Focal Mechanism and Focal Depth Determination of Yunnan Yangbi M_S5.1 and M_S4.8 Earthquakes in 2017
PAN Rui;JIANG Jinzhong;FU Hong;LI Jiao;Colledge of Resources,Environment and Geosciences,Yunnan University;Yunnan Earthquake Agency;
Since different earthquake research institutes provided different focal depths of the Yunnan Yangbi M_S5.1 and M_S4.8 earthquakes occurring on Mar.27,2017,we refine the focal depths and focal mechanisms of these two earthquakes by using the broadband earthquake waveforms recorded by Yunnan Seismic Networks and Sichuan Seismic Networks in Cut-and-Paste(CAP)inversions with three different velocity models. We also employ the sPn depth-phase to double-check the focal depths of the Yangbi M_S5.1 and M_S4.8 earthquakes. The results are as follows:①Owing to we used the broadband waveform of near-earthquakes with better azimuth coverage and the phase data of sPn depth,the obtained focal depths of the two earthquakes(5 km and 6 km)are more reliable. ②Based on the broadband waveforms recorded by more stations,the double-couple focal mechanisms we obtained from CAP inversions are consistent with the focal mechanisms provided by both the Global Centroid-Moment-Tensor(GCMT),but slightly better than the focal mechanism solution given by the Institute of Geophysics,China Earthquake Administration(CEA-IGP)based on limited stations on the day after the earthquake occurred. The focal mechanism solutions of five M≥ 3.0 aftershocks obtained by CAP method are basically consistent with that of the two earthquakes,which indicated that these earthquakes may occur in the same fault. ③According to the DD relocation results and distribution of the quaternary active faults in Yunnan area,we preliminarily infer that the middle-south segment of the Weixi-Qiaohou fault,i. e. the plane Ⅱ(312°/80°/166°)could be the seismogenic fault of the 2017 Yangbi M_S5.1 and M_S4.8 earthquakes.