Imaging the Western Edge of the Aegean Shear Zone: The South Evia 2022-2023 Seismic Sequence

This report presents the 2022-2023 South Evia island seismic sequence, in the western Aegean sea. An automated workflow, undergoing testing for efficient observatory monitoring in the wake of dense aftershock sequences, was employed to enhance the seismic catalog. It includes a deep-learning phase picker, absolute and relative hypocenter relocation, and moment tensor automatic calculations. The relocated catalog reveals a concentration of earthquake epicenters in a narrow NW-SE zone, with sinistral strike-slip fault movement. The findings of the study indicate the occurrence of an asymmetric rupture within conjugate fault structures in the western Aegean region. These fault structures, although not necessarily both active, play a significant role in marking the transition from dextral (SW-NE) to sinistral (NW-SE) strike-slip ruptures, connecting the Aegean shear zone with normal faulting in mainland Greece. The South Evia 2022-2023 seismic sequence has revealed the activation of this NW-SE strike-slip structure, contrary to previous assumptions of low seismicity in the region. The study highlights the importance of reassessing seismic hazard maps and considering the potential activation of similar zones further south in the future. It also emphasizes the need for the expansion and the densification of seismic networks within the Aegean.