Scientists simulated what would happen if a magnitude 7 earthquake occurred beneath the Mediterranean sea off Sicily or Crete.
The results showed that low-lying areas up to five metres (16 feet) above sea level would be swamped by the resulting tsunami.
Italy, Greece and Libya could all be hit by the waves, with up to 3.5 square kilometres (1.35 sq miles) of the island of Crete almost certainly submerged.
A large tsunami occurs in the Mediterranean once a century on average.
In 1908, thousands of people died when a magnitude seven earthquake struck the Messina region of Italy, generating waves more than 10 metres (33 feet) high.
In the year 365 AD, a cluster of strong tremors off the coast of Crete triggered a tsunami that destroyed ancient cities in Greece, Italy and Egypt, killing some 5,000 people in Alexandria alone.
About 130 million people live around the rim of the Mediterranean.