Microseismic detection and relocation of the 2017 M_S4.8 and M_S5.1 Yangbi earthquake sequence，Yunnan

Based on the earthquake catalog and waveforms of 2017 M_S4.8 and M_S5.1 Yangbi earthquake sequence recorded by Yunnan Seismic Network, we relocate 258 earthquakes occurring one week before and one month after the Yangbi M_S5.1 mainshock by simultaneously using P- and S-wave travel times and waveform cross-correlation data in the double-difference relocation. We then use the 258 earthquakes as template events and scan through the continuous waveforms to search for weak events by using the match and locate method. Using our new catalog, we preliminarily analyze the spatio-temporal evolution characteristics of Yangbi earthquake sequence. We obtain refined hypocenters of 193 earthquakes with location errors of about 1.3 km in the horizontal direction and 1.9 km in the depth, respectively. According to the double-difference relocation and focal mechanisms of the mainshock and early M_L≥3.0 aftershocks, we preliminarily conclude that the middle-south segment of the Weixi-Qiaohou fault may account for the occurrence of the M_S5.1 Yangbi earthquake. A total of 1 625 events are detected by 258 template events, which is about six times as many as the events of Yangbi earthquake sequence listed in the Yunnan Seismic Network catalog. And the detected events are mainly the early aftershocks and M_L≤0 micro events. By comparison with the 2016 M_S5.0 Yunlong earthquake, we conclude that less number and faster decay of aftershocks may be the main difference between the multiple mainshock type of sequence and the mainshock-aftershock type of sequence.