Surface Wavefield Tomography of the Alpine Region to Constrain Slab Geometries, Lithospheric Deformation and Asthenospheric Flow

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Surface waves are ideally suited to constrain isotropic and anisotropic elastic properties of the lithosphere and asthenosphere. The Alpine region is characterized by relatively small-scale structural variations. To answer key questions regarding its lithospheric dynamics requires particularly high imaging resolution. Such resolution can be provided by the wavefield tomography, able to extract highly complete structural information from data recorded by a large-aperture, dense array. Recordings of the AlpArray Seismic Network, including its marine part, and of the Swaths C and D (AF A, B, C, D) will be analyzed to image both the local propagation of teleseismic Rayleigh and Love waves and crustal and mantle structure, with a lateral resolution below 50 km. The resulting shear-wave velocity model for the Earths upper 300 km will image the subducting Adriatic and Eurasian mantle lithospheres, as well as the forelands. It will resolve the slab geometry in the regions of polarity switches (SW Alps to Apennines, western to eastern Alps), of slab gaps (central Alps), of slab break-off (SW Alps), and in the transition from the eastern Alps towards the Dinarides (RT1, Reorg. of Lithosphere). Conversion into density anomalies will enable us to estimate slab-pull and buoyancy forces in the Alpine region and quantify the contribution of endogenous forces to surface uplift and subsidence (RT2, Surface Response). Seismic anisotropy reveals imprints of recent and past deformation on the lithosphere as well as mantle flow in the asthenosphere. We will compute a 3D model of seismic anisotropy within the lithosphere and the asthenosphere, offering new evidence on the deformation of the crust and on the coupling/decoupling between the curst and mantle and between plate motion and mantle flow (RT3, Deform. of Crust + Mantle). It will further serve as observational evidence to evaluate predictions by numerical modelling for different evolution scenarios (RT1, Reorg. of Lithosphere).New method development will focus on the measurement of Rayleigh and Love phases and amplitudes and their use in the imaging of the curvature, amplitude variations, and direcionality of the wavefields and of the seismic velocity structure beneath the arrays footprint. In order to cope with the large amount of recordings, automated measurement methods will be developed. Helmholtz and eikonal tomography will be extended to the anisotropic case. Phase velocity maps will be inverted for a radially and azimuthally anisotropic shear-wave velocity model of the Alpine region embedded into regional models and constrained by a-priori knowledge on the crust. Tools for efficient numerical forward modelling of the interaction of teleseismic surface waves with the deep structure of the Alps based on discontinuous Galerkin methods will be developed. The methods will allow the imaging of the Alps and their forelands that is both high-resolution and whole-region-scale.