moho

Moho, short for the Mohorovičić discontinuity, is the boundary between Earth's crust and the mantle. It is named after Croatian seismologist Andrija Mohorovičić, who in 1909 identified a distinct increase in seismic wave speed at a certain depth when analyzing earthquake data. The discontinuity reflects a change in rock composition and density from crustal rocks to denser mantle rocks.

Depths and variation: In continental regions the Moho lies roughly 30 to 50 kilometers beneath the surface, while under oceans it is much shallower, about 5 to 10 kilometers deep. The depth varies with tectonic setting and crustal thickness, and local topography of the Moho can be irregular.

Detection and significance: The Moho is detected primarily by seismology, using abrupt changes in the travel times of P-waves and S-waves, as well as receiver-function analyses and seismic tomography. Its presence defines the crust–mantle boundary, informs estimates of crustal thickness, and supports models of crust formation, differentiation, and tectonic processes such as subduction and continental collision.

Additional note: The term Moho is commonly used as shorthand for the Mohorovičić discontinuity in geophysical literature. It is one of the fundamental boundaries described in the standard model of Earth’s internal structure.