著者
岸上 冬彦 小坂 丈予
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 (ISSN:00408972)
巻号頁・発行日
vol.33, no.1, pp.153-161, 1955-06-25

1953年7月26日箱根早雲山において山津波が発生し,人員及び建造物に対して相当の損害をあたえた(第1図).我々は7月29日, 31日, 8月5日及び11月11日に現地を調査する機会を得たので,その結果を報告する.
著者
中西 一郎
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.74, no.3/4, pp.301-310, 2000-03-30

It is mentioned in several earthquake catalogues of historical earthquakes that two earthquakes occurred in May, 1685 and on October 3, 1686 in the Toyohashi region, central Japan. We have recently found historical documents recording the latter earthquake in the Toyohashi region where previous studies located the epicenter of the 1686 earthquake without documents. Our analysis of the documents suggests that the 1685 earthquake did not occur. The damage recorded in the historical documents on the 1686 earthquake was large in villages on the Pacific side of the Toyohashi region. According to this evidence we consider that the epicenter of the 1686 earthquake may be located near the Pacific coast to the south of the town of Toyohashi. This large earthquake, the magnitude of which is estimated to be about 7, occurred 21 years before the great Hoei earthquake of October 28, 1707 (M=8.4). In the eastern part of Aichi prefecture, including the Toyohashi region and the offshore region of the Atsumi peninsula, moderate earthquakes have recently occurred. It is possible that the 1686 earthquake was a seismic precursor to the great 1707 earthquake. The eastern part of Aichi prefecture and the offshore region of the Atsumi peninsula in Aichi prefecture may be regions where we should carefully observe seismic activity, and other geophysical and geochemical phenomena.
著者
宇佐美 龍夫 茅野 一郎
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.5, pp.923-933, 1970-12-05

The relation between Mk and MJ MJ=0.5Mk+4.35 is obtained by the method of least squares, using data from 1926 to 1943. It is shown that the relation can also be applied to earthquakes between 1885-1925. However, for earthquakes before 1885, the relation seems to hold for only large earthquakes with magnitude M(=0.5 Mk+4.85) larger than 8.0. MJ of the great Kanto earthquake of 1923 is given as 7.83 from the seismograms recorded at 3 Japanese stations.
著者
羽鳥 徳太郎
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.60, no.1, pp.p87-95, 1985

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.
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.56, no.2, pp.367-390, 1981-09-30

地震断層モデルを波源とする津波数値実験が,東海道沖においても有用であることは,1944年東南海津波の例によって認められた.ここでは数値実験によって,1854年安政東海津波,1707年宝永津波,1605年慶長津波,1498年明応津波の波源断層モデルのパラメータを求めた.いずれも東海道に問題を限って議論される.この中,安政,宝永津波については,かなり信頼度の高いモデルが確定された.しかし慶長,明応津波については,史料の乏しいことなどもあって,信頼度が低いことは否めない.これらの津波の特徴を比較すると,地域によっては明応津波が最も高く,災害予測の面から見落すことのできない津波であると考えられる.また局地モデルによる清水港の陸上遡上計算の結果,防波堤,埋立地などの港湾工事が,津波の高さを軽減するのにかなり効果を持っていることがわかった.また津波危険度の局地性についても,計算上の結果が得られた.
著者
NAKAMURA Kazuaki
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.42, no.4, pp.649-728, 1965-03-15

Oshima Volcano is a basaltic, insular stratovolcano with a summit caldera within which lies an active cone Mihara-yama. Izu- Oshima island is situated on the northern part of a volcanic chain extending from central Honshu to Marianas. Oshima Volcano consists an essential part of Izu-Oshima island which is the largest of the seven Izu-islands, being 92km2 in area and 22.5km3 in volume above sea-level. Volcanic products of the volcano were studied stratigraphically. The method and results of the study are summarized and discussed in this paper. A group of erupted material, including lava-flows, scoria- andash-falls, which successively accumulated without any weatheringbreak is called a member in this paper. A member is the basic stratigraphic unit which is proved to be the product of a singleeruptive cycle. Within a member, there is a definite succession oferupted material, scoria-falls→lava-flows→alternation of ash-falls in ascending order. The time needed for the deposition of amember is considered to be 10 years or less from an examinationof the latest two records of major eruption(1777~1792 and 1684~1690). The time needed for the deposition of the basal scoria of amember is far shorter than that for the deposition of the alternating ash-falls. This is evidenced partly by the examination of historical documents and partly by the simple elliptic shape of the distribution of the basal scoria. Eruptive activity represented bya member may be a continuous process in which the magma in the central conduit rises with explosive eruptions of scoria, overflows and then gradually falls with an ejection of ash formany years. Oshima Volcano is composed of more than a hundred members. The youngest twelve members are lumped into the Younger Oshima Group, with which this paper is chiefly concerned. Dates of the deposition of the twelve members are inferred bythe correlation with historical documents and excavated fragmentalpottery remains and by radiocarbon measurements. As a result, the Younger Oshima Group is found to consist of the deposits during the last 1500 years or so, and the deposition of each member, in other words .major eruption, to have taken place periodically with an interval of about 135±50 years. The volume of individual members is calculated to range from 0.1 to 0.7km3. The volume of the Younger Oshima Group is estimated to be 3.6km3, of which only 0.7km3 is now accumulated on the slope of the main cone. The rest is the caldera fill (ca. 2.2km3) and the deposits outside the island. The explosion index is calculated to be, about 60 for the Younger Oshima Group. Thermal energy transported by the Younger Oshima Group attains to the order of 1×1026 erg and the rate of energy release is 8.7~6.0×1024 erg/100 years. More than forty parasitic volcanoes are distributed within two narrow fracture zones. They are monogenetic, that is, the entire erupted material of each is incorporated within a single member. The summit caldera was formed after the deposition of the twelveth member(S2) from the surface and prior to that of the tenth member(N4), or some fourteen centuries ago. The volume of the twelveth and the eleventh member(S2 and S1), which are considered to have deposited just before the caldera formation, is estimated to be 0.4km3 i. e. one-eighth of the volume of the decapitated summit(3.1km3). These are mainly steam explosion breccias and ash-falls with accretionary lapilli. This will indicate that the summit was engulfed associated with intense explosions. The actual course of the engulfment is inferred to be like the eruption of Kilauea in 1924, after a consideration of the similarity of the sequence of events for the both activities. Recent eruptions of Oshima Volcano after the last major activity(1777~1792, the product of which is the uppermost member Y1), are very different in nature from those represented by members. Recent eruptions are more effusive(explosion index 10±), smaller in the volume of erupted material(less than 0.03km3) and have affected only the interior of the caldera or even of the crater of Mihara-yama. The rate of thermal energy release is also lower(2.7×1024 erg/100 years). Moreover, the period after the last major activity is that of repose judging from the deposits on the slope of the main cone.
著者
早川 由紀夫
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.60, no.4, pp.507-592, 1986-03-31

The eruptive activity of Towada Volcano is documented by the tephrostratigraphic study. More than 20 eruptive episodes are described in detail with isopach maps and isograde maps of maximum pumice size, maximum lithic size, and median diameter for the individual fallout deposits. The activity of the volcano started about 200,000 years ago along the NE-SW trending line crossing the present lake Towadako and relatively small-scale volcanoes were formed. A caldera 11km×11km wide was formed as a result of several eruptive episodes during the period about 55,000 to 13,000 years ago, three of which included voluminous pyroclastic flow eruptions. The post-caldera activity occured at a rate of one eruptive episode every 1,000 to 2,000 years and a stratovolcano and two lava domes were formed in the caldera. The latest eruptive episode was dated 1,250 y B. P. by the radiocarbon method. Rocks of Towada Volcano cover a wide range from basaltic andesite to rhyodacite (SiO2 : 51-70wt.%) with phenocrysts of plagioclase, augite, hypersthene, and magnetite with occasional olivine. Horn-blende is characteristically found in the pyroclastic deposits of 13,000 years old and in some earlier deposits. Volumes, V, of two plinian deposits are determined by the crystal method : 6.7km3 for the Chuseri deposit and 2.2km3 for the Nambu deposit. Then an empirical formula, V=12.2 TS, is obtained for the practical volume estimation, where T is the thickness of an isopach and S is the area enclosed by the isopach. Application of the formula to the fallout deposits of Towada Volcano suggests that the total magma erupted during the past 55,000 years amounts to 1.5×1017g. This corresponds to the discharge rate of dense rock equivalent to 1.1km3 per thousand years. The cross-wind range, Rc, of the pyroclasts of a given size may be a good indicator of the maximum height reached by the pyroclasts in the eruption column. It is found that the Rc is relatively large for those deposits whose erupted masses are relatively large. The dispersal of a fallout deposit is also seriously affected by winds. A plausible solution of the eruption condition for the Nambu deposit is that 4mm size lithic fragments reached the maximum height of 15km in the eruption column, then they were detached from the column and displaced by winds having an average velocity of 30m/s. After a 20 min flight, they fell upon the ground 48km east of the source. Whole-deposit grain size populations are determined for the Chuseri and Nambu plinian deposits. The Chuseri population is similar to the New Zealand examples. However, the Nambu population is distinctly coarser than the others.
著者
羽鳥 徳太郎
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.60, no.1, pp.87-95, 1985-09-05

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.
著者
都司 嘉宣 日野 貴之
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.68, no.2, pp.91-176, 1993-09-30

寛政4年4月1日(1792年)に,普賢岳の火山活動の終期に島原市付近に生じた地震に誘発された島原半島眉山の東斜面の崩壊によって,多量の土砂が有明海に流入し,有明海に大きな津波を生じた.この津波によって,島原半島側と,対岸の熊本県側の海岸は大きな津波被害を被った.近年,このときの熊本県側の津波被害の状況を伝える文書が数多く発掘された.この研究では,津波による死者数,家屋被害,田畑の浸水範囲と面積を確定し,あわせて被災現地での伝承,津波の浸水限界を示す「津波留石」などの知識を加えて,津波の浸水高の測定を行った.この津波による,肥後国の被害は,武士僧侶を除く死者が玉名郡で2,221人,飽田郡で1,166人,宇土郡で1,221人で肥後3郡合計で4,653人.このほかに武士僧侶とその家族たち162人を加え,4,815人が肥後三郡の死者総数となる.また,大矢野島を含む天草諸島では343人で,結局現在の熊本県がわ海岸全体で5,158人の死者があったものと見積られる.肥後三郡のけが人は811人,流失破損家屋2,252軒,浸水田畑3,848町歩であった.津波高さは熊本市の河内,塩屋,近津付近で15mから20mに達し,また三角半島北岸の細田,大田尾などで高く,三角町大田尾で22.5mに達した.
著者
石原 吉明 束田 進也 酒井 慎一 平松 良浩 古本 宗充
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.76, no.1, pp.87-92, 2001-07-25

Fireballs, which are caused by high-velocity passages of meteorites through the atmosphere, generate shock waves. It has been known that such shock waves are often recorded on seismograms. It is possible to determine the trajectories and the sizes of a fireball using seismological records. We have searched shock wave signals from many bright fireballs observed in the period from September 1996 to November 1998, and the 1999 Kobe meteorite. The shock waves from one large fireball, which is called the Miyako fireball, and the Kobe meteorite are clearly recorded on many seismograms. In particular, the shock waves from the former fireball are widely recorded by the dense seismic array of 1997-98 joint seismic observations in the Tohoku Backbone Range. We determine their trajectories. Amplitudes of the shock waves are found to be possibly correlated with the masses of the meteorites. It is also indicated that the shock waves from fireballs, which are darker than brightness magnitude -10, are too weak to be recognized on the seismograms of ordinary seismic stations in Japan.
著者
羽鳥 徳太郎
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.60, no.3, pp.429-438, 1986-02-07

津波史料をもとに別府湾沿岸を現地調査し,地盤高をふまえて各地の津波の高さ(平均海面上)や浸水域の広がりを検討した.大分市内では,流失した寺院の分布から津波の高さは4~5.5mに推定され,地盤高ぶおよそ4m以内の範囲が浸水域とみなされる.別府湾口の奈多と佐賀関ではそれぞれ7~8mと6~7mの波高に達し,湾外の上浦で4m,臼杵では3~4mと推定される.津波マグニチュードは今村・飯田スケールでm=2と格付けされる.津波・震度分布および周辺のテクトニクスから判断すれば,波源域は別府湾を包み東西方向に50km程度の長さがあったと推定される.また,瓜生島・神場洲の地盤沈降の記録は別府湾が陥没したことを暗示し,高角正断層の地震により津波が発生したと考える.
著者
宍倉 正展
出版者
東京大学地震研究所
雑誌
地震研究所彙報 (ISSN:00408972)
巻号頁・発行日
vol.78, no.3, pp.245-254, 2003

A tectonic geomorphological study is one of the best methods of evaluating the timing and the crustal deformation of pre-historic earthquake. To reveal the cycle of interplate earthquakes along the Sagami Trough, I investigatedthe emergedshoreline topography andthe fossilizedsessile assemblages in the Miura Peninsula andthe Boso Peninsula. The distribution pattern of coseismic vertical displacement during the 1703 Genroku Kanto Earthquake inferredfrom the height distribution of the paleo-shoreline suggests that the fault source model consists of a dual fault system of the Fault A andB. Fault A is also the source of the 1923 Taisho Kanto Earthquake. The geometry and ages of the emerged shoreline topography divided into several levels indicate that the characteristic earthquake generatedfrom Fault A has occurredabout every 400 years. One of several events, it is accompaniedwith a slip of Fault B, which has a recurrence interval of 2000-2700 years.
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.56, no.4, pp.713-730, 1982-03-31

南海道沖におこる巨大地震による津波の波源断層モデルを数値実験によって検討した.1946年南海地震を東西二つの断層によってあらわす.今回求められた断層モデルの特徴は,西側断層の西端が,足摺岬の東側約30kmにあること,東側の断層面の傾斜角が10°と低角であることである.また西側断層による海底変動継続時間を断定することはむずかしいが,3~10分程度と,普通の地震より長い方が,計算波形と実際記録の一致がよい.1854年安政南海地震津波の波源断層モデルは,南海地震の断層とくらべて,東側断層が北側に位置し,西側断層が30km長く求められた.また,ずれの量は約15%大きい.このモデルで大阪の津波の高さは2.4mとなるが,従来の推定値よりやや低い.しかし海岸においてこの程度の高さがあるならば,堀に津波が侵入する際,多くの船を上流に押し込み,地震をおそれて船上に避難していた人多数を犠牲にする可能性は十分あると考えられる.1707年宝永津波の場合は,足摺岬付近の津波の高さが,安政津波の約1.5倍もあり,また室戸岬,高知の地盤変動量が安政地震の際の約2倍といわれている.このため安政津波と相似形の波源断層モデルではよく近似できない.ここでは西側断層を更に二つに分割して三つの断層面をもうモデルによってこれを説明した.
著者
羽鳥 徳太郎
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.62, no.3, pp.p297-309, 1988-01

寛政5年1月7日(1793年2月17日)宮城沖に発生した地震の震度分布およびそれに伴う津波の高さを,新史料をもとに調べ,近年の宮城沖地震との比較から地震と津波の規模および波源域を考察した.各地の史料を調べた結果,震度5の範囲は岩手県中部から福島県北部に至る内陸部に分布し,震度4の範囲は東北地方から関東地方に広くまたがることが示された.1933年三陸地震・1978年宮城県沖地震などの震度分布との比較から,寛政地震のマグニチュードはM=7.8と推定された.一方,この地震に伴う津波の高さは,岩手県中部~牡鹿半島沿岸で3~5m,福島県沿岸では2~3mと推定された.筆者の方法(羽鳥,1986)によれば,津波マグュチュード(今村・飯田スケール)はm=2.5と見つもられ(1968年十勝沖津波と同じ規模),従来推定されていた値よりもやや大きい.震度および津波の高さの分布から,波源域は1897年8月の宮城沖津波の波源域を含むかたちで海溝付近にあり,長さ200km,幅80km程度の大きさであったと考えられる.The Miyagi-Oki tsunamigenic earthquake of Feb. 17, 1793 (Jan. 7, Kansei 5) hit the Tohoku district, and its aftershock activity continued for a long time. According to the old documents, in the Sendai region 12 persons were killed and 1060 houses were destroyed by the earthquake. Along the Pacific coast from Aomori to Fukushima 22 or more persons were drowned and about 500 houses and many ships were damaged by the tsunami. In this paper the distributions of the seismic intensity and tsunami behavior are investigated with the addition of newly collected data. The results are summarized as follows: 1) A seismic intensity of 5 (JMA scale) occurred inland for 230 km from Morioka to Fukushima, and an intensity of 4 was widely distributed in the Tohoku to Kanto districts. The earthquake magnitude is inferred as M=7.8 via a comparison with the seismic intensity pattern of other Miyagi-Oki earthquakes. The epicenter is estimated to have been 38.5°N, 143.5°E near the trench. 2) Considering the ground level of the damaged regions, the tsunami heights were inferred to have been three meters (above M.S.L.) along the Iwate to Miyagi coasts and locally to have reached 4~5 meters. The tsunami heights along the Fukushima coast were 2~3 meters. The head of the large bay with seiche periods of 30min or more was con- spicuously damaged, suggesting that the longperiod waves were predominant. By use of the author's method based on the classification of tsunami heights along the coast, the tsunami magnitude (Imamura-Iida scale) is determined as being m=2.5. 3) The estimated source area is lapped on the tsunami source of Aug. 5, 1897, lies near the trench. According to the statistical relation of tsunami magnitude, the source area may be 80×200 km2. It is pointed out by many seismologists that a seismic gap exists near the trench far east of Miyagi Prefecture. For future tsunamis generated in this region, the behaviors of the 1793 tsunami suggest useful information.
著者
羽鳥 徳太郎
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.60, no.4, pp.p643-655, 1985

1985年3月3日,チリのバルパライソ沖でおきた地震(M=7.8)により,約23時間後に日本の太平洋沿岸各地の検潮所で全振幅10~30cmの津波が観測された.太平洋各地の検潮記録から判定すれば,津波マグニチュードはm=1.5と格付けされる.日本沿岸では津波の周期15分が卓越したが,最大波に60分の長周期波も含まれている.津波初動から最大波が現われた時間は,3時間と7時間前後のところがあり,3時間後に最大波を記録した1960年チリ津波の波形パターンと多少異なった.1700年以降の日本の記録によれば,チリでM8以上の巨大地震が発生して,チリ沿岸で波高が6~8mの場合,日本沿岸では1m程度の波高になり,10mをこえると日本では3m以上に達して被害をもたらした.また,ハワイでは常に日本より波高が大きい.これは,日本の津波予報を適確に判断する上で,チリおよびハワイの津波情報がきわめて重要であることを示している.