Real-time monitoring of seismic velocity variations during the 2025 Aegean Sea seismic swarm

Monitoring seismic velocity variations in the shallow crust using noise-based techniques has emerged as an effective approach for tracking temporal changes in the local stress field. Despite their potential, real-time implementations of these methods have so far been mostly restricted to volcanic areas and are operational at only a limited number of volcano observatories due to the relative simplicity and speed of application in those contexts. In this work, we present the first real-time monitoring of seismic velocity variations applied to a tectonic seismic swarm in the Aegean Sea, which initiated on January 31, 2025. We introduce objective and rapid procedures to identify the key parameters necessary for the analysis and to compute the probability that new observations belong to the same statistical distribution as the background, allowing us to highlight potential anomalies as they occur. Finally, we interpret the processes driving the Aegean seismic swarm and suggest the presence of distinct recovery patterns in relative velocity variations following the abrupt drops typically observed during co-seismic effects.