We investigate a seismic crisis that occurred in the western Gulf of Corinth (Greece) between December 2020 and February 2021. This area is the main focus of the Corinth Rift Laboratory (CRL) network, and has been closely monitored with local seismological and geodetic networks for 20 yr. The 2020–2021 seismic crisis evolved in three stages: It started with an $Mw$ 4.6 event near the northern shore of the Gulf, opposite of Aigion, then migrated eastward toward Trizonia Island after an $Mw$ 5.0 event, and eventually culminated with an $Mw$ 5.3 event, $∼3km$ northeast of the Psathopyrgos fault. Aftershocks gradually migrated westward, triggering another cluster near the junction with the Rion–Patras fault. Moment tensor inversion revealed mainly normal faulting; however, some strike‐slip mechanisms also exist, composing a complex tectonic regime in this region dominated by east–west normal faults. We employ seismic and geodetic observations to constrain the geometry and kinematics of the structures that hosted the major events. We discuss possible triggering mechanisms of the second and third stages of the sequence, including fluids migration and aseismic creep, and propose potential implications of the $Mw$ 5.3 mainshock for the seismic hazard of the region.

On 30 October 2020 11:51 UTC, a Mw=6.9 earthquake struck the offshore region north of Samos Island, Greece, in the Gulf of Ephesos/Kuşadasi, causing two fatalities and 19 minor injuries at Samos Island, as well as 115 casualties and over 1,030 injuries in Western Turkey. Preliminary results indicate that the mainshock occurred on a north-dipping normal fault, with a focal mechanism of 270º/50º/-81º. The selection of the fault plane is supported by evidence of uplift at western Samos and over 10 cm of subsidence at the northernmost edge of the central part of the island. The distribution of relocated hypocenters shows clustering of events, east of the mainshock’s epicenter, where most major aftershocks have occurred. To the west, a smaller group of aftershocks is observed, separated by a spatial gap in seismicity. The latter is likely related to the region of the fault plane where most of the co-seismic slip occurred, with Coulomb stress-transfer towards the western and eastern margins of the rupture triggering aftershock activity. The apparent complexity of the mainshock’s source time function, supported by preliminary results, could indicate the rupture of more than one structures. This could explain the relatively weak magnitude of the largest aftershock (Mw=5.0). The mainshock caused damage mainly to non-engineered constructions, i.e. old residential buildings, churches and monuments in Samos Island, and minor damage to the majority of the building stock of the island built according to the National Seismic Code. On the other hand, it caused severe damage at Izmir, especially to high-rise buildings. The mainshock also triggered a small tsunami that reached heights of over 1 m, mainly affecting the Turkish coast.

Seismicity in the Ionian Sea (W. Greece) is mainly generated along the Cephalonia–Lefkada Transform Fault Zone (CLTFZ) in the central Ionian, and on the northwestern termination of the Hellenic subduction margin in the south. Joint pre-, co- and post-seismic ground deformation and seismological analysis is performed at the broad Ionian area, aiming to homogeneously study the spatiotemporal evolution of the activity prior to and after the occurrence of strong (M > 6) earthquakes during the period of 2014–2018. The 2014 Cephalonia earthquakes (Mw6.1 and Mw5.9) were generated on a faulting system adjacent to CLTFZ, causing local ground deformation. The post-seismic sequence is coupled in space and time with the 2015 Lefkada earthquake (Mw6.4), which occurred on the Lefkada segment of the CLTFZ. Co-seismic displacement was recorded in the broader area. Seismicity was concentrated along the CLTFZ, while its temporal evolution lasted for several months. The 2018 Zakynthos earthquake (Mw6.7) caused regional deformation and alterations on the near-velocity field, with the seismicity rate remaining above background levels until the end of 2021. In the northern Ionian, convergence between the Apulian platform and the Hellenic foreland occurs, exhibiting low seismicity. Seismic hazard assessment revealed high PGA and PGV expected values in the central Ionian.