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  • 1
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    In:  Bull. Seism. Soc. Am., New York, Scientific American, vol. 95, no. 4, pp. 1495-1509, pp. B11404, (ISSN: 1340-4202)
    Publication Date: 2005
    Keywords: Seismology ; Seismic networks ; Location ; Travel time ; Non-linear effects ; Acoustics ; Inversion ; Data analysis / ~ processing ; BSSA
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  • 2
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    In:  Geophysics, Basel, Inst. f. Geophys., Ruhr-Univ. Bochum, vol. 69, no. 2, pp. 583-591, pp. L14310, (ISSN: 1340-4202)
    Publication Date: 2004
    Keywords: Finite difference method ; Modelling ; Synthetic seismograms ; Inelastic ; Rheology ; Anisotropy
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  • 3
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    Math.-Natw. Fak., C.-A.-Univ.
    In:  Dissertation, Kiel, Math.-Natw. Fak., C.-A.-Univ., vol. 10, no. 9, pp. 177-185
    Publication Date: 1998
    Keywords: Synthetic seismograms ; Finite difference method ; Modelling ; Inelastic
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  • 4
    Publication Date: 2019
    Description: ABSTRACT Over the last years, full‐waveform inversion has become an important tool in the list of processing and imaging technologies available to the industry. For marine towed‐streamer data, full‐waveform inversion is typically applied using an acoustic approximation because S‐waves do not propagate in water and elastic effects in recorded data are generally assumed to be small. We compare acoustic and elastic modelling and full‐waveform inversion for a field data set acquired offshore Angola over sediments containing a salt body with significant topology. Forward modelling tests reveal that such geological structures lead to significant mode conversions at interfaces and, consequently, to significant relative amplitude differences when elastically and acoustically modelled traces are compared. Using an acoustic approach for modelling in full‐waveform inversion therefore leads to problems matching the synthetic data with the field data, even for recorded pressure data and with trace normalization applied. Full‐waveform inversion is unable to find consistent model updates. Applying elastic full‐waveform inversion leads to more consistent and reliable model updates with less artefacts, at the expense of additional computation cost. Although two‐dimensional marine towed‐streamer data are least favourable for the application of full‐waveform inversion compared to three‐dimensional data or ocean‐bottom data, it is recommended to check on the existence of elastic effects before deciding on the final processing and imaging approach.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
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  • 5
    Publication Date: 2011-04-05
    Description: ABSTRACT In order to keep up with the economic and safety demands of modern tunnel construction projects, especially in urban areas, there is a need to detect safety threats in real time while the construction is advancing. Tunnel prediction methods accompanying the drilling process can help to correlate and update a priori information on expected geological structures with their actual spatial location or even existence ahead of the tunnel face. We recently presented a seismic prediction approach using tunnel surface waves, which has already proven its potential during field surveys. However, common tunnel seismic data interpretation, regardless of the prediction method, requires human interaction. Either a specially trained field technician have to be present at the construction site or the data has to be uploaded to an office for further interpretation. In this work we present a simple but stable approach to automatically detect major geological structures ahead of the tunnel face. We focus on the accurate determination of the distance of fault zones or lithological boundaries from the tunnel face without any a priori information. By 3D seismic finite difference modelling we simulated a synthetic tunnel seismic survey that includes typical features encountered in tunnel construction. The developed prediction sequence was tested on these data and later successfully applied to two different tunnel data sets acquired at the Gotthard Base Tunnel (Switzerland) and during the construction of the ‘Neuer Schlüchterner Tunnel’ close to Fulda (Germany).
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
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  • 6
    Publication Date: 2013-01-22
    Description: Ultrasonic echo testing is a more and more frequently used technique in civil engineering to investigate concrete building elements, to measure thickness as well as to locate and characterise built-in components or inhomogeneities. Currently the Synthetic Aperture Focusing Technique (SAFT), which is closely related to Kirchhoff migration, is used in most cases for imaging. However, this method is known to have difficulties to image steeply dipping interfaces as well as lower boundaries of tubes, voids or similar objects. We have transferred a processing technique from geophysics, the Reverse Time Migration (RTM) method, to improve the imaging of complicated geometries. By using the information from wide angle reflections as well as from multiple events there are fewer limitations compared to SAFT. As a drawback the required computing power is significantly higher compared to the techniques currently used. Synthetic experiments have been performed on polyamide and concrete specimens to show the improvements compared to SAFT. We have been able to image vertical interfaces of step-like structures as well as the lower boundaries of circular objects. It has been shown that RTM is a step forward for ultrasonic testing in civil engineering.
    Print ISSN: 1687-885X
    Electronic ISSN: 1687-8868
    Topics: Geosciences
    Published by Hindawi
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  • 7
    Publication Date: 2013-01-02
    Description: Ultrasonic echo testing is a more and more frequently used technique in civil engineering to investigate concrete building elements, to measure thickness as well as to locate and characterise built-in components or inhomogeneities. Currently the Synthetic Aperture Focusing Technique (SAFT), which is closely related to Kirchhoff migration, is used in most cases for imaging. However, this method is known to have difficulties to image steeply dipping interfaces as well as lower boundaries of tubes, voids or similar objects. We have transferred a processing technique from geophysics, the Reverse Time Migration (RTM) method, to improve the imaging of complicated geometries. By using the information from wide angle reflections as well as from multiple events there are fewer limitations compared to SAFT. As a drawback the required computing power is significantly higher compared to the techniques currently used. Synthetic experiments have been performed on polyamide and concrete specimens to show the improvements compared to SAFT. We have been able to image vertical interfaces of step-like structures as well as the lower boundaries of circular objects. It has been shown that RTM is a step forward for ultrasonic testing in civil engineering.
    Print ISSN: 1687-885X
    Electronic ISSN: 1687-8868
    Topics: Geosciences
    Published by Hindawi
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