著者

糸魚川 淳二

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.4, pp.726-731, 2009-08-25

著者

氏家 恒太郎 山口 飛鳥 木村 学 久光 敏夫 平 朝彦

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.115, no.3, pp.353-366, 2006-06-25 (Released:2009-11-12)

参考文献数

34

被引用文献数

3 3

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Fluid behavior during the evolution of the plate boundary fault (pbf) from a trench to seismogenic depths is the central problem when evaluating the relationship between fluids and seismicity in subduction zones. Ocean Drilling Program Legs 190 and 196 at the toe region of the Nankai accretionary margin reveal that fluid-filled dilatant fractures and underconsolidated underthrust sediments lead to an elevated fluid pressure in and below the pbf, respectively. The pbf with elevated fluid pressure extends down-dip to 35 km, resulting in the absence of seismic behavior at shallow depths and mechanical decoupling between accreted and underthrust sediments. Underconsolidated underthrust sediments are primarily caused by rapid tectonic loading compared to the rate of fluid escape in underthrust sediments and secondarily by a lowpermeability cap due to the compactively deformed pbf. Fluid-filled dilatant fractures represent the overconsolidate state within the pbf, which is caused by the generation of high fluid pressure after compactive deformations.The exhumed plate boundary rocks (i.e., tectonic melange) in the Shimanto accretionary complex indicate that the underthrust sediments became rocks due to dewatering, pressure solution, and other diagenetic reactions, thus acquiring elastic strength. The pbf in the upper part of the seismogenic depths was weak due to elevated fluid pressure, this facilitated the downward step of the pbf and the underplating of underthrust rocks. The pbf under low effective stress was unlikely to nucleate the instability; however the fluid-related repeated deformations, which probably reflect the seismic cycle in the subduction zone, could be recorded. The coseismic deformations were attributed to hydraulic implosion breccias, injection of ultracataclasite, and fluid inclusion stretching in the pbf. Implosion breccias suggest rapid depressurization associated with the passage of the rupture through dilational jog. Other deformations represent shear heating and fluidization along the narrow ultracataclasite layer, which could enhance the propagation of instability at the pbf in the upper parts of the seismogenic depths.

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.119, no.1, pp.Cover01_1-Cover01_2, 2010-02-15 (Released:2010-05-21)

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伊豆半島の東半分およびその沖合の相模湾底に100個程度の単成火山の群れである伊豆東部火山群が分布している.大室山(標高580m.写真右上の薄茶色の小山)は,底径1km,比高300mほどの美しいプリン状のスコリア丘で,およそ4,000年前の噴火によってできた.山頂には直径250m,深さ40mのスリバチ状の火口があり,観光リフトによって簡単に登山・散策できる.山頂からの360度のパノラマは見事である. 大室山から流出した溶岩は北方・東方・南方へと流れ下り,地形の凹凸を埋めて伊豆高原(写真中央から右にかけての台地)をつくるとともに,幅4kmほどの範囲で相模湾に流れこんで城ヶ崎海岸(写真左から下にかけての凹凸の激しい海岸)をつくった.海岸ぞいでは,柱状節理・溶岩じわなどのさまざまな溶岩流の造形を観察することができる.写真左上の山は,第四紀火山のひとつである天城山.(写真:白尾元理,2010年1月7日撮影;解説:小山真人)

著者

尾池 和夫

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.97, no.7, pp.Plate1-Plate4, 1988-12-25 (Released:2009-11-12)

著者

石川 晃 金子 慶之 太田 努 磯崎 行雄

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.120, no.1, pp.52-64, 2011-02-25 (Released:2011-05-20)

参考文献数

59

被引用文献数

2 2 3

---

The western Pacific region, where the Eurasia, Australia, and Pacific plates currently interact, has been recognized as an important site for constraining the origins and emplacement of ophiolites (particularly for island-arc or supra-subduction zone types), because the spatial distribution of oceanic micro-plates and numerous ophiolitic rocks along their convergent margins infers possible genetic linkages among them. Mafic-ultramafic rocks distributed in the Timor-Tanimbar island chain, eastern Indonesia may be a good example of the on-going emplacement of the marginal basin lithosphere on the continental margin in the arc-continent collision zone, and are recognized as a possible modern analogue for Mesozoic Tethyan-type ophiolites (e.g. Troodos and Oman) in the Alpine-Himalayan orogenic system. Geological occurrence suggests that the buoyant subduction of the Australian continent uplifted fragments of newly formed mantle-crust section, which extends to neighboring pre-emplaced forearc marginal basins. However, from petrological and geochemical points of view, young pillowed basalt, dolerite, and gabbroic cumulate commonly possess island-arc signatures, whereas structurally underlying peridotites are mostly fertile (lherzolitic) in composition. This suggests that the crustal section is not linked to the underlying mantle by a genetic melt-and-residua relationship, as inferred from the lack of complete succession and the presence of abundant crosscutting structures. This inconsistency leads to the emergence of two contrasting models accounting for the unusual occurrence of a fertile mantle in the forearc setting of the Timor-Tanimbar region: (1) thrust-stacked fragments of the subcontinental mantle originally exhumed in the rifting stage of Australia; (2) depth-related heterogeneities in the lithospheric part of the mantle wedge. We note that the current debates on the origins of fertile lherzolites found throughout the Tethyan sutures and western Pacific regions can be settled through a better understanding of Timor-Tanimbar peridotite masses by age-dating studies employing several radiogenic isotope systematics.

著者

中田 高 島崎 邦彦

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.59-69, 1997-02-25 (Released:2009-11-12)

参考文献数

4

被引用文献数

31 53

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We invented a completely new simple method and new equipment necessary for high-resolution active fault studies. Vertical thin sections of unconsolidated soil layers are extracted by a newly invented sampler named “Geo-slicer”.Extracted sections can be taken to a laboratory for close examination or can be displayed at a meeting or even stored for future re-examinations (Fig. 1). This method enables us to carry on high-resolution analyses not only in active fault studies but also in other fields of Quaternary sciences with less expenditure of time, labor and money.We made three different-sized Geo-slicers and tested them successfully in the field. A Geo-slicer is made of steel and has a simple structure composed of a box and its shutter (Figs. 2 and 3). Several devices are implemented to the box and the shutter, such as wedge-shaped side walls and a stopper at the bottom of the box for easy pull-out of the equipment and steady-holding of samples (Fig. 4).For sampling, we firstly intrude the box vertically down into the ground by using a vibro-hammer (Photo 1) and then shutter sliding along the thin slits attached to the both sides of the box, and pull out the equipment containing samples.The extracted layers of sediments are surprisingly undisturbed and show almost the same features as previously observed on trench walls excavated close to the extraction sites (Photos 2 and 3). The largest sample collected by this method is 150 cm wide, 270 cm long (deep) and 8-15 cm thick (Photo 4).This sampling method is far more effective on active fault studies than the conventional trench excavation technique and we will be able to carry out three-dimensional analysis of active faulting, restoration of horizontal fault slips and so on for paleoseismological studies (Fig. 6).

著者

溝上 恵

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.73, no.4, pp.224-242, 1964-08-30 (Released:2009-11-12)

参考文献数

5

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As the present crustal structures have been formed by the tectonic movements through the long geological age, problems of the crustal movements must be studied in connection with the information of the present crustal structures obtained from geological, geomorphological and geophysical methods. In this paper, the relation between the crustal structures and the crustal movements in Japanese islands found by geodetic methods is investigated from the following three points.1) The relation between the changes of the intensity of crustal movements with time and those in space.2) The relation between the horizontal variations of the crustal movements and crustal structures.3) The difference of the characteristics of the crustal movements in orogenic regions (Japanese islands) and in continental platform.

著者

石本 巳四雄

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.48, no.9, pp.399-412, 1936-09-15 (Released:2010-10-13)

著者

松本 至巨 尾方 隆幸 内川 啓

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.115, no.2, pp.221-235, 2006-04-25

被引用文献数

1 1

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The Northern Japanese Alps (Chubusangaku National Park) has experienced a dramatic increase in the number of visitors since the boom referred to as "the Japanese hundred mountains". The Ushiro-Tateyama Range, located in the northernmost area of the Japanese Alps, provides various alpine landscapes such as cirques, asymmetrical ridges, patterned ground, perennial snow patches and alpine plant communities. Data from 6922 trekkers indicate that the distribution of mountain huts and accessibility to trails control their trekking courses, and that the trekkers concentrate in three mountain areas : Shirouma-mountain area, Goryu-mountain area and Kashima-mountain area. These areas are divided by a landform called kiretto, where a col with steep rockwalls lies along a main ridge, operating as a natural obstacle. Such a concentration suggests that human impacts on mountain geoecosystem occur locally, but intensively.

著者

田村 芳彦

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.112, no.5, pp.Plate4-Plate4, 2003-10-25 (Released:2009-11-12)

著者

石渡 明 平島 崇男 野坂 俊夫 坂野 昇平

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.99, no.4, pp.382-387, 1990-08-25 (Released:2009-11-12)

参考文献数

15

被引用文献数

1 1

著者

小野 有五

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.121, no.2, pp.187-214, 2012-04-25

被引用文献数

1 4 2

---

Fifty years of studies on glacial landforms in Japan between 1960 and 2010 are reviewed from the personal perspective of a researcher who devoted a major part of his life to these studies. The 1960s was a period in which there was a paradigm shift in the history of glacial landform studies in Japan. This resulted from a series of studies by Tomoya Iozawa using aerial photograph interpretation. He was the first researcher to observe and identify all of the glacial landforms in Japan using aerial photographs, and divided them into two groups: the older and more widespread (Yokoo Stage) and the younger and much less widespread (Karasawa Stage). Following his methodology and staging, extensive research was done in the 1970s, and tephrochronological studies revealed that the older and younger stages correspond to MIS 4 and 2 respectively, although MIS 3 glaciation was recognized later in the Hidaka Range, Hokkaido. A researchers union of glacial and periglacial landforms called <i>Kanrei-chikei Danwakai</i> was established in 1972, Proposed and organized by Isozawa and other young students including the author, it stimulated research. In the 1980s, a reconstruction of the mass balance and flows of past glaciers from glacial landforms was attempted by the author and other researchers. This led to the estimation of the Equilibrium Line Altitude (ELA) of former glaciers in Japan. Inventory work and monitoring of perennial snow patches in the Japanese Alps were also begun in the 1980s, and they encouraged studies on the transformation from perennial snow patch to glacier. In addition, the discovery of an ice body at the bottom of Kuranosuke Cirque, Mt. Tateyama, Northern Japanese Alps gave an important hint to estimating the present (topographical) snowline altitude, which could be much lower than the former evaluation determined only from free air temperature. Both the study of perennial snow patches and mapping of the former ELA clarified the importance of precipitation when determining snowline altitude, and the present ELA was estimated at 2970 m just below the peak of Mt. Tateyama (3003 m). Since the 1990s, glacial landform studies became more closely related to global climatic change within the framework of IGBP-PAGES. Glacial fluctuations in Japan in the last glacial period were mainly controlled by monsoon changes and migration of westerlies, which caused a southern migration of the polar frontal zone. Although the glaciers in Japan were small, even in the glacial period, it is now believed that they are an important indicator of climatic changes because they are very sensitive to monsoon and westerly changes.

著者

茂木 清夫

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.92, no.7, pp.547-554, 1984-01-25 (Released:2009-11-12)

参考文献数

13

著者

木村 学 玉木 賢策

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.94, no.2, pp.69-83, 1985-04-25 (Released:2010-10-13)

参考文献数

52

被引用文献数

1 4

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The Kuril basin was formed by back-arc spreading in Oligo-Miocene time which is deduced from bottom depth, heat flow and geological data in and around the basin. The b sin has a shape of fan which diminishes northeastward and closes just southwestern end of Kamchatka Peninsula.The fan shape strongly suggests that the basin was formed by the rotation of backarc plate (the Okhotsk Plate) around a relative rotation pole located between the Kuril Basin and Kamchatka Peninsula. Geology around the Sea of Okhotsk indicates that the clockwise rotation of the Okhotsk Plate and the fan spreading of the Kuril Basin concurrently took place in Oligo-Miocene time.

著者

横山

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.4, no.1, pp.44-44, 1892-01-25 (Released:2010-12-22)

著者

岩生 周一

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.55, no.3, pp.115-117, 1943-03-15 (Released:2010-10-13)

著者

白尾 元理 佐藤 正

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.6, pp.Plate1-Plate2, 1999-12-25 (Released:2009-11-12)

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.25, no.12, pp.885-886, 1913-12-15 (Released:2010-12-22)

著者

浜野 洋三 柳澤 孝寿 山岸 保子

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.114, no.2, pp.142-150, 2005-04-25 (Released:2009-11-12)

参考文献数

7

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Recent progress of numerical simulations on the dynamo process in the core and the mantle convection provides a clue to understanding the origin of global variations of the Earth system during the last 150 Ma, in which long-term variations of geomagnetic reversal frequency and mantle activity are closely related in time. Recent MHD dynamo simulations suggest that the increase of the total heat flow through the CMB changes the geodynamo from stable dipolar dynamos to unstable multipolar dynamos, and on axially symmetric and equatorial symmetric pattern of heat flux produces stable dipolar dynamos. Numerical modelings of mantle convection indicate 3 convection regimes, whole-mantle, intermittent, and 2-layer convections, in a parameter space of the Rayleigh number (Ra) and the Clapeyron slope (dP/dT) of the phase transition at a depth of 660 km. In the intermittent convection regime, the convection vacillates between wholelayer and the 2-layer regimes, and the surface and CMB heat flows fluctuate with time. The global variation of the Earth system might be attributed to this intermittent convection mode of the present Earth. However, the apparent out of phase variation of the total heat flow through the CMB inferred from the reversal frequency and the mantle activity requires some mechanism for the phase shift of the variations..

著者

山下 傳吉

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.6, no.5, pp.252-258, 1894-05-25 (Released:2010-10-13)