Abstract:Based on dense array data in northwest Yunnan, using absolute positioning combined with the relative positioning method, we relocate the foreshocks, main shock, and aftershocks of the Yangbi M6.4 earthquake sequence. Simultaneously, we use the CAP full waveform inversion method to obtain the focal mechanism solution and centroid depth of M≥5.0 earthquakes. Combined with the accurate positioning results of the earthquake sequence, we analyze the Yangbi M6.4 earthquake. The results show that the Yangbi earthquake sequence presents a NW distribution with a length of 25~30 km and a width of about 5 km. The main shock is at the northern end of the whole sequence, and aftershocks are concentrated in the north. The moment magnitude of Yangbi M6.4 main shock is MW6.03, the centroid depth is 5.8 km, and the strike, dip, slip angle of the nodal plane Ⅱ is 133°, 75°, -164°, respectively, which is consistent with the NW-SE direction of earthquake sequence. Both the focal mechanism solution and focal depth profile of M≥5.0 earthquakes show high dip angles, and there is a slowing trend from northwest to southeast. The M6.4 earthquake has the characteristics of unilateral rupture on the southeast side, and the nodal plane Ⅱ is the seismogenic fault plane. The Yangbi M6.4 earthquake is a right-lateral strike-slip earthquake with NW-trending high-dip. Its seismogenic structure is a northwest-trending hidden fault or a secondary fault on the west side of the Weixi-Qiaohou-Weishan fault zone. The fault may not be completely parallel to the Weixi-Qiaohou fault zone, and there is a certain angle.
LI Jian,CHEN Jia,JIN Mingpei et al. Focal Mechanism Solutions and Structural Characteristics of M≥5.0 in the Yangbi M6.4 Earthquake Sequence[J]. jgg, 2022, 42(7): 680-686.