Seismic Evidence for Gas Hydrates

Although some details of the seismic reflection properties are not yet fully understood, it appears that the strength and the characteristics of the BSR is determined by the presence of free gas below the gas hydrate zone (Pauli et al. 1996). The presence of free gas represents a very laige change in seismic velocity, and therefore produces a very strong and sharply defined reflection. Theoretical models (Xu and Ruppel 

1999) and synthetic studies (Wood and Ruppel 2000) indicate that the BSR is not a necessary condition for the presence of hydrate, as it only occurs when there is free gas beneath the distinct gas hydrate phase boundary. If there is no free gas below a deposit of gas hydrate, there will be no BSR. Indeed, sediments containing gas hydrate liave been recovered from areas where there is no BSR (Mathews and vonHuene 1985). 

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