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  • Drift tube  (1)
  • Key words Cascadia accretionary prism  (1)
  • bottom shots  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Implications for focused fluid transport at the northern Cascadia accretionary prism from a correlation between BSR occurrence a d near-sea-floor reflectivity anomalies imaged in a multi-frequency seismic data set (2000)
    Springer
    International journal of earth sciences 88 (2000), S. 655-667 
    Details
    ISSN: 1437-3262
    Keywords: Key words Cascadia accretionary prism ; Very high-resolution seismics ; Fluid migration ; Bottom simulating reflector ; Near-surface reflectivity anomalies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A high-resolution seismic survey was carried out at the accretionary prism on the continental slope off Vancouver Island, Canada. Two GI-Gun data sets with different source frequency ranges of 50–150 and 100–500 Hz were combined with 4 kHz narrow-beam echosounding data (Parasound). The data allow spatial correlation between a gas hydrate bottom simulating reflector (BSR) and distinct areas of high near-sea-floor reflectivity. An integrated interpretation of the multi-frequency data set provides insight into the regional distribution of tectonically induced fluid migration and gas hydrate formation in the vicinity of ODP Leg 146 Sites 889 and 890. The BSR at the base of the gas hydrate stability field is observed within accreted and deformed sediments, but appears to be absent within bedded slope basin deposits. It is suggested that these basin deposits inhibit vertical fluid flow and prevent the formation of a BSR, whereas the hydraulic conductivity of the accreted sediments is sufficiently high to allow for pervasive gas migration. An elevation of the BSR beneath the flanks of a topographic high is interpreted as an indicator for local upflow of warm fluids along permeable pathways within outcropping accreted sediments. Parasound data reveal discontinuous zones of high reflectivity at or directly beneath the sea floor, which may indicate local cementation of surface sediments. In combination with GI-Gun data, the occurrence of these reflective areas can be related to the location of slope sedimentary basins acting as hydraulic seals. It is proposed that the seals sometimes fail along faults extending beneath the BSR, leading to focused upflow of methane-bearing fluid and the formation of carbonate pavements at the sea floor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050295
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    An implosive seismoacoustic source for seismic experiments on the ocean floor (1998)
    Springer
    Marine geophysical researches 20 (1998), S. 239-247 
    Details
    ISSN: 1573-0581
    Keywords: bottom shots ; implosive sources ; P-waves ; Scholte waves ; seismic velocities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Bottom shots have been used for a number of years in seismic studies on the ocean floor. Most experiments utilized explosives as the energy source, though researchers have recognized the usefulness of collapsing water voids to produce seismoacoustic signals. Implosive sources, however, suffered generally from a lack of control of source depth. We present a new experimental tool, called SEEBOSEIS, to carry out seismic experiments on the seafloor utilizing hollow glass spheres as controlled implosive sources. The source is a 10-inch BENTHOS float with penetrator. Inside the sphere we place a small explosive charge (two detonators) to destabilize the glass wall. The time of detonation is controlled by an external shooting device. Test measurements on the Ninetyeast Ridge, Indian Ocean, show that the implosive sources can be used in seismic refraction experiments to image the subbottom P-wave velocity structure in detail beyond that possible with traditional marine seismic techniques. Additionally, the implosions permit the efficient generation of dispersed Scholte waves, revealing upper crustal S-wave velocities. The frequency band of seismic energy ranges from less than 1 Hz for Scholte modes up to 1000 Hz for diving P-waves. Therefore, broadband recording units with sampling rates 〉2000 Hz are recommended to sample the entire wave field radiated by implosive sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004552406168
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  • 3
    Electronic Resource
    Electronic Resource
    Drift tube investigations on the reactions of O 2 + with CH4 and of CO 2 + with NO in various buffer gases (1981)
    Springer
    Plasma chemistry and plasma processing 1 (1981), S. 65-71 
    Details
    ISSN: 1572-8986
    Keywords: Drift tube ; rate coefficients ; internal excitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The influence of internal excitation on the reactions of O 2 + + CH4 and of CO 2 + + NO has been investigated using a slow flow drift tube. The rate coefficients for these reactions obtained as a function of relative kinetic energy in various buffer gases like He, Ne, Ar, and Kr showed higher values under conditions where the internal excitation of the reactant ions was enhanced. For both reactions the lowest reactivity at all kinetic energies was observed to occur in He, indicating that He is the least effective buffer for collisionally inducing internal excitation of molecular ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566376
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    Paper (German National Licenses)
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