Which named seismic discontinuity is located at the greatest depth inside the Earth?

Correct answer: Lehmann discontinuity

The correct answer is D, the Lehmann discontinuity. A seismic discontinuity is a boundary where seismic-wave speed or direction changes because the material or physical state changes. The Moho lies between the crust and mantle, so it is relatively shallow. The Repetti discontinuity lies within the mantle. The Gutenberg discontinuity marks the boundary between the mantle and the liquid outer core and is much deeper, but it is still outside the inner core. The Lehmann discontinuity separates the liquid outer core from the solid inner core, close to Earth’s centre, so it is deepest among these choices. A, B, and C are therefore shallower boundaries. Memory cue: “Lehmann leads to the inner core.”