For seven weeks, a temporary network of 68 seismological stations was operated in Central Greece, in the region of Thessaly and Evia, located at the western termination of the North Anatolian Fault system. We recorded 510 earthquakes and computed 80 focal mechanisms. Seismic activity is associated with the NE–SW dextral North Aegean Fault, or with very young E–W‐striking normal faults that are located around the Gulf of Volos and the Gulf of Lamia. The important NW–SE‐striking faults bounding the Pilion, or the basins of Larissa and Karditsa, are not seismically active, suggesting that it is easier to break continental crust, creating new faults perpendicular to the principal stresses, than to reactivate faults that strike obliquely to the principal stress axes

The Galaxidi earthquake that occurred in the Gulf of Corinth on 18 November 1992 was not followed by a noticeable aftershock sequence, a fact that was also observed for the 1965 Eratini event in the same area. The temporary network of 35 stations that we installed 5 days after the mainshock did not help to identify a cluster of activity related to the mainshock. In a section across the epicentral zone, the focal mechanism of the mainshock and the distribution of a few aftershocks define a plane dipping north, consistent with the nearby Helike fault. We propose that the Galaxidi earthquake was related to an asperity located between the Helike and Xilokastro faults.

<p>Intense and continuous seismicity in the last two years (October 2020 – September 2022) that took place in a rather small area near the city of Thiva is investigated here. The activity started with an M4.6 earthquake (2 of December 2020) followed by its own aftershock sequence. The activity migrated slightly to the west, with a persistent swarm in July 2021-September 2022 (largest magnitudes M4.3, on 11 July 2021, M4.0 on 2 September 2021 and M4.3, on 10 April 2022). Aiming to constrain the geometry and kinematics of the activated fault segments along with the spatiotemporal evolution of the seismic activity, processing of the recording of the regional seismological network was accomplished that includes the determination of the focal coordinates using the HYPODD software. The above information will provide a better understanding of the seismic sequence and seismic hazard in the region so that there is better prevention and preparation against a future strong earthquake. Aiming to study in detail the properties of this seismicity manifestation, the recordings of the Hellenic Unified Seismological Network (HUSN) are used to accurately determine the seismic parameters of earthquakes with magnitudes M≥1.5. Phases (P, S phases) are gathered from the Geophysical Department of the Aristotle University of Thessaloniki and the Geodynamics Institute of National Observatory of Athens from October 2020 to September 20212. Then, the bulletins were merged, and an initial earthquake catalogue was compiled containing ~6000 events. Earthquake relocation was initially performed using HYPOINVERSE software and all the available manually picked P and S phases. An appropriate local velocity model and the V<sub>P</sub>/V<sub>S</sub> ratio were necessary to defined. The Wadati method was applied to the dataset and the resulting V<sub>P</sub>/V<sub>S</sub> ratio equals to 1.76. The one-dimensional velocity model used for this study is calculating by the VELEST software. Time corrections relative to the crustal model were calculated considering the mean residual for each station. For the relocation of the events the calculated time delays were taken into account. To improve the obtained locations, we relocate the earthquakes using the double difference inversion algorithm, hypoDD with differential times derived from phase-picked data.</p> <p>Τo define the stress regime in the area, the moment tensors of earthquakes with ML ≥ 3.5 were estimated using the ISOLA and FPFIT software. The fault plane solutions from the largest earthquakes of the seismic sequence have been used for Coulomb stress changes calculation. The stress field is calculated according to the focal mechanism of the next large event, whose triggering is inspected, so it can be checked if foreshocks contributed to the occurrence of the largest earthquakes of the sequence and the possible sites for future strong earthquakes can be assessed as well.</p>