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  • American Geophysical Union (AGU)  (2)
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  • American Geophysical Union (AGU)  (2)
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  • 1
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 1999
    In:  Journal of Geophysical Research: Solid Earth Vol. 104, No. B7 ( 1999-07-10), p. 15351-15364
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 104, No. B7 ( 1999-07-10), p. 15351-15364
    Abstract: A high‐resolution seismic survey was carried out in the vicinity of Ocean Drilling Program (ODP) Leg 168 drill sites at the eastern flank of the Juan de Fuca Ridge. Three seismic systems with different source frequencies up to 4000 Hz were used simultaneously along each seismic line. The data sets were combined to provide the best possible resolution at any given depth level. An integrated interpretation of narrow zones of low reflection amplitudes is presented, which are related to basement highs but are independent of seafloor topography. The effect is most pronounced above a buried basement ridge in the vicinity of ODP Sites 1030 and 1031, where higher porosity values are present. Higher porosities can reduce seismic impedance contrasts and may therefore cause the observed low reflection amplitudes. In addition, Biot‐Stoll's [ Biot , 1956a, b; Stoll , 1989] model suggests that attenuation coefficients are porosity dependent and reflection amplitudes are further decreased at higher seismic frequencies when porosity increases. Since zones of higher porosities are potential pathways for fluids, they may be associated with hydrothermally driven fluid discharge, which was previously predicted above the buried basement ridge. It is therefore proposed that the observed seismic amplitude reduction in the vicinity of ODP Sites 1030 and 1031 indicates zones of upward fluid migration.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1999
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    SSG: 16,13
    Location Call Number Limitation Availability
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  • 2
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Solid Earth Vol. 105, No. B9 ( 2000-09-10), p. 21411-21430
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 105, No. B9 ( 2000-09-10), p. 21411-21430
    Abstract: Ultrasonic P wave transmission seismograms recorded on sediment cores have been analyzed to study the acoustic and estimate the elastic properties of marine sediments from different provinces dominated by terrigenous, calcareous, and diatomaceous sedimentation. Instantaneous frequencies computed from the transmission seismograms are displayed as gray‐shaded images to give an acoustic overview of the lithology of each core. Centimeter‐scale variations in the ultrasonic waveforms associated with lithological changes are illustrated by wiggle traces in detail. Cross‐correlation, multiple‐filter, and spectral ratio techniques are applied to derive P wave velocities and attenuation coefficients. S wave velocities and attenuation coefficients, elastic moduli, and permeabilities are calculated by an inversion scheme based on the Biot‐Stoll viscoelastic model. Together with porosity measurements, P and S wave scatter diagrams are constructed to characterize different sediment types by their velocity‐ and attenuation‐porosity relationships. They demonstrate that terrigenous, calcareous, and diatomaceous sediments cover different velocity‐ and attenuation‐porosity ranges. In terrigenous sediments, P wave velocities and attenuation coefficients decrease rapidly with increasing porosity, whereas S wave velocities and shear moduli are very low. Calcareous sediments behave similarly at relatively higher porosities. Foraminifera skeletons in compositions of terrigenous mud and calcareous ooze cause a stiffening of the frame accompanied by higher shear moduli, P wave velocities, and attenuation coefficients. In diatomaceous ooze the contribution of the shear modulus becomes increasingly important and is controlled by the opal content, whereas attenuation is very low. This leads to the opportunity to predict the opal content from nondestructive P wave velocity measurements at centimeter‐scale resolution.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
    detail.hit.zdb_id: 2033040-6
    detail.hit.zdb_id: 3094104-0
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    detail.hit.zdb_id: 2016810-X
    detail.hit.zdb_id: 2403298-0
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    detail.hit.zdb_id: 161666-3
    detail.hit.zdb_id: 161667-5
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    detail.hit.zdb_id: 161665-1
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016804-4
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    detail.hit.zdb_id: 3094219-6
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    SSG: 16,13
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
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