Thermal and Compositional Characterization of the Greater Alpine Crust Using Seismic Observables

The Greater Alpine crust provides a natural laboratory for investigating tectonic and geodynamic processes owing to its strong structural and lithological heterogeneity. A key challenge is constraining its thermal and compositional properties, given the limited direct observations and the uncertainties of existing models. We analyze two years of seismic ambient noise recorded at about 700 broadband seismic stations, and eight years of teleseismic earthquakes recorded at approximately 400 broadband stations. Using ambient noise tomography and receiver functions, we derive the Vs of the crust, the average Vp/Vs ratio, and a new Moho depth map for the Greater Alpine region. Moho depths range from 15 to 55 km, and Vp/Vs ratios vary from <1.65 in the Variscan domain to >1.8 in the Apennines, Dinarides and sedimentary basins. Thermodynamic modeling translates these seismic results into quantitative estimates of silica content and linear thermal gradients. We find that the Variscan crust is relatively cold (<20°C/km) and silica-rich (>62 wt% (Formula presented.)), in contrast with Alpine–Apenninic domains that show elevated thermal gradients (>25°C/km) and more mafic compositions (<60 wt% (Formula presented.)). However, elastic velocities predicted by mineral physics systematically exceed observed seismic velocities, reflecting effects of sediments, porosity, anelastic relaxation, and non-equilibrium processes not captured in thermodynamic equilibrium models. We apply empirical corrections to address these discrepancies, emphasizing caution when interpreting seismic velocities from mineral physics models. These quantitative constraints refine the thermal and chemical distinction between stable Paleozoic lithosphere and actively deforming orogens in the Greater Alpine crust.