关键词: 海原断裂带, SBAS-InSAR, 震间反演, 滑动亏损, 地震危险性

Abstract:

Owing to the ongoing collision between the Indian and Eurasian plates, the Tibetan block manifests as the most intensely deforming intracontinental tectonic unit globally. The interseismic phase, defined as the protracted stable period between characteristic earthquakes, features persistent relative movement of fault-bounded blocks driven by plate convergence or strike-slip motion. Locked segments at depth impede shallow slip, resulting in sustained accumulation of elastic strain within the crustal medium. This strain buildup manifests as long-term, stable tectonic deformation within the surface displacement field, known as interseismic deformation. As the critical phase for seismic energy accumulation, the Haiyuan fault zone(HYFZ)has historically experienced two major earthquakes: the 1920 Haiyuan and 1927 Gulang events. As a significant active block boundary and intense seismicity zone in the northeastern Tibetan margin, and one of China's most earthquake-prone regions, monitoring the HYFZ's interseismic deformation is particularly crucial.
This study employs Small Baseline Subset Interferometric Synthetic Aperture Radar(SBAS-InSAR)technology with Sentinel-1A T135 and T62 track data(2018-2024) to monitor the HYFZ's interseismic deformation. The resulting deformation field covering the entire HYFZ was analyzed using cross-fault techniques, with emphasis on deformation at structural step-overs. Results indicate minimal deformation-rate differences(characteristic of interseismic locking) across the central-eastern Lenglongling, Jinqianghe, Maomaoshan, and western Laohushan segments. Notably, near the 2022 Menyuan earthquake hypocenter, the Lenglongling Fault exhibited a significant differential rate reaching 4mm/a. Shallow creep was observed along the eastern Laohushan segment, while the central Haiyuan strand showed an obvious maximum differential rate of 3.7mm/a with left-lateral strike-slip characteristics.
Time-series analysis of a near western Lenglongling cross-fault profile revealed an accelerated trend on the southern block approximately two years before the 2022 Menyuan earthquake, with notably higher acceleration compared to the northern block. This suggests the southern block acted as the driving block. Subsequent slip-rate inversion for each HYFZ segment utilized the arctangent elastic dislocation model. Integrating InSAR and GPS data, the study transformed the deformation field into the Eurasian reference frame. Tectonic blocks adjacent to the HYFZ were defined as the Lanzhou, Qilian Shan, Ordos, and Alashan blocks. A block-based negative dislocation model inversion yielded locking depths and slip deficits along the entire HYFZ. Results indicate: maximum locking depth(16km) at the Lenglongling-Jinqianghe junction, minimum depth(<1km) in western Laohushan, and overall slip deficit rates decreasing eastward within the range of 1.9-5.2 mm/a.
The comprehensive seismic hazard assessment suggests that the Lenglongling segment(deep locking, large slip deficit)faces significant hazard potential despite small earthquakes, requiring vigilance for large events. The Jinqianghe, Maomaoshan, and western Laohushan segments(constituting the “Tianzhu Seismic Gap”)exhibit deep locking, substantial slip deficits, and no major earthquakes in several centuries, indicating high risk. The eastern Laohushan and central Haiyuan segments(shallow locking, small deficits) are likely undergoing post-seismic adjustment, primarily experiencing small earthquakes with minimal potential for large events.

Key words: Haiyuan fault zone, SBAS-InSAR, interseismic inversion, slip deficit, earthquake risk