Wednesday 17 February 2021

Magnitude 5.5 Earthquake to the north of the Gulf of Corinth, Greece.

The United States Geological Survey detected a Magnitude 5.5 Earthquake at a depth of 10 km close to the northern shore of the Gulf of Corinth, slightly after 5.35 am local time (slightly after 3.35 am GMT) on Wednesday 17 February 2021. There are no reports of any damage or casualties associated with this event, but people have reported feeling it locally.

The location of the 17 February 2021 Gulf of Corinth Earthquake. USGS.
The geology beneath the Gulf of Corinth is slightly complicated. The Gulf forms part of the boundary between the Aegean and Eurasian Plates. This is a divergent margin, with the two plates moving apart, causing sinking in the centre of the Gulf, with the rocks on either side sinking along a series of faults, a structure known as a graben to geologists.
The graben beneath the Gulf of Corinth. The drawing apart of the Aegean and Eurasian Plates causes the lithosphere under the Gulf to thin, and the rocks of the crust to sink, splitting along a series of concentric faults on either side of the Gulf. Moretti et al. (2003).
However this is not the whole story, as to the south of the Peloponnese the African Plate is being subducted beneath the Aegean Plate along the Hellenic Subduction Zone, passing under The Peloponnese and the Gulf of Corinth (note this is oceanic plate attached to the north of Africa, not the continental African Plate).
The subduction of the African Plate beneath the Aegean Plate and the Gulf of Corinth. Turner et al. (2010).
 Thus there are two potential causes of Earthquakes beneath the Gulf of Corinth; shallow faulting associated with the graben caused by the drawing apart of the Aegean and Eurasian Plates, and a deeper zone where friction between the subducting African Plate and the overlying Aegean and Eurasian Plates can lead to quakes. However, depth is not the only guide to the cause of a quake, as the friction of the African Plate passing under the Aegean and Eurasian Plates also exerts stresses on the rocks in the graben, and can contribute to quakes there.
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