First i was a mine-sweep electrician in the US navy and am familiar with the damage caused by mines and torpedoes and how they work.
Mines are of three types
moored mines are contact or acoustic or magnetic influence
bottom mine are acoustic, magnetic or pressure influence or a combination
Contact mine for the most part take out the bow of a ship.
Moored or bottom acoustic, magnetic or pressure influence or a combination mine takes out the aft third of the ship.
This gets the engine room. shafts props and rudders.
Even if the ship does not sink its not going anywhere.
Acoustic, pressure or magnetic influence mines take out the ship about 2/3 of the way back under the engine room aft to the area or the screws.
acoustic mines read the sound if the screws and as it just starts to drop the mine goes off.
Pressure or magnetic influence read the signature of pressure or the magnetic field of the ship as a bell curve and just after it reaches max and
starts to drop is when the mine goes off.
Torpedoes are of two types strait line runners and guided acoustic.
Strait line runners can go off anywhere under the ship and are contact or magnetic influence fused. the magnetic influence fused go off under the keel
and in many cases on smaller ship break the ship in half.
Acoustic torpedoes will target the props as this is the biggest sound source.
and that is about 2/3 of the way back on the ship.
Now as to the south Korean ship.
reports are the water in the area was shallow and parts of the ship are still visible above water.
This most likely rules out torpedo attack from a sub. the water is not deep enough to safely run or hid a sub.
But this is perfect waters for using mines both moored or contact with acoustic,or magnetic fuses.You get two shock waves from the explosion.
a direct and reflected wave off the sea bed.
But this ship also has 4 gun mounts two forward and two aft. that means 4 magazines for ammo.
Though there are not any reports of the ship breaking in two like you would have from a ammo magazine explosion. light load out of ammo??????
All they can do now is to get divers down and see of the hull sheathing is bent inwards(mine or torpedo) or outwards(magazine explosion).