The survivors of a tsunami that killed thousands living on the shores of the Mediterranean in AD 365 called it the "day of horror". Worryingly, history may be due to repeat itself, say geologists who have located the source of the wave.Nature Geoscience doi:10.1038/ngeo151
No one had been able to find evidence pinpointing the earthquake that caused the tsunami, which struck the Egyptian city of Alexandria and the Nile Delta in AD 365. The mainstream view was that a series of quakes had struck the region – cumulatively thrusting a section of western Crete upwards by 10 metres.
Beth Shaw and colleagues at the University of Cambridge carbon-dated a section of corals on the coast of Crete that were lifted clear of the water during the upheavals.
The corals' distribution and identical age revealed that one giant quake must have lifted all of them by 10 metres in one massive push – revealing the tsunami's source.
The only thing that could have generated such a large uplift at that location is an earthquake in a steep fault in the Hellenic trench, near Crete, says Shaw.
Eastern Mediterranean tectonics and tsunami hazard inferred from the AD 365 earthquake
B. Shaw et al.
Historical accounts describe an earthquake and tsunami on 21 July AD 365 that destroyed cities and drowned thousands of people in coastal regions from the Nile Delta to modern-day Dubrovnik. The location and tectonic setting of this earthquake have been uncertain until now. Here, we present evidence from radiocarbon data and field observations that western Crete was lifted above sea level, by up to 10 m, synchronously with the AD 365 earthquake. The distribution of uplift, combined with observations of present-day seismicity, suggest that this earthquake occurred not on the subduction interface beneath Crete, but on a fault dipping at about 30° within the overriding plate. Calculations of tsunami propagation show that the uplift of the sea floor associated with such an earthquake would have generated a damaging tsunami through much of the eastern Mediterranean. Measurement of the present rate of crustal shortening near Crete yields an estimate of approx5,000 yr for the repeat time of tsunamigenic events on this single fault in western Crete, but if the same process takes place along the entire Hellenic subduction zone, such events may occur approximately once every 800 yr.