Stress drop variations of the 2019 ML 6.0 Changning earthquake and its aftershock sequence in the southern Sichuan Basin, China
Stress drop variations of the 2019 ML 6.0 Changning earthquake and its aftershock sequence in the southern Sichuan Basin, China
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DOI：
10.1016/j.tecto.2023.230139
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发表时间：
2023-11
期刊：
影响因子：
2.9
通讯作者：
Lin Shen;Lian‐Feng Zhao;Xiao-Bi Xie;Xi He;Wei-Min Wang;Zhen-Xing Yao
中科院分区：
文献类型：
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作者：
Lin Shen;Lian‐Feng Zhao;Xiao-Bi Xie;Xi He;Wei-Min Wang;Zhen-Xing Yao
对发生在四川盆地南部的2019年长宁6.0级地震及其94次2.8级以上余震的长波谱进行了研究。这次地震序列可能与附近盐矿开采活动的注水有关。基于建立的区域高分辨率宽带长波衰减模型，对观测光谱进行了沿传播路径衰减效应校正。通过对长宁地震序列观测谱与理论震源模型的拟合，估计了地震矩和角频率，并由此计算了整个地震序列的应力降。结果表明：应力降分布较分散，范围为0.16 ~ 32 MPa，中位数为0.78 MPa；应力降的时空变化反映了断层的强非均质性和复杂的应力释放过程，可能受到注水和扩散的影响。应力降与震源深度、应力降与震级呈正相关。对于大多数浅层事件，相对较低的应力降可能表明长期流体注入降低了正常应力。应力降与注入水的双河盐矿距离无明显关系。结合实际注水数据和前人数值模拟研究，我们认为，2019年长宁地震震源区以外，与采盐有关的注水可能导致孔隙压力升高。不断积累的地下水可能已经形成了连接多个断层系统的通道，因此不能排除未来发生大型诱发地震的可能性。
The Lg-wave spectra are investigated for the 2019 Changning M L 6.0 earthquake and its 94 aftershocks with magnitudes above M L 2.8, which occurred in the southern Sichuan Basin, Southwest China. This earthquake sequence is potentially related to the water injection from nearby salt mining activities. Based on an established regional high-resolution broadband Lg-wave attenuation model, we correct the observed spectra for the attenuation effect along the propagation path. By fitting the observed spectra from the Changning earthquake sequence with the theoretical source model, we estimate seismic moments and corner frequencies, from which the stress drops are calculated for the entire earthquake sequence. The results show that the stress drops are rather scattered, ranging from 0.16 MPa to 32 MPa with a median value of 0.78 MPa. Spatiotemporal variation of stress drops reflects strong fault heterogeneity and a complex stress release process, which is likely influenced by water injection and diffusion. Positive trends are observed between the stress drop and focal depth and between the stress drop and seismic magnitude. Relatively lower stress drops for most shallow events are possibly the indication of lowered normal stress by long-term fluid injection. No apparent relation is observed between the stress drop and the distance to the Shuanghe salt mine, where water was injected. Combining the actual water injection data and previous numerical simulation studies, we suggest that the salt mining-related water injection may lead to elevated pore pressure beyond the source region of the 2019 Changning earthquake. The increasingly cumulated underground water may have created pathways linking multiple fault systems, thus the possibility of future large induced-earthquakes cannot be ruled out.