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'ab-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 regions of the inner core which have been identified as strongly anisotropic (similar to 3.5%), respectively beneath the Central Pacific and Africa, and should arrive some similar to 6s earlier than predicted by a standard model. Absolute and differential travel times do not appear to be anomalous. A very complex texture and/or heterogeneity of the top similar to 400km of the inner core, or a significant contribution from the strongly heterogeneous D ", is required to explain this discrepancy.