Monitoring for mountain slope failures and earthquake damage caused by the Hyogoken-Nanbu Earthquake on artificial of topography and the further failures by subsequent rainfalls

神户市区按地质条件可分为丘陵地带和冲积地层两个区域。丘陵手由上新世-更新世大阪群组成。小古间-南部地震对这片丘陵地带造成了各种破坏。许多坐落在河岸上的木制建筑在这次地震中倒塌了。人为改变地形对地面造成了严重破坏。造成木质建筑严重损坏的原因是垃圾填埋场，其主要构成是软土地基和高地下水位。堆填区上部存在较多张拉裂缝，下部侧缘道路膨胀明显。地震造成的破坏与地质背景和地下水位密切相关。六甲山因地震造成多处边坡破坏。过于陡峭的斜坡集中在六甲山脉的东部。造成这些过陡坡分布的原因，可以认为是由于东段的风化作用较东段严重。神户市区有大约39个危险的过陡斜坡。其中，在神户地区，许多陡峭的山坡上，风化的花岗岩都有开放的裂缝。地震后的坡面破坏和坡面运动主要是在强降雨条件下沿张性断裂带发生的，这是由于陡坡的上部沿断裂带发生了断裂。这些边坡破坏受地形和地质特征的控制。

Kobe city area can be divided into two areas on the basis of geological conditions, hilly lands and alluvial formation area. The hilly hands consists of Plio-Pleistocene Osaka Group. The Hyogoken-Nanbu Earthquake had caused various damages on this hilly lands. Many wooden buildings which were located on the banking were collapsed by this Earthquake. Serious damaged grounds were observed on artificial alteration of topography. The reason for this seriously damaged wooden buildings is landfill which mainly composed of soft ground and high groundwater level. In the upper part of landfill many tension cracks were observed, and in the lower part the swell of road was significant at lateral margins. The damage associated with the Earthquake had close relation to the geological background and groundwater level.Rokko Mountains had many slope failure caused by the Earthquake. The over-steep slopes appear to concentrated eastern part of Rokko Mountains. The reason for these over-steep slope distribution is thought to be heavy weathering in eastern part of Rokko Mountains compared with that of another part of Rokko Mountains. There are about 39 dangerous over-steep slopes at Kobe city area. Among them, many steep slopes have open cracks in heavy weathered granite in Kobe area. The slope failures and slope movements have taken place after the Earthquake along the tension fractures during heavy rainfalls, because the upper part of the steep slopes have broken along fracture. These slope failures are controlled by topographic and geological characteristics.