Neotectonic characteristics along the eastern flank of the Central Range in the active Taiwan orogen inferred from fluvial channel morphology

The tectonic activity of the Taiwan orogenic belt has been studied by different methods over various timescales. Constraints on tectonic characteristics over timescales of 10³-10⁵ years, however, are rather limited. To further understand the tectonic forcing over this timescale, we analyzed 20 major river basins along the eastern flank of the Central Range, the mountainous core of the orogen. The results of river steepness index (k_sn) values and the distribution patterns of knickpoints are consistent with the patterns of tectonic evolution in Taiwan. On both ends of the orogen, the rivers have low k_sn values that indicate low uplift rates throughout the area. In the central part of the island where the orogen is under rapid collisional processes, the rivers are steeper and are characterized by many tectonic knickpoints. Our results show different patterns from both short-term and long-term uplift and denudation rate patterns. This suggests that these rates change temporally and spatially. Moreover, the steepness indexes of rivers in the Taiwan orogen show the same increasing trend with erosion rates as those in other active orogens but correspond to significantly higher erosion rates. This is likely produced by the frequent debris flow and landslide events in Taiwan, a character that makes the island distinctive from other active orogens in the world.