

View full abstract

From the considerations on GRÜNEISEN's parameter, it has been found that the condition of hydrostatic equilibrium is satisfied beneath the depth of 90 km. from the earth's surface, although it is not satisfied above that level. This depth can be interpreted as representing that of the isostatic compensation. The value of 90 km. was deduced by using the velocities of seismic waves in Japan, so that it can claim no general validity. Nevertheless, this line of approach may afford a new method for estimating the depth of compensation from data other than gravimetric.

View full abstract

Based on the considerations on GRÜNEISEN's parameter as in the preceding paper, it has been shown that three types of the distributions of density and temperature in the interior of the earth can be considered according to the following three suppositions.
(a) GRÜNEISEN's parameter has an extraordinary value throughout the earth's mantle.
(b) In the stratum between the depths of 400 km. and 800 km., GRÜNEISEN's parameter has an extraordinary value.
(c) GRÜNEISEN's parameter has an ordinary value in the part shallower than the depth of 400 km. and an extraordinary value in the deeper parts.
In (a), the temperature decreases with increasing depth between the depths of 400 km. and 800 km. In (c), the physical states or chemical compositions of material change at the depth of 400 km. dividing the earth's mantle into two parts.

View full abstract

The earth's crust is generally divided into three layers, the upper two of which are called granitic and intermediate layers, while the deepest is believed to be composed of peridotite. The visco-elastic properties of the three layers have been studied in the present paper from the velocities and amplitude changes of seismic waves which are propagated through them. Principal results obtained are as follows. propagated through them. Principal results obtained are as follows. 1. The attenuation coefficient and relaxation time in each of the three layers were computed from the amplitude changes of initial P-waves in case of near earthquakes with the results as follows: 2. The velocity of P in the granitic layer is about 5.4-5.75km./sec. from natural earthquakes (P_g seis.), while it is 6.0km./sec. from explosion experiments (P_g expl.). This difference can be accounted for by the dispersion of seismic waves in the visco-elastic medium, since the periods of the waves in the two cases are decidedly different. On the other hand, scarecely any difference can be found between P-wave velocities from natural earthquakes and artificial explosions in the intermediate and peridotite layers. 3. The viscosities of the layers were calculated by the methods recently developed and were compared with the values obtained by other authors. 4. Similar studies were made of the results of artificial explosion experiments on alluvial layers, such as have recently been attempted at various places in Japan by members of our institute. It was found that earthquake damages on the surface of the alluvial layers are closely connected with the rheological properties of the layers.

View full abstract

A sensitive torsion balance was installed at a place of Inuyama town and continuous observations have been made of the change in its equilibrium position. The instrument was placed at a point on the bank of the Kisogawa river, which flows through the town, with the intention to investigate the change in the gravitational potential around the instrument caused by the rise and fall of the level of the river water, especially at the times of flood flows.
Calculations have shown that the observed deflections fall much short of those expected from the visible changes in the level of the river water, thus suggesting there are notable changes in the underground water conditions associated with the floods.

View full abstract

1. The vertical displacements of the ground surface in the central part of the city of Tokyo, which have been detected by levelling surveys repeated recently, consist of two components, namely, the sinking due to the shrinkage of the soft superficial soil layer and the displacement resulting from tilt of the underlying layer of harder material. The former is progressive as a whole, while the latter is quasi-periodic with respect to time. The vertical displacements measured for longer intervals of time are proceeding in one direction, although those measured for shorter intervals show more or less irregular fluctuations. 2. As a whole, the rate of sinking has been evidently decreasing. 3. The rate of sinking during the intervals involving summer is larger than that involving winter.

View full abstract

By means of the formulas determined by the present author previously, the magnitudes of 735 shallow earthquakes which took place in and near Japan during 1931-1950 were determined. The mean annual numbers of earthquakes having the magnitude M were found to be expressed by log N= -1.60+1.06 (8-M), for the area A, log N= -1.57+0.72 (8-M), for the area B, log N= -1.61+0.66 (8-M), for the area C, log N= -1.46+1.04 (8-M), for the area (A+B), log N= -1.33+1.01 (8-M), for the area (A+B+C), the class interval of M being taken as 0.1. It is interesting to note that while the first constant does not differ much from area to area, the second does so. The second constant for an area is nearly proportional to the total number of earthquakes which occurred in that area.

View full abstract

An apparatus is described by which earthquake motions are recorded photographically with a certain time lag. The initial parts of the motions do not fail to be recorded and the speed of recording can be increased as much as desired.

View full abstract