A three‐dimensional seismic tomographic study of the gas hydrate stability zone, offshore Vancouver Island

Hobro, James; Minshull, T. A.; Singh, S. C.; Chand, Shyam

doi:10.1029/2004jb003477

Cited by 21 publications

(9 citation statements)

References 31 publications

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“…Our hydrate estimate is higher because it accounts for broad zones of previously undetected hydrate across the region (Fig. 4); however, it is notably consistent with more recent mean hydrate estimates of 2%-4% to the north, offshore Cascadia (Hobro et al, 2005;Torres et al, 2008). Global hydrate estimates based on drilling results at Hydrate Ridge are likely too low by a factor of three because they fail to account accurately for 3-D variability of hydrate (e.g., Milkov et al, 2003).…”

Section: Implications For Hydrate Quantifi Cationsupporting

confidence: 69%

Detecting hydrate and fluid flow from bottom simulating reflector depth anomalies

Hornbach

Bangs

Berndt

2012

Geology

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Methane hydrates, ice-like compounds that consist of water and methane, represent a potentially enormous unconventional methane resource that may play a critical role in climate change and ocean acidifi cation; however, it remains unclear how much hydrate exists. Here, using a newly developed three-dimensional (3-D) thermal technique, we reveal a novel method for detecting and quantifying methane hydrate. The analysis reveals where fl uids migrate in three dimensions across a continental margin and is used to quantify hydrate with meter-scale horizontal resolution. Our study, located at Hydrate Ridge, offshore Oregon (United States), suggests that heat fl ow and hydrate concentrations are coupled and that 3-D thermal analysis can be used to constrain hydrate and fl uid fl ow in 3-D seismic data. Hydrate estimates using this technique are consistent with 1-D drilling results, but reveal large, previously unrecognized swaths of hydrate-rich sediments that have gone undetected due to spatially limited drilling and sampling techniques used in past studies. The 3-D analysis suggests that previous hydrate estimates based on drilling at this site are low by a factor of approximately three. 2000 3-D Survey 2008 3-D Survey

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Section: Implications For Hydrate Quantifi Cationsupporting

confidence: 69%

Detecting hydrate and fluid flow from bottom simulating reflector depth anomalies

Hornbach

Bangs

Berndt

2012

Geology

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“…Wide‐angle data from all ten OBSs were used in the velocity analysis. The OBS data in the mid‐slope region contain only reflections and almost no refraction events, consistent with other OBS surveys in this area (Hobro et al 2005; Zykov 2006). Hydrophone (pressure) components were chosen for picking.…”

Section: P‐wave Velocity Modellingsupporting

confidence: 89%

“…OBS surveys with hydrate targets have been carried out on the Cascadia margin off Oregon (Tréhu & Flueh 2001; Kumar et al . 2006a,b) and off Vancouver Island (Hobro et al . 2005; Zykov 2006).…”

Section: Introductionmentioning

confidence: 99%

P-wave and S-wave velocity structure of northern Cascadia margin gas hydrates

Dash¹,

Spence²

2011

Geophysical Journal International

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S U M M A R YSingle-channel seismic and wide-angle reflection data collected in September 2005 were analysed along a 2-D profile of 10 ocean bottom seismometers (OBSs) on the continental slope region off Vancouver Island, near ODP Site 889 and IODP Site U1327. The objectives were to determine the shallow P-wave and S-wave velocity structure associated with marine gas hydrates and to estimate the hydrate concentration and distribution in the sediment pore space. Combined traveltime inversion of single-channel and OBS data produced a P-wave velocity model down to the depth of the bottom-simulating reflector (BSR) at 230(±5) m below the seafloor (mbsf). Mean velocities, which increased from 1.50 km s -1 at the seafloor to 1.88 km s -1 at the BSR, are in good agreement with the sonic log data from Sites 889 and U1327. The increase in P-wave velocity of the hydrate-bearing sediments relative to a background no-hydrate velocity was utilized to estimate the hydrate concentration by using effective medium theory. An average concentration of 13 per cent in the interval from 120-230 mbsf was estimated from the P-wave velocity model. Lateral continuity of the model data confirms that these average hydrate concentrations are also found around the drillsites out to distances of a few kilometres. Forward modelling of S-waves was carried out using the data from the OBS horizontal components. Above the BSR, S-wave velocities are higher than a background velocity profile based on a rock physics model and on global averages for unconsolidated sediments. This increase in velocity suggests that the hydrate is distributed as part of the load-bearing matrix to increase the rigidity of the sediment.

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“…• Deployment of ocean-bottom seismographs for 2-D and 3-D traveltime inversion (Hobro et al, 2005;Spence et al, 1995),…”

Section: Background and Objectivesmentioning

confidence: 99%

Site U1327

2006

Proceedings of the IODP

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A three‐dimensional seismic tomographic study of the gas hydrate stability zone, offshore Vancouver Island

Cited by 21 publications

References 31 publications

Detecting hydrate and fluid flow from bottom simulating reflector depth anomalies

Detecting hydrate and fluid flow from bottom simulating reflector depth anomalies

P-wave and S-wave velocity structure of northern Cascadia margin gas hydrates

Site U1327

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