著者

笹井 洋一 上嶋 誠 歌田 久司 鍵山 恒臣 Jacques ZLOTNICKI 橋本 武志 高橋 優志

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.110, no.2, pp.226-244, 2001-04-25 (Released:2009-11-12)

参考文献数

31

被引用文献数

8 10

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Electric and magnetic field observations have been extensively carried out since 1995. A precursory magnetic anomaly was detected in July 1996, which was ascribed to thermal demagnetization at a depth of several hundreds of meters beneath the southern periphery of the summit Hatcho-taira caldera. Magnetic data revealed that the large depression at the summit associated with the steam explosion on July 8, 2000 had been completed within four minutes. Since the beginning of July, anomalous magnetic changes were observed at several magnetometer sites along the central N-S line of Miyake-jima volcano, which indicated the rise of a demagnetized area from depth to the summit. On July 4, a few days before the steam explosion, an area survey of SP in the summit caldera was conducted, discovering an extremely negative zone around the forthcoming depression, which suggested the intense absorption of ground water. Tilt-step events; i.e., abrupt uplifts around the summit area, were accompanied by electric field variations, which were very similar to the velocity waveform of the ground motion, as well as magnetic variations with step-like changes. An electric field can be interpreted as being due to electric currents generated by the forced injection of steam and/or water from the pressure source (electrokinetic phenomena). Magnetic changes are attributed to the piezomagnetic effect of rocks due to increased stresses. The geomagnetic total intensity showed large variations after the July 8 eruption, the typical feature of which was positive at the east and west sides and negative along the central north-south line of the volcano. They are ascribed to 1) the loss of magnetic mass from the summit and 2) the thermal demagnetization at depth. After the August 18 eruption, which was the largest, the steep changes in total intensity became flat, which suggested that the temperature rise at depth had weakened. At the time of the August 18 eruption, a large increase in self-potential was observed around the southwestern foot of the central cone Oyama : This implies that a definite change occurred in the hydrothermal system of the volcano.

著者

笹井 洋一 上嶋 誠 歌田 久司 鍵山 恒臣 Jacques ZLOTNICKI 橋本 武志 高橋 優志

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.110, no.2, pp.Plate7-Plate8, 2001-04-25 (Released:2009-11-12)

著者

中田 節也 長井 雅史 安田 敦 嶋野 岳人 下司 信夫 大野 希一 秋政 貴子 金子 隆之 藤井 敏嗣

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.110, no.2, pp.168-180, 2001-04-25 (Released:2009-11-12)

参考文献数

18

被引用文献数

41 43

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The 2000 eruption of Miyakejima volcano started with a submarine eruption of basaltic andesite on the morning of June 27, which occurred following earthquake swarms during the previous night. The main phase of the summit eruption began, being associated by a sudden subsidence of the summit area on July 8. Continuous collapsing of the summit area that had continued until midAugust, resulted in the formation of a caldera with the volume of about 0.6 km3. Phreatic (or phreatomagmatic) eruptions took places during the growth of the caldera, although the total volume of eruptives was about 11 million m3. which is smaller by one magnitude than the caldera volume. Eruptives are enriched with hydrothermally altered materials such as smectite and kaolinite.The manner of the first collapse suggests the existence of a large open space under the summit just before the subsidence. Judging from geophysical observation results, the open space may have ascended in the manner of stoping. Successive formation of open spaces at deeper levels is likely to have caused the continuous collapse of the summit area. These open spaces may have been generated by magma's migration from under Miyakejima to the west. The migration is considered to have continued by August 18.It is likely that an inflow of underground water to the open spaces generated a hydrothermal system, where the open spaces acted as a sort of pressure cooker that built up overpressure of eruptions. The hydrothermal system was broken by the largest eruption on August 18, and the eruption column rose about 15 km above the summit. A boiling-over type of eruption occurred on August 29, whereby sufficient overpressure of steam was not built up, resulting in the generation of low-temperature ash cloud surges moving very slowly.

著者

酒井 慎一 山田 知朗 井出 哲 望月 将志 塩原 肇 卜部 卓 平田 直 篠原 雅尚 金沢 敏彦 西澤 あずさ 藤江 剛 三ヶ田 均

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.110, no.2, pp.145-155, 2001-04-25 (Released:2009-11-12)

参考文献数

6

被引用文献数

38 54

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From June 26, 2000, an intensive earthquake swarm started under Miyake-jima Island, 180 km south off Japan. This swarm was closely related to the eruption of Miyake-jima Island, probably dominated by underground magmatic activity. The swarm spread toward the northwestern ocean region from Miyake-jima Island, in which a huge number of earthquakes (over 100, 000) including five large events of M>6.0 were detected over about two months. This earthquake swarm was the most active since we started seismic observations in the 1970's.Although there are some telemetered observation stations on the Izu volcanic islands, no offshore instruments were operated in the area of this earthquake swarm. To understand both the spatial and temporal changes of this activity, we conducted a series of ocean bottom seismometer observations. According to the variation in the seismic activity with time, we changed the array configuration of OBSs six times. Furthermore, real-time seismic observations were undertaken using a buoy-telemetering OBS system.Combining the OBS data with those of the island stations, very precise earthquake locations were determined. The epicenter distribution obtained strongly indicates a northwest-southeastern lineament. The vertical cross-section of the events shows two characteristic trends. Deeper (7- 13km) events are forming a very thin (2-km thick) plane, while shallower ones (< 7 km) show a much thicker distribution. These distribution patterns will provide important constraints on the physical mechanism for understaning magma migration.

著者

宮下 由香里 市川 清士 田中 竹延

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.3-4, pp.380-386, 2007-08-25 (Released:2009-11-12)

参考文献数

13

---

The Tachikawa fault, which is the only active fault in the Tokyo Metropolis, is expected to be the source of shallow intra-plate earthquakes in the future. We performed additional trenching surveys at the northwestern part of the fault to obtain the paleoseismological parameters for evaluating earthquake potential caused by the fault. Trench wall observation, radiocarbon dating, and tephra analyses constrained the last surface-rupturing event at the Tachikawa fault between about 13, 700 cal yBP and 12, 800 cal yBP. The vertical separation of the event is estimated to be more than 2.6 meters.

著者

瀬戸 寿一 村中 亮夫 谷端 郷 中谷 友樹

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.121, no.6, pp.946-961, 2012-12-25 (Released:2013-01-07)

参考文献数

27

---

This study explores how to use geospatial information for residential safety and security activities, such as patrolling a community, from the perspective of PPGIS. The study takes Shino-town, Kameoka City as a case study, where a neighborhood community association held a workshop in 2009 for residents to collect geospatial information for use in disaster prevention and daily security. Because they made a hard-copy “Safety-security Map,” we first converted it into a web-based map with functions that help a user prepare a walking route using Google Maps API. Using the web-based map, some Kameoka residents developed routes for patrolling the community. Then, we walked through the routes with them, conducting interviews on how they felt about risks and attractive features along the routes. Analyzing the results of the field research and interviews, we identified substantial differences in risk perception and interest in the possibility of using web-based safety-security maps by local community residents. Compared to the male representative group of the residents' association, female members of the welfare commission and the PTA representative group were more interested in community safety and disaster prevention information, and the web-based map containing information. They hope to use the web-based map to exchange information among residents. Besides, they showed a keen interest in using the web-based map for walking exercise to raise their awareness of community-safety and disaster-prevention information on a daily basis. It is vital to integrate different interests and needs for safety-security geospatial information of local resident groups to carry out effective residential safety and security activities.

著者

Phil R. CUMMINS 馬場 俊孝 堀 高峰 金田 義行

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.110, no.4, pp.498-509, 2001-08-25 (Released:2009-11-12)

参考文献数

39

被引用文献数

2 2

---

By carefully analyzing the source process of the 1946 Nankai earthquake and its correlation with plate boundary structure, we attempt to explain the occurrence pattern of historical earthquakes in the Nankai Trough, in which great earthquakes tend to rupture separately either the western or eastern portions of the Nankai Trough. The source process of the 1946 earthquake consists of two major subevents, each corresponding to segments A and B, defined by Ando (1975), which have long been thought to correspond to units of earthquake rupture in the western Nankai Trough. Furthermore, rupture in each subevent begins near the eastern edge of the respective segment, where there are pronounced contortions of the plate boundary : a subducting seamount chain off Cape Muroto and a rapid change in subduction angle beneath the Kii Peninsula. We suggest that these seismotectonic features of the plate boundary shape control to some extent the pattern of great earthquake occurrence in the Nankai Trough.

著者

大島 規江

出版者

学術雑誌目次速報データベース由来

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.5, pp.661-679, 2000

被引用文献数

1 1

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In this paper I analyze the social space of Muslim inhabitants in Amsterdam, paying particular attention to differences of residential area around the city center and its suburbs. This study is based on my fieldwork carried out from February to March 1997 in Amsterdam. The materials were collected through personal interviews.<BR>The result of the analysis showed that the residential pattern of Amsterdam experienced great change between 1990 and 1995. Since 1990, the Dutch have tended to concentrate in the northern and southern suburbs and inflow into the area. On the other hand, Moroccan and Turkish inhabitants have concentrated in eastern and western part around the city center. It is pointed out minorities concentrate in CBD and inner city, which often have low-wage jobs and low-rent housings. Lobar and housing market in Amsterdam also affected residential pattern. Ethnic clusters are located around the city center where the ratio of private let and deteriorated housing are relatively high. However, the concentrated area of ethnic minorities has gradually expanded into the suburbs in recent years.<BR>According to past studies, it is interpreted that the expansion of ethnic clusters comes from on upgrading of social and economic status. To consider whether or not the same factors also operate on or not in Amsterdam, it is necessary to look at the social space of Muslim inhabitants in two areas around the city center and the suburbs. From the responses to questions, Muslim inhabitants were classified into four types. For the sake of brevity, the members of cluster one can be labeled 'Inhabitants of the first generation live in around the city center'. Cluster two identifies 'Inhabitants of the first generation live in the suburbs'. In contrast, members falling into cluster three could be representing 'Inhabitants of the second generation live in the suburbs'. And, cluster four might be express 'Inhabitants of the second generation live in all areas of the city'.<BR>The result of the analysis clearly shows that the expansion of Muslim clusters does not originate from social and economic factors in the Dutch welfare state. More than half of the housing is managed by housing associations in Amsterdam. Because Amsterdam is situated on former marshland, building poses special problems. As Amsterdam developed concentrically, the suburban area has great number of social housing. But, most of the Muslim ingabitants have to lie in private lets around the city center. However, they have opportunities to move into social housing, due to decreas of the Dutch population from 1990 to 1995. For this reason, ethnic clusters have expanded into the suburbs in recent years. The differences between the environs of the city center and the suburbs are family constitution and years residing in Amsterdam. Muslim inhabitants live in suburban areas together with the first generation and the second generation. However, research reveals that social space in two areas consisted of similar social and economic conditions.

著者

仰天子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.2, no.6, pp.310-310, 1890

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

大石 雅之

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.118, no.6, pp.1237-1246, 2009-12-25 (Released:2010-03-23)

参考文献数

19

被引用文献数

1 4

---

Azumaya Volcano is a stratovolcano located slightly at the back arc side of the volcanic front in central Japan. Previous studies led to the publication of a geologic map and the K-Ar age of some lavas, but the stratigraphic relationships of the volcanic products and their eruptive history are still unclear. Some tephras that possibly erupted from Azumaya Volcano have been found in the North Kanto region. But, there are relatively few descriptions of pyroclastic products. This study presents the lithological and petrographical characteristics of products from Azumaya Volcano, especially the refractive indices of phenocrysts, because these data are very important for identifying products and reconstructing eruptive history. This study examined the adequacy of the identification of tephras of the previous studies and whether the source of these tephras is Azumaya Volcano from the distribution of tephra and comparing mineral composition and refractive indices of orthopyroxene, plagioclase, hornblende, and cummingtonite phenocrysts in proximal products and distal tephras. Because the refractive indices of the phenocrysts in the products distributed in Azumaya Volcano have unique characteristics, refractive indices are useful for identifying and correlating products. Distal tephras correlated in previous studies have similar characteristics, increasing the probability that the source of the SgP.2 tephra bed is the Azumaya Volcano. In addition, the volume of the SgP.2 tephra bed was calculated to be 0.85 km3 dense-rock equivalents (DRE) using its distribution.

著者

竹中 克行

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.121, no.4, pp.650-663, 2012-08-25 (Released:2012-09-03)

参考文献数

27

---

Since its beginnings, geography in Spain has followed a particular development course, defined mainly by a close and ever evolving relationship between academic geography and professional geography. Over the last few decades, the two geographies have been mutually involved, creating a situation in which the professional practice of geography, originating with cartographers and engineers in the late nineteenth century, has become an increasingly important factor for the renewal of academic research, mostly undertaken in universities. Innovation was possible, on the one hand, thanks to the consolidation of academic geography, which today concerns not only traditional areas of knowledge, but also fields where there is growing social demand, such as environment, landscape management, regional planning, urbanism or risk analysis. All these themes, on the other hand, have opened up new professional opportunities for geography graduates, who have been contributing with their practice in administration and private enterprises to make more people aware of the importance of geography as a useful science. The fruitful relationship between the two geographies briefly described above is the main concern of this article, which introduces a mixed approach of science historiography and radiography. After analyzing the evolution of academic geography through doctoral theses and major journals specialized in geography, the author highlights the role of professional geography, focusing on how geographers are entering in new fields of the labor market and are defending their interests as a professional group. The analysis is complemented by reference to successive new plans of studies launched in university geographical education, an important reform accelerated by the so-called Bologna process. The article concludes by pointing out some of the research lines that have great potential for future development with international repercussions.

著者

早津 賢二

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.101, no.1, pp.59-70, 1992-02-25 (Released:2010-10-13)

参考文献数

18

被引用文献数

3 3

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Myoko volcano, situated in the northern part of Central Japan, is one of the composit stratovolcanoes whose life histories have been studied in detail. In this paper, ten volcanic ash layers belonging to the central cone stage of Myoko volcano are described, and more detailed volcanic history of the central cone stage is compiled in connection with the informations already known.The result are summarized as follows:(1) The central cone stage started ca. 5, 800 years ago. The central cone, Mt. Myoko, was almost built at the early time of the stage.(2) The youngest magmatic eruption of Myoko volcano took place ca. 4, 200 years ago, and produced pyroclastic flows and pyroclastic surges.(3) The youngest steam explosion of Myoko that was confirmed took place ca. 3, 000 years ago, and produced small pyroclastic surges.(4) For 1, 600 years between 5, 800 and 4, 200 years ago, a series of eruption whose ejecta were kept as an obvious stratum at the foot of Myoko volcano took place at the average rate of once for 200 or 300 years. After the violent eruption of ca. 4, 200 years ago, Myoko rapidly became less active, and the eruption in the similar scale took place only once or twice for ca. 4, 200 years up to the present.(5) The central cone stage was dominated mainly by the activity of dacitic magma, and coincided with the time when pyroclastic flows and pyroclastic surges were apt to be produced by explosive eruptions.

著者

斎藤 功 矢ヶ崎 典隆

出版者

学術雑誌目次速報データベース由来

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.3, pp.293-313, 2001

被引用文献数

2

---

Covered with short grass and bushes and called llano estacado by Spanish explorers, the Texas Panhandle constitutes the southern part of the American High Plains. Following the decline of the open range cattle industry in the late nineteenth century, large-scale cattle ranches appeared, such as LIT, LS, and XIT. Irrigation has rapidly expanded in the region during the past fifty years. It supports production of corn and grain sorghum (milo) in the flat plains of the northern Panhandle and wheat and cotton in the southern Panhandle. Cattle ranches still dominate in the undulating and sloping country of the Canadian River valley. This paper examines the nature of cattle ranching in the Texas Panhandle during the age of irrigation that promoted differentiation of land use.<BR>Hartley and Oldham counties are chosen for our intensive field study. Large-scale ranches are identified on the map using farm plats, topographic maps, and aerial photographs. They vary in size, from family-operated ranches of 2, 000 hectares to corporate ranches exceeding 40, 000 hectares. Historic ranch names such as LIT and LS are still maintained by contemporary owners. The cow-calf operation is still the basic method in this region, while some beef cattle ranches, not owning cows, depend on purchased yearlings. Others combine cow-calf operations with raising yearlings. As a single animal is given 12 hectares of pasture, 150 to 200 head are grazed on a 4, 000 hectares ranch. Calves born on the ranch during the spring are sold at livestock auctions in Dalhart and Amarillo to farmers, who graze them in wheat fields during the winter. In March, farmers sell their yearlings weighing around 200 kilograms at livestock auctions to ranchers. After being grazed on pasture and reaching 300 kilograms in the fall, they are finally sold to the neighboring feedlots for finishing. Therefore, cattle transactions at the Dalhart livestock auction have peak periods in March and October.<BR>The Texas Panhandle has a concentration of feedlots. They fatten two-year old cattle weighing 300 kilograms for four months until they reach 570 kilograms. They are large-scale commercial feeders, with the largest raising 85, 000 head. Agribusiness companies such as Continental Grain and Cargill operate large feedlots. Some local feedlot owners operate large ranches in order to secure a supply of cattle. Large beef packing plants are also concentrated in the Texas Panhandle for processing locally finished beef cattle.<BR>Beef packers, feedlots, ranches and wheat growers of the Texas Panhandle are interrelated, taking advantage of the groundwater resources of Ogallala Aquifer. Cattle ranches are the basis of the feedlot and beef-packing industries, while they depend on local wheat growers for winter grazing. Unlike the cattle industry in the late nineteenth century and first half of the twentieth century, contemporary cattle-ranching industry in the Texas Panhandle represents a regional change that took place in the American High Plains in response to the opportunities offered by groundwater exploitation.

著者

白尾 元理

出版者

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.103, no.1, pp.plate1-plate2, 1994

著者

木村 昌三

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.110, no.4, pp.581-591, 2001-08-25 (Released:2009-11-12)

参考文献数

32

被引用文献数

2 2

---

Seismicity characteristics in and around Shikoku, southwest Japan are investigated using recent data from microearthquake observations. Earthquakes occurring in the regions are distinctly divided into crustal and mantle earthquakes according to about 22 km in focal depth. Crustal and mantle earthquakes have predominantly the strike-slip type with P axes in the east-west and north-south directions, respectively. Although the Philippine Sea plate is subducting under Shikoku in the northwest direction from the Nankai trough, the P axis of mantle earthquakes in eastern Shikoku is inferred to be stable in the N-S direction during the period before the 1946 Nankai earthquake until today. On the other hand, earthquakes with normal fault type occur infrequently in the aseismic portion deeper than the north dipping mantle earthquake zone.A gradual lowering of crustal earthquake activity has continued since 1968 in which our microearthquake observation started in central Shikoku. Taking the abrupt decreasing of events in Shikoku before the 1946 Nankai earthquake by JMA data into consideration, the present activity is expected to become lower extremely just before the next Nankai earthquake.

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

---

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

---

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.