In early 1981 the eastern

Gulf of Corinth The Gulf of Corinth or the Corinthian Gulf ( el, Κορινθιακός Kόλπος, ''Korinthiakόs Kόlpos'', ) is a deep inlet of the Ionian Sea, separating the Peloponnese from western mainland Greece. It is bounded in the east by the Isth ...

, Greece was struck by three earthquakes with a magnitude greater than 6 over a period of 11 days. The earthquake sequence caused widespread damage in the

Corinth Corinth ( ; el, Κόρινθος, Kórinthos, ) is the successor to an ancient city, and is a former municipality in Corinthia, Peloponnese, which is located in south-central Greece. Since the 2011 local government reform, it has been part o ...

–

Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates ...

area, destroying nearly 8,000 houses and causing 20–22 deaths.

Tectonic setting

The Gulf of Corinth is an area of active

extensional tectonics Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere. Deformation styles The types of structure and the geometries formed depend on ...

. The underlying cause of this extension has been attributed to rollback of the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...

as it subducts northwards beneath the Aegean Plate. Other possible mechanisms include

gravitational collapse Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formatio ...

of crust overthickened during the

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

to early

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

or the effects of the continuing propagation of the

North Anatolian Fault The North Anatolian Fault (NAF) ( tr, Kuzey Anadolu Fay Hattı) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian Plate and the Anatolian Plate. The fault extends westward fro ...

towards the southwest. The

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

that formed the Gulf of Corinth is bounded by large

normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

s that vary in their polarity ( dip direction) along its length. The eastern end of the rift, which forms the

Alkyonides Gulf The Alkyonides Gulf ( el, Κόλπος Αλκυονίδων - ''Kolpos Alkyonidon'') is a bay that connects with the Gulf of Corinth to the west. The bay is approximately 20 to 25 km long and 20 km wide. It stretches from Aigosthena to ...

, is dominated by north-dipping faults, including the Perachora, Straya, Skinos, Pisia, West Alkyonides and East Alkyonides faults. Immediately to the east, the large south-dipping Kaparelli Fault forms the northern boundary to the onshore continuation of the rift zone.

Earthquake sequence

The first earthquake in the sequence occurred at 20:53 UTC on 24 February. It had a magnitude of 6.7 and a maximum felt intensity of IX (''violent'') on the

Modified Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

(MMI). The epicentre was at the western end of the Alkyonides Gulf and involved rupture of the Pisia Fault and possibly the Skinos Fault. The assignment of the observed surface ruptures to the first two earthquakes in the sequence remains uncertain as they occurred over the same night. The maximum measured offset on the Pisia Fault was 150 cm, while that on the Skinos Fault was 100 cm. The second earthquake occurred less than 6 hours later at 02:35 UTC on 25 February, with a magnitude of 6.4 , also with a maximum felt intensity of IX (MMI). The epicentre was in the central part of the Alkyonides Gulf and involved the rupture of the Skinos Fault and possibly the Pisia Fault. The final earthquake in the sequence occurred over ten days later at 21:58 UTC on 4 March, also with a magnitude of 6.4 and a maximum felt intensity of IX (MMI). The epicentre was just to the east of the Alkyonides Gulf and involved the rupture of the Kaparelli Fault, with a maximum observed displacement of 100 cm. Analysis of stress changes associated with the February 24 earthquake show increases on the fault segments that ruptured during the other two events.

Damage

The effects of the first two earthquakes are treated together due to their close spacing, with a single

isoseismal map In seismology, an isoseismal map is used to show lines of equally felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters, particularly where no instrumental records exist, such as ...

being produced. The area of violent shaking (level IX MMI) was along the southern coast of the Akyonides Gulf, with a much larger area experiencing severe shaking (level VIII MMI) extending from

Xylokastro Xylokastro ( el, Ξυλόκαστρο) is a seaside town or village and a former municipality in Corinthia in the Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Xylokastro-Evrostina, of which it is a unit ...

in the west to beyond

Megara Megara (; el, Μέγαρα, ) is a historic town and a municipality in West Attica, Greece. It lies in the northern section of the Isthmus of Corinth opposite the island of Salamis Island, Salamis, which belonged to Megara in archaic times, befo ...

in the east, including the city of Corinth. The area of very strong shaking (level VII MMI) included Athens, with some parts of the city experiencing shaking of VIII to IX depending on ground conditions. The final earthquake also produced an area that experienced shaking of IX MMI, including the villages of Kalamaki and

Plataies Plataies ( el, Πλαταιές), anciently Kokhla, is a village and a former municipality in Boeotia, Greece. Since the 2011 local government reform it is part of the municipality Thebes, of which it is a municipal unit. The municipal unit has an ...

. The area of level VIII shaking included the city of Thebes. In total the earthquake sequence caused the destruction of 7,701 buildings (of which 1,175 were in Athens) with a further 20,954 being seriously affected (7,824 in Athens). Three administrative areas were affected,

Attica Attica ( el, Αττική, Ancient Greek ''Attikḗ'' or , or ), or the Attic Peninsula, is a historical region that encompasses the city of Athens, the capital of Greece and its countryside. It is a peninsula projecting into the Aegean Se ...

Beotia Boeotia ( ), sometimes Latinized as Boiotia or Beotia ( el, Βοιωτία; modern: ; ancient: ), formerly known as Cadmeis, is one of the regional units of Greece. It is part of the region of Central Greece. Its capital is Livadeia, and its lar ...

and

Corinthia Corinthia ( el, Κορινθία ''Korinthía'') is one of the regional units of Greece. It is part of the region of Peloponnese. It is situated around the city of Corinth, in the north-eastern part of the Peloponnese peninsula. Geography Cori ...

. The number of fatalities was in the range 20–22, with between a further 400 and 500 people injured. Both onshore and offshore areas were affected by landslides with one large underwater slump possibly the cause of the observed local

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

Liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of the ...

and ground fissures were reported from several areas.

References

{{Earthquakes in Greece 1981 earthquakes Earthquakes in Greece Gulf of Corinth 1981 in Greece Modern history of Thessaly History of Central Greece Tsunamis in Greece 1980s in Athens History of Corinth 1981 disasters in Greece

Tectonic setting

Earthquake sequence

Damage

See also

References