Relocation and seismogenic structure analysis of the M_S5.5 Ninglang earthquake sequence on January 2，2022

On January 2, 2022, a M_S5.5 earthquake occurred in the Ninglang County, Lijiang City, Yunnan Province. Using the P and S phase arrival data of this M_S5.5 earthquake provided by the Seismic Catalogue System, the high-precision relative positions of 694 earthquakes in Ninglang M_S5.5 earthquake sequence are obtained by using the double difference relocation algorithm. In general, the relocations reveal a 11 km-long, linear NNE−NS seismicity trend concentrating in the 4—11 km depth range, which is consistent with the NNE nodal plane （191°） of the mainshock focal mechanism solution. The mainshock is located in the southern segment of the earthquake sequence. The earthquake sequence shows two groups of active branches with different tendencies on the depth profiles, in which the east branch is consistent with the dip angle of the nodal plane Ⅱ （81°） of the mainshock focal mechanism solution. In addition, the earthquake may have triggered local fault activity in the adjacent area. According to the comprehensive analysis, the seismogenic structure of the M_S5.5 Ninglang earthquake sequence should be a NNE−NS trending left-lateral strike-slip fault, with normal component, and the fault plane dips to the WNW at 81° angle. The properties of the seismogenic fault are not completely consistent with any mapped faults in this area. Although the M_S5.5 Ninglang earthquake sequence is located to the north of the M_S5.7 Ninglang-Yanyuan earthquake sequence in 2012, they have different seismogenic structures. The result of Coulomb failure stress shows that the M_S5.7 Ninglang-Yanyuan earthquake in 2012 promoted the occurrence of the M_S5.5 Ninglang earthquake.