Zisin (Journal of the Seismological Society of Japan. 2nd ser.)

Direction of Approach of Microseisms Observed in Kyushu

Kennosuke OKANO, Kosuke KAMO

1961 Volume 14 Issue 3 Pages 131-137
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_131

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Direction of Approach of microseismic waves was investigated in Kyushu by means of vector seismographs. It was found that no microseismic wave comes from the west direction even when typhoons were situated in the south-west direction. The frequency of arrival directions was distributed partially for the direction of the Hyuga Sea where the continental margin is near to the coast.
From these distributions and those at the Abuyama Observatory, it is reasonably concluded that the nearer the continental margin is to the coast, the more frequently microseismic waves are generated.

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May M-waves be classified into two major branches?

Kyozi TAZIME

1961 Volume 14 Issue 3 Pages 138-149
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_138

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In the characteristic equation (1·1) of M-waves, two major branches, M ⁽¹⁾ and M ⁽²⁾, have been defined by (3·7) or (4·4) which is deduced from (2·1) for the case of a plate. Calculated results are shown in Figs. 5, 6 and 7 by thick full lines for M ⁽¹⁾ and by thick dotted lines for M ⁽²⁾.
The next two points must be noticed.
1) No dispersion curves, but for a plate, intersect each other on one c/v_p-Tv_p/H plane, if they correspond to a certain real structure of media.
2) Any dispersion curve changes from M ⁽¹⁾ to M ⁽²⁾ or from M ⁽²⁾ to M ⁽¹⁾, when it crosses chain lines which were given by the first equation in (3·5) or (4·8).
No criterion has been found for classification of continuous dispersion curves. In the present stage, the author thinks, notation (5·1) or (5·2) will be better than (5·3) or (5·4).

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Crustal Structure in Central Japan as Derived from the Miboro Explosion-Seismic Observations

Part 1. Explosions and Seismic Observations

The Research Group for Explosion Seismology

1961 Volume 14 Issue 3 Pages 150-167
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_150

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Since September 1957, several scores of tons of explosives have been detonated many times, for quarrying purpose connected with construction of a rock-fill dam at the site of Miboro-valley, Gihu Prefecture.
The Research Group for Explosion Seismology has carried out successfully systematic observations of seismic waves from the six quarry blasts, in order to get information about the crustal structure in central Japan, over Kwantô, Tyûbu, Kinki and Tyûgoku Districts. Our temporary observation stations, 75 in total, were spread to a distance of about 300km mainly along the Eastern profile and the Western profiles A and B, as shown in Figs. 4 and 5. Observed data and time-distance graphs of first seismic arrivals are given in this paper.

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Crustal Structure in Central Japan as Derived from the Miboro Explosion-Seismic Observations

Part 2. On the Crustal Structure

Takeshi MIKUMO, Michio OTSUKA, Tokuzi UTSU, Tsutomu TERASHIMA, Atusi O ...

1961 Volume 14 Issue 3 Pages 168-188
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_168

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From the observed results of seismic waves from the Miboro Explosions, two probable models of crustal structure as shown in Figs. 5, 8 and 9 were derived for the Eastern and Western profiles, respectively.
The time-distance plot of first seismic arrivals shows the following apparent velocities for the respective branches; in Model I: 5.55, 5.86, 6.33 and 7.91km/sec in the Eastern profile, 5.55, 5.92, 6.32 and 7.52km/sec in the Western profile A, 5.55, 5.81, 6.16 and 7.45km/sec in the Western profile B; in Model II: 5.5, 6.0 and 7.9km/sec in the former profile, 5.5, 6.0 and 7.5km/sec in the latter two profiles.
These data are interpreted to indicate three crustal layers with a compressional velocity of 5.55, 6.00 and 7.70km/sec, taking the results obtained in Kwantô District into consideration.
The first layer is thickest in Tyûbu region and in the northern part of the Lake Biwa. Comparing the results in two Western profiles the layer is considered to taper northwards (toward the Japan-Sea coast). The boundary surface between the 2nd and 3rd layers (probably, the Mohorovicic discontinuity) becomes deeper westwards from Kwantô District with the deepest value of about 38km in the Tyûbu mountain regions, and in turn becomes shallower to 28km at Miboro. This deepens again toward Kinki District with the deepest value of 36km. but seems to be shallower in the Awazi Island.

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Elastic Wave Propagation in a Liquid Layer Overlying a Sloping Rigid Bottom

Shozaburo NAGUMO

1961 Volume 14 Issue 3 Pages 189-197
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_189

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2 dimentional elastic wave propagation in a liquid layer overlying a sloping rigid bottom is studied. Mode solutions exst. Elastic wave propagation in the layer is described by superposing the normal modes. The mode solutions take the forms of progressive wave in the range h_r>|ξ|>0, namely in the range r (θ₁+θ₂) / (2n-1) λ/4>1. Normal mode wave has dual dispersive property; phase velocity varies not only with frequency but also with distance. When the interface is inclined apparent phase velocity, which will be observed at a certain station, is expected to be generally different from the formal phase velocity, which is defined in the representation of progressive wave. However, in the special case of sloping rigid bottom, apparent phase velocity becomes equal to the formal phase velocity. Dispersion curve of the formal phase velocity corresponds to that of parrarell interface when r (θ₁+θ₂) is understood as the depth at the station. Apparent phase velocity increases as the mode wave progresses towards shallower direction, and decreases towards deeper direction. Apparent phase velocity at a certain station however does not depend upon the direction of the wave propagation. Apparent group velocity, which will be observed at a certain station, depends upon the location of the source.

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Normal Mode Interpretation of the Sound Propagation in Whispering Galleries

Yasuo SATO

1961 Volume 14 Issue 3 Pages 198-199
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_198

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Correlation between coefficients determined by the least squares method

Keiiti AKI

1961 Volume 14 Issue 3 Pages 199-201
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_199

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On the Longitudinal Wave Velocity in the Moist Granular Media (I)

Takao MOMOI

1961 Volume 14 Issue 3 Pages 201-202
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_201

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On the Longitudinal Wave Velocity in the Moist Granular Media (II)

Takao MOMOI

1961 Volume 14 Issue 3 Pages 203
Published: September 25, 1961
Released on J-STAGE: March 09, 2010

DOIhttps://doi.org/10.4294/zisin1948.14.3_203

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