S-Wave Velocities and Anisotropy in Methane Hydrate- and Gas- Bearing Sediments Offshore Svalbard - the HYDRATECH Project <p> HR: <span class="hr"> 14:40h<br></span> AN: <span class="an"> OS42B-05 <a href="../absbook/fm03-OS42B.pdf">[PDF]</a><br></span> TI: <span class="ti"> S-Wave Velocities and Anisotropy in Methane Hydrate- and Gas- Bearing Sediments Offshore Svalbard - the HYDRATECH Project <br></span> AU: <span class="au"> * Westbrook, G K<br></span> EM: <span class="em"> G.K.Westbrook@bham.ac.uk<br></span> AF: <span class="af"> School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT United Kingdom <br></span> AU: <span class="au"> Long, C <br></span> EM: <span class="em"> C.Long@bham.ac.uk<br></span> AF: <span class="af"> School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT United Kingdom <br></span> AU: <span class="au"> Peacock, S <br></span> EM: <span class="em"> S.Peacock@bham.ac.uk<br></span> AF: <span class="af"> School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT United Kingdom <br></span> AU: <span class="au"> Haacke, R <br></span> EM: <span class="em"> RRH826@bham.ac.uk<br></span> AF: <span class="af"> School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT United Kingdom <br></span> AU: <span class="au"> Rossi, G <br></span> EM: <span class="em"> grossi@ogs.trieste.it<br></span> AF: <span class="af"> Istituto Nazionale di Ocenografia e di Geofisica Sperimentale, Sgonico (TS), Trieste, I-34010 Italy <br></span> AU: <span class="au"> Madrussani, G <br></span> EM: <span class="em"> gmadrussani@ogs.trieste.it<br></span> AF: <span class="af"> Istituto Nazionale di Ocenografia e di Geofisica Sperimentale, Sgonico (TS), Trieste, I-34010 Italy <br></span> AU: <span class="au"> Foucher, J P<br></span> EM: <span class="em"> jfoucher@ifremer.fr<br></span> AF: <span class="af"> IFREMER, Plouzane, Brest, 29280 France <br></span> AU: <span class="au"> Nouze, H <br></span> EM: <span class="em"> Herve.Nouze@ifremer.fr<br></span> AF: <span class="af"> Istituto Nazionale di Ocenografia e di Geofisica Sperimentale, Sgonico (TS), Trieste, I-34010 Italy <br></span> AU: <span class="au"> Reston, T <br></span> EM: <span class="em"> treston@geomar.de<br></span> AF: <span class="af"> GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany <br></span> AU: <span class="au"> Zillmer, M <br></span> EM: <span class="em"> MZillmer@geomar.de<br></span> AF: <span class="af"> GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany <br></span> AU: <span class="au"> Mienert, J <br></span> EM: <span class="em"> Juergen.Mienert@ig.uit.no<br></span> AF: <span class="af"> Department of Geology, University of Tromsoe, Tromsoe, 9037 Norway <br></span> AU: <span class="au"> Vanneste, M <br></span> EM: <span class="em"> Maarten.Vanneste@ig.uit.no<br></span> AF: <span class="af"> Department of Geology, University of Tromsoe, Tromsoe, 9037 Norway <br></span> AU: <span class="au"> Buenz, S <br></span> EM: <span class="em"> Stefan.Buenz@ig.uit.no<br></span> AF: <span class="af"> Department of Geology, University of Tromsoe, Tromsoe, 9037 Norway <br></span> AB: <span class="ab"> As part of the HYDRATECH project, an EC Framework-5 research project devoted to the development of techniques for the quantification of methane hydrate in European continental margins, seismic experiments were conducted at two sites in the continental margin off western Svalbard. At each site, an array of 20 four-component OBS at 400-m spacing was deployed at the centre of a grid of seismic lines shot with 200-m line spacing and a 20-m shot spacing. The seismic source comprised two 0.65-litre sleeve guns, and single-channel reflection profiles were recorded along each shot line. The bottom-simulating reflector [BSR] lies about 200 m below the seabed. The BSR, with opposite polarity to the seabed reflector, cuts obliquely across the reflectors related to bedding, which show increased relative amplitude and lower frequency content beneath the BSR. Some of these reflectors show a change in polarity where they cross the BSR, and in places the hydrate/gas transition is only evident from the change in amplitude of the bedding reflectors. Seismic velocity was obtained in 2D and 3D by ray-tracing and tomographic inversion of travel times. In a zone about 50-m thick above the BSR, P-wave velocity is increased above that expected for a typical increase of velocity with depth from compaction. It decreases sharply beneath the BSR, and returns to more normal values, with increasing depth, over the next 150 m. Clear S-waves were generated by P-to-S conversion on reflection. Poisson's ratio decreases rapidly in a 50-m thick zone beneath the BSR, in response to a reduction in the bulk modulus caused by the presence of free gas, whereas the shear modulus increases consistently with depth. At this location, the presence of hydrate seems not to have increased the shear modulus of sediment significantly. Travel-time anomalies and S-wave splitting indicate anisotropy that is probably caused by vertical cracks in the gas-bearing sediments beneath the BSR. These cracks may provide the principal route for the upward migration of methane. <br></span> UR: <span class="one"> <a href='http://www.hydratech.bham.ac.uk' >http://www.hydratech.bham.ac.uk</a> <br></span> DE: <span class="de"> 1724 Ocean sciences<br></span> DE: <span class="de"> 3000 MARINE GEOLOGY AND GEOPHYSICS<br></span> DE: <span class="de"> 3025 Marine seismics (0935)<br></span> SC: <span class="sc"> Ocean Sciences [OS]<br></span> MN: <span class="mn"> 2003 Fall Meeting<br></span></p></body></html>