Quantifying the transient landscape response to active faulting using fluvial geomorphic analysis in the Qianhe Graben on the southwest margin of Ordos, China

Abstract

River morphology has been widely used to record and track the transient landscape response to active faulting. Here we evaluate the landscape response to active faulting in the Qianhe Graben of southwest Ordos, China. In this region, it has been difficult to determine the activity of mapped faults because of the presence of thick Quaternary Loess; however, by analysing the presence and distribution of slope-break knickpoints in river longitudinal profiles, the ongoing tectonic uplift of the Qianhe Graben can be investigated. The alignment of vertical-step knickpoints gives a new insight into the location of an active fault on the southern margin of Qianhe Graben. Additionally, slope-break knickpoints, typical of fault controlled landscape change, were identified from 24 river longitudinal profiles that drain across normal faults along both graben margins. Along strike from north to south, the knickpoints varied systematically with relief, and the height of the knickpoints also decrease to the southeast. Indicating that the rate of motion on the faults, likely is greater in the northwest and decays southeastwards. The horizontal knickpoint retreat rates range from 0.3 to 27.3 mm/yr, constraining the landscape response time with fault initiation at 1.2–1.4 Myr. In comparison with other studies, the knickpoint recession triggered by base-level fall as a result of faulting is relatively lower than when the base-level fall is the result of sea-level fall potentially the result of different mechanism of retreat. Finally, the potential for earthquakes along the Taoyuan-Guichuansi Fault (TGF) before and after fault linkage was assessed, indicating the potential for earthquakes of Mw of 6.3–6.7 and 6.8–7.0, respectively. These observations not only suggest the knickpoints are recording fault evolution in Qianhe Graben, but also provide information on seismic hazard in this populous region.