著者

木村 敏雄

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.44, no.2, pp.561-607, 1966-10

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Turbidites are developed in the Permian-Triassic Sambosan and the Jurassic-Cretaceous Shimanto group in Japan. The Turbidite sequences are well distributed in the Tamagawa district, the Kanto mountainous land, and in the Oigawa district (Fig. 1). The sequence in the latter district occupies the southern wing of a grand recumbent fold. Here, turbidite-poor shale, turbidite (the A formation), non-turbidite with turbidite (the B), turbidite (the C) and turbidite-poor shale formations are distributed. Average thickness and standard deviation of the sandstone and shale beds within each 5m column of strata were measured (Tables 1-3). Average thickness of sandstone beds varies with the horizon, especially with the major cyclic sedimentation. On the other hand the average thickness of shale beds is fairly constant in the turbidite sequences (the A and C formations). Thickness of the sandstone beds in the turbidite sequences shows log-normal distributions (Figs. 16, 17). However, that of the shale in the turbidite sequences shows distributions similar to the normal ones. The distributions are probably due to the fact that the shale deposition is proportional to time and that the time interval of turbidity currents is fair constant. This is confirmed by a fact that the number of turbidites during the deposition of a unit shale is fairly constant (Table 4). The standard deviation of thickness distribution is related to the thickest bed within each 5m column, especially for the sandstone beds. Thickness distributions of sandstone and shale beds in the turbidite-poor and the turbidite-rich sequences (the B formation) are quite different from those of the turbidite sequence (the A and the C formation) in the Oigawa (Fig. 18, Table 2) and show much wider distribution. The thickness of sandstone beds is not related to that of the overlying and the underlying shale beds in the A and C formation (Figs. 22, 23). However, turbidite beds in the turbidite-poor shale formation underlying the A formation are composed of a very thin sandstone part and rather thick silt part. In this case thickness of the overlying silt and shale appears to be related to that of the underlying sandstone part. The thickness of turbidite sandstone beds is also related to the clasticity (Fig. 24) and sedimentary structures. Sole marking is not common on the underside of the thinner beds (70cm or less). Laminated structures, convolute structures and other are common in the thinner beds (10cm or less), but not common in the thicker beds. In the turbidite together with the non-turbidite sequences there are cyclic sedimentations. Sandstone-shale diagrams (Figs. 6, 10, 11, 14, 15), total thickness (Figs. 4, 7, 13), average thickness and the thickest bed (Fig. 26) within 5m column, and accumulation of sandstone during the deposition of a unit thick shale (Figs. 8, 10, 15) show the cyclic sedimentations which are classified into major and minor ones. The major cyclic sedimentation is most well shown by the distribution of thickest bed within each 5m column (Fig. 26). The bed usually corresponds to the thickest bed within each minor cycle (Fig. 19). The major cycle may be related to transgression and regression and is not related to the chert deposition at Unazawa (Fig. 7). Minor cyclic sedimentations are further classified into "increasing" and "decreasing" types (Fig. 12). The "increasing" type appears to be generally formed during the regression, the "decreasing" type during the transgression. The minor cyclic sedimentations are well shown by the sandstone-shale diagrams as well as by the thickness distribution of sandstone beds according to the sedimentation order (Figs. 12, 20). There was a basin of the normal sedimentation with some steep cliffs at the regressional stage (Fig. 27), a part of this basin becoming the drainage of turbidity currents when the sea level was rather high. At the stage of transgression, shale deposited principally with muddy turbidites. The major cyclic sedimentation may have been formed under such a circumstance. The frequency of great earthquakes and the tectonic position in the westernmost Pacific near Japan are comparable with those of turbidite sequences in the Oigawa district, the turbidites having been probably produced by such earthquakes.二畳紀-三畳紀の三宝山層群,ジュラ紀-白亜紀の四万十層群にはTurbidites層が発達している.このTurbidite層は多摩川地域・南部大井川地域によく見られる(Fig. 1).大井川地域のこの層群は大きな横臥せしゅう曲の南翼をなしており, Turbiditeの少ない頁岩層, Turbidite層(A層), Turbiditeを伴うnon-Turbidite層(B層), Turbidite層(C層), Turbiditeの少ない頁岩層からなつている. 5mの厚さの地層の中の砂岩層の平均層厚(Table 1-3)は層準に応じて,特に堆積の大りんねに応じて変化する.一方頁岩層の平均屈厚はA, C層内では層準にかかわらずほぼ一定である.

著者

長沢 工

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.53, no.1, pp.p271-280, 1978

著者

鈴木 貞臣 サイエド モハムド ファテミ アグダ 中村 武史 松島 健 伊藤 喜宏 ホセイン サデギ メヒデ マレキ アラシュ ジャファー ガンドミ サイエド セイバン ホセイニ

出版者

東京大学

雑誌

東京大學地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.79, no.3, pp.37-45, 2005-03-23

著者

Ando Masataka

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.49, no.1/3, pp.19-32, 1971-09-30

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The writer determined fault parameters of the great Kanto earthquake of 1923 on the basis of the geodetic data by triangulation and levelling. Thus he attempted to establish a dislocation model which reasonably explains all the available data on the surface displacements associated with this earthquake. Basically the fault line is assumed to extend from the Kozu area southeastward with its strike N45°W, parallel to the trend of the Sagami trough. The shape of the fault plane is assumed to be a rectangular plane. The fault models which was finally accepted is as follows. total length: 130km, width: 65km, dip. 45° and a fault displacement : 6 m (right lateral strike slip) and 3 m (reverse dip slip). Generally speaking, this earthquake seems to indicate a differential movements of the two crustal plates bounded by the Sagami trough. The fault's dimension, geometry and direction of the slip are all in good harmony with the seismological evidence on wave radiation.|1923年の関東大地震の震源パラノーターを地殻変動を使つて推定した.

著者

佃 為成 酒井 要 橋本 信一 羽田 敏夫 小林 勝

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.63, no.3, pp.p237-272, 1988-12

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北部フォッサマグナの中央隆起帯を横断する千曲川構造線の東端に位置する長野県小県郡丸子町付近で1986年8月24日,M4.9の地震が発生した.ここは2つの火山前線がぶつかる点のすぐ背後でもある.通常の地震活動レベルは低いが,過去には1912年の上田市付近の地震(M5.2)がある.丸子町の地震活動は前震・本震・余震系列と本震の10日後から始まった群発地震が重なったものであった.2回の主要な活動ピークをもつ例は,北部フォッサマグナ地域では少なくなく,ピーク間の間隔は1918年大町地震の13時間,1969年焼岳の地震の2日,1912年上田の地震の5日,今回の地震の12日,1963年燕岳の地震の20日,1897年上高井の地震の104日というように様々である.2回目が群発地震であったのは丸子の地震と,燕岳の地震,上田の地震である.現地における臨時観測によって精密な震源分布が得られた.震源域は時間とともに拡大したが群発地震後最終的には東西3km,南北2km,深さは6kmを中心に3kmの幅をもつ拡がりであった.定常観測網で求めた震源との比較を行い,観測網に依存する震源の系統的なずれやその値のバラツキから震源の絶対精度と相対精度を推定した.MO~4.5の間のM別頻度分布はGutenberg-Richterの関係から少しずれる.群発地震の回数の減衰(p~2)は本震直後の余震のそれ(p~1)と比べ大きい.燕岳の地震ではどちらもp~2であった.本震の震源断層は発震機構及び余震分布の特性から西上り東落ちの高角逆断層である.これは中央隆起帯東縁でのテクトニックな変動と調和する.1986年の千曲構造線の地震活動はそのピークが東南東から西北西へ約150km/yearの速度で伝播した.1912年~1918年にもこの構造線の両端付近で地震があった.約70年の間隔を置いて同じような活動を繰り返したことになる.The earthquake of M 4.9 which occurred at Maruko town, eastern part of Nagano prefecture, at 11 h 34 m on August 24, 1986, was accompanied by foreshocks, ordinary aftershocks just after the main shock and peculiar swarm-like aftershocks that began 10 days after the event. Seismic sequences with double high adtivity peaks have occurred frequently in and around the northern Fossa Magna region; the intervals between the two peaks ranege from 13 hours to 104 days.

著者

Kanamori Hiroo Miyamura Setumi

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.48, no.2, pp.115-125, 1970-06-10

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Old seismological data were used to re-evaluate the Great Kanto Earthquake of September 1, 1923. On the basis of reported P times at about one hundred stations the hypocenter parameters were determined as: origin time, 2h58m32s; latitude 35.4°N; longitude, 139.2°E; depth, 0 to 10km. The above epicenter may be uncertain by ±15 km. The surface-wave magnitude was re-evaluated using seismograms from 17 stations. The average value of 8.16 was obtained.|1923年9月1日の関東大地震の震源とマグニチュードを再決定した.震源決定に用いた資料はInternational Seismological Summaryや日本の文献に発表されているP波の発震時で約100の観測点の値を用いた.再決定された震源要素は次の通りである.震源時:02時58分32秒,震央緯度:35.4°N,震央経度:139.2°E,深さ:O~10km.この震央の誤差は±15km位である.マグニチュードの決定は,17ケ所の観測所で記録された周期20秒程度の表面波の振幅を用いて行なつた.平均値として8.16が得られた.

著者

佃 為成 和田 博夫 酒井 要 伊藤 潔

出版者

東京大学

雑誌

東京大學地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.69, no.1, pp.1-18, 1994

被引用文献数

2

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An M6.6 earthquake occurred on February 7,1993, around a sea rise extending southwest-northeast direction off the northeastern tip of Noto Peninsula. The hypocenters of the mainshock and aftershocks were located using telemetered data from university stations. The aftershocks during the first two days are concentrated in the narrow active fault zone along the northwest side of the rise. Other concentrations occurred along active faults on the southeast side of the rise. Most of the focal depths are 10-15km, consistent with the interpretation of T phases and pP phases recorded at some stations. Northwestward dipping 3-dimensional distributions for large aftershocks suggest two possible fault planes, which coincide well with the two fault planes of the CMT solution. The gross nature of the seismic fault is of a thrust type, which contradicts the strike slip solution estimated from the initial motions. The Noto region is part of the tectonic zone along the eastern margin of the Japan Sea, where zonal shortening due to compression is predominant as in the Japan Sea coast region in northern Honshu, Japan. The alignment of aftershocks along the topographic lineaments and submarine active faults may reflect this tectonism.1993年2月7日の能登半島沖地震は,禄剛崎沖の南西から北東へ伸びる海底の高まり付近で発生した.この余震の分布をできるだけ精密に求めるため京大防災研上宝観測所と東大地震研信越地震観測所の観測網のデータを統合して震源計算した.この地域の構造はきわめて不均質であり,その影響を極力さけるためもっとも震源域に近い観測点を用いて地震決定を行なった.

著者

相田 勇

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.59, no.4, pp.p519-531, 1984

被引用文献数

4

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1741年北海道渡島半島沿岸から津軽地方にかけて襲った津波は,その規模の大きさからみて,地震によるものとする方が考え易い.しかし地震があったとする確かな古記録が,現在のところ見当っていない.そこで渡島大島の噴火によって発生するとしたら,どの程度の津波が期待できるかを見積った.渡島大島北側の大崩壊地形に見合う量の,土石なだれと,空気と混合した大規模な粉体流を仮定して,津波発生の数値実験を行った,結果は渡島沿岸の津波の高さが,1741年津波の1/3~1/4にしかならず,また津波のエネルギーも2桁位小さい.A great tsunami hit the Japan sea coast of Oshima and Tsugaru Peninsulas on Aug. 29, 1741. The idea that the tsunami was caused by the bottom deformation due to a large earthquake might be reasonable because the tsunami was ranked as one of the largest in the sea of Japan. However, there were no old records to prove the tremor or damage due to an earthquake, in contrast with the existence of many records on the eruption of the Oshima-Ohshima volcano.

著者

山科 健一郎 村井 勇

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.50, no.3, pp.295-302, 1976-03-31

著者

宇津 徳治

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.60, no.4, pp.639-642, 1986-03-31

著者

宇佐美 龍夫

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.52, no.2, pp.333-342, 1978-03-15

著者

宇佐美 龍夫

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.52, no.2, pp.333-342, 1978-03-15

著者

相田 勇

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.52, no.1, pp.p71-101, 1977

被引用文献数

14

著者

羽鳥 徳太郎

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.60, no.3, pp.439-459, 1986-02-07

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寛文・明和日向灘津波および宝永・安政南海道津波について,史料をもとに大分・宮崎県沿岸各地を現地調査し,津波の高さ,浸水域の広がりを考察した.寛文津波は宮崎平野に広く浸水し,津波の高さは4~5mと推定される.明和津波は大分県沿岸で2~2.5mの波高があり,津波よりむしろ地震災害が上回った.津波マグニチュードは,それぞれm=2と1に格付けできる.両津波の震度・波高分布および地殻変動の記録を近年の日向灘津波と比べると,波源域はいずれも沿岸付近にあったとみなされる.一方,宝永南海道津波は大分・宮崎県沿岸各地の集落に溢れ,津波の高さは3~4.5mに達している.また,熊本・長崎県沿岸にも浸水記録があり,30分程度の長周期波が卓越したことを暗示する.安政南海道津波は宝永津波よりやや小さく,大分・宮崎県沿岸の波高は2~3mと推定される.両津波の規模および震度が1946年南海道津波を上回り,予想以上に九州各地に強い影響を与えていることから,波源域が1946年津波のものより四国の南西沖に伸びていたことを考えさせる.

著者

羽鳥 徳太郎

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.56, no.3, pp.547-570, 1982-01-08

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The west coast of Kii Peninsula and Shikoku, western Japan, suffered severe damage from the three Nankaido tsunamis of 1707, 1854 and 1946. There are many old monuments of the 1854 Ansei tsunami along the Kochi coast. Old documents on the Hoei (Oct. 28, 1707) and Ansei (Dec. 24, 1854) tsunamis along the southwest coast of Kochi Prefecture were collected during the present field investigation and illustrated in this paper. Based on the documents, the inundation heights of the 1707 Hoei and 1854 Ansei tsunamis were surveyed by handlevel and compared with those of the 1946 Nankaido tsunami (Dec. 21, 1946). The inundation heights (above M. S. L.) of the 1854 Ansei tsunami along the southwest coast of Kochi averaged 5.5 meters. Those of the 1707 Hoei tsunami averaged 7.7 meters with maximums of 10 meters at places. Although the inundation heights of the 1946 tsunami along the entire Pacific side of Shikoku were nearly uniform, the patterns of height distribution along the west coast of Shikoku for the 1707 and 1854 tsunamis differ significantly from those of the 1946 tsunami. The inundation heights of the 1854 Ansei and 1707 Hoei tsunamis on the western Shikoku coast were 1.5 and 2.1 times respectively, higher than those of the 1946 tsunami. This suggests that the rise times and/or the amount of the slip displacements on the west part of the fault might be different.

著者

羽鳥 徳太郎 相田 勇 坂下 至功 日比谷 紀之

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.58, no.1, pp.187-206, 1983-07-28

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Yuasa and Hiro located on the west side of Kii Peninsula, western Japan, have been hit by many large tsunamis which were generated about every 100 to 150 years. Sources of all these tsunamis were offshore between Wakayama and Shikoku along the Nankai Trough. Traces of the inundated level on many houses in the two towns caused by the 1946 Nankaido tsunami (Dec. 21, 1946) were surveyed, using the automatic level from Oct. 18 to 23, 1982. The behavior of the 1946 tsunami run-up on land was investigated and compared with the two historical tsunamis of Hoei (Oct. 28, 1707) and Ansei (Dec. 24, 1854). The results of the present survey are as follows: (1) At Yuasa, the inundation heights of the 1946 tsunami were 3.0-3.5 meters above M.S.L. Ground about 3.0 meters above M.S.L. was inundated, so that 450 houses were inundated but hardly any were washed away. At Hiro, the sea wall strongly protected the main part of town from the 1946 tsunami (This bank was constructed just after the 1854 Ansei tsunami from Mr. Goryo Hamaguchi's personal funds). However, the tsunami energy concentrated at the head of bay along the Egami River. The inundation heights locally reached 5 meters (above M.S.L.) or more and 22 persons were killed. (2) According to old documents, the inundation area of the 1707 Hoei tsunami elongated along the Yamada, Hiro and Egami Rivers. Forty-one lives were lost at Yuasa and 192 at Hiro. Inundation heights above M.S.L. were estimated 4-5 meters at Yuasa and 5-6 meters at Hiro. (3) By the 1854 Ansei tsunami, 28 lives were lost at Yuasa and 36 at Him. The patterns of damage at Yuasa and Hiro are similar to those of the 1707 Hoei tsunami. There remain even now traces of the inundation level on a few old houses in both towns. Inundation heights above M.S.L. were 4.0-4.7 meters at Yuasa and 5.0 meters in the center of Hiro town. Ground about 4.0 meters above M.S.L. was inundated, 0.7 to 1 meter higher than that during the 1946 Nankaido tsunami.

著者

葉室 和親 荒牧 重雄 加賀美 英雄 藤岡 換太郎

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.55, no.1, pp.259-297, 1980-08-25

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More than 40 topographic highs resembling conical submarine volcanoes in the area between the eastern coast of the Izu Peninsula and the Izu-Oshima island, are identified by the detailed submarine topographic maps recently published. 17 dredge hauls were recovered from 26 dredge stations occupied during cruise KT78-10 of S.S. Tansei Maru of the Ocean Research Institute, University of Tokyo. Most of the rock samples are fresh basalts from the top part of the isolated peaks indicating that many of these topographic highs are young submarine volcanoes. They are very likely to be the submarine counterparts of the subaerial Higashi-Izu Monogenetic Volcano Group distributed on land just west of the dredge area. Most of them are high-alkali tholeiitic basalts with phenocrysts of olivine and plagiocalse. Augite phenocrysts may be present and some specimens contain abundant quartz and plagioclase xenocrysts derived from felsic plutonic rocks, a feature very similar to that found of the Higashi-Izu Monogenetic Volcano Group. Many are nearly aphyric and high in Al2O3 (19-17%) which is in strong contrast with the low alumina, low alkali tholeiites of Izu-Oshima island. In the Harker variation diagrasm, the highalumina, high-alkali tholeiites, both on land and under the sea, have distinctly high Na2O as compared with the basalts of Izu-Oshima. There seems no compositional gradation between the two although they are contemporaneous and occurring in adjacent areas.

著者

中村 一明

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.58, no.3, pp.711-722, 1984-01-14

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富山トラフ以東の日本海東縁の大陸斜面と陸上の瑞穂摺曲帯よりなる日本海東縁変動帯は北米・ユーラシア両プレート間の1~2Ma前以降の収束(力学)境界域であるという考えが説明される.日本海盆東縁と富山トラフ内に点在する凹地を連ねた地帯は沈み込みを示唆する構造を伴うので新生の海溝である可能性がある.

著者

村井 勇 金子 史朗

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.50, no.3, pp.329-342, 1976-03-31

著者

羽鳥 徳太郎

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.60, no.1, pp.87-95, 1985-09-05

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1984月6年13日,鳥島近海地震(M=5.9)によって,伊豆諸島をはじめ,房総から四国に至る沿岸各地の検潮所で全振幅10~57cm,周期5~9分の津波が観測された.また,八丈島の八重根漁港では,最大波の全振幅130~150cmの津波が目撃された.検潮記録によれば,津波マグニチュードはm=0と格付けされ,地震規模に対して津波が異常に大きい“津波地震”であった.波源域は須美寿島(八丈島南方190km)西側の水深1,000mの伊豆・小笠原海嶺にあり,波源域の長さは25kmと推定される.津波初動の押し引き分布から判断して,波源の西側の海底が隆起し,東側が沈降したとみなされる.