Abstract:

The Tarim Basin, a typical small cratonic basin and the largest inland basin in China, is bordered by three major orogenic belts: the Kunlun, Altun, and Tianshan Mountains. Prior to 2000, seismic activity within the basin was sparse. However, with the ongoing development of oil and gas exploration and extraction after 2000, seismicity began to increase, forming a distinct pattern of earthquake swarms—referred to as the Tarim earthquake swarm. Notably, since 2017, both the frequency and magnitude of earthquakes have risen significantly. Major events include the Kuqa M5.6 earthquake on January 16, 2020, the Shaya M6.1 earthquake on January 30, 2023, and three M5.0 earthquakes in the Yuli-Kuqa area in 2024. The rising seismicity has drawn increasing attention, particularly due to heightened activity in the Yuli region since June 2024, now considered the most seismically active area in both Xinjiang and China.
This study applies the Cut and Paste(CAP)method to invert focal mechanisms for three M5.0 earthquakes and other events above M_L4.0 within the Yuli earthquake swarm. The double-difference relocation method was employed to refine the hypocentral locations of earthquakes above M_L2.0. Furthermore, by analyzing the spatial distribution of smaller events and modeling the regional stress field, the study infers plausible parameters for seismogenic fault planes and investigates the faults responsible for the swarm. Among the 44 earthquakes analyzed, 42 exhibit strike-slip focal mechanisms. Cluster analysis reveals the presence of nearly north-south(NS)oriented nodal planes, consistent with regional strike-slip faulting trends in the NS to NNE direction. The relocated seismic sequence shows a clear division into eastern and western branches, both exhibiting linear NNE-trending patterns. Initially, seismic activity was concentrated in the eastern segment, but both branches demonstrated a northward migration over time. Based on the focal mechanisms, relocation data, and inferred fault plane parameters—combined with known fault structures in the region—it is preliminarily concluded that the Yuli earthquake swarm occurred along two nearly parallel, NNE-trending, right-lateral strike-slip faults: F₁(east)and F₂(west). Both faults are nearly vertical, with F₁ exhibiting a steeper dip. The fault depths are estimated at 20~25km. The previously mapped faults F_Ⅰ18 and F_Ⅰ16 near the Yuli swarm may correspond to the shallow and deep sections of faults F₁ and F₂, respectively. The eastern fault(F_Ⅰ18/F₁) maintains consistent dip characteristics from shallow to deep levels, whereas the western fault(F_Ⅰ16/F₂)displays a gentler dip at depth compared to the surface.
In addition to the Yuli swarm, the Tarim Basin has recently experienced the 2012 Luopu M6.0 earthquake(thrust)and the 2023 Shaya M6.1 earthquake(strike-slip), reflecting diverse faulting mechanisms driven by a common regional tectonic regime. The Luopu event resulted from thrusting of the Bachu Uplift toward the Awati Depression, induced by the ongoing convergence of the Indian and Eurasian plates. In contrast, the Shaya earthquake and the Yuli swarm likely represent secondary strike-slip structures accommodating crustal deformation from northward-directed compressive stress associated with NW- and EW-trending thrust belts in the basin interior. The Yuli earthquake swarm is located in the Yuke region of eastern Tarim, an area rich in oil and gas resources. In recent years, extraction activities have intensified, raising questions about a potential link between these activities and the increased seismicity. Further investigation is required to clarify the relationship between industrial activity and the occurrence of the Yuli earthquake swarm.

Key words: The Tarim Basin, Yuli earthquake swarm, focal mechanism solution, relocation, NNE-trending strike-slip faults

摘要：

2024年6月以来, 塔里木盆地内部尉犁地区地震活动异常活跃, 是新疆甚至中国地震活动最主要的地区。文中采用CAP方法反演了尉犁震群中3次5级地震及M_L4.0以上地震的震源机制; 采用双差定位方法对该震群中M_L2.0以上地震进行了重新定位, 并利用小地震分布和区域应力场拟合了可能的发震断层面参数, 在此基础上分析了震群活动可能的发震断层。结果显示, 44次地震中有42次为走滑型, 经聚类分析均存在近SN向的节面, 与震中附近近SN向或NNE向分布的走滑断裂特征较为一致。重新定位后的震群序列明显分为东、 西2支, 且均呈现NNE向线性分布特征。震群早期地震主要集中在东区, 随着时间的推移, 东区和西区地震均呈现向N迁移的特征。根据序列震源机制、 重定位结果及利用小地震约束得到的断层面参数, 结合震区的断层信息, 初步推断此次尉犁震群发生在近平行的NNE向右旋走滑断裂F₁(东区)和F₂(西区)上, 2条断裂均呈近直立(略微W倾)特征, 且F₁较F₂断层面更陡, 断裂深度可达20~25km。尉犁震群附近已知的断裂F_Ⅰ18和F_Ⅰ16与F₁和F₂断裂可能分别对应震区附近走滑断裂的浅部和深部, 其中东区断裂(F_Ⅰ18和F₁)深、 浅部的产状特征基本一致, 而西区断裂(F_Ⅰ16和F₂)深部的倾角较浅部更小。受印度板块对欧亚板块的推挤, 塔里木震群区的一系列走滑断裂成为盆地中部NW向和近EW向大型逆冲带向N推挤时形成的伴生调节构造, 是调节区域挤压缩短变形的代表性构造样式。此外尉犁震群位于塔里木盆地东部的玉科地区, 该区油气资源相对富集, 此次震群是否与油气开采相关仍需进一步考证。

关键词: 塔里木盆地, 尉犁5级震群, 震源机制解, 重新定位, NNE向走滑断裂