Local Seismicity and Sediment Deformation in the West Svalbard Margin: Implications of Neotectonics for Seafloor Seepage

Abstract

In the Fram Strait, mid‐ocean ridge spreading is represented by the ultra‐slow system of the Molloy Ridge, the Molloy Transform Fault and the Knipovich Ridge. Sediments on oceanic and continental crust are gas charged and there are several locations with documented seafloor seepage. Sedimentary faulting shows recent stress release in the sub‐surface, but the drivers of stress change and its influence on fluid flow are not entirely understood. We present here the results of an 11‐month‐long ocean bottom seismometer survey conducted over the highly faulted sediment drift northwards from the Knipovich Ridge to monitor seismicity and infer the regional state of stress. We obtain a detailed earthquake catalog that improves the spatial resolution of mid‐ocean ridge seismicity compared with published data. Seismicity at the Molloy Transform Fault is occurring southwards from the bathymetric imprint of the fault, as supported by a seismic profile. Earthquakes in the northern termination of the Knipovich Ridge extend eastwards from the ridge valley, which together with syn‐rift faulting identified in seismic reflection data, suggests that a portion of the currently active spreading center is buried under sediments away from the bathymetric expression of the rift valley. This hints at the direct link between crustal rifting processes and faulting in shallow sediments. Two earthquakes occur close to the seepage system of the Vestnesa Ridge further north from the network. We suggest that deeper rift structures, reactivated by gravity and/or post‐glacial subsidence, may lead to accommodation of stress through shallow extensional faults, therefore impacting seepage dynamics.

Variations in deep-sea methane seepage linked to millennial-scale changes in bottom water temperatures ~50–6 ka, NW Svalbard margin

“…Widespread occurrences of low δ 13 C values during the Bølling-Allerød interstadials indicate that similar emissions occurred simultaneously over large areas of the western Svalbard margin 40,55 including shelf areas 29 . Another contributory cause to the widespread and strong emission of methane during the Bølling and Allerød interstadials could be tectonic movements due to the proximity of the Knipovich Ridge spreading zone 37,45,70 , isostatic rebound [71][72][73] and/or high sedimentation rates 35 .…”

Glacial-interglacial sedimentation control on gas seepage exemplified by Vestnesa Ridge off NW Svalbard margin

“…According to our results the change from advective to diffusive seepage probably occurred at ∼10 ka. Nevertheless, active tectonism and onshore and offshore isostatic rebound continued after ∼10 ka and until today (e.g., Forman et al, 2004;Vachon et al, 2022;Domel et al, 2023). Fine-grained drift sediments can often seal fractured or coarse, porous glacial sediments in contourites exampled by studies of the very seismically active Hikurangi Margin, New Zealand (Bailey et al, 2021).…”