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  • 1
    Electronic Resource
    Electronic Resource
    Elastic Kirchhoff-Helmholtz Synthetic Seismograms (1998)
    Springer
    Pure and applied geophysics 151 (1998), S. 17-45 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Synthetic seismograms, elastic waves, Kirchhoff, Green's function, inhomogeneity, anisotropy, hybrid.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. —An approximate hybrid formulation of the elastic Kirchhoff-Helmholtz theory for numerical simulation of seismic wave propagation in multilayered inhomogeneous and transversely isotropic media is developed. The layer boundaries can be curved or irregular. We insert a general computational ansatz into the basic elastodynamic divergence theorem to express the unknown variables in terms of slowly varying amplitude and phase functions. In situations where the geometrical optics approximation becomes invalid, more accurate methods can be applied to compute these functions. In particular, the kernel remains regular when rays have caustics on the target integral surface. Branch points are taken into account to include head waves. Both elementary solutions and WKBJ expansion are employed to compute the Green’s function. To reduce the resulting integral to a numerical form, the surface is divided into a set of segments and the above functions are replaced by their local polynomial series in the vicinity of each segment. It allows us to construct an error-predictive numerical algorithm in which the truncation error is prescribed via the higher order terms of such series. We show, using geologically relevant synthetic models, the performance of the proposed technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050103
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  • 2
    Electronic Resource
    Electronic Resource
    Crustal wave propagation anomaly across the Pyrenean Range. Comparison between observations and numerical simulations (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 115 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Lg records analysis and numerical modelling of Lg propagation are used to find out to what extent this phase can be seen as a marker of unidentified structural anomalies in the crust. This study is based on Lg propagation through the Pyrenean range from earthquakes located in Spain.We have first evaluated the mean value of the S-wave quality factor for central Spain. We have computed simultaneously the seismic station responses and the source functions. The correction for propagation effects, assuming a homogeneous attenuation and the theoretical calculation of the Lg excitation, lead to the seismic moment of each event. The moment magnitude obtained correlates well with the magnitude proposed by the local networks. This gives a confirmation of the Q model in the low-frequency range (1-5 Hz). As we intended to compare traces of different Spanish earthquakes recorded in France at different epicentral distances, we had to make amplitudes independent of propagation and source effects. Therefore, we corrected the spectral amplitudes for geometrical spreading, anelastic attenuation and normalized them to equal seismic moment.We then plotted the records as a function of group velocity, in order to make up a fan profile along the Pyrenean axis. The resulting section reveals that in the central and the eastern parts of the range, neither the North Pyrenean Fault, nor the Moho jump deduced from seismic-refraction experiments and vertical seismics, seem to affect Lg propagation. However, there is an extinction of the Lg phase in the western part of the chain. The lateral extent of this area is correlated with a zone of positive gravity anomaly, probably linked to the presence of dense material of mantle origin. A numerical simulation in the low-frequency band indicates that the Moho topography inferred from deep seismic soundings does not explain the strength of the observed attenuation. Ray-tracing seismograms show that, at high frequency, the conclusion is the same. The attenuation effect due to lateral variation of structure should not be so strong. We, therefore, think that attenuation of guided waves is not due to large-scale geometry effects, but is due to local properties of the crustal materials, possibly apparent attenuation due to scattering on small-scale heterogeneities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb01495.x
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  • 3
    Electronic Resource
    Electronic Resource
    Wave Diffraction In Multilayered Media With the Indirect Boundary Element Method: Application to 3-D Diffraction of Long-Period Surface Waves By 2-D Lithospheric Structures (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An indirect boundary-element method is presented for simulating seismic wave diffraction in layered media with irregular interfaces. Recursive formulae are developed to take into account an arbitrary number of layers without increasing the size of the problem in terms of computer memory. the interfaces between layers are of variable geometry, and interfaces can be superposed to introduce horizontally finite structures. such as lenses or sedimentary basins. In the present implementation, we study three-dimensional (3-D) diffraction of plane waves by two-dimensional (2-D) structures. the formulation is nevertheless sufficiently general to include the complete 3-D case. Even though the method can be used at all scales, the main purpose of the theoretical development is to simulate diffraction of long-period surface waves by heterogeneous lithospheric structures. A new approach to treat incident surface waves in multilayered media is therefore developed, but other wave types, such as body-waves and internal seismic sources, can easily be introduced. the method is verified by transparency tests and comparison with other simulation methods. the application on the 3-D diffraction of plane Rayleigh waves by a major lithospheric boundary shows that significant conversions between wave types are present, and that the diffracted waves influence the apparent phase velocities measured at the surface above the heterogeneity and several wavelengths behind it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb00017.x
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  • 4
    Electronic Resource
    Electronic Resource
    Modelling long-term phosphorus leaching and changes in phosphorus fertility in excessively fertilized acid sandy soils (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The sound management of agricultural soils that are heavily loaded with phosphorus (P) involves minimizing the losses of P responsible for eutrophication of surface waters, while ensuring enough P for crops. This paper describes a simple model to examine the compatibility of these two objectives in acid sandy soils in a temperate humid climate. The model is based on several assumptions regarding reversible and irreversible P sorption by P-reactive soil compounds (mainly poorly crystalline Fe and Al oxides) and release of P to water (water-P test). Model inputs are amount of P leached, P uptake by crops, and contents of poorly crystalline Fe and Al oxides in soil. The model predicts that reducing the amount of leached P to what is environmentally acceptable (e.g. 0.44 kg P ha–1 year–1, equivalent to 1 kg P2O5 ha–1 year–1) results in the long run in available soil P test values below target concentrations for optimum crop growth. When the amount of leached P is set to a fixed value the model predicts that soils with large contents of Fe and Al oxides can maintain the initial soil P test values for longer periods than other soils. The content in available P decreases if fertilizer P is applied to the soil at a rate equal to P uptake by crops. These results stress the difficulties involved in trying to make agricultural and environmental needs compatible in acid sandy soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1999.00244.x
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  • 5
    Electronic Resource
    Electronic Resource
    MODELING OF SH-WAVE PROPAGATION IN AN IRREGULARLY LAYERED MEDIUM-APPLICATION TO SEISMIC PROFILES NEAR A DOME (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 35 (1987), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: An approach that relies on a discrete representation of seismic wavefields allows the computation of synthetic SH-seismograms in a laterally varying medium with plane and curved interfaces in the two dimensional (2-D) case. The diffracting interface is represented by an array of body forces located along the interface at equal spacing. The numerical treatment is limited to the irregular boundary while the propagation in flat layered zones is obtained by the reflection-transmission matrix method. As an example we have studied the case of a dome in a stratified medium. The solutions obtained verify the reciprocity theorem with good accuracy. The computation of vertical profiles and of surface reflection profiles illustrates the effects of diffraction and the importance of lateral propagation in such a structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1987.tb00815.x
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  • 6
    Electronic Resource
    Electronic Resource
    Modeling crystal phases in southeast France for focal depth determination
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 95 (1989), S. 341-358 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0012-821X(89)90109-X
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  • 7
    Electronic Resource
    Electronic Resource
    Changes in the lithospheric structure across the Sorgenfrei-Tornquist Zone inferred from dispersion of Rayleigh waves
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 128 (1994), S. 37-46 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0012-821X(94)90024-8
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  • 8
    Electronic Resource
    Electronic Resource
    Population variability of Cernuella arigonis (Haas, 1929) (Mollusca: Helicidae) experimentally infected with Muellerius capillaris (Mueller, 1889) (Nematoda: Protostrongylidae)
    Amsterdam : Elsevier
    Veterinary Parasitology 53 (1994), S. 101-108 
    Details
    ISSN: 0304-4017
    Keywords: Cernuella arigonis ; Epidemiology-Nematoda ; Muellerius capillaris
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0304-4017(94)90022-1
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical studies of transplantation antigens: Predicted conformation and structure-function relationship of the murine MHC class i antigen H-2K^b
    Amsterdam : Elsevier
    Journal of Molecular Structure: THEOCHEM 179 (1988), S. 27-39 
    Details
    ISSN: 0166-1280
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0166-1280(88)80111-8
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  • 10
    Electronic Resource
    Electronic Resource
    Frequency dependence and spatial distribution of seismic attenuation in France: experimental results and possible interpretations
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 67 (1991), S. 48-64 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(91)90059-Q
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