致震斷層錯動所造成近地表面劇烈變形是造成嚴重地震災害的主因之一，且因地震的週期性發生其地表破裂跡沿線會重覆地遭受地變災害的威脅，因此精準地判定斷層地表跡的位置及得宜地規避建設，將有助於減緩未來的地震災情。致震逆斷層錯動後常形成連續性的地形崖，此地形崖位置及形貌等可能會隨時間而大有變化，集集地震發生至今已17年，其破裂跡沿線的斷層引致地形崖，將為檢核現行利用地形崖判定活動斷層地表跡位置之精確性的最佳例子。本研究利用野外調查及無人飛行載具攝影等方法，詳細追蹤、紀錄集集地震時引致的地形崖現今的延伸性及樣貌，再利用一米網格空載光達資料，比較集集地震引致地形崖與其破裂跡沿線附近地形崖之特徵。 依據集集地震引致地形崖的地理位置，將其分成河道、非河道兩大類，非河道類又細分成房屋建造區、平地農田、平坦野地類及既存坡地四類。調查結果顯示：河道中的地形崖明顯後退亦或被夷平；房屋建造區的地形崖修整較平緩或被剷除，地形崖腳變得斷斷續續；平地農田的地形崖被抹平或被築成圍牆；平坦野地類的地形崖坡度變緩，但其位置及高度差，則無可察覺的變化；既存坡地的例子，則甚難判別出集集地震引致的地形崖。 本研究認為至今17年的集集地震引致地形崖變化，主要來自於人為活動的因素，其中僅河道類，河水侵蝕因素也同等重要。因此歸結，人為活動不頻繁的地區地形崖不失為活動斷層地表跡判定的依據。然而必須留意部分地區集集地震破裂跡附近無法證實與活動斷層活動有關的地形線形，有比集集地震引致的地形崖線形明顯的現象。 ;The intense ground distortion induced by earthquake faulting is one of the major causes of earthquake disaster. Such ground distortion periodically occurs along active fault traces. Construction avoidance from such fault traces will mitigate the effects of earthquakes. Hence, a precise map of active fault traces becomes critical. Commonly, earthquake-induced reverse faulting results in typical escarpment within its resultant deformation zone. However, the position and the morphology of such escarpment can evolve with time at different rates. The 1999 Chi-Chi earthquake-induced escarpment can serve as a rare and good example for geologists to examine a presumption that the toe of escarpment is equivalent to active fault trace appearing at an area covered by unconsolidated sediments or vegetation. In this study, we document the change of position and morphology of escarpment induced during the Chi-Chi earthquake in detail by field investigation and UAV photography. In addition, we compare Chi-Chi earthquake-induced escarpment with its adjacent pre-existing escarpment by using 1m resolution LiDAR data. The escarpments induced during the Chi-Chi earthquake can be divided into two main categories, i.e. riverbed type and non-riverbed type. The escarpments formed in the river either have retreated upstream or been wiped out. The non-riverbed escarpments can be further classified into 4 kinds, which formed in residential areas, farmlands, wild lands, and pre-existing slopes, respectively. The escarpments at the residential areas have been either smoothed or completely wiped out. The escarpments in the farmlands have been either flattened or turned into a retaining wall. The escarpments in the wild lands have relatively gentle change in their profile shape and no observable change on their positions and height. The escarpment on a pre-existing slope no longer can be recognized. This study suggests that human activity is the main cause of the change on the Chi-Chi earthquake-induced escarpments in terms of profile shape and position except that erosion may also play an important role for the escarpments formed on the riverbeds. In summary, the toe of escarpment may serve as a good counterpart of fault trace at an area with low human activity. Furthermore, be aware that some escarpments with unknown cause at a few places are more distinct than the adjacent the Chi-Chi earthquake-induced escarpments.
