The Hellenic arc or Aegean arc is an arcuate tectonic feature of the eastern Mediterranean Sea related to the subduction of the African Plate beneath the Aegean Sea Plate. It consists of an oceanic trench, the Hellenic Trench, on its outer side; two arcs—a non-volcanic outer arc and an inner volcanic arc, the South Aegean Volcanic Arc; and a marginal sea on its inner side.
The Hellenic ocean trench is not the surface expression of the subduction zone but is better understood as a sediment-starved part of a fore-arc basin. The Mediterranean Ridge, which forms the southern boundary of the trench is the accretionary complex that marks the subduction zone. The northern boundary of the Mediterranean Ridge is formed by a major backthrust. The Hellenic trench is most clearly developed in the western part of the arc, splitting into the Pliny and Strabo trenches to the east.
The non-volcanic arc consists of a raised topographic feature running the full length of the Hellenic arc, occasionally above sea level, forming the Ionian islands, Crete and Rhodes. This zone represents an uplifted part of the fore-arc.
The inner or volcanic arc extends for 450 km from Methana on the eastern coast of the Peloponnese in the west to the island of Nisyros off the Aegean coast of Turkey in the east. It consists of a series of dormant or active volcanic islands including Santorini, the site of the catastrophic Minoan-era eruption.
The current geometry of the Hellenic arc is a result of the southwards migration of the subduction zone. This has led to extension both along the line of the arc as it bulged out and extension perpendicular to the arc, which is the current tectonic state.
The Hellenic arc is one of the most active seismic zones in western Eurasia. It has regularly been the source for magnitude 7 earthquakes in the last hundred years of instrumental recording and the location for at least two historical events that were probably of about magnitude 8 or more, the 365 Crete earthquake and the 1303 Crete earthquake.
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