For the purpose of determining the epicentre of the destructive earthquake which occurred on Jan. 15th, 1924 in Sagami district, the author of the present paper has drawn a series of isochronal lines using the results of seismic observations made at the meteorological stations in our country. The isochronal lines thus obtained is shown by full lines in Fig. 1. The general form of the lines are coaxial ellipses, their minor axes coinciding with the tangent at the epicentre to the arc of the Japanese Islands and their major axes being perpendicular to the tangent. This means that the velocity of condensational seismic wave differs with the direction of propagation relative to the general feature of our islands. Nextly, the author has drawn a series of lines which connect the stations having the equal duration of preliminary tremor. For simplicity, we call them, iso-PL-lines. The general feature of these curves show also a series of coaxial ellipses, their major axes coinciding with the tangent at the epicentre drawn to the arc of the Japanese Islands and their minor axes being perpendicular to it (dotted lines in Fig. 1). In other words, the elliptical isochronal lines are nearly perpendicular to the elliptical iso-PL-lines. This striking results are varified by a few more examples, two of which are shown in Figs. 2 and 3. To explain this phenomena, isochronal lines for L-phase were drawn in the same earthquake and is shown in Fig. 4. This curves are composed of a number of concentric circles with the epicentrum as its centre. From this fact, we may conclude that the L-phase wave travels with equal velocity in all directions from the origin of earthquake. According to this fact, which is also borne out by a few other semidestructive earthquakes, it becomes certain that the velocity (V1) of condensational seismic wave propagating in the direction perpendicular to the tangent at the epicentre drawn to the arc of the Japanese Islands is greater than that (V2) of the wave propagating along it. Nextly, the mean velocities of condensational wave V1 and V2 estimated from isochronal lines are Again, the mean velocity of L-wave is estimated from the isochronal lines for L-phase (U1) and U2=4.1km/sec is obtained. Then, if we accept the fact that L-phase coincides with S-phase in a near earthquake, the value of U may be taken as the velocity of transverse seismic wave. So, we may calculate from V1, V2, and U, the elastic constants of the portion of the upper layer of the earth crust under consideration from tbe following formulae: where σ1, and σ2, represent Poisson's ratio of the upper layer of the earth crust in the direction perpendicular and parallel to the tangent drawn to the arc of Honsyu respectively. Values of σ1 and σ2 thus calculated are as follows: This irregularity of elastic property of the earth crust of our great island may perhaps be explained by the continental stress which acts radially on this islands, but confirmation of this conclusion is left to my further studies.
On January 30th snow fell in Tokyo nearly all day long. The author measured the density of snow on the ground while snow was still falling. The result of his measurements is depth of snow from its surface 2.5 7.5 10 12.5 15 20 24cm density 0.033 0.065 0.074 0.080 0.081 0.081 0.084 These values are very near but a little less than those for new snow, given by K. Abe at Sapporo and nearly 1/3 of those for old snow given by T. Okada and by K. Abe in Hokkaido. The author believes that an exponential law hold good hetween the density and depth.
The visibility at Tateno is good during autumn, winter and early spring and bad from mid spring to summer. It is good with north to west wind and bad with SE to SW winds both at 1, 000m level, with stronger NWly wind at that level visibility is better and with stronger southerly wind visibility is worse.
There is a phenomenon called “kasumi” in Japan, which appears mainly in Spring and makes atmosphere opaque. The general feature of this phenomenon is that objects at distance-say one, two or more miles gradually become hidden from the sight as the day advances. Objects near horizon become usually invisible but not those with greater height such as mountain tops. In Japanese picture of “kasumi” are often represented cherry trees in full blossoms hidden, however, by kasumi at their middle branches, exposing their trunks and top parts. Kasumi has a tint very thin and somewhat bluish. It always extends horizontally like a sheet of evening smoke, but on approaching it, no body has ever perceived any material particles floating there, as it is the cases in smoke, haze or mist. It is something like optical turbidity, an allied phenomenon of scintillation and mirage, but hitherto there has been no research on this direction. Only a vague idea that it might be a product of very fine particles of water in air is generally prevailing. The author wishes to define the phenomenon scientifically by fixing up the conviction of “kasumi” taking old Japanese verses into consideration, which refer the phenomenon. He collected 72 ‘Utas’. By adding his own observations, he drew conclusion from these verses that “kasumi” is the phenomenon appearing most in Spring, seldom in winter and Autumn, and most seldom in Summer. It Sometimes settles over along river and sometimes emigrates along coastal line, mostly encircle_??_ hills round its slope. The height at which kasumi is stratifying is from 10 m to 200 m above the ground. The author left the problem on the physical nature of “kasumi” to future investigation. (Fujiwhara)