I'm not sure exactly what you are trying to get at here scientifically. The earth's crust is always under tremendous stress. Each point is being gravitationally attracted to the center, the pressure from lower layers is holding it up, and it is being pulled on by the moon and other bodies. If you can simply relax the pressure some how in a small area, you can tap tremendous amounts of energy as the forces readjust to a new equilibrium. You don't need to feed the system with the amount of energy you get out.

So we, i.e. humans, don't need to input that energy. Earthquakes merely release the energy that is stored from all kinds of gravitational energy sources that have been present for eons. All we need to do is provide the activation energy. After that it is fully exothermic. It's like saying a toddler can't fire a gun because he didn't create the bullet. All he needs is enough strength to pull the trigger. The potential energy for the devastation is already present in the environment.