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Mohorovičić discontinuity[‚mō·hō′rō·və‚chich dis‚känt·ən′ü·əd·ē]
(also “Moho,” M-discontinuity), the boundary surface between the earth’s crust and mantle. The existence of the Mohorovičić discontinuity has been determined from seismic data; the velocity of longitudinal seismic waves passing downward through the Mohorovičić discontinuity jumps from 6.7–7.6 to 7.9–8.2 km/sec, and that of transverse waves jumps from 3.6–4.2 to 4.4—4.7 km/sec. Various geophysical, geological, and other data seem to indicate that the earth’s density at the discontinuity also increases substantially, from 2.9–3 to 3.1–3.5 t/m3. It is virtually certain that the Mohorovičić discontinuity separates strata of different chemical composition. The Mohorovičić discontinuity was named after A. Mohorovičić, who discovered it.