Composition of the Earth's inner core from high-pressure sound velocity measurements in Fe-Ni-Si alloys

摘要

We performed room-temperature sound velocity and density measurements on a polycrystalline alloy, Fe_(0.89)Ni_(0.04)Si_(0.07), in the hexagonal close-packed (hcp) phase up to 108GPa. Over the investigated pressure range the aggregate compressional sound velocity is ~9% higher than in pure iron at the same density. The measured aggregate compressional (V_P) and shear (V_S) sound velocities, extrapolated to core densities and corrected for anharmonic temperature effects, are compared with seismic profiles. Our results provide constraints on the silicon abundance in the core, suggesting a model that simultaneously matches the primary seismic observables, density, P-wave and S-wave velocities, for an inner core containing 4 to 5wt.% of Ni and 1 to 2wt.% of Si.