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Mohorovičić discontinuity
The Mohorovičić discontinuity (), usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. Named after the pioneering Croatian seismologist Andrija Mohorovičić, the Moho separates both the oceanic crust and continental crust from underlying mantle. The Moho lies almost entirely within the lithosphere; only beneath mid-ocean ridges does it define the lithosphere–asthenosphere boundary. The Mohorovičić discontinuity was first identified in 1909 by Mohorovičić, when he observed that seismograms from shallow-focus earthquakes had two sets of P-waves and S-waves, one that followed a direct path near the Earth's surface and the other refracted by a high-velocity medium.
The Mohorovičić discontinuity is below the ocean floor, and , with an average of , beneath typical continents.
==Nature==
Immediately above the Moho, the velocities of primary seismic waves (P-waves) are consistent with those through basalt (6.7–7.2 km/s), and below they are similar to those through peridotite or dunite (7.6–8.6 km/s). That suggests the Moho marks a change of composition, but the interface appears to be too even for any believable sorting mechanism within the Earth. Near-surface observations suggest such sorting produces an irregular surface.
The Moho is characterized by a transition zone of up to 500 m thick.〔(D.P. McKenzie - The Mohorovičić Discontinuity )〕 Ancient Moho zones are exposed above-ground in numerous ophiolites around the world.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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