Tectonic deformation of northeastern Taiwan revealed by geomorphic indices

Abstract

Abstract In northeast Taiwan, many areas are affected by various tectonic forcings. Some areas appear to have a subsidence tendency, whereas others reflect uplift activities on the surface, due to tectonic northward compressive forcing growth and decline. Owing to the presence of widespread mountain areas, limited geodetic surveys in the field have made data scarce in this area in the past decades. In addition, most upstream streams in northeastern Taiwan originate from the Backbone Range and flow immediately into the ocean. Because of the steep topography, field investigations on land have been restricted, and in situ surveys are usually limited usually by obstruction. Therefore, the long-term landscape evolution of drainage basins can record topographic changes through the river channels. The distribution of the geomorphic indices, which were calculated along the river channels, were used to analyze the activities on a regional scale. In this study, the results of the geomorphic indices were based on the calculation of published digital elevation models by utilizing the function library TopoToolBox2. The geomorphic indices, which include knickpoints and the normalized steepness index (\({K}_{sn}\)), can indicate the unequilibrium state of the river system and can be used as topographic indicators. The magnitude of knickpoints represents the degree of abrupt changes in the river longitudinal profile, and the\({K}_{sn}\) value variation can be used as quantitative index of river topography. The geomorphic indices synthetically suggest that the landscape evolution of the studied drainage basins is influenced by geological structures, tectonic activity, various lithologies and potential surface ruptures.