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Volume 48, Issue 1
Displaying 1-4 of 4 articles from this issue
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Hisanori WAKAMATSU, Kunio WATANABE, Hiroyasu TAKASE, Hiroya MATSUI2007 Volume 48 Issue 1 Pages 2-14
Published: April 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSThe influence of any construction work on underground environment should be properly assessed prior to the start of the construction. The evidences used in the assessment and the process of the decision making should be properly documented to ensure the traceability. The difficulty in the assessment of underground environment is arisen from the fact that the hydro-geological information generally includes uncertainties. Evidential Support Logic (ESL) that was recently proposed as an effective tool for the environmental assessment can treat the uncertainties contained in the hydro-geological information. For the reason, ESL was adopted in this study for the evaluation of groundwater flow changes induced by the construction of two underground structures. At the first, the preliminary assessment on the impacts of underground construction to groundwater environment was performed by using ESL with focusing the potential occurrence of groundwater hazards, such as land subsidence, groundwater pollution and so forth. Information on the hydro-geological condition, the water use and the construction plan were used in the assessment. It was found that the effects of the additional survey and the modification of construction plan on the decrease of uncertainties could be well evaluated. At the second, the reliability of conceptual models for groundwater flow analysis around a large underground research laboratory was evaluated by using ESL. The uncertainty on the geometry and the hydraulic feature of a big fault existing around the laboratory was well examined. It was also found that the additional hydrogeological research could be properly planed on the basis of the evaluation. As the conclusion of this study, it can be said that ESL can be well applied to the assessment of construction on the underground environment.View full abstractDownload PDF (2982K) -
Comparisons among the Landslide Topographies in Tertiary Formation (Yuya), Crystalline Schist (Syunan) and Gneiss (Yanai) AreasHidenori TSUDA, Takashi KANO2007 Volume 48 Issue 1 Pages 15-26
Published: April 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSThis paper describes geomorphological and geological characteristics of landslide topographies in the Yuya Tertiary Formation, Shunan crystalline schist and Yanai gneiss areas, Yamaguchi Prefecture. They are classified into four geomorphological types of landslides; the simple type and complex type including subdivisions of nested type, parallel type and clustered type. The geomorphological development of landslides types is discussed from the view point of the topographic over-lapping of landslides units. The Tertiary landslides in the Yuya area are predominated in the nested and parallel types with large dimensions (more than 10 hectares). They occur as the simple type landslide controlled by the bedding plane, and develop into the nested type, then into the parallel type with complex inner structure. The landslides in the Shunan crystalline schist and Yanai gneiss areas, on the other hand, are mostly clustered type with smaller dimensions (less than ca. 3 hectares), and have somewhat slope-failure features. Landslide units in these areas are generated in detritus deposits, and gather into a clustered type along the valley.View full abstractDownload PDF (4058K) -
Takashi ITO, Hideo SAKAI, Mayumi MORIMOTO, Masanobu SHISHIKURA, Shinji ...2007 Volume 48 Issue 1 Pages 27-34
Published: April 10, 2007
Released on J-STAGE: March 25, 2010
JOURNAL FREE ACCESSA paleomagnetic method was applied to decipher the origin of a dipping layer of the Agematsu fault at Oki trench sites (Si, S2). In S1 and S2 trenches, a sedimentary layer dipping up to 40 degrees was observed on the slope of bulge. It was discussed if the origin of dipping layer was due to tectonic deformation or to primary sedimentary structure. Oriented samples were collected from the same stratigraphic horizon. Alternating field (AF) demagnetization revealed that the remanent magnetization was divided into the stable primary component and the secondary component that could be cleaned by demagnetization at low AF levels. The primary component was estimated to be of DRM origin from low Qratio and high ARM/NRM ratio. The origin of dips of the sedimentary layer is considered to be primary sedimentary structure, because the scatter of the directions of remanent magnetization after the tilt correction is larger than that before the correction. There were large differences in the mean directions and the scatters of the secondary components between S1 and S2 trenches. In S2 trench, the secondary component showed less scatter than primary component and eastward deflection. The secondary component of S1 was regarded as VRM. There is a possibility that the origin of the secondary component in the S2 trench is due to lightning-induced remanent magnetization.View full abstractDownload PDF (1471K) -
Tatsuya MORIOKA, Atsushi SAGAWA, Yuji KANAORI, Takenobu TANAKA2007 Volume 48 Issue 1 Pages 35-47
Published: April 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSWe conducted a topographical survey, an investigation of fault outcrops, a trench survey, and/or an array drilling survey at the Shinome and Tashiro areas, Ato Town, central Yamaguchi Prefecture, in order to clarify characteristics and activity of the Tokusa-Jifuku and Western Mt. Kido faults. In the Shinome area, an excellent exposure of the Western Mt. Kido fault is found on a slope excavated during a road cutting work. In this outcrop, a gravel bed is cut clearly by a fault accompanied by white fault gouge approximately ten centimeters wide. By 14C age dating of samples from slope sediments in a footwall of the fault, it is judged that the Western Mt. Kido fault moved during past 5, 400 years. In contrast, a fault with approximately 70 centimeters of a south-side-up displacement was identified by the trench excavation for the Tokusa-Jifuku fault in the Shinome area. Based on 14C age dating of samples obtained from the gravel bed with clay and sand matrix overlaying the fault, it is pointed out two possibilities of the last movement of the Tokusa-Jifuku fault: the one is no movement during the past 7, 600 years; and the other is the movement during the past 6, 300 years. In the Tashiro area, 14C age dating of a silt sample collected in gravel bed overlaying the fault by the trench excavation reveals that no movement occurred on the Tokusa-Jifuku fault during the past 5, 200 years. The array drilling indicates that the basement rock developing in the southeast side from the fault is displaced upward about 30 centimeters on a presumed fault. By the 14C age date of humus silt samples obtained from the gravel bed with clay matrix covering the fault and silty samples with gavel in a hanging wall of the fault, there are two possibilities of the last movement of the Tokusa-Jifuku fault: the one is no movement during the past 7, 000 or 5, 200 years; and the other is the movement between past 6, 700 and 5, 200 years. In conclusion, the combination of the array drilling with the trench survey suggests the Tokusa-Jifuku fault did not move at least during the past 5, 200 years.View full abstractDownload PDF (10006K)
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