Preliminary 3D isotropic full-waveform inversion model of the Alpine lithosphere from assimilation of AlpArray teleseismic body waves

The Alps, which result from the convergence between the African and Eurasian plates, are an ideal natural laboratory to study the dynamics and evolution of continental orogens. This mountain range is indeed well documented both by geology and geophysics, which have notably allowed to highlight the different stages of continental subduction and collision during its formation. Nevertheless, large uncertainties remain about the 3D shape of structures and the internal composition of the Alps at crustal and upper mantle scales. This context motivated the European initiative AlpArray which deployed a dense array of more than 600 seismic sensors in the Alps and its periphery paving the way for the application of advanced seismic imaging techniques such as teleseismic waveform inversion (FWI). FWI is becoming a state-of-the-art method for lithospheric imaging as it allows the determination of various subsurface properties (seismic wavespeed, density, anisotropy or even attenuation) with high resolution and accuracy. In this study, we present the preliminary results of the LisAlps project which aimed at applying teleseismic FWI to the AlpArray  dataset to build isotropic and anisotropic high-resolution seismic models of the Alps from the surface down to the transition zone. Our preliminary application successfully built an isotropic (P and S seismic wave-speeds and density) model of the entire Alpine lithosphere from the assimilation of the first 60 s of the direct P waveforms of 18 teleseismic events within a period band ranging from 30 to 10 seconds. The resulting models recover large crustal structures of the Alpine range. In the crust, it recovers the surroundings sedimentary basins, crustal thickening in the internal part of the Alps as well as crustal thinning in the Ligurian sea and in the Ivrea zone. In the upper-mantle, where only the P wave-speed model is currently resolved, our model recovers large-scale mantle structures of the European and Apennines slabs.