著者
石戸 経士
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.114, no.6, pp.885-900, 2005-12-25
参考文献数
29
被引用文献数
6 2

Characterizing the transport properties of reservoir-forming rocks is one of the most important tasks in reservoir engineering. We review the relationships among permeability, porosity, electrical formation factor, and electrokinetic coupling coefficient under saturated and unsaturated conditions on the basis of the capillary tube model of porous medium, by which one can relate the microscopic physics of the transport properties to the macroscopic behaviors described by Darcy's and Ohm's laws and the cross-coupling effects. These relationships together with the recent models of clay rich sandstones provide a useful guideline for interpreting core, logging, and geophysical survey data. Among various rock properties, permeability in particular needs in situ measurements such as pressure transient tests, because <I>in situ</I>i values are usually at least a few orders of magnitude larger than those measured for intact core samples due to the presence of discontinuities such as fractures in reservoirs. Concerning this topic, the concept of fractured rocks, <I>i.e.</I>, the double porosity medium and how to characterize fractured reservoirs are described.<BR>Even if the results of extensive field-wide pressure transient tests are available, in addition to drilling and various exploration data, numerical models of reservoirs are never precise, due to the problem of non-uniqueness. However, once exploitation begins in earnest, additional data become available such as temporal trends in downhole flowing pressure and enthalpy (in case of geothermal reservoirs), which may be used in history-matching studies. Because uncertainty in predictions of numerical reservoir models is directly related to the amount of field data available against which the models can be tested, it is clear that the addition of repeat geophysical survey data to the list of pertinent field measurements is likely to improve the reliability of these forecasts. Recently developed computational tools such as the EKP-postprocessor, which can calculate changes in self-potential distribution through electrokinetic coupling caused by changing underground conditions computed by reservoir simulation, enable us to use geophysical monitoring data in history-matching studies.
著者
庄子 仁 Jin Young K. Obzhirov Anatoly SALOMATIN Alexander BARANOV Boris GLADYSH Vyacheslav 八久保 晶弘 南 尚嗣 山下 総 高橋 信夫
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.118, no.1, pp.175-193, 2009-03-25
参考文献数
35
被引用文献数
5 6

Methane hydrates exist beneath the sea bottom near cold seeps NE off the Sakhalin in the Sea of Okhotsk. Multidisciplinary field operations were performed at a study area (approximately 16 × 20 km<sup>2</sup>) to investigate seepage characteristics and understand gas hydrate formation mechanisms. A continuous profiling survey was conducted to obtain a distribution map of seepage structures on the floor by using a deep-tow, side-scan-sonar equipment. The distribution map reveals that the dense area of seepage structures coincides with a sea-floor area of deformed sediments caused possibly by repeated sediment slumping and debris flows in the past. We speculate that this deformation may have created shallow faults that are suitable to conduits for the migration and discharge of gas and fluid.<br> Three seepage structures were selected to study about their fluid-seep conditions around the sea floor level. Hieroglyph seepage structure is located at the northern end of the dense area of the structures. Kitami and Chaos structures are located about 2 and 7 km respectively apart from the Hieroglyph structure within the dense area. Large plumes on echograms and higher methane contents in the water column confirm gas seepage activities at the three structures. There observed at least two and four plumes at the Hieroglyph and Chaos structures, respectively. Each gas chimney image in seismic reflection profiles was traced to connect each BSR and seepage structure. Both pull-up and disturbed structures of BSR around the gas chimney images were interpreted as to be indications of significant heat flows caused by ascending fluid at both Kitami and Chaos structures. On the other hand, almost no pull-up/disturbance of BSR was observed at the Hieroglyph structure, suggesting little water seepage.<br> The seep activity may vary with time off the Sakhalin. The Hieroglyph structure is located at the edge of a dense area of the seepage structures. It might serve as an indicator for the long-term activity of the fluid seepage system off the Sakhalin.
著者
吉田 明夫 高山 博之
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.6, pp.696-705, 1994-12-10
参考文献数
12
被引用文献数
1 1

We show that seismic activity decreased clearly in a wide area before the 1953 Boso-oki earthquake and the 1972 Hechijojima-toho-oki earthquake. In both cases the seismic quiescence extended to the Tokyo Metropolitan area. Marking precursory activity appeared several years before the Boso-oki earthquake in the Chiba prefecture and in the sea region off-Ibaraki prefecture. It is also noted that the seismicity in the Kanto region as well as in the sea region south off-Boso Peninsula decreased conspicuously after the Boso-oki earthquake. On the contrary an increase of the seismicity was observed after the Hachijojima-toho-oki earthquake, although deep seismic activities decreased remarkably. We show that seismic quiescences preceding the Boso-oki earthquake and the Hachijojima-toho-oki earthquake were detectable before their occurrences, and no other statistically significant quiescence has appeared in the south off-Kanto region since 1926. It is proposed that the occurrence of a large earthquake may be predicted by monitoring changes of the seismicity in a wide area.
著者
宇都宮 陽二朗
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.101, no.2, pp.117-126, 1992
参考文献数
26
被引用文献数
3

Numajiri Bokusen invented an epochal terrestrial globe made from wood, bamboo nd Japanese paper in 1800 and published details of it in 1855. The globe was similar to a coarse Japanese oilpaper umbrella, and in fact was called the "umberlla-like globe" later. Previously, the author has described the form of this globe.<BR>The present paper describes the geometrical features of Bokusen's globe, especially, the shapes of shorelines and national boundaries. The world map on the 1855 globe had obviously been revised since that appearing on the globe invented in 1800, based on the latest information on the shorelines available at the time.<BR>Since the Japan Archipelago was set in the center of the world, the axis of the globe was declined at 36 degrees. Therefore, the ground level sinusoidally rounds the globe according to its declination.<BR>Lines of latitude were shown every 10 degrees. The interval of the lines of longitude was also 10 degrees. While the value of latitude was written, that of longitude was not shown anywhere on the globe. Between the lines of longitude, marks were inserted every one degree along the equator, resembling the symbol used for railways in recent maps.<BR>Despite the lack of a base for the median line of the globe, the base was expected to pass through Ferro Island in the Canary Islands. Thus, it is assumed that values were intended to be written every 10 degrees according to the distance from the Island. The location of the Japan Archipelago at the center, and the declination of the earth's axis seem to have been important political matters influenced by attitudes such as reverence for the Emperor and exclusion of foreigners during the late Edo period in Japan.<BR>On this globe, the center of the Japan Archipelago was intended to be just under the zenith, and set at 130°(actual value 132° in recent maps) E and 36 N. This location was selected as the place nearest to Miyako (Kyoto), which is placed at 135°46'E and 35°00'N. On the other hand, Edo is at 139°40'E and 35°42'N (almost equal to 36 degrees) based on values in recent maps. Therefore, the base of latitude at the center of the 1855 map seems to have been unchanged since that on the 1800 globe. If Bokusen used the value of Miyako, the inclination of the earth's axis was set at 35 degrees.<BR>On the other hand, the base of longitude was altered to a new location near Miyako. Ne-vertheless, Bokusen could not help including some of the base of the median line of the world maps established in the western Europe. Thus, the center was not set in Miyako, but was moved to the west.<BR>Some compass lines drawn from the center were made on assumptions, and some remarks about astronomical phenomena such as sunrise and sunset at the winter/summer solstices and the vernal/autumnal equinoxes were written on these lines and assumed lines.<BR>Most of the shapes of the shorelines closely resembled those on recent maps. Although the Australian continent was correctly shaped, the Antarctic continent was not shown. In the Arctic region, the shape of the northern coast of the Eurasian continent was relatively correct compared with that of the North American continent. Especially, the areas in the vicinity of Hudson's Bay and the District of Franklin were obscure, and their shapes were expressed using broken lines. This seems to reflect Bokusen's scientific standpoint, which excluded any uncertainty.<BR>Between 80°N and 80°S, the coast lines including Korea and the California Peninsula and other continents were correctly shown. On the other hand, the shapes of national boundaries of inland areas were drawn as rough lines framed by colors including blue, red, violet, yellow and black. Some of the shapes appear to be scribbled. Therefore, the decisions regarding boundaries seem to have been less confident.
著者
若林 芳樹 伊藤 悟
出版者
東京地学協会 = Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.3, pp.221-232, 1994-06-25
参考文献数
34
被引用文献数
4 2

Geographical approach to cognitive maps has mainly focused on measurement of their spatial patterns. Recently Lloyd (1989) devised a useful method for analyzing the components of distortions in cognitive maps by means of Euclidean regression. Until now, however, this method has not yet been validated. The purpose of this study was to reexamine his concepts about the distortions in cognitive maps and to test their validity.We pointed out several discrepancies between the concepts of distortions and their operational definitions given by Lloyd (1989). To overcome this problem, the absolute distortion that appears in the configuration before Euclidean regression ought to be distinguished from the systematic distortion that is measured by the parameters of Euclidean regression. While the systematic distortion that indicates a Euclidean property of the distortion can be explained by alignment and rotation heuristics (Tversky, 1981) and implicit scaling model (Holyoak and Mah, 1982), the relative distortion that remains after Euclidean regression cannot be explained by general theories. In addition, these geometrical components of distortion ought to be distinguished from statistical ones, namely, distortion (central tendency) and fuzziness (dispersion) defined by Gale (1982).On the basis of this conceptualization, we carried out an empirical analysis of the distortion in the cognitive map of Kanazawa City. The data used in this study were obtained by a conditional sketch mapping drawn from 113 students of Kanazawa University. Locations to be answered were 21 transportation nodes within the central part of the city known by more than 90 percent of the students. From these locations, two major landmarks of CBD were selected as reference points. Subjects were asked to indicate the remaining 19 locations on the legal-size sheet in which the two reference points were printed.We detected the absolute distortions, overlaying the cognitive maps for all samples on the actual map so as to fit the locations of two reference points into the actual ones. The patterns of the absolute distortion indicated that the amount of errors increased with distance from the reference points, and that the locations in cognitive maps commonly shifted outward from the actual ones. Specifically, these displaced locations in southern or eastern part of the city indicated a counterclockwise shift, which suggested a directional bias in cognitive maps.In order to separate the systematic distortion from the relative one, each of the cognitive configurations was fitted into the actual map by Euclidean regression. Parameter estimates of the scale change averaged 0.593, which suggested that cognitive maps were enlarged about twice the size of the actual map. Mean direction of the rotated angle amounted to-22.2 degrees, which implied that cognitive maps were rotated counterclockwise about 20 degrees from the actual map so as to coordinate the cardinal directions of the cognitive map with the actual one. This tendency can be due to the displacement of two river channels as major reference lines in Kanazawa from cardinal directions.After eliminating the systematic distortions by Euclidean regression, the actual map was overlaid with all the cognitive maps. The overlaid maps indicated that the local patterns of relative distortions reflected hierarchical structure of cognitive maps (Stevens and Coupe, 1978) although the amount of them was smaller than that of the systematic distortions.
著者
松本 剛 宮下 純夫 荒井 章司 森下 知晃 前田 仁一郎 熊谷 英憲 大友 幸子 DICK Henry J. B.
出版者
東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.112, no.5, pp.705-719, 2003-10-25
参考文献数
20
被引用文献数
6

To characterise the crust-mantle boundary (petrological Moho) and to find evidence of ophiolite model, we investigated the lithology and the development process of the oceanic crust. We carried out geological and geophysical studies of Atlantis Bank core complex located at the eastern margin of the Atlantis-II active transform in the Southwest Indian Ridge (SWIR) using deep sea submersibles and remotely operated vehicles. Unaltered lower crust and uppermost mantle rocks were observed at the southwestern slope of Atlantis Bank. The lower crust of this part of Atlantis Bank is similar to the ophiolite exposed ashore. On the other hand, a large number of dike intrusions into gabbroic massifs were observed at the eastern wall and at the southern slope of the bank. This corresponds to the dike-gabbro transition in the ophiolite model. Dike intrusions were also observed in the mantle peridotite domains. This may, however, suggest melt intrusions into the bank near the spreading axis posterior to the mantle peridotite that was dragged out along the detachment faults, or may suggest possible horizontal melt intrusion from the segment centre to the segment edge characterised by a thin plutonic layer. The northern ridge-transform intersection RTI of the Atlantis-II active transform presents an L-shaped nodal basin, while the southern RTI presents a V-shaped one. The difference between northern and southern RTI types suggests differences in the structure and basement rock types. A fossil transform fault and RTI relics at the northern side of the spreading axis west of the Atlantis-II active transform were observed, suggesting a sudden change of the spreading direction in SWIR from 20 Ma
著者
吉村 稔
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.102, no.2, pp.131-143, 1993-04-25
参考文献数
11
被引用文献数
7 9

In order to reconstruct the march of climate before instrumental observations in Japan, Historical Weather Data Base has been constructed. Weather descriptions in historical documents, such as official diaries of Feudal Clans in Edo Era, or of local offices in each clan, are objects of the data base. Other descriptions are in those diaries of large temples, large shrines and large farmers, and in some of private diaries Considering the description of weather phenomena in old diaries, they were grouped into 13 weather conditions In this data base, "weather range" means weather conditions in a day. A rough tendency of the weather in a day (HN), or remarkable conditions such as hot, cold, dry and wet (HT), are also important to understand weather conditions for each day. Accompanied phenomena (TK) and wind conditions (KT, TT, KH) are also objects to encode. Daily weather records for the years from 1700 to 1889 are mainly under collections. So far, more than 2, 500 years weather records have been inputted in the daily data base. The main files of the system are PC-DA (paleo climatic data), and PC-REC (paleo climatic record). The former consists of encoded weather data which will be used chiefly to retrieve weather conditions and to draw maps or to make tables. The latter contains weather descriptions in each day with Katakana, one of the Japanese characters. This will support detailed investigation<BR>As an index of wet or dry condition for each month, "PI" is proposed. Weather conditions having some relations with precipitation are grouped to three kinds. Monthly frequencies of each type are multiplied by constants. These are 1 for "little rain", 2 for "rain" and 5 for "much rain". The total value in each month in each day is "PI", which is useful for the comparison within the same daily series. The scatter diagrams of PI in Kokura Kita Kyushu City and Precipitation at Moji for each season are shown in Fig. 4. Time series of PI in 6 cities show the existence of different march in summer precipitations over Japan (Fig. 5). The monthly conditions in summer months from 1781 to 1789 are reconstructed in Fig. 6.
著者
都司 嘉宣
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.106, no.4, pp.486-502, 1997-08-25
参考文献数
12
被引用文献数
2 3

A field survey of the damage of the Amami-Oshima-Kinkai earthquake (<I>M</I><SUB>w</SUB> 7.1) and its tsunami of October 18, 1995 was conducted for four days from the next day of the main shock. A large aftershock (<I>M</I><SUB>w</SUB> 6.8) occurred in the next day and was also accompanied with a small tsunami. We conducted interviews of the inhabitants, and measured heights of the both tsunamis. The maximum height of the tsunami of the main shock was 3.0 m at Urahara Port on the south coast of Kikai-jima. Earthquake damage mainly occurred on Kikai-jima, where stone walls were fallen down at 91 places, the water supply facility of the island was disordered, and several concrete slabs slid down at Wan Port. Several fishing boats were wrecked due to the both tsunamis at ports on Kikai-jima and Amami-Oshima. Imamura-Hatori's magnitudes of the main shock and the large aftershock are <I>m</I>=1.0 and <I>m</I>=0.0, respectively. Abe's magnitude of the tsunamis the main shock is estimated to be <I>M</I><SUB>t</SUB>=7.6 and is large for the earthquake magnitude. A gigantic earthquake (<I>M</I>8.0) with a larger tsunami occurred on June 15, 1911 in the sea region close to the present event, and its folktale is handed down by the inhabitants of Kikai-jima.
著者
漆原 和子 鹿島 愛彦 榎本 浩之 庫本 正 フランツ ディーター ミオトケ 仲程 正 比嘉 正弘
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.108, no.1, pp.45-58, 1999
参考文献数
38
被引用文献数
2 3

Observations of the solution rate of limestone tablets from 1993 to 1997 have been utilized to clarify the degree of karstification from northern to southern Japan.<BR>Limestone tablets were placed at seven observation points stretching from northern to southern Japan : Toma, Abukuma, Chichibu, Akiyoshidai, Shikoku Onogahara, Ryugado, and Minamidaito. Three groups of four limestone tablets from Slovenia, Guilin (China), Chichibu, and the fourth tablet from limestone indigenous to the obsevation point, were arranged on three levels at each observation point : 1.5m above the ground, the A3 horizon, and the B<SUB>2</SUB> horizon. Measurements were taken of the solution rates of the tablets at each observation point from 1993 to 1997. Thornthwaite's method was used for calculating water balance to ascertain the relation between solution rate and water balance factors. The solution rates of limestone tablets placed 1.5m above the ground show a high correlation coefficient between (water surplus (WS) minus water deficit (WD)). On the other hand, limestone tablets planted in the soil had a solution rate from two to three times higher than those suspended in the air. The solution rates of limestone tablets located in the A<SUB>3</SUB> and B<SUB>2</SUB> horizons exhibited the highest annual precipitation correlation coefficient. The high CO<SUB>2</SUB>values under warm, humid conditions may account for the higher solution rates of the tablets planted in the soil.<BR>The solution rate tendency curve achieved its greatest range during the five years in direct proportion to the WS-WD ratio in 1993, when a cool, humid summer prevailed throughout most of Japan. The solution rate tendency curve marked its smallest range during the five years in proportion to the WS-WD ratio at all locations for limestone tablets suspended in air in 1994, under conditions of an extremely hot and dry summer, such as occurs only once in a hundred years. In general, however, the solution rates of the limestone tablets were high when the WS-WD ratio ranged between 1, 000 to 1, 600mm. Within this range, the solution rates at each observation point decreased slightly as the WS-WD ratio decreased.
著者
菊地 正幸 山中 佳子 纐纈 一起
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.2, pp.204-216, 2001
参考文献数
12
被引用文献数
1 16

A sudden collapse of the summit of Miyake-jima occurred on July 8, 2000, together with intermittent eruptions. This collapse generated long-period seismic waves with a dominant period of about 10s. Following this event, very long-period seismic pulses (VLP pulses) with a duration of about 50s were observed a few times a day until they ceased at the largest summit eruption on August 18. We analyzed these seismic pulses using waveform data recorded at several domestic stations for broadband seismographs and strong motion seismometers on Miyake-jima. The July 8 event is well characterized by a single-force directed initially upward and later downward during 12 sec. The single-force is interpreted as an abrupt collapse of massive rock. The total mass is estimated to be about 5 × 10<SUP>10</SUP> kg with fall of about 300 m. On the other hand, VLP pulses are modeled by moment-tensors with an isotropic component. They are located about 1 km southwest from the summit and 2 to 3 km deep. All three principal values are positive. The largest one is horizontal and the smallest one is near vertical. The total volume change due to 39 VLP pulses is 2.6× 10<SUP>8</SUP>m<SUP>3</SUP>, amounting to nearly one half of the total volume of the summit collapse. Based on theresults, we propose a buried geyser model. A large reservoir of hot water was formed just after the summit collapse on July 8. The ground water poured into the reservoir, being rapidly heated by hot rock underneath, and evaporated to form a highly pressurized steam, which pushed a lower conduit piston into the magma reservoir to generate VLP pulses. Non-isotropic expansion of the VLP pulses may be ascribed to the shape of the magma reservoir.
著者
石原 舜三
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.117, no.3, pp.674-677, 2008-06-25
参考文献数
15

Worldwide, HREEs are not abundant, but LREEs are. HREEs are limited to certain weathered crust deposits in China where the original granites are rich in HREEs and surface weathering is intense. Because of environmental limitations on mining, it is necessary to discover the primary sources of REEs in alkaline igneous rock provinces. Indium can be recycled easily, and primary sources can be found in Sn-Zn-sulfides deposits of both volcanic and subvolcanic settings. Tungsten and bismuth are also limited mineral resources, but can be found in carbonate rocks with fractionated ilmenite-series granite intrusions. Molybdenum can be supplied sufficiently from porphyry-type deposits.
著者
長沼 毅
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.112, no.2, pp.226-233, 2003-04-25
参考文献数
45
被引用文献数
4 1

The search for life on the edges (frontiers) of the global biosphere bridges earth-bound biology and exobiology. This communication reviews recent microbiological studies on selected "frontiers", <I>i.e</I>., deep-sea, deep subsurface, and Antarctica. Deep-sea is characterized as the aphotic (non-photosynthetic) habitat, and the primary production is mostly due to the chemosynthetic autotrophy at the hydrothermal vents and methane-rich seeps. Formation of the chemosynthesis-dependent animal communities in the deep leads to the idea that such communities may be found in the "ocean" of the Jovian satellite, Europa. An anoxic (no-O<SUB>2</SUB>), as well as aphotic, condition is characteristic of the deep subsurface biosphere. Microorganisms in the deep subsurface biosphere exploit every available oxidant for anaerobic respiration. Sulfate, nitrate, iron (III) and CO<SUB>2</SUB> are the representative oxidants in the deep subsurface. Below the 3000 m-thick glacier on Antarctica, >70 lakes having liquid water are entombed. One of such sub-glacial lakes, Lake Vostok, has been a target of "life in extreme environments" and is about to be drill-penetrated for microbiological studies. These biospheric frontiers will provide new knowledge about the diversity and the potential of life on Earth and facilitate the capability of astrobiologial exploration.
著者
本井 達夫 鬼頭 昭雄 緑川 貴 荒川 理 笹井 義一 陳 永利
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.117, no.6, pp.1015-1028, 2008-12-25
被引用文献数
1 1 1

Climate model experiments are carried out to understand the relationship between large-scale topography and climate variation. Mountain uplift experiments show that sea surface temperature, surface wind fields, precipitation and sea surface salinity are strongly influenced by mountain uplift. An enhanced Asian monsoon due to mountain uplift causes stronger seasonal coastal upwelling in the Indian Ocean and freshening in the Bay of Bengal, Yellow Sea and East China Sea. Mountain uplift experiments using a higher resolution atmospheric general circulation model reveal that the spatial pattern of precipitation becomes finer as resolution increases, and that there is a sharper contrast in the salinity distribution near coastal regions. Experiments in which the Panamanian Gateway is closed, opened and re-closed suggest that reorganization of the ocean current due to closure of the Panamanian Gateway induces a cooler and drier climate with a permanent halocline and sea ice in the subarctic Pacific.
著者
丸山 茂徳 大森 聡一 千秋 博紀 河合 研志 WINDLEY B. F.
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.120, no.1, pp.115-223, 2011-02-25
被引用文献数
5 25

Pacific-type orogeny (PTO) has long been recognized as a contrasting accretionary alternative to continent-continent collisional orogeny. However, since the original concept was proposed, there have many new developments, which make it timely to produce a new re-evaluated model, in which we emphasize the following new aspects. First, substantial growth of Tonarite–Trondhjemite–Granite (TTG) crust, and second the reductive effect of tectonic erosion. The modern analog of a Pacific-type orogen developed through six stages of growth exemplified by specific regions; initial stage 1: the southern end of the Andes; stage 2: exhumation to the mid-crustal level at Indonesia outer arc; stage 3: the Barrovian hydration stage at Kii Peninsula, SW Japan; stage 4: the initial stage of surface exposure of the high-P/T regional metamorphic belt at Olympic Peninsula, south of Seattle, USA; stage 5: exposure of the orogenic core at the surface at the Shimanto metamorphic belt, SW Japan; and stage 6: post-orogenic processes including tectonic erosion at the Mariana and Japan trench and the Nankai trough.<br> The fundamental framework of a Pacific-type orogen is an accretionary complex, which includes limited ocean floor material, much terrigenous trench sediment, plus island arc, oceanic plateau, and intra-oceanic basaltic material from the ocean. The classic concept of a PTO stresses the importance of the addition within accreted rocks of new subduction-generated arcs and TTGs, which were added along the continental margins particularly during the Cretaceous. Besides the above additional or positive aspects of a PTO, here we emphasize the negative effects of previously little-considered tectonic erosion caused by subduction over time. The evaluation of such extensive tectonic erosion leads a prospect of the presence of huge quantities of TTG material in the lower transition zone, where many subducted slabs have ponded, as illustrated by mantle tomography. This is confirmed by density profiles of the mantle, which show that TTGs are abundant only along the bottom of the upper mantle accompanied by slab peridotite, lherzolite, and MORB. The major velocity anomaly in the lower transition zone is best explained by the predominance of SiO<sub>2</sub> phases, hence TTG, and not by MORB or ultramafic rocks. Reasonable calculations indicate that at a depth range of 520-660 km TTG material amounts to 6-7 times more than the total mass of the surface continental crust.<br> The traditional view is that the Japanese islands evolved since 520 Ma through five Pacific-type orogenies, which grew oceanward, thus creating a continuous accretionary complex <i>ca.</i> 400-500 km wide, with TTG growth at the continental side of each orogen. However, the subducting oceanic lithosphere has produced five times more TTG crust compared with the present TTG crust in the Japan islands. This is explained by the fact that over time tectonic erosion has dominated the increasing arc-TTG crust. Accordingly, Japan has lost four arc-TTG crusts to tectonic erosion. TTG material, such as trench sediment, arc crust, and continental margin crust, was fragmented by tectonic erosion and transported into the bottom of the upper mantle at depths of 520-660 km. Worldwide data suggest that tectonic erosion destroyed and fragmented most of the Pacific-type orogens.<br>(View PDF for the rest of the abstract.)
著者
山田 周二
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.110, no.1, pp.79-93, 2001-02-25
被引用文献数
1

This study classified Japanese mountains based on mountain ordering using 1 : 500000 topographic maps, and examined the relationships of relief, relative relief and perimeter fractal dimension for the classified mountains. Mountain order was defined in terms of closed contour lines on the topographic map. A set of closed, concentric contour lines defines a first-order mountain. Higher-order mountains can be defined as a set of closed contour lines that contain lower-order mountains and that have only one closed contour line for each elevation. Relief, relative relief and fractal dimension were measured for ordered mountains using personal computer, and were defined as follows : relief <I>E = H/A</I><SUP>1/2</SUP>, where <I>H</I> and <I>A</I> are the height and area of each ordered mountain, respectively; relative relief <I>R</I>= ∑ <I>h<SUB>i</SUB>/H</I>, where <I>h<SUB>i</SUB></I> is the height of the enclosed, lower-order mountains, and represents the degree of vertical roughness of the ordered mountain; fractal dimension was measured for perimeter contour line by the pixel dilation method, and represents the degree of horizontal roughness of the ordered mountain. Japanese mountains were classified into 74 third order mountains and 11 fourth order mountains. The area of a third order mountain varies from 50 to 4712 km<SUP>2</SUP>, and that of a fourth order mountain is 2498 to 15563 km<SUP>2</SUP>. A significant relationship was found among relief <I>E</I>, relative relief <I>R</I>, and fractal dimension <I>D</I> for the ordered mountains (r=0.91, n=85), and can be defined by the expression : <BR>Log<I>E</I>=-a<I>D</I>-bLog<I>R</I>-c<BR>This relationship shows that Japanese mountains have the following morphological characteristics : a high relief mountain has low vertical and horizontal roughness, and a low relief mountain has high vertical and horizontal roughness. These characteristics suggest that slope angle of Japanese mountains converges within a certain range.
著者
宮縁 育夫
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.125, no.3, pp.421-429, 2016
被引用文献数
6

The Kumamoto earthquake(Mj7.3) on April 16, 2016 triggered numerous landslides in and around Minamiaso Village, which is located at the western part of Aso caldera, southwestern Japan. The landslides were divided into two types:landslides occurring at steep caldera walls and landslides generated on the slopes of post-caldera central cones of Aso Volcano. Several landslides occurred on slopes steeper than 25°at the northwestern to western caldera walls, which comprise pre-Aso volcanic rocks (lavas and pyroclastics). The largest landslide (ca. 300m high, 130-200m wide) occurred on the western caldera wall, damaging National Route 57 and the Hohi line of the Japan Railway. Because a clear rupture surface could not be observed, unstable blocks which had been divided by cracks, were likely to collapse due to the intense earthquake on April 16. At the post-caldera central cones of Aso Volcano, earthquake-induced landslides were generated not only on steep slopes but also on slopes gentler than 10°. They occurred in unconsolidated superficial tephra deposits overlying lavas and agglutinates, and the thickness of the slides usually ranged from 4 to 8 m. The sliding masses traveled long distances (<600m), compared to small differences in elevation. The deposits were composed of tephra blocks of a few meters and there was no evidence that they were transported by water. These facts suggest that some landslides mobilized rapidly into debris avalanches, traveling a few hundred meters. The associated debris avalanche resulted in five casualties and severe damage to houses at the foot of the Takanoobane lava dome. The characteristics of the April 16, 2016 earthquake-induced landslides differ from those of rainfall-induced landslides in July 2012, June 2001, and July 1990 at Aso Volcano, and provide important imformation for preventing or mitigating future landslide disasters in the Aso caldera region.
著者
渡辺 満久 齋藤 勝
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.115, no.6, pp.727-736, 2006-12-25

The eastern margin of Echigo Plain, central Japan, is characterized by NNE-SSW trending active faults. The Anchi fault is made up of two segments : the Anchi-nishi fault and the Anchi-higashi fault. Each fault trace is approximately 2-km long. They may be short subsidiary faults on the hanging wall of the master fault in this region (the Tsukioka fault). Trench investigations across the Anchi fault reveal its rupture history as follows : 1) the Anchi-nishi fault and the Anchi-higashi fault are west-dipping reverse faults; 2) the Anchi-nishi fault shows a vertical offset of 1.3-1.9 m after ca. 30 ka; and, 3) the vertical displacement of 3.5 m is associated with two faulting events along the Anchi-higashi fault, one between ca. 30 and 60 ka and the other younger than ca. 30 ka. Geomorphic features indicate that a reverse fault branches into these two faults at a certain depth. Thus, the total vertical offset for the last ca. 30 ky is between 3.1 to 3.7 m. This value is one third of that along the master active fault. If the source fault consists of these active faults, we should evaluate the activity of the master fault taking account of the activity of the Anchi fault. It is very important to know the nature of subsidiary faults, even if they display very short traces.