Inversion for regional tectonic stress field in the North-South Seismic Belt of China
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摘要: 利用区域应力张量阻尼方法，使用南北地震带及其邻近区域2009年1月—2017年8月466次ML≥3.5地震的震源机制解，及1976年1月—2017年8月GCMT公布的259次M≥4.5地震的震源机制解，反演得到研究区1.0°×1.0°网格大小区域的构造应力场。应力场空间分布特征显示，南北地震带作为青藏高原的东边界，由于所处动力环境复杂，其内部最大主应力方向具有明显的空间差异性。这种差异主要表现为：南北地震带北段最大主应力方向为NE向；南北地震带中段及周边除龙门山断裂带NE段最大主应力为NW-NNW向外，其它地段最大主应力近EW向；南北地震带中南段最大主应力方向逐渐由近EW向到NW或NE向，再到近NS向。整体而言，南北地震带及邻近区域最大主应力方向由北到南发生了顺时针旋转。川滇菱形块体内部最大主应力方向为NNW向，应力方向转换带与块体边界基本一致，其东边界以东最大主应力方向为NW向，西边界以西为NNE向。从区域构造应力场的角度分析，难以将“南北地震带”作为一个统一的地震带应用于中长期地震预测的研究与实践中。Abstract: Using the regional stress tensor damping inversion method and focal mechanism data （466 ML≥3.5 earthquakes focal mechanism solutions from January 2009 to August 2017 and 259 M≥4.5 earthquakes focal mechanism solutions from January 1976 to August 2017 from the GCMT）, we have obtained the distribution of the stress field by 1.0°×1.0° grid region in the North-South Seismic Belt and its adjacent regions. The spatial distributions of stress field show that, because of the complex dynamic environment, there are differences between the maximum principal stress direction inside the North-South Seismic Belt which is the east boundary of the Tibetan Plateau. The maximum principal stress direction in the northern segment of the North-South Seismic Belt is NE. In and surround the middle segment of the North-South Seismic Belt, the maximum principal stress direction is nearly EW except the NE segment of the Longmenshan fault zone whose direction is NW-NNW. The direction of the maximum principal stress in the middle and southern segments of the North-South Seismic Belt changes gradually, from nearly EW to NW/NE then to nearly NS. Overall, the maximum principal stress in the North-South Seismic Belt and its adjacent regions has a clockwise rotational pattern from north to south. Inside the Sichuan-Yunnan rhombic block the maximum principal stress is in NNW direction, while to the west of the west boundary the direction is NNE, to the east of the east boundary the direction is NW. The stress direction transition bands have well corresponded with the Sichuan-Yunnan rhombic block boundary. According to the analysis of regional tectonic stress field, it is difficult to apply the North-South Seismic Belt as a unified seismic belt to the medium and long-term earthquake prediction.
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图 1 本研究所用震源机制解空间分布图
Figure 1. Spatial distribution of the focal mechanism solutions used in this study
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图 2 南北地震带震源机制解P （a），T （b）轴分布图
Figure 2. P axes （a） and T axes （b） of focal mechanism solutions in North-South Seismic Belt
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