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  • 1
    Electronic Resource
    Electronic Resource
    A MAN/COMPUTER INTERPRETATION SYSTEM FOR RESISTIVITY SOUNDINGS OVER A HORIZONTALLY STRAFIFIED EARTH (1977)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 25 (1977), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The proposed system works as follows:〈list xml:id="l1" style="custom"〉1By a trial-and-error procedure using a graphic display terminal a geologically relevant layer sequence with parameters (ρj, dj) is adjusted to yield roughly the measured curve.2The resulting layer sequence is used as starting model for an iterative least squares procedure with singular value decomposition. Minimization of the sum of the squares of the logarithmic differences between measured and calculated values with respect to the logarithms of the resistivities and thicknesses as parameters linearizes the problem to a great extent, with two important implications:〈list xml:id="l2" style="custom"〉a) a considerable increase in speed (the number of iterations goes down), thus making it cheap to achieve the optimum solution;b) the confidence surfaces in parameter space are well approximated by the hyper-ellipsoids defined by the eigenvalues and eigenvectors of the normal equations.Since these are known from the singular value decomposition we do in fact know all possible solutions compatible with the measured curve and the geological concept.〈list xml:id="l3" style="custom"〉3It is possible to “freeze” any combination of parameters at predetermined values. Thus extra knowledge and/or hypotheses are easily incorporated and can be tested by rerunning step (2). The overall computing time for a practical case is of the order of 10 sec on a CDC 6400.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1977.tb01196.x
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  • 2
    Electronic Resource
    Electronic Resource
    AN INTERACTIVE COMPUTER/GRAPHIC-DISPLAY-TERMINAL SYSTEM FOR INTERPRETATION OF RESISTIVITY SOUNDINGS (1975)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 23 (1975), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A fast computer-procedure giving the apparent resistivity curve as well as the partial derivatives with respect to the layer-parameters is presented. It is based on the linear filter method developed by D. P. Ghosh in 1971.The sampling frequency is 10 points per decade, and 3 decades are covered. The maximum relative error is less than 10−3, and in most cases orders of magnitude smaller. The computation time on a CDC 6400 for one curve given in 30 points ranges linearly from .17s for a two-layer case to .36s for a ten-layer case.The procedure is used to plot master curves interactively on a graphic display terminal (Tektronix 4010) connected to the CDC 6400. By trial-and-error adjustments a set of layer-parameters is found, giving essentially the measured curve.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1975.tb01541.x
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  • 3
    Electronic Resource
    Electronic Resource
    FAST HANKEL TRANSFORMS (1979)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 27 (1979), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Inspired by the linear filter method introduced by D. P. Ghosh in 1970 we have developed a general theory for numerical evaluation of integrals of the Hankel type:〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR876:GPR_876_mu1"/〉Replacing the usual sine interpolating function by sinsh (x) =a· sin (ρx)/sinh (aρx), where the smoothness parameter a is chosen to be “small”, we obtain explicit series expansions for the sinsh-response or filter function H*.If the input function f(λ exp (iω)) is known to be analytic in the region o 〈 λ 〈 ∞, |ω|≤ω0 of the complex plane, we can show that the absolute error on the output function is less than (K(ω0)/r) · exp (−ρω0/Δ), Δ being the logarthmic sampling distance.Due to the explicit expansions of H* the tails of the infinite summation 〈displayedItem type="mathematics" xml:id="mu2" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR876:GPR_876_mu2"/〉 ((m−n)Δ) can be handled analytically.Since the only restriction on the order is ν 〉 − 1, the Fourier transform is a special case of the theory, ν=± 1/2 giving the sine- and cosine transform, respectively. In theoretical model calculations the present method is considerably more efficient than the Fast Fourier Transform (FFT).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1979.tb01005.x
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  • 4
    Electronic Resource
    Electronic Resource
    Diagenesis of a mixed siliciclastic/evaporitic sequence of the Middle Muschelkalk (Middle Triassic), the Catalan Coastal Range, NE Spain (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 42 (1995), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Middle Muschelkalk (Middle Triassic) of the Catalan Coastal Range (north-east Spain) comprises sandstone, mudstone, anhydrite and minor carbonate layers. Interbedded sandstones and mudstones which are dominant in the north-eastern parts of the basin are terminal alluvial fan deposits. South-westward in the basin, the rocks become dominated by interbedded evaporites and mudstones deposited in sabkha/mudflat environments. The diagenetic and pore water evolution patterns of the Middle Muschelkalk suggest a strong facies control. During eodiagenesis, formation of microdolomite, anhydrite, baryte, magnesite, K-feldspar and mixed-layer chlorite/smectite was favoured within and adjacent to the sabkha/mudflat facies, whereas calcite, haematite, mixed-layer illite/smectite and quartz formed mainly in the alluvial facies. Low δ18OSMOW values for microdolomite (+23.7 to +28.4%) and K-feldspar overgrowths (+17.3 to +17.7%) suggest either low-temperature, isotopic disequilibrium or precipitation from low-18O porewaters. Low-18O waters might have developed, at least in part, during low-temperature alteration of volcanic rock fragments. During mesodiagenesis, precipitation of quartz overgrowths and coarse dolomite occurred in the alluvial sandstones, whereas recrystallization of microdolomite was dominant in the sabkha/mudflat facies. The isotopic compositions of these mesogenetic phases reflect increasing temperature during burial. Upon uplift and erosion, telogenetic calcite and trace haematite precipitated in fractures and replaced dolomite. The isotopic composition of the calcite (δ18OSMOW=+21.5 to +25.6%o; δ13C= 7.7 to - 5.6%o) and presence of haematite indicate infiltration of meteoric waters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1995.tb00407.x
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