Spatiotemporal variations in b-value suggest an evolving mechanical state of the crust in the southeastern Alps

Understanding whether and how the mechanical state of the crust evolves is a central challenge in intraplate regions. We investigate the southeastern Alps region by analyzing the frequency-magnitude distribution of ten years of seismicity (14776 earthquakes) with magnitudes in the range 0 ≤ M L ≤ 4.5. We analyze the spatio-temporal evolution of the b-value, a proxy for crustal stress and strength. Using the b-positive method and Singular Spectrum Analysis, we observe a persistent b-value decrease since 2020 in the Friuli region, which we interpret as evidence of the evolving stress state of the system towards crustal weakening. . By linking b-value trends to the Hoek–Brown failure criterion, we interpret the crustal stress evolution in terms of rock mass disturbance. Our results suggest that, even under low loading rates, distinct crustal volumes may evolve differently over time, with some potentially approaching critical conditions while others remain stable. Whitin this framework, b-value variations may provide a physically grounded approach to monitor fault weakening and assess seismic hazard in slowly deforming continental regions.