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Volume 37, Issue 1
Displaying 1-8 of 8 articles from this issue
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Tertiary Mudstone Landslide Slope in Itakura, Niigata PrefectureMasayuki IMAIZUMI1996 Volume 37 Issue 1 Pages 2-18
Published: April 10, 1996
Released on J-STAGE: March 25, 2010
JOURNAL FREE ACCESSThe underground temperature survey and radioactivity prospecting had shown that three groundwater veinstreams are caused by different origin on Ohoike landslide slope in Itakura Town, Niigata Prefecture; west groundwater vein-stream by fault, center groundwater vein-stream by fissures zone of combination of small landslides, and east groundwater vein-stream by the fissures zone and underflow of stream water. It may be inferred that the shallow ground water flow downstream through the zone of strongly weathered mudstone and the veinstreams.
The relationship between geochemistry of shallow groundwater and groundwater vein-streams, and the variation of shallow ground water geochemistry as groundwater flow downstream has been studied.
The shallow groundwater is divided into high silica concentration group: Group 1, and low silica concentration group: Group 2. The Group 1 is subdivided into two subgroups: Group in and Group 1b, on the basis of its rate of electrical conductivity and Na+ concentration increase in proportion to groundwater flow distance. The Group 1a is high rate of increase. The Group 1b is low rate of that.
The distribution areas of Group 1a, Group 1b, and Group 2 practically coincide with the area of west groundwater vein-stream, that of center groundwater vein-stream, and that of east groundwater vein-stream, individually. The different origin of vein-streams is presumably related to the diffrent variation of geochemistry of groundwater.View full abstractDownload PDF (3765K) -
Yutaka SASAKI1996 Volume 37 Issue 1 Pages 19-28
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSIn 2-D resistivity surveys, it is important to use the electrode array yielding the highest resolution and accuracy. Although a number of studies have been done to examine the characteristics of various electrode arrays, it is not well known how the electrode array affects the resolution and accuracy of 2-D inversion. In this paper, the relationship between the electrode arrays and the accuracy of 2-D resistivity surveys is analysed through numerical simulation. In addition, the performances of 2-D resistivity and CSAMT methods are compared. It is shown that if the data accuracy is about the same, the dipole-dipole array is superior to the pole-pole and pole-dipole arrays. However, if the signal level is considered, the pole-dipole array gives the best result. It is also shown that the synthesis of pole-dipole data from pole-pole data is effective in improving the accuracy of 2-D inversion if the original pole-pole data have an relative error of about 1%. Comparison of resistivity and CSAMT methods shows that CSAMT method may be superior to resistivity method in resolving vertically extending structures when the scale of exploration is relatively large. It is also expected that resistivity and CSAMT methods complement each other in defining the structures showing pseudo-anisotropy, such as fractured zones.View full abstractDownload PDF (1996K) -
Yoshihiro YOKOI, R. James, J. Robert1996 Volume 37 Issue 1 Pages 29-39
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSWe collected data on 39 landslides and analyzed the fractal character of their block distributions and block development process. Correspondence analysis revealed that the fractal dimension correlates to the geometry of the landslide, discontinuities of the base rock, and activity level of the landslide. The fractal dimension is independent of the size of the landslide, angle of slide surface and slope, and geology of the base rock.
The fractal character of landslide block distribution can be explained by self-similar geometry, the unique fractal dimension made by combining second and third level blocks, and the fractal erosional process. The preceding block's geometry influences propagation of subsequent blocks. Lineaments influence the propagation process of second level blocks. As erosion progresses, the fractal dimension decreases. The fractal character of landslide block distribution can be used to identify potential landslides and as a numerical index to describe landslides including their level of activity.View full abstractDownload PDF (2253K) -
Yoshiaki TAINOSHO1996 Volume 37 Issue 1 Pages 40-47
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSNagata district can be divided into two areas on the basis of geological conditions, particularly, Jyomon coast line which was formed by Jyomon transgression about 6000 years ago.
The first area is the northern part which is characterized by the uplift of Suma Fault which forms mountains and hilly lands. The mountains are composed of Cretaceous granitic rocks. This area has very weak earthquake disasters except for slope failure, even though active fault (Suma Fault) is located on this area. The hilly lands consist of Plio-Pleistocene Osaka Group. This earthquake had caused various damages on this hilly lands. Many wooden buildings which were located on the bankings were collapsed by the 1995 Hyogoken-Nanbu Earthquake. Serious damaged grounds were observed on the margin of the hilly lands.
The second area is alluvial formation which is located in southern part of the Jyomon coast line. This area is composed of clay rich deposits. Concentrative damaged area caused by the 1995 Hyogoken-Nanbu Earthquake is located in this area. About 70% of Wooden buildings were collapsed and elevated-railroads were destroyed by the 1995 Hyogoken-Nanbu Earthquake. The reason for this seriously damaged wooden buildings is soft ground which is mainly composed of clay. Geologic hazards associated with this great earthquake are slightly weak in sand rich alluvial formation area compared with those of the clay rich alluvial formation area.
The 1995 Hyogoken-Nanbu Earthquake had caused various damages. The damage associated with the earthquake had close relation to the geologic conditions and the ground.View full abstractDownload PDF (2904K) -
Toshio FUKUMA, Masato SANO, Muneki MITAMURA, Sigeru TODA, Hideo UDA1996 Volume 37 Issue 1 Pages 48-56
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSSeismic reflection survey and boring were performed in Hikami Drainage Basin in Hyogo Prefecture.
Surveyed area is located near Iso where the lowest watershed in the main devide of the Honshu Island is located.
Seismic profiles of the reflection survey show that unconsolidated sediments is 80 to 90 meters thick. The cored boring was drilled to depth of 100 meters on the profile line of the survey. This boring reached green rock of Tanba group at the depth of 96.6 meters (TP-5.92m).
Cored samples contain a volcanic ash layer in depths ranging from 4.10 meters to 4.30 meters. As a result of Tephra analysis, it became clear that this volcanic ash was Aira-Tn (AT) tuff having ages of 22, 000 year. Therefore Holocene sediments are less than 4.1 meters in thick in this boring point. It is considered that almost unconsolidated sediments are Pleistocene.
Sedimennts in depth from 0.6 meters to 6.5 meters contains rich silt and clays. Almost sediments under depth 6.5 meters are gravel and sand. The value of coefficient of permeability of these gravel and sand is 10-2-10-3cm/s which was obtained by the permeability test.
This stratum of gravel is aquifer which provide much ground water in this area.View full abstractDownload PDF (1975K) -
Caused by the Heavy Rain of 6 August 1993Seiji TAKAYA1996 Volume 37 Issue 1 Pages 57-63
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSOn 6 August 1993, Kagoshima City was struck by the record-high torrential rain of 90mm/hour. A number of landslides occurred along Route 10, leaving some 800 vehicles confined in an 8-kilometer distance between Iso and Hiramatsu. Also, Ryugamizu railroad station, where a train had made an emergency stop, was hit by one of debris flows and buried in earth and sand with the crashed train.
Investigations of the Ryugamizu area after the accident show that its geological formation consists of andesite, basalt, Kekura formation and welded tuff. It was also found that the collapse was triggered by Iso tuffaceous member, component of the upper Kekura formation. Most of debris flows were identified as basalt and welded tuff. In addition, it was revealed that the Hiramatsu area geologically consists of Osakibana andesite, clastic andesite and tuiTaceous sand layer. Another finding was that a large amount of collapse occured to the Osakibana andesite which is featured by its platy joints.View full abstractDownload PDF (1646K) -
Ryuji KITAGAWA1996 Volume 37 Issue 1 Pages 64-72
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSDownload PDF (2919K) -
[in Japanese]1996 Volume 37 Issue 1 Pages 73-76
Published: April 10, 1996
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSDownload PDF (700K)
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