What part of earths interior cause the diffraction of P waves made by earthquake?

The diffraction of P waves, or primary waves, during an earthquake occurs primarily at the boundary between the Earth's solid inner core and its liquid outer core. As P waves encounter this boundary, their speed changes due to the differing densities and states of the materials, causing them to bend or refract. Additionally, P waves can also be affected by variations in the Earth's crust and mantle, leading to further diffraction. This behavior helps seismologists understand the Earth's internal structure.