Northern gravity gradient changes of the Nepal M_S8.1 earthquake derived from GRACE data

Based on the RL05 monthly gravity field model released by Center for Space Research, University of Texas at Austin (UTCSR), the spatio-temporal distribution of northern gravity gradient of the Nepal M_S8.1 earthquake is successfully obtained by using 300 km Fan filter. Then we analyzed both the long term change tendency in Nepal and its vicinity areas and monthly time series at six feature points of the northern gravity gradient by the least-squares fitting method. Furthermore, the possibility of the detection on coseismic change of the northern gravity gradient in the Nepal M_S8.1 earthquake by GRACE is discussed combined with the viscoelastic-gravitational dislocation theory as well. The results show that, the positive and negative anomaly of the northern gravity gradient is obvious before the Nepal M_S8.1 earthquake, which occurred in the vicinity of the zero line; the annual change rate of the northern gravity gradient presents positive and negative distribution in the four quadrants along the Indian Plate boundary and its vertical direction in the studied area, and the northern gravity gradient at the six feature points shows obvious jump in April 2012. Therefore, it is deduced that the dynamic change process of northern gravity gradient reflects mass migration before the earthquake and viscosity adjustment of crust and mantle after the earthquake in Nepal and its vicinity areas.