著者

田島 広一 井筒屋 貞勝

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.17, no.4, pp.187-190, 1972-08-02 (Released:2011-03-01)

参考文献数

4

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Measurements of vertical gradient of gravity carried out at Keio Plaza Hotel Building which was built recently. This building is in Tokyo (latitude: 35°41.2'E longitude: 139°41.9'N) and its height is about 170 m above the ground. The mean value of the gradient measured was 0.3049 mgal/m ± 0.00032SD. There are four stations where the vertical gradients of gravity have been measured in and around Tokyo. The distribution has a tendency to increase toward north in this area same as the free air anomaly distribution.

著者

森本 良平 小坂 丈予 羽鳥 徳太郎 井筒屋 貞勝 浦部 和順 高橋 春男 岡田 義光 平林 順一 伊佐 喬三 磯部 宏

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.77, no.5, pp.255-283, 1968-10-25 (Released:2009-11-12)

参考文献数

25

被引用文献数

3 3

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Unusual uplift of the land was found about an insular active volcano Iwo-jima, Ogasawara archipelago, 1, 200 km south of Tokyo. Remarkable retreat of shore line was revealed by reviewing topographic maps and aerophotographs of the island. Some upward movements of the island are to be one of the most principal reasons of the retreat. As the clear evidences of the upheaval of the land, following phenomena were observed by the writers who investigated the island five times from 4th July to 23rd August 1968 : a) Sunken vessels and a landing craft have emerged on the western coastal beach of the island : b) Faults and cracks appeared on the abandoned run-way of the former Japanese Navy in the central part of the island ; c) Coastal reef emerged on the sea to connect off shore islet with the island ; d) New coastal terraces were formed on the sand beaches ; e) Fresh living corals were exposed on the sea.Results of the investigations are enumerated as follows : 1) About 8 m upheaval of the land since 1953-4 was revealed by levelling survey at the western coast of the island. 2) Amount of uplift observed on the above-mentioned run-way is smaller in its central part than in both terminals, maximum vertical displacement of the fault being 3 m. 3) Tide gauge installed at the western rocky coastrecorded slight relative down of sea level but further observation should be continued without disturbance by typhoon to obtain more reliable data. 4) No expected microseisms were recorded on the high sensitive electro-magnetic seismographs except 2 or 3 per day. 5) Temperature of the fumarolic gases were 95-123°C, 10-25°C higher than that observed in 1935. In spite of the rise in temperature, gases of so called high temperature type, such as sulphur dioxide and halogens, were not contained. 6) Composition of the sublimates also accords with these results of chemical analyses of the gases. 7) Content of each main component element and its ratio to other ones is quite variable in several hot springs whose pH values range from 2.1 to 6.8. 8) Analcite was identified by X-ray and DTA analyses in the tuff forming Moto-yama, an eastern main flat cone of the island. Genetic condition of the mineral inferred from its chemical composition may indicate submarine eruption of the volcano. 9) Three weak zones were recognized by the present investigations in addition to the two ones previously reported by Tsuya. Thus three are arranged radially through the center of the eastern main cone and the two are arranged concentrically around the foot of the same cone. From these weak zones phreatic explosions are expected in future, if they occur. 10) Nothing more than mere weak phreatic explosion was recorded through the historic activity of the volcano. Artificial filling up of the vent, such as the pavement of the surface often causes the small explosion at fumarole. 11) Submarine eruption recently found at the sea bottom, about 5.4 km NNE of the South Sulphur Island, about 50 km south of the island did not occur recently but must have repeated rather stationarily.According to the present investigations, no remarkable magmatic explosion could be expected except those small phreatic ones, same one of which has often occurred on the island. Chemical composition of the gases does not indicate any approach of hot magma to the surface.

著者

萩原 幸男 村田 一郎 田島 広一 長沢 工 井筒屋 貞勝 大久保 修平

出版者

東京大学地震研究所

雑誌

東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.61, no.4, pp.563-586, 1987-03-31

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埼玉県北西部の関東山地北東縁部には,深谷断層,櫛挽断層,江南断層,今市-菅谷断層等の活断層が密集している.この地帯に7回にわたって合計約630点の重力測定を実施した.得られたブーゲー異常から,地質地形調査ではかつて指摘されたことのない断層を児玉町に発見した.また櫛挽断層は従来考えられていた規模より遙かに大きく,北西にはこの児玉町の断層に,南東には荒川を越えて今市-菅谷断層に連続していることが判明した.1931年西埼玉地震(M7.0)の震源断層は恐らくこの一連の断層と関連があるものと思われる.

著者

萩原 幸男 村田 一郎 田島 広一 長沢 工 井筒屋 貞勝 大久保 修平

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.61, no.4, pp.563-586, 1987-03-31

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埼玉県北西部の関東山地北東縁部には,深谷断層,櫛挽断層,江南断層,今市-菅谷断層等の活断層が密集している.この地帯に7回にわたって合計約630点の重力測定を実施した.得られたブーゲー異常から,地質地形調査ではかつて指摘されたことのない断層を児玉町に発見した.また櫛挽断層は従来考えられていた規模より遙かに大きく,北西にはこの児玉町の断層に,南東には荒川を越えて今市-菅谷断層に連続していることが判明した.1931年西埼玉地震(M7.0)の震源断層は恐らくこの一連の断層と関連があるものと思われる.