Abstract:

At 09:05a.m. on January 7, 2025, a magnitude M_S6.8 earthquake struck Dingri County, Xizang, China, resulting in 126 fatalities and a maximum seismic intensity of Ⅸ. Occurring within a seismically active and tectonically complex region, this event drew significant attention from both the scientific community and the public. The epicenter was located near the Dengmecuo Fault, which has been preliminarily identified as the seismogenic fault.

This study utilized publicly available geological survey data, aftershock relocations, and focal mechanism solutions to construct a detailed three-dimensional geometric model of the Dengmecuo Fault. The model was developed using the SKUA-GOCAD 3D modeling platform, enabling a comprehensive analysis of the fault’s geometry. Results reveal pronounced geometric segmentation along the fault plane, with the spatial distribution of these structural features closely correlating with observed seismicity, highlighting the influence of fault geometry on earthquake generation.

The M_S6.8 Dingri earthquake occurred near a prominent structural irregularity on the Dengmecuo Fault, at point P3, where the fault plane bends into an eastward-projecting arc. This three-dimensional structural mutation likely played a role in the nucleation of the event, underscoring the relationship between fault complexity and seismic rupture. The Dengmecuo Fault, situated in the southern Tibetan plateau, is a listric normal fault characterized by a steep upper section and a gentler lower section that terminates within a detachment layer in the upper crust. It does not extend into the deeper lithosphere, indicating that it is part of the region’s shallow normal fault system. The earthquake is interpreted as the release of accumulated stress along this shallow fault structure.

To evaluate post-earthquake stress transfer and seismic hazard, Coulomb stress modeling(Coulomb 3.4)was conducted. The analysis indicates that several regional faults are now in a state of increased Coulomb stress, including the southern segment of the Dengmecuo Fault, the middle segment of the south Xizang detachment system, the southern segment of the Shenzha-Dingjie Fault, the central Yarlung-Zangbo Fault, and the midsection of the Dajiling-Angren-Renbu Fault. These fault segments are identified as potential sites for future seismic activity and merit heightened monitoring.

This study presents a detailed characterization of the three-dimensional geometry of the seismogenic fault responsible for the Dingri M_S6.8 earthquake and offers a preliminary analysis of regional seismogenic structures. The findings provide valuable insights into the tectonic setting of southern Xizang and contribute to the assessment of regional seismic hazard.

Key words: Dingri M_S6.8 Earthquake, focal mechanism solution, seismic structure, Three-Dimensional fault model, Coulomb stress analysis

摘要：

2025年1月7日, 西藏定日县发生 M_S6.8 强震, 造成126人死亡, 最大烈度达Ⅸ度, 引起广泛关注。定日 M_S6.8 地震的震中位于登么错断裂附近, 初步推断该断裂为发震断裂。文中根据公开获取的地表地质调查结果、 余震重定位和震源机制解数据, 基于SKUA-GOCAD三维建模平台, 构建了登么错断裂的三维几何模型, 揭示了定日 M_S6.8 强震发震断层在三维空间展布的几何学特征。研究表明, 登么错断裂具有明显的几何分段性, 断裂的几何结构和地震活动在空间中的分布具有一定的关联性。此次地震的主震发生在登么错断裂(P3段)三维结构突变的位置(断层面呈向东凸出的弧形), 该地震的孕育和发生可能与断层面复杂的几何结构有关。震中所处的藏南地区深部发育大型拆离层, 登么错断裂为上陡下缓的铲式正断层, 断层底部在上地壳拆离层下方消失, 并未进一步向下延伸, 属于藏南地区浅部正断层系统, 此次地震是浅部正断层应力释放的结果。通过Coulomb 3.4程序计算得到不同深度的库仑应力变化表明: 登么错断裂南段、 藏南滑脱拆离系断裂中段、 申扎-定结断裂南段、 雅鲁藏布江断裂中段、 达吉岭-昂仁-仁布断裂中段处于震后应力加载状态。因此, 建议对余震进行监测和开展地震危险性分析时重点关注上述区域。文中刻画了三维发震断裂模型, 初步分析了发震构造, 为该区域孕震环境以及地震危险性评估提供了依据与参考。

关键词: 定日M_S6.8强震, 震源机制, 发震构造, 三维断层模型, 库仑应力分析