Analysis of Earthquake Sequence and Seismogenic Structure of the 2025 MS6.8 Dingri Earthquake in Tibetan Plateau
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摘要:
2025年1月7日9时5分，西藏定日发生MS6.8强震，造成了重大人员伤亡和财产损失.震中位于藏南申扎‒定结裂谷南段西部的丁木错地堑内，其震源机制为典型的正断型地震.此次地震的发震断层为丁木错断裂，但地震形成的地表破裂展布特征、断裂带的几何结构以及地堑的演化模式等还有待深入研究.根据野外地表破裂调查和余震序列重定位，探讨了此次地震的变形特征及丁木错地堑的演化模式.震后科考发现，丁木错东、西两侧均发育有明显的地表破裂，为典型的地堑结构，尼辖错仅在东部发育地表位错，位错量较大，为典型的半地堑结构，地表破裂总长~30 km，且表现出了边界断裂向盆地内部迁移的特征.基于双差定位方法，结合固定台网和流动观测台网，对震后13 d的地震序列进行了重定位，共获得4 312个高精度定位结果，主震震中位置28.51°N，87.52°E，震源深度为11.3 km.余震序列与地表破裂走向一致，呈~NS向分布，深度集中在~4~17 km，余震分布揭示了断层东倾和西倾并存的特征.结合地表破裂和余震序列分布，认为此次地震的发震断层为丁木错断裂的东部边界断裂，倾角~60°~70°.地震序列主要集中在上地壳，此次地震可能是对喜马拉雅弧形逆冲形成的边界应力的响应.
Abstract:On January 7, 2025, at 09:05, an MS6.8 earthquake struck Dingri County in the Xizang Autonomous Region, resulting in significant casualties and property damage. The epicenter of the main shock was located in the Dingmucuo graben, in the western segment of the southern Shenzha-Dingjie rift zone in the southern Tibetan Plateau, and the focal mechanism was identified as a typical normal faulting earthquake. The seismogenic fault is the normal faults in Dingmucuo graben, however, the distribution of surface rupture and geometry of normal faults, as well as the evolution model of this graben is relatively limited. This study discusses the seismogenic fault of the earthquake and the evolution model of the Shenzha-Dingjie rift through the interpretation of remote sensing images before and after the event, field investigations of surface ruptures, and the relocation of the seismic sequence. Earthquake investigations revealed significant surface ruptures developed on both the eastern and western sides of Dingmucuo, forming a typical graben structure, while the northern segment primarily developed in the eastern part of the Nixiacuo, exhibiting significant displacement and resembling a half-graben structure. Notably, the surface rupture extends about 30 km in the graben showing a migration of the graben boundary fault into the basin. Furthermore, based on the seismic phase data recorded by the permanent and temporary stations, 4 312 high-precision location results were determined by using a double-difference relocation method. The epicenter of the main shock was determined to be at 28.51°N, 87.52°E, with a focal depth of 11.3 km. The aftershock sequence was consistent with the direction of the surface rupture, showing a ~NS distribution, with depths concentrated around ~4‒17 km. The aftershock distribution revealed the coexistence of east-dipping and west-dipping fault characteristics. Based on the surface rupture and aftershock sequence, it concludes that the seismogenic fault for this earthquake is the eastern boundary fault of the Dingmucuo graben, with a dip angle of approximately 60°‒70°. The earthquake sequence is primarily concentrated in the upper crust and is likely a response to boundary stress resulting from the thrusting along Himalayan arc.
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Key words:
- Shenzha‒Dingjie rift /
- earthquakes /
- Dingmucuo graben /
- surface rupture /
- aftershock sequence /
- tectonics
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图 1 青藏高原内部活动断裂及震源机制解分布
断层引自 Tapponnier et al.，2001； Wang et al.，2024；红色断层线为申扎‒定结裂谷内的主要断裂带；震源机制解引自GCMT（
https://www.globalcmt.org/CMTsearch.html ）Fig. 1. Tectonic map and focal mechanism in the interior of Tibetan Plateau
图 2 申扎‒定结裂谷主要活动断裂和历史地震分布
断层引自 Tapponnier et al.，2001； Wang et al.，2024；红色断层线为申扎‒定结裂谷内的主要断裂带；地震数据为公元前780年至今M5.0以上地震，历史地震来源顾功叙（1983）；现代地震据中国地震台网中心（
http://www.ceic.ac.cn ）Fig. 2. Map showing the major active faults and epicenters of historical earthquake along Shenzha-Dingjie rift
图 4 丁木错西地表破裂野外照片
a.无人机正射影像显示两条近~NS走向的平行地表破裂错断了废弃河道（位置见图 3）；b.丁木错西单支地表破裂沿先前陡坎发育，垂直位错达0.13 m（位置见a）；c.丁木错西单支地表破裂的垂直位错达0.12 m（位置见a），红色倒三角指示地表破裂位置
Fig. 4. Surface rupture along west of Dingmucuo
图 5 尼辖错北地表破裂野外照片
a.尼辖错北地表破裂的无人机照片（位置见图 3），红色倒三角表示地表破裂位置，白色倒三角表示先存断层陡坎；b.尼辖错北地表破裂呈右阶分布，最宽地表变形~50 m（位置见a）；c.尼辖错北地表破裂的垂直位错达~2.5 m（位置见a）
Fig. 5. Surface rupture along north of Nixiaco
图 6 丁木错东地表破裂和滑塌变形照片
a.丁木错东地表破裂和滑塌变形无人机照片（位置见图 3）；b.丁木错东地表破裂/滑塌变形和挤压鼓包野外照片（位置见a）；c.丁木错东地表破裂野外照片.绿色倒三角表示滑塌变形带，红色倒三角表示地表破裂位置，白色倒三角表示地表裂隙，黑色倒三角表示先存断层陡坎
Fig. 6. Surface rupture and landslide deformation in the east of Dingmucuo
图 7 台站分布（a）、余震震级‒频度（b）和定位时采用的一维P波速度模型（c）
Fig. 7. Station distribution map (a), aftershock magnitude-frequency distribution (b) and 1-D P-wave velocity model used in earthquake location (c)
图 8 地震余震序列在平面上（a）和剖面上（b~d）随时间的分布
黄色五角星表示主震位置，黄色圆圈表示M3.5级以上余震的位置，绿色三角形表示震区周边的流动台站. 余震颜色表示距离主震发生的时间. 震源机制解由中国地震台网中心的马亚伟博士提供. 图中黑色断层线为先存断层，红色断层线为形成地表破裂的断层
Fig. 8. Map (a) and profile (b‒d) views of the Dingri aftershock sequence
图 9 丁木错地堑演化模式（修改自Kapp et al., 2008）
a.丁木错断裂半地堑初始形成阶段；b.丁木错断裂迁移过程；c.丁木错断裂现今演化阶段
Fig. 9. Evolution model of Dingmucuo rift (modified after Kapp et al., 2008)
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