HR: 10:35h
AN: OS42A-02    [Abstracts]
TI: Amplitude Variation With Offset (AVO) Inversion in Marine Gas Hydrate Studies
AU: * Chen, M P
EM: mchen@uvic.ca
AF: University of Victoria, School of Earth and Ocean Sciences, P.O. Box 3055, Victoria, BC V8W 3P6 Canada
AU: * Chen, M P
EM: mchen@uvic.ca
AF: Geological Survey of Canada, Pacific Geoscience Center, P.O. Box 6000, 9860 W. Saanich Road, Sidney, BC V8L 4B2 Canada
AU: Riedel, M
OS42A-02 AF: Geological Survey of Canada, Pacific Geoscience Center, P.O. Box 6000, 9860 W. Saanich Road, Sidney, BC V8L 4B2 Canada
AU: Dosso, S E
OS42A-02 AF: University of Victoria, School of Earth and Ocean Sciences, P.O. Box 3055, Victoria, BC V8W 3P6 Canada
AU: Hyndman, R D
OS42A-02 AF: University of Victoria, School of Earth and Ocean Sciences, P.O. Box 3055, Victoria, BC V8W 3P6 Canada
AU: Hyndman, R D
OS42A-02 AF: Geological Survey of Canada, Pacific Geoscience Center, P.O. Box 6000, 9860 W. Saanich Road, Sidney, BC V8L 4B2 Canada
AU: Spence, G D
OS42A-02 AF: University of Victoria, School of Earth and Ocean Sciences, P.O. Box 3055, Victoria, BC V8W 3P6 Canada
AB: Seismic amplitude versus offset (AVO) analysis is one of several tools for estimation of gas hydrate and free gas concentrations at the base of a gas hydrate stability field. From AVO data, a Bayesian inversion approach is used to obtain estimates and uncertainties of the physical parameters at an interface corresponding to a bottom-simulating reflector (BSR), related to gas hydrate occurrences. The way in which the amplitude of a seismic reflection varies with angle of incidence, described by the Zoeppritz (1919) equations, depends on P- and S-wave seismic velocities, and densities of both media. These physical parameters can in turn be related to hydrate and free gas concentration. The inversion is based on Gibbs' sampling approach to determine properties of the posterior probability distribution, such as marginal probability distributions (MPDs) for each physical parameter, which allows for an assessment of the uncertainty in the inversion results. Synthetic test cases are generated, designed to emulate the geometry and quality of available multi-channel seismic (MCS) data. For synthetic test cases representing MCS data with incidence angles up to 40°, the MPDs of the physical parameters are too wide to confidently determine their values. The problem is deemed underdetermined, because the range of incidence angles available is too small to fully characterize the AVO behavior of the interface. Synthetic cases representative of MCS data with incidence angles up to 80° give MPDs of physical parameters with significantly lower uncertainties. This Bayesian inversion approach is then applied to expanding spread profile data (with incidence angles up to 80°) from northern Cascadia, where a BSR reflection is present. The inversion yields estimates and uncertainties of physical parameters at the BSR, from which gas hydrate and free gas concentrations are in turn estimated, based on the supporting matrix/grain rock physics model for gas hydrate bearing sediments.
DE: 3004 Gas and hydrate systems
DE: 3025 Marine seismics (0935, 7294)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005