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Volume 50 (2009 - 201･･･
- Issue 6 Pages 319-
- Issue 5 Pages 262-
- Issue 4 Pages 202-
- Issue 3 Pages 126-
- Issue 2 Pages 70-
- Issue 1 Pages 2-
Volume 50, Issue 4
Displaying 1-4 of 4 articles from this issue
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Original Article
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Atsushi FUJIYAMA, Yuji KANAORI2009 Volume 50 Issue 4 Pages 202-215
Published: 2009
Released on J-STAGE: March 31, 2013
JOURNAL FREE ACCESSBased on geomorphologic and geologic investigations, small-scale fluvial terraces along Rivers Yugawa and Shiwarigawa in Ikachi Basin, southeastern Yamaguchi Prefecture, southwestern Japan are identified. Such terraces are classified into six surfaces defined as Ikachi I to VI surfaces in an order of the altitude and the relative height above the present river bed. Distribution and inclination of the terraces, and differences in terrace deposits overlaying their bedrock of Ikachi II and III surfaces, which are developed in an approximately 5km reach along the upstream to midstream of River Yugawa, suggest that the direction of a paleocurrent was in the opposite to that of the present stream before the formation of Ikachi II surface. By an aerial photo-interpretation and field survey, the geomorphic features showing a fault displacement was identified, and a fault outcrop which cutting terrace deposits was discovered in Ikachi Basin, and the existence of the NE-SW-trending active fault (Hizumi Fault: a new designation) was clarified. Change in the paleocurrent might be controlled by the river capture which was caused by the riverbed lowering with an incision of River Yugawa. It was suggested that the river capture resulted mainly from regional tectonics which caused the bedrock uplift and the active fault movement.View full abstractDownload PDF (6779K) -
—Based on Temporal Changes of Electric Resistivity Distribution and Surface Soil Moisture—Tetsuya FUKUDA, Shuichiro YOKOTA, Akira IWAMATSU, Takuya WADA2009 Volume 50 Issue 4 Pages 216-227
Published: 2009
Released on J-STAGE: March 31, 2013
JOURNAL FREE ACCESSInfiltration of rainwater into slope surface is one of the fundamental factors for the occurrence of slope failures in monsoon regions. In addition to this, seepage water from the steep slope may also be an important factor because such seepage water changes depending on the infiltrated water from the upper horizontal surface, and sometimes it rapidly increases with rainfall. To understand these processes, the authors analyzed some fundamental data including continuous electric resistivity measurements, soil water, temperature and conductivity of seepage water from the slopes. A target slope is underlain by the Quaternary ignimbrites characterized by soft and permeable properties in southern Kyushu, Japan.
Apparent resistivity changes depending of rainfall with surface soil moisture. Based on the resistivity data measured during about one year, temporal changes of contents of water of the slope materials become rapidly and largely in the surface portion, whereas slow and small in the inner portion. These changes have a high correlation with the Antecedent Precipitation Index which was calculated from the daily rainfall and proper reducing coefficients. Then, applying these coefficients to the daily rainfall data for the day when many slope failures occurred, it may be possible to obtain a pattern of rainfall which bring about the occurrence of slope failures. If a proper unstable model and the influence of water contents to the safety factor Fs are obtained, it may be possible to predict the occurrence of slope failures on the basis of daily rainfall.View full abstractDownload PDF (6893K) -
Ryo TAKAHASHI, Junko HARA, Takeshi KOMAI, Masahiro YAHATA, Yuuji ENDOU2009 Volume 50 Issue 4 Pages 228-237
Published: 2009
Released on J-STAGE: March 31, 2013
JOURNAL FREE ACCESSClarifying the leaching behavior of arsenic and heavy metals from hydrothermal altered rocks at mine areas is important to deduce the water quality of mine drainage. Using drill core samples, we discussed geological features of hydrothermal altered rocks which considerably leach toxic elements, especially arsenic, at the Horobetsu sulfur mine area, southwestern Hokkaido. Two Pleistocene andesite lava layers and a volcanic breccia layer have undergone sulfuric acid hydrothermal alteration. The lower part of the volcanic breccia layer particularly shows strongly altered features, consisting of the sulfide zone, acid leached silicified zone and argillic zone. The arsenic concentration in the leachate is different according to alteration mineral assemblages, thus the mineral assemblages would be an important clue to estimate the degree of arsenic leaching. Compared with other alteration zones, the sulfide zone is rich in arsenic content (∼965ppm) and leaches it remarkably (∼113mg/l). Moreover, large amounts of pyrite are contained in the sulfide zone, and a high concentration of arsenic was recognized in the pyrite. These indicate that arsenic was supplied by hydrothermal activities and was added with pyrite precipitation. Silicified veins are sometimes observed in the sulfide zone and contain Fe-sulphate mineral (rhomboclase) which was formed by the hydrolysis of pyrite. Since rhomboclase generates ferric ion by dissolution, it would promote pyrite oxidation accompanied with the release of arsenic.View full abstractDownload PDF (2901K)
Report
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Hironori FUNAKI, Eiichi ISHII, Testuya TOKIWA2009 Volume 50 Issue 4 Pages 238-247
Published: 2009
Released on J-STAGE: March 31, 2013
JOURNAL FREE ACCESSEvaluation of the role of fractures as major water-conducting features in sedimentary rocks is indispensable for modelling and analyses of groundwater flow. We conducted core logging, acoustic televiewer logging and fluid electric conductivity logging in a borehole in Neogene sedimentary rocks, i.e., in the Koetoi and Wakkanai Formations in the Horonobe area Hokkaido, Japan, to evaluate the role of fractures as major water-conducting features. Few of the fractures in the Koetoi Formation are associated with water inflow points into the borehole, in contrast to the number of flowing fractures in the Wakkanai Formation. The relationship of fracture distributions and apertures to inflow points suggests that: 1) fracture interconnections in the Koetoi Formation are poor, while those in the Wakkanai Formation are expected to be more developed, at least more than in the Koetoi Formation, 2) fracture apertures in the Wakkanai Formation tend to be larger than those in the Koetoi Formation. These suggest that the Koetoi Formation would behave as a porous medium whereas the Wakkanai Formation would be behave hydrogeologically as a heterogeneous, fractured medium.View full abstractDownload PDF (4287K)
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