Seismological studies (via travel-time analysis and models like PREM) show that P-wave velocity increases steadily with depth through the solid lower mantle, then drops sharply at the core-mantle boundary upon entering the liquid outer core (which cannot support shear and has a notably lower P-wave velocity than the base of the mantle), before rising again at the inner core boundary into the solid inner core, though the inner core's P-wave velocity remains lower than that of the deep lower mantle.