In the present paper are treated the problems concerning the mechanism of earthquakes from the stand point of the seismological observation of earthquake waves. First of all the importance of generation of a fault is discussed for the occurrence of earthquakes. Then the fact so-called “quadrant distribution of first motion” which is observed in almost all cases of earthquakes of both shallow and deep origins can be considered as a naturally expected phenomenon if earthquakes occur first in the crust by breaking, in other words by fault, and the conservation of angular momentum be hold. Hitherto, oscillators are sometimes considered at the source of earthquakes to interpret the distribution of the first motion, such as “center of compression or dilatation” “doublet with moment” or “a pair of doublet with (without) moment” etc. Yet we have perhaps never heard of the simple explanation mentioned above that the distribution of the first motion can be interpreted by the motion caused by a doublet (with moment) and adding to it by that of the opposite sign caused by the reaction of the former. Although the first motion of earthquakes can be considered to be caused by a pair of doublet oscillator, it is quite another phenomenon as to the crustal deformation observed in the epicentral region where sometimes a remarkable fault may be found in the case of large earthquakes. The latter phenomenon cannot be satisfactorily interpreted by the assumption that a pair of doublet nuclei of force act in the crust, but rather explained by the assumption that there exists only one doublet nuclei of force in the crust, each of them lies on each side of the fault surface in a certain depth. A trial is made to obtain mathematically the crustal deformation at the surface occurred near the fault by a great earthquake. For the simplest case, the following assumptions are made. In a semi-infinite elastic body, surface. being z=0, the fault surface y=0 and z axis taken positive downwards, a nucleus of force exists at (0, -b, b.) and a force X0 acts horizontally to x-direction, another nucleus at (0, -b, b), force acts there -X0. As boundary conditions, stress must be vanish at z=0 and also at the fault surface y=0. The method used for this calculation is similar to that made by F. I. W. Whipple (M. N. of R. A. S. Geo. Sup. Vol. 3, No.6) and the approximate solutions obtained. The crustal deformation thus obtained resembles much to that actually observed. In the last part, the problem of the wave propagation of shallow earthquakes is treated. Dr. H. Nakano treated theoretically this problem assuming oscillators in a general form at the origin. Dr. H. Honda proved that the actually observed result of seismic waves agrees just well with a special case of this theoretical result. Of couse this proof is good in general tendency but if we examine precisely the observed result, it may be found that the problem of propagation of seismic waves issued from a very shallow origin can not be treated under such a simple conditions as assumed by Dr. Nakano that the medium is uniform and perfect elastic and the origin lies just on the surface. He obtained that the amplitude of solid seismic waves decreases with epicentral distance as AP∝Δ-2, AT∝-1 in their principal directions respectively, and this theoretial result ascertained by Dr. Honda using many observational data. But in the practical case, the earth's crust is not homogeneous, the seismic-focus does not lie strictly on the surface and therefore the conditions of wave propagation must be somewhat different from this theoretical result.
The author of the present paper observed the change of the electrical resistance of soil, when it froze in the natural state, at Toyohara, Karahuto (Sakhalien), by a simple method. Pairs of electrodes, consisting of stretched twisted copper wires of 0.5m length, had been buried horizontally at the depths 0.0, 0.1, 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8m from the surface of the earth. One end of leading wire of every set was soldered to each of the electrode and the other end was brought in the room. The intensity of the electric current was observed by a milliammeter when the current was supplied from a dry cell of known voltage in the circuit consisting of the dry cell-milliammeter-leading wire-electrode-earth-electrode-leading wire. The effective resistivity was calculated as (Voltage of the dry cell)⁄(Intensity of the current). General aspects of the change of the resistivity in the cold season (Nov. 1932-May, 1933) are shown in Fig. 1 in the text. The possibility of finding the depth of frozen soil without turning up the ground is suggested from the figure. Similar observations were tried in case of heavy rainfall of Aug. 6-7th, 1933. Results of them are shown in Fig. 3 in the text, from which we can find to what depth the rain water per_??_o lated at any time.
The change of electrical resistance with the depression of temperature is obsfrved on several specimens of soil. The sample is contained in a wide glass tube, two concentric copper tubes and a thermometer being inserted in it, and kept in a freezing mixture. The resistance is measured by a D. C. ohm-meter of the type MAI of TSK. The freezing point is estimated dilatometrically on another sample of the same specimen. Some of the specimens show an abrupt increase of resistance upon freezing while the others do not reveal the same tendency. The phenomenon is mainly attributed to the sudden decrease of mobile electrolyte ions upon freezing. The soil which contains much saline matter shows freezing when it is cooled in the dilatometer but the electrical resistance do not change considerably upon freezing. The result can be applied to the estimation of the depth of the soil frozen whithout turning up the ground.
H. Jeffreys' theory on the maintenance of westerly currents in middle and higher latitudes is reexamined from another point of view. He discussed the general circulation of the atmosphere based on the idea of geostrophic wind and arrived at the conclusion that there prevail the high pressure areas near the polar regions and the low pressure over the equatorial region, which, however, contradicts with to the actual atmosphere. The frictional term is only neglected and Jeffreys emphasized that frictional effect is sufficient enough to destroy the easterly wind theoretically deduced and creat the westerly wind. (In Oberbeck's theory such a difficulty does not occur, since in his theory the westerlies prevails throughout the latitudes in case of no friction.) The present author reexamined this theory by making use of H. Lettau's result recently published (Luftmassen-und Energieaustausch zwischen niederen and hohen Breiten der Nordhalbkugel während des Polarjahres 1932/33 Beitr. z. Phys. d. f. Atm., Bd. 23, 1935) and concluded that the supply of angular momentum through “grosse Austausch” just cancels, with the energy dissipation due to skin friction. Thermodynamically speaking the circulation in temperate latitudes denotes “eine arbeitvernichtende Maschine, ” but this difficulty may be removed to some degree by the supply of angular momentum through “grosse Austausch” element as a cyclone or an anticyclone.
The apparatus illustrated by Fig. I is a Pendulum-anemometer. From the experiments made by the present author it is shown that this anomometer with the plate A of 200 gram in weight and of 30cm in length, 15cm in breadth is able to be used for the measurements of wind-velocity up to 25m/s. Fig. II shows the result results obtained by the Pendulum-anemometer, compared with that obtained by the Dines' pressure tube anemometer. As we easily notice fro_??_ Fig. 2, the Pendulum anemometer is not so good for the accurate measurements of wind-velocity, and hence it may be used only for the measurement of wind-force or so. Now we consider the case of Dines' anemometer. Taking the mean value of the maximum wind-velocity Mx, and that of the minimum wind-velocity for M_??_, the present author defines the mean wind-velocity Vaby Let the wind-velocity measured by the Robinson's cup anemometer be Vrm/s, the following empirical formula betwe_??_n V_??_ and V_??_ was obtained. In the experiments made by the present author was used the secondary Robinson's cup anemometer which belongs to the Central Meteorological Observatory and several Dines' pressure tube anemometers. If we follow the relation between V_??_ and the true air speed V: we obtain From this relation we easily notice that when the Dines' pressure tube anemometer is rightly used, the mean wind-velocity measured by Dines anemometer will coincide with the approximately true air speed.
By spherical harmonic analysis it is possible to distinguish between the_??_arts of the earth's magnetic field, at any time, which originate respectively within and above the earth's surface. A. Schuster, S. Chapman and others, applying this method, found that the major parts are of external origin, but that there are also parts produced within the earth so far as the diurnal and the storm-time variations concern. They attributed the parts due to the inner part of the earth to electric currents inducd in the earth by the outer varing field. They considered that the earth is a uniformly conducting sphere, but in reality, there exist oceans and continents of wide extentions over the globe. When we consider the effect of land and ocean the problem becomes too complex to be treated easily, And if we consider the magnetic variation at the middle part of ocean or continent, it will be not so much unreasonable though we do not consider the effects of both, Therefore the present author considered the electromagnetic induction within the earth's crust consisted of many consentric shells, each of which is of uniform nature, putting the ocean and land out of consideration. The earth is considerd to be constructed from m's concentric conducting shells and a non-conducting medium outside the conducting shells. (radius being _??_a) The typical forms of the magnetic potential of the external and internal origins are indicated respectively by (1) and (2) (page. 294) at the earth's surface. While in the core the potential becomes (3). Applying the adequate boundary conditions we have the relations (6) to be fulfilled at the boundaries. Successive application of (6) we have the relation I0/E0as a function of κ electric conductivity, μ magnetic permeability, and ξ depth of conducting shell. If we consider the periodic variation of short period (6) becomes (8) and if the period is sufficiently small we have a functional relation of κ/μ and ξ only. Therefore in the stratum near the earth's surface we can obtain κ/μ and ξ. For the variation of the period little longer than before we should use (9) instead of (10) and then we can obtain κ, μ and ξ separately. On the other hand if we consider the periodic variation of long period we must use (11) instead of (7). Hence in this case if the period is so long to be able to neglect the term L in (11), the resultant expression of I0/E0 contains only μ and ξ. Therefore in this case we can not know κ. Namely as in this case the electromagnetic induction penetrates far deep in the interior of the earth crust, in such a region we can assume the permeability only. The discussions made hitherto are all based on the supposition that the magnetic variation observed on the earth are mainly of external origin and their internal parts should be interpretted as the effect of the electromagnetic induction within the earth. If we have ample data of the magnetic variation of external origin at stations at almost middle part of land or ocean, we can estimate the electric and magnetic states of the upper stratum of the earth from the variation of short period and the magnetic state of the relatively inner core of the earth from the variation of long period. As to the variation of the intermediate period, not so long nor so short, the treatment becomes rather complex.