Abstract: Menyuan M_S6.4 earthquake occurred on 21 January 2016 in Menyuan County of Qinghai Province. We collected all GPS data during the period from 1999 to 2015 in the seismic source area and its vicinity, and estimated GPS velocity field by the weighted least square method and cross-fault GPS site baseline time series and GPS strain rate field by multi-scale spherical wavelet method. The results indicate that the Qilian fault zone was characterized by ~60 wide continuous belts. In the south side of the Qilian fault zone, GPS velocity field is featured by clockwise rotation, whereas, the vaule shows no significant change. Across the Qilian fault zone and to its north side, the size of GPS velocity is significantly reduced, which shows that the Qilian fault zone is an active tectonic belt. The sinistral strike-slip rate along the West segment of Lenglongling fault is 6.17±0.41 mm/a, with the compressive rate of 1.83±0.38 mm/a and the locking depth of 22.1±3.1 km. by calculating the coseismic displacements measured by fiducial GPS caused by the earthquake. We found that it is significant only at QHME site that is 26.8 km southwest of the epicenter. The northeast movement of the hozizontal coseismic displacement at QHME site is in agreement with the focal mechanism from the inversion of seismic data.

Key words: Strain rate field, Co-seismic displacements, GPS observation, Menyuan M_S6.4 earthquake