Moisture content has a very significant impact on shock propagation.
Nuclear blasts in regions with a high water table exhibit shallower crater
depth, but a significantly larger shock damage radius. Water transmits
shock much better than either air or dry soil. However, this is mostly of
concern to underground structures since ground shock propagation is their
only significant threat other than overpressure. For most structures,
overpressure is the primary threat, not ground shock.
FYI, as a rule, conventional explosives have a 50% greater damage radius
underwater as they do in air due to differences in hydrostatic shock
propagation efficiency.
-James Rogers
jamesr@best.com