Scientists are sounding the alarm over how much damage could be inflicted by a big earthquake in Istanbul, a city of 15mn full of unregulated construction and old building stock.

They have warned, reported Reuters, that the government urgently needs to act on the city's earthquake preparedness plans to reduce the risk of mass casualties. "We have the rules, recommendations and road map," Haluk Eyidogan, an expert in seismology engineering and member of the Chamber of Geophysical Engineers of Turkey, a nonprofit organisation, was quoted as saying.

"We have to [start] immediately ... to make a disaster-resilient society and system," he added.

Earthquake researchers have predicted that there is a 95% chance that an earthquake of magnitude 7.0 or stronger will strike the city within the next 70 years. And, according to the latest version of Istanbul's Earthquake Master Plan, published in 2018, an earthquake that strong would heavily damage or destroy an estimated 194,000 buildings. That would leave more than 10% of Istanbul's inhabitants homeless, Eyidogan was cited as saying.

Rapid, largely unregulated development has taken place in Turkey’s commercial and cultural capital during the past 15 years, with the city beset by difficulties in accommodating all of the people migrating from the Anatolia region to find work in the metropolis.

In the rush to house the city's growing population, many construction projects—such as adding floors onto existing buildings—are unplanned and skirt building standards, Dogan Kalafat of the Kandilli Observatory and Earthquake Research Institute (KOERI), told Reuters.

The government launched a building amnesty in February 2019 in an attempt at tackling the wave of illegal construction. It received applications as regards 7.4mn illegal structures. But work towards restrengthening or reconstructing where it is necessary appears to be progressing much too slowly.

In 1999, Istanbul felt the effects of a magnitude-7.4 earthquake that struck the city of Izmit, killing more than 17,000 people. Though Izmit is more than 100km (62 miles) away, shocks caused severe damage to Istanbul.

In October, a magnitude-6.9 earthquake destroyed or heavily damaged more than 340 buildings and killed 115 people in the city of Izmir on the Aegean coast.