The velocity structure and heterogeneity of the upper mantle

https://doi.org/10.1016/0031-9201(90)90220-RGet rights and content

Abstract

In a particular region a smoothed and averaged representation of the velocity structure in the upper mantle can be derived from long-period body wave and higher-mode surface wave observations. The vertical resolving power of such techniques is limited by the relatively long wavelengths used. In contrast, short-period studies show considerable complexities in postulated one-dimensional models which are unresolvable in the long-period band. However, these may be associated with the mapping of lateral heterogeneity into a vertical profile.

To assess the extent to which lateral heterogeneity in the mantle can be resolved, we have attempted to model the features seen on recordings of earthquakes in the Indonesia/New Guinea region at large-aperture (400–1000 km) arrays of portable seismic recorders. With horizontal heterogeneity scales of the order of 300–500 km and velocity perturbations up to 2%, the amplitude deviations from those predicted for a stratified model can be considerable and fit in well with the pattern of observations. For long-period waves such laterally heterogeneous structures have only a modest effect, with weak inter-mode coupling resulting from the heterogeneity. As a result, a one-dimensional model may still be a useful approximation for long-period studies, but will not be adequate for broad-band or short-period work.

References (23)

  • A.M. Dziewonski et al.

    Preliminary reference earth model

    Phys. Earth Planet. Inter.

    (1981)
  • A.L. Hales et al.

    A compressional velocity distribution for the upper mantle

    Tectonophysics

    (1980)
  • B.L.N. Kennett

    Observational and theoretical constraints on crustal and upper mantle heterogeneity

    Phys. Earth Planet Inter.

    (1987)
  • L.J. Burdick

    A comparison of the upper mantle structure between America and Europe

    J. Geophys. Res.

    (1981)
  • J. Cleary et al.

    The effect of local structure on measurements of the travel time gradient at the Warramunga seismic array

    Geophys. J. R. Astron. Soc.

    (1968)
  • S.P. Grand

    Tomographic inversion for shear velocity beneath the North American plate

    J. Geophys. Res.

    (1987)
  • S.P. Grand et al.

    Upper mantle shear structure of North America

    Geophys. J.R. Astron. Soc.

    (1984)
  • E. Herrin

    Regional variation of P-wave velocity in the upper mantle beneath North America

  • S. Ingate et al.

    Limitations of waveform modelling of long-period seismograms

    Geophys. J. R. Astron. Soc.

    (1986)
  • B.L.N. Kennett

    A comparison of travel time inversion

    Geophys. J. R. Astron. Soc.

    (1976)
  • B.L.N. Kennett

    Guided wave propagation in laterally varying media—I

  • Cited by (0)

    Presented at IASPEI symposium; Computation and Interpretation of Seismic Waveform in 2-Dimensional and 3-Dimensional Structures, held at the IUGG meeting 1987, Vancouver, Canada.

    View full text