We have this big roiling Earth, and what does that have to do with earthquakes? Simply that the earth has gone with the most efficient method of heat removal which is convection, and transfers that heat to the radiator fins of the ocean crust. It's an operating air conditioner. The upper convection is in the mantle, just below the solid crust, and is responsible for our earthquakes. There may be lower convection cells that give us our magnetic field, and the Earth's core may be a nuclear reactor. :)
Who cares about deeper convection, it's the mantle that does all the interesting stuff to us on the surface. Because of the convection all our continents move around like floating scum, and the oceanic crust gets recycled. The whole thing is called Plate Tectonics, which is a rather surface-oriented expression. I'd rather call it Convection Collision.
You can read all about Plate Tectonics without once thinking about the whole 3-d mechanism. This would be rather shallow of you. :) As I have said, this would be all quiet grinding if it were not for the interaction of quartz and water. That gives us earthquakes, and nobody would care about them if we could all live on high rock.
All the details of Convection Collision (my new theory) are horribly boring. There's subduction, spreading, transform faults, etc. The only thing interesting are the formation of diamonds as the big chunks go down.
Bye for now.