Can the Next Tsunami Strike Home?

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On the morning of 21 July 365 CE, a powerful earthquake off the coast of Greece triggered a killer Mediterranean tsunami, more than 30 m high, that devastated our home city of Alexandria. Thousands were killed in what is considered to be one of the most devastating events in the Ancient World.

Artistic rendition of Crete Earthquake and Alexandria Tsunami, 21 July 365 CE

The catastrophic event was repeated, in the year 1303, when an earthquake of magnitude around 8.5 and a tsunami to match hit the Mediterranean Coast once more. New research now claims that it is likely to happen again.

Scientists who led the study claim they have pinpointed the geological fault that lies off the coast of Crete which likely slipped during a huge quake and led to the ancient tsunami.

The findings of the study, published in Nature Geoscience Journal, confirm that massive earthquakes greater than magnitude 8 are likely to strike the Mediterranean, approximately every 800 years, bringing with them killer tsunami waves along the shores of Alexandria.

Other scientists disagree on this prediction, arguing that not enough evidence is known about the faults that caused the earthquakes to predict how often they may strike. 

The new study pinpoints the date to when western Crete was suddenly lifted up, as the date of the 365 CE tsunami, confirming the link between the uplift and the tsunami.

The team also linked the earthquake to a previously unknown fault1 along an underwater rift called the Hellenic Trench2. The newfound fault is near a larger fault known to run along the region, where two continental plates run into each other.

"One fault is lubricated, slipping quietly without earthquakes," said Beth Shaw of the University of Cambridge in England, lead author of the study. "The other slips infrequently in large earthquakes, which can cause tsunamis”.

Using Global Positioning System (GPS) measurements of the movement of the continental plates, the team estimated how much energy builds up in the "sticky" fault and estimated it could slip and cause a massive earthquake about once every 800 years.

Roger Bilham is a geophysicist at the University of Colorado in Boulder, who was not involved in the new study. He said that the study presents "bad news"—"That the Mediterranean, with its growing coastal population in excess of 130 million … could host a large tsunami at any moment is cause for considerable unease," he added.

Paolo Pirazzoli of the National Center for Scientific Research in Meudon, France, who led the first study linking the uplift in Crete to the 365 CE earthquake, says he is skeptical of the new estimate of earthquake frequency in the area, and believes the ancient earthquake is unique.

"Earthquakes tend to repeat along the same fault or set of faults. So it would be highly unusual to have one unique event." concludes Shaw.

Glossary

1) Fault: In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement.

2) Hellenic Trench: A linear depression between the Ionian Basin and Crete which forms the boundary between the Hellenic Plate and the African Plate.

References
www.nature.com
news.nationalgeographic.com

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