REFERENCES

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Ecker, C., Dvorkin, J., and Nur, A., 1996, Sediments with gas hydrates: Internal structure from seismic AVO: Geophysics, submitted for publication.

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Korenaga, J., Holbrook, W. S., Singh, S. C., and Minshull, T. A., 1997, Natural gas hydrates on the southeast U.S. margin: Constraints from full-waveform and travel time inversions of wide-angle seismic data: Jour. Geophys. Res., 102, 15345-15365.

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A

The Parameters S_n and S_tau are calculated as follows:

$$\begin{eqnarray} S_n&=&\:A_n (\Lambda_n)\:\alpha^2\:+\:B_n (\Lambda_n)\:\alpha\:... ...pha& = &\: \left[{{2\:S_h\:\phi}\over{3\:(1-\phi)}}\right ]^{0.5};\end{eqnarray}$$

where G and $\nu$ are the shear modulus and Poisson's ratio, respectively, of the sediment. The hydrate properties are given by its shear moduli G_h and Poisson's ratio $\nu_h$. The parameter $\alpha$ is the ratio of the cemented contact radius to the grain radius in case of hydrate evenly enveloping the sediment grains.

B

Here we give the calculation parameters for the sediment, hydrate, water, and gas properties used in the forward modeling approach.

Substance Bulk Modulus [GPa] Shear Modulus [GPa] Density [g/cm³]

Calcite 76.8 32 2.71

Clay 20.9 6.85 2.58

Quartz 36 45 2.65

Water 2.5 1.032

Pure Hydrate 5.6 2.4 0.9

Gas 0.1 0.235

Table 1: Properties of sediment mineralogy, water, gas and pure hydrate and

C

Here we describe the calculation parameters used for the synthetic modeling.

Layer Thickness [km] Saturation (Model 1) (Model 2) (Model 3)

Water 3.315 100% brine

Brine sediment 0.2 100% brine

Hydrate sediment 0.3 31% 23% 0.08%

Gas sediment 0.3 2% gas

Brine sediment 0.5 100% brine

Table 2: Model used to calculate synthetic seismograms.