In the early morning of December 28, 1908 a 30 to 42 seconds long earthquake with a reconstructed magnitude of 6.7-7.2 hit the Italian cities of Messina and Reggio Calabria. The earthquake damaged 90% of the buildings and broken pipes fuelled a firestorm, an aftereffect known from many other earthquakes; however one of the most unusual effects of this earthquake was an 8 meter high tsunami which killed almost 2.000 people.
The earthquake killed estimated 40.000 people in the two cities alone, 27.000 people along the shores of the Strait of Messina - some historic documents claim 100.000 to 200.000 victims - one of the deadliest natural disasters recorded during historic times in Europe.
Fig.1. A historical representation - a "Vue de l'Optique composition" (a hand-coloured copper engraving used in a Laterna magica) - shows ships on the Strait of Messina during a sequence of earthquakes in 1783 with more than 35.000 victims.
South Italy is located between the borders of the two major continental plates of Europe and Africa and several microplates of the Mediterranean Sea. This geometry forms "belts" with intense tectonic activity, recognized already in 1862.
The origin of the tsunami of Messina is still today an unsolved geological problem. The entire region is dominated by the large rift-zone of the Calabrian Arc, formed by the slow rollback of the oceanic crust of the Ionian Sea.
Fig.2. Simplified tectonic settings of South Italy and the intensity of the December 1908 earthquake after the modified Mercalli scale (data from INGV site). In this model the earthquakes of Calabria and Sicily are mostly associated with a rift valley formed by the rollback of the Ionian Sea.
This tectonic setting is characterized by faults with downwards movements, unusual to produce the upward push needed to generate a tsunami. Also no prominent fault or escarpment was until today discovered in the Strait of Messina or along the coasts of Sicily. Finally it is strange that the tsunami hit the shores 8 to 10 minutes after the quake, too late according to some researchers to be associated directly to the quake. A new hypothesis proposes that the tsunami of 1908 was therefore the result of a large underwater landslide, triggered by the earthquake.
The bottom of the sea revealed also that tsunami are frequent (in geologic time) catastrophes in the Mediterranean Sea. In sediments of the bay of Augusta (Sicily) researches discovered twelve layers, dated to 4.500 years, with microorganisms, especially foraminifers, living along the shores of the island. These layers were probably formed during past tsunami, when sediments were eroded from the beach and then transported by the backwash currents into the bay.
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