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Volume 25, Issue 2
Displaying 1-10 of 10 articles from this issue
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Seismicity of Microearthquakes in Western Part of Sizuoka PrefectureIsao YAMADA, Tooru OOIDA1972 Volume 25 Issue 2 Pages 115-123
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSWe set up a temporary seismographic network with four stations in the western part of Sizuoka Prefecture, central Japan, for the observation of microearthquakes during the period from July to August in 1970.
The results obtained in the observation were as follows; very shallow earthquakes occurred to the east side of the Tenryu river. But in the north-west side of the Median Tectonic Line and in the vicinity of Lake Hamana, many earthquakes were located as deep as Moho discontinuity showing a systematic focal mechanism.
These distributions of focal depths were similar to those in Inuyama area where many earthquakes occurred at shallow depths in Mino-Tanba belt and those in Ryoke belt were below the Moho discontinuity.View full abstractDownload PDF (996K) -
Isao YAMADA, Rikio MIYAJIMA, Iwao FUJII, Masaru NAKAMURA1972 Volume 25 Issue 2 Pages 124-133
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSWe set up a temporary seismographical network in northern part of Gifu Prefecture, central Japan, and carried out an observation in July and August, 1971.
Only a few hypocenters could be determined in the vicinity of active faults such as Atotsugawa and Atera faults. Whereas other shocks were mainly located in the vicinity of Mt. Yake, south-west side of Mt. Norikura, and in the vicinity of the aftershock region of the earthquake of central part of Gifu Pref. (Sept. 9, 1969). These earthquakes were very shallow, less than 15km in depth.
Aftershocks of the earthquake mentioned above were still active in the same region in the early stage of the aftershock sequence.View full abstractDownload PDF (1059K) -
Kazunari FUJII, Masayoshi NAKANO1972 Volume 25 Issue 2 Pages 134-154
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe amplitudes of body-waves, P and SV, are approximately obtained in the case that they are radiated from a cylindrical hole in an infinite elastic medium. It is assumed that two axially symmetric pressures, g (z) p (t) and f (ρ) p (t), are acting on the side-wall and the bases of cylinder, and the amplitudes can be expressed in common by three factors F1, F2 and θ. Detailed discussions are made with respect to directivity of P, P/P, and relative predominance of SV, S/P, especially in either extreme cases of the shape of cylinder being very flat or very slim. A few explicit forms of g (z) and f (ρ) are taken up as models of actual wave source in explosion and the variations of P/P and S/P are examined, being connected with the change of r2/r1, the ratio of mean (Model 1) or maximal (Model 2 and 3) intensities of both pressures.View full abstractDownload PDF (2027K) -
Takashi TADA1972 Volume 25 Issue 2 Pages 155-163
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSIn 1966, the artificial explosions off the Atsumi Peninsula were carried out by the Reserch Group for Explosion Seismology (R.G.E.S.). At the same time, many Matsushiro earthquakes were recorded at the temporary stations of the R.G.E.S. These stations and the Matsushiro earthquakes form ray paths like those in a fan shooting.
The travel times derived from these earthquakes were analyzed and the following conclusions were obtained. The observed appearent velocities are 6.1 km/sec and 7.7km/sec, respectively. However, the intermeditate appearent velocity has not been observed. These evidences agree with the results which are obtained by the R.G.E.S.
The lack of the intermeditate appearent velocity may suggest that the intermeditate crustal layer (the so called basaltic layer) does not exist, or it is masked in the Central Japan. These travel time curves are explained by the crustal structure obtained by the R.G.E.S..View full abstractDownload PDF (1090K) -
Michio OTSUKA, Akira KUBOTERA, Tsuyoshi HIGAKI1972 Volume 25 Issue 2 Pages 164-171
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSA test experiment has been carried out to apply audio tape recorder directly to seismic observations. Parallel seismic observation by use of the new technique with the traditional drum system and with data recorder system has proved its utility especially toward the micro seismic observations.
The sharp cut-off against the extra low-frequency signal which is inherent to audio tape recorders is a key to obtain high S/N ratio of seismic signal from extraneous noises.
The feasibility of tape recorders together with their low costs and light weight is expected to facilitate seismic observations particularly of aftershocks and swarms which require rapid mobilities of observation.View full abstractDownload PDF (2776K) -
Part 3. Characteristic Bent in the Magnitude Frequency Relation of EarthquakesMichio OTSUKA1972 Volume 25 Issue 2 Pages 172-177
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSMagnitude frequency relation of earthquakes expected from the Go game model which was proposed in the second part of this paper is compared with actual data with special emphasis on the characteristic bent of magnitude frequency relations. Of particular interest is that the multiplicity of magnitude frequency curves as well as the characteristic bent can be expressed by assigning proper values of p to the Go game model.
It is also demonstrated that a formula recently presented by Utsu to express general downward bent of the magnitude frequency relations yields almost identical solution with Go game solution when parameters are properly chosen.View full abstractDownload PDF (768K) -
Tooru OOIDA, Kiyoshi ITO1972 Volume 25 Issue 2 Pages 178-186
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSAn earthquake of magnitude 6.1 occurred off the Atsumi Peninsula on January 5, 1971. A few foreshocks and many aftershocks were recorded at many seismological stations of both the Wakayama Micro-earthquake and the Inuyama Seismological Observatories. The distribution of hypocenters and nodal plane solutions were examined with the following results:
1) The epicenters of foreshocks, the main and large aftershocks were located along the line N 60°W-S 60°E across the Median Tectonic Line. The foreshocks occurred in the northern side of the Median Tectonic Line were very shallow as deep as 2km. However, the main shock and most of the aftershocks occurred in the southern side of the Median Tectonic Line were rather deep, about 30km in depth. But some of focal depths of aftershocks occurred near the largest foreshock were about 5km.
2) It seems that there were two types of earthquake mechanism in this region. The mechanisms of foreshocks and the aftershocks which occurred in the foreshock region were dip-slip-fault type with the pressure axes of N 90°W. On the contrary, those of the main shock and the deep aftershocks which occurred near the main shock were strike-slip-fault type with the pressure axes of N 30°W.
3) The daily frequency distribution of aftershocks was well represented by the Omori's formula N (t) =k. t-p for the first fifteen days, where p=1.2.View full abstractDownload PDF (1057K) -
Akira IKAMI, Harumi AOKI1972 Volume 25 Issue 2 Pages 187-189
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSDownload PDF (532K) -
Yasuo SATO1972 Volume 25 Issue 2 Pages 189-191
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSDownload PDF (442K) -
Hitoshi TAKEUCHI, Naoyuki FUJII1972 Volume 25 Issue 2 Pages 191-192
Published: September 30, 1972
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSDownload PDF (280K)
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