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Volume 46 (2005 - 200･･･
- Issue 6 Pages 311-
- Issue 5 Pages 250-
- Issue 4 Pages 190-
- Issue 3 Pages 115-
- Issue 2 Pages 72-
- Issue 1 Pages 2-
Volume 46, Issue 3
Displaying 1-5 of 5 articles from this issue
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Masahiro CHIGIRA2005 Volume 46 Issue 3 Pages 115-124
Published: August 10, 2005
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSThe Mid Niigata prefacture Earthquake in 2004 (M6.8) triggered thousands of landslides in the Miocene to Quaternary sedimentary rocks in Japan. The most common landslides were shallow disrupted landslides on steep slopes without geologic preference, but deep, coherent landslides also occurred in many locations. We studied about 100 deep, coherent landslides by field investigation and by interpretation of aerial photographs and found that many of them had occurred due to the reactivation of previous landslides. These had planar sliding surfaces along bedding planes or slope-parallel oxidation fronts. Planar, bedding-parallel sliding surfaces were exposed or inferred from the geometry of the deformed ground surface, such as “horsts and grabens” and “roll-over antiform”. The bedding-parallel sliding surfaces were made at the boundary between the overlying sandstone and underlying siltstone or along the bedding planes of the alternated beds of sandstone and siltstone. Sliding surfaces along the oxidation front w re made in the area of black mudstone. New landslides (rockslide-avalanches) occurred with the sliding surfaces of several-cm thick tuff interbedded in siltstone. Most of the deep landslides occurred on slopes undercut by erosion or artificial excavation, notwithstanding they are reactivated or new ones. One rockslide-avalanche occurred on a slope where buckling deformation preceded the earthquake. Gentle valley bottom sediments were mobilized in many locations, probably because they were saturated and partial liquefaction occurred by the earthquake.View full abstractDownload PDF (6447K) -
Ken TSUTSUI, Sanae MIYAZAKI, Shuichi ROKUGAWA, Hideaki NAKAGAWA2005 Volume 46 Issue 3 Pages 125-137
Published: August 10, 2005
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSThe volume of landslides generated by the Mid Niigata prefecture Earthquake in 2004 was estimated by the elevation change detection based on the high-accurate DEM extraction techniques using high-resolution satellite images. Two 5 mmesh DEM data, which showed the elevation model on the Niigata Prefecture before and after the disaster, were extracted from SPOT 5 satellite stereo pair images, and the elevation changes were analyzed by the difference of two DEM data. The landslides were detected as the high elevation change area, and the landslides volume was estimated by the totaling the elevation changes. As a result, maximum ±50m of elevation change was measured on the largestscale landslide and about 25 million m3 in total volume of landslides was estimated on the Mid Niigata prefecture.View full abstractDownload PDF (6190K) -
Toshitaka KAMAI2005 Volume 46 Issue 3 Pages 138-144
Published: August 10, 2005
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSLandslides triggered by the Chuetsu earthquake occurred in artificial slopes of some new developments in suburban Nagaoka, the largest city in the affected area. The landslides occurred in hilly terrain of the eastern part of Nagaoka between the alluvial plain and Tertiary folded mountains of Yamakoshi. Although the extent of landslides in urban Nagaoka was small compared with landslides on natural slopes (especially near Yamakoshi), they represent an important case study for urban landslide disasters. Slope instabilities in urban residential areas were classified as: A) landslides in steep embankments; B) landslides in gently sloping artificial valley fills; C) re-activation of old landslides; and D) liquefaction in deep artificial valley fills. These failures all occurred in relatively uniform suburban landscapes, which were significantly modified from the original landforms. Recent destructive earthquakes in Japan caused the similar types of slope failures in urban regions, suggesting that lessons from past earthquakes were not implemented. Governmental reconstruction assistances for urban residential areas are insufficient comparing to the generous assistance for mountainous district. The earthquake disaster should provide a momentum to consider the effective policy of distributing the limited resources.View full abstractDownload PDF (3622K) -
Hiroshi YAGI, Takanari YAMASAKI, Tsutomu IWAMORI, Kentaku ATSUMI2005 Volume 46 Issue 3 Pages 145-152
Published: August 10, 2005
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSLarge scale earthquake of Mg 6.8 (on 23rd Oct.) and a series of aftershocks more than Mg 6 in a scale occurred in Chuetsu, Niigata Pref., Central Japan, in the end of October. It severely damaged allover the hill and caused enormous landslides. This study clarified the distribution of the landslides by aerial photo interpretation. Characteristics of landslide in this study area are summarized as follows;
1) Landslides of rotational or translational slide type, wider than 1 hectare, are concentrated in a NNE-SSW belt between Imo River and Shiotani River. It just coincides with a synclinal zone named Kajikane syncline (Fig. 2). It has been filled with sand stone or alternatives of sand and mud/silt stones overlaying mudstone. Imo River incises sand dominant area in eastern wing of the syncline. Their landslide masses consist of sand layers and they slid down on a westward dip slope consisted of mudstone. They are dip slope landslides. However, they are not landslides of primary movement. Many of them reactivated due to earthquake tremor within trans-accumulation areas of previous landslides.
2) Topographic feature in the western part of this study area is Questa. Westward gentle slope and eastward steep slope alternately develop in the western wing of Higashiyama Anticline that characterizes the outline of landform in this study area. Shallow sheeted slope failures are widely distributed on eastward anti-dip slopes. Detritus from slope failure turned to high speed debris flows, capturing reservoir water on the way.View full abstractDownload PDF (5501K) -
The Relation of the Current Processes of the Flood to the LandformsYukiko HIRAMATSU, Satoshi YASUI, Atsushi URABE, Misao HONGO2005 Volume 46 Issue 3 Pages 153-161
Published: August 10, 2005
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSA huge flood disaster was caused by a heavy rainfall around the Chuetsu area of Niigata Prefecture on July 13, 2004. The flood breached the levees in many places along Ikarashi-, Kariyata-, and Chigoshimizu Rivers, so that many houses were swept away and wide areas were under muddy flood water in Sanjo and Mitsuke Cities and Nakanoshima Town.
In this study, we describe the damages sustained by the flood in Nakanoshima Town area and the southern area of Mitsuke City along Kariyata River, and discuss the current processes of the flood at these areas. It is clear that a surge of the flood attacked houses near by the point of levee breach at Nakanoshima Town, judging from the evidences such as the directions of scours and the traces of flood current toward the houses. The preferred orientations of inclined or felldown houses, traffic signs, fens, etc., indicated the direction change of flood current. Though the primary surge ran powerfully toward southwest, the flood flowed westward being led to the lower topography until the direction changed toward northwest by an obstruction of natural levee. On the other hand, in the southern area of Mitsuke City, the flood current direction was restricted so much by the narrow valley plain that its flood strength increased much more. As the levee of Chigoshimizu River also breached, the older levee, which remained between the present one and fluvial terrace, was collapsed immediately. The flood current did not only lose its power when it had reached at the lowest terrace but also run up beyond the terrace and destroyed some houses standing on it.View full abstractDownload PDF (2309K)
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