2020年6月9日中卫M_(L)3.4地震的震源机制及其中心解的测定

Determination on the focal mechanism and central focal mechanism of Zhongwei M_(L)3.4 earthquake on June 9,2020

2020年6月9日宁夏中卫市沙坡头区发生M_(L)3.4地震,该地震发生在1709年中卫南7½级地震的极震区内,且震中位于以往弱震相对偏少的地区。本文利用宁夏区域地震台网的波形记录,采用gCAP方法反演了2020年6月9日中卫ML3.4地震的震源机制解及震源矩心深度,并用Hash方法计算其震源机制解,且得出了两种方法的震源机制中心解。结果表明,gCAP方法的震源机制解为:节面I走向255°,倾角79°,滑动角−20°;节面II走向348°,倾角70°,滑动角−168°,震源矩心深度为12 km。而Hash方法的震源机制解为:节面I走向344°,倾角89°,滑动角176°;节面II走向74°,倾角86°,滑动角1°。两种方法的震源机制中心解为:节面I走向255°,倾角87°,滑动角−11°;节面II走向346°,倾角80°,滑动角−176°,主压应力轴走向主要为NE向,其中gCAP方法结果与震源机制中心解的最小空间旋转角相对最小,为12.09°。结合过去地质构造资料,推测2020年6月9日中卫M_(L)3.4地震的主要错动方式为左旋走滑,且断层面为NEE向节面的可能性较大。

On June 9,2020,an earthquake measuring M_(L)3.4 occurred in Shapotou District,Zhongwei City,Ningxia.The earthquake occurred in the meizoseismal area of the 1709 M7½earthquake of South Zhongwei,and its epicenter is located in an area where there were relatively few weak earthquakes in the past.In this paper,based on the waveform records of the Ningxia regional seismic network,the focal mechanism solution and focal centroid depth of the Zhongwei ML3.4 earthquake on June 9,2020 are inversed using the gCAP method.The focal mechanism solution is also calculated by the Hash method,and the central focal mechanism of these two methods is obtained.The result shows that the focal mechanism solution of gCAP method is strike 255°,dip 79°,rake−20°for nodal plane I,and strike 348°,dip 70°,rake−160°for nodal plane II,and the centroid depth is 12 km,and that the focal mechanism solution of Hash method is strike 344°,dip 89°,rake 176°for nodal plane I,and strike 74°,dip 86°,rake 1°for nodal plane II.The central focal mechanism solution of the two methods is strike 255°,dip 87°,rake−11°for nodal plane I,and strike 346°,dip 80°,rake−176°for nodal plane II,and the principal stress axis is mainly in NE direction.The minimum 3-D rotation angle between the gCAP method result and the central focal mechanism is relative small,which is 12.09°.Combing the past geologic structure data,we deduces that the main dislocation of Zhongwei M_(L)3.4 earthquake on June 9,2020 is the left-lateral slip,and that the fault is more likely to belong to the nodal plane in NEE direction.