Prediction of potential landslide sites on Shirasu steep slopes applying the landslide periodicity

本研究的目的是根据日本九州南部白苏（Aira火山火山碎屑流沉积）陡坡坡面滑坡疤痕年代学、表土深度和滑坡周期特征，编制一幅预测高潜在浅层滑坡地点的实用地图。研究结果如下：1。利用全球定位系统（GPS）和光电测量仪分别对研究区进行了骨架和细部地形测量，绘制了研究区的大比例尺地形图。将浅层滑坡疤痕图、表土深度图和植被图叠加在地形图上。年龄小于60年、表土较薄的较年轻滑坡疤痕上的森林植被与年龄大于60年、表土较厚的较老滑坡疤痕上的森林植被在树种组成和植物演替上存在差异。这表明，通过对坡面植被的区分，可以间接预测高潜力浅层滑坡场地。利用大尺度航拍图像分析，可以区分较年轻滑坡疤痕上的森林植被和较老滑坡疤痕上的森林植被。根据坡面形态将研究区白苏坡面划分为6个部分。其中，坡度超过40度的最陡地段以凹或直的形式被选定为高潜在浅层滑坡场地。这部分坡陡，广泛分布在沿沟壑和河道的斜坡上。根据边坡形态划分预测的高潜势浅层滑坡位点上，大部分较年轻和较老的浅层滑坡都留下了疤痕。

The purpose of this study is to prepare a practical map for predicting high potential shallow landslide sites on Shirasu (pyroclastic flow deposits from Aira volcano) steep slopes based on the landslide scar chronology and topsoil depth on the slopes and the landslide periodicity in the southern part of Kyushu, Japan. The results are as follows :1. A large scale topographic map of the study area was made based on skeleton and detail topographical surveying using the global positioning system (GPS) and electro-optical survey instrument, respectively. Each map of the shallow landslide scars, topsoil depth and vegetation was superimposed on the topographic map.2. The forest vegetation on younger landslide scar of less than 60 years in age with thinner topsoil and older landslide scar of more than 60 years in age with thicker topsoil differ from each other in tree species composition and plant succession. This suggests that the high potential shallow landslide sites can be indirectly predicted through distinction of the vegetation grown on the slopes.3. It is possible to distinguish between the forest vegetation on the younger landslide scar and the one on the older scar based on the image analysis using large-scale aerial photographs.4. The Shirasu slopes in the study area were divided into six parts based on the slope morphology. Of these parts, a part consisting of steepest slopes of over 40 degrees in gradient with a form of concave or straight was selected as the high potential shallow landslide site. This part with steep slopes are widely distributed on the slopes along ravines and river channels. A most parts of the younger and older shallow landslide have been scarred on the high potential shallow landslide sites predicted based on the division of slope morphology.