New Slip Rate of the Central Gulang-Zhongwei Fault determined from high resolution topography and, OSL and 14C dating

    The Gulang-Zhongwei Fault is a northeast splay of the Haiyuan fault (east of 102°E) accommodating mostly left-lateral slip and some thrusting. Its slip history and kinematics are critical for understanding the mechanisms of slip partitioning along the oblique convergence at the margin of the plateau. Up to now, a consensus on its slip rate remains elusive; previous investigations have yielded divergent estimates ranging from <1 to 6 mm/yr. The central segment of the Gulang–Zhongwei Fault has been targeted for a detailed geomorphological and paleoseismological study. We used drone-based lidar to collect aerial imagery and dense point cloud to generate a digital elevation model (DEM) with a spatial resolution of better than 6 cm. The DEM clearly reveals the fault trace with faulted geomorphic features such as offset terraces and alluvial fans along the southern piedmont of Jingtai Xiaohongshan and Guanguan Ling . We performed detailed geomorphological mapping and displacement measurements at five sites over a fault length of ~6 km. The initiation time of fault slip accumulation was constrained by sub-surface 14C and OSL dating of various terraces and fan surfaces. Systematic and repeated offsets of multiple alluvial fans and terraces, with an average displacement of 12 m, postdating their emplacement in the early Holocene (8–10 ka), imply a millennial slip rate of 0.9–1.5 mm/yr. Altogether, our results indicate that the long-term left-lateral strike-slip rate of the Gulang-Zhongwei Fault ranges from 0.9 to 1.5 mm/yr. Although it accommodates only 10 % to 15 %of the left-lateral shear between Gobi-Ala Shan to the north and northeast Tibet to the south, it has been responsible for some major earthquakes in the past (1709 and 1920). Determination of its slip rate at various time scales is paramount for understanding how northeast convergent strain is distributed along the various faults at the regional scale and is key to seismic hazard assessment.