3-D Seismic Imaging of an Active Margin Hydrate System - Oregon Continental Margin

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99-06990 Trehu99-07205 BangsRecommended project is for a high-resolution, 3-D marine seismic survey of a 9 x 4 km area on the crest of Hydrate Ridge, on the Cascadia accretionary complex of the offshore Oregon continental margin. The survey will use ocean bottom seismometers (OBS's) to optimize recording of the seismic signals, and will focus on mapping the presence of gas hydrate within the accretionary sediments in this region of high fluid flux. Other goals center on defining the gas hydrate stability conditions; estimation of gas hydrate and free gas volumes, with the free gas trapped beneath bottom simulating reflectors (BSR's) associated with gas hydrate presence; defining pathways of fluid flux and their importance in gas hydrate formation; and slope stability (or instability) related to gas hydrate presence on the Cascadia margin. Specific hypotheses to be tested by the research include: 1) do bright stratigraphic reflections represent developing zones of focused fluid flow; 2) does a double BSR imaged in previous multichannel work within an anticline in the study region represent destabilization of hydrate in response to folding; 3) can tomographic inversion of refracted arrivals image the sub-BSR volume in which free gas is present; and 4) does the presence of hydrate and free gas affect the mechanical properties and thus slope stability and morphology of accretionary complexes. This work will provide the 3-dimensional stratigraphic and structural context for the proposed Ocean Drilling Program drilling (ODP proposal 546-Full) on Hydrate Ridge, which is designed to "ground truth" the factors related to gas hydrate formation and stability.***