some engineers and seismologists. "Since AD 342, it has seen large earthquakes that each claimed more than 10,000 lives." Some scientists have estimated a 77% probability that, at some time in the next 30 years, Istanbul will suffer an earthquake measuring 7.0 or more on the Richter magnitude scale. The waterlogged, silty soil on which the tunnel is constructed has been known to liquefy during an earthquake so engineers injected industrial grout to below the seabed to keep it stable. The walls of the tunnel are made of waterproof concrete coated with a steel shell, each section independently watertight. The tunnel is made to flex and bend in the way that tall buildings are constructed to react if an earthquake hits. Floodgates at the joints of the tunnel are able to close and isolate water in the event of the walls' failing. Steen Lykke, project manager for Avrasyaconsult, the international consortium that oversaw the construction, summed the problems up by saying, "I can't think of any challenge this project lacks". Marmaray in numbers Some figures of the project are as follows: Overall length: Tunnel section: Immersed tube: Deepest point: Minimum curve radius: Maximum gradient: 1.8% Surface stations: 37 Underground stations: 3 Interchanges: 4 Inter-city stations: 8 Minimum platform length: Average station spacing: Maximum speed: Commercial speed: Headway: 2–10 minutes Passengers per hour and direction: 75,000 Number of passenger cars: 440 Passengers When the Marmaray finally opened, 4.5 million passengers traveled through the tunnel in the first 15 days when travel was free of charge. There were 10 million passengers in the beginning of 2014, 13.5 million in first four months and 21.4 million in first six months. The Marmaray is expected to carry 1.5 million passengers per day. See also Eurasia Tunnel Great Istanbul Tunnel, a proposed three-level road-rail undersea tunnel Public transport in Istanbul Rail transport in Turkey Turkish Straits References External links Overview of the Marmary history, justification, and construction process with pictures Marmaray Project: L. C. F. Ingerslev, 2005, "Considerations and strategies behind the design and construction requirements of the Istanbul Strait immersed tunnel," Tunnelling and Underground Space Technology 20: 604–08. Steen Lykke and Hüseyin Belkaya, 2005, "The project and its management," Tunnelling and Underground Space Technology 20: 600–03. Steen Lykke and Frits van de Kerk, 2005, "Marine operations, the Bosphorus Crossing," Tunnelling and Underground Space Technology 20: 609–11. Hideki Sakaeda, 2005, "Tunnels and stations in BC