For reference the Tunguska event, which was projected to be a 5MT explosion on the low end, flattened about 2000 square kilometers when it airburst. If this hits the ocean it would no doubt cause some large tsunamis.
Only very locally, the Japan tsunami was an order of magnitude more energy and aiui earthquake tsunamis happen particularly with certain kinds of seafloor displacement. It's not just about the amount of energy but how that energy is applied, impact energies dissipate quickly with distance.
It depends, on where exactly will hit. Similar to nuclear explosions, if one happen over sea or ocean near coast, it will cause extremely large wave, which will be similar to tsunami. If it will hit land, will be small earthquake.
This is why nearly all nuclear explosions was over land or far from coast. Few experiments near some coast or island, created tsunami-like wave on those coast (island), which considerable widen polluted territory (ocean is usually considered as self-cleaning).
https://en.m.wikipedia.org/wiki/Tunguska_event