11 0 0 0 OA 新任教官紹介

著者
橘 和夫 深谷 賢治 駒宮 幸男 池田 安隆 馳澤 盛一郎
出版者
東京大学理学部
雑誌
東京大学理学部廣報
巻号頁・発行日
vol.23, no.2, pp.6-16, 1991-09

変り者の本音/アメリカの数学教育に関して(など)/新任のご挨拶/トルコでの活断層調査/本郷再見

5 0 0 0 OA 研究ニュース

著者
茅根 創 池田 安隆 川島 隆幸 狩野 直和 尾中 敬
出版者
東京大学大学院理学系研究科・理学部
雑誌
東京大学理学系研究科・理学部ニュース
巻号頁・発行日
vol.39, no.1, pp.6-8, 2007-05

2004年スマトラ島沖地震で干上がったサンゴ礁/史上最高の蛍光量子収率を示すアゾベンゼンの合成/「あかり」が見た星生成領域、終末期の星、超新星残骸、活動銀河核、遠方銀河
著者
池田 安隆 岡田 真介 田力 正好
出版者
一般社団法人 日本地質学会
雑誌
地質学雑誌 (ISSN:00167630)
巻号頁・発行日
vol.118, no.5, pp.294-312, 2012-05-15 (Released:2012-10-05)
参考文献数
100
被引用文献数
10 22 5

東北日本弧においては,測地学的観測で検出された水平短縮歪み速度が地質学的に観測される歪み速度よりおよそ一桁大きい.同様の不一致は垂直変動速度に関しても存在する;太平洋岸で急速な沈降が観測される一方で,第四紀後期の旧汀線高度は緩慢な隆起を示す.これは現在急速に蓄積している地殻歪みの大部分が弾性歪みであり,プレート境界の固着部分がすべることで解消されるということを示している.しかし,過去100年間に起こったMw 708級の海溝型地震は歪み解放に寄与していない.したがって,プレート境界の固着面全体がすべる巨大歪み解放イベントが存在するはずであり,2011年東北地方太平洋沖地震はこのような固着解放イベントであると考えられる.東北日本では幅広い固着領域の浅部のみが地震時にすべり,割れ残った深部固着域で余効すべりが起こるらしい.このような深部固着は,他の超巨大地震発生帯には存在しない可能性が高い.日本海溝に沈み込んでいるプレートの年齢は極めて古く従って低温であるから,このように深い固着域が存在するのは熱的な原因によると考えられる.
著者
鈴木 康弘 池田 安隆 渡辺 満久 須貝 俊彦 米倉 伸之
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.42, no.2, pp.151-159, 1989-06-24 (Released:2010-03-11)
参考文献数
17
被引用文献数
5 2

Many active faults trending N-S along basin-mountain boundaries are recognized in Northeast Japan, but only a few of them have experienced surface faulting in historical time; most of them seem to have been quiescent in the past several hundred years or more. Thus earthquakes are anticipated to occur from these active faults in the near future. To detect the recurrence intervals of faulting, which can be obtained by the excavation study, is indispensable for the long term prediction of earthquakes.We excavated a trench at Kitasakai, Sakata City, across the Kannonji fault, one of the eastern boundary faults of the Shonai plain, Northeast Japan, in order to reveal its late Holocene activity including a possible faulting event associated with the Shonai earthquake (M=7.0) of 1894 A. D., which caused severe damage along this fault.Our excavation has revealed that (1) the last surface faulting event on the Kannonji fault occurred in a period from 2, 500 years B. P. to 1894 A. D., and that (2) no surface faulting occurred (at least at the trenching site) in association with the Shonai earthquake of 1894. Careful examination of historical records, however, strongly suggests that the earthquake of 1894 was also generated from this fault; it is likely that thick, unconsolidated sediments prevented the rupture from propagating up-dip to the surface. These results indicate that the interval between the last two earthquakes originating from the Kannonji fault is less than 2, 500 years. It could be 1, 000 years, because the event revealed by excavation is possibly correlated to the historically-documented earthquake of 850 A. D..
著者
東郷 正美 佐藤 比呂志 池田 安隆 松多 信尚 増淵 和夫 高野 繁昭
出版者
日本活断層学会
雑誌
活断層研究 (ISSN:09181024)
巻号頁・発行日
vol.1996, no.15, pp.1-8, 1996-11-29 (Released:2012-11-13)
参考文献数
16

By excavation of the Ochikawa-Ichinomiya remain located on the flood plain along Tama River near the boundary between Tama City and Hino City, Tokyo metropolitan area, a fault was found in young alluvium. This fault is regarded as the continuation of Tachikawa fault, a major active fault existing in the left bank area of Tama River, because it is located on the southeastern extension of Tachikawa fault line, and its strike is almost parallel to the Tachikawa fault.Detailed investigation of the fault outcrop made it clear that the last faulting event on the Tachikawa fault had occurred after A. D.1020-1158, the mid-Heian period. At this place, the last faulting event was dominantly strike slip with horizontal shortening of about 0.6 m.
著者
高田 圭太 中田 高 野原 壯 原口 強 池田 安隆 伊藤 潔 今泉 俊文 大槻 憲四郎 鷺谷 威 堤 浩之
出版者
一般社団法人 日本活断層学会
雑誌
活断層研究 (ISSN:09181024)
巻号頁・発行日
vol.2003, no.23, pp.77-91, 2003-06-30 (Released:2012-11-13)
参考文献数
28

Large inland earthquakes bigger than Mj 7.2 during the historical past on Japanese islands have mostly been generated from active faults (Matsuda,1998). The 2000 Tottoriken-seibu earthquake of Mj 7.3 (Mw 6.6), however, occurred in the area where distinctive active faults were not mapped before the earthquake, and the surface ruptures associated with the earthquake were small and sparse. Active faults are hardly recognized even by detailed interpretation of aerial photographs after the earthquake but sharp lineaments. In Chugoku district in southwest Japan is characterized by less densely-distributed active faults with lower activities than other areas in Japan, and the 1943 Tottori earthquake of M 7 occurred by reactivation of the Shikano fault with rather obscure fault traces.Taking this condition, in mind, we carried out detailed mapping of active faults and lineaments, and compared with their topographical, geological, seismological and tectonic settings, in order to develop a new technique to find potential seismogenic faults.The results obtained are as follows;1) Active faults and lineaments were not evenly distributed, and the dense zone is recognized along the Japan Sea while the sparse zone in the central part of the district. The active faults known before are mainly located in the dense zone (Fig.1).2) The lineaments mapped are mostly less than 10km long, and half of them strike to NE-SW or ENE-WSW and 30 per cent to NW-SE or WNW-ESE (Fig.2). NE-SW lineaments prevail in the western part of the district, and NW-SW lineaments are systematically distributed only in the western-most and eastern-most area of the district probably reflecting their tectonic setting under the present stress condition.3) Lineaments with poor topographical manifest were not commonly recognized by individual geologist, and were generally short, scattered, isolated, random in strike, and independent from geological structures. These lineaments will not be considered as potential seismogenic faults.4) Epicenters of the small earthquakes are characteristically distributed to the north of the backbone range probably coincided with the past volcanic front. On the contrary, the area to the south of the backbone range the seismicity is sparse, except for several swarms. These seismic condition well matches with the distribution of active faults and well-defined lineaments (Fig.3).5) Most of the active faults and lineaments follow the pre-existed geological faults that had moved opposite direction to the active faulting, indicating their inversion movements under the present stress field.6) Surface ruptures reported as earthquake faults associated with the 2000 Tottoriken-seibu earthquake are considered as results of subsidiary shallow-sheeted faulting spontaneously caused by stain release around the seismogenic faulting in depth, because many of them appeared spontaneously, and not always along rather well-defined lineaments. They are small in extent and displacement. Therefore, it is rather difficult for evaluate such minor surface fault ruptures, but such ruptures may not displace the surface in large extent.
著者
池田 安隆
出版者
一般社団法人 日本活断層学会
雑誌
活断層研究 (ISSN:09181024)
巻号頁・発行日
vol.1996, no.15, pp.93-99, 1996-11-29 (Released:2012-11-13)
参考文献数
28

Faulting and other surface deformations in recent geologic time are essentially relevant to understanding present-day tectonic processes, which in turn are a key to scientific, not empirical, earthquake prediction. Geologic records are indispensable because instrumentally observed records, such as geodetic measurements and microseismicity, are not sufficient in time to cover a whole cycle of strain buildup and release in a orogenic zone.Rheological structure of the Japan arc b ased on explosion seismology, heat-flow measurements, and laboratory experiments indicates that the western half of central and northern Honshu, including continental slopes on the Japan Sea side, is mechanically very weak; only the upper 15 kilometers of crustal rocks behaves elastic, and ductile lower crust is underlain directly by asthenospheric mantle. This zone of weakness was rifted and stretched during the early Miocene back-arc spreading event, and coincides broadly with the distribution of active faults. Since late Miocene time up to the present, the Japan arc has been subjected to east-west compression due principally to the westward convergence of the Pacific plate at Japan trench at a rate as high as ∼90 millimeters per year.If the megathrust at the Japan trench is locked, the plate convergence is to be ac c ommodated mainly in this zone of weakness. Actually, geodetic observations in the last 100 years have revealed that strain accumulation rates over the mechanically weak zone are on the order as high as 10-7 per year. However, geologically observed strain rates, based on slip rates on active faults and folding rates, are one order of magnitude lower than the geodetic rates. A possible explanation for this discrepancy between short-term (geodetic) and long-term (geologic) observations is that the strain accumulated in the last 100 years at abnormally high rates is likely to be released by slip on the megathrust at Japan trench, which would produce big earthquake(s) with magnitude 8 or greater. Only a fraction of plate convergence may be accommodated within the Japan arc as long-term deformation.Whether or not the above scenario is real, the process of strain buildup and release in the Japan arc-trench system is unique, and should be understood with more geologic, as well as geophysical, observations.
著者
千田 昇 竹村 恵二 松田 時彦 島崎 邦彦 池田 安隆 岡村 眞 水野 清秀 松山 尚典 首藤 次男
出版者
一般社団法人 日本活断層学会
雑誌
活断層研究 (ISSN:09181024)
巻号頁・発行日
vol.2003, no.23, pp.93-108, 2003-06-30 (Released:2013-03-22)
参考文献数
11

The writers describe the location and active mode of a fault (Funai fault) lying concealed under the town area of Oita City, by analyzing lots of the drilling survey, the reflection method and the Geo-slicer investigation.The Funai fault is the eastern part of“Beppu bay south coast fault group”, which com p osed of the Horita-Asamigawaa fault, Beppu bay south coast fault and Funai fault, extended from west to east with extension about 20km.The very position in Oita plain is considered from Kasugaura to the south of Maizuru bridge located at the left bank of Oita river.It was c o nfirmed in the drilling survey, and the amount of vertical displacement of the K-Ah volcanic ash layer in a main fault is 16m at the Funai castle traverse line. According to existing bore hole data, the maximum amount of displacement of the Funai fault is 18m to the west of Funai castle. The average rate of vertical displacement after the K-Ah volcanic ash (6,300 years BP) is 2.2-2.5m/1000 year, and the Funai fault is estimated one of the A class active faults in Kyushu.The latest activity of the Funaifault is thought to be time between before 1,540yBP dated at the lower part of the uppermost mud layer which does not show the displacement and after 2,350yBP dated in the peat layer in upper sand and gravel bed which shows displacement.The problem in the future is the clarification of the fault continuation to the further east, and it is necessary to elucidate accurate distribution and the activity history of the concealed faults lying under whole the Oita plain.
著者
東郷 正美 池田 安隆 今泉 俊文 佐藤 比呂志
出版者
一般社団法人 日本活断層学会
雑誌
活断層研究 (ISSN:09181024)
巻号頁・発行日
vol.1996, no.15, pp.9-16, 1996-11-29 (Released:2012-11-13)
参考文献数
14
被引用文献数
1

The Kamishiro fault, extending for at least 20 km from the north Hokujyo basin to the south of Lake Kizaki, is one of major active faults along the Itoigawa-Shizuoka Tectonic Line in central Japan. We investigated detailed features of fault morphology along this fault, by interpretation of large scale aerial photographs. It became clear that faulting characteristics at the both ends of the Kamishiro fault are essentially different. At its northern end, the fault has become inactive progressively southward with time. However, the southernmost portion of the fault is still active in Holocene time, and continues southeastward to the Eastern Boundary fault of Matsumoto basin.At the southernmost portion of the Kamishiro fault, we also found evidence that remarkable thrust-front migration have occurred recently. Young offset features along the main portion of the Kamishiro fault suggest that at least one or two faulting events have occurred in Holocene time, and the latest event occurred probably in historic time.
著者
松多 信尚 池田 安隆 今泉 俊文 佐藤 比呂志
出版者
日本活断層学会
雑誌
活断層研究 (ISSN:09181024)
巻号頁・発行日
vol.2001, no.20, pp.59-70, 2001 (Released:2013-03-22)
参考文献数
12
被引用文献数
1

The Kamishiro fault is one of the major active faults constituting the Itoigawa-Shizuoka Tectonic Line (ISTL) in central Japan. The Kamishiro fault is an east-dipping reverse fault. This fault cuts and warped the young lake deposits (late Pleistocene and Holocene in age) in the Kamishiro basin. The slip rate on the Kamishiro fault near the surface has been estimated by Geo-Slicer and shallow drillings survey, but was found to be significantly smaller than the vertical slip-rate that was estimated from the displacement of the AT volcanic ash. We carried out a 55 m deep drilling and a seismic reflection profiling using S-waves in this basin to clarify the subsurface structure of the Kamishiro fault. As a result, it was clarified that the Kamishiro fault is associated with drag folding near the surface. If we take the drag folding into account, the overall rate of slip on the fault would be as high as 4.4-5.2mmlyr during the past 28ka.
著者
佐藤 比呂志 岩瀬 貴哉 池田 安隆 今泉 俊文 吉田 武義 佐藤 時幸 伊藤 谷生
出版者
東京大学
雑誌
基盤研究(A)
巻号頁・発行日
2002

平成16年度には、2003年7月26日に発生した宮城県北部地震の震源域を横断する反射法地震探査を行い、中新世に形成された正断層が逆断層として再活動することによって発生した地震であったことが判明した。この北方の宮城県北部で1900年以降に発生したM6.5を越える内陸地震は、2003年の震源域の北方の領域から、南方に破壊してきたことが明らかになった。この一連の地震は、中新世の日本海の拡大時の最末期に形成された北部本州リフトの東縁のリフト系の再活動によるものであった。このリフト系の延長である水沢地域における石油公団が実施した反射法地震探査データと、現地の活断層調査によって、この地域の活断層はリフト系のハーフグラーベンを限る西傾斜の正断層が逆断層として再活動して形成されたものであることが明らかになった。また、リストリックな形状の正断層の再活動に伴って、浅層の高魚部分をショートカットして形成された、footwall short cut thrustも見いだされた。同様の再活動は、このリフト系の東縁の延長である三戸地域でも見いだされ、地表地質と重力から推定される密度構造から、中新世初期に活動したハーフグラーベンの東縁の断層が鮮新世以降再活動し、現在、活断層として知られる折爪断層はこの再活動によって形成されている。東北日本の太平洋側に分布する活断層は、仙台市周辺の長町-利府断層も含め、こうした中新世の背弧海盆の拡大に伴って形成されたかつての正断層が再活動したものである。したがって、震源断層は均質な物質中で形成される30度前後の傾斜を有するものではなく、50度前後の高角度のものとなる。本研究プロジェクトで検討した、中央構造線活断層系や糸魚川-静岡構造線活断層などの成果も含め、現在の大規模な内陸地震は、既存の断層の再活動によって発生しており、深部の断層の形状は地質学的なプロセスと密接に関連している。