Study of the Songyuan, Jilin, earthquake sequence in 2017−2018

Using the master event relative location method, the earthquakes near the Songyuan M_S5.7 earthquake occurred from 18 July 2017 to 15 July 2018 have been relocated. The Song-yuan earthquake sequence was analyzed. The results show that: ① The rupture plane for the Songyuan M_S5.7 earthquake strikes south-west direction with deep angle and dips to north-west, nearly upright. ② Most of earthquakes are located above the main shock. There are very few earthquakes with the focal depth greater than that of the main shock. ③ The focal depths of the earthquakes increase with time prior to the main shock and decrease with time after the main shock. According to the above results, combining with tectonic conditions and focal mechanisms, we can infer that the rupture surface of the Songyuan M_S5.7 earthquake strikes NE−SW, and a blind fault with a strike of NE−SW could be the seismogenic fault.