Impact of dynamic stress on aftershock triggering of the 2021 Yunnan Yangbi MS6.4 earthquake
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摘要: 选取IRIS远震台站波形数据，反演了云南漾濞MS6.4地震震源破裂过程，计算了断层破裂在近场产生的动态库仑破裂应力变化，并讨论了主震对近场余震活动的动态应力触发作用。结果显示：动态库仑应力演化过程与震源破裂特征反演结果一致，其大小分布与地震序列分布的疏密程度也具有较好的相关性。主震产生的静态和动态库仑破裂应力均促进余震的发生，但相比静态应力，余震位于库仑破裂应力正值区域的比例提高了21%，余震与动态库仑应力变化的正负区域有更好的一致性，动态应力能更好地解释震后余震分布的空间特征。垂直于地震序列主干10 km处出现小震丛集，该现象可能是由主震产生的动态库仑破裂应力占主导作用所致。定量分析主震对余震的动态应力触发结果显示，主震后一周内MS4.0以上的8次余震接收点均受到了动态库仑破裂应力的触发作用。Abstract: Based on the waveform data of IRIS teleseismic station, this paper inversed the focal rupture process of Yunnan Yangbi MS6.4 earthquake, calculated the dynamic Coulomb rupture stress change caused by fault rupture in near field and discussed the dynamic stress triggering effect of main shock on near-field aftershock activity. The results show that the evolution process of dynamic Coulomb stress is consistent with the inversion results of source fracture characteristics, and its size distribution is also well correlated with the density of seismic sequence distribution. The static and dynamic Coulomb rupture stress produced by the main shock promote the occurrence of aftershocks, but compared with the static stress, the proportion of aftershocks located in the positive Coulomb rupture stress area is increased by 21%, and the positive and negative areas of aftershocks and dynamic Coulomb stress change have better consistency. The dynamic stress can better explain the spatial characteristics of aftershocks distribution after the earthquake. Small earthquakes cluster at 10 km perpendicular to the main trunk of the earthquake sequence, which may be caused by the dominant dynamic Coulomb fracture stress produced by the main earthquake. Quantitative analysis of the dynamic stress triggering of the main shock to the aftershock shows that within one week after the main shock, eight aftershocks receiving points bigger than MS4.0 are triggered by the dynamic Coulomb rupture stress.
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图 3 云南漾濞MS6.4地震静态应力变化（a）和地震序列密度分布及MS4.0以上余震震源机制（b）
Figure 3. Static stress change of the Yunnan Yangbi MS6.4 earthquake （a） and density distribution of the earthquake sequence and focal mechanisms of aftershocks above MS4.0
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图 1 云南漾濞MS6.4地震震中区构造背景（a）、地震序列空间分布（b）及剖面上的投影（c）
Figure 1. Tectonic setting （a） of the epicentral area and spatial distribution （b） for Yunnan Yangbi MS6.4 earthquake sequence and its projection on profile （c）
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图 2 台站分布和P波垂向位移理论图（红线）与观测波形（黑线）的拟合情况（a）以及每2秒破裂快照（b）
Figure 2. Station distribution and the fitting of P-wave vertical displacement theoretical graph （red line） and observed waveform （black line） （a） and snapshot shown every 2 s （b）
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图 4 ∆CFS动态演化
图中百分数表示余震位于动态库仑破裂应力正值区域的比例
Figure 4. Dynamic evolution of ∆CFS
The percentage in the figure shows the proportion of aftershocks in the positive value area of dynamic Coulomb stress
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图 4 ∆CFS动态演化
图中百分数表示余震位于动态库仑破裂应力正值区域的比例
Figure 4. Dynamic evolution of ∆CFS
The percentage in the figure shows the proportion of aftershocks in the positive value area of dynamic Coulomb stress
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表 1 云南漾濞MS6.4地震震源参数
Table 1 Focal mechanism parameters of the Yunnan Yangbi MS6.4 earthquake
发震日期 震中位置 MW 深度/km 节面Ⅰ 节面Ⅱ 来源 年-月-日 北纬/° 东经/° 走向/° 倾角/° 滑动角/° 走向/° 倾角/° 滑动角/° 25.61 100.02 6.1 15.0 46 78 4 315 86 168 GCMT （2021） 2021-05-21 25.73 100.01 6.1 9.0 135 82 −165 43 75 −9 USGS （2021） 25.69 99.88 5.9 7.8 135 75 −168 42 78 −15 重定位（龙锋等，2021） 
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表 2 云南漾濞MS6.4地震震源附近地壳分层模型
Table 2 Crustal layered model near the seismic source of the Yunnan Yangbi MS6.4 earthquake
深度/km vP/（km·s−1） vS/（km·s−1） 地壳密度/（g·cm−3） QP QS 0 7.75 4.47 3.37 600 300 4 4.85 2.80 3.37 600 300 16 6.25 3.61 3.37 600 300 22 6.40 3.70 3.37 600 300
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表 3 主震对MS≥4.0余震应力触发情况
Table 3 The stress trigger of the main shock to MS≥4.0 aftershocks
地震序号 与主震震中的
距离/km开始变化
时间/s达到峰值
时间/s∆CFS峰值
/MPa趋于稳定
时间/s稳定值
/MPa应力触发 1 8.67 2.0 3.7 0.13 13 0.09 动态、静态应力触发 2 12.68 1.7 5.3 0.83 16 −0.001 动态应力触发 3 13.49 2.0 5.3 0.47 13 0.01 动态应力触发，静态应力可能触发 4 13.49 1.9 5.7 0.27 14 −0.02 动态应力触发 5 2.22 3.0 3.5 0.39 动态应力触发 6 1.00 1.8 8.4 0.50 12 0.48 动态、静态应力触发 7 8.98 2.0 7.4 0.12 11 0.09 动态、静态应力触发 8 11.17 5.0 7.5 0.18 13 0.02 动态应力触发，静态应力可能触发
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