If you live in Istanbul, you should put an earthquake backpack next to your front door: money, biscuits, water, telephone and flashlight, bandages, the essentials for survival. After the severe earthquake to be expected in the coming years or decades, the chaos in the city of 16 million will be unimaginable, experts say.
There was a possible foretaste of this recently on June 19: a quake with a magnitude of 4.2 hit the city. No houses collapsed, nobody was killed. Nevertheless, the panic was widespread and the media read of the harbinger of a catastrophe. The fear of earthquakes is now being fed by the construction of a “second Bosporus” planned by the government in Ankara: the new canal that is to cut through Istanbul on the European side parallel to the strait.
The so-called North Anatolian Fault runs along the Turkish north, under the Marmara Sea and into the Aegean Sea. Roughly speaking, the Anatolian tectonic plate is pushed westward by the Arabian plate, by around 2.5 centimeters per year. Because it is hooked to the Eurasian plate in the north, this creates pressure in the subsurface. Keep going until a wedged point gives way and the plates jerk off – then there is an earthquake and the process starts all over again.
In the 20th century there were a number of major earthquakes along the fault. In 1912 a severe earthquake struck Ganos, at the western end of the Marmara Sea. In 1939 the earth shook in Erzincan in Eastern Anatolia, at the other end of Turkey, then the violent quakes moved further and further west towards Istanbul until the chain finally reached Gölcük and Izmit in 1999, about 100 kilometers southeast of the metropolis. Around 17,000 people died at the time, and around 1,000 were also killed in Istanbul itself. But the region under the Sea of Marmara was spared from severe earthquakes for a suspiciously long time; the last major event there was in 1766.
Geologists call something like this “earthquake deficit”: It means that tension has built up there for a long time, like an arc that is stretched further and further. The only question is when the arrow will come loose and hit Istanbul.
Apartments for half a million people are to be built near the possible epicenter
“The probability that a quake under the Sea of Marmara will reach magnitude seven or more at some point in the next 30 years is around 40 percent,” says Marco Bohnhoff from the Potsdam Geo Research Center, who also heads the Gonaf earthquake observatory near Istanbul. A severe tsunami would not be expected with such an earthquake, because the earth would move in a horizontal direction rather than vertically. But the effects would still be catastrophic, with estimates suggesting tens of thousands of deaths.
Against this background, the planned channel is now being discussed. In addition to significant environmental concerns due to the consequences for nature and the ecological balance of the Marmara Sea, the risk of earthquakes also plays a role. The geology professor Naci Görür, who is considered a leading Turkish earthquake expert, recently pointed out that the mouth of the planned canal into the Sea of Marmara would be very close to the presumed epicenter of the future earthquake. This makes any large-scale change in the earth’s surface structure through the construction of canals dangerous. This is particularly true if extensive blasting is carried out during the excavations.
However, other experts consider this risk to be manageable. “You can say a lot against the planned channel,” says Bohnhoff. “But it is very unlikely that this will promote a major quake.” Compared to the tectonic energy in the subsurface, the mass redistribution caused by the construction is relatively small.
But the risk assessment also depends on what is happening on the banks of the canal. Apartments for 500,000 people are to be built there, in the middle of the zone that is likely to be affected by a Marmara quake. In principle, you can build earthquake-proof, as shown by countries like Japan, where buildings can withstand even the heaviest tremors. In Turkey, however, the regulations have been tightened time and again, but so far they have often not been complied with.
Critics like Istanbul’s mayor Ekrem İmamoğlu are therefore calling for the estimated 65 billion euros in construction costs for the canal to be invested in the overdue renovation of existing buildings. For a long time, experts have been calling for old, cheaply constructed reinforced concrete buildings to be stabilized, clearing equipment to be provided and collection points to be created. But the government is not pushing this forward with determination.
One thing is certain: if the earthquake comes, it will come without warning. “The prerequisites for an earthquake early warning system are very poor in Istanbul,” says Bohnhoff. The fault is simply too close to the city, seconds after the first measurable vibration, the more energetic secondary and surface waves would reach the city. “That might be enough to close gas pipes and turn traffic lights to red, but not for more.”