From Internet:
The heat from the mantle makes the rocks at the bottom of the lithosphere slightly elastic, which allows the plates to move. The movement of these plates is known as plate tectonics. Most tectonic activity takes place at the boundaries of these plates, where they may collide, tear apart, or slide against each other.
What is the driving force for the movement of the lithospheric plates?
3 answers
@PsyDAG no the answer idiot
The tilt of the earth causes a very strong centrifugal force on the asthenosphere magma as explained in my article : The driving forces of tectonics, freely availible.