著者
田中 圭 中田 高 松浦 律子 田力 正好 松田 時彦
出版者
公益社団法人 東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.127, no.3, pp.305-323, 2018
被引用文献数
1

<p> <i>Kambara Jishinyama</i> (earthquake-mound) located on the west bank of lower reach of the Fujikawa river, is widely believed to be a mound that was tectonically formed at the time of the 1854 Ansei Tokai earthquake. Using old maps and aerial photogtaphs, geomorphological changes around <i>Kambara Jishinyama</i> before and after the earthquake are examined. The Fujikawa river frequently flooded and the course on its west bank changed especially after construction of the <i>Karigane-zutsumi</i> (big bank) in order to protect farmland on its east bank. The area around the lower reach of the river was surveyed in 1803 for the <i>Dai Nihon Enkai Yochizu</i> large-scale map, which is the so-called <i>Ino-Daizu</i>. On that map, the river was at almost the same location as its present course. The historical road map (<i>Kaido-Ezu</i>) of <i>Tokaido</i>, which was the trunk road connecting Edo and Kyoto, illustrated in the same period as <i>Ino-Daizu</i>, shows that the Fujikawa river shifted its course close to the foot of river terraces at the west bank. Due to lateral erosion of the river, part of the <i>Tokaido</i> between the towns of Iwabuchi and Kambara collapsed several times. Subsequently, the road was diverted to the new route via Shinzaka as shown on the 1:20,000 scale topographic map published in 1890. A micro-landform classification map of the alluvial lowland of the west bank of the Fujikawa river based on interpretations of aerial photographs taken in 1952 and 1953 reveals that <i>Kambara Jishinyama</i> was located on one of the former mid-channel bars in the braided channels of the river before the 1854 Ansei Tokai earthquake. The earthquake caused a large landslide that dammed the Fujikawa river for a short period at the foot of Shiratori-yama to the north of Iwabuchi. The discharged flood water changed the river course close to the present stream. Geomorphic evidence for tectonic uplift does not exist around <i>Kambara Jishinyama</i>. The Koike river, a small stream flowing in the former main stream of the Fujikawa river, abandoned at the time of the Ansei Tokai earthquake, concordantly flows into the present main stream of the Fujikawa river showing that co-seismic uplift did not take place at the west bank. We conclude that <i>Kambara Jishinyama</i> was not tectonically formed by the earthquake, but is a product of the river course change.</p>
著者
久野 久
出版者
公益社団法人 東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.73, no.5, pp.279-280, 1964
被引用文献数
1

Basalt magmas in Japan range in composition from tholeiite, passing through high-alumina basalt, to alkali basalt. Picrite basalt related to either of these three basalt magmas is scarcely represented. In Hawaii, both tholeiite and alkali basalt are closely associated with picrite basalt having bulk compositions intermediate between the ordinary basalt and peridotite. The Japanese basalt magmas are supposed to be produced by sudden release of stress attending the generation of the intermediate to deep-focus earthquakes. In such a case, there may be a certain limitation of the heat energy supply for melting the mantle peridotite ; only a few per cent of the peridotite would be melted to form the basalt magmas.<BR>The Hawaiian basalt magmas are supposed to be produced by the heat transfer due to convection current within the mantle. In such a case, there would be less limitation of the heat energy supply for melting ; a greater per cent of the peridotite would be melted, resulting in the production of picrite basalt magmas.
著者
新谷 俊一 田中 和広
出版者
公益社団法人 東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.118, no.3, pp.340-349, 2009-07-07
参考文献数
20
被引用文献数
3 12

&emsp;Mud volcanoes are structures formed as a result of the emissions on a land surface or the sea floor of argillaceous material, which is composed of erupting remobilized mud, petroliferous or magmatic gases, and high-salinity water. Recently, large constructions have been planned deep underground besed on the expectation of geological stability. Therefore, it is important to study the origin of erupted mud and groundwater and the depths from which they ascend when evaluating long-term stability. Three active mud volcanoes and a passive mud volcano are found in the Tertiary Shiiya Formation distributed in Tokamachi City, southern part of Niigata Prefecture. Detailed descriptions of the mud volcanoes are provided by Shinya and Tanaka (2005). However, the origin of erupted mud and the formation mechanism of abnormal pore water pressure have not yet been identified. The authors measured the oxygen and hydrogen isotopic ratio of groundwater and vitrinite reflectance of coal fragments separated from erupted mud of an active mud volcano to investigate the origin of erupted mud, particularly the depth of the origin, and the formation mechanism of abnormal pore water pressure. As a result, &delta;<sup>18</sup>O and &delta;D values of erupted water are 1.2&permil;, -5&permil; respectively, showing good agreement with those of the Nanatani Formation distributed at a depth of 3400 m in depth in the studied area. Vitrinite reflectance (Ro) shows a bimodal distribution (<i>i.e.</i>, 0.3-1.2% and 1.5-1.8%). Ro value of coal fragments sampled from the Shiiya Formation at the outcrop in the studied area are 0.3-0.45%. High Ro (1.5-1.8%) values of coal fragments are obtained in core samples at a depth of 4000 m in the Gimyo SK-1 oil well, which was excavated 2 km NW from the mud volcano. As a result of an investigation of erupted materials at the mud volcano, they were found to have originated at depths of from 3400 m to 4000 m in the studied area. Geothermal temperature of underground at depth of 3400 m to 4000 m in the in the studied area is estimated to be about 120&deg;C to 150&deg;C. Estimated temperature is high enough to cause diagenetic transition from smectite to illite. Transition from smectite to illite results in the release of a large volume of pore water into the sediment. It is concluded that dehydration due to mineral transition might be the major reason for abnormal pore water pressure formation at depths of 3500 m to 4000 m in the study area.
著者
小山 真人
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.5, pp.576-590, 1994-10-25 (Released:2009-11-12)
参考文献数
56
被引用文献数
4 7

Izu Peninsula and adjacent areas, which are located on the northern tip of the Izu-Bonin volcanic arc, are characterized by intense crustal movements and volcanic activity. Many geomorphological, geological, and geophysical data were collected from this area and various tectonic models were proposed to explain them systematically. These tectonic models can be classified into two categories : models 1 and 2. While model 1 regards the area as a single tectonic province, model 2 proposes two or more tectonic provinces, which are bounded by tectonic lines. Models 1 and 2 can be classified into models 1A and 1B, models 2A, 2B, 2C, and 2D, respectively. Model 1A hypothesizes an anticlinal bend of the Philippine Sea plate, which is being generated by the subductions along the Suruga and Sagami troughs. Model 1B emphasizes the crustal stress field generated by the collision of the Izu-Bonin volcanic arc with Japan arc and the slab-pull force along the Sagami trough. Since there are many local tectonic features that cannot be explained by model 1A or 1B, models 2A-2D were proposed. Model 2A divides the study area into two tectonic provinces : the northern province of compressive deformation by conjugate faults and the southern province of right-lateral shearing deformation. Model 2B divides the area into the eastern and western provinces, which are defined by sharp contrasts in the geologic structure, seismicity, crustal stress field, crustal movements, focal mechanisms of earthquakes, paleomagnetic directions, and volcanic activity. Many observations support the validity of the model 2B tectonic provinces. Model 2C introduces the hypothesis that the Izu-Bonin arc is being fractured into the inner and outer arcs because of a contrast in buoyancy. The existence of the estimated model 2C fracture, W est Sagami Bay Fracture, is still under debate. Model 2D regards the Higashi-Izu monogenetic volcano field, located in the eastern Izu Peninsula, as a field of crustal spreading. Model 2D proposes a key to understanding a sharp contrast in tectonic features between the eastern and western provinces of model 2B as well as the complex geometry of the Philippine Sea slab beneath the Japan arc.
著者
西村 昭
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.1, pp.134-136, 1998-02-25 (Released:2009-11-12)
参考文献数
2

深海の海底堆積物は, かつては微化石の標準層序の確立やマンガン団塊など海底鉱物資源関連の研究対象とされていたが, 現在では, 古気候や古環境の研究が活発になっている。海底堆積物の研究を古気候と関連させて考えると2つの視点がある。一つは古気候や環境変遷の記録としての堆積物で, もう一つは, 地球のシステムの物質循環の中で気候や環境の変化にかかわる堆積物である。地球環境問題の関連研究として, 深海堆積物の種類や分布, 形成過程と環境変遷について紹介した。
著者
横山 祐典
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.111, no.6, pp.883-899, 2002-12-25 (Released:2009-11-12)
参考文献数
62
被引用文献数
9 7

Global ice volume during the last glacial stage was obtained using geological observations from the sites located away from the former glaciated regions. The advantage using such records is that the area has been less influenced from the readjustments of the crust due to glacial isostasy. However the effect is still not negligible in those areas and hence it is required to correct sea-level records for both glacio-and hydro-isostatic effect to extract past global ice volume information. The record shows progressive growth of global ice volume since the end of the Last Interglacial. Rapid fluctuations of the volume were also observed during the last ice age corresponding to the Heinrich events observed in the North Atlantic ocean as well as Dansgaard-Oschgar events seen in the Greenland Ice cores. The Last Glacial Maximum was ranged between 30, 000 years ago to 19, 000 years ago and ended by the rapid disintegration of the ice volume that corresponding to decrease of the ca. 10 m of ice-volume equivalent sea-level. Gradual sea-level rise was seen during the late glacial stage, except the time known as melt-water pulse la in the Barbados coral, but other catastrophic rises were not found in the records. Main phase of deglaciation was ended until ca. 7000 years ago, yet slight decrease in ice volume equivalent to the 3 m global sea-level has been occurred since then. Sea-level change namely global ice volume fluctuations had been played as major role for human migration from Africa to the other parts of the world during the last ice age. Therefore studies on coastline changes will provide an useful information for the research on spatial and temporal histories of past human life styles.
著者
宮下 純夫
出版者
公益社団法人 東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.98, no.3, pp.213-230, 1989
被引用文献数
5

Magma reservoir models beneath ocean ridges are reviewed with reference to the spreading rates and the mode of fractional crystallization. Faster spreading rates (5cm/year) cause a large and long-lived magma chamber in which a thick plutonic sequence would be succesively produced away laterally from the chamber. Basalts extruded at fastspreading ridges underwent various degrees of low pressure fractionation causing conspicious chemical zonation in the chambers. On the other hand, small and transient magma chambers may be present beneath slow-spreading ridges. Comparatively less-evolved basalts, where petrological characteristics are governed mostly by the deep-seated processes such as degree of partial melting and polybaric fractionation, could appear at slow-spreading ridges because of absence of a large crustal magma chamber.<BR>Since sheeted dikes in ophiolites intruded vertically and the foliation of mantle tectonites were approximately horizontal in original, the configuration of the magma chamber interlayered between the tectonites and sheeted dike complex, if it existed, can be infered from the structure of a cumulate-gabbro sequence. The appearance of a thick plutonic sequence in the ophiolite where the crystallization order is olivine-plagioclase-clinopyroxene-orthopyroxene suggests that it was generated at a fast-spreading ridge. In such thick plutonic sequence, the fine-scale igneous layering (=time plane) obliquely across the major lithologic boundary of the plutonic sequence may reflect the horizontal chemical zonation of the magma chamber. On the other hand, the appearance of abundant whelritic cumulates crystallized at mantle deths and suffered high temperature deformation suggests that the ophiolite was generated at a slow-spreding ridge.<BR>Spreading rates of ancient ocean ridges at which the ophiolites were generated may be roughly estimated from the considerations on geochemical variation of the basaltic rocks. The occurrence of evolved basalts interpreted by extensive low pressure fractional crystallization suggests fast spreading rates, whereas the appearance of less evolved basalts showing complicated geochemical features such as different incompatible element ratios and crossing REE pattern suggests rather slow spreading rates.<BR>The studies on ophiolites would bring significant informations not only on the dynamic process beneath present-day ocean ridges but also on the tectonic framework and the evolution of ancient spreading center.
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.128, no.1, pp.Cover01_01-Cover01_02, 2019

<p> 台風22号の通過後に冬型の気圧配置が強まり,近畿・東京地方では木枯らし1号が発表された.長野県北部にも季節風に伴う雪雲が侵入し,根子岳中腹から山頂では弱い降雪と霧氷が発生した.霧氷は短時間で広範囲の樹木に付着するため,低地から見上げると山頂が冠雪したと誤認されることもある.雪雲は背が低く,上空には青空が時折現れ,一方で上田盆地周辺は紅葉が見ごろだ.晩秋は中部山岳域北部の山々が彩を豊かにする季節である.</p><p>(写真・解説:上野健一 2017年10月30日撮影)</p>
著者
森本 良平 小坂 丈予 羽鳥 徳太郎 井筒屋 貞勝 浦部 和順 高橋 春男 岡田 義光 平林 順一 伊佐 喬三 磯部 宏
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.77, no.5, pp.255-283, 1968-10-25 (Released:2009-11-12)
参考文献数
25
被引用文献数
3 3

Unusual uplift of the land was found about an insular active volcano Iwo-jima, Ogasawara archipelago, 1, 200 km south of Tokyo. Remarkable retreat of shore line was revealed by reviewing topographic maps and aerophotographs of the island. Some upward movements of the island are to be one of the most principal reasons of the retreat. As the clear evidences of the upheaval of the land, following phenomena were observed by the writers who investigated the island five times from 4th July to 23rd August 1968 : a) Sunken vessels and a landing craft have emerged on the western coastal beach of the island : b) Faults and cracks appeared on the abandoned run-way of the former Japanese Navy in the central part of the island ; c) Coastal reef emerged on the sea to connect off shore islet with the island ; d) New coastal terraces were formed on the sand beaches ; e) Fresh living corals were exposed on the sea.Results of the investigations are enumerated as follows : 1) About 8 m upheaval of the land since 1953-4 was revealed by levelling survey at the western coast of the island. 2) Amount of uplift observed on the above-mentioned run-way is smaller in its central part than in both terminals, maximum vertical displacement of the fault being 3 m. 3) Tide gauge installed at the western rocky coastrecorded slight relative down of sea level but further observation should be continued without disturbance by typhoon to obtain more reliable data. 4) No expected microseisms were recorded on the high sensitive electro-magnetic seismographs except 2 or 3 per day. 5) Temperature of the fumarolic gases were 95-123°C, 10-25°C higher than that observed in 1935. In spite of the rise in temperature, gases of so called high temperature type, such as sulphur dioxide and halogens, were not contained. 6) Composition of the sublimates also accords with these results of chemical analyses of the gases. 7) Content of each main component element and its ratio to other ones is quite variable in several hot springs whose pH values range from 2.1 to 6.8. 8) Analcite was identified by X-ray and DTA analyses in the tuff forming Moto-yama, an eastern main flat cone of the island. Genetic condition of the mineral inferred from its chemical composition may indicate submarine eruption of the volcano. 9) Three weak zones were recognized by the present investigations in addition to the two ones previously reported by Tsuya. Thus three are arranged radially through the center of the eastern main cone and the two are arranged concentrically around the foot of the same cone. From these weak zones phreatic explosions are expected in future, if they occur. 10) Nothing more than mere weak phreatic explosion was recorded through the historic activity of the volcano. Artificial filling up of the vent, such as the pavement of the surface often causes the small explosion at fumarole. 11) Submarine eruption recently found at the sea bottom, about 5.4 km NNE of the South Sulphur Island, about 50 km south of the island did not occur recently but must have repeated rather stationarily.According to the present investigations, no remarkable magmatic explosion could be expected except those small phreatic ones, same one of which has often occurred on the island. Chemical composition of the gases does not indicate any approach of hot magma to the surface.