Kuo-Jen Chang

Active interseismic shallow deformation of the Pingting terraces (Longitudinal Valley – Eastern Taiwan) from UAV high-resolution topographic data combined with InSAR time series

ABSTRACT We focus herein on the location, characterization and the quantification of the most active structural feature of Taiwan: the Longitudinal Valley Fault that corresponds to the suture in between the Philippine and Eurasian Plates. In order to determine and monitor its present inter-seismic deformation, we focus on the Pingting Terraces area, situated in the South Longitudinal Valley (Eastern Taiwan). We first determine the structural geometry issued from both photo-interpretation deduced from new unmanned aerial vehicle (UAV) high-resolution Digital Terrain Model data that we acquired (34.78 km2 with 7.73 cm ground sampling distance), combined with geological field work. In order to characterize and quantify the present deformational patterns over the Pingting terraces, we used an InSAR time series Interferometry algorithm (MT-InSAR) applied to nine L-band SAR images from ALOS satellite acquired over the period 2007–2010. The unprecedented density of measurements (about 120 points per km2 for a total of 6,400 points) gives a continuous overview of the inter-seismic shallow deformation. The structural geometry combined with the mean velocity map (MT-InSAR) reveals two clear active faults situated above the scarps of the Pingting terraces and responsible for up to 7 and 20 mm/yr velocity offset along the radar line of sight. A temporal analysis of the deformation is performed with one measurement at each SAR acquisition date, giving major improvements in the characterization and quantification of the Longitudinal Valley active Fault trace.

Empirical Modal Decomposition of Near Field Seismic Signals of Tsaoling Landslide

Giant landslides can achieve high-speed sliding and long run out distances and estimating the kinematic is crucial for the next generation of the hazard mitigation system. Direct measurement data when landslides are in motion are valuable for the purpose. However, because of their scarce occurrences and short flow durations, such measurements are rarely recorded with instruments. In 1999, the Chi–Chi earthquake triggered a major landslide in this area, with a source volume 125×106 m3. Near the scar area, there is a strong ground motion station, CHY080, recorded the seismic signals during the earthquake and the recorded data exhibit some distinctive signatures. We analyze the polarizations of the seismic waves and use Ensemble Empirical Mode Decomposition (EEMD) with an additional clustering analysis to decompose the seismic signals. Series of peculiar wave packets associated with the landslide are identified. Based on these results, a complementary rigid sliding model is deployed to verify the sliding process. The results reveal that with the sliding distance 1,990 m, the maximum velocity reaches 78 m/s, and the mass generates a large collision impact against the riverbed and the steep slope on the other side of the river. The friction angle of the sliding surface could be as low as 6.9o. These results are agreeable with the numerical simulation of the landslide. These findings provide the evidence that the earthquake and the landslide induced ground motion coexist in the seismogram records.

The 1999 Tsao-Ling Rockslide: Source Area, Debris, and Life Cycle of Associated Rockslide-Dammed Lake (Central Taiwan)

The Tsao-Ling rock avalanche was the largest landslide triggered by the 1999 Chi–Chi earthquake in central Taiwan. In addition to detailed and extensive field observations, several Digital Elevation Models (DEMs) generated from sets of aerial photos have been utilized to document and measure the coseismic and post-seismic morphological changes at Tsao-Ling. The estimated volume of the initial rock avalanche is about 125.5 and 138 Mm3 for the depleted and accumulated zones, respectively, indicating an increase in volume due to fragmentation. The average thickness was about 150–170 m, up to 195 m of the slid mass–over 140 m on the Chingshui River channel while between 30 and 90 m debris covered on the preexisting debris deposit hill. The landslide debris blocked the river channel and formed a dammed lake, with a maximum volume of 45 Mm3. In the deposit area, strong river erosion has removed 72 Mm3 of the debris since the earthquake. By August 2004, the rockslide-dammed lake had filled up completely with sediment. The filling materials originated in numerous landslides in the upstream area.

Use of Multiple Digital Terrain Models and Aerial Orthophotos for Landscape Evolution in Tsaoling Landslide Area

Tsaoling is an important area for landslide studies in Taiwan because of its repetitive occurrences of landslides. In 1999, the Chi-Chi earthquake triggered a dip slope failure and the landslide mass deposit in the channel and opposite bank of the Chinshui River. Long-term (3 decades) as well as the rapid landscape evolution after the Chi-Chi earthquake is inspected in the present study, by using a total number of ten high-resolution digital terrain models (DTMs). These DTMs were constructed by using aerial orthophotos dated between 1979 and 2009 and they were calibrated against the 2009 DTM, with the root mean square error controlled to be less than 1 m. The focus is on the surface elevation changes of two representative cross-sections and recession of the Chunqui Cliff in the landslide scarp zone. Because the Chinshui River cuts through the loose deposit, significant incision was found and the incision undergoes a common exponential natural process. The half-life time is estimated about 3.2–4.3 years. On the other hand, cliff recession is associated with the extreme climate events and the recession rate is found to increase after 2003.