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The Northern Thessaly Basin in central Greece ranks amongst the most well pronounced extensional (graben) basins in the backarc 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 (M 6 to M 7) 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 3 d, to an M w 6.3 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 w 6.0 main shock associated with a 13-km-long NE dipping fault segment and 9 d later by an M w 5.5 earthquake associated with an 8-km-long SW dipping fault segment, with its aligned epicentres, 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 Interferometric Synthetic Aperture Radar (InSAR) methodology and Global Navigation Satellite System (GNSS) 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 neighbouring faults. [ABSTRACT FROM AUTHOR]

On October 30, 2020, a strong earthquake (Mw6.6-7.0) occurred offshore, just north of Samos Island, causing life losses, injuries and damages, especially on the Turkish side. The broader area is characterized by a complex geodynamic setting with both rich seismic history and numerous active faults of different direction and kinematics. The first aim of this study is to define the seismic source of the mainshock, based on seismological and geodetic data (GPS measurements and originally processed GNSS records), as well as our field observations on Samos Island few days after the mainshock. The integration of this information leads to a N-dipping normal fault (Kaystrios fault) that controls the central-northern coast of Samos Island. We modelled the seismic source and calculated the theoretical dislocation (using the Okada formulae) on the surrounding GPS/GNSS stations, comparing it with the measured values. The results are very encouraging, especially on the station installed on Samos Island, giving confidence to our source model. We then used our seismic source to study the spatiotemporal evolution of the aftershock sequence by exploiting published seismological data (focal mechanisms and two seismic catalogues, one of which with relocated hypocentres) and our calculated Coulomb static stress changes caused by the mainshock. This comparison suggests that more faults than the Kaystrios fault were involved in the aftershock sequence. In order to investigate possible triggering and/or delay scenarios of the mainshock on nearby faults, the Coulomb stress changes are also studied showing various results according to each receiver fault. [ABSTRACT FROM AUTHOR]

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Thessaly lies on the Aegean (micro-)plate, undergoing internal crustal deformation due to the plate relative motion against the adjacent Anatolian and Nubian plates. As a result, the whole Thessalian Basin was supposed to be under an extensional tectonic regime of N-S direction. However, the recent earthquake sequence of March 2021 which occurred close to the northwestern margin of the basin revealed NE-SW direction of extension. Based on 7-year GPS measurements recorded by stations installed within and around the basin we assessed four deformational parameters for Thessaly aiming at the understanding of the deformation processes that control the region. These parameters are i) the Maximum Horizontal Extension (MAHE), ii) the Total Velocity (TV), iii) the Maximum Shear Strain (MSS), and iv) the Area Strain (AS). The results show that during the monitoring period, Thessaly moved toward the S-SW with a simultaneous clockwise rotation and underwent dispersed deformation mostly associated with dilatation. Focusing on the epicentral area of the 2021 sequence, strain during the 7-year period was rather low in all three strain parameters, implying a mature stage of elastic strain accumulation before the fault rupture. [ABSTRACT FROM AUTHOR]

The broader Corinth Gulf region is characterized by a notable active tectonic regime, associated with multiple active fault zones. The continuous N-S extensional tectonics of the area is responsible for the roughly E-W trending active normal fault zones, while individual fault segments are associated with seismic events. Satellite geodesy is a qualitative and quantitative means of estimating the tectonically active setting, based on the recorded motions. The study area is monitored by 14 permanent GPS/GNSS stations, collecting primary geodetic data for a 7-year time period (2008-2014). A 30-sec observation rate was performed, resulting in the extraction of the GPS/GNSS velocity values. The primary geodetic data were processed by applying the triangulation methodology, based on the combination of three different GPS/GNSS stations data, which were considered as the triangle vertices. Triangulation methodology led to the construction of 26 different triangles, while for each of them a series of parameters was determined. In particular, the extracted parameters are: a) Maximum Horizontal Extension, b) Total Velocity, c) Maximum Shear Strain and d) Area Strain. The extracted results are expected to approach, qualitatively and quantitatively, the interpretation of the tectonic regime, as well as to determine new, seismic-related, tectonic features. [ABSTRACT FROM AUTHOR]