Seismogenic structure identification of the 2013 Eryuan MS5.5 and MS5.0 earthquake sequence
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摘要: 采用Hypo2000和双差定位方法对2013年云南洱源MS5.5和MS5.0地震序列进行了重新定位. 结果显示: 精定位后洱源地震序列分布优势方向集中在160°； 用CAP方法反演了两次5级地震震源机制， 节面Ⅱ的走向158°和157°与余震优势分布方向一致； 现场考察MS5.5和MS5.0地震极震区的长轴方向也是NW向. 上述结果与维西—乔后断裂NNW走向一致， 据此判定该断裂为洱源MS5.5和MS5.0地震的发震构造. 序列震源机制解显示， 洱源地震序列表现出不同的错断性质以及不同方向主压应力， 可能与维西—乔后断裂所处区域复杂构造应力场有关.Abstract: The Eryuan MS5.5 and MS5.0 earthquake sequence are relocated by using absolute location (Hypo2000) and double-difference earthquake location (HypoDD) methods. The results show that the dominant direction of relocated aftershocks concentrated at 160°. Focal mechanisms of the MS5.5 and MS5.0 earthquakes are inverted by CAP method. The inversion result shows that the strike angles of the nodal plane Ⅱ were 158° and 157°, respectively, which are consistent with dominant distribution direction of aftershocks. Field survey suggests that the major axis of the meizoseismal region was also in NW direction. The above three directions were consistent with the NNW strike orientation of Weixi--Qiaohou fault, which can be considered as the seismogenic structure of the Eryuan earthquake sequence. Focal mechanisms of the sequence indicate that different focal dislocations and different orientations of principal compression stresses, may have relationship with the complex regional structural stress field of Weixi--Qiaohou fault.
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图 1 洱源地震序列M-t图(a)、 目录完整性分析(b)和精定位前序列震中分布图(c)
图(a)中横坐标为距离2013年3月3日洱源MS5.5地震天数； 图(b)中正方形为累计 频度，斜线为累计频度-震级最大似然法拟合曲线； 图(c)中红色圆为3月3日洱源 MS5.5及其后续地震，蓝色圆为4月17日洱源MS5.0及其后续地震
Figure 1. M-t diagram of Eryuan earthquake sequence; (b) Completeness of earthquake catalogues; (c) Epicentral distribution of Eryuan sequence before accurate location
The x-axis in Fig.(a) means the days from Eryuan MS5.5 earthquake on March 3, 2013; squares in Fig.(b) are accumulative frequency, the black line is accumulative frequency-magnitude fitting curve using maximum likelihood method; in Fig.(c) red circles are the epicenters of MS5.5 and its following shocks, blue circles are those of MS5.0 and its following shocks
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图 2 精定位后洱源地震序列(a)和震中分布(b)图
实心圆表示余震震中，红色星表示主震震中位置． 色标表示距离两次5级地震发震时刻 的时间差． AB为沿着维西—乔后断裂的剖面，CD为垂直于该断裂的剖面
Figure 2. The epicentral distribution of the Eryuan earthquake sequence after accurate location
Solid circles denote epicenters of aftershocks; red stars mean epicenters of the main shocks; the color scale represents the difference of occurrence times between two main shocks. AB is the section along the Weixi-Qiaohou fault， and CD is the section perpendicular to the fault
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图 3 震源深度沿AB剖面(a)与CD剖面(b)的分布
实心圆表示余震震中， 星号表示两次5级地震震中， 其余图注同图2
Figure 3. Focal depths along the sections AB, CD
Solid circles denote epicenters of aftershocks; stars denote the epicenters of two main shocks; the other legends are the same as those in Fig.2
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图 4 洱源MS5.5地震震源机制解反演中的误差-深度分布图
Figure 4. Misfit error as a function of depth in the focal mechanism inversion of the Eryuan MS5.5 earthquake
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图 5 洱源MS5.5地震的理论地震波形(红色)与实际观测地震波形(黑色)
波形下面第一行数字为理论地震图相对观测地震图的移动时间； 第二行数字为二者的相关系数； 波形 左侧的字母和数字分别为台站名称和震中距(km); 图中V表示垂直向，R表示径向，T表示切向
Figure 5. Comparison between synthetic (red) and observed (black) seismograms of Eryuan MS5.5 earthquake
Numbers in the first line below the waveform curves are the time shifts(in unit of s)between the two kinds of seismograms， and those in the second lines are correlation coefficients of the theoretical and observed seismograms; station’s symbol and its distance are given on the left of each line of the waveforms，respectively
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图 6 洱源地震序列12次ML≥2.9地震震源机制解
蓝色表示洱源MS5.5地震及其余震， 酒红色表示洱源MS5.0地震及其余震
Figure 6. Focal mechanism solutions of 12 ML≥2.9 Eryuan earthquakes
Blue circles denote epicenters of MS5.5 and its aftershocks; wine red circles denote epicenters of MS5.0 and its aftershocks
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图 7 2013年洱源地震序列主震位置及其震源机制解、 烈度及台站分布图
① 维西—乔后断裂； ② 红河断裂； ③ 程海断裂； ④ 龙蟠—乔后断裂； ⑤ 澜沧江断裂； ⑥ 怒江断裂
Figure 7. Distribution of 2013 Eryuan main shocks，focal mechanism solutions， seismic intensity and seismographic stations
① Weixi-Qiaohou fault; ② Honghe fault; ③ Chenghai fault; ④ Longpan-Qiaohou fault; ⑤ Lancangjiang fault; ⑥ Nujiang fault
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图 8 洱源地震序列优势分布方位(a)和确定序列余震优势分布方位示意图(b)
星号为示意性的主震位置，θ含义参见正文
Figure 8. The dominant distribution orientation of Eryuan earthquake sequence(a) and schematic diagram for determination of the sequence dominant distribution orientation(b)
The star denotes the main shock location，the meaning of θ can be found in this paper
表 1 本文与GCMT、 CEA-IGP得到的震源机制解比较
Table 1 A comparison among focal mechanism solutions from this study, GCMT and CEA-IGP
下载: 导出CSV
表 3 2013年洱源地震序列震源机制解
Table 3 Focal mechanism solutions of Eryuan earthquake sequences in 2013
下载: 导出CSV
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