Kinematics of the ∼1000 km Haiyuan fault system in northeastern Tibet from high-resolution Sentinel-1 InSAR velocities: Fault architecture, slip rates, and partitioning

Abstract

The 1000-km-long Haiyuan fault system on the northeastern edge of the Tibetan Plateau contributes to accommodating the deformation in response to the India/Asia collision. In spite of its importance, the kinematics of the fault including the geometry and along-strike slip rate have not been completely defined. In this study, we use synthetic aperture radar data acquired between 2014 and 2021 by Sentinel-1 satellites to investigate the present-day strain accumulation on the Haiyuan fault system. We produce a high-resolution velocity map for the ∼300,000 km2 Haiyuan region using the Small BAseline Subset method. Our new velocity fields reveal deformation patterns dominated by the eastward motion of Tibet relative to Alaxan and localised strain accumulation along the Haiyuan, Gulang and Xiangshan-Tianjingshan faults. The western ∼300-km-long section of the Haiyuan fault, which was previously unmapped, seems to follow Tuolaishan and terminate at Halahu. We compute the along-strike slip rate using a Bayesian Markov Chain Monte Carlo inversion approach, and find that the overall strike-slip rate along the Haiyuan fault system gradually increases from the western end (1.8±0.3 mm/yr close to Halahu) to the east (6.4±0.5 mm/yr before entering Liupanshan), and further east, it decreases from 6.4±0.5 mm/yr to 1.3±0.7 mm/yr. The Haiyuan fault absorbs most of the left-lateral strike-slip motion with a rate of ∼4.2±0.4 mm/yr, and the Gulang and Xiangshan-Tianjingshan faults take up a fraction of 2.2±0.6 mm/yr. We re-map the previously identified shallow creeping zone on the Laohushan segment for a length of 45 km, slightly larger than the previous estimate of 35 km. The average shallow creep rate, 3 mm/yr between 2014–2021, is consistent with the rate before 2007 (2–3 mm/yr), implying that the shallow creep is a steady behaviour.