Greetings;

yes, we have a very good idea of the effect on the earth's crust.

Nothing.

Nuclear explosions are rated in kilotons. Hiroshima was about 20 kilotons.

The Amchitka explosion buried in a very seismic area was one of the biggest tests ever conducted and had negigible results on the seismicity.

War explosions will be surface or even air bursts, transferring very little energy to the ground.

Roger