Progress in the seismological study of the Earth′s inner core

This paper reviewed the recent results concerning the Earth's inner core, as inferred from seismological observations. The claim that the inner core is differently rotating is under debate. Souriau and Song Xiaodong have respectively estimated rotation speed as (0±0.2)°/a and (0.15-1.1)°/a. The eastern hemisphere is less anisotropic than the western hemisphere in the uppermost several hundred kilometers of the inner core, namely, the hemispherical pattern is well observed. According to some results, it is nearly isotropic in the top of the inner core, but significantly anisotropic in the rest of the inner core. These observations lead to an inner core model with a transition zone to uniformly explain both radial variation and lateral variation in anisotropy data. Based on an extensive seismic data set, an innermost inner core, with a radius of nearly 300 km, was found, and within it the anisotropy is stronger than outside. Thereby, a new structure model of the Earth′s inner core was suggested as to include an upper inner core, a transition\|zone, a lower inner core and an innermost inner core. The specific studies of Q\|value reveal high velocity regions correspond to that of high wave attenuation in the inner core, however, the positive correlation between velocity and attenuation is different from the opposite in the mantle. A few attempts have been made to investigate the propagation and attenuation of S\|wave inside the inner core, although it is a very hard project.