Sure... but that doesn't mean the whole plate moves. If it did... you would notice more than one earthquake.
Also, I think it was the Indian Ocean side of the fault that slipped - different plate.
The underlying plate (compression) moves under the upper VERY slowly building up forces on the upper plate.
Also, I think it was the Indian Ocean side of the fault that slipped - different plate.
I think you are correct from my memory. When it 'slipped', the mass 'fell' causing a water displacement.