Quantifying the response of bankfull channel width to active faulting in the Qianhe Graben on the southwest margin of Ordos Block, China

River longitudinal profiles have been widely used to quantify the transient landscape response to active faulting, but the fluvial cross-section is often ignored, yet width can also reveal river incision and tectonic activity. Channel width responds to tectonic forcing through flow concentration effects resulting in channel narrowing where vertical incision dominates during uplift acceleration. Here we employ a novel bankfull channel width extraction method using Landsat and ZY-3 satellite images, and SRTM DEM data to evaluate the cross-section landscape response to active faulting in the Qianhe Graben of southwest Ordos, China. Although some areas are difficult to access (e.g., thick Quaternary Loess and vegetation cover), limiting the possibility of measuring river widths in the field, the remote sensing width extraction method provides a complete river width evaluation. Twenty-four rivers known to be responding to ongoing tectonic uplift that drain across normal faults were extracted, and demonstrate that the width tends to be narrower in the footwall of faults. Along strike from north to south, the channel widths varied systematically with the distance to the river source, and the normalized wideness index (kwn) of the rivers also decreases to the southeast. In combination, with the distribution of the widths, kwn, exponential of channel width (b’), the main morphologies of the study area are controlled by the lithologies and faults. Additionally, the peak of unit stream power and boundary shear stress gives a new insight into the location of an active fault in this area and overall suggest that uplift rates are higher along the southern graben margin. In regions of tectonic uplift, channel narrowing and steepening are the main modes of channel morphology adjustment, and the timescale of channel width adjustment is usually much shorter than that of gradient adjustment. All of these observations indicate the river channel widths are tracing fault evolution in Qianhe Graben.