We present the results of a dense seismological experiment in the western part of the Gulf of Corinth (Psathopyrgos-Aigion area), one of the most active rifts in the Aegean region for which we have precise tectonic information. The network included 51 digital stations that operated during July and August 1991, covering a surface of 40 x 40 km2.Among the 5000 recorded events with M L ranging between 1.0 and 3.0, we precisely located 774 events. We obtained 148 well-constrained focal mechanisms using P-wave first motions. Of these, 60 also have mechanisms obtained by combining the P-wave first motions with the S-wave polarization directions. The observed seismicity is mainly located between 6 and 11 km depth. Most of the fault-plane solutions correspond to E-W-striking normal faulting, in agreement with the geological evidence. Most of the well-determined mechanisms indicate a nodal plane dipping 10-25" due north and a steep south-dipping plane. A similar asymmetry is also seen in the seismicity distribution and in the overall geological structure of the Corinth Rift. We discuss this evidence and the inference of a deep detachment zone, a structure where the major faults seen at the surface appear to root. A large part of the microseismic activity appears to cluster in regions near the junctions of the main faults with the proposed detachment zone. This feature of the microseismicity is interpreted in terms of stress transfer and stress concentration in regions of probable nucleation of future large earthquakes.

During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al. (1985) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 (Rigo et al. 1996), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes (Hatzfeld et al. 1996; Bernard et al. 1997) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic–aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).

During a 7‐week microearthquake experiment conducted in Epirus, Akarnania, and the Ionian islands of western Greece, we located approximately 600 earthquakes with magnitudes between 2 and 4.2. No event was deeper than 40 km. The seismicity cannot be clearly associated with any single fault except the Lixourion right‐lateral fault located west of the Ionian islands. Focal mechanisms of about 100 earthquakes show, for a narrow band of earthquakes located along the coast, ENE–WSW shortening consistent with the surface tectonics. Farther east, focal mechanisms show NNW–SSE extension beneath the foothills of the Pindus mountains, which is unrelated to surface faulting but is consistent with the presently subsiding basins. This strain pattern is seen far north and south of the Lixourion fault and is similar to the one observed in the Peloponnese. It suggests that a large‐scale mechanism is responsible for the recent geodynamics of both the northwestern and southwestern Aegean

Abstract. Seismic anisotropy, deduced from SKS splitting measured at 25 stations installed in the Aegean, does not show a homogeneous pattern. It is not restricted to the North Anatolian Fault but is distributed over a region several hundreds kilometers wide. Little anisotropy is observed in continental Greece or along the Hellenic arc; however, significant anisotropy is observed in the north Aegean Sea. Large values of delay times suggest that anisotropy is due to a long path within the upper mantle and to strong intrinsic anisotropy. Our results, both in fast polarization directions and in values of delay time, do not support the idea that anisotropy is associated with inherited tectonic fabric nor are they consistent with the present-day Aegean motion relative to an absolute frame. In contrast, the direction of fast polarization and the magnitude of delay times correlate well with the present-day strain rate observed at the surface deduced from both geodetic measurements and seismicity. This anisotropy is not horizontally restricted to major surface faults but is spread over a wide region.

Abstract. We report here the results of a tomegraphic lithospheric study in the area of the Corinth and Evvia rifts (Greece), designed to constrain the mechanism of continental extension. Sixty seismological stations were deployed in the area for a period of 6 months, and 177 teleseismic events were recorded by more than five stations and gave more than

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Here we present a joint analysis of the geodetic, seismological and geological data of the March 2021 Northern Thessaly seismic sequence, that were gathered and processed as of April 30, 2021. First, we relocated seismicity data from regional and local networks and inferred the dip-direction (NE) and dip-angle (38°) of the March 3, 2021 rupture plane. Furthermore, we used ascending and descending SAR images acquired by the Sentinel-1 satellites to map the co-seismic displacement field. Our results indicate that the March 3, 2021 Mw=6.3 rupture occurred on a NE-dipping, 39° normal fault located between the villages Zarko (Trikala) and Damasi (Larissa). The event of March 4, 2021 occurred northwest of Damasi, along a fault oriented WNW-ESE and produced less deformation than the event of the previous day. The third event occurred on March 12, 2021 along a south-dipping normal fault. We computed 22 focal mechanisms of aftershocks with M≥4.0 using P-wave first motion polarities. Nearly all focal mechanisms exhibit normal kinematics or have a dominant normal dip-slip component. The use of InSAR was crucial to differentiate the ground deformation between the ruptures. The majority of deformation occurs in the vertical component, with a maximum of 0.39 m of subsidence over the Mw=6.3 rupture plane, south and west of Damasi. A total amount of 0.3 m horizontal displacement (E-W) was measured. We also used GNSS data (at 30-s sampling interval) from twelve permanent stations near the epicentres to obtain 3D seismic offsets of station positions. Only the first event produces significant displacement at the GNSS stations (as predicted by the fault models, themselves very well constrained by InSAR). We calculated several post-seismic interferograms, yet we have observed that there is almost no post-seismic deformation, except in the footwall area (Zarkos mountain). This post-seismic deformation is below the 7 mm level (quarter of a fringe) in the near field and below the 1 mm level at the GNSS sites. The cascading activation of the three events in a SE to NW direction points to a pattern of domino-style earthquakes, along neighbouring fault segments. The kinematics of the ruptures point to a counter-clockwise change in the extension direction of the upper crust (from NE-SW near Damasi to N-S towards northwest, near Verdikoussa).

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