Forward modelling of regional <i>S</i> -waveforms in the central-southern Apennines (Italy): evidences for lateral crustal velocity contrasts and shallow axial attenuation

SUMMARY We present a forward waveform modelling study to investigate the regional crustal structure of the central-southern Apennines, along a NNE-SSW profile. The profile cross-cuts the Apenninic chain axis and extends from the eastern Adriatic domain, characterized by a thick crust and thick seismogenic layer, to the western Tyrrhenian domain, dominated by tectonic thinning, distributed CO2 gas emissions at the surface and volcanic structures. This region hosted the largest earthquakes in recent history, making precise knowledge of the crustal structure crucial for a comprehensive understanding of seismogenesis and seismic hazard assessment. We analysed and modelled seismic data from two lower crustal strike-slip earthquakes in the eastern segment of the profile (2018 Mw 5.1 and 2023 Mw 4.6), recorded by the Italian National Seismic Network (IV). The two events, located along the target NNE-SSW linear profile, provide a unique opportunity to study the westward propagation and evolution of seismic phases. Using a 2-D numerical modelling approach, we modelled direct (Sg) and Moho-reflected (SmS) phases on transverse component seismograms, comparing the synthetic to the observed waveforms in terms of arrival times and waveform shapes. A faster Adriatic lower crust with an average shear-wave velocity of 3.85 km s−1 supports the hypothesis of distributed crustal mafic intrusions at the margin between the Apenninic chain and Adriatic foreland. We estimate a local Adriatic Moho depth of 38 km, in agreement with previous investigations. Furthermore, we identify a strong attenuation zone across the Apenninic chain axis, extending directly from the surface down to 10 km depth, significantly impacting both seismogenic processes and waveform propagation. This first, regional-scale waveform study highlights the significance of waveform analysis for constraining seismic velocities and interface velocity contrasts in the Southern Apennines mountain range.