3D Elastic Full Waveform Inversion of Teleseismic Data for High-resolution Ospheric Imaging

Abstract

We present a 3D time-domain target-oriented elastic full-waveform inversion method well-adapted to the reconstruction of lithospheric images from passive teleseismic data. In teleseismic configurations, sources no longer correspond to point sources embedded in the lithospheric target but rather correspond to a nearly plane wavefronts generated by distant Earthquake incoming from the outside of the targeted medium. To save computation time and apply FWI in the lithospheric target, we follow a two steps strategy based on grid-injection technics. First, wavefields generated by earthquake are propagated in axisymmetric global Earth model with AxiSEM to be stored on the target boundaries. Then, these wawefields are injected within the lithospheric medium and propagated with a spectral element method. We efficiently compute the gradient of the misfit function with the adjoint-state method in time domain. We assess the feasibility of the method on two synthetic models: a cubic inclusion and a realistic lithospheric model representative of the Western Alps. Preliminary results suggest that, despite a weak number of sources and a a coarse aperture illumination, our FWI implementation succeed in reconstructing the initial model thanks to the contribution of both forward and backward scattering regimes.