georefid:2012-020901SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2013-07-08T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=10.1111/j.1365-246X.2011.05215.x2011-01-01publicationgeorefid:2012-020901doi:10.1111/j.1365-246X.2011.05215.xDash, RanjanUniversity of Victoria, School of Earth and Ocean Sciences, Victoria, BC, CanadaauthorSpence, GeorgeauthorWiley-Blackwell on behalf of The Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft and the European Geophysical Society, InternationalpublisherdocumentHardcopyGeophysical Journal International187 (3)1363-1377Single-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(+ or -5) m below the seafloor (mbsf). Mean velocities, which increased from 1.50 km s (super -1) at the seafloor to 1.88 km s (super -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. Abstract Copyright (2011), RAS.completedSolid-earth geophysicsApplied geophysicsattenuationbody wavesBritish ColumbiaCanadaCascadia BasincrustEast Pacificelastic wavesExpedition 311gas hydratesgeophysical methodsgeophysical profilesgeophysical surveysIntegrated Ocean Drilling ProgramIODP Site U1327Leg 146North PacificNortheast PacificOcean Drilling ProgramODP Site 889offshoreP-wavesPacific Oceanpermeabilityporosityreflection methodsS-wavesseismic methodsseismic profilesseismic wavessimulationsurveystomographyVancouver Islandvelocity structureWestern Canadaurn:org.iodp:exp:311urnlargerWorkCitationcampaignurn:org.iodp:exp:146urnlargerWorkCitationcampaignurn:org.iodp:exp:311:site:U1327urnlargerWorkCitationstudyurn:org.iodp:exp:311urnlargerWorkCitationcampaignurn:org.iodp:exp:146:site:889urnlargerWorkCitationstudyurn:org.iodp:exp:146urnlargerWorkCitationcampaignEnglishgeoscientificInformation-126.5223-126.520048.415148.4200