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  • 1
    Online Resource
    Online Resource
    High-resolution, deep tow, multichannel seismic and sidescan sonar survey of the submarine mounds and associated BSR off Nicaragua pacific margin (2007)
    Associated volumes
    Details Availability
    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 241(2007), 1/4, Seite 33-43, 1872-6151
    In: volume:241
    In: year:2007
    In: number:1/4
    In: pages:33-43
    Description / Table of Contents: Bathymetric and conventional multichannel seismic surveys offshore Nicaragua and Costa Rica have revealed numerous mud mounds beneath which the generally widespread BSR is not well imaged. However, many of the mounds are partially capped by patches of authigenic carbonate crusts, so it was not clear if the semitransparent seismic facies and the apparent gaps in the BSR beneath the mounds are real or due to poor normal-incidence seismic penetration through the cap rocks. To address these problems, a high-resolution seismic survey was carried out over the continental slope of the Nicaraguan Pacific margin using a deep towed multichannel seismic streamer (DTMCS) along with a sidescan sonar system (DTS) to image submarine mud mounds and the associated BSR. The proximity of the very short (39 m active length) but high-resolution 17 channel streamer to the seafloor of the deep towed system allows greatly improved lateral resolution whereas the relatively large sourcereceiver offset allows the undershooting of the cap rocks. For the first time our data show that the BSR in many cases continues but rises beneath the mounds. This is consistent with the advection of deep warm fluids and thus increased heat flow through the mounds. The occurrence of mud mounds seems to be controlled by the locations of faults.
    Type of Medium: Online Resource
    Pages: graph. Darst., Kt
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2007.03.002
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    LOVE-TYPE SEAM-WAVES IN WASHOUT MODELS OF COAL SEAMS (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 34 (1986), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The propagation of Love seam-waves across washouts of coal seams was studied by calculating synthetic seismograms with a finite-difference method. Seam interruption, seam end and seam thinning models were investigated. The horizontal offset, the dip of the discontinuities and the degree of erosion served as variable parameters. Maximum displacement amplitudes, relative spectral amplitudes and phase and group slowness curves were extracted from the synthetic seismograms.Both seam interruption and seam thinning reduce the maximum displacement amplitudes of the transmitted Love seam-waves. The degree of amplitude reduction depends on the horizontal offset and the degree of erosion. It is four times greater for a total seam interruption than for an equivalent seam thinning with a horizontal offset of four times the seam thickness. In a seam cut vertically, the impedance contrast between the coal and the washout filling determines the maximum displacement amplitudes of the reflected Love seam-waves. They diminish by a maximum factor of four in oblique interruption zone discontinuities with a dip of maximum 27°, and by a maximum factor of ten in a seam thinning with a degree of erosion of at least 22%.The analysis of the relative spectral amplitudes indicates a preferential transmission of those phases with frequencies below, and a preferential reflection of those phases with frequencies above the first mode Airy-phase. The relative spectral amplitudes of the reflected Love seam-waves show a distinct interference pattern of the waves reflected at both interruption zone discontinuities.The dispersion analysis reveals a flattening of the phase and group slowness curves with increasing frequencies, horizontal offset and degrees of erosion.These results imply that a detection of washouts in-mine will be possible in a frequency range including at least the first mode Airy-phase. An interference pattern and a flattening of the dispersion curve indicate a washout rather than other seam obstructions and leads to an estimate of the washout dimension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1986.tb00521.x
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  • 3
    Electronic Resource
    Electronic Resource
    PARAMETER ESTIMATION AND FAULT DETECTION BY THREE-COMPONENT SEISMIC AND GEOELECTRICAL SURVEYS IN A COAL MINE (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 35 (1987), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Three-component seismic and geoelectrical in-mine surveys were carried out in Lyukobanya colliery near Miskolc, Hungary to determine the in situ petrophysical parameter distributions and to detect inhomogeneities in the coal seam. The seismic measurements comprise an underground vertical seismic profile, using body waves, and an in-seam seismic amplitude-depth distribution and transmission survey, using channel waves. The geoelectrical measurements are based on the drift- and seam-sounding method.Interval traveltime-, amplitude-, multiple-filter- and polarization analysis methods are applied to the seismic data. They lead to a five-layer model for the strata including the coal seam. The coal seam and two underlying beds act as a seismic waveguide. The layer sequence supports the propagation of both normal and leaky mode channel waves of the Love- and Rayleigh type. A calculation of the total reflected energy for each interface using Knott's energy coefficients shows that the velocity ranges of high reflection energy and of normal and leaky mode wavegroups coincide. The excitation of wavegroups strongly depends on the seismic source. A simultaneous inversion of a geoelectrical drift- and seam-sounding survey prevents misinterpretations of the seismic data by clearly identifying the low-velocity coal seam as a high-resistivity bed. Calculations of dispersion and sounding curves improve the resolution of the slowness and resistivity in each layer.Both diminished amplitudes and distortions in the polarization of transmission seismo-grams and decreasing resistivities in a geoelectrical pseudosection of the coal seam are related to an inhomogeneity.A calculation of synthetic seismograms for Love and Rayleigh channel waves with the finite-difference and the Alekseev-Mikhailenko method agrees well with the field data for the main features, i.e., particular arrivals in the wave train, wavegroups, velocities and symmetries or asymmetries.This in-mine experiment demonstrates that the simultaneous acquisition, processing and interpretation of seismic and geoelectrical data improve the lithological interpretation of petrophysical parameter distributions. Coal seam inhomogeneities can also be detected more reliably by the two independent surveys than by one alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1987.tb02261.x
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  • 4
    Electronic Resource
    Electronic Resource
    Late Quaternary Seismic Stratigraphy of the Eastern Bengal Shelf (1998)
    Springer
    Marine geophysical researches 20 (1998), S. 57-71 
    Details
    ISSN: 1573-0581
    Keywords: Bengal Shelf ; seismic stratigraphy ; Parasound ; Late Quaternary ; subaqueous delta ; lowstand delta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An ultra-high-resolution seismic study of the eastern Bengal Shelf with the parametric narrow-beam echosounder Parasound allows the interpretation of late Quaternary depositional patterns in terms of seismic stratigraphy. Accommodation space was still present on the outer shelf during the last lowstand, where a prograding delta developed in the western survey area. Oolitic beach ridges were later formed on top of this lowstand delta. Farther east, large parts of the shelf were exposed to subaerial erosion and a river system extended seaward across the area. A subaqueous highstand delta prograded southwards following the maximum transgression about 7,000 years ago. Its foreset beds exhibit acoustic voids very likely generated by sediment liquefaction, possibly caused by episodic energetic events such as major cyclones and/or earthquakes. Bottomset sediments extend seaward close to the shelf break in the west, whereas no Holocene sediments cover the outer shelf in the east.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004375908399
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  • 5
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    Tectonic framework of the mud mounds, associated BSRs and submarine landslides on the Pacific margin off Nicaragua (2006)
    In:  [Invited talk] In: AGU Fall Meeting, 14.12, San Francisco, USA .
    Details
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    A deep-towed multichannel seismic streamer for very high-resolution surveys in full ocean depth (2003)
    EAGE
    In:  First Break, 21 . pp. 59-65.
    Details
    Publication Date: 2019-03-01
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Acoustic facies and depositional processes in the upper submarine canyon Swatch of No Ground (Bay of Bengal) (2003)
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 50 (5). pp. 979-1001.
    Details
    Publication Date: 2016-10-12
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(02)00617-3
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  • 8
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    Sediment transport in the shelf canyon "Swatch of No Ground" (Bay of Bengal) (2003)
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 50 (5). pp. 1003-1022.
    Details
    Publication Date: 2016-10-12
    Description: The Swatch of No Ground is a shelf canyon that deeply incises the Bengal shelf near the Ganges–Brahmaputra river mouth, cuts the foreset beds of the subaqueous river delta and acts as temporary depocenter between river mouth and Bengal fan. Sedimentation rates in the Swatch of No Ground are highest near the canyon head at ∼50 cm a−1, decreasing to ∼15 cm a−1 in 600 m water depth. The canyon deposits consist of intercalated fine (silt–clay) and coarse (silt–sand) grained deposits. In seismic profiles, small-scale sedimentary structures and parallel-bedded layers reveal that sediment in the canyon is mainly deposited from suspension. During fair weather conditions tidal currents are the dominant mechanism that transports plumes of suspended river load towards the canyon, forming fine-grained silt–clay layers. During storm conditions, sediment is resuspended on the inner shelf and subaqueous delta east of the canyon. Storm-generated bottom currents transport the resuspended sediment alongshelf to the canyon where the particles are trapped and form graded coarse silt–sand layers. Channels and gullies in the Swatch of No Ground indicate active gravity-driven currents with an erosional character in the upper canyon and non-depositional character below ∼450 m, suggesting that persistent or ephemeral currents presently export sediment to the Bengal fan. Numerous slumps and slides observed in the canyon show small-scale acoustically transparent layers that indicate sediment liquefaction presumably initiated along the steep canyon margin. These mudflows move downslope and halt where the canyon gradient decreases. One widespread acoustically transparent layer with an age of approximately 140–160 years BP can be traced throughout much of the canyon and is probably the result of large-scale sediment remobilization triggered by a catastrophic event like an earthquake. This may represent decennial-to-centennial scale events that remove large quantities of sediment and prevent the canyon from rapid infilling.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(02)00617-3
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  • 9
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    Fast static correction methods for high-frequency multichannel marine seismic reflection data: A high-resolution seismic study of channel-levee systems on the Bengal Fan (2002)
    Springer
    In:  Marine Geophysical Research, 23 . pp. 57-75.
    Details
    Publication Date: 2017-06-22
    Description: Very high-frequency marine multichannel seismic reflection data generated by small-volume air- or waterguns allow detailed, high-resolution studies of sedimentary structures of the order of one to few metres wavelength. The high-frequency content, however, requires (1) a very exact knowledge of the source and receiver positions, and (2) the development of data processing methods which take this exact geometry into account. Static corrections are crucial for the quality of very high-frequency stacked data because static shifts caused by variations of the source and streamer depths are of the order of half to one dominant wavelength, so that they can lead to destructive interference during stacking of CDP sorted traces. As common surface-consistent residual static correction methods developed for land seismic data require fixed shot and receiver locations two simple and fast techniques have been developed for marine seismic data with moving sources and receivers to correct such static shifts. The first method – called CDP static correction method – is based on a simultaneous recording of Parasound sediment echosounder and multichannel seismic reflection data. It compares the depth information derived from the first arrivals of both data sets to calculate static correction time shifts for each seismic channel relative to the Parasound water depths. The second method – called average static correction method – utilises the fact that the streamer depth is mainly controlled by bird units, which keep the streamer in a predefined depth at certain increments but do not prevent the streamer from being slightly buoyant in-between. In case of calm weather conditions these streamer bendings mainly contribute to the overall static time shifts, whereas depth variations of the source are negligible. Hence, mean static correction time shifts are calculated for each channel by averaging the depth values determined at each geophone group position for several subsequent shots. Application of both methods to data of a high-resolution seismic survey of channel-levee systems on the Bengal Fan shows that the quality of the stacked section can be improved significantly compared to stacking results achieved without preceding static corrections. The optimised records show sedimentary features in great detail, that are not visible without static corrections. Limitations only result from the sea floor topography. The CDP static correction method generally provides more coherent reflections than the average static correction method but can only be applied in areas with rather flat sea floor, where no diffraction hyperbolae occur. In contrast, the average static correction method can also be used in regions with rough morphology, but the coherency of reflections is slightly reduced compared to the results of the CDP static correction method.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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