BharatNotes Mohorovicic
noun (proper noun; chiefly attributive, as in "Mohorovicic discontinuity")Usage in a UPSC answer
Just as the Mohorovicic discontinuity marks the hidden seismic boundary where the Earth's crust yields abruptly to a denser mantle, the transition from welfare populism to fiscal prudence in Indian budgeting is rarely visible on the surface yet decisively governs how shocks propagate through the wider economy.
Synonyms
Word Family
Mohorovicic discontinuity (n phrase), Moho (n abbrev), No standard derived forms
Root
Proper noun: named after Croatian seismologist Andrija Mohorovičić (1857–1936); entered scientific literature 1930s
Etymology
Named after Croatian seismologist Andrija Mohorovicic (1857-1936), who first identified this boundary in 1909 by studying seismic waves from a Zagreb earthquake; the term entered scientific literature in the 1930s.
Memory Hook
"MOHO" = the boundary where the crust says "no more" and the MOre-dense mantle begins; recall Mohorovicic as the man who heard the Earth's seismic waves "echo" (-vicic ~ "vich-itch") off this hidden floor.
How This Word Works in UPSC Writing
The discontinuity separating the crust from the mantle, universally shortened to the Moho. Its discovery is the standard illustration of how anything is known about the Earth's interior at all, since no one has ever drilled through it: in 1909 Andrija Mohorovicic noticed that seismic waves from an earthquake reached distant stations sooner than expected, which could only be explained if they had passed through a deeper layer of higher velocity and been refracted back to the surface, so the boundary was inferred entirely from the behaviour of waves rather than observed directly. That method underlies the whole picture of the deep interior, including the shadow zone which reveals a liquid outer core, because S-waves are transverse and cannot travel through liquid. The difference in Moho depth beneath continents and oceans is itself the evidence for the compositional contrast between thick low-density continental crust and thin dense oceanic crust.
Don’t Confuse It With
The Mohorovicic discontinuity separates crust from mantle and is compositional, whereas the lithosphere-asthenosphere boundary is mechanical and lies deeper, so the two are frequently confused. The Gutenberg discontinuity separates mantle from outer core and the Lehmann discontinuity the outer core from the inner. P-waves are longitudinal and pass through both solids and liquids, while S-waves are transverse and cannot cross a liquid, which is precisely what reveals the liquid outer core. The shadow zone is the belt receiving no direct waves, and its geometry gives the core's dimensions.
Hindi Meaning
मोहो असातत्य (moho asātatya); भूकंपीय छाया क्षेत्र (bhūkampīya chhāyā kshetra) for the shadow zone.
Common Questions
- How was the Moho discovered without drilling?
- Mohorovicic found in 1909 that seismic waves arrived at distant stations earlier than expected, which implied a deeper high-velocity layer refracting them back, so the boundary was inferred from wave behaviour alone.
- How does the Moho differ from the lithosphere-asthenosphere boundary?
- The Moho is a compositional boundary between crust and mantle, while the lithosphere-asthenosphere boundary is mechanical, marking where rigid rock gives way to ductile flow, and it lies deeper.
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