No. Not really. Sounds a bit uneducated to me, which "underground" is this??
A sonic boom will not create a tsunami.
A nuclear weapon will not create a tsunami. We have tested nuclear weapons for naval warfare and it never caused a tsunami.
Blast waves are circular. If you detonate a blast affixed to a solid object that wouldn't be disrupted by the blast, you can direct the explosion.
In water the blast wave move faster and stronger and in all directions because the mass of the water is equal on all sides.
So, if theoretically you could do as you say, detonate a bomb and it send a tsunami, then detonate on the other side to protect your self, the other
side of the blast radius coming from your bomb will still send a tsunami at you anyways.
Sending subs to flood all the worlds coastlines?

Right.