著者
木村政昭
出版者
海洋科学技術センター
雑誌
JAMSTEC
巻号頁・発行日
vol.5(4), no.20, 1993-10-01
著者
木村 政昭
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.105, no.3, pp.259-285, 1996-06-25 (Released:2009-11-12)
参考文献数
53
被引用文献数
76 82

Compilation of seismic reflection profiles, rock sample analyses and manned and non manned diving observations revealed that land bridges, connecting the Ryukyu Arc to the Chinese continent, have appeared in two stages since the late Pliocene. The first stage occurred before the deposition of Pleistocene Ryukyu Limestone and ceased in the early stages of deposition, while the second was apparent during the middle and late stages of the Ryukyu Limestone. The land bridge in the first stage may have appeared between 2.0-1.0 Ma and is well identified by the unconformity between Shimajiri and Ryukyu Groups before the deposition of Ryukyu Limestone. The land bridges may have appeared two or three times in the second stage during or after deposition of Ryukyu Limestone between 0.4-0.02 Ma. The last land bridge may have appeared during the Würm glacial stage in the late Pleistocene, connecting the Chinese continent through Taiwan, Okinawa and Amami-Oshima to the Kyushu main land. This supports the hypothesis that the Minatogawa Man migrated to Nansei-shoto Islands passing through the land bridge in the Late Pleistocene.
著者
木村 政昭 笠原 順三 麻植 誠二郎
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.91, no.4, pp.217-238, 1982-08-25 (Released:2009-11-12)
参考文献数
22

Spatial and temporal relations between large interplate earthquakes and eruptive activities along Northeast Japan was studied by means of a two-dimensional model using the finite element method. Stress fields were calculated using seismological data in Northeast Japan. The stress value for each earthquake was normalized by using the seismic moment Mo instead of earthquake magnitude M. Stress differences before and after great earthquakes show close relationships with eruptive activities in Northeast Japan. The results suggest that eruptive activities increase under the increased compressive strain of pre-seismic conditions and their activities abruptly decrease under post-seismic conditions.
著者
松本 剛 木村 政昭 仲村 明子 青木 美澄
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.105, no.3, pp.286-296, 1996-06-25 (Released:2009-11-12)
参考文献数
27
被引用文献数
6 11

Precise topographic features at the two major structural boundaries in the Ryukyu Arc, Tokara Gap and Kerama Gap, revealed that there exists a ridge feature of the Ryukyu Arc as a saddle topography. The feature supports the idea recently proposed that a landbridge connecting the Chinese continent, Ryukyu Islands and Japanese Islands, is thought to have been subsided since Late Pleistocene. The saddle is offset by large-scale left-lateral normal faults both of which are related to the opening of the Okinawa Trough. These topographic features and geological structure together with the gravity anomaly and regional tectonics in the Ryukyu area suggest that a north-south tensional stress regime, due to the rolling buck of the Philippine Sea Plate at the Ryukyu Trench, has dominated in this region since last 20, 000 years.
著者
松本 剛 木村 政昭
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.45, no.4, pp.417-426, 1993-03-24 (Released:2010-03-11)
参考文献数
20
被引用文献数
5

Historical record shows that a large-scale tsunami named “the Great Meiwa Tsunami” or “the Yaeyama Earthquake Tsunami” occurred on 24th April 1771 in the sea region of Miyako and Yaeyama Islands, westernmost part of Ryukyu District caused by a large earthquake and the tsunami inundated up to the inside of the islands. Swath bathymetric survey in this area was conducted by the use of SEABEAM and HS-10 systems on board the Research Vessels KAIYO and YOKOSUKA, in November 1990, April 1991, January and April 1992. Precise topographic contour map was completed in the area of 22°40′N-24°10′N, 122°50′E-126°20′E, including the westernmost part of the Ryukyu Trench and tsunami source area (around 24.0°N, 124.3°E). The survey area is classified into five different topographic domains which are arranged zonally. Those are:Zone 1: north of 24°00′N, which is characterised by the distribution of well developed submarine canyons along the southern coasts of Yaeyama Islands.Zone 2: 23°40′N-24°00′N, which is characterised by deep sea fans and its large-scale subsidence edged by steep scarp near 23°55′N-24°00′N, 124°10′E-124°20′E. The observed relative height of the depression is about 200-300m.Zone 3: south of 23°40′N on the landward slope of the trench, which is characterised by quite complicated topography such as several escarpments and ridges and troughs of which trend is not clearly recognized.Zone 4: trench axis area with depth about 6500-6600m, which is characterised by broad plain. Maximum width of the axial plain is about 40km.Zone 5: seaward slope of the trench, which is characterised by horsts and grabens which are samely distributed in the sea area of the south of Okinawa Island. The strike direction of the horsts and grabens is NW-SE off Miyako Islands, and WNW-ESE off Yaeyama Islands.The 1771 Meiwa Tsunami is considered to be originated by the large-scale subsidence of the deep sea fans which is composed of soft sediment derived from the submarine canyons just north of the fans, and the wave might be propagated along the canyons from the position of the tsunami source.Tention of N-S direction is suggested by the topographic features in the survey area, and the tention stress in this area is considered to be the origin of the large-scale subsidence which induced the tsunami.
著者
徳山 英一 本座 栄一 木村 政昭 倉本 真一 芦 寿一郎 岡村 行信 荒戸 裕之 伊藤 康人 除 垣 日野 亮太 野原 壮 阿部 寛信 坂井 眞一 向山 建二郎
出版者
海洋調査技術学会
雑誌
海洋調査技術 (ISSN:09152997)
巻号頁・発行日
vol.13, no.1, pp.27-53, 2001-03-31
参考文献数
56
被引用文献数
6

We propose the guideline to identify fault in offshore region mainly based on MCS profiles, combining high resolution bathymetric maps and geological data such as bore hole results. Based on the guideline we distinguished total 776 faults developing around Japan since the latest Miocene and 753 faults out of total numbers of faults are interpreted to have been active by Quaternary. Together with distinguishment of fault we examined the attributes of each faults such as surface and vertical distribution, criteria of offset, age of movement, certainty of a fault and so on. <br>The results of the distinguishment and examination of the fault leads to the conclusion that the ongoing tectonic framework around Japan characterized by 1) oblique Subduction along the Nankai Trough, 2) rifting at the Okinawa Trough, 3) E-W compressionl regeme along the Japan Sea margin, 4) E-W compressionl regeme along southwestern margin of the Okhotsk Sea and off southern Hokkaido, 5) E-W compressionl regeme along the Japan Trench, 6) rifting in the central arc of the Izu-Ogasawara Arc has been established since 3 Ma, at the earliest 6 Ma. <br>We utilized high resolution data set which we enable to access. Tow big problems, however, still remain in terms of reliability of fault recognition. Those are 1) age of fault movement and 2) spatial distribution of fault. To solve the first one, new technique is required in order to obtain core samples which provide critical evidence to determine age of fault movement. As is second problem concerned, new intensive seismic survey is indispensable to make a precise fault distribution map, especially in the boundary area between land and sea.
著者
木村 政昭
出版者
京都大学防災研究所
雑誌
京都大学防災研究所年報 (ISSN:0386412X)
巻号頁・発行日
no.37, pp.p293-317, 1994-04
被引用文献数
1

Seismic and volcanic data during this century reveals that most of all eruptions in Japan should be followed by large earthquakes (M ≧7.0) in concerned places. The time-space relation between major eruptions and great earthquakes larger than M7.7 in Japan shows a reverse correlation given by the following equation.T=50.61-18.17logDT: Interval from the starting time of an eruption to the occurrence time of the earthquake. D: Distance from the concerned volcano to the epicenter of the shock. This implies that the eruption occurs in earlier time prior to the concerned shock if the epicenter of the earthquake is nearer from the volcano. Based on this relation, the crustal breaking time in the estimated epicenter should be known. This suggests that the eruption occurs by the increased stress generated from the epicentral region. The increased strain should squeeze up magmas before breaking the crust. Recent eruptive activities strongly suggest that the strain has been critically accumulated in several regions such as northern and southern parts of central Japan and eastern Kyushu.
著者
木村 政昭 上田 誠也 山里 清 加藤 祐三 大森 保
出版者
琉球大学
雑誌
一般研究(A)
巻号頁・発行日
1988

1986年に世界の背弧海盆に先駆けて中央地溝の一つである伊平屋海凹内で研究者らにより、低温で非晶質の熱水性マウンドが発見された。そこで、本研究においては、大洋中央海嶺で発見されたような硫化鉱床や大型生物コロニ-が認められるような高温の熱水性ベント・システムが背弧海盆にも認められるのかということを世界に先駆けて検証することを目標の一つとした。そして、それによって背弧海盆が大洋中央海嶺と同じ様な拡大メカニズムにより形成されたのかどうかということを明らかにしようと努めた。その結果、研究者らが参加・協力した調査・研究において以下に述べるような成果があげられた。昭和63(1988)年度:4ー6月、伊平屋海凹と伊是名海穴で熱水性生ベント・システム発見。ドレッジにより大型生物や硫化鉱床採取(ゾンネ号:「かいよう」)。9月には、前記熱水域に潜航し、熱水性鉱床・生物コロニ-等のサンプル採取に成功(「しんかい2000」)。平成元(1989)年度:4ー5月、伊是名海穴で高温熱水を噴出するブラックスモ-カ-が発見され、さらに新熱水域を発見する(「しんかい2000」)、1990ー91年の調査により、さらに北方の奄西海丘でも熱水性鉱床が発見された。1991年6月、沖縄トラフ南部北縁の潜水調査。トラフ縁の沈水時期を明らかにする(「スコ-ピオン」)。平成4年1月、南西諸島南方海域の海底地形精密調査。海溝運動と島弧・背弧海盆形成メカニズムを探る(「よこすか」)。以上、本研究により、発見された鉱床は、わが国経済水域内にあり、いわゆる黒鉱型鉱床に酷似し、金・銀を多量に含む珍しいものである。そして、シロウリ貝やバクテリア等も発見採取され、生命の起源解明にも寄与した。更に今後熱水域が新たに発見される可能性も指摘することができた。一方、構造探査の方では、沖縄トラフは典型的な大陸性地殻構造を持っていることが明らかになったが、鉱床の性質はそれと予盾しない。
著者
木村 政昭
出版者
日本熱帯生態学会
雑誌
Tropics (ISSN:0917415X)
巻号頁・発行日
vol.10, no.1, pp.5-24, 2000 (Released:2009-01-31)
参考文献数
41
被引用文献数
86 144

近年の潜水調査を含む海底の地質・地球物理学的研究成果をまとめることにより,琉球弧および東シナ海の海底地質の地史を明らかにした。琉球弧の形成過程では2つのステージが基本的である。第1 ステージには,東シナ海東縁域の地殻の薄化とそれに伴う琉球弧の東方への移動が,中新世後期から鮮新世中期の聞に生じた。その後, 160 万-130 万年前に,東シナ海域が広範に陸化した。これには現在の沖縄トラフのかなりな部分を含む。その時琉球弧はユーラシア大陸の一部であった。その後,更新世初期の今からおよそ130 万年前に,第2 ステージが発生した。そして現在の琉球弧(海底地形的には琉球海嶺)が形成された。琉球弧は2 つの主な時期に,台湾を通って中国大陸と陸橋としてほぼ連続していたとみられる(たとえば160 万-100 万年前と20 万-2.5 万年前)。この琉球古陸はおよそ2.5 万年前以降,地殻変動と後氷期の海面変動の両者によって段階的に沈水していった。琉球弧の水深10-35 m の海底には複数の鍾乳洞が発見された。それらの洞穴はウルム氷期以降に沈水したものである。そのうちの1 つからは石器が得られた。さらに6,000 年より古い時期に形成されたと推定される階段ピラミッドのような形をした人工的な遺構が与那国島沖の海底から発見された。そのような遺跡の存在は琉球弧の沈水過程を解明する手がかりを与えるものとなろう。