Apart from the usual challenges that come along with the construction of a sub-sea tunnel, the contractors and the developers of the Marmaray project have had to sort out one challenge, which is left unaccounted for, could put the project in jeopardy.

The tunnel passes through an earthquake zone – the North Anatolian Fault – and experts believe that there is a 62 per cent chance of a strong one erupting along the fault line within the next couple of decades.
Since the disastrous 1939 Erzincan earthquake, the region has been hit by as many as seven earthquakes measuring over 7.0 on the Richter scale. Each quake has happened at a point progressively further west. Seismologists studying quake patterns believe that they happen in storms spread over decades, with one quake triggering the next. The last quake in the region, which the scientists were able to predict after analysing the stresses caused along the fault by preceding quakes, hit the town of Izmit with devastating effect in August 1999. It is thought that the chain is not complete, and that an earthquake will soon strike further west along the fault – perhaps in the heavily populated city of Istanbul.

The solution
While most of the tunnel will be bored through solid rock, the central mile-long section under the Bosphorus will consist of an “immersed tube” fabricated in sections on the surface and then sunk and joined together on the seabed.
The immersed tube tunnel technique has been developed since late in the 19th century. The first immersed tube tunnel ever built was constructed in North America for sewer purposes in 1894. The first tunnels for traffic purposes constructed using this technique were also built in the US.
Unlike a tunnel bored through rigid rock, the submersed sections will be connected by flexible joints made of thick, rubber-reinforced steel plates, which can absorb quake movement without breaking.