I once read somewhere that 4 or so of those 50MT firecrackers ,if they were detonated in a short span of time, placed correctly, could split the planet apart. Of course we have all read all sorts of things about nukes over the years, I just remember that as I thought it was interesting. No doubt, a 50MT is a big bang. Isn’t that what the Tsar was rated? Or was it more? Didn’t they actually reduce it some, because they were afraid the bomber couldn’t get away?
Hardly, Tsar Bomba create a five mile diameter fireball in open air. Below-ground crater size, for a buried detonation, might be a little bigger. Zone of total destruction above ground (burning; pressure damage) was about a 50 mile radius. Earth is just under 8,000 miles diameter. Not much chance a rock that size is going to crumble based on those little firecrackers.
Tsar Bomba was originally designed to be 100MT(I think) but then they reduced it to 50-57MT (I think) I think another reason for reduction was the level of fallout created.
I don’t think the theory about four well placed 50MT is correct. Super volcanoes, say Yellowstone caldera, are believed to be around 200 or so Megatons.