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  • 1
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    Combined seismic and borehole investigation of the deep granite weathering structure—Santa Gracia Reserve case in Chile (2022)
    Details
    Publication Date: 2022-12-10
    Description: Imaging the critical zone at depth, where intact bedrock transforms into regolith, is critical in understanding the interaction between geological and biological processes. We acquired a 500 m‐long near‐surface seismic profile to investigate the weathering structure in the Santa Gracia National Reserve, Chile, which is located in a granitic environment in an arid climate. Data processing comprised the combination of two seismic approaches: (1) body wave tomography and (2) multichannel analysis of surface wave (MASW) with Bayesian inversion. This allowed us to derive P‐wave and S‐wave velocity models down to 90 and 70 m depth, respectively. By calibrating the seismic results with those from an 87 m‐deep borehole that is crossed by the profile. We identified the boundaries of saprolite, weathered bedrock, and bedrock. These divisions are indicated in the seismic velocity variations and refer to weathering effects at depth. The thereby determined weathering front in the borehole location can be traced down to 30 m depth. The modelled lateral extent of the weathering front, however, cannot be described by an established weathering front model. The discrepancies suggest a more complex interaction between different aspects such as precipitation and topography in controlling the weathering front depth.
    Description: Combined seismic approaches of body wave tomography and MASW method revealed the upper 90 m of the critical zone down to the bedrock. The integration of the borehole data with the resulting P‐ and S‐wave velocity model, as well as the vertical velocity gradient model, provides a strong constraint in identifying the different lithologies. The resulting conceptual model shows the extent of the critical zone in Santa Gracia Reserve, Chile and its relation to topography.
    Description: German Science Foundation (DFG) priority research programme SPP‐1803 ‘EarthShape: Earth Surface Shaping by Biota’
    Keywords: ddc:622.15 ; borehole ; geophysics ; Bayesian inversion ; body wave tomography ; critical zone ; geomorphology ; geophysics ; Rayleigh wave ; regolith ; seismic survey ; surface wave tomography ; velocity gradient ; weathering front
    Language: English
    Type: doc-type:article
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  • 2
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    TERTIARY SEA LEVEL CHANGES ON THE ICELAND-FAEROE RIDGE (1992)
    In:  [Talk] In: 4. International Conference on Paleoceanography (ICP IV), 21.09.-25.09.1992, Kiel .
    Details
    Publication Date: 2014-05-26
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 3
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    Detachment tectonics during continental rifting off the west Iberia Margin: seismic reflection and drilling constraints (1995)
    GEOMAR Forschungszentrum für marine Geowissenschaften
    In:  (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 142 pp . GEOMAR-Report, 037 . DOI 10.3289/geomar_rep_37_1995 〈http://dx.doi.org/10.3289/geomar_rep_37_1995〉.
    Details
    Publication Date: 2015-02-11
    Type: Thesis , NonPeerReviewed
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  • 4
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    Shear wave reflection seismic yields subsurface dissolution and subrosion patterns: application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan (2018)
    Copernicus Publications (EGU)
    In:  Solid Earth, 9 (5). pp. 1079-1098.
    Details
    Publication Date: 2021-08-26
    Description: Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development. For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area. The most surprising result of the survey is the absence of evidence of a thick (〉 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth. Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.
    Type: Article , PeerReviewed
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  • 5
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    Dynamics of hydrological and geomorphological processes in evaporite karst at the eastern Dead Sea – a multidisciplinary study (2021)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Karst groundwater systems are characterized by the presence of multiple porosity types. Of these, subsurface conduits that facilitate concentrated, heterogeneous flow are challenging to resolve geologically and geophysically. This is especially the case in evaporite karst systems, such as those present on the shores of the Dead Sea, where rapid geomorphological changes are linked to a fall in base level by over 35 m since 1967. Here we combine field observations, remote-sensing analysis, and multiple geophysical surveying methods (shear wave reflection seismics, electrical resistivity tomography, ERT, self-potential, SP, and ground-penetrating radar, GPR) to investigate the nature of subsurface groundwater flow and its interaction with hypersaline Dead Sea water on the rapidly retreating eastern shoreline, near Ghor Al-Haditha in Jordan. Remote-sensing data highlight links between the evolution of surface stream channels fed by groundwater springs and the development of surface subsidence patterns over a 25-year period. ERT and SP data from the head of one groundwater-fed channel adjacent to the former lakeshore show anomalies that point to concentrated, multidirectional water flow in conduits located in the shallow subsurface (〈 25 m depth). ERT surveys further inland show anomalies that are coincident with the axis of a major depression and that we interpret as representing subsurface water flow. Low-frequency GPR surveys reveal the limit between unsaturated and saturated zones (〈 30 m depth) surrounding the main depression area. Shear wave seismic reflection data nearly 1 km further inland reveal buried paleochannels within alluvial fan deposits, which we interpret as pathways for groundwater flow from the main wadi in the area towards the springs feeding the surface streams. Finally, simulations of density-driven flow of hypersaline and undersaturated groundwaters in response to base-level fall perform realistically if they include the generation of karst conduits near the shoreline. The combined approaches lead to a refined conceptual model of the hydrological and geomorphological processes developed at this part of the Dead Sea, whereby matrix flow through the superficial aquifer inland transitions to conduit flow nearer the shore where evaporite deposits are encountered. These conduits play a key role in the development of springs, stream channels and subsidence across the study area.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
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  • 6
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    Cable reverberations during wireline distributed acoustic sensing measurements: their nature and methods for elimination (2021)
    Details
    Publication Date: 2021-07-21
    Description: The application of distributed acoustic sensing in borehole measurements allows for the use of fibre optic cables to measure strain. This is more efficient in terms of time and costs compared with the deploying of conventional borehole seismometers. Nevertheless, one known drawback for temporary deployment is represented by the freely hanging wireline cable slapping and ringing inside the casing, which introduces additional coherent coupling noise to the data. The present study proposes an explanation for the mechanism of noise generation and draws an analogy with similar wave propagation processes and phenomena, such as ghost waves in marine seismics. This observation allows to derive a ringing noise filter function, to study its behaviour and to consider known effects of the gauge length filter. After examining existing methods aimed at eliminating ringing noise and results of their application, we propose a two‐step approach: (1) developing a denoising method based on a matching pursuit decomposition with Gabor atoms and (2) subtracting the noise model for imaging improvement. The matching pursuit method focuses on decomposing the original input signal into a weighted sum of Gabor functions. Analysing Gabor atoms properties for frequency, amplitude and position in time provides the opportunity to distinguish parts of the original signal denoting noise caused by the vibrating cable. The matching pursuit decomposition applied to the distributed acoustic sensing‐vertical seismic profiling data at the geothermal test site Groß Schönebeck provides a versatile processing instrument for noise suppression.
    Description: German Federal Ministry of Economic Affairs and Energy
    Keywords: 550 ; Borehole geophysics ; Distributed acoustic sensing ; Noise ; Signal processing ; Vertical seismic profiling
    Type: article
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  • 7
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    Wavelet transform‐based seismic facies classification and modelling: application to a geothermal target horizon in the NE German Basin (2021)
    Details
    Publication Date: 2021-07-03
    Description: At the geothermal test site near Groß Schönebeck (NE German Basin), a new 3D seismic reflection survey was conducted to study geothermal target layers at around 4 km depth and 150°C. We present a workflow for seismic facies classification and modelling which is applied to a prospective sandstone horizon within the Rotliegend formation. Signal attributes are calculated along the horizon using the continuous Morlet wavelet transform. We use a short mother wavelet to allow for the temporal resolution of the relatively short reflection signals to be analysed. Time‐frequency domain data patterns form the input of a neural network clustering using self‐organizing maps. Neural model patterns are adopted during iterative learning to simulate the information inherent in the input data. After training we determine a gradient function across the self‐organizing maps and apply an image processing technique called watershed segmentation. The result is a pattern clustering based on similarities in wavelet transform characteristics. Three different types of wavelet transform patterns were found for the sandstone horizon. We apply seismic waveform modelling to improve the understanding of the classification results. The modelling tests indicate that thickness variations have a much stronger influence on the wavelet transform response of the sandstone horizon compared with reasonable variations of seismic attenuation. In our interpretation, the assumed thickness variations could be a result of variable paleo‐topography during deposition of predominantly fluvial sediments. A distinct seismic facies distribution is interpreted as a system of thicker paleo‐channels deposited within a deepened landscape. The results provide constraints for the ongoing development of the geothermal test site.
    Description: Federal Ministry for Economic Affairs and Energy http://dx.doi.org/10.13039/501100006360
    Keywords: 622.15 ; 550.83 ; Full waveform ; Interpretation ; Reservoir geophysics
    Type: article
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  • 8
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    Structural investigation and strain analysis of a polyphase flower structure in the Lower Saxony Basin, Germany (2010)
    Universitätsverlag Göttingen
    Details
    Publication Date: 2021-03-29
    Description: The Lower Saxony Basin (LSB) is a part of the post-Variscan Central European Basin System. We used a 3-D reflection seismic dataset in the northern LSB, provided by RWE-DEA AG, Hamburg (c.f. Lohr et al. submitted) for our investigation, which is concerned with the detailed structural and kinematic analysis of a flower structure within Mesozoic strata. This data is used in turn to determine input parameters for further 3-D geometrical retro-deformation. The retro-deformation verifies our assumptions about the structure and tectonic processes, and gives further information about sub-seismic strain distribution with respect to the branch faults of the flower structure.
    Description: conference
    Keywords: 551 ; TQC 220 ; TSB 000 ; VAE 820 ; VAE 830 ; VEB 110 ; VAE 120 ; VBE 000 ; Reflexionsseismik {Geophysik} ; Mitteleuropa {Geophysik} ; Sedimentationsbecken als Erdkrustentypen {Geologie} ; Bruchschollenstrukturen {Geologie} ; Norddeutsche Senke {Geologie} ; Methodik {Strukturgeologie} ; Modellierung von Prozessen in der Geosphäre ; Niedersächsiches Becken ; Dreidimensionale Seismik ; Strukturgeologie ; Modell
    Language: German
    Type: anthologyArticle , publishedVersion
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  • 9
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    Kinematic 3D Retro-Deformation of Fault Blocks Picked from 3D Seismics (2010)
    Universitätsverlag Göttingen
    Details
    Publication Date: 2021-03-29
    Description: Movement on fault planes causes a large amount of smaller-scale deformation, ductile or brittle, in the area surrounding the fault. Much of this deformation is below the resolution of reflection seismics (i.e. sub-seismic, 〈10m displacement), but it is important to determine this deformation, since it can make up a large portion of the total bulk strain, for instance in a developing sedimentary basin. Calculation of the amount of sub-seismic strain around a fault by 3-D geometrical kinematic retro-deformation can also be used to predict the orientation and magnitude of these smaller-scale structures. However, firstly a 3-D model of the fault and its faulted horizons must be constructed at a high enough resolution to be able to preserve fault and horizon morphology with a grid spacing of less than 10 m. Secondly, the kinematics of the fault need to be determined, and thirdly a suitable deformation algorithm chosen to fit the deformation style. Then by restoring the faulted horizons to their pre-deformation state (a ‘regional’), the moved horizons can be interrogated as to the strain they underwent. Since strain is commutative, the deformation demonstrated during this retro-deformation is equivalent to that during the natural, forward deformation...
    Description: conference
    Keywords: 551 ; TQC 220 ; TSB 000 ; VAE 200 ; VAE 400 ; VBE 000 ; Reflexionsseismik {Geophysik} ; Mitteleuropa {Geophysik} ; Geodynamik der Lithosphäre {Geologie} ; Tektogenese {Geologie} ; Modellierung von Prozessen in der Geosphäre ; Niedersächsiches Becken ; Dreidimensionale Seismik ; Störung 〈Geologie〉 ; Kinematik ; Modell
    Language: German
    Type: anthologyArticle , publishedVersion
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  • 10
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    Structural Evolution at the Northeast North German Basin Margin: From Initial Triassic Salt Movement to Late Cretaceous‐Cenozoic Remobilization (2021)
    Details
    Publication Date: 2021-07-04
    Description: In this study, we investigate the regional tectonic impact on salt movement at the northeastern margin of the intracontinental North German Basin. We discuss the evolution of salt pillows in the Bay of Mecklenburg in the light of thick‐ and thin‐skinned tectonics, including gravity gliding, and differential loading using seismic imaging. Stratigraphic and structural interpretation of a 170 km long, multichannel seismic line, extending from the Bay of Mecklenburg to northeast of Rügen Island, incorporates well information of nearby onshore wells. This new high‐resolution seismic line completely images the stratigraphic and tectonic pattern of the subsurface, from the base of the Zechstein to the seafloor. Our analysis reveals that subsidence during Late Triassic to Early Cretaceous at the northeastern basin margin was associated with transtensional dextral strike slip movement within the Trans‐European Suture Zone. We reinterpret the Werre and Prerow Fault Zones west of Rügen Island as an inverted, thin‐skinned normal fault system associated with the formation of the Western Pomeranian Fault System. Salt movement in the Bay of Mecklenburg was initiated in the Late Triassic and lasted until the Early Jurassic. A second phase of salt pillow growth occurred during the Coniacian until Cenozoic and correlates with compression‐related regional basin inversion due to the onset of the Africa‐Iberia‐Europe convergence. Thin‐skinned extensional initialization of salt pillow growth and compressional salt remobilization explains salt pillow evolution in the Bay of Mecklenburg. Additionally, we discuss an impact of gravity gliding on salt pillow evolution induced by basin margin tilt.
    Description: Key Points: A regional high‐resolution seismic profile continuously images the SW Baltic Sea subsurface from the Zechstein salt base to the seafloor. Late Triassic salt movement and Late Cretaceous‐Cenozoic remobilization correlate with regional tectonics at the North German Basin margin The tectonic evolution of salt pillows is discussed in terms of thin‐skinned. extensional/compressional deformation and gravity gliding.
    Description: Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) http://dx.doi.org/10.13039/501100001659
    Keywords: 551.8 ; Mesozoic structural evolution ; salt tectonics ; Baltic Sea ; faults ; seismic imaging ; gravity gliding
    Type: article
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