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

摘要： 海原断裂带是青藏高原东北缘重要的块体活动边界和强震活动带, 是中国地震发生最频繁的地区之一。文中基于短基线集干涉测量(Small baseline subsets interferometric synthetic aperture radar, SBAS-InSAR)技术, 采用2018-2024年Sentinel-1A T135、 T62 2个轨道的数据监测海原断裂带震间形变。对形变速率场进行跨断层分析, 并重点分析了断裂转换带处形变, 发现冷龙岭断裂中东段、 金强河断裂、 毛毛山断裂和老虎山西段断裂南、 北2盘形变速率差较小, 符合震间闭锁特征, 其中, 靠近2022年门源地震震源处的冷龙岭断裂剖面南、 北2盘形变速率差较大, 达4mm/a。老虎山断裂东段存在浅层蠕滑现象, 海原断裂南、 北2盘形变速率差明显, 最大相差3.7mm/a, 表现为左旋走滑的运动特征。联合InSAR与GPS数据进行震间反演, 得到海原断裂带闭锁和滑动亏损分布, 结果显示, 闭锁最深处(深度为16km)位于冷龙岭与金强河断裂交界处, 最浅处(深度<1km)位于老虎山西段, 滑动亏损速率为1.9~5.2mm/a, 大致呈自西向东递减的趋势。综合分析海原断裂带地震危险性, 冷龙岭断裂、 金强河断裂、 毛毛山断裂闭锁较深, 滑动亏损较大, 地震危险性较高; 老虎山、 海原断裂闭锁较浅, 滑动亏损较小, 发生大地震可能性较小。

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