巻号一覧
28 巻 (1975)
- 4 号 p. 373-
- 3 号 p. 239-
- 2 号 p. 113-
- 1 号 p. 1-
前身誌
28 巻, 4 号
選択された号の論文の13件中1～13を表示しています
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坂部 和夫, 飯田 汲事1975 年 28 巻 4 号 p. 373-378
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーThe secondary fault of the Fukozu fault associated with the Mikawa earthquake in 1945 was investigated by the present geological survey. The secondary fault is a reverse fault with the south side as the hanging wall amounting up to about 1m, accompanied by lesser left-lateral component. It was ascertained that the secondary fault is of an active type and its vertical displacement at least since the formation of high terrace have accumulated in the same direction.
The strike of the secondary fault is nearly parallel with that of the northern wing of the Fukozu fault, and both faults are reverse type with the south side as the hanging wall, accompanied by lesser left-lateral component.
Western extension of the secondary fault had not been traced farther than the village Tenjin by the earlier investigators. Our survey, however, revealed that the fault extended at least 1km more to the west as far as Tomokuni. As the result of this survey, a total length of the secondary fault formed by the Mikawa earthquake in 1945 became about 5km.抄録全体を表示PDF形式でダウンロード (2353K) -
TOSBAC-3400, TOSBAC-40 SYSTEM とそのA/D, D/A変換器の利用勝山 ヨシ子, 浜田 和郎, 福井 隆文, 渡辺 一郎1975 年 28 巻 4 号 p. 379-386
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーMethods of earthquake detection from a long time analog tape recording have been developed. In these methods, the detection of earthquakes is done by an interpreter looking at the display on the memory-scope of storage type, then the selected seismogram is picked up and stored on digital magnetic tapes by the instruction through an on-line console typewriter. The hardware system for the methods consists of an additional memory-scope of low price and an ordinary computer system including A/D and D/A converters. By the present technique, 7-days data which includes 30 earthquakes is processed within several hours.
We have developed two methods. In the first step of the first method, all analog records are once digitized and stored on digital magnetic tapes with a high speed of 50 times that of recording. Then in the second step, the converted digital data are displayed on the memory-scope with a high speed of 80 times that of recording. Data of the recognized earthquakes are eddited and stored on a new digital magnetic tape by the interpreter's instruction.
In the second method, analog data are digitized with a speed of 50 times that of recording and displayed on the memory-scope simultaneously. Selected data are eddited and stored on a new digital magnetic tape when needed.
In the first method, it takes 4 hours for the first step and 2.5 hours for the second step in processing the data of one week which contains about 30 earthquakes, while in the second method it takes 4.5 hours for the same data. In the first method, a monitor's working time is shorter and its first step can be carried out by the use of a mini-computer semi-automatically, although the total time is longer than in the second method.
The importance of eye inspection of the visible record shall remain in the future, even if an effective automatic earthquake detection method is developed.抄録全体を表示PDF形式でダウンロード (2985K) -
岡田 義光1975 年 28 巻 4 号 p. 387-413
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーTwo earthquakes, which occurred in the east off Hachijojima, Japan (Feb. 29, 1972 (M=7.0) and Dec. 4, 1972 (M=7.2)) are studied with respect to their source mechanisms. For this purpose, the writer collected the strain- and tilt-steps observed in Japan, and compared them to theoretical steps based on fault-origin models.
Generally, the strain data seem systematic and consistent, to some extent, to the theoretical models. It is remarkable that patterns of the spatial distribution of steps, which characterized the two events, are very different to one another. This may be naturally attributed to the difference in their source mechanisms as derived from the radiation pattern of the P-waves.
Direct plots of the step amplitude versus epicentral distance showed large scattering of data. It is rather difficult to explain this relation by a simple formula.
The writer refers to the fault-plane solutions by Ichikawa and calculated the theoretical steps at the observational sites, by use of the explicit expressions for surface strains and tilts due to an arbitrarily oriented double couple source buried in a semi-infinite elastic medium. Comparison of the theory with the observation seems to suggest the moments of the two earthquakes, as 2.3×1027, 1.2×1027 c. g. s., respectively, though these values are erroneous due to considerable scattering of the data.
Tilt-step data seem more erroneous, sometimes the observations show the amplitude ten or more times as large as the theory, and hard to explain by a simple model. Various sorts of causes may be suspected for this trouble. One of the likely causes is that the continuous tilt observations are worked out, at present, mainly with small-size pendulumtype tiltmeters, which may be disturbed by local conditions more easily than such large-size instruments as water-tube tiltmeters. For further discussion, therefore, careful selection of data in account to the instrumental conditions at each station must be provided.抄録全体を表示PDF形式でダウンロード (2161K) -
山科 健一郎1975 年 28 巻 4 号 p. 415-427
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーThe fault parameters of earthquakes in the Japan area (1926-1948) are referred to, and their contribution to strain accumulation is computed in the Fukui area, Honshu, Japan, where a big earthquake occurred in 1948 (M=7.3, 136.2°E, 36.1°N, depth about 20km, after JMA). Taking the focal mechanism of the Fukui earthquake (strike-slip type) into consideration, the discussion is developed with respect to the increase or decrease of the strain component, εYY-εXX, which would play an essential role in the present faulting.
Especially remarkable is the contribution by several major shocks, such as the Tottori (1943), the Tonankai (1944), and the Nankai (1946) earthquakes, which immediately preceded the present event and resulted in significant increase of the strain component. Quantitatively, the present effect may cause the changes of 6×10-7 in strain, and 200mb in stress, approximately. It is questionable that small disturbances of this magnitude can be a definitive trigger, always. In some critical cases, however, a fractional change in strain or stress may play an essential role. Further knowledges about the present effect are needed for better understanding of the focal processes.抄録全体を表示PDF形式でダウンロード (1476K) -
松浦 充宏, 佐藤 良輔1975 年 28 巻 4 号 p. 429-434_4
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーDisplacement field due to some typical dimensional faults in a semi-infinite medium are shown systematically, by exhibiting contour maps for vertical components and vector maps for horizontal components, which provide helpful guide when estimating focal parameters such as dip-angle and slip direction from observed data on static deformations.
Computations and mappings are carried out by the machine program developed by SATO and MATSU'URA (1974).
For a pure dip-slip reverse fault (Fig. 3), main upheaval appears on the area of projection of the fault to the surface and spreads over the hanging wall side as the dip-angle increases. For small dip-angle, subsidence is found on the hanging wall side, while for large dip-angle, it is observed on the foot wall side.
For a pure strike-slip fault (Fig. 4), there appear subsidence and upheaval at two ends of the fault projection. As the dip-angle increases, the area with opposite deformation to that on the hanging wall side spreads on the foot wall side.
Horizontal displacements do not show quite a different pattern between fault models with different slip directions (Fig. 6). Hence it may be difficult to get unique fault solution from observation of only horizontal displacements unless precise and dense data around the fault are available.抄録全体を表示PDF形式でダウンロード (2353K) -
宇津 徳治1975 年 28 巻 4 号 p. 435-448
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーAbout 400 shallow earthquakes in central Japan occurring during 1967-1974 have been relocated using data supplied by the Japan Meteorological Agency and several university seismic stations. About 4200 P-residuals are obtained in the relocation. The residual is approximately normally distributed with a mean of 0.0sec and a standard deviation of 0.59sec. Therefore, the probability that a residual exceeds 0.4sec is 0.25. If the actual travel-time for paths crossing the focal region of an impending earthquake is increased by 0.4sec, the probability that an observed residual for one of these paths exceeds 0.4sec will be 0.50. Let R denotes the ratio of the number of paths with residuals larger than 0.4sec to the total number of the paths crossing a certain region. The R-values for the focal regions of the central Gifu earthquake of 1969 (M=6.6), the Izu-hanto-oki earthquake of 1974 (M=6.9), and other 24 earthquakes of smaller magnitudes during some time-intervals before the occurrence of them have been determined to be about 0.5 or more. These values suggest the decrease in P-velocity before the earthquakes. A map has been made showing the distribution of R-values in 204 areas of 0.2°×0.2° in central Japan. Significantly high R-values are found in the areas containing the focal regions of the above-mentioned two earthquakes in the maps covering certain periods before the earthquakes. However, there are many other areas of high R-values, which are not connected with the occurrence of large earthquakes until now. Most of these areas may correspond to inherent low-velocity regions in the crust.抄録全体を表示PDF形式でダウンロード (1351K) -
相田 勇1975 年 28 巻 4 号 p. 449-460
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーOn May 21, 1792, a gigantic collapse of Mt. Mayuyama in Shimabara Peninsula, Kyushu, occurred. Following this event, a severe tsunami of about 10 meters in height was generated by the landslide and attacked the coast of Ariake-kai, killing more than 14, 500 persons. Many historical documents tell us the phenomena of this tsunami in fair details, so that we attempted to reconstruct a numerical model of the tsunami consistent with the historical data. In the numerical computation, a finite difference method with a leap-frog system is adapted, and two kinds of source input are tried; one is the prescrived water mass transport normal to shore line and the other the vertical displacement of sea bottom. When the transport of 18, 000m3/min (current speed-20m/sec) per unit length of shore on the center line of landslide area is assumed to be continued during 2 to 4 min, the computed waves agree fairly well with the real tsunami behaviors, the height of tsunami in various places along the coast and the order of the maximum crest in the sequence of a wave train. Therefore, it seems probable that the extraordinary flow of water normal to the shore occurred by some physical mechanisms of the mountain collapse.
The energy of this tsunami is estimated to be about 5×1019erg, and this is about 1/100-1/1000 of the available potential energy of the slided material due to the collapse of the mountain. It is significant that the tsunami energy is several times larger than that of the 1968 Hyuganada Earthquake (M=7.5). The wave spreaded over a wide area and gave distructive damages to the coast more than 120km on both side of Ariake-kai.抄録全体を表示PDF形式でダウンロード (1210K) -
羽鳥 徳太郎1975 年 28 巻 4 号 p. 461-471
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーAdding mareographic data at the Kuril Islands, the source areas of the 1973 Nemuro-oki tsunami and the 2nd tsunami accompanying the largest aftershock on June 24, 1973 are reanalyzed. The result is the same as shown in the preliminary report: The source length of the 1973 Nemuro-oki tsunami is 130km long parallel to Nemuro Peninsula and the area is 7.2×103km2. The source length of the 2nd tsunami is 100km which is longer than the aftershock area reported by NOAA, and the western half of the source area seems to overlap with the source area of the first tsunami.
The 3rd tsunami of Sept. 27, 1974 was observed with small amplitude at Hanasaki. The estimated source area of this tsunami is within the source area of the 1973 tsunami. The 4th tsunami of June 10, 1975 was generated by an earthquake with the magnitude of about 7 (JMA), but the tsunami magnitude was relatively large. According to the author's method based on the attenuation of tsunami height with distance, the tsunami magnitude (Imamura-Iida scale) is m=1.5. This magnitude is the same grade to that of the 1973 Nemuro-oki tsunami. The estimated source area falls inside the source area of the 1969 Shikotan tsunami. The source length is about 100km long and its area is 6.3×103km2. The sea-bottom of this area may be uplifted, judging from the initial motion of the tsunami observed at Hokkaido and Sanriku.
The source areas of the tsunamis generated after the 1973 Nemuro-oki tsunami moved to the north-eastern direction along the continental slope. Within the source area of the 1969 Shikotan tsunami, many tsunami sources are located. On the contrary, there is a remarkable gap of the tsunami source area between the 1952 Tokachi-oki and the 1973 Nemuro-oki tsunamis. The source area of the 1973 tsunami occupies only the eastern half of the 1894 tsunami source. The area to the south-west of the 1973 tsunami may be considered a region of relatively high tsunami risk.抄録全体を表示PDF形式でダウンロード (1031K) -
島津 康男1975 年 28 巻 4 号 p. 473-481
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーDisaster due to earthquake in Japan is characterized by indirect and long-term impacts by collapse in administration, information, and communication systems. Damages and corresponding actions are discussed based on a systems concept. Four types of actions are distinguished as: destruction proof, dispersion, fail safe, and repair. The latter two are espcially important to protect systems function. Earthquake prediction is also discussed in relation to possible actions. The prediction at one year before the zero day is significant with respect to systems protection. Mass evacuation appears to be impossible. An interdisciplinary research of prediction connecting seismology and social-human sciences is proposed.抄録全体を表示PDF形式でダウンロード (779K) -
石井 清1975 年 28 巻 4 号 p. 483-486
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (498K) -
佐藤 良輔1975 年 28 巻 4 号 p. 486-489
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (9660K) -
佐藤 裕, 井内 登1975 年 28 巻 4 号 p. 489-491
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (334K) -
竹内 均, 横倉 隆伸, 菊地 正幸1975 年 28 巻 4 号 p. 491-492
発行日: 1975/12/10
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (226K)
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