BEIRUT: A new underwater survey has revealed that Lebanon lies dangerously close to a fault that could soon generate a catastrophic tsunami, according to a report by Discovery News channel. The fault, which according to the survey lies just four miles off Lebanon's coast, caused a tsunami-generating earthquake in 551 A.D. that devastated the coastal cities of Phonecia, or modern-day Lebanon.

The underwater survey was carried out by a team of international geophysicists, Discovery wrote in an article published on Thursday.

The previously unknown submarine fault is responsible for the build-up of the Mount Lebanon range that towers around 10,000 meters above sea level, Discovery said.

The fault moves approximately every 1,500 years, meaning that a disaster of the same magnitude as the earthquake and tsunami that destroyed coastal cities on July 9, 551, could be due any day.

According to historical accounts, that ancient event caused the sea to retreat up to 10,000 meters, Discovery said.

Tripoli was reported to have "drowned," while Beirut took nearly 1,300 years to recover from the cataclysm.

"It was arguably one of the most devastating historical submarine earthquakes in the eastern Mediterranean," Ata Elias of the National Center for Geophysical Research in Beirut, Lebanon, and colleagues wrote in the current issue of the journal Geology.

To trace the origin of the disaster, Elias and colleagues used high-resolution sonar to map the contours of the sea floor between the Lebanese coastal towns of Enfeh and Damour.

"The images show details of spectacular submarine ruptures ... that cut the smoothly sediment-mantled seafloor," the researchers wrote.

Along the coast offshore of Mount Lebanon, the team of researchers found relatively fresh seafloor seismic breaks, indicating that an active thrust fault is responsible for major earthquakes there.

Based on their research, the team estimated that the 551 disaster was caused by a rupture at least 62 miles long on the offshore Mount Lebanon thrust.

The rupture caused a magnitude 7.5 quake. Part of the seafloor collapsed by 5 to 10 feet, triggering a tsunami.

Their research also revealed that at least four earthquakes similar to the 551 event have occurred over the past 6,000 to 7,000 years, suggesting that the seismic behavior of the Mount Lebanon thrust is characterized by a series of clustered quakes separated by 1,500 to 1,750 years of relative calm.

If so, the quakes in 1837, 1918 and 1956 "might be forerunners of worse to come," the researchers concluded.

According to Rob Butler of University of Leeds's Institute of Geophysics and Tectonics, the researchers "make a convincing case about the source of the A.D. 551 earthquake."

But he is not convinced that earthquakes of the last few decades might be harbingers of the next "big one."

"There is an unavoidable certainty that the [area] will be struck by a devastating earthquake. But it could be any time, perhaps within the next few years, perhaps a hundred years from now," he told Discovery.

"The bottom line is, we don't know the odds. In the case of Lebanon, people are literally betting their lives and houses on it," he added. - The Daily Star