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  • 1
    Electronic Resource
    Electronic Resource
    Aeromagnetic reconnaissance over the Riiser-Larsen Ice Shelf, east Antarctica (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Polar research 6 (1988), S. 0 
    Details
    ISSN: 1751-8369
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Geosciences
    Notes: A single 160 km long aeromagnetic profile across the Riiser-Larsen Ice Shelf from the coast to Vestfjella, indicates shallowing of the depth to the magnetic source from about 2 km below the sea floor at the ice front to a depth equivalent to ice thickness at the position of the grounding line about 80 km farther south. Adjoining marine multichannel seismic data and sonobuoy measurements suggest that the material below the ice shelf may be a prograding wedge of sediments of seismic velocity less than 3.5km/s. Parallel northeast trending magnetic anomalies between the Plogen and Dagvola nunataks in Vestfjella can best be modelled as three large dyke swarms at depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1751-8369.1988.tb00587.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    An analysis of shear waves observed in VSP data from the superdeep well at Kola, Russia (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Two VSPs have been analysed from the Kola superdeep borehole, located on the Kola Peninsula. The Kola borehole was drilled down to a depth of 12 260 m and VSPs were recorded in the interval 2150 to 6000 m. The VSPs sample the Proterozoic Pechenga complex, which consists of alternating metasedimentary and metavolcanic layers that range from greenschist to amphibolite-grade fades. The structural dip is 28–45° to the SSW, and a major shear zone (the Luchlompolsky fault) occurs at 4.5 km depth.The VSPs display strong transmitted- and reflected-mode converted energy from structural and lithologic boundaries. A kinematic (traveltime) ray-tracing modelling of the main compressional- (P-) and shear- (S-) wave events was performed to define the seismic boundaries. P- and S-wave velocities were estimated from the near-offset data, and Vp/Vs ratios were related to the lithology. A significant increase in the Vp/Vs ratio is observed in the main shear zone at 4.5 km depth. Shear-wave splitting is identified by traveltime divergence (different apparent velocites) and orthogonal polarization of S phases in the far-offset VSP. The inferred polarization direction for the fast shear wave is N160°W, clearly observed below 4400 m depth. Two models are suggested to explain the observed shear-wave splitting: intrinsic anisotropy caused by aligned hornblende minerals in the amphibolite-grade facies; and vertical cracks aligned N160°W. The direction of crack alignment is not consistent with the present-day NW-SE maximum compressive stress field. However, it is consistent with the direction of the palaeostress, the direction of crack alignment at the surface and the fast direction obtained from analysis of shear waves in shallow VSPs. The velocity anisotropy is estimated to be 4–5 per cent with a local increase to 10 per cent in the Luchlompolsky fault zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb05309.x
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  • 3
    Electronic Resource
    Electronic Resource
    Geophysical evidence for the East Antarctic plate boundary in the Weddell Sea (1986)
    [s.l.] : Nature Publishing Group
    Nature 322 (1986), S. 538-541 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Major linear basement highs have been found below the lower continental slope of the southeastern Weddell Sea margin (Fig. 1). In the north-east, the Explora Escarpment4-is characterized by a well-defined 10-20-km-wide basement ridge of 1-2 km elevation with respect to hyperbolated acoustic ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/322538a0
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  • 4
    Electronic Resource
    Electronic Resource
    Use of mode-converted waves in marine seismic data to investigate the lithology of the sub-bottom sediments in Isfjorden, Svalbard (1995)
    Springer
    Pure and applied geophysics 145 (1995), S. 313-325 
    Details
    ISSN: 1420-9136
    Keywords: Mode-conversion ; marine/land geometry ; V p /V s ratios ; lithology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstracts The compression wavefield is efficiently converted to shear-wave energy at post-critical angles in areas of high impedance contrast at the sea floor. We have analysed mode-converted shear waves in a data set acquired with a hybrid marine/land geometry in Isfjorden, Svalbard. Through a kinematic 2D ray-tracing modellingV p/Vs ratios for part of the uppermost 5km of the crust are obtained. Low values (V p /V s =1.65) are tentatively associated with the section of Devonian sandstones which appears to attain a minimum thickness of 1.5km below 3 km depth about 10km west of Kapp Thorden.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00880273
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  • 5
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    Frequency power analyses of seismic sources on firn (2013)
    Geophysical Research Abstracts Vol. 15, EGU2013-8035-1
    In:  EPIC3EGU General Assembly, Vienna, 2013-04-07-2013-04-12Geophysical Research Abstracts Vol. 15, EGU2013-8035-1
    Details
    Publication Date: 2019-07-17
    Description: A great obstacle for seismic surveys on firn-covered ice masses is the ability of firn to strongly attenuate seismic energy and divert downward ray paths away from the vertical because of the velocity gradient. The standard way to overcome these limitations is the drilling of shotholes about 10-30 m deep. However, drilling of shotholes is a time and energy consuming task. Another possibility is to use vibroseismic sources at the surface and increase the signal-to-noise ratio by repeated stacking. However, compared to explosive charges, vibroseismic signals are bandlimited per se. As a third variant, we investigate the usage of ordered patterns of surface charges consisting of detonation cord. Previous applications of detonation cord only explored their general comparison to bulk explosives when deployed in a linear fashion, i.e. a single line. Our approach extends these results to other geometries, like fan- or comb-shaped patterns. These have two advantages: first, over the pattern area a locally plane wave is generated, limiting the spherical and velocity-gradient induced spreading of energy during propagation; second, the ratio between seismic wave speed of the firn and the detonation cord of typically about 1:5 causes the wave to propagate in an angle downward. When using large offsets like a snow streamer, it is possible to direct the refected energy towards the streamer, depending on offset range and reflector depth. We compare the different source types for several surveys conducted in Antarctica in terms of frequency spectra. Our results show that ordered patterns of detonation cord serve as suitable seismic surface charges, avoiding the need to drill shotholes. Moreover, an example of a short profile with patterned surface charges is presented. The technique can be of advantage for surveys in remote areas, which can only be accessed by aircrafts.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    Scientists spend Arctic winter adrift on sea ice (2016)
    American Geophysical Union
    In:  EPIC3EOS, American Geophysical Union
    Details
    Publication Date: 2017-01-19
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 7
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    Advances in seismic data acqiuisition and interpretation for glaciological research on glaciers, ice sheets and shelves (2012)
    In:  EPIC3IEEE Geoscience and Remote Sensing Symposium, Munich, Germany, 2012-07-22-2012-07-27
    Details
    Publication Date: 2019-07-17
    Description: Seismic data acquisition and interpretation belongs to the oldest geophysical methods used in glaciological research. Its has been in use since the beginning of the 20th century. However, since the advent of airborne radio-echo sounding (or radar), the amount of seismic work carried out on polar ice masses and glaciers has been decreasing. The reasons is that airborne radars can acquire much more data in a very short time, especially when it comes to sounding ice thicknesses, than ever possible with seismics. Seismic data can only be acquired with the seismic source and recorders, i.e. geophones, on the ground. Moreover, as the top tens of meters of polar ice masses consist of porous firn, the traditional application of explosive seismic sources require drilling of shot holes about 10 to 50 m deep into the firn to overcome strong wave attenuation. Such constraints make seismic works comparably slower than radar data acquisition. Despite such disadvantages, the mutual application of seismic and radar methods provide a strong synergy for enlighting the internal structure and property of ice masses, important for determining ice-dynamic flow parameters, as well as the properties of the sub-ice geology. A considerable improvement in seismic data acqiusition has been achieved over the last two years with the successful application of standard vibroseismic methods on cold firn, both, in the polar regions as well as on high-altitude Alpine glaciers. In this contribution we provide an overview over the achievments, both, technically and scientifically, obtained in the last two years.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
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    Investigating englacial reflections with vibro- and explosive-seismic surveys at Halvfarryggen ice dome, Antarctica (2013)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 54(64), pp. 189-200, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: Explosive seismic reflection data from Halvfarryggen, a 910m thick local ice dome of the Antarctic ice sheet, show numerous laterally continuous reflections within the ice between 300 and 870m depth.We compare the quality of data obtained with explosive sources with that obtained using a vibroseis source for detecting englacial reflections with a snowstreamer, and investigate the origin of englacial reflections. We find vibroseis in combination with a snowstreamer is ten times more productive than explosive seismics. However, englacial reflections are more clearly visible with explosives, which have a broader bandwidth signature, than the vibroseis, which is band-limited at the high-frequency end to 100 Hz. Only the strongest and deepest englacial reflection is detected with vibroseis. We interpret the majority of englacial reflections to originate from changes in the crystal orientation fabric in closely spaced layers, less than the vibro-seismic tuning thickness of 13.5 m. Phase analysis of the lowermost englacial reflector, 40m above the bed, indicates a sharp increase in seismic wave speed. We interpret this reflector as a transition to a vertical single-maximum fabric. Our findings support current results from anisotropic ice-flow models, that crystal fabric is highly anisotropic at ice domes, both laterally and vertically.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
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    Potential for Drilling Cainozoic Sediments below the Ekström Ice Shelf, Dronning Maud Land, East Antarctica (2015)
    In:  EPIC3XII International Symposium on Antarctic Earth Sciences, Goa, India, 2015-07-13-2015-07-17
    Details
    Publication Date: 2018-08-10
    Description: The Explora Wedge (Hinz and Krause, 1982; Hinz et al., 2004) represents a prominent morphological and structural feature of Earth crust in the north eastern Weddell Sea. Marine geophysical data reveal that it constitutes East Antarctica's volcanic rift margin, with seaward dipping reflectors buried below sediments and floating ice shelves on the continental margin of Dronning Maud Land. Using a vibroseis source on the Antarctic continent for the first time, together with regional aeromagnetic data, these new results show the southward extent of the more than 1000 m thick Explora Wedge (EW) volcanic deposit below the Ekström Ice Shelf (Kristoffersen et al., 2014). While up to now the landward extent of the wedge had been less clearly defined, the new data indicates the top of the wedge outcrop to be about 36 km landward off the shelf edge, or 14 km south of Neumayer III station. One target of the geo-scientific studies will be the top of the EW sequence, which represents the final phase of the initial continent break up and is presumed to be of an Upper Jurassic age. Genesis, magma differentiation, and precise age of the EW volcanics are largely unknown and high-ranking research objectives. The upper boundary of the EW forms a distinct unconformity to the overlaying younger, wedge-shaped sedimentary unit, which reaches about 800 m in thickness close to the Neumayer III station. The age of these sediments is unknown and could be all from Mesozoic to Recent. Considering this largely unexplored Antarctic continental margin, any high latitude palaeo-environmental information about the Mesozoic und lower Cainozoic greenhouse world prior to the start of Antarctic glaciation, the onset of glaciation, and up to the glacial/interglacial variability of the East Antarctic Ice Shield during the Quaternary can best be gathered through drilling at the proposed site. Perhaps we will be able to drill one never reached target of former ODP Leg 113, the Cretaceous black shales that sparsely were dredged from the scarps of the Wegener Canyon close by (Fütterer et al. 1990).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 10
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    Reconstruction of changes in the Weddell Sea sector of the Antarctic Ice Sheet since the Last Glacial Maximum (2014)
    Elsevier
    In:  EPIC3Quaternary Science Reviews, Elsevier, 100, pp. 111- 136, ISSN: 0277-3791
    Details
    Publication Date: 2018-08-10
    Description: Abstract The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica's continental ice volume. Over the last few decades, studies on glacial–geological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23–19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on the Weddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different ice-sheet models have reconstructed conflicting {LGM} ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the {LGM} sea-level low-stand of ~130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past ice-sheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the {LGM} ice-sheet configuration, including time-slice reconstructions for post-LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. The aim of our study is to provide two alternative interpretations of glacial–geological datasets on Antarctic Ice-Sheet History for the Weddell Sea sector, which can be utilised to test and improve numerical ice-sheet models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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