Changes of sediment disaster and topography following the ChiChi Taiwan Earthquake on September 21,1999

1999年9月21日台湾集集大地震造成多人死亡，财产损失惨重。此外，它还在山区引发了许多滑坡和泥石流。由此产生的泥沙运动在每一次暴雨中都会造成泥沙灾害。本研究在实地考察的基础上，探讨震后泥沙灾害与地形之变化。主要研究结果如下：1.定量阐明了台湾中部研究区域(10.76平方公里~2)地震后坡面和河道地形的变化。通过航空摄影解译，已识别出131多个斜坡破坏伤疤。滑坡面积1.35平方公里，占研究区面积的12.5%。每下一场大雨，山坡崩塌的泥沙就会流到下游。泥沙外流在造成泥沙灾害的同时，也改变了河流地貌。2.虽然震前研究区每年发生一次泥石流，但震后2000年泥石流发生了20次以上。在研究区的河流沿线观察到了更古老和更新的泥石流梯田。台湾过去曾多次发生强烈地震，地震引起的泥沙运动被认为是山河地形变化的主要原因。3.探讨了滑坡的机制、降雨扩大滑坡伤痕、以及一些滑坡(九峰二山、枣岭、火焰山)的对策。4.对2002-2004年受地震影响地区的台风泥沙灾害进行了调查。分析了地震前后降雨条件与滑坡破坏的关系。5.对日本和台湾泥沙灾害的应对措施和预警疏散系统进行了比较。

The Chi-Chi Taiwan Earthquake on September 21,1999 killed many people and involved great property loss. Also, it triggered many slope failures and debris flows in the mountainous regions. The resulting sediment movement caused sediment disasters at every heavy rain. This study aimed to examine the changes of sediment disaster and topography following the earthquake based on the field investigations. The results are summarized as follows :1.Changes of topography of slopes and river channels following the earthquake ware clarified quantitatively in the study area (10.76km^2) in central Taiwan. More than 131 slope-failure scars have been identified through aerial photographic interpretation. The slope-failure area is 1.35km^2, representing 12.5% of the study area. The sediment from slope failures flows out to the lower reaches of the river at every heavy rain. The outflow of the sediment changes the river topography at the same time as it causes sediment disasters.2.Although debris flows had occurred about once per year in the study area before the earthquake, they occurred 20 times or more in 2000 after the earthquake. Older and more recent debris-flow terraces are observed along the river in the study area. In Taiwan, severe earthquakes have occurred repeatedly in the past, and sediment movement resulting from earthquakes is considered to be the main cause of change in mountain and river topography.3.The mechanisms of slope failures, expansion of slope-failure scars by rainfall, and the countermeasure were examined for some slope failures (Jiu-Feng-Er-Shan, Tzao-Ling, Huo-Yan-Shan).4.The sediment disasters by typhoons of the period in 2002 to 2004 were investigated in the areas influenced by the earthquake. The relationships between slope failure and rainfall conditions were analyzed before and behind the earthquake.5.The countermeasures and warning evacuation systems for the sediment disaster were compared between Japan and Taiwan.