Crustal structure and the seismogenic environment in Yunnan imaged by double-difference tomography
Crustal structure and the seismogenic environment in Yunnan imaged by double-difference tomography
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DOI：
10.3389/feart.2023.1149932
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发表时间：
2023-05
期刊：
影响因子：
17.6
通讯作者：
Yanpeng Sun;Shilin Deng;Jiwen Huang
中科院分区：
文献类型：
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作者：
Yanpeng Sun;Shilin Deng;Jiwen Huang
云南地区广泛发育的大规模断裂活动和地震活动与印度板块和欧亚板块的碰撞有关。精细地壳结构可以提供更好的了解地壳变形，孕震环境和破裂过程。利用双差层析成像技术，在地震观测的基础上，进行了新的三维P波速度结构和地震重定位。层析成像结果显示，川滇地块南部边缘、小江断裂、丽江-小金河断裂在中、下地壳范围内分布有大规模的低速异常。峨眉山大火成岩省（ELIP）存在明显的高速异常。LJ-XJHF带下方的低速异常可能是来自青藏高原中部的下地壳流被ELIP遮挡，而XJF带附近的速度异常可能是剪切加热引起的，与大深大的走滑断层和东南方向的应力传递有关。反演结果还表明，漾濞地震发生在上、下地壳高、低速的北西-南东向分界线上，与漾濞地震序列和维西-桥后断裂的位置吻合较好。同时，地震重定位显示余震主要分布在低速区。上述研究结果表明，漾濞地震可能是由沿维西-桥后断裂沿着的软物质流向北西-南东方向侵入所致。这些低粘度的地壳物质会引起脆性破裂，并导致NW-SE左旋走滑断层。
The large-scale faulting and earthquake activities that developed extensively in the Yunnan area are associated with the collision of India and Eurasia. The fine crustal structure can provide a better understanding of the crustal deformation, seismogenic environment, and rupture processes. We performed a new 3-dimensional (3D) P wave velocity structure and seismic relocation using double-difference tomography based on seismic observations. The tomography images show that large-scale low-velocity anomalies spread around the margin of the south Chuan–Dian Block, Xiaojiang fault (XJF), and the Lijiang–Xiaojinhe fault (LJ-XJHF) in the middle and lower crust. There is an obvious high-speed anomaly in the Emeishan large igneous province (ELIP). We infer that the low-velocity anomaly under the LJ-XJHF zone may be derived from the lower crustal flow extruded from the central Tibetan plateau and obstructed by the ELIP, while the velocity anomalies around the XJF might be caused by shear heating, which is associated with the large-deep strike–slip fault and the transmission of stress in the southeast direction. The inversion results also show that the Yangbi earthquake occurred at the NW–SE boundary of high and low velocity from the upper crust to the lower crust, which coincides well with the location of the Yangbi earthquake sequence and the Weixi–Qiaohou fault. Meanwhile, the earthquake relocations show that the aftershocks are mainly distributed at low velocities. All the aforementioned research results indicate that the Yangbi earthquake might be attributed to the intrusion of the soft material flow along the Weixi–Qiaohou fault in the NW–SE direction. These low-viscosity crustal materials would cause brittle fractures and result in NW–SE sinistral strike–slip faults.