Stress Drop and Seismic Efficiency Distributions Over the Adriatic Indenter (European Southeastern Alps)

Seismic source parameters, such as seismic moment, stress drop, and radiated energy, are key to understanding earthquake dynamics and rupture processes. In this study, we apply a non-parametric Generalized Inversion Technique (GIT) to characterize the source properties of 735 earthquakes (local magnitudes 1.65 ≤ ML ≤ 4.55) recorded between 2016 and 2024 in the area of the European Southeastern Alps characterized by the presence of the Adriatic indenter. The high-density seismic network coverage in the region allows for a robust, data-driven inversion of Fourier amplitude spectra to separate source, path, and site effects. Our results highlight significant spatial variations in seismic source parameters, revealing distinct mechanical properties of fault systems. We find a general increase in stress drop with depth and observe deviations from self-similar scaling, with apparent stress increasing with event size. The spatial distribution of the Savage-Wood efficiency suggests differences in dynamic fault strength, with high-efficiency events concentrated in the northeastern Italian Alps and Snežnik Mt. seismic area, respectively located in the Southeastern Alps Western sector and in the Dinarides seismotectonic domains, while lower-efficiency events are more common along the Tolmin-Idrija and Gemona-Tarcento fault systems and in the Schio-Vicenza-Lessini seismotectonic domain. These findings provide new constraints on the mechanical behavior of faults in the northeastern Adriatic indenter section and have implications for seismic hazard assessment and ground motion modeling. The study underscores the importance of accurate source parameter estimation in improving our understanding of regional seismotectonic and earthquake generation processes.