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  • 1965-1969  (5)
Document type
Year
  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 13 (1965), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A description and classification is given for those later events in seismograms of refraction–and wide angle reflection shooting which travel nearly parallel and at constant time intervals behind the first arrivals and which are frequently observed in field surveys. Multiple events with the velocity V1 of the uppermost layer may be caused by multiple P-reflections and certain velocity conditions or by PS-conversions. In addition to these types multiple events with the velocity V2 or Vn may be caused by reflected refractions or by reflected diving waves. The different types will be distinguished mainly by means of travel time–and amplitude-considerations.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 13 (1965), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Uphole recordings in sediments very often reveal shear waves. With their velocity and that of the P-waves Poisson's ratio may be determined, this usually has unexpectedly high values.A number of up-hole shots were recorded with a linear spread of geophones and with constant gain amplifiers. Calculations were made to show the effect of the free surface and ray divergence (the spread factor). The theoretical, relative amplitudes of the ground motion were plotted together with the observed values. In general, there is good agreement between theory and observation which is better for the P-waves than for the S-waves. The reasons for this difference are discussed.Finally, an absorption coefficient is calculated from the amplitudes measured at the surface.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 15 (1967), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Amplitudes of the vertical ground motion are larger in the critical angle region than in the near vertical region, especially amplitudes coming from deeper boundaries or interfaces with small velocity contrast. Four basic boundary models are used to derive specific travel time patterns for first order and higher order interfaces. The transition from reflected waves to diving waves in the supercritical angle region is shown for the different models.Examples from wide angle surveys in Bavaria and in the Buchara region in the USSR have many characteristic similarities. Travel time patterns and asymptotic velocities are almost identical. The most important boundaries of the continental crust - the Mohorovč Ić discontinuity and the top of the crystalline basement - correspond to two boundary models mentioned before. Amplitude and frequency investigations have been used to derive items of the M-discontinuity. It is certainly a gradient zone and seems to have a lenticular structure with material of stepwise different velocities.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 14 (1966), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: From travel time observations on a test profile ranging from o to 145 km four main events can be distinguished. They represent reflections and diving waves from various discontinuities within the earth crust. A low-velocity zone of a few kilometres thickness begins at a depth of about 10 km, another one probably at 25 km.For the MohoričIć discontinuity (=MD) a gradient zone with a large velocity gradient instead of a first order interface is postulated in order to explain some irregularities of the travel time curve. Comparisons between the to-time of the MD with the statistical data from Dohr and Liebscher show an excellent correlation.〈section xml:id="abs1-2"〉〈title type="main"〉ZusammenfassungAufgrund von Laufzeitbeobachtungen eines Weitwinkelprofils in der Bayrischen Molasse von o bis 145 km Länge können im wesentlichen vier verschiedene Einsätze unterschieden werden, die sich aus Reflexionen bzw. aus Tauchwellen zusammensetzen. Eine Zone geringerer Geschwindigkeit beginnt bei etwa 10 km Tiefe. eine weitere liegt wahr-scheinlich unterhalb 25 km Tiefe. Von den Unregelmäßigkeiten der Laufzeitkurve der MohorovičIć-Diskontinuität (=MD) wird eine Zone mit einem starken Geschwindigkeits-gradienten anstelle einer “scharfen” Grenzfläche abgeleitet. Vergleiche zwischen der to- Zeit der MD-Reflexionskurve mit den statistischen Untersuchungen von Dohr und Liebscher zeigen eine sehr gute Übereinstimmung.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 17 (1969), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Using plane wave theory and assuming a given input wavelet the shape of the reflected (or transmitted) wavelet from a layered boundary is derived. Several types of boundaries are considered, among them the weathered layer and a wedge shaped intermediate layer. Different angles of incidence and all internal multiples are taken into account. The examples shown in the figures can be used for a direct comparison between theoretical and observed shapes of reflected (or transmitted) wavelets from special boundaries.
    Type of Medium: Electronic Resource
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