Crustal and Upper Mantle Structure Variation Along the Alpine Chain Using Teleseismic Full Waveform Inversion

The geodynamics of the Alps result from the collision and interaction of the African and Eurasian plates, starting with the closure of the Neo-Tethys Ocean in the Middle Jurassic. This led to subduction, mountain formation, and tectonic shifts, including slab rollback and back-arc basin formation. These processes shaped the complex geological structure of the Alps. Simultaneously investigating the crustal and upper mantle structures is crucial for seismologists to gain a deeper understanding of the geodynamic processes shaping the study region. To reach this aim, we employ Full Waveform Inversion (FWI) on teleseismic earthquakes recorded by AlpArray, SWATH-D, and CIFALPS2 networks to develop the first 3D high-resolution elastic multiparameter FWI model, including Vp , Vs, and density, extending from the surface to 700 km depth. The analysis of FWI models at the crustal scale along the Alps captures small-scale anomalies and velocity variations along fault zones, and reveals the subducted European lithosphere beneath the Adriatic. Our results show that Moho depth increases from the southwestern to the northwestern Alps, with a deeper Moho in the Central Alps compared to the Western Alps. In the Eastern Alps, two distinct Moho structures are identified: the Adriatic Moho, which remains flat at 40 km depth, and the European Moho, which extends southward to 60–65 km and subducts along the Penninic Front. At the upper mantle scale, FWI results show continuous subduction of the European slab beneath the Po Basin to 250 km in the Western Alps, with steeper subduction in the southwest and shallower dips in the north. In the Central Alps, the slab reaches 250 km without detaching, though low-velocity anomalies suggest potential slab tearing. In the Eastern Alps, FWI models indicate vertical slab extension beneath the Tauern window, with a low-velocity anomaly hinting at asthenospheric upwelling due to slab retreat.