“We live in distress,” said Aysegul Rahvanci, a lifetime Istanbul resident, of her fears about a possible strong earthquake in the city.

“Our life equals to anxiety.”

Many people living in Turkey’s largest city shared Rahvanci’s feelings, in particular following the massive earthquakes – with magnitudes of 7.8 and 7.6 –  on Monday that killed more than 21,000 people and wounded more than 80,000 others in southeastern Turkey as of Saturday. Thousands of others were killed in Syria. Officials said they expect the death toll to continue to rise.

The country is particularly prone to earthquakes, as it lies in an area where several tectonic plates meet. Quakes usually occur along the boundaries between plates. The North Anatolian Fault, which divides the Eurasian and Anatolian plates, runs close to Istanbul.

According to Sukru Ersoy, a professor of geology from Istanbul’s Yildiz Technical University, the question is when a powerful earthquake will hit Istanbul, not if it will happen.

“With the data we have on the past earthquakes, and through certain modellings, we can say that an Istanbul earthquake is near and we would not even be surprised if the city is hit by it today,” he told Al Jazeera, adding that it was impossible to know when the disaster would take place.

Istanbul Mayor Ekrem Imamoglu said in a recent interview that there were some 90,000 buildings that were highly vulnerable to earthquakes in the megalopolis with a population of some 20 million people.

The mayor said another 170,000 buildings were in the medium-risk status in case of a strong earthquake, according to research conducted by Istanbul Municipality.

After Monday’s earthquakes, more than 6,400 buildings have reportedly collapsed in southeastern Turkey.

Many victims are still thought to be stuck in the rubble of collapsed buildings across the region, as search and rescue efforts continue despite fading hopes of finding survivors.

‘Living in new buildings expensive’

Istanbul residents watched the news coming from southeastern Turkey in shock, knowing that experts have said an earthquake in Istanbul is highly likely.

Rahvanci, who lives in the Kadikoy district and works as a sales attendant, said she lives in a building that is approximately 25 years old.

“I cannot afford to live in a newer building as rents are very high in those,” the 41-year-old told Al Jazeera.

Zeynep Urs, who lives in a more than 50-year-old building in the Beyoglu district of the city, agreed, “I would consider moving to a newer building but it is currently very hard to find one with reasonable prices.”

“I generally trust my building, but I am not positive that it can handle a very strong earthquake. And of course, I have worries because of my building’s age,” Urs told Al Jazeera.

The government improved its construction regulations after a magnitude-7.6 quake hit the western part of Turkey’s Marmara region, where Istanbul is also located, in 1999 and killed some 17,500 people.

After that earthquake, the Turkish seismic design code was enhanced and in late 2000s, the Turkish government launched a large-scale urban transformation plan to replace the buildings unsafe for earthquakes with new seismically improved ones.

Both Rahvanci and Urs said that their buildings did not have the necessary document, the so-called “earthquake report”, showing that the buildings were in line with the new regulations adopted after the earthquake in the Marmara region.

Another Kadikoy resident, Ugur Kumtas, said that he partially trusted the safety of the building he lived in with his family.

The building’s construction was finished in late 2020 and it is built according to the new regulations, according to 57-year-old Kumtas, who works as a mechanical engineer.

“I feel 80 percent safe about the building I live in,” he told Al Jazeera. “The building might get damaged in case of a powerful earthquake, but I believe it will not collapse.”

Nonetheless, Kumtas expressed his worries over the risk of being caught by an earthquake in another building when he is out with his family.

All three Istanbul residents who talked to Al Jazeera said that they did not have any preparation for a possible tremor apart from having an emergency bag at home.

According to official data, there are 817,000 buildings in Istanbul that were built before 2000, which corresponds to 70.2 percent of all the buildings in the city.

New buildings collapsed

After the tremors in southeastern Turkey last week, some buildings that were built after 2000 collapsed. However, reports have said the majority of the damaged buildings were built before the year 2000.

Sukru Ersoy said that the majority of the buildings constructed after the 1999 earthquake across Turkey were in line with the new regulations and consist of improved materials.

“However, corruption is high in the construction sector in Turkey. And therefore, there were abuses,” he told Al Jazeera, adding that these happened particularly during building inspections in the past.

“And we see this in the earthquake in southeastern Turkey. Some new and luxurious buildings also collapsed,” Ersoy said.