Seismic attenuation tomography: new insights into fluid dynamics in the Northern Calabrian region (Italy)

In recent years, 3D seismic velocity models of the southern Apennines–Calabrian Arc border region have improved the definition of crustal structures at the northern edge of the Ionian subduction zone (see, e.g., Totaro et al., JoG, 2014). In this sector, a seismic gap, supported by the absence of major earthquakes in historical catalogues (https://emidius.mi.ingv.it/CPTI15-DBMI15/), was previously hypothesized by paleoseismological evidence (Cinti et al., SRL, 2015). In the upper crust, a low-velocity anomaly of both P- and S-waves was detected between the Calabrian and southern Apennines domains, characterized by higher velocities (Totaro et al., JoG, 2014). The low velocity- anomaly may be related to fluid rising along several SW-NE-oriented faults crossing Italy from the Tyrrhenian to the Ionian coasts (Minissale et al., Earth-Sci Rev, 2019). Seismic-wave attenuation is highly sensitive to fluid storage within geological structures. When scattering attenuation and absorption, the two primary attenuation mechanisms, are separated and mapped in space and time, they can constrain fluid migrations through tectonic structures (Reiss et al., GRL, 2022; Gabrielli et al., GRL  2023). For this study, we collected 3690 waveforms from 112 earthquakes (M≥3.0, hypocentral depth≤20km) that occurred in the area between September 2004 and October 2024. We used the MuRAT3.0 suite (De Siena et al., JVGR, 2014; Napolitano et al., SR, 2024) to map proxies of scattering attenuation and absorption (peak-delay times and late-time coda attenuation) in space. The results mark the presence of high-attenuation anomalies, potentially associated with sources of geothermal energy comprised in the low-velocity anomaly described by Totaro et al. (JoG, 2014). Seismic attenuation models provide complementary information to velocity tomography on the area's complex 3D structure. The results are jointly interpreted with those coming from geophysical and geological investigations (e.g., Totaro et al., BSSA, 2015; Brozzetti et al., JStructGeol, 2017; De Ritis et al., Tectonics, 2019), fully characterizing the crustal structure of the study area.