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  • 1
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    Characterization of the seismic velocities in a gas chimney blow the actively seeping Lunde pockmark, Vestnesa Ridge, Svalbard Margin: Preliminary results (2021)
    In:  [Poster] In: 81. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG), 01.03.-05.03.2021, Kiel (online) .
    Details
    Publication Date: 2021-07-09
    Description: Hydrocarbon gases are actively seeping from pockmarks in the eastern part of the Vestnesa Ridge, western-Svalbard Margin. One of these is Lunde pockmark which is characterized by a seismic chimney below. Such seismic anomalies are widely believed to represent fluid migration pathways. However, their detailed structure and the physical properties of such structures is poorly understood and might be highly variable. Tomographic seismic velocity analysis can resolve the inner structure of the chimney beneath the Lunde pockmark. The aim is to understand the distribution of gas hydrate, free gas and carbonates within the gas chimney. Here, we present first results of our detailed 3D seismic travel time tomography using newly acquired high-resolution ocean bottom seismometer data guided by high-resolution 3D multi-channel seismic data. These models were generated with the Jive3D software. Our initial results show the variability of the seismic velocity structure beneath the Lunde pockmark. Our analysis, combined with earlier datasets and results shows that fluid pathways through the gas hydrate stability zone are anything but simple and highlights the importance of understanding the evolution of methane seepage pathways through time.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
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    Origin and periodic behavior of short duration signals recorded by seismometers at Vestnesa Ridge, an active seepage site on the west-Svalbard continental margin (2022)
    In:  EPIC3Frontiers in Earth Science
    Details
    Publication Date: 2022-03-13
    Description: Short duration events (SDEs) are reported worldwide from ocean-bottom seismometers (OBSs). Due to their high frequency (4–30 Hz) and short duration, they are commonly attributed to aseismic sources, such as fluid migration related processes from cold seeps, biological signals, or noise. We present the results of a passive seismic experiment that deployed an OBS network for 10-month (October 2015–July 2016) at an active seepage site on Vestnesa Ridge, West Svalbard continental margin.We characterize SDEs and their temporal occurrence using the conventional short-time-average over long-time-average approach. Signal periodograms show that SDEs have periodic patterns related to solar and lunar cycles. A monthly correlation between SDE occurrences and modelled tides for the area indicates that tides have a partial control on SDEs recorded over 10 months. The numbers of SDEs increase close to the tidal minima and maxima, although a correlation with tidal highs appears more robust. Large bursts of SDEs are separated by interim quiet cycles. In contrast, the periodicity analysis of tremors shows a different pattern, likely caused by the effect of tidally controlled underwater currents on the instrumentation. We suggest that SDEs at Vestnesa Ridge may be related to the dynamics of the methane seepage system which is characterized by a complex interaction between migration of deep sourced fluids, gas hydrate formation and seafloor gas advection through cracks. Our observation from this investigated area offshore west-Svalbard, is in line with the documentation of SDEs from other continental margins, where micro-seismicity and gas release into the water column are seemingly connected.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Local Seismicity and Sediment Deformation in the West Svalbard Margin: Implications of Neotectonics for Seafloor Seepage (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry Geophysics Geosystems, American Geophysical Union (AGU), 24(12), ISSN: 1525-2027
    Details
    Publication Date: 2024-01-22
    Description: 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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    SEAMSTRESS: DEPAS ocean-bottom seismometer operations on Vestnesa Ridge in 2020-2021 (2023)
    GFZ Data Services
    Details
    Publication Date: 2023-11-06
    Description: “This ocean-bottom seismometer deployment is part of the SEAMSTRESS project examining tectonic stress effects on Arctic methane seepage. The project is led by PI Andreia Plaza-Faverola at the Centre for Arctic Gas Hydrates, University of Tromsö, Norway. A total of 10 ocean bottom seismometers (OBS) were deployed on Vestnesa Ridge, a sediment drift body just north Knipovich Ridge at its intersection with the Molloy Transform fault (cruise CAGE-20-5). The aim of the experiment was to look for stress release along faults that control seepage sites on Vestnesa Ridge. The network consisted of 8 Lobster type broadband OBS from the German Instrument Pool for Amphibian Seismology (DEPAS) and 2 3C geophones provided by the University of Tromsö. Instruments were free-fall deployed and spaced by about 10 km. They recorded continuously at 100 Hz for 11 months between August 2020 and July 2021.Short, intersecting refraction profiles were shot across all OBS stations, such that OBS positions at the seafloor could be determined within 10 m (cruise CAGE-21-3). Clock drift in this experiment was nonlinear and skew values were only obtained for 6 of the stations. Skew-corrected station VSN01 served as reference station to obtain the clock drift of all other stations using noise cross-correlation and subsequently correct also for the thus determined nonlinearity of time drift. Waveform data are available from the GEOFON data centre, under network code Y9 and are embargoed until July 2025.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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