state-of-the-art underwater robot called BOB may hold the key to protecting millions of people around Turkey's biggest city against a massive earthquake scientists say is all but inevitable.
Submersed into the dark waters of the Marmara Sea off Istanbul, BOB is a sophisticated turning sonar device similar to the kind of equipment used to detect shoals of fish.
Working at a depth of around 1,200 metres (3,960 feet), its mission however is not to track the movements of fish but to observe the expulsion of bubbles of gas, notably methane, from the seabed.
BOB -- which stands for Bubbles OBservatory module -- is the key piece of equipment on board the Suroit, an oceanographic vessel of the French Research Institute for Exploitation of the Sea (IFREMER).
The mission, which lasts until December 14, is aimed at observing possible clues emerging from the North Anatolian fault.
"We know that after earthquakes, there are significant emissions of gas," said Louis Geli, a geophysicist from IFREMER.
"What we would like to know is whether emissions like this occur before earthquakes or whether there are variations in emissions before earthquakes, which would work as a kind of alert."
Pointing to a map of the Marmara Sea, which connects the Black Sea to the Mediterranean, Geli explains the threat facing Istanbul, a crowded metropolis where mass emigration has led to rapid growth.
Some 15 million people live in and around Istanbul, but there is a lot of ramshackle planning and illegal construction, suggesting many homes would be vulnerable to a large quake.
The North Anatolia fault lies some 20 kilometres (12 miles) to the south of Istanbul.
Its eastern strand, the Izmit fault, ruptured in 1999 in two huge quakes that killed about 20,000 people in Turkey's densely-populated northwest, while its western strand, the Ganos fault, was responsible for a big quake in 1912.
"Between those two strands, there has been no movement since 1766. This is the most dangerous segment of the fault today," Geli said.
Pierre Henrym from France's National Centre for Scientific Research (CNRS), warned that the earthquake expected to hit Istanbul -- dubbed the "Big One" -- would be of a major magnitude
