Prediction of Sediment Yield by Shallow Landslide Based on Landslide Periodicity

本研究的目的是建立一种基于滑坡周期性的浅层滑坡产沙量预测新方法。主要研究区域为日本九州南部的石野山、Yaku-Aina岛、lichifusa山、鹿儿岛（Shirasu）和Aso-Nekodake。通过航空摄影判读和野外调查，确定了滑坡疤痕，并在研究点使用锥形金属棒测量了边坡表土厚度。根据滑坡年代学，各研究区的0级盆地中分布着许多不同年代的滑坡瘢痕，虽然大部分瘢痕是在不同的坡址上形成的，但在火山研究区，同一坡址上的新旧瘢痕重叠时间不到100年。陡坡上的表层土有一个浅层滑坡的临界厚度，超过这个厚度表层土就不能大量生长。临界厚度取决于斜坡的地质和地形环境。在其他因素相同的情况下，森林盆地滑坡发生的频率不仅与降雨有关，还与滑坡周期有关。森林盆地浅层滑坡潜力用表土厚度的概率密度函数表示。概率函数是时间相关的。如果在暴雨条件下发生多次浅层滑坡，则表层土厚度大于临界厚度的密度会降低，从而导致滑坡危险性下降。反之，如果长期不发生滑坡，则表层土厚度大于临界厚度的密度增大，滑坡危险性增大。

The purpose of this study is to develop a new method for prediction of sediment Yield by shallow landslide based on landslide periodicity. The main research areas are Mt. Shibisan, Yaku-Aina island, Mt. lichifusa-yama, Kagoshima-shi(Shirasu)and Aso-Nekodake, Southern Kyushu, Japan. Landslide scars were made out by interpretation of aerophotographs and field survey and topsoil thickness on the slopes was wmured using a cone-tipped metal stick in the research sites.1. Many landslide sears with different ages distribute at the 0-order basins in each research area according to the landslide chronological sap. Although the greater part of scars has been formed on different slope site each other, in the volcanic research areas the newer and older scars overlap on a same slope site during less than 100 years.2. The topsoil on the steep slope has a critical thickness for shallow landsliding beyond which the tpsoil can not grow up largely. The critical-thickness depends on geological and topographical setting of the slopes.3. The frequency of landslide in the forested basins depends on the landslide periodicity as well as rainfall if other factors are same.4. The shallow landslide potential in a forested basin is expressed by probability density function of the topsoil thickness. The probability function is time dependence. If many shallow landslides occur under a heavy rain, the density of topsoil thickness more than critical one is reduced and as a result of that the landslide potential falls off. On the contrary if the landslide does not occur during a long period, the density of topsoil thickness more than critical one increases and as a result of that the landslide potential rises.