2020年2月18日长清M_(S)4.1地震发震构造研究

Study on the Seismotectonics of the M_(S)4.1 Changqing Earthquake on 18 February,2020

本文利用基于波形互相关的双差定位方法对2020年2月18日长清M_(S)4.1地震序列进行了精定位计算,共得到33个地震事件的精定位结果。结果显示,地震序列主要沿NW向分布,在水平方向上具有自NW向SE迁移,在深度上具有由浅向深迁移的特征;序列震源深度主要集中在2~7 km,其中,主震的震源深度约2.8 km。由于长清地震序列的地震数量较少,为了更准确地了解长清地震序列的发震构造、探索该序列的发生和发展过程,本文采用CAP方法反演了主震的震源机制解,其中,节面Ⅰ走向223°、倾角42°、滑动角-160°,节面Ⅱ走向117.9°、倾角76.8°、滑动角-49.8°,最佳拟合震源矩心深度约2.8 km,矩震级M_(S)4.2。结合区域构造特征分析认为,长清M_(S)4.1地震的发震断裂为孝里铺断裂和东阿断裂之间发育的一条浅层次生断裂。在ENE向区域应力场作用下,发震断裂产生高角度正断滑动,并伴有左旋走滑分量,从而引发长清地震序列。

The Changqing M_(S)4.1 earthquake and its aftershocks have been precisely relocated by the double-difference earthquake location method in this paper, and the accurate locations of 33 events have been obtained. The results show that the earthquakes are mainly distributed along the NW direction, with the characteristics of migrating from NW to SE in the horizontal direction and from shallow to deep in depth direction. The focal depth are mainly concentrated in 2~7 km, and the main shock is about 2.8 km depth. In order to more accurately understand the seismogenic structure, we also inverted the focal mechanism of the M_(S)4.1 earthquake with the “Cut and Paste”(CAP) method. The best double couple solution of the mainshock shows that the best-fit moment magnitude and focal depth are M_(S)4.2 and 2.8 km respectively. Nodal plane Ⅰ of the focal mechanism is 223°, 42° and-160° for strike, dip and rake angle respectively, while Nodal plane Ⅱ is 117.9°, 76.8° and-49.8°. According to the distribution of earthquakes and the focal mechanism, combining with the regional structural characteristics, it suggests that the seismogenic fault of the Changqing M_(S)4.1 earthquake is a shallow secondary fault developed between the xiaolipu fault and the dong’a fault. Under the action of regional stress field in ENE direction, the seismogenic fault produce a high angle, normal-slip with left strike-slip dislocation which lead to the Changqing M_(S)4.1 earthquake and its aftershocks.