The 1956 Amorgos earthquake occurred at 03:11 UTC on July 9. It had a magnitude of 7.7 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

and a maximum perceived intensity of IX on the Mercalli intensity scale. The

epicentre The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

was to the south of the island of

Amorgos Amorgos ( el, Αμοργός, ; ) is the easternmost island of the Cyclades island group and the nearest island to the neighboring Dodecanese island group in Greece. Along with 16 neighboring islets, the largest of which (by land area) is Nik ...

, the easternmost island of the

Cyclades The Cyclades (; el, Κυκλάδες, ) are an island group in the Aegean Sea, southeast of mainland Greece and a former administrative prefecture of Greece. They are one of the island groups which constitute the Aegean archipelago. The name ...

in the

Aegean Sea The Aegean Sea ; tr, Ege Denizi (Greek: Αιγαίο Πέλαγος: "Egéo Pélagos", Turkish: "Ege Denizi" or "Adalar Denizi") is an elongated embayment of the Mediterranean Sea between Europe and Asia. It is located between the Balkans ...

. There was significant damage on Amorgos and the neighbouring island of Santorini. It was the largest earthquake in Greece in the 20th century. It was followed 13 minutes later by a magnitude 7.2 earthquake near Santorini. It triggered a major

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 exp ...

with a maximum run-up of 30 m. The combined effects of the earthquake shaking and the tsunami caused the deaths of 53 people with a further 100 injured.

Tectonic setting

The Cyclades island group lies within a zone of extensional tectonics in the

Aegean Sea Plate The Aegean Sea Plate (also called the Hellenic Plate or Aegean Plate) is a small tectonic plate located in the eastern Mediterranean Sea under southern Greece and western Turkey. Its southern edge is the Hellenic subduction zone south of Crete, ...

, between the

South Aegean Volcanic Arc The South Aegean Volcanic Arc is a volcanic arc (chain of volcanoes) in the South Aegean Sea formed by plate tectonics. The prior cause was the subduction of the African plate beneath the Eurasian plate, raising the Aegean arc across what is n ...

to the south and the continuation 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 ...

to the north. The extension is a result of the bulging out of the

Hellenic arc The Hellenic arc or Aegean arc is an arcuate mountain chain of the southern Aegean Sea located on the southern margin of the Aegean Sea Plate. Geologically it results from the subduction of the African Plate under it along the Hellenic subductio ...

due to

flat-slab subduction Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the seismogenic layer and a resumption of normal ...

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 Plate ...

Earthquake

The earthquake's focal mechanism is consistent with normal faulting, trending SW-NE. From the distribution of aftershocks, it is possible to discriminate between the two nodal planes implied by the focal mechanism, indicating that the fault plane dips to the southeast at about 25°. The rupture area is estimated to be about 110 km along strike and 26 km in depth, extending into the

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from appr ...

Tsunami

The tsunami affected a large part of the Aegean Sea. The variable distribution of the observed run-ups, combined with inconsistent timing of the wave arrivals at different locations, suggest that earthquake-triggered underwater landslides were the main cause of the observed tsunami.

Damage

Damage was severe, particularly on Santorini. The earthquake demolished 529 houses and left many others damaged. Fifty-three people were killed as a result of the earthquake, with another three killed by the associated tsunami.

References

External links