Non-Catastrophic Landslides Induced by the Mw 7.6 Chi-Chi Earthquake in Central Taiwan Revealed by the PIV Analysis

Phenomena of natural disasters, such as landslide and debris flow torrents, are very common in Taiwan due to the rugged mountains and large precipitation during the typhoon season every year. After the 1999 Mw 7.6 Chi-Chi earthquake, the catastrophic landslides and debris flow torrents occur more frequently. However, the non-catastrophic Hongtsaiping landslide triggered by the Chi-Chi earthquake in Central Taiwan is less reported and documented. To understand the characteristics of the non-catastrophic Hongtsaiping landslide, several pairs of gray-scale aerial photographs of the study area are compared and analyzed. They are first precisely orthorectified in order to correct geometric distortion of the aerial photographs. These images are then analyzed by cross-correlation using the Particle Image Velocimetry (PIV) technique. And the directions, magnitude as well as the boundary of the non-catastrophic Hongtsaiping landslide are revealed.
The calculated results reveal that the maximum horizontal displacement is about 24 m, and directions of displacement lie between north and west. Specific boundary of the landslide can be confirmed, and the dimension of the Hongtsaiping landslide area is measured about 1.2 km2. In addition to the main landslide area, a minor landslide area east of the main landslide area is also detected. The small landslide moved toward the west and the magnitude of displacement is measured about 10 m.
According to the results, it is inferred that there are two different sliding blocks in the northern and southern parts of the Hongtaiping landslide area. Based on the patterns of topography within the Hongtsaiping area, the non-catastrophic Hongtsaiping landslide appears to fit the type of circular failure. However, the detailed mechanism of the Hongtsaiping landslide needs more geological survey and data to be understood.