玛曲M_(S)4.4地震震源机制解及其构造意义探讨

Focal mechanism solution of the Maqu M_(S)4.4 earthquake and associated tectonic significance

2021年5月22日青海省玛多县发生M_(S)7.4地震,数小时后在距离震中两百多公里的甘肃玛曲县发生了M_(S)4.4地震。利用甘肃、青海和四川区域测震台网记录的三分向宽频带数字波形资料,反演甘肃玛曲M_(S)4.4地震的震源机制解,结果显示此次地震活动面走向、倾角和滑动角分别为105.6°、74.1°和-38.7°。参考玛多M_(S)7.4地震的震源机制解,发现两次地震震源机制解具有较好的一致性,均呈现明显的左旋走滑特征。静态库伦破裂应力改变量分布计算结果表明,玛曲M_(S)4.4地震震中位置单位面积(m2)受到来自玛多地震震中方向的拉应力约为0.02 MPa。综合两次地震的震中距、发震时刻和断层分布等情况,初步判断甘肃玛曲M_(S)4.4地震应为青海玛多M_(S)7.4强震的一次触发地震。

On May 22,2021,an M_(S)7.4 earthquake occurred in Maduo County,Qinghai Province.A few hours later,an M_(S)4.4 earthquake occurred in Maqu County,Gansu Province,200 kilometers away from the epicenter.In this paper,the focal mechanism solution of the Maqu M_(S)4.4 earthquake was inverted by using the data of three-component broadband digital waveform recorded by regional seismic networks in Gansu,Qinghai,and Sichuan Province.The results showed that the strike,dip,and slip angle of the seismic plane are 105.6°,74.1°,and-38.7°,respectively.Referring to the focal mechanism solution of the Maduo M_(S)7.4 earthquake,it is found that the focal mechanism solutions of the two earthquakes are in good agreement,showing obvious characteristics of left-lateral strike-slip.The calculation results of static Coulomb failure stress showed that the tensile stress on the unit area(m2)of the epicenter of the Maqu M_(S)4.4 earthquake from the epicenter direction of the Maduo earthquake is about 0.2 bar(≈0.02 MPa).Based on the epicentral distance,occurrence time and fault distribution of the two earthquakes,it is preliminarily determined that the Maqu M_(S)4.4 earthquake should be a triggered earthquake of the Maduo M_(S)7.4 earthquake in Qinghai Province.