Using pre-critical PKiKP-PcP phases to constrain the regional structures of the inner core boundary beneath East Asia

We collected 177 pre-critical PKiKP-PcP records, assembling a wealth of traveltime and amplitude data. These observations sample the inner core boundary (ICB) beneath East Asia with good spatial coverage. Combined with previous studies, our results demonstrate a 100-km-wide anomaly with positive PKiKP-PcP traveltime residuals surrounded by negatives beneath the Yellow Sea area (123°E, 33°N) (Yellow Sea anomaly). After correcting the elliptic effects and mantle Vp heterogeneities based on the tomography models, the residuals of the Yellow Sea anomaly remain at least 0.6 s faster than those of the surrounding areas, suggesting a thickening of 2-3 km between the ICB and core mantle boundary (CMB). Due to the negative CMB topography along the western Pacific rim, we attribute this anomaly mainly to negative ICB topography. Across the northern border of the Yellow Sea anomaly, PKiKP/PcP amplitude ratios increase by approximately 50% from north to south, which can be explained by an approximately 0.6 g/cm3 raise in ICB density contrast. These traveltime and amplitude features suggest a mosaic structure at the ICB beneath the Yellow Sea areas.