The novels are canon, you say? Good, chew on this. Direct quotation from X-Wing: Wedge's Gamble.
Ackbar sat back in his eggshell repulsorlift chair. "You have the basics: one standard day ago Warlord Zsinj showed up in the system with the Iron Fist, launched a wing of TIEs, and proceeded with a planetary bombardment. Our base there was hit hard, but since it was underground, not as hard as Zsinj would undoubtedly like to think..."
"...How badly was Noquivzor hit?"
Ackbar's eyes half-closed. "We had major damage to the barracks complex. Multiple floors collapsed one atop the other. We will be a long time digging bodies out. Rogue Squadron lost a significant portion of their support staff. The hanger complex, on the other horizon, escaped damage. When we get them back from Coruscant they will have ships to fly."
Noquivzor Base had no shields, and was the only target of any significance on the world. If a Super Star Destroyer was unable to dig it out, a SUPER STAR DESTROYER with a minimum broadside of 450 heavy turbolasers, was unable to dig it out completely, 200 gigatons is utterly impossible. 200 gigatons would exacavate to a ridiculous depth, a half-kilometer at least. With an opening volley of 450 heavy turbolasers, at 200 gigatons the Iron Fist's first broadside should have blasted straight through the planetary crust and annihilated everything for a conservative minimum of twenty kilometers in every direction. It didn't. Major parts of the base survived, including the hanger and powerplant.
Before you say that they simply glassed the planet, they did not. Noquivzor was still habitable after the bombardment ended and Noquivzor Base was eventually fully repaired.
Another interesting little factoid: cruising about Babylon 5 tech sites, I ran across a reference to the power of a Shadow Battlecrab's Death Ray. There is visual evidence from the series that they can blow a good-sized plantoid (650 meters judging from size in relation to the Battlecrab) in half, and dialouge that suggests they are capable of glassing a planetary surface in a little more then a day. Using only a single weapon.