as a bunker buster but more powerful and with a lot of splash damage because they work producing mini earthquakes.
the splash damage should be greater than the direct impact damage because what destroys the target is the earthquake.
the explosion not.
link:
http://en.wikipedia.org/wiki/Earth_quake_bomb
http://en.wikipedia.org/wiki/Tallboy_bomb
http://en.wikipedia.org/wiki/Grand_Slam_bomb
the bomb should outweigh the plasma bomb and do more damage with a similar or larger area damage