Abstract:

Based on the seismic data from temporary stations and regional stations in the northwestern area of Yunnan, the paper performs high-resolution detection and high-precision location on continuous waveforms recorded from February 25, 2018 to July 31, 2019 using waveform correlation methods and analyzes the seismicity characteristics of the Weixi-Qiaohou Fault in the northern section of the Red River fault zone. Studies have shown that the Weixi-Qiaohou Fault exhibits weak seismic activity currently, except for some special fault locations(such as terraces, intersections, etc.), but there may be a hidden steep-dip right-lateral strike-slip fault along the west side of the fault. Small earthquakes are frequent along the fault. The distribution of seismic activity and focal mechanism solutions indicate that this fault is a right-lateral strike-slip fault with a steep dip. Statistical parameters, such as seismic frequency, energy release rate and b-value, indicate that the seismic activity in the Weixi-Qiaohou Fault and its surrounding areas is relatively stable, and the regional stress enhancement is not obvious. The b-value is relatively high in most areas, and low b-value areas are mainly distributed in some special fault locations(such as terraces, intersections, etc.), but the scale is generally small. The statistical results of the ETAS model show that more than 40% of seismic activity may be affected by external factors such as deep fluid disturbance and remote strong earthquake triggering. This shows that the role of external trigger mechanisms in seismic activity cannot be ignored. The external triggering seismic activity factors are related to the disturbance of deep fluid activity and the dynamic triggering of long-distance strong earthquakes. Therefore, we believe that the Weixi-Qiaohou Fault is currently not active, but on the hidden branch fault to its west, small earthquake activity is clustering and has a tendency to increase. So, when assessing the seismic risk of the fault, comprehensive analysis shall be made on the activity of the main fault and the branch fault to its west.

Key words: seismicity, Weixi-Qiaohou Fault, branch fault

摘要：

文中基于滇西北地区临时加密台站和区域固定台站地震观测资料, 利用波形相关方法对2018年2月25日—2019年7月31日记录的连续波形进行高分辨率地震检测和高精度地震定位, 据此分析红河断裂带北段维西-乔后断层的地震活动性特征。研究表明, 目前维西-乔后断层除了一些特殊的断层部位(交会区、 阶区等)外, 地震活动微弱, 但在其西侧可能存在一条隐伏的陡倾角右旋走滑断层, 沿该断层小地震活动活跃。地震频度、 能量释放率、 b值等统计参数及其随时间的变化表明, 维西-乔后断层及其附近地区的地震活动相对稳定, 区域应力增强不明显; 空间上大部分区域的b值较高, 低b值区主要分布在一些特殊的断层部位(如断层交会区、 阶区等), 但尺度一般较小。ETAS模型统计结果表明, 40%以上的地震活动受外部因素触发, 包括深层流体扰动和远程强地震触发等。由此我们认为, 维西-乔后断层主断层目前的地震活动性较弱, 但其西侧的隐伏分支断层小地震活动丛集且有增强趋势, 需要综合分析主断层及其西侧隐伏分支断层的活动性, 以评估其地震危险性。

关键词: 地震活动性, 维西-乔后断层, 分支断层