9:50 AM - 10:05 AM
[HCG25-04] Developmental process of landform in drainage basin dominated by fault movement: case study of Yasuda River, Eastern Kochi, Japan
Keywords:watershed topography, divide, fault
Events such as divide migration and river capture are considered to have a significant impact on the development of watershed topography. In addition, it has been pointed out that landforms change in response to external factors such as uplift rates and climate change, and that divide migration and river capture occur during this process. In this study, we examine the topographic processes in the western part of the Muroto Peninsula in Shikoku Island, Japan, where marine terraces formed by seismic crustal movements are widely distributed, and where many geological and geodetic studies of uplift rates have been conducted. The Yasuda Fault, which is an active fault located, and the Yasuda and Namura Rivers, which are located in the vicinity of the Yasuda Fault, were selected as the area for analysis. The Yasuda Fault is a westward-trending reverse fault with the Namura River on the west side and the Yasuda River on the east side of the fault. The shape of the Namura River basin is narrow and long, and the Yasuda River basin is relatively large compared to the Namura River basin.
For the target area,χmaps were produced using 10 m mesh DEM. The χ parameter is an integral-form index based on the stream power incision model (SPIM), which is used to evaluate whether the equilibrium or transition state of topography. In many previous studies, the uplift rate is not included in the integrand, assuming a uniform uplift rate. In this study, the spatial variation of uplift rate is taken into accounts by substituting the denudation rate as a surrogate of uplift rate, tentatively assuming an equilibrium state. The denudation rate can be estimated from the relief of landform. If there is a difference in χ parameter value across the divide, it implies that the divide moves in the direction to the watershed with the larger χ value from that with the smaller (Willet et al., 2014). In the case of the present target area, the Namura River shows relatively higher χ value than the Yasuda River, which suggests that the divide is moving from the Yasuda to the Namura. Thus, the topography responds to the tilting uplift produced by the Yasuda Fault, and the divide moves in response to the tilting uplift, which exemplifies the watershed-scale topographic process controlled by fault movement.
For the target area,χmaps were produced using 10 m mesh DEM. The χ parameter is an integral-form index based on the stream power incision model (SPIM), which is used to evaluate whether the equilibrium or transition state of topography. In many previous studies, the uplift rate is not included in the integrand, assuming a uniform uplift rate. In this study, the spatial variation of uplift rate is taken into accounts by substituting the denudation rate as a surrogate of uplift rate, tentatively assuming an equilibrium state. The denudation rate can be estimated from the relief of landform. If there is a difference in χ parameter value across the divide, it implies that the divide moves in the direction to the watershed with the larger χ value from that with the smaller (Willet et al., 2014). In the case of the present target area, the Namura River shows relatively higher χ value than the Yasuda River, which suggests that the divide is moving from the Yasuda to the Namura. Thus, the topography responds to the tilting uplift produced by the Yasuda Fault, and the divide moves in response to the tilting uplift, which exemplifies the watershed-scale topographic process controlled by fault movement.