Over the years several technical papers have
asserted that there are noticeable variances in the
size and number of gas bubbles being emitted
from sediments before an earthquake. Four gases
are involved: methane, radon, hydrogen sulfide
and carbon dioxide. Shown to the left is an
underwater methane sensor from Franatech in
Germany. Results from Taiwan indicate gross
changes a week before a major earthquake with
profound changes about 30 hours before the
actual seismic event.
Note that the changes can be no bubbles where there had been bubbles previously; bubbles where there had
not been bubbles previously; or drastic changes in bubble size, velocity and creation rate.

For an admiral or other leader, a week or even 24 hours of warning would make a world of
difference. There is time to clear any straits, evacuate endangered people, finish loading or
unloading ships; and disperse vessels into deeper water.