Effect of Regional Forcing on Fault-related Seepage off West-Svalbard

Abstract:

Here we present the main results of a cross-disciplinary study that aims at quantifying the effect of regional processes (i.e., glacial isostatic adjustment, mid-ocean ridge spreading, tides, sedimentation) on faults and associated seepage dynamics along the west-Svalbard margin in the Fram Strait. We integrate high-resolution 3D P-Cable seismic imaging, long-term and short term ocean bottom seismic experiments and geomechanical tests, with stress field modeling (i.e., glacial and ridge push stress) to constrain the pressure field that controls seepage along this Arctic margin. The study puts special emphasis on explaining spatial and temporal variations in the release of methane along the Vestnesa ridge since the onset of glaciations at 2.7 Ma. The Vestnesa Ridge is a contourite drift deposited mostly over oceanic crust and it is bounded by the Svalbard continental shelf, the Molloy and Knipovich mid-ocean ridges and the Molloy and Spitsbergen transform faults. Field data reveal a close link between faults and fractures and seepage periodicity. Stress modeling shows patterns of stress magnitude and orientation that may have affected fault behavior and hence exerted a control on seepage distribution over geological time. In-situ sediment property data and geomechanical tests suggest sediment overpressure in the near-surface. We use the generated multi-disciplinary data and stress modeling information to constrain timing and pressure thresholds for the vertical migration of fluids through brecciated strata (gas chimneys) that sustain seabed seepage.