The AD 365 Ammianus tsunami in Alexandria, Egypt, and the Crete ca. 365 fault and tsunami

摘要

The traditional interpretation of a legendary, though controversial, fourth century text of Ammianus Marcellinus is that an earthquake-generated tsunami hit Alexandria on 21 July 365. The causative earthquake is usually associated with the Aegean Arc, and it has been modeled through elastic dislocation of the up to 9 m uplift of Crete which occurred in ca. 365. A rather steep, intra-plate fault was inferred, and this predicts a regional tsunami, with about 0.6-m-high waves just offshore Alexandria. However, modeling does not reproduce the tsunami polarity clearly described by Ammianus, first major retreat of the sea and then flooding; this polarity can better be explained by a slump-generated tsunami in the eastern part of the Nile Delta. On the other hand, analysis of historical and archaeological evidence excludes the possibility of a major destruction of Alexandria in 365. The possible explanation for this puzzle is that Ammianus mixes at least two events: a slump-generated, locally impressive tsunami to east and a regional tsunami from Crete. None of these events produced significant destruction in Alexandria, which was protected by fortification walls and by an islet to the north, and in addition, it was exposed mostly to longshore waves of the 365 tsunami. These results do not mean that Alexandria has not been affected by other historical tsunamis and that the modern town is not exposed to earthquake and tsunami hazards.