Surface Wave Tomography
Using recording from portable and permanent seismic stations across Australia, the large amplitude surface waves from regional earthquakes are analysed to determine 3-dimensional structure in seismic wavespeed. For each path from a source to a receiver an average velocity model is determined and these constraints on the 3-D structure are finally combined to produce the 3-D image.
(now) EOST CNRS
Significant Achievements, Anticipated Outcomes and Future Work
We have been able to derive the first 3-D representation of both seismic wavespeed and anisotropy in the shear wave velocity beneath the Australian continent. We are able to demonstrate both the presence of high seismic wavespeeds beneath the Precambrian part of the continent, and a change in the nature of anisotropy with depth. Shallow anisotropy reflects past deformation, but the deep part which is nearly aligned with the motion of the Australian plate indicates current deformation at the bottom of the mechanical lithosphere. As time progressed we have incorporated larger volumes of data and improved the methods used to generate and assess the 3-D image.
Computational Techniques Used
The process requires both the inversion of seismic waveforms to extract a velocity model with depth and the combination of such models to retrieve the 3-D structure. The wavespeed inversion is nonlinear, whereas the second step is linear but involves a very large system of equations. We have used a continuous representation of the 3-D model and this requires extensive computation but includes the influence of the neighbourhood of the propagation paths and thereby produces more reliable models.
Publications, Awards and External Funding
E. Debayle, B.L.N. Kennett , The Australian continental upper mantle - structure and deformation inferred from surface waves, J. Geophys. Res., 2000, 105, 25443-25540.
E. Debayle, B.L.N. Kennett, Anisotropy in the Australian upper mantle from Love and Rayleigh wave inversion, Earth Planet. Sci. Lett., 184, 2001, 339-351.