High-resolution 3D-seismic data indicate focussed fluid migration pathways above polygonal fault systems of the mid-Norwegian margin

Seismic attribute analysis and interpretation of high-resolution 3D- and 2D-seismic data reveal focussed fluid flow processes through the gas hydrate stability zone (GHSZ) at the northern flank of the giant Storegga Slide. Diffusive fluid migration predominantly starts from a widespread polygonal fault system in fine-grained sediments of the Miocene Kai Formation. The overlying 600-700 m thick Plio-Pleistocene Naust Formation shows spatially related soft-sediment deformation and overlying fluid conduits. A low relief antiform structure connects to an overlying 250 m high, 300 m wide and 3 km elongated columnar zone, where seismic signatures suggest self-enhanced permeability, i.e. natural hydraulic fracturing. "Push-down" effects create an elongated depression caused by increased gas accumulations where a cluster of vertical cylindrical acoustic pipe structures originates. These pipe clusters pierce the GHSZ and indicate focussed fluid flow pathways originating from potentially overpressured sediments. High seismic reflection amplitudes at the seafloor above the pipe structures may indicate pockmarks with authigenic carbonates and/or gas hydrates. The observed objects and seismic features presented are not stand-alone indicators for fluid flow, but a joint perspective illustrates that they are vertically tied together providing new insights to the effects of focussed fluid flow. (C) 2007 Elsevier B.V. All rights reserved.