Posted on 07/26/2007 1:42:31 PM PDT by blam
Major Quake Likely in Middle East, Survey Finds
Kate Ravilious
for National Geographic News
July 26, 2007
In A.D. 551, a massive earthquake devastated the coast of Phoenicia, now Lebanon. The disaster is well-documented, but scientists had struggled over the years to locate the earthquake fault.
Now a new underwater survey has uncovered the fault and shown that it moves approximately every 1,500 years—which means a disaster is due any day now.
"It is just a matter of time before a destructive tsunami hits this region again," said Iain Stewart, an earthquake expert at the University of Plymouth in the United Kingdom not involved in the underwater survey.
Hitting the Jackpot
Earthquakes are common in Lebanon, but many of the faults remain unidentified, hidden beneath the deep waters of the Mediterranean Sea.
Surveying this region is difficult because some of the continental shelf drops off very quickly, reaching water depths of around 4,921 feet (1,500 meters) only five miles (eight kilometers) from the shore. (See a Lebanon map.)
Ata Elias of the National Center for Geophysical Research in Beirut, Lebanon, and his colleagues had a hunch that the fault responsible for the A.D. 551 earthquake would lie in this offshore region, so they did an underwater geophysical survey—and "hit the jackpot," Elias said.
By bouncing radio waves off the seafloor and studying the reflection patterns, Elias and his team were able to build a three-dimensional map showing all the lumps and bumps on the seafloor.
Running parallel to the Middle Eastern coast, they discovered a distinctive stepped ridge—the shape made by a "thrust" fault when one of Earth's tectonic plates shoves its way underneath another.
"We inferred that this thrust fault is the source of major earthquakes," Elias said.
The team was able to trace this fault along the coast for more than 62 miles (a hundred kilometers).
The findings are published in the August issue of the journal Geology.
Shell Secrets
Back on land the team found additional evidence to link this fault to the A.D. 551 earthquake. A "staircase" of platforms rising from present-day sea level showed how the land had moved upwards each time the thrust fault moved.
Enlarge Photo
When the thrust fault ruptured it uplifted the coastline by around three feet (one meter), Elias said.
When the platforms were at sea level they were colonized by mollusks. But as soon as they were thrust out of the water by the earthquake the mollusks died.
By dating the mollusk shells on the raised platforms, Elias and his colleagues determined when the thrust fault moved.
At least four earthquakes similar to the A.D. 551 quake have occurred over the last six to seven thousand years, the team found—suggesting a 1,500- to 1,750-year recurrence time for destructive quakes.
From the length of the thrust fault and the amount of uplift of the platforms on land, Elias and his colleagues estimate that the A.D. 551 earthquake must have had a magnitude of about 7.5 on the Moment magnitude scale, a more modern form of measurement than the Richter scale. (What is an earthquake?.)
When the fault ruptured in A.D. 551, part of the the seafloor block collapsed by around 5 to 10 feet (1.5 to 3 meters). This vertical drop in the water triggered a surging tsunami, which gained height rapidly as it pushed toward land.
Stewart of the University of Plymouth said the study is interesting, but remains cautious about blaming the newfound thrust fault for the A.D. 551 event.
"The Mediterranean has a lot of big earthquakes and there are lots of benches [unstable, newly formed fronts of lava deltas] everywhere. It is hard to link those benches to a particular fault," he said. (Related: "Ancient Tsunami Smashed Europe, Middle East, Study Says" [December 4, 2006].)
Nonetheless, he believes that the risk of another big earthquake occurring is very high, and should be taken seriously.
"In the past this area has had a lot of big earthquakes and tsunamis, but in modern history it has been quite quiet," Stewart said.
"We have been lulled into a false sense of security, just like we were in the [2004 Indian Ocean earthquake]."
Drowned Cities
Archaeological and historical evidence of the A.D. 551 earthquake indicate that this was truly a catastrophic event.
All the major coastal cities between Tripoli and Tyr suffered heavy damage, with Tripoli reported to have "drowned."
Historical records describe "the complete ruin of Berytus (Beirut), Jewel of Phoenicia, and the sea retreating one to two Roman miles, or 4,921 to 9,842 feet (1500 to 3000 meters) from shore. That's enough to ground mooring ships and uncover sunken ones. More than 30,000 people died in Beirut alone. (Who were the Phoenicians?)
"If this earthquake and tsunami were repeated today, it would be a disaster of enormous proportions," said Sanford Holst, an author and expert on ancient Phoenicia.
More than 70 percent of the Lebanese population lives along the coast: Beirut has a population of 1.5 million.
What's more, much of the country's infrastructure is also located along the coast. The main highways, electrical power stations, airports and economic centers are all next to the sea, Elias said.
To prepare for the next big quake, many of the tall buildings that line the coast need to be re-enforced to withstand earthquakes. New buildings need to be built with large earthquakes in mind. And people need to be informed. "We need an earthquake and tsunami alert system and proper emergency plans," Elias said.
How so?
From Wikipedia:
“The most common estimate of Christianity in Lebanon is about 40-45%. It has the largest number of Christians of all the Arab nations.”
Coming at the beginning of the scientific revolution the total devastation of the powerful Lisbon was a shock to all. Many re-evaluated their philosophical and even theological stance.
This topic was posted , thanks blam.
Just a refresher ping and update.
Free beer tomorrow..................
As if things weren’t getting weird enough...
If you look at the top of Africa it clearly shows that some huge wave swept over it.
The ‘eye of the Sahara’ might have been Atlantis, and the ‘single day and night of misfortune’ was whatever wave swept over the whole continent. I am thinking a huge meteor burst over the Indian ocean. (??)
Also, the bottom half of Africa clearly shows man-made waterways in a grid (mostly filled in, now)
They stone you when you're tryin' to go home.
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