Mediterranean Quake - Tsunami that devastated the ancient world could return

The 365 AD Crete earthquake was an undersea earthquake that occurred close to the end of the night of 21 July 365 AD in the Eastern Mediterranean, with an assumed epicentre near Crete. Geologists today estimate the quake to have been magnitude 8 or higher on the Richter scale, causing widespread destruction in central and southern Greece, northern Libya, Cyprus, and Sicily. In Crete, nearly all towns were destroyed.

The Crete earthquake was followed by a tsunami which devastated the eastern coasts of the Mediterranean, particularly Alexandria and the Nile Delta, killing thousands and hurling ships nearly two miles inland. The quake left a deep impression on the late antique mind, and numerous writers of the time referred in their works to the event.

Studying an ancient earthquake has enabled Oxford University researchers to quantify the likelihood of a tsunami in the Eastern Mediterranean. They estimate that a ring of faults around the south of Greece and the Aegean Sea generates tsunami earthquakes approximately once every 800 years and, because the last such earthquake took place in 1303, the probability of a tsunami affecting the region is much higher than had been thought.

Reporting in Nature Geoscience, the group describe how they tracked down the origin of this ancient quake to a fault beneath western Crete. Very precise radiocarbon dates of uplifted shorelines show that western Crete was lifted by about ten metres within a few decades of AD 365, and the shape of the uplifted shorelines is diagnostic of distortion of the land surface by an earthquake.

The researchers then used GPS stations to take very precise measurements of how the Earth’s surface is being slowly compressed all around the southern Aegean Sea today. From these measurements they predict that the energy being built up will be released in tsunami-earthquakes somewhere along this fault approximately every 800 years.

The AD 365 event is important because it is the only earthquake in the Mediterranean where the evidence can be studied on land, rather than being hidden under the ocean. It was one of the most devastating events in the ancient world, destroying cities and drowning thousands of people in coastal regions from the Nile Delta to modern day Dubrovnik.

Calculations suggest that, as it crossed the open ocean, the wave height of the AD 365 tsunami was similar to that of the 2004 Sumatra tsunami – around one metre high. This leads the researchers to believe that, when it hit the shore, this sea wave would have been highly destructive.