Mohoroviidiszkontinuitás

The Mohorovičić discontinuity, commonly referred to as the Moho, is a seismic boundary that separates the Earth's crust from the mantle. The term originates from the name of its discoverer, Croatian seismologist Andrija Mohorovičić, who first identified it in 1909 during the study of earthquake waves. The discontinuity is characterized by a sudden increase in seismic wave velocities, indicating a change in the composition and density of the underlying material.

The Moho is typically found at a depth of about 5–10 kilometers beneath the oceanic crust and 30–50 kilometers beneath the continental crust, though these depths can vary significantly depending on geological features such as mountain ranges or rift zones. The boundary itself is not a sharp, well-defined plane but rather a transitional zone where the composition shifts from crustal rocks, primarily granitic and basaltic in nature, to ultramafic mantle rocks like peridotite.

Seismic waves, particularly primary (P) and secondary (S) waves, exhibit distinct changes in velocity at the Moho due to the increased density and rigidity of the mantle compared to the crust. P-waves accelerate from roughly 6.5–7.0 km/s in the crust to about 8.0–8.5 km/s in the mantle, while S-waves, which do not propagate through liquids, appear only below the Moho. This behavior provides a key tool for geophysicists in mapping the Earth's internal structure.

The Moho plays a crucial role in understanding tectonic processes, as it marks the boundary where the lithosphere, the rigid outer layer of the Earth, transitions into the more ductile asthenosphere. Variations in the depth and structure of the Moho can provide insights into tectonic activity, such as subduction zones, where one tectonic plate descends beneath another, or regions of continental rifting. While the Moho is a fundamental concept in geophysics, its exact nature—whether it represents a true compositional boundary or a gradual transition—remains an area of ongoing research.