Constraints on fluid flow pathways from shear wave splitting in and around an active fluid-escape structure: Scanner Pockmark, North Sea

SUMMARY Vertical fluid-escape structures observed in seismic reflection data represent an important class of potentially active fluid flow pathways. An understanding the mechanism these types is needed to assess risk natural gas venting from potential subsurface carbon dioxide storage operations. The Scanner Pockmark Complex a 22 m deep, 900 × 450 seabed depression North Sea, which actively vents methane, and underlain by chimney structure with horizontal dimensions ?300 600 m. Gas accumulation evidenced presence bright reflectors at top this chimney, depth ?50 below seabed. Here, we analyse anisotropy shallow sediments using shear wave splitting on ocean bottom seismographs (OBS). Anisotropy varies spatially, strength ?1–4 per cent, several OBS located around pockmark complex. By correlating observations calculated P- S-wave velocities, show that there present throughout through passes, are interpreted as relating syn- post-depositional glaciomarine processes. However, within itself orientation fast direction different outside degree lower. We attribute difference indicating associated formation continued migration system, overprints background depositional anisotropy.