This sentence is from an article about "Earthquakes":

The surface of the earth, about 100 kilometers thick, is made of large pieces. When they move against each other, an earthquake happens.

What does "move against each other" mean? Does it mean "move in the opposite direction and hit"?


The phrase 'move against each other ' literally means they come in contact and collide with each other so as to create an earthquake.

The word against may be the confusion, but look at the below definition (taken from Google):

in or into physical contact with (something), so as to be supported by or collide with it.

"she stood with her back against the door"


"she leaned against the wall"

The same meaning is applied in the example given.


I can see the confusion. In most cases, "move against" means to oppose something, or even attack something, for example:

Syrian troops moved against rebel strongholds in the city of Aleppo.

We should quickly move against the enemy's advance through this valley.


When describing tectonic plates, however, the authors wanted to say something akin to "rub against". As with many English phrases, the challenge is to use a verb that conveys the right image. Rub implies a gentle motion, like a cat against your leg. "Grind against" might work, like a car wheel scraping along a curb, but for whatever reason the authors chose the generic "move against", despite its alternate meanings.

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