滇西南地区深浅部构造变形特征

doi:10.12196/j.issn.1000-3274.2023.01.007

摘要/Abstract

摘要： 滇西南地区是地震多发区, 研究该区的岩石圈深浅部变形特征是认识其孕震环境和地震成因的重要途径。基于自主观测和收集的GNSS观测资料, 通过融合给出滇西南地区最新的GNSS速度场。采用多尺度球面小波方法计算应变率张量, 分析主应变率、面应变率和最大剪应变率的空间分布特征。结果表明, 滇西南地区表现出近NNE—SSW向的挤压和NNW—SSE向的拉张。近EW向断层表现为左旋走滑, 近NS向断层表现为右旋走滑, 黑河断裂和无量山断裂之间的区域具有明显的面压缩与面膨胀转换, 畹町断裂、龙陵—瑞丽断裂东部、南汀河断裂东部、黑河断裂、澜沧断裂和小江断裂跨过红河断裂延伸到孟连、孟兴断裂区域具有较高的剪应变率, 最高达到50 nstrain/a。利用1976—2020年的震源机制解, 采用区域阻尼应力反演方法反演应力张量, 并解算反映主应力相对大小的R值分布, 反演结果表明, 滇西南地区受到NNE—SSW向的主压应力作用, 整体上处于走滑应力状态, 而大盈江断裂东部腾冲火山附近的南北向断层存在正断兼斜滑的特点。滇西南地区的主应力大小在空间上具有明显的差异性, 南汀河断裂以南是主应力最大的区域, 其走滑特征也更加明显。此外, 还收集了滇西南地震波各向异性数据, 分别对比主应力方向和主应变率方向的夹角、主应力方向和Pms快波偏振方向的夹角、主应力方向和XKS快波偏振方向的夹角、 Pms快波方向和XKS快波偏振方向的夹角, 得到地表和中上地壳、中上地壳和下地壳、下地壳和上地幔构造变形的差异性, 发现滇西南地区下地壳和上地幔变形机制不相同, 解耦并不全部位于下地壳和上地幔之间。在龙陵—瑞丽断裂、南汀河断裂, 孟连断裂附近下地壳和中上地壳之间存在变形差异, 下地壳与上地幔变形一致, 表明该区域下地壳与中上地壳发生解耦, 滇西南部分区域可能存在上地幔涌入下地壳的热物质流动通道, 存在局部的下地壳流。

关键词: 滇西南地区, 应变率场, 应力场, 多尺度球面小波法, 地震各向异性

Abstract: Southwest Yunnan is an earthquake active area. The deep and shallow deformation characteristics of the lithosphere in this area is of great significance to understand its seismogenic environment and mechanism. This study is based on independent observation and collected regional GNSS data, the GNSS velocity field in Southwest Yunnan is studied. Then the multi-scale spherical wavelet method is used to calculate the strain rate tensor, and the spatial distribution characteristics of principal strain rate, surface strain rate and maximum shear strain rate are analyzed. The results show that the southwest of Yunnan is compressed by nearly NNE—SSW, and the surface compressibility is ~10 nstrain/a. The near east-west fault is characterized by left-hand strike slip, and the near north-south fault is characterized by right-hand strike slip. There is an obvious transformation between surface compression and surface expansion in the area between Heihe fault and Wuliangshan fault. Wanding fault, east of Longling-Ruili fault, east of Nantinghefault, Heihe fault, Lancang fault and Xiaojiang fault extend across Honghe fault to Menglian-Mengxing fault area has high shear strain rate, up to 50 nstrain/a. The focal mechanism solutions of the study area from 1976 to 2020 are collected, the regional damping stress inversion method is used to invert the stress tensor, and the R-value distribution reflecting the relative size of the principal stress is attained. The inversion results show that the southwest of Yunnan is affected by the principal compressive stress in the NNE—SSW direction, and the area is in the state of strike slip stress as a whole, The North-south fault near Tengchong volcano in the east of Dayingjiang fault has the characteristics of normal fault and oblique slip. The magnitude of principal stress in Southwest Yunnan is obviously different in space. The south of Nantinghe fault is the area with the largest principal stress, and its strike slip characteristics are more obvious. In addition, this study also collects seismic wave anisotropy data in the study area, compares the angle between the direction of the principal stress axis and the principal strain rate axis, the angle between the direction of the principal stress axis and the polarization direction of Pms fast wave, the angle between the direction of the principal stress axis and the polarization direction of XKS fast wave, the angle between Pms fast wave direction and XKS fast wave polarization direction, we obtains the structural deformation differences between the surface and middle upper crust, middle upper crust and lower crust, lower crust and upper mantle respectively, It is found that the lower crust and upper mantle are decoupled in Southwest Yunnan. At the same time, it is found that the difference in deformation between the lower crust and the middle upper crust near Longling-Ruili fault, Nantinghe fault and Menglian fault, indicating that the lower crust and the middle upper crust are decoupled in this area, and there may be a hot material flow channel in the lower crust, with localized lower crustal flow in partial zones of southwestern Yunnan.

Key words: Southwest Yunnan, Strain rate field, Stress field, Multiscale spherical wavelet, Seismic anisotropy

中图分类号:

P315.7

杨业鑫, 孟国杰, 吴伟伟, 罗艳, Thant Myo. 滇西南地区深浅部构造变形特征[J]. 地震, 2023, 43(1): 74-92.

YANG Ye-xin, MENG Guo-jie, WU Wei-wei, LUO Yan, Thant Myo. Characteristics of Deep and Shallow Tectonics Deformation in Southwest Yunnan[J]. EARTHQUAKE, 2023, 43(1): 74-92.

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