Clear PKKP,a P wave reflects of the core-mantle boundary on the core side,is recorded by the transcontinental USArray from two deep earthquakes occurred in South America and Tonga,and one intermediate-depth earthquake in the Hindu Kush region.We compare the PKKP waveforms with the direct P waves to investigate the fine structures near the core-mantle boundary,with a primary focus on the core side.We find no evidence for the existence of a sedimentary layer of lighter elements with a thickness above a few hundreds of meters beneath the reflection points of the two deep events,which are located at the Ninety-East Ridge and South Africa.On the other hand the PKKP wave duration of the Hindu Kush event is almost twice as long as that of the P wave,suggesting that multiple reflections may be occurring at the core-mantle boundary located beneath the Antarctic,which is located inside the so-called tangent cylinder of the outer core.The tangent cylinder is an imaginary cylindrical region suggested by geodynamics studies,which has different flow pattern and may have a higher concentration in lighter elements as compared to the rest of the outer core.One possible explanation of the elongated PKKP is a thin distinct layer with a thickness of a few kilometers at the top of the outer core,suggesting that precipitation of lighter elements may occur at the core-mantle boundary.Our data also indicate an extremely low QP of 312,approximately 40%of the PREM average(～780),within the large-scale low-velocity anomaly in the lowermost mantle beneath Pacific. Clear PKKP, a P wave reflects of the core-mantle boundary on the core side, is recorded by the transcontinental USArray from two deep earthquakes occurred in South America and Tonga, and one intermediate-depth earthquake in the Hindu Kush region. We compare the PKKP waveforms with the direct P waves to investigate the fine structures near the core-mantle boundary, with a primary focus on the core side. We find no evidence for the existence of a sedimentary layer of lighter elements with a thickness above a few hundreds of meters beneath the reflection points of the two deep events, which are located at the Ninety-East Ridge and South Africa. On the other hand the PKKP wave duration of the Hindu Kush event is almost twice as long as that of the P wave, suggesting that multiple reflections may be occurring at the core-mantle boundary located beneath the Antarctic, which is located inside the so-called tangent cylinder of the outer core. tangent cylinder is an imaginary cylindrical region sugges ted by geodynamics studies, which has different flow pattern and may have a higher concentration in lighter elements as compared to the rest of the outer core. One possible explanation of the elongated PKKP is a thin distinct layer with a thickness of a few kilometers at the top of the outer core, suggesting that precipitation of lighter elements may occur at the core-mantle boundary. Our data also indicate an extremely low QP of 312, approximately 40% of the PREM average (~ 780), within the large-scale low -velocity anomaly in the lowermost mantle beneath Pacific.