Earthquake in Turkey a warning for Istanbul, which faces much larger death toll if quake strikes

The high death toll from the massive earthquake in southeastern Turkey and northern Syria is in large part a result of the poor structural integrity of thousands of buildings, experts say.

This is why Istanbul, a city of 15 million people which geologists predict will eventually get hit by a strong quake, could see tens of thousands of deaths unless action is taken on the thousands of buildings in the city that aren't earthquake proof or resistant.

"What we see today in [southeastern] Turkey is just a preview of what will happen in Istanbul," said, Ihsan Engin Bal,  a professor of the Research Group on Earthquake Resistant Structures at the Hanze University of Applied Sciences in the Netherlands.

"I'm not saying what may happen. I say what will happen. What will happen in Istanbul is way bigger than this. Way bigger."

While efforts have been made to modernize building codes and protect against tremors, researchers say there is a vast challenge getting older buildings safe enough to withstand a quake.

More than 17,000 people have been killed by the 7.8-magnitude tremor that hit earlier this week about 26 km east of the Turkish city of Nurdagi at a depth of about 18 km on the East Anatolian Fault.

Turkey lies on two major fault systems, the North Anatolian Fault and East Anatolian Fault, making it the country in that area with the highest risk to be affected by a quake. Earthquake researchers predict that an earthquake of magnitude 7.0 or stronger is very likely to strike Istanbul, which is close to the North Anatolian Fault, within the next 70 years.

"If that that happens, we're talking hundreds of thousands [of fatalities] potentially because of the population of Istanbul. And those buildings are not ready," said Joanna Faure Walker, a professor of earthquake geology and disaster risk reduction at University College London's Institute for Risk & Disaster Reduction.

"That is definitely somewhere where the [geological] community is worried about because the earthquakes are progressing along that fault and because the buildings in Istanbul are not designed to be seismic resistant."

Estimates vary as to potential losses of life if an earthquake struck Istanbul. The municipality of Istanbul conducted its own study estimating that 14,500 people will die if a magnitude 7.5 earthquake happens at night. One study by a group of European researchers projected 30,000 to 40,000 would be killed.

But Bal believes those estimates are low, with his own study estimating 47,000 buildings would be destroyed, with the possibility of 150,000 people killed.

The problems in Istanbul are the same problems that have come to light in this most recent earthquake — many of the buildings in Turkey appear to be extremely vulnerable.

Just from her initial observations of the damage, Faure Walker said the destroyed buildings she sees in pictures and video seem to lack basic earthquake-resistant structures, like reinforced concrete or column bracing.

Another problem, she said, is the issue of "pancaking," where essentially the inside of the building collapses, a sign that the internal floors and structures aren't connected strongly enough to the outer wall.