Seismogenic structure of the Qingshiling, Gaizhou, earthquake swarm

Using double difference earthquake location algorithm, we relocated the Qingshiling earthquake swarm which lasted from February 2012 to August 2015. We also obtained the earthquake focal mechanism solutions of the swarm by cut and paste (CAP) method and the P-wave first motion method, and then according to the seismo-geological conditions, we discussed the seismogenic structure of the sequence. The results demonstrated that the distribution direction of the relocated earthquakes is NW, and the earthquakes of the swarm mainly distributed in a scope of 6 km×3 km with the focal depths varied from 7 km to 10 km. The strike of some large earthquakes coincided with the predominant distribution direction of the relocated swarm. Based on double difference results, focal mechanisms and local geological conditions, we preliminarily surmised that there lies a listric secondary normal fault of NW trending to the northwest side of the Jiuzhai-Gaixianbei fault, and Qingshiling earthquake swarm may be caused by that listric normal fault which is controlled by continuous left-lateral strike slip motion under regional stress field.