The Northern Thessaly Basin in central Greece ranks amongst the most well pronounced extensional (graben) basins in the back-arc Aegean Sea region, with well–mapped faults having an ∼E–W orientation, compatible with the ongoing predominant ∼N–S extension. The southern margin of the basin is bounded by major faults associated with strong (M6 to M7) earthquakes, whereas along its northern margin, strong events are more scarce, in the documented catalogues. Along this northern margin, a weak, albeit persisting foreshock activity, culminated within three days, to an M_w6.3 earthquake on 3 March 2021 associated with a 15 km–long NE dipping fault segment. It was followed the next day, by the second M_w6.0 main shock associated with a 13 km–long NE dipping fault segment and nine days later by an M_w5.5 earthquake associated with an 8 km–long SW dipping fault segment, with its aligned epicenters, showcasing the cascade type activation of adjacent fault segments. The sequence, evolved to be very productive, with aftershocks extending ∼50 km along a ∼NW–SE trending narrow seismic zone. All events indicate pure normal faulting, with an NNE–SSW oriented extensional axis, oblique to our previous consensus of the prevalence of ∼N–S extension. This observation documents that inherited fault fabric can be reactivated within the modern tectonic stress field. We use high–quality seismological data, alongside InSAR (Interferometric Synthetic Aperture Radar) methodology and GNSS (Global Navigation Satellite System) data, to study the temporal and spatial evolution of the sequence, and to provide inferred kinematic models that describe the complexity of the seismic process, in terms of heterogeneous slip distribution, activated fault planes, fault geometry, and displacement field. Cross–sections show that the activity defines the crustal seismogenic layer at depths between 5 and 10 km, associated with low–angle fault segments dipping to the NE. Other faults, both antithetic and secondary ones, appear active and accommodated aftershocks clusters. Using our preferred finite fault source model, we calculated the changes of Coulomb failure stress on the neighboring faults.

An effort is exerted to investigate the recurrence pattern of large earthquakes (M_w ≥ 6.0) in the Kefalonia Transform Fault Zone (KTFZ), Greece, by considering the incorporation of the 74-year (1948–2022) evolving stress field. Four earthquake occurrence models—the Poisson, Poisson with the incorporation of the static stress changes (Poisson + ΔCFF), Brownian passage time (BPT) and Brownian passage time with the incorporation of the static stress changes (BPT + ΔCFF)—have been applied to estimate the occurrence probabilities of nearly characteristic earthquakes for the seven fault segments of the study area. The mean recurrence time, T_r, is estimated using the physics-based seismic moment rate conservation method. The results show large variability depending upon fault parameters. Incorporating the state of stress into T_r results in both advanced and delayed recurrence patterns. The occurrence probability estimates for the next 10, 20 and 30 years indicate that the fault segment most likely to be ruptured is the Paliki North fault segment in all models. Overall, the occurrence probabilities, combined with the state of stress along the fault segments, emphasize the high seismic moment rate of the study area. The application of time-dependent models (BPT, BPT + ΔCFF) resulted in significant increases or decreases in the associated seismic hazard.