The seismic discontinuity that marks the boundary between the Earth’s crust and mantle. The mantle has P-wave velocities of about 8.1 km/s, higher than that of the lower-density crustal rocks. The Moho was originally recognized at a depth of some 20 km in Europe by A. Mohorovičić on the basis of the arrival of refracted P-waves before direct P-waves. Previously considered to be very sharp, the discontinuity is now known to be more complex.