Relocations and focal mechanism solutions characteristics of 2012 Yiliang M_S5.7 and M_S5.6 earthquake sequence

Based on the recordings of 17 portable seismographs of ChinArray deployed in Yunnan-Guizhou region, the Yiliang M_S5.7 and M_S5.6 earthquakes happened on September 7, 2012 and the aftershocks with M_L≥1.0 were relocated by double-difference hypocenter location algorithm (hypoDD), and then the focal mechanism solutions of earthquakes (M_S≥4.0) were determined by CAP (cut and paste) method. Our results show that the Yiliang M_S5.7 mainshock is located at (27.509°N, 103.971°E) with initial rupture depth of 9.7 km. The best double-couple solutions for the Yiliang M_S5.7 earthquake have one nodal plane with strike 251°, dip 66°, rake 150°, and another plane with strike 354°, dip 63° and rake 27°. The Yiliang M_S5.6 mainshock is relocated at (27.563°N, 104.034°E) with initial rupture depth of 10.0 km, and the mechanism solutions of two nodal planes are 235°, 39°, 147° and 352°, 70°, 56°, respectively. The fault geometry, aftershock distribution characteristics, focal mechanism solutions and the tectonic stress field are in good consistency. Combining with the characteristic of fault kinematic, seismicity and the geological structure, we infer that Yiliang M_S5.7 and M_S5.6 earthquakes occurred on the NE-striking Shimen fault which is the leading edge of Zhaotong fracture. The shallow focal depth of Yiliang earthquake and the energy release occurred in shallow crust are the major reasons for serious damage in the hypocentral region.