Geometry, slip rate, and the latest earthquake of the Jinta Nanshan Fault: Interactions of the Altyn Tagh Fault and the Qilian Shan at the northern margin of the Tibetan Plateau

Abstract

This work presents a study of late Quaternary activity on the Jinta Nanshan Fault (JTF), to constrain its properties including seismic hazard, and to understand the tectonic evolution of the northern edge of the Tibetan Plateau. The JTF has developed during northeastward growth of the Qilian fold-and-thrust belt and eastward growth of the Altyn Tagh Fault. Based on remotely-sensed image interpretation and field investigation, trench studies, high-resolution terrain construction and Optical Stimulated Luminescence dating, we study the fault geometry and slip motion, and constrain the slip rate and the latest earthquake for the JTF. The JTF continues as far southeast as the Heihe River and shows predominantly left-lateral strike-slip displacement. The left-lateral slip rate is 0.27–0.48 mm/yr since late Pleistocene, much larger than the vertical slip rate of 0.05 ± 0.01 mm/yr. The latest rupture event of the JTF is slightly before 1 ka, which could be related to the poorly-recorded 756 CE earthquake in Hexi Corridor, and is also associated with fresh offset during this earthquake in the geomorphology of the east segment of the JTF. Strike-slip offset in this earthquake is estimated as 3.2 ± 0.4 m, with a rupture length of at least ∼13 km, indicating a moment magnitude of 6.4–7.2. We estimate the recurrence interval as 8–13 ka, based on the size of the latest offset and the slip rate of 0.27–0.48 mm/yr. These results indicate that the strike-slip continuation of the Altyn Tagh Fault dominates the slip behaviour of the JTF. The small strike-slip rate, and the match between the strike-slip of the JTF and the vertical slip of the North-South Normal Faults (NSF) at its eastern end, permit the interpretation that the slip of Altyn Tagh Fault is completely accommodated by crustal extension at the NSF, and dies out at the eastern end of the Jinta Nanshan region.