Depth extent of hemispherical inner core from PKP(DF) and PKP(Cdiff) for equatorial paths

Differential travel times and amplitude ratios of PKP(DF) and PKP(Cdiff) (partly including PKP(BC)) for equatorial paths at epicentral distances from 150° to 160° are examined to discuss the radial structure of the uppermost 500 km of the inner core. By using seismograms with a predominant frequency of approximately 0.5 Hz, 649 measurements are successfully collected, including 295 and 354 readings for the Eastern and Western hemispheres, respectively. Forward modeling with the reflectivity method suggests that the best-fit velocity structures in the Eastern and Western hemispheres are 0.5% faster and 0.9% slower, respectively, than an average structure at the inner core boundary (ICB), and that the velocity perturbations become linearly closer to the average with depth, finally coinciding with the average at 400 km and 250 km below the ICB, respectively, if ak135 is adopted for the structure above the ICB. In the Eastern hemisphere, the Q values in the uppermost 250 km of the inner core and that in the range from 300 to 450 km below the ICB are approximately 180 and 1000, respectively. In contrast, the Q value in the Western hemisphere is almost constant at approximately 300–400 in the uppermost 450 km of the inner core.