Sitting at the crossroads of Europe and Asia, the ancient city of Istanbul has seen thousands of years of trade, battles and invasions. Now it is the scene of one of the most audacious engineering projects in the world.
Istanbul is divided by the Bosporus strait that connects the Black Sea to the north of the city with the Sea of Marmara to the south. Part of the city lies in Europe, on the western side of the strait, while the rest is in Asia.
Recently, a mix of technical expertise, foreign investment and national pride finally came together to make the sultan’s dream a reality. This time the plan is not so much to unite an empire as to deliver modern Turks from traffic hell.
The plan is first to improve the existing railways on both sides of the strait and then extend them to the coast via tunnels bored through the bedrock. The cen-tre section, under the Bosporus, will be a 1.4-kilometre tube made up of several shorter sections that will be built on land, floated into position and sunk into place. End to end, the tunnel will be 12 kilometres long.
The result is what geologists refer to as a right-lateral strike-slip fault, similar in size and type to the San Andreas fault in California. The NAF runs for 1600 kilo-metres across northern Turkey, and the abutting plates move about 2 to 3 centimetres relative to each other every year.
Almost every quake along the NAF in the past 100 years seems to have set up a larger one, to the west. The process appears cyclic: quakes march along the fault in sequence until stress falls below a certain threshold, and then start again after a period of quiet. In 1997, geologists studying the most recent cycle predicted that the next shock would hit near the port city of lzmit, 80 kilometres east of Istanbul. Sure enough, a major quake of magnitude 7.4 struck close to lzmit in August 1999, followed by another in Duzce in December, together killing over 18,000 people and causing $10 to $25 billion of damage.
Recent estimates by the US Geological Survey, the University of Tokyo and Istanbul Technical University estimate that the probability of a strong quake hitting Istanbul is up to 44 per cent in the next decade and as much as 77 per cent in the next 30 years. A major earthquake and accompanying tsunami are considered inevitable within a generation.