| 摘要: | 摘要 前人對於山崩特性之統計分析往往針對較大區域進行。由於臺灣處於褶皺造山帶上，地質狀況複雜，地形、岩性、氣候可能存在著區域性的差異，故在不同區域影響山崩之因子及其影響程度可能有所不同，所表現出來的山崩特性亦可能不同。本研究希望瞭解山崩特性是否具有區域內的均質性及區域間的變化性。若然，則未來在進行山崩潛感分析時可以考慮分區為之，以期能夠有效地評估及預測各分區之山崩危害度。 本研究首先透過主成份分析檢討劃分地形與地質均質區所需的因子，目的在於尋找可解釋較大變異量之因子，供進一步分類之用。接著，在ERDAS IMAGINE系統中將各因子圖層資料疊合，透過ISODATA分類法進行地形均質區之劃分，再以山崩特性將地形均質區予以歸類，得到本研究所謂之山崩因子特性均質區。 本研究由原21個因子經主成份分析篩選出山頂標高、全坡高、地形粗糙度、比高、坡度、總曲率及坡度粗糙度等7個因子，並利用ISODATA分類法進行均質區劃分。分區結果顯示已可反應地質及地形之特性。本研究之山崩因子特性均質區，共分為四區。第一區主要分布於車籠埔斷層以西的台中盆地區及新社河階。第二區位於車籠埔斷層以東至雙冬斷層以西之間，為地勢低緩之丘陵區。第三區主要分布於頭嵙山層火炎山相地區。第四區分布於雙冬斷層以東之山地。由各區之統計特性顯示，第二區之山崩多分布於河谷附近，第三區之山崩多發生於坡頂附近，第四區之山崩亦多發生於坡頂附近，但第四區之山崩高度較高，而第三區之山崩坡度則較陡。 研究結果顯示各均質區間具區域差異，且各均質區間山崩特性亦不同。同時各均質區內能區分山崩與非山崩特性之因子並不一致，顯示各均質區山崩因子重要性有不同。建議未來山崩潛感分析應分區考慮。 Abstract Statistical analyses on landslide susceptibility factors were usually performed over a broad region in the past. Taiwan is located at the folded mountain belt. Due to the complexity of the geological condition, regional differences may exist in geomorphologic characteristics, lithology, and climate. Therefore, factors affecting landslides and their extent of influence may be different among regions, and the characteristics of the landslides may also be different. This research attempts to test the hypothesis of the existence of homogeneity on landslide characteristics for a single region, as well as difference among regions. If our hypothesis is tested to be true, we suggest that zoning should be performed prior to the landslide susceptibility analysis in order to obtain better landslide hazard prediction in a region. Geomorphologic-geologic factors that explain more variances were evaluated and selected using principle component analysis (PCA). These factor layers were stacked and classified using ISODATA algorithm in ERDAS IMAGINE software to obtain the geomorphologic-geologic homogeneous sub-zones. These sub-zones were merged into the so-called homogeneous areas of landslide characteristic according to the similarities in the statistics of landslides. Seven from twenty one factors were selected by using PCA, they are elevation of crest, total slope height, standard deviation of elevation, relative height to riverbed, slope angle, total curvature, and standard deviation of slope angle. ISODATA classification was then used to obtain fifty homogenous sub-zones. Results show that these sub-zones can reflect the difference in geologic and geomorphologic characteristics. We further merged the fifty sub-zones into four homogenous areas for reflecting homogeneity in landslides characteristics. The first area is mainly located in the Taichung basin and the Hsinshe terraces. The second area is located in hilly region between the Chelungpu fault and the Shuantung fault, and mainly composed of Plio-Pleistocene sedimentary strata. Most of the third area falls on the Houyeushan member of the Tokoshan Formation. And most of the fourth area is located in mountainous area east of the Shuantung fault, and mainly composed of Oligo-Miocene sedimentary strata. Statistics shows that landslides in the second area tended to concentrate near the bottom of river valley, and landslides in the third and fourth area often close to the ridge crest. Meanwhile, elevation of the landslides in the fourth area is higher then other areas, and slope angle of landslides in the third area is usually steeper. The results of this study show that regional variation in geomorphologic-geologic factors does exist among different homogenous areas, and characteristics of landslide in different homogenous area are also different. Meanwhile, factors that can distinguish landslide and non-landslide are different in each homogenous area, and the importance of landslide susceptibility factors is also different. We recommend that the concept of homogeneous area may be adopted in a future landslide susceptibility analysis. |
