Table 1. List of parameters included in the theoretical velocity equations used in this study.

Symbols	Definitions
	Porosity
s	Proportion of solid
h	Proportion of gas hydrate
w	Proportion of water
g	Proportion of free gas
ch = s / (w + h)	Gas hydrate concentration
ss = s / (s + h)	Grain saturation
sh = s / (s + h)	Gas hydrate saturation
sw = w / (w+ g)	Water saturation
sg = g / (w + g)	Free gas saturation
eff = (1 - ch)	Effective porosity
s	Density of grain
h	Density of gas hydrate
w	Density of water
g	Density of free gas
b = sss + shh	Density of solid part
f = sww + sgg	Density of fluid part
m= (1 - eff)b + efff	Total density
Cs	Compressibility of grain
Ch	Compressibility of gas hydrate
Cw	Compressibility of water
Cg	Compressibility of free gas
Cb = (ssCs + shCh) + (ss/Cs + sh/Ch)-1	Average compressibility of the solid part (Schön, 1996)
Cf = (swCw + sgCg) + (sw/Cw + sg/Cg)-1	Average compressibility of the fluid part (Schön, 1996)
z	Depth below sea floor
g	Acceleration of gravity
	Differential pressure
Pd0	Differential pressure immediately below sea floor
0	Porosity immediately below sea floor
Cp = (1 - eff/0)/(Pd - Pd0)	Pore compressibility
Cm = (1 - eff)Cb + effCp	Compressibility of the matrix
ß = Cb/Cm	Compressibility ratio
µsm0	Shear modulus for matrix without gas hydrate
µsmKT	Kuster-Toksöz's shear modulus (Kuster-Toksöz, 1974)
µ = [µsmKT - µsm0][h/(1 - s)]3.8 + µsm0	Solid matrix shear modulus (Leclaire, 1992)
µs	Rigidity of grains
µh	Rigidity of gas hydrate
µ = (s + h)(sss/µsm + sh/µh)-1	Average rigidity of the skeleton
k	Coupling factor