Imaging the Crust and Upper Mantle in the Southern Central Mediterranean with Joint Ambient Noise and Earthquake Surface Wave Tomography

Surface wave tomography has proven to be a very powerful tool for discerning complex crustal and upper mantle structures since it bypasses the necessity for local seismic sources and crustal corrections. This study presents a refined 3D model encompassing the crust and uppermost mantle in Southern Italy and the broader southern Central Mediterranean region, achieved through the joint inversion of ambient noise and earthquake data. Our dataset comprises 11,900 phase velocity dispersion curves, spanning 2 to 100 seconds, derived from ambient noise cross-correlations. Additionally, we incorporate 81,000 phase velocity curves covering 8 to 250 seconds, obtained through inter-station cross-correlations and averaging over single earthquake measurements. A thorough quality control process ensures the reliability of both datasets, which are seamlessly integrated using a correction factor derived from inter-station paths with overlapping measurements. Azimuthally anisotropic Rayleigh wave phase velocity maps are computed using a regularized least-square approach. These maps, showcasing directional variations in wave velocities, serve as the foundation for our 3D model. The inversion process employs a stochastic particle swarm optimization algorithm, enhancing the robustness and accuracy of the final model. The resulting 3D velocity model brings to light significant subsurface features, notably the subducted Calabrian and Hellenic slabs, alongside the identification of a delaminated high-velocity anomaly beneath Sicily. Additionally, the model captures details such as the transition from the Ionian Lithosphere to the Calabrian Slab, deformation of the Adriatic Lithosphere, and the dynamic flow of the asthenosphere beneath the Tyrrhenian Sea.