Introduction
The Aegean Sea plate (also termed the Hellenic or Aegean plate) is a relatively small lithospheric block beneath southern Greece and western Turkey that forms a discrete tectonic element within the eastern Mediterranean. Its southern margin is defined by the Hellenic subduction zone south of Crete, where the African Plate descends beneath the Aegean plate and drives active convergent tectonics; the plate’s northern edge, by contrast, is characterized by a divergent boundary with the Eurasian Plate and reflects an overall extensional regime along that margin.
Bathymetric and geophysical observations indicate the Aegean region occupies a comparatively shallow seafloor—on the order of ~350 m depth—making it a topographic high relative to the deeper Black Sea and Mediterranean basins (circa 1,300–1,500 m). Subsurface imaging and crustal studies show the block is underlain by thinned continental crust rather than true oceanic lithosphere, so it exhibits continental rheological properties despite its offshore position.
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The plate’s crust has undergone substantial thinning since its formation through processes including post‑orogenic collapse and continued extensional deformation; this extension has generated major structural features such as the Gulf of Corinth. Historically the Aegean crust was sometimes grouped with the Anatolian Plate, with observed motion differences attributed to rotation of that larger block, but more precise geodetic and kinematic data have demonstrated that the Aegean region moves distinctly and is best treated as a separate tectonic plate.
The Aegean Sea is an actively extending back‑arc region whose present tectonic regime is driven by slab rollback at the Hellenic subduction zone. Retreat of the subducting slab forces trench migration and imposes extensional stresses on the overriding plate, producing large‑scale crustal stretching across the Aegean domain and sustaining ongoing back‑arc extension.
This extension has been accommodated by pervasive normal faulting and rifting, producing a back‑arc basin characterized by alternating uplifted and down‑dropped fault blocks. Seafloor morphology is therefore dominated by horsts and grabens, a submarine analogue of continental basin‑and‑range topography. Many Aegean islands are the emergent crests of these horst blocks; their distribution and size reflect the spatial pattern of normal faults, differential rift subsidence, and relative sea level, so islands mark the highest portions of an actively extending fault‑block system.
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Spatial variations in crustal thickness record the differential expression of extension across the plate: southern Aegean crust is markedly thinned (≈20–22 km) while northern crust remains thicker (≈32–40 km), indicating that extension has been most intense in the south and is only more recently affecting the northern regions.
The current extensional architecture overprints an earlier orogenic history. The Aegean Orogeny (c. 70–14 Ma) produced regional mountain belts; subsequent post‑orogenic collapse and gravitational extension of the thickened crust initiated significant thinning and unroofing. These processes facilitated widespread metamorphism and exhumation, so the bedrock exposed on many islands preserves both orogenic and post‑orogenic/extensional histories.
Viewed as a spatio‑temporal sequence—Aegean Orogeny → post‑orogenic collapse and crustal thinning → slab rollback and active back‑arc extension—this evolution explains the region’s bathymetry, the pattern of island emergence, the north–south crustal thickness contrast, and the continued structural activity throughout the Aegean.
Seismic activity
The Aegean region is characterized by persistent seismicity resulting from the interaction of an active subduction system and contemporaneous internal extension. Along the Hellenic subduction zone the African Plate converges on and descends beneath the Aegean Plate at roughly 40 mm yr−1, producing concentrated strain and frequent earthquakes along the plate interface. Seismicity associated with this slab shows a clear depth segmentation: shallow events cluster near the plate boundary, whereas deeper earthquakes occur beneath and immediately landward of the Greek volcanic arc, reflecting progressive slab descent beneath the overriding plate. Superimposed on this subduction-driven regime, the Aegean Plate is undergoing internal extension that is accommodated on predominately east–west–trending normal-fault systems. Slip on these faults generates additional earthquakes and, together with subduction-related events, defines the Aegean Sea’s multi-source seismic hazard, with earthquakes occurring over a broad range of depths and mechanisms.