Multiscale seismic heterogeneity in the continental lithosphere

We examine the nature of seismic heterogeneity in the continental lithosphere, with particular reference to Australia. With the inclusion of deterministic large-scale structure and realistic medium-scale features, there is not a need for strong fine-scale variations. The resulting multiscale heterogeneity model gives a good representation of the character of observed seismograms and their geographic variation, and is also in good agreement with recent direct results on P wave reflectivity in the lithosphere. Fine-scale heterogeneity is pervasive, but strongest in the crust. There is a weak quasi-laminar component above the lithosphere-asthenosphere transition with horizontal correlation length of 10 km and vertical correlation length of 0.5 km. Within the transition, the aspect ratio of heterogeneity changes and can be well represented with a horizontal correlation length of 5 km and vertical correlation length of 1 km. For the Australian cratons, this transition zone needs low intrinsic attenuation (high Q) to sustain the long high-frequency coda of both P and S waves. The interaction of the different aspects of the heterogeneity is complex and produces a diversity of behavior depending on the relative thickness of the different lithospheric zones. The multiscale model reconciles many of the divergent concepts of the character of heterogeneity based on interpretations of particular aspects of the seismic wavefield. The varying nature of the heterogeneity also ties well with the variations in tectonic character across the Australian continent.