In the Star Trek: Deep Space Nine episode The Die is Cast. A planetary bombardment scene occured where 17 shots was stated to have destroyed 30% of a planet's crust. Now obviously that's a HUGE amount of firepower, but it's not unrealistic for Star Trek as since the pilot episode of the original series they stated they had enough firepower to blast a continent.
So what kind of firepower are we talking about here?
Specifically if the entire crust were destroyed right down to the mantle. As in what kind of energy levels are we talking about (preferably in tnt equivalent) would be necessary to destroy completely or severely extrude the crust of 30% of a planet's surface area? What about the entire planet?
To make things easier lets just assume values for Earth.