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  • Articles  (709)
  • Blackwell Publishing Ltd  (709)
  • 1990-1994  (682)
  • 1955-1959  (27)
  • Geosciences  (709)
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  • Articles  (709)
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  • 1
    Electronic Resource
    Electronic Resource
    Coda-Q Distribution In the Iberian Peninsula (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 100 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Several attenuation studies have established a frequency dependence law of the anelastic attenuation factor Q in the form Q=Qo(f/fo)v for the approximate 1–10 Hz frequency range. We propose a method that leads to the determination of Qo, which is a function of the reference frequency fo, and the real exponent v with a single station. to carry out the problem we determine a set of master curves as a function of v. We discuss the method, and the different features of the master curves, when it is applied to the complicated regions of the Iberian Peninsula and to several instruments with different responses. Using this new method and the seismographic stations available in the Iberian Peninsula we have mapped iso-Q0 lines, at a reference frequency of 1 Hz, applying inversion methods. the Q0 values determined for Iberia vary between about 100 and about 600. Values close to 100 correspond to the southern part of Iberia. In general, Qo values increase from south to north with values about 600 near the NW part of Iberia. the Pyrenees Mountains and adjacent areas present Q0 values between about 200 and about 350. These results suggest a strong Q0 lateral variation in Iberia. A considerable frequency dependence of coda-Q has also been determined. the v values vary between 0.3 and 0.8. the Q0 values obtained in the Iberian Peninsula show very good agreement with several Q0 values obtained in other regions of the world. Comparison between the iso-Q0 lines and other geophysical parameters, like regional variations of Pn velocities, heat flow, isoseimal intensity distribution and crustal thickness, indicates that lower Q0 values are associated with higher isoseismal intensity attenuation, higher heat flow, lower Pn velocities and thinner crust.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb02486.x
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  • 2
    Electronic Resource
    Electronic Resource
    Deep-crustal granulites with migmatitic and mylonitic fabrics from the Zambezi Belt, northeastern Zimbabwe (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 9 (1991), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract High-P granulites contained in two allochthonous tectonic units were thrust southwards onto the northern margin of the Zimbabwe craton during the Pan-African Zambezi orogeny. In the lower sheet, the Masoso Metamorphic Suite contains mafic garnet granulite assemblages formed during a high-P-T metamorphic event, although the suite as a whole is predominantly granitic. The garnet granulites occur as relicts within narrow mafic layers characterized by migmatitic and mylonitic fabrics. The annealed mylonites represent surfaces of deep-crustal tectonic imbrication that formed immediately before the Pan-African orogeny. Gabbros which intruded the granulites after the main phase of migmatization have formed corona textures that document a low-P-T metamorphic event at mid-crustal levels. The style of deformation then changed and the Masoso Suite with its mylonitic layers was folded and thrusted southwards onto the Archaean Zimbabwe craton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1991.tb00540.x
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  • 3
    Electronic Resource
    Electronic Resource
    1–18 Hz Lg attenuation in the Granada Basin (southern Spain) (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 111 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The attenuation of the Lg waves for the Granada Basin has been analysed. This study has been done in the frequency domain, eliminating the influences of the source, the instrumental response and the local site response, using the Reverse Two-Station Method (RTSM). The average QLg value for the whole region, obtained for all the paths is: QLg= (105 ± 25)∞(0.93±0.14).The average values of QLg determined for this region are lower than those corresponding to other areas of Spain, and are similar to those of coda-Q obtained using local coda and single scattering methods, for some determined focal depth and for some lapse times (50 and 70 s). Small differences of the attenuation are observed between paths that cross the central part and the edges of the basin. A detailed analysis showed that the E-W and the N-S directions have differences between attenuation values; in the E-W direction Q0Lg (the QLg value at 1 Hz of frequency) is 131 ± 7 and in the N-S one Q0Lg is 88 ± 21. The frequency dependence is similar to the average QLg value. These values may indicate that the attenuation of the Lg waves, at least for this region, may not be affected by only the anelastic dissipation, but also by scattering process. The N-S direction is normal to the dominating fault systems and seems to provide a greater scattering effect than the E-W direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00576.x
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  • 4
    Electronic Resource
    Electronic Resource
    The fit of polar wander curves by small circles using Marquardt's algorithm: statistical properties (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The method of constructing smooth apparent polar wander paths by fitting to small circle arcs is re-examined. The calculation of the best fitting small circle axis and angle is carried out by means of an iterative, rapidly convergent method. In addition, statistical properties are derived for the various estimated parameters in the linear asymptotic approximation, which allows, in particular, the determination of ellipses of confidence around the calculated poles of the model. Applications to the North American apparent polar wander path using previously published data sets are given as illustrations. In each case, the consistency of the inferred statistics has been checked by simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb00808.x
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  • 5
    Electronic Resource
    Electronic Resource
    Results of the DEKORP 1 (BELCORP-DEKORP) deep seismic reflection studies in the western part of the Rhenish Massif (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 106 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Within the DEKORP project (DEKORP: Deutsches Kontinentales Reflexionsseismisches Programm) a joint deep seismic reflection venture with the BELCORP (Belgian Continental Reflection Seismic Programme) group of the Belgian Geological Survey was carried out in 1987 across the Rhenish Massif, a part of the mid-European Variscides. This orogenic belt developed in the Upper Devonian/Carboniferous. Mostly Devonian rocks crop out at the surface. The Rhenish Massif is bordered by two sedimentary troughs: the sub-Variscan Foredeep in the north and the Permo-Carboniferous Saar-Nahe Basin in the south. In the east-west direction it is subdivided by the axial depression of the Eifel Nord-Süd Zone.The aim of the survey which totals almost 220 km of seismic profiling, was to investigate the crustal structure of the western part of the Rhenish Massif and to compare it with the line DEKORP 2-N which crosses the eastern portion of the massif. The results indicate the presence of NW-vergent tectonics of various styles that can often be traced down to deep parts of the crust. Horizontal Variscan compression plays a dominant role in the northern part while post-Variscan extension seems to dominate in the Saar-Nahe Basin, although even there traces of Variscan compression seem to be preserved in the middle crust. Common characteristics of the pre-Palaeozoic basement, differences between the western and eastern parts of the Rhenish Massif, and the deep extension of the Aachen Thrust (Faille du Midi) have been clearly observed. This prominent thrust in the north with its characteristic ramp and flat structure has been followed over 100 km length down
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb04612.x
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  • 6
    Electronic Resource
    Electronic Resource
    Using expert systems and simulation modelling for land evaluation at farm level: a case study from New York State (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 9 (1993), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. A land evaluation at farm level was made for a toposequence of three New York soils, using the FAO framework and the LEACHN simulation model. The land utilization type (LUT) was continuous corn, using three varieties with different growing periods. Ten experts identified the same land qualities but three different types of land characteristics, as derived from soil survey data, field observations and simulation modelling. Differences could be explained by the backgrounds of the experts. A land evaluation procedure according to framework criteria using decision trees rather than matching tables was more accessible and transparent. Simulation of the soil-water regime provided quantitative data for all land qualities considered, and this procedure was preferred to qualitative estimates based on poorly defined procedures. When some land qualities cannot be characterized by simulation, however, a mix of qualitative and quantitative decision tree branches may be considered. The standard scheme of land evaluation, which is scale independent, provides irrelevant results at farm level because farmers’ questions are different from those of regional planners who are well served by the traditional land evaluation procedure. For the farmer, development of decision support systems should be focused on optimal management decisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1993.tb00942.x
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  • 7
    Electronic Resource
    Electronic Resource
    A comparison of qualitative and quantitative physical land evaluations, using an assessment of the potential for sugar-beet growth in the European Community (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 8 (1992), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Qualitative and quantitative physical land evaluations differ in their technical procedures, i.e. use of expert knowledge versus process-orientated simulation models. This paper compares the results of both procedures using the growth potential for sugar-beet in the European Community. Qualitative procedures give suitability expressions, such as land being well suited or moderately suited for a given land use. Less than 30% of EC land was found to be well suited or moderately suited under water-limited conditions. No quantitative expressions for the crop yield potential are, however, produced. The quantitative procedure describes suitability in terms of average crop yield and its temporal variability. Water-limited and potential dry matter yields of sugar-beet were estimated to range from 3.5 to 20 t/ha, and from 6 to 25 t/ha, respectively.Comparison of results of the qualitative and quantitative procedures for regions showed that the suitability classes obtained by the former can be characterized by different yield distributions derived from the latter. These yield assessments showed that results of qualitative land evaluation procedures aimed at assessing yield potential are meaningful only when they are linked to agroclimatic zones. The comparison also showed that some moderate restrictions, which often can be counteracted by adequate farm management, are not incorporated into the quantitative procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1992.tb00899.x
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  • 8
    Electronic Resource
    Electronic Resource
    PULSE DISTORTION IN CAUSTIC REGIONS (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 39 (1991), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: It is well known that there is a phase shift of π associated with the propagation of a seismic pulse through a focus. But this simple behaviour is true only if the two points at which the pulse is observed lie sufficiently far from the focus, one on either side. Near the focus matters are more complicated and the shape of the pulse may be severely distorted because of diffraction. To examine this problem we consider a pulse generated by a point source and focused by a spherical reflector. Using a general combined method of ray tracing and diffraction, we compute seismograms for receivers lying both inside and outside the focal region, and determine how the shape of the pulse changes on propagation through the focus. To assist the physical interpretation of the numerical results, we also present relevant exact and asymptotic results for comparison.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1991.tb00300.x
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  • 9
    Electronic Resource
    Electronic Resource
    The fossil vertebrates from Lano (Basque Country, Spain); new evidence on the composition and affinities of the Late Cretaceous continental faunas of Europe (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 2 (1990), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A newly discovered fossil locality at Lano (Basque Country) has yielded a vertebrate assemblage of probably Maastrichtian age comprising fishes, amphibians, reptiles and mammals. It considerably enlarges our knowledge of the Late Cretaceous continental faunas of Europe, hitherto based on a much less complete record. Some taxa are recorded for the first time in Europe, and the fauna also contains the oldest known representatives of some groups (amphisbaenians, salamandrids). The Lan assemblage reveals an original fauna comprising both forms related to Asian and North American groups and elements with Gondwanan affinities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1990.tb00103.x
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  • 10
    Electronic Resource
    Electronic Resource
    Modeling Free Product Migration and Recovery at Hydrocarbon Spill Sites (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 32 (1994), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The numerical model ARMOS, which simulates areal flow of water and light hydrocarbon in an unconiined aquifer, isdescribed. Based on the assumption of local vertical equilibrium, area! flow equations for water and hydrocarbon are derived which exhibit reduced dimensionality and nonlinearity. A finite-element method is used to solve the water and oil equations using an efficient semidecoupled approach. Input required by the model includes area! boundaries, elevations of the aquifer lower boundary, and initial water and hydrocarbon levels in monitoring wells. Soil and fluid properties include hydrocarbon density, viscosity and surface tension, saturated hydraulic conductivity, van Genuchten air-water capillary pressure curve parameters, and the maximum residual hydrocarbon saturations in the saturated and unsaturated zones. Fluid heads or fluxes may be specified on the domain perimeter and pumping rates are prescribed at recovery wells. The water pumping rate is automatically limited when drawdown reaches a pump-off set point (or the screen bottom), and hydrocarbon recovery is limited when well hydrocarbon thickness becomes zero. Model output includes water and hydrocarbon levels in monitoring wells, cumulative product recovery, and free and residual hydrocarbon volumes in the soil. A hypothetical problem involving optimization of free product recovery and a field application of the model to a large pipeline leak are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1994.tb00619.x
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