Evidence for inner core super-rotation from time-dependent differential PKP traveltimes observed at Beijing Seismic Network

In an effort to confirm and constrain inner core rotation, we examine earthquakes from the South Sandwich Islands recorded at the Beijing Seismic Network. We obtained a total of 109 high-quality measurements of PKP(BC)-PKP(DF) differential traveltimes by waveform cross-correlations from earthquakes spanning over 30 years. The results show robust temporal changes in PKP(BC)-PKP(DF) residuals along this pathway, providing new support for the differential inner core hypothesis. We also observed evidence for a lateral velocity gradient in this part of the inner core. Assuming that the temporal changes result from a shift of a lateral structure due to an inner core rotation, we estimate the inner core rotation rate to be about 0.41 +/- 0.12° yr^-1 faster than the mantle.