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  • 1
    Publication Date: 2018-12-04
    Description: Highlights • Increased glacial sedimentation rates do not generate sufficient overpressure to trigger a landslide. • Simulated overpressures for different sedimentation scenarios do not significantly differ. • A glacimarine layer underneath rapidly-deposited sediments is important for overpressure build-up. • An earthquake of M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the Tampen Slide. Abstract Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries. In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment. Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 2
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    In:  [Talk] In: 3. Applied Shallow Marine Geophysics Conference, 09.-13.09.2018, Porto, Portugal .
    Publication Date: 2019-01-10
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] During a recent cruise in the Porcupine Basin, off southwest Ireland, we discovered two extensive and hitherto largely unsuspected deep-water reef provinces, including a giant cluster of hundreds of buried mounds. The ring shapes of many reefs suggest that they are caused by an axial fluid ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Analytical Biochemistry 107 (1980), S. 86-95 
    ISSN: 0003-2697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Insurance Mathematics and Economics 15 (1994), S. 37-48 
    ISSN: 0167-6687
    Keywords: Annuities ; Functional integration ; Random interest rate
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mathematics , Economics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0167-6687
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mathematics , Economics
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2017-07-21
    Description: A multi-component Ocean Bottom Seismometer (OBS) survey in the Ormen Lange area of the Storegga Slide constrained the existence of free gas and possibly gas hydrates in the shallow subsurface. The three investigated areas (A, B, C) lie in close vicinity to the slide scar above one of the largest deep-water gas reservoirs on the mid-Norwegian margin. Generally, P-wave and S-wave velocities are high compared to average velocities at a given burial depth due to an exposure of deeper sediments as a consequence of sediment mass movement by the Storegga slide. Indications for the presence of gas within the sediments exist for two of the three investigated areas. The gas accumulates beneath less permeable layers of glacigenic debris flow deposits. Average gas concentration of pore space in both areas is 0.9% (area A) and 0.15% (area B). The geophysical data do not allow a conclusive answer about the occurrence of gas hydrates. Their presence might be masked by high-velocity debris flow deposits, which occur in the subsurface. Nevertheless, gas hydrate concentrations of pore space have been estimated to about 9% in area A and 7% in area B.
    Type: Article , PeerReviewed
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  • 8
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    In:  [Talk] In: Near Surface Geoscience 2016 - Second Applied Shallow Marine Geophysics Conference, 04.-08.09.2016, Barcelona, Spain .
    Publication Date: 2017-01-02
    Description: We created a two-dimensional geomechanical model to analyse the hazard of hydrate production induced slope failures in a channel-levee system of the Danube paleo-fan in the Black Sea. Gas hydrates presumably have accumulated in coarse-grained sediments at the base of a paleo channel. The exploitation scenario is based on depressurization of the reservoir along a vertical drill hole. The model geometry is based on high resolution reflection seismic data. Initial results estimated the failure surface at the steepest part of the levee slope (〉8° dip) with a Factor of Safety of 1.254, which is considered to be critically affected by seabed subsidence. Preliminary results show that the estimated subsidence at the seafloor after pore pressure depletion of the gas hydrate reservoir is only in the order of centimeters. The effect of production-induced subsidence on the stability of critical slopes will be minor. However, the inherent stability of the slope is still under marginal ranges, and the material properties and production scenario still have big uncertainties due to lack of information.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
    Publication Date: 2001-01-01
    Description: High-resolution reflection seismic investigations carried out in the Porcupine Basin, SW of Ireland, have shed light on the presence of several provinces of giant carbonate mounds. An intriguing setting is found on the northern slope of the basin. A cluster of surface mounds appears to be flanked by a large upslope, crescent-shaped province of buried mounds. Below the transitional zone, large imbricated slide scars suggest repeated failures. The buried mounds rise from an undisturbed basal horizon and seem to represent a single event, confined in time and space. Both high-resolution and industrial seismic data reveal a close vertical match of the mound cluster with a lower, buried sea-bed failure, where hydrate build-up may have played a role. The latter association may not be entirely fortuitous. It is suggested that gas venting may have triggered the formation of the mound clusters, and that the underlying sea-bed failure forms a previous but different expression of gas venting, on a common, episodic fluid migration pathway but under strongly contrasting bottom water temperature conditions.
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  • 10
    Publication Date: 2017-07-21
    Description: High-resolution seismic experiments, employing arrays of closely spaced, four-component ocean-bottom seismic recorders, were conducted at a site off western Svalbard and a site on the northern margin of the Storegga slide, off Norway to investigate how well seismic data can be used to determine the concentration of methane hydrate beneath the seabed. Data from P-waves and from S-waves generated by P–S conversion on reflection were inverted for P- and S-wave velocity (Vp and Vs), using 3D travel-time tomography, 2D ray-tracing inversion and 1D waveform inversion. At the NW Svalbard site, positive Vp anomalies above a sea-bottom-simulating reflector (BSR) indicate the presence of gas hydrate. A zone containing free gas up to 150-m thick, lying immediately beneath the BSR, is indicated by a large reduction in Vp without significant reduction in Vs. At the Storegga site, the lateral and vertical variation in Vp and Vs and the variation in amplitude and polarity of reflectors indicate a heterogeneous distribution of hydrate that is related to a stratigraphically mediated distribution of free gas beneath the BSR. Derivation of hydrate content from Vp and Vs was evaluated, using different models for how hydrate affects the seismic properties of the sediment host and different approaches for estimating the background-velocity of the sediment host. The error in the average Vp of an interval of 20-m thickness is about 2.5%, at 95% confidence, and yields a resolution of hydrate concentration of about 3%, if hydrate forms a connected framework, or about 7%, if it is both pore-filling and framework-forming. At NW Svalbard, in a zone about 90-m thick above the BSR, a Biot-theory-based method predicts hydrate concentrations of up to 11% of pore space, and an effective-medium-based method predicts concentrations of up to 6%, if hydrate forms a connected framework, or 12%, if hydrate is both pore-filling and framework-forming. At Storegga, hydrate concentrations of up to 10% or 20% were predicted, depending on the hydrate model, in a zone about 120-m thick above a BSR. With seismic techniques alone, we can only estimate with any confidence the average hydrate content of broad intervals containing more than one layer, not only because of the uncertainty in the layer-by-layer variation in lithology, but also because of the negative correlation in the errors of estimation of velocity between adjacent layers. In this investigation, an interval of about 20-m thickness (equivalent to between 2 and 5 layers in the model used for waveform inversion) was the smallest within which one could sensibly estimate the hydrate content. If lithological layering much thinner than 20-m thickness controls hydrate content, then hydrate concentrations within layers could significantly exceed or fall below the average values derived from seismic data.
    Type: Article , PeerReviewed
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