Hellenic subduction zone
The Hellenic subduction zone is where the African plate dives north‑northeast under the Aegean Sea plate. The southern part is hidden beneath thick sediments that form the Mediterranean Ridge, the world’s fastest‑growing accretionary complex.
A Wadati–Benioff zone of earthquakes marks the dipping subduction slab, with a relatively shallow dip in the south that steepens toward the north. Seismic imaging has traced the descending slab down to about 410 km depth, into the upper mantle.
When the zone was first identified in the 1970s, many scientists thought the surface trench was the boundary of subduction. After the Mediterranean Ridge was recognized as an accretionary complex, most geoscientists began to treat the Hellenic trenches as features in the forearc region, caused by crustal processes in the Aegean plate. Some researchers still call the trench the surface expression of the subduction zone.
The Mediterranean Ridge is about 2,000 km long and grows quickly because the convergence is fast and a thick sequence of sediments sits on the old Neotethyan ocean crust. Its northern edge is often seen as a backthrust moving northward. The links between the ridge’s thrusts and the main subduction interface are not clear, partly because a thick layer of Messinian salt makes imaging difficult. Tomography shows no direct connection between the Hellenic subduction slab and the slabs at the Calabrian or Cyprus arcs, though earthquake data suggest the shallower part of the zone continues with the Cyprus‑west subduction system, and a deeper tear may be developing northward.
The Hellenic subduction zone slab has two main parts, western and eastern, separated roughly along central Crete. The western segment dips about 30° from 20 to 100 km depth and about 45° from 100 to 150 km depth; the boundary between the two is interpreted as a slab tear.
Subduction of the African plate has created the South Aegean Volcanic Arc (SAVA). Volcanism began in the early Pliocene, with arc‑like rocks from the Saronic Gulf to Santorini. In the mid to late Quaternary, activity spread eastward with more varied chemistry, reflecting regional extension.
Geologists estimate that more than about 1,500 km of Neotethyan oceanic crust has been subducted along this structure or its earlier versions. Broadly, Neotethys moved north under Eurasia since the Late Cretaceous, with the subduction zone retreating and crustal blocks accreting to Eurasia, keeping a continuous slab through backstepping and rollback.
Subduction began at different times along the zone: the eastern part under Crete in the latest Eocene (about 35 million years ago), the eastern part under Crete in the early Miocene, and the western end under the Ionian Islands in the Pliocene (about 4 million years ago). The initially near‑planar slab began to fold in the late Oligocene (around 25–23 million years ago) as the slab rolled back and the trench retreated, driving clockwise rotation of western Greece. From the mid‑Miocene (around 15 million years ago) the curvature increased and southwestern Turkey rotated anticlockwise. A major tear developed between the main HSZ and the Western Cyprus zone, creating a deep slab window.
Today, the Hellenic subduction zone moves at about 35 mm per year, while the overall Africa–Eurasia convergence is only about 5 mm per year. The difference is explained by continual slab rollback and fast southward movement of the Aegean plate, along with ongoing extension inside the Aegean region.
This page was last edited on 2 February 2026, at 17:28 (CET).