著者

つち山 明 上杉 健太朗 中野 司

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.6, pp.845-858, 2000-12-01

被引用文献数

6 6

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X-ray computerized tomography (CT) is a non-destructive method by which crosssectional images of rocks and minerals are obtained using X-ray attenuation. Threedimensional structures of samples can also be obtained by constructing a number of successive images. This review discusses high-resolution X-ray CT machines including an industrial machine in commercial use and that developed by our group at SPring-8, which is the largest synchrotron radiation facility in Japan. Spatial resolution of CT images, which is determined by X-ray detectors and X-ray beam size, is practically limited by sample size due to the limited numbers of X-ray detectors. A resolution of about 1 μm was realized at SPring-8. This resolution is the lower limit for imaging with simple optics. The contrast of an X-ray CT image is expressed as a two-dimensional distribution of CT values, which related to the X-ray linear attenuation coefficient (LAC), , μ. CT values of standard minerals were measured to compare with their values of μ. As μ is a function of X-ray photon energies, beamhardening occurs when we use polychromatic beams. Thus, we cannot compare CT and μ values directly with the industrial scanner, which aplies a polychromatic X-ray beam. If the CT and μ values are normalized by a standard mineral having similar size as samples for the photon energy or the accelerating voltage of an X-ray tube, both values agree well as long asμis less than about 2.5 × μ of Fo<SUB>92</SUB> olivine. We can compare CT and μ values directly in the SPring-8 machine, where monochromatic X-ray beams are available. In this case, normalized CT and μ values agree well in various materials havinga large μ at least including metallic iron. However, absolute CT values are slightly smaller than μ by about 10%, which is probably due to scattered X-ray beams, although the exact reason is not known at present. The high-resolution X-ray method was applied to three-dimensional structures of chondrules, which are characteristic constituents of primitive meteorites, named chondrites. It is known from external shapes and internal textures, which are related to distributions of voids and platy olivine crystals, that chondrules spin at high revolutions of about 50-500 rps during their formation in the primordial solar nebula. This greatly constrains the formation mechanism of chondrules.

著者

斎藤 文紀

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.98, no.3, pp.350-365, 1989

被引用文献数

25 16

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The criteria for the classification of present shelf sediments are summarized, and the classification of sedimentary environments and the facies of their sediments in a stormdominated shelf are presented.<BR>The present shelf sediments are classified by the seven criteria as follows.(1) Are the sediments modern or relict? and when were the sediments supplied? (2) Are the sediments palimpsest or not? (3) By which kind of physical processes were they deposited? (e. g. density currents, flood, tidal currents, geostrophic currents, oceanic currents, tsumanis, etc.)(4) What type of sedimentary environment? (e. g. foreshore, shoreface, inner shelf, outershelf, etc.)(5) What is the grain size? (6) What is the natur e of the constituents? (e. g. authigenic, biogenic, volcanic, clastic, etc.)(7) What is the sedimentary structure or bedform of the sediments? These classification criteria of the present shelf sediments are the key to the interpretation of the environment of ancient sedimentary rocks.<BR>The storm-dominated and siliciclastic shelf sediments are divided into nearshor e (foreshore and shoreface), inner shelf and outer shelf facies. Foreshore is the zone of beach and the facies is characterized by well-sorted sand and seaward dipping, low-angle wedge-shaped cross- or parallel-bedding. Upper shoreface is the zone in which longshore bars and troughs are recognized within water depth of less than about 6m, and the facies consists of coarse to pebbly sand with cosets of high -angle tabular or trough cross-bedding of 10 to 100cm thickness. Lower shoreface is the zone which is between 6 to about 20m of water depth, and the facies is comprised of well-sorted fine to very fine sand with amalgamated hummocky cross- or parallel-stratification. Inner shelf is the zone which ranges from 20 to about 70m of water depth, and the facies is made up of interbedded sand and mud. Also, hummocky cross-stratification is recognized in the sand beds deposited in a zone less than about 50m of water depth. Outer shelf is the zone below about 70m of water depth, and the facies is composed of bioturbated mud. The boundary between shoreface and innershelf corresponds to the mean fairweather wave base and the boundary between inner shelf and outer shelf to the mean storm wave base.

著者

森田 利仁

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.107, no.6, pp.862-871, 1998-12-01

著者

鈴木 和恵 丸山 茂徳 山本 伸次 大森 聡一

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.6, pp.1173-1196, 2010-12-25

被引用文献数

11 35

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The Japanese Islands have long been considered to be the most evolved of all the island arcs in the oceans. A simple scenario has been implicitly accepted for the growth of the Japanese Islands: since subduction started sometime around 520 Ma, the TTG crust has increased over time in association with the steady-state growth of the accretionary prism in front. Here, we show very different dynamic growths of TTG crusts over time than previously thought, <i>i.e.</i>, four times more TTG crusts than at present must have gone into the deep mantle due to tectonic erosion, which occurred six times since subduction was initiated at 520 Ma. Tectonic erosion is a major process that has controlled the development history of the Japanese islands. It can be traced as a serpentinite mélange belt, which indicates the upper boundary of past extensive tectonic erosion.

著者

岩崎 正吾 平川 一臣 澤柿 教伸

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.1, pp.37-55, 2000-02-25

被引用文献数

14 7

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Late Quaternary glacial fluctuations in the Esaoman-Tottabetsu Valley, inthe northern Hidaka Range, central Hokkaido were reconstructed based on stratigraphy of glacial landforms and sediments. By mean of tephrochronology, the two previously known stadials of the Last Glacial Stage, the Poroshiri and Tottabetsu Stadials, were reassessed. Shikotsu 1 tephra overlain by the terminal moraine of the Poroshiri Stadial at the river bed of 850m a. s. l. indicates that the glacier reached its maximum at around 40ka (Oxygen Isotopic Stage 3: OIS-3). This advance should have been initiated in the preceding cold period of 01S-4. Kuttara 6 tephra (86 ka) in the proglacial outwash deposits indicates that a glacier fluctuated in the vicinity of the cirque bottom even in the relatively warm period of the early Last Glacial Stage (01S-5b). Contrary to this stadial, the glacial and proglacial deposits including Eniwa a tephra (18 ka) show that the glacial advance during the Tottabetsu Stadial (LGM) in this region was restricted within the cirque bottom. The penultimate glaciation, named the Esaoman Glaciation in this study, was suggested by the discontinuously traceable remnant bed topography along the river basin. These features recommend that the glacial advance of this stage reached at 750m a. s. l., lower than during the Last Glacial Stage.

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.7, no.3, pp.169b-169b, 1895

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.8, no.4, pp.225a-228, 1896

著者

小山 真人

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.108, no.4, pp.346-369, 1999-08-25

被引用文献数

4 14

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There remain many challenges in using historical documents to reconstruct a reliable history of earthquakes in Japan. Previous catalogs of historical earthquakes in Japan are not conclusive and contain uncertainties about date, hypocenter, magnitude, and tectonic interpretation of each earthquake. There is no database of digital texts of historical documents, which describe each earthquake. Since the density of historical records in Japan is temporally and spatially heterogeneous, seismologists should carefully remove apparent changes of earthquake frequency, which are caused by the heterogeneity of record density. There is, however, no detailed database of the density variation of historical records. The number of researchers, who are interested in historical earthquakes, is small.<BR>The situation stated above is caused mainly by the multi-disciplinary character of historical seismology. Japanese seismologists, who usually have little knowledge of history and classical literature, are not qualified to read a historical document and evaluate its reliability.<BR>The environment for research on historical seismology is, however, getting better. Japanese historians have published and are still publishing many historical documents, sometimes with translations into modern language. Evaluations of the reliability of each document can easily be done by referring to historical dictionaries or other databases. All these publications and information are available in many libraries. It is now easy and stimulating for many seismologists to read, evaluate, and interpret historical documents.

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.20, no.3, pp.217-218, 1908

著者

鶴我 佳代子 笠原 順三 三ケ田 均 山岡 耕春 藤井 直之

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.115, no.1, pp.51-71, 2006-02-25

被引用文献数

3

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Large earthquakes along the subducting plate boundary occur repeatedly in the area of an asperity that consists of a strongly coupled zone between two plates. Other areas along the subduction zone are considered to be stable-quasi-stable slip region, which is called a non-asperity, might release strain energy caused by oceanic plate subduction. The physical states of large asperities under the ocean are not well known at present because of the lack of offshore stationary observation networks (e.g., geodetic, seismic and electromagnetic networks).<BR>Strong PP reflections from the subducting plate boundary were found in aseismic zones along the Japan Trench and in the slow slip region in the Tokai region. These features suggest the presence of low-Vp/soft materials and/or fluid along the subducting plate boundary. Such regions might cause continuous or intermittent aseismic slow-slips. If we can map areas of strong PP reflections from observations such as refraction-reflection studies using Ocean Bottom Seismometer (OBS) -airgun surveys, we will be able to obtain the distribution of asperities along the plate boundary.<BR>Assuming that slip acceleration at non-asperity regions might trigger a large earthquake at adjacent asperities, a sudden change of physical states in a non-asperity region might suggest a high probability of plate-boundary earthquakes. Changes due to slip acceleration might be detected by continuously monitoring seismic reflection intensity at non-asperity regions. To perform continuous monitoring, we propose the Accurately Controlled Routinely Operated Signal System (ACROSS), with an integrated active monitoring method using continuously transmitting seismic and electromagnetic sinusoidal waves, which are accurately controlledby a GPS clock with a sophisticated signal analysis method.<BR>The ACROSS seismic source at Toki city in central Japan has been operated continuously for more than 2 years. A field experiment in the Tokai region, central Japan, using this transmission method provided sufficient S/N ratios for the Pg phase traveling 60 km through stacking the data for one month.<BR>Submarine cable OBS systems near the trenches enable us to continuously monitor seismic reflection signatures provided by ACROSS systems located on land. The planned submarine cable OBS in the Tonankaki region might be a good real-time receiver system.<BR>The Exploration of Asperities-Reflectors System (EARS) is proposed for integrating the necessary research components-mapping, monitoring, and real-time continuous monitoring of the Earth's crust. In this paper, we describe the analytical method and important points in such a study.

著者

小林 貞一

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.62, no.4, pp.167-171, 1953

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1952年9月8日以降1週間に亘り, Algeriaの首都Algerで開催された第19回万国地質学会議に, 私は三土知芳・渡辺武男両氏とともに日本代表として列席する栄誉を得た。この会議前のGeneral Excursion には日本代表3名が参加した。会議後の地質巡検には3名の代表は, それぞれ別の班に加わつた。小林はモロッコの地質巡検C33に参加した。会議前のGeneral Excursion は会議前後約50班の地質巡検中最も大がかりなもので, その指揮者はM. Roubault教授で参加者約300名はChampolion号に便乗して, 8月24日にマルセイユを解纜してから9月7日朝アルゼールに投錨するまでの2週間の間, チュニス・アルゼリアの沿岸地帯を遍歴した。これは大体テルアトラスおよびカビレ海岸山脈に属する地帯で, 高アトラスはその背後に位している。<BR>Les Chaines Littorales Kabyles は主に古い地塊とその被覆層からなり Chaine Calcaire の称がある。Les Chaines telliennes は褶曲山脈である。われわれはまずこの褶曲山脈の北東端をチュニスにおいて見, それからアルゼリアにおいて海岸山脈の基盤変成岩類, その古第三紀被覆層, これを貫ぬく火成岩, 新第三紀以後の火山岩を, そしてアルゼリア西部でテルアトラスを見た。これらの巡検はTunis, Bizerte, Bone, Bougie, Oran などに寄港し, 8台の大型自動車に分乗し, 1日200~300哩を走り要所々々にはとまつて見聞する。連日の巡検は相当の体力を要するので, 老人婦人は分かれて名所見物に行くこともあつた。また時には汽車で山脈を横切り, Onenza鉄山や Constantine の旧都を訪れることもあつた。<BR>会議後のモロッコの地質巡検C33は, L. Neltzner, R. Ambroggi の両氏が指揮者で, 時にはM. Gigoux, R. Bourgin らの諸氏も案内に加わつた。参加者は英国からの3名, フランス本国からの1名, モロッコ地質調査所の婦人1名と小林を合して僅かに6名で, 一行約10数名が2台あるいは3台の自動車に分乗して, 高アトラスおよび後アトラス両山地西部地域層序と地質構造とを巡検した。万国地質学会議が終了すると翌朝早々アルゼールから汽車でオランまで, それから先きは飛行機でCasublancaに至り, 休養して9月18日からSafi, Magador, Agadirなどを経て太平洋岸を南下し, 後アトラス山地西端部を巡つてSous河中流のTaroudantにいで, 高アトラスを越えて旧都Marrakechで1日休養, 再度同山脈を越えてOuarzazateの盆地に行き, Marrakechを経て10月2日夜Rahatに帰つた。この間小林はモロッコ地質調査所および巡検班指揮者の好意によつて, Sout河の南岸後アトラス北方に位するl'Amouslek の下部寒武系層序の検討を行なうために, 案内者とともに2日間 Taroudant から族行團の一行とは別れて特別の地質調査を行つた。そして10月3日4日の両日に調査所所藏の寒武系下部三葉虫を見た。L'Amouslek丘陵地では最近, Redtichia様の三葉虫がOlenellidaeの三葉虫とともに産出するので, 極めて興味ある層序で世界の寒武系研究家間の注目の的となつている。この層序に対する私の所見は, A brief Note on the Lower Cambrian of Morocco としてモロッコ地質調査所から出版されるはずであるからここには省略し, 以下主にモロッコのアトラス山系の地質について述べる。

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.26, no.9, pp.729-729, 1914

著者

田中 阿歌麻呂

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.17, no.10, pp.741-743_1, 1905

著者

田中 阿歌麻呂

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.17, no.9, pp.660-663, 1905

著者

田中 阿歌麻呂

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.17, no.8, pp.594-598, 1905

著者

倉本 真一 平 朝彦 Bangs Nathan L. SHIPLEY Thomas H. MOORE Gregory F. EW99-07 08 航海乗船研究者

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.4, pp.531-539, 2000-08-25

被引用文献数

10 19

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A three-dimensional seismic survey was carried out at the western Nankai Trough accretionary wedge from June 18 to August 18, 1999. This experiment was Japan-U.S. collaborative investigation on seismogenic zones. The cruise imaged an 8 X 80 km area with 81, 80km-long, high quality, seismic reflection lines, all of which have nearly continuous coverage.<BR>The main objective of our experiment was to image the plate boundary fault at which major earthquakes and tsunamis are generated. Our primary goal is to image the thrust and identify the boundary between aseismic and seismic zones for a large inter-plate earthquake.<BR>On-board two-dimensional data processing has been carried out. This gives us a significantly clear image of the inner structure of the accretionary wedge at our survey area. One impressive image of the profile shows the large thrust slice zone that is classified by our interpretation. A number of out-of-sequence thrusts have developed and are concentrated in the area where the water depth is approximately 4, 000 to 3, 000m. A decollement plane touches the oceanic plate (layer II) down at there in first. We identified that the boundary between the stable sliding zone (ocean-ward) and the unstable stick slip zone (landward) is located there. We propose that the boundary is the up-dip limit of the seismogenic zone. Further data processing is ongoing. A true three-dimensional structure will reveal much more details and a clear image of seismogenic zone at the Nankai subduction margin.

著者

八木 貞助

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.44, no.3, pp.126-132_1, 1932

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長野市を東北に距ること約二十粁の庭山岳に園まれた小盆地に古來著名なる温泉郷がある。名づけて山之内温泉といふ。昭和三年長野屋代等から此地に電車が通するに至つて頓に資展の機蓮を将來して居る。山之内温泉とは下ヒラすアンダイカノバヤシホノポカクマ高井郡平穏村の湯田中、安代、澁、上林、地獄谷、登補、熊之湯の七湯と穗波村の角問との入湯を包括したもので、燥田中、安代、澁の三湯は相連績して湯町をなし、他のものは近きは三十分遠きも三四時間を以て互に幸絡せられ、附近には琵琶池、幕岩及志賀高原の湖沼、燒額ヤケピタイ山、岩菅山、笠岳、白根山等散策探勝する所に富み、其標高大孚は六七百米に幸するから盛夏暑熱を知らす、冬も寒氣激しとはいはす、白雪にスキーを走らすの快もあり、遠ぐは西に日本アルプス及飯網、黒姫、妙高、戸隙、斑尾ママドロ等五岳の秀麗を望み、近くは夜間瀬に俗耳を洗ひ得るのである。四時の風光亦明媚人情は素朴で宿含も近代的に施設されて、社會の各階級を迎ふに遺憾はない。今其各湯に亙つて大要を録したいと思ふ。<BR>本文に記載した事項及棄温度、湧出攣水素イオン濃度 (P. H.) 等各種の測定は昭和二年以降のものが大部分である。調査上多くの人々の助力を得たことを戚謝するものである。

著者

青木 一勝 大藤 茂 柳井 修一 丸山 茂徳

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.2, pp.313-332, 2010-04-25

被引用文献数

10 24

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The Sanbagawa metamorphic belt in SW Japan was previously considered to extend in the E-W direction from the Kanto Mountains to Kyushu Island, a distance > 800 km. However, Aoki <i>et al.</i> (2007) recently demonstrated that protoliths of metamorphic rocks in the Oboke area of the belt in central Shikoku accumulated at the trench after <i>ca.</i> 90-80 Ma. Furthermore, Aoki <i>et al.</i> (2008) showed that these rocks suffered blueschist metamorphism at 66-61 Ma, which differs from the timing of the Sanbagawa metamorphism. Thus, these results show that the Sanbagawa belt in Shikoku is a composite metamorphic belt. We, therefore, redefine the traditional Sanbagawa belt; the structurally upper part is the Sanbagawa metamorphic belt (<i>sensu stricto</i>). It formed as an accretionary complex at <i>ca.</i> 140-130 Ma and subsequently experienced BS-EC facies metamorphism at <i>ca.</i> 120-110 Ma (Okamoto <i>et al.</i>, 2004). By contrast, the structurally lower segment termed the Shimanto BS facies metamorphic belt, formed as an accretionary complex after <i>ca.</i> 90-80 Ma and experienced peak metamorphism at <i>ca.</i> 60 Ma. Our observations have important implications for the lateral extension of these two metamorphic belts in SW Japan. The accretionary ages of the traditional Sanbagawa belt in the Kanto Mountains are younger than the Sanbagawa peak metamorphic age (Tsutsumi <i>et al.</i>, 2009), clearly indicating that the entire region of Kanto Mountains Sanbagawa must belong to the Shimanto metamorphic belt. The same timing relationships were also found for the Sanbagawa belt on Kii Peninsula (Otoh <i>et al.</i>, 2010). These results, therefore, indicate that the Shimanto metamorphic belt is exposed in Shikoku, Kii, and Kanto, thus the spatial distribution of Sanbagawa belt (<i>ss</i>) is less than half of its previous extent. The metamorphic grade of the Kanto Mountains in the Shimanto metamorphic belt ranges from pumpellyite-actinolite facies to epidote-amphibolite facies. Therefore, the higher-grade rocks of the Shimanto metamorphic rocks are exposed in the Kanto Mountains in comparison with Shikoku and Kii Peninsula. Hence, these two distinct BS-EA-EC (?) metamorphic belts are virtually equivalent in terms of spatial distribution, metamorphic range of grade, and facies series. Pacific-type orogenic belts typically comprise accretionary complex, high-P/T metamorphic belt, fore-arc sediments, and batholith belt landward from the trench (Maruyama <i>et al.</i>, 1996). In SW Japan, the Sanbagawa belt (<i>ss</i>) is paired with the Ryoke low-P/T metamorphic belt and with the <i>ca.</i> 120-70 Ma Sanyo TTG batholith belt. Furthermore the related fore-arc basin may have developed penecontemporaneously with the Shimanto BS-EA orogeny, which is paired with the late Cretaceous to early Tertiary San-in TTG belt, which extending along the Japan Sea coast. In-between the intervening Izumi Group, a fore-arc basin deposit formed during the Campanian to Maastrichtian. Thus, these two groups of orogenic units, which formed during independent orogenies were both extensively modified during the opening of the Japan Sea <i>ca.</i> 20 Ma. The southward thrusting of the Ryoke and Cretaceous TTG belts over the Sanbagawa extended beyond the southern limit of the Sanbagawa, leading the up-down relationship of the Sanbagawa (<i>ss</i>) and the Ryoke belts.

著者

中田 高 蓬田 清 尾高 潤一郎 坂本 晃章 朝日 克彦 千田 昇

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.104, no.1, pp.127-142, 1995

被引用文献数

30 48

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Distinctive ruptures of the surface faulting which generated the destructive 1995 Hyogoken-Nanbu Earthquake (M<SUB>s</SUB>=7.2) appeared along the Nojima fault, an active fault on the northwestern coast of Awaji island, Japan. The surface fault ruptures in Awaji island extend southwestward continuously for about 9km from Easki near the epicenter to Toshima in Hokudan town, and caused prominent right-latearl off-sets of 1.9m at maximum on roads, paddy dikes with vertical displacement of 1.2m at maximum, while no large surface faulting has been reported in Kobe where major damage and casualties have appeared.<BR>Most of the surface ruptures follow along the pre-existing active fault traces of the Nojima fault. The ruptures are generally arranged in left-stepping echelon, and local extensional and compressional jog forms such as trenches, mole tracks, buldges are sometimes related to changes in fault strikes.<BR>The earthquake fault seems to have propagated bilaterally northeastward and southwestward from the hypocenter in the Straits of Akashi near the major jog of the earthquake fault system. The source process of the earthquake deduced from the slip distribution along the earthquake fault in Awaji island well explains near-field P-waveforms of broad-band seismometers for early part in about 4 seconds. The later part of much larger amplitude should attribute to the northeast fault ruptures toward Kobe.

著者

青山 千春 松本 良

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.1, pp.156-174, 2009-03-25

参考文献数

28

被引用文献数

6 15

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During methane hydrate exploration and research, remote and on-board acoustic surveying and monitoring of methane hydrate can be easily and economically conducted using a quantitative echo sounder. Simultaneously, the structure and the floating-up speed of methane plumes can be obtained from an analysis of acoustic data.<br> We conducted a survey of methane plumes from 2004 through 2008 at a spur situated southwest off the coast of Sado Island (tentatively called Umitaka Spur) and at the Joetsu Knoll. In 2007 and 2008, we performed experiments by releasing methane hydrate bubbles and methane hydrate, and letting them float upward. Consequently, we demonstrated that acoustical reflection from the methane plumes correlates with water temperature and depth, that the floating-up speed is constant but depends on the conditions of methane hydrate, that the discharge of methane hydrate bubbles changes, and that there is a wide scattering of materials below the seafloor where methane plumes are located. Furthermore, the amount of methane hydrate bubbles seeping was estimated by a preliminary calculation.<br> The method will be applied not only to basic research on methane hydrate but also to assessments of the environmental impact of methane hydrate exploitation.