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My book explains that "Tidal waves are the result of an abrupt shift in the underwater movement of the Earth".

It seems to me that the words shift and movement have similar meanings in this sentence. Could you explain the differences of those words in this context? Thank you.

5

Shift means a change.

It may mean a move, some movement that displaced a thing that normally was in one position, and placed it in another. But a train on a railway track in the middle of 6-hour journey is not shifting. It may shift tracks - move from one track to the other, but it's not shifting from 786th kilometer to 787th.

A shift in the movement means the movement changes. The tectonic plates moving 3cm a year for past millennium suddenly skipped 2 meters. That was a shift that caused the waves. The movement was building tension, storing energy, and once something snapped, the rapid change occurs - the movement caused the shift.

  • Although technically correct, with respect to tectonic movement, this sentence does sound redundant to me, and I would find "shift in the underwater configuration" less surprising. – barbara beeton Feb 28 '13 at 16:53
3

"Shift" means "change" in your textbook's sentence. When driving a car with a standard transmission, the driver has to shift gears, which means change gears.

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