“Seismicity in the Gulf of Corinth and the Recent Seismic Crisis in Santorini”

The Gulf of Corinth is a “natural laboratory” for seismology and geosciences, as it is characterized by high tectonic activity, with the bulk of earthquakes occurring close to its western border. Active normal faults, oriented in an approximately E-W direction, dominate the Gulf of Corinth. Regarding the morphology of the gulf, it is an E-W trending asymmetric graben, with the major active faults outcropping at the southern coast and dipping north, resulting in a long record of rifting in the center of the gulf. GNSS measurements have revealed a high extension rate in a NNE-SSW direction, which increases from the east to the west. Since the historical era, strong earthquakes have occurred in the western part of the Gulf, as the 373 BC Helike earthquake that was accompanied by a tsunami wave. Large events have also occurred during the instrumental period, causing severe damage to urban areas in the broader region, e.g. Eratini, M=6.3, 1965; Antikyra, M=6.2, 1970; Aigion, Ms=6.2, 1995. Regarding the eastern part of the gulf, large earthquakes are also present, however rarer. In 1981, on February 24, 25 and March 4, a seismic sequence with three major earthquakes of Ms = 6.7, 6.4 and 6.4 occurred in the Alkyonides Gulf, causing significant damage to Athens. It is worth noting that the seismicity in the WGoC is mostly expressed through the occurrence of seismic swarms, as the one close to Helike in 2013. A seismic crisis occurred at the western part of the Gulf during 2020–2021, which evolved in three stages. It started with an Mw 4.6 event near the northern shore of the Gulf, then migrated eastward toward Trizonia Island after an Mw 5.0 event, and eventually culminated with an Mw 5.3 event, ∼3 km northeast of the Psathopyrgos fault. The intense seismicity in the Gulf of Corinth has resulted in the installation of a permanent network in the area, with stations belonging to the Hellenic Unified Seismological Network (HUSN). Furthermore, the international initiative of the Corinth Rift Laboratory (CRL) has greatly increased the density of local station coverage and has led to the prompt provision of seismological data to the scientific community. This permits the identification of seismogenic faults through seismological observations, in combination with GNSS and tectonics.