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The Australian National University
Research School of Earth Sciences
Earth Physics - Prof. B.L.N. Kennett

B.L.N. Kennett


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Research Interests

The development of interpretational techniques for seismic records, with the object of extracting detailed information about the nature of the structure within the Earth, and the character of seismic sources.

a) The Structure of the Earth

  • Structure of the Upper Mantle
    • Velocity and attenuation structure from refracted body waves
    • Nature of heterogeneity in upper mantle
      • Pervasive presence of medium-scale heterogeneity
      • 3-D structure in transition zone beneath Australian region
      • exploiting velocities, attenuation, anisotropy
    • Development of systematic studies of a Australian region using arrays of portable broad-band instruments
        • SKIPPY experiment 1993-1996 - whole continent
        • KIMBA 1997-1998 more detailed experiment in Kimberley WA
        • QUOLL 1999 - south-eastern Australia
        • WACRATON 2000-2001 - Western Australia
        • TasmaL 2003-2005 - bracketing Tasman Line in Australia
        • CAPRA 2006-2007 - north-western Australia
      • surface wave tomography
      • body wave studies
      • attenuation (body wave and surface waves)
      • anisotropy (SKS splitting, direct S and surface waves
      • receiver function studies
  • Structure of whole Earth
    • 1-dimensional Earth models from travel times
      • iasp91 - improved earthquake locations and hence empirical travel times
      • ak135 - fit to a wide range of empirical travel times, improved core model and S model
      • have formed the reference models for recent high-resolution travel- time tomography
      • allowed the exploitation of S wave times for tomography (by eliminating baseline discrepancy in earlier models)
    • 3-dimensional shear wavespeed variation
      • combining S and SKS information to provide better resolution of lower mantle
    • 3-dimensional variation of bulk-sound and shear wavespeeds
      • exploit data set with common source/receiver for both P and S about 1 million times for each exploiting together to produce 3-D images of variation of bulk-sound and shear velocities.
      • The combination of two wavespeed imagesallows the delineation of different heterogeneity regimes
    • Relation of Seismic Structure and underlying processes

b) Seismic Wave Propagation

  • Systematic treatment of stratified media
    • Development of a representation of the seismic wavefield which is both physically based and numerically stable
    • Approximations to seismic response tuned to different classes of seismic phases
    • Forms basis of most work on anisotropic stratification
  • Operator development for heterogeneous media
    • Extension of stratified media techniques via operators
    • Representations through coupled wavenumbers
    • Stochastic wave propagation
  • Guided waves in heterogeneous media
    • Coupled mode techniques for surface waves in varying waveguides including transmission and reflection (2-D)
    • Synthetic seismograms for transmission through heterogeneous regions applied to analysis of surface wave tomography
    • Coupled mode and plane wave method for description of surface in 3-D varying media

c) Inverse Theory

    Nearly all seismic observations are indirect and the properties of the interior of the Earth have to be deduced from analysis of extensive data sets with relatively subtle dependence on the distribution of seismic wave velocities. There is therefore a major need to develop improved algorithms for the solution of such 'inverse problems'.

  • Development of methods for multi-parameter inverse problems
    • Application of subspace expansion techniques to geophysical problems
    • Dual wavespeed tomography (bulk-sound and shear from P and S times)
  • Earthquake location
    • Nonlinear methods for earthquake location exploiting multi-phase information.

d) Applied Seismology:

  • Discrimination of underground nuclear explosions re Comprehensive Test Ban Treaty
    • the iasp91 travel times have been adopted as the standard for event location in the International Data Centre for the Comprehensive Test Ban Treaty
    • a shift to ak135 to improve later phases is under discussion
    • studies of the regional wavefield and the influence of lateral heterogeneity
    • improved regional discriminants incorporating corrections for the influence of the free surface
    • techniques for characterising later seismic phases, using arrays or single stations, to improve location accuracy
  • Reflection Seismology
    • Techniques for multiple suppression for multi-component land records
    • The importance of the shear wavespeed in marine work with hard seafloor
    • Techniques for processing deep-crustal reflection profiles
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