HR: 09:45h
AN: OS21A-08    [Abstracts]
TI: High-Resolution 3D-Seismic Investigations Indicate Focused Fluid Flow Systems in Hydrated Sediments at the Vestnesa Ridge off the W-Svalbard Margin.
AU: * Petersen, C
EM: joerg.petersen@ig.uit.no
AF: University of Tromsoe, Department of Geology, Drammsveien 201, Tromsoe, 9037, Norway
AU: Buenz, S
EM: stefan.buenz@ig.uit.no
AF: University of Tromsoe, Department of Geology, Drammsveien 201, Tromsoe, 9037, Norway
AU: Hustoft, S
EM: steinar.hustoft@ig.uit.no
AF: University of Tromsoe, Department of Geology, Drammsveien 201, Tromsoe, 9037, Norway
AU: Mienert, J
EM: juergen.mienert@ig.uit.no
AF: University of Tromsoe, Department of Geology, Drammsveien 201, Tromsoe, 9037, Norway
AB: High-resolution seismic data were acquired using the 3D seismic P-Cable system of the University of Tromsoe to investigate how the fluid flow penetrates gas hydrate systems of the Vestnesa Ridge. The ridge represents a current-controlled sediment drift on the continental margin offshore western Svalbard. The survey area is located at the northwestern part of the Vestnesa Ridge and centered at the ridge crest that resembles an anticline in a water depth of 1250-1320 m. The seafloor morphology at the crest is characterized by an abundance of pockmarks with a diameter between 50-500 m indicating recent fluid flow activity. Since the area is within the gas hydrate stability zone (GHSZ), it is an ideal site to understand where and how fluids escape through a hydrated sediment drift. 35 reflection seismic profiles with a spacing of about 40-60 m were shot resulting in a seismic cube covering an area of approximately 22 km². In addition, regional single channel streamer (SCS) seismic lines were acquired across the ridge perpendicular to the crest to connect the 3D area with the regional structural setting. The seismic data provide images of the subsurface to about 500 ms TWT (two-way time) below the seafloor (bsf), where gas accumulations cause acoustic attenuations that hinder deeper acoustic signal penetration. The well-stratified sediments exhibit a bottom simulating reflector (BSR) at about 200 ms TWT bsf at the base of the GHSZ. The BSR is difficult to identify due to the stratification, but it is accompanied by the onset of an ubiquitous band of strong reflectivity indicating free gas accumulation zones beneath the GHSZ. Fluid flow activity is evident from a link between gas accumulations (bright spots), gas wipeouts and disturbed reflectivity in the seismic data. These features are observed not only beneath the pockmark structures, but also in the sediment without seafloor expressions of fluid venting. The fluid source might be related to deep tectonic processes at the sedimented ocean ridge. Regional faults seen in the bathymetry data running across the Vestnesa Ridge are located beneath the pockmark fields. They may provide major fluid migration pathways, and in addition, heat flow driven hydrate dissociation is likely to play a significant role in fluid flow dynamics.
DE: 0935 Seismic methods (3025, 7294)
DE: 3004 Gas and hydrate systems
DE: 3025 Marine seismics (0935, 7294)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting