HR: 14:15h
AN: NS13A-04 INVITED     [Abstracts]
TI: Assessing Deep Water Gas Hydrate Systems and Seafloor Stability
AU: * Hardage, B A
EM: bob.hardage@beg.utexas.edu
AF: Bureau of Economic Geology, University Station, Box X, Austin, Tx 78713 United States
AU: Roberts, H H
EM: hrober3@lsu.edu
AF: Coastal Studies Institute, Louisiana State University, Baton Rouge, La 70803 United States
AB: We demonstrate how four-component ocean-bottom-cable (4-C OBC) seismic data acquired in deep water can be used to study near-seafloor strata and the geologic characteristics of fluid and gas expulsion systems that extend to the seafloor and become thermogenic sources of gas hydrates. We document the importance of the converted-shear (P-SV) mode extracted from 4-C OBC data. We show that P-SV data provide a spatial resolution of deep-water, near-seafloor strata that is an order of magnitude better than the resolution of the compressional (P-P) mode. Shear wave velocities less than 100 m/s in unconsolidated near-seafloor sediments produce scattered SV wavelengths of meter scale even when long-range surface-based air guns illuminate the seafloor with frequencies that do not exceed 100 Hz. These short wavelengths allow the P-SV mode to define geologic detail that cannot be detected with P-P scattered data. The geomechanical properties of the seafloor strata are determined by transforming seismic measurements of compressional and shear velocities into estimates of compressional and shear moduli. Current 4-C OBC technology available from major seismic contractors allows deep-water gas hydrate systems and seafloor stability to now be studied over large areas of many hundreds of square kilometers.
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 4820 Gases
DE: 7203 Body wave propagation
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly