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

神户城区根据地质条件可分为丘陵地段和冲积层地段。丘陵地带由上更新世大阪群组成。仙谷地震对这片丘陵地带造成了不同程度的破坏。许多位于河岸上的木制建筑在这次地震中倒塌了。人工改变地貌，地面破坏严重。造成这一严重破坏的原因是垃圾填埋场，主要由软弱地基和高地下水位组成。垃圾填埋场上部有较多的拉裂，下部侧缘路面膨胀明显。震害与地质背景和地下水位密切相关，六甲山曾多次因地震而发生边坡崩塌。过陡峭的山坡似乎集中在六歌山脉的东部。这些过陡坡分布的原因被认为是罗科山东部与罗科山另一部分相比风化严重所致。神户市区大约有39个危险的过陡坡。其中，神户地区重风化花岗岩中有许多陡坡存在裂隙。地震发生后，由于陡坡上部沿裂隙断裂，在暴雨过程中发生了沿张性裂隙的坡体破坏和坡体移动。这些边坡的破坏受地形和地质特征控制。

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.