Detection of a D″ discontinuity in the south Atlantic using PKKP

A strong arrival in the early coda of major‐arc PKKP ab is observed on recordings of earthquakes in the Banda Sea region from the short‐period, small‐aperture Yellowknife array. The arrival has a move‐out close to PKKP ab with an average delay of ∼12 s. We show that the phase is most likely an underside reflection from a D″ discontinuity above the PKKP reflection point at the core‐mantle boundary beneath the southern Atlantic on the edge of the African superplume. Differential travel times between PKKP ab and PK d KP (the underside reflection at the D″ discontinuity) is used to constrain potential D″ velocity models. The high amplitude of PK d KP requires proximity to the b ‐caustic adding further velocity control. We find that a P‐velocity model with a sharp positive velocity jump ∼280 km above the core‐mantle boundary, and a negative velocity gradient closer to the core‐mantle boundary, fits the data well.