splash = splash effect when torpedo is dropped into the water (so that's pretty much only useful for air torpedoes or playable ship torps)
dud_effect = probably the effect spawned if the torpedo is a dud, by default it links to a dummy node in particles.dat though so atm it doesn't do anything
water_explosion = column of water launched into the air by the explosion, like what you see above the surface if a depth charge explodes
under_explosion = explosion effect if detonation occurs below the surface, so that's the under water 'fireball'
above_explosion = probably explosion effect if detonation occurs above the surface, so that's the above water 'fireball'
I'm almost completely sure about splash, water_explosion and under_explosion. I'm pretty sure about the other two, though I've never seen them happen
I hope this helped
