A powerful earthquake of magnitude 7 or greater may be building up along a now-quiet fault on the coast of Istanbul, a new study finds. Turkey's latest large quake shook Izmit in 1999 with a force of 7.6, killing 30,000 people and causing $6.5 billion in damages.
Different segments of the North Anatolian Fault, one of the most energetic and longest earthquake faults in the world, have fallen silent. This silence may mean that the segment could be building tension that accrues over decades and may eventually release it in a large, seismic event.
The North Anatolian Fault is more than 1,500 kilometers long and stretches from northern Turkey to the Aegean Sea. An analysis of 20 years' worth of GPS data along the fault shows that a seismic gap under the Sea of Marmara at Princes Island, just 8 kilometers west of Istanbul, is likely to cause the next big earthquake. Of course, it is impossible to predict when such an earthquake might exactly happen.
The Princes Island segment should have slipped about 2.4 to 3.4 meters since its last major earthquake 121 years ago, but it hasn't, researchers found. Instead, tension is building up more and more. If that tension were released in a giant, single earthquake, the Earth could move as much as 11 feet in a few seconds, the study found.
Such a blow could destroy Istanbul, a city of about 14 million people. "Istanbul is a large city, and many of the buildings are very old and not built to the highest modern standards," Michael Floyd, a research scientist in MIT's department of earth, atmospheric and planetary sciences, said in a statement.
Marco Bohnhoff, a professor at the German Research Center for Geosciences in Potsdam, Germany, said that "unfortunately 90 percent of buildings in Istanbul do not fulfill building codes and might not resist the expected earthquake."
The more time passes before the quake strikes, the more devastating the quake will be. Tick, tack. Tick, tack. Tick tack.
 Egintav et al: Istanbul's earthquake hot spots: Geodetic constraints on strain accumulation along faults in the Marmara seismic gap in Geophysical Research Letters – 2014
 Parsons: Recalculated probability of M7+ earthquakes beneath the Sea of Marmara, Turkey in Journal of Geophysical Research - 2004. See here.