|dc.description.abstract||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.