A new-generation multiparameter elastic model of the crust and upper mantle of the Greater Alpine area and the Apennines using teleseismic Full Waveform Inversion: data, method and models

Summary The collision between the European plate and the Adria microplate during the Cenozoic led to the formation and uplift of key mountain belts, including the Alps, Apennines, and Dinarides. This convergence also resulted in a highly complex assemblage of tectonic units, each characterized by distinct geological and geophysical properties within the accreted crustal domains. A comprehensive understanding of the geodynamic evolution of this region requires integrated imaging of both the crust and upper mantle. To achieve this goal, we apply Teleseismic Full Waveform Inversion (TFWI) to P-wave seismic data recorded by permanent European broadband stations, supplemented by the dense temporary deployments of the AlpArray initiative, SWATH-D, and CIFALPS-2 projects. Leveraging this unprecedented seismological coverage, our study aims to design a suitable TFWI workflow to develop a multiparameter model defined by P- and S-wave velocities and density of the Alpine orogen down to 500-km depth. The critical importance of high-quality data for ensuring the reliability of TFWI results first prompts us to develop a semi-automated workflow for data selection and quality control, from which we select 84 teleseismic events for inversion. The seismograms were filtered within the 5-to-25-s period band, and a 30-s time window from the first arrival was used for inversion. Other critical aspects are the assessment of the resolution power of TFWI provided by the field acquisition geometry, as well as potential sources of artefacts. We review the key theoretical factors controlling resolution and imaging artefacts, and further illustrate these issues with numerical experiments designed with the field acquisition geometry to provide the necessary guidelines for sound geological interpretation of the TFWI models. The reconstructed TFWI models effectively capture key crustal features, including low-velocity sedimentary basins, high-velocity anomalies like the Ivrea Body, deep mountain roots beneath the Alpine and Apennine chains, and the signature of the continental subduction. The TFWI models also reveal small-scale anomalies previously identified by local tomography studies. Then, we extend the analysis at upper-mantle depths by comparing the footprint of the subducting slabs in the P and S velocity TFWI models with previous ones obtained by surface wave tomography and teleseismic body-wave traveltime tomography. These comparative analyses highlight the incomparable power of TFWI to resolve multiparameter models of the Earth’s interior from the surface down to the upper mantle. From this first critical analysis of the TFWI results, a comprehensive geological survey of the reconstructed structures will be presented in a companion paper.