STRUCTURAL GEOLOGY IMPLICATIONS AS CRUCIAL FACTORS TO FACILITATE FORMING TYPHOON-TRIGGERED LANDSLIDES: CASE FROM HSIAOLIN VILLAGE DURING TYPHOON MORAKOT, 2009

摘要

Typhoon Morakot had invaded and caused catastrophic hazard in southern Taiwan between 8th and 11th of August 2009. Exceeding rainfall threshold in many sides in mountainous areas triggered slope failure leading to widespread damage and loss of life. In our study we focused on one particular event, which was tragic in consequences. Hsiaolin Village located at the foothills of Shiendu Shan on the third day typhoon existence was entirely buried by massive landslide. We also utilize satellite images to analysis terrain deformations immediately during the event, collecting more information by extracting high resolution digital elevation model (DEM) and field working in study area, aim to figure out the relation between geologic conditions and landslides. According to result, Two geological formations were involved in this incident- Tangenshan sandstone and Yenshuikeng shale. The boundary between those two formations propagated along the axis of the landslide. Wedge failure direction produced by bedding and fault surface system was almost parallel to the slope angle, which in some areas of the landslide could have happen even in dry conditions. Local uplift of the southern region of Hsiaolin village with assumed constant incision rate of the Chishan River seems to be quite noticeable. This assumption agrees with tilting of terraces, which we divided into three stages. After measurements of tectonic situation of this area we came to a conclusion that structure geological setting played a major role as an indirect factor creating mechanism of the Hsiaolin landslide.