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  • 1
    Online Resource
    Online Resource
    SO 258 - INGON - The Indian-Antartic Break-up Engima : Schlussbericht : Laufzeit des Vorhabens: 01.03.2017-31.07.2019, Berichtszeitraum: 01.03.2017-31.07.2019 (2020)
    Bremerhaven : Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
    Details Availability
    Keywords: Forschungsbericht
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (24 Seiten, 12,70 MB) , Illustrationen, Diagramme
    URL: https://doi.org/10.2314/KXP:1692956914
    DOI: 10.2314/KXP:1692956914
    Language: German
    Note: Förderkennzeichen BMBF 03G0258A , Verbundnummer 01177085 , Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden
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  • 2
    Electronic Resource
    Electronic Resource
    The Moho Structure in The Western Eger Rift: A Receiver Function Experiment (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 188-194 
    Details
    ISSN: 1573-1626
    Keywords: Eger Rift ; Moho conversions ; receiver function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract We used teleseismic recordings of a temporary deployment of seismic stations and of permanent short period stations in the western Eger Rift system to study the lithosphere with the help of Receiver Functions. The crust-mantle boundary (Moho) is observed at almost all stations by strong P-to-S converted phases. The Moho is basically flat between about 26 – 30 km depth in the entire region. At one station in the Eger Rift (BOH-1, Loket castle) no Moho is observed. We interpret this with the existence of a broad gradient zone there, instead of a sharp discontinuity. This observation, however, needs to be confirmed by more data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022158725170
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    Paper (German National Licenses)
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  • 3
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    Submarine slope failures due to pipe structure formation (2018)
    Nature Research
    In:  Nature Communications, 9 (Art.No. 715).
    Details
    Publication Date: 2021-03-19
    Description: There is a strong spatial correlation between submarine slope failures and the occurrence of gas hydrates. This has been attributed to the dynamic nature of gas hydrate systems and the potential reduction of slope stability due to bottom water warming or sea level drop. However, 30 years of research into this process found no solid supporting evidence. Here we present new reflection seismic data from the Arctic Ocean and numerical modelling results supporting a different link between hydrates and slope stability. Hydrates reduce sediment permeability and cause build-up of overpressure at the base of the gas hydrate stability zone. Resulting hydro-fracturing forms pipe structures as pathways for overpressured fluids to migrate upward. Where these pipe structures reach shallow permeable beds, this overpressure transfers laterally and destabilises the slope. This process reconciles the spatial correlation of submarine landslides and gas hydrate, and it is independent of environmental change and water depth.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41467-018-03176-1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Seismicity in the vicinity of the Tristan da Cunha hotspot: Particular plate tectonics and mantle plume presence (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 122 (12). pp. 10427-10439.
    Details
    Publication Date: 2020-02-06
    Description: Earthquake locations along the southern Mid-Atlantic Ridge have large uncertainties due to the sparse distribution of permanent seismological stations in and around the South Atlantic Ocean. Most of the earthquakes are associated with plate tectonic processes related to the formation of new oceanic lithosphere, as they are located close to the ridge axis or in the immediate vicinity of transform faults. A local seismological network of ocean-bottom seismometers and land stations on and around the archipelago of Tristan da Cunha, allowed for the first time a local earthquake survey for one year. We relate intra-plate seismicity within the African oceanic plate segment north of the island partly to extensional stresses induced by a bordering large transform fault and to the existence of the Tristan mantle plume. The temporal propagation of earthquakes within the segment reflects the prevailing stress field. The strong extensional stresses in addition with the plume weaken the lithosphere and might hint at an incipient ridge jump. An apparently aseismic zone coincides with the proposed location of the Tristan conduit in the upper mantle southwest of the islands. The margins of this zone describe the transition between the ductile and the surrounding brittle regime. Moreover, we observe seismicity close to the islands of Tristan da Cunha and nearby seamounts, which we relate to ongoing tectono-magmatic activity.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1002/2017JB015017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Micro-seismicity in the Gulf of Cadiz: Is there a link between micro-seismicity, high magnitude earthquakes and active faults? (2017)
    Elsevier
    In:  Tectonophysics, 717 . pp. 226-241.
    Details
    Publication Date: 2020-02-06
    Description: The Gulf of Cadiz seismicity is characterized by persistent low to intermediate magnitude earthquakes, occasionally punctuated by high magnitude events such as the M ~ 8.7 1755 Great Lisbon earthquake and the M = 7.9 event of February 28th, 1969. Micro-seismicity was recorded during 11 months by a temporary network of 25 ocean bottom seismometers (OBSs) in an area of high seismic activity, encompassing the potential source areas of the mentioned large magnitude earthquakes. We combined micro-seismicity analysis with processing and interpretation of deep crustal seismic reflection profiles and available refraction data to investigate the possible tectonic control of the seismicity in the Gulf of Cadiz area. Three controlling mechanisms are explored: i) active tectonic structures, ii) transitions between different lithospheric domains and inherited Mesozoic structures, and iii) fault weakening mechanisms. Our results show that micro-seismicity is mostly located in the upper mantle and is associated with tectonic inversion of extensional rift structures and to the transition between different lithospheric/rheological domains. Even though the crustal structure is well imaged in the seismic profiles and in the bathymetry, crustal faults show low to negligible seismic activity. A possible explanation for this is that the crustal thrusts are thin-skinned structures rooting in relatively shallow sub-horizontal décollements associated with (aseismic) serpentinization levels at the top of the lithospheric mantle. Therefore, co-seismic slip along crustal thrusts may only occur during large magnitude events, while for most of the inter-seismic cycle these thrusts remain locked, or slip aseismically. We further speculate that high magnitude earthquake's ruptures may only nucleate in the lithospheric mantle and then propagate into the crust across the serpentinized layers.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.tecto.2017.07.026
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Gas hydrate distribution and hydrocarbon maturation north of the Knipovich Ridge, western Svalbard margin (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 121 (3). pp. 1405-1424.
    Details
    Publication Date: 2019-09-23
    Description: A bottom-simulating reflector (BSR) occurs west of Svalbard in water depths exceeding 600 m, indicating that gas hydrate occurrence in marine sediments is more widespread in this region than anywhere else on the eastern North Atlantic margin. Regional BSR mapping shows the presence of hydrate and free gas in several areas, with the largest area located north of the Knipovich Ridge, a slow-spreading ridge segment of the Mid Atlantic Ridge system. Here, heat flow is high (up to 330 mW m-2), increasing towards the ridge axis. The coinciding maxima in across-margin BSR width and heat flow suggest that the Knipovich Ridge influenced methane generation in this area. This is supported by recent finds of thermogenic methane at cold seeps north of the ridge termination. To evaluate the source rock potential on the western Svalbard margin, we applied 1D petroleum system modeling at three sites. The modeling shows that temperature and burial conditions near the ridge were sufficient to produce hydrocarbons. The bulk petroleum mass produced since the Eocene is at least 5 kt and could be as high as ~0.2 Mt. Most likely, source rocks are Miocene organic-rich sediments and a potential Eocene source rock that may exist in the area if early rifting created sufficiently deep depocenters. Thermogenic methane production could thus explain the more widespread presence of gas hydrates north of the Knipovich Ridge. The presence of microbial methane on the upper continental slope and shelf indicates that the origin of methane on the Svalbard margin varies spatially.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1002/2015JB012083
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Chronology of the Fram Slide Complex offshore NW Svalbard and its implications for local and regional slope stability (2017)
    Elsevier
    In:  Marine Geology, 393 . pp. 141-155.
    Details
    Publication Date: 2020-02-06
    Description: Highlights • The Fram Slide Complex has been active from late Miocene to late Pleistocene. • Local processes were critical for slope stability in the Fram Strait area. • Toe erosion caused by normal faulting may have led to retrogressive failure. • Low gradient contourite drifts might smooth and stabilize submarine slopes. • Low tsunami potential from the Fram Slide Complex could increase in the future. Abstract The best known submarine landslides on the glaciated NW European continental margins are those at the front of cross-shelf troughs, where the alternation of rapidly deposited glycogenic and hemi pelagic material generates sedimentary overpressure. Here, we investigate landslides in two areas built of contourite drifts bounded seaward by a ridge-transform junction. Seismic and bathymetric data from the Fram Slide Complex are compared with the tectonically similar Vastness area ~ 120 km to the south, to analyze the influence of local and regional processes on slope stability. These processes include tectonic activity, changes of climate and oceanography, gas hydrates and fluid migration systems, slope gradient, toe erosion and style of contourite deposition. Two areas within the Fram Slide Complex underwent different phases of slope failures, whereas there is no evidence at all for major slope failures in the Vastness area. The comparison cannot reveal the distinct reason for slope failure but demonstrates the strong impact of variation in the local controls on slope stability. The different failure chronologies suggest that toe erosion, which is dependent on the throw of normal faults, and the different thickness and geometry of contourite deposits can result in a critical slope morphology and exert pronounced effects on slope stability. These results highlight the limitations of regional hazard assessments and the need for multi-disciplinary investigations, as small differences in local controlling factors led to substantially different slope failure histories.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.margeo.2016.11.003
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Hunting for the Tristan Mantle Plume - An upper mantle tomography around the volcanic island of Tristan da Cunha (2017)
    Elsevier
    In:  Earth and Planetary Science Letters, 462 . pp. 122-131.
    Details
    Publication Date: 2020-02-06
    Description: The active volcanic island Tristan da Cunha, located at the southwestern and youngest end of the Walvis Ridge - Tristan/Gough hotspot track, is believed to be the surface expression of a huge thermal mantle anomaly. While several criteria for the diagnosis of a classical hotspot track are met, the Tristan region also shows some peculiarities. Consequently it is vigorously debated if the active volcanism in this region is the expression of a deep mantle plume, or if it is caused by shallow plate tectonics and the interaction with the nearby Mid-Atlantic Ridge. Because of a lack of geophysical data in the study area, no model or assumption has been completely confirmed. We present the first amphibian P-wave finite-frequency travel time tomography of the Tristan da Cunha region, based on cross-correlated travel time residuals of teleseismic earthquakes recorded by 24 ocean-bottom seismometers. The data can be used to image a low velocity structure southwest of the island. The feature is cylindrical with a radius of ~ 100 km down to a depth of 250 km. We relate this structure to the origin of Tristan da Cunha and name it the Tristan conduit. Below 250 km the low velocity structure ramifies into narrow veins, each with a radius of ~ 50 km. Furthermore, we imaged a linkage between young seamounts southeast of Tristan da Cunha and the Tristan conduit.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.epsl.2016.12.028
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  • 9
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    Marine magnetotellurics imaged no distinct plume beneath the Tristan da Cunha hotspot in the southern Atlantic Ocean (2017)
    Elsevier
    In:  Tectonophysics, 716 . pp. 52-63.
    Details
    Publication Date: 2020-02-06
    Description: Highlights • The electrical structure beneath the Tristan da Cunha (TDC) hotspot was investigated. • Plume-like structure was not imaged beneath TDC by 3-D inversion analysis. • The plume may be small and/or weak or take place elsewhere outside of the study area. • Conductivity and bathymetry anomalies show a contrast across the TDC fracture zone. • Mantle temperature and melting process at ridge may cause the conductivity anomaly. Abstract The Tristan da Cunha (TDC) is a volcanic island located above a prominent hotspot in the Atlantic Ocean. Many geological and geochemical evidences support a deep origin of the mantle material feeding the hotspot. However, the existence of a plume has not been confirmed as an anomalous structure in the mantle resolved by geophysical data because of lack of the observations in the area. Marine magnetotelluric and seismological observations were conducted in 2012–2013 to examine the upper mantle structure adjacent to TDC. The electrical conductivity structure of the upper mantle beneath the area was investigated in this study. Three-dimensional inversion analysis depicted a high conductive layer at ~ 120 km depth but no distinct plume-like vertical structure. The conductive layer is mostly flat independently on seafloor age and bulges upward beneath the lithospheric segment where the TDC islands are located compared to younger segment south of the TDC Fracture Zone, while the bathymetry is rather deeper than prediction for the northern segment. The apparent inconsistency between the absence of vertical structure in this study and geochemical evidences on deep origin materials suggests that either the upwelling is too small and/or weak to be resolved by the current data set or that the upwelling takes place elsewhere outside of the study area. Other observations suggest that 1) the conductivity of the upper mantle can be explained by the fact that the mantle above the high conductivity layer is depleted in volatiles as the result of partial melting beneath the spreading ridge, 2) the potential temperature of the segments north of the TDC Fracture Zone is lower than that of the southern segment at least during the past ~ 30 Myr.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.tecto.2016.09.033
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Arctic megaslide at presumed rest (2016)
    Nature Research
    In:  Scientific Reports, 6 (38529).
    Details
    Publication Date: 2019-07-19
    Description: Slope failure like in the Hinlopen/Yermak Megaslide is one of the major geohazards in a changing Arctic environment. We analysed hydroacoustic and 2D high-resolution seismic data from the apparently intact continental slope immediately north of the Hinlopen/Yermak Megaslide for signs of past and future instabilities. Our new bathymetry and seismic data show clear evidence for incipient slope instability. Minor slide deposits and an internally-deformed sedimentary layer near the base of the gas hydrate stability zone imply an incomplete failure event, most probably about 30000 years ago, contemporaneous to or shortly after the Hinlopen/Yermak Megaslide. An active gas reservoir at the base of the gas hydrate stability zone demonstrate that over-pressured fluids might have played a key role in the initiation of slope failure at the studied slope, but more importantly also for the giant HYM slope failure. To date, it is not clear, if the studied slope is fully preconditioned to fail completely in future or if it might be slowly deforming and creeping at present. We detected widespread methane seepage on the adjacent shallow shelf areas not sealed by gas hydrates.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/srep38529
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