Late Quaternary slip rate of the Fengmenkou-Wuzhiling fault at the southern margin of North China block (S-NCB)

The regional crustal slipping behaviour within the interaction zone of the North China and Qinling blocks reveals the pattern of extensional grabens merging with strike-slip faults and establishes the contribution of these faults to the regional basin generation. In this study, we aimed to assess the active slipping at the Laojing Gou site along the Fengmenkou-Wuzhiling fault (FMK-WZLF), one of the main active faults at the southern margin of North China block (S-NCB), by setting a three-dimensional measurement of the offset in buried paleochannels. Mapping, trenching, and age constraints of the geomorphic and stratigraphy units illustrate three offset paleo-fluvial surfaces since the Late Pleistocene, named S1, S2, and S3, along the fault strike direction. Beneath the surface, the structure of isolated confined paleo-channels C1 and C3 was exposed on the stratigraphy profile, and they were active during 130–75 ka and 2.8–3.0 ka, respectively. We presented a set of adapted scripts for three-dimensional measurements to calculate the lateral and normal tectonic components. The left lateral slip rate for the FMK-WZLF was estimated to be 0.25–0.45 mm/a, and the long-term oblique slipping behaviour generated the scarps in a dip of 70° ± 5° across the fault plane. The oblique slip of the FMK-WZLF, together with the regional E-W and SW-NE striking normal fault system, shapes the northeastward flowing Yiluo river and the southeastward flowing Huai river at S-NCB.