ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Keywords: seismology ; reflection profiles ; seismic waves ; seismic tomography ; Australia
    Description / Table of Contents: Deep Crustal Seismic Reflection Profiling: Australia 1978–2015 presents the full suite of reflection profiles penetrating the whole crust carried in Australia by Geoscience Australia and various partners. The set of reflection data comprises over 16,000 km of coverage across the whole continent, and provides an insight into the variations in crustal architecture in the varied geological domains. Each reflection profile is presented at approximately true scale with up to 220 km of profile per page and overlap between pages. Each reflection section is accompanied by a geological strip map showing the configuration of the line superimposed on 1:1M geology. The compilation includes a suite of large-scale reflection transects groups of 1,000 km or more that link across major geological provinces, and an extensive bibliography of reports and relevant publications.
    Pages: Online-Ressource (V, 224 Seiten)
    Edition: 2nd ed.
    ISBN: 9781760460853
    Language: English
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 114 (1976), S. 747-751 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations of surface waves depend both on the structure traversed and the nature of the source, and therefore inversion of surface wave data can yield information about both structure and sources. The available methods for structural inversion are compared and discussed and a suggestion made for improved source inversion.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 114 (1976), S. 647-652 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The effects of unsuspected lateral variation in seismic velocities at depth on the interpretation of a seismic refraction profile are discussed with the aid of a numerical experiment. The results show that there will be bias in any velocity depth models derived by travel time analysis based on the assumption of horizontally layered media. This bias is examined for a lithospheric profile using both extremal and linearised travel time inversion. In addition quite mild subsurvace topography can have an appreciable effect on the amplitude distribution along the profile.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 422 (2003), S. 674-675 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Over the past three decades there has been vigorous debate over how thick the continents can be — that is, the depth to which the rigid crust and upper mantle reach before meeting convecting mantle that can flow and drive tectonic motion. On page 707 of this issue, Gung and colleagues ...
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 123 (1995), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The location of seismic events can be improved if accurate picks can be assigned for later seismic phases, which requires both the detection of an arrival and the recognition of its character. Such phase identifications are particularly valuable if they can be provided in real-time as the seismic disturbance passes across a broad-band seismic recording station.A simple but promising scheme for characterizing arrivals can be constructed by analysing the energy content of the seismic trace as a function of time. Such an approach can be used to detect arrivals by using a method comparing the short-term average energy to a long-term average, with averaging windows that are adaptive to the local frequency of the seismic disturbance. The phase detector can be tuned to different classes of arrivals by utilizing three-component records. By comparing the energy on the vertical component of motion to that in the horizontal plane, it is possible to start to separate P and S arrivals. Phase assignments can be refined by the use of adaptive filtering and by including polarization information.With an estimate of the azimuth of propagation it is possible to use approximate projection methods which attempt to compensate for the influence of the free surface, since the surface corrections are not a strong function of slowness for teleseismic arrivals. By this means, an instantaneous estimate can be made of the relative contributions of P, SV and SH arrivals which can be very helpful in determining the phase assignment for a particular arrival.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 122 (1995), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: New empirical traveltime curves for the major seismic phases have been derived from the catalogues of the International Seismological Centre by relocating events by using P readings, depth phases and the iasp91 traveltimes, and then re-associating phase picks. A smoothed set of traveltime tables is extracted by a robust procedure which gives estimates of the variance of the traveltimes for each phase branch. This set of smoothed empirical times is then used to construct a range of radial velocity profiles, which are assessed against a number of different measures of the level of fit between the empirical times and the predictions of the models. These measures are constructed from weighted sums of L2 misfits for individual phases. The weights are chosen to provide a measure of the probable reliability of the picks for the different phases.A preferred model, ak135, is proposed which gives a significantly better fit to a broad range of phases than is provided by the iasp91 and sp6 models. The differences in velocity between ak135 and these models are generally quite small except at the boundary of the inner core, where reduced velocity gradients are needed to achieve satisfactory performance for PKP differential time data.The potential resolution of velocity structure has been assessed with the aid of a non-linear search procedure in which 5000 models have been generated in bounds about ak135. Msfit calculations are performed for each of the phases in the empirical traveltime sets, and the models are then sorted using different overall measures of misfit. The best 100 models for each criterion are displayed in a model density plot which indicates the consistency of the different models. The interaction of information from different phases can be analysed by comparing the different misfit measures. Structure in the mantle is well resolved except at the base, and ak135 provides a good representation of core velocities.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 118 (1994), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Many techniques for the solution of seismic-wave propagation problems depend on the representation of the seismic wavefield in terms of a linear combination of basis functions, as for example in Fourier or Gaussian Beam expansions. A common formal representation encompasses such methods when a preferred coordinate is isolated to track the propagation path. Different techniques can be classified by the dependence of the basis functions on this preferred coordinate. The common representation provides useful insight into the relation between apparently disparate methods and can guide the development of computational techniques. This common framework allows the development of generalized propagator methods and a compact formulation of reflection and transmission problems. A general perturbation approach can be used either to add heterogeneity to an existing structure or to restore features, such as coupling between P and S waves, which have been ignored in an approximate development.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 124 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Much modelling of the seismic wavefield is undertaken with an acoustic approximation in which the influence of shear waves is neglected. Although such calculations can predict the correct traveltimes for compressional-(P-) wave propagation, they can he very misleading with respect to the distribution of seismic amplitudes, especially at larger offsets. At the seabed, the acoustic approximation predicts total reflection for P waves incident beyond the critical angle. However, once the presence of shear waves in the solid material below the sea-floor is taken into account, P waves in the sea water incident beyond the critical angle can give rise to transmitted S waves, with a consequent major change in the propagation pattern. Such effects are very important for areas with high velocities at the sea-floor, as commonly occurs in tropical waters, such as the north-west shelf of Australia. The character of the water-borne noise in these conditions depends on whether the shear wavespeed at the seabed lies above or below the P-wave velocity in the sea water above. For high shear velocities, two distinct sets of critically reflected multiples can be produced to give a very energetic noise train trapped in the water column. Conversion of P to S in transmission at the sea-floor can often be important and give rise to significant arrivals on the outer traces from long marine cables. Further, the conversion of energy to S waves reduces the energy available for P-wave multiples and dramatically reduces the influence of waterbottom multiples compared with a purely acoustic situation. Synthetic seismogram calculations for large offsets and equivalent calculations in the slowness-times domain, with selective control of the level of multiples and conversion at each interface, provide a convenient tool for characterizing the expected water-borne energy and the influence of converted shear waves on the pressure field recorded in the water.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 108 (1992), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Earthquakes in oceanic areas are normally located using traveltime tables which are representative of continental paths, since most seismic stations lie on continents. It should therefore be possible to improve such locations by employing a set of traveltimes more appropriate to paths from oceanic events to continental stations.A comparison has therefore been made between locations for a number of oceanic events using the recent iasp91 global traveltimes and the times for the pac91 model derived from observations of events in the Pacific. Although there were often significant differences in the location estimates for the two models, these were often no larger than the shifts induced by changing the misfit criterion used for determining the location.For events in purely oceanic regions such as Tonga and the Marianas with little nearby continent, the results from the pac91 model either provided a significantly better fit to the data or produced depth estimates in close accord with independent constraints (e.g. centroid moment tensor locations). In these cases the use of a specific set of ‘oceanic’ traveltimes can be recommended. However for marginal zones and island arcs, the situation is less clear and it is probably best to employ the global traveltime set with the use of additional phases to improve depth estimates.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 100 (1990), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Coupled mode techniques for guided wave propagation are extended to 2-D stochastic heterogeneity superimposed on a stratified medium. This approach requires the variations to be smoothly varying and of modest size (less than ±2 per cent). By averaging over an ensemble of statistically similar models, coupled equations for the modal energy transport can be generated. The intermode coupling depends on the horizontal correlation functions for the heterogeneity in the crust and mantle, and the integrated effect of the vertical variations in velocity and the modal eigenfunctions.For a particular stochastic model, the attenuation of a single mode as a function of distance can be calculated as a superposition of intrinsic attenuation and scattering loss by energy transfer to other modes of propagation. These statistical estimates of attenuation can be compared with observations of regional phases travelling over a variety of paths in a single region. For Lg and Sn phases, intermode scattering may represent up to 30 per cent of the apparent loss.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...