2021-09-29宁夏中宁M_(L)3.6地震震源参数测定

Source Parameters Determination of the Zhongning M_(L)3.6 Earthquake in Ningxia on September 29,2021

基于宁夏区域地震台网资料,采用初至P震相定位法测定2021-09-29中宁M_(L)3.6地震震源深度,同时利用gCAP反演方法测定该地震震源机制解及矩张量解,然后根据震源机制与应力场模拟方法计算现今应力场体系在中宁M_(L)3.6地震震源机制两个节面的相对剪应力和正应力。结果表明,初至P震相定位法和gCAP方法测定的中宁M_(L)3.6地震震源深度均为11 km,震源机制节面Ⅰ走向242°、倾角63°、滑动角8°,节面Ⅱ走向148°、倾角83°、滑动角153°,矩张量解结果表明该地震的双力偶成分占全矩张量解的97.07%,表明该地震为天然地震。结合震中附近2009年以来M_(L)1.0以上地震重定位后的空间分布、区域地质构造和相对剪应力等分析推测,中宁M_(L)3.6地震发震断层可能与天景山断裂东南段附近NNW向断裂薄弱带有关,该地震是在青藏高原东北缘NE向挤压作用下,沿着NNW向断裂剪切滑动引起的一次右旋走滑型地震事件。

Based on the data from Ningxia regional seismic network,we determine the focal depth of the Zhongning M_(L)3.6 earthquake using the first arrival P phase locating method,and the focal mechanism and moment tensor solution of the earthquake using gCAP inversion method.Then,using the simulation method of focal mechanisms and stress field,we calculate the relative shear stress and normal stress on the two nodal planes of focal mechanism of the Zhongning M_(L)3.6 earthquake under current stress systems.The results show that the focal depth of the Zhongning M_(L)3.6 earthquake measured by the first arrival P phase locating method and gCAP method are both 11 km.The focal mechanism of the earthquake is strike 242°,dip 63°,rake 8°for nodal planeⅠ,and strike 148°,dip 83°,rake 153°for nodal planeⅡ.The moment tensor result reveals that double couple component of the earthquake accounts for 97.07%of total moment tensor solution,indicating that the earthquake is a natural earthquake.Combined with spatial distribution of relocation of M_(L)≥1.0 earthquakes from 2009 near the epicentre,regional geological structure,and relative shear stress,we conclude that the seismogenic fault of the Zhongning M L3.6 earthquake may be related to the NNW trending weak fault zone near the southeast segment of Tianjingshan fault.Under the NE direction compression of the northeastern Tibetan plateau,the earthquake is a right-lateral strike-slip seismic event caused by shear slip along NNW direction fault.