Bibliothek

X
feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
Filter
Datenquelle
Materialart
Erscheinungszeitraum
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    Dynamic composite elastic medium theory. Part I. One-dimensional media (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5451-5457 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Wave propagation in stratified media may be described by scattering theory, effective medium theory or ray theory, depending upon the frequency range. We present a dynamic composite elastic medium theory which describes wave propagation at all frequencies. In the first part of the series we consider randomly layered one-dimensional media and in the second part media with three-dimensional inclusions. Non-self-consistent and self-consistent methods using the scattering functions of the individual layers are formulated which allow the calculation of phase velocity, attenuation and wave forms. In the low frequency limit only the self-consistent method agrees with the Reuss average and in the high frequency limit it yields the correct ray theory average velocity. The comparison with complete numerical solutions shows that our theory predicts the coherent wave through randomly layered media. Hence, the dynamic composite elastic medium theory can be used to compute frequency dependent elastic properties of randomly layered media without calculating the complete wave propagation solution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368307
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 2
    Digitale Medien
    Digitale Medien
    Dynamic composite elastic medium theory. Part II. Three-dimensional media (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5458-5468 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Non-self-consistent and self-consistent methods of estimating velocity and attenuation of P waves and S waves at all frequencies for heterogeneous media with three-dimensional inclusions are formulated using the scattering functions of the individual inclusions. The methods are the generalization of methods for one-dimensional media presented in the first paper of this series. The specific case of spherical inclusions is calculated with the exact scattering function and compared with several low frequency approximations. The self-consistent estimates are consistent with Berryman's low frequency approximation. We present spectra and wave forms of materials with solid and liquid inclusions in a solid matrix. The results show that the exact scattering functions are required to adequately describe wave propagation at all frequencies. The analysis of liquid inclusions demonstrates that viscous damping may become important only if scattering attenuation due to spherical pores is small.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368308
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 3
    Digitale Medien
    Digitale Medien
    Ensemble inference in geophysical inverse problems (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 115 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Non-invasive studies of the shallow Earth are an essential element in a broad range of earth science disciplines. Such studies are usually accomplished using geophysical techniques, which means that a geophysical inverse problem must be solved. Unfortunately, non-uniqueness is a basic property of almost all solutions to geophysical inverse problems. In this paper we describe a method of dealing with this non-uniqueness which we believe is more direct, more complete, and more informative than previous attempts in this area. Instead of using regularization methods to constrain the non-uniqueness of geophysical inverse problems, we confront directly the non-uniqueness and attempt to describe it. The basic technique is to generate and describe a collection of models that fit the data within acceptable limits based upon observational errors. This collection of models, called an ensemble, is analysed with statistical methods in order to characterize the uncertainty in the solution and also make inferences about properties that are shared by all acceptable models. A by-product of this approach is that it produces basic information about the degree of linearity contained in the problem and maps trade-offs between various parameters. The method proposed is quite general and should be applicable to a broad range of geophysical inverse problems. We illustrate the basic method by applying it to two typical geophysical problems. The first application is to a set of cross-borehole traveltime observations gathered in Kesterson, California. The small deviations of the observed traveltime residuals from those predicted by a uniform half-space indicates that the velocity contrasts are not large. The set of acceptable models appears to form a non-degenerate hyperellipsoid in the model space. The mean of the velocity models converges quite rapidly to a smoothed version of a linearized singular-value decomposition solution. The velocity variations agree very well with the results of a hydrological tracer test conducted prior to the seismic experiment. The second application is to the problem of simultaneously estimating the shape and density of a constant density body using surface gravity measurements. In this case a linear analysis is found to be inadequate. A quadratic formulation is necessary to accurately represent the trade-off between the magnitude of the density perturbation and the depth extent of the body.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb01489.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    A stable method for linearized inversion of elastic parameters (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 115 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: An inversion method that stabilizes the multiparameter inverse problem for a constant background elastic isotropic medium is developed. The inverse problem is formulated in the wavenumber domain and the operators acting on the individual elastic parameters are displayed and analysed. From here it is noticed that for certain scattering angles some parameters produce no scattering. This scattering angle dependence is combined with the frequency dependence of the parameters to reduce the multiparameter inverse problem to a single parameter inversion problem, which is known to yield stable results. The method developed here is an extension of an acoustical medical imaging method by Norton (1983) to the elastic seismic imaging problem which inherits limited view constraints. This method is compared to the elastic extension of a multiparameter acoustic inversion method developed by Devaney (1985) and the resulting improvements in stability are demonstrated on synthetic examples.From the theory it is observed that a fixed 90° scattering angle can be used with multiple frequencies to achieve highly stable inversion results of all elastic parameters provided specific elastic parameters are extracted from specific scattering modes. The attempt to extract all elastic parameters from the P-to-P scattering mode using multiple scattering angles is seen to be very ill-conditioned and not recommended.For the 90° scattering angle we find that surface reflection profiling (SRP) and cross-hole geometries have the same wavenumber domain coverage and the multi-offset vertical seismic profiling (MVSP) geometries give a better coverage than only a SRP or cross-hole geometry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb05585.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 5
    Digitale Medien
    Digitale Medien
    Low-frequency elastic-wave scattering by an inclusion: limits of applications (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The present investigation considers various approximations for the problem of low-frequency elastic waves scattered by a single, small inclusion of constant elastic parameters. For the Rayleigh approximation containing both near- and far-field terms, the scattered amplitudes are investigated as a function of distance from the scatterer. Near-field terms are found to be dominant for distances up to two wavelengths, after which far-field solutions correctly describe the scattered field. At a distance of two wavelengths the relative error between the total and the far-field solution is about 15 per cent and decreases with increasing distance. Deriving solutions for the linear and quadratic Rayleigh–Born approximation, the relative error between the non-linear Rayleigh approximation and the linear and quadratic Rayleigh–Born approximation as a function of the scattering angle and the parameter perturbation is investigated. The relative error reveals a strong dependence on the scattering angle, while the addition of the quadratic term significantly improves the approximation for all scattering angles and parameter perturbations. An approximation for the error caused by linearization of the problem, based entirely on the perturbations of the parameters from the background medium, and its validity range are given. We also investigate the limit of the wave parameter for Rayleigh scattering and find higher values than previously assumed. By choosing relative errors of 5 per cent, 10 per cent and 20 per cent between the exact solution and the Rayleigh approximation, we find the upper limits for the parameter kpR to be 0.55, 0.7 and 9.9, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb01845.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 6
    Digitale Medien
    Digitale Medien
    Scattering of elastic waves by a spherical inclusion—I. Theory and numerical results (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 115 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: A complete and exact solution for the problem of an incident P wave scattered by an elastic spherical inclusion is presented and described. The solution can be obtained from either analytical formulae or stable numerical procedures. A method of estimating the number of terms that must be retained in the harmonic series in order to achieve a specified accuracy is given. The results are investigated by calculating synthetic seismograms, scattering diagrams, and scattering cross-sections for a broad frequency band and for both low-velocity and high-velocity inclusions. The fields within the shadow zone are formed primarily from three different types of waves, P waves transmitted through the sphere, P waves diffracted around the sphere, and S waves converted at the boundary of the sphere. The relative contribution from these different waves depends upon the distance of the observation point from the sphere.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb05601.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 7
    Digitale Medien
    Digitale Medien
    Scattering of elastic waves by a spherical inclusion–II. Limitations of asymptotic solutions (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 115 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Starting with the exact solution for the scattering of a plane P wave by a homogeneous spherical inclusion, various types of approximate solutions are developed and discussed. The standard Rayleigh and Mie approximations are extended to the case of inclusions having arbitrary contrasts in material properties. For the low-contrast case, solutions are developed which are valid over a wide frequency range. Several aspects of these solutions are discussed, including the importance of near-field terms and the relative strength of the scattered P and S fields. The various types of approximate solutions are compared with each other and with the exact solution by calculating and displaying their normalized scattering cross-sections.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb05602.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 8
    Digitale Medien
    Digitale Medien
    Isotropic and deviatoric characterization of the Coalora nuclear explosion in Yucca Flats (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 116 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Near-source data from the nuclear explosion Coalora detonated at Yucca Flats, Nevada Test Site (NTS), are utilized to constrain the seismic-source function. The equivalent seismic source is interpreted in terms of physical processes in the source region with the aid of data from within the explosion's non-linear region. The isotropic, deviatoric and spall contributions are separated and quantified. Standard spectral interpretations of the radiated wavefield for source parameterization are contrasted with complete waveform modelling with moment tensor determination. Individual waveform spectra (source-receiver offsets 〈 2 km) can be interpreted in terms of an isotropic source model, which is in agreement with a Mueller-Murphy model, including f−2 high-frequency decay and source corner frequency of 1.8 Hz. The deviatoric component of the moment tensor is a factor of 5–10 times smaller than the isotropic component. Deviatoric source radius, as estimated from the spectral data, is 125 m, smaller than the equivalent elastic source radius, which is bounded between 133 and 202 m. Stress drop estimated with the Brune source model is 45 bars with an average slip of 17 cm. Moment tensor inversion produces an isotropic source strength of 8 × 1020 dyne cm, while scalar moments from the spectral interpretation are a factor of 2.5 larger. This difference is attributed to the application of whole-space propagation path corrections with a free-surface amplification to the spectral interpretation. The spall source is longer period and delayed in time from the initial explosion. Its contribution to the diagonal elements of the moment tensor is dominant on the Mzz component, a factor of 3 larger than the Myy and Mxx components. Spall source strength from waveform inversion is within a factor of 2 of forward models developed from acceleration data within the spall zone. It is longer in duration than the forward prediction, reflecting the effect of a quasi-point source assumption in the forward model. Complex propagation effects extend in time and homogenize the data beyond 2 km as exemplified by wave trains at 5 km that are 20 s in duration and similarity of radial, vertical and transverse acceleration spectra. In contrast, observations at 2 km or less are short in duration with strong differences between transverse and radial-vertical spectra. These apparent propagation path effects suggest that source biases can develop at ranges as close as 2–5 km.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb03278.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 9
    Digitale Medien
    Digitale Medien
    Formal inversion of ISC arrival times for mantle P-velocity structure (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 113 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Seismic traveltime data are used to determine and assess a weighted least-squares model of the 3-D P-velocity structure of the Earth's mantle. A total of 682090 summary rays constructed from over three million ISC traveltime observations are used to constrain velocity perturbations in 12496 6° by 6° cells. An iterative block LU decomposition procedure, applied on the massively parallel Connection Machine 2 (CM-2), is used to compute a formal weighted least-squares model of P-velocity variations as well as the full resolution and covariance matrices. It is found that the shallow mantle beneath the continents of the northern hemisphere is well resolved. However, the majority of mid-oceanic features, such as spreading ridges and hot spots, are not well constrained. As a function of depth, the resolution is highest in the upper to mid-mantle, due to variations in ray coverage. Primarily because of ray geometry, single blocks are not resolved below 1870 km. The estimates of spatial resolution, constructed from the complete resolution matrix, are useful in judging whether subducting lithosphere extends into the lower mantle. The results indicate that possible extensions of subduction zones in the northern hemisphere are imaged reliably down to at least 1470 km. However, areas beneath most subduction zones in the southern hemisphere are averaged over scale lengths of 800 km or more below a depth of 1070 km. Velocity estimates for the mid to lower mantle beneath Hawaii are the result of averaging over 1900 km or more. Generally, vertical and lateral averaging of 600 to 1000 km is occurring in the depth range 2270 to 2670 km. P-wave velocity values in the region just above the Core-Mantle Boundary (CMB) are large-scale spatial averages (1500 km or more) and individual cells are poorly resolved. The model parameter standard error remains moderate throughout the lower mantle due to smaller traveltime errors associated with rays that bottom in this region. These standard errors reach no more than 0.3 per cent of the Jeffreys-Bullen average velocity. The greatest standard errors, 0.9 per cent of the average velocity, are found in the upper mantle underlying the Pacific basin. These large parameter errors are due primarily to the poor ray coverage in the Pacific coupled with the large arrival-time uncertainties for P recordings in the epicentral distance range 0° to 20°.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb04654.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 10
    Digitale Medien
    Digitale Medien
    Scattering ofP andS waves by a spherically symmetric inclusion (1996)
    Springer
    Pure and applied geophysics 147 (1996), S. 675-718 
    Details
    ISSN: 1420-9136
    Schlagwort(e): Elastic waves ; sphere ; scattering ; diffraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract Scattering of an arbitrary elastic wave incident upon a spherically symmetric inclusion is considered and solutions are developed in terms of the spherical vector system of Petrashen, which produces results in terms of displacements rather than displacement potentials and in a form suitable for accurate numerical computations. Analytical expressions for canonical scattering coefficients are obtained for both the cases of incidentP waves and incidentS waves. Calculations of energy flux in the scattered waves lead to elastic optical theorems for bothP andS waves, which relate the scattering cross sections to the amplitude of the scattered fields in the forward direction. The properties of the solutions for a homogeneous elastic sphere, a sphere filled by fluid, and a spherical cavity are illustrated with scattering cross sections that demonstrate important differences between these types of obstacles. A general result is that the frequency dependence of the scattering is defined by the wavelength of the scattered wave rather than the wavelength of the incident wave. This is consistent with the finding that the intensity of theP→S scattering is generally much stronger than theS→P scattering. When averaged over all scattering angles, the mean intensity of theP→S converted waves is2V p 2 /V s 4 times the mean intensity of theS→P converted waves, and this ratio is independent of frequency. The exact solutions reduce to simple and easily used expressions in the case of the low frequency (Rayleigh) approximation and the low contrast (Rayleigh-Born) approximation. The case of energy absorbing inclusions can also be obtained by assigning complex values to the elastic parameters, which leads to the result that an increase in attenuation within the inclusion causes an increased scattering cross section with a marked preference for scatteredS waves. The complete generality of the results is demonstrated by showing waves scattered by the earth's core in the time domain, an example of high-frequency scattering that reveals a very complex relationship between geometrical arrivals and diffracted waves.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01089697
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...