Abstract: The Changqing M_S4.1 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_S4.1 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_W4.2 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_S4.1 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_S4.1 earthquake and its aftershocks.

Key words: Double-difference location, CAP method, Focal mechanism, Seismogenic structure, 2020 Changqing M_S4.1 earthquake