Characteristics of seismogenic faults and stress fields of the Songyuan M_S5.7 earthquake sequence in May 2018

In recent years, moderate-strong earthquakes in Songyuan area of Jilin Province are active. Studying the fault structure and stress field characteristics of the earthquake sequence in Songyuan area is of great significance for scientific understanding of the earthquake-preserving environment in Northeast China and earthquake prevention. The M_L≥1.0 earthquakes are relocated by the method of double difference relocation, the focal mechanism solutions of the strong earthquakes are determined by the CAP method, and the stress field is determined by the FMSI method.According to the results, we realize that: ① The Songyuan M_S5.7 earthquake sequence occurred at the intersection of the Second Songhuajiang fault trending NW and Fuyu-Zhaodong fault trending NE. The results of earthquakes relocation are analyzed along the two faults. The length of the NW axis is about 5 km, the same as to NE axis. The epicenters on the profile of NW axis have a high inclination distribution, while the NE axis is uniform. ② The focal mechanism solutions of four M_L≥3.7 earthquakes are all of strike-slip type with high dip angles and good consistency: The strike of nodal plane Ⅰ is NE, and the other is NW. The focal mechanisms of the moderate-strong earthquakes are basically consistent with the Second Songhuajiang fault, and it is concluded that the Second Songhuajiang fault is the seismogenic fault of the Songyuan M_S5.7 earthquake; ③ The principal compressive stress azimuth and the inclination angle of Songyuan area are N86°E and 7°, respectively, and the principal tensile stress azimuth and the inclination angle are N24°E and 71°, respectively. The regional stress field in Songyuan area is controlled by both large-scale plate tectonic movement and regional tectonic movement. Under the westward subduction of the Pacific Plate, the Northeast Asia Plate’s principal compressive stress near the EW direction is generated, which is controlled by the surrounding geological structure. The strike-slip type earthquake is prone to occur at the intersection of the NE-trending fault and the NW-trending fault in the Songliao basin, while the 2018 Songyuan M_S5.7 earthquake is a moderate-strong earthquake that occurred under the control of such tectonic action.