I'm not an expert, so had to do some research after the previous thread closed @AcrossthePond55.
Q.Are MOABs those 'ultra-percussion' bombs that destroy using sound waves?
A.The MOAB is a conventional explosive weapon. It results in an initial fireball from the explosion and a subsequent pressure wave caused by the creation of large quantities of gases at high temperatures. The MOAB is an air burst weapon, that is, it detonates above the ground. The MOAB must be distinguished from the class of volumetric weapons, such as thermobaric weapons and fuel-air explosive weapons that have been used against fighters within cave complexes in Afghanistan.
On MOAB and civilians. It's not a straightforward 'Illegal'.
As with any weapon, however, its use in particular situations may be unlawful. Of note in this regard are the rule of proportionality and the requirement to take precautions in attack. But these IHL(International Humanitarian Law) rules are always context-dependent. Consider the rule of proportionality, which prohibits “an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.” Using a MOAB in a populated urban area, for instance, would generally violate the rule except in circumstances where the military advantage sought is enormous.
Finally, IHL forbids the use, or threat of use, of any weapon or tactic when the primary purpose of the operation is to terrorize the civilian population. This is so even if the operation would otherwise comply with all other IHL requirements. The MOAB could obviously be used in this fashion, as its immediate effects are stunning. However, violation of the prohibition requires an intent to terrorize. Absent such an intent, and without prejudice to other requirements of IHL, a decision to resort to the MOAB would be lawful. Relatedly, IHL does not currently consider unintended or incidental mental harm to civilians as part of proportionality analysis, though some might wish for the law to move in that direction.
It must be cautioned that this prohibition applies only to those operations designed to terrorize the civilian population. There is no equivalent prohibition on employing a weapon or engaging in tactics in order to terrorize enemy forces. Therefore, the fact that the MOAB was designed in part as a “shock and awe” effect weapon and may effectively demoralize, and even terrify, the enemy has no bearing on the legality of its use.
Extracted from
https://www.justsecurity.org/40022/the-mother-bombs-understanding-massive-ordnance-air-blast-weapon/