地震研究

鉴于国内外地震研究机构给出的2017年云南漾濞MS4.8和MS5.1这2次地震的震源深度存在较大差异,利用云南和部分四川地震台网宽频带数字地震波形资料,采用CAP方法和3种不同速度模型对这2次地震进行震源机制解反演,并结合sPn深度震相对其震源深度进行了再次测定。结果表明:①由于利用了台站方位覆盖更好的近震宽频带波形和sPn深度震相数据,最终获得了2次地震的震源深度(5 km和6 km); ②基于更多台站记录的宽频带波形,利用CAP方法得到的双力偶震源机制解与Global CMT利用全球宽频带台站记录波形得到的反演结果更为一致,并且利用CAP方法得到5次M≥ 3.0余震事件的震源机制解与这2次地震的结果基本一致,表明这些地震事件可能发生于同一断层; ③经初步分析认为,2017年漾濞地震的发震断层可能是维西—乔后断裂中南段,即节面Ⅱ(312°/80°/166°)为真正的发震断层面。

Since different earthquake research institutes provided different focal depths of the Yunnan Yangbi MS5.1 and MS4.8 earthquakes occurring on Mar.27,2017,we refine the focal depths and focal mechanisms of these two earthquakes by using the broadband earthquake waveforms recorded by Yunnan Seismic Networks and Sichuan Seismic Networks in Cut-and-Paste(CAP)inversions with three different velocity models. We also employ the sPn depth-phase to double-check the focal depths of the Yangbi MS5.1 and MS4.8 earthquakes. The results are as follows:①Owing to we used the broadband waveform of near-earthquakes with better azimuth coverage and the phase data of sPn depth,the obtained focal depths of the two earthquakes(5 km and 6 km)are more reliable. ②Based on the broadband waveforms recorded by more stations,the double-couple focal mechanisms we obtained from CAP inversions are consistent with the focal mechanisms provided by both the Global Centroid-Moment-Tensor(GCMT),but slightly better than the focal mechanism solution given by the Institute of Geophysics,China Earthquake Administration(CEA-IGP)based on limited stations on the day after the earthquake occurred. The focal mechanism solutions of five M≥ 3.0 aftershocks obtained by CAP method are basically consistent with that of the two earthquakes,which indicated that these earthquakes may occur in the same fault. ③According to the DD relocation results and distribution of the quaternary active faults in Yunnan area,we preliminarily infer that the middle-south segment of the Weixi-Qiaohou fault,i. e. the plane II(312°/80°/166°)could be the seismogenic fault of the 2017 Yangbi MS5.1 and MS4.8 earthquakes.

引言
1 方法原理
2 利用CAP方法确定震源机制解及震源深度
3 利用sPn深度震相确定震源深度
4 讨论
5 结论

图1 单层地壳模型sPn传播路径<br/>Fig.1 The sPn propagation path in the single layer crust

图1 单层地壳模型sPn传播路径
Fig.1 The sPn propagation path in the single layer crust

图2 不同深度、不同震中距下的sPn和Pn震相理论走时差Δt(a),及Δt 的中值在不同震源深度下的拟合(b)<br/>Fig.2 Theoretical travel time difference Δt of sPn and Pn phases in different source depths and epicentral distances(a)and the fitting of median values of Δt in different source depths(b)

图2 不同深度、不同震中距下的sPn和Pn震相理论走时差Δt(a),及Δt 的中值在不同震源深度下的拟合(b)
Fig.2 Theoretical travel time difference Δt of sPn and Pn phases in different source depths and epicentral distances(a)and the fitting of median values of Δt in different source depths(b)

图3 研究区断裂、台站以及漾濞及附近地震的分布图<br/>Fig.3 Distribution of the faults,stations and epicentres of Yangbi earthquakes in the study area

图3 研究区断裂、台站以及漾濞及附近地震的分布图
Fig.3 Distribution of the faults,stations and epicentres of Yangbi earthquakes in the study area

图4 用于CAP反演的3个P波(实线)、S波(虚线)速度模型<br/>Fig.4 Three P-wave(solid lines)and S-wave(dashed lines)velocity models used in our CAP inversions

图4 用于CAP反演的3个P波(实线)、S波(虚线)速度模型
Fig.4 Three P-wave(solid lines)and S-wave(dashed lines)velocity models used in our CAP inversions

表1 利用3种速度模型反演漾濞2次地震震源机制解及震源深度<br/>Tab.1 Focal mechanisms and focal depths of the Yangbi MS5.1 and MS4.8 earthquakes inverted by 3 velocity models

表1 利用3种速度模型反演漾濞2次地震震源机制解及震源深度
Tab.1 Focal mechanisms and focal depths of the Yangbi MS5.1 and MS4.8 earthquakes inverted by 3 velocity models

图5 利用3种速度模型反演漾濞MS5.1(a)和MS4.8(b)地震震源深度拟合误差图<br/>Fig.5 Focal depths fitting errors of the Yangbi MS5.1(a)and MS4.8(b)earthquakes inverted by using three velocity models

图5 利用3种速度模型反演漾濞MS5.1(a)和MS4.8(b)地震震源深度拟合误差图
Fig.5 Focal depths fitting errors of the Yangbi MS5.1(a)and MS4.8(b)earthquakes inverted by using three velocity models

表2 不同机构给出的漾濞2次地震的震源机制解及震源深度<br/>Tab.2 Focal mechanisms and focal depths of Yangbi MS5.1 and MS4.8 earthquakes provided by different institutes

表2 不同机构给出的漾濞2次地震的震源机制解及震源深度
Tab.2 Focal mechanisms and focal depths of Yangbi MS5.1 and MS4.8 earthquakes provided by different institutes

图6 采用2号模型反演得到震源深度为6 km时漾濞MS5.1地震观测波形(黑线)及理论波形(红线)对比图<br/>Fig.6 Comparison between observed(black line)and synthetic(red line)seismograms at 6.0 km depth for the Yangbi MS5.1 earthquake by using No.2 model

图6 采用2号模型反演得到震源深度为6 km时漾濞MS5.1地震观测波形(黑线)及理论波形(红线)对比图
Fig.6 Comparison between observed(black line)and synthetic(red line)seismograms at 6.0 km depth for the Yangbi MS5.1 earthquake by using No.2 model

表3 利用2号速度模型反演5次M≥3.0余震的震源机制解及深度<br/>Tab.3 Focal mechanisms and depths of the M≥3.0 aftershocks by using No.2 velocity model

表3 利用2号速度模型反演5次M≥3.0余震的震源机制解及深度
Tab.3 Focal mechanisms and depths of the M≥3.0 aftershocks by using No.2 velocity model

图7 不同台站记录到的漾濞MS4.8地震(a)MS5.1地震(b)Pn及sPn震相<br/>Fig.7 The Pn and sPn phases of Yangbi MS4.8(a)and MS5.1(b)earthquakes recorded by different stations

图7 不同台站记录到的漾濞MS4.8地震(a)MS5.1地震(b)Pn及sPn震相
Fig.7 The Pn and sPn phases of Yangbi MS4.8(a)and MS5.1(b)earthquakes recorded by different stations

图8 漾濞地震序列双差精定位震中、定位台站及主要断裂分布(a),虚线方框放大后的震中分布(b)<br/>Fig.8 Epicentral distribution of the Yangbi earthquake sequence after Double-difference relocation,stations,distribution of main faults(a)and epicental distribution in dotted fram(b)

图8 漾濞地震序列双差精定位震中、定位台站及主要断裂分布(a),虚线方框放大后的震中分布(b)
Fig.8 Epicentral distribution of the Yangbi earthquake sequence after Double-difference relocation,stations,distribution of main faults(a)and epicental distribution in dotted fram(b)

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备注

引言

1 方法原理

2 利用CAP方法确定震源机制解及震源深度

3 利用sPn深度震相确定震源深度

4 讨论

5 结论

期刊信息