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Volume 21, Issue 2
Displaying 1-10 of 10 articles from this issue
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Rayleigh WavesYûkô OGUCHI, Hitoshi TAKEUCHI1968 Volume 21 Issue 2 Pages 89-96
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSPhase velocity of plane Rayleigh waves on a transversely isotropic, heterogeneous medium is calculated by integrating directly the equations of motion. The group velocity is calculated directly from the energy equation.
The increments of the phase velocity with respect to the changes of the physical parameters are calculated by the variational calculus. It is shown that this prediction of the phase velocity increment is useful for small changes (up to 10%) of the physical parameters.View full abstractDownload PDF (602K) -
Akira KUBOTERA, Yutaka OHTA1968 Volume 21 Issue 2 Pages 97-108
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe problem related to seismic waves generated by small dynamite explosions has been investigated, based upon the experiment carried out by the Exploration Group of Japan at Shirane City, Niigata Pref, in 1965.
There are four different types of wave groups, namely, wave groups of I, II, III and IV. On the wave groups III and IV, comparative investigations were made from theoretical and experimental view points by several authors. Consequently, in the present paper, characteristics of the wave groups I and II have been mainly treated.
The wave group I is concluded to be composed of various kinds of converted waves generated at the interfaces beneath the surface. While, in the wave group II, three different kinds of waves are found; a kind of surface waves having the longest wave length, a wavelet of direct P waves and refracted SV waves. Among these the first one, corresponding to the main part of this wave group, is most interesting.
In order to make clear the mechanism of development of this type of waves, the observed data have been compared with the computed results of amplitudes and velocities (phase- and group-) of the normal mode waves in the liquid layers, and it is ascertained that they have many points of similarity to the normal mode waves in the liquid medium.
When the Poisson's ratios of the experimental fields are nearly equal to 0.5 the observed seismic records may seem to be divided into two, that is, P-and S-zones before and after the head part of the critically refracted SV waves.
Through the computations of the amplitudes of the converted waves at the interfaces it was proved that in the P-zone the converted SV waves have a negligibly small amplitude compared with the P waves in the medium of which the Poisson's ratio is almost 0.5. Thus in the P-zone the circumstances resemble to the liquid conditions. The surface waves under consideration can be looked upon as the normal mode waves mentioned above. While, in the S-zone both P and SV waves are coexisting. The surface waves (wave groups III and IV) in this zone belong to the usual elastic waves in solid.
In connection with the propagation phenomena of the seismic waves, the medium, especially in the physical condition that the Poisson's ratio is near to 0.5, can have two different properties such as fluidity and elasticity.View full abstractDownload PDF (3002K) -
Yutaka OHTA, Akira KUBOTERA1968 Volume 21 Issue 2 Pages 109-120
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA wave group which is most attractive in the transversal component and is dispersed has been observed on the occasion of the experiment of seismic waves generated by small sized simple explosions using three-component seismometers.
For the purpose to ascertain that this type of wave group is a kind of Love waves, the following investigations were made; i) whether SH waves are produced simultaneously or not, ii) the comparison of the observed dispersion curve to the calculated, iii) generation characteristics of the waves in question, with special respect to the differences of shot depths and of charge amounts, and iv) the coherence of the other surface waves.
Finally, remarks on excitation mechanism of the Love waves by means of the explosions are added.View full abstractDownload PDF (1055K) -
Hisashi MIYOSHI1968 Volume 21 Issue 2 Pages 121-138
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTwo reasons which intensified the Chilean tsunami of 1960 along the Japanese coast, have been supposed as follows;
(1) The distance between the Chilean coast and the Japanese coast is 17, 100km. (which is roughly 20, 000km) —Antipode Effect—
(2) The Hawaiian Islands and the shallows around them have the convex-lens effect on the orthogonals of the tsunami wave. And the energy converges into Japan.
The present author, in this paper, pursues the primary reason, regarding the abovementioned two reasons as the secondary ones. The thought that the bottom topography causes refraction of the tsunami wave and much energy is radiated at right angles to the bottom contour lines around the origin, was picked up. Many past examples, such as the tsunami caused by the Lisbon earthquake of 1755 and that was generated at the Aleutian Trough on April 1, 1946, support this thought impressively.
After some analyses, the relation between m (the ratio of water depth at the origin to that of the deep-sea floor) and r (the ratio of off-shore energy of the tsunami to the whole) was calculated and shown in a table and a figure. Most tsunamis radiate off-shore a quarter of the whole energy or so. And it is natural that the deeper is the origin depth, the bigger is the ratio of off-shore energy.
Then we calculated the directivity of this off-shore energy, and found that the shallower is the origin depth, the sharper is the directivity. Directivities of many tsunamis, the origin depths of which are various, are shown in a table and a figure.
These two facts of rather opposite meanings shown in two tables, are combined into new theorem that “the deeper is the origin depth, the larger are the energy radiated in any direction”. This theorem suggests the possibility of the larger (along the Japanese coast) Chilean tsunami than that of 1960, in future.
Two important conclusions of this paper are as follows;
(1) The energy radiated from Chile in 1960, had a remarkable directivity towards Hawaii. Passing through Hawaii, it was intensified doubly at most—more accurately, maintaining its energy owing to the antipode effect, it came to Japan.
(2) The angle Θ between the great circle drawn from Japan and the line of circum Pacific coast, can be observed or calculated. The tsunami generated near the coast whereΘis approximately 90°, is dangerous for Japan. And we need not feel nervous about other coasts. Along the coast of South America, there is a far-stretching area whereΘis approximately 90°. And there are dangerous coasts fragmentarily, in other areas. The warnings against the tsunamis from these fragmentary areas are haunted with some probabilitiesView full abstractDownload PDF (1455K) -
Sigeru KANDA1968 Volume 21 Issue 2 Pages 139-140
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
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Sigeru KANDA1968 Volume 21 Issue 2 Pages 141-142
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
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Sigeru KANDA1968 Volume 21 Issue 2 Pages 142-143
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
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Tatsuo USAMI1968 Volume 21 Issue 2 Pages 143-146
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
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1. The PentateuchIkuko OZAKI, Yasuo SATÔ1968 Volume 21 Issue 2 Pages 147-150
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
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Yoshimitsu OKADA1968 Volume 21 Issue 2 Pages 151-153
Published: August 30, 1968
Released on J-STAGE: March 11, 2010
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