Active deformation front delineated by drainage pattern analysis and vertical movement rates, southwestern Coastal Plain of Taiwan

Orogenesis in Taiwan results from an arc-continent collision between the Eurasian plate and the Philippine Sea plate. The southwestern part of Taiwan absorbs active shortening as evidenced by rapid crustal deformation and frequent earthquakes. Southwestern Taiwan may be subdivided into three tectonic–geomorphic domains, including the plain (PL), the tilted tableland (TT), and the low hills (LH), based on geomorphology, drainage pattern and stratigraphic records. The PL domain is the westernmost and is characterized by meandering rivers with relatively low surface slope and river gradient, but high river sinuosity. The TT domain has slightly tilted terraces with river meanders and many tributaries are developed on its surface. Anomalous river sinuosity occurs as a result of active tectonics. The LH domain has higher elevation and deformed geomorphic surfaces associated with a dissected landscape. This domain also has high stream gradients with low sinuosity which may indicate active deformation. We define crustal deformation, using Holocene deposits and radiocarbon dating in addition to geomorphic analysis that suggests a blind thrust may exist between the PL and TT domains. This blind thrust may indicate the position of the active deformation front of the orogenic belt of southwest Taiwan.