New constraints on the structure of the inner core from P ' P '

We measured absolute P'P'df as well as differential P'P'bc-P'P'df and P'P'a b-P'P'df travel time residuals for earthquakes in Alaska and the Aleutians recorded at NORSAR array (Norway). For such paths, P'P'df samples two regio ns of the inner core which have been identified as strongly anisotropic (si milar to 3.5%), respectively beneath the Central Pacific and Africa, and sh ould arrive some similar to 6s earlier than predicted by a standard model. Absolute and differential travel times do not appear to be anomalous. A ver y complex texture and/or heterogeneity of the top similar to 400km of the i nner core, or a significant contribution from the strongly heterogeneous D ", is required to explain this discrepancy.