地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
95 巻 , 3 号
選択された号の論文の6件中1~6を表示しています
  • 徳山 明
    1986 年 95 巻 3 号 p. 155-166
    発行日: 1986/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    Weathering crusts of various sedimentary rocks are described and the relation between geomorphology and deterioration of rocks are discussed in part II.
    In folded zones, which are composed mainly of deformed sandstone, slate, chert and schalstein, weathering crusts are made up of two layers : upper leached zone and lower precipitate zone.
    In the upper layer, leaching is predominant and the top of crusts are truncated by aeolian surfaces. Because a sandstone mainly composed of clastic quartz and feldspar, the reaction to weathering is similar to granitic rocks. Halloysite is found as replaced products of feldspar in sandstone, and the density of weathered regolith attains often 1.2g/cm3.
    Black slates, consiting of illite, chlorite and noncrystallised silica (a kind of chert), beside clastic quartz and feldspar, are stable to chemical reaction of ground water, but they are leached and lightned. Chert is one of the most stable rock against weathering, but also leached in the top of the layer. Density of a fresh chert (2.7g/cm3) is reduced to 1.6g/cm3 in the top of the layer. In this case more than 40% of the total mass is leached out. In X-ray defraction, removed kaolinite is identified beside residual illite and chlorite.
    In the second layer, the leaching is less dominant, and density of the crust is about 2.3 g/cm3 and larger than the upper layer. In the bottom of the layer montmorillonite or a kind of mixed-layer mineral of illite/montmorillonite are deposited. Along the clay layer, often total mass of the weathering crust is slided as bed rock slide (Fig. 2).
    In NE Japan, the Neogene contains acidic to intermediate tuffs and volcanics, which are easily weathered. The weathering crust is also composed of two layers as folded zones. Because Neogene beds are nearly flat, the aquifer is flat, wide-spread and forms very wide topography of weathering. As Neogene rocks are less deformed and therefore more porous (originally 1.8-2.0g/cm3 in density) than folded rocks, reaction of weathering is more penetrated to form thicker crusts in late Neogene, under hot and humid climates. Leached and porous regolith, containing halloysite and kaolinite is predominant in the lower precipitate layer.
    During dry and cold glacial ages, aeolian surface truncates the upper leached layer of the crust, and downward caving of valley is predominant due to lowering of the sea level. After the glacial age, where the lower layer sunk once more in the ground water due to upheaval of the sea level, large bed rock sliding occurred in NE Japan. (Fig. 1 5 on opening plate of this volume).
    Flat-topped weathering crusts, deep-carved valleys and large bed rock slides are characteristic in the Quaternary and recent geomorphogeny of Japan.
  • 大竹 政和
    1986 年 95 巻 3 号 p. 167-185
    発行日: 1986/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    The essential role of interstitial fluid pressure (pore pressure) in earthquake occurrence is strongly suggested by the observational fact that seismic activity was induced by water injection into a deep well and water impounding of an artificial reservoir. Elaborate studies related to water injection revealed following important characteristics of the induced seismicity : (1) Earthquakes are triggered to occur when the interstitial fluid pressure of the basement rock exceeds some threshold level ; (2) Focal mechanisms of induced earthquakes are in good harmony with the regional stress field ; and (3) Seismic activity propagates as far as several kilometers from the injection well. Based on those observational facts, we conclude that the injected water raising the interstitial fluid pressure releases the tectonic stress naturally accumulated. The effect of pressure change on the fracture strength of rock S is formulated in terms of the effective stress hypothesis as
    S=τ0+ (σn-P0) tanφ
    where σn and P0 are normal stress and interstitial fluid pressure, and τ0 and φ are the coefficient of cohesive strength and internal friction angle, respectively. This criterion of rock fracture may also be applied to account for the reservoir induced seismicity. For the case of reservoir induced seismicity, however, the loading effect of water mass should be taken into consideration since some of the artificial reservoirs exhibit induced aseismicity.
    The effect of interstitial fluid pressure seems to be essential even for occurrence of natural earthquakes. Detailed studies on the Matsushiro earthquake swarm revealed that the earthquake swarm was brought about by the “water eruption”; high pressure water supplied at the depth beneath Matsushiro erupted to the ground surface accompanying a large number of small earthquakes which were generated by the increase of interstitial fluid pressure. Remarkable upheaval of the focal area, gushing out of large amount of water, and other associated phenomena are consistently interpreted by the water eruption model. It will be of great value for deeply understanding the nature of swarm activity to investigate whether such a mechanism is common or not to other earthquake swarms.
    The dilatancy-diffusion model of earthquake occurrence is briefly discussed from the viewpoint of the effect of interstitial fluid pressure. The model is a fascinating product of the effective stress hypothesis and results of laboratory experiments of rock fracture. It, however, is still dubious if the results obtained in the laboratory can directly be applied to the earthquake phenomenon occurring in the natural environment. We, therefore, emphasize the especial importance of advanced studies on induced earthquakes which occur under the half-natural and half-controlled circumstances.
  • 小林 貞一
    1986 年 95 巻 3 号 p. 186-198
    発行日: 1986/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    In Japan biostratigraphic studies were began with R. PUMPELLY's route survey in South Hokkaido in 1862 and A. M. EDWARDS' identification of diatoms collected therefrom in 1866. B. S. LYMAN's A general Report of the Geology of Yesso was printed in 1877. About 10 centuries before this, however, elephant bones were already used in Japan for medicine. In 1870 geology was first taught in South College of Kaisei. The geological institute, University of Tokio was founded in 1877, followed by the Geological Survey of Japan in 1882. The geology of the Japanese islands was outlined by E. NAUMANN in 1885 and the geological sequence figured out in 1890 in Die japanische Inseln by T. HARADA. Since the discovery of the recumbent fold of the Akiyoshi limestone in Province Nagato by Y. OZAWA, 1923, geological studies improved rapidly with the result that the growth of the islands by Mesozoic orogenies was schematized in 1941. Considerable advancements were made since then in various ways.
    C. GOTTSCHE was first to publish Geologische Skizze von Korea in 1886 and her orographic Sketch by KOTO 1904 was the second contribution. The geological survey of Korea was founded in 1922 and her geological sequence schematized by KAWASAKI in 1926. The complicate geological structure of the Phyeongyang coal-filed, North Korea was clarified by NAKAMURA and his students and the geology of the Ogcheon folded zone in South Korea by KOBAYASHI and his students. The Triassic Songrim and late Jurassic Daebo orogenies are responsible for the intricate deformation of these areas. In the Cretaceous period there was the Tsushima basin between South Korea and West Japan where the thick pygoclastic non-marine sediments were accumulated. Latir the peninsular outline was figured out by the repeated upheavals with the elevating axis near the Sea of Japan.
  • 中島 峰広
    1986 年 95 巻 3 号 p. 199-219
    発行日: 1986/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    This paper deals with upland field irrigation in Aichi Prefecture. In 1975, Aichi Prefecture had the highest ratio of upland fields equipped with irrigation facilities to total available upland field area. This high ratio was accomplished due to large-scale projects such as the Aichi, Nobi, and Toyokawa irrigation canal projects.
    At present, the degree to which the upland field irrigation sheme is successful and to which the upland field irrigation facilities are useful vary widely among the areas where the three canals are intended to benefit. For example, in the region served by the Aichi Canal (Aichi Canal Area = Aichi C. A.), the scheme's size has been reduced and, for the most part, the upland field irrigation facilities have been abandoned. The project scheme in the Nobi C.A. has been similarly unsuccessful, and, furthermore, upland field irrigation facilities lie idle. But, in the Toyokawa C.A., the scheme has been greatly expanded and maximum use is being made through the scheme's facilities.
    A study conducted to find the causes of such big differences in success and in usefulness clarified the following points :
    1. The reaction of farmers toward the upland field irrigation project can be understood by seeing the extent they promote the project and make use of the upland field irrigation facilities after they are completed. The main factor influencing whether or not the farmers will use the irrigation facilities is based on their previous experience with upland field irrigation using small-scale facilities, not their intentions to promote upland field irrigation themselves.
    2. In the Aichi C.A., land has not been consolidated and, to make things worse, the surface irrigation facilities were provided with scheduled watering of upland rice. Consequently, the secondary canals and the channels located in the lower stream of the trunk canals are basically non-pressured open type channels, and channels equipped with low-pressure delivery valves are used in both paddy and upland fields. The watering method's uses are, therefore, limited, and the extent to which the upland field irrigation facilities can be used is restricted because the facilities are used jointly both for paddy and for upland fields.
    In the Nobi and Toyokawa C.A.s, on the other hand, pressurized closed type pipelines, used exclusively for upland field irrigation, are extensively provided. This is especially true in the Toyokawa C.A., where a complete set, consisting of farm pond, pump station, pressure increasing tank and duster, is located in each section of the upland field iriigation system. The system can, therefore, make use of various irrigation methods, depending on whether high or medium pressure delivery valves are in operation.
    Nevertheless, upland field irrigation facilities and land consolidation alone cannot adequately explain the differences in the extent to which the upland field irrigation facilities have been used in their respective areas. In the Nobi C.A., for example, although land was consolidated and flawless upland field irrigation facilities were made available, the facilities are still lying idle.
    3. As an example of a regional agricultural management base accepting upland field irrigation in the Aichi C.A., the number of part-time farmers has increased bacause of the accelerated pace of industrialization within the area. As a result, the number of agricultural laborers has noticeably decreased. In the Nobi C.A., the widespread conversion of farmland into housing lots, the widespread abandonment of farming, and the large reduction in farming area and agricultural labor, all indicate the widespread lack of enthusiasm for running farms. As explained above, the agricultural management base in both regions-the Aichi C. A. and the Nobi C.A.-is weak and fragile. Except in a few areas, this results in upland field irrigation facilities are being abandoned and have been left unused.
  • 神戸 信和
    1986 年 95 巻 3 号 p. 220-221
    発行日: 1986/06/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 徳山 明
    1986 年 95 巻 3 号 p. Plate1-Plate2
    発行日: 1986/06/25
    公開日: 2009/11/12
    ジャーナル フリー
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