| dc.description.abstract | 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. | en_US |