河南淅川2019年M_L 4.2地震与2018年M_L 4.6地震对比分析

2019年11月30日河南淅川发生M_(L )4.2地震，是淅川区域自2018年2月9日M_(L )4.6地震以来发生的又一次显著地震事件，采用Snoke方法，计算2次地震的震源机制解，结果显示，2次地震震源错动类型均表现为走滑兼正断，其中M_(L )4.6地震节面I性质与新野断裂破裂特征及切错方式符合，而M_(L )4.2地震不符合，可能与附近隐伏未命名的走向NNW、倾向S的左旋正断层有关；采用震源谱进行拟合计算，得到淅川M_(L )4.2地震应力降为0.879 MPa，与淅川M_(L )4.6地震应力降0.24 MPa相比，地震应力释放更充分；2次地震震中均位于丹江口水库库区，分析发现，2次地震均发生在水库蓄水位下降阶段，初步认为，地震的发生与水库蓄放水有关。

Comparative analysis of the 2019 Xichuan ML 4.2 earthquake and the 2018 Xichuan ML 4.6 earthquake in Henan Province

An M_L 4.2 earthquake occurred in Xichuan on November 30, 2019, which is a significant earthquake after the M_L 4.6 earthquake that occurred on February 9, 2018, in the Xichuan area. We calculated the focal mechanism solutions for the two earthquakes by using the Snoke method. The result shows that the source rupture types of the two earthquakes are both strike-slip with normal fault. The focal mechanism solution for the Xichuan M_L 4.6 earthquake is consistent with the fracture features and cutting modes of the Xinye fault, which is the nearest one to the epicenter; however, the focal mechanism solution for the Xichuan M_L 4.2 earthquake is not, which may be related to the hidden unnamed left lateral normal fault that has an NNW strike and a southward dip. Using the method of source spectrum fitting, we calculated the stress drop for the Xichuan M_L 4.2 earthquake to be 0.879 MPa, which indicates a more sufficient stress release than that of the Xichuan M_L 4.6 earthquake. The epicenters of the two earthquakes are located in the Danjiangkou reservoir area. It is found that both earthquakes occurred in the stage of reservoir water level decline. It is preliminarily considered that the occurrence of earthquakes is related to reservoir water storage and release.