Seismogenic Structure of Gaoling Seismic Swarm in Weihe Basin
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摘要: 渭河断陷盆地中东部的高陵周边地区近年来小地震频发，成为渭河盆地的地震高发区.为了解该区的发震构造及发震背景，对研究区内235个地震进行了小震精定位，通过重新拾取震相，计算了研究区内26个ML≥2.0的地震震源机制解.结果表明该区震源深度基本在15 km以内，深度上呈N倾的铲状形态；研究区以NNW的水平拉张和NW向的倾向压缩为主，地震活动以正断为主兼左旋走滑.综合地震分布形态、断层规模与活动性、极震区位置，认为高陵震群发震断裂为泾阳‒渭南断裂.GPS数据显示研究区应变呈复杂的四象限分布，高陵震群正处于四象限的中心区域，推测正是这种复杂的应力背景导致了高陵震群的活动.Abstract: In recent years, small and moderate earthquakes have occurred frequently around Gaoling county, making it a high-incidence area in the Weihe Basin. In order to understand the seismogenic structure and seismogenic background of the seismic area, this paper uses the VELEST and typoDD programs to relocate 235 earthquakes of recent years in the area. By re-picking the seismic phases, GPAT method is applied to calculate 26 focal mechanism solutions of the earthquakes with ML≥2.0. The precision positioning results of small earthquakes indicate that the earthquakes in this area are basically distributed above 15 km, and the vertical profile shows a northward shovel-like fault. Based on the distribution of earthquakes, the scale and activity of faults, and the location of the extreme earthquake zone, this paper considers the seismogenic fault of the Gaoling earthquake group to be the Jingyang-Weinan fault. The calculation results of the focal mechanism of small earthquakes show that the area is dominated by horizontal extension of NNW and tendency of compression in NW direction. The dominant direction of the comprehensive slip angle indicates that the seismogenic fault is dominated by normal fault activity and left-lateral strike-slip. GPS data show that the stress in the study area has a complex four-quadrant distribution, and the Gaoling seismic swarm is in the center of the four quadrants. The article speculates that it is this complex stress background that led to the activity of the Gaoling seismic swarm.
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Key words:
- Weihe Basin /
- Gaoling seismic swarm /
- seismic relocation /
- focal mechanism solution /
- seismology
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图 4 研究区地震和达曲线
图中纵坐标为P波到时，横坐标为S波和P波的到时差.通过线性拟合可求得研究区Vp/Vs值
Fig. 4. Wadati diagram for earthquakes in research area
图 6 定位残差统计图
图a为台网定位残差；图b为VELEST反演结果定位残差；图c为hypoDD定位残差
Fig. 6. Statistics of localization residuals
图 7 重定位后水平方向和垂直方向的误差柱状分布图
Fig. 7. Histograms of horizontal and vertical error distribution after relocation
图 8 精定位后的地震分布及高陵震群M-T图
Fig. 8. Distribution of earthquake epicenter after seismic relocation and M-T diagrams of Gaoling seismic swarm
图 9 研究区ML≥2.0地震震源机制分布
红色和蓝色震源球分别表示发震时间为2013年1月1日以前和以后
Fig. 9. Spatial distribution of focal mechanisms of earthquakes (ML≥2.0) in research area
图 10 P轴、T轴方位及断层滑动角分布统计图
Fig. 10. Statistical analysis of azimuth of P-axis, T-axis and rake angles
图 12 研究区活动构造和整体无旋转GPS速度场示意
图中应变率与GPS速度场引用自张永奇等（2021）
Fig. 12. Distribution of active structures and the entire non-rotating GPS velocity field in study area
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