地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
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121 巻 , 6 号
選択された号の論文の17件中1~17を表示しています
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論説
  • 舟木 泰智, 石山 宏二, 早稲田 周, 加藤 進, 渡辺 邦夫
    121 巻 (2012) 6 号 p. 929-945
    公開日: 2013/01/07
    ジャーナル フリー
     We conducted headspace gas analyses using cores from two 520 m boreholes to evaluate the gas permeability of Neogene sedimentary rocks in Horonobe, Hokkaido, Japan.
     Analytical data suggest that most hydrocarbon gases are microbial methane. Further analyses of these data indicated that the low concentration and heavy carbon isotope composition of methane could be explained by carbon isotopic fractionation during migration near fractures. The high residual volume of microbial methane observed in the study area suggests that the sedimentary layers have low gas permeability, and are affected less by secondary post-generation processes.
     The headspace gas analysis is an effective approach for detecting sedimentary layers having a high confinement capability.
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  • 瀬戸 寿一, 村中 亮夫, 谷端 郷, 中谷 友樹
    121 巻 (2012) 6 号 p. 946-961
    公開日: 2013/01/07
    ジャーナル フリー
     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.
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  • 林 辰弥, 谷村 好洋, 桑原 義博, 牧 武志, 藤井 理恵, 萬福 真美, 山中 寿朗, 大野 正夫, 酒井 治孝
    121 巻 (2012) 6 号 p. 962-985
    公開日: 2013/01/07
    ジャーナル フリー
     Planktonic and benthic diatom assemblages in the Paleo-Kathmandu Lake, Central Himalaya, were examined to reveal predominant factors of productivity and species diversity between 600 and 15 ka. The productivity of planktonic diatoms fluctuated synchronously with Milankovitch cycles, and increased during interglacial and interstadial periods. This is probably because of variations in nutrient loadings from the catchment area controlled by the Indian monsoon climate (especially wet and dry) changes. In contrast to planktonic diatoms, the productivity of benthic diatoms tended to increase during glacial and stadial periods. The increases in benthic diatom productivity seem to be attributable to lake-level declines and associated habitat diversification (increases in resources) on the lake bottom. On the other hand, species diversity (number of taxa and evenness) of planktonic diatoms did not respond directly to global climate changes, and was characterized by a very low average from about 600 to 300 ka, accompanied by the formation of monospecific assemblages by Cyclotella kathmanduensis and Puncticulata versiformis. Probably, the very low average species diversity is attributable to less frequent lake-level declines (ecological disturbances), which may have allowed C. kathmanduensis and P. versiformis to dominate through competition processes on glacial and interglacial time scales. Species diversity of benthic diatoms remained high from 600 to 15 ka. However, the number of taxa and evenness (two component factors of species diversity) of benthic diatoms were negatively correlated and varied with lake-level fluctuations. For example, the number of taxa increased and evenness decreased with lake-level declines. It is suggested that benthic diatoms increased the number of taxa and decreased evenness when using and competing for increased resources in shallow habitats.
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  • 内山 真悟, 松本 淳, 高橋 洋, 金森 大成
    121 巻 (2012) 6 号 p. 986-997
    公開日: 2013/01/07
    ジャーナル フリー
     We analyzed seasonal variations of lightning activity in continental tropical Africa using 10-day, monthly, and seasonal data observed by the Tropical Rainfall Measuring Mission (TRMM) satellite. The data collected were flash counts obtained with Lightning Imaging Sensor (LIS), and total rainfall, convective rainfall, and stratiform rainfall obtained with Precipitation Radar (PR) for the 10-year period 1998-2007.
     The overall flash count migrates seasonally and meridionally following the solar angle, while it is abundant throughout the year at low latitudes near the equator. Flash count maximum areas generally occur over mountainous regions and the maximum frequency is observed in the Mitumba Mountains east of the Congo Basin. The flash count is also high in the central Congo Basin regardless of season. In the central region (7.5–12.5°N, along 20–22.5°E) of the African Continent, another maximum flash count area is observed during the period May–October. The maximum zone of total rainfall from May to August occurs between these two maxima of the flash count. The peak region of the flash count from December to March does not coincide with that of total rainfall. The maximum region of the flash count occurs from the equator to 2.5°S, while that of total rainfall occurs between 7.5° and 12.5°S. The maximum region of the flash count and total rainfall in January and March is separated by about 10° of latitude.
     Along 22.5°E, in the central region of the African Continent, the flash count at 10°N is higher both at the beginning and final stages of the warm season rainfall. In contrast, the flash count is high only at the beginning of the warm season rainfall at 10°S. The beginning of warm season rainfall relative to the solar angle is 2 months earlier at 10°S.
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  • 伊津野 郡平
    121 巻 (2012) 6 号 p. 998-1009
    公開日: 2013/01/07
    ジャーナル フリー
     Hamelin Pool is well known as one of the best and most extensive localities of modern stromatolites. The distribution of stromatolites at this locality can be explained by the existence of a high-salinity environment. Salinity variations reflect sea-level fluctuations combined with changes in landform during the post-glacial period. Stromatolite formation apparently began at 1250 BP in Hamelin Pool. It has been assumed that this event was also related to salinity changes. Focusing on Fragum erugatum (Bivalvia: Cardiidae), which is known to change the height/length ratio of shells with salinity, the author attempted to reconstruct paleosalinity over a period of 4000 years at Hamelin Pool. Shells were sampled at 13 points along a 500-m transect perpendicular to the coastline on a ridge northeast of Flagpole Landing. The height/length ratio was measured and the 14C age was determined. Furthermore, the height/length ratio was converted into a salinity scale based on several previous studies showing the relationship between ratio and salinity. Results showed that salinity rose rapidly to 58‰ when stromatolites first developed at Hamelin Pool.
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  • 市川 康夫
    121 巻 (2012) 6 号 p. 1010-1029
    公開日: 2013/01/07
    ジャーナル フリー
     Less favored areas are the main focus of the common agricultural policy (CAP) of the EU. However, there is insufficient research on the economic strategies of farmers in mountainous regions of France. The objective of this study is to understand the management strategies of mountain farmers in mountainous regions of Mézenc in Massif Central of France.
     The results can be summarized as follows. First, each farmer is classified into five types: dairy farmer, beef cattle farmer, mixed bovid farmer, mixed sheep farmer, and other farmers. Their farm product market has two characteristics. One type of farm trades with large companies such as Danone or Soddial, and the other type trades with local organizations or associations in Haute-Loire. Second, value-added farm products are an important component for farmers in Mézenc when formulating their economic strategies. This region is covered by two types of geographical denomination of the Appellations d'Origine Contrôlée (AOC). Efforts to ensure value-additions to farm produce are important for farmers in Mézenc. However, some farmers with large farms, such as farms belonging to mixed bovid farmers, are dependent not on value-additions but on expansion of their livestock and farmlands.
     An important issue for these farmers when formulating their management strategies is the subsidies they receive under agricultural policies. The policies alter the agricultural structure of Mézenc and the economic strategies of mountain farmers. Farming techniques of less favored areas in France are regulated by the natural, social, and economic conditions of this mountain region.
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短報
  • 長沼 佐枝, 荒井 良雄
    121 巻 (2012) 6 号 p. 1030-1042
    公開日: 2013/01/07
    ジャーナル フリー
     Seaside-Momochi, now an affluent residential area in the waterfront district of Fukuoka City, Kyusyu, Japan, was originally designed for middle-class inhabitants. This paper examines why the government of Fukuoka City changed the original concept of the residential development plan for Seaside-Momochi to cater for higher-income households.
     At the initial stages of the planning process in 1984, the Fukuoka City government focused on the welfare of middle-class inhabitants. However, the government found it difficult to find buyers for the land due to a decrease in housing demand among the middle class, and the project was in danger of stalling. A few years later, land prices in the city rose in the context of a property boom. This suddenly increased the development potential of the Seaside-Momochi area, and several private housing companies became interested in the Seaside-Momochi development project.
     However, the companies joining the project proposed modifying the original development plan to focus more on attracting affluent buyers. Despite this being a departure from its original intentions, the Fukuoka City government decided to alter the plan in order to avoid losing the development plan.
     The government modified the original plans and land-sale strategies. This resulted in a development plan that focused not on middle-class inhabitants but on higher income households.
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  • 小元 久仁夫
    121 巻 (2012) 6 号 p. 1043-1051
    公開日: 2013/01/07
    ジャーナル フリー
     A large number of coral boulders are scattered on reef flats and along the shores of Sakishima Islands, SW of Japan. Many were considered to have been cast ashore by huge tsunamis. In this report the author analyzes the distribution and calibrates the 14C ages of coral boulders collected from Maibahbama, southeast of Miyako Island. The calibrated 14C ages indicate a random distribution; however, some coincided exactly with the 1771 Meiwa tsunami. The tsunami travelled from the epicenter northeast and struck the Higashihenna Promontory, then turned westward leaving a large numbers of coral boulders on Maibahbama. Judging from tsunami deposits overlaying the lowest marine terrace the wave height seems not to have exceeded 10m.
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  • 中村 洋介, 水野 清秀
    121 巻 (2012) 6 号 p. 1052-1062
    公開日: 2013/01/07
    ジャーナル フリー
     A new outcrop of a reverse active fault was observed at Ikeda, Munakata City, Fukuoka Prefecture. Late Quaternary fluvial terraces in this area are divided into five levels: Ikeda I terrace to Ikeda V terrace in descending order. Ikeda III Terrace, near the outcrop, is covered with a loamy soil and aqueous silt. Kikai-Tozurahara tephra (95ka) is contained at the middle of the silt. We estimate that the Ikeda III terrace was formed at approximately 100ka. The strike and dip of the fault plane are N20°W and 28°W, respectively. Terrace gravels (Ikeda III terrace gravel), Ikeda Formation (Paleogene) and Kitazaki Granodiorite (Cretaceous) in this outcrop were deformed. The displacement of terrace gravels on this thrust is about 3.2m in the vertical component. From the approximate age of the terrace and the vertical displacement of active faults, the average long-term vertical slip rates is estimated to be 0.03mm/yr. This outcrop overlaps with geologic boundary fault and there is reactivity along the scar of the geologic boundary fault between the Paleogene and Mesozoic basement rocks.
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寄書
追記
  • 磯﨑 行雄
    121 巻 (2012) 6 号 p. 1081-1089
    公開日: 2013/01/07
    ジャーナル フリー
     In response to comments by Ishiwatari and Tsujimori (2012) on the position of the geotectonic boundary between the North China and South China blocks in easternmost Asia, i.e., in Japan, some additional remarks are presented here to supplement our previous article (Omori and Isozaki, 2011). The 230 Ma ultrahigh-pressure metamorphic belt (the Dabieshan-Sulu collision suture) extends from Shaanxi province to the Shandong peninsula in mainland China, but is not recognized to the east on the Korean peninsula and in Japan. There are two contrasting interpretations of the further extension; (1) a continuity to the east through the Korean peninsula and Japan (Omori and Isozaki, 2011); and (2) a large-scale deviation south to the Ishigaki Island of the Ryukyus and a connection to the 210 Ma high-pressure Suo metamorphic belt in the northern Kyushu and Chugoku districts of SW Japan (Ishiwatari and Tsujimori, 2012). There are two essential differences between the interpretations; a) assuming the eastern margin of South China block per se extends to NE Japan (Omori and Isozaki, 2011) or up to the Shandong peninsula and no further to the east (Ishiwatari and Tsujimori, 2012); and b) assuming two parallel-running geotectonic boundaries (collision suture and oceanic-subduction zone) (Omori and Isozaki, 2011) or one boundary (collison suture changing laterally into an oceanic-subduction zone) (Ishiwatari and Tsujimori, 2012) in Triassic East Asia. Regarding the geotectonic framework around Japan, the northern Kyushu and Chugoku districts belong to the South China block according to the former, whereas they belong to the North China block together with the eastern half of East China Sea and the entire Korean peninsula according to the latter. The traditional paleo-biogeographical data of Paleozoic fauna and the recently dated detrital zircon ages of the Neoproterozoic from non-metamorphosed Silurian, Devonian, and Carboniferous fore-arc sediments prove that Paleozoic Japan was located along the active margin of South China. In addition, NE Japan with the Paleozoic fauna having a South China affinity represents the eastern extremity of the South China block as hitherto known. These potentially require a continuation of the collision suture between the two China blocks to NE Japan. These facts and discussion clearly deny the unusual assumptions of Ishiwatari and Tsujimori (2003). Instead, the following conclusions are confirmed; (1) the South China block extends to NE Japan, (2) the 230 Ma UHP-bearing collision suture between the two China blocks continues to NE Japan; and (3) Triassic East Asia had two parallel-aligned major plate boundaries, i.e., collision suture and the oceanic trench.
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  • 丸山 茂徳
    121 巻 (2012) 6 号 p. 1090-1106
    公開日: 2013/01/07
    ジャーナル フリー
     The geotectonic division of the Japanese islands has been proposed by Isozaki and Maruyama (1991) such that the eastern extension of the Dabie-Sulu 240-220 Ma collisional UHP-HP belt (DSB) passes through the Korean peninsula to Japan. The corresponding belt in Japan is the Higo-Unazuki-Hitachi-Takanuki belt (HUHTB), because the protoliths are a unique A-type (platform sediments) and the metamorphic facies series belongs to the intermediate-pressure type, in addition to 240-220 Ma of metamorphic ages.
     Ishiwatari and Tsujimori (2012) claim that Maruyama et al. (2011) did not evaluate a new proposal by Ishiwatri and Tsujimori (2003), who proposed that the DSB extends not to the HUHTB but to the Sangun belt in a complex manner because of the promontory nature of the continental margin.
     This is a Q-A report requested by Ishiwatari and Tsujimori (2012). In this paper the author first introduces a classification of orogenic belts based on protoliths and its great significance for understanding the history of complex orogenic belts, following the original article by Maruyama et al. (1996), in addition to current topics on the role of tectonic erosion. Preceding the final formation of the collisional orogen, the Pacific-type orogen must have been present structurally above the collisional orogen against the hanging wall of the continent or arc. If not, it suggests the presence of tectonic erosion. Moreover, the size of any of regional metamorphic belt, arc, and TTG belt could be an excellent indicator of the scale of tectonic erosion.
     The Triassic DSB continues not to Sangun belt, but to the HUHTB, for four reasons: first, the protolith of those belts, second; the nature of regional metamorphism along intermediate-pressure type; third, structural units above and below the HUHTB; and finally, paleogeographic reconstruction of the Triassic North and South China cratons. The tectonic juxtapositions of the four so-called Sangun BS belts —450 Ma, 340 Ma, 250-210 Ma, and 170-180 Ma— against the HUHTB in a narrow zone as klippes can best be interpreted by extensive tectonic erosion.
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