應用地理資訊系統於九九峰九二一地震崩塌分析

Geographic Information System Analyses for Landslide from the 921 Earthquake at Mt. Jiujiufong

本研究主要蒐集九九峰地區相關圖層資料，使用地理資訊系統（geographic information system）及影像處理軟體進行處理與分析，以瞭解該區九二一地震崩塌特性。本研究區以埔里事業區第8至20林班為研究分析範圍，海拔高度位於300m至500m間之面積將近占61.57%，坡度為五級坡以上面積約占68.34%，顯見該區多為陡峭尖銳之山峰與深溝。該區土壤類型大多為棕色森林土，少部分位於溪谷旁區域為石質土，土層淺薄，甚易崩塌。研究區九二一大地震前之土地利用類型大部分區域仍為天然植被，人為開墾區域多位於鄰近村落或溪谷較平緩之處，其中以天然闊葉混淆林面積最大，將近占58.65%。九九峰研究區崩塌大多位於海拔高度400m以上或坡度六級坡以上陡峭之山峰。自然保留區內海拔高度大多超過400m，坡度為六級坡以上面積占70.10%，顯示保留區內地勢較區外高且陡峭，甚易崩塌，保留區內崩塌面積為729.36 ha，占保留區面積之60.86%，而占研究區總崩塌面積之71.11%，為九二一地震主要崩塌區域。研究區與保留區崩塌地之平均海拔高度，較非崩塌地分別高出114.52m與84.79m；在平均坡度上，研究區與保留區之崩塌地較非崩塌地分別多出38.13%與27.93%，顯示海拔高度及坡度皆與地震造成之崩塌有密切相關。 Landslides occurred at Mt. Jiujiufong in the 921 earthquake of Taiwan was analyzed with map data,using the geographic information system (GIS) and the image processing software. The study areacovered the 8-20th forest compartments in the Puli Working Circle, where 61.57% had elevations of300m to 500m and 68.34% had the 5th class slopes. The land was covered mainly with thin brown forestsoils and natural forests, of which natural hardwood mixed forests occupied 58.65% of the area prior to the earthquake. The landslide areas occupied 33.63% of the total study area, and were located atelevations mostly above 400m with the 6th class slopes or higher, where the Jiujiufong Nature Reservewas located. A total area of landslides in the nature reserve was 729.36 ha, occupying 60.86% of thereserve area and 71.11% of the total landslide areas in the study area. As compared to the non-landslideareas, the mean elevation of the landslide areas was 114.52m higher for the study area and 84.79m higherfor the reserve area, while the mean slope was 38.13% higher for the study area and 27.93% higher forthe reserve area. The above results indicated that elevation and slope were two major factors associatedwith the occurrence of landslides at Mt. Jiujiufong in the 921 earthquake.