What does the mantle have to do with the 2011 tsunami in Japan?

The mantle has everything to do with this earthquake, without the convection currents in the mantle the plates would have not moved to cause the earthquake in the first place. The problem is that Japan is at a destructive (also called compressional) plate boundry, not just that but there is another four plate boundaries quite close by to magnify the effect of the earthquake, the movement of the crust could also mean that there could be magma rising through the crust ready for an eruption. The earthquake caused the ocean crust to move 10m which displaced the water to create the tsunami.