莫拉克颱風於 2009年8月8日侵台，短時間的強大降雨在全島造成許多重大災害，其中位於獻度山下的小林村在颱風登台的第三天遭大規模的山崩完全掩埋，災後我們在高屏溪上游的旗山溪與荖濃溪流域的崩塌區及周圍山區進行了詳細的地質調查，藉以探討地質構造在颱風誘發山崩中所扮演的角色。研究結果顯示，小林村後山之地層層面與節理暨小斷層共同構成一組向下坡傾斜之不利岩楔，此類岩楔在崩前已呈虛懸狀態，即使在乾燥狀態下也非常不穩定。除了小林村地區，高屏溪流域其他地區的所有地質證據也都支持：地質構造是促進山崩發生的重要因子。地層層面、斷層及地形等基本條件，應廣泛調查作為預測山崩發生可能性的重要參考依據。此外，根據斷層擦痕測量資料計算，研究區域整體受到的主壓應力大致為西北－東南向，這個方向的壓應力也暗示此地區應普遍存在一組東西走向及西北－東南走向的共軛破裂，沿著破裂方向如有地形或地層條件配合，則極易產生山崩，此點是未來防災或地質評估中值得特別注意的條件。Typhoon Morakot invading Taiwan on August 8th, 2009 caused numerous major disasters throughout the island. Hsiaolin village located at the foothills of Shiendu Shan on the third day typhoon existence was entirely buried by massive landslide. A detail field investigation focused on structural measurement, around whole the Hsiaolin landslide as well as its surrounding area and the drainage area of the Kaoping River, has been carried out in this study. In order to realize the landslide mechanism of regional settings, we focused on the affect of geological structures and stress analysis around the study area. Wedge failure had been observed at numerous outcrops, which produced by bedding and fault systems’ inter-cutting at the dip-slope area of the mountains. Therefore, in some areas landslide could have happen even in dry season with relative stable condition. After a detailed investigation from Hsiaolin and all other landslides of the Kaoping drainage basin, we came to a conclusion that structure geological setting played a major role as a direct factor for creating the regional landslide. By considering the geometric correlation between geological structure, strata attitude and topography, an objective hazard map can be provided. Besides, based on the slickenside data measured from the fault planes of fresh outcrops, a NW-SE compressional tectonic regime can be reconstructed. Associated with this compression, a conjugated fault system, which is composed of a E-W striking right-lateral fault and a NW-SE striking left-lateral fault, is also expectable in all this area. This fault system caused the slope failure and easy to lead big landslide. The results derived from the structural analysis can also be applied for improving advanced estimations of other related studies.
