Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Volume 119, Issue 1, Pages 99-115Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2013JB010101
Keywords
carbonate mound; gas hydrate; heat flux; fluid flow; 3-D FEA modeling
Categories
Funding
- National Natural Science Foundation of China [40830423, 40904029]
- Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China
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The bottom-simulating reflector (BSR) of gas hydrate is well imaged from two perpendicular seismic grids in the region of a large carbonate mound, informally called Cucumber Ridge off Vancouver Island. We use a new method to calculate 3-D heat flow map from the BSR depths, in which we incorporate 3-D topographic corrections after calibrated by the drilling results from nearby (Integrated) Ocean Drilling Program Site 889 and Site U1327. We then estimate the associated fluid flow by relating it to the topographically corrected heat flux anomalies. In the midslope region, a heat flux anomaly of 1mW/m(2) can be associated with an approximate focused fluid flow rate of 0.09 mm/yr. Around Cucumber Ridge, high rates of focused fluid flow were observed at steep slopes with values more than double the average regional diffusive fluid discharge rate of 0.56 mm/yr. As well, in some areas of relatively flat seafloor, the focused fluid flow rates still exceeded 0.5 mm/yr. On the seismic lines the regions of focused fluid flow were commonly associated with seismic blanking zones above the BSR and sometimes with strong reflectors below the BSR, indicating that the faults/fractures provide high-permeability pathways for fluids to carry methane from BSR depths to the seafloor. These high fluid flow regions cover mostly the western portion of our area with gas hydrate concentration estimations of similar to 6% based on empirical correlations from Hydrate Ridge in south off Oregon, significantly higher than previously recognized values of similar to 2.5% in the eastern portion determined from Site U1327.
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