Seismic waveform tomography on continental scales based on the spectral-element and adjoint methods

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Recent progress in numerical seismology and computer science enables today s seismologists to model elastic wave propagation through heterogeneous media routinely with high accuracy. This development suggests to go beyond the common data reduction (e.g. extracting travel times) and to analyse full waveforms for the purpose of high-resolution seismic tomography. Our research project is focused on the development of a full waveform inversion (FWI) technique for the detailed imaging of upper mantle structure and its application to the Australian continent. For this we propose (1) to compile a database of highquality waveform data for the Australian continent; (2) to design full waveform misfits in order to extract as much robust information as possible from the seismograms; (3) to employ a spectral-element method in conjunction with the adjoint method for the computation of tomographic images; (4) to assess the importance of correctly accounting for 3D Earth structure in general and for ocean-continent boundaries in particular, and (5) to compare the resolution capabilities of a FWI with those of classical ray tomographies. Key innovations of the FWI are that the forward modelling is accurate in media with lateral variations such as ocean-continent transitions. The synthetic waveforms and the resulting tomographic images can therefore be expected to be more realistic. Moreover, the amount of exploited information is significantly higher than in classical inversion methods based on ray or normal mode theory. Exploiting this wealth of information will lead to better constrained models of upper mantle structure with impact on the related geodynamic issues.