2021年青海玛多MS7.4地震序列精定位与震源机制研究

利用双差定位法对2021年5月22日玛多M_S7.4地震序列中1 434个地震进行重新定位,使用TDMT矩张量反演方法求解玛多地震序列M≥4.5地震的震源机制解,综合分析得到如下结论:(1)玛多地震序列震中整体走向为NWW-SEE向,与昆仑山口—江错断裂展布方向相吻合,序列总长度170 km,呈NWW向和SEE向双侧破裂,主震西北侧存在NW向条带,可能是此次地震的分支断裂活动,在南东侧存在余震稀疏段以及横穿玛多—甘德断裂的余震分布带,推测可能是地下速度结构差异所致;(2)主震附近地震序列以左旋走滑型地震为主,优势走向为NWW向,倾向NE,倾角较高,与昆仑山口—江错断裂性质基本一致,结合余震定位结果推断昆仑山口—江错断裂为本次地震的发震断层;(3)主震附近地震序列P轴平均方位角为237°,P轴,T轴平均倾角分别为15°、16°,N轴平均倾角为65°,结合研究区构造特征推断,本次地震是由NEE-SWW向水平挤压应力推动NWW-SEE向断裂发生左旋走滑错动所致。

Precise location and focal mechanism solutions of the 2021 Maduo,Qinghai MS7.4 earthquake sequence

In this paper,1434 earthquakes of the Maduo M_S7.4 earthquake sequence on May 22,2021 were relocated using the double-difference location method,and the focal mechanism solutions of M≥4.5 earthquakes were also obtained by TDMT inversion method.Through a comprehensive analysis,following conclusions were obtained:(1)The overall trend of the Maduo earthquake sequence is NWW-SEE,which is consistent with the orientation of Kunlun Pass-Jiangcuo fault.There is a NW-trending band on the northwest side of the main shock,and a sparse segment of aftershocks and a distribution zone across the Maduo-Gande fault on the southeast side,which may be caused by the difference of underground velocity structure.(2)The seismic sequence is mainly left-lateral strike-slip type,with the dominant direction of NWW,NE tendency,and high dip angle.Combined with the aftershock positioning results,it is inferred that the Kunlun Pass-Jiangcuo fault is the seismogenic fault of this earthquake.(3)The average azimuth of P axis near the main shock is 237°;the average dip angles of P axis and T axis are 15°and 16°,respectively;the average dip angle of N axis is 65°.Combined with the structural characteristics of the study area,it is inferred that the earthquake is caused by the left-lateral strike-slip dislocation of the NWW-SEE trending fault driven by the NEE-SWW horizontal compressive stress.