著者

吉野 正敏

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.116, no.6, pp.836-850, 2007-12-25 (Released:2009-11-12)

参考文献数

91

被引用文献数

3 4

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Recent studies on climate change during the historical period are reviewed in this paper. Firstly, methods, limitations and materials for reconstructing past climates are summarized. Historic diaries and old documents are useful particularly for the period of the past 500 years. Some indices for expressing the climatic conditions found in the historic materials are introduced. Historic documents and materials found in China since 4, 000 BP were published in 2004. On the other hand, daily weather data at several stations for the 15 and 16 centuries in Japan were published in 2004 and 2006, respectively. Secondly, the “Little hypsithermal (warm) period” during the period from the 4th century to the 10th century is described. In the final part of the present paper, examples of an ancient central government in Japan, planning of Heijoukyou (an old center of government), settlements developed on the Boso Peninsula, Chiba, Japan, and parallel activities in Southeast Asia are discussed in relation to the changing climate during the “Little climatic optimum” from the 8th century to 9th century, which was the peak of the “Little hypsithermal (warm) period”. It is pointed out that the changes were roughly in parallel.

著者

大和 広明 三上 岳彦 高橋 日出男

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.2, pp.325-340, 2011-04-25

参考文献数

12

被引用文献数

3 18

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We analyze the influence of sea breeze on temperature distribution in the Kanto Plain (central Japan) on a day that a sea breeze front was detected (known as sea-breeze front days) using high-resolution temperature data observed by our research team.<br> The high-temperature area on sea breeze front days moves northwest from central Tokyo, and was located at Kawagoe city (middle Kanto Plain) at 14 JST, and the northern Kanto Plain at 16 to 18 JST, respectively. This high-temperature area appears at the head of the sea breeze front to the leeward of central Tokyo, where the daily maximum temperature is highest in Kawagoe city and the northern Kanto Plain. After the sea breeze front passes, the area where the temperature is higher than that at the circumference is distributed in the shape of a wedge. This wedge-shaped area is located to the leeward of central Tokyo where the wind from Tokyo Bay and Sagami Bay forms a convergence zone. The high-temperature area around Kawagoe city, which cannot be found on days with strong winds, is formed from the hindrance of cold air advection caused by sea breeze front penetration.<br> On the other hand, high temperatures in the northern Kanto Plain may not be related to the penetration of sea breeze fronts, which do not reach the northern Kanto Plain on days when the daily maximum temperature is recorded. However, the temperature in the northern Kanto Plain is higher on sea breeze days than on strong southerly wind days, and this suggests that local circulation plays an important role in causing high temperatures in the northern Kanto.

著者

澤柿 教伸 平川 一臣

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.107, no.4, pp.469-492, 1998-08-25 (Released:2010-10-13)

参考文献数

120

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Geomorphological and sedimentological processes beneath modern glaciers and ice sheet s have not been observed directly and are poorly understood. On the contrary, abundant glacial landscapes can be observed, which provide us with evidence about processes underway at the beds of the past ice sheets. Consequently, careful studies of glacial landforms and sediments provide a wealth of information of these processes.During the last decade, there have been various debates regarding subglacial landforms and their formation processes: drumlins is a major issue, and no satisfactorye xplanation of their mode of formation has yet been obtained. By overviewing recent research on the drumlin problem, this article attempts to draw attention to the major concepts and controversies behind the formation of subglacial landform, together with new developments in understanding the subglacial environment. The most recent explanations for drumlin formation have been examined in the light of our knowledge of the subglacial environment. In particular, J. Shaw and his co-workers draw attention to the significance and the implication of subglacial meltwater processes. They suggested that large-scale meltwater floods were responsible for the formation of some drumlins. Later, erosional drumlins, bedrock erosional marks, tunnel channels, and Rogen moraine were added to the forms resulting from catastrophic floods. Conversely, G.S. Boulton developed a semi-quantitative flow model for the deformation of rapidly deforming soft sediments (A-horizon) on the basis of field observations.The drumlin problem stands as a conspicuous instance of how much there is still to understand about the interplay of glacier motion, sediments, topography, and subglacial environmental conditions. It is thus emphasized that accumrate explanations of the complexities of subglacial environments are necessary to understand subglacial landform development, sediment deposition, and other geomorphic processes at the ice/bed interface, together with extraglacial effects of ice sheet dynamics on fluvial systems, marine sedimentation, ocean currents, and climate.

著者

丸山 茂徳 宇都宮 敦 石川 晃

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.120, no.6, pp.1035-1044, 2011-12-25 (Released:2012-03-05)

参考文献数

16

被引用文献数

1

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オントンジャワ海台は太平洋中央部の太平洋スーパープルームによって白亜紀(122 Maと90 Ma)につくられた巨大な海台である。形成後,西方に移動し,オーストラリアプレートが北上することによってプレート相対運動が変化して,20-25 Maごろから海溝に沈み込みはじめた。その結果,ソロモン諸島には,それらの海台の破片が付加体として露出している。付加しはじめた時期については異論があり,これまでの多くの研究者は2 Ma 以降であると考えてきた。 しかしながら,われわれは地質調査と文献に基づいた証拠,すなわち一連の逆断層の形成と構造浸食,および20-25 Ma以降の沈み込み帯火山活動の停止から以下の解釈を行った。海台が25-20 Maに海溝に沈み込みを開始すると,海台のその浮力のために、沈み込み角度が低角度になり島弧火山活動が停止した。そして始新世以降の付加体を構造浸食して,崩壊物をマントルへと運んだ。また中新世におけるオントンジャワ海台の衝突と沈み込みが背後のウッドラーク海盆の拡大の開始のトリガーになったと思われる。 過去25-20 Maにわたるオントンジャワ海台の沈み込みは,付加体としては海台のごく一部(< 1%)のみを上盤側のプレートに付加したのみで,主要部のほとんどはマントル深部へ沈み込んだと思われる。これは顕生代の環太平洋造山帯に普通にみられる現象である。

著者

山口 貞雄

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.44, no.10, pp.549-561, 1932-10-15 (Released:2010-10-13)

参考文献数

12

著者

早川 由紀夫

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.108, no.4, pp.472-488, 1999-08-25 (Released:2009-11-12)

参考文献数

94

被引用文献数

3 9

著者

小口 高 斉藤 享治 原 美登里 門村 浩 林 舟

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.109, no.1, pp.120-125, 2000-02-25 (Released:2010-10-13)

参考文献数

18

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Data for Japanese alluvial fans have been made available on the Internet using ArcView IMS, a GIS-based map server software package. This system permits easy on-line browsing of the data from anywhere in the world and the creation of thematic maps at various scales for the area around an alluvial fan.

著者

早川 由紀夫 藤根 久 伊藤 茂 Lomtatize ZAUR 尾嵜 大真 小林 紘一 中村 賢太郎 黒沼 保子 宮島 宏 竹之内 耕

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.120, no.3, pp.536-546, 2011-06-25 (Released:2011-09-06)

参考文献数

11

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Two wood trunks, one charred and 75 years old and the other not charred and more than 199 years old, were collected from Hayakawa ignimbrite of Niigata Yakeyama Volcano. They were investigated using the radiocarbon wiggle-matching method to determine the age of the eruption. The result was 1225-1244 cal AD (95.4%), which is over 200 years younger than previous estimates. The eruption, including the Hayakawa ignimbrite, was the largest during the volcano's life period of 3000 years. Co-ignimbrite fallout KGc ash has been found at many archaeological sites spreading on the eastern flanks of Myoko Volcano and the Takada Plain. The age obtained here will provide a useful time constraint for archaeologists and volcanologists studying this area.

著者

林 上

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.106, no.6, pp.794-798, 1997-12-25 (Released:2009-11-12)

被引用文献数

1 1 1

著者

浦 環

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.109, no.6, pp.900-906, 2000-12-25 (Released:2009-11-12)

参考文献数

12

被引用文献数

3

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The autonomous underwater vehicle (AUV) has been recognized as a new platform for observing the underwater world. It can dive freely around the target of the mission prescribed in its computer prior to launching.Throughout a dive, it does not require the operator and the support vessel to help it to execute its mission. It has no umbilical cable, which is fitted to remotely operated vehicles currently used for underwater operations and observations and usually causes problems for the operator. This paper presents the state of the art of the AUV and how it can be used in underwater science.

著者

貝塚 爽平

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.66, no.4, pp.217-230, 1957-12-30 (Released:2009-11-12)

参考文献数

23

被引用文献数

2 2

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The northeastern part of the Kantô plain, which is the largest plain in Japan, has many terraces as shown in the geomorphological map (fig. 1).In this paper, the landdforms and the geological structures of these terraces are described as below.(1) General characteristics of the terraces.The above area is divi ed into two topographic regions by the Yamizo mountain range running from north to south. The estern part is practically made up of marine Pleistocene strata. On the other hand, the western part has many river terraces which are formed by fluvial gravels and volcanic ashes.(2) Dating of the terraces by tephrochronology (tehro means volcanic ashes).During the Quaternary period, the terraces had been covered by volcanic ash layers called Kanto Loam. Presently the older terraces and the newer ones both are covered by thick and thin Loams respectively. This relationship between terrace and Loam makes it possible to date the land surfaces chronologically. Through this the author obtained the following chronological table.(3) The river terraces built by eolian volcanic ashes.The western area is chiseled off by many river terraces. In the northern part of this terraces region, the relative heights of terrace surfaces from the preseat flood plain are higher than that of the southern part. But, if the volcanic ashes on the whole terraces are stripped off, the surfaces of the terraces have practically no significant heights, In other words, the higher the terraces, the thicker the volcanic ashes are as shown in Fig. 4, In conclusion, these river terraces would be called “Eolian volcanic ash terraces”.

著者

杉戸 信彦 松多 信尚 石黒 聡士 内田 主税 千田 良道 鈴木 康弘

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.124, no.2, pp.157-176, 2015-04-25 (Released:2015-05-14)

参考文献数

15

被引用文献数

5 8

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Spatial variations of hazards such as strong ground motion and tsunami inundation are a key element for obtaining a geographical understanding of natural disasters. However, detailed distribution of tsunami run-up heights for the devastating tsunami associated with the 2011 off the Pacific coast of Tohoku earthquake is not available. A GIS analysis of tsunami inundation areas is conducted from data collected by the Tsunami Damage Mapping Team and from post-tsunami 2-m mesh and 5-m mesh digital elevation models (DEM) after the Geospatial Information Authority of Japan, in order to produce the Tsunami Run-up Height Map, which includes polygon data of inundation areas with elevation data at each point. Horizontal shifts of orthophotos taken just after the tsunami are corrected using a Helmert transformation. The map covers Iwate Prefecture, Miyagi Prefecture, and the northern part of Fukushima Prefecture continuously at high resolutions, and reveals spatial variations of tsunami run-up heights in detail. These variations are caused by: 1) landforms at each site, such as coastal plains, valleys, bays, and beach ridges, as well as their directions and magnitudes, and 2) source locations, interference, and wavelengths of the tsunami, as implied by a previous study. The map supports examination carried out on source fault models and simulation results of tsunamis from a geographical viewpoint. At the same time, the methodology to produce the map would be useful for systematically revealing run-up height distribution, in addition to inundation areas immediately after future tsunamis.

著者

森川 洋

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.106, no.1, pp.10-30, 1997-02-25 (Released:2009-11-12)

参考文献数

27

被引用文献数

1 1

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This paper is focused on the modernizing process of urban functions in Japanese cities which should remarkably transformed since the end of feudal age ; the transformation of dominant urban functions from parasitic character through central function to management function in main cities of nonmetropolitan areas.First, examining the comparative descriptions between the end of Edo Period and the early Meiji Era mentioned in 'the Annual Report of Commercial Situation (Shokyo Nenpo)' published in 1877 and 1878, we can often reveal the properties of urban functions and urban systems in the comparative descriptions with the end of Edo Period. According to such an analysis the castle towns forming the main element of Japanese urban system in feudal age can be recognized as a kind of parasitic cities, because the merchants of castle towns mainly supplied the necessary goods to samurais inhabited in their own towns. While foods and fuels were transported into castle towns from the surrounding rural areas, the merchants of castle towns could not supply many goods with the same intensity to inhabitants of the rural areas. Besides the circulation of commodities controlled within the territory of clans, Edo (the old name of Tokyo), Osaka and Kyoto functioned as the triple centers within the whole country through oversea transportation of goods. Accordingly, the hierarchical structure of two strata can be recognized in the urban system in those days : national urban system due to the triple centers and the regional and local urban systems in clan territories. The latter usually consisted of smaller areas with castle towns as a center than in the present prefectural areas.Since the Meiji Restauration in 1868 the free economic competition has become active among cities or towns. As the merchants of castle towns lost their privileges, most of castle towns declined, at least temporally. Although there are no adequate materials to analyze central place functions, it can be estimated that they played an especially important role as urban functions in the early Meiji Era except for traffic functions because manufacturing industry has still not developed. Central place functions such as administration, education, health service, etc. were gradually established in larger centers, especially in prefectural capitals. Japanese industrial revolution occurred with singular form about from 1887 to 1907. Usually, larger centers grew and smaller ones declined, although a few new industrial towns appeared.Next, the author analyzed the branch offices of companies registered in Tokyo and Hiroshima Prefectures in 'the Main Staff List of Most Companies in Japan (Nihon Zenkoku Shohaisha Yakuinroku) in 1908 and 1935 in order to investigate firm activities in both periods. In 1908 the insurance companies located in Tokyo Prefecture already formed a network of branch offices in the main cities of the whole country including the present provincial capitals, but other firms such as manufacturing, wholesale-retail companies, etc. had only a few branch offices, mainly located in Osaka. During the period 1908 to 1935 firm activities were largely developed and the number of branch offices increased evidently.We can classify the location patterns of branch offices in those days into 4 types, apart from the present location patterns in which their location in provincial capitals is dominant : the types located 1) in large markets or large cities such as Osaka, 2) in large cities in foreign countries or colonial capitals in those days, 3) in port towns such as Yokohama, Kobe, Moji, Shimonoseki, Otaru and Hakodate, and 4) in the present provincial capitals such as Sapporo, Sendai, Hiroshima and Fukuoka. Therefore, the present provincial capitals were still not so developed for the location of branch offices in 1935 as nowadays. In the years 1908 and 1935 Kanazawa was still an significant center.

著者

佃 為成

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.99, no.1, pp.32-42, 1990-02-25 (Released:2010-11-18)

参考文献数

39

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The geologic feature of the northern Fossa Magna region is characterized by a well developed folded belt system. Recent microseismicity over 10 years and historic earthquakes reveal that there are seismic zones pararell to the axes of this structure: Itoigawa-Shizuoka Tectonic Line, the western side of Shinano River, the western margin of the Central Belt of Uplift, and the eastern margin of the Central Belt of Uplift. The last zone was recently recognized by the earthquake sequence with the main shock of M 4.9 in 1986. The fcal mechanism solutions and other geologic and geodetic evidence indicate the region is compressed in the direction perpendicular to the folded belts. We can also find seismic activity lines perpendicular to or oblique to these folding axes: the Chikumagawa Tectonic Line separates the Central Belt of Uplift with a left lateral offset of 10km; the seismic line along the eastern side of the volcanic line of Myoko-san, Kurohime-yama and Iizuna-yama makes the eastern edge of the seismic gap around the northern end of the Itoigawa-Shizuoka Line.A 20-25 years recurrence time is found in the occurrence of the major earthquake events in the central part of the northern Fossa Magna in recent 140 years.Seismic active regions are grouped into some rectangular blocks with their bases being either pararell or perpendicular to the folded belts. The activity in a block became active nearly simultaneously, and it sometimes migrated to other blocks with some delay time. The high activity migrated from the block region around the Chikumagawa Tectonic Line to both the northern activity block around the Japan Sea coast and the active region in the southern Fossa Magna during the period from 1986 to 1987.The migration of the seismic activity along the Fossa Magna region may be due to delayed transmission of the stress field in the viscoelastic or elastoviscous medium. The exponential time dependence of the decay rate of the Matsushiro swarm activity for a long period more than 20 years since 1965 is found to be reasonably interpreted by the relaxation process of stresses within the elastoviscous medium. The viscosity changed from 1.1×1019 poise to 2.7×1020 poise as time elapsed. The first value is comparable with that of a ground surface rock body estimated by secular ground tilts and strains. The latter is the same order of the values obtained in the long period second creep experiments using granite and gabbro. The Matsushiro region is one of the region where the viscosity might have been very low due to numerous micro-cracks.

著者

小泉 格

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.1, pp.62-78, 2007-02-25

被引用文献数

3 8

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The results of hydro-environment researches into marine and lacustrine sediments revealed climatic variations which seem to have some relationships between turns in world history and climatic changes. In the Japan Sea and northeast Pacific off Kashima from the Late Glacial to the Holocene, diatom temperature, <I>Td</I>' = (frequency of warm-water species) - (frequency of warm-and cold-water species) <SUP>-1</SUP>?100, values show rhythmic fluctuations with durations of 1 kyr and 400-500 yrs (Koizumi et al., 2004, 2006). This indicates a strong and regular inflow of the warm Tsushima Current into the Japan Sea as a branch of the warm Kuroshio Current. The decreases of <I>Td</I>' values correspond to a period of climatic deterioration under which cultural changes occurred in Japan. The paleoclimatic variations and the triple events of high <SUP>14</SUP>C in the atmospheric residual <SUP>14</SUP>C record denoted by Stuiver <I>et al</I>. (1991) are recognized in the diatom variations.<BR>A similar periodicity is also recognized in North Atlantic drift ice (Bond <I>et al</I>., 2001), concentrations of sea salt and terrestrial dust in the GISP2 ice core (O'Brien <I>et al</I>., 1995), in lake deposits from the Jura in France (Magny, 1995), Tibet (Gasse et al., 1991; Ji <I>et al</I>., 2005), and Alaska (Hu <I>et al</I>., 2003), and oxygen isotope variations from stalagmites in southern China (Wang <I>et al</I>., 2005) and Oman (Neff <I>et al</I>., 2001).<BR>Climatic deteriorations are synchronous with periods when serious changes occurred in human intellectual achievements during the Holocene. The Agricultural Revolution (11, 000-10, 000yr BC), with the cultivation of wild plants and domestication of wild animals to produce and secure food, seems to coincide with the Younger Dryas event. Increased agricultural production made it possible to afford a population not engaged in agriculture, for example, people engaged in handicrafts, festivals, and politics. This seems to occur in the period coinciding with T<SUB>2</SUB> event in the T<SUB>1</SUB>-T<SUB>4</SUB> triplets, which have Maunder-and Sporer-type patterns occurring in sets of three, denoted by Stuiver and Braziunas (1993). The religious courtesy belief in the recycling and the reinforcing of life was converted into a rational and systematic consideration of life based on universal theory. This conversion of thinking seems to coincide with the T<SUB>3</SUB> event. Modern science was established in Europe in the 17th century. And now human beings are destroying natural environments using highly developed scientific technologies of their own. This is a negative revolution that human beings have never previously experienced.<BR>In the south-to-north transect of the cores from both the Pacific and Japan Sea sides of Honshu, <I>Td</I>' values indicate that the Kuroshio Current and Tsushima Warm Current are both weakening at present. The present interglacial period might end and become a cooler climatic condition like a Little Ice Age within 300 years. The insolation at 37°N among the Earth's orbital parameters is weak at present (Koizumi and Ikeda, 1997). However, the mean global temperature has risen about 0.5°C during the last century. Warming of the Earth, which is caused mainly by carbon dioxide in the atmosphere, has made natural environments unstable.

著者

柳井 修一 青木 一勝 赤堀 良光

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.1079-1124, 2010-12-25

被引用文献数

8 64

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Median Tectonic Line (MTL) and Fossa Magna (Itoigawa-Shizuoka Tectonic Line) had long been considered to be the most critical fault boundaries controlling development of the Japanese Islands since Naumann (1885) and Kobayashi (1941). After the appearance of plate tectonics, several new interpretations emerged, <i>e.g.</i>, sub-surface Benioff plane for the MTL. In this paper, we propose that those tectonic lines, major faults, and Tanakura Tectonic Line (TTL) were formed through a process at micro-plate boundaries during the opening of the Japan Sea in the Miocene.<br> MTL could have been formed along the consuming boundary between the PHS plate and Japan Sea microplate, which has shifted southward to the Nankai trough, accompanying large-scale tectonic erosion. Fossa Magna was formed as a gigantic transform fault with a transtension component in the Medial-Japan Sea when opening was initiated. The eastern and western boundaries of the Japan Sea must be a strike-slip fault, corresponding to TTL to the east, and a newly proposed strike-slip fault called the West Kyushu Tectonic Line, respectively. Fossa Magna, a medial region defined by two NS-trending Miocene parallel faults in central Honshu, defined by Nauman (1885) could be interpreted to be the largest transform fault in the Medial-Japan Sea to offset the spreading axis when the Japan Sea opened.<br> It should be emphasized that large-scale tectonic erosion occurred in front of consuming plate boundaries facing the PHS and PAC plates oceanward during the opening of the Japan Sea. The volume of tectonic erosion is calculated to be 17,581,500 km³, which is equivalent to 2/3 of the present-day Japan arc crust, which is sufficient to reach the depth of the megalith between the upper and lower mantle boundary, even with 10 km thickness of materials eroded and transported along the Benioff zone.<br> Although MTL, Fossa Magna, and TTL are remarkable in the geology of Japan, these young faults never affected the orogeneses of Japan back to 520 Ma, which grew the continental crust of Japan. We propose that microplate boundary processes decreased the volume of the Japan crust.

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.122, no.3, pp.Cover01_1-Cover01_3, 2013

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(表面)太平洋プレート上部境界面から10km上方の曲面(地表面からほぼ40–120kmの深さ範囲)に沿うS波速度の分布(Nakajima and Hasegawa, 2010).S波速度をカラースケールで示す.太平洋プレートとフィリピン海プレートの接触域を2本の太い黒破線で囲んで示す.赤星印は1885年以降に南関東で発生した5つのM7級地震.ビーチボールは1921年竜ヶ崎地震(M7.0)(2通りの解を示す)と1987年千葉県東方沖地震(M6.7)のメカニズム解.黒丸は1987年千葉県東方沖地震の余震.(裏面)フィリピン海プレート東端部の蛇紋岩化域(茶色の領域).ピンク色の太い破線は蛇紋岩化域の西縁.フィリピン海プレート上面の深さ分布を灰色破線のコンターで示す.緑色の四角と丸は太平洋プレート上部境界面で発生した地震,灰色の点はフィリピン海プレートマントル内の地震.1921年竜ヶ崎地震と1987年千葉県東方沖地震に加え,フィリピン海プレートのマントル内の4つの地震のメカニズム解もビーチボールで示す.紫色の丸は1923年関東地震の約30時間後に発生したM7.1の余震.フィリピン海プレートはピンク色の太い破線を境にして2つに裂け,東側の蛇紋岩化域は西側の本体部分からとり残され,より遅い速度で沈み込んでいる.ピンク色の細い破線で囲んだ楕円はOkada and Kasahara(1990)が指摘した地震の空白域.(長谷川 昭)

著者

熊谷 博之

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.108, no.4, pp.424-432, 1999-08-25 (Released:2009-11-12)

参考文献数

27

被引用文献数

9 12

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Possible tsunami deposits were found at two archeological sites along the Pacific coast near Hamana Lake in central Japan. This region has frequently suffered heavy damage from large earthquakes along the Nankai trough. Three sand deposits covering layers that include archeological remains were found at one of the sites. The ages of the sand deposits were constrained by remains just below the sand deposits, which showed good correspondence to the ages of three major historic earthquakes that seriously damaged this area, i.e., A.D. 1707, 1605, and 1498. These features strongly suggest that the sand deposits were caused by tsunami from the historic earthquakes. Core samples obtained near this site showed that a similar sequence continues into a deeper part, suggesting the existence of tsunami deposits of events older than A.D. 1498, before which few historical records are available in the Tokaido side. Further investigation of tsunami deposits in this area would yield useful information on the reconstruction of large earthquakes along the Nankai trough.

著者

矢島 道子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.1, pp.237-238, 2011

著者

伊神 輝

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.99, no.1, pp.61-71, 1990-02-25 (Released:2010-11-18)

参考文献数

40

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Newly developed idea of the nascent plate boundary along the eastern Japan Sea has become to be discussed in the last five years. The boundary extends southwards through central Japan, where the Itoigawa-Shizuoka Tectonic Line (ISTL), one of the great tectonic lines in Japan, traverses to Suruga Bay. In the south of central Japan, the Philippine Sea plate is subducting under Japanese Islands, which lie on the North American plate and the Eurasia plate, and, therefore, a triple junction is formed there, if we acceptthe new idea of the plate boundary. Central Japan is, then, considered to be situated under the complex tectonic stress fields due to the plate interactions, and has the structures resulting from ongoing or past geodynamical process.Many seismic probings have been undertaken in central Japan and the derived structure will open informations on the geodynamic process and verifications of the nascent boundary. New resolution methods in seismic probing of the crust and the upper mantle can derive a three-dimensional velocity structure. The derived structure in central Japan, including ISTL, shows a low velocity body beneath the Hida mountains at the east of ISTL. However, the difference between the North American plate and the Eurasia plate has not beenresolved over the whole area along ISTL from the P-wave velocity of viewpoint. Many explosion profiles have been conducted in central Japan, some of which cross ISTL. The result at the north of ISTL shows a distinctive reverse fault dipping east near the Matsumoto Basin, though the fault location is slightly different eastwards from the geologically estimated tectonic line. The dip of the fault is concordant to that derived from the newidea of subducting the Eurasia plate under the North American plate. We cannot find other seismic profiles showing the similar structure in this area. In the southern part of ISTL, the northsouth fault is derived, which may be deformed by the plate interaction between thePhilippine Sea plate and the Eurasia plate.Unraveling a highly and widely resolved structure will be required to step forward to verify the new plate boundary hypothesis, and to put it practice, it is necessary to develop observation systems as well as the processing techniques. We address a request ofdeep seismic sounding which has controlled sources on a long-range profile with seismic waves penetrating deep into the crust and the upper mantle on a scale to discusss the new plate boundary hypothesis. Almost simultaneously, seismic tomography using natural sources, having a resolution of a three-dimensional image, will provide important information for better understanding of the geodynamical process in central Japan.