Abstract A M5.9 earthquake occurred on 29 March 2024, offshore near the Strofades Islands, in the western Hellenic Subduction System. Here we present high‐precision earthquake locations and focal mechanisms that suggest the rupture of a NNE‐SSW striking, left‐lateral strike‐slip fault. Both the aftershock depth distribution, and roughly orthogonal focal mechanism P‐axes relative to the upper‐plate shortening direction suggest that the sequence occurred within the slab. The stress pattern inferred from the M5.9 sequence is consistent with arc‐parallel shortening in the lower plate, similar to other intraslab, intermediate‐depth earthquakes in the Aegean. The lack of triggered upper‐plate seismicity, together with the contrasting stress orientations between overriding and subducting plates, suggests a decoupled upper‐lower plate stress field that can be explained by a weak megathrust interface.
Bocchini et al. (2026) studied this question.