Abstract：We compare observation data of Wuhan and Lhasa superconducting gravimeters with free oscillations simulated by 14 different focal mechanisms of the 2015-09-16 Illapel earthquake. The focal mechanism solutions of the Illapel earthquake are analyzed and constrained by spherical normal modes in 1.5-5.3 mHz frequency band. We compare observed value with simulated value to search the more accurate scalar seismic moment and fault dip angle based on the optimal focal mechanism solutions. The results show that the scalar seismic moment of the 2015 Illapel earthquake is (3.0±0.2)×1021 Nm, corresponding to MW8.3, and the optimal dip angle is 19°. This shows that the focal mechanism solution of Illapel earthquake can be evaluated based on superconducting gravity observation, and the reliable magnitude can be obtained by inversion based on long-period seismic wave signals or multiple observation data.
