Abstract:According to Chinese seismological station net determination, a MS6.4 earthquake occurred at 01:13, Beijing time on Jan. 21, 2016 in Menyuan county of Qinghai province. By the end of Feb. 11, 475 aftershocks of ML ≥ 1.0 had occurred in the seismic region of the Menyuan 6.4 earthquake, including 4.0~4.9 level 1 and 3.0~3.9 level 17 times. The largest magnitude of ML4.4 occurred at 01:18 on Jan 21, and the Menyuan earthquake caused heavy economic losses. The CAP method is one entire profile inversion method, its inversion result has an advantages of relatively small merit which relies on the speed model and the earth's crust lateral change. The core idea is as follows:we split the seismic broadband waveform data into Pnl and surface wave parts, calculate the objective error function of the observed and the theoretical seismograms, perform the grid search in the assigned parameter space, and search the focal mechanism and the focal centroid depth of the two global minimum variances. In the paper, using the wave data from "the fifth" Seismological Network of Gansu province and Qinghai province, we adopted the CAP method to obtain the focal mechanism of the 6.4 earthquake occurred at Menyuan on Jan. 21, 2016. The results show that the focal character of the earthquake is thrust, MW 5.9 and the focal depth of the event is 9 km. The nodal plane I parameters of the best double-couple are strike 339°, dip 49°, and rake 111°, respectively. The strike of the nodal plane is the same trend with the strike of the Lenglongling fault; the characteristics of the dip are according to the properties of the Lenglongling fault. The nodal plane has been identified to be representative of the seismogenic fault plane. Analysis considers that the occurrence of Menyuan 6.4 earthquake has osculating correlation with the activity of the fault.
