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Volume 29, Issue 2
Displaying 1-12 of 12 articles from this issue
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Shoji SAKATA1976 Volume 29 Issue 2 Pages 93-98
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSStatic dislocation distributions along two-dimensional dip-slip faults in prestressed semiinfinite Poisson material were calculated as simple inverse problems using the stress expressions derivated from MANSINHA & SMYLIE'S formulas.
The dislocation distribution is well coincident with the STARR'S result as long as the fault is located in the relatively deep part. The nearer to the free surface the upper edge approaches, the more the symmetry of the dislocation distribution of a fault becomes deformed.
The displacements on the free surface were also calculated. The result will be applicated to explain preseismic land deformations.View full abstractDownload PDF (399K) -
Sadaomi SUZUKI1976 Volume 29 Issue 2 Pages 99-116
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTravel times of seven shallow earthquakes having the hypocentral parameters redetermined are analysed to reveal the spatial distribution of P-wave velocity in the upper mantle beneath the Japanese islands and their margin. Regional variation of P-wave velocity in the upper mantle is derived from the areal distribution of P-wave travel time residuals, which is characterized by the arrivals being early in the eastern half of the Japanese arc and late in the western half of Japanese arc.
Analysis of travel times of the 1973 Nemuro-Oki earthquake and its aftershocks reveals that a P-wave velocity in the upper mantle beneath the Pacific coast between the Japan trench and the Aseismic Front is 8.1km/sec just below the Moho interface and increases from that value as a depth increases; the velocity increase to a depth of about 100km in the upper mantle is deduced, which is slightly lower than that obtained from the J-B table.
A Pn velocity of 7.59km/sec is derived as an average velocity beneath the northern region in the Honshu island, using the travel times of the 1970 Southeastern Akita and the 1974 Southern Izu earthquakes. In derivation of the Pn velocities, the reduction of the Moho time terms at stations and epicenters from the actual travel times is made beforehand to have the velocities more accurate. Although the abnormal distributions of seismic intensities suggest a regional variation of Pn velocities, the Pn velocities significantly lower than the average are not confirmed within that region.View full abstractDownload PDF (1650K) -
Takashi TADA1976 Volume 29 Issue 2 Pages 117-126
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA fault model of the 1974 Izu-Oki Earthquake was studied by the vertical crustal movement and the distribution of the after shocks.
An assumed fault type is the right lateral pure strike slip, and the fault parameters are as follows, length=15km, width=8km, dip angle=75°, and dislocation=130cm.
The stress field in the southern part of the Izu peninsula deduced from this fault motion is the north-south directional compressive field. This stress field represents that the Izu peninsula is compressed from south to north by the movement of the Philippine Sea Plate.View full abstractDownload PDF (736K) -
Kazuo OIKE, Kazuo MATSUMURA, Fumiaki TAKEUCHI, Shigemitsu MATSUO, Nobo ...1976 Volume 29 Issue 2 Pages 127-135
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA new type of the ink-writing recorder for the continuous obsevration of earthquakes is developed. Main principles of this recording system are as follows.
1. Recording paper size is as same as a standard from of the line-printer system of the computer.
2. The recording paper is feeded by the similar method as the line-printer system.
3. Two pen-galvanometers are drived at right angles to the feeding direction of the recording paper.
4. The same signal that is recorded at the ending part of a line by one galvanometer is recorded at the beginning part of a next line by the other galvanometer.
By these principles the recording pattern on the paper is designed to be convenient for analyses. Recorded papers by this new recording system are efficiently stacked in the standard shelves, easily used and can be conveniently copied.
Using one case of standard recording paper which has two-thousands pages, continuous observatition of about five months can be done if the recording speed is 4mm/sec, the interval of recording lines is 2mm and the signal for two hours is recorded on a page.
Various applications can be utilized by controlling the paper feeder by the trigger signals from the seismic waves.View full abstractDownload PDF (2745K) -
Part 5 An Interpretation of Aftershock PhenomenaMichio OTSUKA1976 Volume 29 Issue 2 Pages 137-145
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAccording to the chain-reaction type source model which the author has proposed throughout this series of paper, areas of variety of size in which seismic energy is still left unliberated are known to be dispersed within the source domain of the main shock. The assumption that these regions are cause of aftershock is shown to be successfully applied in explaining various aspects of the phenomena.View full abstractDownload PDF (970K) -
Comparison with the SMAC Type Accelerograph Records in Tokachi-oki Earthquake of 1968Hiroshi KAGAMI, Yutaka OHTA, Noritoshi GOTO, Keishi SHIONO, Kazuyoshi ...1976 Volume 29 Issue 2 Pages 147-158
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSContinued to the previous papers observations of the long-period microtremors were carried out in Aomori and Miyako cities for a farther comparative research of their characteristics to the SMAC type accelerograph records in Tokachi-oki earthquake of 1968. The purpose we extended the observations from Hachinohe to these areas is following. The very large acceleration amplitudes in 1- to 5-sec in period were recorded more clearly in Aomori than in Hachinohe, but no significant indication was seen on the accelerograph record in Miyako. Still the differences were seemed too extreme to be explained by the epicentral distances. In Hachinohe we successfully gave an interpretation that the predominancy of the earthquake motions in the long period was considerably due to a large amplification effect by the deep soils. But we did not know if this was true in general.
The observation and the analysis of the microtremors were performed in 1975 with a similar manner to those reported in the previous papers.
The SMAC site in Aomori is situated on the ground of which depth to the bed rock is around 600m, and the predominant period of microtremors, obtained by a series of careful observations from bed rock to the SMAC site, was 3.0sec. This is nothing but a predominant period in the strong motions of the Tokachi-oki earthquake.
On the contrary to this, the SMAC accelerograph in Miyako has been installed above the hard rock with a very thin superficial layer, and no predominant period in the long-period range was observed in the microtremors. This must be the same reason why there were no long-period amplitudes in the acceleration records in Miyako.
Combining these results with that in Hachinohe we can conclude that the correspondency of the predominancy and the predominant period between the microtremors and the strong motion records is very remarkable and thus the observation of the long-period microtremors is a good alternative to estimate the long-period input motions to large-scale structures by future earthquakes.
Finally a short recommendation on the observation schema of long-period microtremors was added. The problem left untouched is the wave-theoretical considerations of the microtremors, which will be scheduled before long.View full abstractDownload PDF (1145K) -
Mitsuo NOGOSHI1976 Volume 29 Issue 2 Pages 159-178
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe distribution of seismic intensities was investigated by means of a mail survey at about 500 locations distributed in Tohoku district, when an earthquake with magnitude 6.2 occured at southeastern part of Akita Prefecture on october 16, 1970. The details of the mail were determined by subdividing the descriptive items of JMA intensity scale, arranging the modified and expanded items which were made by UTSU (1969). The purposes were an investigation of microzoning map by the mail survey method, of anomalous vibrational characteristics of subsoil layer over all Tohoku district and of forms of contours of the larger seismic intensity by the mail survey method, as the epicenter was roughly in the center of Tohoku district.
In this paper, we tried to investigate a few main factors of the seismic intensity structure subdivided into many descriptive items. And we used a factor analysis to invesigate them. In other words, it is one of the main objects of the factor analysis in the multivariate analysis method to make clear interdependence among the multivariate (descriptive items in seismic intensity) and to find out some significant informations for interpretation of the seismic intensity structure. As a result of analysis, it was found that a model of the seismic intensity structure agreed well with a factor model which was composed of degree of human feeling, effects on indoor objects, effects on buildings and the damages, and effects on other structure and nature (cracks and fissures on land, falling stones, landslides and slumps, and cracks on paved and unpaved roads), etc.. And it was found that the first factor loading determining the seismic intensity was mainly the effects on indoor objects (especially, objects on shelves such as flower vases, tableware, books, articles in stores, and water in open vessels such as goldfish bowls). Furthermore, it was shown that a score table which was here used to determine the detailed distribution of seismic intensities did not apply to the seismic intensities 1, 6-and 6+.
Next to the factor loadings, factor scores were computed about each sample (location where the mail survey was made). As a resul of the computation, it was found that such an analysis method as a factor analysis is useful for finding out some characteristics of the locations, i. e., the ground vibration and the effects on buildings and nature, etc..View full abstractDownload PDF (1759K) -
Tokutaro HATORI1976 Volume 29 Issue 2 Pages 179-190
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe source mechanisms of eight tsunamis generated off Fukushima, the Pacific side of northeast Japan, in May to November 1938 are re-studied, making use of tide gauge records. The source areas for each tsunami inferred from the inverse refraction diagrams are shown in the bathymetric charts. The source locations moved to the north direction along the continental shelf, and the north end was in contact with the source area of the tsunami at Nov. 3, 1936. Among these tsunamis, three tsunamis were recorded in a downward direction at Onahama located near the sources, but other tsunamis began with an upward motion. According to the seismic wave data, the tsunamis of downward and upward initial motions correspond to the normal and reverse fault earthquakes, respectively. Tsunamis accompanied by earthquake of the normal fault type were generated later than those for the reverce fault earthquakes, and these source areas are located in the deep sea-bottom side. The source lengths of tsunami are 60-130km, corresponding to earthquake magnitude. A whole length from north to south ends of the sources is 200km.
The calculated sea-level disturbances at the sources for each tsunami are in the range of 10-50cm which the heights nearly agree with the seismic fault models. The whole volume of the displaced water in the tsunami sources is 13×1015cm3 which is comparable to that of the 1968 Tokachi-oki tsunami (tsunami magnitude of Imamura-Iida scale m=2.5).View full abstractDownload PDF (1012K) -
Yutaka OHTA1976 Volume 29 Issue 2 Pages 191-193
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (429K) -
Tatsuo USAMI1976 Volume 29 Issue 2 Pages 194-197
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (388K) -
Tetsuzoh SENO1976 Volume 29 Issue 2 Pages 197-200
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (488K) -
Katsutada KAMINUMA1976 Volume 29 Issue 2 Pages 200-202
Published: May 15, 1976
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (2918K)
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