著者

三浪 俊夫 久保寺 章

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.30, no.1, pp.73-90, 1977-04-05 (Released:2010-03-11)

参考文献数

19

被引用文献数

1

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An earthquake swarm started its activity in the northern somma of the Aso caldera on January 20, 1975. In the course of the earthquake swarm activity, on January 23, an earthquake of magnitude 6.0 representing the largest one among the whole earthquake swarm took place. After this earthquake, the activity of the earthquake swarm declined gradually until the end of January. By using available data obtained from all the seismological stations in the Kyushu district, 120 foci of these earthquake swarm were determined with fairly a high accuracy.Analysing the time variation of the frequency of earthquakes, the migration of their foci, the variation of b-values, and so on, it was found that these features seen in the earthquake swarm were having quite a similar character in the fracturing of the stressed rocks.1) The b-values showed fairly a large differrence in the two periods, i. e. before and after the largest earthquake. Before the earthquake, b=0.73 while after the earthquake b=1.01.2) The series of the earthquake swarm activity can be divided into 6 stages, from the consideration of the migration of the earthquake foci or their characters. The temporal change in the spatial distribution of these foci was noteworthy. In the early stage of the activity a void space (seismicity gap) was observed in the central part of the area in which many foci were distributed. In the next stage, small earthquakes began to take place inside of the above mentioned void space, then at last the largest earthquake occurred at the edge of the void space.3) A volume of the void space may be taken to be 1.8×1017cm3 from the locations of foci during the stage II and the ultimate stress energy that can be stored up in the void space until a break-down takes place can be estimated to be 5.65×1020 erg. According to the relation between the energy of an earthquake and its magnitude i. e. log E=11.8+1.5M, the magnitude of the largest possible earthquake M=5.97 is obtained. This value agrees with the magnitude which has been determined from the maximum amplitude on the seismograph of the above mentioned largest earthquake (M=6.0) among the whole swarm.4) Considering the migration of the earthquake foci, it may be concluded that this earthquake swarm activity have not been related to a volcanic activity of the Volcano Aso.

著者

久保寺 章

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.4, 1981-12-28

著者

益川 敏雄 表 俊一郎 久保寺 章 三浪 俊夫

出版者

日本地熱学会

雑誌

日本地熱学会誌 (ISSN:03886735)

巻号頁・発行日

vol.1, no.1, pp.3-14, 1979-06-30 (Released:2009-08-07)

参考文献数

5

被引用文献数

1

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Recently, the Hatchobaru geothermal electric power station of Kyushu Electric Power Co. started its commertial operation on June 1977, under the prescribed power of 50, 000KW. In prior to the completion of the full scale Hatchobaru Power Station, a geothermal power station had been operated since August 1963 at Ohtake, about 2 km distant from the new station to the north. Together with the increase in the development of power production it was planned to improve the micro-earthquake observation network. A new network is composed by one base station and 6 branch stations distributed within an area of 20×20km, in which the Hatchobaru station is acting as the base station locating nearly in the center of the other stations. Each branch station is equipped with one vertical seismometer and is connected to the base station by telephone lines. In the base station all neccesarry devices for micro-earthquake observations are prepared including memory unit, trigger unit, amplifying unit, for-each respective station and a cloock system as well as a recording system. The recording system in Hatchobaru base station is so arranged that the six seismograms of all the seismic stations could be reproduced on one sheet of paper side by side. In doing so reading of seismograms and locating of epicenters could be realized most easily with high acculacy. In this report there are described the newly developed telemeter system for observing the micro-earthquakes in the Hatchobaru geothermal area, together with the some results obtained in the course of the first 8 months test run. These results fairly a satisfactory operation.

著者

三浪 俊夫 久保寺 章 表 俊一郎 木下 保美

出版者

日本地熱学会

雑誌

日本地熱学会誌 (ISSN:03886735)

巻号頁・発行日

vol.3, no.1, pp.43-53, 1981-04-20 (Released:2010-02-05)

参考文献数

20

被引用文献数

1

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The area around the Kujyu volcanic mountains that is locating just in the central part of Kyushu Island is named as the Hohi geothermal area. In this region, the Ohtake and the Hatchobaru geothermal electric power stations are currently in operation. In this region, the micro-earthquake observation system has been set up providing six satelite stations connected to the Hatchobaru central station by public cable lines and giving seismograph records displayed on one sheet of paper in the central station. The operation of this micro-earthquake system has started July 1977 with highly increased time accuracy.Analysis of the seismic records for the last two years has yield following results.i) In these two years, about 200 foci of the earthquakes that occurred in this region have been located. All of these earthquakes gave the magnitudes smaller than M=3. These earthquakes could be classified into two groups. One was a group of earthquakes that might be related to the characteristic tectonics in the geothermal area, and the other were the earthquake that may be related either to the earthquake swarm activity in the northern part of the Aso caldera or the aftershock activity of the Oita earthquake of 1975.ii) The micro-earthquakes that are proper to the geothermal area were seen arranged in a belt zone along fault lines that are developed clearly in this region. In this belt zone swarm type microearthquake activities were observed showing the short duration period of swarm occurrence and shifting the swarm activity from one place to another.iii) For the purpose of obtaining more accurate focal locations, re-determination of the foci of all these swarm earthquakes were carried out by the aid of the improved master event method.As the result of which, it was made clear that foci distribution of each of these earthquake swarm was bounded in a narrow volume having the horizontal and vertial dimensions of 500 m x 2 km, extending almost vertically.iv) With regard to these earthquakes in the swarm, the study was carried out for making clear the earthquake occurrence mechanism of these earthquakes. It was found that earthquakes that occurred in the area near the Aso caldera, showed a mechanism represented by the right-lateral fault movement and for the earthquakes that took place along the geological fault zone, they showed a normal fault type mechanism.v) Within the low gravity area represented by the Kujyu caldera, locating in the north-eastern part of the Kujyu mountain range, almost any micro-earthquake activity is not observed.

著者

久保寺 章 岡野 健之助

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.13, no.4, pp.210-218, 1960-12-25 (Released:2010-03-11)

参考文献数

5

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The seismic waves due to the great nuclear explosions in the central Pacific Ocean (Bikini Atoll) in June and July 1958 were recorded by routine seismographs at the Abuyama Seismological Observatory of Kyoto University.The remarkable result was that we found a new kind of wave-group which has the following properties on the records of long-period seismograph. The wave in this group is of a period 9 to 1 minute and its propagation velocity is about 300m/s. The arrival time is about 3 hours later than that of seismic P-wave. These properties are similar to those of the microbarographic oscillations produced by the nuclear explosions, and the phenomena can hence be attributed to the effect of atmospheric pressure fluctuations upon the inertia mass of the seismograph.

著者

久保寺 章

出版者

日本地震学会

雑誌

地震 (ISSN:00371114)

巻号頁・発行日

vol.13, no.4, 1960-12